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The effects of food and slug density on slug movement Hamilton, Peter A. 1981

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THE EFFECTS OF FOOD AND SLUG DENSITY ON SLUG MOVEMENT by PETER A. HAMILTON B.Sc.,Toronto Univ.,1977 A^THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA 2 March 1981 © Peter A. Hamilton, 1981 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements for an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of th is t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that copying or pub l ica t ion of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f Zoology  The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date 9 March 1981 i i ABSTRACT I i n v e s t i g a t e d the e f f e c t s of food, crowding, and weather on the behaviour of the s l u g s , A r i o n a t e r and A r i o l i m a x columbianus . F i e l d experiments demonstrated that A r i o n based i t s migratory response on the d e n s i t y of c o n s p e c i f i c s and the q u a l i t y and q u a n t i t y of a v a i l a b l e food. M i g r a t i o n was most r a p i d from areas of high s l u g d e n s i t y and scar c e poor q u a l i t y food. The m i g r a t i o n response of A r i o l i m a x was e x c l u s i v e l y based on d e n s i t y . Although high s l u g d e n s i t y induced m i g r a t i o n by t h i s s p e c i e s , i t s r a t e of m i g r a t i o n was lower than that of A r i o n . M i g r a t i n g A r i o n a t e r were he a v i e r than non-migrating s l u g s . There was no such r e l a t i o n s h i p between body weight and locomotory or migratory a b i l i t y of A r i o l i m a x columbianus . Both s p e c i e s e x h i b i t e d seasonal v a r i a t i o n i n t h e i r behaviour. Hot, dry weather d u r i n g mid-summer c u r t a i l e d t h e i r f o r a g i n g and migratory a c t i v i t y . C o o l e r , wetter weather i n l a t e s p r i n g and l a t e summer lengthened n o c t u r n a l a c t i v i t y p e r i o d s . Average d a i l y temperature and p r e c i p i t a t i o n were poor p r e d i c t o r s of migratory a c t i v i t y . M u l t i p l e r e g r e s s i o n a n a l y s i s of ho u r l y a c t i v i t y p a t t e r n s and weather showed t h a t , time of day, a i r temperature, and atmospheric moisture accounted f o r most of the v a r i a t i o n i n hourl y n o c t u r n a l behaviour. V a r i a t i o n i n s l u g d e n s i t y and food a c c e p t a b i l i t y had no i i i e f f e c t on p o p u l a t i o n a c t i v i t y i n A r i o n a t e r . However, the treatments d i d i n f l u e n c e p a r t i c u l a r kinds of behaviour. A r i o n provided with poor food moved and r e s t e d more, but fed l e s s , than slugs r e c e i v i n g good food. The e f f e c t s of d e n s i t y were not s i g n i f i c a n t . Poor food and high s l u g d e n s i t y i n c r e a s e d the a c t i v i t y of A r i o l i m a x columbianus . T h i s e f f e c t was a l s o evident in the component behaviours of t o t a l a c t i v i t y . A r i o l i m a x moved, re s t e d , and fed more in high d e n s i t y s i t u a t i o n s . These slugs fed more when good food was a v a i l a b l e , but the other behaviours were u n a f f e c t e d by t h i s f a c t o r . On an h o u r l y b a s i s Ar ion a t e r ' s a c t i v i t y p a t t e r n appeared to be based on food a q u i s i t i o n . Over days and weeks, however, t h i s s p e c i e s used both p o p u l a t i o n d e n s i t y and food a c c e p t a b i l i t y to decide to migrate. Ar iolimax columbianus' hourl y behaviour p a t t e r n was most c l o s e l y r e l a t e d to the d e n s i t y of c o n s p e c i f i e s . T h i s response to d e n s i t y p e r s i s t e d over days and weeks, and was the most important f a c t o r a f f e c t i n g the migratory behaviour of these s l u g s . i v TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i LIST OF FIGURES x ACKNOWLEDGEMENTS x i i INTRODUCTION 1 PART 1. SLUG DENSITY AND FOOD MANIPULATION EXPERIMENTS ... 8 1.1 I n t r o d u c t i o n 8 1.2 Methods 8 1.3 R e s u l t s 26 1.3.1 M i g r a t i o n Measures 26 1.3.2 M o r t a l i t y 51 1.3.3 Days to Migrate 57 1.3.4 Weight of Migrants 64 1.3.5 Weather and M i g r a t i o n 75 1.3.6 Summary 83 1.4 D i s c u s s i o n 89 1.4.1 Density E f f e c t s 89 1.4.2 Food E f f e c t s 91 1.4.3 M o r t a l i t y 93 1.4.4 Weather E f f e c t s 96 1.4.5 General D i s c u s s i o n 99 V 1.4.6 Summary 101 PART 2. ARENA STUDIES OF LOCOMOTORY BEHAVIOUR 102 2.1 I n t r o d u c t i o n 102 2.2 Methods 102 2.3 R e s u l t s 109 2.3.1 S i z e and Distance T r a v e l l e d 109 2.3.2 Comparison Between Species 121 2.4 D i s c u s s i o n 125 2.4.1 S i z e and Distanc e T r a v e l l e d 125 2.4.2 Comparison Between Species 128 2.4.3 Summary 129 PART 3. NOCTURNAL BEHAVIOUR OBERSERVATIONS 130 3.1 I n t r o d u c t i o n 130 3.2 Methods 130 3.3 R e s u l t s 134 3.3.1 Treatment E f f e c t s on N o c t u r a l Behaviour 134 3.3.2 Weather E f f e c t s on No c t u r n a l Behaviour: General 167 3.3.3 Weather E f f e c t s on Nocturnal Behaviour: C o r r e l a t i o n - R e g r e s s i o n 177 3.3.4 Feeding Preferences 180 3.4 D i s c u s s i o n 186 3.4.1 Treatment E f f e c t s on Nocturnal Behaviour 186 3.4.2 Weather E f f e c t s on Nocturnal Behaviour 190 v i Time 191 Temperature 193 Atmospheric Moisture 194 Barometric Pressure 195 Other F a c t o r s 196 3.4.3 Food P r e f e r e n c e s 198 3.4.4 Summary 199 GENERAL DISCUSSION 202 REFERENCES 208 APPENDIX A 218 APPENDIX B 223 APPENDIX C 228 APPENDIX D 237 LIST OF TABLES Table I. Dates of D e n s i t y and Food M a n i p u l a t i o n Experiments 15 Table I I . A n a l y s i s of v a r i a n c e : P r o b a b i l i t y of A r i o n a t e r M i g r a t i n g 30 Table I I I . A n a l y s i s of v a r i a n c e : P r o b a b i l i t y of A r i o l i m a x columbianus M i g r a t i n g 30 Table IV. A n a l y s i s of V a r i a n c e : M i g r a t i o n Rate, A r i o n a t e r 32 Table V. A n a l y s i s of V a r i a n c e : M i g r a t i o n Rate, A r i o l i m a x columbianus 32 Table VI. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : P r o p o r t i o n of A r i o n a t e r M i g r a t i n g to S e c t i o n 5 34 Table V I I . K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : P r o p o r t i o n of A r i o l i m a x columbianus M i g r a t i n g to S e c t i o n 5 34 Table V I I I . K r u s k a l - W a l l i s Nonparametric A n a l y s i s of V a r i a n c e : A r i o n a t e r M o r t a l i t y 52 Table IX. K r u s k a l - W a l l i s Nonparametric A n a l y s i s of V a r i a n c e : A r i o l i m a x columbianus M o r t a l i t y 52 Table X. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : M i g r a t i o n time A r i o n a t e r 59 VI 1 1 Table XI. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : M i g r a t i o n time A r i o l i m a x columbianus 59 Table X I I . K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight of M i g r a t i n g A r i o n a t e r 68 Table X I I I . K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight of M i g r a t i n g A r i o l i m a x columbianus ... 68 Table XIV. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight Change of M i g r a t i n g A r i o n a t e r 73 Table XV. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight Change of M i g r a t i n g A r i o l i m a x columbianus 73 Table XVI. C o r r e l a t i o n C o e f f i c i e n t s 77 Table XVII. C o r r e l a t i o n C o e f f i c i e n t s 77 Table XVIII. Ar ion a t e r : Summary of R e s u l t s 85 Table XIX. A r i o l i m a x columbianus : Summary of R e s u l t s .... 87 Table XX. L i n e a r Regression A n a l y s i s of Data from Arena Experiments: A r i o n a t e r 117 Table XXI. L i n e a r Regression A n a l y s i s of Data from Arena Experiments: A r i o l i m a x columbianus 119 Table XXII. D e s c r i p t i v e S t a t i s t i c s of Data from Arena Experiments 122 Table XXIII. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e of Frequency D i s t r i b u t i o n of Behaviours Recorded f o r A r i o n a t e r 135 Table XXIV. A n a l y s i s of v a r i a n c e : Nocturnal O b s e r v a t i o n s of A r i o n a t e r Behaviour 143 Table XXV. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e of Frequency D i s t r i b u t i o n s of Behaviours Recorded f o r A r i o l i m a x columbianus 151 Table XXVI. A n a l y s i s of v a r i a n c e : Nocturnal Observations of A r i o l i m a x columbianus Behaviour 160 Table XXVII. Pair w i s e t - t e s t s : P r o p o r t i o n of Feeders E a t i n g Foods A v a i l a b l e 184 X LIST OF FIGURES F i g u r e 1. Layout of Experimental Cages at the P l a n t Science F i e l d S t a t i o n 17 F i g u r e 2. Slug I d e n t i f i c a t i o n Technique 23 F i g u r e 3. M i g r a t i o n Measures P a r t i t i o n e d by Density 39 F i g u r e 4. M i g r a t i o n Measures P a r t i t i o n e d by Food 42 F i g u r e 5. M i g r a t i o n Measures P a r t i t i o n e d by the Food-D e n s i t y I n t e r a c t i o n 45 F i g u r e 6. M i g r a t i o n Measures P a r t i t i o n e d by the Food-Density-Time I n t e r a c t i o n 48 F i g u r e 7. Mean M o r t a l i t y 54 F i g u r e 8. Mean Number of Days to M i g r a t e 61 F i g u r e 9. Mean Weight of Migrants Versus Non-migrants .... 65 F i g u r e 10. Food and Crowding E f f e c t s on Migrant Weight ... 70 F i g u r e 11. Mean M i g r a t i o n Rate of A r i o n a t e r from a l l Treatments P l o t t e d Against Time 79 F i g u r e 12. Mean M i g r a t i o n Rate of A r i o l i m a x columbianus from a l l Treatments P l o t t e d a g a i n s t Time 81 F i g u r e 13. D i s t a n c e Moved per Gram Body Weight Versus Body Weight; A r i o n a t e r I l l F i g u r e 14. D i s t a n c e Moved per Gram Body Weight Versus Body Weight; A r i o l i m a x columbianus 113 x i F i g u r e 15. Distanc e T r a v e l l e d i n One Night Versus Number of Turns 115 F i g u r e 16. Frequency D i s t r i b u t i o n of the Mean P r o p o r t i o n of Ar ion a t e r A c t i v e 137 F i g u r e 17. Mean P r o p o r t i o n of A r i o n a t e r A c t i v e During the Obse r v a t i o n P e r i o d 139 F i g u r e 18. Mean P r o p o r t i o n of A r i o n a t e r Engaged i n Moving, R e s t i n g , and Feeding 145 F i g u r e 19. Frequency D i s t r i b u t i o n of the Mean P r o p o r t i o n of A r i o l i m a x columbianus A c t i v e 153 F i g u r e 20. Mean P r o p o r t i o n of A r i o l i m a x columbianus A c t i v e During the Observation P e r i o d ......155 F i g u r e 21. Mean P r o p o r t i o n of A r i o l i m a x columbianus Engaged i n Moving, R e s t i n g , and Feeding 162 F i g u r e 22. Nocturnal A c t i v i t y on Nights During the Experimental P e r i o d 170 F i g u r e 23. Mean P r o p o r t i o n of P o p u l a t i o n Feeding on A v a i l a b l e Foods 182 x i i Acknowledgements I would l i k e to thank Dr. W. G. W e l l i n g t o n f o r h i s p a t i e n c e , encouragement, and f i n a n c i a l support d u r i n g the work on t h i s t h e s i s . I am indebted to C h a r l e s Hamilton and C y r i l Chui f o r t h e i r h elp i n data c o l l e c t i o n and maintenance of the " s l u g ranch". I t was my p r i v i l e g e to h o l d a U n i v e r s i t y Graduate F e l l o w s h i p d u r i n g my s t u d i e s . F i n a l l y , s p e c i a l thanks to Marnie Parton f o r her support and good humour d u r i n g my bleaker moments. 1 INTRODUCTION Movement i s an animal c h a r a c t e r i s t i c . Even among the s e s s i l e animals, there i s u s u a l l y a m o t i l e l i f e s t a g e . The range of movement may be r e s t r i c t e d to the immediate v i c i n i t y of an animal's roost or burrow, or may cover thousands of k i l o m e t r e s across c o n t i n e n t s or through oceans. Animal movement, i t s causes and e f f e c t s , have i n t r i g u e d r e a s e a r c h e r s f o r many ye a r s . The s u b j e c t has r e c e i v e d much experimental and t h e o r e t i c a l a t t e n t i o n (Baker 1978; Bovbjerg 1959,1975; Cook 1979; Cook et a l . 1969; D i n g l e 1968,1972; G a d g i l 1971; Hamilton and May 1977; Lees 1966,1967). Movement of m o l l u s c s w i t h i n and between h a b i t a t s has not r e c e i v e d much a t t e n t i o n , with most of the emphasis being on homing and t e r r i t o r i a l i t y i n l i m p e t s (Blackford-Cook 1969; Branch 1975; Cook 1971; Cook et a l . 1969; G a l b r a i t h 1965; Stimson 1973). T i d a l m i g r a t i o n s of the s n a i l , Hydrobia ulvae (Newell 1962) and the clam Donax d e n t i c u l a t u s (Trueman 1971) have been i n v e s t i g a t e d . Squires (1957) documented movements of the s q u i d I I l e x i l l e c b r o s u s i n a f i s h i n g a r e a. Edelstam and Palmer (1950) presented evidence of homing by the s n a i l , H e l i x  a s p e r s a . Homing was a l s o found i n the s n a i l , A l l o g o n a profunda by B l i n n (1963). Climbing behaviour of Cepea nemoralis has been i n v e s t i g a t e d by Jaremovic and R o l l o (1979). S t u d i e s on s l u g movement are l i m i t e d to l a b o r a t o r y experiments i n cages designed to i n v e s t i g a t 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 s (Lewis 1969a,b; R o l l o 1978); homing (Cook 2 1979, G e l p e r i n 1974, Newell 1966) and t r a i l f o l l o w i n g (Cook 1977) . L i t t l e work has been done on the movement of s l u g s between h a b i t a t s . T h i s n e g l e c t e d aspect of s l u g ecology needs i n v e s t i g a t i o n i n view of the f a c t that s l u g s can be severe p e s t s i n f i e l d and vegetable crops (Banham and Arrand 1970; Burch 1960; Hanna 1966; Hunter 1968; Hunter et a l . 1968; Hunter and Runham 1971; Runham and Hunter 1970; Stephenson 1968; W i l k i n s o n 1964). Some slug s are intermediate hosts of p a r a s i t e s of w i l d l i f e and can transmit p l a n t d i s e a s e s (Runham and Hunter 1970). More e f f e c t i v e c o n t r o l measures c o u l d be developed i f the f a c t o r s i n i t i a t i n g m i g r a t i o n and the weather c o n d i t i o n s most s u i t a b l e f o r m i g r a t i o n were known. Baker (1978) hypothesized that animals i n i t i a t i n g f a c u l t a t i v e m i g r a t i o n responded to h a b i t a t v a r i a b l e s which s i g n a l the onset of d e c l i n e i n q u a l i t y of the o l d h a b i t a t . S e l e c t i o n should favour animals which assess h a b i t a t s u i t a b i l i t y by the v a r i a b l e s t h a t are most c l o s e l y c o r r e l a t e d with h a b i t a t q u a l i t y . I propose to i n v e s t i g a t e two f a c t o r s that may serve to i n i t i a t e s l u g m i g r a t i o n . Food and p o p u l a t i o n d e n s i t y are thought to a f f e c t the migratory response of animals (Bovjberg 1959,1975; Lees 1966,1967; Rose 1972). Th e r e f o r e , I have focused my r e s e a r c h on s l u g migratory behaviour on these two f a c t o r s . Food may a l s o i n i t i a t e m i g r a t i o n . P r o p o r t i o n a t e l y more s t a r v e d than fed milkweed bugs made long f l i g h t s (Dingle 1968). 3 Haufe (1962) found that s t a r v a t i o n a l t e r e d the f l i g h t t h r e s h o l d s of the mosquito, Aedes a e g y p t i . Food may have a s i m i l a r e f f e c t on slug s and I inte n d to i n v e s t i g a t e t h i s e f f e c t with my experiments. Baker (1978) s t a t e d that the r a t e of cont a c t with s u i t a b l e food was one of two h a b i t a t v a r i a b l e s which was c o r r e l a t e d with h a b i t a t s u i t a b i l i t y . The r a t e of contact with c o n s p e c i f i c s was the other. Cohen (1967) made a s i m i l a r statement regarding food and p o p u l a t i o n d e n s i t y . Although v a r i o u s foods i n s l u g h a b i t a t s appear s e a s o n a l l y , the p e r i o d s when they are u n a v a i l a b l e or u n s u i t a b l e may not be p r e c i s e l y p r e d i c t a b l e . Changes i n a c c e p t a b i l i t y may be due to senescence and decay, p r o d u c t i o n of t o x i c secondary p l a n t products, or consumption by competitors (Cates and Ori a n s 1975). Slug m i g r a t i o n would probably be i n response to c u r r e n t a d v e r s i t y r a t h e r than an innate response independent of c u r r e n t c o n d i t i o n s . Encounters between c o n s p e c i f i c s w i l l i n c r e a s e as p o p u l a t i o n d e n s i t y i n c r e a s e s . Contact between c o n s p e c i f i c s may not be necessary f o r gauging p o p u l a t i o n d e n s i t y . I n d i v i d u a l s c o u l d a l s o o b t a i n i n f o r m a t i o n about d e n s i t y from t r a c k s , faeces, pheromones, or p a r t i a l l y consumed food l e f t behind by c o n s p e c i f i c s . P o p u l a t i o n d e n s i t y i s an important h a b i t a t v a r i a b l e i n f l u e n c i n g m i g r a t i o n . M i g r a t i o n i n the European r a b b i t , O r y c t o l a g u s c u n i c u l u s , was i n i t i a t e d by inadequate food, but the d i r e c t i o n of movement was always from h i g h - to low-density p o p u l a t i o n s (Myers and Poole 1961). Bovbjerg (1959) 4 demonstrated t h a t high c r a y f i s h d e n s i t i e s i n the l a b o r a t o r y r e s u l t e d i n higher d i s p e r s a l r a t e s than low d e n s i t i e s . P o p u l a t i o n d e n s i t y may a l s o i n i t i a t e s l u g m i g r a t i o n , e s p e c i a l l y i n l i g h t of R o l l o ' s (1978) d i s c o v e r y of t e r r i t o r i a l l y i n some s l u g s p e c i e s . Weather i s a d r i v i n g v a r i a b l e and may a f f e c t a l l of these f a c t o r s . Weather can change the s t r u c t u r e of a h a b i t a t , but weather and p o p u l a t i o n d e n s i t y a c t i n g together can a f f e c t the s u i t a b i l i t y and a v a i l a b i l i t y of s h e l t e r s ( B i r c h 1957, Thompson et a l . 1976). S h e l t e r i s important to s l u g s because a good s h e l t e r p r o t e c t s them from the heat of the day and helps them maintain adequate h y d r a t i o n . Weather a l s o p r o v i d e s a range of c l i m a t i c c o n d i t i o n s which l i m i t s l u g a c t i v i t y . Since s l u g s have no p h y s i o l o g i c a l mechanism to p r o t e c t them from c o l d or d e s i c c a t i o n , t h e i r behaviour i s c l o s e l y c o n s t r a i n e d on a d a i l y and y e a r l y b a s i s by changing weather and c l i m a t e . A number of q u e s t i o n s arose from t h i s assumption. Would d i f f e r e n t food and d e n s i t y regimes have any e f f e c t on n i g h t l y , weekly, and seasonal behaviour of slugs? Could s t r e s s f u l food and d e n s i t y c o n d i t i o n s induce m i g r a t i o n i n s l u g s ? Which f a c t o r i s more important in i n i t i a t i n g m i g r a t i o n ? Is there a p a r t i c u l a r type of s l u g that i s most l i k e l y to migrate? What e f f e c t does weather have on the migratory response? Is t h i s type of behaviour adaptive? 5 My experiments designed to answer these q u e s t i o n s are d i v i d e d i n t o three groups. The f i r s t group d e a l s with the e f f e c t s of d i f f e r e n t food and d e n s i t y regimes on the migratory behaviour of A r i o n a t e r and A r i o l i m a x columbianus. T h i s s e c t i o n a l s o p r e s e n t s evidence of seasonal p a t t e r n s i n migratory behaviour and m e t e o r o l o g i c a l c o n s t r i a n t s on a c t i v i t y . Part two i s concerned with i n v e s t i g a t i n g the r e l a t i o n s h i p between s l u g weight and locomotory behaviour and r e l a t i n g i t to d i f f e r e n c e s between migrants and non-migrants. In p a r t three, n o c t u r n a l behaviour of both s p e c i e s i s i n v e s t i g a t e d h o u r l y . The e f f e c t s of d i f f e r e n t food and d e n s i t y regimes on the p a t t e r n of a c t i v i t y and the time devoted to v a r i o u s behaviours are d i s c u s s e d . C o r r e l a t i o n and r e g r e s s i o n a n a l y s i s i s used to determine which weather f a c t o r s best account f o r v a r i a t i o n i n s l u g a c t i v i t y , and the importance of weather i n r e g u l a t i n g s l u g a c t i v i t y i s d i s c u s s e d . The terminology I have adopted f o r t h i s work r e q u i r e s some i n t r o d u c t i o n and e x p l a n a t i o n . Baker (1978) and Cloudsey-Thompson (1978) p o i n t out that movement forms a continuum from change i n p o s i t i o n between one p a r t of a p l a n t and another, to p e r i o d i c r e t u r n between widely separated geographic areas, and that c l e a r d i f f e r e n c e s between these v a r i o u s types of movement do not e x i s t . Terms used to d e s c r i b e such movement o f t e n o v e r l a p or c o n f l i c t i n t h e i r d e f i n i t i o n s . Baker (1978) p o i n t e d out that W i l l i a m s ' (1960) d e f i n i t i o n 6 of m i g r a t i o n as s t r a i g h t e n e d - o u t f l i g h t under an animal's c o n t r o l was out of favour because there were many counter-examples of l e s s - t h a n - s t r a i g h t migratory paths and examples of many i n s e c t s that were d i s p l a c e d by wind c u r r e n t s over which they had no c o n t r o l once they were caught up i n them. P e r s i s t e n t f l i g h t and a t t e n u a t i o n of v e g e t a t i v e f u n c t i o n s , which formed the b a s i s of Kennedy's (1961) d e f i n i t i o n was u n s u i t a b l e because many swarming i n s e c t s f l y p e r s i s t e n t l y over a marker and go nowhere. In a d d i t i o n , the d e f i n i t i o n f a i l s to account f o r r o o s t i n g behaviour d u r i n g m i g r a t i o n , and the f a c t that l o c u s t s feed while m i g r a t i n g and many f l i e s , b u t t e r f l i e s , and d r a g o n f l i e s mate duri n g m i g r a t i o n . Baker (1978) s t a t e d that although Johnson (1969) was c o r r e c t i n m a i n t a i n i n g t h a t a b e h a v i o u r a l d e f i n i t i o n c o u l d only p a r t i a l l y d e s c r i b e m i g r a t i o n , h i s d e f i n i t i o n of m i g r a t i o n as a d a p t i v e change of breeding h a b i t a t was hampered by the f a c t t h a t the d e f i n i t i o n excluded a l l of the r e t u r n m i g r a t i o n s shown by v e r t e b r a t e s and the vagueness a s s o c i a t e d with the term " h a b i t a t " . Baker (1978) has produced the f o l l o w i n g d e f i n i t i o n s : Movement- change in p o s i t i o n Locomotion- movement of an animal achieved by f o r c e e x e r t e d by the animal T r i v i a l movement- movement of an animal from one p o i n t to another i n which the end p o i n t was w i t h i n the sensory range of 7 the animal before i t vacated i t s s t a r t i n g p o i n t M i g r a t i o n - the act of moving from one s p a t i a l u n i t to another T h i s d e f i n i t i o n of m i g r a t i o n seems vague and a l l - i n c l u s i v e because of the f l e x i b i l i t y i n d e f i n i n g the term " s p a t i a l u n i t " . Baker defended h i s c h o i c e by s t a t i n g that " s p a t i a l u n i t " was not laden with overtones a s s o c i a t e d with words such as " h a b i t a t " or "place of abode". However, he r e v e r t s to using " h a b i t a t " f o r " s p a t i a l u n i t " throughout h i s t e x t . Baker sharpens h i s d e f i n i t i o n of m i g r a t i o n by c r e a t i n g a h e i r a r c h y of types of m i g r a t i o n based on f a c t o r s i n i t i a t i n g i t , the d e s t i n a t i o n , and p e r i o d i c i t y of m i g r a t i o n . Since Baker's i s the most up-to-date and comprehensive t r e a t i s e on m i g r a t i o n , I w i l l use h i s d e f i n i t i o n i n t h i s t h e s i s . 8 PART 1. SLUG DENSITY AND FOOD MANIPULATION EXPERIMENTS 1.1 I n t r o d u c t i o n The experiments in t h i s s e c t i o n were conducted to i n v e s t i g a t e the e f f e c t s of food q u a l i t y and q u a n t i t y and s l u g d e n s i t y on the migratory behaviour of A r i o n a t e r and A r i o l i m a x columbianus . The e f f e c t i v e n e s s of each f a c t o r i n i n d u c i n g m i g r a t i o n was assessed. The data were a l s o analysed to d e t e c t seasonal trends i n m i g r a t i o n . A c l a s s i f i c a t i o n of migrants and non-migrants on the b a s i s of weight was i n v e s t i g a t e d . 