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UBC Theses and Dissertations

Population processes in Peromyscus: an experimental approach Fairbairn, Daphne Janice 1976

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POPULATION PROCESS ES IN PERCMYSCUS: AN EXPERIMENTAL APPROACH BY DAPHNE J . FAIRBAIRN B. S c . (Hons.) , C a r l e t o n U n i v e r s i t y , 1971 A THESIS SUBMITTED IN PARTIAL FULFILLMENT THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e De p a r t m e n t o f Z o o l o q y We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRI T I S H COLUMBIA MARCH, 1976 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 r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e 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 r e f e r e n c e and s t u d y . 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 o f t h i s 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 o f my Department o r 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 c o p y i n g o r p u b l i c a t i o n o f 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 ten pe rm i ss i on . Department o f "2Lc>. ^ oc^K/  The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 D a t e 4p-> I \/'7L A B S T R A C T T h i s s t u d y e x a m i n e d s e a s o n a l v a r i a b i l i t y i n d e m o g r a p h y , g e n e t i c c o m p o s i t i o n , a n d b e h a v i o r , i n p o p u l a t i o n s o f d e e r m i c e ( P e r o m y s c u s m a n i c u l a t u s ) , P a r t i c u l a r a t t e n t i o n was p a i d t o t h e p o s s i b l e r o l e o f a g g r e s s i o n a n d d i s p e r s a l i n d e t e r m i n i n g d e n s i t i e s . T h r e e t y p e s o f p o p u l a t i o n s w e r e e x a m i n e d b y m e a n s o f b i w e e k l y l i v e - t r a p p i n g : u n d i s t u r b e d p o p u l a t i o n s , a p o p u l a t i o n r e m o v e d c o n t i n u o u s l y , a n d a p o p u l a t i o n r e m o v e d a n n u a l l y , a t t h e o n s e t o f b r e e d i n g . T h e t w o r e m o v a l e x p e r i m e n t s s a m p l e d d i s p e r s i n g m i c e . T h e g e n e t i c d a t a c o n s i s t e d o f a l l e l i c f r e q u e n c i e s a t t h r e e b l o o d p r o t e i n l o c i , d e t e c t e d b y s t a r c h g e l e l e c t r o p h o r e s i s : t r a n s f e r r i n , a n e s t e r a s e , a n d g l u t a m a t e o x a l a t e t r a n s a m i n a s e . B e h a v i o r o f f i e l d a n i m a l s w a s e x a m i n e d i n t h r e e l a b o r a t o r y t e s t s . F e m a l e s w h i c h b e g a n b r e e d i n g i n e a r l y s p r i n g s u f f e r e d h e a v y m o r t a l i t y , a n d t h i s r e s u l t e d i n a d e c l i n e i n f e m a l e d e n s i t y . F e m a l e s h e t e r o z y g o u s a t o n l y o n e l o c u s w e r e s e l e c t e d f o r o v e r t h i s p e r i o d . M a l e s b e c a m e a g g r e s s i v e a n d s p a c e d t h e m s e l v e s o u t a s t h e y b e g a n b r e e d i n g , a n d l i g h t - w e i g h t , l e s s a g g r e s s i v e m a l e s d i s p e r s e d . T h i s r e s u l t e d i n a d e c l i n e i n m a l e d e n s i t y . W h i l e m a l e s w e r e b r e e d i n g , j u v e n i l e s , p a r t i c u l a r l y j u v e n i l e m a l e s , s u r v i v e d p o o r l y , a n d f e w e n t e r e d t h e p o p u l a t i o n s . L i g h t , n o n - b r e e d i n g , s u b o r d i n a t e m a l e s c o n t i n u e d t o d i s p e r s e . A s b r e e d i n g s t o p p e d , m a l e s w h i c h c o n t i n u e d t o b r e e d m o v e d a r o u n d , a n d j u v e n i l e s s u r v i v e d w e l l . T h e p o p u l a t i o n i n c r e a s e d t o i t s m a x i m u m d e n s i t y i n l a t e f a l l . i i Over the winter, s u r v i v a l was good, d i s p e r s a l low, and spacing behavior at i t s minimum. D i s p e r s i n g males were l i g h t e r , showed l e s s aggression i n a n e u t r a l arena, and were more a c t i v e than r e s i d e n t males. They d i f f e r e d g e n e t i c a l l y from r e s i d e n t s , although t h e r e was no evidence of s e l e c t i o n on males i n c o n t r o l p o p u l a t i o n s . D i s p e r s i n g females were l i g h t e r , showed l e s s e x p l o r a t o r y behavior i n an u n f a m i l i a r maze, and were mora a c t i v e than r e s i d e n t females. D i s p e r s a l was not s e l e c t i v e i n females. P o p u l a t i o n s s e t t l i n g i n a depopulated area continued to d i f f e r g e n e t i c a l l y from c o n t r o l p o p u l a t i o n s , but w i t h i n two months resembled c o n t r o l p o p u l a t i o n s demographically and b e h a v i o r a l l y . The only d i f f e r e n c e was that a lower p r o p o r t i o n of c o l o n i s t s bred, and t h i s was compensated f o r by r e c r u i t m e n t of j u v e n i l e s from surrounding areas. The major hypotheses suggested by t h i s study a r e : 1) Spacing out and d i s p e r s a l of males i n the s p r i n q i s a response t o m o r t a l i t y of e a r l y - b r e e d i n g females, and thus i t i s t h i s l a t t e r m o r t a l i t y which determines breeding d e n s i t i e s . 2) D i s p e r s a l has two components: d i s p e r s a l o f s u b o r d i n a t e mice i n response to s o c i a l pressure, and i n n a t e d i s p e r s a l of more spontaneously a c t i v e mice. i i i TABLE OF CONTENTS LIST OF FIGURES . V LIST OF TABLES . . . v i i i AO KNGWIEEGEMENTS . . x i i i CHAPTEE 1: GENERAL INTRODUCTION 1 CHAPTER 2: EXPERIMENTAL DESIGN 11 Study Area and T r a p p i n g Techn iques . . 1 3 Exper iments 15 CHAPTER 3: DEMOGRAPHY-CGNTRGL DATA 20 I n t r o d u c t i o n 20 A n a l y s e s and R e s u l t s S p r i n g R e o r g a n i z a t i o n 23 Main Breed ing P e r i o d 33 F a l l Increase P e r i o d 43 Overwinter P e r i o d 51 G e n e r a l D i s c u s s i o n 52 CHAPTER 4: DEMOGRAPHY-EXPERIMENTAL DATA 60 Exper iment 1 60 Exper iment 2 74 Summary and D i s c u s s i o n . . . . 9 1 CHAPTER 5: GENETICS . . . 98 E l e c t i c p h o r e t i c Methods . . . . . . . . . . . . . . . . . . . . . . . . . 98 R e s u l t s - C o n t r o l G r i d s . . . . . 9 9 R e s u l t s - R e m o v a l Exper iments .104 D i s c u s s i o n . . . . . . . . . . . 1 0 8 i v CHAPTER 6: BEHAVIOR . . . .114 Eehav io r i n the N e u t r a l Arena . , . . 1 1 4 B e h a v i o r i n the D i s p e r s a l Haze .125 G e n e r a l A c t i v i t y . . . . . . . . . . . . 1 3 1 D i s c u s s i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 CHAPTER 7: SUMMARY AND CONCLUSIONS . . . . . 1 4 5 FIGURES . .157 TABLES .179 REFERENCES 205 V L I S T 01 F IGURES Figure 1. General model of seasonal f l u c t u a t i o n s i n a population of deermice. .....158 2. Locations of the 4 trapping g r i d s on the U n i v e r s i t y of B r i t i s h Columbia Endowment Lands, Vancouver, B.C. ....159 3. Minimum number known to be a l i v e and proportion breeding cn center c l g r i d 1. ...........160 4. Minimum number known to be a l i v e and pr o p o r t i o n breeding on c o n t r o l g r i d 3. ....161 5. Seasonal estimates of s u r v i v a l r a t e , recruitment r a t e , and trap-overlap i n d i c e s , f o r c o n t r o l populations. S u r v i v a l and recruitment estimates were obtained from the reg r e s s i o n models described i n the t e x t . ............. 162 6. Observed and expected proportions of various p a i r - t y p e s i n the t o t a l t r a p - o v e r l a p sample f o r each season. .......163 7. Mean weights of males from c o n t r o l areas and the pulsed removal area. ..........164 8. Mean weights of non-pregnant females from c o n t r o l areas and the pulsed removal area. ......................... 165 9. Proportions of males and females, a d u l t s and j u v e n i l e s , i n the t o t a l trap-overlap sample f o r each season, on the pulsed removal g r i d . .....166 10, Minimum number known to be a l i v e on the c o n t r o l and pulsed removal g r i d s . .....167 v i 11. S e a s o n a l e s t i m a t e s of s u r v i v a l r a t e and r e c r u i t m e n t r a t e f o r the p u l s e d removal g r i d . These e s t i m a t e s were o b t a i n e d from the r e g r e s s i o n models d e s c r i b e d i n the t e x t . 168 12. P r o p o r t i o n s of s c r o t a l males and l a c t a t i n g females i n p o p u l a t i o n s on the c o n t r o l and p u l s e d removal g r i d s . 169 13. Mean weights (+2 s tandard e r r o r s ) of males c o l o n i z i n g the c o n t i n u o u s removal area and r e s i d e n t males from c o n t r o l a r e a s . . . . . . . . . . . . 1 7 0 14. Mean weights (+2 s tandard e r r o r s ) of non-pregnant females c o l o r i z i n g the c o n t i n u o u s removal and r e s i d e n t females from c o n t r o l g r i d s . . . . . . . 1 7 1 15. Minimum number known to be a l i v e on the c o n t r o l g r i d s and the c o n t i n u o u s removal g r i d . . . . . . . . . . . . . . . . . . . . . . . . . . 172 16. S t a r c h g e l showing e s t e r a s e g e n o t y p e s . 173 17. G e n o t y p i c p r o p o r t i o n s i n the o v e r w i n t e r , b reed ing peak, and f a l l peak samples from c o n t r o l p o p u l a t i o n s . . . . . . . 1 7 4 18. P r o p o r t i o n s of mice heterozygous at 0 , 1 , 2 , and 3 l o c i , a t o v e r w i n t e r , b reed ing peak, and f a l l peak samples . . . . . 1 7 5 19. Genotyp ic p r o p o r t i o n s of males on c o n t r o l a reas and the c o n t i n u o u s removal g r i d . 176 20. P r o p o r t i o n s of males from the c o n t r o l g r i d and c o n t i n u o u s removal g r i d s he te rozygous at 0 , 1 , 2 , and 3 l o c i . . . . . . 1 7 6 21 . H o r i z o n t a l maze des igned f o r s t u d y i n g the tendency of a mouse to l e a v e a f a m i l i a r a rea and e x p l o r e an u n f a m i l i a r one ( e x p l o r a t o r y b e h a v i o r ) . . . . . . . 1 7 7 v i i 2 2 . Schematic r e p r e s e n t a t i o n of s e a s o n a l changes i n p o p u l a t i o n s of Peromjscus j a n i c u l a t u s . ......178 v i i i LIST Of TABLES T a b l e Page 1. Mean number caught/minimum number a l i v e on c o n t r o l g r i d s . . 180 2. Observed r a t e s o f s u r v i v a l and r e c r u i t m e n t , and t r a p -o v e r l a p i n d i c e s , i n c o n t r o l p o p u l a t i o n s . . . . . . . . . . . . . . 1 8 0 3. Number of r e s i d e n t s , d i s a p p e a r i n g m i c e , r e c r u i t s , and t r a n s i e n t s with weights g r e a t e r and l e s s than the weekly mean w e i g h t s , over a l l seasons (males o n l y ) . . . . . . . . . . 1 8 1 4. Number of r e s i d e n t s , d i s a p p e a r i n g m i c e , r e c r u i t s , and t r a n s i e n t s h a v i n g weights above and below the weekly mean w e i g h t s , over a l l seasons ( females o n l y ) . . . 1 8 2 5. Capture f r e q u e n c i e s of b r e e d i n g and n o n - b r e e d i n g mice d u r i n g the s p r i n g r e o r g a n i z a t i o n . . . . . . . . . . . . . . . . 1 8 3 6. Observed and expected numbers of j u v e n i l e r e c r u i t s on c o n t r o l a reas d u r i n g the main b r e e d i n g season .183 7. Number of a d u l t r e s i d e n t s , d i s a p p e a r i n g m i c e , r e c r u i t s , and t r a n s i e n t s with weights g r e a t e r and l e s s than the weekly means. A l l j u v e n i l e s have been removed from the sample . 184 8. Capture f r e q u e n c i e s of b reed ing and n o n - b r e e d i n g mice cn c o n t r o l a reas d u r i n g the main b r e e d i n g and f a l l i n c r e a s e p e r i o d s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 8 4 i x 9 , Breed ing c o n d i t i o n on f i r s t c a p t u r e of r e c r u i t s and t r a n s i e n t s i n the main b r e e d i n g and f a l l i n c r e a s e p e r i o d s . 185 10. Observed and expected t r a p - o v e r l a p f r e q u e n c i e s fcy sex and age , i n the f a l l i n c r e a s e p e r i o d . . . . . 1 8 5 11. Observed and expected numbers o f j u v e n i l e r e c r u i t s on c o n t r o l a reas i n the f a l l i n c r e a s e p e r i o d . . . . . . . . . . . . 1 8 6 12. Gomparison of j u v e n i l e r e c r u i t m e n t i n the main b r e e d i n g and f a l l i n c r e a s e p e r i o d s . 186 13. l o s s of p o t e n t i a l j u v e n i l e r e c r u i t s between pregnancy and r e c r u i t m e n t . . . . . . . 1 8 7 14. T r a p - o v e r l a p f r e g u e n c i e s in the o v e r w i n t e r p e r i o d . . . . 1 8 7 15. D i s t r i b u t i o n of d u r a t i o n s of l i f e of females b e f o r e the s t a r t of the o v e r w i n t e r p e r i o d ( females o n l y ) . . . . . . . . 1 8 7 16. Sex r a t i o s (males per female) o f mice moving onto the removal a r e a s , and of r e s i d e n t s cn c o n t r o l a r e a s , d u r i n g the s p r i n g r e o r g a n i z a t i o n . . . . 1 8 8 17. Number of r e s i d e n t s on c o n t r o l a reas and c o l o n i s t s to removal a reas with weights g r e a t e r and l e s s than the weekly mean weights on c o n t r o l a r e a s . . . . . . 1 8 8 18. P r o p o r t i o n s of r e s i d e n t c o n t r o l mice and removal c o l o n i s t s caught i n b r e e d i n g c o n d i t i o n at l e a s t once d u r i n g the s p r i n g r e o r g a n i z a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 8 9 19. T r a p - o v e r l a p f r e g u e n c i e s on the p u l s e d removal and c o n t r o l g r i d s (sexes combined) . . . . . 1 8 9 20 . Observed and expected numbers of j u v e n i l e r e c r u i t s on the c o n t r o l and p u l s e d removal g r i d s ...............190 21. Capture f r e g u e n c i e s of b r e e d i n g and non-breeding mice: c o n t r o l r e s i d e n t s , t o t a l c o n t r o l p o p u l a t i o n , and c o l o n i s t s t o the c o n t i n u o u s removal g r i d ................190 22. The p r o p o r t i o n s of mice weighing l e s s than 15g, and between 15 and 16 g, which were b r e e d i n g when caught on the c o n t i n u o u s removal and c o n t r o l a r e a s . ............191 23. R e c r u i t m e n t o f j u v e n i l e s onto c o n t r o l a r e a s and the c o n t i n u o u s removal a r e a , d u r i n g the main b r e e d i n g and f a l l i n c r e a s e p e r i o d s . The c a l c u l a t i o n of expected v a l u e s i s e x p l a i n e d i n the t e x t . ...............191 24. C h a r a c t e r i s t i c s of d i s p e r s i n g mice (mice moving onto and o f f c o n t r o l a r e a s , and mice c o l o n i z i n g r e m o v a l areas) when compared t o mice r e s i d e n t on c o n t r o l a r e a s . ....192 25. R e g r e s s i o n s of number caught on the c o n t i n u o u s removal g r i d a g a i n s t minimum number known to be a l i v e on the two c o n t r o l a r e a s . .....192 26. R e g r e s s i o n s of number caught cn t h e c o n t i n u o u s removal g r i d a g a i n s t d e n s i t y and r a t e of i n c r e a s e on the c o n t r o l a r e a s . 193 27. R e g r e s s i o n s of r e c o v e r y r a t i o on the c o n t i n u o u s removal a r e a a g a i n s t d e n s i t y and r a t e o f i n c r e a s e oh t h e c o n t r o l a r e a s . 193 28. The r e s u l t s of l a b o r a t o r y c r o s s e s showing the i n h e r i t a n c e of the two a l l e l e s a t the t r a n s f e r r i n l o c u s . .........194 29. The r e s u l t s of l a b o r a t o r y c r e s s e s showing the i n h e r i t a n c e x i of the two a l l e l e s at the e s t e r a s e l o c u s . . . 194 30. The r e s u l t s of l a b o r a t o r y c r o s s e s showing the i n h e r i t a n c e of the a l l e l e s at the g lutamate o x a l a t e t ransaminase l o c u s . . . . . . . 1 9 5 31. Genotypes used in the g e n e t i c a n a l y s e s . . . . . . . 1 9 5 32 . Observed and expected g e n o t y p i c f r e q u e n c i e s cn c o n t r o l a r e a s . . . . . . . . . . . . . . . . . . . . . . . . . . 1 9 6 33. Observed and expected numbers of mice hav ing 0 , 1 , 2 , a n d 3 he te rozygous l o c i . . . . . . . . . . 1 9 7 34. S u r v i v a l r a t e s e s t i m a t e d from r e g r e s s i o n models with g e n o t y p i c f r e q u e n c i e s a l lowed to vary ( s e a s c n s - o n l y model) or he ld c o n s t a n t at t h e i r mean v a l u e s . . . . 1 9 8 35. P r o p o r t i o n s of mice he terozygous at 0 , 1 , 2 , a n d 3 l o c i i n peak b r e e d i n g , f a l l peak, and overw in te r samples . . . . . 1 9 8 36. A g o n i s t i c and s o c i a l b e h a v i o r s r e c o r d e d d u r i n g the n e u t r a l arena e n c o u n t e r s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 37 . F a c t o r s o l u t i o n f o r a g o n i s t i c b e h a v i o r s . .199 38. F a c t o r s o l u t i o n f o r s o c i a l b e h a v i o r s . , . . . . . . . . . . . . . . . . 2 0 0 39 . Comparison of f a c t o r s c o r e s f o r b r e e d i n g and n o n - b r e e d i n g males . 200 40 . Comparison of f a c t o r s c c r e s of r e s i d e n t B a l e s with those c f c o l o n i s t s on the c o n t i n u o u s removal a r e a .201 41. C l a s s i f i c a t i o n f u n c t i o n s d e r i v e d from d i s c r i m i n a n t a n a l y s i s of r e s i d e n t males cn c o n t r o l g r i d s and c o l o n i s t s to the c o n t i n u o u s removal g r i d , u s i n g f a c t o r s AF1 and S F 1 . 201 x i i 42. Summary of a n a l y s i s of f a c t o r s c o r e s f o r a g o n i s t i c and s o c i a l f a c t o r s . 202 43. Mean s c o r e s i n the maze t e s t f o r males and females from c o n t r o l g r i d s . 202 44. Comparisons of maze b e h a v i o r of b r e e d i n g and no n - b r e e d i n g mice from c o n t r o l g r i d s . 203 45. Comparisons o f maze b e h a v i o r of mice from c o n t r o l ; p u l s e d r e m o v a l , and c o n t i n u o u s removal g r i d s . ............... 203 46. Comparisons of g e n e r a l a c t i v i t y s c o r e s o f mice from c o n t r o l , p u l s e d r e m o v a l , and c o n t i n u o u s removal g r i d s . .204 x i i i ACKNOWLEDGEMENTS D u r i n g the course of t h i s s t u d y , I r e c e i v e d h e l p and encouragement from many p e o p l e . I am e s p e c i a l l y g r a t e f u l to my s u p e r v i s o r , Dr . C h a r l e s K r e b s , f o r a lways be ing both w i l l i n g and a b l e t o help me, and f o r h i s example of p e r s i s t e n t c h e e r f u l n e s s i n the face of e v e r y t h i n g from wasps' n e s t s to s t a t i s t i c a l s e t - b a c k s . I would a l s o l i k e to thank Dr . Dennis C h i t t y f c r h i s c o n s t a n t i n t e r e s t i n the p r o g r e s s of t h i s work, encouragement , and many v a l u a b l e s u g g e s t i o n s . I am g r a t e f u l to Dr . E r n s t Bernt o f the economics department f o r h i s a d v i c e on t e c h n i g u e s of a n a l y s i s of t i m e -s e r i e s d a t a , and to Dr . A l l a n B i r d s a l l f o r h i s h e l p with e l e c t r o p h o r e t i c t e c h n i g u e s . Hugh B i c k n e r , C a r l E l l i n g s e n , Tom S u l l i v a n , and C a r l B h i t n e y he lped me with my f i e l d work and the maintenance of my l a b o r a t o r y c o l o n y . I am g r a t e f u l f o r t h e i r h e l p and good humor. I would a l s o l i k e to thank Dr . J u d i t h Myers , Dr . James S m i t h , Dr. Dixon j c n e s , Dr . Dennis C h i t t y , and D r . C h a r l e s Krebs f o r c r i t i c a l l y r e a d i n g e a r l i e r {and longer ) d r a f t s of t h i s t h e s i s . I r e c e i v e d f i n a n c i a l suppor t and r e s e a r c h funds from the N a t i o n a l Research C o u n c i l of Canada from 1971 to 1975. A t e a c h i n g a s s i s t a n t s h i p from the U n i v e r s i t y o f B r i t i s h Columbia p r o v i d e d s u p p o r t f o r 1975-76. 1 CHAPTER 1 GEHEBAL INTRODUCTION Animal p o p u l a t i o n s have the c a p a c i t y to i n c r e a s e e x p o n e n t i a l l y , but seldom do s o . What p r e v e n t s u n l i m i t e d i n c r e a s e s ? One h y p o t h e s i s i s t h a t some p o p u l a t i o n s have e v o l v e d i n t r i n s i c b e h a v i o r a l mechanisms which l i m i t r e p r o d u c t i o n , and ma in ta in b r e e d i n g d e n s i t i e s below those at which r e s o u r c e s , such as food or n e s t i n g s p a c e , would be d i r e c t l y l i m i t i n g . A c c o r d i n g t o t h i s h y p o t h e s i s , i n t e r a c t i o n s between i n d i v i d u a l s i n the p o p u l a t i o n a f f e c t r e p r o d u c t i o n and s u r v i v a l . A g g r e s s i v e b e h a v i o r , a s s o c i a t e d with c o m p e t i t i o n between i n d i v i d u a l s f o r b r e e d i n g t e r r i t o r i e s or p o s i t i o n s i n a s o c i a l h i e r a r c h y , can have such a l i m i t i n g e f f e c t , s i n c e l e s s s u c c e s s f u l c o m p e t i t o r s o f t e n have a reduced chance of s u r v i v i n g and b r e e d i n g . A l though many f a c t o r s w i l l i n f l u e n c e the l e v e l of a g g r e s s i o n i n a p o p u l a t i o n , i f a g g r e s s i v e i n t e r a c t i o n s r e g u l a t e b r e e d i n g d e n s i t i e s , a g g r e s s i o n must be l i n k e d to d e n s i t y i n some s y s t e m a t i c manner. What i s the na tu re of t h i s l i n k ? C h i t t y (1967) proposed a model which s t r e s s e s the g e n e t i c b a s i s o f b e h a v i o r a l v a r i a b i l i t y . T h i s model was proposed t o e x p l a i n the r e g u l a r c y c l e s observed i n p o p u l a t i o n s of many m i c r o t i n e r o d e n t s and sncwshoe h a r e s , but C h i t t y assumed t h a t the p o p u l a t i o n d e c l i n e s observed i n these s p e c i e s a re merely wel l -marked e f f e c t s of the g e n e r a l p r o c e s s o f 2 p o p u l a t i o n l i m i t a t i o n , and hence tha t the model can be g e n e r a l i z e d to a l l p o p u l a t i o n s which are l i m i t e d by i n t r a s p e c i f i c a g g r e s s i o n . The h y p o t h e s i s i s t h a t a d e c l i n e i n numbers i s a n e c e s s a r y conseguence o f s e l e c t i o n , i n i n c r e a s i n g p o p u l a t i o n s , f o r an imals which can w i ths tand c r o w d i n g . When d e n s i t y i s low, genotypes with h igh r e p r o d u c t i v e p o t e n t i a l a re f a v o r e d , b u t , as d e n s i t y i n c r e a s e s , mutual i n t e r f e r e n c e i n c r e a s e s , r e s u l t i n g i n s e l e c t i o n f o r an ima ls which can w i t h s t a n d c r o w d i n g . A g g r e s s i v e an imals are f a v o r e d a t t h i s t i m e , and i n c r e a s e d s p a c i n g out o f i n d i v i d u a l s r e s u l t s i n a r e d u c t i o n i n p o p u l a t i o n d e n s i t y . S e l e c t i o n a c t s through reduced r e p r o d u c t i o n , i n c r e a s e d m o r t a l i t y and i n c r e a s e d e m i g r a t i o n , p a r t i c u l a r l y of l e s s a g g r e s s i v e i n d i v i d u a l s . T h i s h y p o t h e s i s , the major o b j e c t i o n s t o i t , and the e v i d e n c e s u p p o r t i n g , i t have been rev iewed by Krebs and Myers (1974). A l though no study has demonstrated r a p i d s e l e c t i o n f o r g e n e t i c a l l y determined b e h a v i o r a l t y p e s i n a n a t u r a l p o p u l a t i o n , o t h e r ev idence i n d i c a t e s tha t such s e l e c t i o n c o u l d o c c u r . For example , a g g r e s s i v e b e h a v i o r i s under g e n e t i c c o n t r o l , and s e l e c t i o n of a g g r e s s i v e types can occur w i t h i n two or th ree g e n e r a t i o n s ( l a g e r s p e t z e , 1968; B a r n e t t , 1968; C r a i g , Ortman and G u h l , 1968); and both a g o n i s t i c b e h a v i o r (Krebs , 1970; S a d l e i r , 1965) , and f r e g u e n c i e s of g e n e t i c types (Tamarin and K r e b s , 1969; Gaines and K r e b s , 1970) vary with p o p u l a t i o n d e n s i t y . The l i m i t a t i o n of p o p u l a t i o n i n c r e a s e by i n t r a - s p e c i f i c 3 a g g r e s s i o n i s c e n t r a l to C h i t t y ' s b e h a v i o r a l - g e n e t i c feedback h y p o t h e s i s . D i s p e r s a l o f i n d i v i d u a l s from conges ted a r e a s i s one consequence of t h i s mechanism. However, some e m i g r a t i o n may be independent of i n t r a s p e c i f i c a g g r e s s i o n . Howard (1960) p o s t u l a t e d t h a t s m a l l mammals may sometimes make e x t e n s i v e d i s p e r s a l movements as a r e s u l t of an " i n n a t e " or i n h e r i t e d tendency to d i s p e r s e . l i d i c k e r (1962) expanded on t h i s i d e a , and suggested t h a t , when 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 or c a r r y i n g c a p a c i t y d e c r e a s e s , i n d i v i d u a l s which d i s p e r s e from the a r e a may be a t a s e l e c t i v e advantage . T h i s i s a g e n e t i c feedback mechanism of p o p u l a t i o n r e g u l a t i o n which i s s i m i l a r to t h a t proposed by C h i t t y (1967), but which emphasizes v a r y i n g s e l e c t i o n f o r d i s p e r s a l tendency r a t h e r than a g g r e s s i v e b e h a v i o r . Other a u t h o r s have used mathemat ica l models to i n v e s t i g a t e d i s p e r s a l as a response t c p o p u l a t i o n d e n s i t y . They have suggested tha t s p a t i a l v a r i a t i o n i n c a r r y i n g c a p a c i t i e s w i l l f a v o r a r a p i d i n c r e a s e i n d i s p e r s a l with i n c r e a s i n g d e n s i t y ( G a d g i l , 1971) , and t h a t a polymorphism f o r tendency to d i s p e r s e c c u l d be mainta ined i n a p o p u l a t i o n i f t h e r e were a p r o b a b i l i t y of l o c a l e x t i n c t i o n (Van V a l e n , 1971). D i s p e r s a l b e h a v i o r p l a y s an impor tant r o l e i n l i m i t i n g p o p u l a t i o n s of f i e l d v o l e s , M i c r o t u s f - e n n s y l y a n i c u s and M i c r g t u s o c h r o g a s t e r (Krebs , K e l l e r and T a m a r i n , 1969). Myers and Krebs (1971) s t u d i e d the d i s p e r s a l of these v o l e s i n t o 4 depopulated areas. They found that the number of i n d i v i d u a l s d i s p e r s i n g was not d i r e c t l y c o r r e l a t e d with d e n s i t y , but occurred l a r g e l y d u r i n g the phase of p o p u l a t i o n i n c r e a s e , and t h a t d i s p e r s i n g v o l e s d i f f e r e d b e h a v i o r a l l y and g e n e t i c a l l y from v o l e s i n r e s i d e n t p o p u l a t i o n s . These r e s u l t s are c o n s i s t e n t with both C h i t t y ' s and L i d i c k e r ' s hypotheses. Although the proposed b e h a v i o r a l - g e n e t i c feedback mechanisms co u l d l i m i t p o p u l a t i o n s which remain s t a b l e from year to year, a l l f i e l d s t u d i e s conducted to date have been concerned with p o p u l a t i o n s of m i c r c t i n e rodents which are assumed to undergo r e g u l a r c y c l e s i n d e n s i t y . T h i s t h e s i s examines g e n e t i c and b e h a v i o r a l v a r i a b i l i t y w i t h i n a p o p u l a t i o n of deermice (ferom.yscus maniculatus) , a s p e c i e s which i s noted f o r constancy of p o p u l a t i o n d e n s i t y from year to year, area to area, and h a b i t a t to h a b i t a t (Terman, 1S68). The g u e s t i c n s which I asked a r e : 1) Could t h i s ' s t a b l e 1 p o p u l a t i o n be' l i m i t e d by a mechanism i n v o l v i n g v a r y i n g s e l e c t i o n pressures on g e n e t i c a l l y determined b e h a v i o r a l t y p e s ? ; and, 2) I f such a mechanism i s o p e r a t i n g , what r o l e does d i s p e r s a l play? £S£2JIscus p o p u l a t i o n s are good s u b j e c t s f o r t h i s study because not only do they maintain r e l a t i v e l y constant breeding d e n s i t i e s from year to year, but they show r e g u l a r seasonal f l u c t u a t i o n s (Terman, 1968), so that the phenomenon of l i m i t a t i o n of p o p u l a t i o n i n c r e a s e can be s t u d i e d each year. F u r t h e r , s e v e r a l l i n e s of evidence i n d i c a t e that a g g r e s s i v e 5 b e h a v i o r i s i n v o l v e d i n t h e r e g u l a t i o n o f t h e s e p o p u l a t i o n s . One l i n e o f e v i d e n c e comes f r o m s t u d i e s o f t h e g r o w t h o f l a b o r a t o r y p o p u l a t i o n s o f P e r o m ^ s c u s i n t h e p r e s e n c e o f e x c e s s f o o d and w a t e r ( T e r m a n , 1 9 6 5 a ; l i d i c k e r , 1 9 6 5 ) . The d e n s i t y o f t h e s e p o p u l a t i o n s i n i t i a l l y i n c r e a s e d r a p i d l y and t h e n l e v e l e d c u t b e c a u s e o f a r e d u c t i o n i n t h e p r o p o r t i o n o f f e m a l e s b r e e d i n g , d e l a y i n m a t u r a t i o n o f young m i c e , and i n c r e a s e i n l i t t e r m o r t a l i t y . No d i s p e r s a l was a l l o w e d i n t h e s e e x p e r i m e n t s . A l t h o u g h l i d i c k e r and Terman d i d n o t m easure a g o n i s t i c b e h a v i o r , t h e y s u g g e s t e d t h a t b e h a v i o r a l i n t e r a c t i o n s were r e s p o n s i b l e f o r t h e o b s e r v e d l i m i t a t i o n o f g r o w t h i n t h e i r p o p u l a t i o n s . A s t u d y by G r e g o r e t a l . . (1972) s u p p o r t s t h i s v i e w . They s e t up p o p u l a t i o n s o f £eromjsc_us j a n i c u l a t u s a t two d e n s i t i e s , f o u r p e r c a g e and t w e l v e p e r c a g e , a n d o b s e r v e d t h e b e h a v i o r o f t h e s e m i c e i n t h e i r heme c a g e s and i n n e u t r a l a r e n a e n c o u n t e r s . I n b o t h p l a c e s , m i c e f r o m t h e h i g h d e n s i t y p o p u l a t i o n s showed more a g o n i s t i c and c o n t a c t b e h a v i o r t h a n d i d m i c e f r o m l o w d e n s i t y p o p u l a t i o n s . I n a d d i t i o n , h i g h d e n s i t y f e m a l e s had f e w e r l i t t e r s and r a i s e d them l e s s s u c c e s s f u l l y t h a n d i d l o w d e n s i t y f e m a l e s . T h u s , t h e r e i s good e v i d e n c e t h a t l a b o r a t o r y p o p u l a t i o n s o f P e r o m j s c u s c a n r e g u l a t e t h e i r d e n s i t y b e l o w t h a t a t w h i c h f o o d becomes l i m i t i n g , and t h a t t h i s r e g u l a t i o n i s p r o b a b l y a c h i e v e d by b e h a v i o r a l m echanisms i n v o l v i n g a g g r e s s i o n . I n t h e s e s t u d i e s , r e g u l a t i o n o c c u r r e d i n t h e a b s e n c e o f 6 d i s p e r s a l . D i s p e r s a l behav io r i s t h e r e f o r e not n e c e s s a r y f o r r e g u l a t i o n . However, s i n c e i n h i b i t i o n of r e p r o d u c t i o n o c c u r s a t h i g h d e n s i t i e s , i n d i v i d u a l s i n n a t u r a l p o p u l a t i o n s n i g h t i n c r e a s e t h e i r f i t n e s s by d i s p e r s i n g to a reas c f lower d e n s i t y ( L i d i c k e r , 1962) . A l s o , the l a b o r a t o r y p o p u l a t i o n s s t a b i l i z e d a t much h i g h e r d e n s i t i e s than have ever been observed i n n a t u r a l p o p u l a t i o n s . T h i s i s p r o b a b l y ana lagous to the " f e n c e e f f e c t " observed i n e n c l o s e d f i e l d p o p u l a t i o n s of M i c r o t u s ( K r e b s , K e l l e r , and T a m a r i n , 1969) , and s i m i l a r l y , s u g g e s t s t h a t d i s p e r s a l p l a y s an impor tan t r o l e i n r e g u l a t i o n of u n r e s t r i c t e d n a t u r a l p o p u l a t i o n s . L a b o r a t o r y p o p u l a t i o n s of Peromyscus appear to be l i m i t e d by mechanisms i n v o l v i n g i n t r a s p e c i f i c a g g r e s s i o n , but can we i n f e r tha t such a g g r e s s i o n p l a y s a pa r t i n the r e g u l a t i o n of numbers i n n a t u r a l p o p u l a t i o n s ? S t u d i e s by S a d l e i r (1965) and Healey (1967) i n d i c a t e tha t we c a n . S a d l e i r s t u d i e d p o p u l a t i o n s of P.. I S f i i c u l a t u s on the Endowment Lands at the U n i v e r s i t y of E r i t i s h C o l u m b i a . These p o p u l a t i o n s showed the s e a s o n a l v a r i a b i l i t y c h a r a c t e r i s t i c of the genus , wi th low s p r i n g b r e e d i n g d e n s i t i e s and h i g h e r d e n s i t i e s through the f a l l and w i n t e r . Dur ing the b r e e d i n g s e a s o n , r e c r u i t m e n t was very low and few j u v e n i l e s s u r v i v e d to t r a p p a b l e a g e . However, the en,d of b reed ing i n the f a l l was a s s o c i a t e d with a marked i n c r e a s e i n j u v e n i l e s u r v i v a l and r e c r u i t m e n t . fldult male a g g r e s s i o n , as measured by p a i r e d encounte rs i n the l a b o r a t o r y , was h i g h l y c o r r e l a t e d wi th b r e e d i n g c o n d i t i o n , and 7 v a r i e d i n v e r s e l y with p o p u l a t i o n d e n s i t y . A l l of the p o p u l a t i o n s d e c l i n e d , and showed a r i s e i n male a g g r e s s i o n , wi th the onse t of b r e e d i n g i n the s p r i n g . The most s e v e r e d e c l i n e s were a s s o c i a t e d with the h i g h e s t l e v e l s of a g g r e s s i o n observed i n the s t u d y . Ey a s e r i e s of f i e l d and l a b o r a t o r y e x p e r i m e n t s , S a d l e i r was ab le to show tha t a g g r e s s i o n of a d u l t males r e s t r i c t e d the s u r v i v a l , and r e c r u i t m e n t o f j u v e n i l e s , d u r i n g the b r e e d i n g s e a s o n . Men-breeding males d i d not behave a g g r e s s i v e l y toward j u v e n i l e s . Healey (1967) v e r i f i e d S a d l e i r ' s c o n c l u s i o n s and f u r t h e r examined the i n t e r a c t i o n s between a d u l t s and j u v e n i l e s . He found tha t a g g r e s s i v e males more s e v e r e l y a f f e c t e d j u v e n i l e s than d i d d o c i l e m a l e s , and that r e s i d e n t a d u l t s mere s e v e r e l y r e s t r i c t e d j u v e n i l e growth and s u r v i v a l than d i d a d u l t s i n u n f a m i l i a r s u r r o u n d i n g s . A g g r e s s i v e b e h a v i o r of r e s i d e n t b r e e d i n g a d u l t s c l e a r l y prevented j u v e n i l e s from s u c c e s s f u l l y e n t e r i n g the p o p u l a t i o n s d u r i n g the b r e e d i n g s e a s o n . The r i s e i n male a g g r e s s i o n , which accompanied the s p r i n g p o p u l a t i o n d e c l i n e s ( S a d l e i r , 1 9 6 5 ) , sugges ts t h a t a d u l t a g g r e s s i o n may a l s o be impor tant i n e s t a b l i s h i n g the d e n s i t y o f b r e e d i n g a d u l t s . Healey i n v e s t i g a t e d i n t e r a c t i o n s between a d u l t s i n the f i e l d , and found t h a t , d u r i n g the b r e e d i n g s e a s o n , the presence of r e s i d e n t a d u l t s on an area r e s t r i c t e d i n t r o d u c e d a d u l t s from s e t t l i n g . T h u s , i t appears t h a t the b r e e d i n g d e n s i t y e s t a b l i s h e d at the end of the s p r i n g d e c l i n e was ma in ta ined by a g g r e s s i v e b e h a v i o r of r e s i d e n t , b r e e d i n g 8 males . F u r t h e r , a l t h o u g h n e i t h e r S a d l e i r nor flealey made a d e t a i l e d i n v e s t i g a t i o n of i n t e r a c t i o n s a t the s t a r t of the b r e e d i n g s e a s o n , t h e i r r e s u l t s suggest t h a t the s p r i n g p o p u l a t i o n d e c l i n e s may r e s u l t , a t l e a s t i n p a r t , from the e x p u l s i o n of l e s s a g g r e s s i v e males from the p o p u l a t i o n . Many a u t h o r s (see Terman, 1968) have r e p o r t e d t h a t j u v e n i l e s dc not d i s p e r s e from the p a r e n t a l home range u n t i l they become s e x u a l l y mature. Howard (1949) r e p o r t e d tha t a g g r e g a t i o n s of j u v e n i l e s were s t a b l e throughout the w i n t e r , and d i d not break up u n t i l the s t a r t of the b r e e d i n g s e a s o n . E x t e n s i v e d i s p e r s a l o c c u r r e d at t h i s t i m e . Smith (1968) made s i m i l a r o b s e r v a t i o n s on a p o p u l a t i o n of P A ficlionctus. Sav idge (1974) d e m o n s t r a t e d , i n the l a b o r a t o r y , tha t j u v e n i l e P j , manic u l at us d i s p e r s e i n response to a g g r e s s i o n of t h e i r mother with the a r r i v a l o f a new l i t t e r . In the f i e l d , the l a s t l i t t e r s o f a season would not e x p e r i e n c e t h i s a g g r e s s i o n and would t h e r e f o r e tend not to d i s p e r s e . I f the l a s t l i t t e r s o f the season do net d i s p e r s e u n t i l the f o l l o w i n g s p r i n g , then one would expect a r e o r g a n i z a t i o n of the p o p u l a t i o n every s p r i n g , merely as a r e s u l t of d i s p e r s a l movements of the newly mature, o v e r w i n t e r e d j u v e n i l e s . T h e r e f o r e , a l t h o u g h t h e r e i s good e v i d e n c e t h a t the low d e n s i t y of b r e e d i n g p o p u l a t i o n s i s ma in ta ined by the a g g r e s s i v e b e h a v i o r of r e s i d e n t b r e e d i n g males , d i s p e r s a l p r o b a b l y p l a y s an impor tant r o l e i n de te rmin ing not o n l y how many, but a l s o what k i n d s of o v e r w i n t e r e d an imals remain to 9 b r e e d . There i s a l s o e v i d e n c e , from the l a b . and the f i e l d , t h a t d e n s i t i e s of some Percmyscus p o p u l a t i o n s may be r e l a t e d to the g e n e t i c c o m p o s i t i o n of the p o p u l a t i o n . When Pergm^scus p o p u l a t i o n s are a l lowed to grow i n the l a b o r a t o r y , i n the p resence of excess f o o d , the a s y m p t o t i c d e n s i t y v a r i e s c o n s i d e r a b l y among p o p u l a t i o n s (Terman, 1965; L i d i c k e r , 1 S 6 5 ) . L i d i c k e r (1965) has suggested t h a t t h i s v a r i a b i l i t y may be due i n p a r t to g e n e t i c d i f f e r e n c e s among the mice f o u n d i n g the d i f f e r e n t p o p u l a t i o n s . Ev idence f o r g e n e t i c i n f l u e n c e s on f i e l d p o p u l a t i o n s comes from s t u d i e s by Canham (1969) and B i r d s a l l (1972), which showed tha t s e l e c t i o n at b lood p r o t e i n l o c i o c c u r s both between and w i t h i n g e n e r a t i o n s , i n p o p u l a t i o n s of Pergm^scus man icu la tus . F u r t h e r , Canham found t h a t the s e l e c t i o n p r e s s u r e v a r i e d with p o p u l a t i o n d e n s i t y -a n i m a l s he te rozygous at both p r o t e i n l o c i examined were f a v o r e d when the p o p u l a t i o n was d e c l i n i n g , wh i le h e t e r o z y g o t e s were s e l e c t e d a g a i n s t i n i n c r e a s i n g p o p u l a t i o n s . N e i t h e r Canham nor B i r d s a l l s t u d i e d b a h a v i o r a l changes i n t h e i r p o p u l a t i o n s , so we cannot connect the observed g e n e t i c changes wi th b e h a v i o r , nor can we assume that these p o p u l a t i o n s are r e g u l a t e d by the same mechanisms as p o p u l a t i o n s i n the Vancouver a r e a . However, these s t u d i e s do i n d i c a t e both t h a t s e l e c t i o n goes on over the annual ' c y c l e ' , and tha t there i s some r e l a t i o n s h i p between the g e n e t i c c o m p o s i t i o n of the p o p u l a t i o n s and t h e i r d e n s i t y . I began t h i s s tudy i n the 10 b e l i e f t h a t , i f s i m i l a r r e l a t i o n s h i p s h e l d f o r P e r o j ^ s c u s on the U . B . C . Endowment L a n d s , which are r e g u l a t e d a t l e a s t p a r t l y by b e h a v i o r a l mechanisms, they might we l l be r e g u l a t e d by b e h a v i o r a l - g e n e t i c ' feedback mechanisms of the s o r t s proposed by C h i t t y and L i d i c k e r . In summary, t h e r e i s good e v i d e n c e t h a t p o p u l a t i o n s of Peromxscus, i n both the l a b o r a t o r y and the f i e l d , are r e g u l a t e d by i n t r i n s i c b e h a v i o r a l mechanisms which c e r t a i n l y i n v o l v e a g g r e s s i o n and may i n v o l v e d i s p e r s a l as w e l l . F i e l d p o p u l a t i o n s show p r e d i c t a b l e s e a s o n a l i n c r e a s e s and d e c l i n e s , so t h a t the r e g u l a t o r y p r o c e s s can be observed each y e a r , and these d e n s i t y changes are a s s o c i a t e d wi th g e n e t i c changes i n at l e a s t some p o p u l a t i o n s . A l l of these f a c t o r s make Peromyscus an e x c e l l e n t s u b j e c t f o r an i n v e s t i g a t i o n of the p o s s i b l e r o l e of b e h a v i o r a l - g e n e t i c feedback mechanisms i n r e g u l a t i n g a ' n o n - c y c l i c * p o p u l a t i o n of s m a l l mammals. 