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The behavioral ecology and terrestrial slugs Rollo, Christopher David 1978

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THE BEHAVIORAL ECOLOGY OF TERRESTRIAL SLUGS by CHRISTOPHER DAVID ROLLO B.Sc. {Agr.), University of Guelph, 1972 H.Sc, University of Guelph, 1974 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES in the Department of Plant Science we accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1978 (Q C. David Hollo, 1978 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T-1W5 Date ABSTRACT The behavior of eight species of slug ( Dergceras reticulatum^ Dj_ caruanae, Arion a tar^ A^ subfusc.us.jt 4.*. circumscri£tus x A._ h g r t a n s i s x Lim ax saximus,. and Ariglimax cglumbianus ) and the s n a i l , Cepaea nemoralis, was studied in re l a t i o n to weather, shelter, food, and competition. Experiments that depended on a r t i f i c i a l shelters quickly showed how the d i s t r i b u t i o n and abundance of slug populations could vary within large outdoor enclosures. I f undisturbed by aggressive individuals, the molluscs selected shelters closest to the i r food. A l l species were capable of returning to shelters by homing on an odor they deposited there, and by following slime t r a i l s . During hot, dry weather the animals usually returned to the same shelter repeatedly, but they were less l i k e l y to do so in the wet, cool weather of spring and f a l l . Adult L„_ 3iaximust Qu caruanae t and A^ subfuscus became highly aggressive during the summer months.,Their attacks caused smaller conspecifics and other non-aggressive species to avoid shelters they occupied. Slugs were not so aggressive in spring and f a l l , and not at a l l i n winter. Three hundred and f i f t y eight hourly observations of molluscan a c t i v i t y and weather were made on 21 nights from May u n t i l October, 1976. Factors causally important to the a c t i v i t y patterns of the molluscs were determined by controlled laboratory experiments. These factors were included i n a multiple correlation-regression analysis of daily and seasonal a c t i v i t y patterns in rel a t i o n to weather. The analysis was also performed for each species using weather data from the previous hour's observation. Equations incorporating lag-weather explained s l i g h t l y more v a r i a b i l i t y than did those that used concurrent weather. The best r 2 values obtained for the subterranean species, A.4. hortensis and ftt circumscrijtus were 0.2269 and 0. 5533 respectively..For the other species studied, r 2 values ranged from 0.7283 to 0.8966. Factors included in the regression equations, i n descending order of importance, were: time of day (circadian rhythm), surface temperature, l i g h t i n t e n s i t y , photoperiod, time of sunset, temperature qradient (shelter to ground surface), wind speed, moon phase, atmospheric moisture, changes i n l i g h t i n t e n s i t y , barometric pressure, shelter temperature (acclimation), changes in barometric pressure, and temperature changes, age and hydration were also shown to be key factors i n other experiments. fi model incorporating weather thresholds estimated from f i e l d data explained 83.06% of the v a r i a b i l i t y i n the a c t i v i t y of Limax maximus over the season. The values predicted from the model did not d i f f e r s i g n i f i c a n t l y from those actually observed i n the f i e l d (Kolmogorov-Smirnov test, p>0.50). Seasonal changes in the strength of the homing response, a c t i v i t y patterns, and the aggressiveness of the three species noted above were closely related to one another through their mutual association with weather. i v TABLE OF CONTENTS A b s t r a c t i i L i s t Of T a b l e s And Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v i i L i s t Of F i g u r e s ............. ....»..............*..........xxv Acknowledgements . ... . x v i i i I n t r o d u c t i o n - J u s t i f i c a t i o n ................................ 1 S e c t i o n I : F a c t o r s I n f l u e n c i n g The A c t i v i t y Of M o l l u s c s On The S o i l S u r f a c e ....................................... 3 F i e l d Methods .......................................... 3 L a b o r a t o r y Methods ..................................... 19 I n n a t e Bhythms ......................................... 21 I n t r o d u c t i o n : Seme G e n e r a l P r o p e r t i e s Of Bhythms .... 21 Endogenous B h y t h m i c i t y Of M o l l u s c a .................. 30 D e s c r i b i n g The C i r c a d i a n Rhythm In The F i e l d ........... 53 The A c t i v i t y P a t t e r n Over Time ...................... 53 The A c t i v i t y P a t t e r n Of Deroceras r e t i e u l a t u p , . . . . . . 55 The A c t i v i t y P a t t e r n Of l£ion a t e r .................. 59 The A c t i v i t y P a t t e r n Of Cepaca n e m o r a l i s ............ 63 The A c t i v i t y P a t t e r n Of Limax maxiaus ....... ........ 66 The A c t i v i t y P a t t e r n Of A r i o l i m a x Columbianus ....... 69 The A c t i v i t y P a t t e r n Of A r i o n s u b f u s c u s ............. 72 The A c t i v i t y P a t t e r n Of Deroceras c a r u a n a e . . . . . . . . . . 75 The A c t i v i t y P a t t e r n Of A r i o n h o r t e n s i s And A r i o n c i r c u m s c r i p t u s ... .... ...... 78 I n f l u e n c e Of Ambient Temperature On The Form Of The V Rhythm .. ... .... 80 Photoperiod And Phase .................................. 84 Ac t i v i t y As A Foraging Besponse ........................ 94 A ge ..........«•.*•......;....'.'•.'•...*....».••'..:. ......... • 98 Light Intensity ........................................ 105 Phase Cf The Scon ..122 T € m per at u re .................... ................... ..... 123 General Discussion .... • 123 The Relationship Of A c t i v i t y To Temperature In The F i e l d 126 Acclimation ............................................ 157 Temperature Gradients .................................. 160 Temperature Changes ............................ ........ 164 Barometric Pressure .................................... 168 Atmospheric Moisture ........... ........................ 170 Hydration .......................................•...... 195 B a i n f a l l .. .. 207 Hind .....«:.. .... .... . . . . . . . . . ...... *.«.'. •.... 208 Correlation-Begression Models .......................... 213 Threshold Model , .. 269 Section I I : Environmental Orientation ..................... 276 Beview Of Literature ...................................276 Methods And Results 283 Pheromone Experiment ................................ 283 Homing Behavior In The F i e l d ........................ 285 Seasonal Homing Changes ............................. 291 Twelve-Hour Observations Of Individual Slugs ........ 298 Discussion ................................. ............3C7 v i Orientation To Substrate Cues: T r a i l s And Topography 307 Orientation To Air-Eorne Cues 314 Section I I I : Intra- and I n t e r s p e c i f i c Agonistic Behavior Among T e r r e s t r i a l Mollusca 337 Literature Review ...................................... 337 Methods and Results ....................................340 Discussion ............................................. 370 Variations In Aggressiveness Among Species ..........370 Maturation, Mating And Aggression ................... 380 Laboratory Study Of Aggression ...................... 387 Aggression In F i e l d Environments .................... 392 General Discussion ........................................ 403 Bib11ography ..............................................406 LIST OF TABLES AND APPENDICES Table I. Regression Eguation Relating the A c t i v i t y of peroceras reticulatum to Time. ..... .... ................ 56 Table II. Regression Eguation Relating A c t i v i t y of Arion ater to Time ........................................... 60 Table I I I . Regression Eguation Relating the A c t i v i t y of Cejaea nemoralis to Time. ............................... 63 Table IV. Regression Eguation Relating the A c t i v i t y of Limax maximus to Time..................................66 Table V. Regression Equation Relating the A c t i v i t y of Ariolimax cplufbianus to Time.......................... 69 Table VI. Regression Eguation Relating the A c t i v i t y of Arion §ubfuscus to Time. 12 Table VII. Regression Eguation Relating the A c t i v i t y of Dergceras caruanae to Time. ............................ 75 Table VIII. Regression Equation Relating the A c t i v i t y of Arion hortensis to Time. ...............................79 Table IX. Regression Eguation Relating the A c t i v i t y of Arion circumscriptus to Time. 79 Table X. Bes t - F i t t i n g Regression Equation Describing the A c t i v i t y Pattern of Limax maximus in Relation to Time. .93 Table XI. Response of Dercceras reti.cuj.atum to Light. .....111 Table XII. Outer Limits of A c t i v i t y for Light Intensity. ..118 Table XIII. Regression Equation Relating A c t i v i t y of Peroceras caruane to Surface Temperature. .............. 129 Table XIV. Limits of A c t i v i t y f o r Surface Temperature. ....132 Table XV. Regression Equation Relating A c t i v i t y of Deroceras reticulatum and Temperature...................133 Table XVI. Regression Equation for i i m a j maximus and Surface Temperature. ...................................137 Table XVII. Regression Equation f o r Cepaea -neforalis-and Surface Temperature ....................................141 Table XVIII. Regression Equation for Ariolimax cclumbianus and Surface Temperature. ..........145 Table XIX. Regression Eguation for Arion ater and Surface Temperature ............................................ 149 Tafcle XX. Regression Eguation for Arion subfuscus and Surface Temperature. ................................... 153 Table XXI. Regression Eguation for Arion circumscriptus and Surface Temperature. 156 Table XXII. Changes i n Behavior of Arion ater Subjected to a Temperature Increase. ................................167 Table XXIII. A c t i v i t y Limits Associated with Evaporation. .195 Table XXIV, Influence of Hydration on A c t i v i t y , ........... 204 Table XXV. Correlation C o e f f i c i e n t s Relating the A c t i v i t y of Molluscs to Environmental Parameters. ............... 216 Table XXVI. Summary of C o e f f i c i e n t s of Determination for Correlation-Regression Models Relating Molluscan A c t i v i t y to Environmental Parameters. .................. 231 Table XXVII. Frequency that Independent Factors Here Included i n Eguations Describinq A c t i v i t y of Nine Molluscan Species. .....................................232 Table XXVIII. Beqression Analysis Relating the A c t i v i t y of ix Peroceras reticulaturn to Concurrent Environmental Factors. 233 Table XXIX. Degression Analysis Relating the A c t i v i t y of A rion ater to Concurrent Environmental Factors. ........ 234 Table XXX, Regression Analysis Relating the A c t i v i t y of £££§.§5 nemoralis to Concurrent Environmental Factors. ..235 Table XXXI. Regression Analysis Relating the A c t i v i t y of Arielimax columbianus to Concurrent Environmental Factors. .... 2 3 6 Table XXXII. Regression Analysis Relating the A c t i v i t y of Limax Kaximus to Concurrent Environmental Factors....... 2 3 7 Table XXXIII. Regression Analysis Relating the A c t i v i t y of Arion subfuscus to Concurrent Environmental Factors. ...238 Table XXXIV, Regression Analysis Relating the A c t i v i t y of JLEISII hortensis to Concurrent Environmental Factors. . . , 2 3 9 Table XXXV, Regression Analysis Relating the A c t i v i t y of Arion circumscriptus • to Concurrent Environmental Factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 0 Table XXXVI. Regression Analysis Relating the A c t i v i t y of Peroceras caruanae to Concurrent Environmental Factors. 241 Table XXXVII. Regression Analysis Relating the Logarithm of Ac t i v i t y of Peroceras reticulaturn to Concurrent Heather. ..... ............... .................. ...................,,242 Table XXXVIII. Regression Analysis Relating the Logarithm of A c t i v i t y of Arion ater to Concurrent Heather.,,.,..,.243 Table XXXIX. Regression Analysis Relating the Logarithm of Ac t i v i t y of Cepaea nemoralis t o Concurrent Weather. ....244 Table XL. Regression Analysis Relating the Logarithm of X A c t i v i t y of Ariolimax columbianus to Concurrent Weather. .......... .................,...........................245 Table XLI. Regression Analysis Relating the Logarithm of A c t i v i t y of Limax maximus to Concurrent Heather. ....... 246 Table XLII. Regression Analysis Relating the Logarithm cf A c t i v i t y of Arjon subfuscus to Concurrent Heather. .....247 Table X1III. Regression Analysis Relating the Logarithm of A c t i v i t y of Arion hortensis to Concurrent Heather. ..... 248 Table XLIV. Regression Analysis Relating the Logarithm of A c t i v i t y of Arion cir^umscriptus •••to Concurrent Heather. 249 Table XIV. Regression Analysis Relating the Logarithm of A c t i v i t y of Deroceras caruanae to Concurrent Heather. .,250 Table XLVI. Regression Analysis Relating the A c t i v i t y of Deroceras retlculatum to Environmental Factors Hith lag-Heather ............................ .... .. 251 Table XLVII. Regression Analysis Relating the A c t i v i t y of Arion ater to Environmental Factors Hith Lag-Heather .,,252 Table XLVIII. Regression Analysis Relating the A c t i v i t y of Cegaea nemoralis to Environmental Factors Hith Lag-Heather ....................... ..... ...... .............. 253 Table XIIX. Regression Analysis Relating the A c t i v i t y cf Ariglimax Columbianus to Environmental Factors Hith Lag-Heather ......... .... 254 Table L. Regression Analysis Relating the A c t i v i t y of Limax JJSiSJH to Environmental Factors Hith Lag-Heather ......255 Table LI. Regression Analysis Relating the A c t i v i t y of Arion subfuscus to Environmental Factors Hith l a g -Heather ............. ......... .. ..256 Table I I I . Regression Analysis Relating the A c t i v i t y of Arign hortensis to Environmental Factors With lag-Weather 257 Table I I I I . Regression Analysis Relating the A c t i v i t y of hEJLQM circumscriptas to Environmental Factors With l a g -S € citing IT •* • • * * * « « * • •» •»• •«• • • *• # • •* # • •••••• * # • •- • «•••* *****^58 Table LIV, Regression Analysis Relating the A c t i v i t y of peroceras caruanae to Environmental Factors With Lag-Weather ... .............................................259 Table IV. Regression Analysis Relating the Logarithm of A c t i v i t y of Peroceras retlculatum to Environmental Factors With Lag-Weather .....260 Table IVI. Regression Analysis Relating the Logarithm cf Ac t i v i t y of Arion ater to Environmental Factors With Lag-Weather ..........................,,.•.....«..........261 Table LVII. Regression Analysis Relating the Logarithm cf A c t i v i t y of Cepaea nemoralis to Environmental Factors With Lag-Weather ...... .....262 Table IVIII. Regression Analysis Relating the Logarithm of A c t i v i t y of Ariolimax columbianus to Environmental Factors With Lag-Weather ............................... 263 Table LIX, Regression Analysis Relating the Logarithm of A c t i v i t y of Limax maximus to Environmental Factors With Lag-Weather ..................................,......... 264 Table IX. Regression Analysis Relating the Logarithm of A c t i v i t y of Arion subfuseus to Environmental Factors With Lag-Weather ..................«...... ...... ........ 265 Table LXI. Regression Analysis Relating the Logarithm cf x i i a c t i v i t y of Arion hortensis to Environmental Factors With Lag-Weather .............,......... ................266 Table LXII. Regression Analysis Relating the logarithm cf A c t i v i t y of Arion circumscriptus to Environmental Factors With Lag-Weather 267 Table LXIII. Regression Analysis Relating the Logarithm of A c t i v i t y of Dercceras caruanae to Environmental Factors With Lag-Weather ...............................,.......268 Table LXIV. Faeces and Homing of Arion a t e r . . . . . . . . . . . . . . . 285 Table LXV. History of Shelter Occupancy by Marked Ariolimax cclumbianus i n F i e l d Cages. ............................ 288 Table LXVI. Mann-Whitney O-Test of Whether Hoaing by ftJEi.oli5§x cclumbianus was Influenced by Conspecifics. ,.. 291 Table LXVII. Proportions of the Mollusc Populations that did not Return to Shelters i n F i e l d Cages During 1976. .293 Table LXVIII. Sheltering Locations of Limax•maxim us over a 39-day Period i n Cages With Either Five or Ten Shelters. , ... ,. 343 Table LXIX. Regression of Size of Limax maximus with the Sum of Their Positive and Negative Displacements from Ten Shelters. ..........................................345 Table LXX. Regression of Size of Limax maximus with the Sum of Their Positive and Negative Displacements from Five Shelters. .346 Table LXXI. Displacements from Shelter and Size of Limax-maximus. 347 Table LXXII. Displacement Interactions of Limax maximus i n Treatments with Five or Ten Shelters. .................. 351 x i i i Table LXXIII. Positive Associations of Limax maximus i n Treatments with Five cr Ten Shelters. .................. 352 Appendix I. Total Number of Each Hcllusc Species Present in Fi e l d Cages for Observation Days During 1976. .......... 443 xiv LIST OF FIGURES Figure 1. F i e l d Cages Used to Study T e r r e s t r i a l Molluscs During 1976. ...................... ..................... 7 Figure 2. F i e l d Cage I l l u s t r a t i n g the General Design and Method of Access. .......................,. ............. 7 Figure 3. A Typical A r t i f i c i a l S h e l t e r . . . . . . . . . . . . . . . . . . . . 7 Figure 4. Layout cf F i e l d Cages Used to Study the A c t i v i t y of T e r r e s t r i a l Molluscs During 1976. ................... 9 Figure 5. "Wellington" Evaporimeter used to Obtain a Relative Measure of Evaporation i n the F i e l d . .......... 15 Figure 6. General Features of Innate Rhythms of Motivation and A c t i v i t y . 23 Figure 7. A c t i v i t y Pattern of a Natural Population of Arion-ater. ....... ....................................,......28 Figure 8. Individual A c t i v i t y Patterns of Deroceras reticulatum. ............... ... .........................35 Figure 9. A c t i v i t y Pattern of Deroceras reticulatum entrained to L:D 800:0 f t - c . .....41 Figure 10. A c t i v i t y of Deroceras reticulatum i n the F i e l d . 43 Figure 11. A c t i v i t y Pattern of D§ rocgra s re t i culatum i n a L:£ 16:8 Photoperiod at 15° C. ......................... 47 Figure 12. A c t i v i t y of Deroceras reticulatum i n a Photo-Thermoperiod. .......................................... 49 Figure 13. A c t i v i t y of Deroceras reticulatum and Time. ....57 Figure 14. A c t i v i t y of Arion ater and Time. ............... 61 XV F i g u r e 15. A c t i v i t y o f Cepaea n e m o r a l i s and Time. .........64 F i g u r e 16. A c t i v i t y of Limax maximus and Time. ............67 F i g u r e 17. A c t i v i t y P a t t e r n of A r i c l i m a x columbianus and Time. ..............,................................... 70 F i g u r e 18. A c t i v i t y of A r i o n s u b f u s c u s and Time. .......... 73 F i g u r e 19. A c t i v i t y o f Deroceras caruanae and Time. ....... 76 F i g u r e 20. S e a s o n a l Changes i n P a t t e r n s o f A c t i v i t y . ......87 F i g u r e 21. S e a s o n a l Trends i n S c o t o p e r i o d and S h e l t e r Temperature. 89 F i g u r e 22. I n f l u e n c e o f Food on A c t i v i t y . ................. 96 F i g u r e 23. I n d i v i d u a l A c t i v i t y P a t t e r n s and Age. .......... 101 F i g u r e 24. A c t i v i t y o f A d u l t v s J u v e n i l e L i j n a j maximus on Two N i g h t s i n the F i e l d Cages. ......................... 103 F i g u r e 25. A c t i v i t y of Limax maximus and L i g h t . . . . . . . . . . . . 112 F i g u r e 26. A c t i v i t y of D e i p c e r a s r e t i c u l a t u m and L i g h t . ...114 F i g u r e 27. A c t i v i t y o f Ceuaea. ngmo.ralis and L i g h t . . . . . . . . . 116 F i g u r e 28. A c t i v i t y o f Deroqeras r e t i c u l a t u m i n R e l a t i o n t o Changes i n L i g h t I n t e n s i t y . ............................120 F i g u r e 29. A c t i v i t y of D e r o c e r a s caruanae and S u r f a c e Temperature. ............................,.............. 130 F i g u r e 30. A c t i v i t y o f Deroceras R e t i c u l a t u m and Temperature. 134 F i g u r e 31. A c t i v i t y o f L i n a x maximus and S u r f a c e Tern per a t ur e. ...»..««.«.,..««*.,.,««•«.*,,**......««**•.•* ,13 8 F i g u r e 32. A c t i v i t y o f Cepaea n e m p r a l l s and S u r f a c e Temperature. 142 F i g u r e 33. A c t i v i t y of A r i o l i m a x c c l u m b i a n u s and Temperature. 146 x v i F i g u r e 34. A c t i v i t y o f A r i o n a t e r and S u r f a c e Temperature. 150 F i g u r e 35. A c t i v i t y of Ajcion. s u b f u s c u s and S u r f a c e Temperature.,........................................... 154 F i g u r e 36. The I n f l u e n c e c f E v a p o r a t i v e S t r e s s Upon t h e A c t i v i t y o f p e r o c e r a s retjcula.tjum. ..................... 176 F i g u r e 37. The R e l a t i o n s h i p Between Vapor P r e s s u r e and Temperature a t 100% and 50% S a t u r a t i o n s . ....179 F i g u r e 38. C o r r e l a t i o n o f R e l a t i v e Humidity and Vapor P r e s s u r e D e f i c i t i n the F i e l d .......183 F i g u r e 39. c o r r e l a t i o n o f Vapor P r e s s u r e D e f i c i t w i t h E v a p o r a t i o n i n t h e F i e l d . ..............................185 F i g u r e 40. C o r r e l a t i o n o f R e l a t i v e H umidity w i t h E v a p o r a t i o n i n t h e F i e l d . .............................. 187 F i g u r e 41, A c t i v i t y of P e r o c e r a s r e t i c u l a t u m i n R e l a t i o n t o E v a p o r a t i o n Rate i n t h e F i e l d . ......................... 189 F i g u r e 42. A c t i v i t y o f P e r o c e r a s r e t i c u l a t u m i n R e l a t i o n t o R e l a t i v e Humidity i n t h e F i e l d . 191 F i g u r e 43. R e l a t i o n s h i p of A c t i v i t y of Dero.cer,as E S i i s a J a t u m t o Vapor P r e s s u r e D e f i c i t i n the F i e l d . ....193 F i g u r e 44. A e s t i v a t i o n Chamber of A r i o n s u b f u s c u s . ,.198 F i g u r e 45. A c t i v i t y of P e r o c e r a s r e t i c u l a t u m and Hind . ....211 F i g u r e 46. Flow C h a r t of the T h r e s h o l d A c t i v i t y M o d e l . . . . . 272 F i g u r e 47. P r e d i c t i o n s of A c t i v i t y f o r Limax maximus. ..... 274 F i g u r e 48. Homing o f M o l l u s c s Over t h e Season. ............ 294 F i g u r e 49. Temperature and H o l l u s c a n Homing. .............. 296 F i g u r e 50. T r a c k s of an I n d i v i d u a l Limax maximus- (Slug E) During i t s A c t i v i t y P e r i o d . ............................303 F i g u r e 51. T r a c k s of an I n d i v i d u a l Limax maximas (S l u g C) x v i i During i t s A c t i v i t y Period. ...............3C5 Figure 52. Relationship Between Size of Umax maximus and Displacements from Shelters. ........................... 348 Figure 53. Avoidance of Limax maximus by AgiSiilSJE cclumbianus. ........................................... 355 Figure 54. Avoidance of Limax maximus by Ar4P n ater. and Aricliraax Columbianus.............. ....................357 Figure 55a-e. Influence of Food and Aggression on the Distr i b u t i o n of Slugs. , 359 Figure 56. Limax maximus attacking an Arion ater. .........362 Figure 57. Sounds on Arion ater Resulting From Attacks by Ijpax maximus. ..,,............................w........ 362 Figure 58. Courtship of Peroceras caruanae. I l l u s t r a t i n g a Lunge. ,...... ... ,......,.... 362 Figure 59, Mantle-flapping Defense of Limax maximus Against an Attack by Carabus nemoralis. ........................ 364 Figure 60. I n i t i a l Stages of Mating of Limax maximus. .....364 Figure 61. Advanced Stages of Mating of Limatx ma.xigus. .. ..364 Figure 62. Courtship of Peroceras reticulatum. ............366 Figure 63. Mating of Arion ater...........................366 Figure 64. Mating of Arion subf uscus. ..................... 366 Figure 65. Mating of Cepaea nemoralis. ....................368 x v i i i ACKNOWLEDGEMENTS Very s p e c i a l t h a n k s are due t o my s u p e r v i s o r . Dr. If. G. W e l l i n g t o n , a thaumaturge o f s c i e n c e who t a u g h t me much of h i s magic. T h i s t h e s i s owes a g r e a t debt t o h i s e n t h u s i a s m , c o n s t r u c t i v e c r i t i c i s m , and f i n a n c i a l a s s i s t a n c e . My o t h e r committee members. Dr. ...V. R u n e c k l e s , Dr. J . H. Myers, and Dr. J . P. Kimmins a l s o c o n t r i b u t e d many i d e a s and h e l p f u l a d v i c e , Mr. R. B e r e s k a , Miss R. J a r e m o v i c , and Mis s S. E l l i o t t , s hared many o f t h e b o r i n g t a s k s and o f f e r e d many u s e f u l s u g g e s t i o n s . Mr.,Bereska, M i s s J a r e m o v i c , M i s s A. M a r i e , and Mrs. R, I y e r t r a n s l a t e d a number c f papers from French and German. I must a l s o thank Dr. G. Eaton f o r h i s i n v a l u a b l e s t a t i s t i c a l a d v i c e , and Mr. D. P i e r s e f o r h i s a s s i s t a n c e i n c o l l e c t i n g m e t e o r o l o g i c a l d a t a , and c a r r y i n g out t h e f i e l d s t u d i e s . Mr, S, Borden h e l p e d me w i t h t h e i n i t i a l p r e p a r a t i o n o f a c o m p u t e r i z e d d a t a - r e t r i e v a l system b e f o r e h i s d e a t h . Mrs, S, H a r r i s o n c a r r i e d on t h i s work. F i n a n c i a l a s s i s t a n c e f o r t h i s p r o j e c t was p r o v i d e d by the N a t i o n a l Research C o u n c i l c f Canada (NRC 67-6239), and t h e Canadian Department o f A g r i c u l t u r e (CDA 65-1016). S c h o l a r s h i p s were awarded by t h e N a t i o n a l Research C o u n c i l and by t h e U n i v e r s i t y of B r i t i s h Columbia ( K l l n k - M a c M i l l a n S c h o l a r s h i p ) . A l t h o u g h many c o l l e a g u e s p r o v i d e d t r a n s l a t i o n s , r e p r i n t s , and u s e f u l d i a l o g u e t h a t c o n t r i b u t e d t o t h i s t h e s i s . Dr. K. .Richter and Mr. M. Denny deserve s p e c i a l t hanks. x i x ' F i n a l l y I wish t o ' t n a n k s u p p o r t and e n d l e s s p a t i e n c e , company was the s l u g s i n the my w i f e , b i a n a , f o r her t i r e l e s s On many l o n g n i g h t s her o n l y r e f r i g e r a t o r , ; 1 INTRODUCTION-JOSTIFICATION L i t t l e i s known about s l u g s i n B r i t i s h Columbia (Hanna, 1966), a l t h o u g h t h e y a r e s e r i o u s a g r i c u l t u r a l and h o r t i c u l t u r a l p e s t s here ( B o l l o and W e l l i n g t o n , 1975), and thr o u g h o u t t h e w o r l d {Hunter and Bunham, 1971) . The development and a p p l i c a t i o n of s l u g c o n t r o l programs r e q u i r e s d e t a i l e d knowledge of t h e i r e c o l o g y and e t h o l o g y . E f f e c t i v e use of poisoned b a i t s , t h e most cooson c o n t r o l p r a c t i c e , r e q u i r e s d e t a i l e d knowledge o f t h e p a t t e r n s of a c t i v i t y and d i s p e r s i o n of t h e a n i m a l s , e s p e c i a l l y w i t h r e s p e c t t o weather. Knowledge o f t h e i n f l u e n c e o f m i c r o c l i m a t e on c r o p p e s t s i s a l s o n e c e s s a r y f o r c u l t u r a l c o n t r o l s d e s i g n e d t o a l t e r t he microenvironment o f t h e t a r g e t a n i m a l (reviewed by P i n t e r e t a l * . * . 1975) . a c t i v i t y p a t t e r n s , however, a r e t y p i c a l l y i d i s c o n t i n u o u s , and a r e i n f l u e n c e d by a v a r i e t y o f i n t e r a c t i n g exogenous and endogenous f a c t o r s . P r e d i c t i n g a c t i v i t y and i t s c o n c u r r e n t r a m i f i c a t i o n s has been d i f f i c u l t f o r a l m o s t e v e r y k i n d of a n i m a l because knowledge o f even t h e most t h o r o u g h l y s t u d i e d s p e c i e s o f t e n p e r m i t s o n l y broad g e n e r a l i z a t i o n s t h a t l e a d t o c o n f l i c t i n g i n t e r p r e t a t i o n s . For example, Johnson (1969) showed t h a t much o f e a r l i e r work on f l i g h t a c t i v i t y of i n s e c t s i s i n v a l i d due t o f a u l t y c o n c e p t u a l models (do t h e y f l y and r e t u r n , o r do t h e y f l y away?) and s t a t i s t i c a l t e c h n i q u e s ( t h r e s h o l d s vs r e g r e s s i o n s ) , ; Endogenous rhythms a f f e c t t he p r o b a b i l i t y o f a c t i v i t y i n d e p e n d e n t l y o f immediate weather f a c t o r s . T h e r e f o r e s t i m u l u s - r e s p o n s e 2 i n t e r p r e t a t i o n s o f f i e l d s i t u a t i o n s o f t e n prove f r u s t r a t i n g l y u n s u c c e s s f u l o r , i f a p p a r e n t l y s u c c e s s f u l , the approach may fee u l t i m a t e l y a i s l e a d i n g ( E n r i g h t , 1970). I n a r e c e n t comprehensive t r e a t m e n t o f s l u g a c t i v i t y , Crawford-Sidebotham (1971) c o n c l u d e d : " The d i f f i c u l t i e s e x p e r i e n c e d i n a t t e m p t i n g t o r e l a t e i t s f D e r o c e r a s r e t i c u l a t u m T a c t i v i t y t o a p a r t i c u l a r s e t o f weather parameters are i n agreement w i t h p r e v i o u s l y p u b l i s h e d o b s e r v a t i o n s . M I have f o c u s e d on t h r e e main a r e a s r e l e v a n t t o t h e a c t i v i t y and d i s p e r s i o n o f t e r r e s t r i a l m o l l u s c s . S e c t i o n I d e t a i l s t h e a c t i v i t y p a t t e r n s of t e r r e s t r i a l m o l l u s c s i n r e l a t i o n t o weather, and t h e f i n d i n g s a r e s y n t h e s i z e d w i t h p r e v i o u s l y p u b l i s h e d a c c o u n t s . I t i s i n t e n d e d as a model f o r f u t u r e s t u d i e s c o n c e r n e d w i t h t e r r e s t r i a l m o l l u s c s and o t h e r s h e l t e r - d e p e n d e n t a n i m a l s . S e c t i o n I I d e s c r i b e s homing b e h a v i o r , and f a c t o r s t h a t i n f l u e n c e i t . , S e c t i o n I I I i s a s t u d y of the a g o n i s t i c b e h a v i o r o f c e r t a i n s p e c i e s , an a s p e c t o f s l u g e t h o l o g y which has never b e f o r e been r e c o g n i z e d , b u t which promises t o be c r u c i a l t o u n d e r s t a n d i n g t h e i r d i s t r i b u t i o n and abundance. A l t h o u g h each of t h e s e s e c t i o n s i s a b l e t o s t a n d i n d e p e n d e n t l y o f t h e o t h e r s , t h e i r i n t e r r e l a t i o n s h i p p r e s e n t s an o v e r a l l p i c t u r e o f t h e b e h a v i o r a l e c o l o g y o f s l u g s . , 3 SECTION -Ji FACTORS INFLU ENCING THE ACTIVITY OF HOLLflSCS Ofi THE SOIL SUHIi£J FIELD MJTHOfiS. One problem greatly hampering f i e l d studies of animal a c t i v i t y i s the d i f f i c u l t y of accurately and guickly estimating population size. Without such information, errors r e s u l t i n g from immigration, emigration and recruitment cannot be eliminated from successive samples. To accurately estimate populations of most slugs requires the laborious procedures of s o i l sampling, flooding, and wet-sieve extraction (Thomas, 1944; South, 1964; Hunter, 1968a; Hollo and E l l i s , 1974). Most previous f i e l d studies of slug a c t i v i t y used a catch per unit e f f o r t method for estimating numbers; slugs along a predetermined route were counted at convenient i n t e r v a l s of time (e.g. Barnes and Weil, 1944,1945; White, 1959; Bett, 1960; Crawford-Sidebotham, 1972) . This method was c r i t i c i z e d by Van den Bruel and Moens (1958), South (1964), and Hunter (1968a) since l i g h t e r coloured species tend to be observed i n higher proportions than dark species, surface dwelling species are more l i k e l y to be found than subterranean species, and smaller species or immatures are less l i k e l y to be seen. But a major drawback of t h i s method for a c t i v i t y studies i s that data cannot be compared from d i f f e r e n t habitats or from di f f e r e n t sampling dates, because the counts are only r e l a t i v e . The number of slugs attracted to poisoned b a i t s i s another 4 c r i t e r i o n of a c t i v i t y (Hebley, 1962,1964) . However, baits r e f l e c t the a c t i v i t y of slugs more than the population s i z e (Sebley, 1962), and attra c t d i f f e r e n t species to varying degrees (Crawford-Sidebotham, 1970)., Mature slugs of some species are captured more readily than are immatures (Crawford-Sidebotham, 1971), and many slugs recover from the poison and escape-some species more than others (Crawford-Sidebotham, 1970). In addition, varying weather not only influences the a c t i v i t y of slugs, but also the e f f i c i e n c y of the baits (Cragg and Vincent, 1952) .u Richter (1973,1976b) found that slugs can be marked by branding them with l i q u i d nitrogen. He used marks to monitor the a c t i v i t y of s p e c i f i c i n d i v i d u a l s and to estimate population size by capture-release-recapture methods (eichter, 1976a). Marking i s suitable for observing the behavior of p a r t i c u l a r i n d i v i d u a l s , but when inferences at the population l e v e l , are required, and large numbers of animals must be counted in a short period, t h i s method becomes cumbersome. In the present study, i t had the further drawback that smaller species could not be e f f e c t i v e l y marked for quick i d e n t i f i c a t i o n at night. Hunter (1968a) found that mark-release-recapture methods underestimated populations of slugs compared with s o i l sampling. In a heterogeneous environment, slug shelters w i l l vary considerably i n quality with respect to water, temperature, brightness, and food, and consequently the behavior of slugs inhabiting them w i l l vary.„- Besides food i n s i d e shelters, the distance that the organise must t r a v e l to food i n the v i c i n i t y , and the qua l i t y and quantity obtained w i l l also vary i n such a 5 h a b i t a t , and may i n t r o d u c e f u r t h e r c o n f o u n d i n g v a r i a t i o n i n b e h a v i o r . I n o r d e r t o a v o i d t h e problems a s s o c i a t e d w i t h n a t u r a l s h e l t e r s , I d e s i g n e d e x p e r i m e n t a l cages i n which I c o u l d c o n t r o l t h e e n v i r o n m e n t a l f e a t u r e s t h o u g h t t o be i m p o r t a n t t o t e r r e s t r i a l s l u g s . Four cages were c o n s t r u c t e d about 50 m from t h e 'Plant S c i e n c e Weather S t a t i o n a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , such t h a t f o u r 1.4 m x 5 m a r e a s o f s h o r t - c u t s o d were e n c l o s e d i n . s l u g - p r o o f 40 mesh/cm w h i t e p o l y e s t e r f i b r e c a n o p i e s ( F i g u r e 1).,Any s l u g s a c t i v e on t h e s h o r t - c u t sod c o u l d be e a s i l y o b s e r v e d , and i t p r o v i d e d v i r t u a l l y no n a t u r a l s h e l t e r s . S l u g s do n o t a c t i v e l y burrow, but use n a t u r a l c r e v i c e s i n t h e s o i l ( f i o l l o , 1974) so p o s s i b l e s u b t e r r a n e a n s h e l t e r s were e l i m i n a t e d by compressing t h e sod. The p e r i m e t e r o f t h e cage was surrounded by a wooden r i m 10 cm h i g h X 2 cm wide. T h i s r i m was h e l d f l u s h t o the s o i l s u r f a c e by 30 cm s t a k e s hammered i n t o t h e ground. & l a y e r o f f i n e sand about 6 cm deep was p l a c e d a l o n g i t s i n s i d e edge t o p r e v e n t s l u g s from e s c a p i n g underneath o r from s h e l t e r i n g t h e r e . T h i s c o m b i n a t i o n proved t o be an i m p e n e t r a b l e b a r r i e r f o r a l l t h e mo l l u s c a n s p e c i e s s t u d i e d . S e m i c i r c u l a r a r c h e s of bent 2.2 m l e n g t h s o f f l a t i r o n (6 cm X 0.5 cm), p a i n t e d w i t h r u s t - r e s i s t a n t p a i n t were a t t a c h e d t o the wooden r i a a t e g u a l i n t e r v a l s i n each cage (6 per c a g e ) . T h e maximum h e i g h t o f t h e cage was 70 cm. On one s i d e o f t h e cage, a p o l y e s t e r canopy was a t t a c h e d d i r e c t l y t o the wooden r i m , whereas on the o t h e r s i d e , t h e canopy was a t t a c h e d t o a 5 m l e n g t h o f 5 cm X 2 cm wood t h a t was 6 f a s t e n e d t o the r i m w i t h wing n u t s and b o l t s . L i f t i n g t h i s s i d e of the canopy gave a c c e s s t o t h e cages ( F i g u r e 2 ) . The ends of t h e cages were s e a l e d w i t h c u t p i e c e s o f p o l y e s t e r f i b r e . Ten p o t t e r y f l o w e r p o t s ; 19 cm i n d i a m e t e r X 19.5 cm deep, were e q u a l l y spaced i n s i d e each cage and s e t i n t o t h e ground so t h a t a 30 cm X 30 cm X 5 cm wooden pl a n k c o v e r i n g each pot was l e v e l w i t h t h e s u r f a c e o f t h e sod. The p o t s were l i n e d w i t h a r o l l o f m oist newspaper t o i n c r e a s e i n s u l a t i o n and h u m i d i t y . ( F i g u r e 3) . l e t t u c e and c a r r o t r o o t were p r o v i d e d between the s h e l t e r s a t f o u r e q u i d i s t a n t l o c a t i o n s i n each cage. S l u g s r a r e l y a t e t h e g r a s s , and t h e o n l y o t h e r greens a v a i l a b l e were o c c a s i o n a l d a n d e l i o n l e a v e s . A l l s p e c i e s a t e some, of the newspaper i n s i d e the s h e l t e r s , but t h e more s u b t e r r a n e a n s p e c i e s a t e more of i t . Dead s l u g s o r s n a i l s were a l s o e a t e n , b u t I removed t h e s e when p o s s i b l e . si S i n c e l e t t u c e and c a r r o t were t h e p r e f e r r e d v e g e t a b l e foods,, t h e e x p e r i m e n t a l d e s i g n a l l o w e d c l o s e c o n t r o l of the a v a i l a b l e f o o d . The l a y o u t o f t h e cages i s shown i n F i g u r e 4. 7 F i g u r e 1. F i e l d Cages Used t o Study T e r r e s t r i a l M o l l u s c s D u r i n g 1S76, Showing t h e P l a n t S c i e n c e Heather S t a t i o n i n t h e Background, F i g u r e 2, F i e l d Cage I l l u s t r a t i n g t h e G e n e r a l D e s i g n and Method of A c c e s s , F i g u r e 3, A T y p i c a l A r t i f i c i a l S h e l t e r w i t h t h e C o v e r i n g Plank Bemoved t o show t h e C l a y Flower P o t and Paper Liner.,, 9 Figure 4, Layout of Field Cages Used to Study the Activity of Terrestrial Molluscs During 1976. .0-65 m 0 - 8 5 m •00 m •I ! m 1 0 0 m f 0 - 8 5 m f 0- 6 5 m 1 K)-55m-» • m o . o H a o 00 o I 1= SHELTERS W 3 AREAS n m CAGES O = FOOD LOCATIONS 1-4 m-5 m Z 2 11 I c o l l e c t e d s l u g s e a r l y i n May from v a r i o u s h a b i t a t s around Vancouver, and d i s t r i b u t e d them e q u a l l y among t h e s h e l t e r s w i t h i n t h e cages. Seven s p e c i e s were used i n i t i a l l y : t he s l u g s Decoceras r e t i c u l a t u m ^ A r i o n a t e r rufus^. A r i 2 i i h 2 r t g u s i s x JrJ&n. c i r c u m s c r i p t u s , Ariolima,x sp2umjbi,an,usx and Lim, ax. majijuis.* and t h e s n a i l Cegaga n e m o r a l i s . I n June, •Derocer.as carunae- and A r i o n s u b f u s c u s were added, b r i n g i n g the t o t a l t o n i n e s p e c i e s . I n J u l y and August, IJL c^r^umsc£i£tu§ and I x hjaj&ensis d i e d i n the f i e l d cages and r e p l a c e m e n t s c o u l d not be o b t a i n e d u n t i l f a l l when t h e s e s p e c i e s a g a i n moved c l o s e r t o t h e s o i l s u r f a c e . However, t h e s e s l u g s proved t o be almost t o t a l l y s u b t e r r a n e a n i n h a b i t except d u r i n g s p r i n g and f a l l , so the l o s s of d a t a d u r i n g summer was n o t c o n s i d e r e d i m p o r t a n t . Only cages 2 and 4 were used d u r i n g May. Cages 1 and 3 were r e s e r v e d f o r s t u d y i n g t h e homing b e h a v i o r of A. colu m b i a n u s and the i n t e r a c t i o n s o f A. c o l u m b i a n u s . J j i l a ^ i i u s ^ and A, 7;gter,.-A c t i v i t y was mon i t o r e d i n a l l cages on each o b s e r v a t i o n n i g h t . The a c t i v i t y of s l u g s was m o n i t o r e d o v e r 24-hour p e r i o d s i n August and September, 1975, i n n a t u r a l h a b i t a t s , and i n May, 1976 i n the cages. These t r i a l s showed t h a t an o b s e r v a t i o n p e r i o d from 4:00 pm u n t i l 9:00 am the next morninq i n c l u d e d t h e major a c t i v i t y p e r i o d o f t h e s p e c i e s under i n v e s t i g a t i o n , b u t sometimes o b s e r v a t i o n s c o n t i n u e d u n t i l 10:00 am. The a n i m a l s r e a d i l y a c c e p t e d t h e a r t i f i c i a l s h e l t e r s , and a l l s p e c i e s r e t u r n e d t o t h e i r s h e l t e r s a f t e r f o r a q i n g a t the f e e d i n g s t a t i o n s a t n i g h t . One n i g h t ' s d a t a c o n s i s t e d o f c o u n t i n g how many s l u g s were a c t i v e (=outside s h e l t e r s ) e v e r y hour from 4:00 pm u n t i l 9:00 am. In t h e case of Cepaea. a n i m a l s 12 were termed a c t i v e i f the body was e x t r u d e d from t h e s h e l l , s i n c e i n d i v i d u a l s f r e q u e n t l y c l i m b e d t h e canopy and a t t a c h e d t h e m s e l v e s t h e r e , r a t h e r than r e t u r n i n g t o the s h e l t e r s , Heather parameters measured d u r i n g each o b s e r v a t i o n i n c l u d e d ! L i g h t i n t e n s i t y Hind speed Temperature ( i n s i d e s h e l t e r , and a t h e i g h t s of Ocm, 10cm and 30cm) E v a p o r a t i o n (a r e l a t i v e measure u s i n g a i e l l i n g t o n e v a p o r i m e t e r ( B e l l i n q t o n , 1949a)) R e l a t i v e h u m i d i t y vapor p r e s s u r e d e f i c i t B a r o m e t r i c p r e s s u r e A l l weather f a c t o r s e x c e p t wind speed and b a r o m e t r i c p r e s s u r e were measured i n s i d e the cage. O b s e r v a t i o n s on Hay, 1 1 r 1 2 were made t o det e r m i n e t h e e f f e c t o f t h e canopy on l i g h t and t e m p e r a t u r e . /During the day t h e g r e a t e s t d i f f e r e n c e i n s o d te m p e r a t u r e w i t h i n and o u t s i d e t h e canopy o c c u r r e d a t ground l e v e l . Daytime s u r f a c e t e m p e r a t u r e s were as much as 6.9° C h i g h e r on t h e unshaded sod. L i g h t i n t e n s i t y was reduced by as much as 50%. At n i g h t , t h e r e was a "greenhouse" e f f e c t w i t h i n t h e cage so t h a t s u r f a c e t e m p e r a t u r e s were as much as 2° C h i g h e r under t h e canopy. Soo d f o r d (1973) s t u d i e d t h e e f f e c t of a s i m i l a r w h i t e t e r y l e n e canopy on t h e c l i m a t e w i t h i n a 3.7m X 3.7m X 1.8m h i g h f i e l d c age, and r e s u l t s o f the p r e s e n t s t u d y agree w i t h h i s ( l i g h t , r e d u c t i o n from 42% up t o 5 8 % ) . A l t h o u g h wind speed was 13 not measured i n s i d e t h e canopy i n t h e p r e s e n t s t u d y , Woodford (1973) found t h a t t h i s f a c t o r was s i g n i f i c a n t l y a f f e c t e d i n h i s ca g e s , w i t h a g r e a t e r t h a n 851 r e d u c t i o n . A l t h o u g h r e l a t i v e h u m i d i t y was s i m i l a r i n s i d e and o u t s i d e t h e f i e l d c a g e s , t h e r e d u c t i o n of wi n d , l i g h t , and r e s u l t i n g t e m p e r a t u r e g r a d i e n t s would be. expected t o reduce e v a p o r a t i o n r a t e . ,. I n o r d e r t o a c c u r a t e l y measure the environment e x p e r i e n c e d hy t h e s l u g s and s n a i l s , most weather f a c t o r s were measured i n s i d e of t h e cage, Heasurements i n cage 2 were t a k e n t o r e p r e s e n t c o n d i t i o n s i n the o t h e r c a g e s , and s h e l t e r t e m p e r a t u r e was always o b t a i n e d from a probe l o c a t e d a t the bottom o f s h e l t e r 2. S i n c e b a r o m e t r i c p r e s s u r e was not i n f l u e n c e d by t h e cages, i t was o b t a i n e d from a B e l f o r t m icrobarograph a t t h e Weather S t a t i o n . A r e l a t i v e measure o f wind was o b t a i n e d frcm a G a s s e l l a 3 cup anemometer, l o c a t e d 0.91 m above s h o r t - c u t s o d a t the Weather S t a t i o n . S i n c e wind speed was o n l y a r e l a t i v e measure, n ot t a k e n a t t h e a n i m a l s ' l e v e l , i t was not measured i n s i d e t h e cage. Summer o b s e r v a t i o n s s u g g e s t e d t h a t , w i t h o u t the a m e l i o r a t i n g i n f l u e n c e o f the cage canopy, the h a b i t a t would be too s e v e r e f o r some o f t h e s p e c i e s , i f s h e l t e r s a l o n e were p r o v i d e d . The i n f l u e n c e o f the p o l y e s t e r canopy was n o t u n l i k e the e f f e c t o f a r e l a t i v e l y s p a r s e p l a n t canopy, a common a s p e c t of t h e h a b i t a t o f s l u g s and s n a i l s . T h e r e f o r e t h e d e p a r t u r e o f c o n d i t i o n s i n s i d e t h e cage from t h e exposed s u r r o u n d i n g s was not t o o a r t i f i c i a l . A r e l a t i v e measure o f e v a p o r a t i o n r a t e was o b t a i n e d u s i n g an e v a p o r i f f l e t e r s i m i l a r t o t h a t d e s c r i b e d by W e l l i n g t o n (1949a), 14 c o n s t r u c t e d from 15 ca-20 cm l e n g t h s o f 0.5 mm bore c a p i l l a r y t u b i n g ( F i g u r e 5 ) . One s i d e of the tube was co v e r e d w i t h masking t a p e , t h u s p r o v i d i n g a background t o view the p o s i t i o n o f t h e water column i n the tub e . T r a n s p a r e n t c e l l o p h a n e tape was p l a c e d on a m e t a l t r a y , and a mm s c a l e was drawn on i t w i t h I n d i a i n k . The tape was then p e e l e d o f f t h e m e t a l and t r a n s f e r r e d t o the uncovered s i d e o f t h e c a p i l l a r y tube. The e n t i r e t u b e , e x c e p t f o r t h e ends, was then c o a t e d i n s e v e r a l l a y e r s o f t r a n s p a r e n t n a i l p o l i s h t o water proof i t . A s u p p l y o f 6mm paper d i s c s was made w i t h a paper punch. A s t a n d was c o n s t r u c t e d by c u t t i n g one deep, and one s h a l l o w *V* on o p p o s i t e s i d e s o f the r i m of a p l a s t i c cup. D u r i n g measurements t h e e v a p o r a t i n g s u r f a c e was kept a t the same h e i g h t above t h e ground as t h e i n l e t f o r t h e m o t o r r d r i v e n psychrometer (used t o o b t a i n measurements o f B.H. and V. P. D.) s i n c e Humphreys (1975) found t h a t l a r g e B.H., d i f f e r e n c e s o c c u r r e d by moving t h e i n l e t v e r t i c a l l y by as l i t t l e as 0.5cm. 15 F i q u r e 5. " W e l l i n g t o n " E v a p o r i m e t e r used t o O b t a i n a R e l a t i v e Measure of E v a p o r a t i o n i n the F i e l d . ! FILTER PAPER D I S C (6mm 0 ) P L A S T I C S T A N D 0-5 mm B O R E C A P I L L A R Y T U B E WITH mm S C A L E 17 The e v a p o r i m e t e r was f u n c t i o n a l when a f i l t e r - p a p e r d i s c was a t t a c h e d t o one end of the w a t e r - f i l l e d c a p i l l a r y t u b e . E v a p o r a t i o n r a t e c o u l d then be measured as fflm3/minute. ^The tube was f i l l e d by p l a c i n g t h e f i l t e r - p a p e r d i s c on one end and t h e n t r a n s f e r r i n g water t o i t u s i n g a b r u s h , so i t f i l l e d by c a p i l l a r y a c t i o n . I f t h i s f a i l e d , a hypodermic n e e d l e was used, Another problem not mentioned by W e l l i n g t o n (1949a) was t h a t t h e r e was u s u a l l y an excess o f water on t h e d i s c i n i t i a l l y , and t h i s had t o e v a p o r a t e b e f o r e t h e column began t o move. T h i s was e s p e c i a l l y i m p o r t a n t when e v a p o r a t i o n r a t e s were v e r y low. T i n y a i r spaces sometimes o c c u r r e d between t h e paper and the water column so t h a t t h e y were net connected. These had t o foe removed b e f o r e the a p p a r a t u s c o u l d be used.. The c a p i l l a r y tube was always mounted s o t h a t i t s l o p e d downwards towards t h e f i l t e r paper d i s c . O b s e r v i n g the water column a t n i g h t w i t h a f l a s h l i g h t proved d i f f i c u l t , e s p e c i a l l y i f c o n d e n s a t i o n formed on t h e i n s t r u m e n t . Adding s e v e r a l drops of r e d food c o l o u r i n g t o a l i t r e o f water p r o v i d e d a s o l u t i o n e a s i l y v i s i b l e i n t h e column. Machin (1975) p o i n t e d o u t t h a t t h e presence o f d i s s o l v e d s o l u t e s has a l m o s t no i n f l u e n c e on e v a p o r a t i o n r a t e , e x cept a t h u m i d i t i e s v e r y near 100%, when the e f f e c t i s v e r y s m a l l . T h e r e f o r e , a d d i n g a s m a l l amount o f f o o d c o l o u r i n g would not be expected t o i n f l u e n c e the performance o f th e e v a p o r i m e t e r s i g n i f i c a n t l y . L i g h t i n t e n s i t y was measured i n f t - r c a n d l e s w i t h a K a h l s i c o model 268WA620 l i g h t meter e g u i p e d w i t h a 17.6X r e d u c t i o n f i l t e r f o r i n t e n s i t i e s o v e r 500 f t - c a n d l e s . Temperature was r e c o r d e d w i t h a YSI model 42SC t e l e - t h e r m o m e t e r and a model 4002 m u l t i p l e 18 s w i t c h box. R e l a t i v e h u m i d i t y (R.H.) was o b t a i n e d w i t h a Bendex model 566 m o t o r - v e n t i l l a t e d psychrGmeter. Vapor p r e s s u r e d e f i c i t was then c a l c u l a t e d from t h e s a t u r a t e d vapor p r e s s u r e (S.v.P.) f o r t h e a p p r o p r i a t e t e m p e r a t u r e , o b t a i n e d from t a b l e s a c c o r d i n g t o the f o r m u l a : V.P.D. = S. V.P.