1.2 Methods These experiments were conducted outdoors i n wooden e n c l o s u r e s i n a f a l l o w f i e l d near the U n i v e r s i t y of B r i t i s h Columbia P l a n t Science F i e l d L a b o r a t o r y . The e n c l o s u r e s were 15 cm hi g h , 1 m wide, and 5 m long, d i v i d e d along t h e i r long a x i s i n t o f i v e e q i v a l e n t 1 m2 s e c t i o n s by a ramp of sod and a s t r i p of plywood 1 m wide and 7.6 cm hig h ( P l a t e 1 ) . The ramp was c o n s t r u c t e d so that the slugs c o u l d only move over i t away from t h e i r s t a r t i n g a r e a . T h i s u n i d i r e c t i o n a l arrangement was ach i e v e d by p l a c i n g the s t r i p of wood at an acute angle to the ground on the o u t s i d e of the sod ramp (P l a t e 1 ) . T h i s slope allowed the s l u g s to climb up and f a l l or s t r e t c h down to the ground i n the next s e c t i o n . Once the s l u g s were over, although 9 they c o u l d have returned, they seemed r e l u c t a n t to climb back up the wood on the o u t s i d e of the ramp, perhaps because the angle of the wooden s t r i p would have f o r c e d them to bend too s h a r p l y i f they attempted to climb i t . The e n c l o s u r e s were open to the elements. Escape was prevented by a simple e l e c t r i c a l system. Two stra n d s of 20-gauge t i n n e d copper wire were s t a p l e d 2 cm apart and 4 cm from the top edge along the i n s i d e perimeter of each cage. The p a i r of wires from a cage were a t t a c h e d to the p o s i t i v e and negative t e r m i n a l of a 12 v, 4 amp g e l storage b a t t e r y to c r e a t e an open c i r c u i t . When a s l u g attempted to leave the cage the c i r c u i t was c l o s e d as soon as the s l u g c r o s s e d the w i r e s . The e l e c t r i c shock caused the s l u g to s e c r e t e copious amounts of mucus, withdraw i t s head and t e n t a c l e s under i t s mantle, and q u i c k l y c o n t r a c t i t s body. T h i s a v e r s i v e stimulus was u s u a l l y enough to make the s l u g turn back i n t o the cage or drop from the w a l l . T h i s system worked w e l l f o r most s i z e s of s l u g s used i n these experiments, but dur i n g the e a r l y s p r i n g some small A r i o n a t e r were k i l l e d because they were trapped on the wires by t h e i r s l i m e . In a d d i t i o n , some very l a r g e A r i o l i m a x columbianus were able to arch t h e i r bodies over the wires and thereby escape without r e c e i v i n g a shock. A 3-cm wide cap was p l a c e d around the top perimeter of each cage to p r o t e c t the wires from r a i n or dew which c o u l d cause short c i r c u i t s . In the s p r i n g the i n s i d e perimeter of the cages and the s i d e s of the ramp f a c i n g away from the treatment areas were 10 sprayed with Paraquot to k i l l the grass , then the e a r t h along the edges of the cages was compressed to remove any c r e v i c e s i n which the s l u g s might s h e l t e r . The remaining grass was c l i p p e d s h o r t to remove p o t e n t i a l s h e l t e r s at the base of the clumps, and any p o t e n t i a l food. The grass was not otherwise maintained. Each 1 m* s e c t i o n of each cage was s u p p l i e d with at l e a s t one s h e l t e r ; 45.7 cm long X 15.2 cm o u t s i d e diameter concrete drainage t i l e p l a c e d v e r t i c a l l y i n a c y l i n d r i c a l h o l e . Each s h e l t e r had a 15.2 X 15.2 cm l i d of plywood with a 1.9 cm hole i n i t s c e n t r e to serve as an e n t r a n c e / e x i t . The treatment areas each c o n t a i n e d three such s h e l t e r s ( P l a t e 2 ) . I f a l l three were not needed f o r a p a r t i c u l a r experiment, the s h e l t e r s c o u l d be c l o s e d with s o l i d squares of plywood that had no e n t r a n c e / e x i t h o l e . E a r t h was p i l e d around the edges of these c l o s e d s h e l t e r s to prevent the s l u g s from e n t e r i n g through the spaces between the plywood and the t i l e s . Since moles sometimes caused problems by f i l l i n g the s h e l t e r s with d i r t from t h e i r e x c a v a t i o n s , d i s c s of 0.64 X 0.64 cm g a l v a n i z e d wire mesh were p l a c e d i n the bottom of some s h e l t e r s to prevent access from below. The s h e l t e r s r e c e i v e d no s p e c i a l treatment except removal of dead animals and any l a r g e accumulations of faeces. During the drought the s h e l t e r s were sprayed d a i l y with water to reduce the d e s i c c a t i n g e f f e c t s of low s h e l t e r humidity and h i g h a i r temperatures. Since the cages were l e f t open to the elements to f a c i l i t a t e data c o l l e c t i o n and o b s e r v a t i o n , the s l u g s , e s p e c i a l l y A r i o l i m a x columbianus , 11 were exposed to more severe d a i l y weather c o n d i t i o n s than they would have experienced i n n a t u r a l s i t u a t i o n s . Some consequences of t h i s exposure w i l l be d i s c u s s e d l a t e r . There were s i x t e e n cages ( P l a t e 3). E i g h t were a l l o t t e d to each s p e c i e s t o allow two r e p l i c a t e s of the four experimental treatments to be run sim u l t a n e o u s l y (Figure 1 ) . Four of each set of e i g h t cages had t h e i r long a x i s a l i g n e d i n a N-S d i r e c t i o n , while the other, four were o r i e n t e d E-W to confound any d i r e c t i o n a l b i a s caused by the l o c a l environment or the cages. Slugs were c o l l e c t e d p e r i o d i c a l l y i n excess of those needed c u r r e n t l y and kept i n re s e r v e i n one of two covered f i e l d e n c l o s u r e s . The 1.5 X 4.0 m perimeter of these cages was made of 10 cm corrugated p l a s t i c garden edging m a t e r i a l . A cover of f i n e p l a s t i c window screen was s t a p l e d to each p l a s t i c fence. The c o v e r i n g screen was supported by three arches of 5 X 0.64 cm f l a t s t e e l t r e a t e d with primer to prevent r u s t . Three 20 X 20 cm ceramic pots with 25 X 25 X 2.5 cm wooden l i d s with c e n t r a l e n t r a n c e / e x i t holes p r o v i d e d s h e l t e r i n each cage. The spe c i e s were kept separate, one i n each cage. A r i o n a t e r was c o l l e c t e d at n i g h t on the U n i v e r s i t y of B r i t i s h Columbia Endowment Lands. The best s i t e s f o r c o l l e c t i n g t h i s s p e c i e s were t y p i c a l l y at the forest-meadow i n t e r f a c e . They were r a r e l y found deeper i n the f o r e s t . A r i o n a t e r was u s u a l l y c o l l e c t e d while i t was a c t i v e and f o r a g i n g . Apparently these s l u g s s h e l t e r e d by day at the f o r e s t edge and foraged at 12 night i n the nearby g r a s s . Adequate numbers of A r i o n a t e r were obtained from two adjacent s i t e s on e i t h e r s i d e of a road. A r i o l i m a x columbianus was c o l l e c t e d from s i t e s on the U n i v e r s i t y of B r i t i s h Columbia Endowment Lands d u r i n g the daytime p e r i o d of i n a c t i v i t y . T h i s s p e c i e s was e a s i l y found throughout the f o r e s t , t y p i c a l l y s h e l t e r i n g on f a l l e n , moist, moss-covered r o t t i n g l o g s . Before the s l u g s were p l a c e d i n the reserve cages they were kept ov e r n i g h t i n a growth chamber at 15°C. In the morning the slugs were i n d i v i d u a l l y marked by means of a l i q u i d n i t r o g e n branding technique developed by R i c h t e r (1973,1976b) (Figure 2, P l a t e 4 ) . A r i o l i m a x columbianus r e t a i n e d i t s mark longer and with b e t t e r c l a r i t y than A r i o n a t e r , s i n c e t i s s u e r e g e n e r a t i o n i n the l a t t e r o f t e n o b l i t e r a t e d the brand w i t h i n four to s i x weeks. A f t e r being marked, the s l u g s were p l a c e d as needed i n the reserve cages or experimental cages. In the present experiments the q u a n t i t y and q u a l i t y of the food regime v a r i e d simultaneously so t h e i r separate e f f e c t s on s l u g behaviour c o u l d not be d i s t i n g u i s h e d . Two food regimes were e s t a b l i s h e d at op p o s i t e ends of a food s u i t a b i l i t y s c a l e to e s t a b l i s h b a s e l i n e responses to food m a n i p u l a t i o n . Slugs that experienced a " Good " food regime were given more wheat b r a n , c a r r o t root,and potato tuber than they c o u l d consume i n one sample p e r i o d . A " Poor " food regime p r o v i d e d the s l u g s with i n s u f f i c i e n t c e l e r y s t a l k s f o r one sample p e r i o d . The foods were chosen a f t e r a p r e l i m i n a r y f e e d i n g study, and by 13 comparing the t a b u l a t e d v a l u e s of t h e i r v a r i o u s n u t r i t i o n a l a s p e c t s , such as amount of p r o t e i n , f a t , carbohydrate, and c a l o r i c value per gram. The amounts of food s u p p l i e d were determined beforehand by t r i a l and e r r o r . I n t e r a c t i o n s between c o n s p e c i f i c s p l a y an important r o l e in the spacing behaviour of many animals (Brown and Orians 1970; Hunter 1968b,c; Watson and Moss 1970). An i n c r e a s e i n p o p u l a t i o n d e n s i t y i n a f i n i t e area may r e s u l t i n more p o s s i b l e c o n t a c t s between i n d i v i d u a l s . The outcome of i n c r e a s e d c o n t a c t depends on the b i o l o g y of the s p e c i e s . R o l l o ' s (1978) r e p o r t of a g g r e s s i v e n e s s i n s l u g s l e d me to b e l i e v e that the degree of crowding i n a c o n f i n e d area might be an important f a c t o r m ediating s l u g movement. Two d e n s i t i e s of s l u g s and s h e l t e r s were used. The " Crowded " s i t u a t i o n comprised twenty slu g s p r o v i d e d with only one s h e l t e r , whereas the " Uncrowded " s i t u a t i o n used ten s l u g s and t h r e e s h e l t e r s . Hence, s h e l t e r q u a l i t y was a f u n c t i o n of q u a n t i t y . The number of s l u g s i n each regime was chosen mainly f o r convenience, but i t should be noted that under c e r t a i n n a t u r a l c o n d i t i o n s with i d e a l food and s h e l t e r , ten s l u g s per m2 would not be unusual. The occurrence of twenty s l u g s per m2 of the s p e c i e s used i n these experiments would be h i g h l y u n l i k e l y i n most f i e l d s i t u a t i o n s . The Food and D e n s i t y f a c t o r s were arranged i n four experimental treatments as f o l l o w s : In the A treatment the s l u g s were "uncrowded" and r e c e i v e d 14 "good food". The B treatment s l u g s were "crowded" and r e c e i v e d "good food". The d e n s i t y f a c t o r was "uncrowded" and the food f a c t o r was "poor food" i n treatment C. The D treatment sl u g s were "crowded" and r e c e i v e d "poor food". The treatments w i l l subsequently be i d e n t i f i e d as A, B, C, or D. The f o l l o w i n g experimental d e s i g n was used to i n v e s t i g a t e the e f f e c t s of food and d e n s i t y m a n i p u l a t i o n on A r i o n a t e r and A r i o l i m a x columbianus . Two r e p l i c a t e s of each of the four treatments were e s t a b l i s h e d i n the e i g h t e n c l o s u r e s a v a i l a b l e f o r each s p e c i e s . The treatments were assigned to the four cages at random with the s t i p u l a t i o n that one of each treatment was i n the N-S and one i n the E-W o r i e n t e d cages r e s p e c t i v e l y . The experiment ran f o r 36 days, a f t e r which a l l the s l u g s were removed, the e n c l o s u r e s were cl e a n e d , and another 36-day set of r e p l i c a t e s was begun. T h i s experiment was r e p l i c a t e d twice f o r A r i o l i m a x columbianus and three times f o r A r i o n a t e r , g i v i n g a t o t a l of four and s i x r e p l i c a t e s r e s p e c t i v e l y (see F i g u r e 1). Data were c o l l e c t e d on every t h i r d day, food was renewed, and enough s l u g s were added to each e n c l o s u r e so that t h e i r numbers were e q u i v a l e n t to the number d i c t a t e d by the type of treatment. 15 Table I. Dates of D e n s i t y and Food M a n i p u l a t i o n Experiments A r i o n a t e r R e p l i c a t e s Dates D u r a t i o n 1,2 May 27 - J u l y 2, 1979 36 day 3,4 J u l y 2 - August 7, 1979 36 day 5,6 August 8 - September 12, 1979 35 day A r i o l i m a x columbianus R e p l i c a t e s Dates D u r a t i o n 1,2 June 14 - J u l y 20, 1979 36 day 3,4 J u l y 21 - August 25, 1979 36 day 17 F i g u r e 1. Layout of Experimental Cages at the P l a n t Science F i e l d S t a t i o n A: e i g h t cages used f o r A r i o n a t e r B: reserve cages C: e i g h t cages used f o r A r i o l i m a x columbianus /\: i n d i c a t e s treatment area and d i r e c t i o n of s l u g movement P l a t e 1. Long View of an Experimental Cage P l a t e 2. View of Treatment Area of a Cage 21 P l a t e 3. Experimental S i t e at U n i v e r s i t y of B r i t i s h Columbia P l a n t Science F i e l d S t a t i o n P l a t e 4. F i v e A r i o l i m a x columbianus Feeding on C a r r o t Note brand marks on mantles 23 F i g u r e 2. Slug I d e n t i f i c a t i o n Technique upper: numbering sequence f o r brand lower: s l u g with 945 branded on i t s mantle 24 25 The f o l l o w i n g data were c o l l e c t e d on each sampling day: the number of s l u g s i n each compartment, the numbers of dead or unaccounted, and the number of eggs i n each of the f i v e compartments of the e n c l o s u r e s , as w e l l as the weight and i d e n t i f i c a t i o n number of any s l u g s i n the compartment f a r t h e s t from the treatment a r e a . D a i l y maximum and minimum temperatures, n o c t u r n a l minimum temperature, minimum grass temperature, and d a i l y p r e c i p i t a t i o n were obtained from the U n i v e r s i t y of B r i t i s h Columbia Weather S t a t i o n l o c a t e d at the U n i v e r s i t y of B r i t i s h Columbia P l a n t Science F i e l d Laboratory, which was about 100 m from the e n c l o s u r e s . A l l data were entered on coding sheets f o r subsequent keypunching and a n a l y s i s . 26 1.3 R e s u l t s 1.3.1 M i g r a t i o n Measures In order to d i s c e r n any e f f e c t s of the food and d e n s i t y manipulations on s l u g movement the raw data were used to c a l c u l a t e three i n d i c a t o r s of migr a t o r y movement. The f i r s t was the p r o b a b i l i t y of m i g r a t i o n c a l c u l a t e d f o l l o w i n g the formula given by Roff (1977): P=l-(n/N)T (1) Where P i s the p r o b a b i l i t y of m i g r a t i o n , N i s the i n i t i a l number of s l u g s i n the treatment a r e a , and n i s the number of slugs remaining i n the treatment area a f t e r T days. T h i s d e s c r i p t i v e s t a t i s t i c gave the p r o b a b i l i t y that s l u g s had l e f t the treatment a r e a . The second i n d i c a t o r expressed the m i g r a t i o n r a t e as the p r o p o r t i o n of the p o p u l a t i o n moving per day and was determined by equation 2: R=[N2/N1+(N3/(N1+N2))+(N4/(Nl+N2+N3))+( N5/(N1+N2+N3+N4))]/D (2) 27 Where R i s the m i g r a t i o n r a t e , Ni i s i s the number of s l u g s i n each s e c t i o n on the sampling days, i = l - 5 . D i s the l e n g t h of the sample p e r i o d , which f o r these experiments i s three days. Nl i s e i t h e r 10.0 or 20.0 depending on the treatment. The t h i r d i n d i c a t o r of m i g r a t i o n c a l c u l a t e d was the p r o p o r t i o n of the p o p u l a t i o n found i n s e c t i o n 5 (the f a r t h e s t from the treatment area) on the sampling day. T h i s p r o p o r t i o n was c a l c u l a t e d from equation 3. Pr=N5/Nl (3) Pr i s the p r o p o r t i o n of slugs r e a c h i n g s e c t i o n 5, N5 i s the number of s l u g s i n s e c t i o n 5 on the sampling day, and Nl i s the i n i t i a l number of s l u g s i n the treatment area, e i t h e r 10.0 or 20.0, depending on the treatment. The number of dead slugs was c a l c u l a t e d f o r each sample p e r i o d by summing the number of dead found i n each s e c t i o n of the e n c l o s u r e . The weather data c o l l e c t e d were averaged so that they c o i n c i d e d with the three-day sampling p e r i o d of the experiment. The mean d a i l y temperature, d a i l y maximum temperature, and d a i l y p r e c i p i t a t i o n f o r the three-day p e r i o d before the data c o l l e c t i o n were each summed and d i v i d e d by 3.0 to give the r e s p e c t i v e means f o r the sample p e r i o d . 28 A n a l y s i s of v a r i a n c e and K r u s k a l - W a l l i s nonparametric a n a l y s i s Of v a r i a n c e were used to determine s i g n i f i c a n c e . Table II summarizes the a n a l y s i s of v a r i a n c e f o r the p r o b a b i l i t y of m i g r a t i o n f o r A r i o n a t e r . D e n s i t y , food, time, and the d e n s i t y - f o o d and d e n s i t y - f o o d - t i m e i n t e r a c t i o n s a l l had s i g n i f i c a n t e f f e c t s on the p r o b a b i l i t y of A r i o n m i g r a t i n g . Table I I I c o n t a i n s the r e s u l t s of the a n a l y s i s of v a r i a n c e of the p r o b a b i l i t y of m i g r a t i o n f o r A r i o l i m a x columbianus Only the food f a c t o r and the f o o d - d e n s i t y i n t e r a c t i o n were not s i g n i f i c a n t , l e a v i n g the b i o l o g i c a l s i g n i f i c a n c e of the d e n s i t y f a c t o r , time and the i n t e r a c t i o n of d e n s i t y , food, and time to be e x p l a i n e d . Tables IV and V present the r e s u l t s of the a n a l y s i s of v a r i a n c e f o r the r e s p e c t i v e m i g r a t i o n r a t e s of A r i o n a t e r and A r i o l i m a x columbianus . The two s p e c i e s d i f f e r e d i n the i n t e n s i t y of t h e i r r e a c t i o n s to the v a r i o u s f a c t o r s . For A r i o n , the only n o n s i g n i f i c a n t i n t e r a c t i o n was between food and d e n s i t y . D e n s i t y , food, and time and the i n t e r a c t i o n of d e n s i t y , food, and time a l l s i g n i f i c a n t l y a f f e c t e d the m i g r a t i o n r a t e of A r i o n . S i m i l a r analyses on the m i g r a t i o n r a t e of A r i o l i m a x i n d i c a t e d that only the i n t e r a c t i o n of d e n s i t y , food, and time was s i g n i f i c a n t . The p r o p o r t i o n of the p o p u l a t i o n reaching s e c t i o n 5 was a n a l y s e d by the K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e . The r e s u l t s f o r A r i o n are shown i n Table VI. The 29 d e n s i t y f a c t o r had a s i g n i f i c a n t e f f e c t on the number of slug s reaching the l a s t s e c t i o n of the e n c l o s u r e s . Although food alone had no e f f e c t on t h i s measure i t s i n t e r a c t i o n with d e n s i t y and time d i d . The comparable a n a l y s i s of the p r o p o r t i o n of A r i o l i m a x columbianus reaching s e c t i o n 5 i s shown in Table V I I . For A r i o l i m a x , only the d e n s i t y f a c t o r had any s i g n i f i c a n t i n f l u e n c e on t h i s measure, the other f a c t o r s d i d not warrant c o n s i d e r a t i o n . 30 Table I I . A n a l y s i s of v a r i a n c e : P r o b a b i l i t y of A r i o n a t e r Migrat ing Table I I I . A n a l y s i s of v a r i a n c e : P r o b a b i l i t y of A r i o l i m a x columbianus M i g r a t i n g Source DF f-v a l u e p r o b a b i l i t y d e n s i t y 1 10. 286 <.001 food 1 10. 286 <.001 time 5 4. 593 <.001 d e n s i t y -food 1 3. 993 .01 d e n s i t y -food-t ime 16 3. 993 <.001 E r r o r 263 T o t a l 287 Source DF f-v a l u e p r o b a b i l i t y d e n s i t y 1 49.321 < .001 food 1 0.265 0 .607 time 3 2.818 0 .041 d e n s i t y -food 1 1.129 0 .290 d e n s i t y -food-t ime 10 3.778 < .001 E r r o r 175 T o t a l 191 32 Table IV. A n a l y s i s of V a r i a n c e : M i g r a t i o n Rate, A r i o n a t e r Table V. A n a l y s i s of V a r i a n c e : M i g r a t i o n Rate, A r i o l i m a x columbianus Source DF f-value p r o b a b i l i t y d e n s i t y 1 21 .407 <. 001 food 1 30 .484 <. 001 time 5 7 .148 <. 001 d e n s i t y -food 1 0 .023 0. 879 d e n s i t y -food-time 16 4 .501 <. 001 E r r o r 263 T o t a l 287 Source DF f-value p r o b a b i l i t y d e n s i t y 1 0 .949 0. 338 food 1 0 .189 0. 112 time 3 2 .547 0. 715 d e n s i t y -food 1 0 .376 0. 540 d e n s i t y -food-time 10 2 .236 0. 018 E r r o r 175 T o t a l 191 34 Table VI. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : P r o p o r t i o n of A r i o n a t e r M i g r a t i n g to S e c t i o n 5. Table V I I . K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : P r o p o r t i o n of A r i o l i m a x columbianus M i g r a t i n g to S e c t i o n 5. Source DF k-value p r o b a b i l i t y d e n s i t y food d e n s i t y -food d e n s i t y -food-t ime 1 1 3 23 13.735 0.702 14.521 72.055 <.001 0.402 0.002 <.001 Source DF k-value p r o b a b i l i t y d e n s i t y 1 4.961 0.026 food 1 0.542 0.462 d e n s i t y -food 3 5.526 0.137 d e n s i t y food-time 15 20.328 0.160 36 The food and d e n s i t y manipulations on A r i o n a t e r and Ar i o l i m a x columbianus r e v e a l e d c e r t a i n t r e n d s . F i g u r e 3a shows the means of the three m i g r a t i o n measures f o r A r i o n p a r t i t i o n e d by the d e n s i t y f a c t o r . On average the crowded c o n d i t i o n s evoked more m i g r a t i o n than the uncrowded c o n d i t i o n s . The same tendency was found i n A r i o l i m a x (Figure 3b); crowded slug s produced higher m i g r a t i o n v a l u e s , except m i g r a t i o n r a t e , than the uncrowded ones. When the r e s u l t s were p a r t i t i o n e d by the food f a c t o r i t was ev i d e n t that the poor food regime had higher mean m i g r a t i o n measures than the good food regime f o r A r i o n ( F i g u r e 4a). A r i o l i m a x data were not s i g n i f i c a n t ( F i gure 4b). F i g u r e 5a shows a s i m i l a r t r e n d f o r each m i g r a t i o n measure of A r i o n when the data are p a r t i t i o n e d by both the food and d e n s i t y f a c t o r s . In most cases the mean m i g r a t i o n measures f o r the treatments can be ordered: A, C, B, D. T h i s o r d e r i n g r e v e a l s that the two treatments with the lowest m i g r a t i o n measures (A,C) shared a common d e n s i t y l e v e l . Both treatments s u b j e c t e d the slug s to lower d e n s i t y l e v e l s than the B and D treatments, although they had d i f f e r e n t food regimes. T h i s f i n d i n g may i n d i c a t e the r e l a t i v e importance of the d e n s i t y and food f a c t o r s on the movement of the s l u g s . T h i s i n t e r a c t i o n had no e f f e c t on the Ar iolimax m i g r a t i o n measures ( F i g u r e 5b). When simultaneous r e p l i c a t e s were averaged by treatment and p l o t t e d over time ( F i g u r e 6) the f o l l o w i n g g e n e r a l i z a t i o n s emerged. The p r o b a b i l i t y of m i g r a t i o n f o r A r i o n a t e r showed two t r e n d s . The C and D treatments showed i n c r e a s i n g mean 37 p r o b a b i l i t y of m i g r a t i o n over the whole experimental p e r i o d , whereas A and B treatments d e c l i n e d from t h e i r i n i t i a l values in the second experimental p e r i o d and in c r e a s e d again i n the f i n a l p e r i o d (Figure 6 a i ) . The mi g r a t i o n r a t e of A r i o n (Figure 6 a i i ) d i d not show such c l e a r trends as the p r o b a b i l i t y of m i g r a t i o n . However, both C and D treatments f o l l o w e d a s i m i l a r t r e n d over time. The mean mig r a t i o n r a t e i n c r e a s e d from the f i r s t to second experimental p e r i o d s and began to p l a t e a u through the t h i r d . A and B treatments d i d not show such a c l o s e r e l a t i o n s h i p . The m i g r a t i o n r a t e of A dropped a s y m p t o t i c a l l y from i t s i n i t i a l value to lower v a l u e s i n the second and t h i r d experimental p e r i o d s , while B remained about the same from the f i r s t to second p e r i o d s and rose i n the t h i r d p e r i o d . The mean p r o p o r t i o n of A r i o n reaching s e c t i o n 5 (Figure 6 a i i i ) showed a c o n s i s t e n t t r e n d . Except i n the D treatment, only small numbers reached the terminus of the enc l o s u r e s d u r i n g the f i r s t two experimental p e r i o d s . A l l treatments showed some i n c r e a s e i n t h i s v a r i a b l e d u r i n g the t h i r d p e r i o d . The mean p r o p o r t i o n of A r i o n r e a c h i n g s e c t i o n 5 in the D treatment i n c r e a s e d from the f i r s t to second p e r i o d and then d e c l i n e d i n the t h i r d , but i t should be noted that i n t h i s as i n a l l other measures, the D treatment u s u a l l y had the high e s t v a l u e s , followed by B or C, with A u s u a l l y having the lowest v a l u e s . Although the experiments with A r i o l i m a x columbianus were sh o r t e r than those f o r A r i o n a t e r , s i m i l a r groupings of treatments with d i f f e r e n t trends over time c o u l d be d e t e c t e d . 38 As with A r i o n , the A and B treatments of A r i o l i m a x v a r i e d i n the same way, and d i f f e r e d from the C and D treatments. The A and B treatments showed an i n c r e a s e over time i n a l l three m i g r a t i o n measures, while the C and D treatments d e c l i n e d ( F i g u r e 6b). The only i n c o n s i s t e n t r e s u l t was the s l i g h t i n c r e a s e of the mean p r o p o r t i o n of m i g r a t i o n i n the C treatments (Figure 6 b i ) . When p a t t e r n s evident i n F i g u r e s 5 and 6 were compared, i t was c l e a r t h a t i f the treatments were not p a r t i t i o n e d by time (Figure 5), the o r d e r i n g was d e n s i t y -based; e.g., as i n F i g u r e 3. If time was i n c l u d e d i n the p a r t i t i o n i n g , then the trends over time appeared to be food-based ( F i g u r e 6). The good-food treatments f o l l o w e d a d i f f e r e n t p a t t e r n than the poor-food treatments. There are seasonal trends i n A r i o n and A r i o l i m a x behaviour and they appear to be m o d i f i e d by the d e n s i t y and food f a c t o r s . 