11 CHAPTER 2 EXPERIMENTAL DESIGN A grea t d e a l of work has been done on the p o p u l a t i o n b i o l o g y of Psrcm^scus (see rev iews by Terman, Basmussen, S t i c k e l , E i s e n b e r g , and F a l l s , in - B i o l o g y of P e rpjn yj=c us , 1968, J . A . . K i n g , e d , ) . Only those s t u d i e s t h a t most d i r e c t l y a f f e c t e d the development of my i d e a s and the d e s i g n of my exper iments have been c i t e d i n the i n t r o d u c t o r y c h a p t e r . In d e v e l o p i n g the c o n c e p t u a l model of s e a s o n a l f l u c t u a t i o n s i n Peromyscus p o p u l a t i o n s ( F i g . 1 ) , I r e l i e d h e a v i l y on the s t u d i e s of S a d l e i r (1965) and Healey (1967) , but the demographic and b e h a v i o r a l changes proposed i n t h i s model are c o n s i s t e n t with o b s e r v a t i o n s on £££cmyscus p o p u l a t i o n s throughout North A m e r i c a , (see rev iews by S t i c k e l and Terman, o p ; c t . ) . Peromx§cus i n a reas wi th hot dry summers ( i . e . c e n t r a l C a l i f o r n i a ) breed i n the w i n t e r r a t h e r than the summer, but show the same r e l a t i o n s h i p s between p o p u l a t i o n s i z e , b e h a v i o r , and b r e e d i n g season as do the more temperate p o p u l a t i o n s r e p r e s e n t e d i n the model . In F i g u r e 1, the f i r s t season i s r e p r e s e n t e d as a d e c l i n e i n d e n s i t y . However, I have l a b e l e d t h i s season the ' s p r i n g r e o r g a n i z a t i o n ' r a t h e r than the ' s p r i n g d e c l i n e * . T h i s i s b e c a u s e , a l t h o u g h I would expect the onset o f b r e e d i n g t o be a s s o c i a t e d with a r e o r g a n i z a t i o n of p o p u l a t i o n s t r u c t u r e , due to a g g r e s s i v e i n t e r a c t i o n s between males and d i s p e r s a l of o v e r w i n t e r e d j u v e n i l e s , i t need not always r e s u l t i n a d e c l i n e 12 i n numbers. The r e o r g a n i z a t i o n shou ld a lways be a s s o c i a t e d with the e m i g r a t i o n of some o v e r w i n t e r e d r e s i d e n t s , but i f the moni tored p o p u l a t i o n i s p a r t o f a l a r g e r , c o n t i n u o u s p o p u l a t i o n , some new an imals can be expected t o come i n from the s u r r o u n d i n g a r e a . I f the r e o r g a n i z a t i o n a c t s as a r e g u l a t o r y mechanism, the e m i g r a t i o n s h o u l d exceed i m m i g r a t i o n o n l y when more i n d i v i d u a l s have s u r v i v e d the winter than can s u c c e s s f u l l y breed i n tha t a r e a . T h e r e f o r e , i n examining p o p u l a t i o n p r o c e s s e s , I w i l l i d e n t i f y the ' s p r i n g r e o r g a n i z a t i o n ' by i n c r e a s e d e m i g r a t i o n and i m m i g r a t i o n a s s o c i a t e d with the onset of b r e e d i n g : p o p u l a t i o n d e n s i t y cou ld -show any t r e n d , i n c l u d i n g no net change , over t h i s p e r i o d . I have not i n c l u d e d g e n o t y p i c changes i n F i g u r e 1. A l though B i r d s a l l (1972) and Canham (1969) showed t h a t s e l e c t i o n does o c c u r i n p o p u l a t i o n s of P e r o i j s c u s , and t h a t s e l e c t i o n p r e s s u r e v a r i e s with p o p u l a t i o n t r e n d , they were concerned with compar isons between y e a r s , a r e a s , and g e n e r a t i o n s , r a t h e r than with d e t a i l s of the r e l a t i o n s h i p s between genotype and d e n s i t y w i t h i n the annual c y c l e . The demographic and b e h a v i o r a l components of the model have been gathered from v a r i o u s f i e l d and l a b o r a t o r y s t u d i e s , but the g e n e t i c component would have been mere s p e c u l a t i o n . The c o m p o s i t i o n of the p o p u l a t i o n changes most r a p i d l y d u r i n g the s p r i n g r e o r g a n i z a t i o n and the f a l l i n c r e a s e p e r i o d . The o n l y • g e n e t i c 1 p r e d i c t i o n tha t I made at the s t a r t of my s tudy was 13 t h a t , i f s e l e c t i o n d i d occur over the annual ' c y c l e ' , i t would p r o b a b l y be most obv ious d u r i n g cne or both of these p e r i o d s . Having s y n t h e s i z e d what was a l r e a d y known about Peromjscus p o p u l a t i o n s i n t o a c o n c e p t u a l model , I proceeded to d e s i g n exper iments to a c c o m p l i s h my major o b j e c t i v e : to determine i f a p o p u l a t i o n of s m a l l mammals which main ta ined a r e l a t i v e l y c o n s t a n t b reed ing d e n s i t y from year to y e a r , c o u l d be r e g u l a t e d by a b e h a v i o r a l - g e n e t i c feedback mechanism, such as those proposed by C h i t t y (1967) and l i d i c k e r (1962). The components which I f e l t were n e c e s s a r y f o r such a mechanism were v a r i a b i l i t y in a g g r e s s i o n , d i s p e r s a l , and g e n e t i c c o m p o s i t i o n over the annual c y c l e . S a d l e i r and Healey had a l r e a d y shown tha t b r e e d i n g d e n s i t i e s were d e t e r m i n e d , at l e a s t p a r t l y , by a g g r e s s i v e b e h a v i o r of r e s i d e n t a d u l t males . T h e r e f o r e , I c o n c e n t r a t e d on d e t e r m i n i n g i f d i s p e r s a l and g e n e t i c c o m p o s i t i o n of the p o p u l a t i o n were r e l a t e d i n any s y s t e m a t i c manner to the p o p u l a t i o n p r o c e s s e s presented i n F i g u r e 1. STUD! flEEfl AND TRAPPING TECHNIQUES: The s tudy area i s a 1700-acre t r a c t o f second growth c o a s t a l r a i n f o r e s t s u r r o u n d i n g the campus of the U n i v e r s i t y of B r i t i s h C o l u m b i a , on the western edge of Vancouver , B . C . The dominant t r e e s are Douglas F i r , Western Bed C e d a r , S i t k a S p r u c e , Western Hemlock, and Bed A l d e r , and the s tands i n which I worked v a r i e d i n age from 60 to 150 y e a r s . The 14 u n d e r s t o r y i s s p a r s e and c o n s i s t s mainly of s a l a l , red h u c k l e b e r r y , v a r i o u s f e r n s p e c i e s , a n d , where more s u n l i g h t p e n e t r a t e s , v ine maple and s a l m c n b e r r y . The c l i m a t e i s c o a s t a l , with m i l d , r a i n y w i n t e r s , c o o l , dry summers, and r e l a t i v e l y s l i g h t annual v a r i a t i o n i n t e m p e r a t u r e . F i g u r e 2 shows the approximate l o c a t i o n s of my s tudy p l o t s . Each p l o t i s a 7 x 7 g r i d of t r a p p i n g s t a t i o n s p l a c e d at 15-meter i n t e r v a l s . T h i s area i n c l u d e s .8 h e c t a r e s , and i f each s t a t i o n i s c o n s i d e r e d to be the c e n t e r o f a 15-meter s g u a r e , c o v e r s 1.1 h e c t a r e s . G r i d s 1 and 2 are s e p a r a t e d by 153 mete rs ; g r i d s 2 and 3 by 61 meters; and g r i d 4 i s s e p a r a t e d from t h i s c l u s t e r of g r i d s by at l e a s t 1.6 km. Animals were c a p t u r e d i n s tandard s i z e d (3 x 3 x 10 i n c h e s ) Sherman l i v e t r a p s , b a i t e d with f r e s h peanut b u t t e r and one or two p i e c e s of E u r i n a l a b o r a t o r y chow. T h i s was enough food to suppor t one mouse f c r 24 h o u r s , but I f e l t i t was not enough to c r e a t e a s i g n i f i c a n t i n c r e a s e i n the food a v a i l a b l e on the s tudy a r e a s . The t r a p s on each g r i d were s e t f o r two n i g h t s every second week, a n d , through most of the s t u d y , a l l g r i d s were t rapped i n the same week. The t r a p s were checked on ly i n the morn ings . I r e c o r d e d the w e i g h t , b r e e d i n g c o n d i t i o n , and g r i d p o s i t i o n of every animal c a p t u r e d , and i f the animal had not been p r e v i o u s l y c a p t u r e d , I marked i t with a numbered metal ear t a g , and took a b lood sample (approx. 0.3 o l . ) from the s u b o r b i t a l c a n t h a l s i n u s . I n d i v i d u a l s were then e i t h e r r e l e a s e d where they were c a u g h t . 15 t e m p o r a r i l y removed to the l a b o r a t o r y f o r b e h a v i o r t e s t i n g , or removed permanent ly from the g r i d . EXPERIMENTS I gathered data i n th ree b l o c k s . The major b lock c o n s i s t e d of c o n t i n u o u s o b s e r v a t i o n s of b e h a v i o r , genotype f r e g u e n c i e s , and demographic v a r i a b l e s i n a r e l a t i v e l y u n d i s t u r b e d p o p u l a t i o n . Eor t h i s p u r p o s e , I ma in ta ined two g r i d s , which I d i s t u r b e d on ly by my b iweek ly t r a p p i n g . These • c o n t r o l ' g r i d s {gr ids 1 and 3) were t rapped from J u l y 1972 to November 1974. Animals caught on these a reas c o u l d be removed t e m p o r a r i l y f o r b e h a v i o r t e s t i n g , but no an imals were p u r p o s e l y removed permanent ly from the p o p u l a t i o n . I i n t e n d e d to use the data from these c o n t r o l a r e a s to answer the f o l l o w i n g q u e s t i o n s : 1. How c l o s e l y do these p o p u l a t i o n s resemble the model p o p u l a t i o n with r e s p e c t to d e n s i t y , r e p r o d u c t i o n , s u r v i v a l , and r e c r u i t m e n t ? 2. Do r a t e s of e m i g r a t i o n and immigra t ion vary over the annual c y c l e ? 3. Do an imals which d i s p e r s e i n t o and out of the p o p u l a t i o n d i f f e r from r e s i d e n t s , a n d , i f s o , are these d i f f e r e n c e s c o n s t a n t over the year? 4. Does the g e n o t y p i c c o m p o s i t i o n of the p o p u l a t i o n change over the y e a r . 16 5. Bo the sexes d i f f e r ? (The b e h a v i o r a l mechanism proposed by S a d l e i r and H e a l e y , c o n c e r n s on ly males. ) B r i e f l y , I c o l l e c t e d the c o n t r o l data t o v e r i f y the model which I had c o n s t r u c t e d from p r e v i o u s s t u d i e s and t o add to t h i s model i n f o r m a t i o n about d i s p e r s a l , g e n e t i c v a r i a b i l i t y , and the b e h a v i o r and demography of f e m a l e s . The o t h e r two b l o c k s of data are exper iments des igned to gather i n f o r m a t i o n about i n d i v i d u a l s d i s p e r s i n g out of r e s i d e n t p o p u l a t i o n s . One exper iment was conducted on g r i d 2 ( F i g . 2 ) , between the two c o n t r o l a r e a s . I removed the e n t i r e p o p u l a t i o n from t h i s g r i d at the s t a r t of the b r e e d i n g season i n 1973 and 1974. The assumpt ion behind t h i s exper iment was t h a t the emptied a rea would be c o l o n i z e d by an imals which had emigra ted from s u r r o u n d i n g p o p u l a t i o n s d u r i n g the s p r i n g r e o r g a n i z a t i o n . I a l lowed a l l the c o l o n i s t s to s e t t l e on the a r e a , and , f o r the r e s t of the y e a r , the p o p u l a t i o n r e c e i v e d the same t rea tment as the c o n t r o l p o p u l a t i o n s . T h i s exper iment was des igned to answer the f o l l o w i n g q u e s t i o n s : 1. Do the an imals which l eave the t r a p p i n g a reas d u r i n g the s p r i n g r e o r g a n i z a t i o n d i f f e r from those which s t a y ? 2. Are these d i s p e r s i n g an imals capab le of s u c c e s s f u l l y s e t t l i n g and b r e e d i n g on a s u i t a b l e a r e a , i f the r e s i d e n t p o p u l a t i o n i s removed? 17 3. Does a p o p u l a t i o n composed e n t i r e l y o f new c o l o n i s t s J d i s p e r s e r s ) d i f f e r from an u n d i s t u r b e d p o p u l a t i o n ? I s t u d i e d the c o l o n i s t s on t h i s g r i d from F e b r u a r y 1973 to November 1974. The second exper iment was conducted cn G r i d 4 ( F i g . 2 ) . I began t r a p p i n g t h i s area i n February 1973, and immedia te ly began to remove a l l the mice c a p t u r e d . Because I s u s p e c t e d t h a t t h i s c o n t i n u o u s removal might draw an ima ls t h a t would n o r m a l l y have been r e s i d e n t i n the s u r r o u n d i n g p o p u l a t i o n ( S t i c k e l , 1946) , I separa ted t h i s exper iment from the main c l u s t e r of g r i d s by a lmost 2 km. A l though i t i s u n l i k e l y t h a t a l l of the an ima ls which moved onto G r i d 4 were an ima ls which would have been d i s p e r s i n g cut of u n d i s t u r b e d , r e s i d e n t p o p u l a t i o n s , I d i d assume that t h i s sample would c o n t a i n a h i g h e r p r o p o r t i o n of these ' d i s p e r s e r s ' than would the r e s i d e n t samples from the c o n t r o l a r e a s . ( S t i c k e l ' s r e s u l t s (1946) suppor t t h i s assumpt ion . ) I t h e r e f o r e used t h i s exper iment to s tudy the g u a l i t y and g u a n t i t y of d i s p e r s i n g i n d i v i d u a l s i n r e l a t i o n to p o p u l a t i o n p r o c e s s e s on the c o n t r o l a r e a s . While the exper iment on G r i d 2 was des igned to study the c o l o n i z i n g a b i l i t y of d i s p e r s e r s from one t ime of y e a r , t h i s exper iment was des igned t o gather a l a r g e sample of i n d i v i d u a l s d i s p e r s i n g at a l l t imes of the y e a r . The major q u e s t i o n s I asked were: 1. Is the onset o f b r e e d i n g i n the s p r i n g 18 a s s o c i a t e d with i n c r e a s e d d i s p e r s a l ? I f s o , who d i s p e r s e s at t h i s t ime? 2. Do the j u v e n i l e s which are prevented from e n t e r i n g r e s i d e n t p o p u l a t i o n s i n the b r e e d i n g s e a s o n , en te r a reas where r e s i d e n t s have been removed? 3. Do d i s p e r s i n g animals d i f f e r f rom r e s i d e n t a n i m a l s , and i f s o , do d i f f e r e n t t y p e s of an ima ls d i s p e r s e at d i f f e r e n t t imes of year? 4. Is r a t e of d i s p e r s a l onto a vacant area r e l a t e d t o d e n s i t y of s u r r o u n d i n g p o p u l a t i o n s ? T h i s c o n t i n u o u s removal exper iment r a n from F e b r u a r y , 1973, to November, 1974. T h u s , i n t h i s s t u d y , I have gathered i n f o r m a t i o n on three k i n d s of p o p u l a t i o n s : u n d i s t u r b e d p o p u l a t i o n s , p o p u l a t i o n s removed p e r i o d i c a l l y , and p o p u l a t i o n s removed c o n t i n u o u s l y . F u r t h e r , I c o l l e c t e d th ree d i s t i n c t t ypes of data on each p o p u l a t i o n : demograph ic , g e n e t i c , and b e h a v i o r a l . Because each of these types of da ta r e g u i r e d d i f f e r e n t t e c h n i g u e s , assumpt ions and methods of a n a l y s i s , I have o r g a n i z e d the remainder of t h i s r e p o r t on the b a s i s of da ta t y p e . The demographic a n a l y s e s and r e s u l t s are d e s c r i b e d in Chap te rs 3 and 4 . The g e n e t i c data i s d e s c r i b e d i n Chapter 5, and the b e h a v i o r data i n Chapter 6, and the majcr r e s u l t s and c o n c l u s i o n s from these 4 c h a p t e r s are brought t o g e t h e r and summarized i n Chapter 20 CHAPTER 3 DEMOGRAPHY - CONTROL DATA INTRODUCTION: I ma in ta ined G r i d s 1 and 3 not on ly as c o n t r o l s f o r the two e x p e r i m e n t a l g r i d s , but a l s o as r e p r e s e n t a t i v e u n d i s t u r b e d p o p u l a t i o n s comparable to the model p o p u l a t i o n presented i n F i g u r e 1. In t h i s c h a p t e r , I w i l l examine these u n d i s t u r b e d p o p u l a t i o n s i n d e t a i l , and compare my o b s e r v a t i o n s with the model . F o r ease o f a n a l y s i s , I have d i v i d e d the Peromjscus year i n t o f o u r seasons c o r r e s p o n d i n g to the seasons d e s c r i b e d i n F i g u r e 1. The d e f i n i t i o n s of these seasons f o l l o w : S p r i n g l ^ g r g a n i z a t iorji. the th ree c o n s e c u t i v e t r a p p i n g p e r i o d s i n c l u d i n g and immedia te ly a f t e r the f i r s t male b r e e d i n g a c t i v i t y . 2. Main Breed ing P e r i o d j; the p e r i o d from the end of the s p r i n g r e o r g a n i z a t i o n to the t r a p p i n g p e r i o d immediate ly b e f o r e the f i n a l d e c l i n e i n male b r e e d i n g a c t i v i t y . 3. f a l l I nc rease Per iod j , the p e r i o d from the end of the main b reed ing p e r i o d to peak p o p u l a t i o n d e n s i t y . (If males and fema les reach maximum d e n s i t i e s a t d i f f e r e n t t i m e s , the r e c r u i t m e n t p e r i o d i n c l u d e s both peaks 4* Overwin ter Per iod . : a l l t r a p p i n g weeks 21 between the f a l l peak i n d e n s i t y and the f i r s t s i g n of male b r e e d i n g . The r e l a t i o n s h i p s of these seasons t o d e n s i t y and r e p r o d u c t i o n on the two c c n t r o l a reas can be seen i n F i g u r e s 3 and 4. Throughout t h i s a n a l y s i s , I have c l a s s i f i e d a l l i n d i v i d u a l s as e i t h e r ' b r e e d i n g 1 or ' no t b r e e d i n g ' . Males were c l a s s i f i e d as b reed ing i f t h e i r t e s t e s were e i t h e r s c r o t a l or s e m i s c r o t a l . T e s t e s p o s i t i o n was a s c e r t a i n e d v i s u a l l y and by m a n i p u l a t i o n . A female was c l a s s i f i e d as b r e e d i n g i f she was l a c t a t i n g or o b v i o u s l y p r e g n a n t . Dur ing seasons 2 and 3, I wanted to d i s t i n g u i s h between a d u l t and j u v e n i l e m i c e , where a d u l t s were d e f i n e d as mice which were capab le of b r e e d i n g , and j u v e n i l e s as mice which were no t . For t h e s e two s e a s o n s , I d e f i n e d a j u v e n i l e as any mouse weighing l e s s than 15 grams. By d e f i n i t i o n , no b r e e d i n g o c c u r s d u r i n g the overw in te r p e r i o d , and no j u v e n i l e s a re a v a i l a b l e to e n t e r the p o p u l a t i o n at t h i s t ime or d u r i n g the f i r s t f o u r weeks of uale breed ing (spr ing r e o r g a n i z a t i o n ) . Dur ing these s e a s o n s , I c l a s s i f i e d a l l an ima ls as a d u l t s . Throughout t h i s s t u d y , I have used 'minimum number known to be a l i v e * as an es t imate of d e n s i t y on my g r i d s . F o r any g i v e n week, t h i s es t imate c o n s i s t s of the number of an ima ls caught t h a t weex, p l u s those i n d i v i d u a l s not caught t h a t week, but caught both b e f o r e and a f t e r t h a t week. I have used t h i s e s t i m a t e because i t i s f r e e from the assumpt ion of e q u a l 22 c a t c h a b i l i t y , and w i l l approach the t r u e d e n s i t y when an imals a re c o n t i n u o u s l y t rapped over l o n g p e r i o d s , and when a h i g h p r o p o r t i o n of the an imals i n the p o p u l a t i o n i s c a p t u r e d each t i m e . fl rev iew of t o t a l and s e a s o n a l means of c a t c h a b i l i t y (Table 1) shows both that a h igh p r o p o r t i o n cf an ima ls were caught each week, and t h a t c a t c h a b i l i t y v a r i e d with sex and season Both sexes show lower c a t c h a b i l i t y i n the w in ter (November -February ) , a n d , i n winter females show lower c a t c h a b i l i t y than males. Under t h e s e c o n d i t i o n s , I f e l t t h a t the best e s t i m a t e of d e n s i t y would be minimum number a l i v e . I had o r i g i n a l l y in tended to examine each season s e p a r a t e l y f o r each g r i d , s e x , and y e a r . However, because c f s m a l l sample s i z e s ( F i g u r e s 3 and 4 ) , I d e c i d e d t o c o n s i d e r each observed season as a sample , and to poo l these samples i n my a n a l y s e s . For example, c o n s i d e r the s p r i n g r e o r g a n i z a t i o n . I c o l l e c t e d data d u r i n g t h i s season i n both 1973 and 1974. Each y e a r ' s o b s e r v a t i o n s c o n s i s t of t h r e e t r a p p i n g weeks on each of two g r i d s . I c o n s i d e r each t r a p p i n g week w i t h i n a s p r i n g r e o r g a n i z a t i o n p e r i o d t o be a sample of p o p u l a t i o n b e h a v i o r d u r i n g that p e r i o d , and so the t o t a l s p r i n g r e o r g a n i z a t i o n sample c o n s i s t s of 12 t r a p p i n g weeks. In most c a s e s , I a n a l y z e d each g r i d and year s e p a r a t e l y , and then compared them by i n s p e c t i o n , c r , where p o s s i b l e , by s t a t i s t i c a l methods, be fore p o o l i n g them i n t o one l a r g e sample of the s e a s o n . In the f o l l o w i n g p a g e s , I w i l l p resent the a n a l y s e s and 23 r e s u l t s f o r each season i n t u r n . Tab le 2 summarizes the observed s u r v i v a l and r e c r u i t m e n t r a t e s , and the i n d i c e s of s p a c i n g b e h a v i o r , f o r the c o n t r o l g r i d s , i n a l l s e a s o n s . ANALYSES AND RESULTS: SPRING REORGANIZATION S u r v i v a l and Recru i tment^ The g e n e r a l model makes no p r e d i c t i o n s f o r females i n t h i s s e a s o n , but p r e d i c t s i n c r e a s e d e m i g r a t i o n , i m m i g r a t i o n , and a g g r e s s i o n i n males. Immigrat ion r a t e can be determined d i r e c t l y from the number of new an ima ls caught each week, but e m i g r a t i o n ra te and r e l a t i v e a g g r e s s i o n must be e s t i m a t e d from o t h e r demographic v a r i a b l e s . E m i g r a t i o n i s a component o f the m o r t a l i t y e s t i m a t e ga ined from l i v e t r a p p i n g : when an animal d i s a p p e a r s from the g r i d , i t has e i t h e r d ied on the g r i d or e m i g r a t e d . I t i s i m p o s s i b l e t o s e p a r a t e these two s o u r c e s of ' m o r t a l i t y * , b u t , i f one assumes tha t i n c r e a s e d e m i g r a t i o n r e f l e c t s i n c r e a s e d movement of an imals i n the s u r r o u n d i n g p o p u l a t i o n , as w e l l as on the t r a p p i n g g r i d , then h igh r a t e s of e m i g r a t i o n s h o u l d be a s s o c i a t e d wi th h igh r a t e s of i m m i g r a t i o n . T h i s i m m i g r a t i o n may r e s u l t i n the s e t t l i n g of new an imals i n the p o p u l a t i o n , or may be r e p r e s e n t e d on ly as s i n g l e c a p t u r e s of ' t r a n s i e n t ' i n d i v i d u a l s . In e i t h e r c a s e , i n c r e a s e d movement of an imals i n the p o p u l a t i o n s h o u l d be r e f l e c t e d i n both i n c r e a s e d l o s s of a n i m a l s and i n c r e a s e d r a t e of c a p t u r e of new an ima ls ( rec ru i tment r a t e ) . 24 I f t h i s argument i s c o r r e c t , then the s p r i n g r e o r g a n i z a t i o n shou ld be c h a r a c t e r i z e d by r e l a t i v e l y h igh r e c r u i t m e n t and low s u r v i v a l r a t e s . To t e s t t h i s p r e d i c t i o n , I c o n s t r u c t e d l i n e a r r e g r e s s i o n models of s e a s o n a l v a r i a t i o n i n s u r v i v a l and r e c r u i t m e n t . Le t us c o n s i d e r s u r v i v a l f i r s t . I e s t i m a t e d minimum s u r v i v a l r a t e s f o r each 14-day p e r i o d by d e t e r m i n i n g the p r o p o r t i o n of the an ima ls caught i n one week which was known to be a l i v e two weeks l a t e r . The g e n e r a l model f o r each sex i n c l u d e d g r i d and y e a r , and can be seen below: Minimum 14-day s u r v i v a l = Constant + a (Gr id ) + b(Year2) + c (Year3) + d (Season 2) + e (Season 3) + f (Season 4) A l l o f the v a r i a b l e s i n t h i s model are 'dummy v a r i a b l e s ' (see J o h n s t o n , 1972). B r i e f l y , these are ' t r u e or f a l s e ' v a r i a b l e s which take on the va lue 1 when t r u e , and 0 when f a l s e . For example , i n the egua t ion above , an an imal caught i n year 2, season 3, cn g r i d 3 , would have the f o l l o w i n g va lues f o r the 6 v a r i a b l e s : g r i d (1 ) , year 2 (1 ) , year 3 (0) , season 2 (0 ) , season 3 (1 ) , season 4 (0). The e g u a t i o n f o r t h a t animal would t h e r e f o r e reduce t o : Minimum 14 day s u r i v a l = Constant + a + b + e S i m i l a r l y , the e g u a t i o n f o r an animal caught cn g r i d 1, i n season 4, year 1 would reduce t o : Minimum 14 day s u r v i v a l = Constant + f By u s i n g dummy v a r i a b l e s , I was a b l e to use l i n e a r r e g r e s s i o n 25 models f c r f a c t o r s which are not d i r e c t l y q u a n t i f i a b l e , such as seasons and g r i d s . N e i t h e r g r i d nor year c o n t r i b u t e d s i g n i f i c a n t l y t o the r e g r e s s i o n f c r e i t h e r sex ( m a l e s , P > . 5 0 ; f e m a l e s , P> .20 ) , which i n d i c a t e s t h a t s u r v i v a l d i d not d i f f e r s i g n i f i c a n t l y between a r e a s or y e a r s . The ' s e a s o n s o n l y * models were s i g n i f i c a n t f o r both males ( F - 6 . 8 3 8 , d f=3 ,109 , p<.001 ) and females ( f=3 .901, d f=3 ,109 , p=.011 ) , and i n d i c a t e tha t s u r v i v a l does vary s i g n i f i c a n t l y with season on the c o n t r o l a r e a s . F i g u r e 5 shows the s e a s o n a l s u r v i v a l e s t i m a t e s o b t a i n e d from the r e g r e s s i o n s , and T a b l e 2 shows the observed s u r v i v a l r a t e s . For both sexes s u r v i v a l i n both the o v e r w i n t e r and main b r e e d i n g p e r i o d s i s g o o d , and season 1 i s c h a r a c t e r i z e d by a s h o r t p e r i o d o f low s u r v i v a l . I c o n s t r u c t e d the r e g r e s s i o n models f c r r e c r u i t m e n t i n the same manner as the s u r v i v a l models , my e s t i m a t e of b iweek ly r e c r u i t m e n t be ing the number of new an ima ls caught each t r a p p i n g week d i v i d e d by the t o t a l number caught t h a t week. a l though the g e n e r a l r e g r e s s i o n model i n d i c a t e s t h a t male r e c r u i t m e n t v a r i e s with year and a r e a , the s e a s o n s - o n l y mode l , with these components e x t r a c t e d , produces a h i g h l y s i g n i f i c a n t r e g r e s s i o n ( F - 1 3 . 3 2 1 , df=3 ,107, p=.0001). The p r e d i c t e d s e a s o n a l r e c r u i t m e n t r a t e s can be seen i n F i g u r e 5. Male Recru i tment i s h i g h e s t i n season 3 , when j u v e n i l e s are b e i n g r e c r u i t e d , b u t , as p r e d i c t e d , i t i s a l s o h i g h i n season 1. The r a t e o f r e c r u i t m e n t d u r i n g the s p r i n g r e o r g a n i z a t i o n 26 p e r i o d appears p a r t i c u l a r l y h igh when compared to the r a t e s i n s e a s o n s 2 an 4 , which immedia te ly precede and f o l l o w season 1. S i m i l a r r e l a t i o n s h i p s h o l d f o r the observed r e c r u i t m e n t r a t e s (Table 2 ) . In males , the s p r i n g r e o r g a n i z a t i o n p e r i o d i s a s s o c i a t e d with both decreased s u r v i v a l and i n c r e a s e d r e c r u i t m e n t . I c o n c l u d e from t h i s t h a t the onset of male b r e e d i n g i s a s s o c i a t e d , as p r e d i c t e d , with i n c r e a s e d movement of males. Recru i tment i n females i s not s i g n i f i c a n t l y i n f l u e n c e d by a rea or year (p>.25) , but does vary s i g n i f i c a n t l y with seasons ( f=8 .418, d f=3 ,107 , P<.0001) . F i g u r e 5 shows the s e a s o n a l r e c r u i t m e n t r a t e s p r e d i c t e d by t h i s model and Table 2 shows the observed s e a s o n a l r e c r u i t m e n t r a t e s . . As i n m a l e s , female r e c r u i t m e n t i s h i g h e s t d u r i n g season 3, b u t , u n l i k e ma les , females do not shew r a p i d r e c r u i t m e n t i n season 1. Female r e c r u i t m e n t r a t e does not change wi th the onset of b r e e d i n g . I t does not begin to i n c r e a s e u n t i l season 2, when j u v e n i l e females are a v a i l a b l e to en te r the p o p u l a t i o n . T h e r e f o r e , i n f e m a l e s , season 1 i s a s s o c i a t e d with low s u r v i v a l and low r e c r u i t m e n t . I c o n c l u d e t h a t females are d y i n g at t h i s t i m e , r a t h e r than moving around as males d o . In summary, the s p r i n g r e o r g a n i z a t i o n p e r i o d appears to be a s s o c i a t e d with movement i n males and m o r t a l i t y i n f e m a l e s . Spac ing E e h a v i o r ^ A l though I cannot get a d i r e c t measure of a g g r e s s i o n from 27 the demographic d a t a , I can get an index of how much an imals space themselves out on the s tudy a r e a . S i n c e there i s abundant e v i d e n c e i n P e r o r y s c u s of mutua l ly e x c l u s i v e home ranges ( S t i c k e l , 1 9 6 8 ) , the bes t e s t i m a t e of s p a c i n g would have been an a c c u r a t e e s t i m a t e of the degree of o v e r l a p of these home r a n g e s . U n f o r t u n a t e l y , my t r a p p i n g program was not s u i t a b l e f o r a c c u r a t e home range e s t i m a t i o n . For t h i s r e a s o n , I d i d not attempt to es t imate range o v e r l a p , but used the f r e q u e n c y of c a p t u r e of two an imals i n the same t r a p w i t h i n any t r a p p i n g p e r i o d (two t r a p n igh ts ) as a r e l a t i v e e s t i m a t e of the degree of s p a c i n g i n the p o p u l a t i o n . T h i s i s a r e l a t i v e l y s t r a i g h t - f o r w a r d i n d e x . I f two d i f f e r e n t an ima ls are c a p t u r e d i n the same t r a p cn s u c c e s s i v e n i g h t s , they must both be a c t i v e i n the a rea of the t r a p . T h e r e f o r e , the number of t imes tha t two an imals are caught at a s i n g l e t r a p s t a t i o n (number of double cap tures ) i n d i c a t e s the r e l a t i v e amount of home range o v e r l a p . I w i l l c a l l t h i s index the * t r a p - o v e r l a p ' i n d e x . To get the index of t r ap o v e r l a p , I compared the observed number of double c a p t u r e s i n any week with the maximum number of double c a p t u r e s which c o u l d have o c c u r r e d tha t week. The maximum number of double c a p t u r e s i s the number of p o s s i b l e d i f f e r e n t combina t ions of the mice caught on the f i r s t day of t r a p p i n g with the mice caught the second day. Tab le 2 shows t h e s e r a t i o s , by s e a s o n , f o r males and f e m a l e s . The index r a t i o s are a l s o presented g r a p h i c a l l y i n F i g u r e 5. F i g u r e 6 28 shows the p r o p o r t i o n s of t o t a l double c a p t u r e s which were two m a l e s , two f e m a l e s , and a male with a f e m a l e . Double c a p t u r e i n d i c e s f o r both sexes vary s i g n i f i c a n t l y with season (males:xz=53.935 , df 3 , P< .0005; females:X2=17 .536 , df 3 , P< .001) . In season 1 females tend to be c a p t u r e d i n the same t r a p s as o ther mice more o f t e n than males are (X 2 =21.411 ,P<.001) , and both males and females are more o f t e n c a p t u r e d with females than with males (X 2 =10 .400 ,< .01 ) . The two sexes show d i f f e r e n t s e a s o n a l t r e n d s . a h i l e the t r a p -o v e r l a p i n d i c e s of both males and females g r a d u a l l y i n c r e a s e from season 2 to 4 , the index drops s e v e r e l y from season 4 to season 1 i n males , but remains n e a r l y c o n s t a n t i n f e m a l e s . The onse t of male b r e e d i n g appears to be a s s o c i a t e d with i n c r e a s e d s p a c i n g out of m a l e s , b u t not of f e m a l e s . In summary, the onset c f male b r e e d i n g i s a s s o c i a t e d with i n c r e a s e d s p a c i n g out of ma les , and i n c r e a s e d d i s p e r s a l o f males onto and o f f of the t r a p p i n g g r i d s . T h i s season appears to be t r u l y a p e r i o d of r e o r g a n i z a t i o n f o r the male p o p u l a t i o n . However, a l though females beg in breed ing a t t h i s t i m e , there i s no ev idence tha t they e x p e r i e n c e the same r e o r g a n i z a t i o n c f p o p u l a t i o n s t r u c t u r e t h a t males d c . Females s u r v i v e p o o r l y at t h i s t i m e , and n e i t h e r space out nor d i s p e r s e . T h e r e f o r e , a l though the i n t e r a c t i o n of a g g r e s s i v e and d i s p e r s a l b e h a v i o r i n males may d i r e c t l y determine the number of males which breed on the a r e a s , i t seems u n l i k e l y t h a t such b e h a v i o r a l mechanisms determine the number o f 29 females which b r e e d , £2!Eaxa£i!€ Jn .a ly .s is c f B e e r u i t s ^ T r a n s i e n t s x R e fiisajjpearina Mice.: B i t h the onset of b r e e d i n g i n the s p r i n g , some an ima ls which have s u c c e s s f u l l y s u r v i v e d the w i n t e r , d i s a p p e a r from the s tudy a r e a s . What determines i f an animal w i l l remain on the a reas at t h i s t ime? Do mice which d i s a p p e a r d i f f e r from those which remain? Do mice which en te r the p o p u l a t i o n s resemble those tha t d i s a p p e a r , as you would expect i f those t h a t d i s a p p e a r are a c t u a l l y d i s p e r s i n g ? fo answer these q u e s t i o n s , " I compared the w e i g h t , and b r e e d i n g c o n d i t i o n of mice which remained on my areas throughout the s p r i n g r e o r g a n i z a t i o n p e r i o d ( c a l l e d r e s i d e n t s ) , mice which d i s a p p e a r e d d u r i n g t h i s p e r i o d , mice which s u c c e s s f u l l y e n t e r e d the p o p u l a t i o n s d u r i n g t h i s p e r i o d , a n d mice which e n t e r e d the p o p u l a t i o n but remained cn the area on ly two weeks o r l e s s ( c a l l e d t r a n s i e n t s ) . The subsamples of r e s i d e n t s , t r a n s i e n t s , r e c r u i t s and d i s a p p e a r i n g mice were too s m a l l t o a l low independent compar isons f o r each g r i d and y e a r . I t h e r e f o r e d e c i d e d to c o r r e c t f o r d i f f e r e n c e s between g r i d s and years and then p o o l a l l f o u r s p r i n g s o b s e r v e d , b e f o r e making compar isons among the s u b s a m p l e s . These c o r r e c t i o n s were made f o r the weight data i n the f o l l o w i n g manner. I c a l c u l a t e d mean weights of a l l mice caught on each g r i d , f o r each t r a p p i n g week. I then took 30 the weight of each mouse at f i r s t cap tu re i n t h a t p e r i o d , and c o r r e c t e d i t f o r v a r i a t i o n w i t h i n t h a t p e r i o d , and between g r i d s and y e a r s , by e x p r e s s i n g i t as a d e v i a t i o n from the mean weight f o r the week o f f i r s t c a p t u r e . However, the d i s t r i b u t i o n s of these c o r r e c t e d weights were not n o r m a l , and the sample s i z e s , even a f t e r p o o l i n g g r i d s and y e a r s , were very s m a l l . S i n c e my b a s i c h y p t h e s i s was tha t some groups would be h e a v i e r than o t h e r s , I dec ided to t e s t t h i s us ing a very s i m p l e method i n v o l v i n g o n l y i n f o r m a t i o n about whether a g i v e n weight was g r e a t e r than or l e s s than the mean weight f o r the g i v e n year and g r i d . T h i s i n f o r m a t i o n c o n s i s t e d , f o r each subsample , of the number of i n d i v i d u a l s whose weights were below the mean and the number whose weights were above the mean. I then compared the v a r i o u s subsamples The compar isons f o r season 1 we ights can be seen i n T a b l e s 3 and 4. S u r v i v i n g r e s i d e n t males tend t o be h e a v i e r than those which d i s a p p e a r , but t h e r e i s no d i f f e r e n c e between r e s i d e n t and d i s a p p e a r i n g f e m a l e s . The r e c r u i t s which remained on the a reas do not d i f f e r i n weight from t r a n s i e n t m i c e , f o r e i t h e r s e x . The weights of newly c a p t u r e d males ( r e c r u i t s p l u s t r a n s i e n t s ) resemble those of d i s a p p e a r i n g males more than those of r e s i d e n t ma les . These r e s u l t s i n d i c a t e tha t the l i g h t e r males are moving around i n t h i s s e a s o n . The s u c c e s s of females appears t o be u n r e l a t e d to we ight . Is b r e e d i n g c o n d i t i o n r e l a t e d to s u c c e s s f u l r e s i d e n c y 31 over season 1? Tab le 5 shows that the re are no d i f f e r e n c e s i n p r o p o r t i o n b r e e d i n g among the f o u r c l a s s e s of males. However, the fema les which d i s a p p e a r c l e a r l y tend to be t h o s e which come i n t o b reed ing c o n d i t i o n . F u r t h e r , females which e n t e r the p o p u l a t i o n s a t t h i s t ime resemble r e s i d e n t s i n hav ing low p r o p o r t i o n s b r e e d i n g : the b r e e d i n g females which d i s a p p e a r are not r e p l a c e d by b r e e d i n g r e c r u i t s . These o b s e r v a t i o n s suggest t h a t b r e e d i n g females s u f f e r heavy m o r t a l i t y at t h i s t ime of y e a r . (Ten of the 15 females which came i n t o b r e e d i n g c o n d i t i o n i n season 1 d i s a p p e a r e d from the a r e a . T h i s r e p r e s e n t s 67% l e s s of b r e e d i n g f e m a l e s . ) D i s c u s s i o n : : 8hen I combine the r e s u l t s from the p r e c e d i n g a n a l y s e s , 1 b e g i n to understand what i s going on i n p o p u l a t i o n s d u r i n g the s p r i n g r e o r g a n i z a t i o n . Eoth males and females come i n t o b r e e d i n g c o n d i t i o n at t h i s t i m e . T h i s i s a s s o c i a t e d with a r i s e i n a g g r e s s i o n i n males ( S a d l e i r , 1965 ;H ea ley ,1967 ) , which b e g i n to space themselves out and e s t a b l i s h the t e r r i t o r i e s they w i l l occupy d u r i n g the b r e e d i n g s e a s o n . Heavy males tend to e s t a b l i s h t e r r i t o r i e s on the area where they o v e r w i n t e r e d . I suggest tha t these are p robab ly the dominant i n d i v i d u a l s i n the p o p u l a t i o n . l i g h t e r males d i s p e r s e away from t h e i r o v e r w i n t e r i n g a reas at t h i s t i m e , and some of them are r e p l a c e d on the study a reas by s i m i l a r i n d i v i d u a l s d i s p e r s i n g from s u r r o u n d i n g a r e a s . Females which come i n t o b r e e d i n g 32 c o n d i t i o n d u r i n g season 1 tend t o d i s a p p e a r from the t r a p p i n g a r e a , R e c r u i t m e n t i s low, but some of the s e b r e e d i n g f e m a l e s a r e r e p l a c e d by mice from s u r r o u n d i n g a r e a s , and t h e s e mice a r e not i n b r e e d i n g c o n d i t i o n . R e s i d e n t f e m a l e s d i f f e r from t h o s e t h a t d i s a p p e a r o n l y i n b r e e d i n g c o n d i t i o n , and r e c r u i t s r esemble r e s i d e n t s i n t h i s r e s p e c t . T h i s l e a d s me t o c o n c l u d e t h a t f e m a l e s do not move around much d u r i n g season 1, and t h a t t h o s e which come i n t o b r e e d i n g c o n d i t i o n a t the s t a r t o f t h e b r e e d i n g season s u f f e r heavy m o r t a l i t y . T h i s heavy m o r t a l i t y s u f f e r e d by b r e e d i n g females i n t h e e a r l y s p r i n g d e t e r m i n e s the b r e e d i n g d e n s i t i e s o f f e m a l e s , but t h e r e i s no i n d i c a t i o n t h a t t h i s m o r t a l i t y i s a s s o c i a t e d w i t h e i t h e r a g g r e s s i o n o r d i s p e r s a l . S a d l e i r (1973) has suggested t h a t female E§I2IX§cus are e n e r g y - l i m i t e d d u r i n g the e a r l y s p r i n g : t h e energy demands o f t h e r m o r e g u l a t i o n and f o r a g i n g p r e c l u d e r e p r o d u c t i o n . T h i s h y p o t h e s i s i s s u p p o r t e d Jby t h e o b s e r v a t i o n t h a t female Peromyscus on my s t u d y a r e a s w i l l s u c c e s s f u l l y breed i n the w i n t e r i f they are p r o v i d e d w i t h excess f o o d (Hary T a i t t , p e r s . comm.). I f t h i s h y p o t h e s i s i s c o r r e c t , then f e m a l e s which begin b r e e d i n g i n the e a r l y s p r i n g on my a r e a s may have d i e d because they d i d not have enough r e s e r v e e n e r g y , and c o u l d not o b t a i n enough f o o d , t o s u p p o r t pregnancy and l a c t a t i o n at t h i s t i m e . D u r i n g t h e s p r i n g r e o r g a n i z a t i o n , a t l e a s t , males and fe m a l e s appear t o be doing d i f f e r e n t t h i n g s . The d e n s i t y of males at the end of t h i s p e r i o d i s p r o b a b l y determined m a i n l y 33 by b e h a v i o r a l i n t e r a c t i o n s d u r i n g the p e r i o d , but the d e n s i t y o f f e m a l e s , determined by m o r t a l i t y of e a r l y breed ing f e m a l e s , i s more d i r e c t l y r e l a t e d to e x t e r n a l f a c t o r s such as weather and food a v a i l a b i l i t y . ANALYSIS AND BESOLTS: MAIN BBEEDTNG PEBIGD. S u r v i v a l and Hecrui tmei i t^ The g e n e r a l model p r e d i c t s good s u r v i v a l o f r e s i d e n t males and lew r e c r u i t m e n t of new males d u r i n g the main b r e e d i n g p e r i o d . I examined s u r v i v a l and r e c r u i t m e n t d u r i n g t h i s p e r i o d u s i n g the l i n e a r r e g r e s s i o n models d i s c u s s e d i n the l a s t s e c t i o n . The s u r v i v a l and r e c r u i t m e n t r a t e s p r e d i c t e d by these models are presented i n F i g u r e 5, and Table 2 shows the observed r a t e s . In ma les , the main b r e e d i n g p e r i o d i s a s s o c i a t e d with both the h i g h e s t s u r v i v a l r a t e and the lowest r e c r u i t m e n t r a t e observed ever the y e a r . Males which are p resent on the a reas a t the s t a r t o f t h i s p e r i o d tend to remain on the a r e a s , and very few new an ima ls enter the p o p u l a t i o n . T h i s i s c o n s i s t e n t wi th the model . Females a l s o show t h e i r h i g h e s t s u r v i v a l d u r i n g the main b r e e d i n g p e r i o d . However, u n l i k e i n males , t h i s good s u r v i v a l i s a s s o c i a t e d wi th the second h i g h e s t r e c r u i t m e n t r a t e observed over the y e a r , and , female r e c r u i t m e n t i n c r e a s e s from season 1 to season 2. Females which are p r e s e n t on the a reas 3a at the s t a r t o f season 2 t e n d , l i k e ma les , to remain on the a r e a s , but new fema les en te r the p o p u l a t i o n at a r e l a t i v e l y h igh r a t e . J u v e n i l e B e c r u i t m e n t j An i n s p e c t i o n o f F i g u r e s 3 and a shows t h a t some females b e g i n l a c t a t i o n b e f o r e the s t a r t of the main b r e e d i n g p e r i o d . We saw tha t these e a r l y b r e e d i n g females s u r v i v e d very p o o r l y , and a r e t h e r e f o r e u n l i k e l y to have produced very many o f f s p r i n g . Few females l a c t a t e d d u r i n g the e a r l y p a r t of the main b r e e d i n g s e a s o n , but the p r o p o r t i o n l a c t a t i n g r o s e s h a r p l y towards the end of the s e a s o n . Peromyscys mainta ined i n the l a b . appear to be l a c t a t i n g 3 to 5 days p r i o r to the b i r t h of t h e i r l i t t e r s , and c o n t i n u e to l a c t a t e f o r at l e a s t 4 weeks. T h e r e f o r e , l a c t a t i o n on my study a reas i n d i c a t e s tha t l i t t e r s are born and n u r s e d , and are p robab ly e n t e r i n g the p o p u l a t i o n . S i n c e the g e n e r a l model p r e d i c t s t h a t a d u l t r e s i d e n t males w i l l r e s t r i c t the r e c r u i t m e n t o f these j u v e n i l e s , I examined j u v e n i l e r e c r u i t m e n t i n some d e t a i l . The f i r s t t ask i n s t u d y i n g j u v e n i l e r e c r u i t m e n t i s to determine the maximum number of j u v e n i l e r e c r u i t s which c o u l d be e x p e c t e d . T h i s expected number of j u v e n i l e s can be c a l c u l a t e d as f o l l o w s : Number of J u v e n i l e s = number of l i t t e r s X number of young per l i t t e r . S i n c e I c o u l d not observe the b i r t h and e a r l y l i f e of l i t t e r s i n the f i e l d , I had to es t imate both the number of l i t t e r s born and the number of young per l i t t e r . An o v e r e s t i n a t e of e i t h e r of t h e s e parameters would r e s u l t i n an o v e r e s t i m a t e of the expected number of j u v e n i l e r e c r u i t s , and so b i a s the a n a l y s i s i n f a v o r o f f i n d i n g fewer r e c r u i t s than e x p e c t e d . S a d l e i r {1965) cap tured o n l y 39% of expected j u v e n i l e s d u r i n g the main b r e e d i n g p e r i o d . He c a l c u l a t e d the expected number of j u v e n i l e s as f o l l o w s : Number of j u v e n i l e s = number of p r e g n a n c i e s x 5 .5 The e s t i m a t e of 5.5 f o r l i t t e r s i z e i s from Sheppe (1961) , and i s an average v a l u e f o r Egrom^scus man icu la tus throughout B r i t i s h Columbia (sample s i z e = 53 ) . T h i s i s probab ly an o v e r e s t i m a t e f o r mice on tne Endowment l a n d s . I c a l c u l a t e d a mean l i t t e r s i z e of 4.33 ± . 