-((S.V.P. X B. H. )/100) Vapor p r e s s u r e d e f i c i t s were c a l c u l a t e d f o r one s t a n d a r d atmosphere, s i n c e Humphreys (1915) p o i n t e d out t h a t t h e c o m p r e s s i b i l i t y f a c t o r i s very s m a l l over a wide range o f b a r o m e t r i c p r e s s u r e s , t e m p e r a t u r e s , and r e l a t i v e h u m i d i t i e s . The l e n g t h of t h e n i g h t { s c o t o p e r i o d ) , the time o f s u n s e t ( p h a s e ) , and t h e p e r c e n t a g e o f f u l l moon were o b t a i n e d from t a b l e s and c a l e n d a r s a t the Heather S t a t i o n . O b s e r v a t i o n s began i n mid-May, about one month a f t e r s l u g s became f u l l y a c t i v e i n t h e f i e l d , and c o n t i n u e d u n t i l most a c t i v i t y had c e a s e d i n l a t e O c t o b e r . The s h e l t e r s were watered the day b e f o r e an e x p e r i a e n t , u n l e s s t h e y were a l r e a d y damp, t o ensure t h a t a l l the m o l l u s c s were f u l l y h y d r a t e d • The g r a s s was c u t a t t h e same ti m e i n o r d e r t o f a c i l i t a t e o b s e r v a t i o n o f a c t i v e , a n i m a l s . H o u r l y o b s e r v a t i o n s were made d u r i n g 21 n i g h t s , a l t h o u g h on some o c c a s i o n s r a i n or f r o s t d i s r u p t e d a sequence (the p o l y e s t e r canopy became t r a n s l u c e n t when wet, so o b s e r v a t i o n s were t e r m i n a t e d ) . I m m e d i a t e l y f o l l o w i n g a n i g h t ' s o b s e r v a t i o n s the s h e l t e r s were opened and t h e t o t a l p o p u l a t i o n o f s l u g s and s n a i l s was t a b u l a t e d . . C a r e f u l s e a r c h e s were c a r r i e d out f o r any s l u g s or s n a i l s t h a t had not r e t u r n e d t o s h e l t e r s . £ep.aea s n a i l s were a s p e c i a l problem s i n c e they f r e g u e n t l y c l i m b e d the cage canopy and 19 a t t a c h e d t h e r e , or e l s e formed a s h a l l o w d e p r e s s i o n on t h e s o i l s u r f a c e and r e s t e d t h e r e , o r i e n t e d w i t h t h e a p e r t u r e d i r e c t e d upwards and co v e r e d w i t h an epiphragm. Any a n i m a l s found o u t s i d e the s h e l t e r s were r e t u r n e d t o t h e n e a r e s t one, and t h e p r o p o r t i o n of t h e p o p u l a t i o n which had f a i l e d t o r e t u r n home was re c o r d e d . O b s e r v a t i o n s from week t o week showed t h a t t h e a c c u r a c y o f the census was 100$ f o r t h e l a r g e r s p e c i e s i n v o l v e d . Even f o r s m a l l e r s l u g s , which sometimes found s h e l t e r i n s o i l f i s s u r e s o r earthworm burrows, a c c u r a c y was very c l o s e to 100%. Appendix I g i v e s the o b s e r v a t i o n d a t e s and t h e t o t a l number o f s l u g s and s n a i l s i n v o l v e d f o r each s p e c i e s . The d a t a from a l l the cages were p o o l e d d u r i n g the f i n a l a n a l y s i s , and t h e p r o p o r t i o n o f the p o p u l a t i o n a c t i v e was used as t h e dependent v a r i a b l e . T h i s a l l o w e d comparison o f d a t a among d i f f e r e n t s p e c i e s , and from d i f f e r e n t s a m p l i n g d a t e s . , LABORA2211 l i lHQpS I t was d e s i r a b l e t h a t l a b o r a t o r y r e s u l t s be d i r e c t l y comparable t o t h e f i e l d s t u d y . I n most e x p e r i m e n t s , t h e r e f o r e , t h e s l u g s were p r o v i d e d w i t h cages t h a t had s h e l t e r s and a f o r a g i n g a r e n a c o n t a i n i n g t h e f o o d s u p p l y . Two cage d e s i g n s were used i n the m a j o r i t y of l a b o r a t o r y e x p e r i m e n t s . In t h e f i r s t t h e s h e l t e r c o n s i s t e d o f a s t r a i g h t - s i d e d bowl, 9 cm deep, and 18 cm i n d i a m e t e r . / The bottom was l i n e d w i t h moistened paper t o w e l s t o ensure 100% RH. A c i r c u l a r p i e c e 20 of p l e x i g l a s s was c o t t o c o v e r the t o p of t h i s b o w l , w i t h a 2.5 cm h o l e t o a l l o w the s l u g s t o emerge from t h e s h e l t e r . T h i s l i d was s p r a y - p a i n t e d opaque b l a c k . , A t u b e was c o n s t r u c t e d from 1 mm t h i c k , t r a n s p a r e n t p l a s t i c t o f i t over t h e bowl and extend 15 cm above the l e v e l of the l i d . That p a r t o f the tube t h a t surrounded the bowl was a l s o p a i n t e d b l a c k t o keep t h e s h e l t e r dark. Another t r a n s p a r e n t bowl was i n v e r t e d over t h e open end of the t u b e , t o p r e v e n t s l u g s from e s c a p i n g when t h e y emerged from t h e dark s h e l t e r t o the upper, t r a n s p a r e n t s e c t i o n . The l i d c o v e r i n g t h e s h e l t e r was c o v e r e d w i t h paper t o w e l s on i t s upper s i d e , so t h a t s l u g s emerging from t h e s h e l t e r had a damp s u b s t r a t e t o c r a w l on. S l i c e d c a r r o t r o o t was u s u a l l y p r o v i d e d i n a s m a l l d i s h i n t h e upper s e c t i o n of t h e cage.. The a c t i v i t y cages were s e t i n s i d e growth chambers upon 3 cm t h i c k p i e c e s of foam r u b b e r , so t h a t t h e s l u g s were i s o l a t e d from v i b r a t i o n s ( i n t h e f i e l d c a g e s , A. c o l u m f r i a B U s f r e q u e n t l y became a c t i v e when I c u t t h e g r a s s i n t h e m i d d l e o f the day). S l u g s were i n i t i a l l y p l a c e d i n s i d e t h e s h e l t e r s , and the cages were t h e n p l a c e d i n t h e d e s i r e d e x p e r i m e n t a l c o n d i t i o n s . ( I f t h e s l u g s were not p l a c e d i n s i d e t h e s h e l t e r i n i t i a l l y , some i n d i v i d u a l s r e q u i r e d a number o f days t o d i s c o v e r i t and r e t u r n at t h e a p p r o p r i a t e t i m e s ) . S i n c e the growth chambers were f r e q u e n t l y opened f o r o b s e r v a t i o n s , a sheet o f t r a n s p a r e n t p l a s t i c was a t t a c h e d i n s i d e t h e door of the chambers, so t h a t t h e r e was l i t t l e exchange o f a i r between the chamber and t h e room when t h e door was open. F i n a l l y , t h e chambers were housed i n s i d e a dark room so t h a t t h e r e was not much change i n l i g h t 21 i n t e n s i t y when t h e door was opened. In t h e second t y p e o f cage, wooden boxes were l i n e d w i t h p l a s t i c sheet t o p r o t e c t them from m o i s t u r e and f a c i l i t a t e c l e a n i n g . M o i s t e n e d paper t o w e l s were p l a c e d o v e r t h e bottom o f t h e box, and c l a y f l o w e r p o t s , w i t h two n o t c h e s c u t i n o p p o s i t e s i d e s o f t h e i r r i m s t o s e r v e as d o o r s , were i n v e r t e d i n the box as s h e l t e r s . These were a l s o l i n e d w i t h moistened paper t o w e l s . The p o t s were t y p i c a l l y a r r a n g e d i n a c i r c l e around a c e n t r a l d i s h o f c a r r o t r o o t and/or l e t t u c e . A l t h o u g h t h e s i z e o f t h e boxes, and t h e number and s i z e o f t h e s h e l t e r s v a r i e d among e x p e r i m e n t s , most boxes were 61 cm X 61 cm X 12 cm h i g h , w i t h f l o w e r p o t s about 10 cm deep X 8 cm i n d i a m e t e r . Each box had a g l a s s l i d . ( The cages were p l a c e d i n a w a l k - i n e n v i r o n m e n t a l chamber s e t t o t h e d e s i r e d c o n d i t i o n s o f temperature and photo p e r i o d . INNATE BHYTHMS In t r o d u c t i o n : Serne G e n e r a l P r o p e r t i e s Of Bhythms P h y s i o l o g i c a l and b e h a v i o r a l a c t i v i t i e s of most a n i m a l s e x h i b i t endogenous r h y t h m i c i t y (Saunders, 1976). Bhythms of v a r i o u s l e n g t h s a l l o w a n i m a l s t o s y n c h r o n i z e i m p o r t a n t f u n c t i o n s w i t h e n v i r o n m e n t a l parameters which c y c l e a t p a r t i c u l a r p e r i o d i c i t i e s . Thus, c i r c a n n u a l rhythms have a p e r i o d of about one y e a r , l u n a r rhythms 29.75 days, c i r c a d i a n rhythms 24 hours and t i d a l rhythms 12,4 h o u r s . A 27-day rhythm c o r r e s p o n d i n g t o t h e r o t a t i o n o f t h e sun on i t s a x i s has been proposed as w e l l 22 {Bennett, 1974). The l i t e r a t u r e concerned w i t h " c h r o n o b i o l o g y " i s voluminous. Some major works o r r e v i e w s of r e l e v a n c e t o t h e p r e s e n t s t u d y a r e B a r k e r (1958, 1961,1964),, papers c o n t a i n e d i n t h e 1960 C o l d S p r i n g Harbor symposium on b i o l o g i c a l c l o c k s (Chovnick, 1960) , Cloudsley-Thompson (1961K, S s c h o f f (1965), S o l l b e r g e r (1965), Beck (1968), D a n i l e s k y e t a l ^ ( 1 9 7 0 ) , Palmer (1970), Bunning (1973), Bennett (1974), and Saunders (1976). The f o l l o w i n g g e n e r a l d i s c u s s i o n i s a s y n t h e s i s o f i n f o r m a t i o n from t h e s e v a r i o u s works, C i r c a d i a n rhythms are most r e l e v a n t t o t h e p r e s e n t s t u d y , a l t h o u g h c i r c a n n u a l and l u n a r rhythms may e v e n t u a l l y be shown t o be i m p o r t a n t i n t e r r e s t r i a l m o l l u s c s . The g e n e r a l p r o p e r t i e s o f a l l rhythms a r e s i m i l a r , however. To f a c i l i t a t e d i s c u s s i o n . F i g u r e 6 p r o v i d e s a g e n e r a l model of t h e c i r c a d i a n rhythm of a p o p u l a t i o n of n o c t u r n a l a n i m a l s . The phase o f t h e rhythm r e f e r s to i t s r e l a t i o n s h i p i n time t o the e n t r a i n i n g e n v i r o n m e n t a l parameter, i n t h i s c a s e l i g h t . Thus t h e peak i n a c t i v i t y o c c u r s at a s p e c i f i c t i m e a f t e r l i g h t i n t e n s i t y f a l l s below a c r i t i c a l v a l u e . . The p e r i o d o f t h e rhythm i s t h e time between s u c c e s s i v e r e c u r r e n c e s of some f e a t u r e such as the peak i n a c t i v i t y . The a c t i v i t y p e r i o d r e f e r s t o t h e t i m e t h a t t h e a n i m a l s a r e a c t i v e . , 23 Figure 6.. General Features of Innate Rhythms of Motivation and Activity. T l V E 25 The number of animals active can never be less than zero and thus i s represented by a square wave. However, i t i s conventional to represent the rhythm as a complete oscillation. On a physiological level this i s probably justified since Bunning (1973), Bennett (1974), and Saunders (1976) offer numerous examples of rhythms of responsiveness to various factors, that show the complete range of oscillation. Thus, sensitivity to light, temperature, and various poisons or drugs frequently cycle with a sinusoidal wave form. Similarly, the locomotor speed or reaction time of certain snails and earthworms are known to vary so that they are greatest durinq the normal activity period.,Bunning (1973) further notes that the sensitivity of the rhythm to be entrained by appropriate environmental factors i s i t s e l f a response rhythm, beinq much more sensitive durinq some phases of the rhythm. The complete oscil l a t i o n , shown on the l e f t hand axis, represents the animal's readiness and abi l i t y to respond to appropriate stimuli. The right what would actually be observed in the f i e l d , "amplitude", according, to most authors refers to the range between the peak and the trough of any entrained response. /In the present study, however, amplitude will refer to the degree of activity of the population of animals. Circadian rhythms have several important properties which should be discussed. F i r s t l y the period of the rhythi i s relatively independent of temperature (0.10=0.8-1.3) , over a wide range. Thus, temperature does not cause the clock tc slow or accelerate appreciably except at the extremes of the organism's physiological range. The peak in activity w i l l occur at the same 26 t i m e each n i g h t d e s p i t e i n t e r v e n i n g hot or c o l d days. An e n v i r o n m e n t a l f a c t o r t h a t e n t r a i n s an endogenous rhythm i s termed a " z e i t g e b e r " . The z e i t g e b e r i s a s t a n d a r d which t h e organism u t i l i z e s t o keep i t s s c h e d u l e i n phase w i t h the environment. F o r example, the rhythm might be an a d a p t a t i o n t o a v o i d p e r i o d s o f i n t o l e r a b l e heat or e v a p o r a t i o n , whereas t h e z e i t g e b e r c o u l d be l i g h t c y c l e s , f a r more p r e d i c t a b l e as a t i m e -s e t t e r (Cloudsley-Thompson, 1962). A l a r g e number o f p e r i o d i c a l l y r e c u r r i n g e n v i r o n m e n t a l f a c t o r s a r e c a p a b l e of f u n c t i o n i n g as z e i t g e b e r s i n v a r i o u s s p e c i e s . L i g h t and t e m p e r a t u r e c y c l e s , i n t h a t o r d e r , a r e the two most i m p o r t a n t o f t h e s e , a l t h o u g h such d i v e r s e t h i n g s as r e l a t i v e h u m i d i t y , sound, e l e c t r i c f i e l d s , f o o d , and s o c i a l cues a l s o may s y n c h r o n i z e rhythms. I f t h e t i m i n g of a z e i t g e b e r changes, the i n t e r n a l rhythm a d j u s t s i t s e l f so t h a t i t s phase i s once a g a i n p r o p e r l y a l i g n e d (termed a phase s h i f t ) . I f t h e s h i f t i n t h e e n t r a i n i n g c y c l e i s v e r y g r e a t , t h e rhythm r e q u i r e s s e v e r a l days t o become p r o p e r l y read-justed. The i n t e r v e n i n g , i n c o r r e c t l y phased p a t t e r n s a r e c a l l e d t r a n s i e n t s . I n the f i e l d , s m a l l phase s h i f t s a l l o w p l a n t s and a n i m a l s t o a d j u s t t o s e a s o n a l changes i n t h e d r i v i n g e n v i r o n m e n t a l c y c l e s . More t h a n one z e i t g e b e r may s i m u l t a n e o u s l y e n t r a i n t h e same rhythm, and t h i s can l e a d t o c o m p l i c a t e d i n t e r a c t i o n s i f t h e e n t r a i n i n g c y c l e s become g r e a t l y d i s s o c i a t e d . Host i m p o r t a n t from a s t a n d p o i n t o f p r e d i c t i n g a c t i v i t y i n the f i e l d i s t h a t t h e rhythm has a d e f i n i t e p a t t e r n . Most t y p i c a l i s the unimodal peaJt i l l u s t r a t e d i n F i g u r e 6. However, 27 b imodal rhythms are common ( A s c h o f f , 1966), and rhythms of even g r e a t e r m o d a l i t y a r e known ( B a r k e r , 1964) . The peak ; may o c c u r e a r l y or l a t e i n t h e a c t i v i t y p e r i o d . A n i m a l s w i t h bimodal rhythms, when one peak i s l a r g e r t h e y a r e s a i d t o have a " bigeminus" p a t t e r n (second peak s m a l l e r ) , o r an " a l t e r n a n s " p a t t e r n (second peak l a r g e r ) ( A s c h o f f , 1966). The i n f l u e n c e o f weather f a c t o r s i s superimposed upon t h i s endogenous b e h a v i o r a l p a t t e r n i n f i e l d s i t u a t i o n s , and a t t e m p t s t o i n t e r p r e t a c t i v i t y i n terms o f weather w i t h o u t c o n s i d e r i n g t h e i n n a t e rhythm can l e a d t o b a f f l i n g or m i s l e a d i n g r e s u l t s ( E n r i g h t , 1970). F i g u r e 7 p r o v i d e s an example from a n a t u r a l p o p u l a t i o n of A r i o n a t e r . T h e a c t i v i t y p a t t e r n a f t e r s u n s e t shows a r a p i d i n c r e a s e i n a c t i v i t y t o an e a r l y e v e n i n g peak. A c t i v i t y t h e n f a l l s o f f g r a d u a l l y throughout t h e n i g h t . S i n c e t emperature f a l l s t h r o u g h o u t t h e n i g h t , a r e s e a r c h e r working from 6:00 pm t o m i d n i g h t would o b t a i n e x c e l l e n t n e g a t i v e c o r r e l a t i o n s o f a c t i v i t y w i t h t e m p e r a t u r e . The same o b s e r v e r w o r k i n g from m i d n i g h t u n t i l 9:00 am would o b t a i n p o s i t i v e c o r r e l a t i o n s . The g r a d u a l f a l l i n a c t i v i t y f o l l o w i n g the e a r l y peak was not e x p l a i n e d by l i g h t i n t e n s i t y , t e m p e r a t u r e , o r e v a p o r a t i o n r a t e s which were monitored c o n c u r r e n t l y . White (1959) observed a s i m i l a r f a l l i n numbers o f D. r e t i c u l a t u m as t h e n i g h t p r o g r e s s e d . As w i l l be shown, the p a t t e r n o f a c t i v i t y d e p i c t e d i n F i g u r e 7 i s t y p i c a l o f t h e c i r c a d i a n a c t i v i t y rhythm o f s l u g s e n t r a i n e d t o l i g h t o r t e m p e r a t u r e c y c l e s . 28 Figure 7 . , a c t i v i t y Pattern of a Natural Population of Arion /ater on a Vancouver Lawn, August 21-22, 1975. 3AI10V y31V NOTW dO H39WnN 30 Heather f a c t o r s tend t o a l t e r the a m p l i t u d e of s l u g s ' i n n a t e rhythms of a c t i v i t y . D e s p i t e t h e v a s t l i t e r a t u r e c oncerned w i t h c h r o n o b i c l o g y , most o f the r e s e a r c h i s c o n cerned with t h e mechanism of t h e c l o c k ( e . g . , I s i t endogenous? How i s i t t emperature compensated?), or c h a r a c t e r i s t i c s o f t h e f r e e r u n n i n g rhythms ( i n t h e absence o f z e i t g e b e r s ) , e s p e c i a l l y t h e l e n g t h of the p e r i o d . B a r k e r (1961) obs e r v e d t h a t v e r y l i t t l e work had been done on t h e f a c t o r s t h a t i n f l u e n c e the a m p l i t u d e of t h e rhythm, and t h i s i s s t i l l t r u e today. While c h r o n o b i o l o g i s t s have c o n c e n t r a t e d upon l a b o r a t o r y s t u d i e s o f t h e c l o c k i t s e l f , most f i e l d e c o l o g i s t s have c o n t i n u e d a t t e m p t s t o r e l a t e a c t i v i t y d i r e c t l y t o weather i n t y p i c a l F r a n k e l and Gunn (1940) s t y l e , d e s p i t e warnings by A s c h o f f (1966), Johnson (1969), and E n r i g h t (1970) t h a t changes i n the a m p l i t u d e and t i m i n g o f a c t i v i t y may not be c l o s e l y r e l a t e d t o c o n c u r r e n t weather c o n d i t i o n s a t a l l . I have attempted t o a n a l y s e t h e a c t i v i t y p a t t e r n s o f t e r r e s t r i a l m o l l u s c s w h i l e c o n s i d e r i n g b o t h endogenous r h y t h m i c i t y and t h e i n f l u e n c e o f weather. Endogenous R h y t h m i c i t v Of M o l l u s c a Bennett (1974) has a c h a p t e r r e v i e w i n g some l i t e r a t u r e concerned w i t h r h y t h m i c i t y o f M o l l u s c a , e s p e c i a l l y marine forms. C o n c e r n i n g t e r r e s t r i a l m o l l u s c s , Szymanski (1918) found a daytime a c t i v i t y p a t t e r n i n t h e s n a i l H e l i x pomatia s u b 1 e c t e d t o d a y - n i g h t changes i n i l l u m i n a t i o n and temperature./Howes and H e l l s (1934a,b). H e l l s (1944) , and B i c h a r d s o n (1972) found e v i d e n c e f o r endogenous r h y t h m i c i t y i n weight f l u c t u a t i o n s o f H, p c m a t i a . Cepaea n e m o r a l i s . A r i o n a t e r . and Ij.ma.x-' f l a v u s 31 a l t h o u g h of a n o n - c i r c a d i a n n a t u r e ( P e r i o d l e n g t h o f s e v e r a l days f o r the s n a i l s ) . T e r c a f s (1961) demonstrated t h a t t h e d i u r n a l rhythm of t h e s n a i l , ' O x jchij-us q e j l a r i u s . p e r s i s t e d i n t h e c o n s t a n t c o n d i t i o n s of s u b t e r r a n e a n c a v e s . Henne (1963) found t h a t t h e a c t i v i t y p a t t e r n of - Polygyra•-••albo.lafrris-- (Say) was e n t r a i n e d by l i g h t c y c l e s , and Stephens and Stephens (1966) found endogenous rhythms i n ; H e l i x a s p e r s a . Cameron (1970a) s i m i l a r l y showed t h a t t h e a c t i v i t y rhythms o f Cepaea h o r t e n s i s , •• - ^ ^ i ^ e m o r a l i s ^ -and- Arian§av :ar-bustQ:rum- .-.were:: e n t r a i n e d by l i g h t c y c l e s . B a i l e y (1975) found t h a t a c t i v i t y o f <- r a s p e r s a -e n t r a i n e d t o l i g h t c y c l e s but he a l s o found e v i d e n c e t h a t t emperature c y c l e s f u n c t i o n e d a s a z e i t g e b e r . I n c o n t r a s t t o t h e e a r l y r e s u l t s o f Szymanski (1918), o t h e r a u t h o r s have found p r e d o m i n a n t l y n o c t u r n a l a c t i v i t y i n s n a i l s . The o n l y e v i d e n c e f o r rhythms o f a n o n - c i r c a d i a n p e r i o d i c i t y among s l u g s i s i n S e g a l ' s s t u d y (1959) showing t h a t Limax f l a v u s m a i n t a i n s an a n n u a l rhythm o f egg l a y i n g under c o n s t a n t c o n d i t i o n s . An annual rhythm of oxygen consumption has a l s o been r e p o r t e d f o r the s n a i l , A r i a n t a arbustorum. by Wieser e t a l . • (1970). D a i n t o n (1954a) f i r s t d i s c o v e r e d t h a t s l u g s possessed an i n n a t e c i r c a d i a n rhythm. She f o u n d t h a t D. r e t i c u l a t u m was e n t r a i n e d by temperature c y c l e s , and t h a t t h e rhythm p e r s i s t e d i n c o n s t a n t c o n d i t i o n s f o r 4-5 d ays.^Attempts t o e n t r a i n the s l u g s t o l i g h t c y c l e s a t c o n s t a n t t e m p e r a t u r e s were not s u c c e s s f u l . / S e w e l l (1965a,b,1968) o b s e r v e d t h a t t h e a c t i v i t y p a t t e r n o f p. - i-rgtlcu|aturn • was c l o s e l y t i e d t o l i g h t c y c l e s , and suggested t h a t t h e s e e n t r a i n e d a d i u r n a l rhythm o f p o s i t i v e and n e g a t i v e 32 r e s p o n s e s t o g r a v i t y which a l l o w e d s l u g s t o emerge a t t h e p r o p e r time from s h e l t e r s remote from immediate changes of l i g h t and tempe r a t u r e on the s o i l s u r f a c e . T h i s was based on t h e o b s e r v a t i o n by Frandsen (1901) t h a t l i g h t caused Limax mafi,mcs t o move towards t h e e a r t h . That l i g h t c y c l e s w i l l e n t r a i n the c i r c a d i a n rhythms of s l u g s was demonstrated by Lewis (1967,1969b) w i t h jS^ a t e r . He was unable t o show e n t r a i n m e n t by temperature c y c l e s , as was p r e v i o u s l y c l a i m e d by D a i n t o n (1954 ) . Lewis (1967,1969b) found t h a t t h e rhythm p e r s i s t e d i n c o n s t a n t c o n d i t i o n s f o r s e v e r a l days, and c o u l d not be e n t r a i n e d t o c y c l e s o f l i g h t much d i f f e r e n t t h a n t h o s e o f 24 hours (e.g. 18.5-30.0 h ) , b o t h o f which f i n d i n g s i n d i c a t e a t r u l y endogenous rhythm (Bunning, 1973). The f r e e - r u n n i n g rhythm had a p e r i o d o f 22-23.5 h, a f a c t t h a t Lewis (1967,1969b) suggested would h e l p t h e s l u g s a d j u s t t o s e a s o n a l changes i n t h e environment. However, such d e v i a t i o n s from e x a c t l y 24 h a r e common i n f r e e - r u n n i n g rhythms, whereas i n t h e f i e l d t h e p e r i o d i s e x a c t l y e n t r a i n e d ( H a r k e r , 1964; Bu n n i n g , 1973). a l t h o u g h a r r h y t h m i c s l u g s r e a d i l y s y n c h r o n i z e d t o 1:D c y c l e s w i t h i n about f o u r days, an i n c o n s i s t e n t r e s u l t was o b t a i n e d when e n t r a i n e d s l u g s were exposed t o a 6 hour phase s h i f t of t h e p h o t o p e r i o d . Even a f t e r 11 days t h e a c t i v i t y p a t t e r n had n o t r e s y n c h r o n i z e d ( L e w i s , 1967). A t r u l y c i r c a d i a n rhythm s h o u l d have e x h i b i t e d a t l e a s t some phase s h i f t i n g i n r e s p o n s e t o such a s t i m u l u s , so t h i s work d e s e r v e s r e p e a t i n g * ( P i n d e r (1969) performed an i n t e r e s t i n g e x periment u s i n g D e r o c e r a s reticu1atum» a l t h o u g h h i s s m a l l sample s i z e w a r r a n t s some c a u t i o n . He found t h a t both temperature and l i g h t c y c l e s 33 e n t r a i n e d t h e a c t i v i t y o f t h e -slugs• Hhen t h e t e m p e r a t u r e c y c l e was s h i f t e d out of phase w i t h t h e l i g h t c y c l e by 12 h, the s l u g s p a t t e r n o f a c t i v i t y s h i f t e d t o c o i n c i d e w i t h t h e t e m p e r a t u r e c y c l e . , A g a i n t h e rhythm p e r s i s t e d f o r 3-4 days i n c o n s t a n t c o n d i t i o n s . I n e x p e r i m e n t s on t h e homing b e h a v i o r of Lt, ym^xjmus, G e l p e r i n (1974) found t h a t t h e s l u g s were a c t i v e o n l y d u r i n g t h e dark p e r i o d o f a L:D 12:12 p h o t o p e r i o d . , T h e most d e t a i l e d s t u d y o f c i r c a d i a n r h y t h m i c i t y i n a s l u g i s t h a t of S o k o l c v e g t al*. (1977) on L t maximus. The a c t i v i t y rhythm was found t o be endogenous, temperature-compensated (Q1Q=G.99+/-0.01 SE) and e n t r a i n e d by l i g h t c y c l e s . The rhythm p h a s e - s h i f t e d i n r e s p o n s e to s h i f t s i n t h e e n t r a i n i n g l i g h t c y c l e , and t r a n s i e n t s o c c u r r e d when the s h i f t s were r e l a t i v e l y g r e a t . The f r e e - r u n n i n g rhythm showed a p e r i o d s l i g h t l y l e s s than 24 h o u r s . A l t h o u g h t h e p o s s e s s i o n of a c i r c a d i a n rhythm by s l u g s has been d e f i n i t e l y e s t a b l i s h e d , no s t u d y has r e c o g n i z e d t h e f u l l i m p o r t a n c e o f t h i s rhythm when r e l a t i n g s l u g a c t i v i t y t o weather. At b e s t , s e v e r a l a u t h o r s have suggested t h a t t h e rhythm a l l o w s s l u g s t o *know» when t o emerge from s h e l t e r , a f t e r which they have been assumed t o r e a c t o n l y t o weather i n a s t i m u l u s -response manner (e.g. N e w e l l , 1965a,1968; L e w i s , 1967,1969a,b). The most d e t a i l e d s t u d i e s d e a l i n g w i t h t h e c i r c a d i a n a c t i v i t y rhythms have been m a i n l y concerned w i t h c h a r a c t e r i z i n g t h e rhythm, o r p r o v i n g t h a t i t i s endogenous (L e w i s , 1967,1969b; Sokolove g t 1977) . The a c t i v i t y p a t t e r n e x h i b i t e d i n F i g u r e 7 i s a p o p u l a t i o n p a t t e r n , and t h e main t h r u s t of t h e p r e s e n t s t u d y has been a t 34 that level. However, the pattern of activity of individual slugs i s discontinuous, a fact previously noted by Newell (1965a,1966), and Daxl (1969). Figure 8 provides some examples of the activity pattern of individual r p« -} re ti,c ulaturn - en tr ained to a L:D 12:12 photoperiod in the laboratory. The slugs were housed individually in cages constructed from two jars, each 8.5 cm in diameter and 10 cm deep. The lower jar was painted black and was lined with moist paper towels. The upper jar was inverted over this to form a transparent enclosure. The two jars were separated by an opague floor i n which there was a small hole to allow the slugs access either way. Carrot root was placed on the floor in the upper jar. The slugs typically rested in the lower jar when the lights were on, and emerged to feed during the dark period. There are distinct individual differences in the pattern of activity i n the Figure./ For example, slug #2 tended to have short intervals of activity interspersed with short intervals inside the shelter. In contrast, slug #4 had much longer periods of activity, interspersed with short returns to shelter. 35 Figure 8. Individual Activity Patterns of Ten Peroceras reticulatum. Observed on Three Different pays. CJ ro — CJ ro w N - u ro — w ro <J> ro C J r o — o j r o — OJ ro S L U G DAY r 8:00 am 9:00 LIGHTS OFF 1 0 0 0 l|:00 - 12:00 - hOOpm —t 2 0 0 3:00 h 4:00 5:00 (- 6:00 7:00 8:00 9:00 LIGHTS ON L I0:00 37 C o r r e c t l y d e c i p h e r i n g the o v e r a l l a c t i v i t y p a t t e r n s o f s l u g s w i l l u l t i m a t e l y depend on a knowledge o f t h e a c t i v i t i e s o f t h e i n d i v i d u a l s c o m p r i s i n g the p o p u l a t i o n , and how t h e y p a r t i t i o n t h e i r v a r i o u s a c t i v i t i e s i n time, Among c e r t a i n i n s e c t s , v a r i o u s a c t i v i t i e s such as f e e d i n g , m a t i n g , o v i p c s i t i o n , and t r a v e l are r i g i d l y sequenced i n a c i r c a d i a n p a t t e r n (e.g. C a l d w e l l and ; D i n g l e , 1967) . R e s e a r c h e f f o r t s a r e now b e i n g f o c u s e d on t h e r e l a t i o n s h i p of s h o r t - t e r m rhythms ( p e r i o d s o f a c t i v i t y a s s o c i a t e d w i t h f e e d i n g , e x c r e t i o n , l o c o m o t i o n e t c . ) , and the o v e r a l l c i r c a d i a n p a t t e r n , e s p e c i a l l y among a n i m a l s t h a t show r e g u l a r l y r e c u r r i n g .short, a c t i v i t y p a t t e r n s (e.g. S t e b b i n s , 1975; Lehmann, 1976). A l t h o u g h t h e p a t t e r n s i l l u s t r a t e d i n F i g u r e 8 show t h a t s l u g a c t i v i t y i s d i s c o n t i n u o u s , and t h a t t h e r e i s l e s s v a r i a t i o n w i t h i n i n d i v i d u a l s than among them, t h e r e does not appear t c be much r e g u l a r i t y of s p e c i f i c a c t i v i t i e s w i t h i n or between days. The v a r i o u s k i n d s o f a c t i v i t i e s f o l l o w g e n e r a l , but n o t r i g i d , p a t t e r n s i n s l u g s . D e f e c a t i o n o c c u r r e d m o s t l y d u r i n g t h e day when s l u g s were i n s h e l t e r s . F e e d i n g and mating o c c u r r e d most f r e q u e n t l y d u r i n g the peaks of g e n e r a l a c t i v i t y , but a l s o l e s s f r e q u e n t l y t h r o u g h o u t t h e d i e ! c y c l e . For example, P* E f j i c u l a t u m and A. columbianus were observed mating i n s i d e s h e l t e r s a t midday. F o r t h e most p a r t , however, s l u g s remained i n a r e s t i n g p o s i t i o n d u r i n g t h e day (body c o n t r a c t e d and t e n t a c l e s w i t h d r a w n ) , moving o r f e e d i n g v e r y l i t t l e . R i c h t e r (1976a), showed t h a t the p r o p o r t i o n o f A, c o l u m b i a n u s engaged i n v a r i o u s t y p e s o f a c t i v i t i e s v a r i e d w i t h d i f f e r e n t k i n d s o f weather. O b s e r v a t i o n s i n both t h e 38 l a b o r a t o r y and f i e l d by t h e p r e s e n t a u t h o r showed t h a t when g e n e r a l a c t i v i t y was l i m i t e d by u n f a v o u r a b l e weather, s l u g s c o n c e n t r a t e d upon o b t a i n i n g f o o d . Much o f t h e time n o r s a l l y spent c r a w l i n g o r " r e s t i n g " was e l i m i n a t e d . Thus t h e r e d u c t i o n o f the a m p l i t u d e o f t h e p o p u l a t i o n rhythm may i n v o l v e q u a l i t a t i v e as w e l l a s q u a n t i t a t i v e changes i n a c t i v i t y . An e x t e n s i o n of t h e p r e s e n t s t u d y i s examining the a c t i v i t y of t h r e e s l u g s p e c i e s w i t h t h i s d i s t i n c t i o n i n mind. , The d i s c o n t i n u i t i e s i n t h e i n d i v i d u a l a c t i v i t y p a t t e r n s u s u a l l y p r e v e n t t h e a m p l i t u d e o f a p o p u l a t i o n p a t t e r n from r e a c h i n g 100%.,Each s p e c i e s appears t o e x h i b i t a c h a r a c t e r i s t i c .Population p a t t e r n . For example. L. maximus tends t o have a s h o r t a c t i v i t y p e r i o d o f h i g h a m p l i t u d e ( F i g u r e 1 6 ) , whereas &. c c l u m b i a n u s tends t o have a l o n g a c t i v i t y p e r i o d o f low a m p l i t u d e ( F i g u r e 17). D a x l (1969) showed t h a t d i f f e r e n c e s i n t h e i n d i v i d u a l p a t t e r n s o f a c t i v i t y c o u l d account f o r d i f f e r e n c e s i n p o p u l a t i o n p a t t e r n s among s e v e r a l s p e c i e s o f s l u g s . / • • • I n l a b o r a t o r y e x p e r i m e n t s , s l u g s seemed t o e x h i b i t v a r i o u s degrees of e n t r a i n m e n t t o l i g h t c y c l e s , i n a L:D 12:12 (L:D=300:0 f t - c ) p h o t o p e r i o d a t 15° C, • B. r e t i c u l a t u m and A. a t e r were most a c t i v e d u r i n g t h e dark phase o f t h e c y c l e , b u t t h e i n c r e a s e i n a c t i v i t y l a g g e d c o n s i d e r a b l y behind l i g h t s - o f f , and o f t e n peaked l a t e i n t h e dark phase. C o n s i d e r a b l e a c t i v i t y a l s o extended i n t o t h e l i g h t phase. L e w i s (1967) s i m i l a r l y found t h a t a c t i v i t y o f e n t r a i n e d --Ay-vater o f t e n c o n t i n u e d i n t o t h e l i g h t p e r i o d , a l t h o u g h i n the f i e l d a c t i v i t y was m a i n l y f i n i s h e d by s u n r i s e . N e w e l l (1968) r e c o r d e d t h a t Df ^ r e t i c u l a t u m o f t e n 39 r e t u r n e d home b e f o r e s u n r i s e . I n t h e p r e s e n t s t u d y , mggimns proved t o be much more s e n s i t i v e t o l i g h t t h a n t h e o t h e r s p e c i e s (see T a b l e XXV), and was r e a d i l y e n t r a i n e d . Sokolove e t a l A (1977) found good e n t r a i n m e n t t o l i g h t c y c l e s u s i n g t h i s s p e c i e s , but t h e r e was o f t e n a b u r s t of a c t i v i t y a t l i g h t s - o n u n t i l t h e a n i m a l a p p a r e n t l y a d a p t e d t o the r u n n i n g wheels used as a c t o g r a p h s . I have never o b s e r v e d such b u r s t s i n t h e f i e l d * The b e h a v i o r o f D. r e t i c u l a t u m and A f a t e r i n t h e p r e s e n t s t u d y s u ggested t h a t t h e y were r e a c t i n g i n a p a r t i a l l y exogenous manner t o t h e l i g h t c y c l e , and t h a t t h e i r a c t i v i t y rhythm was not w e l l e n t r a i n e d . ^ D u r i n g t h e s e i n i t i a l e x p e r i m e n t s c a r e had been t a k e n t o remove t h e p o s s i b l e i n f l u e n c e of temperature c y c l e s i n o r d e r t o s t u d y t h e i r b e h a v i o r s t r i c t l y i n response t o l i g h t . The p h o t o p e r i o d was m a i n t a i n e d u s i n g f l o u r e s c e n t l i g h t s , s u f f i c i e n t l y removed from the s l u g s t o minimize h e a t i n g e f f e c t s , and t h e e x p e r i m e n t s were c a r r i e d out i n c o n t r o l l e d e n v i r o n m e n t a l chambers. n e a r l y " t y p i c a l " a c t i v i t y p a t t e r n s c o u l d o n l y be o b t a i n e d by moving t h e s l u g s much c l o s e r t o t h e l i g h t s , i n o r d e r t o i n c r e a s e t h e l i g h t i n t e n s i t y t o about 800 f t - c a n d l e s d u r i n g t h e l i g h t p h a s e . . F i g u r e 9 shows a t y p i c a l l a b o r a t o r y p a t t e r n f o r HM. I§ii£fllaiai i n such c o n d i t i o n s . The f a c t t h a t a c t i v i t y b e g i n s s l i g h t l y b e f o r e the l i g h t s go o f f , and dec r e a s e s r a p i d l y j u s t b e f o r e they come on a g a i n , i n d i c a t e s t h e o p e r a t i o n o f t h e endogenous c l o c k . I n o r d e r t o o b t a i n such l i g h t i n t e n s i t i e s , t h e i n t r o d u c t i o n of some temperature f l u c t u a t i o n s were u n f o r t u n a t e l y u n a v o i d a b l e * F i g u r e 10 i l l u s t r a t e s t h e t y p i c a l a c t i v i t y p a t t e r n of D. r e t i c u l a t u m from the f i e l d . The l a b o r a t o r y r e s u l t s ( F i g u r e 40 9 ) , although showing entrainment to the light cycle, s t i l l depart considerably from the f i e l d pattern. The early peak of activity, followed by a decrease through the night, i s missing. 41 Figure 9. A c t i v i t y Pattern of Dercceras• -.retj.c;alatflm entrained to L:D 800:0 f t - c . PROPORTION OF POPULAT ION A C T I V E (N=2I) 43 Figure 10. Activity Pattern of pe'roqer^ s---yretic-ul.atqm;^ .. on •• Two Nights in May and June, Showing Concurrent Evaporative Bates. 44 o o o o o o O o o c o CD r~ cr> tn ro c\J _ — 6 6 6 6 6 6 6 6 6 3 A 10V N O I l V i n d O d dO NOIiyOdOHd o o 45 The c o n c l u s i o n drawn from t h e l a b o r a t o r y e x p e r i m e n t s was t h a t t h e c r i t i c a l l i g h t t h r e s h o l d which e n t r a i n s the c i r c a d i a n rhythm v a r i e s w i t h t h e s p e c i e s , and i s u n u s u a l l y h i g h f o r some. Lx J i l i i a S nas the l o w e s t t h r e s h o l d ( l e s s t h a n about 200 f t -c a n d l e s ) , whereas, A. c o l u m b i a n u s appears t o have one c l o s e t o or s l i g h t l y h i g h e r t h a n that,, o f A.A ater, • J u a t e r . a n d £4./£§ti£alat!li appear t o have a c r i t i c a l t h r e s h o l d between 400-600 f t - c a n d l e s . N o t i c e i n F i g u r e 7 t h a t even i n t h e middle o f the day, one A. a t e r became a c t i v e as t h e l i g h t i n t e n s i t y f e l l t hrough t h i s v a l u e . , Getz (1963) p r e v i o u s l y f o u n d e v i d e n c e o f d i f f e r e n c e s i n t h r e s h o l d s among v a r i o u s s p e c i e s o f m o l l u s c s . I t i s l i k e l y t h a t l i g h t and t e m p e r a t u r e e f f e c t s a r e never t r u l y s e p a r a t e d i n t h e f i e l d . F i g u r e 11 shows the a c t i v i t y p a t t e r n o f 24 D. r e t i c u l a t u m i n L:D 16:8 (300:0 f t - c ) a t 15° C. They. had been i n these c o n d i t i o n s f o r 5 days b e f o r e t h e o b s e r v a t i o n s and i t i s c l e a r t h a t , a l t h o u g h a c t i v i t y i s g r e a t e r i n t h e dark and d e c r e a s e s a f t e r t h e l i g h t s come on, t h e r e i s no d ecrease b e f o r e t h e l i g h t s come on as t y p i c a l l y o c c u r s i n t h e f i e l d . The same c o n d i t i o n s e n t r a i n e d - L t maximus and C. n e m o r a l j s s u c c e s s f u l l y . D a i n t o n (1954a) p r e v i o u s l y found t h a t r e t i c u l a t u m had a c i r c a d i a n a c t i v i t y rhythm t h a t was e n t r a i n e d by t e m p e r a t u r e c y c l e s . A t e m p e r a t u r e o f 21° C appeared t o be a c r i t i c a l t h r e s h o l d , r i s i n g t e m p e r a t u r e s above t h i s t h r e s h o l d , and f a l l i n g ones below i t , i n d u c i n g movement. D a i n t o n (1954a) d i d not p r o v i d e s h e l t e r s f o r h e r a n i m a l s * and a c t i v i t y was s c o r e d as t o whether t h e s l u g s were moving o r not. .Thus her r e s u l t s were not i n a form t h a t c o u l d be d i r e c t l y compared w i t h f i e l d a c t i v i t y 4 6 patterns. In addition, Lewis (1967,1969a,b), has questioned whether temperature cycles . entrain slugs at a l l , since he was unable to entrain A,^  ater with temperature c y c l e s . A temperature cycle, r i s i n g and f a l l i n g through the c r i t i c a l threshold of 21° C, was tested i n the present study to provide further information on t h i s aspect of entrainment. Figure 12 shows the a c t i v i t y pattern of 12 D. reticulatum entrained to i d e n t i c a l conditions as those i n Figure 11, but with a H:L 16:8 (23-15° C) thermoperiod reinfor c i n g the l i g h t regime. Only with the associated thermoperiod does the a c t i v i t y pattern of t h i s species resemble that occurring i n the f i e l d ; an early peak after sunset, followed by a decline throughout the night (Figure 10). 47 F i g u r e 11. A c t i v i t y P a t t e r n o f P e r o c e r a s r e t i c u l a t u m i n a L:P 16:8 P h o t o p e r i o d at 15° C. P R O P O R T I O N OF P O P U L A T I O N A C T I V E 7:00 8:00 9:00 10:00 11=00 12:00 | 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 49 F i g u r e 12. A c t i v i t y P a t t e r n o f D e r o c e r a s r e t i c u l a t u m i n L:D 16:8 P h o t o p e r i o d and H:L 16:8 <23°-15° C) Thermo p e r i o d . P R O P O R T I O N OF P O P U L A T I O N A C T I V E NO DATA 51 I n summary, the e v i d e n c e shows t h a t t h e a c t i v i t y rhythm o f s l u g s can be e n t r a i n e d t o l i g h t c y c l e s . T h i s r e s p o n s e was shown by t h e f a c t t h a t L. maximus was e n t r a i n e d by l i g h t i n t e n s i t i e s so low t h a t t e m p e r a t u r e f l u c t u a t i o n s c o u l d be e l i m i n a t e d , . However, i n o t h e r s p e c i e s t h e t h r e s h o l d s a r e so h i g h t h a t t h e p o s s i b i l i t y o f t h e i r r e a c t i n g t o s l i g h t temperature f l u c t u a t i o n s c o u l d n o t be t o t a l l y e l i m i n a t e d . I n a l a t e r s e c t i o n on t h e e f f e c t s o f l i g h t , an experiment i s d e s c r i b e d which shows t h a t s l u g s w i l l d e f i n i t e l y r e s p o n d t o l i g h t i n t e n s i t y when tempe r a t u r e i s c a r e f u l l y c o n t r o l l e d , so i t i s l i k e l y t h a t e n t r a i n m e n t t o l i g h t c y c l e s i s a common f e a t u r e of the a c t i v i t y rhythms of a l l s p e c i e s i n t h e f i e l d . A lthough L e w i s (1967,1969 ) does not s a y what l i g h t i n t e n s i t y was used f o r e n t r a i n m e n t , he s t a t e s i n h i s t h e s i s t h a t he c o u l d not i n d u c e the rhythm w i t h o u t using i n c a n d e s c e n t as w e l l as f l o u r e s c e n t l i g h t s , which s u g g e s t s t h a t he used a f a i r l y h i g h l i g h t i n t e n s i t y . T h e h i g h l i g h t t h r e s h o l d f r e q u e n t l y r e q u i r e d t o e n t r a i n t h e rhythm undoubtedly e x p l a i n s why D a i n t o n (1954a) c o u l d not e n t r a i n DyNretiteu/l^tum-to l i g h t c y c l e s . She used an i n t e n s i t y of o n l y 40 f t - c , c l e a r l y t o o low t o have any e f f e c t , as p r e s e n t r e s u l t s i n d i c a t e . , S i m i l a r l y , L ewis (1967,1969 ) was unable t o e n t r a i n J ^ M a i t o t e m p e r a t u r e c y c l e s . However, he used t e m p e r a t u r e s i n t h e range o f 12-189 c. Even f o r D. r e t i c u l a t u m the t h r e s h o l d i s 2 1 * C, and my f i e l d o b s e r v a t i o n s s u ggest t h a t ?a€§r i s more t o l e r a n t o f h i g h t e m p e r a t u r e s t h a n i s - --D> ^ ^ e t j c y l ^ t ^ f . - . . i n - a l a t e r s e c t i o n an e x p e r i m e n t i s d e s c r i b e d which shows t h a t ^*§^er.~ w i l l i n f a c t r e s pond t o t e m p e r a t u r e changes, but i n a range h i g h e r 52 than that fox .^^reticulatum. ,f It i s likely that lewis (1967,1969b) fai l e d to show entrainment to temperature cycles because he did not use the range of temperature that included the c r i t i c a l threshold for his species. i r. . . Although the present few experiments with the innate rhythm have not answered a l l the guestions raised, they do emphatically demonstrate the point of key importance to the present study; i.e., the activity pattern exhibited in the f i e l d can be duplicated in the laboratory by entrainment of the circadian rhythm to appropriate zeitgebers, thus permitting discussion of activity rhythms in f i e l d situations. Host previous studies have attempted to describe the activity of animals in the f i e l d using correlation-regression techniques. Johnson (1969) argued that f i e l d activity resulted from an interaction of various thresholds which were not well described by a correlation-regression model. The experimental design used in the present study allowed the estimation of apparent thresholds associated with several key factors governing mollusc activity in the f i e l d . Therefore, the data were analysed in two ways: f i r s t l y by conventional correlation-regression, incorporating a l l the factors of possible importance, and secondly by a threshold model* Due to time constraints, i t was not logistxcally feasible to construct i threshold models for a l l the species studied, so L,« maximus was selected for this purpose./The various factors included in the two models are discussed serially i n the following text. After this, the regression models for a l l the species are given and compared, and then the threshold model for L. maximus i s i 53 d i s c u s s e d . , DESCRIBING THE CJRCJDIAN MIWM& M M I f i l i l T h e A c t i v i t y P a t t e r n Oyer, fAge Time was i n c l u d e d i n the c o r r e l a t i o n - r e g r e s s i o n a n a l y s i s a s a v a r i a b l e t o account f o r the v a r i a t i o n i n a c t i v i t y e x p l a i n e d by the i n n a t e rhythm. The o n l y o t h e r work t o i n c l u d e t i m e seems t o be t h e u n p u b l i s h e d t h e s i s by A r c h b o l d (1974) , on w o o d l i c e . Because t h e s l u g s a r e n o c t u r n a l , hours were counted from 1 pm r a t h e r t h a n 1 am so t h a t 1 am was hour 13./Thus time was a c o n t i n u o u s l y i n c r e a s i n g v a r i a b l e o v e r t h e o b s e r v a t i o n p e r i o d f o r t h e purposes o f a n a l y s i s . The d a i l y p a t t e r n of a c t i v i t y f o r •B^^EgtiSftiUMa* ~ "&x-;MtoBE.± ^ e a o r a l i s ^ Ls. i a x i j a u s x -4* c^ l a j b j ^ n j i s * ijiysaMasjsa§^ and PA garu§nae over the e n t i r e c o u r s e o f t h e experiment i s i l l u s t r a t e d i n F i g u r e s 13, 14, 15, 16, 17, 18, and 19 r e s p e c t i v e l y . The c o r r e l a t i o n of time w i t h the v a r i o u s s p e c i e s o f s l u g s i s g i v e n i n T a b l e XXV, and i t i s c l e a r l y u n e x p e c t e d l y low. A l o g a r i t h m i c t r a n s f o r m a t i o n improved t h e r e l a t i o n s h i p o n l y s l i g h t l y . The s c a t t e r diagrams showed t h a t t h e low c o r r e l a t i o n w i t h a c t i v i t y was due t o t h e n c n - l i n e a r i t y o f t h e r e l a t i o n s h i p , and a g u a r t i c f i t o f t h e d a t a (see L i t t l e and H i l l s , 1975) was su g g e s t e d . The computer r e c o g n i z e d t h e 3 r d power as b e i n g p e r f e c t l y c o r r e l a t e d w i t h the o t h e r s , and dropped i t from t h e a n a l y s i s . The complex e g u a t i o n t h u s developed was s u p e r i o r t o the s i m p l e l i n e a r e g u a t i o n i n a l l c a s e s (Ta&le XXV). The l o g a r i t h m i c t r a n s f o r m a t i o n o f time was i n i t i a l l y i n c o r p o r a t e d t o h e l p c o r r e c t t h e skewed d i s t r i b u t i o n o f a c t i v i t y t o the l e f t , a p p a r e n t i n most s p e c i e s . Although t h e r e s u l t 54 proved t o be s u p e r i o r t o p o l y n o m i a l e q u a t i o n s i n which t i n e was not t r a n s f o r m e d , i t i s d o u b t f u l t h a t t h e e f f e c t was due t o my o r i g i n a l a s s u m p t i o n , s i n c e a c t i v i t y o f - -., A. C o l u m b i a n us. • which shows a skewed d i s t r i b u t i o n t o the r i g h t , was more h i g h l y c o r r e l a t e d w i t h t h e l o g a r i t h m i c t r a n s f o r m a t i o n o f t i m e than w i t h a complex e g u a t i o n u s i n g an e x p o n e n t i a l t r a n s f o r m a t i o n . The p o l y n o m i a l e x p a n s i o n of time was used t o r e p r e s e n t the c i r c a d i a n rhythm i n t h e f i n a l c o r r e l a t i o n - r r e g r e s s i o n model i n a l l c a s e s . . The r e g r e s s i o n l i n e p r e d i c t e d from t h e c o r r e l a t i o n -r e g r e s s i o n a n a l y s i s p a s s e s t h r o u g h t h e c e n t e r o f the t i m e -a c t i v i t y s c a t t e r diagram ( e . g . . F i g u r e 13). However, f o r any g i v e n t i m e , t h e c i r c a d i a n rhythm o f a c t i v i t y would p r e d i c t a c e r t a i n number o f a n i m a l s a c t i v e ( t e m p o r a r i l y i g n o r i n g s e a s o n a l changes). U n f a v o u r a b l e weather would reduce t h i s , b u t h i g h l y f a v o u r a b l e weather would not i n c r e a s e a c t i v i t y above t h a t i n n a t e l y determined by t h e c l o c k . T h e r e f o r e t h e c o r r e l a t i o n -r e g r e s s i o n model i s u n r e a l i s t i c . Because the e f f e c t s o f weather are confounded w i t h t h e c i r c a d i a n rhythm i n t h e f i e l d d a t a , c o r r e l a t i o n - r e g r e s s i o n u n d e r e s t i m a t e s t h a t a c t i v i t y * a t any g i v e n t i m e due t o the i n n a t e c l o c k . I d e a l l y t h e e x a c t form o f t h e c i r c a d i a n a c t i v i t y p a t t e r n would he d e t a i l e d i n l a b o r a t o r y e x p e r i m e n t s under v a r i o u s c o n d i t i o n s . E q u a t i o n s c o u l d t h e n be developed which would p r e d i c t a c t i v i t y i n t h e f i e l d when weather was not a c o n s t r a i n t . Such d a t a a r e c r u c i a l t o t h e development of a t h r e s h o l d model. A l t h o u g h such e x t e n s i v e d a t a a r e not a v a i l a b l e , t h e r e q u i r e d i n f o r m a t i o n c o u l d be e s t i m a t e d d i r e c t l y from the f i e l d d a t a . The a c t i v i t y o f L. maximus was p l o t t e d f o r 15 days from May 55 1976 u n t i l O ctober 1976. By comparing th e shape of t h e a c t i v i t y p a t t e r n on a g i v e n n i g h t w i t h t h e shape of t h e p a t t e r n d u r i n g p r e v i o u s and subseguent t i m e s , and by a p p l y i n g e x i s t i n g i n f o r m a t i o n on t h e p a t t e r n s e x h i b i t e d i n d i f f e r e n t p h o t o p e r i o d s i n t h e l a b o r a t o r y , t h e e x p e c t e d a c t i v i t y a t any g i v e n time c o u l d be e s t i m a t e d . An e g u a t i o n was t h e n g e n e r a t e d from th e s e e s t i m a t e s by f i t t i n g them t o a p o l y n o m i a l e x p r e s s i o n o f t i m e , as d i s c u s s e d f o r t h e r e g r e s s i o n model. Other f a c t o r s were a l s o i n c l u d e d which w i l l be e l a b o r a t e d l a t e r , I n many c a s e s thesje e s t i m a t e s were c o n s i d e r a b l y g r e a t e r t h a n t h e a c t i v i t y a c t u a l l y observed. T h i s d e v i a t i o n a l s o o c c u r r e d i n e s t i m a t e s o f t h e o t h e r t h r e s h o l d s used f o r t h i s model. The magnitude of such v a r i a t i o n s c o u l d be used t o v a l i d a t e t h e model.,For example, an u n r e a l i s t i c t h r e s h o l d model would d r a s t i c a l l y o v e r e s t i m a t e a c t i v i t y on n e a r l y a l l o c c a s i o n s . I f t h e t h r e s h o l d model does n o t s e r i o u s l y o v e r e s t i m a t e s - a c t i v i t y , t h e n i t p r o b a b l y r e p r e s e n t s a r e a l i s t i c c a u s e - a n d - e f f e e t s i t u a t i o n . The A c t i v i t y P a t t e r n 0 f D e xoce r a s re t i c ulatjam The s c a t t e r diagrams o f a c t i v i t y v e r s u s t i m e a r e u s e f u l f o r c h a r a c t e r i z i n g and comparing t h e a c t i v i t y p a t t e r n s o f the v a r i o u s s p e c i e s . The a c t i v i t y p a t t e r n o f ( F i g u r e 13) shows a r a p i d c l i m b i n numbers t o a peak n e a r 90%. There i s a s t r o n g h i n t o f b i m o d a l i t y , t h a t was more o b v i o u s on some n i g h t s , t h a n on o t h e r s . The f a l l i n a c t i v i t y t h r ough the n i g h t i s l e s s p r e c i p i t o u s than t h e r i s e a t t h e b e g i n n i n g o f a c t i v i t y . I t i s c l e a r from th e f i g u r e t h a t , a l t h o u g h a c t i v i t y i s 56 o c c a s i o n a l l y v e r y low, i t i s never c o m p l e t e l y s u p p r e s s e d between the hours of 9:00 pm and 7:00 am. Barnes and B e i l (1942#1945) obse r v e d t h a t peak a c t i v i t y o f D. r e t i c u l a t u m o c c u r r e d b e f o r e m i d n i g h t . N e w e l l (1965a) found t h a t f j f r e t i c u l a t u m u s u a l l y emerged and c r a w l e d on t h e s u r f a c e a f t e r s u n s e t , and t h a t r e t u r n t r a c k s began b e f o r e s u n r i s e . He agreed t h a t peak a c t i v i t y o c c u r r e d b e f o r e midnight. The b e s t -f i t t i n g c o r r e l a t i o n - r e g r e s s i o n model p r e d i c t i n g a c t i v i t y o f D, r e t i c u l a t u m w i t h time i s g i v e n i n T a b l e I . / T a b l e I. R e g r e s s i o n E g u a t i o n R e l a t i n g t h e A c t i v i t y of B e r o c e r a s r e t i c u l a t u m t o Time. Dependent v a r i a b l e = L o g ( A r c s i n ( S g r t (¥*0. 