39 F i g u r e 3. M i g r a t i o n Measures P a r t i t i o n e d by Densit y a: A r i o n a t e r b: A r i o l i m a x columbianus the v a l u e s p l o t t e d i n t h i s and a l l subsequent f i g u r e s are the means and the v e r t i c a l l i n e s are the Standard E r r o r s of the mean. 40 a i L O W HIGH S L U G D E N S I T Y a n .20 I LU h-< fx .15 < fX o 10 L O W HIGH a m .15 LU o < o D Z LU .10 O t-rx O CL O DC 0- .05 L O W HIGH S L U G D E N S I T Y S L U G D E N S I T Y 41 b i >-_J CO < CQ O DC CL z o h-< cn L O W H I G H S L U G D E N S I T Y b i i .15 f LU < cr o < CC o .10 L O W H I G H S L U G D E N S I T Y b i i i .05 LU O < Q LU O Q .03 LU o cc o CL o cc CL .01 L O W H I G H S L U G D E N S I T Y 42 F i g u r e 4. M i g r a t i o n Measures P a r t i t i o n e d by Food a: A r i o n a t e r b: A r i o l i m a x columbianus a i CQ < CQ o cc CL < rx o GOOD POOR FOOD .20 B-a n GOOD POOR FOOD a m .15 LU < o LL o Q LU .10 fX o 0-O fx 0- .05 I-GOOD POOR FOOD 44 b i .45 4 0 >-- J m < m o £ 3 5 o I -< cc ^ .30 G O O D P O O R F O O D b i i .20 .15 UJ Sc CL z O < cc CD 5 10 G O O D P O O R F O O D b i i i UJ (3 < o LL O 05 LU .03 2 o I-cn O Q. o cr a .01 G O O D P O O R F O O D 45 F i g u r e 5. M i g r a t i o n Measures P a r t i t i o n e d by the Food-Density I n t e r a c t i o n a: A r i o n a t e r b: A r i o l i m a x columbianus treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 46 a i >-t o cr < cr 5 B TREATMENT a n TREATMENT a m CD < o 2 o TREATMENT o cc • 2 B TREATMENT b i i b i i i <2 5 TREATMENT o cr 2 o CC TREATMENT 48 F i g u r e 6. M i g r a t i o n Measures P a r t i t i o n e d by the Food-Density-Time I n t e r a c t i o n a: A r i o n a t e r b: A r i o l i m a x columbianus treatments A: uncrowded, good food © B: crowded, good food 3 C: uncrowded, poor food Q D: crowded, poor food €) MIGRATION RATE u o Jj-m > —< m CO PROPORTION AT END OF CAGE 33 m o > —I m VO bi 51 1.3.2 M o r t a l i t y A K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e of the m o r t a l i t y data i s given i n Tables VIII and IX f o r A r i o n a t e r and A r i o l i m a x columbianus , r e s p e c t i v e l y . The r e s u l t s of the a n a l y s i s were the same f o r both s p e c i e s . The food f a c t o r had no e f f e c t on the mean m o r t a l i t y , whereas the crowding f a c t o r d i d . Mean m o r t a l i t y was higher i n crowded e n c l o s u r e s . The i n t e r a c t i o n between d e n s i t y and food was s i g n i f i c a n t . The lowest mean m o r t a l i t y o c c u r r e d i n the A and C treatments , i n which the s l u g s experienced, low d e n s i t i e s but d i f f e r e n t food regimes. The highest mean m o r t a l i t y o c c u r r e d i n the B and D treatments, which r e c e i v e d d i f f e r e n t food regimes but the same high s l u g d e n s i t i e s (Figure 7 a i i i , b i i i ) . I t i s c l e a r that d e n s i t y s t r o n g l y a f f e c t e d s l u g m o r t a l i t y . Under crowded c o n d i t i o n s there may not have been enough r e s t i n g p o s i t i o n s i n the s h e l t e r s to p r o t e c t a l l of the slug s from heat and e v a p o r a t i v e s t r e s s . I n c r e a s i n g m o r t a l i t y through the summer probably r e s u l t e d from d e t e r i o r a t i n g weather and the n a t u r a l l i f e c y c l e of these s l u g s , e s p e c i a l l y A r i o n a t e r which d i e s s h o r t l y a f t e r e g g - l a y i n g . 52 Table V I I I . K r u s k a l - W a l l i s Nonparametric A n a l y s i s of V a r i a n c e : A r i o n a t e r M o r t a l i t y Table IX. K r u s k a l - W a l l i s Nonparametric A n a l y s i s of V a r i a n c e : A r i o l i m a x columbianus M o r t a l i t y Source DF k-value p r o b a b i l i t y d e n s i t y food d e n s i t y -food d e n s i t y -food-time 1 1 3 23 23.682 0.256 23.982 58.520 <.001 0.613 <.001 <.001 Source DF k-value p r o b a b i l i t y d e n s i t y food d e n s i t y -food d e n s i t y -food-time 1 1 3 12.369 0.256 13.651 15 41.285 <.001 0.613 0.003 <.001 54 F i g u r e 7. Mean M o r t a l i t y a: A r i o n a t e r and b: A r i o l i m a x columbianus treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 55 a i 2.5 1.5 >-2 tr O LOW HIGH SLUG DENSITY a n 18 r 1.4 >-cc .o 1.0 GOOD POOR FOOD aiv LOW HIGH SLUG DENSITY GOOD POOR FOOD 57 1 ._3 . 3 Days to Migrate Since each s l u g was i n d i v i d u a l l y marked i t was p o s s i b l e to determine how many days the s l u g took to move through i t s en c l o s u r e by checking the dates when i t was f i r s t i n t roduced and when i t reached the l a s t compartment. Table X g i v e s the r e s u l t s of a K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e of m i g r a t i o n time f o r A r i o n a t e r . The d e n s i t y f a c t o r had a s i g n i f i c a n t e f f e c t on the m i g r a t i o n time but the food f a c t o r d i d not. Fi g u r e 8ai shows that A r i o n took longer to migrate i n the uncrowded e n c l o s u r e s . The d e n s i t y - f o o d i n t e r a c t i o n and the i n t e r a c t i o n of d e n s i t y , food, and time were a l s o s i g n i f i c a n t . F i g u r e 8 a i i i i l l u s t r a t e s the mean m i g r a t i o n time p l o t t e d by treatment f o r A r i o n a t e r . These data c o u l d be grouped l i k e the m i g r a t i o n measures and the m o r t a l i t y data. The A and C treatments had longer mean m i g r a t i o n times than the B and D treatments. As before, t h i s grouping was based on the d e n s i t y f a c t o r . Slugs took longer to migrate i n the f i r s t and t h i r d experimental p e r i o d s than i n the second ( F i g u r e 8 a i v ) . The i n c r e a s e d u r i n g the l a s t p e r i o d d i d not reach v a l u e s as high as those f o r the f i r s t p e r i o d . There was no grouping of treatments evident i n the f i r s t p e r i o d . In the second p e r i o d , a l l treatments except A shared s i m i l a r low v a l u e s , and the t h i r d p e r i o d means were grouped on the b a s i s of the d e n s i t y f a c t o r . 58 R e s u l t s of a s i m i l a r a n a l y s i s on the m i g r a t i o n time of A r i o l i m a x columbianus are shown i n Table XI. N e i t h e r d e n s i t y nor food had any s i g n i f i c a n t e f f e c t on m i g r a t i o n time ( F i g u r e 8 b i , i i ) ; - only the i n t e r a c t i o n between d e n s i t y , food, and time was s i g n i f i c a n t . F i g u r e 8biv shows the mean m i g r a t i o n time p l o t t e d by treatment f o r A r i o l i m a x columbianus . There were two o p p o s i t e trends i n the data. The groupings had no common f a c t o r , but these r e s u l t s should be i n t e r p r e t e d c a u t i o u s l y because the sample s i z e f o r each p o i n t was s m a l l . Fewer A r i o l i m a x than A r i o n migrated to s e c t i o n 5. 59 Table X. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : M i g r a t i o n time A r i o n a t e r Table XI. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : M i g r a t i o n time A r i o l i m a x columbianus Source DF k-value p r o b a b i l i t y d e n s i t y 1 7.292 0.007 food 1 0.969 0.325 d e n s i t y -food 3 8.294 0.040 d e n s i t y -food-time 23 63.429 <.001 source DF k-value p r o b a b i l i t y d e n s i t y 1 0.002 0.957 food 1 1.692 0.193 d e n s i t y -food 3 3.519 0.318 d e n s i t y -food-time 13 22.405 0.049 61 F i g u r e 8. Mean Number of Days to Migrate a: A r i o n a t e r and b: A r i o l i m a x columbianus treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 62 a i 11 UJ I-< , CC 9 CD ' O I— co > LOW HIGH SLUG DENSITY a n 9 r-UJ h-< CC 8 CD co a 71-GOOD. POOR FOOD 63 b i 20 LU Q a,. L O W HIGH S L U G DENSITY b i i 16 r 12 G O O D POOR F O O D h i i i 18 LU rx 2 CO I 10 h 0 biv 18 10 e / / A B C T R E A T M E N T D 1,2 3,4 R E P L I C A T E S 64 1.3.4 Weight of Migrants F i g u r e 9 compares the mean weights of m i g r a t i n g and non-migrating s l u g s of both species,and shows that m i g r a t i n g s l u g s were he a v i e r than non-migrating s l u g s . A t - t e s t r e v e a l e d that t h i s d i f f e r e n c e was s i g n i f i c a n t only f o r A r i o n a t e r (t= 5.620 p<0.001 df=1768). The d i f f e r e n c e f o r A r i o l i m a x columbianus was not s i g n i f i c a n t (t=0.845 p>0.50 df=769). F i g u r e 9 a l s o demonstrates the f a c t t h a t A r i o l i m a x was a l a r g e r s l u g than A r i o n . Both migrant and non-migrant A r i o l i m a x were more than twice the weight of comparable A r i o n . 65 F i g u r e 9. Mean Weight of Migrants Versus Non-migrants a: A r i o n a t e r and b: A r i o l i m a x columbianus 6. Y x o LU B 16 15. 14. NON-MIGRANTS MIGRANTS 67 The r e s u l t s of K r u s k a l - W a l l i s nonparametric a n a l y s i s of va r i a n c e of the weight of m i g r a t i n g A r i o n a t e r are shown i n Table X I I . Density had a s i g n i f i c a n t e f f e c t on the weight of the migrants, but food d i d not. F i g u r e l O a i demonstrates that m i g r a t i n g Ar ion i n uncrowded e n c l o s u r e s were l i g h t e r than migrants i n the crowded e n c l o s u r e s . The i n t e r a c t i o n of d e n s i t y , food, and time was ! s i . In a l l but the A treatments, there was an increase i n mean m i g r a t i o n weight with time (Figure l O a i v ) . T h i s i n c r e a s e was not s u r p r i s i n g as the s l u g s were growing throughout the summer, so that a gain i n weight should o c c u r . The same a n a l y s i s performed on the weight of mi g r a t i n g A r i o l i m a x columbianus demonstrated that there was no s i g n i f i c a n t e f f e c t f o r any of the treatments (Table X I I I ) . / 68 Table X I I . K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight of M i g r a t i n g A r i o n a t e r Table X I I I . K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight of M i g r a t i n g A r i o l i m a x columbianus Source DF k-value p r o b a b i l i t y d e n s i t y 1 5.086 0.024 food 1 0.000 0.997 d e n s i t y -food 3 6,323 0.101 d e n s i t y -food-time 23 59.434 <.001 Source DF k-value p r o b a b i l i t y d e n s i t y 1 0.490 0.483 food 1 0.957 0.328 d e n s i t y -food 3 2.179 0.536 d e n s i t y -food-time 13 14.289 0.354 70 F i g u r e 10. Food and Crowding E f f e c t s on Migrant Weight A r i o n a t e r treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 71 a i co i -< cr u. O t-X 53 LU 5 LOW HIGH SLUG DENSITY a i i P 2 < fX o O I CD LU 5 » r GOOD POOR FOOD 72 The weight change of each migrant was c a l c u l a t e d by s u b t r a c t i n g the weight on removal from the weight when int r o d u c e d to the e n c l o s u r e . Analyses of these data (Table XIV,XV) suggest that d e n s i t y , food, or t h e i r i n t e r a c t i o n a p p a r e n t l y had no s i g n i f i c a n t e f f e c t on the weight change of m i g r a t i n g i n d i v i d u a l s of e i t h e r s p e c i e s . T h i s problem probably stemmed from the small sample s i z e of each treatment. 73 Table XIV. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight Change of M i g r a t i n g A r i o n a t e r Table XV. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e : Weight Change of M i g r a t i n g A r i o l i m a x columbianus Source DF k-value p r o b a b i l i t y d e n s i t y 1 0 .466 0.495 food 1 1 .926 0.165 d e n s i t y -food 3 2 .572 0.900 d e n s i t y -food-time 23 14 .740 0.900 Source DF k-value p r o b a b i l i t y d e n s i t y 1 0.192 0.661 food 1 0.313 0.576 d e n s i t y -food 3 0.605 0.895 d e n s i t y -food-time 15 6.215 0.976 75 1.3.5 Weather and M i g r a t i o n C o r r e l a t i o n s between m i g r a t i o n r a t e and 3-day mean d a i l y temperature and p r e c i p i t a t i o n were q u i t e low (Table XVI). Fi g u r e 11 shows the mean m i g r a t i o n r a t e of A r i o n when a l l combined treatments were p l o t t e d a g a i n s t time. A l s o i n c l u d e d are the mean d a i l y temperatures and p r e c i p i t a t i o n over the three-day sampling p e r i o d s . The mean m i g r a t i o n r a t e d i d not seem to f o l l o w any r e g u l a r p a t t e r n or c y c l e , but i t should be noted that the peaks i n m i g r a t i o n were a s s o c i a t e d with the occurrence of p r e c i p i t a t i o n . In most cases, however, when the p r e c i p i t a t i o n had ceased the m i g r a t i o n r a t e took longer t o d e c l i n e , suggesting that p r e c i p i t a t i o n , though i t seemed t o i n i t i a t e m i g r a t i o n , was not i t s best p r e d i c t o r . There was no apparent r e l a t i o n s h i p between mean m i g r a t i o n r a t e and mean d a i l y temperature. Mean m i g r a t i o n r a t e and mean d a i l y temperature and p r e c i p i t a t i o n are given i n F i g u r e 12 f o r A r i o l i m a x columbianus. The r e l a t i o n s h i p between mean m i g r a t i o n r a t e and the two weather f a c t o r s was even l e s s c l e a r f o r t h i s s p e c i e s than f o r A r i o n ; s e e , f o r example, the very low c o r r e l a t i o n s i n Table XVII. Both s p e c i e s had s i m i l a r d i s t r i b u t i o n s of mean mi g r a t i o n r a t e over time. Mean m i g r a t i o n r a t e was h i g h through mid-July, d e c l i n i n g to a minimum i n the f i r s t week of August, and then i n c r e a s i n g to pr e v i o u s l e v e l s by l a t e August or e a r l y September. Although there was an obvious seasonal i n f l u e n c e on the m i g r a t i o n r a t e s of these s l u g s , the two 76 weather f a c t o r s presented here d i d not d e s c r i b e such seasonal trends adequately. The data i n the s e c t i o n on behaviour should c l a r i f y the r e l a t i o n s h i p between weather and a c t i v i t y . 77 Table XVI. C o r r e l a t i o n C o e f f i c i e n t s A r i o n a t e r M i g r a t i o n Measures and Weather V a r i a b l e s Table XVII. C o r r e l a t i o n C o e f f i c i e n t s A r i o l i m a x columbianus M i g r a t i o n Measures and Weather V a r i a b l e s 78 N=288 r@0.05=0.1156 r@0 . 001 = 0.1516 P r o b a b i l i t y M i g r a t i o n M i g r a t i o n Rate 3-day Mean D a i l y Temp0 C. 0.124 3-day 3-day Mean D a i l y Mean D a i l y Max. Temp. Prec i p i t a t ion 0.086 0.121 0.057 0.191 0.300 P r o p o r t i o n m i g r a t i n g to Sec. 5. -0.091 -0.009 438 N=192 r@0.05=0.1417 r@0.001=0.1855 P r o b a b i l i t y M i g r a t i o n M i g r a t i o n Rate 3-day Mean D a i l y Temp0 C. -0.043 3-day 3-day Mean D a i l y Mean D a i l y Max. Temp. P r e c i p i t a t i o n 0.060 0.106 -0.230 0.246 0.025 P r o p o r t i o n M i g r a t i n g To Sec. 5, 0.181 -0.029 0.275 79 F i g u r e 11. Mean M i g r a t i o n Rate of A r i o n a t e r from a l l Treatments P l o t t e d Against Time 80 n i i i — i — i i i i — i i — i — i — i — i — i — i — r 30 5 11 17 23 29 5 11 17 23 29 3 10 16 22 28 3 9 JUNE JULX AUGUST DATE 81 F i g u r e 12. Mean M i g r a t i o n Rate of A r i o l i m a x columbianus from a l l Treatments P l o t t e d a g a i n s t Time 82 J U N E J U L Y A U G U S T 83 1.3_.6 Summary Table XVIII summarizes the t e s t s performed on the data from the d e n s i t y and food manipulation experiments on A r i o n a t e r . The t a b l e shows that both d e n s i t y and food had s i g n i f i c a n t e f f e c t s on the m i g r a t i o n of these s l u g s . The i n t e r a c t i o n e f f e c t s were a l s o s i g n i f i c a n t f o r these v a r i a b l e s . D e n s i t y , food, and the two i n t e r a c t i o n s a l s o had s i g n i f i c a n t e f f e c t s on the m o r t a l i t y of A r i o n , but only d e n s i t y and the i n t e r a c t i o n of d e n s i t y , food, and time had any s i g n i f i c a n t e f f e c t on the weight of migrants. Migrants were s i g n i f i c a n t l y h e a v i e r than non-migrants. The d e n s i t y - f o o d - t i m e i n t e r a c t i o n was a l s o the only one that had any e f f e c t on the migrants' weight change. C o r r e l a t i o n s between s l u g movement and average d a i l y temperature and p r e c i p i t a t i o n were weak. O v e r a l l , i t was e v i d e n t that d e n s i t y and the i n t e r a c t i o n of d e n s i t y , food and time had important i n f l u e n c e s on the movement and weight of moving s l u g s , whereas food and the i n t e r a c t i o n of food and d e n s i t y were not so important. S i g n i f i c a n t e f f e c t s of food and of the i n t e r a c t i o n of food and d e n s i t y were l i m i t e d to the movement measurements and even there they were not c o n s i s t e n t . T h i s l i m i t a t i o n may have been due to a d i f f e r e n t i a l s e n s i t i v i t y of the m i g r a t i o n measurements to d i f f e r e n t a s p e c t s of the migratory a c t . Table XIX i n c l u d e s a comparable summary f o r A r i o l i m a x columbianus . The food f a c t o r had no e f f e c t on any of the v a r i a b l e s t e s t e d . D e n s i t y had no e f f e c t on the weight 84 or weight change of the migrants, but had v a r i a b l e e f f e c t s on the m i g r a t i o n measurements. The i n t e r a c t i o n of d e n s i t y and food had no s i g n i f i c a n t e f f e c t on m i g r a t i o n or weight measurements, but i t d i d a f f e c t m o r t a l i t y . Conversely, the i n t e r a c t i o n of d e n s i t y , food and time had e f f e c t s on a l l but two v a r i a b l e s . The weights of A r i o l i m a x migrants and non-migrants d i d not d i f f e r . As with A r i o n a t e r , c o r r e l a t i o n s between m i g r a t i o n measurements and mean temperature and p r e c i p i t a t i o n were weak. On the whole, food was unimportant f o r A r i o l i m a x , but the e f f e c t of d e n s i t y on mi g r a t i o n was n e i t h e r so c l e a r - c u t nor so c o n s i s t e n t f o r a l l mi g r a t i o n measurements f o r t h i s s p e c i e s as i t was f o r A r i o n . 85 Table XVIII. A r i o n a t e r : Summary of R e s u l t s D e n s i t y and Food M a n i p u l a t i o n Experiments 86 V a r i a b l e Source And Status Of E f f e c t d e n s i t y food d e n s i t y - d e n s i t y - f o o d -food time P r o b a b i l i t y M i g r a t i o n M i g r a t i o n Rate P r o p o r t i o n i n S e c t i o n 5. M i g r a t i o n Time M o r t a l i t y Weight of Migrants Weight Change of Migrants s s ns ns ns s ns ns ns s ns ns s s ns weight of migrants i s g r e a t e r than that of non-migrants. c o r r e l a t i o n s between m i g r a t i o n measures and temperature and p r e c i p i t a t i o n are poor. 87 Table XIX. A r i o l i m a x columbianus : Summary of R e s u l t s D e n s i t y and Food M a n i p u l a t i o n Experiments 88 V a r i a b l e Source And Status Of E f f e c t d e n s i t y food d e n s i t y - d e n s i t y - f o o d -food time P r o b a b i l i t y s M i g r a t i o n M i g r a t i o n ns Rate P r o p o r t i o n i n s S e c t i o n 5. M i g r a t i o n ns Time M o r t a l i t y s Weight of ns Migrants Weight Change ns of Migrants ns ns ns ns ns ns ns ns ns ns ns s ns ns ns s ns ns weight of migrants i s not d i f f e r e n t than weight of non-migrants. c o r r e l a t i o n s between m i g r a t i o n measures and temperature and p r e c i p i t a t i o n are poor. 89 1.4 D i s c u s s i o n 1.4.1 D e n s i t y E f f e c t s The r e s u l t s i n d i c a t e that there were very d i f f e r e n t e f f e c t s of d e n s i t y and food on the migratory behaviour of each s p e c i e s . D e n s i t y was c l e a r l y the most important f a c t o r a f f e c t i n g A r i o n a t e r movement. A l l of the m i g r a t i o n measures, m o r t a l i t y , and weight of migrants were s i g n i f i c a n t l y a f f e c t e d by i t . Only m o r t a l i t y and two m i g r a t i o n measures were s i g n i f i c a n t l y a f f e c t e d by the food f a c t o r . The food regime had no s i g n i f i c a n t e f f e c t on any of the migratory measures, m o r t a l i t y , or weight of A r i o l i m a x columbianus . The stronger migratory response of A r i o n a t e r i n crowded s i t u a t i o n s , compared with that of A r i o l i m a x columbianus , may be due to a number of reasons. A r i o n may have had a lower t o l e r a n c e to d e n s i t y than A r i o l i m a x . The p o p u l a t i o n d e n s i t y t h a t i n d i c a t e d an u n s u i t a b l e h a b i t a t may have been lower f o r A r i o n than f o r A r i o l i m a x . A r i o n may have migrated at a h i g h e r r a t e because they were more a c t i v e than A r i o l i m a x (see p a r t 2). A r i o l i m a x has been recorded moving at 0.18 cm/s and A r i o n at 0.12 cm/s at 20°C ( R o l l o 1978) but c r a w l i n g speed alone does not determine the d i s t a n c e a s l u g w i l l move, nor w i l l i t be a f a c t o r i n i n i t i a t i n g m i g r a t i o n . F i n a l l y , m i g r a t i o n of these s l u g s i s tempered by both p h y s i c a l and b i o t i c f a c t o r s . 90 Both s p e c i e s r e a c t e d to the h i g h - d e n s i t y s i t u a t i o n s by m i g r a t i n g . The s i n g l e s h e l t e r (one s h e l t e r f o r twenty sl u g s ) i n the crowded e n c l o s u r e s may not have provided enough adequate r e s t i n g p o s i t i o n s f o r the c o n f i n e d s l u g s , so that some may have l e f t i n search of s a t i s f a c t o r y s h e l t e r . In a d d i t i o n the presence of so many c o n s p e c i f i c s i n the h i g h - d e n s i t y treatment area may have i n d i c a t e d s t r o n g f e e d i n g p r e s s u r e on the a v a i l a b l e r e s o u r c e s , and a h i g h e r p r o b a b i l i t y of f i n d i n g adequate food and fewer competitors elsewhere. T h i s p r o b a b i l i t y would depend on the i n t e r - p a t c h d i s t a n c e and the sensory a b i l i t y of the searcher to d e t e c t food. D e n s i t y a f f e c t e d only two m i g r a t i o n i n d i c a t o r s , as w e l l as the m o r t a l i t y of A r i o l i m a x columbianus . Although both s p e c i e s r e a c t e d to crowding by m i g r a t i n g more than they d i d when they were not crowded, A r i o l i m a x d i d so at a lower r a t e than A r i o n a t e r . S i m i l a r e f f e c t s of d e n s i t y have been demonstrated i n other s p e c i e s , such as c r a y f i s h , Bovbjerg (1959) and aphids, Lees (1966,1967). I n c r e a s i n g the d e n s i t y of c r a y f i s h at one end of an e n c l o s u r e i n c r e a s e d the mean d i s t a n c e the c r a y f i s h moved through the e n c l o s u r e (Bovbjerg 1959). Supplying the e n c l o s u r e s w i t h s h e l t e r s reduced the r a t e of movement. Lees (1966,1967) found that i n c r e a s e d aphid p o p u l a t i o n d e n s i t y r e s u l t e d i n the p r o d u c t i o n of more a l a t e s than lower d e n s i t i e s . G a d g i l (1971) developed a model to r e l a t e s p a t i a l and temporal h e t e r o g e n e i t y of the environment to the e v o l u t i o n of 91 the d e n s i t y response and the magnitude of the d i s p e r s a l r a t e . One of h i s c o n c l u s i o n s was that s p e c i e s occupying h a b i t a t s with v a r i a b l e c a r r y i n g c a p a c i t i e s , which may be l o o s e l y i n t e r p r e t e d as h a b i t a t s u i t a b i l i t y , should be very s e n s i t i v e to the degree of crowding. That i s , as d e n s i t y i n c r e a s e s , so should m i g r a t i o n , thus l e a d i n g to a s i t u a t i o n i n which a g r e a t e r p r o p o r t i o n of the p o p u l a t i o n occupies l e s s crowded s i t e s . The r e l a t i o n s h i p between f l u c t u a t i n g k and i n c r e a s i n g m i g r a t i o n has a l s o been demonstrated mathematically by Cohen (1967), and supported by f i e l d evidence gathered by Brown (1951). 