2 8 , f o r l i t t e r s of Endowment l a n d s mice born i n my l a b . c o l o n y (n=80). T h i s es t imate does not d i f f e r s i g n i f i c a n t l y from the es t imate of 4.60 ± . 2 8 , c a l c u l a t e d by B r i t t o n (1966) from 89 l i t t e r s of Endowment Lands mice born i n the l a b . I have used 4.33 as my e s t i m a t e of mice per l i t t e r . S a d l e i r used the number of observed p r e g n a n c i e s as h i s index of the number of l i t t e r s . However, s i n c e some p r e g n a n c i e s may be u n s u c c e s s f u l , and some l i t t e r s may d i e b e f o r e weaning, the number of p r e g n a n c i e s w i l l tend to be an o v e r e s t i m a t e of the number of l i t t e r s . To get a more a c c u r a t e e s t i m a t e of expected r e c r u i t m e n t , I f o l l o w e d the weights and b r e e d i n g c o n d i t i o n s o f each female . I i d e n t i f i e d s u c c e s s f u l V3'6 p r e g n a n c i e s by i n i t i a l He ight ga in f o l l o w e d by the l o s s of at l e a s t 2 grams and the onse t of l a c t a t i o n . I f a female was r e p o r t e d pregnant i n week n , I d i d not c o n s i d e r the pregnancy s u c c e s s f u l u n l e s s she was l a c t a t i n g i n week n + 2 . I observed 1 5 4 p r e g n a n c i e s , and only 9 4 of these ( 6 1 . 0 % ) were s u c c e s s f u l . Number of p r e g n a n c i e s would c e r t a i n l y have o v e r e s t i m a t e d the expected number of j u v e n i l e r e c r u i t s . U s i n g the above e s t i m a t e s of l i t t e r s i z e and numbers of s u c c e s s f u l p r e g n a n c i e s , I c a l c u l a t e d the expected numbers of r e c r u i t s i n a g i v e n season as f e l l o w s : Le t E be the expected number of j u v e n i l e r e c r u i t s d u r i n g season b , which runs from week i to week j ; and l e t S be the number of s u c c e s s f u l l i t t e r s bcrn i n week i . Then: J B L = X(S. +S. , ) 4 . 3 3 . b n i l *"3 1 . - V T h i s e s t i m a t e w i l l be lower than the e s t i m a t e s used by S a d l e i r , and so t h e r e i s a lower p r o b a b i l i t y tha t the a n a l y s i s w i l l be b i a s e d toward f i n d i n g fewer r e c r u i t s than e x p e c t e d . In o rder to t r e a t the sexes s e p a r a t e l y , I assumed an equa l sex r a t i o among j u v e n i l e s . T h i s assumpt ion i s suppor ted by the data from my breed ing c o l o n y , which showed a r a t i o c f 1 6 9 males to 1 7 7 females ( 4 8 . 9 % males) . T h i s r a t i o does not d i f f e r s i g n i f i c a n t l y from 1 : 1 ( X « = . 1 8 5 , P > . 6 0 ) . T a b l e 6 shows the observed and expected numbers of j u v e n i l e r e c r u i t s i n season 2 . My more c o n s e r v a t i v e e s t i m a t e 37 of expec ted numbers of r e c r u i t s d i d not e l i m i n a t e the d i f f e r e n c e between observed and expected numbers: o n l y 42.6% of a l l j u v e n i l e s expected were a c t u a l l y r e c r u i t e d , and 67.6% of them were f e m a l e s . T h i s d i f f e r s s i g n i f i c a n t l y from the expec ted 50% males (X2= 4 . 5 6 8 , P < . 0 5 ) . These r e s u l t s are c o n s i s t e n t with the h y p o t h e s i s tha t j u v e n i l e s are r e s t r i c t e d from e n t e r i n g the p o p u l a t i o n d u r i n g the main b r e e d i n g s e a s o n , and f u r t h e r suggest tha t male j u v e n i l e s may be more s e v e r e l y r e s t r i c t e d than f e m a l e s . A d u l t males may be s e l e c t i v e l y r e s t r i c t i n g the r e c r u i t m e n t of male j u v e n i l e s . Spac ing B e h a v i o r : Both sexes showed lower t r a p - o v e r l a p i n d i c e s i n season 2 than i n any o ther season (see Tab le 2 and F i g u r e 5 ) . F i g u r e 6 shows the c o m b i n a t i o n s of ages and sexes i n the observed double c a p t u r e s . The l e a s t f r e q u e n t combina t ion i s an a d u l t male with another a d c i t male , and the most common c o m b i n a t i o n i s an a d u l t female with a j u v e n i l e . J u v e n i l e s tended to be caught with o ther mice more o f t e n than e x p e c t e d , wh i le a d u l t males were c a p t u r e d with o ther mice l e s s o f t e n than expected (X 2 =168.223 ,P<.001) . These r e s u l t s i n d i c a t e t h a t a d u l t mice a v o i d o t h e r a d u l t mice at t h i s t i m e , and tha t the s t r o n g e s t a v o i d a n c e i s between a d u l t males . The j u v e n i l e s which e n t e r the p o p u l a t i o n i n t h i s season do not appear to a v o i d e i t h e r a d u l t s or o t h e r j u v e n i l e s , and tend p a r t i c u l a r l y to be caught i n the same t r a p s as a d u l t f e m a l e s . T h i s i s c o n s i s t e n t with 38 t h e o b s e r v a t i o n t h a t j u v e n i l e s t e n d n o t t o l e a v e t h e i r m o t h e r ' s home r a n g e u n t i l t h e y r e a c h s e x u a l m a t u r i t y (see T e r m a n , 1 9 6 8 ) . T h e s e r e s u l t s a r e c o n s i s t e n t w i t h t h e g e n e r a l m o d e l o f t h e main b r e e d i n g s e a s o n i n s h e w i n g t h a t a d u l t m a l e s a v o i d e a c h e t h e r more d u r i n g t h i s s e a s o n t h a n a t a n y o t h e r t i m e . W h i l e a d u l t f e m a l e s a l s o a v o i d e a c h o t h e r , t h e y do s o l e s s t h a n m a l e s , and a d u l t f e m a l e s show a s t r o n g t e n d e n c y t o be c a u g h t i n t h e same t r a p s a s j u v e n i l e s . C o i f i a ^ a t i v e A n a l y s i s o f R e s i d e n t s ^ T r a n s i e n t s t R e c r u i t s a n d M i c e w h i c h d i s a p p e a r ^ I a n a l y s e d t h e s e d a t a i n t h e same manner a s t h e d a t a f r o m s e a s o n 1 ( T a b l e s 3 and 4 ) . R e s i d e n t s c a n n o t be d i s t i n g u i s h e d f r o m d i s a p p e a r i n g m i c e by w e i g h t , f o r e i t h e r s e x . S i m i l a r l y , r e c r u i t s de n o t d i f f e r i n w e i g h t f r o m t r a n s i e n t s . H o w e v e r , t h e r e i s a s l i g h t t e n d e n c y , i n b o t h s e x e s , f o r a n i m a l s w h i c h a r e f i r s t c a p t u r e d i n t h e m a i n b r e e d i n g s e a s o n t o be l i g h t e r t h a n t h o s e w h i c h were p r e s e n t a t t h e s t a r t o f t h e s e a s o n . I s t h i s m e r e l y a f u n c t i o n o f t h e p r e s e n c e o f j u v e n i l e s i n t h e c l a s s o f n e w l y c a p t u r e d a n i m a l s ? T a b l e 7 shows t h e w e i g h t r e l a t i o n s h i p s o f t h e f o u r c l a s s e s o f m i c e , w i t h a l l j u v e n i l e s d e l e t e d f r o m t h e s a m p l e s . W i t h j u v e n i l e s r e m o v e d , t h e t e n d e n c y o f r e c r u i t s and t r a n s i e n t s t o be l i g h t e r t h a n r e s i d e n t s and m i c e w h i c h d i s a p p e a r a l m o s t d i s a p p e a r s . The s u c c e s s o f b o t h m i c e p r e s e n t a t t h e s t a r t o f t h e main b r e e d i n g 39 season and mice which are r e c r u i t e d d u r i n g t h i s s e a s o n , i n rema in ing on the a r e a s f o r the d u r a t i o n of the s e a s o n , seems to be u n r e l a t e d to we ight . I s s u c c e s s f u l r e s i d e n c y or r e c r u i t m e n t r e l a t e d t o b r e e d i n g c o n d i t i o n ? To answer t h i s g u e s t i c n , I counted the number of weeks, w i t h i n season 2, t h a t each an ima l was c a p t u r e d i n b r e e d i n g c o n d i t i o n , and the number of weeks i t was c a p t u r e d not i n b reed ing c o n d i t i o n . I then summed these r a t i o s w i t h i n each of the f o u r c l a s s e s of m i c e , and compared these summed r a t i o s over a l l c l a s s e s (Table 8 ) . Both sexes showed h i g h l y s i g n i f i c a n t h e t e r o g e n e i t y between c l a s s e s i n p r o p o r t i o n of weeks b r e e d i n g . The o v e r a l l r e l a t i o n s h i p of the f o u r c l a s s e s of males wi th r e s p e c t to b r e e d i n g c o n d i t i o n i s : r e s i d e n t s > r e c r u i t s > d i s a p p e a r i n g m i c e > t r a n s i e n t s . The males which remained i n the p o p u l a t i o n , e i t h e r as s u c c e s s f u l r e s i d e n t s c r r e c r u i t s , were those which were most o f t e n i n b r e e d i n g c o n d i t i o n . T h i s i s c o n s i s t e n t with the h y p o t h e s i s t h a t a g g r e s s i v e , b reed ing males space themselves out d u r i n g t h i s s e a s o n , and r e s i s t the r e c r u i t m e n t of new males i n t o the p o p u l a t i o n . I f a g g r e s s i o n i s c o r r e l a t e d with b r e e d i n g c o n d i t i o n (Hea ley , 1967) one would expect t h a t b r e e d i n g males would be more s u c c e s s f u l i n m a i n t a i n i n g t h e i r t e r r i t o r i e s than n c n - b r e e d i n g males , and t h a t , o f mice a t t e m p t i n g to en te r the p o p u l a t i o n , those which were b r e e d i n g , and t h e r e f o r e a g g r e s s i v e , would have a g r e a t e r p r o b a b i l i t y o f overcoming the a g g r e s s i o n o f r e s i d e n t ma les , and e s t a b l i s h i n g 40 themselves i n the p o p u l a t i o n . T h e r e f o r e , i f these p o p u l a t i o n s were behaving as p r e d i c t e d by the model i n F i g u r e 1, I would expect not only the r e l a t i o n s h i p s which I observed between the c l a s s e s with r e s p e c t to breeding c o n d i t i o n , but a l s o t h a t animals were s u c c e s s f u l l y r e c r u i t e d would more o f t e n be breeding when f i r s t captured than would t r a n s i e n t i n d i v i d u a l s . Table 9 shows the breeding c o n d i t i o n of r e c r u i t s and t r a n s i e n t s on f i r s t c a pture. As p r e d i c t e d , males which s u c c e s s f u l l y entered the p o p u l a t i o n tended to be i n breeding c o n d i t i o n when they were f i r s t captured, while t r a n s i e n t males were most o f t e n not i n breeding c o n d i t i o n when f i r s t c a ptured. T h e r e f o r e , i t appears t h a t , during the main breeding season, males which are i n breeding c o n d i t i o n more s u c c e s s f u l l y maintain t h e i r t e r r i t o r i e s , and more o f t e n remain i n the p o p u l a t i o n a f t e r r e c r u i t m e n t . Than dc non-breeding males. The r e l a t i o n s h i p of the four c l a s s e s of females with r e s p e c t to p r o p o r t i o n of time spent breeding was: r e c r u i t s > r e s i d e n t s d i s a p p e a r i n g mice>transients. As i n males, females which s u c c e s s f u l l y remained cn the g r i d s , or s u c c e s s f u l l y entered the p o p u l a t i o n , fended to be breeding more o f t e n than mice which d i d not remain on the a r e a s . Do females breed cn l y once they are e s t a b l i s h e d cn a home area, or can they secure a home area only i f they are breeding? I f the l a t t e r h ypothesis i s c o r r e c t , then, as i n males, animals which s u c c e s s f u l l y enter the p o p u l a t i o n s should tend to be b r e e d i n g when they f i r s t appear. T h i s i s not the case f o r 41 f e m a l e s (Table 9 ) : s u c c e s s f u l r e c r u i t s tend not to be i n b r e e d i n g c o n d i t i o n when they f i r s t appear on the g r i d , and do not d i f f e r f rom u n s u c c e s s f u l r e c r u i t s ( t r a n s i e n t s ) i n t h i s r e s p e c t . T h i s may i n d i c a t e tha t f ema les tend to breed o n l y a f t e r they are e s t a b l i s h e d on a home a r e a . However, t h i s s t r a i g h t f o r w a r d r e l a t i o n s h i p i s somewhat confused by the r e l a t i o n s h i p between the f o u r c l a s s e s o f females and the t i m i n g of r e p r o d u c t i o n w i t h i n season 2. The p r o p o r t i o n of females b r e e d i n g tends t o be very low u n t i l the l a s t h a l f of the main b r e e d i n g s e a s o n , when i t i n c r e a s e s to peak l e v e l s w i t h i n two t o f o u r weeks ( F i g u r e s 3 and 4 ) . Animals which are r e c r u i t e d d u r i n g t h i s season w i l l ' h a v e a h i g h e r p r o p o r t i o n of t h e i r c a p t u r e r e c o r d s i n t h e , l a t t e r pa r t of the season than w i l l an imals r e s i d e n t throughout the s e a s o n . S i m i l a r l y , d i s a p p e a r i n g an ima ls w i l l have a h i g h e r p r o p o r t i o n of t h e i r c a p t u r e s i n the e a r l y pa r t o f the s e a s o n . Ihe observed r e l a t i o n s h i p s between p r o p o r t i o n b r e e d i n g i n r e c r u i t s , r e s i d e n t s , and d i s a p p e a r i n g mice c o u l d be due e n t i r e l y to t h i s . In summary, s u c c e s s f u l r e s i d e n c y and s u c c e s s f u l r e c r u i t m e n t i n the main b r e e d i n g s e a s o n , does not appear to depend on weight f o r e i t h e r s e x . In both sexes b r e e d i n g i s a s s o c i a t e d with rema in ing on the a r e a s . I have suggested t h a t , i n f e m a l e s , t h i s a s s o c i a t i o n may r e s u l t mainly from the t i m i n g of the peak r e p r o d u c t i v e p e r i o d , b u t , i n m a l e s , a g g r e s s i o n , a s s o c i a t e d with b r e e d i n g , may be impor tan t i n 42 d e t e r m i n i n g who s u c c e s s f u l l y e s t a b l i s h e s and m a i n t a i n s a t e r r i t o r y d u r i n g t h i s s e a s o n . fiiscussionj: D u r i n g t h e main b r e e d i n g s e a s o n , a d u l t m a l e s s p a c e o u t f r o m e a c h o t h e r and s u r v i v e v e r y w e l l . J u v e n i l e s , p a r t i c u l a r l y j u v e n i l e m a l e s , a r e r e s t r i c t e d f r o m e n t e r i n g t h e p o p u l a t i o n . B o t h s u c c e s s f u l r e s i d e n c y and s u c c e s s f u l r e c r u i t m e n t a r e a s s o c i a t e d w i t h b e i n g r e p r o d u c t i v e l y a c t i v e . T h e s e o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t t h e r e s i d e n t m a l e s m a i n t a i n t e r r i t o r i e s d u r i n g t h e b r e e d i n g s e a s o n , and t h a t a g g r e s s i v e b e h a v i o r o f t h e s e m a l e s l i m i t s t h e r e c r u i t m e n t o f new a n i m a l s , p a r t i c u l a r l y m a l e s , i n t o t h e p o p u l a t i o n . A t t h i s t i m e , f e m a l e s a r e s p a c i n g o u t f r o m e a c h o t h e r , b u t n o t as much as m a l e s a r e . The r e c r u i t m e n t r a t e o f f e m a l e s i s much h i g h e r t h a n t h a t o f m a l e s , and a much h i g h e r p r o p o r t i o n o f e x p e c t e d f e m a l e j u v e n i l e s t h a n male j u v e n i l e s e n t e r t h e p o p u l a t o n . ' A d u l t ' f e m a l e s a r e c a p t u r e d i n t h e same t r a p s a s j u v e n i l e s much more o f t e n t h a n e x p e c t e d . These r e s u l t s s u g g e s t t h a t , w h i l e a d u l t f e m a l e s a r e s p a c e d o u t f r o m e a c h o t h e r d u r i n g t h e main b r e e d i n g s e a s o n , t h e y do n o t r e s t r i c t t h e r e c r u i t m e n t o f new a n i m a l s i n t o t h e p o p u l a t i o n . F u r t h e r , j u v e n i l e f e m a l e s have a h i g h e r r a t e o f s u c c e s s f u l r e c r u i t m e n t t h a n j u v e n i l e m a l e s , w h i c h s u g g e s t s t h a t a d u l t m a l e s may s e l e c t i v e l y r e s t r i c t t h e r e c r u i t m e n t o f j u v e n i l e 43 males . E e h a v i o r a l i n t e r a c t i o n s do not appear to be very i m p o r t a n t i n d e t e r m i n i n g the r a t e of female r e c r u i t m e n t d u r i n g the main b r e e d i n g season . I f t h i s i s t r u e , the number of females present i n the p o p u l a t i o n at the end c f t h i s season w i l l tend to be a f u n c t i o n of the number a v a i l a b l e , r a t h e r than a f u n c t i o n of the a g g r e s s i v e b e h a v i o r cf r e s i d e n t , b r e e d i n g a d u l t s , as i n ma les . P e t t i c r e w and S a d l e i r ( 1 9 7 4 ) suggested t h a t the numbers of males and females present at the end of the b r e e d i n g season i n the p o p u l a t i o n s which he was s t u d y i n g , f o r t y m i l e s e a s t o f Van c ou v e r , were determined i n the above manner: females by the numbers of j u v e n i l e s which had been a v a i l a b l e to r e c r u i t over the s e a s o n , and males by the a g g r e s s i v e b e h a v i o r c f r e s i d e n t , a d u l t ma les . T h u s , i t seems l i k e l y t h a t , d u r i n g the main b r e e d i n g s e a s o n , as over the s p r i n g r e o r g a n i z a t i o n , we cannot g e n e r a l i z e from o b s e r v a t i o n s c f male b e h a v i o r t o f e m a l e s . Male numbers appear to be l i m i t e d by b e h a v i o r a l i n t e r a c t i o n s , but I have no ev idence tha t t h i s i s t rue f o r f e m a l e s . ANALYSIS AND BESDITS: 1A1L INCREASE EEBIOD. S u r v i v a l and Recrui tment : . The model p r e d i c t s good s u r v i v a l and peak r e c r u i t m e n t i n the f a l l . The p r o p o r t i o n of b r e e d i n g males d e c l i n e s r a p i d l y at the onset o f t h i s s e a s o n , a n d , d u r i n g the l a t t e r pa r t o f the s e a s o n , no males are b r e e d i n g at a l l . In response to the decrease i n male a g g r e s s i o n which i s a s s o c i a t e d with c e s s a t i o n of b r e e d i n g , j u v e n i l e s shou ld f r e e l y en te r the p o p u l a t i o n . I a n a l y s e d s u r v i v a l and r e c r u i t m e n t f o r t h i s p e r i o d us ing the r e g r e s s i o n models p r e v i o u s l y d e s c r i b e d . F i g u r e s 5 and T a b l e 2 i n d i c a t e t h a t , as p r e d i c t e d , r e c r u i t m e n t of both sexes i s h i g h e r than i n any o ther s e a s o n . S u r v i v a l i s not as good as i n the main b r e e d i n g s e a s o n , and t h i s , i n a s s o c i a t i o n wi th h igh recru i tment , - may i n d i c a t e t h a t the s t a b l e p o p u l a t i o n s t r u c t u r e ma in ta ined over the main b r e e d i n g season breaks down d u r i n g the f a l l i n c r e a s e and mice tend to move around more. Spac ing F e h a v i c r : I f the s t a b l e p o p u l a t i o n s t r u c t u r e of season 2 does break down d u r i n g the f a l l i n c r e a s e , and i f male a g g r e s s i o n drops as b r e e d i n g c e a s e s , then the i n c r e a s e p e r i o d shou ld be a s s o c i a t e d wi th reduced s p a c i n g b e h a v i o r f o r both s e x e s . The t r a p -o v e r l a p i n d i c e s f o r both sexes can be seen i n F i g u r e 5. As p r e d i c t e d , n e i t h e r sex s p a c e s cut as much i n season 3 as i n season 2. Males c o n t i n u e to space out more than f e m a l e s . There were fewer double c a p t u r e s of a d u l t s and more of j u v e n i l e s than e x p e c t e d , and j u v e n i l e s tended to be c a p t u r e d with a d u l t females or with e the r j u v e n i l e s (Table 10). However, the d i f f e r e n c e s between observed and expec ted numbers of doub le c a p t u r e s are not as l a r g e i n season 3 as they were i n season 2 ( F i g u r e 6 ) . The same s p a c i n g p a t t e r n s a re e v i d e n t i n the f a l l i n c r e a s e as i n the main b r e e d i n g p e r i o d , b u t , as 45 p r e d i c t e d , the mice tend net to space themselves cut as much d u r i n g the f a l l i n c r e a s e . J u v e n i l e r e c r u i t m e n t ^ I a n a l y s e d j u v e n i l e r e c r u i t m e n t f o r season 3 i n the same manner as d e s c r i b e d f o r season 2. Tab le 11 shows the observed and expected numbers of j u v e n i l e r e c r u i t s i n season 3. The r a t i o of observed to expected was .92 f o r males and 1.00 f o r f e m a l e s , and the sex r a t i o of r e c r u i t e d j u v e n i l e s (47.9$ males) d i d not d i f f e r from 1 (X 2 =.293) . Thus , t h e r e i s no i n d i c a t i o n of j u v e n i l e s c f e i t h e r sex be ing prevented from e n t e r i n g the - p o p u l a t i o n . I compared j u v e n i l e r e c r u i t m e n t i n season 3 with r e c r u i t m e n t i n the main b r e e d i n g p e r i o d . A l though a h i g h e r p r o p o r t i o n of expected j u v e n i l e s were r e c r u i t e d i n season 3 than i n season 2 , the d i f f e r e n c e between seasons was much more pronounced i n males than i n females (Table 12) , T h i s i n d i c a t e s aga in tha t male j u v e n i l e s a re more s e v e r e l y r e s t r i c t e d from e n t e r i n g the p o p u l a t i o n d u r i n g the main b r e e d i n g s e a s o n , than females a r e . The g e n e r a l model (F igure 1) p r e d i c t s tha t p o p u l a t i o n i n c r e a s e over the b r e e d i n g season w i l l be l i m i t e d main ly by the r e s t r i c t i o n of j u v e n i l e r e c r u i t m e n t by a d u l t males . I have found tha t j u v e n i l e r e c r u i t m e n t i s indeed r e s t r i c t e d when a d u l t males are b r e e d i n g , but I have a l s o seen tha t on ly about o n e - t h i r d of the l i t t e r s born over the e n t i r e summer would be 46 r e c r u i t e d i n the main b r e e d i n g season, even i f t h e r e were no r e s t r i c t i o n of r e c r u i t m e n t (20 s u c c e s s f u l p r e g n a n c i e s were obs e r v e d i n season 2, and 40 i n season 3 ) . Giv e n t h a t r e l a t i v e l y few j u v e n i l e s would be r e c r u i t e d w h i l e males were a c t i v e l y b r e e d i n g i n any c a s e , does t h e r e s t r i c t i o n of j u v e n i l e r e c r u i t m e n t by a d u l t males have a s i g n i f i c a n t e f f e c t on p o t e n t i a l i n c r e a s e ? T a b l e 13 shows the numbers and p r o p o r t i o n s of p o t e n t i a l r e c r u i t s which were l o s t owing t o u n s u c c e s s f u l p r e g n a n c i e s and a f t e r b e i n g n u r s e d . l i t t e r s l o s t b e f o r e I d e t e c t e d l a c t a t i o n are c o n s i d e r e d t o have been l o s t owing t o u n s u c c e s s f u l p r e g n a n c i e s , w h i l e l i t t e r s l e s t a f t e r I d e t e c t e d l a c t a t i o n may have been l o s t because o f r e s t r i c t i o n o f j u v e n i l e r e c r u i t m e n t by r e s i d e n t males. The p r o p o r t i o n of l i t t e r s l o s t was much h i g h e r i n season 2 than i n season 3 (70.7% as opposed t o 40.8% ) , and most of t h i s d i f f e r e n c e was due to the d i f f e r e n c e i n l o s s e s a f t e r n u r s i n g . I f a l l l i t t e r s which were nursed were r e c r u i t e d , o n l y 7 (6.6) a d d i t i o n a l mice would have e n t e r e d the p o p u l a t i o n s i n the f a l l i n c r e a s e p e r i o d . S i n c e t h i s i s t o t a l r e c r u i t m e n t over t h r e e y e a r s , on two a r e a s , i t r e p r e s e n t s an average r e c r u i t m e n t of o n l y one mouse per p o p u l a t i o n per y e a r . C l e a r l y , as e x p e c t e d , the r a t e o f p o p u l a t i o n i n c r e a s e i n the f a l l i s not s i g n i f i c a n t l y l i m i t e d by r e s t r i c t i o n of j u v e n i l e r e c r u i t m e n t : a l l j u v e n i l e s which are a v a i l a b l e t o r e c r u i t do so. However, i f a l l o f t h e j u v e n i l e s expected to e n t e r the p o p u l a t i o n d u r i n g the main b r e e d i n g season d i d s o , the p o p u l a t i o n s i z e a t the end of the 47 main b r e e d i n g season would have i n c r e a s e d by a mean of 7 8 . 4 $ . A c c e p t i n g the assumpt ion tha t l e s s of l i t t e r s a f t e r n u r s i n g i s main ly due to r e s t r i c t i o n of j u v e n i l e r e c r u i t m e n t by r e s i d e n t a d u l t m a l e s , i t i s c l e a r t h a t t h i s b e h a v i o r a l i n t e r a c t i o n reduces the r a t e of p o p u l a t i o n i n c r e a s e d u r i n g the p e r i o d of peak male b r e e d i n g . In summary, my o b s e r v a t i o n s of j u v e n i l e r e c r u i t m e n t appear t o f o l l o w the p r e d i c t i o n s based on the g e n e r a l model deve loped from e a r l i e r work on Peromyscus . S h i l e males are a c t i v e l y b r e e d i n g , j u v e n i l e r e c r u i t m e n t i s r e s t r i c t e d , and the r a t e o f i n c r e a s e i n p o p u l a t i o n s i s s i g n i f i c a n t l y r e d u c e d . In the l a t e r p a r t of the b reed ing s e a s o n , when males cease to b r e e d , b e h a v i o r a l i n t e r a c t i o n s between a d u l t s and j u v e n i l e s no l o n g e r l i m i t j u v e n i l e r e c r u i t m e n t , and the r a t e of p o p u l a t i o n i n c r e a s e i s determined main ly by the numbers of l i t t e r s s u c c e s s f u l l y n u r s e d . Comparat ive A n a l y s i s of R e s i d e n t s ^ T r a n s i e n t s ^ R e c r u i t s ^ and D i s a p p e a r i n g Mice.. I compared r e s i d e n t m i c e , r e c r u i t s , t r a n s i e n t s and d i s a p p e a r i n g m i c e , us ing the methods d e s c r i b e d f o r seasons 1 and 2. T a b l e s 3 and 4 show the numbers of mice i n each c a t e g o r y with weights above and below the mean weight f o r week of f i r s t cap tu re i n season 3. Res ident mice cannot be d i s t i n g u i s h e d by weight from mice which d i s a p p e a r d u r i n g season 3. T h i s i n d i c a t e s tha t s u c c e s s f u l r e s i d e n c y does not 48 depend on weight f c r e i t h e r s e x . S i m i l a r l y , s u c c e s s f u l r e c r u i t s dc not d i f f e r s i g n i f i c a n t l y from t r a n s i e n t s , f o r e i t h e r s e x , and so s u c c e s s f u l r e c r u i t m e n t a l s o does not appear t o depend on we ight . However, both males and females which a r e c a p t u r e d f o r the f i r s t t ime i n t h i s seascn are l i g h t e r than mice p r e s e n t at the s t a r t of the s e a s o n . T h i s r e f l e c t s the f a c t t h a t most r e c r u i t s and t r a n s i e n t s are j u v e n i l e s , whi le most r e s i d e n t s and d i s a p p e a r i n g m i c e ; p a r t i c u l a r l y m a l e s , are b r e e d i n g a d u l t s . In g e n e r a l , d u r i n g t h i s p e r i o d of h i g h j u v e n i l e r e c r u i t m e n t and d e c l i n i n g b r e e d i n g a c t i v i t y , n e i t h e r s u c c e s s f u l r e s i d e n c y nor s u c c e s s f u l r e c r u i t m e n t appears t o be r e l a t e d t o we igh t . Do the f o u r c l a s s e s of mice d i f f e r i n b r e e d i n g a c t i v i t y ? I examined t h i s g u e s t i o n , as I d i d f o r season 2, by d e t e r m i n i n g the number of weeks mice were c a p t u r e d i n b r e e d i n g c o n d i t i o n , and the number of weeks they were c a p t u r e d n o n -b r e e d i n g , and comparing these r a t i o s among the f o u r c l a s s e s of m ice . These compar isons can be seen i n Tab le 8. The p r o p o r t i o n of t ime i n b r e e d i n g c o n d i t i o n v a r i e d s i g n i f i c a n t l y over the f o u r c l a s s e s f o r both s e x e s . However, the r e l a t i o n s h i p s of the four c l a s s e s are not the same f o r males and f e m a l e s . Res iden t females breed more than a l l o ther g r o u p s , and females which e n t e r the p o p u l a t i o n t h i s s e a s c n , breed l e a s t . The r e l a t i o n s h i p s of the f o u r c l a s s e s were as f o l l o w s : R e s i d e n t s > D i s a p p e a r i n g m i c e > T r a n s i e n t s > r e c r u i t s . 49 R e s i d e n t females d i d not breed s i g n i f i c a n t l y more o f t e n than d i s a p p e a r i n g females (X 2 = .702 ) , and t r a n s i e n t s d i d not breed s i g n i f i c a n t l y mere o f t e n than r e c r u i t s (X 2= 2 . 2 2 5 , P > . 1 0 ) . However, the mice p resen t at the s t a r t o f the season ( r e s i d e n t s and d i s a p p e a r i n g mice) were i n b r e e d i n g c o n d i t i o n s i g n i f i c a n t l y more o f t e n than mice c a p t u r e d f o r the f i r s t t ime i n t h i s season ( r e c r u i t s and t r a n s i e n t s ) (X 2 =13.799 ,P<.001) . These r e l a t i o n s h i p s d i f f e r from those observed i n s e a s c n 2 on ly in t h a t , i n season 3, r e c r u i t e d females are l e a s t o f t e n b r e e d i n g , r a t h e r than most o f t e n . T h i s d i f f e r e n c e i s p robab ly due to the t i m i n g of r e c r u i t m e n t i n the two s e a s o n s . In season 2, as I have d i s c u s s e d , the p r o p o r t i o n of females b r e e d i n g i n c r e a s e d as the s e a s c n p r o g r e s s e d , and r e c r u i t s may appear to breed more than r e s i d e n t s s imp ly because the r e s i d e n t s were cn the area d u r i n g .the e a r l y pa r t of the s e a s o n . The o p p o s i t e s i t u a t i o n occurs i n season 3. a l l b r e e d i n g a c t i v i t y d e c l i n e s as t h i s season p r o g r e s s e s , and so c l a s s e s with c a p t u r e d i s t r i b u t i o n s skewed toward the l a t e r p a r t o f the season ( r e c r u i t s ) w i l l appear to breed l e s s than c l a s s e s with e v e n l y d i s t r i b u t e d c a p t u r e f r e g u e n c i e s ( r e s i d e n t s ) or c a p t u r e s skewed t o the e a r l y pa r t of the season ( d i s a p p e a r i n g m i c e ) . T h e r e f o r e , d i f f e r e n c e s i n p r o p o r t i o n b r e e d i n g among t h e s e c l a s s e s p robab ly do not r e f l e c t the e f f e c t of b r e e d i n g c o n d i t i o n on s u c c e s s f u l r e s i d e n c y and r e c r u i t m e n t i n t o the p o p u l a t i o n . I s u s p e c t t h a t , i n season 3, as i n season 2, the s u c c e s s of females i n remain ing cn my 50 s tudy areas does not depend cn b reed ing c o n d i t i o n . For ma les : D i s a p p e a r i n g m i c e > f i e s i d e n t s > T r a n s i e n t s > B e c r u i t s . D i s a p p e a r i n g males were i n b r e e d i n g c o n d i t i o n s i g n i f i c a n t l y more o f t e n than r e s i d e n t males (X 2 =5.343,.025>p>.001) , and t r a n s i e n t males were a c t i v e l y b r e e d i n g more o f t e n than s u c c e s s f u l r e c r u i t s (X 2 =6.420, P<.025) . F u r t h e r , t r a n s i e n t males i n season 3 tended to be i n b r e e d i n g c o n d i t i o n when f i r s t cap tu red more o f t e n than were s u c c e s s f u l r e c r u i t s (see T a b l e 9 ) . These r e s u l t s suggest tha t b r e e d i n g males may move « more than n o n - b r e e d i n g males d u r i n g t h i s s e a s o n . However, the r e l a t i o n s h i p s between the f o u r c l a s s e s of m i c e , with r e s p e c t to b r e e d i n g c o n d i t i o n , may a l s o b e , as i n f e m a l e s , p r i m a r i l y an e f f e c t of t i m i n g of c a p t u r e s . S i s c u s s i o n i My o b s e r v a t i o n s of the f a l l i n c r e a s e p e r i o d g e n e r a l l y agree with p r e d i c t i o n s from the model p resented i n F i g u r e 1. The i n c r e a s e i n r e c r u i t m e n t , drop i n s u r v i v a l , and decrease i n s p a c i n g b e h a v i o r i n d i c a t e tha t the p o p u l a t i o n s t r u c t u r e ma in ta ined over the main b r e e d i n g season breaks down as b r e e d i n g c e a s e s . l i t t e r s c o n t i n u e t o be produced d u r i n g most o f t h i s s e a s o n , and a l l j u v e n i l e s which are produced are r e c r u i t e d . I c o u l d not d i s t i n g u i s h r e s i d e n t mice from mice which d i s a p p e a r e d , or r e c r u i t s from t r a n s i e n t s , by weight or b r e e d i n g c o n d i t i o n ( d i f f e r e n c e s i n b r e e d i n g c o n d i t i o n be ing 51 confounded by d i f f e r e n c e s in the t i m i n g of c a p t u r e s ) . ANALYSIS AND RESULTS:CVEEWINTEE PERIOD. The g e n e r a l model p r e d i c t s t h a t the p o p u l a t i o n s w i l l remain r e l a t i v e l y s t a b l e over t h i s p e r i o d , wi th good s u r v i v a l , low r e c r u i t m e n t , and l i t t l e s p a c i n g o u t . S u r v i v a l and Recru i tment^ The s u r v i v a l and r e c r u i t m e n t r a t e s e s t i m a t e d from the r e g r e s s i o n models can be seen i n F i g u r e 5 , and the observed r a t e s , i n T a b l e 2. As p r e d i c t e d , over the w in ter p e r i o d , s u r v i v a l of both sexes i s g c c d , and r e c r u i t m e n t i s low. I f h i g h s u r v i v a l and low r e c r u i t m e n t i n d i c a t e s t a b i l i t y o f p o p u l a t i o n s t r u c t u r e , than t h i s p e r i o d i s as s t a b l e f o r males as the main b r e e d i n g season was, and f o r females i t i s the most s t a b l e p e r i o d of the y e a r . S p a c i n g J e h a v i o r ^ Spac ing b e h a v i o r t h i s season was a n a l y s e d from ' t r a p -o v e r l a p 1 i n d i c e s , as d e s c r i b e d f o r season 1 (F igure 5 ) . As p r e d i c t e d , both males and females show minimal s p a c i n g b e h a v i o r over the winter s e a s o n . F i g u r e 6 shows the observed and expected numbers c f p a i r t y p e s i n season 4, and T a b l e 14 shows the numbers of males and females caught i n t r a p s which a l s o caught o t h e r mice d u r i n g t h a t t r a p p i n g p e r i o d . A l though s p a c i n g b e h a v i c r was at i t s lowest d u r i n g t h i s s e a s o n , males s t i l l tended t o be cap tured i n the same t r a p s as o t h e r males 52 l e s s o f t e n than expected 8X 2 =13 .698 , df 2, P<.005) . Females showed no tendency to space themselves o u t . Comparat ive A n a l y s i s of R e s i d e n t s ^ R e c r u i t s x T r a n s i e n t s ^ and Bi§a££§3li.Dg l i £ § i . I compared the f o u r c l a s s e s o f mice u s i n g the same t e c h n i q u e s d e s c r i b e d f o r p r e v i o u s s e a s o n s . Res ident females tended to be h e a v i e r than females which d i s a p p e a r e d (Table 4 ) , N e i t h e r male nor female r e c r u i t s d i f f e r e d i n weight from t r a n s i e n t s , but the weight d i s t r i b u t i o n s of these newly-c a p t u r e d an imals resembled those c f d i s a p p e a r i n g mice more than they d i d those of r e s i d e n t s . T h i s may i n d i c a t e t h a t l i g h t e r mice move around d u r i n g the o v e r w i n t e r p e r i o d . D i s c u s s i o n In g e n e r a l , the r e s u l t s from the o v e r w i n t e r p e r i o d agree wi th p r e d i c t i o n s from the mcdel : f o r both s e x e s , s u r v i v a l was h i g h , r e c r u i t m e n t low , and s p a c i n g b e h a v i o r a t a minimum. One i n t e r e s t i n g r e s u l t i s t h a t , a l though s p a c i n g behav io r was at i t s minimum d u r i n g t h i s s e a s o n , males s t i l l spaced themse lves out more than expected by c h a n c e , and more than f e m a l e s . The o v e r w i n t e r p e r i o d appears to be a t ime c f p o p u l a t i o n s t a b i l i t y , with l i t t l e movement of i n d i v i d u a l s and low l e v e l s of a g g r e s s i v e i n t e r a c t i o n . L i g h t a n i m a l s , p a r t i c u l a r l y f e m a l e s , may move around over t h i s p e r i o d , but g e n e r a l l y the p o p u l a t i o n of i n d i v i d u a l s p resent a t the end of the f a l l 53 i n c r e a s e p e r i o d w i l l tend t o change r e l a t i v e l y s l o w l y u n t i l t h e onset of b r e e d i n g and the s p r i n g r e o r g a n i z a t i o n p e r i o d . GENERAL DISCUSSION T h i s c h a p t e r has c o n s i s t e d mainly of a d e t a i l e d , season by s e a s c n , a n a l y s i s of the demographic c h a r a c t e r i s t i c s of my c o n t r o l p o p u l a t i o n s . T h i s a n a l y s i s has r e v e a l e d not on ly t h a t t h e r e are l a r g e s e a s o n a l d i f f e r e n c e s i n demography, but a l s o t h a t , i n two o f the f o u r s e a s o n s , males and females appear to be do ing very d i f f e r e n t t h i n g s . I w i l l b e g i n t h i s d i s c u s s i o n with a b r i e f summary o f the s e a s o n a l changes which I suggest are o c c u r r i n g i n male and female demography. Males beg in b reed ing i n the e a r l y s p r i n g (February -March) . As they come i n t o b r e e d i n g c o n d i t i o n they beg in to space themse lves out and e s t a b l i s h b reed ing t e r r i t o r i e s which they w i l l ma in ta in throughout the b r e e d i n g s e a s o n . The r e s u l t i n g r e s t r u c t u r i n g of the p o p u l a t i o n and i n c r e a s e d movement of a n i m a l s , which i s a s s o c i a t e d with the s p a c i n g b e h a v i o r , tends to r e s u l t i n an o v e r a l l d e c r e a s e i n the numbers of males r e s i d e n t on the area (the p o p u l a t i o n d e n s i t y decreased i n t h r e e of the f o u r s p r i n g s o b s e r v e d , and the mean i n s t a n t a n e o u s r a t e of p o p u l a t i o n change , over the f o u r g r i d -s p r i n g s , was - . 