00 1)).-) ra=0.7754 S. E.=0.2737 P=0.00000 V a r i a b l e C o e f f i c i e n t S.E.> F T P r o b a b i l i t y log-Time -20.4244 3.258 0.0000 Log-Time 2 22.086098 2. 564 0.0000 log-Time* -5.2176 0.436 0.0000 Constant 3.3953 1. 129 57 F i g u r e 13. a c t i v i t y o f D e r o c e r a s r e t i c u l a t u m i n F i e l d Cages from Hay u n t i l October 1S76 Showing t h e B e s t - F i t t i n g R e g r e s s i o n L i n e . 89 59 The a c t i v i t y P a t t e r n Of Arion/-ater----L i k e D. r e t i c u l a t u m , members o f an - A,, a t e r p o p u l a t i o n q u i c k l y r e a c h t h e i r peak a c t i v i t y e a r l y i n t h e e v e n i n g ( F i g u r e 14). They show no t r a c e o f a b i m o d a l p a t t e r n , and t h e i r a c t i v i t y f a l l s o f f g r a d u a l l y t h r o u g h o u t the n i g h t . O c c a s i o n a l l y t h e a c t i v i t y p e r i o d o f ft., a t e r Has l o n g e r t h a n t h e o b s e r v a t i o n p e r i o d , i n d i c a t i n g t h a t t h i s s p e c i e s can remain a c t i v e i n a wider range o f cond i t i o n s th a n D. r e t i c u l a t um ./October was t h e o n l y t i m e t h a t a c t i v i t y s u p r e s s e d between the hours of 8:00 pm and 7:00 am, and t h i s was due t o very c o l d t e m p e r a t u r e s . , l e w i s (1967) observed t h a t t h e a c t i v i t y o f a. a t e r i n c r e a s e d r a p i d l y soon a f t e r s u n s e t , r e a c h i n g a maximum around m i d n i g h t . Numbers t h e n : dropped s h a r p l y , so t h a t t h e r e were never many a c t i v e a t s u n r i s e . The b e s t p o l y n o m i a l e q u a t i o n o b t a i n e d by c o r r e l a t i o n r e g r e s s i o n f o r the r e l a t i o n s h i p o f a c t i v i t y on t ime i s p r o v i d e d i n T a b l e I I . 60 T a b l e I I . d e g r e s s i o n E g u a t i o n R e l a t i n g A c t i v i t y of A r i o n a t e r t o Time Dependent variable=Lc£(Arcsin{Sgrt(1+0. 001) ) ) r*-0.6512 S. E.=0.3249 P=0. 00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y Log-Time -12.1982 3.869 0.0019 Log-Time 2 14.6311 3.045 0.0000 l o g - t i m e * -3.6579 0.517 0.0000 , C o n s t a n t 1.0467 1.340 61 Figure 14. A c t i v i t y Pattern of Arion • ater- Over Time, I l l u s t r a t i n g the Bes t - F i t t i n g Regression Line. 29 63 The A c t i v i t y P a t t e r n Of Cepaea nemoralis--The a c t i v i t y o f C. n e m o r a l i s i n c r e a s e s r a p i d l y i n t h e e v e n i n g , o f t e n t o 100S5. A c t i v i t y t h e n d e c r e a s e s g r a d u a l l y t h r o u g h t h e n i g h t , a l t h o u g h t h e r e i s a h i n t o f a bimodal p a t t e r n ( F i g u r e 15) . Low l e v e l s 6 f a c t i v i t y on some o c c a s i o n s were known to be caused by some s n a i l s a e s t i v a t i n g . The b e s t e q u a t i o n g e n e r a t e d by a p o l y n o m i a l f i t o f a c t i v i t y on t i m e i s g i v e n i n T a b l e I I I . T a b l e I I I . R e g r e s s i o n E g u a t i o n R e l a t i n g t h e A c t i v i t y of Cejoaea-•-nemorales t o Time. Dependent v a r i a b l e = L c g ( A r c s i n ( S g r t ( Y + 0 . 0 0 1 ) ) ) r«=0.7110 S.E. =0.3355 P=0.00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y log-Time -38.1856 3.994 0,0000 l o g - T i m e 2 35.1773 3.144 0.0000 Log-Time* -7.0373 0.534 0.0000 Co n s t a n t 9.6559 1. 384 64 F i g u r e 15, A c t i v i t y P a t t e r n o f C e p a e a n e m o r a l i s from May u n t i l i' 1 " j • I October 1976 I l l u s t r a t i n g t h e B e s t - f i t t i n g R e g r e s s i o n L i n e , 65 r I I i i i ' r j — i 1—• i 1 1 r — i r — T 1 1 r\Y O 10 O m o O N i n CM O — 6 6 o 6 3 A I 1 0 V N O I l V i n d O d J O N O I i y O d O U d 66 The-Activity Pattern Of Limax maximus ' The population of 1. maximus (Figure 16) has a short, very nocturnal, activity period. The numbers active peaked rapidly in the evening, after which they, declined less abruptly. The proportion of the population active was most often very high, sometimes reaching 100%. The best eguation predicting the activity- of .- ^../fflaaciiBUS-with time i s given in Table XV.; Table IV. Begression Eguation Beiating-..the .Activity •,--o-f ^MlSS-' majijmus to Time. Dependent variable=Log(Arcsin(Sgrt|¥+0*001))) r2=0.6845 S.E. = 0.3901 F=0.00000 Variable Coefficient S.E. F-ProbaMlit y Log-Tiffle -50.3951 4.644 ;' 0.0000 log-Time* 46. 1935 3.655 0.0000 Leg-Time* -9.4978 0.621 0.0000 Constant 13.3525 1.609 67 Figure 16. a c t i v i t y Pattern of Limax maximus Over Time I l l u s t r a t i n g the Best-Fitting Regression Line. PROPORTION OF POPULATION ACTIVE 69 The A c t i v i t y P a t t e r n Of A r i o l i m a x Columbianus O n l i k e t h e o t h e r m o l l u s c s , A. columbianus e x h i b i t e d an a c t i v i t y p a t t e r n w i t h t h e peak skewed t o t h e r i g h t ( F i g u r e 17). The i n c r e a s e i n a c t i v i t y was g r a d u a l , peaking a t 2zGO or 3:00 am, and then d e c l i n i n g p r e c i p i t o u s l y . The a c t i v i t y p e r i o d t h u s was q u i t e l o n g , sometimes e x c e e d i n g t h e o b s e r v a t i o n p e r i o d . However, t h e a m p l i t u d e of the rhythm was always r e l a t i v e l y l o w , never e x c e e d i n g about 74% a c t i v i t y . The b e s t e g u a t i o n p r e d i c t i n g t h e a c t i v i t y o f A . v c c l u m b i a n u s w i t h t i m e i s g i v e n i n T a b l e V. Tab l e V. E e q r e s s i o n E q u a t i o n R e l a t i n g the A c t i v i t y o f A r j o l i m a x columbianus.-to Time. Dependent variable=Log(Arcsin(Sqrt{¥+0.001))) r2=0.7204 S.E.=0.2725 E=0. 00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y Log-Time — 2 0 . 4 5 4 5 3.244 0.0000 log-Time^ 20.7421 2.553 0.0000 Log-Time* -4.5484 0.434 0.0000 Con s t a n t 3.9743 1.124 70 Figure 17. A c t i v i t y Pattern of Ariolimax columbianus Over Time I l l u s t r a t i n g the B e s t - F i t t i n g Begression Line. 72 The A c t i v i t y P a t t e r n C f A r i o n s u b f uscus The a c t i v i t y p a t t e r n c f A,, subf uscus--was r e m a r k a b l y s i m i l a r t o t h a t of lit maximus ( F i g u r e 18). At no time d u r i n g t h e e n t i r e experiment was a c t i v i t y l e s s than 50% a t 11:00 pm. The l e n g t h o f the a c t i v i t y p e r i o d was s i m i l a r t o t h a t o f L. maximus and a g a i n the a m p l i t u d e sometimes r e a c h e d 100%.: The b e s t - f i t t i n g c o r r e l a t i o n - r e g r e s s i o n e g u a t i o n p r e d i c t i n g t h e a c t i v i t y of A. s u b f u s c u s w i t h time i s p r o v i d e d i n T a b l e VI. T a b l e V I . ; B e g r e s s i o n E q u a t i o n B e l a t i n g , the A c t i v i t y o f ;Arlon s u b f u s c u s t o Time. Dependent v a r i a b l e = L o g ( A r c s i n ( S g r t ( 1 * 0 . 0 0 1 ) ) ) r 2=0.7151 S.E. = 0.3305 E=0. 00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y Log-Time -41.1761 l o g - T i m e 2 39.0781 Log-Time* -8.2957 Con s t a n t 10.1470 4.436 0.0000 3.501 0.0000 0.5980 0.0000 1.533 73 Figure 18. A c t i v i t y Pattern of Arion • • subf uscus - Over Time I l l u s t r a t i n g the Be s t - F i t t i n g Begression Line. >*• If I 75 The A c t i v i t y P a t t e r n Of P e r o c e r a s caruanae The a c t i v i t y p a t t e r n o f P. caruanae showed mo s t l y low numbers a t any g i v e n t i m e { l e s s t h a n 6 0 % ) , w i t h o c c a s i o n a l sharp b u r s t s o f a c t i v i t y . F i g u r e 19 shows t h e r a p i d r i s e i n a c t i v i t y t o an e a r l y - e v e n i n g peak, f o l l o w e d by a more g r a d u a l d e c l i n e . The s p o r a d i c n a t u r e o f t h e p a t t e r n appears t c be due t o the s l u g * s u n u s u a l l y narrow temperature r a n g e , d i s c u s s e d l a t e r . ,. The b e s t e q u a t i o n r e l a t i n g t h e a c t i v i t y o f t h i s s p e c i e s t o time i s g i v e n i n Table V I I . Ta b l e V I I . R e g r e s s i o n E g u a t i o n R e l a t i n g the A c t i v i t y o f E e r o c e r a s caruanae t o Time. Pependent v a r i a b l e = L c g ( A r c s i n (Sgrt(Y+0.001))) r 2 = 0 . 6 3 8 5 S.E. = 0.3 04 3 P=0. 00000 V a r i a b l e c o e f f i c i e n t S.E. F - P r o b a b i l i t y Log-Time 2 5.95634 0.2590 0.0000 Log-Time* -2.5923 0.1188 0.0000 Constant -3.6851 0.1278 76 Figure 19. The A c t i v i t y Pattern of Deroceras caruanae Over Time Showing the Best-Fitting Begression Line. PROPORTION OF POPULATION ACTIVE / / 78 The A c t i v i t y P a t t e r n Of A r i o n h o r t e n s i s And A r i o n c i r c u m s c r i n t u s The s u b t e r r a n e a n h a b i t s of A. h o r t e n s i s and •A±i g i g c u m s c r i p t u s , p r e v e n t e d d e t a i l e d o b s e r v a t i o n of t h e i r p a t t e r n s o f a c t i v i t y , but t h e y were n o c t u r n a l i n t h i s e nvironment. Although v e r y l i t t l e s u r f a c e a c t i v i t y was e v e r observed f o r t h e s e s p e c i e s i n my e x p e r i m e n t a l c a g e s , I have o c c a s i o n a l l y noted e x t e n s i v e a c t i v i t y on t h e s u r f a c e i n e t h e r e n v i r o n m e n t s , such as dense p l a n t c a n o p i e s , compost heaps, and w e l l - w a t e r e d gardens. D a x l (1969) found t h a t h o r t e n s j s would t r a v e l a s h o r t d i s t a n c e from an a r t i f i c i a l s h e l t e r t o f e e d . H i s graph shows t h a t a c t i v i t y i n c r e a s e d g r a d u a l l y t h r o u g h o u t t h e n i g h t and peaked between 6:00 and 7:00 am. „ My c o r r e l a t i o n s o f a c t i v i t y w i t h t i m e were s i g n i f i c a n t , a l b e i t low, f o r both A * h o r t e n s i s and A. c i r c u m s c r i p t u s and are p r o v i d e d i n T a b l e s V I I I , and I X . 79 T a b l e V I I I . R e g r e s s i o n E g u a t i o n R e l a t i n g the A c t i v i t y o f A r i o n h o r t e n s i s t o Time., Dependent variable=Log(Arcsin(Sgrt(¥+0.001))). fi2=0.Q147 S.E. = 0.1689 1=0.02676 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y Log-Time 2 0.05407 0.0246 0.0091 Constant -1.5248 0.0297 T a b l e I X . R e g r e s s i o n E g u a t i o n R e l a t i n g the A c t i v i t y o f I r i o n c i r c u m s c r i p t u s t o Time. Dependent v a r i a b l e = L o g ( A r c s i n ( S g r t ( Y + 0 . 0 0 1 ) ) ). Rz=0.0691 S.E.=0.2395 P=0.00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y Log-Time 2 1.2221 0.2637 0.0000 Log-Time* -0.5064 0.1181 0.0000 Con s t a n t -1.9972 0.1330 80 INFLUENCE OF AMBIENT TEMPERATURE ON 31 HE FORM OF THE BfllTJLM. S l u g s a r e g e n e r a l l y n o c t u r n a l a n i m a l s { T a y l o r , 1907). Getz (1963) s t a t e d t h a t he was unaware of any t e r r e s t r i a l m o l l u s c known t o be s t r i c t l y d i u r n a l i n habit./However, the f a c t t h a t s l u g s f r e q u e n t l y become a c t i v e d u r i n g t h e day, e s p e c i a l l y d u r i n g d u l l , r a i n y weather, has a l s o been f r e q u e n t l y r e p o r t e d <e.g. L o v e t t and B l a c k , 1920; M i l e s e t a l ^ 1931; Ingram, 1941; Ord and »atts, 1949; D a i n t o n , 1954a; Brunson and K e v e r n , 1963; C h i c h e s t e r and Ge t z , 1973). Such o b s e r v a t i o n s t e n d t o c o n t r a d i c t t h e h y p o t h e s i s t h a t t h e c i r c a d i a n rhythm governs the a c t i v i t y p a t t e r n s o f t h e s e a n i m a l s . But a s y n t h e s i s c f my r e s u l t s w i t h t h o s e o f e t h e r a u t h o r s s u g g e s t s hew some d i u r n a l a c t i v i t y may be r e c o n c i l e d w i t h t h e i d e a o f a g o v e r n i n g c i r c a d i a n rhythm. y waste (1940) p r e v i o u s l y observed t h a t A* c s l S l M & B J S i s not s t r i c t l y n o c t u r n a l , but f e e d s i n the shade d u r i n g t h e day. Mead {1942) obse r v e d t h a t A. columbianus was d i u r n a l d u r i n g the w i n t e r , and ex c e p t f o r more s o u t h e r n p o p u l a t i o n s , remained so throughout t h e yea r . S o u t h e r n p o p u l a t i o n s became n o c t u r n a l d u r i n g the dry season. B i c h t e r {1976a) , working w i t h t h i s s p e c i e s i n woodland, found t h a t t b e y were c o m p l e t e l y d i u r n a l d u r i n g t h e s p r i n g and f a l l , whereas t h e y became c r e p u s c u l a r d u r i n g t h e summer. That f i n d i n g c o n t r a s t s s h a r p l y w i t h t h e n o c t u r n a l a c t i v i t y p a t t e r n observed f o r t h i s s p e c i e s i n t h e p r e s e n t s t u d y . T h i s s l u g was a l s o markedly n o c t u r n a l on C l e l a n d I s l a n d , B r i t i s h C o l u m b i a , where t h e r e i s l i t t l e t r e e c o v e r {Campbell and S t i r l i n g , 1967; R. J a r m o v i c , p e r s o n a l communication). 81 Working w i t h i t a t e r i n a garden, Lewis (1967) observed t h a t they were s t r i c t l y -nocturnal,- a l t h o u g h he was aware o f r e p o r t s c f o c c a s i o n a l d i u r n a l a c t i v i t y . P o u l i n (1967), however, found t h a t t h i s s p e c i e s was c r e p u s c u l a r i n woodland. P h i l c n v c u s c a r o l i n J . e n s i s # a woodland s l u g common i n e a s t e r n North A m e r i c a , i s a l s o commonly d i u r n a l (Ingram, 1941,1949). My own o b s e r v a t i o n s c o n f i r m t h a t d a y l i g h t a c t i v i t y of woodland m o l l u s c s i s common ( A^ Columbianus, A. a t e r , D^  r e t i c u l a t u m , Prpphysaon a n d e r s o n i , Monedenia f i d e l i s . cepaea n e m o r a l i s , A. s u b f u s c u s . P o l y g y r a v a n c o u y e r e n s i s x and P a l l i f e r a d o r s a l i s ) , a l t h o u g h even woodland s p e c i e s such as A. columbianus and P. a n d e r s o n i become n o c t u r n a l i n gardens or f i e l d s where t h e r e i s l i t t l e t r e e c o v e r . Dense p l a n t c a n o p i e s such as t h o s e o f c l o v e r o r a l f a l f a , f r e q u e n t l y s u p p o r t d i u r n a l a c t i v i t y , e s p e c i a l l y i n s p r i n g and f a l l . Getz (1963) d i s c o v e r e d t h a t m o l l u s c s p e c i e s commonly a c t i v e d u r i n g t h e day, shewed a p r e f e r e n c e f o r a l i g h t i n t e n s i t y of 35 f t - c v e r s u s 2 f t - c i n a l i g h t - c h o i c e a p p a r a t u s . S n a i l s , not o f t e n a c t i v e d u r i n g the day, and t h r e e s p e c i e s o f s l u g s , were r e p e l l e d . Reports o f s i m i l a r v a r i a t i o n s i n t h e p a t t e r n i n g o f a c t i v i t y among o t h e r k i n d s of a n i m a l s appear throughout t h e l i t e r a t u r e , but t h e i m p l i c a t i o n s have never been r e c o g n i z e d , n or has the t o p i c been r e v i e w e d . When such o b s e r v a t i o n s were made, they were g e n e r a l l y r e g a r d e d as unusual o r e x c e p t i o n a l . Bodenheimer (1935), f o r example, observed t h a t t h e woodlouse. H e m i l e p j s t u s re.aupurj. s h i f t s i t s a c t i v i t y c y c l e d u r i n g t h e year such t h a t i n midsummer i t i s a c t i v e o n l y i n t h e e a r l y morning and e v e n i n g , s i m i l a r t o the s h i f t B i c h t e r (1976) observed f o r A. colu m b i a n u s . 82 Among a n t s , Bodenheimer and K l e i n (1930) o b s e r v e d t h a t l e s s o r s e m i r u f u s Andre was a c t i v e mainly a t noon i n low ambient t e m p e r a t u r e s , but as t e m p e r a t u r e s i n c r e a s e d , i t s h i f t e d i t s a c t i v i t y u n t i l i t was c o m p l e t e l y n o c t u r n a l . The same s i t u a t i o n was d e s c r i b e d f o r c a r p e n t e r a n t s more r e c e n t l y ( S a n d e r s , 1972). W i l l i a m s (1959) observed t h a t the c a r a b i d b e e t l e , F e r o n i a roadida ( F a b r i c i u s ) , was a c t i v e o n l y d u r i n g t h e day on open ground and o n l y a t n i g h t i n woodland. T e n e b r i o n i d b e e t l e s , C a r d i o s i s s£j. a r e n o r m a l l y a c t i v e a t midday i n c o o l e r c o n d i t i o n s , but on hot days t h e a c t i v i t y p a t t e r n becomes b i m o d a l ( H a m i l t o n , 1971). Harker (1964) o b s e r v e d t h a t each s p e c i e s t e n d s to e x h i b i t a c h a r a c t e r i s t i c , unintodal a c t i v i t y p a t t e r n i n t h e l a b o r a t o r y ^ whereas i n the f i e l d , more c o m p l i c a t e d p a t t e r n s are common, p o s s i b l y due t o , an i n t e r a c t i o n of t h o s e f a c t o r s d e t e r m i n i n g the phase. H e c k r o t t e (1962,1975) i n v e s t i g a t e d a c i r c a d i a n system i n t h e p l a i n s g a r t e r s n a k e, t h a t c o u l d e x p l a i n how d i f f e r e n t t e m p o r a l o r s p a t i a l e nvironments produced the phase s h i f t s o f a c t i v i t y I have mentioned f o r m o l l u s c s and o t h e r a n i m a l s . He d i s c o v e r e d t h a t at 35° C , a c t i v i t y was m a i n l y n o c t u r n a l , w i t h a peak o c c u r r i n g a t the end o f t h e 12 h s c o t o p e r i o d , much as I found f o r A. c o l u m b i a n u s i n t h e f i e l d cages. At 15° C, a c t i v i t y of t h e snakes was m a i n l y d i u r n a l . H e c k r o t t e (1975) r e v i e w e d s e v e r a l r e p o r t s t h a t snakes d i s p l a y e d c r e p u s c u l a r or n o c t u r n a l a c t i v i t y a t h i g h t e m p e r a t u r e s , and c o n c l u d e d t h a t such o c c u r r e n c e s were " an e f f e c t t h e t e m p e r a t u r e l e v e l has on t h e b i o l o g i c a l c l o c k and a c t i v i t y c o n t r o l l i n g mechanisms r a t h e r than temperature s e l e c t i o n by t h e snake. 1' 83 Corneal! e t a l . (1976) . a l s o showed t h a t t h e d i e ! p e r i o d i c i t y o f s e x u a l a c t i v i t y among s e v e r a l s p e c i e s of moths was m o d i f i e d by ambient t e m p e r a t u r e . The change from a f t e r n o o n f l i g h t i n s p r i n g t o n i g h t f l i g h t i n summer f o r A r g y r c t a e n i a v e l u t j ^ a n a (Walker) was accounted f o r by d i f f e r e n c e s i n ambient t e m p e r a t u r e , t h e moths f l y i n g l a t e r a t h i g h e r t e m p e r a t u r e s . The g r e a t v a r i e t y of organisms f o r which t h e s e phase s h i f t s have been r e p o r t e d s u g g e s t s t h a t t h e phenomenon i s widespread and, i n f a c t , a common f e a t u r e o f c i r c a d i a n rhythms. Among s l u g s , t h e r e f o r e , one would expect t h a t t h o s e s p e c i e s r e q u i r i n g a h i g h l i g h t i n t e n s i t y t o e n t r a i n t h e i r rhythm would be t h o s e most l i k e l y t o show phase s h i f t s i n response t o changes i n ambient t e m p e r a t u r e s . T h i s e x p e c t a t i o n appears t o be c o n f i r m e d by f i e l d o b s e r v a t i o n s showing t h a t s p e c i e s w i t h h i g h t o l e r a n c e t o l i g h t (e.g. .A. a t e r , c o l u m b i a n u s . and P., r e t i c u l a t u m were more a c t i v e d u r i n g t h e day i n s p r i n g and f a l l t h a n were s p e c i e s w i t h low l i g h t t h r e s h o l d s , such as L. maximus. However, even t h i s l a t t e r s p e c i e s e x h i b i t e d more d a y l i g h t a c t i v i t y d u r i n g t h o s e seasons t h a n i n the summer. P o s s i b l y i t s c r i t i c a l l i g h t t h r e s h o l d i s h i g h e r a t l o w e r t e m p e r a t u r e s . F o r example, i n summer, L. maximus was never a c t i v e i n l i g h t i n t e n s i t i e s g r e a t e r than about 1 f t - c , whereas, i n f a l l some i n d i v i d u a l s were a c t i v e i n i n t e n s i t i e s as h i g h as 500 f t - c . The s h i f t o f a c t i v i t y t o daytime c o n d i t i o n s i n c o o l e n v i r o n m e n t s , and t o n o c t u r n a l a c t i v i t y i n hot environments c e r t a i n l y would have t h e r m o r e g u l a t o r y v a l u e f o r t h e m o l l u s c s . , F u t u r e comparisons o f my d a t a w i t h t h a t o f fiichter's (1976a) may p r o v i d e some i n s i g h t i n t o the f a c t o r s p r o d u c i n g t h e 84 v a r i o u s t y p e s o f a c t i v i t y p a t t e r n s observed f o r flifi c o l u m b i a n u s . A g e n e r a l model of a c t i v i t y f o r s l u g s must be a b l e t o p r e d i c t such changes i n p a t t e r n g i v e n t h e a p p r o p r i a t e e n v i r o n m e n t a l c o n d i t i o n s . Thus, t h e r e s u l t s of t h e p r e s e n t s t u d y must be viewed as a p p l y i n g o n l y t o f i e l d e n v i r o n m e n t s . For t h e c o r r e l a t i o n - r e g r e s s i o n model, s h e l t e r t e m p e r a t u r e was i n c l u d e d as a f a c t o r , p a r t i a l l y t o account f o r v a r i a t i o n s i n t h e a c t i v i t y p a t t e r n t h a t might a r i s e from ambient te m p e r a t u r e s . PHOTOPERIOD AND PHASE Other f a c t o r s b e s i d e s ambient t e m p e r a t u r e ad-just t h e p a t t e r n and t i m i n g o f the a c t i v i t y rhythm. D a x l (1969) showed t h a t t h e time a t which a number o f s l u g s p e c i e s became a c t i v e , v a r i e d w i t h s e a s o n a l changes i n p h o t o p e r i o d . B a i l e y (1975) found t h a t t h e s n a i l H e l i x a s p e r s a . had i t s a c t i v i t y peak 3.5 h a f t e r the end o f a 2 h t w i l i g h t when e n t r a i n e d t o 1:D 10:14, whereas t h o s e e n t r a i n e d t o L:D 14:10 had t h e i r peak o n l y 1.5 h f o l l o w i n g the t w i l i g h t . Using a c t i v i t y wheels, Sokolove e t a l . (1977) found t h a t the phase, a m p l i t u d e , and d u r a t i o n of a c t i v i t y was d i f f e r e n t f o r L. maximus e n t r a i n e d t o LzD 12:12 and L:D 16:8. In the l a t t e r , a c t i v i t y began 2 h b e f o r e l i g h t s o f f , by which time peak a c t i v i t y o c c u r r e d . The a m p l i t u d e was lower i n L:D 16:8, whereas t h e a c t i v i t y p e r i o d was 12 h l o n g . I n L:D 12:12, t h e peak i n a c t i v i t y o c c u r r e d 2 h a f t e r t h e l i g h t - d a r k t r a n s i t i o n , had a c o n s i d e r a b l y h i g h e r a m p l i t u d e , and the whole p e r i o d o f a c t i v i t y l a s t e d o n l y 9-10 h o u r s . 85 Eecause t h e c i r c a d i a n rhythm i s r e p r e s e n t e d i n t h e c o r r e l a t i o n - r e g r e s s i o n model as f i x e d i n t e r v a l s , a change i n t h e phase o f t h e rhythm w i t h r e s p e c t t o t h e s e p e r i o d s w i l l e s s e n t i a l l y change t h e a m p l i t u d e observed i n each. Thus, i f t h e peak i n a c t i v i t y o c c u r r e d a t 12 pm, and the a c t i v i t y rhythm phase s h i f t e d ahead one hour, t h i s s h i f t would have the e f f e c t o f i n c r e a s i n g t h e a m p l i t u d e a t 1 am, and r e d u c i n g i t a t 12 pm. As mentioned above, t h e work o f Sokolove e t a l . . (1977) a l s o s u g g e s t s t h a t t h e a m p l i t u d e can be a f f e c t e d by d i f f e r e n t p h o t c p e r i c d s independent of phase c o n s i d e r a t i o n s . S i n c e I am a t t e m p t i n g t o a n a l y s e t h e i n f l u e n c e o f weather f a c t o r s t h rough t h e i r i n f l u e n c e on t h e a m p l i t u d e o f t h e i n n a t e rhythm, some c o n s i d e r a t i o n must be g i v e n t o t h i s problem. F i g u r e 20 i l l u s t r a t e s t h e i n f l u e n c e o f season on t h e a c t i v i t y p a t t e r n of a s h o r t - p e r i o d s l u g , L.. maximus, and a l o n g -p e r i o d s l u g , A. a t e r . The o n s e t of a c t i v i t y of both s p e c i e s was c l o s e l y a s s o c i a t e d w i t h s u n s e t , a l t h o u g h Aj. a t e r tended t o become a c t i v e s l i g h t l y b e f o r e s u n s e t , whereas L. maximus u s u a l l y was a c t i v e a f t e r s unset.:Even i n s h o r t p h o t o p e r i o d s t h e a c t i v i t y of J-t j a x i j u s was s t r i c t l y n o c t u r n a l , a r e s u l t t h a t s h a r p l y c o n t r a s t s w i t h t h e l a b o r a t o r y s t u d y o f Sokolove ej^ ajL... (1977). The c e s s a t i o n of a c t i v i t y i n L. maximus was c l o s e l y a s s o c i a t e d w i t h s u n r i s e , whereas A*, a t g r was u s u a l l y a c t i v e f o r s e v e r a l hours t h e r e a f t e r . These s p e c i f i c d i f f e r e n c e s p r o b a b l y r e f l e c t the d i f f e r e n c e s i n t h e c r i t i c a l l i g h t t h r e s h o l d s r e q u i r e d f o r e n t r a i n i n g t h e rhythm d i s c u s s e d e a r l i e r . L e wis (1969b) showed t h a t a r t i f i c i a l l y s h o r t e n i n g t h e p h o t o p e r i o d caused c o l o n i e s o f A, a t e r t o become a c t i v e e a r l i e r . 86 Barnes and W e i l {1944) o b s e r v e d t h a t t h e onset o f s l u g a c t i v i t y was more c l o s e l y r e l a t e d t o the t i m e o f s u n s e t d u r i n g summer than i n w i n t e r . Barnes {1949) showed t h a t , a l t h o u g h each s p e c i e s o f s l u g d i d not have t h e same p e r i o d o f a c t i v i t y d u r i n g t h e n i g h t , they were a l l a c t i v e by about t h r e e hours a f t e r s u n s e t d u r i n g w i n t e r , and 2 hours f o l l o w i n g sunset i n summer. B e s u l t s p r e s e n t e d i n F i g u r e 20, however, do not show any c l e a r e v i d e n c e o f a change i n phase o f peak a c t i v i t y w i t h the time o f s u n s e t . A c t i v i t y i s c l o s e l y r e l a t e d t o s u n s e t t h r o u g h o u t t h e se a s o n . The data a l s o do not i n d i c a t e a change i n a m p l i t u d e a s s o c i a t e d w i t h d i f f e r e n t p h o t o p e r i o d s , as was found i n t h e l a b o r a t o r y by Sokolove g t a l ^ {1977). N e v e r t h e l e s s , t h e r e were d e f i n i t e s e a s o n a l changes i n t h e a c t i v i t y p a t t e r n s . Whereas o n l y 3% o f L,, maximus were a c t i v e by 9:00 pm on June 17-18, more th a n 30% were a l r e a d y a c t i v e by 7:00 pm on October 7-8. Although most a c t i v i t y o f L. maximus c e a s e d by 4:00 or 5:00 am i n June and J u l y , a few s l u g s were s t i l l a c t i v e a t 9:00 am i n October. The a c t i v i t y p e r i o d ranged from as low as 8 h i n J u l y , t o as l o n g as 15 h i n O c t o b e r . A. a t e r showed t h e same tendency, but had a l o n g e r a c t i v i t y p e r i o d , e x t e n d i n g w e l l o u t s i d e t h e o b s e r v a t i o n p e r i o d d u r i n g t h e f a l l . The f a c t t h a t t h e s h o r t e s t a c t i v i t y p e r i o d o c c u r r e d i n August (12 h o u r s ) , r a t h e r than i n June (14 h o u r s ) , s u g g e s t s t h a t t e mperature may p l a y a r o l e , s i n c e maximum p h o t o p e r i o d o c c u r r e d on June 2 1 s t , whereas maximum temp e r a t u r e o c c u r r e d i n e a r l y August ( F i g u r e 2 1 ) . 87 Figure 20. A c t i v i t y of Limax maximus and Arion ater from Selected Nights i n 1976 I l l u s t r a t i n g the Seasonal Changes in the A c t i v i t y Pattern. PROPORTION OF POPULATION ACTIVE CC cc 89 Figure 21. Seasonal Trends i n Scotoperiod and Maximum Shelter Temperatures Observed i n the F i e l d Cages During 1976. o o LL) DC h-< tr UJ OL 2-LU © 24 22 20 I 8 I 6 I 4 I 2 I 0 8 6 4 2 0 © © LU O t -_1 o to UJ 01 n— i 1—i—r II 18 27 I 8 9 O 9 a 17 24 n — i — n 1—i—i r— 13 20 2528 5 10 17 24 T T 1 — r H 800 700 600 500 J M A Y J U N E J U L Y A U G U S T 8 16 23 29 7 20 SEPTEMBER O C T O B E R B CO o o - H O "O m o o cz m 400 ^ h 300 D A T E 91 B a i l e y (1975) found t h a t , a l t h o u g h t h e a c t i v i t y p a t t e r n of H. a s p e r s a kept a f a i r l y c o n s t a n t r e l a t i o n s h i p t o s u n s e t , t h e d u r a t i o n of a c t i v i t y was u n r e l a t e d t o t h e t i m e of s u n r i s e , u n l i k e t h e r e s u l t s o b t a i n e d f o r s l u g s i n t h e p r e s e n t s t u d y . N e w e l l (1965a,1966,1968) observed t h a t exposure t o l i g h t i n t h e morning caused JD. r e t i c u l a t u m t o i n c r e a s e i t s r a t e of t u r n i n g and c r a w l i n g , a p p a r e n t l y i n an attempt to q u i c k l y f i n d s h e l t e r . C o n v e r s e l y , Schread (1958) r e c o r d e d t h a t on d u l l , c l o u d y mornings, p a r t i c u l a r l y w i t h s h o r t p h o t o p e r i o d s i n August and September, s l u g s may remain on food l o n g e r t h a n when t h e sun r i s e s e a r l i e r . The c l o s e a s s o c i a t i o n o f changes i n t h e t i m i n g o f m o l l u s c a n a c t i v i t y w i t h t h e time of s u n s e t and s u n r i s e s u g g e s t s s e v e r a l f a c t o r s t h a t may be i m p o r t a n t i n an a c t i v i t y model, l i g h t i n t e n s i t y , i ndependent o f i t s f u n c t i o n as a z e i t g e b e r i s c o n s i d e r e d l a t e r . The l e n g t h o f the n i g h t ( s c o t o p e r i o d ) , and when i t b e g i n s (time o f s u n s e t , o r p h a s e ) , may a l s o be i m p o r t a n t m o d i f i e r s of t h e i n n a t e a c t i v i t y rhythm. I n the c o r r e l a t i o n -r e g r e s s i o n model, s c o t o p e r i o d c o u l d a l s o h e l p t o account f o r p o s s i b l e s e a s o n a l changes i n r e s p o n s i v e n e s s t o v a r i o u s weather parameters (e.g. h u m i d i t y ) , known t o oc c u r i n many a n i m a l s (Cloudsley-Thompson, 1967). S i n c e t h e l e n g t h of t h e n i g h t i s more r e l e v a n t t o t e r r e s t r i a l m o l l u s c s than d a y l e n g t h , the number o f minutes i n the s c o t o p e r i o d ( t e r m i n o l o g y o f Beck, 1968), was c a l c u l a t e d f o r each day o f o b s e r v a t i o n , and was a t t a c h e d t o each h o u r l y o b s e r v a t i o n . C o r r e l a t i o n s o f s c o t o p e r i o d w i t h a c t i v i t y o f s l u g s a r e g i v e n i n T a b l e XXV. I n some c a s e s l o g a r i t h m s o r e x p o n e n t i a l 92 t r a n s f o r m a t i o n s were s u p e r i o r t o s i m p l e s c o t o p e r i o d . The ti m e o f suns e t was a l s o added as a f a c t o r t o each h o u r l y o b s e r v a t i o n , s i n c e t h i s was c l o s e l y r e l a t e d t o the phase o f t h e rhythm. C o r r e l a t i o n s o f phase w i t h a c t i v i t y o f s l u g s are g i v e n i n T a b l e XXV. Because o f the number of f a c t o r s b e i n g c o n s i d e r e d , i t was de c i d e d t o i g n o r e p o s s i b l e i n t e r a c t i o n e f f e c t s i n the c o r r e l a t i o n - r e g r e s s i o n model, However, f o r the t h r e s h o l d model to be r e a l i s t i c , an e g u a t i o n had t o be developed t h a t would g i v e the form of t h e c i r c a d i a n rhythm f o r any c o m b i n a t i o n of phase and s c o t o p e r i o d . As p r e v i o u s l y d i s c u s s e d , ambient t e m p e r a t u r e would p r o b a b l y a l s o be an i m p o r t a n t m o d i f i e r , and t h e maximum d a i l y s h e l t e r t e m p e r a t u r e was s e l e c t e d as t h e b e s t e s t i m a t o r o f average e n v i r o n m e n t a l t e m p e r a t u r e . U s i n g t h e e s t i m a t e d v a l u e s o f a c t i v i t y o f L. -•m§;xiimus-as t h e dependent v a r i a b l e , a r e g r e s s i o n e g u a t i o n was f i t t e d u s i n g a p o l y n o m i a l e x p a n s i o n o f t i m e , s c o t o p e r i o d , phase, maximum s h e l t e r t e m p e r a t u r e , and i n t e r a c t i o n s of t h e s e f a c t o r s . T h i s e g u a t i o n appeared t o f i t the e s t i m a t e d p o i n t s r e a s o n a b l y w e l l ( r 2 = 0 . 8 1 5 ) , and i s g i v e n i n T a b l e X. Due t o the n a t u r e o f t h e c u r v e - f i t t i n g p r o c e d u r e , v a l u e s g r e a t e r t h a n 1.00 o r l e s s t h a n 0.00 sometimes o c c u r r e d . I n t h e f i n a l model t h e s e were a p p r o p r i a t e l y m o d i f i e d w i t h F o r t r a n s t a t e m e n t s . I n summary, d a i l y and s e a s o n a l changes i n the a c t i v i t y o f m o l l u s c s , as r e l a t e d t o the i n n a t e rhythm, were accounted f o r i n t h e models by i n c l u d i n g the f a c t o r s , t i m e , phase, s c o t o p e r i o d , and s h e l t e r t e m p e r a t u r e . 93 T a b l e X. B e s t - F i t t i n g R e g r e s s i o n E g u a t i o n D e s c r i b i n g t h e C i r c a d i a n A c t i v i t y P a t t e r n o f Lj.max j a x i j u s E s t i m a t e d from F i e l d Data from May u n t i l O c t o b e r , 1976. R2=0.8148 S.E.=0.1458 E=0. 00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y Time 33.4770 1.601 0.0000 Time« -17.2957 0.918 0.0000 Phase -0.4306 0.039 0.0000 Phase x T i m e 3 0. 1959 0.017 0.0000 S c o t o p e r i o d x Time - 1 . 2209 0. 103 0.0000 S c o t o . x Time 3 0.3558 0.020 0.0000 Maximum S h e l t e r Temperature -0.17 27 0.0 35 o.qooc Max.Shit, x Scoto. 0.0448 0.005 0.0000 Max.Sh i t , x Time -0.0631 0.018 0.0008 Con s t a n t -8.8887 0.625 94 ACTIVITY AS A FORAGING.RESPONSE The purpose of t h e p r e s e n t study i s t o de v e l o p a model c a p a b l e o f e x p l a i n i n g the a c t i v i t y o f s l u g s , d e f i n e d as t h e numbers on t h e s u r f a c e . An o b v i o u s g u e s t i o n t o ask i s , "why come t o the s u r f a c e a t a l l ? " The most o b v i o u s answer i s t h a t s u r f a c e a c t i v i t y i s m a i n l y f o r f o r a g i n g . To what e x t e n t i s s u r f a c e a c t i v i t y r e l a t e d t o food a g u i s i t i o n , and how w i l l i t be a f f e c t e d by the d i s t a n c e between s h e l t e r s and food? Den Boer (1961), a l s o i n v e s t i g a t e d t h i s g u e s t i o n u s i n g w o o d i i c e and found t h a t t h e i r a c t i v i t y was not c l o s e l y r e l a t e d t o food a g u i s i t i o n . T h i s l e d him t o c o n c l u d e t h a t woodlouse a c t i v i t y was m a i n l y h y g r o r e g u l a t o r y . My e x p e r i m e n t s were t h e r e f o r e d e s i g n e d t o p r o v i d e food i n t h e s h e l t e r , c r on the s u r f a c e w i t h i n l a b o r a t o r y cages. P r e l i m i n a r y r e s u l t s o f t h e s e e x p e r i m e n t s were c o n f u s i n g . Sometimes food w i t h i n t h e s h e l t e r n e a r l y s u p p r e s s e d s u r f a c e a c t i v i t y , whereas a t o t h e r t i m e s such a c t i v i t y was n e a r l y normal. A f u r t h e r experiment showed t h a t food o f t e n l o s t i t s a t t r a c t i v e n e s s w i t h t i m e and thus produced the v a r i a b l e r e s u l t s ( F i g u r e 22). F r e s h c a r r o t s l i c e s i n s i d e t h e s h e l t e r g r e a t l y r educed t h e s u r f a c e a c t i v i t y c f D. r e t i c u l a t u m . As the food d e t e r i o r a t e d , s l u g s emerged more f r e q u e n t l y , but f u l l s u r f a c e a c t i v i t y o c c u r r e d o n l y when a l l t h e a v a i l a b l e f o o d was on t h e s u r f a c e . Thus t h e a v a i l a b i l i t y and q u a l i t y of food i n s i d e the s h e l t e r s w i l l g r e a t l y i n f l u e n c e s l u g a c t i v i t y on t h e s u r f a c e . T h i s r e s u l t s u g g e s t s t h a t s l u g s w i l l behave d i f f e r e n t l y on s o i l s 95 containing d i f f e r e n t amounts of organic material. It also shows that a large amount of v a r i a b i l i t y can r e s u l t i f standardized shelters, with which the food supply can be s t r i c t l y c o n t r o l l e d , are not used i n a c t i v i t y experiments. I t i s l i k e l y that the a v a i l a b i l i t y of food in shelters w i l l interact with weather factors, changing the thresholds at which slugs are w i l l i n g to engage i n surface a c t i v i t y . Heather w i l l have a much greater influence on populations of slugs which must forage on the surface for food than on those which have reserve food in t h e i r shelters. Of relevance here i s the previously unreported fact that slugs deposit nearly a l l of their faeces i n their s helters. Since they rea d i l y eat t h e i r faeces i n the laboratory, t h i s source of food could provide a short-term reserve during periods of intolerable weather. The experiment also i l l u s t r a t e s another point, " a c t i v i t y " has been defined as the number of slugs active on the s o i l surface for the purposes of the present study. However, even "surface" species may actually continue many of t h e i r normal a c t i v i t i e s underground, behaving at times l i k e the t y p i c a l l y subterranean species, I r i o n circumscriptus and arion hortensis . Thus, in some environments, unfavourable weather w i l l not change the amplitude of the a c t i v i t y pattern of the population by d i r e c t l y a f f e c t i n g a c t i v i t y , but i n d i r e c t l y by forcing i t underground. 9 6 Figure 22. Changes i n the A c t i v i t y Pattern of Deroceras reticulatum i n Besponse to the A v a i l a b i l i t y of Food Within Shelter. PROPORTION OF POPULATION ACT IVE o 6 o o o ro o o o o o 0 0 0 0 — 61 oS CO CO 6 o 0 0 0 0 0 0 cn cn LIGHTS ON .10:00 J Z6 98 AGE B l i n n (1961) observed g r e a t e r a c t i v i t y o f younger s n a i l s t h r o u g h o u t the day, and noted t h a t t h e y remained a c t i v e l a t e r i n the year t h a n d i d a d u l t s . B i c h t e r (1976a) s i m i l a r l y observed t h a t young A. c o l u m b i a n u s were a c t i v e a f t e r the a d u l t s had e n t e r e d h i b e r n a t i o n . He h y p o t h e s i z e d t h a t younger s l u g s s h o u l d be more a c t i v e t h a n a d u l t s because t h e y r e g u i r e more food f o r t h e i r h i g h e r metabolism. He s u g g e s t e d t h a t t h e i r extended a c t i v i t y i n the f a l l was thus an a d a p t a t i o n t o o b t a i n the e x t r a r e s e r v e s n e c e s s a r y t o pass t h e w i n t e r . S i n c e age seemed l i k e l y t o a f f e c t a c t i v i t y p a t t e r n s i n t h e f i e l d , t h i s f a c t o r was c o n t r o l l e d by u s i n g o n l y a d u l t s l u g s f o r f i e l d o b s e r v a t i o n s . However, many o b s e r v a t i o n s were made o f t h e d i f f e r e n c e s i n a c t i v i t y w i t h age, and s e v e r a l e x p e r i m e n t s were performed t o g u a n t i f y t h i s r e l a t i o n s h i p . Newly hatched s l u g s r a r e l y became a c t i v e on the s o i l s u r f a c e , a l t h o u g h very s m a l l C. n e m o r a l i s f r e q u e n t l y were a c t i v e . H a t c h l i n g s g e n e r a l l y remained i n t h e f l o w e r - p o t s h e l t e r s , where t h e y f e d on s l u g eggs, humus, p l a n t d e b r i s , and the f a e c e s d e p o s i t e d t h e r e by t h e a d u l t s . O l d e r immatures and j u v e n i l e s f r e q u e n t l y became a c t i v e on t h e s o i l s u r f a c e i n l a r g e numbers. Those of most s p e c i e s (e.g. A. a t e r . r§tisulatum. £x j e mora l i s , , , and A t s u b f u s c u s , ) o f t e n became a c t i v e w e l l b e f o r e t h e a d u l t s , and c o n t i n u e d l a t e r i n t o t h e d a y l i g h t . K a r l i n (1961) a l s o observed t h a t immature Df r e t i c u l a t u m became a c t i v e a t t i m e s when a d u l t s were i n a c t i v e . P o l l a r d (1973) s i m i l a r l y 99 observed differences i n the a c t i v i t y pattern of the s n a i l . Helix poenatia, with age. fly own observations suggested that immatures do not have as pronounced a circadian rhythm as the adults. Their arrhythmic a c t i v i t y , coupled with their high numbers, thus gave the f a l s e impression that the immatures were more active than the adults. This arrhythmic nature of the immatures might also explain Blinn (1961) and Bichter's (1976a) observations that adults hibernated e a r l i e r than the young. Adults may have a more strongly entrained seasonal rhythm. In Lj. maximus, the circadian rhythm of the immatures was as strong as i n the adults. Figure 23 shows the i n d i v i d u a l a c t i v i t y pattern of 26 I f maximus in L:D 12:12 (L=c.a. 300 f t - c , 1=15° C), observed every half hour during t h e i r a c t i v i t y period. Two a c t i v i t y arenas each contained 13 slugs , Ten inverted flower pots served as shelters i n each cage, and a central dish of carrot root was provided. Small slugs were 3-4 cm long when extended, medium slugs, 4-7 cm long, and large slugs were greater than 7 cm. The mean number of times that individuals i n these classes were observed to be active was 3.67, 11.88, and 15.15 f o r the small, medium and large slugs, respectively. There was a very obvious e f f e c t of age upon the amount of time spent outside shelter. On two occasions, the a c t i v i t y of adult L,x iax;imu.s (>10 cm) in f i e l d cages was compared with that of immatures i n the same cages (<4.0 cm). Figure 24 shows that the a c t i v i t y of immatures was considerably l e s s than that of adults cn both of these nights. The immature slugs partitioned t h e i r various a c t i v i t i e s 100 d i f f e r e n t l y than did the adults. Smaller slugs were almost exclusively concerned with obtaining food, whereas adults traveled and rested more, and also exhibited t e r r i t o r i a l and sexual behavior not observed in immatures. I t had been previously assumed that smaller individuals would be more active due to t h e i r higher metabolism, but i t appears that immatures devote t h e i r a c t i v i t y period exclusively to foraging and then rest for most of the remaining time. By minimizing a c t i v i t y , these slugs can probably divert more of their energy into growth. Davidson (1976) recently showed that immature slugs assimilate food more e f f i c i e n t l y than adults, which may further compensate for t h e i r reduced a c t i v i t y . Early authors observed that each species of slug had a p a r t i c u l a r time of year when th e i r greatest a c t i v i t y occurred, and t h i s coincided with that period i n t h e i r l i f e cycle when they reached t h e i r maximum size (Barnes and Weil, 1945; Barnes, 1949). The cause of these seasonal peaks i n a c t i v i t y was obscure, but the present finding, that younger slugs are l e s s active, helps to explain them. 101 F i g u r e 23. I n d i v i d u a l A c t i v i t y P a t t e r n s of Limax maximus I l l u s t r a t i n g t h e R e l a t i o n s h i p o f S i z e t o t h e Amount of A c t i v i t y . 102 T I M E S L U G No. 2 3 4 5 ' 6 7 8 9 10 M E D I U M ( 4 -7 cm 2 3 4 S M A L L ( < 4 ' c m : T O T A L 10 O B S E R V A T I O N S 0 (ZZ i 2 3 4 5 6 7 8 9 10 I I 12 YZZA YZZZZZZA ¥22 nvzzA vzza 0 0 L I G H T S O F F 0 15 13 5 I I 8 6 5-5 4 4 3 3 3 2 1-5 I 0 - L I G H T S ON M E A N No. O B S E R V A T I O N S P E R . S L U G LARGE = 15-05, MEDIUM" 11-88, S M A L L = 3-67 103 Figure 24. activity of adult vs Juvenile Limax maximus on Two flights in the Field Cages. m P R O P O R T I O N OF P O P U L A T I O N A C T I V E o o ° 9 ° — ro o o o CD o oo o o o 105 LIGHT INTENSITJf Frandsen (1901) tested the response of L,«: ^ aximus - to. l i g h t . Most slugs were negatively phototactic, although several were attracted to the strongest i n t e n s i t y used (36,31 f t - c ) . Around 0.00007 f t - c , nearly as many slugs were attracted to the l i g h t as were repelled. He concluded that k l M i i i l »as negatively phototactic to strong l i g h t , p o s i t i v e l y phototactic to weak l i g h t , and neutral at some intermediate i n t e n s i t y . Frandsen (1901) has been widely quoted as showing that slugs are attracted to l i g h t when they are hungry. The basis of t h i s was h i s statement: " I t i s p o s s i b l e — and c e r t a i n observations seem to indicate that i t i s highly probable--that the food conditions of the animals have some influence on t h e i r responses to l i g h t . . . " He l a t e r goes on to say that the a t t r a c t i o n of some slugs to the l i g h t was "probably" because they were hungry. At no time was t h i s point experimentally v e r i f i e d . A number of physiological-behavioral studies u t i l i z i n g L. maximus and Dt laeve were c a r r i e d out by Crazier and h i s collaborators,exploiting the fact that the slugs were repelled by l i g h t (Crozier and Federighi, 1925; Crozier and Xibby, 1925; Crozier, 1926; wolf, 1927; Crozier and Solf, 1928,1929; Holf and Crozier, 1928; Crozier and Cole, 1929) , Crozier and Libby (1925) reported that 1^ maximus no longer responded to l i g h t after eating boiled potato, whereas raw potato did not have t h i s e f f e c t . Feeding sugars or i n j e c t i n g glucose s i m i l a r l y led to a b o l i t i o n of the l i g h t response. 