1.4.2 Food E f f e c t s The e f f e c t of the food regime v a r i e d with s p e c i e s . The food regime had no s i g n i f i c a n t e f f e c t on any of the m i g r a t i o n measures, weight, or m o r t a l i t y of A r i o l i m a x columbianus  A r i o n a t e r ' s p r o b a b i l i t y of m i g r a t i o n , m o r t a l i t y , and the m i g r a t i o n r a t e were s i g n i f i c a n t l y a f f e c t e d . Although A r i o n i n good and poor food regimes took about the same mean time to migrate ( F i g u r e 8 a i i i ) the departure r a t e was higher among slu g s i n the poor food regimes (Figure 6 a i i ) . The numbers of A r i o n l e a v i n g the treatment areas, as r e f l e c t e d by the p r o b a b i l i t y of m i g r a t i o n , a l s o i n d i c a t e d a s t r o n g response to the food regime. C h a t f i e l d (1976) s t a t e d that n u t r i t i o n a l q u a l i t y of food c o u l d a f f e c t s n a i l growth and f e c u n d i t y . A r i o n seemed to be a c t i n g i n a c c o r d with White's (1978) hy p o t h e s i s , that the 92 a v a i l a b i l i t y of nitrogenous food was the s i n g l e l i m i t i n g f a c t o r a f f e c t i n g p o p u l a t i o n s , by l e a v i n g areas where food was scarce and poor i n q u a l i t y . T h i s type of behaviour has a l s o been documented f o r gypsy-moth l a r v a e , which d i s p e r s e d more when they encountered unacceptable food or c o u l d n ' t f i n d food (Capinera and Barbosa 1976). Confinement on d r y i n g p l a n t s , i . e . poor food, s t i m u l a t e d f l i g h t i n l e a f hopper C i c a d u l i n a spp., while confinement on green p l a n t s supressed f l i g h t and induced maturation of ova (Rose 1972). A r i o l i m a x columbianus a l s o migrated f a c u l t a t i v e l y i n the present study, but these s l u g s used only p o p u l a t i o n d e n s i t y to assess the s t a t u s of the h a b i t a t . Although the same f a c t o r s a f f e c t e d the s e n s i t i v i t y of A r i o l i m a x and A r i o n to d e n s i t y changes, what remains to be e x p l a i n e d i s the former's apparent r e l i a n c e on d e n s i t y to assess h a b i t a t s u i t a b i l i t y i n the experiments. The m i g r a t i o n trends i n the data f o r A r i o l i m a x columbianus were s i m i l a r to those i n the A r i o n a t e r data over the same p e r i o d , with the exception of the D treatment data f o r A r i o l i m a x . Both s p e c i e s , however, showed an i n c r e a s e i n m i g r a t i o n i n the l a t e r p a r t of the summer, when the amount of r a i n i n c r e a s e d and c o n d i t i o n s became more favourable f o r movement. R o l l o (1978) and R o l l o and W e l l i n g t o n (1978) observed seasonal changes i n homing behaviour of s l u g s and s n a i l s . When the weather was hot and dry, the animals r e t u r n e d almost 93 e x c l u s i v e l y to the s h e l t e r s p r o v i d e d by the experimenter or were found i n deep s o i l c r e v i c e s and under l o g s . C o o l e r , wetter c o n d i t i o n s r e s u l t e d i n more s l u g s spending the day on the s o i l s u r f a c e s h e l t e r i n g under leaves or the bases of g r a s s e s . Edelstam and Palmer (1950) c l a i m to have demonstrated seasonal homing behaviour i n the s n a i l , H e l i x pomatia. The s n a i l s moved in the d i r e c t i o n of diapause s i t e s , from as f a r away as 40 m, a f t e r they had been d i s p l a c e d from the s i t e s . Slugs become l e s s a c t i v e i n the f a l l as temperatures drop to the lower l i m i t of t h e i r a c t i v i t y range, and s u i t a b l e forage becomes s c a r c e . They then seek s h e l t e r s i n which to r e s t through the w i n t e r . Getz (1959) found that three s p e c i e s of s l u g s no longer appeared in t r a p s i n the autumn and concluded that they had entered h i b e r n a t i o n . The experiment, however, d i d not d i s t i n g u i s h decreases i n s l u g a c t i v i t y from changes i n s l u g d e n s i t y due to m o r t a l i t y . 1.4.3 M o r t a l i t y Both A r i o n a t e r and A r i o l i m a x columbianus showed seasonal trends i n m o r t a l i t y . The m o r t a l i t y p a t t e r n s were a r e s u l t of the s l u g ' s l i f e c y c l e s , the weather, and the experimental c o n d i t i o n s . M o r t a l i t y i n c r e a s e d over time f o r both s p e c i e s . A r i o n u s u a l l y mated i n J u l y and e g g - l a y i n g began i n mid-August. A r i o n , an annual s p e c i e s , d i e d s h o r t l y a f t e r reproducing, which accounted f o r p a r t of the i n c r e a s e i n i t s m o r t a l i t y with 94 time. A r i o l i m a x normally l i v e s f o r 3 or 4 years, so i t d i d not have so great a d i e - o f f as A r i o n at the end of the summer. The v a r y i n g s e v e r i t y of the experimental treatments a l s o a f f e c t e d the m o r t a l i t y of the s l u g s . The treatments with low s l u g d e n s i t y , A and C, had lower mean m o r t a l i t y f o r both s p e c i e s than the high d e n s i t y treatments. Crowding had s i g n i f i c a n t e f f e c t s on m o r t a l i t y i n both s p e c i e s . Crowded sl u g s are not l i k e l y to have been k i l l e d i n f i g h t s , because n e i t h e r A r i o n a t e r nor A r i o l i m a x columbianus are very a g g r e s s i v e ( R o l l o 1978). Examination of dead s l u g s d i d not r e v e a l any evidence of f i g h t i n g . A more l i k e l y e x p l a n a t i o n of the g r e a t e r s l u g m o r t a l i t y i n crowded e n c l o s u r e s i s that they d i e d of d e h y d r a t i o n . More s l u g s migrated from the crowded e n c l o s u r e s and thus more were exposed to d e s i c c a t i n g c o n d i t i o n s . The weight change data f o r A r i o n a t e r i n d i c a t e d that m i g r a t i n g s l u g s l o s t weight, a l o s s that might have been due to lack of food as w e l l as to water l o s s , although Howes and Wells (1934) demonstrated that water l o s s by s l u g s may be r a p i d and of great magnitude. Some of the dead s l u g s found o u t s i d e the s h e l t e r s i n the e n c l o s u r e s c e r t a i n l y d i e d from d e h y d r a t i o n . Although severe water l o s s may not have i n i t i a t e d the death process i t was c e r t a i n l y the f i n a l cause, because such s l u g s had been unable to reach s u i t a b l e s h e l t e r and thus were exposed to the heat of the day, which they c o u l d not t o l e r a t e . C l o s e c o n t a c t between s l u g s i n crowded e n c l o s u r e s probably 95 a l s o f a c i l i t a t e d t r a n s m i s s i o n of p a r a s i t e s and d i s e a s e s . In f a c t , most of the A r i o n a t e r that d i e d w i t h i n t h e i r s h e l t e r s were i n f e c t e d with nematodes. Such p a r a s i t i z e d s l u g s i n a crowded s h e l t e r c o u l d c o n t a c t s e v e r a l i n d i v i d u a l s and t h e i r f a e c e s , i n f e c t e d with nematode eggs, would remain in the s h e l t e r a f t e r the s l u g s had p e r i s h e d . W e l l i n g t o n (1962) found that c o l o n i e s of western tent c a t e r p i l l a r c o n t a i n i n g i n d i v i d u a l s incapable of o r i e n t i n g alone, who were f r e q u e n t l y i n c l o s e c o n t a c t , were those most a f f e c t e d by p o l y h e d r o s i s v i r u s . There may have been scramble competition w i t h i n the s h e l t e r s f o r p o s i t i o n s nearest the bottom. I d i d not observe any c l o s e body contact between A r i o n a t e r i n t h e i r s h e l t e r s , so t h e i r spacing may have f o r c e d some i n d i v i d u a l s to accept l e s s s u i t a b l e r e s t i n g p o s i t i o n s . In c o n t r a s t , A r i o l i m a x columbianus were o f t e n found r e s t i n g with t h e i r bodies touching i n the bottom of t h e i r s h e l t e r s . They were o b v i o u s l y more t o l e r a n t of c l o s e c o n t a c t with c o n s p e c i f i c s . T h i s t o l e r a n c e allowed more s l u g s to occupy the c o o l e s t part of the s h e l t e r . Since the c o n t a c t between t h e i r bodies reduced t h e i r e v a p o r a t i v e s u r f a c e area, t h i s behaviour a l s o would allow A r i o l i m a x to maintain n e a r l y optimal h y d r a t i o n and might be another reason why the m i g r a t i o n r a t e s from A and D treatments were s i m i l a r i n t h i s s p e c i e s . There was c e r t a i n l y a g r a d i e n t of s u i t a b l e r e s t i n g s i t e s w i t h i n the s h e l t e r s , because the bottom of the s h e l t e r s were J 96 c o o l e r than the top few c e n t i m e t r e s of the s o i l . I confirmed t h i s g r a d i e n t by t a k i n g readings with a temperature probe at v a r i o u s depths i n the s h e l t e r s throughout the day. There was an i n v e r s e r e l a t i o n s h i p between s h e l t e r temperature and depth below the s o i l s u r f a c e . T h i s r e l a t i o n s h i p has a l s o been demonstrated by B i l l i n g s (1964). 1.4.4 Weather E f f e c t s The m i g r a t i o n measures ( F i g u r e 6) show t h a t , as the weather became l e s s s u i t a b l e f o r s l u g s , fewer A r i o n a t e r l e f t the A treatment areas of t h e i r cages. Although about the same p r o p o r t i o n of the p o p u l a t i o n moved a l l the way through the cages i n poorer weather, they d i d so more d i r e c t l y , as evidenced by the smaller number of mean days to migrate i n the l a s t two experimental p e r i o d s shown i n F i g u r e 6. During the most unfavourable p a r t of the summer, the number of slu g s moving from the B treatment and the d i s t a n c e they covered d e c l i n e d to a minimum. In c o n t r a s t to the A treatment, which showed l i t t l e or no recovery i n the m i g r a t i o n of A r i o n a t e r , the high d e n s i t i e s i n the B treatments coupled with the improving weather induced more A r i o n to leave t h e i r o r i g i n a l s h e l t e r . More of the m i g r a t i n g A r i o n reached the end of the cages, but took longer to do so i n comparison with m i g r a t i o n s e a r l i e r i n the summer. I t appeared that the unfavourable weather i n the second 97 experimental p e r i o d d i d not deter the A r i o n a t e r from l e a v i n g the C and D treatments. More slu g s moved i n each s u c c e s s i v e experimental p e r i o d and, as i n the other treatments, when the weather was poorest the s l u g s moved most d i r e c t l y to the ends of the e n c l o s u r e s . The m i g r a t i o n measurements from each of the treatments showed c l e a r seasonal trends and a l s o showed that the food or s h e l t e r i n g c o n d i t i o n s i n some of the treatments overrode the e x t e r n a l p h y s i c a l c o n d i t i o n s by i n d u c i n g movement even when the weather was unfavourable. The C and D treatments were most s i m i l a r i n t h e i r seasonal migratory trends but the D and B treatments caused more s l u g s to migrate. More of these l a t t e r migrants reached the end of t h e i r e n c l o s u r e s , compared with those from the A or C treatments. T h i s i l l u s t r a t e s the i n t e r a c t i o n of food and d e n s i t y i n i n i t i a t i n g m i g r a t i o n by A r i o n a t e r . Although there were only two experimental p e r i o d s f o r A r i o l i m a x columbianus , the trends i n m i g r a t i o n over time were c l e a r and c o n s i s t e n t . Compared with A r i o n a t e r , A r i o l i m a x migrated more slowly and i n fewer numbers ( F i g u r e s 5 b i , i i ) . In the A treatment, a l l three m i g r a t i o n i n d i c a t o r s i n c r e a s e d between the f i r s t and second experimental p e r i o d s . The mean time to migrate decreased. As the weather improved at the end of the summer, more A r i o l i m a x l e f t the A treatment and moved through the cages. 98 The m i g r a t i o n i n d i c a t o r s and the m i g r a t i o n time from the B treatment a l l i n c r e a s e d between the f i r s t and second p e r i o d s and, as the weather improved, more slu g s l e f t the crowded c o n d i t i o n s of the treatment a r e a . On average, s l u g s l e a v i n g the B treatment took longer to move through the e n c l o s u r e s than those v a c a t i n g the A treatment. In s p i t e of an i n c r e a s e i n the m i g r a t i o n p r o b a b i l i t y over the whole summer, the number of s l u g s moving to the end of the enc l o s u r e i n the C treatment decreased over time. T h e i r r a t e of movement a l s o decreased and the number of days spent i n m i g r a t i n g i n c r e a s e d . The trends of the data D treatment data were s i m i l a r to the C treatment. A l l of the m i g r a t i o n measures decreased from higher v a l u e s d u r i n g the f i r s t p e r i o d , when the weather was not conducive to movement, to lower v a l u e s d u r i n g the second p e r i o d . A l l of these trends are e v i d e n t i n F i g u r e 6b. On f i r s t i n s p e c t i o n , the trends i n A r i o l i m a x columbianus m i g r a t i o n may seem c o u n t e r - i n t u i t i v e . As the mean d a i l y p r e c i p i t a t i o n i n c r e a s e d , there appeared to be more movement away from the l e a s t s t r e s s f u l treatments and l e s s movement from the most s t r e s s f u l treatment. Even with a decrease i n p r o p o r t i o n of m i g r a t i o n between the two experimental p e r i o d s , the value, f o r the D treatment was higher than those f o r a l l but one of the other treatments ( F i g u r e 6 b i ) . The m i g r a t i o n r a t e i n the D treatment d i d f a l l to l e v e l s below the r a t e s of the other treatments. The paradox of a l a r g e number of slu g s 99 l e a v i n g the D treatment while t h e i r m i g r a t i o n r a t e remained low co u l d be e x p l a i n e d by the high m o r t a l i t y i n t h i s treatment (Figure 7 b i v ) . In a d d i t i o n , once the slugs had l e f t the treatment area they d i d not i n v a r i a b l y move much f a r t h e r ; e.g., note the decrease i n the p r o p o r t i o n of s l u g s reaching the end of the e n c l o s u r e i n F i g u r e 5 b i i i . 1.4.5 General D i s c u s s i o n A r i o l i m a x columbianus's longer l i f e s p a n may a l s o have made i t l e s s i n c l i n e d than A r i o n a t e r to migrate d u r i n g the comparatively b r i e f experimental term. A r i o n has only one summer to grow and reproduce, so i t would not pay A r i o n to remain f o r long i n an area with poor forage or overtaxed r e s o u r c e s . On the other hand, A r i o l i m a x has 3-4 years to accumulate food r e s e r v e s and reproduce. I t i s g e n e r a l l y h e l d that changing h a b i t a t s u i t a b i l i t y i s the u l t i m a t e f a c t o r that i n i t i a t e s m i g r a t i o n (Baker 1978, Ca l d w e l l 1974, Johnson 1969, Southwood 1962) whether or not the mi g r a t i o n response can be d i r e c t l y r e l a t e d to c u r r e n t a d v e r s i t y . Baker (1978) contends t h a t : (a) i n h a b i t a t s which f l u c t u a t e u n p r e d i c t a b l y , there can be no s e l e c t i o n f o r migratory p r e p a r a t i o n or m i g r a t i o n at a f i x e d time because there i s no c o n s i s t e n t l y r e c u r r i n g cue presaging h a b i t a t s u i t a b i l i t y ; and (b) where there i s a c o n s i s t e n t c y c l e of h a b i t a t s u i t a b i l i t y , s e l e c t i o n should favour o b l i g a t o r y migrants that leave before t h e i r h a b i t a t s have s e v e r e l y 100 d e t e r i o r a t e d . The s l u g s i n the present study belong to the f i r s t c a t e g o ry. They had no c o n s i s t e n t cues forewarning that the h a b i t a t was d e t e r i o r a t i n g . They c o u l d only respond to the present s t a t e of t h e i r surroundings. A r i o n a t e r used both food and d e n s i t y cues i n a s s e s s i n g the s u i t a b i l i t y of i t s h a b i t a t . Sampling the food p r o v i d e d d i r e c t i n f o r m a t i o n on i t s q u a n t i t y and q u a l i t y . When t h i s i n f o r m a t i o n was combined with i n f o r m a t i o n on the r e l a t i v e abundance of c o n s p e c i f i e s , an i n d i v i d u a l A r i o n c o u l d use i t to assess the feed i n g pressure that might be exerted on the l o c a l r e s o u r c e s . The i n t e r n a l s e n s i t i v i t y which each s l u g possessed f o r gauging h a b i t a t s u i t a b i l i t y was probably m o d i f i e d by age, s i z e , and the developmental h i s t o r y of the animal. T h i s would e x p l a i n , i n p a r t , why migratory a c t i v i t y was not synchronized. When the v a r i a b l e s measured i n the s t u d i e s of movement were p l o t t e d a g a i n s t time, s i g n i f i c a n t e f f e c t s of season were evi d e n t i n both s p e c i e s . Most workers t r e a t weather as a density-independent f o r c e , but i n cases where there i s com p e t i t i o n f o r s h e l t e r , weather i s at l e a s t p a r t i a l l y d e n s i t y dependent (Andrewartha and B i r c h 1954, Andrewartha 1963). In t h i s study high d e n s i t y s i t u a t i o n s f o r c e d 20 sl u g s to share one s h e l t e r . There may o c c a s i o n a l l y have been some hy g r o r e g u l a t o r y b e n e f i t f o r sl u g s pressed together i n a s h e l t e r , because such co n t a c t would reduce the s u r f a c e area of t h e i r bodies through which e v a p o r a t i v e water l o s s c o u l d take 101 p l a c e . R i c h t e r (1976a) d i s c u s s e d the hypothesis that contact might a f f e c t t hermoregulation i n r e l a t i o n to r e s t i n g p o s i t i o n s of A r i o l i m a x columbianus . 1.4.6 Summary These experiments have demonstrated that both A r i o n a t e r and A r i o l i m a x columbianus are capable of f a c u l t a t i v e m i g r a t i o n . The degree of crowding and the q u a n t i t y and q u a l i t y of food were the cues A r i o n used. In c o n t r a s t , A r i o l i m a x d i d not use i n f o r m a t i o n about i t s food, but only i n f o r m a t i o n about the d e n s i t y of the p o p u l a t i o n i n the e n c l o s u r e . Furthermore, the s i g n a l to migrate came from c u r r e n t c o n d i t i o n s i n the h a b i t a t , and was m o d i f i e d by the e f f e c t s of l o c a l weather. As the weather became hot and dry, fewer s l u g s migrated from the more s t r e s s f u l treatments. In other words, although such s l u g s may have found t h e i r h a b i t a t u n s u i t a b l e , they stayed i n i t while the c o s t s of m i g r a t i o n remained h i g h . The l i f e h i s t o r i e s and b i o l o g i e s of each s p e c i e s a l s o c o n t r i b u t e d to the d i f f e r e n c e s observed in t h e i r migratory behaviour. A r i o n , the smaller s l u g , migrated i n g r e a t e r numbers and at a higher r a t e than A r i o l i m a x . A r i o n i s an annual s p e c i e s , which must mature in one season, and t h e r e f o r e must experience g r e a t e r d r i v e s f o r f e e d i n g than A r i o l i m a x , with a l i f e - s p a n 3-4 times longer. In these experiments A r i o n ' s t h r e s h o l d f o r m i g r a t i o n was c e r t a i n l y lower than A r i o l i m a x ' s , and i t migrated i n weather that prevented A r i o l i m a x from l e a v i n g s h e l t e r . 102 PART 2. ARENA STUDIES OF LOCOMOTORY BEHAVIOUR 2.1 I n t r o d u c t i o n Migrant i n d i v i d u a l s t r a v e l f u r t h e r than non-migrants. There may a l s o be a r e l a t i o n s h i p between m i g r a t i o n and a c t i v i t y . If h e a v i e r s l u g s are the ones to migrate, they may a l s o maintain a higher l e v e l of a c t i v i t y . The experiments d e s c r i b e d here i n v e s t i g a t e d the r e l a t i o n s h i p between s l u g body weight and the d i s t a n c e a s l u g t r a v e l l e d i n one n i g h t . 2.2 Methods These experiments were conducted to i n v e s t i g a t e the range of movement of i n d i v i d u a l s l u g s . The apparatus c o n s i s t e d of a 14 X 60 X 60 cm wooden box with a removable l i d of p l a s t i c mesh screen fastened to a 60 X 60 cm wooden frame ( P l a t e 5). The box was l i n e d with black p l a s t i c , which was o v e r l a i d with a l a y e r of c l e a r p l a s t i c . There were four such arenas. Two were used f o r each s p e c i e s , so that two i n d i v i d u a l s of each s p e c i e s c o u l d be t e s t e d every evening d u r i n g the experimental p e r i o d . Before the s l u g s were put i n the arenas, they were s t a r v e d f o r two days i n 19 X 20 cm p l a s t i c c o n t a i n e r s kept i n a growth chamber h e l d at 15° C. and 16:8 L:D. A f t e r a n i g h t i n the arena the s l u g s were returned to the c o n t a i n e r s i n the growth chamber and s u p p l i e d with food f o r one day. The food was then 103 removed, the s l u g s were s t a r v e d f o r another two days, and then were t e s t e d a g a i n . Before an arena was used i t s l i n e r was sprayed with d i s t i l l e d water to moisten i t . A s l u g was then weighed and introduced i n t o the lower r i g h t - h a n d corner of the arena. The l i d was f a s t e n e d and the arena was l e f t o v e r n i g h t on a l a b o r a t o r y bench, where the ambient a i r temperature ranged between 18° - 21° C. The s l u g s spent approximately 16 hours i n the arenas. They were i n t r o d u c e d before sunset and removed a f t e r s u n r i s e . T h i s p e r i o d bracketed t h e i r normal a c t i v i t y p e r i o d and d i d not a f f e c t t h e i r a c t i v i t y p a t t e r n . None of the s l u g s used i n the experiment was a c t i v e at the time they were removed from the cage i n the morning. A f t e r each s l u g had spent one night i n an arena the c l e a r p l a s t i c l i n e r was removed and r e p l a c e d with a c l e a n sheet f o r the next i n d i v i d u a l . As a s l u g moves i t t r a v e l s over a f i l m of mucus s e c r e t e d by glands i n the pedal e p i t h e l i u m and by the pedal gland. The slime t r a i l l e f t behind d r i e s , but i t i s h y g r o s c o p i c ; i . e., when remoistened the r e s i d u a l s o l i d s r e s o r b water and the mucus becomes s t i c k y a g a i n . By e x p l o i t i n g t h i s tendency with a technique s i m i l a r to Cook's (1977) i t was p o s s i b l e to o b t a i n a r e c o r d of the s l u g ' s n o c t u r n a l movements. A f t e r removal from the arena, the c l e a r p l a s t i c sheet was l a i d on a f l a t s u r f a c e and l i g h t l y sprayed f i r s t with water and then with sodium b i c a r b o n a t e , a f t e r which i t was allowed to dry. When dry, the sheet was shaken to d i s l o d g e the sodium b i c a r b o n a t e on the s l i m e - f r e e areas, thus 104 r e v e a l i n g the slime t r a i l where the powder adhered to the sheet. The s l u g ' s normally c l e a r slime t r a i l thus became h i g h l y v i s i b l e as a white l i n e ( P l a t e s 6 , 7 ) . The sheet was then p l a c e d t r a i l s i d e down on a p i e c e of black p l a s t i c to h i g h l i g h t the white l i n e , so t h a t a map measurer c o u l d be used to c a l c u l a t e the d i s t a n c e the s l u g had t r a v e l l e d d u r i n g one n i g h t . The number of tu r n s was a l s o recorded, so that the number of tu r n s per metre and the d i s t a n c e moved per gram of body weight c o u l d e v e n t u a l l y be c a l c u l a t e d f o r each s l u g f o r subsequent i n t r a - and i n t e r - i n d i v i d u a l comparisons. 105 P l a t e 5. Apparatus used f o r the i n v e s t i g a t i o n of locomotory behaviour P l a t e 6. Slime t r a i l l e f t by a s l u g a f t e r p r o c e s s i n g to render the t r a i l v i s i b l e 106 107 P l a t e 7. D e t a i l of a slime t r a i l a f t e r p r o c e s s i n g to render i t v i s i b l e 1 0 8 109 2.3 R e s u l t s 2.3.1 S i z e and D i s t a n c e T r a v e l l e d Approximately 30 s l u g s of each s p e c i e s were used i n t h i s experiment. About 25 were used twice i n an attempt to reduce the v a r i a t i o n of the r e s u l t s , so that approximately 60 t r i a l s were conducted f o r each s p e c i e s . Since d i s p e r s i n g s l u g s were heavier than t h e i r n o n - d i s p e r s i n g c o u n t e r p a r t s , t h i s experiment was a l s o expected to show whether body weight had any e f f e c t on the d i s t a n c e a s l u g might t r a v e l d u r i n g the n i g h t . D e s c r i p t i v e s t a t i s t i c s of the measured v a r i a b l e s are presented i n Table XXII. Least squares r e g r e s s i o n was used to i n v e s t i g a t e r e l a t i o n s h i p s between s l u g body weight and the v a r i o u s aspects of movement. The r e s u l t s of these r e g r e s s i o n s are given i n Tables XX,XXI f o r A r i o n a t e r and A r i o l i m a x columbianus , r e s p e c t i v e l y . The outcome of each of the r e g r e s s i o n s was the same f o r both s p e c i e s , so they are t r e a t e d together i n the ensuing d i s c u s s i o n . The l e a s t squares r e g r e s s i o n of d i s t a n c e t r a v e l l e d on body weight was not s i g n i f i c a n t f o r e i t h e r s p e c i e s , so i t e x p l a i n s very l i t t l e of the v a r i a t i o n (Table XX, XXI). No c l e a r t r e n d was evident i n the scattergrams of d i s t a n c e t r a v e l l e d versus body weight f o r A r i o n a t e r and A r i o l i m a x columbianus Furthermore, no s i g n i f i c a n t r e g r e s s i o n was obtained when the 110 number of turns per night and number of turns per metre per night were r e g r e s s e d on body weight. The only s i g n i f i c a n t r e g r e s s i o n i n v o l v i n g body weight was that i n which d i s t a n c e t r a v e l l e d per gram body weight was c o n s i d e r e d . Even t h i s r e l a t i o n d i d not e x p l a i n a major p r o p o r t i o n of the v a r i a t i o n i n the data, but the trend i s evident i n F i g u r e s 13,14. There was a strong r e l a t i o n s h i p between the d i s t a n c e t r a v e l l e d and the t o t a l number of turns (Figure 15, Tables XX,XXI) but the small s i z e of the arena c o u l d have been r e s p o n s i b l e f o r t h i s r e l a t i o n s h i p . When the number of turns per metre was regre s s e d on d i s t a n c e t r a v e l l e d the r e s u l t s were s i g n i f i c a n t , but even they e x p l a i n e d very l i t t l e of the v a r i a t i o n i n the data. Apparently some other f a c t o r i n f l u e n c e d the number of turns a s l u g made i n t h i s apparatus. I l l F i g u r e 13. Di s t a n c e Moved per Gram Body Weight Versus Body Weight; A r i o n a t e r see Table XX f o r equation of r e g r e s s i o n l i n e WEIGHT ( g . ) 113 F i g u r e 14. D i s t a n c e Moved per Gram Body Weight Versus Body Weight; A r i o l i m a x columbianus see Table XXI f o r equation of r e g r e s s i o n l i n e DISTANCE / 115 F i g u r e 15. Di s t a n c e T r a v e l l e d i n One Night Versus Number Turns a: A r i o n a t e r b: A r i o l i m a x columbianus r e g r e s s i o n equations i n t a b l e s XX,XXI r e s p e c t i v e l y 116 a 136.1-3.7 10.5 17.2 2 4 . 