0 6 + . 0 0 4 ) . Heavy males tend to be f a v o r e d i n the . c o m p e t i t i o n f c r t e r r i t o r i e s . A f t e r t h i s i n i t i a l r e s t r u c t u r i n g , the male p o p u l a t i o n tends to remain very s t a b l e : r e s i d e n t s s u r v i v e w e l l , and they r e s i s t r e c r u i t m e n t of 5 a any new males, a d u l t cr j u v e n i l e . Over t h i s s t a b l e p e r i o d , having or e s t a b l i s h i n g a t e r r i t o r y i s a s s o c i a t e d with being a c t i v e l y breeding. The p r o p o r t i o n of males breeding d e c l i n e s over the f a l l i n c r e a s e p e r i o d . l i t t e r s born at t h i s time of year are very s u c c e s s f u l at e n t e r i n g the p o p u l a t i o n , and d e n s i t i e s i n c r e a s e to the y e a r l y maximum. A f t e r t h i s surge of j u v e n i l e r e c r u i t m e n t , the p o p u l a t i o n again s t a b i l i z e s . Over the non-breeding seascn males remain s l i g h t l y spaced out from each other, and, r e l a t i v e to the preceding and f o l l o w i n g seasons, tend not to move around. While the s t a b i l i t y observed over the main breeding season appears to r e s u l t from a c t i v e r e s i s t a n c e to change by t e r r i t o r i a l , breeding males, the overwinter s t a b i l i t y probably r e s u l t s because most p o t e n t i a l r e c r u i t s have already been r e c r u i t e d , and male a g g r e s s i o n i s minimal, r e s u l t i n g i n both l i t t l e f o r c e f o r change and l i t t l e p o t e n t i a l r e s i s t a n c e to i t . Females begin breeding i n the s p r i n g approximately when males do. The onset of breeding i s , however, not a s s o c i a t e d with i n c r e a s e d spacing behavior or movement, but r a t h e r with heavy m o r t a l i t y of breeding females. T h i s m o r t a l i t y , combined with a low recruitment r a t e , r e s u l t s i n a decrease i n the number of females on the area (the p o p u l a t i o n s d e c l i n e d over the f i r s t s i x weeks of breeding i n three of the f o u r g r i d -s p r i n g s observed, and the mean instantaneous r a t e of p o p u l a t i o n change over those weeks was -.11+.004). I have proposed t h a t t h i s e a r l y m o r t a l i t y i s due to the i n a b i l i t y of 55 females t o get enough energy (food) i n the e a r l y s p r i n g fo m a i n t a i n themse lves as we l l as suppor t pregnancy and l a c t a t i o n . A f t e r t h i s i n i t i a l p e r i o d of female b r e e d i n g and m o r t a l i t y , the p r o p o r t i o n of females b r e e d i n g tends to f a l l , and the female p o p u l a t i o n s t a b i l i z e s . A l though females are spaced out mere at t h i s t ime than at any o ther t ime of y e a r , and are s u r v i v i n g w e l l , new females do not appear to be r e s t r i c t e d from e n t e r i n g the p o p u l a t i o n . T h e r e f o r e , the number of females p r e s e n t i n the p o p u l a t i o n a t the end of t h i s p e r i o d w i l l be a f u n c t i o n of the number which s u r v i v e d the s p r i n g d e c l i n e p e r i o d p l u s the number from o t h e r a r e a s or from e a r l y l i t t e r s which en te r the p o p u l a t i o n . T h i s i s i n c o n t r a s t to the l i m i t a t i o n of male numbers a t t h i s t ime by the a g g r e s s i v e b e h a v i o r of b r e e d i n g , r e s i d e n t males . P e t t i c r e w and S a d l e i r (1974) proposed a s i m i l a r dichotomy between sexes i n p o p u l a t i o n s at the D . B . C . Research f o r e s t , eas t of Vancouver . Towards the end of the main b r e e d i n g p e r i o d , the p r o p o r t i o n c f females b r e e d i n g i n c r e a s e s to i t s maximum, and fema les c o n t i n u e to have and nurse l i t t e r s w e l l i n t o the f a l l i n c r e a s e p e r i o d . J u v e n i l e s tend to be caught i n the same t r a p s as females more o f t e n than would be expected by c h a n c e , and p r o b a b l y are remain ing on t h e i r m o t h e r ' s home area u n t i l they a re s e x u a l l y mature or she becomes pregnant aga in ( S a v i d g e , 1974) . Dur ing t h i s p e r i o d , females no l o n g e r space out from each o t h e r , and move around more than they d i d d u r i n g the main b r e e d i n g p e r i o d . The p o p u l a t i o n remains r e l a t i v e l y 56 s t a b l e ever the winter months with good s u r v i v a l and low r e c r u i t m e n t , and no ev idence of s p a c i n g b e h a v i o r . The females which do move around d u r i n g t h i s season tend to weigh l e s s than r e s i d e n t f e m a l e s . S i n c e r e s i d e n t females show a s l i g h t tendency to have been on the areas l o n g e r b e f o r e the s t a r t o f season 4 than were females which d i s a p p e a r e d i n t h i s season (Table 15) , the d i f f e r e n c e i n weight between r e s i d e n t s and mice which move around may r e f l e c t age d i f f e r e n c e s , with a d u l t and e a r l y r e c r u i t i n g females t e n d i n g to remain i n a more r e s t r i c t e d a rea over the winter than do l a t e r e c r u i t i n g j u v e n i l e s . I r e g a r d t h i s h y p o t h e s i s as more probab le than one r e l a t i n g weight to a b i l i t y t o f i n d f o o d , because S a d l e i r e t (1873) has shown tha t i t i s u n l i k e l y t h a t n o n - b r e e d i n g £ § f ° I X § £ i i § are l i m i t e d i n any way by shor tage of food o v e r the win ter p e r i o d . A l s o , the mean weight o f both males and females i n c r e a s e d as the winter p r o g r e s s e d ( F i g u r e s 7 and 8). I f e e l t h a t , a l though females which beg in to breed i n the e a r l y s p r i n g p r o b a b l y f a i l because they cannot o b t a i n enough food to meet t h e i r i n c r e a s e d energy demands, n o n - b r e e d i n g females (and males) can o b t a i n more than enough f o o d to ma in ta in t h e m s e l v e s , and even to grow, over the w i n t e r . My p o p u l a t i o n s c l o s e l y resemble the model which P e t t i c r e w and S a d l e i r p r e s e n t i n t h e i r 1974 paper . They base t h e i r model on data ga thered on Percm^scus p o p u l a t i o n s i n s e v e r a l a r e a s near Vancouver , over a span of ten y e a r s , J s e e S a d l e i r , 1965, 1970 and 1974; and S a d l e i r , C a s p e r s c n and H a r l i n g , 57 1973), as w e l l as on data ga thered i n t h i s area by Fiealey (1967) and Fordam (1971), That my p o p u l a t i o n s behaved as P e t t i c r e w and S a d l e i r would have p r e d i c t e d s u p p o r t s t h e i r model and f u r t h e r i n d i c a t e s the s t a b i l i t y over t ime and space of these p a t t e r n s of Peromjjscus demography. In a d d i t i o n to t h i s , I found tha t male j u v e n i l e s are more r e s t r i c t e d from e n t e r i n g the p o p u l a t i o n d u r i n g the main b r e e d i n g season than are female j u v e n i l e s . T h i s o b s e r v a t i o n i s c o n s i s t e n t with the model tha t male b reed ing d e n s i t i e s a r e l i m i t e d by a g g r e s s i v e b e h a v i o r of a d u l t males , and s u p p o r t s the h y p o t h e s i s t h a t female d e n s i t i e s are not as s t r o n g l y i n f l u e n c e d by t h i s b e h a v i o r . I a l s o d i s c o v e r e d tha t females which begin b r e e d i n g i n the e a r l y s p r i n g p robab ly s u f f e r heavy m o r t a l i t y . S a d l e i r has proposed t h a t females might be unable to breed over the winter because of energy c o n s t r a i n t s , but M i l i a r (1975), l o o k i n g a t energy p a r t i t i o n i n g i n Peromyscus l e u c o p u s , found t h a t , when food was s c a r c e , mothers passed the energy d e f i c i e n c i e s onto t h e i r o f f s p r i n g r a t h e r than d e p l e t i n g t h e i r own r e s e r v e s . I would t h e r e f o r e have p r e d i c t e d tha t the energy l i m i t a t i o n on b r e e d i n g females i n s p r i n g would have been r e f l e c t e d i n l i t t e r m o r t a l i t y r a t h e r than i n m o r t a l i t y of a d u l t f e m a l e s . However, the l a t t e r seems to be the c a s e , and t h i s m o r t a l i t y adds t o S a d l e i r * s model a d i r e c t l i m i t a t i o n on both the t i m i n g of the s t a r t of female breed ing and the s t a r t i n g d e n s i t y o f the b r e e d i n g p o p u l a t i o n . 58 The model of Pexcm^scus p o p u l a t i o n s which I p r e s e n t e d i n Chapter 2 p r e d i c t e d tha t b r e e d i n g , r e s i d e n t males would r e s t r i c t the r e c r u i t m e n t of a l l j u v e n i l e s . I f t h a t was t r u e , and o n l y l i t t e r s born l a t e enough to be r e c r u i t e d a f t e r the males had stopped b r e e d i n g had good r e c r u i t m e n t s u c c e s s , I wondered what the advantage was of b r e e d i n g e a r l y . Why expend energy de fend ing a t e r r i t o r y when you were, at the same t i m e , l o w e r i n g the s u r v i v a l of your own o f f s p r i n g by p r e v e n t i n g t h e i r r e c r u i t m e n t i n t o the p o p u l a t i o n ? Shy produce l i t t e r s which w i l l be u n s u c c e s s f u l ? Hy r e s u l t s have he lped me to answer t h a t g u e s t i o n i F i r s t , some female j u v e n i l e s are a b l e to e n t e r the p o p u l a t i o n whi le males are b r e e d i n g , and some of t h e s e e a r l y r e c r u i t e d females mature and breed w i t h i n one summer (7 of 8 females which r e c r u i t e d as j u v e n i l e s d u r i n g the main b r e e d i n g season were observed i n b r e e d i n g c o n d i t i o n b e f o r e the end of the f a l l i n c r e a s e p e r i o d ) . T h e r e f o r e , males and females may i n c r e a s e t h e i r r e p r o d u c t i v e s u c c e s s by b r e e d i n g e a r l y . E a r l y b r e e d i n g males may a l s o be i n c r e a s i n g t h e i r f i t n e s s by r e d u c i n g the r a t i o of males to females i n the p o p u l a t i o n . At the onset of b r e e d i n g , female m o r t a l i t y i s r e l a t i v e l y h i g h , and t h i s would tend to leave more males than fema les in the p o p u l a t i o n . Assuming t h a t males are spaced out over a g i v e n a r e a , and do not e x i s t t o g e t h e r i n a dominance h i e r a r c h y , the more females t h e r e are per male i n the p o p u l a t i o n , the h i g h e r the p r o b a b i l i t y tha t any g i v e n male w i l l s i r e a l i t t e r . Ey s p a c i n g out at the s t a r t o f the 59 b r e e d i n g s e a s o n , males e l i m i n a t e p o t e n t i a l c o m p e t i t o r s f o r females and compensate f o r female m o r t a l i t y a t t h i s t i m e . I f , i n a d d i t i o n to t h i s , they d i s c r i m i n a t e between male and female r e c r u i t s (both a d u l t and j u v e n i l e ) d u r i n g the b r e e d i n g s e a s o n , and a l l o w on ly the females t o s e t t l e , they w i l l f u r t h e r reduce the sex r a t i o i n t h a t a r e a , and thus i n c r e a s e t h e i r f i t n e s s ( p o t e n t i a l number of l i t t e r s s i r e d ) . In a d d i t i o n to these f a c t o r s , i f the t i m i n g of the end of the b r e e d i n g season v a r i e s , males and females which breed e a r l y may o c c a s i o n a l l y c o n t r i b u t e a lmost a l l of the genes i n the next g e n e r a t i o n . S a d l e i r (1974) has shown tha t the t i m i n g of the end of the b r e e d i n g season i n these mice i s , i n f a c t , h i g h l y v a r i a b l e , and i s p robab ly d i r e c t l y a s s o c i a t e d with temperature changes which mice would be unable to p r e d i c t . T h u s , i t appears tha t males can i n c r e a s e t h e i r f i t n e s s by s p a c i n g out and h o l d i n g t e r r i t o r i e s through the breed ing s e a s o n , even though r e l a t i v e l y few females breed d u r i n g much of t h i s s e a s o n . S i m i l a r l y , a l though e a r l y b reed ing i n fema les can be a s s o c i a t e d with heavy m o r t a l i t y , females can a l s o i n c r e a s e t h e i r f i t n e s s by b r e e d i n g e a r l y . 60 CHftFTEE 4 DEMOGRAPHY - EXPERIMENTAL DATA EXPERIMENT 1: Exper iment 1 was the p u l s e d removal exper iment which I conducted on g r i d 2. I removed a l l of the an imals p r e s e n t on t h i s g r i d at the s t a r t of the s p r i n g r e o r g a n i z a t i o n , i n 1973 and 1974, on the assumpt ion tha t the mice which would c o l o n i z e the a rea would be an imals which had been u n s u c c e s s f u l i n the s u r r o u n d i n g , u n d i s t u r b e d p o p u l a t i o n s . I checked t h i s assumpt ion by comparing mice c o l o n i z i n g the removal a reas i n the s p r i n g r e o r g a n i z a t i o n p e r i o d with mice which were r e s i d e n t on the c o n t r o l a reas over t h i s s e a s o n . I f c o l o n i s t s on vacant a reas are the same k i n d s of mice which are moving around i n c o n t r o l p o p u l a t i o n s d u r i n g the s p r i n g r e o r g a n i z a t i o n , than we can expect more males than females on the removal a r e a s , and removal mice of both sexes s h o u l d be l i g h t e r than c o n t r o l r e s i d e n t s . L e t us look a t sex r a t i o f i r s t . The sex r a t i o s of mice moving onto the removal a reas and r e s i d e n t , c o n t r o l m i c e , are p r e s e n t e d i n Tab le 16. As e x p e c t e d , more males than females were r e c r u i t e d to the removal a reas (X 2 =6.564, P<.005) , even though the sex r a t i o of r e s i d e n t mice on the c o n t r o l areas over t h i s p e r i o d i s 1:1. To determine i f removal mice weighed l e s s than r e s i d e n t m i c e , I compared the two groups u s i n g the same methods which I used i n the p r e c e d i n g c h a p t e r to compare r e s i d e n t s with 61 t r a n s i e n t s , r e c r u i t s , and d i s a p p e a r i n g mice (Table 17) . Both male and female c o l o n i s t s are s i g n i f i c a n t l y l i g h t e r than r e s i d e n t mice . I a l s o compared the p r o p o r t i o n s of c o l o n i s t s and r e s i d e n t s which b r e d . The f o u r c l a s s e s o f males on the c o n t r o l a reas d i d not d i f f e r i n p r o p o r t i o n b r e e d i n g . Females which d i s a p p e a r e d over the s p r i n g r e o r g a n i z a t i o n p e r i o d tended to be b r e e d i n g , but new mice appear ing on the areas were not i n b r e e d i n g c o n d i t i o n , and I t h e r e f o r e d i d net p r e d i c t t h a t b r e e d i n g fema les would be r e c r u i t e d to the removal a r e a s . Compar isons c f the p r o p o r t i o n of r e s i d e n t s and c o l o n i s t s caught i n b r e e d i n g c o n d i t i o n at l e a s t once d u r i n g the s p r i n g r e o r g a n i z a t i o n p e r i o d , are p resen ted i n Tab le 18. As e x p e c t e d , the two groups do not d i f f e r (males: P=0.22; f e m a l e s : p=0.67) . The demographic a n a l y s i s i n d i c a t e s that the mice which c o l o n i z e vacant a reas d u r i n g the s p r i n g r e o r g a n i z a t i o n are the same k i n d s of mice as those l e a v i n g u n d i s t u r b e d p o p u l a t i o n s : l i g h t m a l e s , and l i g h t , n o n - b r e e d i n g females are moving around at t h i s t ime o f y e a r . Bo these d i f f e r e n c e s between s u c c e s s f u l r e s i d e n t s and c o l o n i s t s p e r s i s t , and are they r e f l e c t e d i n d i f f e r e n c e s i n p o p u l a t i o n dynamics between the newly c o l o n i z e d area and the u n d i s t u r b e d p o p u l a t i o n s ? I p a r t i c u l a r l y want to know i f the - c o l o n i s t s can s u r v i v e and reproduce as we l l as c o n t r o l mice , l e t us look f i r s t at whether the observed d i f f e r e n c e s i n sex r a t i o and weight p e r s i s t over the e n t i r e 62 y e a r . Weights^ F i g u r e s 7 and 8 show the mean weekly weights of males and females cn g r i d 2, and on the twc c o n t r o l a r e a s . A l though both male and female c o l o n i s t s were i n i t i a l l y l i g h t e r than r e s i d e n t c o n t r o l m i c e , the d i f f e r e n c e s between the c o l o n i s t s and the e n t i r e c o n t r o l p o p u l a t i o n are never l a r g e , and tend not to p e r s i s t beyond the i n i t i a l p e r i o d of c o l o n i z a t i o n . (In 1974, f ema les on g r i d 2 remained l i g h t e r than females on the c o n t r o l a reas u n t i l the end of the main b r e e d i n g s e a s o n , but t h i s was not t r u e f c r females i n 1973, or f o r males i n e i t h e r y e a r . ) The d i f f e r e n c e i n weight between c o l o n i z i n g and r e s i d e n t p o p u l a t i o n s appears to be t r a n s i t o r y . Sex Rat io , : G r i d 2 was i n i t i a l l y c o l o n i z e d by mere males than f e m a l e s . I compared the p r o p o r t i o n of males on the p u l s e d removal and c o n t r o l g r i d s at the end of the main b r e e d i n g s e a s o n , f a l l i n c r e a s e s e a s o n , and o v e r w i n t e r s e a s o n . By the end of the main b r e e d i n g p e r i o d , the sex r a t i o cn g r i d 2 d i d not d i f f e r from 1:1 (X z =1 .815 ) , or from the r a t i o on the c o n t r o l a reas (X 2 =.321) . I t a l s o d i d not d i f f e r from the c o n t r o l a reas at e i t h e r of the l a t e r sampl ing . t i m e s . T h e r e f o r e , the sex r a t i o d i f f e r e n c e , l i k e the weight 63 d i f f e r e n c e , d i d not p e r s i s t . 5J2il£iJ3.9 SS&avior j , S i n c e males c o l o n i z i n g the removal a r e a s i n the s p r i n g may be s u b o r d i n a t e , and thus l e s s a g g r e s s i v e , i n d i v i d u a l s , I a t tempted to look at s p a c i n g b e h a v i o r on g r i d 2, with the e x p e c t a t i o n t h a t males might space out l e s s on the e x p e r i m e n t a l area than on the c o n t r o l a r e a s . However, sample s i z e s f o r g r i d 2 a l o n e are too s m a l l to a l l o w me to make the same compar isons f o r g r i d 2 as I made f o r the c o n t r o l a r e a s . The observed and maximum expected t r a p - o v e r l a p f r e q u e n c i e s f o r v a r i o u s types of mice can be seen i n F i g u r e 9. Males avo ided o t h e r mice i n seasons 1 through 3, but not i n season 4. Females do not appear to a v o i d o ther m i c e , and j u v e n i l e males were c a p t u r e d with o t h e r mice l e s s o f t e n than female j u v e n i l e s were. These r e s u l t s are i n g e n e r a l agreement with the t r e n d s observed on the c o n t r o l a r e a s . The r a t i o s c f observed double c a p t u r e s to maximum expected double c a p t u r e s f o r the p u l s e d removal and c o n t r o l g r i d s appear i n Tab le 19. G r i d 2 showed the same s e a s o n a l t r e n d s as the c o n t r c l a r e a s , a n d , w i t h i n any one s e a s o n , the r a t i o cn g r i d 2 d i d not d i f f e r s i g n i f i c a n t l y from tha t on the c o n t r o l g r i d s . I a l s o compared f r e g u e n c i e s of double c a p t u r e s c f a d u l t and j u v e n i l e , males and f e m a l e s , on c o n t r c l a r e a s and g r i d 2, and a g a i n , p a t t e r n s cn g r i d 2 do not d i f f e r s i g n i f i c a n t l y from these observed cn c o n t r o l areas (P>.30) . T h u s , a l t h o u g h the p o p u l a t i o n on g r i d 2 began wi th 64 s i m u l t a n e o u s c o l o n i z a t i o n of the a r e a , and a l t h o u g h c o l o n i s t s might he expected to be l e s s a g g r e s s i v e than r e s i d e n t s on c o n t r o l a r e a s , I was unable to d e t e c t d i f f e r e n c e s i n s p a c i n g b e h a v i o r between g r i d 2 and u n d i s t u r b e d p o p u l a t i o n s . Minimum Jumber M i v e j : The d i f f e r e n c e s between the i n i t i a l c o l o n i z e r s on g r i d 2 and r e s i d e n t s on c o n t r o l areas d i d not p e r s i s t , and t h e r e f o r e , we might expect the g r o s s demography of the g r i d 2 p o p u l a t i o n to c l o s e l y resemble t h a t of the u n d i s t u r b e d c o n t r o l a r e a s , i n s p i t e of the two complete r e m o v a l s . F i g u r e 10 shows the minimum numbers known to be a l i v e on the c o n t r o l and p u l s e d removal g r i d s . The g r i d 2 p o p u l a t i o n shows the same s e a s o n a l p a t t e r n of d e n s i t y as the c o n t r o l p o p u l a t i o n s do , and the d i f f e r e n c e s i n d e n s i t y between the two c o n t r o l a r e a s are at l e a s t as l a r g e as the d i f f e r e n c e s between g r i d 2 and the c o n t r o l a r e a s . F u r t h e r , the p o p u l a t i o n d e n s i t y on g r i d 2 tended to be lower than c o n t r o l d e n s i t i e s b e f o r e the removal e x p e r i m e n t , a n d , a f t e r both r e m o v a l s , r e t u r n e d to the same r e l a t i v e d e n s i t y . The d e p r e s s i n g e f f e c t of removal on d e n s i t y l a s t e d on ly f o u r weeks: t h i s p o p u l a t i o n r e c o v e r s very g u i c k l y from l o c a l r e d u c t i o n s i n d e n s i t y . G iven t h a t d i f f e r e n c e s between c o l o n i s t s on the removal a r e a and r e s i d e n t s on c o n t r o l a reas dc not p e r s i s t beyond the i n i t i a l p e r i o d o f c o l o n i z a t i o n , and tha t the o n c e - a - y e a r removal appears to have on ly a very t r a n s i e n t e f f e c t on the 6 5 d e n s i t y of the p o p u l a t i o n , we might p r e d i c t the c o l o n i z i n g i n d i v i d u a l s to s u r v i v e and reproduce as w e l l as c o n t r o l a n i m a l s . S u r v i v a l and Becrui tment j : Do mice on the removal area s u r v i v e as w e l l as mice on c o n t r o l a reas? I f mice c o l o n i z i n g the removal a reas have a h i g h e r tendency to d i s p e r s e throughout t h e i r l i v e s than r e s i d e n t mice , we might expect tha t c o l o n i s t s would remain on the new area f o r l e s s time than r e s i d e n t s remained on the c o n t r o l a r e a s . On the o ther hand, i f the c o l o n i z i n g an ima ls were moving i n response to s o c i a l p r e s s u r e on s e t t l e d a r e a s , we would expect no d i f f e r e n c e i n s u r v i v a l between the removal and c o n t r o l a r e a s , a f t e r the s e t t l e m e n t o f the removal a r e a , and perhaps b e t t e r s u r v i v a l cn the removal a rea immedia te ly a f t e r c o l o n i z a t i o n . I a n a l y s e d s u r v i v a l cn g r i d 2 u s i n g a r e g r e s s i o n model i n the manner d e s c r i b e d f o r the c o n t r o l a n a l y s i s i n the p r e v i o u s c h a p t e r . The r e g r e s s i o n i s not s i g n i f i c a n t f o r m a l e s ( F = 1 . 1 1 1 ; df 3 , 3 9 ; P = . 2 5 3 ) , which i n d i c a t e s t h a t the re i s not a s t r o n g s e a s o n a l v a r i a b i l i t y i n male s u r v i v a l . I lumped c o n t r o l and g r i d 2 males i n a g e n e r a l model , and compared the amount of v a r i a n c e accounted f o r by t h i s model wi th an area term i n c l u d e d and not i n c l u d e d . The d i f f e r e n c e between the two r e g r e s s i o n s was not s i g n i f i c a n t (F=.788; df 1 , 1 5 2 ; P > . 2 5 ) , which i n d i c a t e s t h a t the mean and s e a s o n a l t r e n d s i n male s u r v i v a l cn g r i d 2 d i d not d i f f e r 66 s i g n i f i c a n t l y from s u r v i v a l on the c o n t r o l a r e a s . However, the observed s u r v i v a l r a t e s f o r the s p r i n g r e o r g a n i z a t i o n were s l i g h t l y h i g h e r on g r i d 2 (.79) than on the c o n t r o l a reas ( .74) . T h i s i n d i c a t e s tha t males on the removal area had s l i g h t l y b e t t e r s u r v i v a l ' than c o n t r o l males d u r i n g the i n i t i a l p e r i o d of c o l o n i z a t i o n : d u r i n g the s p r i n g r e o r g a n i z a t i o n p e r i o d , poor s u r v i v a l c f males on the c o n t r o l a reas may be due to s o c i a l p r e s s u r e . Males c o l o n i z i n g the removal a rea a r e r e l e a s e d from t h i s p r e s s u r e , and s u r v i v e b e t t e r than males on u n d i s t u r b e d a r e a s . The r e g r e s s i o n of female s u r v i v a l r a t e s cn season i s h i g h l y s i g n i f i c a n t (F -12 .678 ; df 3 , 3 9 ; P<.0001) , i n d i c a t i n g t h a t female s u r v i v a l cn g r i d 2 shows s t r o n g s e a s o n a l v a r i a b i l i t y (F igure 11). fl compar ison of F i g u r e s 11 and 5 shows that females cn g r i d 2 show the same s e a s o n a l t r e n d s i n s u r v i v a l as c o n t r o l f e m a l e s . To c o n f i r m t h i s , I r e g r e s s e d s u r v i v a l on season f o r c o n t r o l females p l u s g r i d 2 f e m a l e s . The a d d i t i o n of an area term to t h i s r e g r e s s i o n , which has the e f f e c t of s e p a r a t i n g c o n t r o l and removal f e m a l e s , d i d not s i g n i f i c a n t l y i n c r e a s e the amount of v a r i a b i l i t y accounted f o r by the r e g r e s s i o n (F=.22;df 1 ,152;P>.50) . Female s u r v i v a l on g r i d 2 does not appear to d i f f e r from female s u r v i v a l on c o n t r o l a r e a s , a n d , u n l i k e m a l e s , females which i n i t i a l l y c o l o n i z e the removal a rea dc not have i n c r e a s e d or decreased s u r v i v a l r e l a t i v e to c o n t r o l f e m a l e s . T h i s l a t t e r o b s e r v a t i o n s u p p o r t s the h y p o t h e s i s tha t poor s u r v i v a l o f f ema les on the 6 7 c o n t r o l a reas d u r i n g the s p r i n g i s not a f u n c t i o n of s o c i a l p r e s s u r e . The above a n a l y s i s of s u r v i v a l r a t e s on g r i d 2 i n d i c a t e s tha t mice i n t h i s p o p u l a t i o n s u r v i v e at l e a s t as we l l as mice i n c o n t r o l p o p u l a t i o n s . F u r t h e r , a l though g r i d 2 males may i n i t i a l l y s u r v i v e b e t t e r than c o n t r o l ma les , t h i s d i f f e r e n c e i s t emporary . T h u s , i t appears t h a t , l i k e sex r a t i o , w e i g h t , and d e n s i t y , s u r v i v a l r a te r e t u r n s to c o n t r o l l e v e l s very soon a f t e r c o l o n i z a t i o n . S i n c e both d e n s i t y and s u r v i v a l r a t e on g r i d 2 r e t u r n to c o n t r o l l e v e l s very scon a f t e r c o l o n i z a t i o n , we might expect t h a t r e c r u i t m e n t p a t t e r n s on the removal g r i d would a l s o resemble those on c o n t r o l a r e a s . To determine i f t h i s was s o , I r e g r e s s e d r e c r u i t m e n t of c o n t r o l p l u s removal mice on s e a s c n . The area term d i d not s i g n i f i c a n t l y i n c r e a s e the amount of v a r i a b i l i t y accounted f o r by the r e g r e s s i o n model f o r males (F=.0447; df 1,15 1; P>.50) . (Recrui tment f o r the f i r s t t r a p p i n g p e r i o d a f t e r the removal was not i n c l u d e d i n these models . ) I then looked at the r e g r e s s i o n f c r g r i d 2 a l o n e . T h i s r e g r e s s i o n i s h i g h l y s i g n i f i c a n t (F=5.208; df 3 , 4 0 ; E - . 0 0 3 9 ) , i n d i c a t i n g t h a t r e c r u i t m e n t of males i n t o the g r i d 2 p o p u l a t i o n v a r i e d s t r o n g l y with s e a s o n . The s e a s o n a l r e c r u i t m e n t r a t e s p r e d i c t e d by t h i s model are p r e s e n t e d i n F i g u r e 11. as e x p e c t e d , r e c r u i t m e n t i s very h i g h d u r i n g season 1, but a f t e r t h i s p e r i o d , the s e a s o n a l t r e n d s i n male r e c r u i t m e n t c l o s e l y resembled those on the c o n t r o l g r i d s (see 68 F i g u r e 5 ) . When I pooled the g r i d 2 females with c o n t r o l f e m a l e s . I d i s c o v e r e d t h a t the area term d i d s i g n i f i c a n t l y i n c r e a s e the amount of v a r i a b i l i t y accounted f o r by the r e g r e s s i o n (F=4.096; df 1 ,151; E<.05) . T h i s i n d i c a t e d t h a t the r e c r u i t m e n t r a t e o f females cn g r i d 2 d i f f e r e d from the r a t e s observed on the c o n t r o l g r i d s . I then l o o k e d at the r e g r e s s i o n model f o r g r i d 2 a l o n e . T h i s r e g r e s s i o n accounted f o r a s i g n i f i c a n t p r o p o r t i o n of the v a r i a b i l i t y observed i n female r e c r u i t m e n t on g r i d 2 (F=5.866; df 3 ,440; P=.002) , and the s e a s o n a l r e c r u i t m e n t r a t e s which i t p r e d i c t e d can be seen i n F i g u r e 11. The mean r e c r u i t m e n t r a t e f o r f ema les was h igher on g r i d 2 than on the c o n t r o l a reas ( . 220 'as opposed to . 1 6 9 ) , a n d , as e x p e c t e d , r e c r u i t m e n t i n season 1 i s very much h i g h e r cn g r i d 2 than on the c o n t r c l a r e a s . Other than t h a t , the s e a s o n a l p a t t e r n of r e c r u i t m e n t d i d not d i f f e r markedly between the two a r e a s . Female r e c r u i t m e n t to g r i d 2 p robab ly d i f f e r s from c o n t r o l r e c r u i t m e n t , whi le male r e c r u i t m e n t does n o t , main ly b e c a u s e , cn c o n t r o l a r e a s , males have a h igh r e c r u i t m e n t r a t e i n season 1, wh i le females do n o t . T h e r e f o r e , the h igh i n i t i a l r e c r u i t m e n t on the removal g r i d , which o c c u r s i n both s e x e s , r e s u l t s i n f e m a l e s appear ing to d i f f e r more from the c o n t r o l p a t t e r n than males do . In summary, r e c r u i t m e n t r a t e , l i k e the o t h e r demographic parameters which I have d i s c u s s e d , appears t o d i f f e r markedly between c o n t r o l and removal areas on ly d u r i n g the i n i t i a l f o u r 69 weeks of c o l o n i z a t i o n . A f t e r t h a t t i m e , the p u l s e d removal a rea resembles the c o n t r o l a r e a s . Breed ing C o n d i t i o n : I have examined s p a c i n g b e h a v i o r , s u r v i v a l , r e c r u i t m e n t , and d e n s i t y , and i n no case d i d g r i d 2 d i f f e r from the c o n t r o l a r e a s beyond the f i r s t f o u r weeks of c o l o n i z a t i o n . However, b e f o r e c o n c l u d i n g that c o l o n i z i n g mice do not d i f f e r from r e s i d e n t mice , I would l i k e to look more c l o s e l y at b r e e d i n g on g r i d 2. Watson and Moss (1970) s t a t e d t h a t , i n o rder to show t h a t a p o p u l a t i o n i s be ing l i m i t e d by s p a c i n g b e h a v i o r , you must show tha t an imals which a re prevented from b r e e d i n g by the b e h a v i o r of r e s i d e n t i n d i v i d u a l s can s e t t l e and breed s u c c e s s f u l l y i f those r e s i d e n t s are removed. The b r e e d i n g s u c c e s s of g r i d 2 an imals i s r e l e v e n t to t h i s c r i t e r i o n . F i g u r e 12 shows the p r o p o r t i o n s of males and females b r e e d i n g on g r i d 2 and the c o n t r o l g r i d s . Both males and females cn g r i d 2 c o n s i s t e n t l y began b r e e d i n g l a t e r than mice on the c o n t r o l g r i d s , which r e s u l t e d i n s h o r t e r b r e e d i n g seasons cn g r i d 2 i n both 1973 and 1974. For both y e a r s , the area under the male curve f o r g r i d 2 i s c l e a r l y s m a l l e r than the a rea under the male c u r v e s f o r each o f the c o n t r o l a reas (the p r o p o r t i o n breedng on g r i d 2 i s lower than on g r i d 1, 22 out of 27 weeks, and than on g r i d 3 , 30 out of 33 weeks: P<.0005) . There i s a s i m i l a r , but n o n - s i g n i f i c a n t , t r e n d i n fema les (the p r o p o r t i o n b r e e d i n g on g r i d 2 i s l e s s than cn 70 g r i d 1,16 out o f 26 weeks, and than on g r i d 3,17 out of 24 weeks) . The g e n e r a l tendency seems to be tha t the re i s l e s s b r e e d i n g on the removal g r i d than on the c o n t r o l a r e a s : b r e e d i n g s t a r t s l a t e r , and the p r o p o r t i o n b r e e d i n g cn the removal g r i d tends to be l e s s than the p r o p o r t i o n b r e e d i n g on the c o n t r c l a r e a s . J u v e n i l e Becrui tment j : A l though there seems tc be l e s s b r e e d i n g on g r i d 2 than on the c o n t r o l a r e a s , the g r i d 2 p o p u l a t i o n i n c r e a s e s as much as the c o n t r o l p o p u l a t i o n s do i n the f a l l i n c r e a s e p e r i o d . T h e r e f o r e , the d i f f e r e n c e i n amount of b r e e d i n g must not a d v e r s e l y a f f e c t j u v e n i l e r e c r u i t m e n t onto g r i d 2. Is t h i s because a h i g h e r p r o p o r t i o n of the p r e g n a n c i e s en g r i d 2 are s u c c e s s f u l , or because j u v e n i l e s born on the g r i d are more s u c c e s s f u l l y r e c r u i t e d on g r i d 2? The p r o p o r t i o n of known p r e g n a n c i e s which are s u c c e s s f u l ( r e s u l t i n l i t t e r s be ing nursed cn the g r i d ) does not d i f f e r between g r i d 2 and the c o n t r o l g r i d s (.36 f o r - c o n t r o l g r i d s , and .41 f o r g r i d 2 , X 2 = . 0 2 9 , n=116). Tab le 20 shows a tendency f o r a h i g h e r p r o p o r t i o n c f expected j u v e n i l e males to be r e c r u i t e d on g r i d 2 than cn the c o n t r o l a r e a s , i n both seasons 2 and 3, and a h i g h e r p r o p o r t i o n o f expected j u v e n i l e f e m a l e s t o be r e c r u i t e d on g r i d 2 i n season 2. A lower p r o p o r t i o n of males b reeds on g r i d 2 i n season 2 than on the c o n t r o l a r e a s , and t h i s may mean t h a t j u v e n i l e s a t t e m p t i n g to e n t e r the g r i d 2 p o p u l a t i o n 71 i n t h i s season are f a c e d with l e s s a g g r e s s i o n by a d u l t males . T h i s c o u l d account f o r the h i g h e r p r o p o r t i o n of expec ted j u v e n i l e s r e c r u i t s on g r i d 2 in season 2. Dur ing season 3 t h e r e i s no r e s t r i c t i o n of j u v e n i l e r e c r u i t m e n t on e i t h e r the c o n t r o l g r i d s or g r i d 2 , and more males are r e c r u i t e d to g r i d 2 than were expected from the number c f l i t t e r s born on the g r i d . T h i s i n d i c a t e s t h a t , d u r i n g the f a l l i n c r e a s e p e r i o d , j u v e n i l e males from s u r r o u n d i n g areas may e n t e r the p u l s e d removal p o p u l a t i o n . Most of the j u v e n i l e r e c r u i t m e n t cn a l l the g r i d s o c c u r r e d d u r i n g the f a l l i n c r e a s e p e r i o d , and the p o p u l a t i o n d e n s i t y at the f a l l peak was determined mainly by the number of j u v e n i l e s r e c r u i t i n g i n the f a l l . A l though more o f the j u v e n i l e s expected i n season 2 were r e c r u i t e d onto g r i d 2 than onto the c o n t r c l a r e a s , i t i s u n l i k e l y t h a t these d i f f e r e n c e s i n e a r l y r e c r u i t m e n t c o u l d account f o r the a b i l i t y o f the g r i d 2 p o p u l a t i o n s to show the same i n c r e a s e i n the f a l l as the c o n t r o l p o p u l a t i o n s d i d . I suggest tha t the g r i d 2' p o p u l a t i o n s were ab le t o show the same r e l a t i v e i n c r e a s e as the c o n t r o l p o p u l a t i o n s , i n s p i t e o f l e s s b r e e d i n g , main ly because d i f f e r e n c e s i n p r o p o r t i o n b r e e d i n g o c c u r r e d e a r l y i n the season when few j u v e n i l e s en te red the c o n t r o l p o p u l a t i o n s , but a l s o because more j u v e n i l e s were r e c r u i t e d onto g r i d 2 i n the f a l l than were born cn the a r e a . The f a l l i n c r e a s e on g r i d 2 was augmented by r e c r u i t s from s u r r o u n d i n g a r e a s . D i s c u s s i o n o f Exper iment 1 A 72 a f t e r the i n i t i a l p e r i o d of c o l o n i z a t i o n , g r i d 2 resembles t h e - - c o n t r o l g r i d s i n a l l aspects which I have s t u d i e d , except breeding c h a r a c t e r i s t i c s . »hy d i d t h i s p o p u l a t i o n not show as much breeding a c t i v i t y as the c o n t r o l p o p u l a t i o n s ? l e t us co n s i d e r females f i r s t . Females which begin breeding i n the e a r l y s p r i n g , on c c n t r c l a r e a s , s u f f e r heavy m o r t a l i t y (67% over 6 weeks), and do not move around. A f t e r t h i s i n i t i a l s purt of breeding a c t i v i t y , there i s l i t t l e or no breeding u n t i l e a r l y summer. The main d i f f e r e n c e between c o n t r o l and g r i d 2 females i s that g r i d 2 females do not show t h i s i n i t i a l peak i n breeding. Since females which began breeding e a r l y on the c c n t r c l areas d i d not move around, the females moving around at t h i s time of year may be mainly those females which tend to begin breeding l a t e r i n the year, r e g a r d l e s s of t h e i r s o c i a l s i t u a t i o n . In any case, females c o l o n i z i n g pulsed removal areas do not f i t the c r i t e r i o n of Satson and Moss: they do not s e t t l e and breed as s u c c e s s f u l l y as c o n t r o l mice when r e s i d e n t mice are removed. I have p o s t u l a t e d , however, that males are l i m i t e d by s o c i a l behavior at t h i s time, and yet they, a l s o , do not s e t t l e and breed as w e l l as c o n t r o l males. During season 2, non-breeding males are not as s u c c e s s f u l at g e t t i n g or maintaining t e r r i t o r i e s as breeding males are, which means t h a t non-breeding males are the ones which are moving around at t h i s time. The males which c o l o n i z e g r i d 2 tend to be these non-breeding males, and there appears to be a l a g p e r i o d before these males begin to 73 b r e e d i n the new p o p u l a t i o n . T h i s may be a p h y s i o l o g i c a l d e l a y due t o the e f f e c t s of b e i n g s o c i a l l y s u b o r d i n a t e i n t h e u n d i s t u r b e d p o p u l a t i o n s (Terman, 1973). However, whatever t h e r e a s o n , t h e males which are u n s u c c e s s f u l i n c o n t r o l p o p u l a t i o n s d u r i n g seasons 1 and 2 do not breed i m m e d i a t e l y upon b e i n g r e l e a s e d from the s o c i a l p r e s s u r e o f r e s i d e n t males. That they do e v e n t u a l l y b r e e d , i n d i c a t e s t h a t t h e y may be l i m i t e d by s o c i a l p r e s s u r e i n u n d i s t u r b e d p o p u l a t i o n s , but t h e u l t i m a t e e f f e c t of the d e l a y i n b r e e d i n g , as f o r f e m a l e s , i s t h a t the p o p u l a t i o n of c o l o n i s t s does not make as l a r g e a r e p r o d u c t i v e e f f o r t as c o n t r o l p o p u l a t i o n s do. I n summary, when I removed a l l the a n i m a l s from an a r e a a t t h e s t a r t of t h e s p r i n g r e o r g a n i z a t i o n p e r i o d , I found t h a t t h e c l e a r e d a r e a was g u i c k l y r e c o l o n i z e d by t h e same s o r t s of mice which were moving i n t o and out of c o n t r c l p o p u l a t i o n s . These were m a i n l y l i g h t - w e i g h t males and a s m a l l e r number c f l i g h t , n on-breeding f e m a l e s . A f t e r s i x weeks, these c o l o n i s t s c o u l d no l o n g e r be d i s t i n g u i s h e d from mice on the c o n t r o l a r e a s , and t h e p o p u l a t i o n on the removal area was behaving i n e s s e n t i a l l y the same manner as t h e c o n t r o l p o p u l a t i o n s : no d i f f e r e n c e was'found i n s u r v i v a l , r e c r u i t m e n t , d e n s i t y , sex r a t i o , weight, or s p a c i n g b e h a v i o r . The o n l y d i f f e r e n c e which I was a b l e d e t e c t between t h e s e two p o p u l a t i o n s was t h a t t h e c o l o n i s t s began b r e e d i n g l a t e r than the c o n t r o l mice, and a l o w e r p r o p o r t i o n of male c o l o n i s t s b r e d . I have suggested t h a t t h e r e s u l t i n g reduced r e p r o d u c t i v e o u t p u t on t h i s g r i d 74 was compensated f o r i n the f a l l by r e c r u i t l e n t of j u v e n i l e males from s u r r o u n d i n g a r e a s , so t h a t , i n s p i t e of reduced b r e e d i n g , the c o l o n i s t p o p u l a t i o n showed the same r e l a t i v e i n c r e a s e i n the f a l l as the c o n t r o l p o p u l a t i o n s d i d . In s h o r t , the removal o f a l l mice from a one h e c t a r e a rea i n the middle of the 1700 a c r e s of Pergmyscus h a b i t a t has o n l y a very s h o r t - l i v e d e f f e c t on the demography of the p o p u l a t i o n on t h a t one h e c t a r e . EXPERIMENT 2: Exper iment 2 was the c o n t i n u o u s removal exper iment which I conducted on g r i d 4. I removed a l l of the an ima ls which I caught on t h i s area from February , 1973, to November, 1974. I w i l l beg in my a n a l y s i s of the data from t h i s exper iment by a s e a s c n by s e a s c n compar ison of removal g r i d mice wi th c o n t r o l g r i d mice . T h i s compar ison shou ld answer three g u e s t i o n s : 1) Are the mice moving onto the removal area the same t y p e s of mice which are moving onto and o f f of c o n t r o l a r e a s , 2) Do mice c o l o n i z i n g a vacant area d i f f e r from mice r e s i d e n t on c o n t r o l a r e a s , and 3) Do d i f f e r e n t t y p e s of an ima ls d i s p e r s e a t d i f f e r e n t t imes of year? S p r i n g R e o r g a n i z a t i o n . : In the p r e v i o u s s e c t i o n , I poo led the r e s u l t s from g r i d 2 and g r i d 4 to get my sample of mice c o l o n i z i n g vacant a reas d u r i n g the s p r i n g r e o r g a n i z a t i o n . T h i s a n a l y s i s showed t h a t 75 the c o l o n i s t s d i d resemble mice which moved onto and o f f of the c o n t r o l a reas d u r i n g t h i s s e a s o n , and they d i d d i f f e r from r e s i d e n t mice. C o l o n i z i n g mice of both sexes tended t o be l i g h t e r than r e s i d e n t s , and the sex r a t i o of the c o l o n i s t s was skewed i n f a v o u r of males . Main B r e e d i n g S e a s o n : Dur ing the main b r e e d i n g s e a s o n , the p o p u l a t i o n s on c o n t r o l a reas were very s t a b l e , w i th both males and f e m a l e s maximal ly spaced o u t . S u c c e s s f u l r e s i d e n c y and r e c r u i t m e n t were a s s o c i a t e d with b r e e d i n g , i n both s e x e s , a l t h o u g h I p o s t u l a t e d t h a t the b a s i s of the a s s o c i a t i o n d i f f e r e d between the s e x e s . Males c o l o n i z i n g the removal g r i d were i n b r e e d i n g c o n d i t i o n l e s s o f t e n than a l l males on c o n t r o l g r i d s (X 2 =11.177 , P<.001) and than r e s i d e n t males cn c o n t r o l g r i d s (X2=31 . 