106 Dainton (1954b) found t h a t t h e e f f e c t o f l i g h t cn da r k -adapted D. r e t i c u l a t u m mas t o a c t i v a t e them f o r l e s s than one hour, b e f o r e which t i m e a d a p t a t i o n was complete and the l i g h t had no f u r t h e r e f f e c t . /Whereas a d a p t a t i o n t o 40 f t - c a t 20° C r e q u i r e d one hour, dark a d a p t a t i o n r e g u i r e d between 1 and 2 hours. C r o z i e r and Wolf (1929) p r e v i o u s l y found t h a t DuJt. l a e v e adapted g u i c k l y t o l i g h t (5 m i n u t e s ) . At 12° e , 3 t o 4 h were r e g u i r e d f o r d a r k a d a p t a t i o n however ( h a l f t h i s time a t 20°-22° C ) . Based on t h e f a c t t h a t s l u g s r a p i d l y adapt t o l i g h t , and t h a t l i g h t c y c l e s d i d not e n t r a i n t h e a c t i v i t y r h y t h a of D. r e t i c u l a t u m . D a i n t o n (1954b) c o n c l u d e d t h a t l i g h t p l a y e d no p a r t i n r e g u l a t i n g t h e a c t i v i t y o f t h a t s p e c i e s . K a r l i n (1961) agreed w i t h D a i n t o n (1954a), t h a t t e m p e r a t u r e c y c l e s were i m p o r t a n t i n d e t e r m i n i n g s l u g a c t i v i t y , but d i s a g r e e d t h a t l i g h t was u n i m p o r t a n t . He found t h a t Ux. r e t i c u l a t u m o n l y became a c t i v e at n i g h t when l i g h t i n t e n s i t y was l e s s t h a n 1 f t - c . A l t h o u g h he p o i n t e d out t h a t such an o b s e r v a t i o n c o u l d have been due t c the c o r r e l a t i o n between l i g h t and t e m p e r a t u r e , he a l s o noted t h a t a c t i v i t y was not i n i t i a t e d i n t h e f i e l d when a i r t e m p e r a t u r e s f e l l below 21° C, i f l i g h t i n t e n s i t y was h i g h . T h i s o b s e r v a t i o n was c o n t r a d i c t o r y t o D a i n t c n * s t h e o r y of r e g u l a t i o n by temperature changes. K a r l i n (1961) and l a t e r , N e w e l l (1965), s u ggested t h a t s l u g s were a c t i v a t e d by some f a c t o r o t h e r than l i g h t i n t e n s i t y , but t h a t h i g h l i g h t i n t e n s i t y c o u l d p r e v e n t them from emerging onto the s o i l s u r f a c e . Getz ( 1 9 6 3 ) found t h a t t h r e e s l u g s p e c i e s , i n c l u d i n g p. r e t i c u l a t u m always moved towards the l o w e s t a v a i l a b l e 107 i n t e n s i t y o f l i g h t . N e w e l l (1965) d i s c o v e r e d t h a t c o n t i n u o u s use of p h o t o f l o o d lamps p r e v e n t e d t h e normal a c t i v i t y o f D. r e t i c u l a t u m on t h e s u r f a c e . Lewis (1967) found t h a t t h e number of A. a t e r f v i s i b l e i n c h o i c e chambers was i n v e r s e l y p r o p o r t i o n a l to the l o g a r i t h m o f l i g h t i n t e n s i t y above an i n t e n s i t y of 20.26 f t - c . Below 20.26 f t - c t h e s l u g s were a t t r a c t e d t o t h e l i g h t , whereas they appeared i n d i f f e r e n t a t t h a t c r i t i c a l i n t e n s i t y . L e w i s (1967) b e l i e v e d t h a t ft* ftfrtr responded mostly t o i n f r a - r e d wavelengths, s i n c e i n c a n d e s c e n t l i g h t was more r e p e l l e n t t h a n f l o u r e s c e n t . L i g h t passed t h r o u g h water t o remove much o f t h e i n f r a - r e d was s i m i l a r l y l e s s r e p e l l e n t . N e w e l l and N e w e l l (19 68) suggested t h a t t h e " a c c e s s o r y r e t i n a " found i n D. r e t i c u l a t u m f u n c t i o n e d as an i n f r a - r e d r e c e p t o r . P o u l i n (1967) conducted a s t u d y o f l i g h t r e sponses o f A i a t e r s i m i l a r t o t h a t of L e w i s (1967). S l u g s had a c h o i c e o f e n t e r i n g darkened o r uncovered a r e a s and the l i g h t i n t e n s i t y i n t h e s e uncovered a r e a s was v a r i e d from 0.5-250 f t - c w i t h a 40 watt i n c a n d e s c e n t l i g h t . P o u l i n * s graph shows, t h a t At, a t e r was a t t r a c t e d t o t h e l i g h t a t i n t e n s i t i e s up t o s l i g h t l y more th a n 1 f t - c . At h i g h e r i n t e n s i t i e s , t h e response was i n v e r s e l y p r o p o r t i o n a l t o t h e l o g a r i t h m of l i g h t . Thus the g e n e r a l p a t t e r n found by P o u l i n (1967) and L e w i s (1967) agree, a l t h o u g h the c r i t i c a l t h r e s h o l d between a t t r a c t i o n and r e p u l s i o n d i f f e r e d c o n s i d e r a b l y . P o s s i b l y t h i s d i s c r e p e n c y was due t o d i f f e r e n c e s i n t h e t e m p e r a t u r e s used i n t h e s t u d i e s . P o u l i n (1967) c a r r i e d out h i s e x p e r i m e n t a t 23.8°-26.7° C, whereas Lewis (1967) d i d most of h i s e x p e r i m e n t s a t 10°-13° C. D a x l (1969) found t h a t 108 even though c o n t i n u o u s l i g h t d i d not prevent a c t i v i t y by P. r e t i c u l a t u m i t d e l a y e d the peak i n a c t i v i t y by two h o u r s . P r o b a b l y a d i f f e r e n c e i n i n t e n s i t y e x p l a i n s t h e d i s c r e p e n c y between t h i s f i n d i n g and t h a t o f N e w e l l (1965), mentioned e a r l i e r . Other i n v e s t i g a t o r s have found t h a t l i g h t a l s o a f f e c t e d the a c t i v i t y o f s n a i l s . Thus E l w e l l and Dimer (1971) c o n c l u d e d t h a t l i g h t was a f a c t o r l i m i t i n g t h e a c t i v i t y o f A n g u i s p j r a a l t e ^ n a t a -. B a c h i n (1975) o b s e r v e d t h a t O t a l a l a c t e a sometimes became a c t i v e when l a b o r a t o r y l i g h t s were t u r n e d o f f . F i n a l l y , Dundee (1977) r e c e n t l y showed t h a t v e r o n i c e l l i d s l u g s were r e p e l l e d by l i g h t i n t e n s i t i e s o f 44-260 f t - c , even i f t h i s meant e n t e r i n g a r e a s o f a v e r s i v e t e m p e r a t u r e . He concluded t h a t t emperature c o n t r o l l e d t h e t i m i n g of a c t i v i t y , but t h a t l i g h t d e t e r m i n e d where i t c o u l d o c c u r . D a i n t o n (1954b) was the o n l y a u t h o r t o immerse h e r a n i m a l s i n a water bath t o s t u d y t h e i r r e a c t i o n t o l i g h t . Getz (1963) p l a c e d a water f i l l e d aguarium between the a n i m a l s and t h e l i g h t s o u r c e , and used a f l u o r e s c e n t l i g h t . He b e l i e v e d t h a t t h e 0.25° C t e m p e r a t u r e v a r i a t i o n between t h e c o v e r e d and uncovered h a l v e s o f t h e c h o i c e chamber had no i n f l u e n c e on the o r i e n t a t i o n o f t h e a n i m a l s . Lewis (1967,1969 ) argued t h a t t e m p e r a t u r e had no s i g n i f i c a n t e f f e c t on the s l u g s , w h i l e s i m u l t a n e o u s l y c l a i m i n g t h a t i t was t h e i n f r a - r e d p o r t i o n o f t h e spectrum t h a t a f f e c t e d them t h e most. S i n c e Dainton (1954a) showed t h a t D A r e t i c u l a t u m c o u l d respond t o temperature changes as s m a l l as 0.1° C/h, and because I was unable t o e n t i r e l y e l i m i n a t e temperature e f f e c t s when e n t r a i n i n g s l u g s such as D. r e t i c u l a t u m and A. a t e r t o 109 l i g h t c y c l e s , i t seemed a d v i s a b l e t o c a r e f u l l y a s c e r t a i n whether l i g h t c o u l d i n f l u e n c e the a c t i v i t y of s l u g s i n d e p e n d e n t l y of a s s o c i a t e d h e a t i n g e f f e c t s . D A r e t i c u l a t u m were p l a c e d i n a l i g h t - c h o i c e box 16 X 20 cm X 4 cm h i g h . H a l f of t h e p l a s t i c box was p a i n t e d b l a c k , whereas the o t h e r h a l f remained t r a n s p a r e n t . The bottom o f t h e box was l i n e d w i t h m o i s t paper t o w e l s t o f a c i l i t a t e l o c o m o t i o n , and t h e edges around t h e l i d were s e a l e d w i t h v a s e l i n e t o p r e v e n t l e a k a g e when t h e c o n t a i n e r was submerged. The box was immersed 10 cm below t h e s u r f a c e of a f a s t - f l o w i n g water bath at 15 •/-1° C, A r h e o s t a t a l l o w e d v a r i a b l e c o n t r o l of a 200 watt i n c a n d e s c e n t b u l b t h a t was suspended 10 cm above the water s u r f a c e , d i r e c t l y o v e r the t r a n s p a r e n t area o f t h e box. Thermocouples i n t h e l i g h t e d a r e a o f t h e box d i d not show any temp e r a t u r e v a r i a t i o n over the range o f l i g h t i n t e n s i t i e s employed. The e n t i r e experiment was conducted i n a s i n k c o v e r e d w i t h a l i g h t - t i g h t box. A s m a l l door a l l o w e d o b s e r v a t i o n o f t h e s l u g s a t t h e h i g h e r l i g h t i n t e n s i t i e s . D. r e t i c u l a t u m c o l l e c t e d from t h e f i e l d were k e p t f o r a t l e a s t one week a t 15° C i n t o t a l d a r k n e s s , and were f e d a s u r p l u s amount o f c a r r o t r o o t . , S l u g s were removed f r c m the r e a r i n g chamber and were i m m e d i a t e l y i n t r o d u c e d t o t h e a p p a r a t u s i n groups o f t e n . A l l the s l u g s were o r i g i n a l l y p l a c e d i n the c e n t e r of the uncovered s i d e o f t h e c h o i c e chamber. The s l u g s were a l l o w e d one hour t o d i s t r i b u t e t h e m s e l v e s , a f t e r which t h e i r p o s i t i o n s were r e c o r d e d . Responses t o l i g h t i n t e n s i t i e s o f 10, 240, and 2,838 f t - c (measured i n s i d e the submerged c h o i c e chamber), were i n v e s t i g a t e d . The a p p a r a t u s proved u n s u i t a b l e f o r a c c u r a t e l y 110 c h a r a c t e r i z i n g the response of p. r e t i c u l a t u m t o l i g h t because some tended t o s h e l t e r i n t h e c o r n e r s o f t h e t r a n s p a r e n t a r e a and d i d not f i n d t h e i r way i n t o the darkened p o r t i o n of the chamber. However, i f the number of s l u g s a c t i v e i n the l i g h t was c o n s i d e r e d , t h e r e s u l t s c l e a r l y show t h a t D. r e t i c u l a t u m responded s t r o n g l y t o l i g h t a t c o n s t a n t temperature (Table X I ) . U n l i k e S a i n t o n ' s a n i m a l s (1954b), the s l u g s i n t h e p r e s e n t s t u d y showed no s i g n s of a d a p t i n g t o the l i g h t , even a f t e r a f u l l hour. at i n t e n s i t i e s as low as 10 f t - c , the r e p e l l e n t e f f e c t was e v i d e n t . At the h i g h i n t e n s i t y a l l a c t i v i t y i n t h e l i g h t e d a r e a ceased. S l u g s i n s t r o n g l i g h t withdrew t h e i r heads beneath t h e i r mantles and always attempted t o b u r y the f r o n t p a r t of t h e i r body i n t h e body o f a n o t h e r s l u g , or i n t h e c o r n e r s of t h e box. Those i n d i v i d u a l s t h a t moved i n t o the darkened a r e a u s u a l l y were s t i l l a c t i v e when t h e box was opened f o r i n s p e c t i o n , but even when th e y were i n a c t i v e , t h e y d i d not push t h e i r r e t r a c t e d heads i n t o c o r n e r s o r a g a i n s t t h e b o d i e s o f o t h e r s l u g s . O b s e r v a t i o n s a t 240 and 2,838 f t - c showed t h a t a s l u g from t h e darkened a r e a o c c a s i o n a l l y v e n t u r e d i n t o the l i g h t f o r a few cm, but t h e n r e t u r n e d t o t h e d a r k . At the h i g h e s t l i g h t i n t e n s i t y , most i n d i v i d u a l s remained a t t h e extreme end of the dark s e c t i o n . The d i f f e r e n c e s i n b e h a v i o r between t h o s e i n t h e l i g h t and d a r k , and t h e i r p r e f e r e n c e f o r t h e d a r k , showed t h a t s l u g s ' a c t i v i t y can be c u r t a i l e d by h i g h l i g h t i n t e n s i t y . S i n c e l i g h t i n t e n s i t y appeared to be an i m p o r t a n t f a c t o r g o v e r n i n g t h e a c t i v i t y o f s l u g s and s n a i l s , i t was i n c l u d e d i n t h e f i n a l c o r r e l a t i o n - r e g r e s s i o n model. I n the m a j o r i t y o f c a s e s the l o g a r i t h m i c t r a n s f o r m a t i o n o f l i g h t proved t o be more h i g h l y 111 correlated with a c t i v i t y than the untransformed value (Table XXV) . The shape of the response to l i g h t was s i m i l a r among a l l the species examined. Figures 25, 26, and 27 provide examples of molluscs with a very low ( - Liif maximus-- ), an intermediate (D. reticulatum ) . and a high threshold { C A n e m o r a l i s ) . Table XI. The Influence of Light Intensity on the A c t i v i t y of Cexoceras reticulatum in a Light-choice Box at 15° C, Light Intensity Number of Proportion i n Proportion (ft-candles) Slugs the Light Active i n Used the Light 0 70 0.500 0.500 (expected) 10 30 0.267 0.267 240 50 0.240 0.102 2,838 50 0. 102 0.000 112 gure 25. Relationship of Activity .of Limax maximus • to Light Intensity, Illustrating the Best-fitting Begression Line and the Threshold Line. PROPORTION OF POPULATION ACTIVE o o ro O U l o o o o CD X H m z CO I o > O r~ m co o o ro o o CD o o o o o o o 03 o o ro ro o o ro cn O O OJ O o O OJ o o » S ro oo OJ cn ro "TJ A O o o o o o m « o m > CO 3) CO o CO o — 2: <2 -< + o 6 o o o m r -9 ro 0> -!> OJ r o a •< —l i> x m oo CO U l 0 ro ui co oo o X + 9 6 o OJ 00 o o X + 9 6 CL L 114 F i g u r e 26. A c t i v i t y of P e r o c e r a s r e t i c u l a t u m i n R e l a t i o n t o L i g h t I n t e n s i t y , I l l u s t r a t i n g the R e g r e s s i o n L i n e and Outer A c t i v i t y L i m i t . . •00 n > l -o < z o h-< •io Q_ O D_ U. O z o I— cr o 0-o cr o_ 0-75 0-50 H 0-25 0 -00 T H R E S H O L D M O D E L Y =-0 0 0 0 5 6 X + 0-8189 REGRESS ION MODEL ARCSIN(V^T )= - 0 1 0 2 0 ( L O G ( X ) )+ 0 - 5 0 0 5 p < 0 0 0 0 0 r 2 = 0-64, • oca *>• «• I I I I I I I I I ! | I I I I | I I I I | I I I—I | I I I I [ I I I I | I I I 500 1000 1500 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 L IGHT INTENS ITY ( F T . - C A N D L E S ) 116 Figure 27. Relationship of the activity of Ce£ae_a nemoralis to Light Intensity, Illustrating the Regression Line and Estimated Outer Threshold, 1-00 -i LU > o < 0-75 1 i ii : i T H R E S H O L D M O D E L Y = I 0 5 5 - 0 - 2 3 7 6 ( L 0 G I 0 ( X + 0 0 0 ) R E G R E S S I O N M O D E L A R C S I N W Y + 0 0 0 I )= 0 - 4 5 7 3 - 0 I 0 3 3 ( L 0 G I 0 ( X +0-001))-0 - 5 4 2 8 P < 0 0 0 0 0 3 a . o C L LL. O H CC o CL o CC CL 0 - 5 0 0 - 2 5 H \ \ 0 0 - 0 0 n—I—i—i—i—i—i—i—i—\—i—\—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—n—i—i—i—i—n 0 2 0 0 6 0 0 1 0 0 0 1 4 0 0 1 8 0 0 2 2 0 0 2 6 0 0 3 0 0 0 3 4 0 0 3 8 0 0 L I G H T I N T E N S I T Y ( F T - C A N D L E S ) 118 Ta b l e X I I . Bes t B e g r e s s i o n E q u a t i o n s E s t i m a t i n g t h e Outer A c t i v i t y L i m i t s of 7 M o l l u s c a n S p e c i e s w i t h L i g h t . Dependent Independent C o e f f i c i e n t C o n s t a n t V a r i a b l e V a r i a b l e P e r o c e r a s r e t i c u l a t u m L i g h t -0.00056 0.8189 Log '.Arion a t e r L i g h t -0,000324 -0.1571 Cejaaea n § nigral i s l o g - L i g h t -0.2376 1.055 A r i o l i m a x columbianus L i q b t -0.000514 -0. 1028 Iima.x maximus L o g - L i g h t -0.2598 0.8358 A r i o n S U b f J 3 S £ U S L o g - L i g h t -0.2581 0.8022 P e r o c e r a s caruanae L o g - L i g h t -0.2428 0.7363 I t can be seen t h a t most a c t i v i t y o c c u r r e d i n da r k n e s s . However, t h e r e appears t o be an upper l i m i t o f a c t i v i t y i n any g i v e n l i g h t i n t e n s i t y , which p r o b a b l y r e p r e s e n t s t h e response t o l i g h t i n t e n s i t y when no o t h e r f a c t o r s are l i m i t i n g . . T h e f a c t t h a t t h i s o u t e r l i m i t i s o f t h e e x a c t form d e s c r i b e d from l a b o r a t o r y s t u d i e s (e.g. P o u l i n , 1967) f u r t h e r s u p p o r t s t h e c o n t e n t i o n t h a t i t i s a t h e s h o l d . In o r d e r t o o b t a i n e g u a t i o n s f o r t h i s parameter t o i n c l u d e i n t h e t h r e s h o l d model, p o i n t s a l o n g t h e boundary were e s t i m a t e d by eye, and a b e s t - f i t t i n g r e g r e s s i o n l i n e was g e n e r a t e d on t h e computer. The e q u a t i o n s f o r seven of t h e m o l l u s c s s t u d i e d a r e p r o v i d e d i n T a b l e X I I , No e g u a t i o n s were e s t i m a t e d f o r A. h o r t e n s i s and A . - c l r c u m s c r i p t u s -because t h e r e were so few o b s e r v a t i o n s of t h e i r a c t i v i t y . , 119 The i n f l u e n c e o f l i g h t c y c l e s on e n t r a i n i n g t h e rhythms of t e r r e s t r i a l m o l l u s c s was c o n s i d e r e d e a r l i e r . J u s t as D a i n t o n (1954a) showed t h a t changes i n t e m p e r a t u r e were more i m p o r t a n t i n s t i m u l a t i n g a c t i v i t y t han was ambient t e m p e r a t u r e (see temperature s e c t i o n ) , i t i s t h e changes i n l i g h t i n t e n s i t y , f a l l i n g o r r i s i n g t h r ough some c r i t i c a l t h r e s h o l d , t h a t a r e i m p o r t a n t when l i g h t i s a z e i t g e b e r . The v a r i a b i l i t y due t o the t i m i n g of t h e c i r c a d i a n rhythm might be b e t t e r e x p l a i n e d by changes i n l i g h t i n t e n s i t y than by ambient l i g h t i n t e n s i t y a l o n e . I n a d d i t i o n , t h e speed o f dark and l i g h t a d a p t a t i o n depends on l i g h t i n t e n s i t y , a p h y s i o l o g i c a l response t h a t c o u l d cause s l u g s t o r e a c t t o the d i r e c t i o n and degree of changes i n l i g h t , as w e l l as t o the ambient i n t e n s i t y . Changes i n l i g h t a l s o c o u l d account f o r v a r i a t i o n i n t h e data due t o the s e a s o n a l changes i n the d u r a t i o n o f t w i l i g h t . The c o r r e l a t i o n o f a c t i v i t y w i t h changes i n l i g h t i n t e n s i t y p,er se was q u i t e low (Table XXV), m a i n l y due t o t h e n o n - l i n e a r i t y o f the r e l a t i o n s h i p ( F i g u r e 2 8 ) . Some improvement was o b t a i n e d by a g u a r t i c f i t ( T a b l e XXV). The d a t a i n d i c a t e a f a s t d e c l i n e i n t h e numbers a c t i v e w i t h i n c r e a s i n g l i g h t i n t e n s i t y (as a n i m a l s homed), and a s l i g h t l y f a s t e r i n c r e a s e i n numbers w i t h d e c r e a s e s i n l i g h t (as a n i m a l s emerged). 120 Figure 28, activity of Deroceras reticulatum i n Belation to Changes in Light Intensity, Illustrating the Best-fitting Begression Eguation. (1=0.1255X-0.6285X2+C.6732X»+0.6037) X «as multiplied by 0.001 before analysis. PROPORTION OF POPULATION ACTIVE 122 PHASE OF THE MOON Newell {1968) observed that D, /reticulatum•• frequently crawled home before sunrise, and postulated that they were responding to increasing brightness of the sky at that time, lewis (1967) found that a. ater preferred low illumination at night to complete darkness. I f slugs respond to low l i g h t i n t e n s i t i e s , as these findings suggest, then the phase of the moon could modify t h e i r behavior. On some nights I found moonlight bright enough f o r reading. However, the l i g h t meter was not sensitive enough to measure the lower i n t e n s i t i e s of moonlight, so the phase cf the moon (35 f u l l moon) was included instead. Using phase cf the moon as a factor also allows one to detect any posssible lunar rhythm, as well as responses to l i g h t i n t e n sity. An innate lunar rhythm w i l l cycle with a lunar p e r i o d i c i t y , even i f the intensity of moonlight cn some observation nights i s modified by cloud cover. Danthanarayana (1976) and Saunders (1976) reviewed some of the l i t e r a t u r e concerned with lunar rhythms among insects. There are more and mere reports of lunar and lunar-day p e r i o d i c i t i e s occurring i n t e r r e s t r i a l animals, p a r t i c u l a r l y nocturnal ones (e.g. Kerfoot, 1967; Kcltermann, 1974: bees; Hadley and Williams, 1968: scorpions; Youthed and Horan, 1969: ant-lions; FitzGerald and Bider, 1974: toads; Danthanarayana, 1976: moths). The correlations of moon-phase with the a c t i v i t y of various molluscan species i s given i n Table XXV. Moonlight was included 123 i i n r e g r e s s i o n e g u a t i o n s as a s i g n i f i c a n t f a c t o r e x p l a i n i n g some of t h e v a r i a t i o n i n t h e a c t i v i t y o f some s p e c i e s (Table X X V I I ) . l E i P J B J T J j f i J G e n e r a l D i s c u s s i o n Shen r e l a t i n g ambient te m p e r a t u r e to b i o l o g i c a l s y s t e m s , i t i s c o n v e n i e n t t o s u b d i v i d e i t i n t o c a t e g o r i e s of s p e c i a l p h y s i o l o g i c a l c r b e h a v i o r a l consequence, as f o l l o w s : Upper l e t h a l t e m p e r a t u r e Upper locomotor l i m i t Upper d e t r i m e n t a l t emperature ( f o r growth o r r e p r o d u c t i o n ) Upper a c t i v i t y l i m i t P r e f e r r e d t e m p e r a t u r e i n a g r a d i e n t (range) O p t i m a l t e m p e r a t u r e f o r r e p r o d u c t i o n and/or growth (range): O p t i m a l t e m p e r a t u r e f o r a c t i v i t y (range) Lower a c t i v i t y l i m i t l o w e r d e t r i m e n t a l t e m p e r a t u r e Lower locomotor l i m i t Lower l e t h a l t e m p e r a t u r e A l t h o u g h o v e r s i m p l i f i e d , such a c l a s s i f i c a t i o n i s a u s e f u l framework f o r d i s c u s s i o n and c l a r i f i c a t i o n o f c e r t a i n p o i n t s . P r o b a b l y t h e most i m p o r t a n t p o i n t f o r t h e p r e s e n t s t u d y i s t h e n e c e s s i t y t o c o n s i d e r l o c o m o t o r and a c t i v i t y l i m i t s s e p a r a t e l y . There has been a tendency f o r a u t h o r s o b s e r v i n g a n i m a l s i n l a b o r a t o r y c o n d i t i o n s t o assume t h a t , s i n c e they a r e a b l e t o move at p a r t i c u l a r t e m p e r a t u r e s , t h e y w i l l n o r m a l l y become 124 a c t i v e a t comparable t e m p e r a t u r e s i n t h e f i e l d ( e . g . , M e l l a n b y , 1961). The f a c t t h a t l o c o m o t o r and a c t i v i t y t h r e s h o l d s may be d i f f e r e n t f i r s t became apparent i n e x p e r i m e n t s w i t h c o c k r o a c h e s , P e r i g l a n e t a a u s t r a l i e n s j s . At a temperature o f a p p r o x i m a t e l y 15° C, t h e roaches d i d not l e a v e t h e i r s h e l t e r s ( s i m i l a r t o t h e a c t i v i t y chambers d e s c r i b e d f o r s l u g s ) a l t h o u g h t h e y remained w i t h o u t f o o d f o r a week. They were c a p a b l e of f a i r l y a d r o i t movement, whenever t h e s h e l t e r was opened, but d i d n o t f o r a g e o u t s i d e i t . When t h e t e m p e r a t u r e was r a i s e d t o 25° C, t h e a n i m a l s e x h i b i t e d a normal a c t i v i t y p a t t e r n . Most p o i k i l i o t h e r m i c a n i m a l s a r e p r o b a b l y i m m o b i l i z e d b e f o r e t h e y r e a c h t h e i r l o w e r or upper l e t h a l t e m p e r a t u r e s , a l t h o u g h , s i n c e t ime i s a f a c t o r * many i n d i v i d u a l s may move f o r a p e r i o d i n t e m p e r a t u r e s t h a t w i l l e v e n t u a l l y prove l e t h a l i f they do not escape. A c t i v i t y p a t t e r n s a r e adapted t o a v o i d exposure t o extremes, and t o pre v e n t a n i m a l s from becoming i m m o b i l i z e d i n u n f a v o u r a b l e l o c a t i o n s . Thus, i t i s e c o l o g i c a l l y i m p o r t a n t t o d i s t i n g u i s h between locomotory and a c t i v i t y l i m i t s . Only D. r e t i c u l a t u m has been s t u d i e d s u f f i c i e n t l y t o a l l o w a comprehensive p i c t u r e o f i t s t e m p e r a t u r e r e l a t i o n s . A b r i e f d e s c r i p t i o n i s i n c l u d e d here t o s e r v e as a model. Temperatures of -10 t o -80 C were always l e t h a l (Hawley, 1922; G e t z , 1959), whereas no m o r t a l i t y o c c u r r e d a t -2.5° C ( P i n d e r , 1969). C h i c h e s t e r (1968) narrowed t h e l e t h a l range (-5 t o -4° C ) , a l t h o u g h C a r r i c k (1942) found t h a t two s l u g s s u r v i v e d e x p osure t o -50 C. P i n d e r (1969) found 50% m o r t a l i t y i n 35 h a t -3.5o C, whereas 100% m o r t a l i t y o c c u r r e d i n 28 h a t -4.5° C. 125 The lower locomotor l i m i t was found to be 0° C (Melanby, 1961), and -2.5° C (air temperature) by lebley (1964) and Baker (1973). Growth i s slow at 5<> C (Arias and Crowell, 1963), and Carrick (1938) considered t h i s to be the developmental threshold for t h i s species. I t i s at t h i s approximate temperature that a c t i v i t y declines r a p i d l y or ceases (Carrick, 1938; Sfhite, 1959; Karlin and Naegel, 1960). Shite (1959) and flelanby (1961), however, claim that marginal amounts of crawling and feeding may persist at temperatures as low as 0.56-0.8° C. Hewell (1965) claimed that a c t i v i t y was independent of temperature between 9-160 c, and Carrick (1942) observed greatest a c t i v i t y between 10-200 c. This range corresponds to the optimum f o r growth, s u r v i v a l , and reproduction (Carrick, 1942; Arias and Crowell, 1963; Judge, 1972a; Bol l o , 1974). The upper a c t i v i t y l i m i t i s just below 25° C, since there i s very l i t t l e movement of slugs at that temperature (Carrick, 1942). Longevity and maximum size were reduced by a temperature of 21.10 c, and 75% mortality occurred i n three days at 26.7« C (Judce, 1972a). At 30» C, 80% mortality occurred i n 4 h and at 3 5 0 c, 100% of the slugs died i n one hour (Carrick, 1942). At 36° C, slugs died with exposures greater than 15 minutes (Getz, 1959). Other species of molluscs have the ranges of the various temperature parameters contracted, expanded and/or s h i f t e d to higher or lower temperatures, as w i l l be noted when relevant. Ambient temperature has long been considered one of the major factors c o n t r o l l i n g the a c t i v i t y of slugs. Positive correlations of numbers of slugs on the s o i l surface with temperature, were observed by Ka r l i n and Naegel (1960), Sebley 126 (1964), and Crawf ord-Sidebotham (1972), Hunter (1968b) found t h a t a t c o n s t a n t t e m p e r a t u r e s r a n g i n g from 0.5° C t o 25° C i n t h e l a b o r a t o r y , a c t i v i t y of P A r e t i c u l a t u m * A. h o r t e n s i s , and M i l a x feudapestensis i n c r e a s e d w i t h i n c r e a s i n g t e m p e r a t u r e t o 20 o C, but was lower a t 25° C. S i g n i f i c a n t r e g r e s s i o n s of f e e d i n g a c t i v i t y w i t h t e m p e r a t u r e were a l s o o b t a i n e d f o r each s p e c i e s i n f i e l d cages, a l t h o u g h the maximum temp e r a t u r e observed i n t h i s case was o n l y 12° C. B a i l e y (1945) showed t h a t t emperature was an i m p o r t a n t f a c t o r g o v e r n i n g the a c t i v i t y o f the s n a i l MJ. a s j p j r s a , and Cameron (1970b) found t h a t t e m p e r a t u r e i n f l u e n c e d t h e a c t i v i t y o f C. n e m o r a l j s . , The B e l a t i o n s h i p Of A c t i v i t y To Temperature I n The F i e l d I n t h e p r e s e n t s t u d y , c o r r e l a t i o n s o f s l u g a c t i v i t y w i t h ambient t e m p e r a t u r e s measured i n s i d e t h e s h e l t e r s , on the s o i l s u r f a c e , and a t h e i g h t s o f 10 cm and 30 cm a r e c o m p i l e d i n T a b l e XXV. I n most c a s e s t h e b e s t l i n e a r c o r r e l a t i o n was o b t a i n e d w i t h s u r f a c e t e m p e r a t u r e . T r a n s f o r m a t i o n s t o l o g a r i t h m s d i d not improve the f i t , a l t h o u g h a l o g a r i t h m i c t r a n s f o r m a t i o n o f t h e dependent v a r i a b l e d i d . The r e l a t i o n s h i p between s l u g a c t i v i t y and ambient s u r f a c e temperature f o r D. r e t i c u l a t u m . S x c a r j i a n a e * L t maximus. Ca n e m o r a l i s x A^ columbianus,, a t e r and A A sujbf uscus a r e shown r e s p e c t i v e l y i n F i g u r e s 29, 30, 31, 32, 33, 34, and 35. JLL c i f c u m s c r i p t u s and kf h o r t e n s i s were not i n c l u d e d because o f too few o b s e r v a t i o n s . These f i g u r e s c l e a r l y show t h a t a l i n e a r model i s a poor 127 d e s c r i p t o r of the s i t u a t i o n . T h e r e f o r e , p r e v i o u s work hy o t h e r a u t h o r s , a l l o f whom used o n l y l i n e a r models, must be viewed w i t h extreme c a u t i o n . The shape of t h e s c a t t e r diagrams suggested t h a t c o n s i d e r a b l e improvement c o u l d be o b t a i n e d by a g u a r t i c f i t of te m p e r a t u r e t o a c t i v i t y , so r e g r e s s i o n models were o b t a i n e d by f i t t i n g a f o u r t h - d e g r e e p o l y n o m i a l f o r each s l u g s p e c i e s (see L i t t l e and H i l l s , 1975) . The computer r e c o g n i z e d t h e f o u r t h power p o l y n o m i a l t o be p e r f e c t l y c o r r e l a t e d w i t h t h e o t h e r s , and dropped i t from t h e e g u a t i o n . V a l u e s of r f o r the r e s u l t i n g c u b i c e g u a t i o n s proved t o be s u p e r i o r t o l i n e a r c o r r e l a t i o n s (Table XXV). T h e r e f o r e , i n th e f i n a l c o r r e l a t i o n - r e g r e s s i o n model, t h r e e p o l y n o m i a l s were i n c l u d e d t o be s t account f o r the i n f l u e n c e of ambient temperature. The r e g r e s s i o n l i n e s p r e d i c t e d by a c u b i c f i t o f temperature on a c t i v i t y pass t h r o u g h t h e c e n t e r o f t h e data (see f i g u r e s ) . However, s c r u t i n y o f t h e f i g u r e s s t r o n g l y s u g g e s t s t h a t the extreme v a l u e s r e p r e s e n t some upper l i m i t of a c t i v i t y f o r any g i v e n t e m p e r a t u r e . S i n c e t h e p l o t t e d p o i n t s r e p r e s e n t t h e f i n a l p r o d u c t o f a l l t h e i n t e r a c t i n g i n t e r n a l and e x t e r n a l f a c t o r s g o v e r n i n g a c t i v i t y , i t i s l i k e l y t h a t t h e maximum v a l u e s of a c t i v i t y a t any g i v e n temperature r e p r e s e n t t h o s e t i m e s when no o t h e r f a c t o r was l i m i t i n g . P o i n t s below t h i s *limit» p r o b a b l y r e p r e s e n t t i m e s when some o t h e r f a c t o r was s u p r e s s i n g a c t i v i t y i n d e p e n d e n t l y of t e m p e r a t u r e . . I f s o , t h e c o r r e l a t i o n - r e g r e s s i o n model b a d l y r e p r e s e n t s t h e d a t a . In o r d e r t o o b t a i n a g u a n t i t a t i v e d e s c r i p t i o n o f the upper a c t i v i t y l i m i t s a s s o c i a t e d w i t h t e m p e r a t u r e , c u r v e s were f i t t e d 128 by ©ye, and p o i n t s from t h e s e c u r v e s were f i t t e d t o a f c u r t h o r d e r p o l y n o m i a l e q u a t i o n by c o r r e l a t i o n - r e g r e s s i o n a n a l y s i s (Table X I V ) . S i n c e t h e s e e g u a t i o n s sometimes produced v a l u e s e x c e e d i n g 1.00 or l e s s than 0.00, t h e s e u n r e a l i s t i c v a l u e s were m o d i f i e d by a p p r o p r i a t e F o r t r a n s t a t e m e n t s f o r the f i n a l t h r e s h o l d model. Thus a c l e a r i n d i c a t i o n of an u n r e a l i s t i c t h r e s h o l d model would be d r a s t i c o v e r e s t i m a t i c n c f t h e degree o f s l u g a c t i v i t y a t any g i v e n t i m e . There appears t o be a t y p i c a l p a t t e r n t o the r e l a t i o n s h i p between s l u g a c t i v i t y and s u r f a c e temperature when the upper l i m i t s a r e examined. T h i s r e l a t i o n s h i p i s most re m a r k a b l e i n p. caruanae which had i t s h i g h e s t a c t i v i t y w i t h i n a narrow band of temperature w i t h an optimum a t 16.1° C ( F i g u r e 2 9 ) . A c t i v i t y d e creased r a p i d l y on e i t h e r s i d e o f t h i s band, b u t t h e d e c r e a s e i n a c t i v i t y a t t e m p e r a t u r e s g r e a t e r than 16° c was more p r e c i p i t o u s t h a n t h a t on the l o w e r s i d e . Such a narrow t e m p e r a t u r e t o l e r a n c e c o u l d account f o r the low l e v e l s o f a c t i v i t y o b s e r v e d f o r t h i s s p e c i e s most o f the t i m e . The b e s t - f i t t i n g m u l t i p l e r e g r e s s i o n e q u a t i o n g e n e r a t e d f o r Ux. caruanae i s g i v e n i n T a b l e X I I I . 129 T a b l e X I I I . R e g r e s s i o n E g u a t i o n R e l a t i n g A c t i v i t y of P e r o c e r a s caruane t o S u r f a c e Temperature. Dependent v a r i a b l e = L o g ( A r c s i n (Sgrt (Y+0.001) )) r 2=0.4763 S.E.=0.3669 P=0.00000 V a r i a b l e C o e f f i c i e n t S.E F - P r o b a b i l i t y S u r f a c e Temperature 34.5971 4.783 0.0000 S u r f . Temp. 2 -215.0091 28.310 0.0000 S u r f . Temp.3 343.3448 51.580 0.0000 Constant -1. 9702 0. 253 tem p e r a t u r e was o r i g i n a l l y m u l t i p l i e d by 0.01 The best f i t t i n g t h r e s h o l d e g u a t i o n f o r P. caruanae i s g i v e n i n T a b l e XIV. 130 Figure 29. A c t i v i t y Pattern of Peroceras caruanae i n Relation to Surface Temperature, I l l u s t r a t i n g the Regression Line and Outer A c t i v i t y Limit. L E I 132 Table XIV. Best Begression Eguations Describing the Outer activity Limits Associated With Temperature for 7 Molluscan Species. -0.01308 0.0 s P € c i e s Coefficients Temperature Temp. * BSfocejcas SttAculaJtum * 0.43479 arion ater * 0.35728 Oepaea JlSlSialiS 0.76256 Ariclimax ZQlM jManus 0. 18968 Limax maximus 0.0 arion subfiscus * 0.155156 Peroceras caruanae * 0.21694 0.0 *. indicates a logarithmic transformation Temp.3 Constant -0.021798 0.000262 -2.48138 0.019616 0.0 -2. 39 812 -0.046182 0.000816 -2.8938 -0.0066769 0.0 -0.59815 -0.0 0094 -0. 15183 -0.000353 - 1 . 15839 -0.000314 -2. 26173 -O.J., reticulatum*s peak activity occurred at 15° C and f e l l rapidly above 18.5° C (Figure 30). Very small amounts of activity were observed at temperatures as high as 27° C, but these slugs were probably going home. Activity diminished more slowly with decreasing temperatures, and no slug emerged below 133 3° C. O b s e r v a t i o n s a t low t e m p e r a t u r e s (3° to 4° c } showed t h a t the s l u g s were a c t i v e f o r o n l y v e r y s h o r t i n t e r v a l s , and d i d not t r a v e l f a r from the e n t r a n c e s of t h e i r s h e l t e r s . These r e s u l t s compare v e r y w e l l w i t h t h e l i t e r a t u r e summary p r o v i d e d e a r l i e r . The b e s t r e g r e s s i o n e g u a t i o n o b t a i n e d f o r t h i s s p e c i e s i s g i v e n i n T a b l e XV. Table XV. R e g r e s s i o n E g u a t i o n R e l a t i n g A c t i v i t y o f P e r o c e r a s r e t i c u l a t u m and Temperature. Dependent v a r i a b l e = l o g ( A r c s i n ( S g r t (Y>0. 00 1)) ) r2=0.5969 S. E. = 0. 3666 P=0.00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l l t y S u r f a c e Temperature 24.5816 3.920 0.0000 S u r f . Temp. 2 -160.67 38 23.500 0.0000 S u r f . Temp.3 250.4263 43.660 0.0000 Co n s t a n t -1.2309 0.2067 Temperature was o r i g i n a l l y m u l t i p l i e d by 0.01 The b e s t - f i t t i n g t h r e s h o l d e g u a t i o n f o r • P f • / r g t i c u l a t u m •• i s g i v e n i n T a b l e XIV. 134 ure 30. The a c t i v i t y of Deroceras reticulatum i n Relation to Temperature, I l l u s t r a t i n g the Begression Line and Cuter Ac t i v i t y Limit., 136 F i g u r e 31 shows t h a t L A maximus has maximal a c t i v i t y between 13.5° and 15.5° C. A c t i v i t y d e c r e a s e s v e r y r a p i d l y w i t h h i g h e r t e m p e r a t u r e s , and t h e upper l i m i t f o r s u s t a i n e d a c t i v i t y i s p r o b a b l y about 19° C. A c t i v i t y d e c r e a s e s more s l o w l y below the optimum so t h a t even at 3.5° C a few s l u g s were a c t i v e . A t these low t e m p e r a t u r e s , however, s l u g s emerged from s h e l t e r s (which had t e m p e r a t u r e s between 13.5° and 15° C), t r a v e l l e d a s h o r t d i s t a n c e , and then r e t u r n e d home. Many s l u g s were observed c l u s t e r i n g i n t h e e n t r a n c e s w i t h t h e i r t e n t a c l e s extended o u t s i d e , a p p a r e n t l y r e l u c t a n t t o go i n t o t h e c o l d . S i m i l a r l y , a t t e m p e r a t u r e s c l o s e t o the upper l i m i t , many o b s e r v a t i o n s o f a c t i v i t y i n v o l v e d s l u g s t h a t were r e t u r n i n g home. The b e s t - f i t t i n g r e g r e s s i o n e g u a t i o n r e l a t i n g a c t i v i t y of L. maximus t o te m p e r a t u r e i s shown i n Ta b l e XVI. 137 Table XVI. R e g r e s s i o n E q u a t i o n f o r l i m a x maximus and S u r f a c e Temperature. Dependent v a r i a b l e = L o g ( f t r c s i n | S q r t (Y+0.001)) ) r2=0.3796 S.E.= 0.5470 1=0.00000 V a r i a b l e C o e f f i c i e n t S.E. ,. F - P r o f c a b i l i t y S u r f a c e Temperature 26.5674 5.849 0.0000 S u r f . Temp.2 -184.4418 35.0600 0.0000 S u r f . Temp. 3 314.2147 65.150 0.0000 Con s t a n t -1.4784 0.309 Temperature was o r i g i n a l l y m u l t i p l i e d by 0.01 The b e s t - f i t t i n g e g u a t i o n of the temperature t h r e s h o l d f o r t h i s s p e c i e s i s g i v e n i n T a b l e XIV. B e s i d e s a d j u s t i n g t h o s e v a l u e s t h a t were g r e a t e r than 1.00 or l e s s than 0.00 f o r t h e f i n a l t h r e s h o l d model, 19° C was s e t as t h e upper a c t i v i t y l i m i t f o r t h i s s p e c i e s . 1 3 8 Figure 31. Relationship of A c t i v i t y of M i a x m a x i m u s to Temperature, I l l u s t r a t i n g the Regression Line and Outer A c t i v i t y Limit. PROPORTION OF POPULATION ACTIVE 140 The r e l a t i o n s h i p o f t h e s n a i l C. n e m o r a l i s . t o temp e r a t u r e was t h e i n v e r s e of t h e t y p i c a l s l u g p a t t e r n (a r a p i d d e c r e a s e wi t h i n c r e a s i n g t e m p e r a t u r e and a s l o w e r d e c l i n e w i t h c o o l e r t e m p e r a t u r e ) . I n t h e s n a i l s , peaks o f a c t i v i t y o c c u r r e d between 11.5° and 14.0° C ( F i g u r e 32). A c t i v i t y decreased r a p i d l y w i t h f a l l i n g t e m p e r a t u r e , t h e r e b e i n g almost none below about 8° C, a l t h o u g h a few s n a i l s were a c t i v e a t as low as 5° C. A c t i v i t y g r a d u a l l y d i m i n i s h e d w i t h i n c r e a s i n g temperature u n t i l o n l y a few s n a i l s were s t i l l c r a w l i n g at 29.5° C. A l t h o u g h t h e s n a i l s * optimum t e m p e r a t u r e f o r a c t i v i t y i s s i m i l a r t o t h a t o f t h e s l u g s , t h e y a r e much more a f f e c t e d by c o l d , but l e s s a f f e c t e d by h i g h temperature. T h i s t o l e r a n c e a c c o u n t s f o r t h e i r a b i l i t y t o s u r v i v e p e r i o d s o f u n f a v o u r a b l y h i g h t e m p e r a t u r e , by c l i m b i n g p l a n t s o r a e s t i v a t i n g on t h e s o i l s u r f a c e , i n s t e a d of moving down s o i l c r e v i c e s l i k e s l u g s (Jarmovic and S o l l o i n p r e p a r a t i o n ) . The s n a i l s upper l e t h a l t e m p e r a t u r e i s c l o s e t o 35° C (Lamotte, 1959). Cameron (1970) found t h a t a c t i v i t y o f n e m o r a l i s decreased s h a r p l y below 8« C, but t h a t an alm o s t e g u a l l e v e l of a c t i v i t y was m a i n t a i n e d between 8° and 27° c. Cameron's a n a l y s i s , however, i n c o r p o r a t e d t h e t o t a l a c t i v i t y of s n a i l s from d i u r n a l l y v a r y i n g p h o t o p e r i o d s a t v a r i o u s c o n s t a n t t e m p e r a t u r e s , and t h u s t h e e f f e c t s of a c c l i m a t i o n would be s t r o n g e r t h a n i n t h e p r e s e n t s t u d y . The b e s t - f i t t i n g r e g r e s s i o n e g u a t i o n r e l a t i n g t he a c t i v i t y of £± n e m o r a l i s t o t e m p e r a t u r e i s found i n Table X V I I . The b e s t -f i t t i n g e g u a t i o n c a l c u l a t e d f o r t h e t h r e s h o l d model i s p r o v i d e d i n T a b l e XIV. 141 Table XVII. Begression Eguation for Cjjjaaea nemoralis and Surface Temperature Dependent variable=Log(Arcsin <Sgrt(1*0.001))) r*=0.5366 S.E.=0.4248 F=0.00000 Variable C o e f f i c i e n t S.E. F-Probability Surface Temperature 42.9446 4.543 o.oooo Surf. Temp.2 -267.5549 27.230 C.0000 Surf. Temp.3 442.5809 50. 600 0.0000 Constant -2.2852 0.2396 Temperature was o r i g i n a l l y multiplied by 0.01. 142 Figure 32. Activity of Ce paea nemoralis in Relation to Temperature, Illustrating the Regression Line and Outer Threshold Line. SURFACE TEMPERATURE (° C) 144 B i c h t e r (1976a) d e s c r i b e d t h e r e l a t i o n s h i p between the a c t i v i t y o f Affi c o l u m b i a n u s and ambient temperature. He s t a t e d t h a t f e e d i n g was g r e a t e s t a t 13° C, g r a d u a l l y d i m i n i s h i n g w i t h f a l l i n g temperature,and r a p i d l y d e c r e a s i n g w i t h r i s i n g ones. No f e e d i n g o c c u r r e d below 8° C o r above 16° C. S l u g s were a c t i v e a t h i g h e r t e m p e r a t u r e s i n d e c r e a s i n g numbers, but t h e y seemed t o be mcvirg t o wards c o o l e r p l a c e s . , Thus R i c h t e r , s o b s e r v a t i o n s conform t o t h e g e n e r a l p a t t e r n f o r s l u g s t h a t I have d e s c r i b e d F i g u r e 33 i l l u s t r a t e s t h e r e s u l t s I o b t a i n e d f o r h» c c l u m b i a n u s . High l e v e l s of a c t i v i t y o c c u r r e d netween 8.5 and 19.0° C, but t h e d i s t r i b u t i o n s u g g e s t s t h a t the a c t i v i t y p a t t e r n may be b i m o d a l . Such b i m o d a l i t y , i f not an a r t i f a c t , might be produced by a temperature polymorphism i n the p o p u l a t i o n . A l t e r n a t i v e l y t h e peaks c o u l d r e p r e s e n t d i f f e r e n t Kinds o f a c t i v i t y . T h i s l a t t e r p o s s i b i l i t y seems most l i k e l y , s i n c e A* goiumbianus appears t o t h e r m o r e g u l a t e b e h a v i o r a l l y a t h i g h e r t e m p e r a t u r e s ( B i c h t e r , 1976a). Thus, t h e lo w e r peak a t 11° C c o u l d r e p r e s e n t f e e d i n g b e h a v i o r , whereas t h a t a t 17° C, might be t h e r m o r e g u l a t o r y ( s h e l t e r t e m p e r a t u r e s d u r i n g summer n i g h t s u s u a l l y exceeded s u r f a c e v a l u e s ) . A s t u d y p r e s e n t l y underway s h o u l d answer t h i s g u e s t i o n . The b e s t c u b i c r e g r e s s i o n model r e l a t i n g numbers of a c t i v e A. c o l u m b i a n u s t o temperature i s g i v e n i n Table X V I I I . 145 Table X V I I I . B e g r e s s i o n E g u a t i o n f o r A r i o l i m a x columbianus and S u r f a c e Temperature. Dependent v a r i a b l e = L c g ( A r c s i n ( S g r t ( Y + 0.001)) ) r*=0.6153 S.E.=0,3197 P=0.00000 V a r i a b l e C o e f f i c i e n t S» 13 • ..: F - P r o b a b i l i t y S u r f a c e Temperature 20.8444 3.418 0.0000 S u r f . Temp.2 -127.1452 20.4 90 0.0000 S u r f . Temp. 3 179.3186 38.070 0.0000 Con s t a n t -1. 1866 0.1803 Temperature was o r i g i n a l l y m u l t i p l i e d by 0.01. S i n c e b i m o d a l i t y o f t h e p a t t e r n o f a c t i v i t y i n r e l a t i o n t o temperature has not been d e f i n i t e l y proven, f o r t h e p r e s e n t I must assume t h a t t h a t the b i m c d a l appearance was an a r t i f a c t f o r the purposes o f c a l c u l a t i n g t h e a c t i v i t y l i m i t (Table X I V ) . 146 Figure 33. A c t i v i t y of Ariolimax ColuiJaianus i n Relation to Temperature, I l l u s t r a t i n g the Regression Line and Outer A c t i v i t y Limit. 100 SURFACE TEMPERATURE C O 148 JU. a t e r was a c t i v e over a g r e a t e r range c f temperature t h a n o t h e r m o l l u s c a n s p e c i e s . Peak a c t i v i t y o c c u r r e d between 9.5 and 170 c ( F i g u r e 3 4 ) . A l t h o u g h a c t i v i t y d i m i n i s h e d p r e c i p i t o u s l y a t tem p e r a t u r e s g r e a t e r than 19° C, 14% o f the p o p u l a t i o n was s t i l l a c t i v e a t 22° C. A l t h o u g h t h e r e was l i t t l e a c t i v i t y a t and above 23° C, some i n d i v i d u a l s were s t i l l o u t s i d e s h e l t e r a t 29 . 7 5 ° C. A c t i v i t y d e c r e a s e d s h a r p l y below 8°, and t h e r e was none below 3° C. L i k e A. co l u m b i a n u s , t h e r e l a t i o n s h i p of J U • a c t i v i t y t o temperature h i n t s a t b i m o d a l i t y . These two s p e c i e s f r e g u e n t l y l i v e i n t h e same h a b i t a t , and e x h i b i t s i m i l a r b e h a v i o r t h e r e ( a l t h o u g h A. colu m b i a n u s c l i m b s more). Both s p e c i e s o f t e n r e s t i n r e l a t i v e l y exposed p l a c e s , e s p e c i a l l y i n woodland, and appear to be l e s s a f f e c t e d by e v a p o r a t i o n than o t h e r s l u g s . T h e i r t o l e r a n c e i s p r o b a b l y due t o t h e i r l a r g e s i z e and p r o p o r t i o n a l l y r e d u c e d s u r f a c e a r e a . L i k e A. c o l u m b i a n u s . A. a t e r may t h e r m o r e g u l a t e b e h a v i o r a l l y , which may acc o u n t f o r one of t h e peaks i n the graph. A l t h o u g h A A a t e r - c o n t a i n s two s u b s p e c i e s , a t e r and r u f u s , o n l y A. a t e r r u f u s was used i n the p r e s e n t s t u d y , so t h e apparent b i m o d a l p a t t e r n i s u n l i k e l y t o be g e n e t i c . The b e s t c u b i c r e g r e s s i o n model o b t a i n e d f o r A A a t e r i s shown i n T a b l e XIX. 149 T a b l e XIX. R e g r e s s i o n E g u a t i o n f o r A r i o n a t e r and S u r f a c e Temperature Dependent v a r i a b l e = L o g ( A r c s i n ( S g r t ( Y + 0 . 0 0 1 ) ) ) . r 2=0.6909 S.E.=0.3059 P=0. 00000 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y S u r f a c e Temperature 34. 3485 3.271 0.0000 S u r f . Temp. 2 -201.1627 19.60 0.0000 S u r f , Temp. 3 298.9339 36.43 0.0000 Con s t a n t -1. 8365 0.1725 Temperature was o r i g i n a l l y m u l t i p l i e d by 0.01. Because t h e b i m o d a l p a t t e r n might be an a r t i f a c t due t o i n s u f f i c i e n t d a t a , a unimodal c u r v e was assumed when the upper a c t i v i t y l i m i t s f o r temperature were p l o t t e d f o r t h i s s p e c i e s (Table X I V ) . 150 F i g u r e 34. A c t i v i t y of A r i o n a t e r i n R e l a t i o n t c Temperature, I l l u s t r a t i n g the R e g r e s s i o n L i n e , and Outer A c t i v i t y L i m i t . PROPORTION OF POPULATION ACTIVE 151 1 5 2 Peak activity of kt subfuscus occurred at 15° C, although activity was s t i l l high between 12° to 19° C (Figure 35), activity dropped precipitously at 19° c, and no slugs emerged above 22,75° C. as with other species, the decline in numbers with lower temperatures was much slower, activity ceased at 3.5° C. The best cubic eguation relating activity.of a . subfuscus to temperature for the correlation-regression model i s given in Table XX. 153 T a b l e XX. R e g r e s s i o n E q u a t i o n f o r A r i o n s u b f u s c u s and S u r f a c e Temperature. Dependent v a r i a b l e = L o g ( A r c s i n { S g r t (x+0, 00 1))) . E 2=0.5154 S.E. = 0.4229 P=0.00000 V a r i a b l e C o e f f i c i e n t S.E. . F - P f o b a b i l i t y S u r f a c e Temperature 23.8301 5.076 0.0000 S u r f . Temp. 2 -166.8451 29.50 0.0000 S u r f . Temp. 3 272. 1006 53.38 0.0000 Co n s t a n t -1.1405 0.2772 Temperature was o r i g i n a l l y m u l t i p l i e d by 0.01. The b e s t - f i t t i n g t h r e s h o l d e g u a t i o n r e l a t i n g a c t i v i t y t o temperature f o r t h i s s p e c i e s was i s g i v e n i n T a b l e XIV. .? 154 F i g u r e 35. A c t i v i t y of • A r i c n s u b f u s c u s i n R e l a t i o n t o Temperature, I l l u s t r a t i n g the R e g r e s s i o n L i n e and Outer A c t i v i t y L i m i t . PROPORTION OF POPULATION ACTIVE 55 L 156 A c u b i c f i t o f temperature and a c t i v i t y of J L a h o r t e n s i s proved t o be n o n - s i g n i f i c a n t . Those f o r JL*. S i i S i J l s f i L r i c i t t i i s were s i g n i f i c a n t , a l t h o u g h t h e y had very low v a l u e s of r 2 . The be s t r e g r e s s i o n e g u a t i o n f o r t h e l a t t e r s p e c i e s i s g i v e n below./ T a b l e XXI. R e g r e s s i o n E q u a t i o n f o r A r i o n c i r c u n s c r j p f t u s - and S u r f a c e Temperature. Dependent v a r i a b l e = L o g ( A r c s i n ( S g r t (Y+0. 001) )••). 82=0.0738 S.E. = 0.2393 P=0. 00002 V a r i a b l e C o e f f i c i e n t S.E. F - P r o b a b i l i t y S u r f a c e Temperature 9.4522 3.75 4 0. 0118 S u r f . Temp. 2 -68.8058 24.35 0.0050 S u r f . Temp. 3 130.7855 48.26 0.0070 Constant -1.6547 0. 1773 Temperature was o r i g i n a l l y m u l t i p l i e d by 0.01. 157 ACCLIMATION Two g e n e r a l phenomena are a s s o c i a t e d w i t h p r o l o n g e d p e r i o d s i n p a r t i c u l a r t e m p e r a t u r e s : 1) the l e t h a l t e m p e r a t u r e s , both h i g h and low, a r e l o w e r f o r t h o s e a n i m a l s adapted t o lower t e m p e r a t u r e s , and 2) a n i m a l s adapted t o c o l d have a h i g h e r metabolism than t h o s e a c c l i m a t e d t o warmer c o n d i t i o n s when t h e m e t a b o l i c d e t e r m i n a t i o n s a r e made a t a common t e m p e r a t u r e (Boy, 1963). On b e i n g p l a c e d i n a new t e m p e r a t u r e , t h e r e i s a r a p i d a l t e r a t i o n o f the r e s p i r a t o r y r a t e over a p e r i o d o f hours, u n t i l a new r a t e i s adopted. Over a l o n g e r p e r i o d , t h i s new r a t e changes g r a d u a l l y and f i n a l l y s t a b i l i z e s (Runham and Hunter, 1970). A c c l i m a t i o n o f m o l l u s c s might be expected t o i n f l u e n c e t h e i r p r e f e r r e d temperature f o r a c t i v i t y , a s w e l l a s t h e i r upper and lower l i m i t s f o r a c t i v i t y . Both t e r r e s t r i a l s l u g s ( S e g a l , 1959,1961; Boy, 1963,1969; R i s i n g and A r m i t a g e , 1969) and s n a i l s ( G e l i n e o and K o l e n d i g , 1953; B l a z k a , 1955), e x h i b i t the second phenomena mentioned above; a l t e r a t i o n of m e t a b o l i c r a t e w i t h temperature (measured as oxygen consumption). R i s i n g and A r m i t a g e (1969) r e l a t e d a c c l i m a t i o n t o temperature p r e f e r e n c e i n two s l u g s p e c i e s , i x j a x i i u e and f h i l o m j f c us c a r o l i n i a n u s . I n b o t h , t h e d i s t r i b u t i o n i n a temperature g r a d i e n t was a l t e r e d by p r e v i o u s a c c l i m a t i o n , i t maximus "tended t o p r e f e r t e m p e r a t u r e s s l i g h t l y h i g h e r than t h o s e a t which t h e y were a c c l i m a t e d . " However, e x a m i n a t i o n o f R i s i n g and A r m i t a g e * s d a t a shows t h a t s l u g s a c c l i m a t e d t o 15° C 158 or 5° C m o s t l y p r e f e r r e d t h e same range o f temperature (between 20-21° C ) , The r e s u l t s c f R i s i n g and Armi t a g e (1969) do, however, i n d i c a t e t h a t t h e r e a r e changes i n t e m p e r a t u r e p r e f e r e n c e s , and t h e r e f o r e i n a c t i v i t y l i m i t s , w i t h a c c l i m a t i o n . For example, o f 28 a n i m a l s from each o f the a c c l i m a t i o n temperatures 25, 15, and 5° C, f o u r , two, and z e r o s l u g s became t o r p i d a t between 5 and 9° C i n a temperature g r a d i e n t . F o u r t e e n out o f 28 L. maximus a c c l i m a t e d t o 25° C s e l e c t e d t e m p e r a t u r e s between 25 and 29° c, whereas o n l y 3 o f th o s e a c c l i m a t e d t o 15 or 5° C d i d so. No s l u g s remained i n t h e range 30 t o 34° C, except one a c c l i m a t e d t o 5° C which d i e d b e f o r e i f c o u l d move. These r e s u l t s c o n f l i c t w i t h t h o s e o f Melanby (1961), who found no d i f f e r e n c e i n t h e l o w e r a c t i v i t y l i m i t of r e t i c u l a t u m - o r A. h o r t e n s i s a c c l i m a t e d t o 5° o r 20° C. , • Xn t h e case c f P h i l c r o y c u s c a r o l i n i a n u s . R i s i n g and Armi t a g e (1969) found l e s s v a r i a t i o n i n p r e f e r r e d temperature. The s l u g s responded as i f t h e y had an optimum tem p e r a t u r e range of about 22° t o 25° C. The a u t h o r s suggested t h a t " o v e r c o m p e n s a t i o n " produced t h e d i s c r e p a n c i e s i n t h e data about t h e h y p o t h e s i z e d optimum. R i s i n g and Armitage (1969) suggested t h a t t h e d i f f e r e n c e s i n r e s u l t s f o r P. c a r o l i n i a n u s and L,x maximus p o s s i b l y a r o s e because o f t h e d i f f e r e n t h a b i t a t s i n which t h e y n o r m a l l y r e s i d e . The former i s a woodland s l u g , whereas the l a t t e r i s most common i n d i s t u r b e d a r e a s a s s o c i a t e d w i t h man. For L. maximus the a b i l i t y t o a c c l i m a t e t o a wide range of temper a t u r e s would be advantageous, s i n c e wide f l u c t u a t i o n s i n temperature a re common i n i t s normal h a b i t a t . The poor r e s p o n s e o f -. c a r p l ^ p j a n j s • t o 159 a c c l i m a t i o n p o s s i b l y r e f l e c t e d the more s t a b l e t e m p e r a t u r e regime found i n woodland h a b i t a t s . I n t i e p r e s e n t s t u d y , a l l t h e s p e c i e s examined were t y p i c a l l y found i n f i e l d s e x c e p t At cclumbuanus. which was n o r m a l l y a woodland s l u g . I n r e c e n t e x p e r i m e n t s , i n which u n u s u a l l y h i g h t e m p e r a t u r e s o c c u r r e d i n t h e f i e l d , A. c o l u m b i a n u s s u f f e r e d v e r y h i g h m o r t a l i t y as t e m p e r a t u r e s i n t h e s h e l t e r s reached a p p r o x i m a t e l y 22° C. S i m i l a r l y s h e l t e r t e m p e r a t u r e s around 20° C were p r o b a b l y t h e cause of death t o At- h o r t e n s i s and •&.