0 3 0.8 b 117.2 t 2 8 6 S 10.1 1 3 b 1 7 5 DISTANCE im\ 117 Table XX. L i n e a r Regression A n a l y s i s of Data from Arena Experiments: A r i o n a t e r 118 X=weight y=distance r 2=0.002 SE=6.578 p<0.710 y=8.944 + 0.073x x=weight y=number of turns r 2<.001 SE=29.546 p<0.936 y=44.533 - 0.071x x=weight y=number of turns per metre r 2=0.008 SE=2.834 p<0.502 y=5.895 - 0.057x x=weight y=distance moved per gram body weight r 2=0.2135 SE=1.089 p<0.001 y=2.515 - 0.130x x=distance y=number of turns r 2=0.8256 SE=12.341 p<0.001 y=5.204 + 4.077x x=distance y=number turns per metre r 2=0.189 SE=2.562 p<0.001 y=7.237 - 0.188x 119 Table XXI. L i n e a r Regression A n a l y s i s of Data from Arena Experiments: A r i o l i m a x columbianus 120 x=weight y=distance r 2=0.0294 SE=3.743 p<0.195 y=8.003 - 0.069x x=weight y=number of turns r 2=0.043 SE=22.151 p<0.115 y=47.766 - 0.501x x=weight y=number turns per metre r 2=0.038 SE=1.408 p<.001 y=6.447 - 0.194x x=weight y=distance moved per gram body weight r 2=0.351 SE=0.418 p<.001 y=1.127 - 0.033x x=distance y=number of tu r n s r 2=0.777 SE=10.676 p<.001 y=3.341 + 5.257x x=distance y=number turns per metre r 2=0.058 SE=1.393 p<0.066 y=6.553 - 0.910x 121 2.3.2 Comparison Between Species When the d e s c r i p t i v e s t a t i s t i c s of v a r i a b l e s measured were compared a c r o s s s p e c i e s (Table XXII) i t was c l e a r that A r i o n a t e r moved f a r t h e r and turned more than A r i o l i m a x columbianus . The number of turns per metre, however, i n d i c a t e d that both s p e c i e s turned about the same amount when the turns were c o r r e c t e d f o r the d i s t a n c e t r a v e l l e d . In a d d i t i o n , A r i o l i m a x moved only about one t h i r d as much per gram of body weight as A r i o n . Under these experimental c o n d i t i o n s i t appeared that A r i o n was more a c t i v e than A r i o l i m a x . 122 Table XXII. D e s c r i p t i v e S t a t i s t i c s of Data from Arena Experiments A r i o n a t e r V a r i a b l e d i s t a n c e number of turns turns per metre d i s t a n c e per gram N Mean SE 59 9.513 0.850 59 43.983 3.814 59 5.451 0.366 58 1.487 0.160 A r i o l i m a x columbianus V a r i a b l e N d i s t a n c e 59 number of 59 turns turns per 59 metre d i s t a n c e 58 per gram Mean SE 6.803 0.490 39.102 5.091 5.934 0.773 0.539 0.068 125 2.4 D i s c u s s i o n 2.4.1 S i z e and Distance T r a v e l l e d I n s p e c t i o n of the weight data of A r i o n a t e r i n d i c a t e d that s l u g s l e a v i n g h i g h - d e n s i t y areas were he a v i e r than s l u g s m i g r a t i n g from low-density areas ( F i g u r e l O a i ) . There was no d i f f e r e n c e between the mean weight of slugs l e a v i n g the good or poor food regimes nor was there any d i f f e r e n c e based on the i n t e r a c t i o n of d e n s i t y and food ( F i g u r e s l O a i i , l O a i i i ) . Over the summer there were s i g n i f i c a n t d i f f e r e n c e s between treatments i n the mean weight of migrants. In c o n t r a s t , n e i t h e r food, d e n s i t y , time, nor t h e i r i n t e r a c t i o n s had any s i g n i f i c a n t e f f e c t on the weight of m i g r a t i n g A r i o l i m a x columbianus ( F i g u r e 10b). T h i s s p e c i e s showed no s i g n i f i c a n t d i f f e r e n c e between the mean weight of migrants and non-migrants. Phenotypic and b e h a v i o u r a l d i f f e r e n c e s between migrants and non-migrants have been demonstrated (Gypsy moths, Barbosa and Capinera 1978, Capinera and Barbosa 1976; Western tent c a t e r p i l l a r s , W e l l i n g t o n 1964; planthoppers, Denno and G r i s s e l l 1979; milkweed bugs, D i n g l e 1968,1974, D i n g l e et a l . 1980). Although m i g r a t i n g A r i o n a t e r were he a v i e r than non-migrants, the arena experiments on locomotory behaviour d i d not pr o v i d e evidence that s l u g body weight had a s i g n i f i c a n t i n f l u e n c e on the d i s t a n c e t r a v e l l e d . There was no s i g n i f i c a n t r e l a t i o n s h i p 126 between body weight and m o b i l i t y f o r A r i o l i m a x columbianus . If h i g h weight was a c h a r a c t e r i s t i c of a migrant, I would have expected to f i n d a p o s i t i v e r e l a t i o n s h i p between s i z e and a c t i v i t y . The experimental design may have c o n t r i b u t e d to t h i s l a c k of evidence. The slugs used i n these experiments were s t a r v e d before being introduced i n t o the arenas so that d i f f e r i n g amounts of food i n t h e i r guts would not b i a s t h e i r movement. T h i s treatment may have induced a l l slugs to i n c r e a s e t h e i r f o r a g i n g behaviour and so masked any weight-based d i f f e r e n c e s i n movement. H o l l i n g (1966) demonstrated that as hunger i n c r e a s e d , the r e a c t i v e d i s t a n c e and s t r i k e d i s t a n c e between a p r e y i n g mantis and i t s prey i n c r e a s e d . Haufe (1962) found that s t a r v e d mosquitoes flew more r e a d i l y than fed mosquitoes. The arenas were not p r o v i d e d with s h e l t e r s , and the s l u g s may have co n t i n u e d moving i n search of s h e l t e r s d u r i n g the e a r l y morning when t h e i r b i o l o g i c a l c l o c k s i n d i c a t e d that i t was time to become i n a c t i v e . T h i s may a l s o have reduced weight-based a c t i v i t y d i f f e r e n c e s . Although the l a b o r a t o r y arena s t u d i e s d i d not support the f i e l d data, I b e l i e v e that the weight d i f f e r e n c e s found between migrant and non-migrant A r i o n a t e r were r e a l . The e x i s t e n c e of d i f f e r e n c e s i s c o n s i s t e n t with the r e f e r e n c e s c i t e d f o r other s p e c i e s . Furthermore the r e s u l t s support R o f f ' s (1977) hypothesis that l a r g e r i n d i v i d u a l s have lower e n e r g e t i c and r e p r o d u c t i v e c o s t s , and thus w i l l be the ones to c o l o n i z e 127 o u t l y i n g h a b i t a t s . Larger A r i o n l e a v i n g the more s t r e s s f u l treatments were b e t t e r equipped than the other s l u g s f o r m i g r a t i o n . The l a r g e r slugs a p p a r e n t l y had s u f f i c i e n t s t o r e d energy reserves to metabolize i f they found no food d u r i n g t h e i r exodus, because the migrants reaching the end of the e n c l o s u r e on average had l o s t weight. Large s l u g s would a l s o be able to t o l e r a t e d e s i c c a t i n g c o n d i t i o n s b e t t e r than small s l u g s , because of t h e i r smaller s u r f a c e a r e a / volume r a t i o . Presumably the l a r g e r A r i o n a t e r were a l s o o l d e r and thus c l o s e r to r e p r o d u c t i v e maturity than the small ones. T h i s d i f f e r e n c e may have a l t e r e d t h e i r p e r c e p t i o n of " s u i t a b l e " h a b i t a t . T h e i r m i g r a t i o n t h r e s h o l d t h e r e f o r e may have s h i f t e d i n favour of o v i p o s i t i o n s i t e s r a t h e r than s h e l t e r i n g or f e e d i n g s i t e s , but i t i s u n l i k e l y that these migrants were d r i v e n out by a g o n i s t i c encounters. A r i o n i s u s u a l l y d o c i l e . But i f there were c o n f l i c t , l a r g e r s l u g s of any s p e c i e s more o f t e n win a f i g h t ( R o l l o 1978, R o l l o and W e l l i n g t o n 1978). A r i o l i m a x columbianus d i d not show any i n d i v i d u a l d i f f e r e n c e s between migrants and non-migrants. I t i s p o s s i b l e that A r i o l i m a x only migrated d u r i n g the most benign weather, that i s , d u r i n g p e r i o d s of c o o l temperatures and low e v a p o r a t i v e s t r e s s . If t h i s were t r u e even l i g h t e r A r i o l i m a x c o u l d migrate with l e s s r i s k of d e s i c c a t i o n . But A r i o l i m a x i s a much l a r g e r s l u g than A r i o n a t e r , so that " l i g h t " A r i o l i m a x c o u l d weigh as much or more than a "heavy" A r i o n . T h e r e f o r e , the l a c k of d i f f e r e n c e i n weight between non-migrating and 128 m i g r a t i n g A r i o l i m a x may stem from the p o s s i b i l i t y t h a t a l l were l a r g e enough to r e s i s t severe d e s i c c a t i o n i n these experiments. If s l u g s do s h i f t t h e i r h a b i t a t p r e f e r e n c e s when s e a r c h i n g f o r o v i p o s i t i o n s i t e s , A r i o l i m a x may not have done so d u r i n g the experiments because o v i p o s i t i o n by t h i s s p e c i e s does not begin u n t i l September (when my experiments ended). 2.4.2 Comparison Between Species The arena experiments showed that A r i o n a t e r was more a c t i v e than A r i o l i m a x columbianus (Table XX). Being s m a l l e r , A r i o n d i d not have to move as great a mass as A r i o l i m a x , which allowed i t to maintain a higher c r a w l i n g speed. A l a r g e r s u r f a c e a r e a / volume r a t i o made d e s i c c a t i o n a g r e a t e r t h r e a t to Ar ion than A r i o l i m a x , which might have been a more important reason f o r the d i f f e r e n c e s i n the amount and speed of movement. When the experiments ended, some A r i o l i m a x were found r e s t i n g on the roof or s i d e s of the arena. A r i o l i m a x i s known to climb o b j e c t s i n order to thermoregulate ( R i c h t e r 1976a), and I have confirmed the occurrence of t h i s behaviour i n the f i e l d . Jaremovic and R o l l o (1979) i n v e s t i g a t e d s i m i l a r behaviour i n Cepea nemoralis. Consequently, while A r i o n might have been a c t i v e l y seeking "ground" s h e l t e r s on the arena f l o o r , A r i o l i m a x might have ob t a i n e d the same r e s u l t s simply by c l i m b i n g the w a l l s of the arena to a zone of d i f f e r e n t temperature. Temperature g r a d i e n t s w i t h i n the arenas were not i n v e s t i g a t e d . 129 2.4.3_ Summary There were d i f f e r e n c e s i n the locomotory behaviour of A r i o n a t e r and A r i o l i m a x columbianus . M i g r a t i n g A r i o n were heavier than non-migrants. In c o n t r a s t , migrant and non-migrant A r i o l i m a x d i d not d i f f e r i n weight. These d i f f e r e n c e s were e x p l a i n a b l e i n terms of each s p e c i e s ' b i o l o g y . 130 PART 3. NOCTURNAL BEHAVIOUR OBERSERVATIONS 3.1 I n t r o d u c t i o n Part 1 i n v e s t i g a t e d the e f f e c t s of food and d e n s i t y on sl u g movement over days and weeks. Part 2 attempted to demonstrate a r e l a t i o n s h i p body weight and a c t i v i t y . T h i s s e c t i o n i s concerned with the e f f e c t s of food and d e n s i t y on the p a t t e r n of hourly n o c t u r n a l a c t i v i t y and the time devoted to v a r i o u s behaviours. Weather data were c o l l e c t e d to d e s c r i b e the a s s o c i a t i o n between c e r t a i n weather f a c t o r s and h o u r l y behaviour. The importance of these f a c t o r s i s d i s c u s s e d . Food p r e f e r e n c e s are i n v e s t i g a t e d to determine whether or not s l u g s s e l e c t e d food on the b a s i s of i t s n u t r i t i o n a l c o n t e n t . 3.2 Methods Hourly records of s l u g behaviour were made throughout the experimental p e r i o d on t h i r t e e n n i g h t s f o r A r i o n a t e r and eleven n i g h t s f o r A r i o l i m a x columbianus . The o b s e r v a t i o n p e r i o d commenced at 20:00h (P.D.T.) and ended at 06:00h (P.D.T.). These eleven-hour r e c o r d i n g s were always s t a r t e d before sunset and ended a f t e r s u n r i s e i n order to o b t a i n complete data on a c t i v i t y f o r the whole s c o t o p e r i o d . The ob s e r v a t i o n s were c o l l e c t e d i n the treatment s e c t i o n s of each of the f i e l d e n c l o s u r e s . The dates f o r the o b s e r v a t i o n s were 131 chosen' to c o i n c i d e with the schedule f o r c o l l e c t i n g data on movement so t h a t the number of s l u g s i n each treatment area would be s t a n d a r d i z e d at ten or twenty, thus f a c i l i t a t i n g t r a n s f o r m a t i o n of the data to p r o p o r t i o n s f o r comparisions. The f o l l o w i n g data were recorded once each hour duri n g an o b s e r v a t i o n n i g h t : the t o t a l number of s l u g s a c t i v e (on the ground o u t s i d e the s h e l t e r ) ; the numbers moving or r e s t i n g ; the number f e e d i n g , and the number fe e d i n g on each of the three foods s u p p l i e d ( b r a n , c a r r o t , p o t a t o ) . In a d d i t i o n , the degree of c l o u d i n e s s was a r b i t r a r i l y recorded on a s c a l e of 1-3; 1-c l e a r ; 2- p a r t l y cloudy; 3- o v e r c a s t . P r e c i p i t a t i o n was scored i n a s i m i l a r manner, 1- no p r e c i p i t a t i o n ; 2- l i g h t r a i n ; 3- heavy r a i n . A i r temperature and r e l a t i v e humidity at ground l e v e l were recorded h o u r l y with a p o r t a b l e temperature and humidity probe. These m e t e o r o l o g i c a l data were supplemented by h o u r l y readings of a i r temperature and barometric pressure c o l l e c t e d a u t o m a t i c a l l y at the U n i v e r s i t y of B r i t i s h Columbia P l a n t Science F i e l d Laboratory Weather S t a t i o n . During each hour's r e c o r d i n g s e s s i o n , each of the s i x t e e n cages was v i s i t e d once and the same set of data was c o l l e c t e d each time. Thus 120 s l u g s of each s p e c i e s c o u l d be observed each hour. The eleven n i g h t s of o b s e r v a t i o n s on A r i o l i m a x columbianus y i e l d e d 121 hours of data c o l l e c t i o n time; i . e . , 968 cage/hours of o b s e r v a t i o n s over e i g h t cages. S i m i l a r l y t h i r t e e n n i g h t s of A r i o n a t e r o b s e r v a t i o n s produced 132 1144 cage/hours of o b s e r v a t i o n s . The data were recorded on coding sheets and subsequently keypunched in p r e p a r a t i o n f o r a n a l y s i s . The s l u g a c t i v i t y data were transformed i n t o p r o p o r t i o n s by d i v i d i n g the o b s e r v a t i o n s by 10.0 or 20.0, depending on the treatment from which they were o b t a i n e d . T h i s f a c i l i t a t e d cross-comparison of the treatments. The p r o p o r t i o n data conformed to a binomial d i s t r i b u t i o n , which was normalized u s i n g the a r c s i n square-root t r a n s f o r m a t i o n . Before t r a n s f o r m a t i o n , 0.001 was added to each value so that zero p r o p o r t i o n s would be i n c l u d e d i n subsequent a n a l y s e s . R e l a t i o n s h i p s between dependent and independent v a r i a b l e s are not always l i n e a r . R o l l o (1978) noted t h i s and i n order to improve the f i t between weather v a r i a b l e s and s l u g behaviour he generated polynomials f o r some of the weather v a r i a b l e s . These c u r v i l i n e a r f i t s improved the p r e d i c t i v e power of h i s equations c o n s i d e r a b l y . Where a p p l i c a b l e , I have f o l l o w e d the same procedure to improve my own r e g r e s s i o n s and f a c i l i t a t e comparisons with R o l l o ' s work. The raw weather data were manipulated to generate the f o l l o w i n g a d d i t i o n a l weather i n d i c a t o r s : t i m e 2 , t i m e 3 , t i m e 4 temperature 2, temperature 3, temperature 4 temperature change, temperature change 2, temperature change 3, temperature change 4 l a g temperature, l a g temperature 2, l a g temperature 3, l a g 133 temperature 4 barometric p r e s s u r e 2 , barometric p r e s s u r e 3 , barometric p r e s s u r e 4 barometric p r e s s u r e change, barometric p r e s s u r e change 2, barometric pressure change 3, barometric pressure change 4 r e l a t i v e humidity change, l a g r e l a t i v e humidity vapour-pressure d e f i c i t vapour-pressure d e f i c i t change, l a g vapour-pressure d e f i c i t Change v a r i a b l e s were obtained by s u b t r a c t i n g the value of the v a r i a b l e at "time+1" from the value at "time". T h i s was done f o r each hour of the o b s e r v a t i o n p e r i o d . The value from the f i r s t hour of a s e s s i o n was not used s i n c e there was no p r e v i o u s value from which to s u b t r a c t i t . Lag v a r i a b l e s were generated simply by p a i r i n g the weather i n d i c a t o r at "time+1" with the behaviour recorded at "time". In t h i s manner the f i n a l hour's o b s e r v a t i o n s were l o s t from the a n a l y s e s . 134 3.3 R e s u l t s 2«3.1 Treatment E f f e c t s on N o c t u r a l Behaviour The frequency d i s t r i b u t i o n of the p r o p o r t i o n of A r i o n a t e r a c t i v e i s presented i n F i g u r e 16. The high frequency of the 0.0, 0.1, and 0.6-0.9 c l a s s e s gave the r e c t a n g u l a r d i s t r i b u t i o n a s l i g h t l y bimodal appearance. N e i t h e r d e n s i t y , food, nor t h e i r i n t e r a c t i o n had s i g n i f i c a n t e f f e c t s on the frequency d i s t r i b u t i o n s of s l u g behaviours (Table X X I I I ) . The mean p r o p o r t i o n of the A r i o n p o p u l a t i o n a c t i v e over the s c o t o p e r i o d i s p l o t t e d by treatment i n F i g u r e 17. The d i s t r i b u t i o n of a c t i v i t y over time appears q u i t e s i m i l a r f o r a l l treatments. With the exce p t i o n of the B treatment, peak a c t i v i t y o c c u r r e d between 03:00h and 04:00h when between 0.52 and 0.68 of the p o p u l a t i o n were a c t i v e . A l l d i s t r i b u t i o n s were b e l l - s h a p e d . The p l o t s of mean p r o p o r t i o n of A r i o n moving, r e s t i n g , or fee d i n g were q u i t e s i m i l a r i n shape to the p l o t showing the t o t a l p r o p o r t i o n that were a c t i v e ( F i g u r e 17) so they were not in c l u d e d here. A l l were b e l l - s h a p e d , but d i f f e r e d from each other i n the times at which t h e i r p a r t i c u l a r kind of a c t i v i t y peaked, and i n the l e v e l s of that a c t i v i t y a chieved. Although s u p e r f i c i a l i n s p e c t i o n suggested there was no str o n g i n f l u e n c e of the v a r i o u s treatments on these behaviours, the a n a l y s i s i n Table XXIV shows that there were, i n f a c t , such i n f l u e n c e s . 135 Table XXIII. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e of Frequency D i s t r i b u t i o n of Behaviours Recorded f o r A r i o n a t e r V a r i a b l e Source DF K-value P r o b a b i l A c t i v e d e n s i t y 1 0.475 0.491 0.768 0.976    food 1 0 .087 d e n s i t y -food 3 0 .210 Moving d e n s i t y food density-food 1 1 3 0.155 0.053 0.549 0.694 0.818 0.908 R e s t i n g d e n s i t y food density-food 1 1 3 0.211 0.276 0.708 0.646 0.599 0.871 Feeding d e n s i t y food density-food 1 0.039 1. 0.528 3 0.281 0.843 0.818 0.964 137 F i g u r e 16. Frequency D i s t r i b u t i o n of the Mean P r o p o r t i o n of A r i o n a t e r A c t i v e treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 25 15 > O Z LU ZD a m tr .6 .8 10 0. .2 4 P R O P O R T I O N A C T I V E 25 15 > o z LU Z3 o LU CC LL 0. .2 . 4 .6 .8 P R O P O R T I O N A C T I V E 25 15 > o z LU o LU CC 5 h J n i i i : i i ; Q .2 4 6 .8 1.0 P R O P O R T I O N A C T I V E 25 15 > o z LU O LU CC 0. .2 4 .6 .8 1 P R O P O R T I O N A C T I V E 139 F i g u r e 17. Mean P r o p o r t i o n of A r i o n a t e r A c t i v e During the Observation P e r i o d treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 140 141 When o v e r a l l a c t i v i t y was c o n s i d e r e d , n e i t h e r d e n s i t y nor food, nor t h e i r i n t e r a c t i o n , had any s i g n i f i c a n t e f f e c t on the p r o p o r t i o n of A r i o n a t e r a c t i v e , but the i n t e r a c t i o n of d e n s i t y , food and time once again was s i g n i f i c a n t ( F i g u r e 18a). F i g u r e 18aiv demonstrates that the t o t a l a c t i v i t y i n a l l treatments but C i n c r e a s e d from the f i r s t to second experimental p e r i o d s , with B and D p l a t e a u i n g i n the t h i r d p e r i o d , while A and C converged at a lower value than D or B. I n v e s t i g a t i o n of the p r o p o r t i o n of A r i o n a t e r moving r e v e a l e d a s i g n i f i c a n t e f f e c t of the food f a c t o r , but no crowding e f f e c t . Both i n t e r a c t i o n s were s i g n i f i c a n t ; (see the means p l o t t e d i n F i g u r e 18b and Table XXIV). Note that i n Fi g u r e 1 8 b i i the treatments with the poor-food regimes had higher p r o p o r t i o n s of the groups moving than those with the good-food regimes. The tr e n d i n F i g u r e 18biv was the same as tha t f o r the p r o p o r t i o n of A r i o n a c t i v e (Figure 1 8 a i v ) . The C treatment stayed much the same over the whole experimental p e r i o d , whereas the other three rose i n the second p e r i o d from t h e i r i n i t i a l v a l u e s . The D treatment i n c r e a s e d i n the t h i r d p e r i o d , B plateaued, and A dropped s l i g h t l y . The r e s u l t s of the a n a l y s i s of the p r o p o r t i o n of A r i o n a t e r r e s t i n g were i d e n t i c a l to those f o r the p r o p o r t i o n of A r i o n moving. D e n s i t y was the only n o n s i g n i f i c a n t f a c t o r f o r r e s t i n g s l u g s , s i n c e food and the two i n t e r a c t i o n s a l l had s i g n i f i c a n t e f f e c t s . The trends i n these data, when p a r t i o n e d by food and the d e n s i t y - f o o d i n t e r a c t i o n , were the same as 142 those i n the movement data. F i g u r e s 2 1 c i i , i i i show that poor-food treatments had higher p r o p o r t i o n s of r e s t i n g s l u g s than good-food treatments. The trends of the p r o p o r t i o n r e s t i n g viewed over time (Figure 18civ) were d i f f e r e n t from those observed f o r the p r o p o r t i o n that was a c t i v e and the p r o p o r t i o n moving. The A treatment showed l i t t l e change over the summer, B i n c r e a s e d through the whole experimental p e r i o d , whereas C and D treatments f e l l from t h e i r i n i t i a l l e v e l s , r i s i n g again i n the t h i r d experimental p e r i o d , but never a c h i e v i n g t h e i r o r i g i n a l l e v e l s . F i n a l l y we co n s i d e r the p r o p o r t i o n of the p o p u l a t i o n f e e d i n g . P a r t i o n i n g f o r d e n s i t y showed no e f f e c t on f e e d i n g (Table XXIV, F i g u r e 1 8 d i ) . The food f a c t o r , however, had a s i g n i f i c a n t e f f e c t , with the good-food treatments showing higher p r o p o r t i o n s f e e d i n g than poor-food treatments (Table XXIV, F i g u r e 1 8 d i i ) . The d e n s i t y - f o o d i n t e r a c t i o n had no s i g n i f i c a n t e f f e c t , but the i n t e r a c t i o n of d e n s i t y , food and time was once again s i g n i f i c a n t (Table XXIV, F i g u r e 1 8 d i i i , i v ) . The trends of the p r o p o r t i o n f e e d i n g i n F i g u r e 18div were s i m i l a r to the trends of o v e r a l l a c t i v i t y over time ( F i g u r e 1 8 a i v ) . A l l treatments showed i n c r e a s e s from the f i r s t to second experimental p e r i o d s and a l l but C showed a d e c l i n e by the t h i r d p e r i o d . XXIV. A n a l y s i s of v a r i a n c e : Nocturnal Observations A r i o n a t e r Behaviour a r c s i n ( s q u a r e - r o o t x+0.001) transform used on data x=mean p r o b a b i l i t y of ( a c t i v e , moving, r e s t i n g , or feeding) from two r e p l i c a t e s 144 V a r i a b l e Source DF F-value P r o b a b i l i t y A c t i v e d e n s i t y food d e n s i t y -food d e n s i t y -food-time 1 1 3 0.002 2.078 1.179 11 3.485 0.962 0.100 0.317 <.001 Moving d e n s i t y food d e n s i t y -food d e n s i t y -food-time 1 1 3 0.112 9.472 3.325 11 3.904 0.738 0.002 0.020 <.001 R e s t i n g d e n s i t y food d e n s i t y -food d e n s i t y -food-time 1 1 3 1.603 10.45 5.402 11 4.644 0.206 0.001 0.001 <.001 Feeding d e n s i t y food d e n s i t y -food d e n s i t y -food-time 1 1 3 0.509 4.361 1.986 11 5.870 0.476 0.037 0.115 <.001 145 F i g u r e 18. Mean P r o p o r t i o n of A r i o n a t e r Engaged i n Moving, R e s t i n g , and Feeding treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food Values on o r d i n a t e a x i s are a r c s i n ( s q u a r e - r o o t ) transforms of p r o p o r t i o n a l data. b i i .50 r-b i .45, .40 ID 2 > o 5 45 1 LOW HIGH SLUG DENSITY .45 .40 45 GOOD. POOR >OOD 148 c i 30 i •25 CO w .20 LOW HIGH SLUG DENSITY c i i 30 .25 .20 GOOD POOR FOOD civ c i i i 35 .25 -o z CO 111 OC .,51 B C TREATMENT D ^ \— ^ 1.2 3,4 REPLICATES 5,6 149 d i .35 r-.30 O 2 Q LU LU LL. .25 LOW HIGH SLUG DENSITY d i i 45 .30 .25 GOOD POOR FOOD 150 The frequency d i s t r i b u t i o n of the p r o p o r t i o n of A r i o l i m a x columbianus a c t i v e i s p l o t t e d i n F i g u r e 19. Very l a r g e f r e q u e n c i e s i n the 0.00 c l a s s and high v a l u e s i n the 0.40-0.60 c l a s s e s gave the d i s t r i b u t i o n s a bimodal appearance in c o n t r a s t to the frequency d i s t r i b u t i o n of the p r o p o r t i o n of A r i o n a t e r a c t i v e ( F i g u r e 16) which appeared r e c t a n g u l a r . There were few o c c a s i o n s when most of the A r i o l i m a x were a c t i v e , which c o n t r i b u t e d to the bimodal appearance of the frequency d i s t r i b u t i o n of the p r o p o r t i o n a c t i v e . The a n a l y s i s of these data based on p a r t i t i o n i n g by d e n s i t y , food, and t h e i r i n t e r a c t i o n i s shown i n Table XXV. None of these f a c t o r s had any s i g n i f i c a n t e f f e c t on the p r o p o r t i o n of A r i o l i m a x a c t i v e . S i m i l a r a n a l yses c a r r i e d out on the p r o p o r t i o n s of A r i o l i m a x moving, r e s t i n g , and f e e d i n g y i e l d e d n o n s i g n i f i c a n t r e s u l t s (Table XXV). The mean p r o p o r t i o n of A r i o l i m a x columbianus a c t i v e were p l o t t e d by hour f o r each experimental treatment i n F i g u r e 20. The p r o p o r t i o n a c t i v e i n c r e a s e d over the o b s e r v a t i o n p e r i o d to maximum l e v e l s between 04:00h and 05:00h. The t r u n c a t e d nature of the p l o t s was due to the f a c t that i n d i v i d u a l A r i o l i m a x were s t i l l a c t i v e when the o b s e r v a t i o n p e r i o d ended. The A r i o l i m a x histograms were l e s s b e l l - s h a p e d than those f o r A r i o n a t e r (Figure 17). Furthermore, the i n c r e a s e i n a c t i v i t y over time was slower f o r A r i o l i m a x than f o r A r i o n . These d i f f e r e n c e s can be e x p l a i n e d by d i f f e r e n c e s i n onset and t i m i n g of a c t i v i t y of A r i o n and A r i o l i m a x . 