2 8 3 , P<.001) (Table 21) . T h i s i s c o n s i s t e n t wi th the h y p o t h e s i s , deve loped i n Chapter 3 , tha t the males which a re moving around at t h i s t ime of year are n o n - b r e e d i n g males which are u n s u c c e s s f u l i n g e t t i n g and m a i n t a i n i n g t e r r i t o r i e s i n u n d i s t u r b e d p o p u l a t i o n s . On the o t h e r hand, the females which c o l o n i z e g r i d 4 were i n b reed ing c o n d i t i o n as o f t e n as c o n t r o l females (X 2 f o r t o t a l c o n t r o l s i s . 7 2 0 , and f o r r e s i d e n t c o n t r o l s i s .418) (Table 21) . In Chapter 3 I noted t h a t , d u r i n g the main breed ing s e a s o n , female r e c r u i t s and r e s i d e n t s tended to be more o f t e n b r e e d i n g than were d i s a p p e a r i n g mice and t r a n s i e n t s . I suggested tha t t h i s may 76 have been s imply a f u n c t i o n of the t i m i n g of female r e p r o d u c t i o n . I f t h i s sere the c a s e , one would e x p e c t the same s e a s o n a l t r e n d s i n r e p r o d u c t i o n on the removal as on the c o n t r o l g r i d s . S i n c e , d u r i n g season 2, removal g r i d fema les do not d i f f e r from e i t h e r r e s i d e n t c o n t r o l f e m a l e s , or the t o t a l p o p u l a t i o n of females on the c o n t r o l a r e a s , i n p r o p o r t i o n b r e e d i n g , I conc lude t h a t the c l a s s d i f f e r e n c e s i n b r e e d i n g which I observed d u r i n g t h i s season on the c o n t r o l g r i d s were a f u n c t i o n of the t i m i n g of female r e p r o d u c t i o n , and d i d not r e f l e c t a r e l a t i o n s h i p between female r e p r o d u c t i o n and r e s i d e n c y . My a n a l y s i s o f the c o n t r o l p o p u l a t i o n s sugges ted t h a t , d u r i n g the main b r e e d i n g s e a s o n , Kales are d e f e n d i n g t e r r i t o r i e s a g a i n s t both a d u l t and j u v e n i l e r e c r u i t s . However, females spaced themselves out l e s s than males at t h i s t ime of y e a r , t h e r e f o r e , one might expect there t o be a l a r g e r number of males than females l o o k i n g f o r a p l a c e t o s e t t l e and b r e e d , and t h a t more males than females would r e c r u i t onto the removal g r i d . As p r e d i c t e d , d u r i n g the main b reed ing s e a s o n , 67 males and 44 females r e c r u i t e d onto g r i d 4. T h i s i s a sex r a t i o o f 1 . 5 2 , and d i f f e r s s i g n i f i c a n t l y from 1 (X 2 =4.766, P<.05) . A l though s u c c e s s f u l r e s i d e n c y and r e c r u i t m e n t on the c o n t r o l g r i d s d i d not appear to be r e l a t e d to weight d u r i n g the main b r e e d i n g p e r i o d , mice c a p t u r e d f o r the f i r s t t ime d u r i n g t h i s season tended to be l i g h t e r than those which were 77 p r e s e n t at the s t a r t c f the s e a s o n . T h e r e f o r e , I would expect t h a t new r e c r u i t s to the removal a rea would be l i g h t e r than c o n t r o l mice . F i g u r e s 13 and 14 compare the weights of g r i d 4 mice with those c f c o n t r o l mice over a l l s e a s o n s . The means and s t a n d a r d e r r o r s were ob ta ined us ing a l l weights r e c o r d e d d u r i n g the g iven s e a s o n , except those of o b v i o u s l y pregnant f e m a l e s . These graphs show a c l e a r tendency f o r removal g r i d mice to be l i g h t e r than r e s i d e n t s on the c o n t r c l a r e a s throughout the y e a r . I f we c o n s i d e r o n l y season 2, males a re c l e a r l y l i g h t e r i n 1973, and females i n 1974. T h u s , t h e r e i s a s l i g h t tendency f o r r e c r u i t s t o the removal a rea to be l i g h t e r than r e s i d e n t c o n t r c l mice d u r i n g the main b r e e d i n g s e a s o n . Both the g e n e r a l model p resented i n Chapter 2 , and my c o n t r o l a n a l y s i s i n Chapter 3, have i n d i c a t e d tha t r e s i d e n t a d u l t males r e s t r i c t the r e c r u i t m e n t o f j u v e n i l e s , and p a r t i c u l a r l y j u v e n i l e ma les , i n t o the c o n t r o l p o p u l a t i o n s d u r i n g the main b r e e d i n g s e a s o n . Do these j u v e n i l e s t u r n up on the vacant area? The sex r a t i o of r e c r u i t i n g j u v e n i l e s on g r i d 4 i s skewed i n f a v o r of females (X 2 =4.000, P<.05) , and does not d i f f e r from the sex r a t i o c f j u v e n i l e s r e c r u i t i n g onto the c o n t r o l a reas (X 2= ^0463). T h i s sugges ts t h a t the removal area does not p i c k up the j u v e n i l e males which are unab le to r e c r u i t i n t o u n d i s t u r b e d p o p u l a t i o n s . T h i s may i n d i c a t e tha t these j u v e n i l e s d i e be fore they reach t r a p p a b l e a g e , or t h a t j u v e n i l e s which have been p e r s e c u t e d tend to 78 a v o i d t r a p s . In any c a s e , I do not have any ev idence to suggest t h a t the j u v e n i l e s which are produced i n u n d i s t u r b e d p o p u l a t i o n s d u r i n g the e a r l y b r e e d i n g s e a s o n , but are unable to r e c r u i t i n t o i n t o these p o p u l a t i o n s because of the a g g r e s s i v e n e s s of t e r r i t o r i a l , b r e e d i n g ma les , are a b l e t o e s t a b l i s h themselves i f these males are removed. Krebs et a l A (1976) found t h a t Microt ias t o w n s e n d i i on removal a reas tended to begin b r e e d i n g at a l i g h t e r weight than females i n c o n t r o l p o p u l a t i o n s . S i n c e the females on my a rea tended to be l i g h t e r than c o n t r o l f e m a l e s , but were i n b r e e d i n g c o n d i t i o n as o f t e n , I s u s p e c t e d t h a t they might a l s o be matur ing at a l i g h t e r weight than c o n t r o l f e m a l e s . However, Tab le 22 shows tha t t h i s i s not the c a s e : n e i t h e r males nor females appear to breed at a l i g h t e r weight on the removal area than they do on the c c n t r c l a r e a s ( t h i s i s da ta f o r a l l b r e e d i n g a n i m a l s i n seasons 2 and 3 ) . The r e s u l t s of my a n a l y s i s of b r e e d i n g c o n d i t i o n , w e i g h t , and sex r a t i o of mice moving onto the c o n t i n u o u s removal a rea d u r i n g the main b r e e d i n g season have g e n e r a l l y been i n agreement with p r e d i c t i o n s made on the b a s i s of the p o p u l a t i o n model p resen ted i n Chapter 2, and the c o n t r o l a n a l y s i s i n Chapter 3. T h e y , t h e r e f o r e , suppor t the hypotheses t h a t a d u l t males defend b r e e d i n g t e r r i t o r i e s a g a i n s t o ther males d u r i n g t h i s s e a s c n , and t h a t there i s a s u r p l u s p o p u l a t i o n of males moving around at t h i s t i m e , l o o k i n g f o r a reas on which to s e t t l e and b r e e d . S i m i l a r l y , the removal data suppor t the 79 h y p o t h e s i s tha t females show l i t t l e s p a c i n g b e h a v i o r a t t h i s t i m e : a l l females which have s u r v i v e d the energy l i m i t a t i o n s of the e a r l y b r e e d i n g season can breed i n r e s i d e n t p o p u l a t i o n s , and few a d u l t females d i s p e r s e . The one s u r p r i s i n g r e s u l t of the main breed ing season a n a l y s i s was t h a t j u v e n i l e s show the same p a t t e r n of r e c r u i t m e n t onto the removal a rea as onto the c o n t r o l a r e a s . The e v i d e n c e from o t h e r s t u d i e s ( S a d l e i r , 196 5, and H e a l e y , 1967) t h a t j u v e n i l e s a re r e s t r i c t e d from e n t e r i n g r e s i d e n t p o p u l a t i o n s because o f the a g g r e s s i o n of r e s i d e n t , a d u l t m a l e s , i s very c o n v i n c i n g , and I do not f e e l tha t my removal g r i d o b s e r v a t i o n s i n v a l i d a t e t h i s e v i d e n c e . B a t h e r , I suggest t h a t the l a c k of j u v e n i l e r e c r u i t m e n t on the vacant area may mean tha t a d u l t s i n u n d i s t u r b e d p o p u l a t i o n s a c t u a l l y reduce the s u r v i v a l of j u v e n i l e s to t r a p p a b l e age ( p u b e r t y ) , so t h a t t h e s e j u v e n i l e s do not d i s p e r s e through the p o p u l a t i o n l o o k i n g f o r empty a reas on which to s e t t l e . The j u v e n i l e s which are born e a r l y i n the b r e e d i n g season do n o t , t h e r e f o r e , r e p r e s e n t a c l a s s of p o t e n t i a l c o l o n i s t s . F a l l I nc rease P e r i o d ^ On the c o n t r c l a r e a s , the f a l l i n c r e a s e p e r i o d was a t ime when the r i g i d s o c i a l s t r u c t u r e of the p r e v i o u s season broke down. A l l the a v a i l a b l e j u v e n i l e s were r e c r u i t e d i n t o the p o p u l a t i o n s , and there was some i n d i c a t i o n c f b r e e d i n g males l e a v i n g t h e i r t e r r i t o r i e s and moving through the p o p u l a t i o n . 80 As i n season 2 , the mice which were f i r s t c a p t u r e d i n the f a l l i n c r e a s e p e r i o d tended to be l i g h t e r than an ima ls p r e s e n t at the s t a r t of the s e a s o n . Given t h i s b e h a v i o r on c o n t r o l a r e a s , I would p r e d i c t i n c r e a s e d r e c r u i t m e n t to the removal g r i d d u r i n g t h i s s e a s o n , with p a r t i c u l a r i n c r e a s e i n the numbers of j u v e n i l e s and of b r e e d i n g , a d u l t m a l e s . Let us look f i r s t at the b reed ing c o n d i t i o n o f r e c r u i t s (Table 21) . Males c o l o n i z i n g the removal g r i d tended to be b r e e d i n g more o f t e n than males on c c n t r c l a reas t h i s season (X 2 =20 .?11 , P<.001) , but not s i g n i f i c a n t l y more than c o n t r o l r e s i d e n t s ( X 2 - 1 . 1 4 4 ) . A l s o , as p r e d i c t e d , s i n c e movement of f e m a l e s cn the c c n t r c l a reas was net a s s o c i a t e d with b r e e d i n g c o n d i t i o n , females on the removal g r i d d i d not d i f f e r from c o n t r o l females i n p r o p o r t i o n b r e e d i n g . I f a d u l t , b r e e d i n g males are moving through the p o p u l a t i o n d u r i n g t h i s s e a s o n , I would expect not o n l y tha t a d u l t males on g r i d 4 shou ld more o f t e n be b r e e d i n g than a re a d u l t males on c c n t r c l a r e a s , but a l s o t h a t the sex r a t i o on the removal area s h o u l d a g a i n be skewed i n f a v o r o f males . T h i s i s , i n f a c t , the c a s e : 78 males and 54 females were caught cn g r i d 4 i n season 3. T h i s g i v e s a sex r a t i o of 1.44, which d i f f e r s s i g n i f i c a n t l y from 1 (X 2 =4.634, P< .05) . F u r t h e r , t h e sex r a t i o of r e s i d e n t c o n t r o l mice d u r i n g t h i s season was o n l y .50 (7 males and 14 f e m a l e s ) . These two r e s u l t s i n d i c a t e t h a t a d u l t males move around more than a d u l t f ema les do d u r i n g the f a l l i n c r e a s e p e r i o d . 81 F i g u r e s 13 and 14 show t h a t , as p r e d i c t e d , r e c r u i t s to the removal area tend to re l i g h t e r than r e s i d e n t s cn c o n t r o l a r e a s d u r i n g the f a l l i n c r e a s e p e r i o d . The p r e d i c t i o n s about a d u l t r e c r u i t m e n t to the removal a rea d u r i n g the f a l l i n c r e a s e p e r i o d seem to have been borne out by the d a t a . Le t us now examine j u v e n i l e r e c r u i t m e n t d u r i n g t h i s s e a s o n . S i n c e j u v e n i l e s f r e e l y e n t e r e d the c o n t r o l a reas at t h i s t i m e , I expect the r e c r u i t m e n t onto g r i d 4 to resemble tha t onto the c o n t r o l a r e a s . F o r t y - n i n e males and 36 females were r e c r u i t e d onto g r i d 4 d u r i n g season 3 , and t h i s sex r a t i o does not d i f f e r s i g n i f i c a n t l y from 1 (X 2 =2 .333 ,P> .10 ) , or from the sex r a t i o of j u v e n i l e r e c r u i t s on c c n t r o l a reas (X 2 =2 .034 ,P> .10) . I compared j u v e n i l e r e c r u i t m e n t on g r i d 4 with tha t on the c o n t r o l a r e a s , i n seasons 2 and 3. U s i n g the expected numbers of r e c r u i t s which I c a l c u l a t e d f o r the c c n t r o l a reas i n Chapter 3 , I determined the p r o p o r t i o n s of t o t a l j u v e n i l e r e c r u i t m e n t which would be expected i n seasons 2 and 3. From these p r o p o r t i o n s and the t o t a l number of r e c r u i t s which I observed on g r i d 4, I c a l c u l a t e d the expected d i s t r i b u t i o n of r e c r u i t s on g r i d 4 over seasons 2 and 3. Fewer j u v e n i l e s of both sexes c o l o n i z e d g r i d 4 i n season 2, and more i n season 3 than expected (Table 2 3 ) . Ss on the c o n t r o l a r e a s , the female d i s t r i b u t i o n much more c l o s e l y approximated the expected than d i d the male d i s t r i b u t i o n (males:X 2 = 15 .921 , P<.0005; f e m a l e s : X 2 = 1 . 3 6 2 , P< .20) . The d i s t r i b u t i o n o f j u v e n i l e c a p t u r e s over the two 82 seasons d i d not d i f f e r between the c c n t r o l and removal areas (males- X 2 = . 5 5 1 ; f e m a l e s - X 2 = . 0 5 U ) . T h i s o b s e r v a t i o n s u p p o r t s the h y p o t h e s i s , deve loped i n the a n a l y s i s c f j u v e n i l e r e c r u i t m e n t to g r i d 4 i n season 2 , tha t the j u v e n i l e s which a r e p revented from e n t e r i n g the c o n t r o l p o p u l a t i o n s d u r i n g the main b r e e d i n g season are not ab le to c o l o n i z e vacant a r e a s . J u v e n i l e r e c r u i t m e n t to the removal a rea shows the same c h a r a c t e r i s t i c s as r e c r u i t m e n t i n t o e s t a b l i s h e d p o p u l a t i o n s . The a n a l y s i s c f c c n t r o l g r i d data i n d i c a t e d t h a t b r e e d i n g males tended t o move through the p o p u l a t i o n s d u r i n g the f a l l i n c r e a s e p e r i o d , and the s e l e c t i v e r e c r u i t m e n t of b r e e d i n g males to g r i d 4 i n t h i s season s u p p o r t s t h i s h y p o t h e s i s . Why would b reed ing m a l e s , which had been t e r r i t o r i a l throughout the s p r i n g r e o r g a n i z a t i o n and main b r e e d i n g p e r i o d s , suddenly a l t e r t h e i r b e h a v i o r ? P e r h a p s , as the b r e e d i n g season comes t o an end , males i n c r e a s e t h e i r p r o b a b i l i t y o f e n c o u n t e r i n g an e s t r o u s female by moving a round . I f a male remains on h i s t e r r i t o r y , he w i l l probably i n t e r a c t with o n l y those females whose home ranges o v e r l a p wi th h i s . Once p r e g n a n t , a female w i l l net come i n t o e s t r o u s a g a i n f o r a t l e a s t t h r e e weeks. F u r t h e r m o r e , s i n c e t h i s i s the end of the b r e e d i n g s e a s o n , i t i s u n l i k e l y t h a t the females would breed a g a i n a f t e r the b i r t h of these l i t t e r s . T h e r e f o r e , once a male has mated with a l l of the females on h i s a r e a , he cannot f u r t h e r i n c r e a s e h i s r e p r o d u c t i v e s u c c e s s by remain ing i n t h a t a r e a . On the c o n t r a r y , he i s p robab ly more l i k e l y to i n c r e a s e the number o f 83 s u c c e s s f u l matings which he has by t r a v e l l i n g through the p o p u l a t i o n i n s e a r c h of e s t r c u s f e m a l e s . T h u s , as the b r e e d i n g season comes to an e n d , b reed ing males probab ly i n c r e a s e t h e i r f i t n e s s by s w i t c h i n g from be ing t e r r i t o r i a l r e s i d e n t s to be ing t r a n s i e n t s . The Overwinter Per iod . : The on ly d i s t i n c t i o n which I was a b l e t c make between r e s i d e n t s on c o n t r o l a reas and mice moving around over t h i s season was tha t females which moved onto and o f f of the c o n t r o l a reas tended to be l i g h t e r than r e s i d e n t s . (There was a s l i g h t , but n o n - s i g n i f i c a n t , tendency f o r t h i s t c be t r u e f o r ma les , as w e l l . ) Eoth males and females which c o l o n i z e d the removal area d u r i n g the overw in te r p e r i o d were l i g h t e r than male and female r e s i d e n t s cn the c o n t r o l a reas ( F i g u r e s 13 and 14) . Over the w i n t e r , there was no i n d i c a t i o n t h a t males were moving around more than females were, or v i c e v e r s a , on the c o n t r o l a r e a s . The sex r a t i o on g r i d 4 o v e r w i n t e r was 51 males to 48 f e m a l e s , or 1.06. T h i s does not d i f f e r from 1 (X 2 =*091) , or from the sex r a t i o of r e s i d e n t , c c n t r c l mice (X*=.139) . As i n seasons 1 through 3, d u r i n g season 4 the removal g r i d seems to be s e l e c t i v e l y p i c k i n g up mice which are moving around i n u n d i s t u r b e d p o p u l a t i o n s . 84 Summary of Seasona l Treatment^ I can now at tempt to answer the t h r e e q u e s t i o n s wi th which I began t h i s s e a s c n - b y - s e a s c n compar ison c f g r i d 4 with the c o n t r o l a r e a s . In a l l s e a s o n s , mice which move onto the removal a rea appear to be the same k i n d s of mice which a re moving around on the c c n t r c l a r e a s , and they do tend to d i f f e r from r e s i d e n t s on the c c n t r c l a reas i n w e i g h t , sex r a t i o , and b r e e d i n g c o n d i t i o n . n i c e c o l o n i z i n g g r i d 4, and moving around on the c o n t r o l areas ( d i s p e r s e r s ) tend t o be l i g h t e r than r e s i d e n t s throughout the y e a r , and more males d i s p e r s e than f e m a l e s . However, the c h a r a c t e r i s t i c s of d i s p e r s e r s (Table 24) do show a s e a s o n a l v a r i a b i l i t y which complements the s e a s o n a l v a r i a t i o n i n the c h a r a c t e r i s t i c s of s u c c e s s f u l r e s i d e n t s . In p a r t i c u l a r , n o n - b r e e d i n g males tend t o d i s p e r s e d u r i n g the main b r e e d i n g s e a s o n , w h i l e b r e e d i n g males a r e the common a d u l t s d i s p e r s i n g d u r i n g the f a l l i n c r e a s e p e r i o d ; and more males d i s p e r s e d than females d u r i n g the th ree s e a s o n s i n which mice are b r e e d i n g , but the sexes d i s p e r s e with egua l f r e g u e n c y d u r i n g the n o n - b r e e d i n g , o v e r w i n t e r p e r i o d . O v e r a l l , the d e s c r i p t i o n of fej:omyscus p o p u l a t i o n d y n a m i c s , deve loped from my c o n t r o l d a t a , has been very w e l l s u p p o r t e d by the data from the c o n t i n u o u s removal g r i d . T h i s suppor t not o n l y g i v e s the ' c c n t r o l s t o r y * more c r e d i b i l i t y , but a l s o i n d i c a t e s t h a t the c o n t i n u o u s removal g r i d d o e s , i n f a c t , s e l e c t i v e l y sample d i s p e r s i n g i n d i v i d u a l s . T h i s l a t t e r assumpt ion w i l l become very impor tant i n my a n a l y s i s of the 8 5 g e n e t i c and b e h a v i o r a l r e s u l t s . £ § U § i i i of Mice on the Removal a r e a : I would l i k e to t u r n my a t t e n t i o n , f o r a w h i l e , from p r e d i c t i n g what t y p e s of mice w i l l d i s p e r s e , to p r e d i c t i n g how many w i l l d i s p e r s e . Is r e c r u i t m e n t to the removal a rea a c o n s t a n t f u n c t i o n of d e n s i t y of the c o n t r o l p o p u l a t i o n s ? F i g u r e 15 shows the numbers of mice which were caught on g r i d 4 , and the minimum number of mice known fo be a l i v e on the two c o n t r o l g r i d s , f o r the d u r a t i o n of the c o n t i n u o u s removal e x p e r i m e n t . as p r e d i c t e d , the s p r i n g r e o r g a n i z a t i o n i s a s s o c i a t e d with decreased d i s p e r s a l of females and r e l a t i v e l y h igh d i s p e r s a l of males. Other than tha t s p e c i f i c o b s e r v a t i o n , the p l o t s show, i n s p i t e of low sample s i z e s and h i g h v a r i a b i l i t y , a g e n e r a l tendency f o r removal g r i d d e n s i t i e s to show s i m i l a r s e a s o n a l t r e n d s to d e n s i t i e s on the c o n t r o l a r e a s . l o determine i f t h i s a s s o c i a t i o n d i d h o l d , and i f I c o u l d p r e d i c t removal g r i d d e n s i t i e s from c c n t r o l g r i d d e n s i t i e s , I r e g r e s s e d the numbers caught on g r i d 4 a g a i n s t the minimum numbers known to be a l i v e on each of the c c n t r o l g r i d s . The model which I used was: N4 = Constant + A (NC) where: N4= number caught on g r i d 4 i n week i , and NC = minimum number known to be a l i v e on one of the c c n t r o l a reas i n week i . 86 The r e s u l t s of these r e g r e s s i o n s f o r t o t a l m i c e , m a l e s , and f e m a l e s , can be seen i n T a b l e 25. A l l o f the r e g r e s s i o n s , except tha t of g r i d 1 f e m a l e s , are s i g n i f i c a n t , but none e x p l a i n more than 35$ of the observed v a r i a t i o n i n weekly c a t c h e s on g r i d 4. T h e r e f o r e , a l though the c a t c h e s cn the removal area are r e l a t e d t o the numbers of mice p resent i n the s u r r o u n d i n g p o p u l a t i o n s , i t i s c l e a r tha t e ther f a c t o r s are a l s o i n f l u e n c i n g these c a t c h e s . Myers and Krebs (1971) found tha t the r a t e c f d i s p e r s a l o f M i c r c t u s p e n n s j l v a n n i c u s was h i g h e s t d u r i n g the phase of p o p u l a t i o n i n c r e a s e on s u r r o u n d i n g a r e a s . Is d i s p e r s a l r e l a t e d to r a t e of i n c r e a s e i n Percmyjscus ? To answer t h i s q u e s t i o n , I c a l c u l a t e d the i n s t a n t a n e o u s r a t e of i n c r e a s e f o r every t r a p p i n g p e r i o d as f o l l o w s : r = [ In (N2/N) ]/2 where r - i n s t a n t a n e o u s r a t e of i n c r e a s e , N=minimum number a l i v e i n t r a p p i n g week T , N2=minimum number a l i v e two weeks l a t e r . Because of s m a l l weekly sample s i z e s , r was h i g h l y v a r i a b l e . To reduce t h i s v a r i a b i l i t y , I c a l c u l a t e d the t h r e e - p o i n t r u n n i n g average f o r r , so t h a t the weekly v a l u e s which I used i n my a n a l y s i s were a c t u a l l y the means of tha t week p l u s the p r e c e d i n g and f o l l o w i n g weeks. I began my a n a l y s i s of the i n f l u e n c e of * r ' on r e c r u i t m e n t to g r i d 4, by do ing a p a r t i a l c o r r e l a t i o n a n a l y s i s of r e c r u i t m e n t on g r i d 4 , d e n s i t i e s on the c o n t r c l a reas (weekly means over two g r i d s ) , and r a t e o f 87 i n c r e a s e on the c o n t r o l a r e a s . Ma les , females and t o t a l mice show a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n between numbers caught on g r i d 4 and d e n s i t i e s on the c o n t r o l a r e a s , when the e f f e c t o f r a t e of i n c r e a s e on the c o n t r o l a reas i s he ld c o n s t a n t ( raales:B=.52, P<.05 ; f e m a l e s : B = . 4 0 , P<.05; t o t a l s : B = . 5 7 , P< .05 ) . T h i s i s what I would have p r e d i c t e d from the above r e g r e s s i o n a n a l y s i s . However, when the e f f e c t o f d e n s i t y i s removed, the c o r r e l a t i o n between numbers on g r i d 4 and r a t e of i n c r e a s e on the c o n t r o l areas i s not s i g n i f i c a n t . T h i s i n d i c a t e s tha t the ra te of r e c r u i t m e n t onto the removal a r e a depends more on the c o n t r o l g r i d d e n s i t i e s than i t does on r a t e o f i n c r e a s e on the c c n t r c l a r e a s . However, t h e r e i s some p o s i t i v e r e l a t i o n s h i p between r e c r u i t m e n t on g r i d 4 and r a t e o f i n c r e a s e i n the c o n t r o l p o p u l a t i o n s , and add ing r a t e of i n c r e a s e to the r e g r e s s i o n model might i n c r e a s e our a b i l i t y to p r e d i c t r e c r u i t m e n t r a t e s onto g r i d 4. I used the f o l l o w i n g model t c t e s t t h i s : N4 = Constant+A (D)+E (r) where B = mean minimum number a l i v e cn the c c n t r c l g r i d s f o r the g iven week, and r = t h r e e - p o i n t runn ing average of r a t e of i n c r e a s e on the c o n t r o l g r i d s . Adding the - r a t e of i n c r e a s e to the r e g r e s s i o n s i g n i f i c a n t l y i n c r e a s e s the amount c f v a r i a b i l i t y accounted f o r by the model f o r a l l mice (F=6.05; df 1 ,37; P<.025) , but not f o r males or f e m a l e s c o n s i d e r e d a lone (males: F=1.51, P>.10; f e m a l e s : 88 F=3 .61 , P>.05) . Adding the r a t e of i n c r e a s e to the r e g r e s s i o n model dees s l i g h t l y i n c r e a s e our a b i l i t y t c p r e d i c t the numbers of mice c o l o n i z i n g g r i d 4, but d e n s i t i e s on the c o n t r o l areas are much b e t t e r p r e d i c t o r s of removal g r i d d e n s i t i e s than are r a t e s of i n c r e a s e on the c o n t r o l a r e a s . These r e s u l t s are i n g e n e r a l agreement with o b s e r v a t i o n s of M i c r o t i s t o w n s e n d i i c o l o n i z i n g vacant a reas (Krebs e t a l , . - , 1976) , but the maximum amount of v a r i a t i o n i n the number of r e c r u i t s to the removal area f o r which I am a b l e tc account i s o n l y 39$, whi le they were ab le to account f o r SU%. T h i s may merely r e f l e c t the d i f f e r e n c e s i n sample s i z e s and t e c h n i g u e s of a n a l y s i s between the two s t u d i e s , or i t may r e f l e c t r e a l d i f f e r e n c e s between the two s p e c i e s . In any c a s e , both s p e c i e s show the same g u a l i t a t i v e r e l a t i o n s h i p s between number of r e c r u i t s onto a vacant a r e a , d e n s i t y on c o n t r o l a r e a s , and r a t e o f i n c r e a s e cn c o n t r o l a r e a s . I have so f a r been t r y i n g to p r e d i c t the numbers of mice r e c r u i t i n g onto the c o n t i n u o u s removal a r e a . T h i s i s an a b s o l u t e measure o f r e c r u i t m e n t or d i s p e r s a l r a t e . Perhaps d e n s i t y and r a t e of p o p u l a t i o n change have a s t r o n g e r i n f l u e n c e cn the p r o p o r t i o n of mice d i s p e r s i n g than on the a c t u a l numbers. To examine t h i s h y p o t h e s i s , I c a l c u l a t e d a weekly r e c o v e r y r a t i o f o r g r i d 4 as f o l l o w s : BB=2 (C4) / (C1 + C3) where BB = r e c o v e r y r a t i o i n a g iven week C4= number of mice c a p t u r e d on g r i d 4 i n 89 a g i v e n week C1 = number of mice captured on g r i d 1 i n a g i v e n week C3 = number of mice cap tured on g r i d 3 i n a g i v e n week The r e c o v e r y r a t i o f o r a l l mice on g r i d 4 i s p o s i t i v e l y c o r r e l a t e d with ra te of i n c r e a s e on the c o n t r o l a r e a s , when the e f f e c t of c o n t r o l d e n s i t y i s h e l d c o n s t a n t <fi=.36, P< .05 ) . ahen the e f f e c t of r a t e of i n c r e a s e i s he ld c o n s t a n t , there remains a s l i g h t n e g a t i v e c o r r e l a t i o n between r e c o v e r y r a t i o and c o n t r o l d e n s i t y (B=- .13) . T h i s i s a very weak r e l a t i o n s h i p , but does i n d i c a t e tha t a s l i g h t l y lower p r o p o r t i o n c f an imals d i s p e r s e when the p o p u l a t i o n d e n s i t i e s a re h i g h , than when they are low. G iven t h a t t h e r e i s some c o r r e l a t i o n between r e c o v e r y r a t i o , r a te o f i n c r e a s e and d e n s i t y on the c o n t r o l a r e a s , can we p r e d i c t r e c o v e r y r a t i o us ing these two c o n t r o l parameters? I at tempted to do t h i s u s i n g the f o l l o w i n g model : BB =Constant+A (D) +B (r) where B B , B , a n d r are as d e f i n e d p r e v i o u s l y . The r e c o v e r y r a t i o of a l l mice and of females a lone can be p r e d i c t e d from c o n t r o l g r i d d e n s i t y and r a t e of i n c r e a s e (Table 27)> but the amount of v a r i a n c e i n r e c o v e r y r a t i o accounted f o r by these r e g r e s s i o n s i s very s m a l l (15.4% o v e r a l l , and 23.3% f o r f e m a l e s ) . As wi th the p r e c e d i n g d e n s i t y a n a l y s i s , my r e g r e s s i o n s 90 a c c o u n t f o r much l e s s of the observed v a r i a b i l i t y i n r e c c v e r y r a t i o than the M i c r o t u s r e g r e s s i o n s d i d . A g a i n , t h i s may merely be a f u n c t i o n of my s m a l l 'week ly sample s i z e s . However, d i s p e r s a l in Eeromjscus p o p u l a t i o n s may a l s o depend more on b e h a v i o r a l i n t e r a c t i o n s w i t h i n the p o p u l a t i o n s and l e s s d i r e c t l y on d e n s i t y and changes i n d e n s i t y , than does d i s p e r s a l i n the p o p u l a t i o n s of v o l e s moni tored by Krebs et a l . , ( 1 9 7 6 ) . T h i s h y p o t h e s i s i s suppor ted by the o b s e r v a t i o n t h a t , even though sample s i z e s on g r i d 4 are s m a l l e r f o r females than f o r m a l e s , more c f the observed v a r i a b i l i t y i n r e c o v e r y r a t i o o f females than c f males i s accounted f o r by d e n s i t y and r a t e of i n c r e a s e on the c o n t r o l a r e a s . . T h i s i n d i c a t e s t h a t male d i s p e r s a l may depend more cn f a c t o r s not d i r e c t l y r e l a t e d to d e n s i t y than does female d i s p e r s a l , and i s c o n s i s t e n t with my h y p o t h e s i s t h a t , dur ing seasons 1 and 2, d i s p e r s a l o f ma les , but not f e m a l e s , i s a f u n c t i o n c f a g g r e s s i v e i n t e r a c t i o n s . Another i n d i c a t i o n that b e h a v i o r a l i n t e r a c t i o n s may be more impor tan t i n d e t e r m i n i n g d i s p e r s a l i n P ejzomy sc us than i n M i c r o t u s i s t h a t r e c c v e r y r a t i o was p o s i t i v e l y c o r r e l a t e d - w i t h c o n t r o l d e n s i t y i n M i c r o t u s , but not i n Percmyscus . T h i s means t h a t , i n Peromyscus , a r e l a t i v e l y h i g h e r p r o p o r t i o n of an imals d i s p e r s e at low d e n s i t i e s than a t h igh d e n s i t i e s . T h i s i s aga in c o n s i s t e n t with the h y p o t h e s i s t h a t , d u r i n g the b r e e d i n g s e a s c n , when d e n s i t i e s are l o w , ' d i s p e r s a l t ends to be h igh due to b e h a v i o r a l i n t e r a c t i o n s . 