«.. c i r c u m s c r i p t u s d u r i n g t h e summer months. These o b s e r v a t i o n s s u p p o r t the i d e a t h a t s p e c i e s t h a t n o r m a l l y i n h a b i t environments w i t h s m a l l t e m p e r a t u r e f l u c t u a t i o n s (e.g. woodland o r s u b t e r r a n e a n ) , a r e unable t o adapt t o as wide a t e m p e r a t u r e range as s p e c i e s t h a t n o r m a l l y l i v e near t h e s u r f a c e i n f i e l d e n v i r o n m e n t s . I n t h e p r e s e n t s t u d y , t h e f l o w e r - p o t s h e l t e r s m a i n t a i n e d a f a i r l y c o n s t a n t t e m p e r a t u r e , not v a r y i n g more t h a n 2° t o 4° C i n 24 h. The t e m p e r a t u r e v a r i e d s e a s o n a l l y ( F i g u r e 2 1 ) , b u t the range among d a i l y maxima was o n l y 8,2° C o v e r the six-month p e r i o d of o b s e r v a t i o n s (14.0-22.2° C ) . T h e r e f o r e t h e use of t h e a r t i f i c i a l s h e l t e r s m i n i m i z e d t h e amount of v a r i a b i l i t y i n the data t h a t would be produced by a c c l i m a t i o n , and s t a n d a r d i z e d t h e a c c l i m a t i o n t h a t c o u l d o c c u r f o r t h e i n d i v i d u a l a n i m a l s i n t h e s t u d y . S l u g s spent most o f t h e day i n s i d e t h e s e a r t i f i c i a l s h e l t e r s . A c c l i m a t i o n can o c c u r g u i c k l y . Boy (1963) c l a i m e d t h a t complete a c c l i m a t i o n o f A,, c i r c u m s c r i p t u s o c c u r r e d i n 5 h. I n the s n a i l , p o m a t i a , s h o r t term a c c l i m a t i o n took 10-15 h (BlazJca, 1955) . On t h e o t h e r hand, complete a c c l i m a t i o n o f 160 La maximus and partial acclimation of Pt carolinianus required one week and cne month respectively (Rising and Armitaqe, 1S69). Inclusion of shelter temperature in the multiple correlation-reqression model would account for variations due to acclimation. As was noted earlier, shelter temperature was also included in the model to account for any changes in the activity pattern that might be associated with adjustment of the circadian rhythm by ambient temperature. Consequently, this factor serves a dual role in the regression models. Photoperiod was unsuitable to account for such seasonal changes in temperature, since the summer solstice lagged about 1.5 months behind maximum shelter temperatures such that they were not linearly related (see Figure 21). Previous studies on the activity patterns of molluscs have not included a factor to account for the effects of acclimation, probably due to the di f f i c u l t y of obtaining an estimate of the temperature in the animal*s resting place. TEMPERATURE GRADIENTS As might be expected, the distribution of slug activity with surface temperature i s similar to the distribution of the animals in a temperature gradient. The gradient of temperature between the shelters and the s o i l surface might be important in determining how many animals emerge. Dainton (1954a) found that D. reticulatum aggregated strongly in the vicinity of 17° to 18" C in a gradient. She 161 proposed a model o f s l u g a c t i v i t y c ased on the v e r t i c a l movement of t h e a n i m a l s t o t h e i r preferendum, and on t h e i n f l u e n c e o f changing t e m p e r a t u r e s . Such v e r t i c a l movements of s l u g s i n response t o t h e a p p l i c a t i o n o f a f r e e z i n g m i x t u r e t o the s o i l was p r e v i o u s l y demonstrated by M i l e s e t a l j t (1931). G e t z {1959) found t h a t D. r e t i c u l a t u m c ongregated at t e m p e r a t u r e s between 180 and 240 c i n a g r a d i e n t . C h i c h e s t e r (1968) f o u n d t h a t 7651 o f t h i s s p e c i e s chose t e m p e r a t u r e s between 13° and 19° C, w i t h 30.6% a g g r e g a t i n g a t 15° t o 16° C, i n c l o s e agreement t o D a i n t o n ' s (1954a) r e s u l t s . , A l t h o u g h D a i n t o n (1954a) and G e t z (1959) found a few s l u g s remained a t h i g h e r t e m p e r a t u r e s , C h i c h e s t e r (1968) found t h a t none remained a t t e m p e r a t u r e s above 21° C, f u r t h e r s u p p o r t i n g t h e i d e a t h a t 21° C i s an i m p o r t a n t t h r e s h o l d f o r t h i s s p e c i e s . The v a r i a t i o n s among t h e s e s t u d i e s may be due t o p r e v i o u s a c c l i m a t i o n o f t h e a n i m a l s ( R i s i n g and A r m i t a g e , 1969), which was not c o n s i d e r e d by the o t h e r a u t h o r s . The peak a c t i v i t y o f D. r e t i c u l a t u m a t 15° C i n t h e p r e s e n t s t u d y ( F i g u r e 30) f i t s the p r e f e r r e d range g i v e n above. However, more s l u g s tended t o remain i n h i g h e r temperatures i n t h e e a r l i e r g r a d i e n t s t u d i e s t h a n would be expected from t h e i r observed p a t t e r n of a c t i v i t y i n t h e f i e l d . The s n a i l , Cepaea n e m o r a l i s , showed a peak o f a c t i v i t y between 12° t o 140 c ( F i g u r e 3 2 ) . S e l d m a i r (1956) found t h a t y e l l o w - s h e l l e d i n d i v i d u a l s s e l e c t e d t emperatures c l o s e t o 20° C i n a g r a d i e n t , whereas p i n k - s h e l l e d s n a i l s chose 140 c . Most of t h e s n a i l s i n t h e p r e s e n t s t u d y were brown or p i n k , and t h u s t h e f i e l d o b s e r v a t i o n s agree w i t h S e l d m a i r * s r e s u l t s . , C h i c h e s t e r (1968) found t h a t J ^ j a x i m u s chose a wide range 162 of temperatures in a gradient, 56.55? s e t t l i n g between 14° to 2 2 ° C. Only 1 5 % were found above 2 2 ° C, and only 1 . 2 % above 26« C. Some 1 2 . 1 % of the animals lay between 5° and 8° C, Such low-temperature clumps of animals are common i n gradient experiments, and have been shown to be due to cold torpor by ¥an der Schalie and Getz ( 1 9 6 3 ) , who provided a more gradual gradient than usual. In these conditions, t h e i r s n a i l s were able to move out of the cold area before becoming trapped. The jresults of Rising and armitage ( 1 9 6 9 ) f o r L, maximus acclimated to 5°and 15° C were s i m i l a r to those of Chichester ( 1 9 6 8 ) . The d i s t r i b u t i o n of a c t i v i t y with temperature of • f.., -/maximus-in the present study showed a peak at 13.5° to 15.5° C, a temperature at the low end of t h e i r preference i n gradients (Rising and armitage, 1 9 6 9 ) . also, t h e i r a c t i v i t y decreased much more rapidly with higher temperatures i n the f i e l d than would be expected from th e i r preferences i n gradients. Chichester ( 1 9 6 8 ) f o u n d that 5 9 * 5 % of AFT, subfuscus distributed themselves i n a gradient between 1 3 ° and 2 0 ° C. , There was a d e f i n i t e peak i n numbers at 15° C, and no slug occurred above 2 8 ° C. These re s u l t s conform almost exactly to the d i s t r i b u t i o n of a c t i v i t y observed i n the f i e l d cages for t h i s species. Peak a c t i v i t y i n the f i e l d was at 1 5 ° , and the highest a c t i v i t y occurred between 12° and 19° c . a. circumscriptus has recently been recognized as a complex of three d i s t i n c t species, a^ circumscriptus £ A. fa s c i a t u s . and 'kx §ilJ[aticusx For the following discussion i t i s assumed that the temperature preferences of these s i b l i n g species w i l l not d i f f e r markedly. 163 Getz (1959) found that A. c j r c u j s c r i p t u s (possibly = A i £jsciatus ), preferred temperatures ranging between 18° to 24° C. Chichester (1968) found that &± fasei£a£u.s mostly chose temperatures between 14° and 17° c . Seventy f i v e percent accumulated between 13 and 19° C. Only 2 out of 200 slugs remained above 23° C, which agrees with the hypothesis that A f circumscriptus has a lower temperature tolerance than most surface-active species. Information on the others i n the complex i s not available. From the above discussion i t i s l i k e l y that knowledge of temperature gradients would explain some of the residual variation i n the multiple correlation-regression model. This would be especially important i f some of the v e r t i c a l movement displayed by slugs (Hunter, 1966; Bollo and E l l i s , 1974), serves a thermoregulatory function. Examination of the temperature gradient between the s o i l surface and heights of 10 cm or 30 cm, or between the shelter and the surface, showed that the shelter-to-surface temperature gradient was most highly correlated with slug a c t i v i t y . The re l a t i o n s h i p was non-linear and a s i g n i f i c a n t improvement was obtained with a guartic expansion of the independent variable. Therefore, i n the f i n a l multiple correlation-regression model, four polynomials of temperature gradient were included to account for the influence of that factor. 164 TEMPERATURE CHAJGES Dainton (1954a) found that the a c t i v i t y of D.:reticulatum was stimulated by temperature changes. F a l l i n g temperatures below and r i s i n g temperatures above 21° C i n i t i a t e d locomotion, whereas r i s i n g temperatures below 21° or f a l l i n g ones above this threshold had no e f f e c t . The strongest response was induced by f a l l i n g temperatures below 21° C., A physiological basis for Dainton*s r e s u l t s was suggested i n work by Kerkut and Taylor (1956), who discovered that cooling produced a transient increase i n both locomotor and ganglionic a c t i v i t y i n QJL £§ticulatum, whereas heat caused a corresponding decrease. Many subseguent studies have attempted to explain slug a c t i v i t y patterns i n terms of changes i n temperature. K a r l i n (1961), for example, found that a c t i v i t y of P. carolinianus. P.*. fgticulatum. and Limax (Lehmannia) p o i r i e r i (Mabille), was associated with temperatures f a l l i n g below 23, 22.3, and 22° C respectively. However, the appropriate a i r temperatures did not activate the slugs i f the sun was shining, filinn (1963) s i m i l a r l y related the a c t i v i t y of two s n a i l species to temperature changes. Both Roy (1963) and Rising and Armitage (1969) found evidence that a c t i v i t y of slugs was increased by moving acclimated animals to a new temperature. S i m i l a r l y , Henne (1963) suggested that small temperature fluctuations i n growth chambers produced great a c t i v i t y i n the s n a i l . Pplygjyra albola.br Is. ..Arias and Crowell (1963) claimed that D x reticjulaturn reared under fluctuating temperatures ate morefood but grew at the same rate as those l i v i n g at a constant temperature. When Hunter (1968b) 165 d i s c o v e r e d t h a t c o v e r i n g s l u g s w i t h a l i g h t - t i g h t box d i d not produce daytime a c t i v i t y , he c o n c l u d e d t h a t t h e s l u g s were r e s p o n d i n g t o t e m p e r a t u r e changes as D a i n t o n (1954a) p r e d i c t e d . Daxl (1969) b e l i e v e d t h a t h i s r e s u l t s on the a c t i v i t y o f s l u g s conformed t o D a i n t o n * s (1954a) h y p o t h e s i s o f r e g u l a t i o n by temperature changes, i f t h e e f f e c t s o f l i g h t were a l s o c o n s i d e r e d . Baker (1973) c o r r e l a t e d the movement o f Dt r e t i c u l a t u m i n an outdoor a c t o g r a p h w i t h d e c l i n i n g t e m p e r a t u r e s , a l t h o u g h he b e l i e v e d t h a t h u m i d i t y was a l s o i m p o r t a n t . H a c h i n (1975) showed t h a t t h e s n a i l , O t a l a l a c t e a , was s t i m u l a t e d t o a c t i v i t y by f a l l i n g t e m p e r a t u r e , a r e s u l t s u b s e q u e n t l y c o n f i r m e d by B e r r e i d and R o k i t k a (1976). Host r e c e n t l y , Dundee (1977), working w i t h the s l u g , J e r o n i c e l i a a m e g h i n i , found t h a t when a i r t e m p e r a t u r e s were above 31° C and d e c r e a s e d , a c t i v i t y g u i c k l y ensued. I f the temperature was below 25° c, however, and i n c r e a s e d , a c t i v i t y d i d n o t b e g i n u n t i l i t rea c h e d 25° C, even though t h i s t e mperature was above t h a t p r e f e r r e d i n a g r a d i e n t . D e s p i t e a l l the e v i d e n c e t h a t t e m p e r a t u r e changes i n f l u e n c e the a c t i v i t y o f t e r r e s t r i a l m o l l u s c s , some doubt a r o s e when Lewis (1969a) was unable t o show t h a t 4 A r a t e r responded t o temperature changes as d i d D. r e t i c u l a t u m - . N e w e l l (1968) had p r e v i o u s l y aurgued t h a t t h e g r a d u a l f a l l of t e m p e r a t u r e throughout t h e n i g h t d i d not appear s u f f i c i e n t t o account f o r the r a p i d a l t e r a t i o n s i n b e h a v i o r observed f o r D „- - r e t i c u l a t u m . Be f a v o u r e d a t h e o r y i n c o r p o r a t i n g l i g h t i n t e n s i t y and t h e c i r c a d i a n rhythm. I n h i s s t u d y , L e w i s (1969a) d i d not c o n s i d e r t h e 1 6 6 p o s s i b i l i t y that J ^ a t e r might have a d i f f e r e n t threshold than Hx. reticulatum . 1 have already discussed how A A ater seems to have a greater temperature tolerance than other species of slugs. Therefore I performed an experiment to determine whether higher temperatures might induce changes i n the behavior of J L s . ater that would conform to Dainton*s (1954a) theory. Twenty A. ater,, entrained to 1:D 12:12 photoperiod at 15° C, were subjected to a rapid increase i n temperature. The experiment was performed i n the middle of the slugs* a c t i v i t y period when 9/20 animals were active on the surface. Three of these nine had not returned to the shelter during the previous scotoperiod, but had remained contracted on the surface throughout the l i g h t period. The temperature change, and the res u l t i n g behavior that was induced are presented i n Table XXII. 167 Table XXII. Changes i n Behavior of Arion ater Subjected to a Temperature Increase. Time Temperature Number Observations (o C) Active 1:15 15 9 a l l resting or feeding 1:20 25 9 s l i g h t increase i n locomotion 1:26 30 9 a l l t r a v e l i n g except one that i s s t i l l feeding 1:30 35 6 a l l moving quickly -three have gone heme 1:34 35 5 one more goes home 1:37 38 3 moving guickly-r a i s i n g heads and extending tentacles-follcwing each other The three slugs that had not returned to shelter the previous night were apparently unable to do so i n the face of adversity, and eventually r o l l e d on t h e i r sides and died at the highest temperature (Table XXII). The experiment shows that Aa ater d e f i n i t e l y can respond to temperature changes, and that the form of t h i s response i s to "go home". The results support my hypothesis that A±. ater behaves s i m i l a r l y to p,, reticulatum. except that the former has a higher threshold temperature for a c t i v i t y . Other evidence frcm the present study suggested that temperature changes play a r o l e i n regulating slug a c t i v i t y . Although temperatures usually f e l l gradually throughout the night, small pockets of warm or cool a i r occasionally passed by and caused temperature t c change as much as 5° C i n l e s s than 168 one hour. Once an a i r pocket had passed, the l o c a l temperature returned rapidly tc the usual l e v e l for the time of the night. Substantial changes in the a c t i v i t y of the various species were associated with these sudden temperature changes. However, no consistant relationship emerged since the deviations from the normal a c t i v i t y pattern were sometimes positive and sometimes negative. This discussion shows the need for considering temperature change i n the multiple correlation-regression model. Temperature-change data were calculated for each hour by subtracting the surface temperature from the previous hour. The f i r s t hour of each day was assigned a blank value which was recognized by the computer as missing data. The cor r e l a t i o n of temperature changes with slug a c t i v i t y was very low due to the non-linearity of the rela t i o n s h i p (Table XX?). A guartic f i t of the same data was a great improvement (Table XXV) , and was therefore included i n the f i n a l regression model. BABCflBTBIC PBESSUJE Barometric pressure i s known to influence the a c t i v i t y of a wide variety of insects {Wellington, 1946a,b; Johnson, 1969). I t freguently varies diurnally, and thus may function as a zeitgeber (Cloudsley-Thcmpson, 1960). However, the most obvious e f f e c t s are associated with the passage of cumulonimbus and large cumulus clouds (Hellington, 1974). On two occasions I observed unusual a c t i v i t y of slugs that 169 suggested that they might be responding to barometric pressure, fit about 2:15 pm, July 4, 1973, p. reticulatum were observed suddenly to become active and climb plant stems, despite the fact that the afternoon was hot and sunny and the entire area was very dry. Hithin 10-15 minutes, however, a large cumulonimbus cloud moved over the area and heavy ra i n f e l l . A similar burst of a c t i v i t y occurred several weeks l a t e r , and was nearly i d e n t i c a l to the f i r s t , except for i t s timing—about 1:30 pm. Each burst of a c t i v i t y occurred before the r a i n f e l l , while the habitat was s t i l l very parched, and slug a c t i v i t y should have remained very low. The best explanations for t h i s unusual a c t i v i t y are that the slugs either respond to barometric pressure or can smell approaching water. The l a t t e r hypothesis seems lea s t l i k e l y since the sun was s t i l l shining when a c t i v i t y began. I have noted, however, that dehydrated ants and cockroaches w i l l leave shelters at almost any time i n response to water placed outside. The possible influence of barometric pressure on slugs has not been previously considered, although Thomas (1856) and Henderson (1905) observed that a number of d i f f e r e n t t e r r e s t r i a l s n a i l s showed periods of marked a c t i v i t y before r a i n , and neither author could discern "meteorological symptoms presaging r a i n . " Henderson (1905) mentioned that the periods of greatest a c t i v i t y of six species of s n a i l s was invariably associated with f a l l i n g barometric pressure, and he also observed that they ceased a c t i v i t y before the sky cleared. Hith t h e i r hydrostatic support system, slugs and s n a i l s may be i d e a l l y suited to detect changes in barometric pressure. 170 T h e r e f o r e , b a r o m e t r i c p r e s s u r e was i n c l u d e d i n t h e f i n a l c o r r e l a t i o n - r e g r e s s i o n model. The c o r r e l a t i o n of ambient p r e s s u r e w i t h s l u g a c t i v i t y was q u i t e low {Table XXV), and was not improved by l o g a r i t h m i c , e x p o n e n t i a l or q u a r t i c t r a n s f o r m a t i o n s . I t i s not t h e ambient b a r o m e t r i c p r e s s u r e t h a t i s u s e f u l f o r p r e d i c t i n g weather, however, but the chanqes of b a r o m e t r i c p r e s s u r e , and i t i s t o t h e s e f l u c t u a t i o n s t h a t i n s e c t s are known t o respond { W e l l i n g t o n , 1974). The h o u r l y changes i n b a r o m e t r i c p r e s s u r e , t h e r e f o r e , were c a l c u l a t e d by s u b t r a c t i n g a g i v e n p r e s s u r e from th e p r e v i o u s h o u r ' s . The f i r s t r e a d i n g f o r each day was a s s i g n e d a m i s s i n g d a t a v a l u e which was r e c o g n i z e d by the computer. T h i s c o r r e l a t i o n of a c t i v i t y w i t h changes i n b a r o m e t r i c p r e s s u r e was an improvement over t h a t w i t h ambient b a r o m e t r i c p r e s s u r e {Table XXV). E x a m i n a t i o n o f the s c a t t e r diagram i n d i c a t e d t h a t a g u a r t i c f i t was even more a p p r o p r i a t e , however {Table XXV). JTMOSPHEfilC JOISTORE S l u g s must d e p o s i t mucus on t h e s u b s t r a t e i n o r d e r t o move { B a r r , 1926). Because s l i m e i s 92 t o 98% water by weight ( D a i n t o n , 1954a; W i l s o n , 1 9 6 8 ) , s l u g s and s n a i l s c o n t i n u o u s l y l o s e water when c r a w l i n g , e s p e c i a l l y on dry s u r f a c e s ( K u n k e l , 1916; D a i n t o n , 1954a; /aachin, 1962; Judge, 1972a). A l t h o u g h a e s t i v a t i n g s n a i l s may p o s s e s s a water b a r r i e r i n the mantle e p i t h e l i u m (Machin, 1974), s l u g s and a c t i v e s n a i l s l o s e water f r e e l y from any exposed s u r f a c e s once t h e ambient h u m i d i t y f a l l s below the b l o o d e q u i l i b r i u m h u m i d i t y o f a p p r o x i m a t e l y 99.5% a t 171 20° C (flachin, 1975). Thus the rate of evaporation from molluscs i s probably unsurpassed by t e r r e s t r i a l animals of any ether group (Howes and Wells, 1934a,b). The evaporation of water from the bodies of t e r r e s t r i a l s n a i l s has been int e n s i v e l y investigated by Machin (1964a,b,c,1965,1866, 1967,1968,1972,1974) , and liewell and Machin (1976), Weight loss of slugs i n evaporation gradients was studied by Kunkel (1916), Howes and Wells (1934b), Dainton (1954a), Getz (1959), Crawford-Sidebotham (1971), Daxl (1972), Judge (1972a), and Rollo (1974). No species displays any resistance to desiccation, although large slugs become dehydrated less guickly than small ones, due to t h e i r proportionally smaller surface area. Dehydrated molluscs guickly regain water when placed i n saturated a i r or on a moist substrate (Kunkel, 1916; Dainton, 1954 ; Judge, 1972). Water absorption i s enhanced by the hydrophilic nature of the mucus, which tends to spread a drop of water over the body as a thin f i l m , thus increasing the area of absorption (Machin, 1962). Dainton (1954a) showed that -Le. IS2Limus that had l o s t 23% of i t s weight through dehydration regained i t s former weight after being suspended in saturated a i r for 2 h. Slugs mainly regulate t h e i r water content behaviorally. Their main physiological adaptation i s an a b i l i t y to withstand wide fluctuations i n water content. Whereas insects are k i l l e d by losses of water exceeding about 15% of their o r i g i n a l weight (Bursell, 1964), p, reticulatum can withstand weight losses by dehydration of 50 to 62% (Dainton, 1954a; Judge, 1972a). Kunkel 172 (1916) recorded that Limax tenellus survived an 80S loss of weight through evaporation. flachin (1975) includes a comprehensive review of the l i t e r a t u r e concerned with the physiological aspects of the water rel a t i o n s of pulmonates, as well as some behavioral aspects. He concluded that environmental water "plays the dominant role i n regulating a c t i v i t y i n t e r r e s t r i a l pulmonates.» For slugs i n par t i c u l a r , Stephenson (1968) concluded that water was the single most important factor a f f e c t i n g reproduction and survival. Slugs and s n a i l s would be expected to avoid areas of high evaporation stress, and Tercafs {1961) and Lewis (1969a) showed that they chose the wetter side i n a humidity choice chamber. However, Bonavita (1967) found that the slug, Milax aaaates, accumulated i n the drie r zone of a humidity gradient during the day, but moved to the damper portion at night, provided the difference between the two zones was less than 33% r.h. Overhydration appears to be deleterious to some molluscs (Runham and Hunter, 1970; Machin, 1975), so that such behavior may represent an e f f o r t to regulate water content. Thus, some aspects of slug a c t i v i t y may be hygro-regulatory, as Den Boer (1961) suggested for woodlice.., Lewis (1967) thought that slugs might measure evaporative rate d i r e c t l y through associated temperature decreases produced by water loss from th e i r epidermis. The behavior of slugs at the boundary of a humidity gradient suggested that the necessary receptors were located on the head, probably on the tentacles. Although slugs generally become active when there i s l i t t l e 173 evaporative stress, Dainton (1954a) demonstrated that high humidity does not stimulate a c t i v i t y . Webley (1964) found l i t t l e r e l a t i o n s h i p between r e l a t i v e humidity (r.h.) and slug a c t i v i t y through correlation-regression analysis. Hunter (1968b), however, found that the number of wheat grains damaged by slugs was reduced at lower humidities. Crawford-Sidebotham (1971,1972) examined the r e l a t i o n s h i p cf slug a c t i v i t y to three measures of atmospheric moisture, r.h., vapor pressure d e f i c i t (v.p.d.), and ambient vapour pressure. His data were collected i n nine dif f e r e n t sets (different locations and days). For the various slugs studied, the b e s t - f i t t i n g regression equations included from none to a l l three of these variables. Of 71 equations from diff e r e n t data sets, v.p.d. was included in 51, r.h. i n 5, and vapor pressure i n 16. Stephenson (1973) observed that the feeding of D. reticulatum was l i t t l e influenced by a v.p.d.,, of 0.8 to 3.8 mm Hg, whereas feeding of JU 1*2 r^ ens. i s decreased rapidly at the larger v.p.d.. Baker (1973) observed that Ht. EJiiSUlatum i n a f i e l d actograph only moved away from shelter when rh was approaching 100%. In the morning, the movement back to shelter appeared to be c l o s e l y associated with changes i n r.h. Lewis (1969a) showed that A,, --ater •• was able to detect areas of low humidity, selecting high humidity when given a choice. However, experimental evidence r e l a t i n g high evaporative stress d i r e c t l y to the a c t i v i t y patterns of slugs i s lacking. Therefore, an experiment was performed to elucidate t h i s r e l a t i o n s h i p . Sixteen D. reticulatum were placed i n each of four a c t i v i t y 174 chambers, and entrained to L:D 12:12 (800:0 ft-c) at 15° C. The slugs were allowed 5 days to entrain to the l i g h t cycle, and then a p e t r i dish 8cm i n diameter containing CaC12 was attached so that i t was suspended about 2 cm from the top of two of the a c t i v i t y chambers. In the other t«o chambers, comparable dishes containing water were s i m i l a r l y suspended. Each p e t r i dish was covered with a fine-mesh screen to exclude the; slugs. Carrot s l i c e s were provided as food i n the upper part of each chamber. One day was allowed f o r the CaCl2 to dry the a i r in the high evaporative stress treatment. The shelters i n a l l of the chambers were kept moist. I t is l i k e l y that the d i f f u s i o n of water vapor from the shelter into the a c t i v i t y areas created a s l i g h t humidity gradient, but the actual humidity was not measured. Two slugs i n the wet-air treatment died during the entrainment period, and thus the f i n a l sample sizes were not i d e n t i c a l . Besults from the chambers with the same treatments were si m i l a r , and were pooled (Figure 36). As predicted, the influence of high evaporative stress was to decrease the amplitude of the a c t i v i t y pattern. In both treatments the peak in the a c t i v i t y pattern occurred early i n the dark period, and then gradually f e l l throughout the night. The reduction i n a c t i v i t y was not caused by to some repellent property of the calcium chloride, since similar r e s u l t s were obtained when the entire experiment was repeated with s i l i c a g el as the drying agent. Slugs in the dry-air treatment behaved d i f f e r e n t l y than those i n the moist a i r . The former confined t h e i r a c t i v i t y to 175 aq.ui.riBg food. They moved quickly to the food supply, ate, and then returned directly to shelter, so that the length of time they remained active was shorter than for slugs in the moist air. In moist air, slugs frequently moved in non-foraging patterns, or remained motionless for varying lengths of time. They were more leisurely in their movements, and ate more slowly than the slugs in dry a i r . The i n i t i a l hydration of the individuals in both treatments was at a maximum when they emerqed, since their shelters were kept well watered. Consequently, activity was not entirely suppressed even in the extreme evaporation gradients. This result suggests that, when adeguately moist shelters are available, some slug activity w i l l occur even in dry weather. In the f i e l d , where wind and convection currents w i l l increase rates cf evaporation above those obtained in the laboratory, slug activity sometimes can be totally suppressed. 176 Figure 36. The Influence cf Evaporative Stress Upon the Activity of peroceras reticulatum. 178 In previous studies of slug activity, and in most of those concerned with other animals, relative humidity and/or vapor pressure deficit have been used to estimate the evaporative stress experienced by the animals. However, the meaning of such measures has been freguently misunderstood, so that seme clarification i s justified here. Evaporation i s a dynamic process representing the net difference between the number of water molecules leaving a surface and the number returning during some unit of time (Anderson, 1936). The rate of evaporation i s proportional to the vapor pressure gradient between the evaporating surface and the air (Leighly, 1937; Thornthwaite, 1940). Figure 37 shows the relationship between vapor pressure and temperature at saturations of 100 and 50%, Since slugs are constantly wet, they are best described by the curve of saturation vapor pressure. 179 Figure 37. The Relationship Between Vapor Pressure and Temperature at 100% and 50% Saturations. 180 45 -i TEMPERATURE (°C) 181 If a slug i s in a i r at 5035 rh, and both have a temperature of 15° c , then the vpd i s 12.771-6.386=6.386 mm Hg. I f both the slug and a i r at 50% rh are at 25° c , however, the vpd i s then 23.729-11.865=11.865 mm Hg. Therefore the evaporative rate i s greater at the higher temperature, even though the r.h. i s the same in both cases. I f i d e n t i c a l atmospheric moisture conditions are desired at d i f f e r e n t temperatures, then d i f f e r e n t r e l a t i v e humidities must be used (Andersen, 19 36; Wellington, 1949a,b). Examining the work of Dainton (1954a), however, we fi n d that she attempted to compare a constant rh of 40% at temperatures of 15.5, 17.5, and 24° C . I f the slugs that she introduced to these various conditions were o r i g i n a l l y at room temperature, then the evaporative rate from t h e i r bodies would have been greater than expected at the lower temperature. If they were f i r s t eguilibrated to the various temperature regimes, then evaporation would have been greatest i n the highest temperature. Since her r e s u l t s were di f f e r e n t at the higher and lower temperatures, her conclusion that evaporation has no influence upon a c t i v i t y of slugs i s not v a l i d . In fact, Lewis (1969a), Judge (1972a), Daxl (1970), and Hollo (1974) have shown that high rates of evaporation do influence the behavior of slugs. Clearly, r. h. i s a poor estimate of evaporation except, when comparing i d e n t i c a l temperatures. Vapor pressure d e f i c i t i s only a good estimator of evaporation when the temperature of the air and the evaporating surface are i d e n t i c a l . Such isothermal conditions rarely p r e v a i l for the climate near the ground (Thornthwaite, 1940; Gieger, 1950) The very process of evaporation can d r a s t i c a l l y a l t e r the body temperature of slugs 182 in relation to ambient temperatures (Hogben and Kirk, 1944), since the slug acts as a net-bulb thermometer. Wellington (1949a,b) clearly demonstrated that direct measurement of evaporation may show relationships which are not apparent when either r.h. or v.p.d. are used. The correlations of these variables with slug activity are shown in Table XXV. Relative humidity generally was the worst. Although relative evaporation was best correlated with activity, v.p.d. was not much inferior in the existing circumstances. This was probably because temperature gradients during the nightime observation period were not very great. Vapor pressure deficit thus would be less reliable during the day when temperature gradients are invariably much steeper. Examination of Figures 38, 39, and 40 shows that, as expected, r.h. and v.p.d. were highly correlated in the f i e l d (r2=0.871). Vapor pressure deficit was less closely correlated with evaporation (r2=0.689), and the relationship between rh and evaporation was the worst (r2=0.585). Relationships of these factors to activity were similar among the various species of molluscs, although there were quantitative differences. Figures 41, 42, and 43 are typical scatter diagrams illustrating the trends. Again there appears to be outer limits possibly representing the action of these variables independently cf other weather factors. Equations for these outer limits were calculated for evaporation, for seven species of the molluscs, by estimating the limits by eye, and obtaining best-fitting regression lines for these points (Table XXIII). 183 Figure 38. Correlation of Relative Humidity and Vapor Pressure D e f i c i t i n the F i e l d . 100 1 9 0 8 0 2 X UJ > < Hi t r 70 H 60 50 96-4 - 5-6419 (X ) r » 0-871 . P <0 0000 2 3 4 5 6 " T " 7 -1 1 10 10-5 co VAPOR P R E S S U R E DEFICIT (mm Hg.) 185 Figure 39. Correlation of Vapor Pressure Deficit with Evaporation in the Field. 187 Figure HO. Correlation of Belative Humidity with Evaporation in the Field. 189 Figure 41. A c t i v i t y of Peroceras reticulatum i n Relation to Evaporation Bate i n the F i e l d . 1 0 0 -, UJ > o < < Z> O. O CL o a . o CC a. 0-75 0-50 4 0-25 J 000 THRESHOLD MODEL Y= 0-9397 - 0-66961X) REGRESSION MODEL LOG I0(ARCSIN(V Y+0-001 )= — 0-2256— 0-7183(X) 2= 0-5172, P < 0 0000 1— I — I — r — i — i — i — i — r 00 0-2 0-4 0-6 0-8 10 "T 1 1 i i i r~i i rn—i—i—I—I—I—I—1—I—l j 1-4 1-6 1-8 2 0 2-2 2-4 . 2-6 2-8 30 3-2 3-4 EVAPORATION ( mm5/minute) O 191 Figure 42. Activity of Deroceras reticulatum in Relation to Relative Humidity in the Field. 192 193 F i g u r e 43, R e l a t i o n s h i p o f A c t i v i t y o f D e r c c e r a s r e t i c u l a t u m t o Vapor P r e s s u r e D e f i c i t i n the F i e l d , , PROPORTION OF POPULATION ACTIVE Ml 195 Table XXIII. Best Regression Equations Describing the Cuter A c t i v i t y l i m i t s Associated With Evaporation for 7 Molluscs. Species C o e f f i c i e n t Constant Deroceras reticulatum -0.6696 0.9397 Arion ater -0.3788 0.7790 Cejjaea nemoralis -0.3936 0.8523 li-iolijnax columbianus -0.5431 0. 7686 Limax maximus -1.244 1.232 iXign subfuscus -1. 111 1. 000 Deroceras caruanae -1.499 1.063 HYDRATION Early authors suggested that the a c t i v i t y of s n a i l s could be stimulated or repressed by t h e i r water content. Howes and Wells (1934a,b), and Hells (1944) reviewed t h i s l i t e r a t u r e and showed that slugs and s n a i l s have c y c l i c a l changes i n body weight that persist even i n saturated a i r . The weight fluctuations were shown tc be primarily due to variations i n the water content of the animals, s n a i l s tended to aestivate at those times when th e i r weight was lowest. In s n a i l s the weight cycles had a period of several days, whereas those of slugs were shorter. Blinn (1964) discovered that s n a i l s store water i n the lung cavity. Variations i n the amount cf t h i s p a l l i a l water 196 appeared to account for the fluctuations of Height. Kurkel (1916) s i m i l a r l y observed that some slugs had a water supply amounting to as much as 10% of their weight. It i s well known that s n a i l s lose water and aestivate during very dry weather (Howes and Wells, 1934a). Major studies concerned with various aspects of aestivation i n s n a i l s include Warburg (1965), Pcmeroy (1968), Cameron (1970a), Schmidt-Nielson et a L (1971), Machin (1975), Herreid and Bokitka (1976) and Jarmovic and Rollo (in preparation). long periods of aestivation (up to a year or more in severe climates), appear to be an i n t e g r a l strategy i n the ecology of many t e r r e s t r i a l s n a i l s . Once they r e t r a c t into t h e i r s h e l l s , water loss i s much reduced (Machin, 1975). By contrast, sheltering slugs move deeper into the s o i l as the upper layers dry cut (Hawley, 1922; Hunter, 1966; Bollo, 1S74). Bailey (1975) noted that a difference i n the ecology of slugs and s n a i l s , i n that s n a i l s can wait several weeks for optimum conditions, whereas slugs, by burrowing, reduce the constraints of surface l i f e . This comment agrees with observations (Barnes, 1949), that slugs were active a l l year round, there being r e l a t i v e l y few nights when none could be found. Barnes (1952) observed that j . reticulatum was active on a l l except 5 out of 214 nights i n B r i t a i n , even when screen temperatures were below freezing. S i m i l a r l y , Bollo (1974) observed that slugs were active nearly every night i n Ontario c o r n f i e l d s u n t i l winter. Despite hot dry weather i n summer, th e i r growth rate was fastest then. Sclem (1974) concluded from a comprehensive taxonomic study that there was considerable s e l e c t i v e pressure upon sn a i l s to reduce t h e i r 197 s h e l l s and become s l u g - l i k e . The a b i l i t y to u t i l i z e environmental resources over a greater range of conditions may represent the major advantage slugs have over s n a i l s . I t appears, however, that slugs may only u t i l i z e t h i s advantage i f s u f f i c i e n t s o i l moisture i s available. Numerous authors have observed that slugs become inactive i n extended periods of hot, dry weather (Tate, 18 66; Hawley, 1922; Carrick, 1938,1942; Mead, 1942; Barnes and Weil, 1944,1945; Ingram and Band, 1949; Howitt and Cole, 1962; Judge, 1S72a,b; Chichester and Getz, 1973; Richter, 1976a). Chichester and Getz (1973) point out that such periods of i n a c t i v i t y may be p a r t i a l l y related to lack of succulent foods then. I t has been suggested that slugs sometimes aestivate in small s o i l chambers, as earthworms are known to do, but t h i s claim has never been well documented. On one occasion I l i f t e d a board and exposed an A, subfuscus contracted within a small 'igloo* of s o i l , with a texture s i m i l a r to eathworm castings. A careful dissection of this structure (Figure 44) revealed no entrances or e x i t s , which suggests that the slug constructed the c e l l . The walls of the structure were completely removed during the examination and the slug was displaced by about 20 cm. The next day I found th i s same indivdual resting i n the same position i n which i t was o r i g i n a l l y discovered, but the c e l l had not been repaired. Similar s o i l capsules are frequently constructed by Jsfioja intermedius as well. 198 Figure 44, Aestivation Chamber of Arion subfuscus. 200 The fact that i r r i g a t i o n freguently leads to increased damage by slugs {e.g. Howitt, 1961; Stephenson, 1965), i s also i n d i r e c t evidence that slug a c t i v i t y i s decreased by dehydration. Likharev and Bammel'meiex {1952) reviewed Soviet l i t e r a t u r e which showed that serious slug damage was mainly associated with areas of high r a i n f a l l . My previous research led me to believe that aestivation did not occur i n slugs {Bollo, 1974). In the most recent major review on slugs, fiunham and Hunter (1970) d i d not discuss aestivation, except to say that "slugs do not feed when the r e l a t i v e humidity of the microhabitat i s less than 100% and there are probably periods during the summer when surface a c t i v i t y i s r e s t r i c t e d . " Hughes and Kerkut (1956), Kerkut and Taylor (1956), and Kerkut (1959) found that the pedal ganglion of slugs was sensitive to changes i n osmotic pressure, and suggested that such changes controlled their activity.,When a l l the evidence i s considered, dehydration during times of drought i s suggested as a major factor r e s t r i c t i n g the a c t i v i t y of slugs. Previous research, however, has focused on the a b i l i t y of slugs to move, and not on the l i k e l i h o o d of becoming active. I t i s u n l i k e l y that a c t i v i t y of slugs in the f i e l d would persist u n t i l they could no longer move. The l e v e l s of dehydration associated with thresholds for movement and a c t i v i t y are probably guite d i f f e r e n t , a p o s s i b i l i t y that has not been previously considered. Unfortunately, no research has been performed with slugs cn t h i s subject, and few authors who claim that slugs aestivate 201 have contributed o r i g i n a l observations. Laboratory studies have demonstrated that the a b i l i t y of slugs to move i s influenced by t h e i r water content. Dainton (1951a) found that a 4% loss of body weight i n water had no e f f e c t on movement of Df reticulatum although, movement was greatly decreased by a 17% l o s s , and t o t a l l y i n h i b i t e d by a loss of 25% of t h e i r weight i n water. She found that movement of L, maxjmus and A A ater was s i m i l a r l y depressed by dehydration. Judge (1972a) found that Dt reticulatum continued locomotion u n t i l they l o s t 44% of the i r weight i n water. In my study, slugs in watered f i e l d cages were active throughout the season, being greatly r e s t r i c t e d at night only when very low temperatures occurred. By contrast, slugs i n adjacent non-irrigated areas were sometimes i n a c t i v e during very hot, dry weather. This difference was especially apparent i n an experiment intended to monitor the growth of Df reticulatum i n various heights cf clover. The slugs were kept i n p l a s t i c p a i l s f u l l cf s o i l which were buried so that the l e v e l of earth i n them was l e v e l with the surrounding s o i l surface, A moistened r o l l of newspaper extended to the bottom of each p a i l , and the slugs were able to crawl down t h i s for shelter, k fine-mesh polyester canopy prevented t h e i r escape. These clover canopies contained a large natural population of D x reticulatum (up to 83 slugs i n 25 sweeps of a net at night), and on most occasions their a c t i v i t y coincided with that of the caged slugs. On several nights after a prolonged hot, dry s p e l l , however, a c t i v i t y of the natural population was strongly reduced or e n t i r e l y suppressed. A c t i v i t y of slugs i n the watered 202 cages continued unabated. These r e s u l t s suggested that the hydration of the molluscs might be the factor most l i k e l y to r e s t r i c t t h e i r a c t i v i t y . , During the summer of 1977, a period of drought and record high temperatures l a s t i n g more than 30 days severely desiccated most of the habitats occupied by slugs. A c t i v i t y i n these habitats was d r a s t i c a l l y reduced or non-existent. This s i t u a t i o n was exploited to test the hypothesis that dehydration causes reduced a c t i v i t y of slugs i n the f i e l d , and to try to determine the l e v e l of hydration at which a c t i v i t y ceases. On the night of August 11, 1977, slugs were sought i n areas known to support large populations. The search was carr i e d out between 11:30 pm and 1:30 am, when the majority of slugs would normally be maximally active. Conditions were extremely dry, so that no dew was deposited during the entire search period. The drought had already been i n e f f e c t for two weeks, and was so severe that c i t y trees were w i l t i n g . Very few slugs could be found. Only i n areas of thick shrub or tree cover were foraging slugs observed, and many slugs were found s i t t i n g immobile close to th e i r shelters, frequently on the tops or sides of loqs. This behavior may have been thermorequlatory, and would also help sluqs t c absorb water on other nights when dew was deposited. For the purpose of the experiment, such resting slugs were ignored. Only animals act i v e l y crawling or feedinq on the s o i l surface were c l a s s i f i e d as active, whereas those found restinq under or within debris were c l a s s i f i e d as ina c t i v e . Each in d i v i d u a l was placed in a snap-tiqht p l a s t i c b o t t l e that had been previously numbered and 203 weighed, to ensure that no water would be l o s t through excretion or mucus production. Only A. ater were obtained i n adequate numbers to be s t a t i s t i c a l l y analysed. \ In the laboratory, the bottle s with the enclosed slugs were weighed and the data recorded. The animals were then k i l l e d by exposure to 85° C for 15 minutes, after which the l i d s were removed from the bottle s and the slugs were dried to constant weight i n an oven at 65° C, The l i d s were then replaced f o r reweighing. The percentage hydration of each slug was calculated by subtracting i t s dry weight frcm i t s wet weight to determine the water loss. This figure was then divided by the wet weight and multiplied by 100. Results are presented i n Table XXIV. 204 Table XXIV. Comparison of the Hydration of Active Versus Inactive Arion ater Collected During Their Normal Time of Peak A c t i v i t y Following an Extended Drought. Null hypothesis: The hydration of active and in a c t i v e slugs i s the same. Alternate hypothesis: The hydration of active and inactive slugs i s d i f f e r e n t . Percentage Hydration Active Inactive 66.9059 78.9342 87.5625 78. 6195 86.2491 86.3707 87.2725 83.0784 84.4362 83.5625 83.4288 88.2749 65.6751 86.1549 89.5564 81.5703 85.3895 85.5971 81.9527 86.2314 90.7527 84.5857 86.3129 81.2259 86.6644 86. 3202 84.0169 82.5574 85.1806 79.6011 N=15 N=15 d.f.-14 d.f.=14 Mean=86.0904 Mean=83.5123 SS=71.1158 SS=128.9101 t=2.6416 t (0.05,28) =2. 048 therefore r e j e c t the n u l l hypothesis (C.0KP<0.02) . The hydration of inactive slugs i s s i g n i f i c a n t l y l e s s than that of active ones. Inactive slugs were s i g n i f i c a n t l y more dehydrated than were active ones (Table XXIV). I f hydration had l i t t l e or no influence we would expect the active slugs to contain l e s s 205 water, because they had to secrete i t i n order to t r a v e l over the dry substrate. Since slugs i n f i e l d cages showed normal a c t i v i t y at t h i s time, the influence of the immediate weather could not account for the dra s t i c reduction i n a c t i v i t y that was observed i n the natural population. The results show conclusively that the slugs with low water content are l e s s l i k e l y to become active than those that are well hydrated. I t i s l i k e l y that maximal hydration of Aj. ater i s between 87 and 91%. The mean hydration (83.51) of the inactive slugs was very s i m i l a r to the hydration of aestivating C. nemoralis (mean=80.05-84.14% depending on th e i r height from the ground), discovered by Jaremovic and Hollo (in preparation). Those aestivating s n a i l s and the i n a c t i v e slugs i n t h i s study, were a l l f u l l y capable of movement when mechanically stimulated, thus supporting the contention that a c t i v i t y i s cu r t a i l e d by a smaller degree of dehydration than i s locomotion. In 1976 there were no high evaporation rates during the nocturnal observations, but some observations i n 1977 showed that high evaporation rates and windy conditions at night can considerably reduce a c t i v i t y . Most of the time, however, f u l l y hydrated slugs probably can feed normally. Dehydration i s the factor causing the greatest depression of slug a c t i v i t y . Blinn (1963) reached a s i m i l a r conclusion a f t e r observing that well-hydrated s n a i l s were freguently active cn dry nights, even crawling over dry surfaces. The slugs i n the present a c t i v i t y study were well watered to ensure t h e i r f u l l hydration on the nights of observation, so t h i s key parameter i s controlled i n the a c t i v i t y model. 206 S o i l moisture probably has the greatest effect co the hydration of these molluscs. Bailey (1975) found that s o i l moisture and r a i n f a l l were the factors which best explained the changes i n a c t i v i t y of Helix aspersa -. Randolph (1973) s i m i l a r l y concluded that s o i l moisture " i s probably a mere important type of moisture than r e l a t i v e humidity to a s n a i l . 