151 Table XXV. K r u s k a l - W a l l i s nonparametric a n a l y s i s of v a r i a n c e of Frequency D i s t r i b u t i o n s of Behaviours Recorded f o r A r i o l i m a x columbianus V a r i a b l e Source DF K-value P r o b a b i l Act i v e d e n s i t y food d e n s i t y -food 1 1 3 0.389 0.004 3.057 0.533 0.948 0.383 Moving d e n s i t y food d e n s i t y -food 1 1 3 0.108 0.873 1.318 0.743 0.768 0.725 Re s t i n g d e n s i t y food d e n s i t y -food 1 1 3 0.004 0.053 0.695 0.948 0.818 0.874 Feeding d e n s i t y food d e n s i t y -food 1 1 3 0.069 0.134 1.431 0.792 0.718 0.698 153 F i g u r e 19. Frequency D i s t r i b u t i o n of the Mean P r o p o r t i o n of A r i o l i m a x columbianus A c t i v e treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 154 77 n 25 15 > o z LU 13 o LU QC LL a .2 4 .6 .8 1.0 P R O P O R T I O N ACTIVE 25 15 > O z LU 13 o LU CC LL a .2 .4 .6 .8 1.0 P R O P O R T I O N A C T I V E 98 25 15 > o z LU Z2 a LU CC ^ SI "1 ^ l I I . a .2 4 .6 .8 10 P R O P O R T I O N A C T I V E 68 r to* 25 15 > o z LU => o LU CC LL i i i r a .2 .4 6 .8 1.0 P R O P O R T I O N A C T I V E 155 F i g u r e 20. Mean P r o p o r t i o n of A r i o l i m a x columbianus A c t i v e During the Observation P e r i o d treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food 156 TIME (RUT) TIME (RD.T) 157 A n a l y s i s of the p r o p o r t i o n of A r i o l i m a x columbianus a c t i v e y i e l d e d the r e s u l t s i n Table XXVI. Both f a c t o r s and t h e i r i n t e r a c t i o n s had s i g n i f i c a n t e f f e c t s on the p r o p o r t i o n a c t i v e . The r e s u l t s are presented i n F i g u r e 21a, which shows that more movement was a s s o c i a t e d with the adverse c o n d i t i o n s of crowding or food. The treatments were s i g n i f i c a n t l y d i f f e r e n t from each other (Table XXVI). The A treatment had the lowest v a l u e s , D the h i g h e s t , and B and C were not very d i f f e r e n t ( F i gure 21ai i i ). The same a n a l y s i s was performed on the transformed p r o p o r t i o n of A r i o l i m a x columbianus moving (Table XXVI). The crowding f a c t o r had a s i g n i f i c a n t e f f e c t on the p r o p o r t i o n moving. The e f f e c t of food was not s i g n i f i c a n t . The i n t e r a c t i o n of d e n s i t y and food was not s i g n i f i c a n t , but the i n t e r a c t i o n of d e n s i t y , food, and time was s i g n i f i c a n t . These r e s u l t s are shown i n (Figure 21b). The crowded group showed a higher mean p r o p o r t i o n a c t i v e than the uncrowded one ( F i g u r e 2 1 b i ) . T h i s d i f f e r e n c e p e r s i s t e d when the experimental treatments were p l o t t e d i n d i v i d u a l l y , ( F igure 2 1 b i i i ) . When the data were viewed by treatment over time ( F i g u r e 21biv) i t i s e v ident t h a t i n a l l treatments but A, . the mean p r o p o r t i o n a c t i v e i n c r e a s e d over time. The d i f f e r e n c e s between the treatments were s i g n i f i c a n t (Table XXVI). Only the d e n s i t y f a c t o r and the d e n s i t y - f o o d i n t e r a c t i o n had any s i g n i f i c a n t e f f e c t s on the p r o p o r t i o n of A r i o l i m a x columbianus r e s t i n g (Table XXVI). The crowded 158 c o n d i t i o n s had l a r g e r p r o p o r t i o n s of slug s r e s t i n g than uncrowded s i t u a t i o n s (Figure 2 1 c i ) . The d i f f e r e n c e i n the p r o p o r t i o n r e s t i n g under the two food regimes was n e g l i g i b l e ( F i g u r e 2 1 c i i ) . F i g u r e 2 1 c i i i shows that the h i g h - d e n s i t y treatments had l a r g e r p r o p o r t i o n s of t h e i r p o p u l a t i o n s r e s t i n g , r e g a r d l e s s of food regime, than the low-density treatments. Although the d e n s i t y - f o o d - t i m e i n t e r a c t i o n was f o r once not s i g n i f i c a n t , a l l treatments showed i n c r e a s e s i n the p r o p o r t i o n r e s t i n g over the whole experimental p e r i o d ( F i g u r e 2 1 c i v ) . The a n a l y s i s of the p r o p o r t i o n of A r i o l i m a x columbianus fe e d i n g y i e l d e d the same r e s u l t s as the a n a l y s i s of the p r o p o r t i o n a c t i v e ; a l l f a c t o r s and i n t e r a c t i o n s had s i g n i f i c a n t e f f e c t s (Table XXVI). The slug s i n the crowded treatments fed more than those i n uncrowded treatments (Figure 2 1 d i ) . Slugs with good food regimes fed more than sl u g s with poor food regimes ( F i g u r e 2 1 d i i ) . Looking at the data by treatment (F i g u r e 2 1 d i i i ) the order of d e c r e a s i n g f e e d i n g i s B, A, D, C. Over time, the p r o p o r t i o n f e e d i n g i n the B treatment decreased, while the other three treatments i n c r e a s e d (Figure 2 1 d i v ) . A noteworthy p a t t e r n i n the A r i o l i m a x columbianus b e h a v i o u r a l data i s that i n each of the a c t i v i t i e s observed the B treatment always had the hi g h e s t mean p r o p o r t i o n of s l u g s engaged (Figure 2 1 a i i i , b i i i , c i i i , d i i i ) . T h i s treatment s u b j e c t e d the s l u g s to high d e n s i t i e s with a good food regime. Commonsense would suggest that t h i s treatment ought to have been l e s s benign than the A treatment, which had low d e n s i t i e s 159 of s l u g s and abundant good food. Consequently, one might expect to f i n d that the A treatment had more slug s a c t i v e than the B treatment. T h i s t r e n d deserves c a r e f u l i n v e s t i g a t i o n , e s p e c i a l l y i n view of the f a c t that there was no s i m i l a r t rend i n the A r i o n a t e r data. 160 Table XXVI. A n a l y s i s of v a r i a n c e : Nocturnal Observations of A r i o l i m a x columbianus Behaviour A r c s i n ( s q u a r e - r o o t x+0.001) t r a n s f o r m a t i o n used on data x=mean p r o b a b i l i t y of ( a c t i v e , moving,resting, or feeding) from two simultaneous r e p l i c a t e s . V a r i a b l e Source DF F-value P r o b a b i l A c t i v e d e n s i t y food d e n s i t y -food d e n s i t y -food-time Moving d e n s i t y food d e n s i t y -food d e n s i t y -food-time R e s t i n g d e n s i t y food d e n s i t y -food d e n s i t y -food-time Feeding d e n s i t y food d e n s i t y -food d e n s i t y -food-time 1 4.527 0.034 I <.001 0.954 3 1.536 0.204 II 3.543 <.001 1 6.822 0.009 I 10.969 0.001 3 5.984 <.001 II 1.880 0.023 1 6.939 0.009 I 0.743 0.389 3 2.989 0.031 II 1.632 0.124 I 3.848 0.050 9.189 0.005 3 4.457 0.004 II 2.397 0.020 162 F i g u r e 21. Mean P r o p o r t i o n of A r i o l i m a x columbianus Engaged i n Moving, R e s t i n g , and Feeding treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food Values on o r d i n a t e a x i s are a r c s i n ( s q u a r e - r o o t ) transforms of p r o p o r t i o n a l data. 163 a i •9r LU > c3 L O W HIGH S L U G DENSITY a i i 9 r G O O D P O O R F O O D 164 b i •56 i b i i .50 i 48 .46 CD > o 2 .401 L O W HIGH S L U G DENSITY 42 G O O D POOR F O O D b i i i B C T R E A T M E N T biv 6 r 5 3 h 1.2 3,4 R E P L I C A T E S 165 c i .25 1 .20 o z r-co Ul CC .15 1 LOW HIGH SLUG DENSITY c i i .25 r .20 •15 GOOD POOR FOOD 166 d i 35 r .30 o 2 a LU LU .25 LOW HIGH SLUG DENSITY d i i 4 5 r .30 .25 GOOD P O O R FOOD d i v d i i i .40 • .35 • 4 0 1 .30 CD 2 Q UJ LU U - .20 B C TREATMENT * 5 .201 V 3,4 REPLICATES 1 6 7 3.3.2 Weather E f f e c t s on N o cturnal Behaviour: General F i g u r e 22 p r o v i d e s a general p i c t u r e of n o c t u r n a l A r i o n a t e r a c t i v i t y d u r i n g the summer. The dates s e l e c t e d f o r t h i s F i g u r e came from the t h i r t e e n n i g h t s of o b s e r v a t i o n s and were chosen such that there was one from each of the experimental p e r i o d s . The histograms p o r t r a y t o t a l s l u g a c t i v i t y i n each of the treatments over the o b s e r v a t i o n p e r i o d and the temperature, vapour-pressure d e f i c i t graph p r o v i d e s a r e f e r e n c e f o r two important weather f a c t o r s . I n s p e c t i o n of these f i g u r e s l e d to the f o l l o w i n g d e s c r i p t i o n s . Cool temperatures d u r i n g most of the night of June 5, 1979, may account f o r the low s l u g a c t i v i t y (Figure 2 2 a i ) . The vapour-pressure d e f i c i t was not e x c e e d i n g l y high but i t may a l s o have reduced a c t i v i t y (compare F i g u r e s 2 6 a i , i i i ) . There was 7.6 mm of r a i n on June 4 and the average d a i l y temperatures on June 4,5 were 15.5° and 15.1°C, r e s p e c t i v e l y . The C and D treatments had about 10% more a c t i v i t y per hour than the A and B treatments. High n o c t u r n a l temperatures and e v a p o r a t i v e s t r e s s c u r t a i l e d a c t i v i t y d u r i n g the n i g h t of August 1, 1979 ( F i g u r e 2 2 a i i ) . Although the average amount of a c t i v i t y i n each treatment was not much reduced ( i n f a c t i t i n c r e a s e d i n the D treatment) i t was compressed i n t o a s h o r t e r p e r i o d than on the other dates f o r which data are presented. There had been no r a i n f o r at l e a s t two weeks p r e v i o u s l y and the average d a i l y 168 temperature had been 18.5° and 21.6°C on the p r e v i o u s two days. High temperature (17.5°C) at 20:00h may have delayed the onset of a c t i v i t y on August 16,1979 (Figure 2 2 a i i i ) . However, temperature and vapour-pressure d e f i c i t dropped r a p i d l y t h e r e a f t e r and plateaued, and near-maximal p o p u l a t i o n a c t i v i t y o c c u r r e d through the r e s t of the n i g h t . D i f f e r e n c e s i n average a c t i v i t y between treatments were not g r e a t . The average d a i l y temperatures of the p r e v i o u s two days (16.9° and 14.0°C) were s i m i l a r to those on June 4 and 5, 1979. Vapour-pressure d e f i c i t on t h i s n i g h t was the lowest of the three days presented, and 26.2 mm of r a i n d u r i n g the p r e v i o u s two days ended a 33-day drought. F i g u r e 22bi shows the a c t i v i t y of A r i o l i m a x columbianus on the n i g h t of June 26,1979. Both temperature and vapour-pressure d e f i c i t dropped s t e a d i l y throughout the evening. Slugs i n the A, C, and D treatments d i d not become a c t i v e u n t i l a f t e r midnight and the l e v e l of a c t i v i t y remained low f o r the d u r a t i o n of the o b s e r v a t i o n p e r i o d . Slugs i n the B treatment became a c t i v e at 22:00h and reached maximum a c t i v i t y at 5:00h. The p a t t e r n f o llowed by temperature and vapour-pressure d e f i c i t on August 1,1979, was s i m i l a r to that of June 26. A r i o l i m a x columbianus's a c t i v i t y p a t t e r n was a l s o s i m i l a r on both n i g h t s (Figure 2 2 b i i ) . A c t i v i t y began a f t e r midnight and l e v e l s of a c t i v i t y were higher than on June 26. A c t i v i t y i n the B treatment was s i m i l a r to the other three on t h i s n i g h t suggesting that the high l e v e l of a c t i v i t y on the f i r s t n i g h t 169 presented may be an a r t e f a c t . The temperature remained higher on August 16,1979, than i t had on p r e v i o u s n i g h t s and the vapour-pressure d e f i c i t r e f l e c t e d a low ev a p o r a t i v e r a t e throughout the n i g h t . Slug a c t i v i t y began sooner i n a l l treatments ( i n f a c t as e a r l y as 21:00h i n the A and B treatments) and was more intense than on other n i g h t s (Figure 2 2 b i i i ) . 170 F i g u r e 22. Nocturnal A c t i v i t y on Nights During the Experimental P e r i o d a: A r i o n a t e r b: A r i o l i m a x columbianus treatments A: uncrowded, good food B: crowded, good food C: uncrowded, poor food D: crowded, poor food Temperature Vapour-pressure d e f i c i t There i s no data at 02:00h f o r F i g u r e 22bi 172 a i l A 1.0 i-20. LU < CC LU CL 10. _I ! 1 1_ 700. 300. 100. Q > 20 22 24 2 4 6 B 1.0 r i • ; 20 22 24 2 4 S 20 22 24 2 4 6 1.0,-2 1-i i i i : 1 i i i , , ; 20 22 24 2 4 6 TIME (RD.T.J D ' • O r ""• I I I I , i , . 20 22 24 2 4 6 TIME (RDT) ACTIVE « « g OJ 174 175 TIME (RD.TJ TIME (ROT.) 177 3.3.2 Weather E f f e c t s on Nocturnal Behaviour; C o r r e l a t i o n - R egression C o r r e l a t i o n and r e g r e s s i o n a n a l y s e s were performed to determine i f any of the weather v a r i a b l e s recorded d u r i n g the behaviour o b s e r v a t i o n s c o u l d be i m p l i c a t e d i n the m o d i f i c a t i o n of the behaviours that make up t o t a l s l u g a c t i v i t y . R o l l o (1978) used t h i s technique with a l a r g e r set of weather v a r i a b l e s and d e r i v e d equations from them to p r e d i c t the l e v e l of s l u g a c t i v i t y . The t h r u s t of my a n a l y s i s has been l e s s concerned with p r e d i c t i o n than with d e s c r i b i n g the a s s o c i a t i o n between weather and s l u g behaviour. C o r r e l a t i o n c o e f f i c i e n t s were c a l c u l a t e d f o r each of the behaviours and a l l of the weather v a r i a b l e s recorded. The c o e f f i c i e n t s are contained i n Appendix A and B f o r A r i o n a t e r and A r i o l i m a x columbianus . Using the c o r r e l a t i o n c o e f f i c i e n t s as guides, stepwise m u l t i p l e r e g r e s s i o n s were c a r r i e d out on the transformed p r o p o r t i o n s of the v a r i o u s a c t i v i t i e s . The best f i t s were obt a i n e d by using data from the A and the D treatments to generate two separate equations that i n c l u d e d the same weather data. By using the most extreme treatments i t was thought that any d i f f e r e n c e s i n response to weather under the d i f f e r e n t treatments would be c l e a r e r . 178 The r e g r e s s i o n analyses f o r A r i o n a t e r can be found i n Appendix C. Time, r e p r e s e n t i n g c i r c a d i a n rhythm, was i n c l u d e d i n every equation generated f o r the behaviour of A r i o n . Some polynomial expansion of time, u s u a l l y q u a r t i c , was used i n each equation. T h i s i n d i c a t e d the n o n - l i n e a r i t y of the time-behaviour r e l a t i o n s h i p . F i g u r e 17 pr o v i d e s an example of t h i s r e l a t i o n s h i p . Temperature was the next most p r e v a l e n t f a c t o r . Temperature polynomials appeared i n a l l but one equa t i o n . The equations f o r t o t a l a c t i v i t y and movement i n c l u d e d the temperature change f a c t o r . Vapour-pressure d e f i c i t was the most common measurement of atmospheric moisture. I t appeared i n 6 of 8 equa t i o n s . R e l a t i v e humidity was a l e s s s u i t a b l e i n d i c a t o r as f a r as these experiments were concerned and i t appeared i n only three e q u a t i o n s . Change i n vapour-pressure d e f i c i t and r e l a t i v e humidity were c o n t a i n e d i n three equations, but t h e i r p a r t i a l c o r r e l a t i o n c o e f f i c i e n t s were s m a l l . Barometric pressure was found only i n equations f o r moving and feeding s l u g s i n the D treatment. Lag temperature v a r i a b l e s were i n c l u d e d i n equations of moving, r e s t i n g , and fe e d i n g and l a g vapour-pressure d e f i c i t and r e l a t i v e humidity appeared i n moving, r e s t i n g , and t o t a l a c t i v i t y . Comparing equations f o r A and D treatments r e g a r d l e s s of the a c t i v i t y i n v o l v e d showed that there was l i t t l e d i f f e r e n c e between the two s e t s of equa t i o n s . Time, temperature, and atmospheric moisture were re p r e s e n t e d i n each e q u a t i o n . The only d i f f e r e n c e between equations from A and D treatments was 179 that barometric pressure was i n c l u d e d only i n moving and r e s t i n g equations from the D treatment. One d i s t i n c t i o n that c o u l d be made between the dependent v a r i a b l e s i n the equations was that the temperature change v a r i a b l e appeared o n l y i n the equations f o r a c t i v e and moving s l u g s . The only other p o i n t needing c l a r i f i c a t i o n i s the composition of the feeding equation from the D treatment. I t i s composed e x c l u s i v e l y of time and barometric p r e s s u r e . The r e g r e s s i o n equations c a l c u l a t e d f o r A r i o l i m a x columbianus (Appendix C) were s i m i l a r to those c a l c u l a t e d f o r A r i o n a t e r i n that they a l l con t a i n e d a polynomial expansion of time. Temperature polynomials appeared i n a l l but one equation. In c o n t r a s t with the A r i o n equations, temperature change and lag-temperature were i n c l u d e d i n the equations generated f o r A r i o l i m a x . Vapour-pressure d e f i c i t , vapour-pressure d e f i c i t change, and lag-vapour-pressure d e f i c i t were the most common i n d i c a t o r s of atmospheric moisture o c c u r r i n g i n the equa t i o n s . A r i o l i m a x showed a gre a t e r s e n s i t i v i t y to barometric p r e s s u r e than A r i o n . T h i s v a r i a b l e was i n c l u d e d i n a l l e i g h t equations. Barometric pressure change appeared i n three equations. Cloud cover appeared i n only three equations, but not at a l l i n the r e g r e s s i o n a n a l y s i s of A r i o n behaviour. There were two d i f f e r e n c e s between equations from A and D treatments. The appearance of lag-temperature was c o n f i n e d to the D treatment equations f o r moving, r e s t i n g , and fe e d i n g . 180 Vapour-pressure d e f i c i t change was found only i n equations from D treatments. The equations f o r each behaviour were b a s i c a l l y s i m i l a r . A l l i n c l u d e d time, temperature, atmospheric moisture, and barometric pressure v a r i a b l e s . The one exception was the equation f o r t o t a l a c t i v i t y by the s l u g s i n the A treatment, which d i d not i n c l u d e temperature. A r i o l i m a x columbianus appeared to be more s e n s i t i v e than A r i o n a t e r to changes i n , and lagged values of, the weather v a r i a b l e s . 3.3.4 Feeding Preferences Although s l u g s are g e n e r a l i s t h e r b i v o r e s they are s e l e c t i v e about what they eat. Food s e l e c t i o n appears to be based on p a l a t a b i l i t y (Cates and Orians 1975, Duval 1973, P a l l a n t 1969). Calow (1975) found a p o s i t i v e c o r r e l a t i o n between food preference and a b s o r p t i o n e f f i c i e n c y i n two s n a i l s p e c i e s , Ancylus f l u v i a t i l i s and P l a n o r b i s c o n t o r t u s . They a l s o ate l e s s of the most h i g h l y d i g e s t a b l e foods. I was i n t e r e s t e d i n the r e l a t i o n s h i p between food c h o i c e and i t s n u t r i t i o n a l value and my b e h a v i o u r a l o b s e r v a t i o n s gave me a crude approach to the q u e s t i o n . The number of s l u g s f e e d i n g d u r i n g each hour's o b s e r v a t i o n s were su b d i v i d e d i n t o the numbers feed i n g on wheat bran, c a r r o t root, and potato tuber. These data were then used to c a l c u l a t e the p r o p o r t i o n of f e e d i n g s l u g s e a t i n g each 181 of these three foods d u r i n g each hour. T h i s a n a l y s i s was performed only f o r the A and B treatments, as slug s i n C and D treatments had only c e l e r y to e a t . The mean p r o p o r t i o n e a t i n g each food i s p l o t t e d i n F i g u r e 23. Both s p e c i e s showed c l e a r p r e f e r e n c e s f o r the v a r i o u s foods a v a i l a b l e . For both s p e c i e s the order of pr e f e r e n c e was wheat bran, c a r r o t r o o t , and potato tuber. P a i r w i s e t - t e s t s were performed on a l l p o s s i b l e combinations, with the r e s u l t s shown i n Table XXVII. A l l p a i r s were q u i t e s i g n i f i c a n t l y d i f f e r e n t , with the exception of the b r a n - c a r r o t p a i r f o r A r i o l i m a x columbianus . Both s p e c i e s of s l u g chose the foods i n order of de c r e a s i n g c a l o r i c value, however, I d i d not determine whether i n d i v i d u a l s l u g s fed on a l l types of food, or i f some s l u g s were excluded from feeding on the most n u t r i t i o u s food. 182 F i g u r e 23. Mean P r o p o r t i o n of P o p u l a t i o n Feeding on A v a i l a b l e Foods a: A r i o n a t e r b: A r i o l i m a x columbianus Q LU LU LU P O T A T O C A R R O T B R A N 2 D LU LU O _1_ POTATO C A R R O T B R A N 184 Table XXVII. P a i r w i s e t - t e s t s : P r o p o r t i o n of Feeders E a t i n g Foods A v a i l a b l e 185 A r i o n a t e r V a r i a b l e Bran/Potato Bran/Carrot P o t a t o / C a r r o t Mean D i f f e r e n c e 0.281 0.123 -0.158 T-value P r o b a b i l i t y 9.437 <.001 3.398 <.001 -5.769 <.001 Ar i o l i m a x columbianus V a r i a b l e Bran/Potato Bran/Carrot P o t a t o / C a r r o t Mean D i f f e r e n c e 0.323 0.069 -0.254 T-value P r o b a b i l i t y 10.519 <.001 1.807 0.072 -8.415 <.001 186 3.4 D i s c u s s i o n 3_.4..1 Treatment E f f e c t s on Nocturnal Behaviour The frequency d i s t r i b u t i o n s of the behaviours recorded f o r A r i o n a t e r were not s i g n i f i c a n t l y d i f f e r e n t among the four experimental treatments. T h i s s i m i l a r i t y i n d i c a t e d that there was no l a r g e s h i f t i n A r i o n ' s a c t i v i t y caused by the treatments. The p l o t of the mean p r o p o r t i o n of A r i o l i m a x columbianus a c t i v e d u r i n g the o b s e r v a t i o n p e r i o d s demonstrated a s i m i l a r absence of any treatment e f f e c t s on t h i s d i s t r i b u t i o n . A r i o n a t e r normally became a c t i v e at about 20:00h i n the summer. I t s a c t i v i t y i n c r e a s e d q u i c k l y through the evening, reachin g i t s peak at 01:00 or 02:00h and s t e a d i l y d e c r e a s i n g t h e r e a f t e r . T h i s p a t t e r n i s s i m i l a r to that of the s l u g Derocerus r e t i c u l a t u m ( R o l l o 1978). R o l l o (1978) and Lewis (1967) found that A r i o n reached peak a c t i v i t y at 24:00h. The f a c t that the p o p u l a t i o n s I used peaked l a t e r may have been due to the experimental c o n d i t i o n s . R o l l o used covered cages which may have mediated the temperature and r e l a t i v e humidity, whereas my cages were uncovered. Optimal m e t e o r o l o g i c a l c o n d i t i o n s f o r a c t i v i t y might have been reached at a l a t e r hour i n the uncovered cages. A r i o l i m a x columbianus a c t i v i t y i n c r e a s e d more slowly than A r i o n a t e r a c t i v i t y . Maximum a c t i v i t y was reached at 03:00 or 187 04:00h. A r i o l i m a x a c t i v i t y sometimes extended beyond the end of the o b s e r v a t i o n p e r i o d , which accounted f o r the t r u n c a t e d r i g h t - h a n d s i d e of the f i g u r e s . R i c h t e r (1976a) found that high temperatures and low r a i n f a l l s e v e r e l y c u r t a i l e d A r i o l i m a x 's f o r a g i n g behaviour and that the s l u g s , which were normally d i u r n a l i n h i s study area, became a c t i v e i n the l a t e evening and e a r l y morning. R o l l o (1978) found peak A r i o l i m a x a c t i v i t y between 02:00 and 03:00h. The d i f f e r e n c e s i n the e n c l o s u r e s again c o u l d account f o r the l a 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 of both s p e c i e s were s i m i l a r to p a t t e r n s f o r these s p e c i e s r e p o r t e d elsewhere ( R i c h t e r 1976a, R o l l o 1978). The abscence of any e f f e c t of d e n s i t y on the h o u r l y a c t i v i t y of A r i o n a t e r was c u r i o u s i n l i g h t of the e f f e c t s of d e n s i t y on migratory a c t i v i t y (see p a r t 1.3). The manner i n which the food regime a f f e c t e d n o c t u r n a l a c t i v i t y was not s u r p r i s i n g . In e n c l o s u r e s where food was s c a r c e and of low q u a l i t y there was bound to be l e s s feeding and more time spent s e a r c h i n g f o r food. In l i g h t of these r e s u l t s i t i s my hypothesis that on a short-term, n i g h t l y b a s i s , A r i o n ' s responses are food-based. Once a c t i v e , a s l u g ' s main concern was the l o c a t i o n and i n g e s t i o n of adequate amounts of s u i t a b l e food. For some animals, g e t t i n g an adequate d a i l y food r a t i o n i s c r i t i c a l f o r s u r v i v a l u n t i l the next day (Gibb 1954, Goss-Custard 1969). Although s l u g s can s u r v i v e f o r long p e r i o d s without food ( C h a t f i e l d 1976) t h e i r growth and development would undoubtedly 188 be slower. C o n s i d e r i n g the b i o l o g y of A r i o n a t e r , i t i s ada p t i v e that i t should be f o o d - o r i e n t e d on a n i g h t l y b a s i s . A r i o n has a one-year l i f e c y c l e (Quick 1949,1960) so i t has but one a c t i v e season to accumulate adequate energy r e s e r v e s f o r maximal egg p r o d u c t i o n . A l s o , f e e d i n g at every a v a i l a b l e o p p o r t u n i t y would i n c r e a s e the s l u g ' s growth r a t e and reduce the t h r e a t of d e s i c c a t i o n through the decrease i n s u r f a c e a r e a / volume r a t i o that i s a s s o c i a t e d with l a r g e r s i z e . B l i n n ' s (1963) o b s e r v a t i o n of higher frequency of a c t i v i t y i n j u v e n i l e than a d u l t Mesodon t h y r o i d u s and Al l o g o n a profunda support these s u g g e s t i o n s . During the present experiments A r i o l i m a x columbianus were not as a c t i v e feeders as A r i o n a t e r . T h i s d i f f e r e n c e may have been because A r i o l i m a x l i v e s e x c l u s i v e l y i n wooded h a b i t a t s , while A r i o n i s found i n meadows and at the edge of f o r e s t s . A r i o l i m a x may have found the experimental h a b i t a t u n s u i t a b l e f o r e x t e n s i v e f o r a g i n g a c t i v i t y . P o s s i b l y , i n d i v i d u a l A r i o l i m a x were only a c t i v e i n sp o r a d i c b u r s t s ; i . e . , a heavy bout of f e e d i n g c o u l d have been f o l l o w e d by a d i g e s t i v e pause that spanned a day or two. T h i s p o s s i b i l i t y was suggested by R o l l o ( p e r s . comm.). Hunter (1968) demonstrated that although the three s p e c i e s of s l u g s he s t u d i e d ate the same amount of food, they fed at d i f f e r e n t r a t e s ; i . e . , those that f e d most o f t e n consumed the l e a s t amount of food d u r i n g each f e e d i n g bout. T h i s may have been the case with A r i o l i m a x . 