91 SUMMARY AND DISCUSSION CF REMOVAL EXPERIMENTS: Beth the p u l s e d and the c o n t i n u o u s removal exper iments have i n d i c a t e d t h a t Pergm^scus which c o l o n i z e vacant a r e a s do d i f f e r from r e s i d e n t s i n u n d i s t u r b e d a r e a s , and f u r t h e r , tha t they tend to be the same t y p e s of mice which are moving i n t o and out c f these u n d i s t u r b e d p o p u l a t i o n s . The va lue of t h i s l a t t e r r e s u l t i s tha t i t shows tha t the removal exper iments a r e s e l e c t i v e l y sampl ing d i s p e r s i n g i n d i v i d u a l s - i n d i v i d u a l s which would have been moving around even i f the removal a rea were not p resent - r a t h e r than j u s t drawing former r e s i d e n t s from s u r r o u n d i n g a r e a s . T h i s has not been shown i n any p r e v i o u s s t u d i e s u s i n g t h i s removal t e c h n i g u e . The pu lsed removal exper iment demonstrated tha t an ima ls moving around i n u n d i s t u r b e d areas d u r i n g the s p r i n g r e o r g a n i z a t i o n , would q u i c k l y c o l o n i z e an area from which the r e s i d e n t s were removed. These an imals were mainly l i g h t -weight males which had presumably been unable t o secure t e r r i t o r i e s i n u n d i s t u r b e d a r e a s , but some l i g h t females which were r e c r u i t e d as w e l l . The p e r i o d of c o l o n i z a t i o n of the removal a rea l a s t e d o n l y about s i x weeks, a f t e r which t ime the removal p o p u l a t i o n c l o s e l y resembled the c o n t r o l p o p u l a t i o n s i n d e n s i t y , s u r v i v a l , r e c r u i t m e n t , sex r a t i o , s p a c i n g p a t t e r n s , and w e i g h t . The o n l y d i f f e r e n c e between the removal and c o n t r o l p o p u l a t i o n s was t h a t b r e e d i n g began l a t e r i n the removal p o p u l a t i o n , and a lower p r o p o r t i o n c f the p o p u l a t i o n tended t o be b r e e d i n g at any g i v e n t i m e . However, t h i s 92 l o w e r e d r e p r o d u c t i v e output on the removal a r e a d i d not r e s u l t i n a reduced d e n s i t y i n c r e a s e i n the f a l l , and I have s u g g e s t e d t h a t t h i s was due mainly t o r e c r u i t m e n t of j u v e n i l e s not born on the g r i d . I f t h i s i s t r u e , then th e r a p i d r e c r u i t m e n t of j u v e n i l e s which c h a r a c t e r i z e s the f a l l i n c r e a s e p e r i o d i n t h e s e p o p u l a t i o n s may s e r v e t o smooth out l o c a l d i f f e r e n c e s i n d e n s i t y and b r e e d i n g s u c c e s s . The r a p i d c o l o n i z a t i o n o f vacant a r e a s , p l a s t i c i t y of c o l o n i z i n g a n i m a l s ( a f t e r s i x weeks they c o u l d not be d i s t i n g u i s h e d from r e s i d e n t c o n t r o l i n d i v i d u a l s ) , and the smoothing of l o c a l d i f f e r e n c e s d u r i n g t h e f a l l i n c r e a s e , a l l combine t o make the p o p u l a t i o n very r e s i l i e n t t o l o c a l e x t i n c t i o n s . The c o n t i n u o u s removal experiment i s i n t e r e s t i n g f o r s e v e r a l r e a s o n s . I t showed t h a t mice c o l o n i z i n g vacant a r e a s a r e the same t y p e s of i n d i v i d u a l s which a r e moving around i n u n d i s t u r b e d a r e a s , throughout the year. F u r t h e r , d i s p e r s i n g mice d i f f e r from season to season, and the n a t u r e of t h e d i s p e r s i n g i n d i v i d u a l s appears t o be a f u n c t i o n c f what i s g o i n g on i n the c c n t r o l p o p u l a t i o n s . The r e l a t i v e and a b s o l u t e number of d i s p e r s e r s a l s o v a r i e s o v er the seasons. The f a i r l y weak r e l a t i o n s h i p s between t h e amount of d i s p e r s a l and d e n s i t i e s cn c o n t r o l areas i n d i c a t e t h a t the q u a n t i t y as w e l l as the g u a l i t y of d i s p e r s i n g i n d i v i d u a l s may be i n f l u e n c e d by i n t e r a c t i o n s w i t h i n u n d i s t u r b e d p o p u l a t i o n s . T h i s h y p o t h e s i s i s s u p p o r t e d by the o b s e r v a t i o n t h a t these c o r r e l a t i o n s are s t r o n g e r f o r f e m a l e s , which I have p o s t u l a t e d 93 a re not d i s p e r s i n g as a r e s u l t of b e h a v i o r a l i n t e r a c t i o n s , than f o r ma les , which a r e . M i c r o t u s which c o l o n i z e vacant a r e a s tend to be i n b r e e d i n g c o n d i t i o n a t a l i g h t e r weight than J J i c r o t u s i n c o n t r o l p o p u l a t i o n s (fSyers and K r e b s , 1971; Krebs et a l . . ^ 1976). T h i s e a r l y matura t ion i n d i s p e r s e r s i s p a r t i c u l a r l y marked i n f e m a l e s . I t has been i n t e r p r e t e d to mean e i t h e r tha t an ima ls which mature e a r l y tend to d i s p e r s e , or t h a t d i s p e r s i n g s u b a d u l t s come i n t o b r e e d i n g c o n d i t i o n on r e a c h i n g the vacant area (the i m p l i c a t i o n be ing tha t they were prevented from b r e e d i n g on c o n t r o l a r e a s by the presence of o t h e r v o l e s ) » I d i d not f i n d tha t d i s p e r s i n g i n d i v i d u a l s were b r e e d i n g a t l i g h t e r weights than c c n t r c l r e s i d e n t s . T h i s d i f f e r e n c e between v o l e s and Peromyscus may be a r e s u l t of the more s e a s o n a l na tu re of Isromyscus p o p u l a t i o n s , and of the r e s t r i c t i o n of j u v e n i l e s u r v i v a l d u r i n g the e a r l y b r e e d i n g s e a s c n . While v o l e s may sometimes breed a l l y e a r , deermice on the Endowment l a n d s have a n o n - b r e e d i n g season over the w i n t e r . A l l the mice p r e s e n t d u r i n g the e a r l y b r e e d i n g season a r e o v e r w i n t e r e d a n i m a l s , most of whom were r e c r u i t e d as j u v e n i l e s the p r e v i o u s f a l l . By the t ime a l a r g e c o h o r t of j u v e n i l e s en te r the p o p u l a t i o n , b r e e d i n g i s d e c l i n i n g , and these r e c r u i t s do net breed u n t i l the f o l l o w i n g s p r i n g . T h i s t i m i n g c f r e p r o d u c t i o n and j u v e n i l e r e c r u i t m e n t p r e c l u d e s adjustment of age at puber ty on the removal a r e a s . In v o l e s , where more than one c o h o r t or age c l a s s i s a v a i l a b l e t c be 94 r e c r u i t e d d u r i n g the b r e e d i n g s e a s o n , such d i f f e r e n c e s i n age a t puber ty c o u l d much more r e a d i l y a r i s e . Both Myers and Krebs (1971), and Krebs et a l . . (1976) , showed tha t a d u l t males d i s p e r s e d more than a d u l t f e m a l e s , and the s u b a d u l t females d i s p e r s e d more than s u b a d u l t ma les . My o b s e r v a t i o n s agree with t h e s e . S t i c k e l (1946) r e p o r t e d t h a t tw ice as many a d u l t male as a d u l t female Perom^scus l eucopus moved.onto a vacant a r e a , and Smith (1968) made s i m i l a r o b s e r v a t i o n s f o r P.. p c l i o n o t u s . S t i c k e l suggested t h a t t h i s excess c f a d u l t males among d i s p e r s e r s , which now seems to be g e n e r a l i z a b l e a c r o s s th ree s p e c i e s of Pergmyscus and two s p e c i e s c f flicrgtus ( c c h r c g a s t e r and t c j n s e n d i i ) , p r o b a b l y was a f u n c t i o n of males hav ing l a r g e r home ranges and a g r e a t e r ' t endency to wander*. However, my a n a l y s e s suggest t h a t t h i s skewed sex r a t i o i n d i s p e r s e r s i s the r e s u l t of d i f f e r e n c e s in p o p u l a t i o n p r o c e s s e s between the two s e x e s . Dur ing most of the t ime t h a t males are b r e e d i n g , t e r r i t o r i a l b e h a v i o r by b r e e d i n g males e x c l u d e s n o n - b r e e d i n g males from the p o p u l a t i o n , and sc c r e a t e s a c l a s s c f p o t e n t i a l d i s p e r s e r s . At the end of the b r e e d i n g s e a s o n , the b e h a v i o r o f b r e e d i n g males c h a n g e s , and they d i s p e r s e . The b r e e d i n g p o p u l a t i o n of f e m a l e s , on the o t h e r hand, i s not p r i m a r i l y l i m i t e d by t e r r i t o r i a l b e h a v i o r , but r a t h e r by m o r t a l i t y of females b r e e d i n g e a r l y i n the s p r i n g . G iven these d i f f e r e n c e s i n the mechanisms l i m i t i n g b r e e d i n g p o p u l a t i o n s of the two s e x e s , i t i s not s u r p r i s i n g t h a t more males than females 95 d i s p e r s e d u r i n g the b r e e d i n g s e a s o n s . T h i s e x p l a n a t i o n of the skewed sex r a t i o o f a d u l t d i s p e r s e r s i s suppor ted by the o b s e r v a t i o n t h a t , d u r i n g the n o n - b r e e d i n g s e a s o n , when the two sexes appear to be doing e s s e n t i a l l y the same t h i n g on the c o n t r o l a r e a s , the sex r a t i o cn the removal g r i d does not d i f f e r from 1. I f my r e s u l t s can be g e n e r a l i z e d to the o ther s p e c i e s in which a d u l t males d i s p e r s e more a d u l t f e m a l e s , than we shou ld look to d i f f e r e n c e s i n the r e g u l a t o r y mechanisms of the two s e x e s , r a t h e r than to d i f f e r e n c e s i n heme range s i z e and a c t i v i t y t c e x p l a i n the skewed sex r a t i o s i n these s p e c i e s , as w e l l . The mice which c o l o n i z e d my removal a r e a s , and which tended t c be moving around i n c o n t r o l p o p u l a t i o n s , tended t o be l i g h t e r than r e s i d e n t s on c o n t r o l a r e a s . Krebs et a l . . (1976) made s i m i l a r o b s e r v a t i o n s f o r d i s p e r s i n g M.. t o w n s e n d i i . and Myers and Krebs (1971) found t h i s to be t r u e f o r female M A o c h r o g a s t e r and MA j e n n s y l y a n n i c u s . I have no s a t i s f a c t o r y e x p l a n a t i o n f o r t h i s weight d i f f e r e n c e , but s u s p e c t tha t the s o u r c e may be both sex and seascn s p e c i f i c . F o r example , b i g g e r males c o u l d be more a g g r e s s i v e and b e t t e r a b l e to s e c u r e b r e e d i n g t e r r i t o r i e s , than l i g h t e r m a l e s . However, even i f t h i s was t r u e , we would s t i l l have t o propose another mechanism f o r females and f o r males over the w i n t e r . Perhaps the weight d i s t r i b u t i o n of a d u l t s at any g i v e n t ime r e f l e c t s r e l a t i v e food i n t a k e , and tha t l i g h t e r mice tend to form a h i g h e r p r o p o r t i o n of the d i s p e r s a l sample because they 9 6 a r e f o r a g i n g f u r t h e r to f i n d enough f o o d . However, t h i s r e l a t i o n s h i p between food i n t a k e , we igh t , and d i s p e r s a l i s l i k e l y to be c o m p l i c a t e d by i n t e r a c t i o n s between we igh t , n u t r i t i o n , a g g r e s s i o n , and b r e e d i n g , a l l of which may vary wi th sex and s e a s o n . In any c a s e , my data o f f e r no s a t i s f a c t o r y e x p l a n a t i o n f o r the o b s e r v a t i o n t h a t d i s p e r s i n g s m a l l mammals tend to be l i g h t e r than r e s i d e n t s . The r e s u l t s of both o f my removal exper iments have been c o n s i s t e n t wi th my d e t a i l e d o b s e r v a t i o n s on the c o n t r o l g r i d s , and have suppor ted the model of geromyscus p o p u l a t i o n dynamics which I deve loped from those r e s u l t s and from e a r l i e r s t u d i e s by o t h e r wor kers . In a d d i t i o n to t h i s , t h e s e exper iments have g i v e n me two major new i n s i g h t s i n t o the dynamics o f . t h e s e p o p u l a t i o n s . One of these i n s i g h t s i s t h a t the j u v e n i l e s which are born i n the main b r e e d i n g season do not appear to d i s p e r s e , and t h e r e f o r e probab ly are not s u r v i v i n g to p u b e r t y . These e a r l y born l i t t e r s are not j u s t sent o f f to be r e c r u i t e d e l s e w h e r e , they are t r u l y l o s t t o the p o p u l a t i o n . The s e l e c t i o n on both sexes to c o n t i n u e b r e e d i n g e a r l y i n the season must be very s t r o n g to overcome t h i s heavy m o r t a l i t y o f e a r l y - b o r n l i t t e r s . The second of these i n s i g h t s i s tha t the d i f f e r e n c e s between r e s i d e n t and d i s p e r s i n g i n d i v i d u a l s are t r a n s i t o r y , and these p o p u l a t i o n s are very r e s i l i e n t to l o c a l r e m o v a l s . The f a c t t h a t the i n i t i a l d i f f e r e n c e s between d i s p e r s e r s and r e s i d e n t s do not p e r s i s t , and t h a t the type of an imals 97 d i s p e r s i n g v a r i e s over t h e y e a r , throws doubt on the h y p o t h e s i s t h a t t h e r e i s a s p e c i f i c d i s p e r s i n g phenotype. My demographic d a t a , from the c o n t r o l and removal a r e a s , i n d i c a t e t h a t d i s p e r s a l i s a f u n c t i o n of p o p u l a t i o n d e n s i t y and r a t e of i n c r e a s e , and b e h a v i o r a l i n t e r a c t i o n s , and t h a t the d i s p e r s i n g i n d i v i d u a l s a r e p r o b a b l y ' e n v i r o n m e n t a l d i s p e r s e r s ' r a t h e r t h a n ' i n n a t e d i s p e r s e r s ' , as d e f i n e d by Howard (1960). 98 CHAPTER 5 GENETICS In a d d i t i o n to c o l l e c t i n g demographic d a t a , I monotored a l l e l i c f r e g u e n c i e s at t h r e e b l o o d p r o t e i n l o c i . These g e n e t i c data were used to l o c k at changes a s s o c i a t e d with the annual c y c l e i n f j r c m ^ s c u s p o p u l a t i o n s , and to determine i f d i s p e r s i n g i n d i v i d u a l s d i f f e r g e n e t i c a l l y from r e s i d e n t s i n u n d i s t u r b e d p o p u l a t i o n s . ELECIROFHORETTC METHODS: I looked at two p r o t e i n s which are found i n the b lood p l a s m a , t r a n s f e r r i n (Tf) and e s t e r a s e (Es ) . I assayed f o r t r a n s f e r r i n u s i n g the v e r t i c a l s t a r c h g e l e l e c t r o p h o r e s i s a p p a r a t u s , b u f f e r s and s t a i n d e s c r i b e d by B i r d s a l l (1972). B i r d s a l l d e s c r i b e d n ine a l l e l e s at t h i s l o c u s , but on ly two of these (J and M) o c c u r r e d i n my p o p u l a t i o n s . To assay f o r e s t e r a s e , I s l i c e d the g e l s which were run f o r t r a n s f e r r i n , and s t a i n e d the bottom s l i c e s u s i n g the s t a i n i n g procedure d e s c r i b e d by S e l a n d e r et a l (1971), i n c l u d i n g i n h i b i t i o n wi th e s e r i n e . T h i s l o c u s had two a l l e l e s , which I l a b e l l e d F and S , and a double banded h e t e r o z y g o t e (F igure 16) . I looked a t a t h i r d l o c u s , g lutamate o x a l a t e t r a n s a m i n a s e , from red b l e e d c e l l s , us ing the method of h o r i z o n t a l s t a r c h g e l e l e c t r o p h o r e s i s d e s c r i b e d by T s u y u k i et 99 a l . . ( 1 9 6 6 ) , w i t h t h e b u f f e r s y s t e m d e s c r i b e d b y S e l a n d e r e t a l . ( 1 9 7 1 ) , T h e g e l s w e r e s t a i n e d a t 37 C . i n a s o l u t i o n o f 5 3 2 mg 1 - a s p a r t i c a c i d , 50 mg p y r i d o x a l - 5 - p h o s p h a t e , 1 5 0 mg ° ( -k e t o g l u t a r i c a c i d , a n d 2 5 0 mg f a s t b l u e E B s a l t , i n 100 m l . o f 0.2-h t r i s - H C l (pH 8 . 0 ) . T h i s l o c u s h a s t w o a l l e l e s (E a n d S) , w i t h a t r i p l e - b a n d e d h e t e r c z y g e t e . T h e d a t a f r o m l a b o r a t o r y c r o s s e s i n d i c a t e d t h a t t h e a l l e l e s a t e a c h o f t h e s e l o c i w e r e i n h e r i t e d i n M e n d e l i a n f a s h i o n ( T a b l e s 28 t o 3 0 ) . T h e g e n o t y p e o f e a c h a n i m a l w a s e s t i m a t e d f r o m a l l e l e s f o u n d a t t h e s e t h r e e l o c i , g i v i n g 27 p o s s i b l e g e n o t y p e s i n t h e p o p u l a t i o n . H o w e v e r , s i n c e o n l y t h e 8 c o m b i n a t i o n s w h i c h l a c k e d a r a r e a l l e l e a t a n y o f t h e t h r e e l o c i o c c u r r e d w i t h a f r e g u e n c y o f o v e r 5 8 , I l u m p e d a l l o f t h e c o m b i n a t i o n s h a v i n g a r a r e a l l e l e i n t o o n e c l a s s . T h i s l e f t o n l y 9 g e n o t y p i c c l a s s e s f o r t h e a n a l y s i s ( T a b l e 3 1 ) . I a l s o l o o k e d a t t h e n u m b e r o f h e t e r o z y g o u s l o c i p e r m o u s e , s i n c e G a r t e n ( 1 9 7 4 ) h a s s u g g e s t e d t h a t t h e r e may b e s e m e r e l a t i o n s h i p b e t w e e n b e h a v i o r a n d p e r c e n t h e t e r o z y g o s i t y i n B e r o m y s c u s p o l i e n o t u s . R E S U L T S - C 0 U T E 0 I G E I E S : T h e s m a l l s a m p l e s i z e s a g a i n made i t n e c e s s a r y t o l u m p y e a r s a n d a r e a s i n t o s i n g l e s e a s o n a l s a m p l e s , B e f o r e d o i n g t h i s , I c o m p a r e d t h e f r e g u e n c i e s o f g e n o t y p e s 1 1 3 , 123 a n d .213 ( d e f i n e d i n T a b l e 31) a n d a l l t h e o t h e r s , b e t w e e n y e a r s a n d a r e a s , a n d f o u n d n o s i g n i f i c a n t d i f f e r e n c e s . 100 The f i r s t g u e s t i c n I asked was whether the g e n o t y p i c f r e g u e n c i e s v a r i e d with s e a s o n . I f s e l e c t i o n i s o c c u r r i n g d u r i n g a g iven s e a s o n , the d i s t r i b u t i o n of the genotypes a t the end of tha t season s h o u l d d i f f e r from t h a t a t the b e g i n n i n g , and we shou ld observe s e a s o n a l v a r i a b i l i t y i n genotype f r e g u e n c i e s . To make these c o m p a r i s o n s , I c o n s i d e r e d samples of a l l mice known to be a l i v e d u r i n g th ree p e r i o d s : f a l l peak, w i n t e r , and b r e e d i n g . The f a l l peak sample i n c l u d e d the th ree t r a p p i n g p e r i o d s immediate ly f o l l o w i n g - the c e s s a t i o n of female b r e e d i n g i n the f a l l , the w in ter sample i n c l u d e d the t h r e e t r a p p i n g p e r i o d s immedia te ly p r e c e d i n g the s t a r t of male b r e e d i n g i n the s p r i n g , and the b r e e d i n g sample i n c l u d e d a l l t r a p p i n g p e r i o d s from the peak i n male b r e e d i n g to the peak i n female b r e e d i n g . The d i s t r i b u t i o n s of genotypes w i t h i n these samples can be seen in F i g u r e 17. Fewer than 4 mice i n the w in ter sample had genotypes 212, 222, and 223, so I have pooled these th ree genotypes f o r the s t a t i s t i c a l c o m p a r i s o n s . Both sexes show s e a s o n a l v a r i a b i l i t y i n the d i s t r i b u t i o n s of the g e n o t y p e s , but t h i s v a r i a b i l i t y i s not s t a t i s t i c a l l y s i g n i f i c a n t f o r e i t h e r sex (males: xz=10.688, df 12, P>.50; f e m a l e s : X 2 =16 .399 , df 12, .20>P>.10). Females show more s e a s o n a l v a r i a b i l i t y than males d o , and the g r e a t e s t d i f f e r e n c e o c c u r s between the win ter and the b r e e d i n g s a m p l e s . Does the d i s t r i b u t i o n of genotypes d i f f e r between sexes? S i n c e the demography of males and females d i f f e r e d , I wondered 101 i f the d i s t r i b u t i o n s of genotypes would a l s o d i f f e r between the s e x e s . The sexes d i d not d i f f e r at the f a l l peak or winter s a m p l i n g s , but d id d i f f e r a t peak b r e e d i n g (X 2 =14 .?6 , df 6 , P<.025) . T h i s i s c o n s i s t e n t wi th both the o b s e r v a t i o n t h a t demographic c h a r a c t e r i s t i c s of the two sexes d i f f e r most markedly d u r i n g the e a r l y b r e e d i n g s e a s o n , and with the above o b s e r v a t i o n t h a t the g r e a t e s t s e a s o n a l change i n genotype f r e q u e n c i e s o c c u r s between the winter and b r e e d i n g s a m p l e s . Us ing the observed a l l e l e f r e q u e n c i e s at each l o c u s , I c a l c u l a t e d the expected g e n o t y p i c f r e g u e n c i e s f o r each sample p e r i o d . Tab le 32 shows the compar isons of observed and expected f r e g u e n c i e s . Only t h e sample o f females from the b r e e d i n g peak d i f f e r s s i g n i f i c a n t l y from e x p e c t e d : females he te rozygous a t o n l y one l o c u s (genotypes 123, 213, and 112) are more common than e x p e c t e d . In t h i s a n a l y s i s of genotype f r e g u e n c i e s , done a d m i t t e d l y w i th very s m a l l sample s i z e s , I have found ho e v i d e n c e f o r s e l e c t i o n over the year i n males. However, females shon more v a r i a b i l i t y i n genotype f r e g u e n c i e s over the y e a r , and the d i s t r i b u t i o n of genotypes i n females d u r i n g the peak o f b r e e d i n g d i f f e r s s i g n i f i c a n t l y from tha t of males and from expected v a l u e s . I w i l l suggest t h a t females h e t e r o z y g o u s at o n l y one l o c u s are s e l e c t e d f o r d u r i n g the e a r l y b r e e d i n g s e a s o n , when female m o r t a l i t y i s h i g h . T a b l e 33 shows the observed and expected numbers of mice h e t e r o z y g o u s at 0, 1, 2 and 3 l o c i , and the p r o p o r t i o n s of 102 mice i n each of these c l a s s e s can te seen i n Figure 18. As expected from the above r e s u l t s , females heterozygous at only one locus are more common, and homozygous females are l e s s common than expected i n the breeding sample. The d i s t r i b u t i o n of numbers of heterozygous l o c i a l s o d i f f e r s between the sexes i n t h i s sample (X 2=8.183, df 2, .05>P>.025), although no d i f f e r e n c e s were found i n the other samples. Neither sex showed s i g n i f i c a n t seasonal v a r i a t i o n (males:X 2=.396; females:X 2=6.750, df 6, p>.40), although females showed more v a r i a t i o n than males d i d . Neither the a n a l y s i s of genotypic freguencies nor the a n a l y s i s of proportion heterozygosity has i n d i c a t e d that male genotypes d i f f e r from expected on the b a s i s of random combinations of a l l e l e s , or that genotype freguencies i n males change over the year. I have no evidence to suggest that s e l e c t i o n i s a c t i n g en the observed genotypes i n males. However, both analyses have i n d i c a t e d that females are s t r o n g l y s e l e c t e d during the period preceding peak breeding. Females heterozygous at only one locus are favored at t h i s time, while homozygous females appear to be s e l e c t e d a g a i n s t . This s e l e c t i o n probably acts through the heavy m o r t a l i t y of earl y - b r e e d i n g females. To determine i f s u r v i v a l does, i n f a c t , depend on genotype, I constructed a r e g r e s s i o n model to p r e d i c t minimum 2-week s u r v i v a l from season and genotype. This i s the same model of s u r v i v a l described i n chapter 3, but with dummy 103 v a r i a b l e s added f o r genotype and g e n o t y p e - s e a s o n i n t e r a c t i o n s . As g e n o t y p e - s e a s o n i n t e r a c t i o n s were not s i g n i f i c a n t f o r e i t h e r sex (males F - . 9 8 9 , df 24, 7 6 , P>.25; females F=1 .201 , df 2 4 , 7 6 , P> .10 ) , the f o l l o w i n g a n a l y s i s c o n c e r n s the s i m p l e r model c o n t a i n i n g o n l y season and genotype v a r i a b l e s : S u r v i v a l ^ Constant+a (S2) +b (S3) +c (S4) +d (G1) +e (G2) +.. .+k (G8) where G1 i s genotype 113, G2 i s 123, e t c . I f i r s t t e s t e d the h y p o t h e s i s that genotype had no e f f e c t on s u r v i v a l by comparing the amount of v a r i a b i l i t y accounted f o r by the r e g r e s s i o n with and without the genotype terms. H h i l e add ing the genotype terms t c the r e g r e s s i o n d i d i n c r e a s e the amount c f v a r i a b i l i t y accounted f o r , t h i s i n c r e a s e was not s i g n i f i c a n t f o r females (F=1.446, df 32 ,76 , .10>P>.05) or f o r males (F=1.1313, df 3 2 , 7 6 , .25>P>.10) . I examined the e f f e c t of genotype on s u r v i v a l i n more d e t a i l by s o l v i n g the r e g r e s s i o n e q u a t i o n f o r s e a s o n s , wi th the g e n o t y p i c p r o p o r t i o n s he ld c o n s t a n t a t t h e i r mean v a l u e s . T h i s a n a l y s i s a s k s what the s u r v i v a l r a t e s would be i f g e n o t y p i c f r e g u e n c i e s d i d not vary over the y e a r . Ey comparing the s u r v i v a l r a t e s p r e d i c t e d here with those p r e d i c t e d i n the seasons on ly model from Chapter 3 , where g e n o t y p i c f r e g u e n c i e s were v a r y i n g , I can l o o k a t the e f f e c t o f genotype on s u r v i v a l . The s u r v i v a l r a t e s of males p r e d i c t e d when genotypes are h e l d c o n s t a n t , a re on ly s l i g h t l y lower than the seasons o n l y s u r v i v a l r a t e s (Table 34 ) . T h i s i n d i c a t e s , as e x p e c t e d , t h a t genotype has very l i t t l e e f f e c t 104 on male s u r v i v a l . Bcwever, female s u r v i v a l r a t e s , p r e d i c t e d when genotypes are he ld c o n s t a n t , a re much lower than the c o n t r o l r a t e s , except d u r i n g the f a l l i n c r e a s e p e r i o d . The d i f f e r e n c e between the two p r e d i c t e d r a t e s i s g r e a t e s t i n season 1, the s p r i n g r e o r g a n i z a t i o n , when female m o r t a l i t y i s h i g h e s t . T h i s r e s u l t s u p p o r t s the h y p o t h e s i s , deve loped a b o v e , tha t females are s t r o n g l y s e l e c t e d at the onse t of b r e e d i n g . The a n a l y s e s of g e n o t y p i c f r e g u e n c i e s and s u r v i v a l by genotype have i n d i c a t e d tha t s e l e c t i o n does occur i n females over the annua l c y c l e , and tha t t h i s s e l e c t i o n i s s t r o n g e s t d u r i n g the e a r l y b r e e d i n g s e a s o n , when there i s s e l e c t i v e m o r t a l i t y . However, I have no ev idence t h a t s e l e c t i o n i s o p e r a t i n g on the observed genotypes i n males . H e r e , as i n the demographic a n a l y s i s , I have found tha t males and females are do ing d i f f e r e n t t h i n g s . BESOITS-BEH0VAL EXPEfi2MENIS: T o t a l Sajrple Comparisons: , I s d i s p e r s a l s e l e c t i v e ? To answer t h i s g u e s t i c n , I began by compar ing the observed g e n o t y p i c f r e q u e n c i e s of a l l the r e s i d e n t s on the c c n t r o l g r i d s with those of an ima ls which d i s p e r s e d onto the c o n t i n u o u s removal g r i d , and with i n i t i a l c o l o n i s t s and subsequent r e s i d e n t s on the p u l s e d removal g r i d . A r e s i d e n t on the c o n t r o l g r i d s was any animal which remained 105 on the g r i d s f o r a t l e a s t f o u r weeks. Males which c o l o n i z e d the c o n t i n u o u s removal a rea d i f f e r e d s i g n i f i c a n t l y from c o n t r o l r e s i d e n t s , bcth i n o v e r a l l g e n o t y p i c d i s t r i b u t i o n (X 2 =23.480 , d f 8, .005>F>.001) , and i n number o f he te rozygous l o c i (X 2 =8.738 , df 3 , .05>P>.025). Males he terozygous a t o n l y one l o c u s , p a r t i c u l a r l y males of the genotypes 112 and 213, were more common on the removal g r i d than on the c o n t r o l a r e a s . (see F i g u r e s 19 and 20) . G r i d 4 females d i d not d i f f e r s i g n i f i c a n t l y from c o n t r o l r e s i d e n t s in e i t h e r o v e r a l l g e n o t y p i c d i s t r i b u t i o n (X 2 =5.901 , df 8) o r i n number of h e t e r o z y g o u s l o c i (X 2 =4.376, df 3 , .30>P>.20) . Owing to the s m a l l sample s i z e f o r g r i d 2 , I c o u l d not compare o v e r a l l g e n o t y p i c d i s t r i b u t i o n s between g r i d 2 and the c o n t r o l a r e a s . However, I d i d compare number of h e t e r o z y g o u s l o c i between the two a r e a s , and found no d i f f e r e n c e f o r males (X 2 =1.451 , df 3) o r f o r females (X 2 =4.338, d f 2, .20>P>.10). S e a s o n a l Comparisons.: The demographic a n a l y s i s i n d i c a t e d that d i f f e r e n t types of i n d i v i d u a l s may d i s p e r s e at d i f f e r e n t t imes c f y e a r . For example , b reed ing males tend to d i s p e r s e i n the f a l l i n c r e a s e p e r i o d , but not d u r i n g the main b r e e d i n g s e a s o n . T h e r e f o r e , i n a d d i t i o n to comparing the t o t a l samples o f d i s p e r s e r s and r e s i d e n t s , I made season by seascn c o m p a r i s o n s . To make these compar isons I used the samples d e s c r i b e d above f o r c o n t r o l a r e a s , s i m i l a r samples f o r the g r i d 2 p o p u l a t i o n , and a l l 106 r e c r u i t s to g r i d 4 from the end of one sampl ing p e r i o d to the end of the next ( t h i s i n c l u d e s a l l the an ima ls which c o u l d have s e t t l e d and e s t a b l i s h e d a r e s i d e n t p o p u l a t i o n b e f o r e and d u r i n g the g i v e n sample p e r i o d . ) I compared the s e a s o n a l samples o n l y with r e s p e c t to number of he te rozygous l o c i . I f mice d i s p e r s i n g d u r i n g the s p r i n g r e o r g a n i z a t i o n and e a r l y b r e e d i n g p e r i o d d i f f e r g e n e t i c a l l y from r e s i d e n t m i c e , these d i f f e r e n c e s shou ld be e v i d e n t i n the b reed ing peak s a m p l e s . T a b l e 35 shews the numbers and p r o p o r t i o n s of mice he te rozygous at 0 , 1 , 2 , and 3 l o c i , i n the g r i d 2, g r i d 4 and c o n t r o l peak b r e e d i n g samples . The t h r e e samples d i d not d i f f e r s i g n i f i c a n t l y f o r males (X*=3.986, df 6, P> .50 ) , but the female samples d i d d i f f e r from each o t h e r (X 2 =15.454, df 6, .025>P>.01). Females he te rozygous at on ly one l o c u s tended to be u n d e r - r e p r e s e n t e d i n both removal s a m p l e s . T h i s may i n d i c a t e t h a t the s e l e c t i o n which o c c u r s on the c o n t r o l a reas a t t h i s t i m e , f a v o r i n g s i n g l e h e t e r o z y g o t e s , i s not o c c u r r i n g on the removal a r e a s . The peak .. b reed ing compar isons are c o n s i s t e n t with the h y p o t h e s i s t h a t females on the c c n t r o l a r e a s are s e l e c t e d i n the s p r i n g , wh i le males are n o t . The males on g r i d 2 do not d i f f e r from c o n t r o l males at e i t h e r the f a l l peak sample (X2= 3 . 9 6 3 , df 2 , .20>P>.10) or the w in ter sample (X*= 1.602, df 2) (Table 3 5 ) . (The 2 and 3 c l a s s e s of h e t e r o z y g o t e s were pooled f o r these c o m p a r i s o n s . ) Females on g r i d 2 c o n t i n u e to d i f f e r from c o n t r o l f ema les at the f a l l peak (X2= 7 . 9 9 2 , df 2, .025>P>.01) and the w in ter 107 sample (X2=9. 352, df 2, P<.01) . a t both of these p e r i o d s t h e r e i s a d e f i c i e n c y of g r i d 2 f e m a l e s i n the 2 and 3 h e t e r o z y g c t e c l a s s e s -{Table 35). T h i s i s the same t r e n d which was e v i d e n t , but net s i g n i f i c a n t , i n males over these two sample p e r i o d s . S i n c e I was unable to d e t e c t any s e l e c t i o n i n males on the c o n t r o l a r e a s , i t i s not s u r p r i s i n g t h a t males cn g r i d 2 d i d not d i f f e r s i g n i f i c a n t l y from c o n t r o l m a l e s , e i t h e r when c o n s i d e r e d as one sample , or when c o n s i d e r e d season by s e a s o n . However, males which appeared on g r i d 2 i n the s p r i n g tended to show the o p p o s i t e r e l a t i o n s h i p to c o n t r o l males than females d i d (more s i n g l e h e t e r o z y g o t e s as opposed to l e s s ) . A f t e r the peak of b r e e d i n g , however , males and females showed the same r e l a t i o n s h i p to c o n t r o l m i c e , and the d i f f e r e n c e s ( s i g n i f i c a n t i n females) p e r s i s t e d th roughout the w i n t e r . T h i s i n d i c a t e s t h a t the l o c a l p o p u l a t i o n on g r i d 2 i s p robab ly composed mainly c f an imals born on the area and i s l e s s i n f l u e n c e d by exchange wi th the s u r r o u n d i n g a reas than the t r a n s i e n c e of demographic d i f f e r e n c e s might have i n d i c a t e d . F u r t h e r , the p e r s i s t e n c e of the g e n e t i c d i f f e r e n c e s i n the f a c e of l o s s c f demographic d i s t i n c t i o n s i n d i c a t e s t h a t the g e n o t y p e s , as measured, may have l i t t l e r e l e v e n c e to f i t n e s s . T h i s view i s suppor ted by the o b s e r v a t i o n t h a t , whi le males on g r i d 2 i n s p r i n g are h e a v i e r and l e s s o f t e n b r e e d i n g than c o n t r o l ma les , they do net d i f f e r g e n e t i c a l l y . The d i s t r i b u t i o n s o f genotypes on the c o n t i n u o u s removal 108 g r i d d i d not d i f f e r from the r e s i d e n t c o n t r o l d i s t r i b u t i o n at the f a l l peak sample (males:X 2=2.971,df 3; females:X 2=4.228, df 3, .30>P>.20), or the winter sample (males:X 2=.387, df 2; females:X 2=3.400, df 2) . D i s p e r s a l does not appear to be s e l e c t i v e a f t e r the peak of breeding. DISCUSSION: H h i l e the genotype sample s i z e s are s m a l l , and the above a n a l y s e s a d m i t t e d l y crude, they give some i n s i g h t i n t o g e n e t i c changes i n the p o p u l a t i o n s . S e l e c t i v e m o r t a l i t y occurs i n e a r l y - b r e e d i n g females, with females heterozygous at only one of the three l o c i being f a v o r e d . Females on removal areas do not breed e a r l y i n the s p r i n g (see chapter 4) and t h e r e f o r e do not experience t h i s s e l e c t i v e m o r t a l i t y . T h i s i s s u f f i c i e n t t o e x p l a i n the d i f f e r e n c e s i n genotype f r e g u e n c i e s between the two a r e a s : there i s no i n d i c a t i o n t h a t s e l e c t i v e d i s p e r s a l of females occurs over t h i s p e r i o d . I have no evidence f o r s e l e c t i v e m o r t a l i t y or d i s p e r s a l i n females over the ether seasons. Males do not undergo any p e r i o d of strong s e l e c t i o n , but there i s some i n d i c a t i o n t h at males of the genotypes 112 and 213 tend to be more common i n the d i s p e r s i n g than the r e s i d e n t samples throughout the period of male breeding. T h e r e f o r e , although the seasonal changes i n male demography do not appear t o be a s s o c i a t e d with s e l e c t i o n cn the c o n t r o l a r e a s , d i s p e r s a l may be s e l e c t i v e , with c e r t a i n genotypes being more l i k e l y t o d i s p e r s e at a l l times of the year. T h i s 109 o b s e r v a t i o n t h a t d i s p e r s a l i s s e l e c t i v e i n males but net i n f e m a l e s , agrees w i t h the demographic o b s e r v a t i o n s which i n d i c a t e d t h a t , d u r i n g t h e b r e e d i n g s e a s o n , t h e r e was a d i s c r e t e c l a s s of n o n - t e r r i t o r i a l , d i s p e r s i n g males, w h i l e t h i s was not t r u e f o r f e m a l e s . The a n a l y s i s of the p u l s e d removal e x p e r i m e n t has i n d i c a t e d t h a t , a l t h o u g h the c o l o n i z i n g p o p u l a t i o n s cannot be d i s t i n g u i s h e d d e m o g r a p h i c a l l y from the u n d i s t u r b e d p o p u l a t i o n s by the f a l l i n c r e a s e p e r i o d , t h e y remain g e n e t i c a l l y d i s t i n c t f o r a t l e a s t a y e a r . T h i s s u g g e s t s two t h i n g s . The f i r s t of thes e i s t h a t t h e f a l l and w i n t e r p o p u l a t i o n s on a g i v e n a r e a a r e p r o b a b l y the product o f b r e e d i n g on t h a t a r e a , and, t h e r e f o r e , t h a t t h e r e i s l e s s i n t e r m i x i n g c f l o c a l p o p u l a t i o n s than the demography would s u g g e s t . The second o f the s e i s t h a t , a l t h o u g h genotype may i n f l u e n c e d i s p e r s a l , s u r v i v a l , o r b r e e d i n g p o t e n t i a l , these a n i m a l s are so p h e n o t y p i c a l l y p l a s t i c t h a t p o p u l a t i o n s can be d e m o g r a p h i c a l l y i n d i s t i n g u i s h a b l e i n s p i t e of l a r g e d i f f e r e n c e s i n g e n o t y p i c c o m p o s i t i o n . Three p r e v i o u s s t u d i e s of genotype f r e g u e n c i e s i n n a t u r a l p o p u l a t i o n s o f Peromysjcus have found e v i d e n c e f o r s e l e c t i o n o c c u r r i n g over the annual c y c l e . Canham (1969) s t u d i e d a p o p u l a t i o n s of | z I S S i c u l a t u s i n a l b e r t a and t h e Nor t h West T e r r i t o r i e s . H i s p o p u l a t i o n s v a r i e d much more from year t o y e a r , i n d e n s i t y and s e a s o n a l t r e n d , than my p o p u l a t i o n s d i d , and he found t h a t the r e l a t i v e f i t n e s s e s o f genotypes v a r i e d 110 from year to y e a r . However, he d i d f i n d , as I d i d , t h a t s e l e c t i o n was sex s p e c i f i c , and , i n one year (1967) he noted t h a t females which were he terozygous at the t r a n s f e r r i n l o c u s were f a v o r e d over the winter and s p r i n g (from f a l l peak to j u v e n i l e r e c r u i t m e n t ) , whi le no such s e l e c t i o n o c c u r r e d i n males . T h i s agrees with my o b s e r v a t i o n t h a t I f f e m a l e s a re s e l e c t e d f o r d u r i n g the e a r l y b r e e d i n g s e a s o n . F u r t h e r , Canham f o u n d , when he c o n s i d e r e d a l l c f the y e a r s of h i s study and both of the marker l o c i ( t r a n s f e r r i n and a l b u m i n ) , tha t homozygotes tended to be f a v o r e d when s u r v i v a l was good and to be the l e a s t f i t when s u r v i v a l was p o o r . T h i s aga in agrees with my o b s e r v a t i o n t h a t females homozygous at th ree l o c i a re s e l e c t e d a g a i n s t i n the e a r l y s p r i n g , when s u r v i v a l i s poor . B i r d s a l l (1972) found ev idence f o r s e l e c t i o n at t h r e e l o c i over the annual c y c l e i n Fero jv .scus p o p u l a t i o n s near Edmonton, A l b e r t a . At two of these l o c i , the Pm b lood group and t r a n s f e r r i n , he found ev idence f o r s e l e c t i o n f a v o r i n g h e t e r o z y g o t e s d u r i n g the winter and e a r l y s p r i n g . Some c l e a r g e n e r a l i t i e s emerge from these two d e t a i l e d g e n e t i c s t u d i e s , and my crude g e n e t i c , but more d e t a i l e d demographic , a n a l y s e s . A l l t h r e e s t u d i e s have shown tha t Tf females are f a v o r e d over the winter and s p r i n g , and my a n a l y s i s i n d i c a t e s that t h i s s e l e c t i o n o c c u r s i n the e a r l y s p r i n g through m o r t a l i t y of b reed ing f e m a l e s . F u r t h e r , o f the f i v e o ther l o c i c o n s i d e r e d i n t h e s e s t u d i e s , f o u r showed s i m i l a r s e l e c t i o n a g a i n s t homozygctes over the w i n t e r and 111 s p r i n g (the t r e n d i s not c l e a r o n l y f o r the Ng l o c u s s t u d i e d by B i r d s a l l ) , and , when more than one l o c u s i s c o n s i d e r e d a t a t ime (Canham and t h i s s t u d y ) , the same t r e n d i s e v i d e n t : homozygous i n d i v i d u a l s , p a r t i c u l a r l y f e m a l e s , are s e l e c t e d a g a i n s t when s u r v i v a l i s poor . Gar ten (1974) l o o k e d at p r o p o r t i o n h e t e r o z y g o s i t y over 31 l o c i i n males of P* poJLiontus from the s o u t h e a s t e r n U.S.A. fie was a b l e to r e l a t e per cent h e t e r o z y g o s i t y to we igh t , b r e e d i n g c o n d i t i o n , and b e h a v i o r . Us ing t h i s r e s u l t , and i n f o r m a t i o n on the demography c f p o p u l a t i o n s of P x p o l i o n t u s gathered from o t h e r a u t h o r s , Gar ten developed a model of r e g u l a t i o n i n these p o p u l a t i o n s . P o p u l a t i o n s of P A p o l i o n t u s show the same s e a s o n a l p a t t e r n s of demography d e s c r i b e d i n my g e n e r a l model ° f JPercjxscus p o p u l a t i o n s (Smith 1971). G a r t e n ' s model p r e d i c t s t h a t h e t e r c z y g o t e s , which are mere a g g r e s s i v e than homozygotes , w i l l be s e l e c t e d f o r d u r i n g the s p r i n g ; whi le homozygotes w i l l be at an advantage i n the f a l l i n c r e a s e p e r i o d because of s e l e c t i v e d i s p e r s a l of h e t e r c z y g o t e s . I t i s impor tan t t c note that t h i s model i s based on a s s o c i a t i o n s between h e t e r o z y g o s i t y , weight and b e h a v i o r i n male mice observed i n the l a b o r a t o r y , not on o b s e r v a t i o n s of g e n e t i c changes i n w i l d p o p u l a t i o n s . These g e n e t i c changes ( s e l e c t i o n f o r h e t e r o z y g o s i t y when s u r v i v a l i s poor and p o p u l a t i o n s are d e c l i n i n g , and f o r homozygosi ty when s u r v i v a l i s good) have been observed i n w i ld p o p u l a t i o n s ( s t u d i e s by Canham and B i r d s a l l and t h i s s t u d y , as d i s c u s s e d a b o v e ) . However, t h i s 112 r e l a t i o n s h i p between s e l e c t i o n and p o p u l a t i o n t r e n d appears to be most obv ious f o r females i n f i e l d p o p u l a t i o n s , whi le G a r t e n ' s model c o n c e r n s r e l a t i o n s h i p s between b e h a v i o r and genotype which were observed o n l y i n m a l e s . F u r t h e r , both demographic and g e n e t i c ev idence i n d i c a t e t h a t female d e n s i t i e s are determined by d i f f e r e n t mechanisms than a r e male d e n s i t i e s . G a r t e n ' s model , based on ly on data from males , cannot be expected to e x p l a i n the r e l a t i o n s h i p s between genotype and demography i n f e m a l e s , and males i n f i e l d p o p u l a t i o n s tend not to show the s e a s o n a l changes i n g e n o t y p i c c o m p o s i t i o n which Gar ten p r e d i c t s . I c o n c l u d e tha t there i s l i t t l e ev idence from f i e l d s t u d i e s to s u p p o r t G a r t e n ' s model . The r e s u l t s c f my study as w e l l as those of Canham, B i r d s a l l and G a r t e n , i n d i c a t e a c o n s i d e r a b l e amount o f g e n e t i c v a r i a b i l i t y i n Peromyscus p o p u l a t i o n s . B i r d s a l l has s u g g e s t e d , t h a t the v a r i a b i l i t y which he found c o u l d have been main ta ined by a c o m b i n a t i o n of s e g r e g a t i o n d i s t o r t i o n and s e l e c t i o n , but my s tudy has suggested another mechanism. T h i s i s s e l e c t i o n f o r d i f f e r e n t genotypes i n males and f e m a l e s . F o r example , d u r i n g the s p r i n g females of the genotypes 112 and 213 are f a v o r e d i n c o n t r o l p o p u l a t i o n s , but males of these genotypes a r e s e l e c t i v e l y d i s p e r s i n g at t h i s t i m e , and so a re l e a v i n g the p o p u l a t i o n s . T h i s s e x - s p e c i f i c s e l e c t i o n s h o u l d reduce the p r o b a b i l i t y t h a t the genotypes f a v o r e d i n e i t h e r sex w i l l f i x i n the p o p u l a t i o n . A l s o , s i n c e these are autosomal l o c i which a s s o r t i n d e p e n d e n t l y of the sex chromosomes, the 113 s e l e c t e d genotypes w i l l not be f i x e d w i t h i n the s e x e s . S e x -s p e c i f i c s e l e c t i o n w i l l tend to main ta in v a r i a b i l i t y w i t h i n the p o p u l a t i o n and w i t h i n each s e x . In summary, my examinat ion of g e n o t y p i c f r e g u e n c i e s i n c o n t r o l and removal p o p u l a t i o n s i n d i c a t e s s e a s o n a l s e l e c t i o n i n females which o p e r a t e s through s e l e c t i v e m o r t a l i t y of e a r l y - b r e e d i n g f e m a l e s , and s e l e c t i v e d i s p e r s a l of ma les . The g e n e t i c c o m p o s i t i o n of the p o p u l a t i o n appears to i n t e r a c t with the demography, f o r both s e x e s , but the na ture of the i n t e r a c t i o n s i s s e x - s p e c i f i c . T h i s i s c o n s i s t e n t wi th the observed d i f f e r e n c e s between male and female demography (see C h a p t e r s 3 and 4 ) , and a l s o with the h y p o t h e s i s tha t g e n e t i c -feedback mechanisms are impor tan t i n d e t e r m i n i n g p o p u l a t i o n p r o c e s s e s i n Percmyscus . 