1 1 The l e v e l s of dehydration associated with a c t i v i t y thresholds also should vary with the species. Getz (1959) and South (1965)--found evidence that indicated A. circumscrjptus i s more sensi t i v e to moisture than Dg reticulatum. Jennings and Barkham (1975) observed that flT ater seemed better able to withstand extremely dry summer conditions than other species of slugs found i n a woodland,, Part of t h i s resistance i s undoubtedly related to s i z e . The large size of slugs such as Afi. ater, Lf ,maximus and A*, columbianus may be a s p e c i f i c adaptation to reduce water loss by decreasing surface area. In the experiment described above, the dry weight of slugs active during the drought was usually greater than the weight of those which were i n a c t i v e , whereas adult slugs usually contain a higher percentage of water than smaller ones (Daxl, 1970: Umax flayus; Richter, personal commun.: A. columbianus ). Information on s o i l moisture alone thus i s not s u f f i c i e n t to predict the hydration of slugs. The length of the dry period, and the size cf the i n d i v i d u a l s , are also important. A direct measurement of the hydration of a sample would be the most useful datum to apply in future a c t i v i t y studies. 207 RAINFALL T e r r e s t r i a l molluscs are generally repelled by heavy r a i n , although they become active i n l i g h t showers (Barnes and Weil, 1945; Whiter 1959; Pinder, 1969). Blinn (1963) observed that i t was the force of the rain drops s t r i k i n g the sensitive tentacles that appeared to deter the a c t i v i t y of s n a i l s ; Bollo (1974) suggested that t h i s was also true of slugs. Bichter (1976) noted that t h i s feature of ra i n appeared to account f o r i t s repellent a f f e c t on At- columbianus . Nevertheless, although spring rain lowered the a c t i v i t y of A x columbianus. even heavy r a i n did not deter these slugs in summer (Richter, 1976a). This difference suggests that the response to rain may depend partly on the dehydration of the animals. I have already noted that some atyp i c a l daytime a c t i v i t y of f i e l d slugs could be a hygro-regulatory response of desiccated animals to rain. Quiescent dehydrated slugs and s n a i l s w i l l become active and move towards pieces of wet paper towelling placed nearby. How such water-covered animals can locate mere point-sources of water i s a mystery. Slugs come to the s o i l surface when i t floods (South, 1964), On several occasions during the winter, I observed I?*, rejbjculatum crawling i n unusually cold and windy conditions. This a c t i v i t y appeared to be a response to flooding of the s o i l by a sudden melting of the snow cover. F i n a l l y , some authors believe that t e r r e s t r i a l molluscs only become active i f the surface of the ground i s covered with a f i l m of moisture (Barnes 208 and Weil, 1944,1945; Shalem, 1949; Rozsa, 1962; Coe, 1971; Randolph, 1973). Although locomotion i s d e f i n i t e l y f a c i l i t a t e d by such conditions (judge, 1972a), the freguency with which I observed slugs crawl on dry substrates demonstrated that an actual f i l m of water on the ground i s not e s s e n t i a l for the a c t i v i t y of well-hydrated animals. WIND Barnes and Weil (19 45) observed that increased wind speed decreased the a c t i v i t y of slugs i n the f i e l d . Kalmus (1942) and Dainton (1943,1954b), showed that slugs were repelled by strong a i r currents i n the laboratory. , In some experiments, Bebley (196 4) found s i g n i f i c a n t correlations of wind speed and the number of slugs attracted to ba i t s . However, some of these correlations were positive, and others were negative. Stephenson (1968) found that the repellent effect of a i r currents made i t impossible to test the response of slugs to odours i n a l-tube olfactometer. On the other hand, Gelperin (1974) noted that L. maximus freguently crawled home against the wind. Richter (1976) found that wind speed influenced the foraging of A. columbianus. Dundee (1977) observed that v e r o n i c e l l i d slugs were repelled by wind, responding either by seeking shelter or by aggregating. Wind has two major e f f e c t s that might be expected to influence the a c t i v i t y of slugs. F i r s t l y , i t modifies their a b i l i t y to orient by o l f a c t i o n . This e f f e c t i s discussed i n more 209 d e t a i l i n the following section. Secondly, wind greatly modifies evaporative rates by decreasing the thickness of the boundary layer over the evaporating surface, and by increasing the movement cf water vapor through turbulent transfer (Leighly, 1937; Thornthwaite, 1940). Machin (1964b) studied the relationship between evaporation and boundary layer thickness by observing the s n a i l , H. aspersa. i n various a i r flows. He discovered that most water was lost by those s n a i l s facing into the wind. Hhen at r i g h t angles to the wind, s n a i l s l o s t 83% of the amount they l o s t when facing into the wind; facing downwind, they l o s t only 68% of the water they l o s t when facing into the wind. These differences were thought to be caused by the asymmetrical aerodynamic properties of the s n a i l - s h e l l , and there would be l e s s pronounced differences f o r s h e l l - l e s s slugs. although evaporation rate i s already included i n the model, and might be expected to account for wind e f f e c t s as well, the p o s s i b i l i t y remains that slugs may respond d i r e c t l y to wind, since Dainton (1952b) demonstrated that even saturated a i r currents could be repellent. In addition, decreases i n a c t i v i t y due to disruption of olfactory orientation could be accounted for by including wind speed as a factor, although t h i s aspect probably would be greatly modified by the immediate surroundings, Barnes (1949) previously observed that on very windy nights, slugs were s t i l l active i n sheltered situations, My f i e l d observations suggest that wind may net a f f e c t the o v e r a l l a c t i v i t y of the animals, but to some extent may determine th e i r l o c a l d i s t r i b u t i o n . In places with considerable topographical complexity, o v e r a l l a c t i v i t y may not be noticeably 210 c u r t a i l e d i n windy weather, whereas the same weather may prevent slugs frcm venturing into open spaces., Correlations of wind speed with the a c t i v i t y of the various species c f slugs are given i n Table XXV. Hind d i r e c t i o n was not taken into account, although i t may have introduced seme variation i n the data, since the shape of the cages would influence a i r flow., Although wind speed was included in some eguations {Table XXVII) as a s i g n i f i c a n t factor related to the a c t i v i t y of some species, the relationship was not c l e a r l y defined. In Figure 45, no apparent threshold of a c t i v i t y with wind was discernible i n contrast to previous factors. 211 Figure 45. A c t i v i t y of Peroceras reticulatum in Relation to Hind Speed i n the F i e l d , I l l u s t r a t i n g the Best Regression Line. PROPORTION OF POPULATION ACTIVE 213 The influence of wind speed may be badly underestimated i n the present study, since the cage canopies considerably reduced a i r currents, and /there were very few r e a l l y windy nights to observe., a single measure of wind speed i s probably inadequate to predict i t s e f f e c t on slug a c t i v i t y due to the high variation of a i r masses with respect t c temperature, water content, d i r e c t i o n , speed , and gustiness. CpJtJMTI^^SEGJ^SSIGN MODELS The correlation-regression analysis was performed using the double-precision triangular regression package, "UBC IBP", written by Le and T e n i s c i at the University of B r i t i s h Columbia, a subroutine was written t c perform the necessary transformations and to ensure that the computer recognized missing data. The degree of a c t i v i t y of slug populations for any given hour was measured as the proportion of the population active. But proportions conform to a binomial, rather than a normal, d i s t r i b u t i o n (a v i o l a t i o n of the assumptions of regression analysis). If the square root of each proportion i s transformed to i t s arcsine, then the r e s u l t i n g data w i l l conform to the normal d i s t r i b u t i o n (Zar, 1974), so t h i s transformation was applied to each observation of slug a c t i v i t y . For those variables that sometimes reached zero (e.g., the proportion of slugs a c t i v e ) , for negative values, such as temperature, for which logarithmic transformations were desired. 214 i t was necessary to add a small number such as 0.001, to each observation of slug a c t i v i t y before the axesine transformation was performed. Because values > 1.00 created by t h i s procedure would then exceed the range of the arcsine function, any that occurred were converted to 0.999 before the operation. In addition, when very large numbers were generated by some of the exponential transformations, i t was necessary to scale down such variables by several powers of 10 before transforming them. This treatment does not a f f e c t t h e i r correlations nor the l i k e l i h o o d of their being selected for the predictive eguations, although i t does change t h e i r means. Such transformations are indicated where appropriate. The correlations of a c t i v i t y of the various slug species with the independent factors discussed u n t i l now are presented in Table XXV. In some cases the logarithmic transformation of the dependent factor provided a better f i t whereas, i n others, the arcsine transformation alone was better. Both p o s s i b i l i t i e s were therefore considered for each species. For each equation to be generated, only one transformation or measure of each independent factor was included for the f i n a l selection by the computer. Thus, i n order to account for evaporative stress on the molluscs, one of r e l a t i v e humidity, vapor pressure d e f i c i t , or r e l a t i v e evaporation was included. Since the c o r r e l a t i o n of these factors with other weather parameters d i f f e r s , i f a l l three were available for s e l e c t i o n , the f i n a l eguation might contain more than one measure of evaporation stress at the expense of a correlated factor that was causally important. 215 The representative factor having the highest correlation with the activity of the particular dependent factor therefore «as the one included for final selection by the computer. Note however, that because of correlations among the various independent parameters, a more significant eguation sometimes might be generated by using the other two possibilities, despite their lower direct correlation with the given dependent variable. Nevertheless, the method choosen appears to be the best alternative to the l o g i s t i c a l l y impractical option of attempting a l l the possible combinations. Table XXV. Correlation Coefficients Relating the A c t i v i t y of Molluscs to Environmental Parameters. Species of Mollusc Time Logarithm Log Time 9 Phase Scoto- Logarithm of Time Log Time^ period Scoto-Log^Time period Deroceras reticulatum a 0. 1834 0. 3505 0. 7970 -0 . 0603 0. 0597 .0. 0615 Logarithm D. reticulatum b 0. 3142 0. 4822 0. 8806 -0 . 0632 0. 0579 0. 0574 Arion ater a 0. 2947 0. 4456 0. 7667 -0 .1486 0 . 1472 0. 1579 Logarithm A. ater b 0. 3879 0. 5315 0 • 8069 -0 .1471 0. 140 8 0. 1469 Cepaea nemoralis a 0. 3259 0. 4539 0. 7489 0. 1162 -0 . 1247 -0 . 1205 Logarithm C. nemoralis b 0. 4828 0. 6057 o. 84 3 2 0. 0398 -0 . 0438 -0 . 0374 Ariolimax columbianus a 0. 4253 0. 5551 0. 7827 -0 . 0704 0. 0778 0. 0867 Logarithm A. columbianus b 0. 4594 0. 5977 0. 8488 -0 .1499 0. 1522 0. 1564 Limax maximus a 0. 0519 0. 2 054 0. 7331 -0 . 1869 0. 1923 0. 2020 Logarithm L. maximus b. 0. 1293 0. 2858 0. 8274 -0 .2656 0. 2684 0. 2726 Arion subfuscus a 0. 0726 0. 2 343 0. 8126 -0 . 1848 Q. 1832 0. 1850 Logarithm A. subfuscus b 0. 2313 0. 3 86 9 0, 84 56 -0 . 2566 0. 2517 0. 2515 Arion hortensis a 0. 1085 0. 1238 0. 1204 0. 1516 -0 . 1600 -0 . 1621 Logarithm A. hortensis b 0. 1108 0. 1268 0. 1213 0. 1535 -0 . 1619 -0 . 1640 Arion circumscriptus a 0. 0871 0. 1349 0. 2312 0. 0743 -0 . 0775 -0 . 0757 Log. A. circumscriptus b 0. 0955 0. 14 7 0 0. 2628 0. 0741 -0 . 0793 -0 . 0776 Deroceras caruanae a 0. 1266 0. 2763 0. 7252 -0 .0446 0. 0523 0. 0695 Logarithm D. caruanae b 0. 1963 0. 3611 0. 7991 -0 . 1066 0. 1112 0. 1199 a Transformation — A r c s i n e (Square root (Proportion slugs active)) +0.001. b Transformation = Logarithm (Arcsine (Square root (Proportion slugs active)) + 0.001. * Value obtained by taking the square root of the value for the best f i t regression equation. T a b l e XXV. ( c o n t i n u e d ) S p e c i e s o f M o l l u s c E x p o n e n t L i g h t . L a g L o g a r i t h m L a g C h a n g e s S c o t o - L i g h t L i g h t L o g a r i t h m L i g h t p e r i o d L i g h t D. r e t i c u l a t u m 0.0579 -0. 6146 -0 . 6508 - o . 7973 - 0 . 6972 0. 0546 L o g . D. r e t i c u l a t u m 0.0578 -0 . 6756 -0 .7167 - 0 . 76 20 - 0 . 6803 0. 0 818 A. a t e r 0.1394 -0. 6415 0. 7115 - 0 . 7850 - 0 . 7165 0. 1105 L o g . A. a t e r 0.1360 -0 . 6913 -0 .7694 - 0 . 6870 - 0 . 6255 0 . 1399 C. n e m o r a l i s -0.1280 -0 . 4874 -0 . 5904 - 0 . 7356 - 0 . 7305 0. 179 5 L o g . C. n e m o r a l i s -0.0488 -0 . 5349 -0 .6905 - 0 . 7163 - 0 . 7019 0. 2812 A. c o l u m b i a n u s 0.0722 - 0 . 6 4 78 -0 . 7342 - 0 . 7 327 - 0 . 7365 0. 1315 L o g . A. c o l u m b i a n u s 0.1494 -0. 7253 -0 . 8220 -o. 7038 - 0 . 6810 0. 1549 L. maximus 0.1852 -0 . 5000 -0 . 5290 - 0 . 8564 - 0 . 7410 0. 0337 L o g . L. maximus 0.2648 - 0 . 5 875 -0 . 6103 -0 . 9144 - 0 . 7967 .0 • 0300 A. s u b f u s c u s 0.1811 -0 . 5307 -0 .5709 - 0 . 8537 - 0 . 7171 0. 0636 L o g . A. s u b f u s c u s 0.2509 -0 . 6182 -0 .6613 - 0 . 8723 - 0 . 7569 0. 1039 A. h o r t e n s i s -0.158.7 -0. 0972 -0 . 1085 - 0 . 0676 - 0 . 1330 0. 0263 L o g . A. h o r t e n s i s -0.1604 -0 . 0960 -0 .1097 - 0 . 0683 - 0 . 1316 0. 0229 A. c i r c u m s c r i p t u s -0.0797 -0 . 1946 -0 .2097 - 0 . 2964 -0 . 2983 0. 0228 L o g . A. c i r c u m s c r i p t u s -0.0813 -0 . 2133 -0 .2272 - o . 2967 - 0 . 3 0 06 0. 0179 D. c a r u a n a e 0.0410 -0 . 5207 -0 .5299 - 0 . 7579 - 0 . 6595 0. 0474 L o g . D. c a r u a n a e 0.1052 -0. 6319 -0 .6507 - 0 . 8311 -0 . 7264 0. 0407 T a b l e XXV. ( c o n t i n u e d ) S p e c i e s o f M o l l u s c C h a n ges Moon L i g h t P o l y n o m i a l * D. r e t i c u l a t u m 0.4565 -0.0536 L o g . D. r e t i c u l a t u m 0.5011 -0.0094 A. a t e r 0.5079 0.0098 L o g . A. a t e r 0.5519 -0.0100 C. n e m o r a l i s 0.4239 0.0511 L o g . C. n e m o r a l i s 0.5189 0.0358 A. c o l u m b i a n u s 0.52 36 0.1100 L o g . A. c o l u m b i a n u s 0.5690 0. 0553 L. maximus 0.3647 0.0298 L o g . L. maximus 0.4350 0.0140 A. s u b f u s c u s 0.5076 0.0293 L o g . A. s u b f u s c u s 0.6075 0.0156 A. h o r t e n s i s 0.0000 -0.1695 L o g . A. h o r t e n s i s 0.0000 -0.1693 A. c i r c u m s c r i p t u s 0.0000 -0.2542 L o g . A. c i r c u m s c r i p t u s 0.0000 -0.2406 D. c a r u a n a e 0.4487 0.0559 L o g . D. c a r u a n a e 0.5604 0.0430 L o g a r i t h m E x p o n e n t B a r o m e t r i c Moon Moon P r e s s u r e L a g B a r o m e t r i c P r e s s u r e -0.0454 -0.0227 -0.0999 -0.1009 -0.0003 -0.0318 -0.0244 -0.0213 -0.1053 -0.0933 -0.0434 -0.0647 0.0008 0.0011 -0.3040 -0.2868 0.0223 -0.0028 -0.0543 -0.0077 0.0162 -0.0033 0.0466 0.0360 0.1075 0.0536 0.0358 0.0189 0.0322 0.0187 -0 . 1 6 7 1 -0.1669 -0.2383 -0.2254 0 .0441 0.0390 - 0 . 0 8 8 1 -0.0237 -0.0818 -0.0389 0.0504 -0.0053 -0.0580 -0.0512 -0.0600 -0.0505 0.0169 -0.0247 -0.0109 -0.0130 -0.0054 0.0108 - 0 . 1 4 1 1 -0.0987 -0.1.022 - 0 . 0 3 7 1 -0.0989 -0.0578 0.0433 -0.0137 -0.0719 -0.0733 -0.0651 -0.0555 -0.0110 -0.0296 -0.0186 - 0 . 0 2 1 1 -0.0164 -0.0020 -0.1426 -0.1054 T a b l e XXV. ( c o n t i n u e d ) S p e c i e s o f M o l l u s c L o g a r i t h m E x p o n e n t L a g L a g L a g Wind Wind Wind L o g a r i t h m E x p o n e n t W i n d . Wind D. r e t i c u l a t u m L o g . D. r e t i c u l a t u m -0 . -0 . 3338 2984 -0 . -0 . 2810 2 380 -0 . -0 . 2947 253 3 -0 . -0 . 3484 3047 -0. -0. 2886 2471 A. a t e r L o g . A. a t e r -0 . - 0 . 2401 2434 -0 . -0 . 2041 2065 -0 . -0 . 2306 2097 -0 . -0 . 2599 2361 -0 . -0 . 2257 2043 C. n e m o r a l i s L o g . C. n e m o r a l i s -0 . -0 . 1295 1521 " -0 . -0 . 1190 12 31 -0 . -0 . 1705 1660 -0 . - o . 1757 1939 -0 . -0 . 1662 1611 A. c o l u m b i a n u s L o g . A. c o l u m b i a n u s -0 . -o -2117 2 456 -0 . -0 . 1675 1917 -0 . -0 . 2078 219 9 -0 . -0 . 2339 2552 -0. -o-2027 2145 L, maximus L o g . L. maximus -0 . -0 . 2023 2490 -0 . - o . 1447 1845 -0 . -0 . 1998 2 42 6 -0 . -0 . 2552 2909 -0 . -0 . 1955 2376 A. s u b f u s c u s L o g . A. s u b f u s c u s -0 . -0 . 2698 2855 -0 . -0 . 2092 2102 -0. -0 . 2398 2239 -0 . -0 . 2980 3005 -0 . -0 . 2348 2171 A. h o r t e n s i s L o g . A. h o r t e n s i s -0 . -0 . 0269 0282 -0 . -0 . 0646 0639 -0 . -0 . 0 7 00 0717 -0 . -0 . 0112 0141 -0. -0 . 0711 0726 A. c i r c u m s c r i p t u s L o g . A. c i r c u m s c r i p t u s -0 . -0 . 1232 1127 -0 . -0 . 18.76 1851 -0 . -0 . 2261 2193 -0 . - o . 1819 1763 - o . -0 . 2251 2222 D. c a r u a n a e L o g . D. c a r u a n a e -0 . -0 . 1924 2573 -0 . -0 . 1814 2216 -0 . -0 . 2183 2539 -0 . -0 . 2376 2934 -0 . -0 . 2140 2515 T a b l e XXV. ( c o n t i n u e d ) S p e c i e s o f M o l l u s c Changes Bardm. Ch.^ S h e l t e r S u r f a c e T e m p e r a t u r e T e m p e r a t u r e B a r o m e t r i c Barom. Ch.^ Temper- Temper- 10 cm above 30 cm above P r e s s u r e Barom. Ch.^ a t u r e a t u r e t h e g r o u n d t h e g r o u n d Barom. Ch. D. r e t i c u l a t u m L o g . D. r e t i c u l a t u m A. a t e r L o g A. a t e r C. n e m o r a l i s L o g . C. n e m o r a l i s A. c o l u m b i a n u s L o g . c o l u m b i a n u s L. maximus L o g . I maximus A. s u b f u s c u s L o g . A. s u b f u s c u s A. h o r t e n s i s L o g . 1 h o r t e n s i s A. c i r c u m s c r i p t u s L o g . A. c i r c u m s c r i p t u s D. c a r u a n a e L o g . D. c a r u a n a e 0.2040 0.2165 0.2382 0.2893 0. 2689 0.3272 0.2005 0.2215 0.1278 0.1419 0.1877 0.2217 0.1324 0.1265 0.2124 0.2331 0.1100 0.1745 0.3826 0.29 77 0.4336 0.3142 0.3787 0.3656 0.4165 0.2624 0.2232 0.2270 0.2932 0. 3289 0.1314 0.1139 0.286 7 0.3382 0.2614 0.2417 •0. 0704 •0.0947 •0. 0811 •0.1067 -0.0608 •0 . 0790 -0. 0778 •0.1050 •0.0 460 •0. 0582 •0 . 0766 •0. 0844 -0 .1656 •0.1718 •0 .1400 •0.1442 •0.0614 •0. 0883 •0.5840 •0.7012 •0.6047 •0 .6786 •0.5447 •0.5920 •0.5924 •0.6942 •0.4431 •0.5628 •0.5488 •0.6742 •0. 1539 •0.1525 •0.2094 •0.2242 •0.4259 •0. 5839 •0.5783 -0.6735 -0.5601 -0. 6274 -0.5202 -0.5483 -0.5287 -0. 6354 -0.4106 -0.5389 -0. 5524 -0.6449 -0.2124 •0.2140 -0. 3115 •0.3221 -0 . 4035 •0.5613 -0.5724 -0.6648 •0.5511 -0.6205 -0.5053 -0.5325 -0.5164 -0.6277 •0.3987 -0.5276 •0.5434 -0.6377 •0.2104 -0. 2115 •0. 3143 -0. 3251 •0. 3957 -0. 5511 T a b l e XXV. ( c o n t i n u e d ) S p e c i e s o f M o l l u s c L a g S u r f a c e T e m p e r a t u r e D. r e t i c u l a t u m -0. 5053 0. 6802 0. 6128 0.0053 0. 4473 L o g . D. r e t i c u l a t u m -0. 6053 0. 7726 0. 6719 -0.3152 0. 3697 A. a t e r -0. 5456 . 0. 7 801 0. 7575 0.0774 0. 4235 L o g . A. a t e r 6067 0. 8312 0. 7853 -0.3203 0. 4227 C. n e m o r a l i s . -o. 5404 0. 6755 0. 6863 0.1770 0. 459 7 L o g . C. n e m o r a l i s -0. 5925 0. 7325 0. 7589 -0.2582 0. 40 61 A. c o l u m b i a n u s -0. 5602 0. 7043 0. 7007 0.1590 0. 4586 L o g . A. c o l u m b i a n u s -0. 6424 0. 7844 0. 7441 -0.3302 0. 4523 L. maximus -0. 3 801 0. 53 31 0. 4945 0.0036 0. 4571 L o g . L. maximus -0. 4774 0. 6162 0. 5372 -0.2097 0. 2891 A. s u b f u s c u s -0. 4984 0. 6236 0. 5681 -0.0195 0. 4704 L o g . A. s u b f u s c u s -0. 6051 0. 7179 0. 6442 -0.2439 0. 3294 A. h o r t e n s i s -0. 1455 0. 1408 o. 1353 0.0249 0. 0000 L o g . A. h o r t e n s i s -0. 1404 0. 1405 0. 1299 -0.0319 0. 0000 A. c i r c u m s c r i p t u s -0. 19 09 0. 2148 0. 2038 0.0358 0. 0000 L o g . A. c i r c u m s c r i p t u s -0. 1918 0 . 2 717 o. 2 5 08 -0.0513 o. 0000 D. c a r u a n a e -0. 3448 0. 6010 0. 56 21 0.0083 0. 4544 L o g . D. c a r u a n a e -0. 4909 0. 6902 0. 6039 -0.2453 0. 3321 S u r f . Temp. 2 L a g Temper- Temp. Changes,, S u r f . Temp.o S u r f . Temp. 2 a t u r e Temp. C h a n g e s 3 S u r f . Temp. S u r f . Temp. 3 Changes Temp. C h a n g e s 4 S u r f . Temp. Temp. Ch a n g e s T a b l e XXV. ( c o n t i n u e d ) S p e c i e s o f M o l l u s c S h e l t e r - L a g S u r f a c e Temper-Temper- a t u r e a t u r e G r a d i e n t G r a d i e n t D. r e t i c u l a t u m 0. 6891 0. 6067 L o g . D. r e t i c u l a t u m 0. 7954 0. 6809 A. a t e r 0... 6 876 0. 6289 L o g . A. a t e r 0. 7476 0. 6621 C. n e m o r a l i s 0. 6052 0. 6076 L o g . C. n e m o r a l i s 0. 6809 0. 6844 A. c o l u m b i a n u s 0. 7242 0. 7056 L o g . A. c o l u m b i a n u s 0. 8125 0. 7575 L. maximus 0. 5579 0. 4 972 L o g . L. maximus 0. 6710 0. 5745 A. s u b f u s c u s 0. 6161 0. 5489 L o g . A. s u b f u s c u s 0. 7383 0. 6386 A. h o r t e n s i s 0. 1043 0. 0 96 0 L o g . A. h o r t e n s i s 0. 1075 0. 09 31 A. c i r c u m s c r i p t u s 0. 1958 0. 1684 L o g . A. c i r c u m s c r i p t u s 0. 2006 0. 1682 D. c a r u a n a e 0. 5305 0. 4530 L o g . D. c a r u a n a e 0. 7021 0. 5928 Temp. G r a d > 2 Temp. G r a d . ^ Temp.. G r a d . ^ Temp. G r a d . L a g Temp. G r a d . 2 Temp. G r a d . ^ Temp. G r a d . ^ Temp. G r a d . R e l a - L o g . t i v e R e l a t i v e H u m i d i t y H u m i d i t y 0.7819 0.6979 0.6028 0.6005 0.8484 0.7245 0.6087 0.6140 0.8132 0.77 7 9 0.6179 0. 6194 0.8349 0.7668 0. 6073 0.6152 0.7246 0.7294 0. 4.677 0.4722 0.7914 0.-7954 0.5371 0.5432 0.7935 0.7880 0.5900 0.5945 0.8617 0.8133 0.6554 0.6644 0.6427 0.5743 0.4898 0.4845 0.7276 0.6096 0.5871 0.5809 0.6841 0.6203 0.5252 0.5180 0.7803 0.6766 0.6065 0.5994 0.0000 0.0000 0.1289 0.1296 0.1075 0.0000 0.1306 0.1314 0.2989 0.3128 0.3598 0.3464 0.3129 0.3237 0.36 52 0.3538 0.6762 0.7835 0.6167 0.6475 0.4669 0.5665 0.4655 0.5636 T a b l e XXV. ( c o n t i n u e d ) S p e c i e s o f M o l l u s c E x p o n e n t L a g . R e l a t i v e E x p o n e n t H u m i d i t y R e l a t i v e H u m i d i t y D. r e t i c u l a t u m 0. 6016 0. 5210 L o g . D. r e t i c u l a t u m 0. 6016 0. 5137 A. a t e r 0. 6136 0. 5560 L o g . A. a t e r 0. 5982 o.. 5393 C. n e m o r a l i s 0. 4618 ol 4540 L o g . C. n e m o r a l i s 0. 5297 0. 5098 A. c o l u m b i a n u s 0. 5835 0. 5442 L o g . A. c o l u m b i a n u s 0. 6451 0. 6025 L. maximus 0. 4916 0. 45 97 L o g . L. maximus 0. 5890 0. 5360 A. s u b f u s c u s 0. 5280 0. 4808 L o g . A. s u b f u s c u s 0. 6090 0. 5536 A. h o r t e n s i s 0. 12 6 8 0. 0939 L o g . A. h o r t e n s i s 0. 1287 0. 0967 A. c i r c u m s c r i p t u s 0. 3681 0. 3439 L o g . A. c i r c u m s c r i p t u s 0. 3721 0. 3563 D. c a r u a n a e 0. 4651 0. 4124 L o g . D. c a r u a n a e 0. 5656 o. 4898 V a p o r P r e s s u r e D e f i c i t L a g V a p o r P r e s s u r e D e f i c i t E v a p o r -a t i o n L a g E v a p o r -a t i o n W ind S p e e d •0. 6419 •0. 6870 •0. 5625 0.5969 •0. 6523 •0.7191 •0 .6216 •0.6535 •0.2869 •0. 2441 •0. 6761 •0. 7043 •0.6193 •0. 6441 •0. 6991 •0. 7548 •0. 6845 •0.7055 0.2092 •0.2177 •0. 5324 •0.6071 •0. 5284 •0. 6012 •0. 5348 •0. 6141 •0. 5769 •0.6644 •0.1231 •0. 1274 •0.6378 •0. 7208 •0. 5976 •0. 6714 •0.7007 •0. 7962 •0.7041 •0. 7631 -0.1727 •0.1973 •0. 4943 •0. 5913 •0. 4619 •0.5432 •0. 5113 •0. 6117 •0.5086 •0. 5830 •0. 1494 •0.1902 •0. 5472 •0.6386 •0.5080 •0. 5916 •0. 5559 •0. 6571 •0. 5580 •0. 6252 •0. 2145 •0.2166 •0.1375 •0.1392 •0.1168 •0. 1184 •0.1249 •0.1262 •0. 1112 •0. 1080 •0. 0637 •0.0633 -0. 3221 •0.3390 0.3143 •0. 3333 •0.2609 •0. 2781 •0. 2561 •0. 2617 •0.1879 •0.1848 •0. 4851 •0. 5967 •0.4341 •0. 5305 •0. 5171 •0. 6417 •0. 5003 •0.5940 •0.1859 •0. 2271 224 Multiple regression eguations may be obtained by a step-down procedure, i n which a l l the independent factors are f i r s t forced into the model, afte r which those that do not make s i g n i f i c a n t contributions are gradually dropped. A l t e r n a t i v e l y , a step-up proceedure may gradually add factors. There i s no universal agreement among s t a t i s t i c i a n s as to which method i s most advantageous (Zar, 197 4). However, i n the present study, the step-down method resulted i n better r 2 values for every eguation except one, i n which the eguations obtained by the two methods were i d e n t i c a l . ; The step-down procedure appeared to account better f o r those parameters represented i n the model by polynomial expressions. The step-up eguations were often very similar to those obtained by the step-down method, but since they contained fewer variables, only the step-down r e s u l t s are presented here. Correlation-regression models r e l a t i n g a c t i v i t y of each molluscan species to the various environmental factors are shown in (Tables XXVIII to XXXVI). Eguations were also generated for the logarithmic transformation of slug a c t i v i t y (Tables XXXVII to XLV)... Holling (1966) pointed out that temporal lags dominate the action of ecological processes. Since slugs have such a slow rate of locomotion, i t seemed l i k e l y that their a c t i v i t y might be better related to previous, rather than concurrent weather. Lag data therefore were obtained by r e l a t i n g the a c t i v i t y of the molluscs at any given time to the weather data collected one hour previously. The f i r s t hour's observations for each day were converted to missing data. Time, and factors representing change (e.g., temperature or l i g h t ) , were not altered. Also, shelter 225 temperatures changed so slowly that lag data were not needed. Once more, one equation was obtained for each species for *ihe arcsine transformation alone, and one for the logarithm of t h i s factor (Tables XLVI to LXIII). To f a c i l i t a t e comparison, the c o e f f i c i e n t s of determination and their standard errors are summarized i n Table XXVI for a l l the regression models. Comparison of the simple correlations of concurrent versus lag data (Table XXV) shows that, although the lag data were more highly correlated i n some cases (e.g. l i g h t i n t e n s i t y , ambient barometric pressure), i n most instances they were lower. Despite t h i s general i n f e r i o r i t y , the b e s t - f i t t i n g regression equations containing lag data, explained a greater amount of the v a r i a b i l i t y i n mollusc a c t i v i t y i n 10 out of 18 cases (Table XXVI). & possible explanation i s that, whereas time was retained in these equations to account for the immediate influence of the circadian rhythm, i t was also higbly correlated with concurrent weather. Thus the equations generated usinq lag data contain components related to both concurrent and previous weather. Although the r e s u l t s show that lagged weather explained an increased amount of the v a r i a b i l i t y in molluscan a c t i v i t y , the improvement was marginal i n most cases. The r e s u l t s f o r l*.£iicaiscrip.tus were a notable exception. Correlation-regression analysis does not demonstrate cause and effect relationships between dependent and independent factors. Due to the high correlations among the independent variables, an unimportant factor could be included i n the f i n a l predictive equation i n place of the actual driving parameter., However, care has been taken to include only those factors that 226 probably causally influence the a c t i v i t y of the molluscs. Even so the importance of the various factors occasionally may be over- or underestimated. For example, l i g h t and evaporation are highly correlated i n the f i e l d (r=0. 8521) . Therefore, i f l i g h t and some other fac t o r s correlated with evaporation are included i n the eguation, there i s a p o s s i b i l i t y that evaporation could be deleted as being non-significant, when i n fact we know that i t i s important, a l t e r n a t i v e l y , an equally s i g n i f i c a n t equation might be qenerated which includes evaporation, but deletes l i q h t i n t e n s i t y . Despite these reservations, the factors consistently included in the various equations seem to be those of importance in the f i e l d . Table XXVII summarizes the frequency with which independent parameters were included i n the b e s t - f i t t i n g regression equations for each species of mollusc. Because the independent factors available for selection d i f f e r e d amonq the regressions for the various species, transformations or d i f f e r e n t representations of each parameter were lumped together (e.g. l i g h t includes l i g h t , l o g - l i g h t , and l a g - l i g h t ; atmospheric moisture includes rh, vpd, evaporation, or transformations of these). For those molluscs which normally foraged on the s o i l surface, the b e s t - f i t t i n g regression models accounted for 72.83 to 89.66% of the variation in the numbers active over the entire season. The frequency with which the various parameters vere included i n the regression equations largely agrees with what would be expected from the previous discussion (Table XXVII). Time, representing the circadian rhythm, and the phase and 227 scotoperiod modifiers are included i n a majority of cases. Surface temperature and l i g h t intensity nearly t i e as the two most important weather factors. The temperature gradient between the shelter and the s o i l surface was the next most important weather factor, followed by wind speed, the phase of the moon, and atmospheric moisture. Within species, particular factors appeared to vary i n importance. For Dt reticulatum. for example, wind speed was included i n a l l four equations. This agrees with observations i n natural habitats that t h i s species i s inhibited more by wind than are larger slugs, such as ft. ater, • A, columbianus or L, maximus (see Table XXVII). For example, on the night of August 22, 1975, wind speeds averaged 40 k/h, and no active D. reticulatum was observed on a lawn. On subseguent nights with lower wind speeds, however, up to 27 Deroceras per hour were observed. There was comparable a c t i v i t y among ft. ater, and i i ja^imus on these occasions. k J t e r was highly s e n s i t i v e to temperature. A l l twelve of the possible polynomials representing surface temperature were included in the eguations f o r t h i s species.. In addition, the temperature gradient was more important for t h i s species than for any other. Despite Lewis*s (1969a) belief that A.* .ater, was not responsive to temperature changes, half of the possible polynomials representing t h i s factor were included i n the eguations f o r t h i s slug. Eguations for C. nemoralis included a l l of those factors representing time, surface temperature, l i g h t i n t e n s i t y , and scotoperiod, and phase, in three out of four eguations. 228 Temperature g r a d i e n t s , wind, and e v a p o r a t i v e s t r e s s a l s o appeared t o be i m p o r t a n t f o r t h i s s n a i l . The phase of the moon was i n c l u d e d i n a l l f o u r e g u a t i o n s f o r the s u b t e r r a n e a n s p e c i e s , as w e l l as f o r A, c o l u m b i a n u s . I n the l a t t e r , t h e p o s i t i v e c o r r e l a t i o n (Table XXV) c o u l d i n d i c a t e a l u n a r rhythm, o r , s i n c e t h i s s p e c i e s i s a woodland a n i m a l , t h e c o r r e l a t i o n may r e p r e s e n t a p r e f e r e n c e f o r a h i g h e r l i g h t i n t e n s i t y as was d i s c u s s e d e a r l i e r (see G e t z , 1963). S i m i l a r l y , t h e n e g a t i v e c o r r e l a t i o n w i t h m o o n l i g h t o b t a i n e d f o r t h e two s u b t e r r a n e a n s p e c i e s p o s s i b l y r e f l e c t s a lo w e r l i g h t p r e f e r e n c e . A c t i v i t y o f L, maximus was g r e a t l y i n f l u e n c e d by l i g h t i n t e n s i t y ( s i m p l e c o r r e l a t i o n of l o g - l i g h t w i t h l o g - Limax was -0.9173). The c i r c a d i a n rhythm, s u r f a c e t e m p e r a t u r e , and l i g h t a r e the most i m p o r t a n t f a c t o r s r e g u l a t i n g t h e a c t i v i t y o f t h i s s l u g . I t was rem a r k a b l y u n r e s p o n s i v e t o any o t h e r f a c t o r s , e x c e p t f o r changes i n l i g h t i n t e n s i t y . f a c t o r s i n c l u d e d i n the e g u a t i o n s f o r A t s u M u s c u s were s i m i l a r to t h o s e f o r L A maximus. but temperature g r a d i e n t s and wind speed were o f g r e a t e r conseguence f o r t h e former. I t . §ufeJHscH§ e g u a t i o n s a l s o i n c l u d e d more o f t h o s e p o l y n o m i a l s r e p r e s e n t i n g changes i n l i g h t i n t e n s i t y t h a n d i d t h o s e of any o t h e r s p e c i e s . The b e s t - f i t t i n g r e g r e s s i o n models o b t a i n e d f o r A. h o r t e n s i s and A. c i r c u m s c r i p t u s , r e p e c t i v e l v . accounted f o r o n l y 22.69% and 55.33% o f t h e ob s e r v e d v a r i a t i o n i n t h e i r a c t i v i t y ( T a b l e s 1X1 and L X I I ) . T h i s l a c k of c o r r e l a t i o n w i t h weather appeared t o be r e l a t e d t o t h e i r s u b t e r r a n e a n h a b i t , a l t h o u g h Hebley (1964) p r e v i o u s l y found low c o r r e l a t i o n s o f 229 a c t i v i t y of A„ hortensis with weather, despite the fac t that many crawled on the s o i l surface. In retrospect, one reason for the lew surface a c t i v i t y observed i n these species, may have been that the food was located too far away from their shelters. Both species have slow rates of locomotion (0.073 cm/sec for ft,, hortensis* and 0.042 cm/sec for A. circumscriptus ), and are thus not well adapted to tr a v e l quickly on the s o i l surface. Although they were both observed to reach the food and return to shelter cn occasion, the t r i p took a considerable amount of time which would not always be available. There i s some support for thi s suggestion. Daxl (1969) obtained an a c t i v i t y curve for A. hortensis similar to that for other slugs when the food was very close to the shelter. Consequently, i f t h i s idea i s correct, the degree of slug a c t i v i t y on the s o i l surface would be expected to change, not only with the a v a i l a b i l i t y of food inside the shelters, as I have already demonstrated, but also with i t s a c c e s s i b i l i t y on the surface. In natural environments, surface a c t i v i t y of A. hortensis and A, circumscriptus as well as that of other subterranean species, such as A. intermedius and A. s i l y a t i c u s . w a s largely limited to the colder months of the year, an observation previously reported for the former two species by Hhite (1959). In the f i e l d cages A. circumscriptus and A. hortensis died during the summer months which suggests that their upper l e t h a l temperature was lower than that of other slugs. Of possible si g n i f i c a n c e i n t h i s respect was the inc l u s i o n of shelter 230 temperature as a s i g n i f i c a n t factor in a l l the eguations f c r Jb. h2I%§H§A§* That such species move deeper in t o the s o i l during the summer (Hunter, 1966; Rollo and E l l i s , 1974) i s probably related to t h e i r temperature preferendum ( although drying of the s o i l surface i s also a factor (Hunter, 1966)]. I t i s s i g n i f i c a n t that the temperature gradient was one of those factors most frequently included i n eguations f o r A, circumscriptus (Table XXVII). The necessity t o move deeper i n the s o i l , combined with the slow rate of movement, could explain the paucity of surface a c t i v i t y by these slugs during the summer. Eguations for A,, circumscriptus included changes i n barometric pressure more freguently than those for any other species. For a subterranean species, l a r g e l y i s o l a t e d from conditions occurring on the s o i l surface, barometric pressure changes could prove a useful factor for predicting favourable periods f o r a c t i v i t y , Eguations f o r D^ . caruanae each included ambient barometric pressure as a factor. A c t i v i t y was l a r g e l y predicted by the circadian rhythm and i t s seasonal adjustment by phase and scotoperiod. Surface temperature, temperature gradients, and temperature changes were a l l important. Changes i n l i g h t i n tensity were included i n eguations more than i n most other species. Table XXVI. Summary of Coefficients of Determination and t h e i r Standard Errors for Correlation-Regression Equations Relating Slug A c t i v i t y to Environmental Parameters. Dependent Concurrent Lag Factors " . Weather ; . Weather  Coef f i c i e n t of C o e f f i c i e n t of Determination S.E. Determination S.E. Deroceras reticulatum a 0. 7989 0.1750 0. 8095 0.1709 Log. D. reticulatum b 0. 8561 0.2254 0. 8657 0.217 7 Arion ater a 0. 8567 0.1425 0. 8787 0.1318 Log. A. ater b 0. 8424 0.2251 0. 8916 0.1870 Cepaea nemoralis a 0. 8324 0.1752 0. 8 09 5 0.1815 Log. C. nemoralis b 0. 8770 0.2275 0. 8592 0.2418 Ariolimax columbianus a 0. 8050 0.1386 0. 8 3 82 0.1266 Log. A. columbianus b 0. 8547 0.2018 0. 8966 0.1717 Limax maximus a 0. 8094 0.2019 0. 7283 0.2399 Log. L. maximus b 0. 8663 . 0.2 5 96 0. 7354 0. 3284 Arion subfuscus a 0. 8183 0.1715 0. 7474 0.2064 Log. A. subfuscus b 0. 8923 0.2054 0-8566 0.2379 Arion hortensis a 0. 2111 0.0494 0. 2263 0.0486 Log. A. hortensis b 0. 1915 0.1579 0-2269 0.1539 Arion circumscriptus a 0. 3553 0. 0813- 0. 5281 0.0700 Log. A. circumscriptus b 0. 3788 0.2026 0. 5533 0.1735 Deroceras caruanae a 0. 7816 0.13 2 9 0. 7637 0.1387 Log. D. caruanae b 0. 8385 0.2113 0. 8321 0.2169 a- Transformation = Arcsine (Square root (Proportion of Slugs Active)) + 0.001. b- Transformation = Logarithm to base 10 o f the above. 232 Table XXVII Frequencies with which Independent Factors were Included i n Regression Models describ-ing the a c t i v i t y of nine Molluscan species. Environ-mental Factors Possible Number Factors/ Species Actual No. of Factors Included Species 3 •p rH • 3 o •H 4-> CD U CO c m •H Xi e rH O 0 CO a u CO m 3 CO CO •H CO CD -p u o CO •J-) a! •H o CO e u u •H O Frequency Factors were i n -cluded i n models (%) Q l <| U l <|. <\ Q l Time 12 12 11 12 12 9 10 12 10 11 91.67 Surface Temperature 12 6 12 12 8 12 9 8 8 10 78.70 Light 4 1 3 4 3 4 4 2 4 2 75.00 Scotoperiod 4 2 3 4 2 2 2 2 2 4 63. 89 Phase 4 1 3 3 2 2 0 2 4 4 58.33 Temperature Gradient 16 8 11 10 9 2 8 6 10 9 50.69 Wind 4 4 1 3 1 0 3 0 2 2 44.44 Moon 4 0 1 0 4 0 0 4 4 2 41. 67 Atmospheric Moisture 4 0 1 3 3 0 2 3 2 0 3 8.89 Changes i n Light 16 6 9 5 2 7 12 2 2 8 36.81 Ambient Barometric Pressure 4 2 2 2 0 0 1 0 0 4 30. 56 Shelter Temperature 4 1 1 0 0 2 0 4 2 0 27.78 Changes i n Barometric Pressure 16 6 2 4 4 0 4 3 12 2 25.69 Temperature Changes 16 5 8 4 5 0 1 2 0 8 22 . 92 T a b l e X X V I I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f D e r o c e r a s r e t i c u l a t u m t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.7989 S t a n d a r d E r r o r = 0.1750 F - P r o b a b i l i t y . = .0000 V a r i a b l e C o e f f i c i e n t S t a n d a r d E r r o r F - P r o b a b i l i t y L o g T i m e 2 L o g T i m e ^ L o g Time L o g S c o t o p e r i o d L o g L i g h t S u r f a c e T e m ? e r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e . T e m p e r a t u r e G r a d i e n t ] T e m p e r a t u r e G r a d i e n t L o g W i n d B a r o m e t r i c P r e s s u r e C o n s t a n t -13.383230 12.843407 -2.7642280 -0.39988238 - 0 . 4 5 6 5 8 2 3 5 E - 0 1 7.0577350 -43.625137 69.362750 -239.23158 - 1 3 8 0 . 7 3 1 3 . -0.12217079 -0.41956214E-02 8.9275588 2.880 2.453 0.4 68 9 0.1521 0.1041E-01 2.285 13. 79 26 . 70 51.06 429.6 0.212 6E-01 0.2141E-02 2.387 0.0000 0.0000 0.0000 0.0088 0.0000 0.0030 0.0022 0.010 6 0.0000 0.0018 0.0000 0.0481 0.0003 Table XXIX. Regression A n a l y s i s R e l a t i n g the A c t i v i t y of A r i o n a t e r to Concurrent Environmental Factors.. r = 0 . 8 5 6 7 Standard E r r o r = 0 . 1 4 2 5 F - P r o b a b i l i t y = . 0 0 0 0 V a r i a b l e Log Time^ Log Time^ Log Time Log S c o t o p e r i o d Phase Log L i g h t 2 Changes L i g h t ^ Changes L i g h t ^ Changes L i g h t Surface Temperature2 Surface Temperature^ Surface Temperature Temperature Gradient^ Temperature Gradient^ Temperature Gradient Temperature Changes 4 Barometric Pressure Constant C o e f f i c i e n t Standard E r r o r F-• P r o b a b i l i t y -6 . 7828717 2.420 . 0. 0054 6.9861201 2.071 0. 0010 -1.5605933 0.39 8 4 0. 0002 . 2.6375504 1.057 0. 0127 . 0.19460957 0.8527E-01 0. 0220 -0.58038476E -01 0..8696E-02 0. 0 00 0 -0.90553820E -01 0.4348E-01 0. 02 45 -0.40465907E -01 0.1579E-01 0. 0065 0. 28800503E-01 0. 7905E-02 0. 0002 14 . 973297 2 . 029 0. 0000 -90.529675 12.3 3 0. 0000 141.29420 23.39 o.. 00 00 -1.4684386 0.6432 0. 0226 -258.35279 58.56 0. oooo--1643.2837 371..7 0. 0000 -4526.3791 .1667. . 0. 0034 -0. 38802254E--0.2 0.1785E-02 0. 02 8 9 -3.4355797 3 .938 0. 3903 T a b l e XXX. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f C e p a e a n e m o r a l i s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.3324 S t a n d a r d E r r o r = 0.175 2 F - P r o b a b i l i t y = .0000 V a r i a b l e C o e f f i c i e n t S t a n d a r d E r r o r . F-• P r o b a b i l i t y L o g T i m e 2 -19.740907 2.997 0. 0000 L o g Tirne^' 1 5 .612281 2.563 ' 0. 0000 L o g Time -2.6562655 0.4923 . .0. 0000 E x p o n e n t S c o t o p e r i o d -3.9044450 1.062 0. 0004 P h a s e -0.66171107 0.2189 0. 0029 L o g L i g h t . -0.10010193 0.1057E-01. 0. 0000 C h a n g e s L i g h t 0.17484354 0.4393E-01 0. 0001 S u r f a c e T e m p e r a t u r e 2 . 12.527240 2.404 0. 0000 S u r f a c e T e m p e r a t u r e ^ -85 . 917294 14.70 0. 0000 S u r f a c e T e m p e r a t u r e ^ 166.99468 .28 .13 0. .0000 T e m p e r a t u r e G r a d i e n t ^ - 170.67089 - 58.54 0. 0044 T e m p e r a t u r e G r a d i e n t - 2 7 1 1 . 0276 .. 4 5 4.7. 0. 0000 T e m p e r a t u r e C hanges 2 .4327500 0.-8031 0. 0 026 E v a p o r a t i o n -0.11963144 0. 3995E-01 0. 0025 L o g W i nd - 0 . 5 1 8 0 1 9 6 9 E - 0 1 0.2219E-01 0. 0184 B a r o m e t r i c P r e s s u r e 0.54802292E-02 0.2228E-02 0. 0139 B a r o m e t r i c Changes 0 . 5.6 520760E-.01 0.3028E-01 0. 0 4 96 C o n s t a n t 13.762749 4.76.6 0. 0042 T a b l e XXXI. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f A r i o l i m a x c o l u m b i a n u s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0 . 8 0 5 0 S t a n d a r d E r r o r = 0.1386 F - P r o b a b i l i t y =..0000 V a r i a b l e C o e f f i c i e n t S t a n d a r d E r r o r F - P r o b a b i l i t y L o g T i r r ^ L o g T i m e ^ L o g Time L o g S c o t o p e r i o d P h a s e L o g L i g h t S u r f a c e T e m p e r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ T e m p e r a t u r e G r a d i e n t E v a p o r a t i o n Moon P h a s e C o n s t a n t - 1 4 . 6 8 4 6 6 2 1 2 . 8 3 4 3 6 5 - 2 . 4 0 6 6 7 7 0 3.2728551 0. 2 7 9 0 8 2 7 5 - 0 . 2 6 9 5 0 7 6 0 E - 0 1 2.4 274935 - 8 . 0 7 4 0 0 0 6 - 1 2 8 . 8 2 0 4 7 - 0 . 1 5 4 8 0 2 1 0 0.93736623E-03 - 6 . 7 3 1 6 3 0 5 2. 304 1.974 0. 3798 1. 005 0.8074E-01 0.8197E-02 0. 6569 1. 907 34.09 0.2 8 01E-01 0.2 410E-03 3.549 0.0000 0.0000 0.0000 0.0014 0.0008 0.0013 0.0005 0.0001 0.0003 0.0000 0.0002 0.0559 u a T a b l e X X X I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f L i m a x maximus t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . " r = 0.8094 S t a n d a r d E r r o r = 0.2019 F - P r o b a b i l i t y = 0.0000 V a r i a b l e L o g T i m e 2 L o g T i m e ^ L o g Time L o g L i g h t C h a n g e s L i g h t ^ C h a n g e s L i g h t ^ C h a n g e s L i g h t S u r f a c e T e m p e r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t C o n s t a n t C o e f f i c i e n t S t a n d a r d . E r r o r F - P r o b a b i l i t y -7.4145236• 3. 228 0. 0212 6.7785111 2. 724 0. 0129 -1.4258493 0. 515 7 0. 0060 - 0 . 1 7 1 6 4 8 7 1 0. 1095E- 01 0. 0000 0 . 19369558 0. 57 4 4 E - 01 0. 0010 -0.85174420E -01 0. 25 8 2 E - 01 0. 0011 0.23548785E- 01 0. 8298E- 02 0. 0041 14.267003 2. 404 0. 0000 -67.996920 14 . 62 0. 0000 99.270362 27 . 03 0. 0005 - 0 . 43859403E -01 0. 1370E- 01 0. 00 27 -2.1879526 0. 6723 0. 0015 1.7664317 1. 055 0. 0869 T a b l e X X X I I I R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f A r i o n s u b f u s c u s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0 . 8 1 8 3 S t a n d a r d E r r o r = 0.1757 F - P r o b a b i l i t y = .0000 V a r i a b l e . 2 Log. T i m e ^ L o g Time L o g L i g h t C h a n g e s L i g h t 2 . • C h a n g e s L i g h t ^ C h a n g e s L i g h t ^ C h a n g e s L i g h t S u r f a c e T e m p e . r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t B a r o m e t r i c P r e s s u r e C o n s t a n t C o e f f i c i e n t 1.2668892 - 0 . 6 0 2 4 6 2 6 1 -0.14376309 0.11469965 -0.25687258. 0.26113027 -0 . 12049986 . 10.855669 - 6 9 . 4 8 0 9 9 1 115.66695 -3.5566510 0. 591910.40E-02 - 6 . 3 6 4 7 5 6 3 S t a n d a r d E r r o r F - P r o b a b i l i t y 0.3107 0.1311 0. 8965E-02 0. 5-8 6 I E - 0 1 0.9158E-01 0 . 6739E-0L". 0.5268E-01 2. 263 13 .46 24.27 0.6207 0. 2831E-02 2.922 0. 0001 0. 0 0 00 0.0000 0.0390 0. 0037 0.0001 0.0164 0.0000 0.0000 0. 0000 0.0000 0.03 53 0.0282 T a b l e XXXIV. R e g r e s s i o n A n a l y s i s R e l a t i n g A c t i v i t y o f A r i o n h o r t e n s i s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.2111 S t a n d a r d E r r o r =. 0.0494 F - P r o b a b i l i t y = .0000 V a r i a b l e C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y L o g Time2 -2.4921168 0. 8068 0. 0024 L o g Time^. 1.9472220 0. 6.465 0. 0030 L o g Time -0.31728593 0. 1148 .0. 0060 L o g S c o t o p e r i o d - 0.20961468 0. 4 381E-01 0. 0 00 0 L i g h t - 0 .42064202E -04 0. 1379E- 04 0. 0026 Changes L i g h t „ 0.51515175E- 01 0. 1982E- 01 0. 0095 S u r f a c e T e m p e r a t u r e ^ -2.7930209 1. 218 0. 0214 S u r f a c e T e m p e r a t u r e 9.6521177 3. 594 0. 0075 S h e l t e r T e m p e r a t u r e - 0.48778073 0. 1998 0. 0146. T e m p e r a t u r e G r a d i e n t -0.64691484 0. 2216 0. 0039 T e m p e r a t u r e Changes -0.61060625 0 . 2540 0. 0159 V.P.D. . -0.27768716. 0. 8990E- 01 0. 0024 B a r o m e t r i c C h a n g e s ^ 0.38832221E- 01 0. 1676E- 01 0. 0200 B a r o m e t r i c Changes 0.38107333E- 01 0. 1778E- 01 0. 030 9 Moon P h a s e -0.35728832E -03 0. 1021E- 03 . 0. 0007 C o n s t a n t 1.6158475 0. 3166 0. 0000 T a b l e XXXV. R e g r e s s i o n A n a l y s i s R e l a t i n g A c t i v i t y o f A r i o n c i r c u m s c r i p t u s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.3553 S t a n d a r d E r r o r = 0.0813 F - P r o b a b i l i t y = .0000 . V a r i a b l e L o g T i m e 2 L o g Time P h a s e L o g L i g h t S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e G r a d i e n t E x p o n e n t W i n d B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c Changes L o g Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F - P r o b a b i l i t y -1.5044178 0.5254 0. 0046 0.70807208 0.2528 0. 0055 0.58565258E-01 0.9168E- 02 0. 0000 - 0 . 2 7 8 0 2 1 5 6 E - 0 1 0.4874E- 02 0. 0000 -1.6726524 0.3860 0. 0000 11.706329 4.137 0. 0 050 - 9 3 . 3 1 7 6 5 1 27. 64 0. 0010 -1168.5817 259. 0 0. 0000 -0.80055593 0.2 206 0. 0004 0. 15758.602 0.3951E- 01 0. 0001 -0.17573294 0.6343E- 01" 0. 0058 -0.17866767 0.2845E- 01 0. 0000 1. 6734982 0.3605 . 0. 0000 T a b l e X X X VI. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f D e r o c e r a s c a r u a n a e t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . " • ~ r = 0.7816 S t a n d a r d E r r o r = 0.1329 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g Time2 L o g T i m e 4 L o g T i m e " L o g S c o t o p e r i o d Phase L o g L i g h t 2 C h a n g e s E i g h t y C h a n ges L i g h t S u r f a c e Temper.ature2 S u r f a c e T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t ^ T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e Changes B a r o m e t r i c P r e s s u r e B a r o m e t r i c Changes C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y -11.347288 2.764 0. 0001 11.457554 2.4 02 0. 0000 -2.5547272 0.4702 0. 0000 5.8510174 1.212 0. 0000 0.44615370 0. 9245E-.01. 0. 0000 -0.59896841E-•01 0.9934E-02 0. 0000 -0.24841229 0.5697E-01 0. 0000 0.10843923 0.3530E-01 0. 0016 2.5321424 0 . 7847 0. 0015 -13.484705 2.101 0. 0000 -3.3149910 0.7010 0. 0000 -292.55640 52.53 0. 0000 -1.6076244 &. 6 7 8 6 0. 0130. - 0 . 6 6 3 4 6 3 4 0 E - 02 0.2343E-02 0. 0050 - 0 . 5 9 3 1 4 5 7 1 E - 01 0.2801E-01 0. 0265 -10.066145 4.619 0. 0283 T a b l e X X X V I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f D e r o c e r a s r e t i c u l a t u m t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s r = 0.8561 S t a n d a r d E r r o r = 0.2254 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g Time2 L o g T i m e ^ L o g Time 2 C h a n g e s L i g h t ^ C h a n ges L i g h t ^ C hanges L i g h t S u r f a c e Temperature2 S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e ^ T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e C h a n g e s L o g W i n d ^ B a r o m e t r i c Changes. C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y - 1 3.358943 2.983 0. 0000 15.835473 2.377 0. 0000 -3.8844555 0.4152 0. 0000 - 0 . 1 4 6 4 5 3 0 2 / 0.6673E-01 0. 0132 -0.45878593E -01 0.2419E-01 0. 0312 0.33636034E- 01 0.1236E-01 0. 0.0 2 5 1.9952953 0.9776 0. 0389 -14.323933 2.931 0. 0000 0.30068655E- 01 0.1396E-01 0. 0302 -433.13912 56.44 0. 0000 - 6 . 6 8 5 6 8 1 1 1.129 0. 0000 710.26835 2 8 3.4 0. 0050 -0.75977099E -01 0.2594E-01 0. 0033 -0.17726564 0.6712E-01 0. 0036 1.1589974 1.002 0. 