189 Increased a c t i v i t y of A r i o l i m a x columbianus r e s u l t i n g from high s l u g d e n s i t y may have been caused by s o c i a l f a c i l i t a t i o n . Because of t h e i r l a r g e s i z e , the slug s were i n c l o s e p r o x i m i t y in the s h e l t e r s , o f t e n p i l e d on top of one another. In t h i s s i t u a t i o n , when one s l u g became a c t i v e i t would d i s t u r b others around i t . T h i s d i s t u r b a n c e c o u l d be t r a n s m i t t e d through the whole p o p u l a t i o n , inducing widespread a c t i v i t y . Such r i p p l e e f f e c t s are known to occur with Western te n t c a t e r p i l l a r s ( W ellington 1974b). Once on the s u r f a c e , repeated c o n t a c t s between s l u g s c o u l d f u r t h e r s t i m u l a t e movement away from s h e l t e r . A r i o l i m a x i n crowded e n c l o s u r e s a l s o spent more time r e s t i n g . T h i s i n a c t i v i t y c o u l d have been f o r thermoregulatory purposes ( R i c h t e r 1976a), h y g r o r e g u l a t i o n (Machin 1975) or a pause t o d i g e s t food. The l a t t e r may be the most l i k e l y e x p l a n a t i o n , s i n c e more fe e d i n g o c c u r r e d i n the crowded treatments. A r i o l i m a x columbianus fed more when good food was a v a i l a b l e . Slugs f e e d i n g on abundant, h i g h - q u a l i t y forage moved as much as those faced with poorer r e s o u r c e s . One might have expected more movement i n poor food areas, as with A r i o n a t e r , s i n c e lack of s u i t a b l e forage ought to induce s e a r c h i n g behaviour. The lack of i n c r e a s e d a c t i v i t y by A r i o l i m a x i n the poor-food e n c l o s u r e s , however, i s c o n s i s t e n t with the lack of i n f l u e n c e of food on i t s m i g r a t i o n . S t a r v a t i o n or dehydration can l e a d to a d e c l i n e i n the metabolic r a t e of pulmonates (Machin 1975), which would reduce 190 a s l u g ' s l e v e l of a c t i v i t y and r e s t r i c t i t s rate of movement. The B treatment, with good food and h i g h s l u g d e n s i t y , had the most a c t i v i t y of any of the treatments. In s p i t e of adequate food, the s l u g s i n t h i s treatment behaved i n the same manner as the A r i o l i m a x i n the D treatment, i n d i c a t i n g that d e n s i t y was more important than food i n i t s e f f e c t s on A r i o l i m a x behaviour over the short and long terms. 3.4.2 Weather E f f e c t s on Nocturnal Behaviour M u l t i p l e l i n e a r r e g r e s s i o n a n a l y s e s c a l c u l a t e d by Crawford-Sidebotham (1972) i n d i c a t e d that s l u g a c t i v i t y c o u l d be r e l a t e d to temperature and vapour-pressure d e f i c i t . He found that A r i o n a t e r a c t i v i t y c o u l d be r e l a t e d s o l e l y to temperature. R o l l o ' s (1978) m u l t i p l e r e g r e s s i o n s c o n f i r m the i n t e r a c t i o n of i n t e r n a l rhythm and weather in the c o n t r o l of s l u g behaviour. In h i s equations, the most important f a c t o r s were those r e p r e s e n t i n g the c i r c a d i a n rhythm. Temperature, barometric p r e s s u r e , and atmospheric moisture were a l s o found to be important f a c t o r s . A r i o n a t e r was very s e n s i t i v e to temperature. Lunar phase was i n c l u d e d i n the equation f o r A r i o l i m a x columbianus and may i n d i c a t e a lunar rhythm or a p r e f e r e n c e f o r a higher l i g h t i n t e n s i t y , s i n c e i t i s a woodland s p e c i e s . The m u l t i p l e r e g r e s s i o n equations generated by my analyses of n o c t u r n a l behaviour d i d not i n c l u d e as many f a c t o r s as those of R o l l o (1978). 191 My methods allowed me to generate equations f o r each behaviour recorded and f o r the most extreme experimental treatments. T h i s allowed me to determine i f there were any s p e c i f i c e f f e c t s of weather on any p a r t i c u l a r type of behaviour. D i f f e r e n c e s i n the e f f e c t s of weather on s t r e s s e d and u n s t r e s s e d s l u g s were a l s o i n v e s t i g a t e d . The most economical and i l l u m i n a t i n g way to e x p l a 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 e s i s to look at each of the weather f a c t o r s as they appear i n the equations. Time In most animals, some form of i n t e r n a l c l o c k i s i m p l i c a t e d i n the c o n t r o l of p h y s i o l o g i c a l p rocesses and a c t i v i t y (Bennet 1974). These i n t e r n a l c l o c k s , when synchronized with some s t i m u l u s , the z i e t g e b e r , mediate the rhythmic a c t i v i t y of animals. Such a c t i v i t y rhythms are synchronized with p e r i o d i c environmental parameters so that the animals are a c t i v e when l o c a l c o n d i t i o n s are most f a v o u r a b l e . L i g h t and temperature are the most important z i e t g e b e r s . The c i r c a d i a n rhythms of v a r i o u s s p e c i e s of slu g s have been i n v e s t i g a t e d (Dainton 1954a,b; G e l p e r i n 1974; Lewis 1969a,b; Pinder 1969; R o l l o 1978; Sokolove e_t a_l. 1977). T h i s e x p l a i n s the i n c l u s i o n of the time v a r i a b l e i n the m u l t i p l e - r e g r e s s i o n equations f o r both A r i o n a t e r and A r i o l i m a x columbianus . Other workers on the e f f e c t s of weather on mollusc behaviour have not i n c l u d e d some aspect of t h e i r animals' 192 i n t e r n a l c l o c k s i n t h e i r a n a l y ses (Crawford-Sidebotham 1972, E n r i g h t 1970). T h i s omission cannot l e a d to r e a l i s t i c d e s c r i p t i o n s of animal behaviour, s i n c e i t n e g l e c t s the i n t e r a c t i o n of the i n t e r n a l c l o c k with weather. To i n t e r p r e t s l u g behaviour i n the f i e l d , both the innate a c t i v i t y of the slugs and the e f f e c t s of weather must be c o n s i d e r e d . The e f f e c t s of weather o v e r l i e the s l u g s ' innate a c t i v i t y p a t t e r n , i n f l u e n c i n g the amplitude of the a c t i v i t y and t h e i r b e h a v i o u r a l r e p e r t o i r e . F i g u r e 22 demonstrates that t h i s i s t r u e f o r A r i o n a t e r and A r i o l i m a x columbianus . When the weather was benign, i . e . , temperatures 8-19°C ( R o l l o 1978) and low vapour-pressure d e f i c i t , p o p u l a t i o n a c t i v i t y was e x t e n s i v e and the i n t e r n a l c l o c k may have had s o l e c o n t r o l of a c t i v i t y . Conversely, when temperatures were higher and the e v a p o r a t i v e s t r e s s g r e a t e r the i n t e r n a l c l o c k was o v e r r i d d e n as evidenced by the delayed onset of a c t i v i t y . R o l l o (1978) contends that entrainment to the z i e t g e b e r may not be r i g i d , which e x p l a i n s o b s e r v a t i o n s of d i u r n a l s l u g a c t i v i t y d u r i n g f a v o u r a b l e weather (Barnes and Weil 1945; C h i c h e s t e r and Getz 1973; Dainton 1954a; R i c h t e r 1976a; p e r s o n a l o b s e r v a t i o n ) , and the a c t i v i t y of A r i o n and A r i o l i m a x past the end of the o b s e r v a t i o n p e r i o d i n t h i s study. 193 Temperature A l l behaviours recorded f o r A r i o n a t e r were i n f l u e n c e d by temperature, and there was no d i f f e r e n c e between the equations f o r the good and poor treatments. Both the t o t a l a c t i v i t y and movement equations i n c l u d e d the temperature change f a c t o r . T h i s o b s e r v a t i o n was c o n s i s t e n t with others i n d i c a t i n g that changing temperatures c o u l d s t i m u l a t e locomotion by m o l l u s c s (Dainton 1954a, Machin 1975, R o l l o 1978). Temperature appeared i n a l l but one of the A r i o l i m a x columbianus equations. In a d d i t i o n , temperature change was i n c l u d e d i n most of i t s eq u a t i o n s . Lag-temperature appeared i n the poor treatment equations of A r i o l i m a x moving, f e e d i n g , and r e s t i n g . A r i o l i m a x was more s e n s i t i v e than A r i o n to temperature under the experimental c o n d i t i o n s . I t i s p o s s i b l e that temperature polynomials appeared i n the equations because other important f a c t o r s , such as l i g h t i n t e n s i t y and scotophase, were not i n c l u d e d f o r s e l e c t i o n . However, A r i o l i m a x i s a woodland s l u g and the e n c l o s u r e s were l o c a t e d i n an open f i e l d , so that n o c t u r n a l temperatures were probably higher than those they would normally e x p e r i e n c e . R i c h t e r (1976a) found that A r i o l i m a x f o r a g i n g behaviour and weight changes c o u l d best be e x p l a i n e d by the weather, e s p e c i a l l y the temperature and p r e c i p i t a t i o n , of the p r e v i o u s week. T h i s r e l a t i o n s h i p may e x p l a i n why the l a g temperature f a c t o r appeared i n my A r i o l i m a x eq u a t i o n s . 194 Atmospheric Moisture C o n t r o l of water content by s l u g s i s achieved b e h a v i o u r a l l y because, other than the a b i l i t y to withstand l a r g e f l u c t u a t i o n s i n water content, they have no p h y s i o l o g i c a l mechanism to c o n t r o l body h y d r a t i o n . I t i s not s u r p r i s i n g that the moisture content of the a i r around them i s of great importance to s l u g a c t i v i t y . Slugs l o s e water from exposed s k i n through evaporation when the ambient humidity f a l l s below t h e i r blood e q u i l i b r i u m humidity of 99.5% at 20°C (Machin 1975). Water i s a l s o l o s t i n the pedal gland s e c r e t i o n s of s t i c k y mucus over which they crawl (Barr 1926). The s l u g ' s body i s kept moist by the s e c r e t i o n of watery mucus, which i s no b a r r i e r t o e v a p o r a t i o n (Barr 1928). A l l the behaviours I recorded were i n f l u e n c e d by atmospheric moisture. The s l u g s must assess t h i s v a r i a b l e before a c t i n g , s i n c e a bad d e c i s i o n c o u l d r e s u l t i n severe water l o s s . R o l l o (1978) observed d i f f e r e n t behaviour p a t t e r n s i n Derocerus r e t i c u l a t u m i n dry and moist a i r . Slugs i n the dry treatment moved q u i c k l y to the food, ate, and returned to t h e i r s h e l t e r s . They were a c t i v e f o r a s h o r t e r p e r i o d of time than s l u g s i n the moist treatment. Slugs i n the moist a i r spent more time i n non-food a c q u i r i n g behaviours, and ate s l o w l y while f e e d i n g . In g e n e r a l , s l u g s a v o i d areas of low atmospheric moisture. They choose the wetter s i d e of humidity choice chambers (Lewis 195 1969a,b; R o l l o 1978). Regression equations generated by Crawford-Sidebotham (1972) r e l a t i n g s l u g a c t i v i t y to v a r i o u s weather f a c t o r s were found to i n c l u d e some measure of atmospheric moisture. Vapour-pressure d e f i c i t was i n c l u d e d most o f t e n i n the equations, f o l l o w e d by ambient vapour pressure and r e l a t i v e humidity. Barometric Pressure Barometric pressure or changes t h e r e i n can s t i m u l a t e a c t i v i t y i n animals (Broadbent 1949, W e l l i n g t o n 1974a). T h i s f a c t o r was i n c l u d e d i n a number of R o l l o ' s (1978) r e g r e s s i o n e q u a t i o n s . Barometric p r e s s u r e appeared i n the present study i n equations f o r A r i o n a t e r movement and f e e d i n g behaviours, and i n a l l equations generated f o r A r i o l i m a x columbianus behaviour. Barometric pressure can give i n f o r m a t i o n about imminent changes i n the weather. I t i s adaptive f o r s l u g s to be s e n s i t i v e to t h i s source of i n f o r m a t i o n , as i t c o u l d warn them of d e t e r i o r a t i n g weather. T h i s type of advance warning would permit them to reach s h e l t e r before c o n d i t i o n s became unfavourable. A r i o l i m a x was more s e n s i t i v e to t h i s weather f a c t o r than A r i o n . A barometric pressure change polynomial appeared i n three of the A r i o l i m a x equations, but there was no e s t a b l i s h e d t r e n d , except f o r the f a c t that both r e s t i n g equations i n c l u d e d t h i s f a c t o r . 196 Other F a c t o r s There are s e v e r a l other weather f a c t o r s not i n c l u d e d i n t h i s study which other authors have found to i n f l u e n c e s l u g a c t i v i t y . Heavy r a i n i s known to i n h i b i t s l u g a c t i v i t y (Barnes and Weil 1945; Pinder 1969; R i c h t e r 1976a). R o l l o (1974) suggested that the f o r c e of the raindr o p s h i t t i n g the s e n s i t i v e t e n t a c l e s of the slugs accounted f o r the r e p e l l e n t e f f e c t of r a i n , s i n c e l i g h t r a i n does not impede the a c t i v i t y of s l u g s . An i n c r e a s e i n a c t i v i t y a f t e r r a i n may have been a hy g r o r e g u l a t o r y response of dehydrated animals ( R o l l o 1978). C o r r e l a t i o n s between a c t i v i t y and r a i n f a l l were weak i n the present work. Lack of a r e l a t i o n s h i p between r a i n and A r i o n a t e r and A r i o l i m a x columbianus a c t i v i t y i n d i c a t e s that r a i n f a l l i s not a good p r e d i c t o r of h o u r l y a c t i v i t y . I t may, however, serve as a t r i g g e r that i n i t i a t e s a c t i v i t y . I t i s q u i t e p o s s i b l e that the s l u g s were r e a c t i n g to s o i l moisture r a t h e r to than r a i n f a l l . Such a response would agree with the o b s e r v a t i o n s of B a i l e y (1975) and Randolph (1973). They found that s o i l moisture and r a i n f a l l best accounted f o r changes i n the behaviour of the s n a i l , H e l i x a s p e r s a . T h i s would a l s o p a r t l y e x p l a i n the gradual decrease i n the m i g r a t i o n r a t e of the slugs, a f t e r the r a i n had ceased. There i s some other evidence of a r e l a t i o n s h i p between s l u g h y d r a t i o n and s o i l moisture. During hot, dry weather there i s probably i n s u f f i c i e n t s o i l moisture a v a i l a b l e f o r 197 e x t e n s i v e a c t i v i t y . As s l u g s become dehydrated they show decreased a c t i v i t y (Dainton 1954a, Howes and Wells 1934). R o l l o (1978) demonstrated that i n a c t i v e A r i o n a t e r c o l l e c t e d from s o i l c r e v i c e s d u r i n g a summer drought p e r i o d were s i g n i f i c a n t l y more dehydrated than a c t i v e i n d i v i d u a l s c o l l e c t e d at the same time, i n d i c a t i n g the importance of h y d r a t i o n f o r s l u g a c t i v i t y . Wind has a r e p e l l e n t e f f e c t on s l u g s i n both the f i e l d and l a b o r a t o r y (Barnes and Weil 1945; Dainton 1954b; Stephenson 1968). Wind a f f e c t s the a b i l i t y of s l u g s to o r i e n t by o l f a c t o r y cues (Cook 1979; G e l p e r i n 1974; R i c h t e r 1976a). Foraging e x c u r s i o n s g e n e r a l l y take p l a c e downwind, while homing behaviour to s h e l t e r i s upwind. Wind a l s o m o d i f i e s the e v a p o r a t i v e r a t e s of water from s n a i l s by d e c r e a s i n g the t h i c k n e s s of the boundary l a y e r with i n c r e a s i n g wind speed (Machin 1964). Machin a l s o found that body shape a f f e c t e d the a i r flow p a t t e r n over the s n a i l s ' bodies. D i f f e r e n t o r i e n t a t i o n s to the wind r e s u l t e d i n d i f f e r e n t amounts of water l o s s through e v a p o r a t i o n . Water l o s s was maximal when H e l i x  aspersa faced i n t o the wind. At r i g h t angles to the wind, l o s s e s were 83% of the maximum, whereas they were 68% of the maximum when f a c i n g downwind (Machin 1964). S i m i l a r r e l a t i o n s h i p s are probably a l s o true f o r s l u g s . R o l l o (1978) found no c l e a r r e l a t i o n s h i p between wind and s l u g a c t i v i t y . R o l l o ' s cages, however, were covered, which would have reduced the e f f e c t s of wind speed. 198 3_.4.3 Food P r e f e r e n c e s Both s p e c i e s of slugs showed c l e a r p r e f e r e n c e s i n t h e i r s e l e c t i o n of food. The order of p r e f e r e n c e was wheat bran, c a r r o t r o o t , and potato tuber. Wheat bran c o n t a i n e d the most c a l o r i e s and p r o t e i n per gram, f o l l o w e d by potato and c a r r o t . T h i s i n d i c a t e d that the s l u g s c o u l d d e t e c t the most n u t r i t i o u s and energy-laden food. The f a c t t h a t the s l u g s d i d not feed e x c l u s i v e l y on bran i n d i c a t e d that the other foods may have been a t t r a c t i v e because of n u t r i e n t s or moisture not a v a i l a b l e i n the bran. Hardness of food may have been important i n l i g h t of Senseman's (1978) demonstration that A r i o l i m a x columbianus consumes s m a l l e r q u a n t i t i e s of hard food. Slugs a l s o choose food on the b a s i s of i t s p a l a t a b i l i t y (Cates and O r i a n s 1975; C h a t f i e l d 1976; Duval 1973; Jennings and Barkham 1975; P a l l a n t 1969,1974a). Davidson (1976) s t a t e d that food q u a l i t y and p a l a t a b i l i t y as w e l l as s l u g age s t r o n g l y i n f l u e n c e d s l u g a s s i m i l a t i o n e f f i c i e n c y . Calow (1975) found t h a t a s s i m i l a t i o n e f f i c i e n c y was p o s i t i v e l y c o r r e l a t e d with p a l a t a b i l i t y f o r the s n a i l s Ancylus f l u v i a t i l i s and P l a n o r b i s  c o n t o r t u s . Other workers have demonstrated food s e l e c t i o n based on q u a l i t y and p a l a t i b i l i t y i n other animals ( s n a i l s . Grime et a l . 1969, Mason 1976; hares, L i n d l o f e_t a l . 1974). Slugs are very e f f i c i e n t d i g e s t e r s and a s s i m i l a t o r s (Davidson 1976; Jennings and Barkham 1976; P a l l a n t 1974a,b; Wieser 1978). Consequently a s l u g can a v o i d long exposure to 199 d e s i c c a t i n g c o n d i t i o n s by e a t i n g h i g h - q u a l i t y food. Since i t can e x t r a c t 50-80% of the energy a v a i l a b l e i n i t s foods (depending on food type) i t can consume l e s s h i g h - than low-q u a l i t y food to e x t r a c t the same amount of energy. In the presence of a good source of energy, t h e r e f o r e , t h i s a b i l i t y a l l o w s the s l u g to devote more of i t s a c t i v i t y p e r i o d to d i g e s t i o n and l e s s time to s e a r c h i n g . In the f i e l d , slugs are o p p o r t u n i s t i c f e e d e r s . A r i o n a t e r and A r i o l i m a x columbianus feed mainly on senescent green p l a n t m a t e r i a l and o c c a s i o n a l l y on fungi ( C h a t f i e l d 1976, Jennings and Barkham 1975,1976). I have seen A r i o n eat dead s l u g s and worms. They are a l s o known to eat dog and s l u g faeces ( R o l l o 1978; p e r s o n a l o b s e r v a t i o n ) . The o b s e r v a t i o n s of s l u g feeding behaviour i n these experiments i n d i c a t e that both s p e c i e s s t r i v e to maximize t h e i r energy i n t a k e . 3.4.4 Summary The behaviour o b s e r v a t i o n s demonstrate that s l u g d e n s i t y and food q u a l i t y and q u a n t i t y have s i g n i f i c a n t e f f e c t s on the h o u r l y n o c t u r n a l behaviour of A r i o n a t e r and A r i o l i m a x columbianus . The p r o p o r t i o n of A r i o n a c t i v e , moving, r e s t i n g , or f e e d i n g was u n a f f e c t e d by the d e n s i t y of c o n s p e c i f i c s . The food regime a f f e c t e d the p r o p o r t i o n of the p o p u l a t i o n moving, r e s t i n g , and f e e d i n g but not o v e r a l l a c t i v i t y . The i n t e r a c t i o n of d e n s i t y and food had s i g n i f i c a n t e f f e c t s on moving and r e s t i n g behaviour, but not t o t a l a c t i v i t y 200 or f e e d i n g . When time was i n c l u d e d i n the d e n s i t y - f o o d i n t e r a c t i o n , s i g n i f i c a n t d i f f e r e n c e s were found f o r a l l behaviours. In c o n t r a s t to the m i g r a t i o n measures, where the d e n s i t y f a c t o r i s q u i t e s i g n i f i c a n t i n i t s e f f e c t s on movement, the n o c t u r n a l non-migratory behaviour of A r i o n was most a f f e c t e d by the food regime they were exposed to and not by the degree of crowding. In c o n t r a s t to the A r i o n a t e r data s e t , d e n s i t y had s i g n i f i c a n t e f f e c t s on a l l behaviours of A r i o l i m a x . Food had s i g n i f i c a n t e f f e c t s on the p r o p o r t i o n a c t i v e and fe e d i n g , but not on the t o t a l p r o p o r t i o n moving or r e s t i n g . The i n t e r a c t i o n of d e n s i t y and food had s i g n i f i c a n t e f f e c t s on the p r o p o r t i o n of A r i o l i m a x a c t i v e , r e s t i n g , and f e e d i n g , but not on the p r o p o r t i o n moving. When time was i n c l u d e d i n the i n t e r a c t i o n , a l l behaviours except the p r o p o r t i o n r e s t i n g were s i g n i f i c a n t l y a f f e c t e d . Step-down m u l t i p l e r e g r e s s i o n s of behaviour and the weather v a r i a b l e s are presented i n Appendices A and B. Time, temperature, and atmospheric moisture accounted f o r most of the v a r i a n c e i n the n o c t u r n a l behaviour of A r i o n a t e r . The behaviour of A r i o l i m a x columbianus was best p r e d i c t e d by a combination of time, temperature, atmospheric moisture, and barometric p r e s s u r e . Polynomial expansions of some of the weather v a r i a b l e s improved the f i t of the r e g r e s s i o n s because they r e f l e c t e d the c u r v i l i n e a r r e l a t i o n s h i p between some p h y s i c a l f a c t o r s and a c t i v i t y . 