114 CHAETEB 6 EEHAVIOB My a n a l y s i s of b e h a v i o r a l v a r i a b i l i t y i n v o l v e d the study o f t h r e e types of b e h a v i o r i n l a b o r a t o r y s i t u a t i o n s . I s t u d i e d a g o n i s t i c b e h a v i o r of male JPeroinyscus from these p o p u l a t i o n s by matching them with l a b o r a t o r y r a i s e d males i n a n e u t r a l a rena . The second t e s t used measured the tendency of an ima ls to l e a v e a" a f a m i l i a r a rea and t r a v e l through an u n f a m i l i a r a r e a , by a l l o w i n g them to d i s p e r s e through a maze. The t h i r d t e s t recorded the g e n e r a l a c t i v i t y of m i c e , i n a f a m i l i a r c a g e , over a 24 -hcur p e r i o d . These t h r e e t e s t s , t h e i r r e s u l t s and s i g n i f i c a n c e , w i l l be d i s c u s s e d i n the f o l l o w i n g pages . BEHAVIOB IN THE NEUTBAI A B E S A : The l a b o r a t o r y t e s t s of a g o n i s t i c b e h a v i o r were d e s i g n e d mainly to determine i f d i s p e r s i n g males (mice c o l o n i z i n g the removal areas) were l e s s a g g r e s s i v e than r e s i d e n t males on the c o n t r o l a r e a s . A male was d e f i n e d as a r e s i d e n t on the c o n t r o l a reas once he had been on the a re a f o r a t l e a s t 4 weeks, and I on ly t e s t e d a d u l t males . A l l a d u l t males c o l o n i z i n g the c o n t i n u o u s removal a rea were e l i g i b l e f o r t e s t i n g . The i n i t i a l c o l o n i s t s to the p u l s e d removal a re a were t e s t e d on f i r s t c a p t u r e , but a f t e r the f i r s t s i x weeks of c o l o n i z a t i o n , on ly r e s i d e n t s on t h i s area were t e s t e d . 115 Because b e h a v i o r i n these t e s t s i t u a t i o n s c o u l d be i n f l u e n c e d by p r e v i o u s e x p e r i e n c e i n the t e s t s , and h a n d l i n g d u r i n g b iweek ly t r a p p i n g , I attempted to t e s t each f i e l d mouse o n l y o n c e , and d u r i n g the f i r s t two months of h i s r e s i d e n c e on the g r i d . However, to i n c r e a s e my sample s i z e , I d i d o c c a s i o n a l l y r e t e s t a n i m a l s . Males became e l i g i b l e f o r r e t e s t i n g two months a f t e r the f i r s t t e s t . The t e s t s were conducted i n a box measuring 61 cm by 30.5 cm (2 f t by 1 f t ) , with a removable p a r t i t i o n d i v i d i n g i t i n t o two 30 .5 cm square a r e a s . The f r o n t of the box was a p l a t e of one-way g l a s s , and the t e s t area was i l l u m i n a t e d by a 60 watt red b u l b . The f l o o r of the box was covered with paper which was r e p l a c e d b e f o r e each t e s t . The f i e l d an ima ls were p a i r e d with l a b o r a t o r y males . These l a b o r a t o r y males had been s e p a r a t e d from t h e i r mothers and l i t t e r mates at three weeks of age , and p l a c e d i n a new cage wi th one o ther male , o f t e n a s i b l i n g . They remained wi th t h i s male u n t i l they weighed 15 g , at which t ime they were p l a c e d i n a cage with another a d u l t male ( n o n - s i b l i n g ) . T h i s a d u l t male p a i r was main ta ined u n t i l the mice reached one y e a r of a g e , as long as both mice remained a c t i v e , and weighed 14 .5 -23 .0 g . Each f i e l d male was t e s t e d with both members of a l a b o r a t o r y p a i r . When an e l i g i b l e f i e l d male was c a p t u r e d , he was brought i n t o the l a b . and p l a c e d a lone i n a cage with food (apple s l i c e s and P u r i n a Mouse Chow), water and b e d d i n g . That 116 e v e n i n g , between 7:00 and 11:00 , he was removed from t h a t cage and p l a c e d in one h a l f of the n e u t r a l a r e n a . One member c f a l a b o r a t o r y p a i r was p l a c e d i n the o t h e r h a l f . A f t e r t h r e e m i n u t e s , I removed the c e n t r a l p a r t i t i o n , and r e c o r d e d the subseguent i n t e r a c t i o n s of the two mice f o r ten minu tes . A f t e r the ten -minu te t e s t p e r i o d , the two mice were r e t u r n e d to t h e i r r e s p e c t i v e c a g e s , and the next e v e n i n g , the f i e l d mouse was t e s t e d with the o ther member of tha t l a b o r a t o r y p a i r . I r e t u r n e d the f i e l d mice to t h e i r p l a c e of c a p t u r e the morning f o l l o w i n g t h i s second t e s t . Dur ing the t e n - m i n u t e t e s t p e r i o d , I r e c o r d e d b e h a v i o r i n 14 c a t e g o r i e s (Table 36) . A b e h a v i o r was counted each t ime i t o c c u r r e d , and when b e h a v i o r s such as mounting and grooming c o n t i n u e d u n i n t e r r u p t e d , they were recorded as new e v e n t s every 5 s e c o n d s . The 14 b e h a v i o r s which appear i n t a b l e 36 a l l o c c u r r e d i n more than 10% of a l l mice t e s t e d . I r ecorded number c f f i g h t s , as w e l l , but on ly 33? of a l l mice t e s t e d f o u g h t , so I have not i n c l u d e d f i g h t i n g i n my a n a l y s i s . Most o f these b e h a v i o r s have been d e s c r i b e d by E i s e n b e r g (1962) and S a d l e i r (1970). S a p i d avo idance i n c l u d e s both avo idance l e a p , as d e s c r i b e d by S a d l e i r , and f l e e i n g from an opponent . Submiss ion i n c l u d e s S a d l e i r ' s s u b m i s s i o n and s u b m i s s i v e u p r i g h t s . An approach was r e c o r d e d only i f the t e s t mouse approached w i t h i n 5 cm o f the c o n t r o l mouse. The f i n a l s c o r e f o r each mouse c o n s i s t e d of the t o t a l number of t imes which he shewed a g iven b e h a v i o r i n the two, 10 minute e n c o u n t e r s . 117 I have d i v i d e d these 14 b e h a v i o r s i n t o a g o n i s t i c b e h a v i o r s , which c l e a r l y have an a g g r e s s i v e - s u b m i s s i v e component, and s o c i a l b e h a v i o r s , and have a n a l y z e d the f r e g u e n c i e s of the two types c f b e h a v i o r s s e p a r a t e l y . Because the da ta were r e c o r d e d as c o u n t s , which i n c l u d e d z e r o v a l u e s , I t rans formed the raw s c o r e s by f i r s t add ing 0.5 to the s c o r e , and then t a k i n g the sguare r o o t of t h i s va lue (Sokal and R o h l f , 1969) . I a n a l y z e d the t rans formed s c o r e s f o r a g o n i s t i c and s o c i a l b e h a v i o r s , us ing the method of f a c t o r a n a l y s i s (Ccoley and l o h n e s , 1962). The two t y p e s of b e h a v i o r s were s u b j e c t e d to s e p a r a t e f a c t o r a n a l y s e s , and the r e s u l t i n g f a c t o r s o l u t i o n s appear i n T a b l e s 37 and 38. These are s o l u t i o n s f o r a l l 217 mice which showed a g o n i s t i c or s o c i a l b e h a v i o r , and i n c l u d e a l l of the f a c t o r s with e i g e n v a l u e s g r e a t e r than 1. The f a c t o r s have been r o t a t e d by the varimax method. The a g o n i s t i c s o l u t i o n c o n s i s t s of two f a c t o r s , one h e a v i l y weighted f o r a g g r e s s i v e b e h a v i o r s , and the o ther f o r s u b m i s s i v e b e h a v i o r s , which t o g e t h e r account f o r 69.2% of the o r i g i n a l v a r i a n c e observed i n the raw s c o r e s . I w i l l r e f e r to t h e s e f a c t o r s as AF1 ( a g g r e s s i v e f a c t o r ) and AF2 (submiss ive f a c t o r ) . The s o l u t i o n f o r s o c i a l b e h a v i o r s c o n s i s t s of three f a c t o r s which account f o r 67.8% of t h e o r i g i n a l v a r i a n c e i n these b e h a v i o r s . The f i r s t s o c i a l f a c t o r (SF1) i s h e a v i l y weighted f o r grooming opponent , mounting opponent , n a s o - a n a l s n i f f i n g , f o l l o w i n g , and a p p r o a c h . These are p r i m a r i l y 118 b e h a v i o r s which i n d i c a t e s o c i a l dominance ( E i s e n b e r g , 1968). The second f a c t o r (SE2) i s h e a v i l y weighted f o r be ing groomed and be ing mounted, b e h a v i o r s which i n d i c a t e s o c i a l s u b o r d i n a t i o n . The t h i r d f a c t o r (SF3) , weighted f o r avo idance and u p r i g h t , i n d i c a t e s a n t i - s o c i a l or avo idance b e h a v i o r . I found tha t the d i s t r i b u t i o n s of s c o r e s were p o s i t i v e l y skewed. To c o r r e c t f o r t h i s , I t r ans formed the f a c t o r s c o r e s i n the f o l l o w i n g manner: Transformed score= ln (old sccre+minimum score) The minimum s c o r e was the lowest s c o r e o b t a i n e d over the e n t i r e sample . T h i s t r a n s f o r m a t i o n s a t i s f a c t o r i l y n o r m a l i z e d the d i s t r i b u t i o n s of s c o r e s on a l l of the f a c t o r s . S i n c e I had t e s t e d some of my an imals more than o n c e , in o rder t c i n c r e a s e my sample s i z e , the f i r s t s t e p i n my a n a l y s i s of the f a c t o r s c o r e s was t o determine i f the s c o r e s on the second t e s t s d i f f e r e d from those on f i r s t t e s t i n g . Twenty-one an ima ls had been t e s t e d more than o n c e . Only the t h i r d s o c i a l f a c t o r d i f f e r e d from f i r s t to second t e s t i n g : an ima ls tended to avo id the l a b o r a t o r y an imal l e s s on the second t e s t ( t=2.324, df 40, E K . 0 5 ) . I had r e t e s t e d a n i m a l s to i n c r e a s e my sample s i z e , and c c n s e g u e n t l y , r e t e s t s tended to be c l u s t e r e d main ly i n seasons 1 and 2, when p o p u l a t i o n d e n s i t i e s were low. To determine i f the d i f f e r e n c e i n s c o r e s on the t h i r d s o c i a l f a c t o r between f i r s t and second t e s t i n g s was an e f f e c t of s e a s c n , r a t h e r than r e t e s t i n g , I compared the f a c t o r s c o r e s c f r e t e s t an imals i n seasons 1 and 2, with 119 s c o r e s of an ima ls f i r s t t e s t e d i n these s e a s o n s . The mean f a c t o r s c o r e f o r r e t e s t an imals was - . 4 0 5 , whi le f o r f i r s t t e s t s i t was . 2 1 1 : r e t e s t e d an ima ls tend to a v o i d l a b o r a t o r y a n i m a l s l e s s than an ima ls t e s t e d f o r the f i r s t t ime d u r i n g the same season (t=1.906> df 49, .10>P>.05). Thus i t seems t h a t r e t e s t i n g does a f f e c t the s c o r e s on the t h i r d s o c i a l f a c t o r (SF3) , and r e t e s t s c o r e s w i l l be c o r r e c t e d by add ing the d i f f e r e n c e between the means to the r e t e s t s c o r e s , i n compar isons of s c o r e s on t h i s f a c t o r between g r i d s and s e a s o n s . However, r e t e s t i n g does not appear to a f f e c t the s c o r e s cn the o ther 4 f a c t o r s , and so r e t e s t s c o r e s need not be c o r r e c t e d i n compar isons of s c o r e s on these f a c t o r s . C o n t r o l J e s u i t s : The two c c n t r o l areas d i d not d i f f e r with r e s p e c t to s c o r e s on any of the f a c t o r s , and the r e m a i n i n g a n a l y s i s was done on the poo led data from both c o n t r o l a r e a s . Does the a g o n i s t i c and s o c i a l b e h a v i o r of males i n u n d i s t u r b e d p o p u l a t i o n s vary with weight and b r e e d i n g c o n d i t i o n ? He ight and b r e e d i n g c o n d i t i o n are not i n d e p e n d e n t : males which were s c r o t a l when t e s t e d tended to be h e a v i e r than n o n - b r e e d i n g males <F=17.181, df 1,103, P<.001) . The demographic a n a l y s i s sugges ts t h a t h e a v y , b r e e d i n g males may be more a g g r e s s i v e than l i g h t e r , n o n - b r e e d i n g males . To t e s t f o r t h i s , I d i d an a n a l y s i s of c o v a r i a n c e , r e g r e s s i n g f a c t o r s c o r e a g a i n s t weight f o r b r e e d i n g and n o n - b r e e d i n g ma les . The 120 mean s c o r e s of b reed ing and n c n - b r e e d i n g males d i d not d i f f e r on f a c t o r AF1 (the a g g r e s s i v e f a c t o r ) (Table 39 ) . The o v e r a l l c o r r e l a t i o n between f a c t o r s c o r e and weight was not s i g n i f i c a n t f o r the t o t a l sample (fl=,045, df 102) or f o r b r e e d i n g and n c n - b r e e d i n g males c o n s i d e r e d a l o n e . A g g r e s s i v e b e h a v i o r of c o n t r o l g r i d males cannot be p r e d i c t e d from b r e e d i n g c o n d i t i o n o r weight . B reed ing males tend to have a s l i g h t l y l cwer s c o r e on AF2 (the s u b m i s s i v e f a c t o r ) than do n o n - b r e e d i n g m a l e s , but t h i s i s not s i g n i f i c a n t (Table 39 ) . The score on t h i s f a c t o r i s n e g a t i v e l y c o r r e l a t e d with weight ( r= - .190 , P< .05) . The s l o p e o f the r e g r e s s i o n c f SF2 s c o r e cn weight i s s t e e p e r f o r b r e e d i n g males (-.15) than f o r n o n - b r e e d i n g males (-.02) (F=3.1€4, df 1 ,103, . 1C>F>.05). The i n t e r c e p t s do not d i f f e r (F=.490) . T h i s i n d i c a t e s t h a t s c o r e s on the s u b m i s s i v e f a c t o r tend t o decrease wi th i n c r e a s i n g w e i g h t , and tha t b r e e d i n g a n i m a l s tend to decrease s u b m i s s i v e b e h a v i o r with weight f a s t e r than n o n - b r e e d i n g males do . S ince the i n t e r c e p t s d i d not d i f f e r , a t low weights b reed ing c o n d i t i o n w i l l not a f f e c t s u b m i s s i v e s c o r e , whi le at h igh weights b r e e d i n g an imals w i l l be l e s s submiss ive than n o n - b r e e d i n g a n i m a l s . S c o r e s on the f i r s t s o c i a l f a c t o r ( s o c i a l dominance) and the t h i r d s o c i a l f a c t o r (avoidance behav ior ) show no s i g n i f i c a n t r e l a t i o n s h i p s to weight or b r e e d i n g c o n d i t i o n . However, b r e e d i n g males tend to s c o r e lower on the second s o c i a l f a c t o r ( s o c i a l s u b o r d i n a t i o n ) than n o n - b r e e d i n g males 121 do (Table 39 ) , and s c o r e on t h i s f a c t o r i s n e g a t i v e l y c o r r e l a t e d wi th weight (B=- .202, df 102, P<.025) . The r e g r e s s i o n s of SF2 s c o r e s on we ight , f o r b r e e d i n g and non-b r e e d i n g ma les , do net d i f f e r i n s l o p e (F=.054, df 1,100) or i n the Y i n t e r c e p t s (F=1.161, df 1 ,100) . T h i s i n d i c a t e s t h a t the observed d i f f e r e n c e between b reed ing and n o n - b r e e d i n g males i s p robab ly a f u n c t i o n of b r e e d i n g males be ing h e a v i e r than n o n - b r e e d i n g males . T h u s , t h i s c o v a r i a n c e a n a l y s i s s u g g e s t s tha t s o c i a l dominance i s c o r r e l a t e d p r i m a r i l y wi th we ight : l i g h t e r an imals tend to show more s u b o r d i n a t e b e h a v i o r than heavy an ima ls d o . The g e n e r a l c o n c l u s i o n from t h i s f a c t o r a n a l y s i s of a g o n i s t i c and s o c i a l b e h a v i o r i s t h a t s u b m i s s i v e and s u b o r d i n a t e b e h a v i o r appears to be n e g a t i v e l y r e l a t e d to we igh t , i n r e s i d e n t mice on c o n t r o l a r e a s . B r e e d i n g c o n d i t i o n does not appear to a f f e c t s u b o r d i n a t e b e h a v i o r i n d e p e n d e n t l y o f we ight , but s u b m i s s i o n i s a f f e c t e d by both b r e e d i n g c o n d i t i o n and weight . J e s u i t s from E x p e r i m e n t a l Areas,: Dc d i s p e r s i n g males show d i f f e r e n t b e h a v i o r i n the n e u t r a l arena than r e s i d e n t males on c o n t r o l a r e a s do? C o n t r o l g r i d r e s i d e n t s tended to show more a g g r e s s i v e b e h a v i o r (AF1) and s l i g h t l y more dominance b e h a v i o r (SF1) than c o l o n i s t s to g r i d 4 (Table 40 ) . I used m u l t i p l e - d i s c r i m i n a n t a n a l y s i s (Bao, 1952; Cooley and L c h n e s , 1962) to d i s c r i m i n a t e 122 between mice from the c o n t r o l and removal g r i d s . The c l a s s i f i c a t i o n f u n c t i o n s which used only the f a c t o r s AF1 and SF1 (Table 41) gave the best s o l u t i o n , and s u c c e s s f u l l y d i s c r i m i n a t e d between r e s i d e n t and c o l o n i z i n g males (F=3.14, df 2,168, P=.04). Males c o l o n i z i n g the continuous removal g r i d tended to show l e s s a g g r e s s i v e behavior ( a t t a c k s , chases and t h r e a t s ) and l e s s dominance behavior (grooming,mounting and f o l l o w i n g the l a b o r a t o r y mouse) i n the n e u t r a l arena t e s t than d i d males which are r e s i d e n t on c c n t r c l areas. I have now d e f i n e d two b e h a v i o r a l t y p e s : c o l o n i s t s which have low scores on AF1 and SF1, and r e s i d e n t s which have higher scores cn these f a c t o r s . I c l a s s i f i e d males on the pulsed removal area using the c l a s s i f i c a t i o n f u n c t i o n s d e r i v e d above. Males on g r i d 2 tended to resemble c o n t r o l males more than they d i d males c o l o n i z i n g the continuous removal area (58.7SS c l a s s i f i e d as c o n t r o l mice), and i n i t i a l c o l o n i s t s to g r i d 2 d i d not d i f f e r from l a t e r r e s i d e n t s i n t h i s r e s p e c t (P=.44 (Fisher exact test),n=46). Ififi.ye.2ce c f Genotypg cn Neutral Arena Scores,: To determine i f the a g o n i s t i c s cores were r e l a t e d to genotype, I c o n s t r u c t e d the f o l l o w i n g r e g r e s s i o n model to p r e d i c t f a c t o r scores from genotype, weight, and g r i d : F a c t o r score=Constant*A (Grid 1 + 3)+B (Grid 4)+C (Breeding) -+D (Height) + E (112)+F (113)+. . . . .+L (223) Where a l l v a r i a b l e s except weight are dummy v a r i a b l e s , t a k i n g 123 the v a l u e 1 when t r u e and 0 when f a l s e , and the numbers 112, 113, e t c . r e f e r t c genotypes as d e f i n e d i n T a b l e 31. T h i s model i s not a s u c c e s s f u l p r e d i c t o r of s c o r e on the f i r s t a g o n i s t i c f a c t o r (AF1) (F=1.076, df 12, 197, P>.25) . Models with on ly g r i d s (1=2.144, df 2 ,207 , .10<P<.25) , and with g r i d s p l u s b r e e d i n g c o n d i t i o n and weight (F= 1. 474, df 4 ,205 , ,25>P>.10) are b e t t e r p r e d i c t o r s o f AF1 s c o r e s than i s the g e n e r a l model , and a model with o n l y genotypes i s the p o o r e s t p r e d i c t o r o f a l l (F=.930, df 8 ,201 , P> .25) . Score on the a g g r e s s i v e f a c t o r does not appear to be r e l a t e d to g e n o t y p e . -Score on the second a g o n i s t i c f a c t o r (AF2) , the f a c t o r which i n d i c a t e s s u b m i s s i v e b e h a v i o r , can be s u c c e s s f u l l y p r e d i c t e d from t h i s g e n e r a l model ( F - 2 . 1 6 8 , df 12 ,197 , . 025>.P>. 01) . F u r t h e r , a model with o n l y genotypes i n c l u d e d s u c c e s s f u l l y p r e d i c t s the s c o r e cn t h i s f a c t o r (F=2.141, df 8,20 1, .025>P>.01) , and accounts f o r more o f the observed v a r i a n c e i n t h i s s c o r e than does a model i n c l u d i n g w e i g h t , b r e e d i n g c o n d i t i o n and g r i d , but not genotype (F=2.177, df 4 , 2 0 5 , .10>P>.05). Score on the f i r s t s o c i a l f a c t o r can a l s o be p r e d i c t e d from the g e n e r a l r e g r e s s i o n model i n c l u d i n g genotypes (F=2.392, df 12 ,197 , .01>P>.005). However, a model i n c l u d i n g o n l y genotypes i s an even b e t t e r p r e d i c t o r of s c o r e on SET than i s the g e n e r a l model (F=3.091, df 8 ,201 , .005>P>,Q0T). N e i t h e r the g e n e r a l model (F=1.551, df 12 ,197 , 124 .25>P>.10) , nor genotypes a lone (F=1.520, df 8 , 2 0 1 , .25>E>.10) , a c c o u n t s f o r a s i g n i f i c a n t p r o p o r t i o n of the observed v a r i a b i l i t y i n the s c o r e s on the second s o c i a l f a c t o r . S i m i l a r l y , the s c o r e s on f a c t o r SF3 cannot be p r e d i c t e d by the g e n e r a l model {F=.608, df 12,197) cr from genotypes a l o n e (F=.716, df 8 ,201 ) . The g e n e r a l model us ing a l l n ine genotypes i s a good p r e d i c t o r of s c o r e s cn f a c t o r s AF2 and SF1 . I s per cen t h e t e r o z y g o s i t y a l s o a good p r e d i c t o r of these s c o r e s ? To answer t h i s q u e s t i o n , I r e g r e s s e d f a c t o r s c o r e a g a i n s t b r e e d i n g c o n d i t i o n , we igh t , g r i d and number of he terozygous l o c i . T h i s model d i d not account f o r a s i g n i f i c a n t p r o p o r t i o n of the v a r i a b i l i t y i n s c o r e on f a c t o r AF1 (F=1.475, df 7 ,202 , . 25>P>.10), and the model i n c l u d i n g o n l y number of he te rozygous l c c i was a l s o not s i g n i f i c a n t ( F - 1 . 3 8 6 , df 3 ,206 , .25>E>.10) . T h u s , n e i t h e r the a c t u a l genotype , not per c e n t h e t e r o z y g o s i t y can p r e d i c t s c o r e s cn the f i r s t a g o n i s t i c f a c t o r . The r e g r e s s i o n s o l u t i o n f o r f a c t o r AF2 s u c c e s s f u l l y p r e d i c t s the f a c t o r score (F=2.047, df 7 ,202 , .05>P>.025) , but number of he te rozygous l o c i a lone cannot p r e d i c t f a c t o r s c o r e (F=2.048, df 3 ,206 , .25>P>.10). The g e n e r a l r e g r e s s i o n models p r e d i c t i n g s c o r e s on the t h r e e s o c i a l f a c t o r s from breed ing c o n d i t i o n , we igh t , g r i d and number o f he te rozygous l o c i , do not account f o r a s i g n i f i c a n t 125 p r o p o r t i o n c f the observed v a r i a b i l i t y i n these s c o r e s . However, the s o l u t i o n us ing on ly number of h e t e r o z y g o u s l o c i does s u c c e s s f u l l y p r e d i c t the s c o r e s on S.F1 (F=2.782, df 3 ,206 , ,05>P>,025) . Summary of N e u t r a l Arena E e s u l t s j , T a b l e 42 summarizes the r e s u l t s of the a n a l y s i s of n e u t r a l arena s c o r e s . Breed ing males tend to be l e s s s u b m i s s i v e and s u b o r d i n a t e than n c n - b r e e d i n g males . S i m i l a r l y , s u b m i s s i v e and s u b o r d i n a t e b e h a v i o r appear to be n e g a t i v e l y c o r r e l a t e d with we ight . Ha les c o l o n i z i n g the c o n t i n u o u s removal g r i d are l e s s a g g r e s s i v e than r e s i d e n t s on c o n t r o l a r e a s . T h i s r e s u l t i s c o n s i s t e n t with the demographic a n a l y s i s which i n d i c a t e d that removal mice were l i g h t e r and l e s s o f t e n i n b r e e d i n g c o n d i t i o n than r e s i d e n t s on the c o n t r o l a r e a s . The s c o r e s on the s u b m i s s i v e and s o c i a l dominance f a c t o r s (AF2 and SF1) v a r i e d with genotype . BEHAVICE IN THE BISEEBSAL MAZE: To measure the tendency c f mice to l eave a f a m i l i a r a rea and e x p l o r e an u n f a m i l i a r one , I des igned the h o r i z o n t a l maze which i s d e p i c t e d i n F i g u r e 21. T h i s appara tus c o n s i s t s of two i d e n t i c a l c a g e s , each measuring 15 cm s g u a r e , connec ted by a t u n n e l with 15 p a r t i a l l y s e p a r a t e d chambers , each 7.6 cm (3 inches ) l o n g . One of the c a g e s , c a l l e d the home c a g e , c o u l d be detached from the maze. A d u l t mice from the f i e l d were 126 p l a c e d s i n g l y i n these d e t a c h a b l e cages f o r 6 fo 8 hours ( u n t i l the e v e n i n g , t e s t p e r i o d ) , and then the cages » e r e p l a c e d , with minimal d i s t u r b a n c e , cn the end of a d i s p e r s a l maze. These home cages c o n t a i n e d apple s l i c e s , P u r i n a House Chow, water amd b e d d i n g . The appara tus was l e f t u n d i s t u r b e d f o r 10 minu tes , and then the door to the maze t u n n e l was l i f t e d and the mouse l e f t a lone f o r one hour . At the end o f the hour t e s t p e r i o d the mouse was removed from the maze and the maze was c l e a n e d i n p r e p a r a t i o n f o r the next s u b j e c t . T i p f l o o r s i n the f i r s t and l a s t s e c t i o n s of the maze t r i p p e d m i c r o s w i t c h e s which were connected t c an E s t e r l i n e Angus event r e c o r d e r (model s -6 20) . These enab led me to determine when and how o f t e n the mouse i n the maze en te red and l e f t the two cages (home cage and s t range c a g e ) . The bottom of the maze t u n n e l was covered with white paper and two ink pads were p l a c e d i n the t u n n e l , one i n f r o n t of the home c a g e , and one h a l f way down the t u n n e l . The t r a c k s which the mouse l e f t on the p a p e r , a f t e r walk ing on the i n k p a d s , enab led me to determine how f a r down the maze t u n n e l i t had t r a v e l l e d . A l l o f the t e s t s were conducted from 7:00 p.m. t c 11:30 p . m . , i n d a r k n e s s . For each t e s t , I r e c o r d e d the l a t e n c y of the mouse to l e a v e the home cage ( L I B ) , i t s l a t e n c y to en te r the s t r a n g e cage (LES), the amount of t ime the mouse spent i n the home cage (THCH), the amount of t ime i t spent i n the s t r a n g e cage (TSTBUG), and the number of s e c t i o n s of the maze t u n n e l which i t en te red (NSECT). 127 A d u l t s of both sexes were t e s t e d i n t h i s a p p a r a t u s . I d i d not t e s t females which were l a c t a t i n g or o b v i o u s l y p r e g n a n t , because I d i d not want to i n c r e a s e l i t t e r m o r t a l i t y by removing these f e i a l e s from the f i e l d . I t e s t e d a l l o ther r e s i d e n t a d u l t s from the c c n t r o l g r i d s , new c o l o n i s t s on the removal g r i d s , and r e s i d e n t s cn the p u l s e d removal g r i d . S i n c e the t e s t was dependent on the an imals e n t e r i n g a s t r a n g e a r e a , each animal was t e s t e d on ly o n c e . D i s p e r s a l Maze J e s u i t s . : A l l of the measurements were e s s e n t i a l l y p r o p o r t i o n s , i n t h a t they were measurements with f i x e d upper bounds which were f r e q u e n t l y r e a c h e d . The d i s t r i b u t i o n s of these parameters over a l l 303 a n i m a l s t e s t e d tended t o be s t r o n g l y U c r J s h a p e d , and c o u l d not be s u c c e s s f u l l y n o r m a l i z e d with a r c s i n e , l o g a r i t h m i c or e x p o n e n t i a l t r a n s f o r m a t i o n s . T h e r e f o r e , I d e c i d e d to a n a l y z e the r e s u l t s of t h i s t e s t u s i n g n o n -p a r a m e t r i c s t a t i s t i c s . Because the males and females behaved d i f f e r e n t l y i n the maze (Table 4 3 ) , I ana lyzed the sexes s e p a r a t e l y . I compared the maze b e h a v i o r c f b r e e d i n g mice with tha t of n o n - b r e e d i n g m i c e , c o n s i d e r i n g o n l y r e s i d e n t s from the c o n t r o l a r e a s . Breed ing mice c f both sexes d i s p e r s e d through the maze more r a p i d l y (had lower 11H,LES and THOM ) than non-b r e e d i n g mice (Table 44) , and b r e e d i n g females a l s o spent more t ime i n the s t r a n g e c a g e , and e n t e r e d more t u n n e l s e c t i o n s 128 than d i d n o n - b r e e d i n g f e m a l e s . To determine i f maze b e h a v i o r was r e l a t e d to we igh t , I c a l c u l a t e d K e n d a l l Bank C o r r e l a t i o n C o e f f i c i e n t s f o r weight and each of the f i v e d i s p e r s a l p a r a m e t e r s , f o r c o n t r o l g r i d mice o n l y . None of these c o r r e l a t i o n s was s i g n i f i c a n t ( p r o b a b i l i t y a lways g r e a t e r than .20): d i s p e r s a l through my maze appears to be independent o f w e i g h t . The above a n a l y s e s have concerned on ly r e s i d e n t mice cn the c o n t r o l a r e a s , but I was most i n t e r e s t e d i n whether c o l o n i z i n g mice behaved d i f f e r e n t l y i n the maze than r e s i d e n t mice d i d . S i n c e maze s c o r e s v a r i e d with b r e e d i n g c o n d i t i o n , I a n a l y z e d b r e e d i n g and n c n - b r e e d i n g mice s e p a r a t e l y . These compar isons appear i n Table 45. B r e e d i n g , r e s i d e n t males tend t o have lower s c o r e s cn the f i r s t t h r e e parameters and h i g h e r s c o r e s on the second two than do b r e e d i n g c o l o n i s t s , but none o f t h e s e d i f f e r e n c e s i s s t a t i s t i c a l l y s i g n i f i c a n t . There i s no c l e a r o v e r a l l t rend i n n o n - b r e e d i n g males . B r e e d i n g r e s i d e n t females d i s p e r s e more r a p i d l y i n the maze than do b r e e d i n g c o l o n i s t s . However, the t r e n d i s not c l e a r f o r n o n -b r e e d i n g f e m a l e s . These r e s u l t s i n d i c a t e tha t b r e e d i n g r e s i d e n t a n i m a l s tend to move more i n the maze than dc b r e e d i n g an ima ls on the c o n t i n u o u s and p u l s e d removal a r e a s . However, d i f f e r e n c e s between g r i d s are not c l e a r f o r n c n - b r e e d i n g mice . I f movement through my maze were ana lagous to d i s p e r s a l i n the f i e l d , I would have expected c o l o n i s t s to the 129 continuous removal area to show the most d i s p e r s a l i n the maze. However, the mice from the removal g r i d tended to move l e s s i n the maze than c o n t r c l mice d i d . S e v e r a l f a c t o r s other than d i s p e r s a l tendency i n the wi l d may be a f f e c t i n g performance i n t h i s maze s i t u a t i o n . The t e s t was designed to measure the w i l l i n g n e s s of a mouse to leave an area with which i t was f a m i l i a r and enter a strange area. Although no ether mice are present t o d i r e c t l y i n f l u e n c e t h i s c h o i c e , i t may be a f f e c t e d by the s o c i a l p o s i t i o n of the mouse i n the f i e l d , A bre e d i n g , r e s i d e n t mouse, probably a g g r e s s i v e and s o c i a l l y dominant, might be expected t o be more c o n f i d e n t i n a strange s i t u a t i o n than would a s o c i a l l y subordinate mouse. Po s s e s s i o n of a home range may a l s o i n f l u e n c e behavior i n the maze i n another way: mice with e s t a b l i s h e d home ranges i n the f i e l d may a c t u a l l y be attempting to home when r e l e a s e d i n t o the maze. These e f f e c t s would tend to r e s u l t i n breeding r e s i d e n t mice d i s p e r s i n g more i n the maze than d i d non-residents and non-breeding mice. Residency on a t r a p p i n g g r i d c ould a l s o be i n f l u e n c i n g d i s p e r s a l score i n a more d i r e c t way: mice which are used to being handled i n the course of being trapped may be l e s s f r i g h t e n e d i n t h i s new, man-made s i t u a t i o n than are mice captured f o r the f i r s t time. Two o b s e r v a t i o n s l e a d me t o b e l i e v e t h at t h i s i s not a good e x p l a n a t i o n f o r the observed r e s u l t s . F i r s t , mice from the pulsed removal area, which are almost a l l r e s i d e n t s , do not c o n s i s t e n t l y d i s p e r s e more i n the maze than do g r i d 4 mice, and, f o r breeding mice, at l e a s t , 130 tend to disperse less than residents on control areas. Second, non-breeding males which colonize grid 4 do not shew less dispersal than ncn-breeding residents do, and, i n f a c t , tend to leave the home cage sooner than residents dc. I think that the observed differences i n maze behavior between breeding and non-breeding residents, and between residents and c o l o n i s t s , probably r e f l e c t differences in the confidence of the mice i n an unfamiliar s e t t i n g , with dominant mice being more confident, and may also r e f l e c t some tendency for t e r r i t o r i a l mice to exhibit homing behavior when released into the maze. Influence cf Genotype on Behavior i n the Dispersal Maze:, Because the variables from the maze test could net be successfully normalized, I was unable to construct regression models to predict behavior from genotype, as I did f o r agonistic behavior. To determine i f genotype influenced behavior, I had to ask whether the mean scores on the f i v e dispersal variables varied over the genotypes. I asked t h i s guestion using a Kruskal-Hallis analysis of variance for the 9 genotypic classes, and for number of heterozygous l o c i . This analysis indicated no s i g n i f i c a n t behavioral v a r i a b i l i t y among genotypes. Summary, cf Dispersal Maze Sesultsj, 131 I examined the behav io r o f 158 r e s i d e n t , a d u l t mice i n the d i s p e r s a l a p p a r a t u s . Females tended to d i s p e r s e more than males d i d , and b r e e d i n g mice of both sexes tended to d i s p e r s e more than n o n - b r e e d i n g mice d i d . D i f f e r e n c e s between r e s i d e n t and c o l o n i z i n g mice were s l i g h t , b u t , w i t h i n the sample of b r e e d i n g mice (n=73), male and female r e s i d e n t s tended to d i s p e r s e more i n the maze than d i d c o l o n i s t s on the removal a r e a s . No r e l a t i o n s h i p was found between genotype and d i s p e r s a l i n the maze. GENERAL ACTIVITY: To measure the g e n e r a l a c t i v i t y cf f i e l d - c a u g h t a n i m a l s , I used two s e l e c t i v e A c t i v i t y Meters (Columbus I n s t r u m e n t s , model S ) . These i n s t r u m e n t s have s i x e l e c t r o m a g n e t i c p r o x i m i t y s e n s o r s which d e t e c t the movements of mice p l a c e d i n p l a s t i c cages on tcp o f the machines . Automat ic d i g i t a l c o u n t e r s r e c o r d these movements. A d u l t males and fema les from my f i e l d g r i d s ( r e s i d e n t s from c o n t r o l g r i d s , c o l o n i z e r s and r e s i d e n t s from g r i d 2, and c o l o n i z e r s from g r i d 4 ) , were p l a c e d s i n g l y i n l a r g e p l a s t i c cages (46 x 35 x 16 cm). These cages c o n t a i n e d a pad of c o t t o n , app le s l i c e s , P u r i n a mouse chow, and water. No bedding was p l a c e d on the bottom of the c a g e s , as t h a t would have i n t e r f e r e d wi th the e l e c t r o n i c s e n s i n g . The mice were l e f t i n the cages f c r 8 to 12 h o u r s , and then the cages were p laced on the a c t i v i t y m e t e r s . A f t e r an ad justment p e r i o d of ten minu tes , a c t i v i t y was recorded f o r 132 e x a c t l y 24 h o u r s . The e n t i r e a c t i v i t y t e s t was done i n comple te d a r k n e s s . Because these mice have a s t r o n g c i r c a d i a n a c t i v i t y rhythm ( F a l l s , 1968), i t was impor tan t to r e c o r d t o t a l a c t i v i t y over 24 h o u r s . The s c o r e s of the 218 mice t e s t e d were n o r m a l i z e d with a l o g t r a n s f o r m a t i o n . R e s u l t s c f A c t i v i t y Tests . : S i n c e some mice were t e s t e d more than o n c e , I t e s t e d f o r d i f f e r e n c e s between t r i a l s , The mean f o r the 9 r e t e s t s was 8 .543 , and f o r the 209 f i r s t t e s t s was 8 .603 . These means were not s i g n i f i c a n t l y d i f f e r e n t (F=.152, df 1 ,216, P> .50 ) , sc r e t e s t s were pooled with f i r s t t e s t s i n the f o l l o w i n g a n a l y s e s . I next t e s t e d f o r d i f f e r e n c e s between the s e x e s . The mean s c o r e f o r males was 8.570 (N=137), and f o r f e m a l e s was 8.652 (8=81). These means d i d not d i f f e r s i g n i f i c a n t l y (F=1.660, df 1 ,216, ,25>P>.10) . However, a l t h o u g h males d i d not d i f f e r f rom females o v e r a l l , I f e l t tha t the r e l a t i o n s h i p s between g r i d s and between b r e e d i n g and n o n - b r e e d i n g mice might be s e x - s p e c i f i c , so I c o n t i n u e d my a n a l y s e s on the sexes s e p a r a t e l y . I s h o u l d note here t h a t , wh i l e females moved more i n my maze than males d i d , they d i d not show a h i g h e r l e v e l of g e n e r a l a c t i v i t y . T h i s i n d i c a t e s t h a t the maze t e s t i s not merely measuring g e n e r a l a c t i v i t y . I compared mean a c t i v i t y s c o r e s of b r e e d i n g and non-1 3 3 b r e e d i n g m i c e , and found t h a t g e n e r a l a c t i v i t y d i d not vary wi th b r e e d i n g c o n d i t i o n . T h i s was t r u e f o r f o r both males (F=.605, df 1 ,58, P> .25 ) , and females (F=1.365, df 1 ,36 , P> .10 ) . T h i s aga in i s a d i f f e r e n t r e s u l t than i n the a n a l y s i s o f maze b e h a v i o r : b r e e d i n g mice move more i n the maze, but a re not more a c t i v e . Nex t , I r e g r e s s e d a c t i v i t y s c o r e s on we igh t . There was a s l i g h t p o s i t i v e r e l a t i o n s h i p between a c t i v i t y and weight f o r males but the r e g r e s s i o n was not s i g n i f i c a n t (F=3.061, df 1 ,57 , .10>P>.05). The c o r r e l a t i o n was even weaker f o r females (F=. 269, df 1 ,36, P>.25) . a c t i v i t y does not appear t c va ry with w e i g h t , f c r e i t h e r s e x . F i n a l l y , I compared a c t i v i t y s c o r e s o f mice from the c o n t r o l , c o n t i n u o u s removal , and pu lsed removal g r i d s (Table 46 ) . Both sexes showed a tendency f o r c o n t r o l r e s i d e n t mice t o be l e s s a c t i v e than c o l o n i s t s to the c o n t i n u o u s removal a r e a , and mice from the p u l s e d removal a rea appear to be the l e a s t a c t i v e . The d i f f e r e n c e between mice on c o n t r o l a reas and the pu lsed removal area was not s i g n i f i c a n t (F=.028, df 1 ,88, P> .25) , whi le the d i f f e r e n c e between these two groups and c o l o n i s t s t o g r i d 4 was h i g h l y s i g n i f i c a n t (F=10.892, df 1 ,135, P<.001) . The g e n e r a l c o n c l u s i o n i s tha t c o l o n i s t s are more a c t i v e than r e s i d e n t s , and tha t t h i s t r e n d i s s t r o n g e r i n males than i n f e m a l e s . I n f l u e n c e of Genotype on Genera l A c t i v i t y ^ 134 To determine i f g e n e r a l a c t i v i t y v a r i e d with genotype , I c o n s t r u c t e d a r e g r e s s i o n model to p r e d i c t g e n e r a l a c t i v i t y from g r i d and genotype . T h i s resembles the model used to p r e d i c t a g o n i s t i c s c o r e s , but does not c o n t a i n terms f o r b r e e d i n g c o n d i t i o n and we ight , s i n c e these f a c t o r s d i d not appear to i n f l u e n c e g e n e r a l a c t i v i t y . T h i s modal : Ac t i v i t y=Constan t+A (Gr id 2)+B (Gr id 4)+C(112) + D (113) 4 . . . . + J (223) where 112, 113, e t c . r e f e r t o the genotypes as d e f i n e d i n T a b l e 3 1 , does account f o r a s i g n i f i c a n t p r o p o r t i o n of the v a r i a b i l i t y i n a c t i v i t y s c o r e s of males (F=1.983, df 10 ,126, ,05>P>.025). However, a model wi th genotypes o n l y (no g r i d terms) has a lmost no p r e d i c t i v e va lue (F=.936, df 8 ,128 , ,50>P>.25) , wh i le the g r i d s on ly model i s h i g h l y s i g n i f i c a n t (F=6.349, df 2 ,134 , .005>P>.001). Adding the genotype terms t o the model does not improve i t s p r e d i c t i v e pcwer, and I w i l l c o n c l u d e tha t g e n e r a l a c t i v i t y of males does not vary with g e n o t y p e . I found the same r e s u l t with number of he te rozygous l o c i . The g e n e r a l model , p r e d i c t i n g a c t i v i t y from g r i d and number of he te rozygous l o c i , was s i g n i f i c a n t (F=3.099, df 5 ,131 , .025>P>.01) , but the model with o n l y number o f he te rozygous l o c i was not (F=.718, df 3 ,133 , P> .50) . The g e n e r a l l e v e l of a c t i v i t y o f males does not appear t o vary with genotype or number of he te rozygous l o c i . The g e n e r a l model p r e d i c t i n g female a c t i v i t y from g r i d and genotype i s s i g n i f i c a n t (F=2.037, df 10 ,70 , .05>P>.025) , 135 whi le n e i t h e r the g r i d s on ly {F=2.709, df 2 , 7 8 , .10>P>.05) , nor the genotypes on ly ( F - 1 . 