2604 T a b l e X X X V I I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o n a t e r t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.8424 S t a n d a r d E r r o r = 0.2251 F - P r o b a b i l i t y = .0000 V a r i a b l e 2 L o g T i m e d L o g Time " L o g S c o t o p e r i o d P h a s e ^ C h a n g e s L i g h t S u r f a c e T e m p e r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t ^ T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e C h a n g e s E v a p o r a t i o n C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F- P r o b a b i l i t y 3.0433177 0.3222 0. 0000 - 1 . 1 8 1 5 5 3 4 0.1319 0. 0000 6.5665213 1.912 0. 0008 0.51092458 0.1554 0. 0013 0 .86561108E- 02 0.3589E-02 0. 0062 16.590957 3.147 0. 0000 - 1 0 7 . 0 2 1 1 5 19.04 0. 0000 148.06374 36.15 0. 0 0 01 0.53842954E- O L 0.1729E-01 0. 0022 - 2 . 6 7 4 7 6 1 0 1. 074 0. 0123 - 3 2 9 . 4 3 7 0 2 80.42 0. 0001 . - 4 . 9 3 1 2 5 9 8 1.176 0. 0000 971.20326 279.1 0. 0001 - 9 9 2 1 . 8 5 4 1 2 5 3 3 . 0. 0000 - 0 . 1 8 4 7 2 3 7 1 0.4957E-01 0. 0002 - 2 4 . 8 1 1 2 3 5 6.432 0. 0002 T a b l e XXXIX. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y . o f C e p a e a n e m o r a l i s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r 2 = 0. 8770 •. . S t a n d a r d E r r o r = 0.2275 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g T i m e 2 L o g T i m e ^ L o g Time E x p o n e n t S c o t o p e r i o d L o g L i g h t C h a n g e s L i g h t ^ Changes. L i g h t ^ C h a n g e s L i g h t S u r f a c e Temperature., S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t . -T e m p e r a t u r e G r a d i e n t ] T e m p e r a t u r e G r a d i e n t ' T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e Changes E v a p o r a t i o n L o g W i n d B a r o m e t r i c .Change s 2 B a r o m e t r i c Changes C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-- P r o b a b i l i t y -16.382449 3. 919 . 0, .0001 12.113516 3. 375 0 .0005 -1.8092197 0 . 6531 0, . 0060 -0.73316030 0. 8 34 6E-•01 0. .0000 -0.12201731 0. 1397E-•01 0. . 0000 0. 29766296 0. 7204E-•01 . 0. 0000 -0 . 54039.296E -01 0. 2957E-•01 0. . 0455 0.26322030E- 01 . 0. 9464E-•02 0. . 0029 21.938345 3. 183 0. .0000 -144.27683 ' 19 . 63 0. .0000 265.42433 37 .25 0. .0000. 3. 6910530 1. 148 0. .0016 -545.82497 94 . 42 0. 0000 -4842.4221 624. 7 0. 0000 4.460287.8 1. 107 0. .0000 -6209.9594 2594. 0. 00 95 -0.14758426 0. 5.4 7 0E- 01 0. 0056 -0.56077968E -01 0. 2 862E-01 0. 0460 0.88654732E- 01 0. 3992E- 01 . 0. 0166 -0.16224573 0. 6477E- 01 0. 0073 5.9529656 1. 221 0. 0000 T a b l e X L . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o l i m a x c o l u m b i a n u s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.3546877 S t a n d a r d E r r o r = 0.2018 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g T i r r ^ L o g T i m e ^ L o g Time S u r f a c e T e m p e r a t u r e 2 S u r f a c e T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e Changes. E v a p o r a t i o n 2 B a r o m e t r i c C h a n g e s Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F - P r o b a b i l i t y - 1 2 . 6 7 2 2 9 2 2. 811 0. 0000 11.993356 2.303 0 . 0000 - 2 . 4 1 4 2 8 2 4 0.4180 0 . 0000 2.5079065 1.088 0. 0200 - 7 . 3 8 1 1 3 8 6 3. 312 0. 0243 4.5451202 0.9624 0. 0 00 0 - 1 7 . 8 5 7 8 8 9 6 .260 0. 0045 - 3 6 6 . 8 5 2 6 7 63.84 0. 0000 - 2 . 4 7 7 7 7 7 4 1.048 0. 0069 1298 . 7207 245.9 0. 0000 - 0 . 2 2 7 7 2 0 1 6 0.-4614E-•01 0. 0 0 00 - 0 . 1 2 3 8 5 7 4 5 0.5559E- 01 0. 0121 0.81101874E-03 0.3514E- 03 0. 0206 2.4935223 0.9549 0. 0096 T a b l e X L I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f L i m a x maximus t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.8663 S t a n d a r d E r r o r = 0.2596 F - P r o b a b i l i t y = .0000 V a r i a b l e E x p o n e n t S c o t o p e r i o d L o g L i g h t C h a n ges L i g h t ^ C h a n g e s L i g h t ^ C h a n g e s L i g h t S u r f a c e T e m p e r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e T e m p e r a t u r e G r a d i e n t C o n s t a n t C o e f f i c i e n t 0.18976902 -0.28201868 0.14678727 - 0 . 9 6 9 8 5 2 5 1 E - 0 1 0.28911372E-01 16.297525 -86.453629 135.92987 - 0 . 3 5 5 3 7 5 0 6 E - 0 1 -1.6195200 -1.8447646 S t a n d a r d E r r o r 0. 7 5 9 3 E - 0 1 0. 9785E-02 0.5192E-01. 0.3187E-01 0.1050E-01 2.952 17. 8 8 33.20 0.1678E-01 0.8076 0.2 466 F - P r o b a b i l i t y 0.0125 . 0.0000 0.0035 0.0018 0.0043 0.0000 0.0000 0.0001 0.0327 0.0425 . 0.0 000 T a b l e X L I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o n s u b f u s c u s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.8923 S t a n d a r d E r r o r F - P r o b a b i l i t y = • 0. 2054 .0000 V a r i a b l e m - 2 L o g T i m e ^ L o g Time S c o t o p e r i o d L o g L i g h t 2 Changes L i g h t ^ C h a n ges L i g h t ^ C h a n g e s L i g h t . S u r f a c e T e m p e r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e ^ T e m p e r a t u r e G r a d i e n t ^ T e m p e r a t u r e G r a d i e n t E v a p o r a t i o n L o g W i n d 2 B a r o m e t r i c C h a n g e s ^ . B a r o m e t r i c Changes C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-- P r o b a b i l i t y 1. 2565244 0. 3703 0. .0008 -0.50855316 0. 1600 0. .0016 0.35968723E-03 0. 1402E- 03 0. ,0096 -0.17297745 0. 1132E- 01 0. ,0000 , -0.50356308 0. 119 0 0. ,0000 0. 5935777.6 0. 7112E- 01 0. , 0000 - 0 . 2 8 2 0 8 3 9 1 0. 6586E- 01 0. . 0000 10.619388 3 . .042 0. ,0007 -78 . 021230 18 . 06 0. ,0000 138.37609 34 . 07 0 . . 0001 - 1 3 . 4 2 2 2 6 1 6 . 485 0. .0366 -264.16204 60 . 26 0. ,0000 0.12830791 0. 5641E- 01 0. ,0188 - 0 . 6 9 1 8 5 5 7 9 E - 0 1 0. 2668E- 01 •o. ,0091 . -0.7 2084221 0. 1537 0. , 0000 0.87468457 0 . 1843 0. ,0000 -1.6957265 0 . 3112 0 . ,0000 T a b l e X L I I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o n h o r t e n s i s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r • 0.1915 S t a n d a r d E r r o r = 0.1579 F - P r o b a b i l i t y = .0000 V a r i a b l e C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y L o g T i m e 2 -7.4468244 2.567 0. 0 0 41 L o g T i m e ^ 5.8117900 2. 059 0. 0051 L o g Time -0.94234295 0.3658 0. 0101 L o g S c o t o p e r i o d -0.66141297 0.1398 0. 0000 L i g h t . - 0 . 1 3 4 4 9 2 0 0 E -03 0. 4365E-03 0. 0024 Changes L i g h t 2 0.15930439 0.6116E-01 0. 0091 . S u r f a c e T e m p e r a t u r e ^ -8.8313762 3.894 0. 0 2 2 8 S u r f a c e T e m p e r a t u r e 30.041326 11.48 0. 0091 S h e l t e r T e m p e r a t u r e -1.5160107 0.6362 0. 017 0 T e m p e r a t u r e G r a d i e n t -2.1552009 0.7069 0 . 0027 T e m p e r a t u r e Changes. - 1 . 8 2 0 3 9 9 1 0.8105 0. 0239. V.P.D. -0.90381804 0.2867 0. 0019 Moon P h a s e - 0 . 1 1 6 2 8 9 2 3 E - 02 0.3254E-03 0. 0005 C o n s t a n t 3. 4676556 1. 004 0. 000 8 T a b l e X L I V . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e ' L o g a r i t h m o f A c t i v i t y o f A r i o n c i r c u m s c r i p t u s t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . r = 0.3788 S t a n d a r d E r r o r = 0 . 2 0 2 6 F - P r o b a b i l i t y =' . 0000 V a r i a b l e L o g T i m e 2 L o g Time P h a s e L o g L i g h t S u r f a c e T e m p e r a t u r e ^ S u r f a c e T e m p e r a t u r e ^ T e m p e r a t u r e G r a d i e n t ^ T e m p e r a t u r e G r a d i e n t E x p o n e n t Wind B a r o m e t r i c C h a n g e s 2 B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c C h a n g e s 4 B a r o m e t r i c C h a nges L o g Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F- P r o b a b i l i t y -4. 2521369. 1. 3 3 6 0. 0018 1.9638523 0.6377 0. 0023 0.15650266 0.2315E-01 . 0. 0000 - 0 . 74722474E-01 0.1248E-01 0. 0000 -4.3509684 0.9523 0. 0000 29.748819 10.69 0. 0057 . -35.811042 7.803 0. 0000 -151.74855 . 63. 17 0. 0161 -1.8314192 0. 5557 0. 0012 0.52529141 0.1005 0. 0000 0.69969964 0.2234 0. 0020 -0.61790868 0.1652 0. 0003 -0.67376429, 0.2465 0. 0064 -0.42403767 0.7071E-01 0. 0000. 2.7343314 0.9097 0. 0032 I I T a b l e XLV. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f D e r o c e r a s c a r u a n a e t o C o n c u r r e n t E n v i r o n m e n t a l F a c t o r s . S t a n d a r d E r r o r = 0.2113 F - P r o b a b i l i t y = .0000 r = 0.8385 V a r i a b l e . 2 L o g T i m e ^ L o g Time L o g S c o t o p e r i o d P h a s e L o g L i g h t 2 Changes L i g h t ^ C h a n ges L i g h t S u r f a c e T e m p e r a t u r e 2 S u r f a c e T e m p e r a t u r e ^ T e m p e r a t u r e G r a d i e n t ^ T e m p e r a t u r e G r a d i e n t • T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e C h anges B a r o m e t r i c P r e s s u r e B a r o m e t r i c C h a n g e s ^ C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-- P r o b a b i l i t y 3.2760941 0 . 420 8 0. . 0000 -1.3035560 0. 1778 0 . ,0000 8.3877580 1. 833 0. .0000 0 . 62642734 0. 1389 0. .0000 -0 . 94802934E-01 0. 1316E- 01 0 . ,0000 -0 . 49011242 0 . 9277 E - 01 0. .0000 0.16728119 0. 5881 E -.01 0. ,0025 6 . 0236553 1. 511 0. ,0001 -25 .498762 4 . 255 0. ,0000 36 .027217 7 . 460 0. ,0000 -632.89694 71 . 30 0 . .0000 -5.9262722 1. 324 0. .0000 592 .25896 284 .6 0 , .0242 -0.75672042E--02 o-. 3633E- 02 0. .0315 -0 .20330046 0 . 7720 E - 01 0. ,0053 -23.415806 6 . 8 59 0. .0007 T a b l e X L V I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f D e r o c e r a s r e t i c u l a t u m t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r 2 = 0.3096 S t a n d a r d E r r o r = 0.1709 F - P r o b a b i l i t y • = .0000 V a r i a b l e L o g T i m e 2 L o g T i m e ^ . L o g Time 2 C h a n g e s L i g h t ^ C h a n g e s L i g h t 2 L a g S u r f a c e T e m p e r a t u r e , L a g T e m p e r a t u r e G r a d i e n t ' L a g T e m p e r a t u r e G r a d i e n t ' T e m p e r a t u r e C h a n g e s 2 T e m p e r a t u r e C hanges L a g L o g Wind L a g B a r o m e t r i c P r e s s u r e B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c C h a nges C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y -20.682752 2 . 312 0. 0000 19.852420 1.853 0. 0000 -4 . 2548194 0.3241 0. 0000 -0.36929381E -01 0.1884E-01 0. 0375 0.14646248E- 01 0.6790E-02 0. 0213 -2.8585394 0.9317 0. 0014 -25.972240 3. 583 0. 0000 -252.00793 44.00 0. 0000 -1.2237198 • 0.6218 0. 0404 -28.901431 11.44 0. 0069 -0.10497973 0.1984E-01 0. 0000 -0 . 45964374E' -02. 0.2170E-02 0. 0249 -0.21930489 0. 1097. 0. 0325 0.23575800 0.1264 0. 0457 10.547665 2.327 0. 0000 T a b l e X L V I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f A r i o n a t e r t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.8787 S t a n d a r d E r r o r = 0.1318 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g Time,, L o g T i m e ^ L o g Time * L o g S c o t o p e r i o d P h a s e L a g L o g L i g h t ^ C h a n g e s L i g h t ^ C h a n g e s L i g h t L a g S u r f a c e T e m p e r a t u r e 2 L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e Lag. T e m p e r a t u r e . G r a d i e n t L a g T e m p e r a t u r e G r a d i e n t L a g T e m p e r a t u r e . G r a d i e n t T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e Changes L a g L o g Wind L a g B a r o m e t r i c P r e s s u r e B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c Changes C o n s t a n t C o e f f i c i e n t • S t a n d a r d E r r o r F-- P r o b a b i l i t y - 15.134740 2. 318 0. ,0000 14.755908 1. 936 0. 0000 -3.1775729 0. 3574 0. 0000 3.808643 0 1. 214 . 0. 0020 0.27326520 0. 9749E- 01 0. , 0054 -0.16463007E -01 0. 7 902E-02 0. ,0243 -0.65527648E -01 •0. 1 4 8 2 E - 01 0. , 0000 0. 234.49479E- 01 0. 5317E- 02 0. , 0000 19.916451 1. 930 0. , 0000 -120.06489 11 . 13 0. ,0000 186.71716 2-1 . 00 0. , 0000 -3.7459377 0. 6083 0. .0000 -25.976393 7. 222 0. .0002 1123.7707 546. 5 0. ,0257 -1.3045535 0. 4911 0. ,0057 -5611.1494 1489. 0. .0001 -0.29591193E -01 0. 1611E- 01 0. , 0457 -0.58856780E -02 0. 17 9 9E- 02 0. , 0007 - 0 . 2 6 6 6 8 9 8 1 0. 8775E- 01 0. , 0014 0.28279389 0. 9936E- 01 0. ,0025 -3.1750267 4. 008 0. .4873 T a b l e X L V I I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f C e p a e a n e m o r a l i s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.8096 S t a n d a r d E r r o r = 0.1855 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g Time2 L o g T i m e ^ L o g Time E x p o n e n t S c o t o p e r i o d P h a s e L a g L o g L i g h t L a g S u r f a c e T e m p e r a t u r e 2 L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t L a g T e m p e r a t u r e G r a d i e n t L a g E v a p o r a t i o n ' L a g B a r o m e t r i c P r e s s u r e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r . F - P r o b a b i l i t y -20.617440 3.192 0. 0000 18.260232 2.664 0. 0000 -3.5558614 0.4894 0. 0000 -3.5596603 1.366 0. 0094 -0.62152075 0.2826 0. 02 71 - 0 . 6 9 8 5 3 0 9 1 E - 0 1 0.1061E- 01 0. 0 00 0 16 . 956886 2.576 0. 0000 -106.15597 16.48 0. 0000 191.80283 30. 77 0. 0000 -2.8177835 0.9867 0. 0 034 -1411.2466 488.4 0. 0030 -0.15600431 0.5042E- 01 0. 0011 0.70000773E-02 .0". 2383E- 02 0. 0028 10.316985 5 .356 0. 058 4 T a b l e X L I X . R e g r e s s i o n A n a l y s i s R e l a t i n g t o t h e . A c t i v i t y o f A r i o l i m a x  c o l u m b i a n u s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.8382 S t a n d a r d E r r o r = 0.1266 F - P r o b a b i l i t y = .0000 V a r i a b l e C o e f f i c i e n t S t a n d a r d E r r o r F- P r o b a b i l i t y L o g T i m e 2 -14.256047 1.8 2-3 0. 0000 Log. Time^. 13.056412 1.482 0. 0000 L o g Time . - 2 . 5 6 4 3 2 9 1 0.2644 0. 0000 L a g L i g h t - 0.10276560E -03 0.2755E- 04 0. 0001 Changes L i g h t - 0.14419817 0.2605E- 01 0. 0000 L a g S u r f a c e Temperature,, 5.4764504 0.6245 0. 0 0 0 0 L a g S u r f a c e T e m p e r a t u r e -12.863773 1.778 0. 0000 L a g T e m p e r a t u r e G r a d i e n t ^ 2.0631953 0.5932 0. 0003 L a g T e m p e r a t u r e G r a d i e n t -157.16625 3 8. 11 0. 0000 T e m p e r a t u r e Changes2 -17.344289 8. 315 0. 0224 L a g L o g Wind -0.31397896E -01 0.1492E- 01 0. 0230 B a r o m e t r i c C h a nges -0.63542257E -01 0.2185E- 01 0. 0021 Moon P h a s e 0.92080827E- 03 0.2239E- 03 0. 00 01 C o n s t a n t 3. 6996651 0.6197 0. 0000 ro cn T a b l e L. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f L i m a x maximus t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.72 8 3 S t a n d a r d E r r o r = 0.2399 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g T i m e 2 L o g Time' 4 L o g Time P h a s e L a g L o g L i g h t C h a n g e s L i g h t . L a g S u r f a c e T e m p e r a t u r e , L a g S u r f a c e T e m p e r a t u r e ! •Lag S u r f a c e T e m p e r a t u r e " C o n s t a n t C o e f f i c i e n t -21.991228. -20.551495 -4 . 3616896 - 0 . 6 8 4 1 4 8 8 3 E - 0 1 - 0 . 6 2 4 4 4 2 0 1 E - 0 1 0.10768269 17.106050 -73.368373 119.54680 5.8746265 S t a n d a r d E r r o r F - P r d b a b i l i t y 4.265 3.548 0.6510 0 . 1 5 5 6 E - 0 1 0.1337E-01 0.4942E-01 3.161 . . 19.04 34. 91 1.429 0.0000 0..0.000 0.0000 0.0000 0.0000 0.0291 0.0000 0.0001 0.0006 0.0001 T a b l e L I . R e g r e s s i o n A n a l y s i s R e l a t i n g , t h e A c t i v i t y o f A r i o n s u b f u s c u s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r =. 0.7474 S t a n d a r d E r r o r = 0.2 064 F - P r o b a b i l i t y . = .0000 V a r i a b l e L o g Time.2 L o g T i m e ^ L o g Time L a g L o g L i g h t ^ C h a n g e s L i g h t ^ C h a n g e s - L i g h t 2 L a g S u r f a c e T e m p e r a t u r e ^ L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t L a g L o g . W i n d C o n s t a n t C o e f f i c i e n t -13.940324 13.955902 - 3 . 2 2 1 8 5 1 4 -0.53164508E-01 0.39244252 -0.26552898 -5.1580516 -18.813780 -350.27188 - 0 . 5 9 7 5 6 7 5 9 E - 0 1 4.0846556 S t a n d a r d . E r r o r 3. 880 3. 215 0.5873 0.1214E-01 0. 6759E-01 0 . 4314E-01 1. 212 4.659 56.15 0. 2543E-01 1.264 F - P r o b a b i l i t y 0.0005 0.0000 0.0000 0.0000 0.0000 0.0 00 0 0.00 0 0 0.0001 0.0000 0.0143 0.0016 ro cn cn T a b l e L I I . R e g r e s s i o n A n a l y s i s Relating A c t i v i t y o f A r i o n h o r t e n s i s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r 2 •• 0. 2263 ' S t a n d a r d E r r o r = 0.0486 F - P r o b a b i l i t y = .0000 V a r i a b l e C o e f f i c i e n t S t a n d a r d E r r o r F - P r o b a b i l i t y L o g Time2 L o g T i m e ^ L o g T i m e " P h a s e L a g S u r f a c e Temperature,, L a g S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t . B a r o m e t r i c C h a n g e s — Moon P h a s e C o n s t a n t -2.3001892 1.8966913 -0.33690157 0.12037067E-01 -2.0517707 4.8483267 -0.43867454 -96.287190 -981.92460 .0.34481720E-01 -0.38210241E-03 0. 95396851 0.7183 0.5 7 34 0.9916E-01 0. 3003E-02 '0. 4108 - -' 1.183 0.1499 18. 01 182. 0 0.1661E-01 0.9994E-04 0.2513 0.0017 0.0012 0.0009 0.0001 0.0000 0.0001 0.0038 0.0000 0.0000 0.0364 0.0002 0.0003 T a b l e L I I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f A r i o n c i r c u m s c r i p t u s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.5281 S t a n d a r d E r r o r = 0.0701 F - P r o b a b i l i t y = . 0000 '. V a r i a b l e L o g Time2 L o g T i m e ^ L o g Time E x p o n e n t S c o t o p e r i o d P h a s e L a g L o g L i g h t L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t L a g E x p o n e n t R.H. B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c C h a nges L o g Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y -4.7883486 1.8 87 0. 0113 3.9983835 1. 565 0. 0108 -0.74405128 0.2842 0. 0091 3.8862757 0.8256 0. 0000 0.89999050 0.1754 0. 0000 . - 0 . 1 7 1 3 2 6 1 7 E - 0 1 . 0.6165E-02 •0. 0056 -4.7736060 0.5473 0. 0000 21.188377 4. 3 97. 0. 0000 -1.0421552 0.3190 0. 0014 -3.2762028 0.5135 0. 0000 -127.89443 37.30 0. 0008 -2036.0642 305.0 0. 0000 0.29507537 0.4118E-01 0. 0000 0.10613085 0 . 3482E-01 0. 0026 -0. 1213223.7 0.5517E-01 0. 0265 -0.20901138 0. 2479E-01 0. 0000 -12.358072 2.914 0. 00 01 T a b l e L I V . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e A c t i v i t y o f D e r o c e r a s c a r u a n a e t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . S t a n d a r d E r r o r F - P r o b a b i l i t y = • 0.138.7 .0000 0.7637 V a r i a b l e L o g Time2 L o g T i m e 4 L o g T i m e " L o g S c o t o p e r i o d P h a s e • . • ' 2 Changes L i g h t ^ C h a n ges L i g h t L a g S u r f a c e T e m p e r a t u r e 2 L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C h a n g e s | T e m p e r a t u r e Changes L a g L o g W i n d L a g B a r o m e t r i c P r e s s u r e Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r . F-P r o b a b i l i t y -21.183070 2 . 3 8 0 0 . 0000 20.087642 1.947 0. 0000 -4.2815660 0.3499 0. 0000 6 .3784449 1.509 0 . 0001 0. 47067384 0.1154 0. 0001 -0.21467816 0.6091E-01 . 0. 0004 0.12278388 . 0.3778E-01 0. 0009 9.3725472 2.325 0 . 0001. -50.405969 .13.47- 0. 0002 57.608698 25.32 0. 0171 -4.7754673 0.7793 .0. 0000 1093.5314 515.3 0 . 0258 - 8 3 . 9 6 9 1 5 1 2-2.4 3 0 . 0002 9722.5577 3411.- 0. 0032 -0 . 42067058E -01 0..1927E-01 0. 0224 -0.8S140030E -02 0.2685E-02 0 . 0012 0 . 62949268E-03 0 . 28 3 3E-03 0 . 0256 -7.2334917 5.0.79 0. 1719 T a b l e LV. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f D e r o c e r a s r e t i c u l a t u m . t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = '0. 8657 S t a n d a r d E r r o r = 0.2177 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g T i r r ^ L o g T i m e ^ L o g Time L o g S c o t o p e r i o d P h a s e C h a n g e s L i g h t L a g T e m p e r a t u r e G r a d i e n t L a g T e m p e r a t u r e G r a d i e n t L a g T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C hanges L a g L o g Wind . ^ B a r o m e t r i c Change's^ B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c Changes C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y - 13.034473 3. I l l 0. 0001 15.103617 2.530 0. 0000 - 3 . 6569324. 0 .4525 0. 0000 -0.52567176E-02 0. 1.526E-02 0. 0008 -0.55811965 0.1683 0. 0012 -0.17152464 0.5131E-01 0. 0003 3.7743068 0.7169 0. 0000 -36.27 88 61 4.689 0. 0 0 0 0 -344.08124 7 0.07 0. 0000 -4.5379136 0.8957 0. 0000 -0.10696892 0.2661E-01 0. 0000 -0.27447822 0.1373 0. 0252 -0.20015750 0.6310E-01 0. 0006 0.32278093 0.1540 0. 0191 8.9273789 2.603 0. 0009 T a b l e L V I . R e g r e s s i o n . A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f - A c t i v i t y o f A r i o n a t e r t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.8916 S t a n d a r d E r r o r = 0.1870 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g T i m e 2 L o g T i m e ^ L o g Time L a g L i g h t C h a n ges L i g h t ^ C h a n g e s L i g h t ^ C h a n g e s L i g h t L a g S u r f a c e Temperature,, L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e . L a g T e m p e r a t u r e . G r a d i e n t . , L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e Changes L o g Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F- P r o b a b i l i t y -5.6695274 2.667 0. 0324 8.1104900 2.164 0. 0003 -2.1662705 0.3857 . 0. 0000 -0.22484086E -03 0.4678E-04 0. 0 0 0 0 -0.24685843 0.5822E-01 0. 0000 -0.41985308E -01 0 . 2410E-01 0. 0448 0.26650341E- 01 0.7744E-02 0. 0002 20.020001 2. 6 0.3 0. 0000 -106.80166 15.53 0. 0000 131.59684 . 2 9.41 0. 0000 -4.3788053 0.8 2 52 0. 0.00 0 - 1 9 . 9 4 2 7 5 1 10.71 0. 0335 1561.7434 773.5 0. 0 214 -1.6918086 0.8012 0. 0155 -11474 . 7.23 2092. 0. 0000 -0.22487466E -01 0.9446E-02 0. 0171 - 1 . 1 6 7 0 0 6 1 0.9397 0. 1616 T a b l e L V I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f C e p a e a n e m o r a l i s t o E n v i r o n m e n t a l F a c t o r s w i t h Lag-Weather.. r 2 = 0.8592 S t a n d a r d E r r o r =• 0.2418 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g Time2 L o g T i m e ^ L o g Time E x p o n e n t S c o t o p e r i o d P h a s e L a g L o g L i g h t ^ C h a n ges L i g h t L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e s -L a g S u r f a c e T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t , L a g T e m p e r a t u r e G r a d i e n t ! L a g T e m p e r a t u r e G r a d i e n t " T e m p e r a t u r e Changes2 L a g L o g W i n d 2 B a r o m e t r i c Changes C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-• P r o b a b i l i t y -25.413799 4.199 0. 0000 22.8 94487 3.506 0. 0000 -4 . 4744809 0.6445 0. 0000- • -4.4724227 1.793 0. 0125 -0.84287945 0.3712 0. 0226 . -0.34470572E -01 0.1455E-01 0. 0106 0.10615900E- 01 0.3891E-02 0. 0034 26. 1406.94 . 4.748 0. 0000 -147.58121 28 . 75 0. 00 00 253.30792 52.45 0. 00 0 0 3.3466911 1.499 0. 015 6 -37.694999 8.779 0. 0000 -.256 . 04199 112.5 0. 0139 -50.257329 16.87. 0. 0015 -0.. 55472213E -01, 0.3017E-01 0. 04 6 0 -0.14713411 0.6759E-01 0. 0188 20.234517 6.295 0. 0017 T a b l e L V I I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o l i m a x c o l u m b i a n u s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.8966 S t a n d a r d E r r o r = 0.17.17 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g Time., L o g T i m e ^ L o g Time L o g S c o t o p e r i o d P h a s e L a g L i g h t C h a n g e s L i g h t 2 L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t 2 L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e Changes L a g E v a p o r a t i o n ^ B a r o m e t r i c Changes.^ B a r o m e t r i c Changes Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F-- P r o b a b i l i t y -6.8048588 2. 486 0. .0065 8.1136283 2. 024 . 0. ,0001 -1.8710549 . 0. 3628 o. .0000 -3.7939606 1. 482 0. ,0106 • -0.31945154 0. 1194 . 0. 00 7 7 -0.13737104E-03 0. 4608E- 04 . . 0. ,0010 -0.28510470 0. 4061E- 01 0. 0000 23.155767 5. 096 0. 0000 -60.537102 14 . 42 0. , 0000 5.0318547 1. 093 0. , 0000 -19.510820 6. 968 0. . 0017 -281.13839 60 . 99 0. , 0000 -3.7925767 0. 9 510 0. .0000 839.62989 213. 3 0. ,000 0 -0.11087283 0. 5243E- 01 0. ,0131 -.0. 22022846 . 0. 5017E- 01 0. ,0000 0.10706075 . 0. 5327E- 01 0. , 0229 0.84374129E-03 0. 2996E- 03 0. ,0052 12.949672 5. 13 6 0. ,0123 T a b l e L I X . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f L i m a x maximus t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.7854. S t a n d a r d E r r o r = 0.3284 F - P r o b a b i l i t y = .00 00 V a r i a b l e L o g Time2 L o g T i m e ^ L o g Time E x p o n e n t S c o t o p e r i o d P h a s e L a g L o g L i g h t L a g S u r f a c e T e m p e r a t u r e . L a g S u r f a c e T e m p e r a t u r e ! L a g S u r f a c e T e m p e r a t u r e " C o n s t a n t C o e f f i c i e n t - 2 9 . 691311 28.250302 - 6 . 0 4 0 6 2 9 1 - 3 . 4 6 3 7 0 4 7 - 0 . 8 4 8 2 8 2 6 0 - 0 . 1 0 7 6 7 4 0 8 15.818082 - 6 6 . 1 5 1 5 2 9 93.363893 1 9 . 2 2 5 2 4 5 S t a n d a r d E r r o r 5.600 4.6.6 9 0.8562 1.667 0.3445 0.1826E-01 4.333 26.51 48. 56 6.168 F - P r o b a b i l i t y 0.0000 0.0000 0.0000 0. 0364 0.0138 0. 00 0,0 0.0002 0. 0092 0.0425 0.0023 T a b l e LX. R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o n s u b f u s c u s t o E n v i r o n m e n t a l F a c t o r s . w i t h L a g - W e a t h e r . r 2 = 0. 8566. S t a n d a r d E r r o r = 0.2379 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g Time2 L o g T i m e ^ L o g . T i m e S c o t o p e r i o d L a g L o g L i g h t 2 C h a n g e s L i g h t ^ C h a n g e s L i g h t ^ C h a n ges L i g h t 2 L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e . ^ L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e Changes L a g E v a p o r a t i o n L a g L o g Wind ^ B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c Changes C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r . F-P r o b a b i l i t y -24.359058 4.755 0. 0000 23.152283 3.926 0. 0000 -5.0268618 0.7 27 6 0. 0000 0.78978582E- 03 . 0.1580E-03 0. 0000 -0.59147881E -01 0. 1539E-01 0. 0001 -0.29094510 0.1233 0. 0116 0.64796947 0.790GE-01 0. 0000 -0.38312082 0..7017E-01 • 0. 00 0 0 -20.251756 6.339 0. 0009 37.856945 20.00 0. 0411 -64.329565 16.32 . 0. 0001 -342.89 48 8 82..84 0. 00 0 0 2694.7328 .1268. 0. 022 3. - 3 . 3 3 2 4 2 3 1 0.9897 0. 0005 . 0. 160123.83 0.7525E-01 0. 0192 -0.64408837E -01 0.3094E-01 . 0. 0262 -0.8 0140790 .0.1766 0. 0000 0. 92096175 0.2104 0. 0000 5.9419602 1.562 0. 0004 T a b l e L X I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o n h o r t e n s i s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.2269 S t a n d a r d E r r o r : F - P r o b a b i l i t y = 0.15 3 9 .0000 V a r i a b l e L o g T i i r ^ L o g T i m e ^ L o g Time. P h a s e L a g S u r f a c e T e m p e r a t u r e 2 L a g S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t " L a g T e m p e r a t u r e G r a d i e n t L a g V.P.D. Moon P h a s e C o n s t a n t C o e f f i c i e n t - 6.2858360 5 .1035217 -0.89189016 0'. 46504375E-01 -6 . 8832106 17.604682 -1.4895295 -297.32942 - 3 0 9 2 . 8 0 0 1 -0.57815296 -0.12138892E-02 1.2358532 S t a n d a r d E r r o r 2.300 1.836 0.3175 0. 1041E-01 1. 319 3. 927 0.4759 57.19 5 7 6.4 0.2812 0 . 3163E-03 0.8064 F - P r o b a b i l i t y 0.0066 0.0057 0.0053 0.0000 0.0000 0.0000 0.0021 0.0000 0.0000 0.0382 0.0002 0.1240 T a b l e L X I I R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f A r i o n c i r c u m s c r i p t u s t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . r = 0.5533 S t a n d a r d E r r o r = 0.1735 F - P r o b a b i l i t y = .0000 V a r i a b l e L o g T i m e 2 L o g T i m e ^ L o g Time E x p o n e n t S c o t o p e r i o d P h a s e L a g L o g L i g h t ^ C h a n g e s L i g h t ^ C h a n g e s L i g h t L a g S u r f a c e T e m p e r a t u r e 2 L a g S u r f a c e T e m p e r a t u r e S h e l t e r T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t . L a g T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t L a g E x p o n e n t R.H. B a r o m e t r i c Changes2 B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c C h a n g e s ^ B a r o m e t r i c Changes L o g Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r . F-• P r o b a b i l i t y - 1 0 . 5400.84 . 4.744 0. 0256 8.7228429 3 . 905 0. 0239 -1.6365146 0.7088 0. 0197 9.0519599 2. 113 0. 0000 2.1109836 0.4486 0. 0000 - 0 . 4 7.81.0295E -01 0.1537E-01 0. 0021 -0.42868871E -01 0. 2043E-01 .0. 0339 0.15257940E- 01 0.7160E-02 0. 0312 -16.332876 2.00 3 0. 0000 27.861521 . 5.791 0. 0000 -2.4401507 0.7938 0. 0025 -7.2468624 . 1.345 0. 0000 -436.62494 98.55 0. 0000 -5767.2428 794.2 0. 0000 0.70416759 0.1030 0. 0000 0.33561868 0.8807E-01 0. 0002 0. 557490.44 0.1954 0. 0045 -0.40710239 0.1485 0. 0062 -0 . 551.63016 0.2229 0. 0129 -0.50023610 0.6158E-01 0. 0000 -30.215009 7.467 0. 0001 T a b l e L X I I I . R e g r e s s i o n A n a l y s i s R e l a t i n g t h e L o g a r i t h m o f A c t i v i t y o f D e r o c e r a s c a r u a n a e t o E n v i r o n m e n t a l F a c t o r s w i t h L a g - W e a t h e r . S t a n d a r d E r r o r =.0.2169 F - P r o b a b i l i t y = .0000 0..8321 V a r i a b l e L o g T i m e ^ L o g T i m e ^ L o g Time L o g S c o t o p e r i o d P h a s e 2 C h a n g e s L i g h t ^ C h a n g e s L i g h t L a g , S u r f a c e T e m p e r a t u r e 2 L a g S u r f a c e T e m p e r a t u r e ^ L a g S u r f a c e T e m p e r a t u r e L a g T e m p e r a t u r e G r a d i e n t ^ L a g . T e m p e r a t u r e G r a d i e n t ^ L a g T e m p e r a t u r e G r a d i e n t T e m p e r a t u r e C h a n g e s 2 T e m p e r a t u r e C h a n g e s ^ T e m p e r a t u r e Changes L a g L o g W i n d L a g B a r o m e t r i c P r e s s u r e Moon P h a s e C o n s t a n t C o e f f i c i e n t S t a n d a r d E r r o r F- P r o b a b i l i t y -25..944563 3.806 0. 0000 24.558125 3.047 0. 000 0 - 5 . 4 4 7 5 7 7 1 0.5542 0. 0000 4.8744083 2.310 0. 0294 0.34069476 0.1767 0. 0460 -0.45235562 0.9594E-01 0. 0000 0.22938557 0.5909E-01 0 . 0001 27.723660 5. 731 0. 0000 - 1 3 2 . 0 3 9 4 1 32.96 0. 0000 166.13522 57.75 0. 0024 -4.4363596 1. 797 0. 00 8 3 402.50519 180.0 0. 016 3 6009.1617 1094 . 0. 0 000 -3.4994309 0.9732 0. 0002 -124,35795 35.73 0. 0003 11223.079 5 4 0 1 . 0. 0244 -0.11389062 0.3043E-01 0. 0001 -0 ..88066192E-02 0. 4226E-02 0. 0254 0.12155187E-02 0.4329E-03 0. 0043 -2.5887673 7.849 0. 6952 269 THRESHOLE MODEL The threshold model developed for L. m a x i m u s i s given i n Figure 46. The circadian rhythm was represented by a 3rd-crder polynomial of time, modified by phase, scotoperiod, shelter temperature, and interactions cf these factors (Table X). As discussed previously, threshold eguations for l i g h t i n t e n s i t y , surface temperature, and evaporative rate were obtained from estimates of the outer a c t i v i t y l i m i t s associated with these factors from f i e l d data (Tables XII, XIV, and XXIII). Five days, June 8-9, July 13-14, August 5-6, September 16-17, and October 7-8, 1976, were selected to test the model's v a l i d i t y . The prediction of the b e s t - f i t t i n g regression model for t h i s species, the threshold model, and the actual a c t i v i t y observed f o r each hour on the selected days are i l l u s t r a t e d i n Figure 47. Regression of the actual observations on those predicted by the threshold model gave an r 2 value of 0.8306 (p=0. 0000001). A Kolmogorov-Smirnov goodness-of-fit t e s t (see Zar, 1974) did not find the predicted values to be s i g n i f i c a n t l y d i f f e r e n t frcm those actually observed at the 5% l e v e l (p>0.50). The way i n which the threshold eguations were obtained suggest that, i f the model i s u n r e a l i s t i c , i t s predicted values should have far exceeded those actually observed. This method appears then, to be a more r e a l i s t i c way of describing a c t i v i t y of animals frcm f i e l d data. Previously, i t was not possible to separate the e f f e c t of a single parameter 270 from a l a r g e number of e t h e r v a r i a b l e s a c t i n g i n c o n c e r t . D e s p i t e i t s v a l u e , i m p l e m e n t a t i o n o f t h i s method r e g u i r e s a c c u r a t e knowledge of d e n s i t y as w e l l as a l a r g e number o f o b s e r v a t i o n s over th e e n t i r e f i e l d s e a s o n . When t h e p r e d i c t i o n s from the v a r i o u s f a c t o r s i n v o l v e d i n the t h r e s h o l d model were examined s e p a r a t e l y , i t was d i s c o v e r e d t h a t t h e key f a c t o r p r e d i c t i n g the numbers a c t i v e was t h e c i r c a d i a n rhythm. The f a c t t h a t most p r e d i c t i o n s of a c t i v i t y were o b t a i n e d from the c i r c a d i a n rhythm i s n o t s u r p r i s i n g , s i n c e the c l o c k i s t h o u g h t t o be an a d a p t a t i o n t c a v o i d a c t i v i t y a t t h o s e t i m e s when l i m i t i n g weather might be e n c o u n t e r e d . The c u r v e s o b t a i n e d by t h e l e a s t s g u a r e s method t o r e p r e s e n t the c i r c a d i a n rhythm were somewhat u n r e a l i s t i c , however. I n s t e a d o f p r e d i c t i n g d e c r e a s i n g v a l u e s of a c t i v i t y a t extreme v a l u e s o f time ( e . g . , near 4:00 pm o r 10:00am), i n c r e a s i n g v a l u e s f o r a c t i v i t y began t o r e c u r . T h i s problem d i d not occur on summer days , however, s i n c e the weather t h r e s h o l d s o v errode t h e t r e n d . The s m a l l peaks i n a c t i v i t y p r e d i c t e d a t 8:00 am f o r September 16-17 and October 7-8 were a r t i f a c t s a r i s i n g from t h i s tendency. I n f u t u r e s t u d i e s , a b e t t e r c u r v e f i t t i n g t e c h n i q u e , f o r example w i t h H e i b u l l c u r v e s (Menon, 1S63), might e l i m i n a t e such a n o m a l i e s . The t h r e s h o l d model p r e d i c t i o n s g e n e r a l l y took th e same form as the a c t u a l l y o b s e r v a t i o n s ( F i g u r e 4 7 ) . August 5-6 was a near p e r f e c t f i t . The p r e d i c t e d v a l u e s d e p a r t e d most from the observed v a l u e s on September 16-17., S i n c e no o t h e r weather f a c t o r appeared t o be u n u s u a l l y s e v e r e t h a t n i g h t , I am unable t o a c c o u n t f o r t h e e x c e p t i o n a l l y low observed a c t i v i t y of the 271 slugs. The regression model illustrated was that obtained with the logarithmic transformation cf the dependent variable (Table ILI, r2=0.8663 for the entire season). This regression model, had a unrealistic form, although accurately predicting the times when activity began or ended. Its sguare form resulted from the lack of time polynomials, other regression models that included time polynomials had a more r e a l i s t i c shape. Nevertheless, the "sguare" regression model had the best r 2 for the species illustrated. Consequently, i f a choice between the threshold and the regression model was required for predictive purposes, the more re a l i s t i c threshold model would seem to be superior, given the present state of the art. 272 Figure 46. Flow Chart of the Threshold Model Developed to Predict A c t i v i t y of Limax, maximus in Response to Environmental Factors. N 273 / R E A D HOURLY , ^ W E A T H E R / ' D A T A , T I M E / C A L C U L A T E A C T I V I T Y FOR C I R C A D I A N R H Y T H M ( A ) C A L C U L A T E A C T I V I T Y FOR L I G H T I N T E N S I T Y ! B) A : T A B L E X. B : T A B L E XII. R E P E A T F O R E A C H HOUR OF T H E N IGHT C A L C U L A T E ACTIV ITY FOR S U R F A C E (C ) T E M P E R A T U R E C : T A B L E X IV . 274 gure 47. A c t i v i t y of Limax maximus over the 1976 Season, with Predictions frcm the Best Regression Model and Threshold Model. PACIFIC STANDARD TIME + I HOUR OBSERVED ACTIVITY REGRESSION MODEL THRESHOLD MODEL 276 SECTION 111-MIlMlMMkh OB IE NT ATION MM1M 9-1 LITERATURE Because slugs have no physiological mechanism for preventing water loss (Machin, 1975), shelter i s a key factor determining t h e i r d i s t r i b u t i o n and abundance. The i n t e n s i t y of the c o n t r o l l i n g e f f e c t s of weather and predators i s lar g e l y determined by the quantity and type of shelter available (Runham and Hunter, 1970). Because adequate food i s not often associated with suitable shelters, the animals must usually emerge and forage i n the surrcundinq area. Thus the environmental complexity relevant to slugs consists of a shelter and the surrcundinq foraqinq area. What are the advantaqes for sluqs to return to particular shelters? The most obvious i s that the molluscs are assured of finding refuge and thus the r i s k of desiccation i s reduced. Since time does not have to be al l o t e d to findinq new shelt e r , the animals can spend le s s time crawling and more time feeding, a r e s u l t confirmed by Newell (1965b, 1966) for D. reticulatum. and by Lewis (1967) for A. ater . Since slugs that home spend less time crawling on the surface after daybreak, they experience less r i s k from diurnal predators (Newell, 1966) as well as from desiccation. Homing behavior of molluscs has never been generally reviewed before, so the l i t e r a t u r e i s detailed here. U n t i l the "landmark" paper of Gelperin (1974) on the homing of I*, maximus , t h i s aspect of the behavior of t e r r e s t r i a l molluscs was known la r g e l y from anecdotal accounts dispersed 277 throughout the l i t e r a t u r e . As early as 1895 C. Ashford (in Edelstam and Palmer, 1953) observed that some i n d i v i d u a l s n a i l s returned d a i l y to the same place following excursions to feed. Frandsen (1901) observed that Lf. maximus showed a strong tendency to t r a v e l i n loops. He pointed out that among many unrelated animals, t r a v e l l i n g i n c i r c l e s or loops was associated with gaining f a m i l i a r i t y with the environment. Accounts of homing behavior for the slugs L ^ m a i i i u s and U f l a y i s , as well as for the s n a i l s fifc asgersa and £ A flglSiaiis were included i n the monographs by Taylor (1900-192 1) . I t was proposed that slugs returned home by following looped paths of a figure "8" pattern. Fischer (1939) stated that the t e r r e s t r i a l s n a i l Succinea putris could return home from a distance of 1-2 m. Other casual observations of homing behavior among slugs were included i n P i l s b r y (1948), Fischer (1950), and Fromming (1954), South (1965) confirmed the e a r l i e r observations of Taylor (1907) that L. flavus showed homing behavior. His studies on the dispersal of £. reticulatum suggested that t h i s slug inhabited a home range rather than a p a r t i c u l a r homesite. Similar dispersal experiments by Pinder (1969) indicated that slugs rapidly s e t t l e d down to a homesite or range. yPotts (1975) believed that H. aspersa inhabited a home range, i n contrast to the observations of precise homing by Taylor (1907-1914)., Newell (1965a, 1966) , using time-lapse photography, observed that f i v e D. reticulatum returned to the same crevices i n the s o i l over several days, and that the choice of holes was very precise. However, slugs also changed shelters p e r i o d i c a l l y . Newell interpreted such homing in the context of the looped-278 track hypothesis proposed by Taylor (1907-1914). He found that about half of the slugs were able to return heme after each night's a c t i v i t y even i n an unfamiliar environment (Newell, 1965b), and he expected that homing would be more accurate once the animals became accustomed to the habitat (Newell, 1965a). Lewis (1967) observed that fl,,. ater returned to i t s previous shelter more often than i f found new ones. He followed four individuals continuously throughout the night. Two of these returned home, but the other two did not. Those which returned home had followed a "U" shaped track with a d e f i n i t e i n f l e c t i o n point. Those that f a i l e d to home showed no such i n f l e c t i o n . There was no evidence of a figure "8" pattern (Lewis, 1969a). Lewis (1969b) proposed that i n A x ater finding shelter was controlled by a "homing a b i l i t y " combined with v i s u a l perception of small differences i n l i g h t and shade at night. Duval (1972) argued that the homing of slugs was mainly fortuitous. Since they t r a v e l i n c i r c u i t o u s patterns, they tend to end t h e i r nightly excursions near where they began and thus may rediscover the same shelter. He stated that slugs exposed to l i g h t made a straight l i n e to any available shelter, and that choice of daytime resting places depended on the nearest regions of shade available when dawn arrived., Bollc (1974) observed that when slugs were offered a choice between a clean container and an i d e n t i c a l one which they had formerly inhabited, 29/29 Dj. reticulatum chose the l a t t e r , indicating the possible presence cf a pheromone or other aeans of recognition such as mixtures of food contained i n their faeces. 279 Gelperin (1974) showed conclusively that most aspects of the betting behavior of L^ . maximus were adequately explained by an olfactory-homing hypothesis. Sluqs were kept in complete darkness durinq the dark phase of a photoperiod except for brief flashes of liqht associated with time-lapse photographic equipment. These flashes were probably faster than the sluqs were able to detect. Individuals travelled directly home without following slime t r a i l s from distances as great as 93 cm. Homing was not impaired by cutting the optic nerves, but i t disappeared entirely i f the olfactory nerves were bilaterally sectioned. Homing was also much better from downwind than from upwind. Gelperin (1974), however, did not speculate as to the source of the attractant. The snail Achat^na fulica also shows a precise homing ability (Southwick and Southwick, 1969), Croll and Chase (1977) found that this species chose the food which i t had previously been raised on when offered a choice in a *i» tube, a response that persisted for 120 days. They reviewed the literature concerned with learning of odors among molluscs and suqqested that the attraction exhibited by the snails miqht not have been solely a response to food, since they may have associated the smell wifh their former heme, Amonq marine prosobranch and pu Intonate Mollusca a relatively larqe amount of research has been accumulated with reqards to behavioral mechanisms involved i n returninq to shelter. The accuracy of hominq varies frcm limpets* precise returns to particular scars worn in the rock (Thorpe, 1963), to the less precise returns to particular areas exhibited by 280 s n a i l s , such as L i t t o r i n a (Newell, 1958a,b). Apparently analagous homing occurs among both prcsobranch and pulmcnate limpets, despite t h e i r divergent ancestory (Cook, 1969). Accurate homing i s also known for chitons (Crozier, 1921; Thorne, 1967,1968; Smith, 1975), i n the s l u g - l i k e pulmonate Onchidium (Qnchidella) floridanum Da11. (Arey and Crozier, 1918,1921), and i n Octopus sp. (Gelperin, 1974). Among sea hares, Afiljsia homes to p a r t i c u l a r positions (Strumwasser, 1971), and Bursatella congregates by following slime t r a i l s (Lowe and Turner, 1976). Thorpe (196 3) reviewed some of the e a r l i e r l i t e r a t u r e , p a r t i c u l a r l y that concerned with homing of limpets. Some of the more important papers published subsequently include Mculton (1962), Frank (1964), Galbraith (1965), Funke (1968), Jessee (1968), Millard (1968), M i l l e r (1968), A. Cook et al^. (1969), S.E. Cook (1969, 1971), Davis (1970), Breen (1971,1972), Seapy and Hoppe (1973), and Cook and Cook (1975). Four major hypotheses have been advanced as mechanisms to explain how marine molluscs home: (1) following external cues (e.g., polarized l i g h t , solar or lunar p o s i t i o n , coastal landmarks, sky brightness); (2) kinaesthetic memory (reverse displacement); (3) topographic memory; (4) cues deposited on the substrate (e.g., mucous t r a i l s ) . External cues and kinaesthetic memory are generally regarded as least l i k e l y . Topographic memory has some support (Jessee, 1968; Davis, 1970), but the most favoured explanation i s that the animals follow mucous t r a i l s , e i t h e r from the outgoing t r i p , or from e a r l i e r excursions (Cook et a l l * 1969; 281 Cock, 1969,1971; Cook and Cook, 1975; Smith, 1975).. I t i s l i k e l y that l o c a t i n g shelter by odor (either emanating from a pcint source or deposited on the substrate while moving), i s a common t a c t i c for nocturnal, shelter-dependent animals. For example, although birds are not generally thought to use ol f a c t o r y guidance to any extent, leache*s p e t r e l locates i t s burrow in the dark by f l y i n g upwind along an odor gradient emanating frcm i t s burrow (Grubb, 1974) . Odor i s also commonly used, either d i r e c t l y or as a "backup** system, for homing by many diurnal invertebrates, such as seme ants and bees (see examples i n Shorey, 1976). An advantage of such olfactory orientation i s that i t does not reguire a well developed memory or the a b i l i t y to integrate complex v i s u a l cues, as does landmark recognition. There i s a tendency i n most research to view orientation mechanisms as either-or a l t e r n a t i v e s , when in f a c t the organism functions as an integrated system. For example, bark beetles tend to orient v i s u a l l y tc v e r t i c a l objects upon encountering high concentrations of the i r aggregation pheromone (reviewed by Shorey, 1S76). Ants which follow t r a i l s lacking d i r e c t i o n a l p o l a r i t y , maintain correct o r i e n t a t i o n by using sun-ccmpass steering (Hclldobler, 1971). In most cases, several i n t e r a c t i n g sensory systems and strategies act conjunctively to determine the f i n a l behavior of the animal. Thus the fact that Gelperin (1974) found that olfactory orientation was adequate to account for most aspects of sluq homing does not mean that i t was also necessary. No tests were performed to determine i f they could home i n the absence of odors, i f there was s u f f i c i e n t l i g h t f or 282 tiiem to employ visual cues, for example. 283 METHODS AND RESULTS Phercmone Experiment Slugs reared i n growth chambers frequently had one place i n t h e i r rearing container where they habitually rested. Such resting places were e a s i l y distinguished by accumulations of faeces. Experiments i n both the laboratory and the f i e l d indicated that nearly 100% of the slugs* defecation took place within t h e i r shelters. Hollo (1974) previously found that D^  reticulatum was attracted to shelters in which they had previously stayed, but the r e s u l t s were confounded by the p o s s i b i l i t y that the slugs were responding tc food odors. Since slugs are believed to orient to shelters mainly through o l f a c t i o n (Gelperin, 1974), and pheromones frequently occur i n the faeces of other animals (Shorey, 1976), A., ater was tested to determine i f i t oriented to the odor of i t s faeces during homing. A 61 X 61 X 10 cm deep box was l i n e d with a clean p l a s t i c sheet, and the f l o o r was then covered with paper towels, moistened to provide a damp substrate. Sixteen consecutively numbered shelters were placed i n a c i r c l e around the perimeter of the box. These were constructed by cutting *0*-shaped holes i n the rims of clay flower pots, to serve as doors when the pots were inverted. The bottom of each pot was stuffed with wet Kimwipes to humidify i t . Carrots were placed in the centre of the arena and a single carrot s l i c e was also placed inside each shelter ensured that any response to faeces placed inside some shelters could not be attributed to hunger. Faeces were collected from a colony of 284 :&,f ater that had been fed carrots i n the laboratory f o r one week without having these containers cleaned. Slugs from t h i s colony were then used i n the t r i a l s that followed. About one teaspoonful of carrot-derived faeces was placed in every other shelter. A plate glass l i d sealed the box but also permitted observations. The box was kept sealed for about one hour to allow the suspected pheromone to diffuse from the shelters, a f t e r which f i v e slugs were placed i n the center of the arena. They were exposed to a bright incandescent l i g h t to induce a homing response, and the remaining 29 slugs from the colony were introduced immediately. The animals were observed for about half an hour, a f t e r which the light, was turned o f f and they were l e f t undisturbed. The following day the number of animals in each shelter was tabulated and a Mann-Whitney U tes t indicated that the r e s u l t s were s i g n i f i c a n t at the 0.001 l e v e l (Table LXIV). 285 T a b l e LXIV. R e l a t i v e Numbers o f firion a t e r Honing t o F l o w e r - P o t S h e l t e r s With and Without Faeces. N u l l h y p o t h e s i s : The presence of f a e c e s i n t h e s h e l t e r s has no i n f l u e n c e on the d i s t r i b u t i o n o f A.* a t e r . A l t e r n a t e h y p o t h e s i s : The presence of f a e c e s i n t h e s h e l t e r s a f f e c t s t h e d i s t r i b u t i o n of A.t- -ater. S h e l t e r S h e l t e r Number T o t a l C o n d i t i o n 1 2 3 4 5 6 7 8 With Faeces 2 5 1 3 3 5 4 3 26 and C a r r o t With C a r r o t 1 3 2 0 0 1 1 0 8 Only S i g n i f i c a n c e l e v e l = 0 . 