201 S t r e s s e d A r i o n d i d not r e a c t to the weather any d i f f e r e n t l y than uns t r e s s e d A r i o n . S t r e s s e d A r i o l i m a x were more s e n s i t i v e than uns t r e s s e d c o n s p e c i f i c s to lag-temperature and vapour-pressure d e f i c i t change. Since the r e l a t i o n s h i p s between weather and each behaviour were not very d i f f e r e n t , i t appears that d e s c r i p t i o n of r e l a t i o n s h i p s between weather and sl u g behaviour need only be concerned with t o t a l a c t i v i t y . Wheat bran was the p r e f e r r e d food of A r i o n a t e r . The slugs chose bran over c a r r o t root and potato tuber i n that order. The order of food p r e f e r e n c e of A r i o l i m a x columbianus was the same. 202 GENERAL DISCUSSION Slug d e n s i t y had s i g n i f i c a n t e f f e c t s on the migratory behaviour and m o r t a l i t y of both A r i o n a t e r and A r i o l i m a x columbianus . M i g r a t i o n was most r a p i d and e x t e n s i v e from areas of high s l u g d e n s i t y . M o r t a l i t y f o l l o w e d the same t r e n d . S e n s i t i v i t y to the d e n s i t y of c o n s p e c i f i c s i s a d a p t i v e i f there i s a r e l a t i o n s h i p between d e n s i t y and f e e d i n g pressure on r e s o u r c e s . I f patches of food are not f a r apart a s l u g may have a b e t t e r chance of consuming an adequate r a t i o n elsewhere r a t h e r than competing with a crowd. A low t o l e r a n c e to the presence of c o n s p e c i f i c s c o u l d r e s u l t i n a more even spacing of i n d i v i d u a l s through a h a b i t a t . On a p o p u l a t i o n l e v e l t h i s may l e a d t o more e f f i c i e n t e x p l o i t a t i o n of patchy resources and may ensure the s u r v i v a l of the p o p u l a t i o n by i n c r e a s i n g the chances that some i n d i v i d u a l s w i l l f i n d s u i t a b l e c o n d i t i o n s f o r growth and r e p r o d u c t i o n . Crowding may a l s o a f f e c t s h e l t e r a v a i l a b i l i t y , which i s c r i t i c a l to shelter-dependent animals l i k e s l u g s . Lack of s u i t a b l e s h e l t e r may induce animals to leave a h a b i t a t . Food s u i t a b i l i t y a f f e c t e d the m i g r a t i o n and m o r t a l i t y of A r i o n a t e r , but not A r i o l i m a x columbianus . More A r i o n migrated from, and d i e d i n , areas of poor food q u a n t i t y and q u a l i t y . Mature A r i o n were about h a l f the s i z e of mature A r i o l i m a x . Although A r i o l i m a x would consume a l a r g e r a b s o l u t e amount of food, i t s per gram metabolic demands would 203 be l e s s than of A r i o n . T h i s i s known to be t r u e f o r homeotherms, and Gould (1966) s t a t e s that the same s i z e -metabolic r e l a t i o n s h i p holds f o r p o i k i l o t h e r m s . Calow (1975) demonstrated that l a r g e r s n a i l s had higher a b s o r p t i o n r a t e s than small ones. He a l s o found that the most p a l a t a b l e food was a l s o most e a s i l y d i g e s t e d . One might p r e d i c t then, that A r i o n would be a more inte n s e and s e l e c t i v e feeder because of i t s s m a l l e r body s i z e and the p a y o f f s a s s o c i a t e d with consuming e a s i l y d i g e s t e d food. T h i s would e x p l a i n A r i o n ' s m i g r a t i o n from areas of poor food s u i t a b i l i t y . Body s i z e may a l s o be a f a c t o r i n determining whether or not a s l u g w i l l migrate. Migrants may be l a r g e r and more robust than non-migrants. D i n g l e et a_l. (1980) found that l a r g e r s p e c i e s of milkweed bug were b e t t e r f l i e r s than small s p e c i e s . Denno and G r i s s e l l (1979) found that migrant planthoppers were l e s s fecund and had more f l i g h t t i s s u e than non-migrants. M i g r a t i n g A r i o n a t e r were he a v i e r than non-migrants, but t h i s d i d not h o l d f o r A r i o l i m a x columbianus Arena experiments i n v e s t i g a t i n g s l u g body weight and d i s t a n c e t r a v e l l e d d i d not support the s i z e - m i g r a n t h y p o t h e s i s f o r these s l u g s . More r e f i n e d experiments may be r e q u i r e d to t e s t t h i s h y p o t h e s i s . M i g r a t i o n by both s p e c i e s of s l u g s v a r i e d over the f i e l d season. The number of s l u g s m i g r a t i n g f e l l to a minimum du r i n g mid-summer when d a i l y a i r temperatures were high and there was no p r e c i p i t a t i o n . The s l u g s that d i d migrate at 204 t h i s time moved q u i c k l y through the cages. More slug s migrated and d i d so more slowly i n e a r l y and l a t e summer when temperatures were lower and r a i n f a l l was more p l e n t i f u l . D a i l y temperature and r a i n f a l l , however, were not s t r o n g l y c o r r e l a t e d with s l u g m i g r a t i o n . I n v e s t i g a t i o n of h o u r l y n o c t u r n a l s l u g behaviour d i d demonstrate weather e f f e c t s on behaviour. Time of day, a i r temperature, and atmospheric moisture e x p l a i n e d most of the v a r i a t i o n i n m u l t i p l e r e g r e s s i o n a n a l y s e s of A r i o n a t e r n o c t u r n a l behaviour and weather. The same f a c t o r s and barometric pressure accounted f o r most of the v a r i a t i o n i n A r i o l i m a x columbianus's n o c t u r n a l behaviour. Time of day represented the c i r c a d i a n rhythm of the s l u g s , which c o n t r o l l e d the onset and t e r m i n a t i o n of n o c t u r n a l a c t i v i t y . Temperature i s an important f a c t o r because i t a f f e c t s the metabolic r a t e of p o i k i l o t h e r m s , which can a l t e r r a t e s of movement and d i g e s t i o n . Temperature i n t e r a c t s with atmospheric moisture to a f f e c t water l o s s from s l u g s . 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 atmospheric moisture i s p o s i t i v e . As the water vapour content of the a i r i n c r e a s e s l e s s water w i l l be l o s t from s l u g s . T h i s i s important f o r s l u g s because dehydration reduces t h e i r a c t i v i t y (Dainton 1954a, R o l l o 1978). A r e d u c t i o n i n a c t i v i t y c o u l d reduce f o r a g i n g thus a f f e c t i n g food i n t a k e and growth. Environmental f a c t o r s such as food and p o p u l a t i o n d e n s i t y can a l s o a f f e c t the behaviour p a t t e r n of animals. D e n s i t y had 205 no e f f e c t on A r i o n a t e r ' s h o u r l y behaviour, but s l u g s r e c e i v i n g poor food foraged and r e s t e d more than those r e c e i v i n g good food. I t appears that A r i o n ' s n o c t u r n a l behaviour i s i n f l u e n c e d most by food and i t s migratory behaviour i s a r e a c t i o n to both food and p o p u l a t i o n d e n s i t y . A r i o l i m a x columbianus's n o c t u r n a l behaviour was i n f l u e n c e d most by s l u g d e n s i t y . Higher s l u g d e n s i t y induced more a c t i v i t y i n t h i s s p e c i e s . Thus both migratory and n o c t u r n a l behaviour of t h i s s p e c i e s seem to be r e a c t i v e to p o p u l a t i o n d e n s i t y . S i z e d i f f e r e n c e s may again be used to e x p l a i n the d i f f e r e n c e s i n behaviour of A r i o n a t e r and A r i o l i m a x columbianus . A r i o n , the smaller s l u g , i s s e n s i t i v e to the food regime because of i t s l a r g e r per gram metabolic requirements and lower a s s i m i l a t i o n r a t e . A r i o n r e a c t e d to food s t r e s s by f o r a g i n g more and when no food c o u l d be found t h i s s p e c i e s migrated. Even though A r i o l i m a x columbianus may have had a smaller i n t e r - i n d i v i d u a l d i s t a n c e than A r i o n a t e r i t was s e n s i t i v e to the d e n s i t y of c o n s p e c i f i c s . Regardless of the q u a l i t y of the food, h i g h d e n s i t i e s of t h i s s p e c i e s may i n d i c a t e heavy feeding p r e s s u r e . As long as the c o s t s of moving between patches of food are not high i t may be more e f f i c i e n t f o r A r i o l i m a x to search f o r food elsewhere r a t h e r than compete f o r a food source that may not l a s t very l o n g . A r i o l i m a x i s a d o c i l e s l u g ( R o l l o 1978). T h i s combined with l a r g e body s i z e , which 206 i m p l i e s a lower metabolic demand, may e x p l a i n why A r i o l i m a x r e a c t s h o u r l y and d a i l y to the d e n s i t y of c o n s p e c i f i c s and not food. I t should be c l e a r that the behaviour of both s p e c i e s of s l u g can be i n f l u e n c e d by food or p o p u l a t i o n d e n s i t y . Slugs' r e a c t i o n s to these f a c t o r s can be i n t e r p r e t e d on both the i n d i v i d u a l and p o p u l a t i o n l e v e l s . Such r e a c t i o n s are not constant over time, they change i n response to weather and changes i n food and p o p u l a t i o n d e n s i t y . The i n d i v i d u a l i s the u n i t of n a t u r a l s e l e c t i o n and the a daptiveness of an animal's behaviour must be judged on t h i s l e v e l . I f , by being s e n s i t i v e to the c u r r e n t c o n d i t i o n s of food or d e n s i t y , a s l u g can vacate or a v o i d poor h a b i t a t s and l i v e to reproduce in another h a b i t a t , i t may improve i t s f i t n e s s as long as the c o s t s of m i g r a t i o n are not too h i g h . There may a l s o be b e n e f i t s of i n c r e a s e d g e n e t i c d i v e r s i t y through outbreeding. At the p o p u l a t i o n l e v e l , s e n s i t i v i t y to food and d e n s i t y c o u l d allow b e t t e r t r a c k i n g of short-term and seasonal f l u c t u a t i o n s i n h a b i t a t r e s o u r c e s . More e f f i c i e n t use of h a b i t a t resources c o u l d be made i f l a r g e clumps of i n d i v i d u a l s , which c o u l d o v e r - e x p l o i t r e s o u r c e s , were avoi d e d . New or vacant h a b i t a t s c o u l d a l s o be c o l o n i z e d , thus extending the range of the s p e c i e s . These s t u d i e s have p r o v i d e d an o p p o r t u n i t y to i n v e s t i g a t e 207 the e f f e c t s of i n d i v i d u a l behaviour on a p o p u l a t i o n l e v e l p r o c e s s . P o p u l a t i o n s are not composed of i d e n t i c a l i n d i v i d u a l s . The d i f f e r e n c e s i n the manner i n which members of a p o p u l a t i o n r e a c t to v a r y i n g environmental f a c t o r s determines the f a t e of the p o p u l a t i o n . 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Proceedings 138:130-156. 218 APPENDIX A: CORRELATION COEFFICIENTS ARION ATER BEHAVIOUR AND WEATHER FACTORS act i v e : A n =108 r@0. 01 = 0 .2469 A c t i v e : D n = 111 r@0. 01 = 0 .2436 Moving: A n =110 r@0. 01= 0 .2446 Moving: D n =111 r@0. 01 = 0 .2436 R e s t i n g : A n = 110 r@0. 01 = 0 .2446 R e s t i n g : D n = 111 r§0. 01 = 0 .2436 Feeding: A n = 110 r@0. 01 = 0 .2446 Feeding: D n = 111 r@0. 01 = 0 .2436 Dependent v a r i a b l e s A c t i v e Moving Weather V a r i a b l e s Good Poor Good ( r - v a l u e s ) Poor time .4116 .5450 .4344 .5665 t ime2 .6318 .7604 .8390 .8792 time3 .5040 .6557 .7123 .7886 time4 .4154 .5784 .6081 .7182 temp -.2679 -.1798 -.1579 -.1962 temp2 -.3033 -.2368 -.1799 -.2482 temp3 -.3287 -.2808 -.2034 -.2887 temp4 -.3402 -.3080 -.2219 -.3126 temp change -.1526 -.2164 -.1481 -.2421 temp change2 -.1994 -.2303 -.2198 -.2986 temp change3 .0460 -.0013 .0172 -.0108 temp change4 -.1949 -.1927 -.1882 -.2375 l a g temp -.1400 -.0311 -.0289 -.0563 l a g temp2 -.1695 -.0848 -.0470 -.1109 l a g temp3 -.1983 -.1312 -.0753 -.1560 l a g temp4 -.2210 -.1652 -.1058 -.1866 R.H. .7691 .6670 .6423 .7001 R.H. change .1607 .2255 .2134 .2082 l a g R.H. .6965 .5407 .5875 .5446 V.P.D. -.6889 -.5944 -.5793 -.6373 V.P.D. change -.3647 -.3217 -.3055 -.3528 l a g V.P.D -.6197 -.4970 -.5085 -.5002 baro p r e s s . -.0967 -.0866 -.0507 -.2130 baro press.2 -.0968 baro press.3 -.0969 baro press.4 -.0970 baro change -.1358 baro change2 .0387 baro change3 -.0720 baro change4 .0812 .0867 -.0508 -.2132 .0868 -.0509 -.2133 .0869 -.0509 -.2134 .1219 -.1056 -.1196 .0089 .0441 .0298 .0341 -.0781 -.0498 .0240 .0763 .0490 Dependent V a r i a b l e s R e s t i n g Feeding Weather Good Poor Good Poor V a r i a b l e s ( r - v a l u e s ) t ime .2936 .3618 .2157 .2400 time2 .2544 .4096 .3741 .3511 time3 .1527 .3227 .2730 .2811 time4 .0911 .2634 .2167 .2304 temp -.2594 -.3590 -.1401 -.1227 temp2 -.2901 -.3787 -.1657 -.0531 temp 3 -.3038 -.3805 -.1890 -.0124 temp4 -.3011 -.3666 -.2060 -.0685 temp change -.1239 -.0256 -.1163 -.1753 temp change2 -.1226 -.0947 -.1402 -.1516 temp change3 -.0293 .0743 .0576 -.0593 temp change4 -.1199 -.1282 -.1528 -.1031 l a g temp -.2079 -.2198 -.0268 .2587 l a g temp2 -.2479 -.2515 -.0453 .2145 l a g temp3 -.2716 -.2701 -.0685 .1621 l a g temp4 -.2788 -.2755 -.0926 .1985 R.H. .4862 .4985 .6372 .3091 R.H. change .1551 .2767 .1196 .1290 l a g R.H. .4792 .4677 .5708 .2111 V.P.D. -.4591 -.4401 -.5333 -.3131 V.P.D. change -.1454 -.2006 -.3241 -.1865 l a g V.P.D. -.4606 -.4642 -.4898 -.1634 baro p r e s s . -.0854 -.1417 -.0362 .1907 baro press.2 -.0855 -.1418 -.0364 .1907 baro press.3 -.0856 -.1419 -.0365 .1907 baro press.4 -.0857 -.1420 -.0367 .1908 baro change -.0222 -.0375 -.2004 -.2027 baro change2 -.1112 -.0576 .1223 -.0173 baro change3 .0795 .0341 -.1289 -.0433 baro change4 -.0800 -.0332 .1450 .0123 223 APPENDIX B: CORRELATION COEFFICIENTS ARIOLIMAX COLUMBIANUS BEHAVIOUR AND WEATHER FACTORS A c t i v e N=77 r@0.01= 0.2919 Moving N=91 r@0.01= 0.2684 Rest i n g N=91 r@0.01= 0.2684 Feeding N=91 r@0.01= 0.2684 Dependent V a r i a b l e s A c t i v e Moving Weather Good Poor Good Poor V a r i a b l e s time .5606 .6515 .6838 .7122 time2 .6060 .6289 .5438 .5092 time3 .4915 .4902 .4712 .3929 t ime4 .4161 .3965 .4049 .3048 temp -.3410 -.2787 -.2338 -.3261 temp2 -.3712 -.3010 -.2460 -.3558 temp3 -.3766 -.3086 -.2466 -.3636 temp4 -.3649 -.3052 -.2397 -.3547 temp change -.1687 -.1325 -.1232 -.1547 temp change2 -.1752 -.1781 -.1417 -.1752 temp change3 .0345 .0437 -.0338 .0344 temp change4 -.1712 -.1794 -.1366 -.1636 l a g temp -.2006 -.1470 -.1629 -.1986 l a g temp2 -.2346 -.1770 -.1765 -.2384 l a g temp3 -.2509 -.1968 -.1832 -.2606 l a g temp4 -.2530 -.2072 -.1852 -.2683 R.H. .7809 .7328 .0441 -.1171 R.H. change .1343 .1812 .1712 .1892 l a g R.H. .6850 .6534 .4903 .5762 V.P.D. -.6974 -.6604 -.5097 -.6154 V.P.D. change -.3579 -.2654 -.3146 -.2847 l a g V.P.D -.5964 -.5765 -.4605 -.5529 baro p r e s s . -.0892 -.0306 .2234 .0510 baro press.2 -.0894 baro press.3 -.0897 baro press.4 -.0899 baro change -.1370 baro change2 .0228 baro change3 -.0784 baro change4 .0506 .0307 .2233 .0509 .0309 .2233 .0508 .0311 .2232 .0507 .1864 -.2231 -.1234 .1557 .1466 .0630 .2184 -.2351 -.1396 .2256 .2245 .1481 Dependent V a r i a b l e s R e s t i n g Feeding Weather Good Poor Good Poor V a r i a b l e s time .4786 .7474 .3636 .4773 time2 .4598 .6432 .6208 .5550 time3 .3493 .5083 .5204 .4471 time4 .2683 .4059 .4451 .3750 temp -.3366 -.2635 -.1174 -.1929 temp2 -.3540 -.2815 -.1534 -.2218 temp3 -.3526 -.2892 -.1775 -.2391 temp4 -.3365 -.2864 -.1919 -.2457 temp change -.1600 -.1039 -.1177 -.1769 temp change2 -.1693 -.1611 -.1497 -.1903 temp change3 -.0060 .0218 .0351 -.0336 temp change4 -.1446 -.1580 -.1509 -.1745 l a g temp -.2833 -.1374 .0260 -.1124 l a g temp2 -.3053 -.1548 -.0004 -.1394 l a g temp3 -.3116 -.1729 -.0259 -.1570 l a g temp4 -.3035 -.1862 -.0481 -.1659 R.H. -.3488 -.1405 .0126 -.0647 R.H. change .3155 .2259 .1016 .1282 l a g R.H. .6396 .6495 .6037 .6549 V.P.D. -.5495 -.6232 -.5786 -.6278 V.P.D. change -.2129 -.2759 -.2670 -.2630 l a g V.P.D. -.5673 -.5627 -.4822 -.5453 baro p r e s s . -.2104 -.1678 -.0093 -.0077 baro press.2 -.2105 -.1679 -.0095 -.0079 baro press.3 -.2106 -.1680 -.0097 -.0081 baro press.4 -.2107 -.1681 -.0099 -.0083 baro change -.0088 -.1238 -.1716 -.1480 baro change2 -.0243 .0824 .1098 .0947 baro change3 -.0851 -.1204 -.1330 -.1277 baro change4 .0907 .1438 .1450 .1261 228 APPENDIX C REGRESSION ANALYSIS: ARION ATER BEHAVIOUR AND WEATHER FACTORS 229 Dependent V a r i a b l e : A c t i v e Treatment: Good m u l t i p l e r=0.90396 r 2 =0.81714 SE=0 .18034 f -value= 51.639 p<0.0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant -.40961 .33419 time2 .47915 16.567 2.9759 time3 -.38596 -45.705 10.712 time4 .32107 34.404 9.9509 temp2 .24755 .97931 -2 .37585 -2 temp3 -.25083 -.92871 -3 .35146 -3 temp4 .24345 .22577 -4 .88203 -5 l a g R.H. .23029 .83745 .34701 V.P.D. -.25286 -.43154 -3 .16.191 -3 l a g V.P.D. .17575 .34904 -3 .19172 -3 Dependent V a r i a b l e : A c t i v e Treatment: Poor m u l t i p l e r=0.93299 r 2=0.87047 SE=0.13453 f-value= 52.210 p<0. 0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant .89939 ' .43066 time .31034 .19800 -1 .60351 -2 time2 .60909 16.004 2.0735 time3 -.48762 -41.934 7.4708 t ime4 .40367 30.806 6.9475 temp2 .22343 .66512 -2 .28872 -2 temp3 -.19298 -.52130 -3 .26374 -3 temp4 .18835 .12843 -4 .66636 -5 temp change -.20378 -.27329 -1 .13064 -1 temp change2 .22533 .11619 -1 .49990 -2 temp change4 -.21597 -.18548 -3 .83437 -4 R.H. -.21192 -.96193 .44140 V.P.D. -.26167 -.10006 -2 .36724 -3 V.P.D. change .17500 .31155 -3 .17441 -3 Dependent V a r i a b l e : Moving Treatment: Good m u l t i p l e r = 0.97013 r 2=0.94115 SE=0.65256 -1 f-value= 213.89 p<0.0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant .17814 .38979 t ime2 .78266 9.4450 .72616 time3 -.67783 -20.895 2.1911 time4 .61956 13.605 1.6663 temp2 .17763 .24694 -2 .13226 -2 temp3 -.18575 -.24025 -3 .12286 -3 temp4 .18305 .59216 -5 .30746 -5 temp change4 -.21494 -.22659 -4 .99532 -5 V.P.D. -.29857 -.14393 -3 .44476 -4 Dependent V a r i a b l e : Moving Treatment: Poor m u l t i p l e r=0.99035 r 2=0.98079 SE=0.37272 -1 f-value= 299.93 p<0. 0001 v a r i a b l e pa r t i a 1 c o e f f i c i e n t SE constant .57500 + 6 .29286 + 6 time .42757 .84798 -2 .18492 -2 time2 .86385 10.056 .60486 time3 -.77606 -25.589 2.1448 time4 .71335 19.509 1.9768 temp2 .26963 .24402 -2 .89888 -3 temp 3 -.28749 -.24067 -3 .82699 -4 temp4 .29461 .61316 -5 .20514 -5 temp change3 .36545 .18520 -3 .48655 -4 l a g temp4 .33418 .77812 -6 .22635 -6 baro p r e s s -.19844 -1691.2 861.52 baro change2 .19841 1.6580 .84477 baro change3 -.19838 -.54184 -3 .27612 -3 R.H. .46729 .35574 .69420 -1 R.H. change .40878 .34699 .79902 -1 l a g R.H. -.46833 -.63677 .12391 l a g V.P.D. -.32098 -.30405 -3 .92533 -4 Dependent V a r i a b l e : R e s t i n g Treatment: Good m u l t i p l e r=0.62070 r 2=0.38527 SE=0.14651 f-value= 9.4904 p<0. 0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant -.31048 .12561 time2 .19678 1.1470 .55508 time3 -.17266 -1.3788 .76399 temp3 -.23454 -.19239 -4 .77453 -5 l a g temp2 .27769 .85448 -2 .28713 -2 l a g temp3 -.27468 -.78364 -3 .26644 -3 l a g temp4 .26857 .18995 -4 .66174 -5 l a g R.H. .34471 .42404 .11216 Dependent V a r i a b l e : R e s t i n g Treatment: Poor m u l t i p l e r=0.68331 r 2=0.46691 SE=0.12206 f-value= 13.138 p<0. 0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant .30422 .46109 -1 t ime2 .30239 2.0957 .64469 time3 -.26839 -2.8075 .98338 temp3 -.19848 -.63349 -4 .30528 -4 temp4 .16260 .24483 -5 .14499 -5 R.H. change .26742 .54979 .19333 V.P.D. -.22028 -.21174 -3 .91503 -4 V.P.D. change .23960 .30651 -3 .12121 -3 Dependent V a r i a b l e : Feeding Treatment: Good m u l t i p l e r=0.67291 r 2=0.45281 SE=0.19519 f-value= 18.371 p<0.0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant .34699 .11172 time 2 .19175 .36248 .17610 temp2 .16115 .65814 -2 .38257 -2 temp3 -.16157 -.61349 -3 .35566 -3 temp4 .17585 .16725 -4 .88870 -5 V.P.D -.56827 -.78329 -3 .10765 -3 Dependent V a r i a b l e : Feeding Treatment: Poor m u l t i p l e r=0.67250 r 2=0.45225 SE=0.13977 f-value= 15.275 p<0. 0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant -10.511 2.6744 time 2 .33314 6.7083 1.8021 time3 -.22941 -17.016 6.8523 time4 .16642 11.649 6.5514 l a g temp .40830 .16197 -1 .34372 -2 baro change -.19549 -.93409 -1 .44479 -1 baro2 .3484 5 .10034 -4 .25618 -5 237 APPENDIX D REGRESSION ANALYSIS: ARIOLIMAX COLUMBIANUS BEHAVIOUR AND WEATHER FACTORS Dependent V a r i a b l e : A c t i v e Treatment: Good m u l t i p l e r= .64387 r 2 = .41457 SE= .31505 f-value= 6.0514 p<0.0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant -38.181 15.097 t ime .27967 .50154 -1 .17759 -1 time2 -.19038 -6.6969 3.5619 time3 .19587 20.080 10.369 time4 -.19659 -15.019 7.7260 temp3 .20016 .51091 -4 .25794 -4 temp change2 .25537 .11708 -1 .45718 -2 baro p r e s s . .25488 .38044 -1 .14887 -1 baro change2 .21030 .84205 .40375 baro change4 -.19789 -.80344 .41048 l a g V.P.D. -.31402 -.81065 -3 .25279 -3 cl o u d -.26396 -.12684 .47802 -1 Dependent V a r i a b l e : A c t i v e Treatment: Poor m u l t i p l e r= .76618 r 2 = .58704 SE= .21562 f-value= 8.2783 p<0.0001 v a r i a b l e p a r t i a l coef f i c i e n t SE constant 57.416 17.329 time .55868 .91144 -1 .13599 -1 time2 .29963 2.4198 .77439 time3 -.28542 -3.1098 1.0495 temp4 -.20275 -.35367 -5 .17167 -5 temp change3 -.20154 -.47738 -2 .23317 -2 temp change4 .32478 .14390 -2 .42115 -3 l a g temp2 .42772 .35643 -1 .75705 -2 l a g temp3 -.39556 -.34386 -2 .80241 -3 l a g temp4 .37303 .96277 -4 .24067 -4 baro p r e s s . -.31270 -.52874 -1 .16142 -1 baro change -.25036 -.25033 .97292 -1 R.H. .26348 .37477 -2 .13790 -2 R.H. change -.22084 -1.5834 .70283 l a g R.H. -.24237 -4.7202 1.8990 V.P.D. .26985 .14641 -2 .52508 -3 l a g V.P.D. -.32286 -.50440 -2 .14861 -2 c l o u d .32808 .11215 .32455 -1 Dependent V a r i a b l e : Moving Treatment: Good m u l t i p l e r= .86066 r 2 = .74074 SE= .20414 f-value= 22.706 p<0.0001 v a r i a b l e p a r t i a l coef f i c i e n t SE constant .46815 + 7 .13757 + 7 time2 .41037 1.0891 .19695 temp .29563 .32866 .86428 -1 temp2 -.32404 -.28570 -1 .67879 -2 temp3 .34487 .80862 -3 .17910 -3 temp change .13841 .33377 -1 .19436 -1 temp change2 .18906 .16884 -1 .71365 -2 temp change3 -.26195 -.18356 -2 .55035 -3 temp change4 -.24904 -.41868 -3 .13250 -3 i a g temp .14716 .54121 -1 .29603 -1 l a g temp2 -.21121 -.36482 -2 .13740 -2 baro p r e s s . -.26695 -13776. 4047.2 baro press2 .26702 13.513 3.9687 baro press3 -.26709 -.44182 -2 .12973 -2 baro change -.20356 -.33221 .13002 baro change3 .18014 .62833 .27921 R.H. change .18381 .94718 .41221 l a g R.H. .28075 1.8984 .52815 V.P.D. -.41086 -.15866 -2 .28651 -3 l a g V.P.D. .31821 .15876 -2 .38490 -3 Dependent V a r i a b l e : Moving Treatment: Poor m u l t i p l e r= .90670 r 2 = .82211 SE= .20550 f-value= 30.906 p<0.0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE c onstant .85650 + 7 .14782 + 7 time .22361 .24561 -1 .10350 -1 time2 .38134 20.433 4.7886 time3 -.26654 -59.692 20.867 time4 .20297 48.855 22.785 temp3 -.30055 -.22800 -3 .69945 -4 temp4 .32348 .10833 -4 .30635 -5 temp change4 -.19206 -.52881 -4 .26123 -4 l a g temp .16091 .14330 .84972 -1 l a g temp2 -.17231 -.11941 -1 .65994 -2 l a g temp3 .17347 .28881 -3 .15851 -3 baro p r e s s . -.48878 -25201. 4348.4 baro press2 .48886 24.716 4.2639 baro press3 -.48893 -.80802 -2 .13937 -2 V.P.D. -.49885 -.10252 -2 .17219 -3 V.P.D. change .31081 .78765 -3 .23286 -3 c l o u d .28954 .87480 -1 .27958 -1 242 Dependent V a r i a b l e : R e s t i n g Treatment: Good m u l t i p l e r= .82995 r 2 = .68882 SE= .10382 f-value= 17.708 p<0.0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant 2.0668 1.7485 time2 .44061 .47192 .10750 temp .32585 .64398 -1 .20890 -1 temp3 -.31663 -.32900 -3 .11019 -3 temp4 .28222 .96214 -5 .36566 -5 l a g temp3 -.33765 -.45568 -4 .14203 -4 baro press3 -.24052 -.35118 -8 .15845 -8 baro change2 -.41599 -.57564 .14069 baro change4 .43928 .68292 .15614 l a g R.H. .50783 1.7359 .32923 l a g V.P.D. .41700 .10551 -2 .25711 -3 Dependent V a r i a b l e : R e s t i n g Treatment: Poor m u l t i p l e r= .91129 r 2 = .83044 SE= .84092 -1 f-value= 15.138 p<0.0001 v a r i a b l e p a r t i a l c o e f f i c i e n t SE constant .17189 + 7 .80161 + 6 time2 .53792 2.0108 .38213 time3 -.41596 -1.9991 .53001 temp2 .24790 .56798 -2 .26917 -2 temp3 -.28822 -.60246 -3 .24273 -3 temp4 .33064 .16919 -4 .58564 -5 temp change .25150 .23904 -1 .11156 -1 temp change2 .23976 .82759 -2 .40637 -2 temp change3 -.37326 -.10537 -2 .31758 -3 temp change4 -.28489 -.18417 -3 .75148 -4 l a g temp -.25929 -.31942 .14428 l a g temp2 .25040 .38476 -1 .18040 -1 l a g temp3 -.24119 -.19034 -2 .92872 -3 l a g temp4 .23263 .33042 -4 .16752 -4 baro p r e s s . -.25162 -5055.6 2358.1 baro press2 .25157 4.9563 2.3123 baro press3 -.25152 -.16196 -2 .75577 -3 baro change -.40645 -.30157 .82210 -1 baro change3 .37978 1.0518 .31069 baro change4 .34566 .76793 .25281 R.H. change .24362 V.P.D. -.59580 V.P.D. change .27892 244 .40791 .19693 .52968 -3 .86585 -4 .34344 -3 .14339 -3 Dependent V a r i a b l e : Feeding Treatment: Good m u l t i p l e r= .90891 r 2 = .82612 SE= .11544 f-value= 14.685 p<0.0001 v a r i a b l e p a r t i a l coef f i c i e n t SE constant .49808 + 7 .12579 + 7 time -.31704 -.19904 -1 .72205 -2 t ime2 .45097 1.2678 .30427 time4 -.20631 -.90863 .52259 temp .40904 .40616 .10988 temp2 -.37909 -.47658 -1 .14107 -1 temp3 .33014 .21793 -2 .75561 -3 temp4 -.26555 -.32371 -4 .14252 -4 temp change .27358 .36798 -1 .15689 -1 temp change2 .26372 .13351 -1 .59219 -2 temp change3 -.40432 -.16872 -2 .46283 -3 temp change4 -.34216 -.32742 -3 .10904 -3 baro p r e s s . -.43300 -14660. 3700.8 baro press2 .43314 14.382 3.6293 baro press3 -.43328 -.47033 -2 .11864 -2 baro change -.35569 -.40816 .13006 baro change3 .31529 1.2583 .45928 baro change4 .28298 .87858 .36112 R.H. -.27427 -.21930 -2 .93242 -3 l a g R.H. .31384 .97223 .35669 246 V.P.D. -.48690 l a g V.P.D. .31479 cl o u d .22926 -.82684 -3 .17987 -3 .45085 -3 .16485 -3 .40045 -1 .20618 -1 Dependent V a r i a b l e m u l t i p l e r= .91680 f-value= v a r i a b l e p a r t i a l constant time2 .43781 time3 -.38497 time4 .36305 temp4 .35213 temp change2 .19972 temp change3 -.30437 temp change4 -.24922 l a g temp .23098 l a g temp2 -.21693 l a g temp3 .20130 l a g temp4 -.19850 baro p r e s s . -.52176 baro press2 .52186 baro press3 -.52197 R.H. -.29289 la g R.H. .42264 V.P.D. -.55484 V.P.D. change .25006 l a g V.P.D. .41649 c l o u d .28817 : Feeding Treatment: Poor r 2 = .84053 SE= .85528 -1 18.447 p<0.0001 c o e f f i c i e n t SE .47258 + 7 .92379 + 6 4.5252 1.1107 -11.560 3.3126 8.1939 2.5135 .18234 -5 .57928 -6 .68382 -2 .40100 -2 -.76151 -3 .28485 -3 -.16769 -3 .77882 -4 .29692 .14949 -.34752 -1 .18692 -1 .16490 -2 .95905 -3 -.29507 -4 .17413 -4 -13907. 2717.7 13.641 2.6650 -.44601 -2 .87112 -3 -.15557 -2 .60703 -3 1.3605 .34870 -.76672 -3 .13741 -3 .30924 -3 .14312 -3 .10381 -2 .27084 -3 .35492 -1 .14096 -1 

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