0 5 U=65.5 (P<0.001) (Mann-Whitney O-Test) T h e r e f o r e , r e j e c t the n u l l h y p o t h e s i s . AH3.QU. a t q r a r e d i f f e r e n t i a l l y a t t r a c t e d t o s h e l t e r s c o n t a i n i n g t h e i r f a e c e s . Homing B e h a v i o r I n The F i e l d A f i e l d s t u d y o f homing b e h a v i o r was i n i t i a t e d i n June, 1976. A,, columbianus was chosen because they c o u l d be very p l a i n l y marked by the l i q u i d - n i t r o g e n b r a n d i n g t e c h n i q u e of R i c h t e r (1973,1976b). T h i r t y - t w o a d u l t s l u g s and e i g h t j u v e n i l e s were marked, and on June 17th 8 a d u l t s and 2 j u v e n i l e s were p l a c e d i n each of s h e l t e r s 1 and 10 i n cage I . I n cage I I I , 2 s l u g s were p l a c e d i n each o f t h e t e n s h e l t e r s ( F i g u r e 4). T h i s d e s i g n was i n t e n d e d t o r e v e a l any s i g n i f i c a n t v a r i a t i o n between 286 the i n i t i a l and the f i n a l d i s t r i b u t i o n s of the slugs, and to detect any differences in t h e i r movements among i n i t i a l l y inhabited and i n i t i a l l y vacant shelters. The o r i g i n a l d i s t r i b u t i o n of the slugs was recorded, and t h e i r i n d i v i d u a l positions were tabulated at 2 to 3-day int e r v a l s u n t i l July 7. From July 7th u n t i l august 11th, observations were made at 5 to 6-day i n t e r v a l s . Since the slugs had to be handled to i d e n t i f y them during the recording sessions, d a i l y observations might have disturbed them too much. Several manipulations were performed during the course of the study. On June 23rd, the l i d s of shelters 1 and 4 and the paper l i n e r s of shelters 10 and 7 were exchanged i n cage I. On July 2nd, the l i d s of shelters 3 and H and the paper l i n e r s of shelters 7 and 8 were also exchanged i n cage I. On July 15th, I J A jaximjas indiv i d u a l s were introduced into shelters 7,8,9, and 10 of cage I and shelters 1,2,3, and 4 of cage I I I to determine whether the two species interacted. On July 21st, a mole p a r t i a l l y f i l l e d shelter 10 i n cage III with s o i l , so the shelters i n the v i c i n i t y were then surrounded by spikes pushed into the ground to deter any further burrowing. The location cf the various i n d i v i d u a l s over time i s given i n Table LXV. To determine whether slugs change shelter more freguently when nearby shelters are inhabited, the number of moves by adult ariolimax were compared in cage I, where there were o r i g i n a l l y only two inhabited shelters, and i n cage III where a l l shelters were inhabited o r i g i n a l l y . The number of changes i n shelter was determined for each i n d i v i d u a l between June 17 and July 7. Only adults were used, and slug #1 was omitted from the analysis 287 because i t died prior to June 21st. A Mann-Whitney U test indicated that there was significantly more movement in cage III where a l l shelters were originally inhabited (P<0.0G1) (Table LXVI) . LEAF Z88 OMITTED IN PAGE NUMBERING. T a b l e LXV. H i s t o r y o f S h e l t e r O c c u p a n c y b y M a r k e d A r i p l i m a x c o l u m b i a n u s i n F i e l d Cages f r o m J u n e 17 u n t i l A u g u s t 1 1 , 1976. S e c t i o n s A-H show D i f f e r e n c e s i n B e h a v i o u r t h a t O c c u r r e d . A. I n d i v i d u a l s s h o w i n g t h e i n i t i a l d i s o r i e n t a t i o n s u f f e r e d b y some s l u g s when f i r s t i n t r o d u c e d t o t h e f i e l d c a g e s , ( s e e a l s o s l u g s 1 1 , and 2 3 ) . B. I n d i v i d u a l s e x h i b i t i n g l o n g - t e r m h o m i n g t o p a r t i c u l a r s h e l t e r s . C. I n d i v i d u a l s t h a t f r e q u e n t l y c h a n g e d s h e l t e r s . D. S l u g s t h a t moved f r o m one end o f c a g e 1 t o t h e o t h e r . E. I n d i v i d u a l s a l t e r n a t i n g b e t w e e n more t h a n one s h e l t e r . F. S l u g s t h a t moved f r o m s h e l t e r 10 t o s h e l t e r 7 a f t e r t h e p a p e r l i n e r s o f t h e s e s h e l t e r s were e x c h a n g e d on J u n e 2 3 , 1976. G. Homing b e h a v i o r o f j u v e n i l e A. c o l u m b i a n u s ( s e e a l s o s l u g s 9 and 1 9 ) . H. E x a m p l e s o f t y p i c a l h o m i n g b e h a v i o r by A. c o l u m b i a n u s f r o m J u n e 17 u n t i l A u g u s t 1 1 , 1976. ro co CO 01 TABLE LXV. (continued) SHELTER OCCUPANCY r-H CT\ rH rH CN m CN in CN CO CN CN tn r- CN rH in rH rH CN VO CN o n vo rH rH Behavior Slug # Cage # Weight (g) <D C 3 •"3 CD 3 D CD C 3 •D ci) C 1-3 CD C 3 h> CD D >1 rH 173 >i rH 3 >i rH 3 1-3 >1 rH 3 1-3 >1 rH 3 >1 rH 3 >1 rH 3 ID >i rH 3 1-3 C7> 3 < CT) 3 < Day: 0 2 4 6 7. 11 15 18 20 25 27 33 3 8 42 49 54 A 1 3 19. 25 8 0 X X X X X X X X X X X X X X 2 3 16. 43 3 0 0 10 8 8 8 8 8 10 8 8 9 9 8 8 3 1 21.01 1 0 1 1 2 1 1 3 1 8 8 8 0 0 0 3 4 1 14. 37 1 0 1 1 2 2 4 3 2 2 2 3 4 0 7 7 B 5 3 14.22 7 7 7 7 7 7 7 7 X X X X X X X X 6 3 23.10 2 2 2 2 2 2 2 2 2 2 4 - - - • OX X 7 3 12.40 2 2 2 2 2 4 2 2 2 2 2 2 p ? 7 7 8 1 21.35 10 10 10 10 10 10 10 10 10 10 9 9 9 10 7 9 3 1. 76 7 7 7 7 7 7 7 7 7 5 7 7 7 7 7 7 C 10 3 9.98 4 6 5 10 6 8 9 9 5 5 6 6 6 6 7 7 11 3 22.78 3 0 8 10 8 6 8 6 8 6 6 5 10 6 8 6 D 12 1 11.63 10 10 10 10 10 7 10 10 1 XI X X X X X X 13 1 13.17 1 1 10 1 1 1 1 1 1 4 .4 4 6 0 p 7 14 1 13. 59 1 1 1 10 10 10 10 10 10 10 10 9 9 9 9 7 E 15 1 11.87 10 10 10 9 9 9 10 9 9 9 9 10 9 9 9 10 16 1 16.53 10 10 10 10 10 10 7 7 10 10 7 10 10 7 7 • 10 17 1 18.16 1 0 1 1 . 4 4 4 4 4 1 1 4 4 4 4 4 18 1 26. 37 10 10 9 9 9 9 10 10 9 9 9 9 •9 9 7 7 X = Dead ~ = n°t found oo 0 = outside shelters ? = identification.uncertain gR TABLE LXV. ( c o n t i n u e d ) SHELTER OCCUPANCY rH CT. rH rH CN m CN LO CN 00 CN CN m r- CN rH m rH rH CN CD CN o ro rH rH B e h a v i o r S l u g # Cage '# " W e i g h t (g) <D C CD c CD c 3 l-J CD c 3 l-J CD c 3 t-j CD C 3 . ^ >1 rH 3 l-J rH 3 I'D > i rH 3 l-J >1 rH 3 >1 rH 3 •"J >1 rH ID >1 rH >i rH l-J tn 3 Cn < Day: 0 2 4 6 7 11 15 18 20 25 27 33 38 42 49 54 F 12 1 11.6 3 10 10 10 10 10 7 10 10 1 X I X X X X X X 16 1 16.53 10 10 10 10 10 10 7 7 10 10 7 10 10 7 7 10 19 1 1. 84 10 10 10 10 10 10 7 7 7 7 10 7 7 7 7 7 20 1 21. 75 10 10 10 10 10 7 10 10 10 7 10 1 1 8 7 7 21 1 27.58 10 10 9 9 9 10 7 0 9 7 7 8 9 0 7 7 G 22 3 3.20 10 10 9 8 8 10 8 9 8 2 2 5 5 2 7 7 23 3 1.37 6 - - 8 8 8 7 7 7 — — _ 7 7 7 7 24 3 2. 10 1 1 1 - 3 1 3 3 3 2 4 7 3 3 7 7 25 1 1.6 8 i 1 X X X X X X X X X X X X X X 26 1 1.78 I 1 2 2 2 1 1 2 .2 7 7 7 7 7 7 7 27 1 1.60 10 10 10 10 10 9 9 9 10 8 9 4 5 - 7 7 H 28 1 17. 11 I 1 1 . 1 1 1 4 1 1 2 2 1 1 . 1 2 2 29 3 27. 70 9 8 8 10 10 4 8 8 8 5 5 5 5 8 7 7 30 3 14. 90 9 9 9 10 10 10 5 6 0 6 8 5 9 7 7 7 31 3 .12.63 4 4 4 4 6 6 8 7 8 8 8 8 p 7 7 7 32 3 21.11 5 5 5 6 6 8 6 5 5 6 6 9 5 8 5 9 33 3 13.00 6 10 10 10 8 8 8 8 8 10 8 8 8 8 8 8 34 3 25.73 5 5 . 5 5 5 5 6 5 2 5 6 8 7 7 7 7 35 3 14.30 1 1 1 1 1 1 3 6 3 3 3 6 6 5 6 6 36 3 17.30 10 10 10 10 9 9 9 10 9 10 10 p 7 7 7 7 37 3 21. 39 8 8 8 9 9 10 8 9 8 8 8 9 9 9 2 9 38 1 15.68 1 1 1 1 2 2 2 1 2 3 4 3 4 2 7 7 39 1 19.58 1 1 1 1 1 - 1 1 1 2 7 5 2 2 2 2 2 40 1 14.19 10 10 10 10 10 10 6 6 6 5 10 6 5 5 7 7 ro oo 290 Table LXVI. Mann-Whitney U-test to Determine i f Accuracy of Homing Behavior by A r i o l i m a x columbianus was in f l u e n c e d by the D i s t r i b u t i o n of C o n s p e c i f i c s . H : A. columbianus' homing behavior i s not i n f l u e n c e d by ° the d i s t r i b u t i o n of other s l u g s . H 2: A. columbianus 1 homing behavior i s i n f l u e n c e d by the d i s t r i b u t i o n of other slugs. a = 0.05 Number of changes Rank of Changes i n s h e l t e r Cage 1 Cage 3 Cage 1 Cage 3 2 4 9.5 6.0 6 4 3.0 6.0 3 0 7.5 12.5 3 3 7.5 7.5 2 8 9.5 1.0 3 4 7.5 6. 0 2 4 9.5 6.0 2 0 9.5 12.5 2 2 9.5 9.5 0 2 12. 5 9.5 5 3 4.5 7.5 3 3 7.5 7.5 6 7 3.0 2.0 3 3 7.5 7.5 1 5 11.0 4.5 1 11. 0 N=16 N=15 Total=130 Total=105.5 P ( U 0 . 0 5 , 1 6 , 1 5 = 2 4 6 > < 0 - 0 0 1 Therefore r e j e c t H q . When other slugs are present, the accuracy of homing by A. columbianus i s s i g n i f i c a n t l y reduced. 291 Seasonal Homing Changes When the slugs and s n a i l s i n the f i e l d a c t i v i t y experiment were counted, each cage was c a r e f u l l y searched for any animals that had remained upon the s o i l surface instead of returning to t h e i r shelters. Such records indicated a remarkable seasonal trend. The average proportion of the mollusc population that had f a i l e d to home i s i l l u s t r a t e d i n figure 48, while Table LXVII gives the numbers of individuals for the species monitored. A regression analysis showed that the change with time i n the numbers of animals sheltering outside was highly s i g n i f i c a n t (P=0,000017, r2=0.7129) (Figure 48). The trend was most evident in the s n a i l C A nemoralis , and guite weak for k i B3x/ilB§ » During hot dry weather the animals returned almost exclusively to p a r t i c u l a r shelters (e.g.. Table LXV ) , but when cooler and wetter conditions prevailed the slugs began to move among shelters more frequently. The seasonal trend in the numbers of molluscs remaining on the s o i l surface r e f l e c t s t h i s tendency, as well as the fac t that shelters occupied during spring and f a l l were often less substantial than those used during the summer (e.g., under leaves of dandelion, or i n tussocks of grass, as opposed to deep s o i l crevices and under large logs). The d a i l y maximum temperature inside the a r t i f i c i a l shelters occurred several hours after dusk. A regression analysis showed that the relationship of shelter abandonment to maximum shelter temperature was highly s i g n i f i c a n t (P=0.00013, r2=0.5556) (Figure 49), supporting my hypothesis that the seasonal trend i n homing behavior was related to severity of weather. T a b l e L X V I I . P r o p o r t i o n s o f t h e M o l l u s c P o p u l a t i o n s t h a t d i d n o t r e t u r n t o S h e l t e r s i n F i e l d C a g e s D u r i n g 1976. D a t e D e r o c e r a s A r i o n A r i o l i m a x L i m a x C e p a e a r e t i c u l a t u m a t e r c o l u m b i a n u s maximus n e m o r a l i s May 12 0. 45 0.2 9 0.17 0. 00 0.90 19 0. 00 0.00 0.00 0.00 0. 53 28 0. 01 0.04 0.02 0.00 0.76 J u n e 2 0.00 0.02 0. 07 0. 00 0.83 9 0.03 0.00 0.00 0. 00 0.53 18 0.00 0.02 0. 00 0. 00 0. 46 25 0.00 0.00 0.00 0.00 0.3 0 J u l y 14 0.00 0.0 0 0.00 0.00 0. 40 21 0.00 0.08 0.01 0.00 0. 20 26 0.00 0.01 0.00 0.00 0.05 29 0. 00 0.00 0. 00 0.00 0.12 Aug. 6 0.00 0.00 0.00 0.00 0. 12 11 0.00 0.00 0.0 0 0.00 0.02 18 0.00 0.10 0.01 0.00 0. 37 25 0.00 0.12 0. 01 0.00 0.13 S e p t . 9 0.00 0.02 0.00 0.00 0.33 17 0. 00 0.09 0.02 0.00 0.09 24 0.00 0. 03 0.05 0.00 0.28 30 0. 00 0. 04 0.0 4 0.04 0.30 O c t . 8 0.04 0.27 0.08 0.07 0.40 20 0.16 0.15 0.18 0.03 0.19 294 Figure 48. Proportions of the Hollusc Population that did not Eetarn to A r t i f i c i a l Shelters at Various Times of the Sear. 962 296 are 49. The Relationship of Maximum Shelter Temperature to the Proportion of Molluscs Remaining Outside Their Shelters. L6Z 298 Twelve^Hour Observations Of |ndivr4dpa3- Slugs In the laboratory, cages similar to those employed i n the phercmcne t r i a l s were used to observe the behavior of slugs during t h e i r a c t i v i t y periods, but the size cf the boxes and number of shelters was varied to s u i t the number and species of slugs. In order to i l l u s t r a t e the usual a c t i v i t y pattern of i n d i v i d u a l animals, the paths of two L±.maximus were monitored continuously on July 18, 1975 throughout the dark phase of a L:D 12:12 photoperiod at 20° C (Figures 50 and 51). These two slugs shared a 120 X 90 X 14 cm deep cage with four others whose pathways were not recorded. A l l six had been i n the cage for a week, so that t h e i r homing behavior was already known. The cage was prepared in the same way as described i n the phercncne experiment. The shelters rested upon pieces of plate glass covered with paper towels so that a shelter and i t s contents could be moved without leaving an olfactory marker. A central board about 25 cm long and 14 cm high provided support for the cage's plate glass roof. The slug's tracks were traced with coloured wax pencils upon a piece of plexiglass l a i d over the cage. Later the t o t a l horizontal distance t r a v e l l e d by the slugs was obtained by following the traces with a map reader. A l l six slugs were continuously observed using the l i g h t of a dim f l a s h l i g h t . Separate dishes of fresh lettuce and s l i c e d carrot were placed in the cage before the beginning of each dark period. At the beginning of the observations slug A was i n shelter 2, B in 1, C i n 3, D in 1, E i n 4, and F in 2. Slugs A and C consistently returned to t h e i r respective shelters. Slugs B and 299 E alternated between shelters 1 and 4, although they actually shared a shelter only once in 8 observations. Slug F had moved to shelter 2 only one day before the observation day. It had previously homed consistently to shelter 4. Slug B was a small, badly injured slug, which had not previously entered shelters. At 8:45 am the dark phase of the photoperiod began. Slug D emerged at 9:15 and slug E at 10:19. Between 9:15 and 10:15 slug D, accurately followed i t s own slime t r a i l over the roof of the cage. It c i r c l e d three times i n an area about 10 cm i n diameter before retracing i t s t r a i l for more than 40 cm. Between 11:14 and 11:21 , slug E exactly followed D's t r a i l for a distance of nearly 50 cm. Between 10:19 and 11:14 slug E was observed to t r a v e l to, but not enter, the other three shelters i n the arena i n an apparently exploratory fashion. By 11:29 slugs C, D, and E were a l l feeding..Slug C attacked E at 11:29, and the l a t t e r defended i t s e l f with a t a i l - s l a p p i n g motion. Slug C then attacked slug D*s slime t r a i l , and then slug D. Slug D waved i t s t a i l i n the ai r and moved away at increased speed while slugs C and E continued feeding. At 11:41, slug E bit slug C, which moved a short distance and resumed feeding.,Between 11:40 and 11:45, slug D again made a number of small orientation c i r c l e s , judging by movements of the tentacles. After t h i s looping behavior, slug D travelled guickly to the food dish, where i t immediately attacked slug E at 12:04. Slug E struck back at slug D which then attacked slug C. Slug C immediately retreated to shelter 3. Meanwhile, slug E again attacked slug D at 12:10, whereupon the l a t t e r returned to 300 s h e l t e r 1. From 12: 22-3:00 pm, slug E remained f a i r l y i n a c t i v e but i t and slug D resumed a c t i v i t y by 3:09 and began to feed again. At 4:02, slug D chased slug E b r i e f l y when they encountered each other at the food dish, whereupon slug E, which had just finished feeding, crawled away. At 4:45 slug D attacked slug C and drove i t from the food dish. Shortly afterwards slug D finished feeding and returned home once more. I t was apparent from the homing tracks (Figures 50 and 51) that slugs go d i r e c t l y home without describing 'figure 8' tracks. Moreover, they usually go to t h e i r former shelters, apparently d i f f e r e n t i a t i n g the various homes. For example, the homing track of slug E at 5:45-5:50 (Figure 50), takes a very di r e c t route. At about 6:00 pm, slug E emerged from shelter 4 and travelled quickly to shelter 1, which i t entered at 6:14. Slug D was s t i l l i n t h i s shelter. Slug E re-emerged at 6:25, but there was no i n d i c a t i o n that i t s e x i t was caused by an i n t e r a c t i o n between the two slugs. Slug D emerged to feed again at 6:42. At t h i s point a manipulation was performed to determine i f slugs homed to the position of t h e i r shelters or to the shelters themselves. At 6:59, the positions of shelters 1 and 2 were reversed while t h e i r inhabitants, slugs D and F, were feeding. By moving the shelters and the glass plates that they rested on, no residual olfactory marker was l e f t behind. Slug F was an immature, non-aggressive Limax whereas slug D was large and highly aggressive. At 7:03, slug F ceased feeding and moved d i r e c t l y to the former position of i t s shelter. Upon reaching the entrance the slug put 301 i t s head inside, raised the fore part of i t s body and swayed i t s head back and forth with i t s tentacles maximally extended. I t then withdrew, crawled to the rear door of the shelter, and repeated t h i s behavior. :Then i t returned to the front and again waved i t s head i n the doorway (7:14), I t then crawled to the back door and repeated the same performance {lz 16) , and at 7:27 pm i t t r i e d the front entrance once more. F i n a l l y the slug abandoned the shelter and moved d i r e c t l y to shelter 4, which had not been moved, entering i t at 7:45 pm. I t had previously used shelter 4 on several occasions. At 7:50 slug E entered shelter 4, and at 7:54 slug D also entered. At 7:55, slug F emerged at top speed. Slug D remained i n shelter 4 and did not return to the o r i g i n a l s i t e of shelter 1 at any time, but alternating between shelters 1 and 4 was not unusual for this i n d i v i d u a l . Interestingly, slug F returned d i r e c t l y to shelter 1, which s t i l l occupied the s i t e of i t s previous shelter. I t again examined both entrances, but remained outside even aft e r the l i g h t s switched on at 8:56. As t h i s slug always returned to shelter before the l i g h t s came on, t h i s behavior was most unusual. At t h i s point, I re-exchanged the positions of shelters 1 and 2, returning them to t h e i r o r i g i n a l s i t e s . Slug F immediately entered shelter 2, but i n a most unexpected manner. The slug quickly climbed to the top of the pot and crawled through the small drainage hole located there. Slugs D and E, meanwhile, were together i n shelter 4. After sharing the shelter f o r only 5 minutes, sluq E was observed squeezinq rapidly out of the drainage hole at the top of shelter 302 4. It moved away in a burst of speed that was only observed in slugs attempting to escape from an attacker. The slug travelled to shelter 3, where i t remained. The total distance travelled by slugs D and E respectively was 12.57 m and 12.08 a, disregarding vertical movements i n the 14 cm deep box. Their normal cruising speed was about 0.10 cm/sec, increasing to nearly 0.50 cm/sec when attacked. 303 Figure 50, Tracks of an Individual Limax maximus (Slug E) During the Dark Phase of a L:D 12: 12 Photoperiod with Darkness Beginning at 8:45 am, July 18, 1975. 305 gure 51. Tracks of an Individual Limax maximus (Slug D) During the Dark Phase of a L:D 12:12 Photoperiod, with Darkness Beginning at 8:45 am, July 18, 1975. 307 DISCUSSION Orientation To Substrate. Cues:. T r a i l s And Xfipoarafiiu: Hells and Buckley (1972) reviewed the evidence and concluded that examples of mucous-trail following within the class flollusca are so diverse that the habit i s probably very widespread, although most of the evidence has been accumulated from studies on aguatic molluscs. T e r r e s t r i a l slugs are known to follow slime t r a i l s i n order to f i n d mates, so t h i s aspect w i l l be considered before discussing the r o l e of t r a i l - f o l l o w i n g for other orientation. Newell (1966) observed that D. reticulatum may follow the slime t r a i l of another i n d i v i d u a l for 1.8 m prior to copulation. He postulated that a pheromone was secreted into the pedal mucus when a slug became receptive to mating. Gelperin (1974) observed similar behavior in L. maximus. Barr (1928) observed an A x ater i n the laboratory inspecting the caudal glands of several other slugs u n t i l i t found one with a globule of mucus, which i t consumed. The slug then began courting that in d i v i d u a l . , Runham and Hunter (1970) observed that the caudal gland becomes maximally developed at maturity, which may help other slugs to i d e n t i f y a potential mate. I have observed mucous-trail following associated with mating in A, ater. A. subfuscus. Lft maximus, P. caruanae. and -D. reticulatum. Other i n d i v i d u a l s were freguently attracted to mating pairs, u n t i l three or four slugs might be occupied i n mutual courtship. On one occasion I placed 20 D. reticulatum together, which had been reared i n i s o l a t i o n from the egg. Within 30 minutes a l l of the slugs had everted their g e n i t a l i a 308 and had formed a large mating aggregation. Instances of apparently pheromone-mediated mating a c t i v i t y i n marine molluscs are discussed by Kohn (1961). Although the evidence suggests the action of a pheromone, I have also observed D. reticulatum dragging i t s g e n i t a l i a over slugs of the wrong species i n t y p i c a l courtship behavior i i * l&fX*. L t maximus. A. fasciatus, and A, columbianus ). On another occasion an A. ater and an A» subfuscus proceeded as f a r as everting t h e i r a t r i a before separating. Such observations, combined with the f a c t that slugs possess very complex courtship r i t u a l s , suggest that there i s no spe c i e s - s p e c i f i c sex pheromone capable of acting as an i s o l a t i n g mechanism, but that there i s probably a generally acting excitant, or a chemical indicating sexual status. Townsend (1S74) found that, although the freshwater s n a i l Bicmphalaria glabrata (Say) followed t r a i l s f o r non-sexual reasons, individuals responded most when seeking mates. H a l l (1973) found no influence of sexual status cn t r a i l following i n L i t t o r i n a . which has well defined male and female stages. Although following slime t r a i l s i s a t a c t i c for finding mates, i t i s not necessarily limited to that function. In laboratory observations of Limax , slugs were freguently observed to follow their own slime t r a i l s or those of other individuals (e.g..Figures 50 and 51). The instance when slug E followed the t r a i l of slug D for nearly 50 cm shows that t r a i l s more than one hour old are perceived. Many of these trackings were not associated with sexual behavior; e.g., when slugs follow t h e i r own t r a i l . 309 I t i s l i k e l y that slugs can fellow slime t r a i l s whenever i t serves t h e i r purpose., Recently Cook (1976,1977) demonstrated that Limax grossui Lupu and Limax flavus L. followed slime t r a i l s when placed under bright l i g h t on a glass sheet. T r a i l s three days old s t i l l e l i c i t e d a response. In the aquatic s n a i l s Physa {Sells and Buckley, 1972) and B ^ a l a b r a t a {Townsend, 1974), mucous t r a i l s more than 30 minutes o l d were ignored. Hells and Buckley {1972) suggested that the behavior of Gastropoda can only be understood i f one takes account of the likel i h o o d that t h e i r environment i s patterned with t r a i l s which may be i n v i s i b l e to us, but which are replete with information for the molluscs. A sim i l a r explanation of homing by limpets was suqqested by Cook et a l t -. {1969) and Cook and Cook {1975). In the present twelve-hour observations of L. maximus. three d e f i n i t e instances of t r a i l following were observed. The sluqs had inhabited the arena for more than a week, however, and possible orientation to previously l a i d t r a i l s could have occurred. Gelperin {1974) observed that JL*. maximus , takes only short excursions from shelter when f i r s t established i n an enclosure. Since such behavior i n other animals i s usually associated with gaining f a m i l i a r i t y with the surroundings, homing to shelter may not be s o l e l y dependent on olfactory cues from the shelter i t s e l f . Hy f i e l d and laboratory observations strongly suggest that slugs can detect d i r e c t i o n a l i t y i n slime t r a i l s , since no individuals were ever observed to travel i n the wrong d i r e c t i o n when seeking a mate. It i s possible that the sex phercmone secreted into the slime t r a i l imparts pola r i t y , however. The 310 I i l a x i i a s observations figured (figures 50 and 51), c l e a r l y shew that slugs w i l l follow single slime t r a i l s in either d i r e c t i o n , but t h i s does not mean that they are unaware of the polarity. Cook (1976,1977), however, believed that i n other species of Limax, the d i r e c t i o n taken was related to the angle of approach and that d i r e c t i o n a l i t y was not perceived. Among other molluscs. Be l l s and Buckley (1972) shewed that Phjjsa was able to detect d i r e c t i o n a l i t y of mucous t r a i l s when tested i n a »T» maze. S i m i l a r l y , Hall (1973) and Townsend (1974) respectively demonstrated, that the marine periwinkle Litterin§-i r r o r a t a Say, and Biomphalaria glabrata were able to detect t r a i l p o l a r i t y . Funke (1968) reported chemical differences i n a wide marginal zone of the " f o o t p r i n t " of P a t e l l a (a limpet), which he postulated could carry d i r e c t i o n a l information. Slugs of one species can also u t i l i z e information i n the slime t r a i l s of another. Thus, i n the present study, L, maximus sometimes followed the tracks of other slugs ( A. ater,,-A t columbianus^ DK reticulatum ). in order to attack them. Cook (1976) found that although L r flavus and L A qjcossui followed one another's t r a i l s , LF grossui did not follow the t r a i l s of D, reticulatum , Peters (1964) previously reported i n t e r s p e c i f i c t r a i l following among periwinkles, L i t t o r i n a spp. . However, Townsend (1974) observed that B. glabrata ignored the t r a i l s of another aguatic s n a i l , Lymnaea staqnalis . Several predaceous s n a i l s , both t e r r e s t r i a l (Wells and Buckley, 1972) and aguatic (Paine, 1963; Gonor, 1965; B l a i r and Seapy, 1972) are known to f i n d t h e i r mclluscan prey by following mucous t r a i l s . Sleeper and 311 Fenical (1977) showed that the marine cpisthobrancb Navanax inermis can secrete a tr a i l - b r e a k i n g alarm pheromone. Even other animals of diverse phylogeny are capable of u t i l i z i n g mucous t r a i l s . Thus I observed the predacious beetle, Carabus nemoralis L., following every curve i n the t r a i l s of A i ater and L. maximus as i t hunted i t s prey. The beetle also appeared to recognize the d i r e c t i o n of the t r a i l , although no c r i t i c a l experiments were performed. Hhile tracking, the beetl e f s antennae vibrated constantly at a high frequency, and the insect oriented to the t r a i l i n quick zig-zags, a strategy commonly observed i n other t r a i l - f o l l o w i n g animals (Shorey, 1976). Interestinqly, slugs do not do t h i s . Perhaps the lower mouth tentacles are of s p e c i a l use i n maintaining a constant orientation to t r a i l s , Bichter (1976a) observed that ft. columbianus does not follow the slime t r a i l s of other individuals i n forests. He sugqested that these slugs actually avoided t r a i l s of others i n order to reduce search redundancy during foraging.,Holda (1971) and Yom-Tov (1972) even suggested that a slime-borne pheromone was responsible for density-dependent regulation of population size i n two species of t e r r e s t r i a l snails, i n contrast to Bichter's (1976a) observations. H a l l (1973) suggested that the main reason f o r t r a i l following by L i t t o r i n a •• was due to conservation of energy. The trail-making s n a i l averaged a speed of only 4.6 cm/minute compared with followers that averaged 6.5 cm/minute u n t i l they overtook the leader. The leadership then was frequently changed. During the experiment to test the att r a c t i o n of faeces to 312 At ater , slugs appeared unable to "home" under the bright l i g h t s . flt that time they exhibited a strong tendency to fellow one another, both by maintaining contact with the t a i l of the slug in front, or by following slime t r a i l s . I t i s noteworthy that the instances of slugs following t r a i l s reported by Cook (1976,1977) also referred to animals placed beneath a bright l i g h t . In the present study, s i m i l a r behavior was previously observed when the temperature was increased i n the middle of the a c t i v i t y cycle of ftt ater. Most slugs went d i r e c t l y home, except for two individuals which had not previously homed to the shelter provided. Instead, these i n d i v i d u a l s spent considerable time following one another. Following other slugs or t h e i r t r a i l s could lead an animal to shelter which i t was unable to locate d i r e c t l y by odor. In the f i e l d , weather conditions can rapidly become unfavourable for long-range olfactory orientation, and such a "backup" system would have high s u r v i v a l value. During observations of I. maximus in laboratory homing experiments, one in d i v i d u a l was found that crawled on the wall, about 5 cm above the f l o o r as i t travelled from i t s corner shelter tc the food dish located i n the opposite corner. I t usually retraced t h i s path going home, and repeatedly used t h i s route around the edge of the arena throughout the week. Shite and Davis (1953) previously stated that slugs returned heme by following their outward path, but the i r contention was i n d i r e c t contrast to a l l other published accounts. In the present instance, the slug appeared to demonstrate a topographical 313 memory, additional evidence for t h i s comes from the behavior described e a r l i e r , of slug F, after i t s shelter had been moved. Slug F appeared to "know" the locations of the shelter entrances. I f t h i s were only a manifestation of t r a i l following, rather than an example of topographical memory, then the slug would require an extremely precise discrimination among the many t r a i l s deposited by i t s e l f and other i n d i v i d u a l s sharing the cage. Cook and Cook (1975) provided evidence that, among limpets, the act of retracing a t r a i l neutralizes i t s p o l a r i t y , a r e s u l t which could p a r t i a l l y explain such behavior. The exact nature of t h i s p o l a r i t y , whether chemical or due to physical structure remains unknown. Gelperin (1974) provided a more or less uniform environment in his study, walls being replaced by a barrier cf s a l t . Thus there was l i t t l e p o s s i b i l i t y that slugs could learn topographical features. It i s also of i n t e r e s t that the homing behavior of limpets disappears on uniformly f l a t substrates (Cook et a l . , 1969) which suggests the hypothesis that orientation to complex patterns of t r a i l s requires a certain amount of topographical heterogeneity. Although following slime t r a i l s could account for the behavior I have described, the directness with which the animals moved to their objectives leads me to conclude that some topographical awareness must be involved. Note, however, that these r e s u l t s do not c o n f l i c t with those of Gelperin (1974) , but merely augment them. Most of my other observations support the idea that d i r e c t o lfactory orientation i s the preferred method of homing, probably because i t i s more economical with regards 314 to locomotion. Orientation Jo Air-Borne Cues Observations in the fie l d and laboratory show that a l l of the slugs included in the f i e l d study exhibited homing behavior, as did Limax (lehmannia) yalentiana^ Prophysaon anderscni. A, intermedius^ and the snails C. nemoralis and Pplyqyra (Vespericola) columbiana pjlosa Henderson. Thus the ability appears to be nearly universal among terrestrial molluscs. The behavior of slugs navigating towards home was similar in a l l the species observed. Two distinct kinds of orientation occurred in every species. The f i r s t type was observed both in the laboratory and f i e l d , and was accurately described by Gelperin (1974) for L. maximus . He observed that the slugs l i f t the anterior part of the body into the air and wave the head from side to side. I also noted that the tentacles become maximally distended, and although they may be moved about considerably in relation to one another, even being bent at right angles near the tips on occasion, they are usually spread as widely as possible when the goal i s far away. When within several cm of the goal the tentacles may be held much closer together. Such behavior i s also typical of molluscs locating food. They may also hold their head up while they are crawling, but more often they l i f t i t at intervals as described above. After their i n i t i a l orientation, the slugs travel guite directly to their apparent goal. -Lx maximcs has been recorded moving directly tc a pile of meat from 180 cm away (L. E. Adams, in Taylor, 1907), and Ar ater can detect certain fungi at 120 cm 315 ( K i t t e l , 1956). Several d i r e c t homing paths are e v i d e n t i n Figures 50 and 51. The f a c t that s l u g s e x h i b i t e d t h i s type of n a v i g a t i o n i n c l o s e d l a b o r a t o r y boxes i n d i c a t e s that they can respond d i r e c t l y t o odor g r a d i e n t s . Gelperin (1974) observed t h a t s l u g s tend to turn i n t o g e n t l e wind to f o l l o w odours and suggested that such anemctaxis would e l i m i n a t e the need f o r a c t u a l l y f o l l o w i n g a g r a d i e n t . Farkas and Shorey (1S76) demonstrated t h a t s i m i l a r anemctaxis occurs i n the t e r r e s t r i a l s n a i l . Helix aspersa. Crisp (1969) found t h a t the a g u a t i c s n a i l Nassar.ius obsgXetus (Say) a l s o turns i n t o c u r r e n t s (rheotaxis) i n which an a t t r a c t i v e odor i s d e t e c t e d . Shorey (1976) g i v e s many examples of i n s e c t s which do the same. The second type of o r i e n t a t i o n was not d i r e c t and was a s s o c i a t e d with windy or r a i n y c o n d i t i o n s . Slugs were f r e q u e n t l y observed t u r n i n g i n c i r c l e s on the planks c o v e r i n g t h e i r f l o w e r -pot s h e l t e r s , a p p a r e n t l y unable t o l o c a t e the c e n t r a l entrance hole. They tended t o f o l l o w c i r c l e s of d i m i n i s h i n g s i z e and thus s p i r a l l e d towards t h e i r g o a l . Slugs have been observed to behave s i m i l a r l y when l o c a t i n g food i n the f i e l d ( K i t t e l , 1956), suggesting t h a t c i r c l i n g i s a d i f f e r e n t m a n i f e s t a t i o n of o l f a c t o r y o r i e n t a t i o n when no obvious or s t a b l e g r a d i e n t can be detected. L i f t i n g and swaying the head again o c c u r s at frequent i n t e r v a l s i n t h i s type o f o r i e n t a t i o n . How the s l u g s approached the planks was not d i s c e r n e d , but they f r e q u e n t l y crawled around the o u t s i d e edges before c l i m b i n g onto them. Their behavior on the planks c l e a r l y i n d i c a t e d the use of o l f a c t o r y n a v i g a t i o n s i n c e they d i d not use the e l d e r slime t r a i l s a v a i l a b l e . 316 Turning in circles may be a tactic to help slugs triangulate on the direction of an olfactory gradient. Duval (1S70), for example, observed that ci r c l i n g movements increased as slugs approach food. Even in cases of direct travel tc a goal, I observed that slugs frequently moved in one or more small circles before embarking in the correct direction. Such circular paths could result i f the molluscs were uti l i z i n g positive anemotaxis in response to the presence of the odour, and negative anemotaxis when the odour was no longer detected., Hindy conditions, and convective currents associated with solar radiation and temperature gradients probably impair olfactory orientation by molluscs. Thus, Griffiths (in Bunham and Hunter, 1970) found that DA geticulatum only responded to food odours in the absence of any wind. Some instances of slugs beccffinq trapped outside their shelters and ultimately killed by the daytime weather are possibly associated with disruption of their olfactory a b i l i t i e s . More knowledge i s needed of the influence of weather on the navigational strategies of molluscs, as was recognized by Chapman (1967) for other animals. In the experiment to detect the use of a pheromone in homing, A. ater apparently was unable to orient directly to shelters containing faeces when the area was l i t by an incandescent lamp. Perhaps olfactory gradients then were disrupted by heat from the lamp. In these conditions the slugs seemed to discover shelters by accident, mainly by following the contours of topographical features, such as walls and flower pots. The animals were apparently unable to see these dccrs, since they freguently passed them by as l i t t l e as 1 cm. Newell 317 and Newell (1968) previously concluded that the eye of Dt reticulatum was probably not sophisticated enough to allow form visio n . At columbianus* prefers to become active i n bright moonlight suggesting that l i g h t may be important as a ,backup» system in orientation. Although the immediate observations suggested that the faeces were unimportant i n orientation to shelters, when the number of slugs i n each shelter was tabulated the next day, s i g n i f i c a n t l y more slugs occupied those which contained faeces (Table LXIX) (P<0.001), despite the fact that some slugs entered shelters without faeces while the incandescent l i g h t was on. Since food was included in a l l the shelters, and the faeces themselves were derived from t h i s same food, i t appears that the attractant i s i n the faeces, and produced by the slugs themselves. Aggregation of the d i s t a n t l y related species of t r o p i c a l slugs >( y^er,snicella ameqhini (Gambetta) and V_j. floridana (Leidy) ] was attributed tc a phercmone contained in t h e i r slime (Dundee, 1973; Dundee j i aJxx 1975). Slugs were attracted to substrates upon which others had formerly aggregated. Nc mention was made as to the d i s t r i b u t i o n of the faeces. Although my r e s u l t s strongly implicate the faeces as the source of the attractant, t i e p o s s i b i l i t y e x i s t s that the faeces were contaminated by a slime-borne chemical. Among other molluscs, Crisp (1969) found that dense aggregations of the marine s n a i l N A obsolej-us- were at least p a r t i a l l y mediated by a chemical produced by the animals. These s n a i l s had no homing behavior and the faeces were not at t r a c t i v e , Dinter and Manos (1973) s i m i l a r l y found that the marine periwinkle, Littcjrina l i t t o r e a L. was attracted 318 p r e f e r e n t i a l l y to tubes containing other members of the same species. Results for females were inconclusive, but sales produced a chemical a t t r a c t i v e to both females and other males (Dinter, 1974). The author favoured the idea that the attractant served a sexual function. Although these s n a i l s do not home precisely, they do tend to return to approximately the same positions for many weeks at a time (Newell, 1958a,b), and the attractant may play an important role i n t h i s . Homing behavior was f i r s t documented for A. columbianus by Ingram and Adolph (1943), who found that slugs returned to concave depressions that they had apparently excavated i n s o i l . These were characterized by the presence of f e c a l masses in a l l stages of drying, and many converging slime t r a i l s . I ncidentally, the accumulation of slime t r a i l s i n shelters may lend the slugs a previously unsuspected advantage. Although hydrated mucus absorbs water from saturated a i r at a very slow rate (0.00323 mg water/mg dry wt. mucus/min), I found that the dry mucus of A. ater was hygroscopic, absorbing water from saturated a i r at a rate of 0.0447 mg water/mg dry wt. mucus/minute. Thus, a slime-coated shelter would dry out less slowly than an unoccupied one, and thereafter, would guickly •recharge 1 i t s water supply whenever moisture became available. I n t e r e s t i n g l y , my observations of woodlice ( Oniscus asellus ), cockroaches ( Periplaneta spp.. B l a t t e l l a qermanjca ) and millipedes (unidentified species) showed sim i l a r accumulations of faeces at t h e i r home s i t e s . Possibly many shelter-dependent species share a common homing strategy. Shorey (1S76) pointed out that among animals i n general, a continuum 319 e x i s t s , from the recognition by an i n d i v i d u a l of i t s own odour, to the recognition of i t s s p e c i f i c home, to recognition of i t s t e r r i t o r y or home range. He suggested that, in some cases, a l l three phenomena may be i d e n t i c a l , but cautioned that not enough i s known about the r o l e of learning scents to make a firm generalization. For woodlice, although there was no evidence that individuals repeatedly used particular shelters, the population as a whole used the same shelters each night (Den Boer, 1961). Kuenen and Nooteboom (1963) found that woodlice tend to aggregate on areas of f i l t e r paper where previous aggregations had formed. Thus they probably recognize a population odor, and do not discriminate the scent of particular individuals or shelters...ft s i m i l a r s i t u a t i o n probably exists f o r earwigs, which Lamb (1974) concluded did not exhibit homing behavior since p a r t i c u l a r i n d i v i d u a l s did not repeatedly use the same shelter (except for females i n brood chambers). He did f i n d , bowever, that when 75 individuals were offered a choice of 4 alternative shelters, a l l the animals were located i n two of these by the end of 13 days. Only f i v e animals did not re-locate at least once. Homing behavior i n the above examples appears to operate at the l e v e l of the population rather than the i n d i v i d u a l , and f a i l u r e to make t h i s d i s t i n c t i o n i n previous studies has frequently led to the conclusion that the animals do not home to shelter (e.g. Collinge, 1942). In fact animals responding to groups probably d i f f e r from those with more precise p o s i t i o n a l homing only i n t h e i r i n a b i l i t y to distinguish i n d i v i d u a l odor., The homing study using A, columbianus in the f i e l d 320 i l l u s t r a t e d that slugs guickly e s t a b l i s h accurate homing to suitable shelters. Most individuals returned to the pots i n which they were o r i g i n a l l y placed. Six out of 40 i n d i v i d u a l s became disoriented i n i t i a l l y (Table LXV-A), and remained on the s o i l surface for several days before re-entering the shelters provided. This resulted i n the death of i n d i v i d u a l #1, apparently from dehydration. Individuals which o r i g i n a l l y became disoriented showed a tendency to move around more than most other slugs (e.g. #11), or were among the f i r s t to show a later breakdown i n homing behavior (#*s 3,4,23), probably due to competition from IJL maximus introduced at that time. Thus they may represent individuals with i n f e r i o r orientation systems, or they may have been inherently more dispersive. Many slugs exhibited long-term homing to i n d i v i d u a l shelters (Table LXV-B), Except for a single observation, slug #9 was found i n the same shelter over a period of 49 days. Other individuals showed considerable movement among shelters (Table LXV-C). Lcmniki (1969) suggested that populations of the s n a i l , H, pematia, were composed of two types of i n d i v i d u a l s ; those with a strong homing tendency, and those with a p r o c l i v i t y to disperse. A s i m i l a r r e s u l t was reported f o r the limpet Acmaea j S i S l t a l i s by Breen (1971). Despite the s t a t i s t i c a l support for t h e i r statements, I believe that defining what appears to be a continuum as a dichotomy, may be a serious conceptual error. In the present study, the strength of the homing response ranged from the majority of i n d i v i d u a l s which showed strong attachment to p a r t i c u l a r shelters, to a few which moved more but s t i l l 321 exhibited homing behavior, but no dichotomy was obvious, fireen (1971) observed a s i m i l a r s i t u a t i o n , stating that most limpets did not migrate, and that there were progressively fewer limpets in each category of higher migration frequency., The dichotomy was only apparent when he compared the d i s t r i b u t i o n of migration frequencies to a Poisson d i s t r i b u t i o n using a Chi square t e s t . S i m i l a r l y Lomniki's (1969) data looked l i k e a continuum of responsiveness, the dichotomy appearing when Chi square was used to test among apparently a r b i t r a r i l y delineated groups. Despite the s t a t i s t i c a l support for t h e i r statements, I believe that defining what appears to be a continuum as a dichotomy, may be a serious conceptual error. In cage I the slugs were o r i g i n a l l y established in shelters at opposite ends of the cage. It was hypothesised that i f slugs homed to a chemical that they produced themselves, then some slugs might exchange shelters, even though they were separated by more than 4 m. Three slugs were found to have i n fact moved from one shelter to the other (Table LXV-D). I t i s unlikely that t h i s was fortuitous, due to the distance involved, and because the only other shelters colonized at that time, at l e a s t i n the case of slugs #13 and #14, were those immediately adjacent to that in which the animals were o r i g i n a l l y established. In the case of slug #13, i t moved to the opposite end of the cage, and then returned to i t s o r i g i n a l shelter. This lends strcnq support to the idea that the homing attractant i s produced by the slugs themselves, and that they recognize the odor of other members of t h e i r species. Whether they can also discern the chemical produced by other species of slugs has not 322 been determined. Among three species of woodlice, i n t r a s p e c i f i c attraction was strongest, but there was also an i n t e r s p e c i f i c attraction i n some cases (Kuenen and Nooteboom, 1963) . An important problem concerned with slug homing i s whether the animals recognize the odour of t h e i r own shelter, or whether they respond on a population l e v e l as was discussed for ether animals. I f slugs react to a chemical i d e n t i c a l among a l l ind i v i d u a l s , then i n cage I, where the slugs o r i g i n a l l y inhabited only two shelters, they should show less movement among shelters than i n cage I I I , where slugs were placed i n a l l 10 shelters i n i t i a l l y * Analysis of the data showed that there was indeed s i g n i f i c a n t l y more movement of slugs i n cage III than in cage I, again supporting the attractant theory (Table IXV.I) (P<0.001), and confirming that individuals can home to the shelters of other members of t h e i r species. Other evidence, however, suggests that slugs have the a b i l i t y to d i f f e r e n t i a t e between their own shelter and that of others. F i r s t l y , many slugs showed long-term homing to pa r t i c u l a r shelters, even i n cage III where such accuracy would be unexpected i f the slugs were e a s i l y confused by alternative choices (Table LXV-B). Furthermore, several slugs exhibited an alternation of homing between two particular shelters. Such s p e c i f i c i t y to more than one shelter also supports the idea that some slugs may inhabit a home range (Table LXV-E). Observations in the laboratory, such as those described in the 12-h observations of L. maximus also indicated that slugs can recognize their i n d i v i d u a l retreats (Figures 50 and 51). The greater movement observed i n cage I I I therefore could have 323 resulted from a deliberate motivation to move, f a c i l i t a t e d by easier recognition of other shelters, rather than from confusion caused by a greater number of attractant sources. Slug homing thus i s more complex than a simple response to a common attractant. Two alternative hypotheses to explain these results are that molluscs can either recognize their i n d i v i d u a l shelters by odour, or some other •backup1 o r i e n t a t i o n a l system helps them arrive at the r i g h t position. This result may seriously c u r t a i l the p o s s i b i l i t y of using the homing chemical as a slug control method. When the paper l i n e r s were exchanged between shelters 10 and 7 in cage I, A. columbianus continued to home to shelter 10 for several days. within the next 9 days, 5 slugs moved to shelter 7 (Table LXV-F). Of the three shelters near shelter 10, shelter 9 was closest (0.55 m), shelter 8 was further away (0.85 m), and shelter 7 was most distant (1.00m). Although several slugs colonized shelter 9 previous to the manipulation, none had moved to shelter 8. Although the sample size was small, when the accuracy of the homing response i s considered, the movement of 5 slugs to shelter 7 could not be due to chance. On July 2nd, the l i n e r s of pots 7 and 8 were exchanged i n cage I. Although two of the three slugs inhabiting shelter 7 remained there subsequently (#16 and #19), slug #21 remained on the s o i l surface for some time before moving to shelter 9. Such apparent disorientation was normally only observed when slugs were f i r s t placed i n shelters, or when they were i n competition with limax * Slugs rested mainly on the paper l i n e r s inside the flower-pot shelters and defecated on them. The r e s u l t s are 324 consistent with the hypothesis that a marker was transferred with the paper l i n e r . The l i d s of shelters 1 and 4 were exchanged i n cage I on June 23rd. Slug #17 moved from shelter 1 to 4 by June 25. By July 2nd, t h i s slug was joined by slugs #4 and #28. Again, although shelter 4 was further away than shelter 3, no slug colonized the l a t t e r during t h i s time. Cn July 2nd, the l i d s between shelters 3 and 4 were exchanged i n the same cage. Slugs #4 and #3 were found there on July 5th, one frcm shelter 4 and one from shelter 1. This evidence suggests that the l i d s of the shelters had also been marked although they had l i t t l e obvious f e c a l material upon them. Possibly they had been impregnated with the attractant, or the animals secreted the attractant in a specialized slime. Exchanging the l i d s of the shelters appeared to invoke a faster response than exchanging the l i n e r s , suggesting that when l i n e r s are exchanged i t takes some time for the odor to d i f f u s e . Homing behavior was also freguently observed i n the laboratory (e.g. Table LXVIII). There were more shelter changes with L., maximus. apparently associated with t h i s species* aggressiveness, but i n d i v i d u a l s tended to return most freguently to particular abodes. The 12-h laboratory observations i l l u s t r a t e d a number of attributes of slug behavior. F i r s t l y , the a c t i v i t y pattern i