652, df 8 ,72 , .25>P>.10} models a r e s i g n i f i c a n t . I a l s o at tempted to p r e d i c t female a c t i v i t y from number of he te rozygous l o c i , but t h i s model i s not s i g n i f i c a n t (F=2.184, df 5 ,75 , .10>P>.05). Summary of G e n e r a l A c t i v i t y ^ I measured the g e n e r a l a c t i v i t y , over 24 h o u r s , o f 218 m i c e . T h i s l e v e l of a c t i v i t y d i d not vary with s e x , w e i g h t , or b r e e d i n g c o n d i t i o n . However, mice c o l o n i z i n g the removal a rea tended to be more a c t i v e than r e s i d e n t mice cn the c o n t r o l a r e a s . T h i s d i f f e r e n c e was g r e a t e r i n males than i n f e m a l e s . The a c t i v i t y s c o r e s o f females were r e l a t e d to g e n o t y p e , but I found no such r e l a t i o n s h i p f o r males . DISCUSSION: In the above s e c t i o n s I have a n a l y s e d data f o r three b e h a v i o r t e s t s , and f o u r t y p e s of b e h a v i o r : a g o n i s t i c and s o c i a l b e h a v i o r , maze b e h a v i o r , and g e n e r a l a c t i v i t y . Both a g o n i s t i c and s o c i a l behav ior were i n f l u e n c e d by b r e e d i n g c o n d i t i o n , we ight , genotype , and whether an i n d i v i d u a l was a r e s i d e n t o r a c o l o n i s t . B e h a v i o r i n the maze was i n f l u e n c e d by s e x , b r e e d i n g c o n d i t i o n , and g r i d , but not by weight or genotype . G e n e r a l a c t i v i t y was i n f l u e n c e d o n l y by g r i d and 136 g e n o t y p e , a n d , whi le c o l o n i s t s moved l e s s than r e s i d e n t s i n the maze, they scored h i g h e r than r e s i d e n t s on g e n e r a l a c t i v i t y . That the i n f l u e n c e of these f a c t o r s v a r i e d o v e r the f o u r b e h a v i o r t y p e s i n d i c a t e s tha t the d i f f e r e n t b e h a v i o r t e s t s were measur ing p r i m a r i l y d i f f e r e n t t h i n g s , and t h a t the d i f f e r e n c e s which I observed between types o f mice were not merely some g e n e r a l f u n c t i o n of g e n e r a l a c t i v i t y l e v e l , f e a r i n new s i t u a t i o n s , or f a m i l i a r i t y wi th be ing h a n d l e d . Beth S a d l e i r (1965) and Healey (1967) measured the a g g r e s s i o n of male Beromyscus from the U . B . C . Endowment L a n d s , us ing home cage e n c o u n t e r s . They found tha t males were more a g g r e s s i v e i n the b r e e d i n g season than over the w i n t e r , and Healey found t h a t b r e e d i n g males tended t c be more a g g r e s s i v e than n o n - b r e e d i n g males . S a d l e i r found some i n d i c a t i o n tha t h i g h body weights were a s s o c i a t e d with h igh l e v e l s of a g g r e s s i o n , p a r t i c u l a r l y i n the e a r l y s p r i n g , but Healey found no such r e l a t i o n s h i p among h i s l a b o r a t o r y males . The r e s u l t s of my n e u t r a l arena t e s t s agree with those of the above a u t h o r s : I found t h a t b r e e d i n g males were more a g g r e s s i v e (shewed l e s s s u b o r d i n a t e behav io r ) than non-b r e e d i n g m a l e s , and that s u b m i s s i v e and s u b o r d i n a t e b e h a v i o r was n e g a t i v e l y r e l a t e d to we ight . The r e l a t i o n s h i p of a g g r e s s i o n and weight may have been obscured i n H e a l e y » s t e s t s by the f a c t t h a t h i s males were h e l d i n the l a b o r a t o r y with excess f o o d , wh i le both S a d l e i r and I t e s t e d males which had j u s t been brought i n from f i e l d p o p u l a t i o n s . 137 Gar ten (1974) made a d e t a i l e d study of the b e h a v i o r of P.ercrny sc us £ o l i o n o t u s males from 8 l o c a l i t i e s i n the s o u t h e a s t e r n U . S . f i . His s tudy i s o f p a r t i c u l a r i n t e r e s t here f o r two r e a s o n s : he s t u d i e d a l l of the f o u r b e h a v i o r types which I examined i n t h i s t h e s i s , us ing very s i m i l a r t e s t s i t u a t i o n s f o r th ree of the b e h a v i o r t y p e s , and he at tempted to r e l a t e these b e h a v i o r s c o r e s t o genotype . Gar ten used n e u t r a l arena e n c c u t e r s , as I d i d , t c measure both a g g r e s s i v e and s o c i a l b e h a v i o r s . He found t h a t both a g g r e s s i o n and dominance were p o s i t i v e l y r e l a t e d to weight and t e s t e s weight (b reed ing c o n d i t i o n ) , and were c o r r e l a t e d with g e n o t y p e . Ely f i n d i n g s are c o n s i s t e n t with t h e s e r e l a t i o n s h i p s . Gar ten used per cent h e t e r o z y g o s i t y over 18 l o c i as h i s index of g e n o t y p e , and found t h a t a g g r e s s i o n , w e i g h t , and t e s t e s weight i n c r e a s e d as per cen t h e t e r o z y g o s i t y i n c r e a s e d . I f e e l t h a t 3 l o c i i s too s m a l l a sample f o r examinat ion of these r e l a t i o n s h i p s , so I w i l l not make a d e t a i l e d compar ison of my g e n o t y p i c r e s u l t s with those of G a r t e n . However, the s i g n i f i c a n t g e n e r a l i t y between the s t u d i e s remains : a g g r e s s i o n and dominance b e h a v i o r i n male fe romyscus from f i e l d p o p u l a t i o n s i s c o r r e l a t e d with g e n o t y p e . Gar ten a l s o measured e x p l o r a t o r y b e h a v i o r i n an open f i e l d s i t u a t i o n . T h i s t e s t resembles my d i s p e r s a l maze t e s t i n t h a t i t measures the tendency of a mouse to e x p l o r e an u n f a m i l i a r a r e a . However, the mice which Garten t e s t e d d i d not have the o p t i o n c f remain ing i n a f a m i l i a r c a g e : the 1 3 8 s u b j e c t s sere g i v e n on ly th ree minutes i n the s t a r t box b e f o r e the doer t c the open f i e l d was opened. A l s o , Gar ten r e c o r d e d e x p l o r a t i o n f o r on ly 5 minutes . In s p i t e of these b a s i c d i f f e r e n c e s between the t e s t s , both measured some component of e x p l o r a t o r y b e h a v i o r , and they can be compared on tha t b a s i s . Gar ten found tha t h i s i n d i c e s of e x p l o r a t i o n were p o s i t i v e l y a s s o c i a t e d with w e i g h t , t e s t e s we igh t , and per cen t h e t e r o z y g o s i t y . I found no r e l a t i o n s h i p between b e h a v i o r i n the maze and weight or genotype , but I d i d f i n d tha t b r e e d i n g males moved more i n the maze than n o n - b r e e d i n g males d i d . T h i s l a t t e r o b s e r v a t i o n , i n combina t ion with my o b s e r v a t i o n t h a t r e s i d e n t mice moved more i n the maze than c o l o n i s t s to the removal a r e a s , l e d me to p o s t u l a t e tha t tha t movement through my maze was some f u n c t i o n of the s o c i a l p o s i t i o n of a mouse i n the source p o p u l a t i o n : dominant mice be ing more c o n f i d e n t to e x p l o r e the u n f a m i l i a r a r e a . G a r t e n ' s o b s e r v a t i o n s tha t e x p l o r a t o r y behav io r shewed the same r e l a t i o n s h i p s to weight and genotype t h a t a g g r e s s i o n and dominance d i d , suppor t t h i s h y p o t h e s i s . The t e s t which Gar ten used to measure g e n e r a l a c t i v i t y was v e r y s i m i l a r to mine: he p l a c e d mice s i n g l y i n a c t i v i t y cages f o r 2 3 • h o u r s . Scores cn t h i s t e s t d i d not vary with b r e e d i n g c o n d i t i o n or we igh t , but were i n v e r s e l y r e l a t e d to per cent h e t e r o z y g o s i t y , Hy a n a l y s i s s i m i l a r l y i n d i c a t e d no r e l a t i o n s h i p between a c t i v i t y and weight or b r e e d i n g c o n d i t i o n . However, I a l s o found no r e l a t i o n s h i p between 139 a c t i v i t y and genotype f o r ma les . T h i s d i f f e r e n c e may r e f l e c t a r e a l d i f f e r e n c e between Percmjscus p g l i c n o t u s and Pergmyscus l i i S i S i J i l i i J s i n the r e l a t i o n s h i p between a c t i v i t y and g e n o t y p e , o r i t may be f u n c t i o n of sample s i z e d i f f e r e n c e s : Gar ten may have been a b l e t o : d e t e c t more s u b t l e r e l a t i o n s h i p s than I c o u l d because he had a very much l a r g e r sample of the genome than I d i d (18 as opposed to 3 l o c i ) . In any c a s e , both s t u d i e s show t h a t g e n e r a l a c t i v i t y i s measuring something f u n d a m e n t a l l y d i f f e r e n t from the o ther two b e h a v i o r t e s t s . In G a r t e n ' s s tudy t h i s i s bes t i n d i c a t e d by the r e l a t i o n s h i p of b e h a v i o r t c per cen t h e t e r o z y g o s i t y : p o s i t i v e f o r a g g r e s s i o n , dominance, and e x p l o r a t o r y b e h a v i o r , and n e g a t i v e f o r a c t i v i t y . In my s t u d y , i t i s best i n d i c a t e d by the g r i d c o m p a r i s o n s : c o l o n i s t s tend t c show l e s s a g g r e s s i v e , dominance and d i s p e r s a l b e h a v i o r , but more g e n e r a l a c t i v i t y than r e s i d e n t s . A l s o , i n both s t u d i e s , a c t i v i t y was the o n l y b e h a v i o r not to be r e l a t e d to weight c r b r e e d i n g c o n d i t i o n . I have p o s t u l a t e d above that the tendency of a mouse to e x p l o r e an u n f a m i l i a r a rea i s some f u n c t i o n of i t s s o c i a l p o s i t i o n i n the f i e l d p o p u l a t i o n , and so can be expected to be r e l a t e d to dominance and a g g r e s s i o n . However, g e n e r a l l e v e l of a c t i v i t y , i n the absence of o ther mice , appears to be fundamenta l l y d i f f e r e n t from t h e s e b e h a v i o r s , and I w i l l p o s t u l a t e tha t g e n e r a l a c t i v i t y i s independent of a g g r e s s i v e i n t e r a c t i o n s i n f i e l d p o p u l a t i o n s . I looked at b e h a v i o r i n my mice main ly to d i s c o v e r i f 140 c o l o n i s t s to removal areas ( d i s p e r s i n g i n d i v i d u a l s ) d i f f e r e d b e h a v i o r a l l y from r e s i d e n t mice . I know of no p r e v i o u s s tudy which has examined the behav io r c f d i s p e r s i n g l e r c m y s c u s , but Hyers and Krebs (1971) d i d look at the b e h a v i o r a l a t t r i b u t e s o f two s p e c i e s of v o l e s c o l o n i z i n g removal a r e a s . They found t h a t d i s p e r s i n g males tended to show l e s s a g g r e s s i o n i n a n e u t r a l arena encounter than d id males from c o n t r o l a r e a s . F u r t h e r , they examined e x p l o r a t o r y b e h a v i o r by a l l o w i n g male v o l e s t c move i n t o a v e r t i c a l maze from the nest b o x , a t e s t which even more c l o s e l y resembles my maze t e s t than does G a r t e n ' s open f i e l d t e s t , and found tha t males c o l o n i z i n g the removal a reas showed l e s s e x p l o r a t o r y b e h a v i o r than d i d males from c o n t r o l a r e a s . I observed the same d i f f e r e n c e between c o l o n i z i n g and r e s i d e n t Jeromyscus i n my d i s p e r s a l maze. T h u s , male v o l e s moving onto a depopula ted area appear to resemble d i s p e r s i n g male Perom^scus i n both a g o n i s t i c and e x p l o r a t o r y behav ior Myers and Krebs (1971) a l s o examined the a c t i v i t y o f male v o l e s by means of a 10 minute open f i e l d t e s t . Vo les d i s p e r s i n g onto depopula ted a reas d i f f e r e d very l i t t l e from v o l e s cn c o n t r o l a r e a s i n s c o r e s on t h i s t e s t , but t h e r e was a s l i g h t tendency f o r the d i s p e r s i n g v o l e s t c be l e s s a c t i v e than the c o n t r o l v o l e s . Male Ps iomyscus c o l o n i z i n g depopu la ted a reas tended t c be more a c t i v e i n my a c t i v i t y t e s t than were r e s i d e n t , c o n t r o l ma les . I s u s p e c t t h a t the d i f f e r e n c e between s p e c i e s i s p robab ly a f u n c t i o n of the 141 nature c f the a c t i v i t y t e s t s u s e d . The open f i e l d t e s t used by Myers and Krebs c l o s e l y resembles the t e s t s which have been t r a d i t i o n a l l y used to measure e x p l o r a t o r y b e h a v i o r i n s m a l l mammals, a n d , i n f a c t , resembles the t e s t which Gar ten used to measure e x p l o r a t o r y a c t i v i t y i n P.. j o l i o n c t u s . S i n c e i t e s s e n t i a l l y r e c o r d s the locomotory response of mice t o a n o v e l e n v i r o n m e n t , i t p r o b a b l y more c l o s e l y resembles my d i s p e r s a l than my a c t i v i t y t e s t . I t i s , t h e r e f o r e , not s u r p r i s i n g tha t d i s p e r s i n g v o l e s s c o r e d lower i n t h i s t e s t than d i d v o l e s from c o n t r o l a r e a s : d i s p e r s i n g Percmyscus a l s o tended to be l e s s a c t i v e i n a n o v e l area than r e s i d e n t Peromyscus were. Myers and Krebs d i d not use a t e s t which can be c o n s i d e r e d e q u i v a l e n t t o the g e n e r a l a c t i v i t y t e s t s used fay myself and by G a r t e n . I t appears tha t we now can make some g e n e r a l i z a t i o n s , a c r o s s s u b - f a m i l i e s , about the c h a r a c t e r i s t i c s of d i s p e r s i n g s m a l l mammals: males which are d i s p e r s i n g tend to be l e s s a g g r e s s i v e , and to show l e s s e x p l o r a t o r y b e h a v i o r { less d i s p e r s a l i n t o a n c v e l e n v i r o n m e n t ) , than males which are r e s i d e n t i n u n d i s t u r b e d p o p u l a t i o n s . These g e n e r a l i t i e s h o l d f o r two s p e c i e s c f M i c r c t u s and one s p e c i e s of Percmyscus . None of the above s t u d i e s of b e h a v i o r i n Peromyscus and M i c r o t u s has examined the b e h a v i o r of f e m a l e s , and t h e r e f o r e , I cannot r e l a t e my o b s e r v a t i o n s of female b e h a v i o r t c those of o ther a u t h o r s . I observed both d i s p e r s a l b e h a v i o r and g e n e r a l a c t i v i t y of females and , on these t e s t s , they showed the same 142 t r e n d s as males d i d : females c o l o n i z i n g removal a reas tended t o shew l e s s e x p l o r a t o r y or d i s p e r s a l b e h a v i o r , and more g e n e r a l a c t i v i t y , than d i d r e s i d e n t f e m a l e s , and b r e e d i n g females showed more e x p l o r a t o r y behav io r than d i d n o n - b r e e d i n g f e m a l e s . My demographic a n a l y s e s have i n d i c a t e d t h a t b e h a v i o r a l i n t e r a c t i o n s among females are not as i m p o r t a n t i n d e t e r m i n i n g female demography as are male i n t e r a c t i o n s i n d e t e r m i n i n g male demography. However, the b e h a v i o r a l v a r i a b i l i t y which I have observed among f e m a l e s , and p a r t i c u l a r l y between d i s p e r s i n g and r e s i d e n t f e m a l e s , s u g g e s t s t h a t s i m i l a r b e h a v i o r a l mechanisms may be o p e r a t i n g i n the two s e x e s . Females i n the f i e l d may, i n f a c t , show the same t y p e s of b e h a v i o r as males do (spac ing out and d i s p e r s a l of s u b o r d i n a t e s ) , but because o ther f a c t o r s , i n p a r t i c u l a r m o r t a l i t y of e a r l y - b r e e d i n g f e m a l e s , account f o r more of the demographic v a r i a b i l i t y i n females than they do i n m a l e s , we seldom see the e f f e c t s of female b e h a v i o r a l i n t e r a c t i o n s i n w i l d p o p u l a t i o n s . The b e h a v i o r a l o b s e r v a t i o n s which I have made i n t h i s c h a p t e r have g e n e r a l l y agreed w e l l with my demographic o b s e r v a t i o n s , and with the g e n e r a l model of Peromyscus demography presented i n Chapter 2. Heavy, b r e e d i n g males are l e s s s u b o r d i n a t e ; and show more e x p l o r a t o r y b e h a v i o r , than l i g h t e r and n o n - b r e e d i n g males . S i m i l a r l y , r e s i d e n t males a r e more a g g r e s s i v e and s o c i a l l y dominant , and show more e x p l o r a t o r y b e h a v i o r , than do d i s p e r s i n g m a l e s . My 143 demographic a n a l y s e s i n d i c a t e d t h a t , d u r i n g the s p r i n g r e o r g a n i z a t i o n and breed ing s e a s o n , r e s i d e n t males tended to be h e a v i e r , and d u r i n g the b r e e d i n g seascn a l s o more o f t e n b r e e d i n g , than d i s p e r s i n g males . These o b s e r v a t i o n s l e d me to p o s t u l a t e tha t l i g h t e r , n c n - b r e e d i n g males were moving around d u r i n g these s e a s o n s . The above a n a l y s i s of b e h a v i o r has i n d i c a t e d t h a t these l i g h t , n o n - b r e e d i n g males are p robab ly n o n - a g g r e s s i v e , s u b o r d i n a t e i n d i v i d u a l s . T h i s s u p p o r t s the h y p o t h e s i s deve loped i n Chapter 4 , t h a t , d u r i n g the s p r i n g r e o r g a n i z a t i o n and main b r e e d i n g s e a s o n s , males are d i s p e r s i n g i n response to the a g g r e s s i v e b e h a v i o r of r e s i d e n t males . T h i s d i s p e r s a l i s a b y - p r o d u c t of a g g r e s s i o n and s p a c i n g b e h a v i o r , and so would be e n v i r o n m e n t a l r a t h e r than i n n a t e d i s p e r s a l , as d e f i n e d by Howard (1960). While a g g r e s s i v e i n t e r a c t i o n s d u r i n g the b r e e d i n g s e a s o n , and p a r t i c u l a r l y among b r e e d i n g m a l e s , may r e s u l t i n d i s p e r s a l of- s u b o r d i n a t e i n d i v i d u a l s , I found no e v i d e n c e , i n my demographic a n a l y s e s , tha t d i s p e r s a l was r e l a t e d t c s p a c i n g b e h a v i o r i n the n o n - b r e e d i n g s e a s o n s . My a n a l y s i s of double c a p t u r e s i n d i c a t e d t h a t both males and females a v o i d each o t h e r l e s s d u r i n g the n c n - b r e e d i n g seasons than d u r i n g the b r e e d i n g s e a s o n s . A l s o , the re was no ev idence t h a t any a n i m a l s were r e s t r i c t e d from e n t e r i n g the p o p u l a t i o n a f t e r males ceased b r e e d i n g i n the f a l l . The h y p o t h e s i s t h a t d i s p e r s a l i s a f u n c t i o n of s p a c i n g b e h a v i o r on ly when males are b r e e d i n g i s suppor ted by the o b s e r v a t i o n that d i f f e r e n c e s na i n maze b e h a v i c r between r e s i d e n t and d i s p e r s i n g mice were much l a r g e r f o r b reed ing than f cr n o n - b r e e d i n g mice. However, the d i f f e r e n c e s i n g e n e r a l a c t i v i t y d i d not depend on b r e e d i n g c o n d i t i o n , w e i g h t , or s e x : a l l c h a r a c t e r i s t i c s which tend to be a s s o c i a t e d with dominance. D i s p e r s i n g i n d i v i d u a l s tended to be more s p o n t a n e o u s l y a c t i v e than r e s i d e n t i n d i v i d u a l s , r e g a r d l e s s of s e a s o n . T h i s s u g g e s t s t h a t the d i f f e r e n c e between r e s i d e n t s and d i s p e r s e r s i n g e n e r a l a c t i v i t y i s independent of s p a c i n g b e h a v i o r , which means tha t t h e r e i s a component of the sample of d i s p e r s e r s which i s independent o f b e h a v i o r a l i n t e r a c t i o n s i n r e s i d e n t p o p u l a t i o n s . T h i s may be a component of the d i s p e r s a l of each i n d i v i d u a l , or i t may be t h a t some i n d i v i d u a l s i n the sample were d i s p e r s i n g i n response to s o c i a l p r e s s u r e , whi le o t h e r s , hav ing a h i g h e r l e v e l of spontaneous a c t i v i t y , were d i s p e r s i n g i n d e p e n d e n t l y o f t h i s . T h u s , the r e s u l t s of the g e n e r a l a c t i v i t y t e s t and the o b s e r v a t i o n t h a t mice c o n t i n u e to d i s p e r s e d u r i n g seasons when s p a c i n g b e h a v i o r i s at a minimum i n c o n t r o l p o p u l a t i o n s , sugges t t h a t not a l l of the d i s p e r s a l which I observed i s e n v i r o n m e n t a l d i s p e r s a l , as d e f i n e d by Howard (1960). F u r t h e r , that an imals c o l o n i z i n g removal a reas tend to d i f f e r g e n e t i c a l l y from r e s i d e n t a n i m a l s , and t h a t g e n e r a l a c t i v i t y o f f ema les i s c o r r e l a t e d with genotype , both i n d i c a t e t h a t t h i s n o n - e n v i r o n m e n t a l d i s p e r s a l may have a g e n e t i c component: some d i s p e r s a l , at l e a s t of f e m a l e s , may be i n n a t e . 145 CHAPTER 7 SUMMARY AND CONCLUSIONS T h i s s tudy was des igned t c d i s c o v e r the r e l a t i o n s h i p s between b e h a v i o r , g e n e t i c c o m p o s i t i o n and demography i n p o p u l a t i o n s of Pergmyscus j a n i c u l a t u s on the U n i v e r s i t y Endowment L a n d s , Vancouver , Canada. I c o l l e c t e d demographic data v i a b iweekly t r a p p i n g from J u l y , 1972 t o November, 1974. Two c o n t r o l a r e a s r e c e i v e d nc t reatment o ther than b iweek ly t r a p p i n g , A l l mice c a p t u r e d were removed from one e x p e r i m e n t a l a rea (the p u l s e d removal area) i n the s p r i n g of 1973 and the s p r i n g of 1974, and from the o t h e r e x p e r i m e n t a l a rea (the c o n t i n u o u s removal area) at each t r a p p i n g . I assumed tha t these e x p e r i m e n t a l a reas would s e l e c t i v e l y sample d i s p e r s i n g mice . I ga thered i n f o r m a t i o n about the b e h a v i o r of mice from both the c o n t r o l and removal a reas by b r i n g i n g mice i n t o the l a b and t e s t i n g them i n three s i t u a t i o n s . Adu l t males were t e s t e d f o r a g o n i s t i c and s o c i a l b e h a v i o r i n n e u t r a l arena encounters with l a b o r a t o r y - r e a r e d m a l e s . I examined the b e h a v i o r of both males and females d i s p e r s i n g through an u n f a m i l i a r maze, and a l s o r e c o r d e d the g e n e r a l l o c c m c t o r y a c t i v i t y of i s o l a t e d males and females over a 24 hour p e r i o d . The g e n e t i c i n f o r m a t i o n was gathered by s t a r c h g e l e l e c t r o p h o r e s i s of b lood samples which were c o l l e c t e d from each mouse at f i r s t c a p t u r e . I r e c o r d e d a l l e l e f r e g u e n c i e s at two p r o t e i n l o c i , t r a n s f e r r i n and an e s t e r a s e , from the p l a s m a , and one l o c u s , g lutamate o x a l a t e t r a n s a m i n a s e , from 146 the red b lood c e l l s . Each c f these th ree l o c i had two a l l e l e s , which l a b o r a t o r y b r e e d i n g exper iments i n d i c a t e d were i n h e r i t e d a c c o r d i n g tc Mendel ian r a t i o s . The r e s u l t s o b t a i n e d from these exper iments , a l o n g with the r e s u l t s of e a r l i e r s t u d i e s , suggest tha t the f o l l o w i n g demographic and g e n e t i c changes occur i n a s s o c i a t i o n with an annua l c y c l e of numbers i n p o p u l a t i o n s of deermice i n the Vancouver a r e a . These changes are summarized s c h e m a t i c a l l y i n F i g u r e 22. In the e a r l y s p r i n g , the onset of b r e e d i n g i n males i s a s s o c i a t e d with reduced s u r v i v a l , i n c r e a s e d r e c r u i t m e n t , and i n c r e a s e d s p a c i n g b e h a v i o r (as measured by t r a p p i n g o v e r l a p ) . L i g h t e r males tend to d i s a p p e a r from c c n t r o l p o p u l a t i o n s and c o l o n i z e removal areas at t h i s t i m e . These o b s e r v a t i o n s , i n c o m b i n a t i o n with the * b e h a v i o r a l ev idence tha t s u b m i s s i v e and s u b o r d i n a t e b e h a v i o r c f males i s n e g a t i v e l y c o r r e l a t e d with weight and b r e e d i n g c o n d i t i o n , i n d i c a t e t h a t males become a g g r e s s i v e with the onset of b r e e d i n g and space cut from each o t h e r . T h i s s p a c i n g b e h a v i o r r e s u l t s i n the d i s p e r s a l of l e s s a g g r e s s i v e ma les , and i n th ree of the f o u r g r i d - s p r i n g s o b s e r v e d , r e s u l t e d i n a r e d u c t i o n i n the number of males on the c c n t r o l a r e a s . A l though t h i s r e o r g a n i z a t i o n p e r i o d r e s u l t s i n s e l e c t i o n f o r a g g r e s s i v e phenotypes on c o n t r o l a r e a s , i t does not r e s u l t i n s i g n i f i c a n t changes i n observed genotype f r e g u e n c i e s on these a r e a s , or i n g e n e t i c d i f f e r e n c e s between r e s i d e n t and d i s p e r s i n g males . 147 A f t e r t h i s i n i t i a l p e r i o d o f r e o r g a n i z a t i o n , the male p o p u l a t i o n s t a b i l i z e s with good s u r v i v a l , low r e c r u i t m e n t , and maximum s p a c i n g - o u t . The males which are r e s i d e n t d u r i n g t h i s p e r i o d tend to be heavy , b r e e d i n g , dominant i n d i v i d u a l s , and l i g h t e r , n o n - b r e e d i n g , l e s s a g g r e s s i v e i n d i v i d u a l s c o n t i n u e to d i s p e r s e through the p o p u l a t i o n . A g a i n , t h i s d i s p e r s a l of s u b o r d i n a t e i n d i v i d u a l s does not seem t c be s e l e c t i v e . A l though some j u v e n i l e s are b o r n , very few of them en te r the p o p u l a t i o n : the r e s i d e n t males appear t o r e s t r i c t r e c r u i t m e n t of j u v e n i l e s , and p a r t i c u l a r l y j u v e n i l e ma les . That these j u v e n i l e s do not c o l o n i z e the removal a r e a s i n d i c a t e s t h a t the r e s i d e n t a d u l t s reduce the s u r v i v a l o f j u v e n i l e s t o weaning , r a t h e r than j u s t r e s t r i c t i n g t h e i r r e c r u i t m e n t . In l a t e summer the a g g r e s s i v e n e s s of r e s i d e n t males d e c l i n e s as they cease b r e e d i n g . S u r v i v a l d rops s l i g h t l y and r e c r u i t m e n t i n c r e a s e s , as males move a round , and a l l j u v e n i l e s which s u r v i v e t c weaning are a l lowed to en te r the p o p u l a t i o n . The l a r g e i n f l u x of j u v e n i l e s and r e d u c t i o n i n s p a c i n g b e h a v i o r of a d u l t s , r e s u l t s in a r a p i d i n c r e a s e i n d e n s i t y , and the p o p u l a t i o n reaches i t s annual maximum i n l a t e f a l l . Over the win ter the p o p u l a t i o n i s composed l a r g e l y of j u v e n i l e s which en te red the p o p u l a t i o n i n the p r e v i o u s f a l l . Males remain s l i g h t l y spaced cut from each o t h e r , but t r a p p i n g o v e r l a p i s a t i t s maximum d u r i n g t h i s s e a s o n . L i g h t e r (subord ina te ) i n d i v i d u a l s c o n t i n u e t c move around throughout the w i n t e r , but s u r v i v a l c f r e s i d e n t s i s h i g h and r e c r u i t m e n t 148 r e l a t i v e l y low , so the p o p u l a t i o n remains q u i t e s t a b l e , d e c l i n i n g s l o w l y , u n t i l the onset c f b r e e d i n g , and r e s u l t i n g r e o r g a n i z a t i o n , i n the e a r l y s p r i n g . The onset o f b r e e d i n g i n females i s a s s o c i a t e d with a decrease i n s u r v i v a l but no i n c r e a s e i n r e c r u i t m e n t or s p a c i n g b e h a v i o r . Breed ing females s u f f e r heavy m o r t a l i t y . T h i s r e s u l t e d i n a d e c l i n e i n the number of females on the c c n t r o l a r e a s i n t h r e e of the f o u r g r i d - s p r i n g s o b s e r v e d . Homozygous females appear to be s e l e c t e d a g a i n s t d u r i n g t h i s p e r i o d o f heavy m o r t a l i t y , whi le females h e t e r o z y g o u s at on ly one l o c u s a r e favored^ A f t e r t h i s p e r i o d of heavy m o r t a l i t y , t h e r e i s a p e r i o d c f 2 t c 3 months i n which females s u r v i v e w e l l , and space out from each e t h e r , though not as much as males d o , but i n which a r e l a t i v e l y s m a l l p r o p o r t i o n b r e e d s . Few l i t t e r s are born d u r i n g t h i s p e r i o d , and a d u l t males reduce the s u r v i v a l of those that a r e . However, some j u v e n i l e females s u r v i v e to e n t e r the p o p u l a t i o n , and these tend to mature and breed l a t e r i n the summer. T h e r e f o r e , there i s some advantage to females which breed e a r l y , i n s p i t e of the r i s k of e a r l y m o r t a l i t y . In e a r l y summer (Kay-Ju ly ) the p r o p o r t i o n of f ema les b r e e d i n g r i s e s r a p i d l y , and i t remains high i n t o the e a r l y f a l l (September-November) . The p r o p o r t i o n of males b r e e d i n g d e c l i n e s r a p i d l y soon a f t e r the summer r i s e i n female b r e e d i n g , and the l a r g e number of l i t t e r s which c o n t i n u e to be born and nursed on the s tudy a reas s u r v i v e w e l l , and are a l l o w e d to e n t e r the p o p u l a t i o n . These j u v e n i l e r e c r u i t s tend 149 t o be f i r s t cap tu red i n t r a p s w i t h i n female home r a n g e s , and t h i s e v i d e n c e , a long with the s t a b i l i t y of g e n e t i c d i f f e r e n c e s between the p u l s e d removal and the c c n t r c l a r e a s o v e r t h i s p e r i o d of j u v e n i l e r e c r u i t m e n t , s u g g e s t s tha t the j u v e n i l e s which en te r the p o p u l a t i o n s at t h i s time were born to mothers w i t h i n these p o p u l a t i o n s . A f t e r t h i s p e r i o d of j u v e n i l e r e c r u i t m e n t , the female p o p u l a t i o n s t a b i l i z e s : s u r v i v a l i s g o o d , r e c r u i t m e n t l o w , and females do not appear to space out from each o t h e r . T h i s p e r i o d of o v e r - w i n t e r s t a b i l i t y l a s t s u n t i l the onset of b r e e d i n g i n the s p r i n g with i t s a s s o c i a t e d heavy m o r t a l i t y of b r e e d i n g f e m a l e s . The major d i f f e r e n c e between female and male demography i s t h a t b r e e d i n g females s u f f e r heavy m o r t a l i t y i n the s p r i n g , whi le males are s p a c i n g out and d i s p e r s i n g . I have suggested t h a t t h i s m o r t a l i t y c f females r e s u l t s from the energy c o n s t r a i n t s of b reed ing i n c o l d weather , and t h e r e f o r e , t h a t the r e s u l t i n g d e c l i n e i n female numbers, i s d i r e c t l y r e l a t e d to f o o d s u p p l y and weather c o n d i t i o n s . T h i s means tha t the number of females which remain t c breed on the s tudy a reas i s a f u n c t i o n of t i m i n g of the onset c f b r e e d i n g i n f e m a l e s , and the p a r t i c u l a r food and weather c o n d i t i o n s of t h a t y e a r . That c e r t a i n genotypes are s e l e c t e d f o r a t t h i s t ime i n d i c a t e s tha t t i m i n g c f onset of b r e e d i n g may have a g e n e t i c b a s i s . I have d i s c u s s e d the p o s s i b l e advantages t c b r e e d i n g e a r l y , which might ac t to ma in ta in the e a r l y b r e e d i n g genotypes i n the p o p u l a t i o n . However, I have sugges ted t h a t the polymorphism 150 may be main ta ined by s e l e c t i o n f o r d i f f e r e n t genotypes i n males and f e m a l e s , and r e c o m b i n a t i o n of these genotypes at b r e e d i n g . Ha les c o n t i n u e to breed a c t i v e l y throughout the s p r i n g , when very few females are b r e e d i n g . C u r i n g t h i s t i m e , males i n h i b i t the s u r v i v a l and r e c r u i t m e n t of those few j u v e n i l e s which are b o r n . I wondered why males s h o u l d breed and space themse lves o u t , whi le at the same t ime r e d u c i n g the s u c c e s s of t h e i r own o f f s p r i n g , and suggested tha t male s p a c i n g b e h a v i o r may be the r e s u l t of c o m p e t i t i o n f o r f e m a l e s . The m o r t a l i t y o f e a r l y b r e e d i n g females w i l l tend to l e a v e more males than females i n the p o p u l a t i o n . T h i s w i l l reduce the p r o b a b i l i t y t h a t any g iven male w i l l f e r t i l i z e a r e c e p t i v e f e m a l e . T h e r e f o r e , i t i s of advantage to a male to become the o n l y male i n as l a r g e an area as p o s s i b l e : t e r r i t o r i a l b e h a v i o r i s s e l e c t e d f o r . The t e r r i t o r i a l males w i l l have an even f u r t h e r advantage i f they can reduce the sex r a t i o on t h e i r a r e a s by a l l o w i n g j u v e n i l e f e m a l e s , but not ma les , to s e t t l e on t h a t a r e a . There i s some ev idence t h a t t h i s s e l e c t i v e r e s t r i c t i o n of j u v e n i l e r e c r u i t m e n t does o c c u r . T h e r e f o r e , I suggest tha t a g g r e s s i o n and s p a c i n g b e h a v i o r o f males i n the e a r l y s p r i n g i s a f u n c t i o n o f c o m p e t i t i o n f o r f ema les , and t h a t the number c f males which remain t o breed on an area i s determined by the number of females which s u r v i v e . T h u s , the i n t e r a c t i o n of the t i m i n g c f onset o f female b r e e d i n g and env i ronmenta l c o n d i t i o n s i s the key which 151 d e t e r m i n e s t h e b r e e d i n g d e n s i t i e s of both males and f e m a l e s . The e a r l y s p r i n g i s not o n l y the p e r i o d i n which t h e numbers and t y p e s o f i n d i v i d u a l s which breed are d e t e r m i n e d , i t i s a l s o t h e o n l y p e r i o d o ver which I d e t e c t e d s e l e c t i o n a t my marker l c c i . I t i s t h e r e f o r e the l o g i c a l p l a c e t o l o o k f o r a c a u s a t i v e a s s o c i a t i o n between genotype and demography. I t i s u n l i k e l y t h a t I would f i n d such an a s s o c i a t i o n i n males, f o r two r e a s o n s . F i r s t , males dc not e x p e r i e n c e s t r o n g s e l e c t i o n over t h i s p e r i o d . Second, I have s u g g e s t e d t h a t s p a c i n g b e h a v i o r and d i s p e r s a l c f males i n the s p r i n g may be a response t o the poor s u r v i v a l and d e c l i n e i n numbers of f e m a l e s . I f t h i s i s t r u e , then male demography would be p r i m a r i l y a f u n c t i o n of female demography, not of male genotype. T h e r e f o r e , even i f a g g r e s s i o n were g e n e t i c a l l y d e t e r m i n e d , any s e l e c t i o n f o r a g g r e s s i v e genotype would be s o f t s e l e c t i o n as d i s c u s s e d by W a l l a c e (1975), and the genotype would not be d i r e c t l y d e t e r m i n i n g d e n s i t i e s . The mean l e v e l o f a g g r e s s i o n may a f f e c t b r e e d i n g s u c c e s s , j u v e n i l e r e c r u i t m e n t , and t h u s the d e n s i t i e s a t the f a l l peak, but s i n c e I have found no e v i d e n c e t h a t males are s e l e c t e d o v e r t h e s p r i n g , t h e r e i s no i n d i c a t i o n t h a t t h i s p o s s i b l e i n t e r a c t i o n of b e h a v i o r and demography has a g e n e t i c component. T h e r e f o r e , i f genotype i s d i r e c t l y a f f e c t i n g e i t h e r b r e e d i n g d e n s i t i e s o r peak d e n s i t i e s , the mechanism i s p r o b a b l y through f e m a l e s r a t h e r t h a n males. The t i m i n g of t h e o n s e t cf b r e e d i n g i n females appears t o be the key which 152 determines female s u r v i v a l and breeding d e n s i t y . U n l i k e the p o s s i b l e s e l e c t i o n on males at t h i s time of year, the s e l e c t i o n on females would be hard s e l e c t i o n (Wallace, 1975): the s u r v i v a l of a given female w i l l depend d i r e c t l y on when she begins t c breed i n r e l a t i o n t c weather c o n d i t i o n s and food supply. Unless mice are competing f o r food ( i . e . the amount of food a v a i l a b l e to a female i s a f u n c t i o n of the number of mice i n the p o p u l a t i o n ) , t h i s s u r v i v a l w i l l probably not be r e l a t e d t o the number of mice i n the p o p u l a t i o n . The s i m p l e s t h y p o t h e s i s i s that mice do compete f o r food over the winter, as Garten suggests. I have already d i s c u s s e d the r e s u l t s of S a d l e i r (1973) and T a i t t (pers. comm.) which i n d i c a t e t h a t the amount of food l i m i t s breeding over the s i n t e r , and T a i t t ' s o b s e r v a t i o n that d e n s i t y i n c r e a s e s when food i s added to o v e r w i n t e r i n g p o p u l a t i o n s i n d i c a t e s that d e n s i t y as well may be f o o d - l i m i t e d over the winter. I f females can s u c c e s s f u l l y breed over the winter i n the presence of excess f o o d , and i f the amount of food a v a i l a b l e to a female i s at l e a s t p a r t l y a f u n c t i o n of the-number of mice i n the p o p u l a t i o n , the success of females breeding e a r l y w i l l be some f u n c t i o n of d e n s i t y of females on the area. I f d e n s i t i e s are high, the amount of food a v a i l a b l e per female w i l l be low, and e a r l y breeding females w i l l s u f f e r heavy m o r t a l i t y . T h i s w i l l r e s u l t i n a d e c l i n e i n d e n s i t y of both males and females i n the e a r l y s p r i n g . However, when d e n s i t i e s are low, the amount of food a v a i l a b l e per female w i l l be r e l a t i v e l y high, and e a r l y -153 b r e e d i n g females w i l l net s u f f e r heavy m o r t a l i t y . T h e r e f o r e , when o v e r w i n t e r d e n s i t i e s are low , I p r e d i c t good s u r v i v a l and r e p r o d u c t i v e s u c c e s s of e a r l y - b r e e d i n g f e m a l e s , l i t t l e s e l e c t i o n over the s p r i n g , and l i t t l e or no s p r i n g d e c l i n e i n numbers. A l t e r n a t i v e l y , when over winter d e n s i t i e s are h i g h , I p r e d i c t poor r e p r o d u c t i v e s u c c e s s and s u r v i v a l o f e a r l y -b r e e d i n g f e m a l e s , s t r o n g s e l e c t i o n over the s p r i n g , and a d e c l i n e i n d e n s i t y . For a g iven s e t of e n v i r o n m e n t a l c i r c u m s t a n c e s , the b r e e d i n g p o p u l a t i o n s i z e (both males and females) w i l l be a f u n c t i o n of the t i m i n g of onset of female b r e e d i n g i n the s p r i n g and the d e n s i t y of the o v e r w i n t e r i n g p o p u l a t i o n . The v a r i a b i l i t y i n t im ing of the onse t o f female b r e e d i n g w i l l tend to damp the e f f e c t s of v a r i a b i l i t y i n food s u p p l y , weather , and o v e r w i n t e r d e n s i t y on b r e e d i n g s u c c e s s (number of l i t t e r s born) and d e n s i t y of b r e e d i n g p o p u l a t i o n . For example , i f food i s s c a r c e or o v e r w i n t e r d e n s i t i e s u n u s u a l l y h i g h , d e n s i t i e s w i l l be reduced by m o r t a l i t y of e a r l y - b r e e d i n g f e m a l e s . On the o t h e r hand , i f ove rw in te r p o p u l a t i o n s are low or food abundant , b r e e d i n g s u c c e s s w i l l be i n c r e a s e d owing to the s u c c e s s o f e a r l y - b r e e d i n g f e m a l e s , and the r e s u l t a n t i n c r e a s e i n the l e n g t h of the b r e e d i n g s e a s o n . T h i s mechanism, which I am p r o p o s i n g i s d e t e r m i n i n g b r e e d i n g d e n s i t i e s i n p o p u l a t i o n s of Peromyscus on the Endowment l a n d s , i s a b e h a v i o r a l mechanism f o r m a l e s , i n v o l v i n g c o m p e t i t i o n f o r f e m a l e s , and a g e n e t i c mechanism f o r 154 f e m a l e s , i n v o l v i n g maintenance c f and s e l e c t i o n on v a r i a b i l i t y i n the onset of b r e e d i n g i n the s p r i n g . A d d i t i o n a l exper iments need to be done to determine i f the b r e e d i n g d e n s i t y of males i s a f u n c t i o n of female d e n s i t y . One c o u l d do t h i s by m a n i p u l a t i n g the sex r a t i o at the end of the o v e r w i n t e r p e r i o d , whi le l e a v i n g d e n s i t y c o n s t a n t . T h i s would be p a r t i c u l a r l y i n s t r u c t i v e i f done i n the presence and absence of e x c e s s f o o d . A d d i t i o n a l work a l s o needs to be done to determine i f the t i m i n g of the onset of b r e e d i n g i n the s p r i n g i s determined g e n e t i c a l l y . My model i s based cn the assumpt ion tha t t h i s t r a i t i s h e r i t a b l e , and t h a t i t has a h igh v a r i a n c e i n the p o p u l a t i o n . I n i t i a l i n v e s t i g a t i o n s of these assumpt ions c o u l d be done i n the l a b o r a t o r y and f o l l o w e d up with s e m i - n a t u r a l f i e l d exper iments such as those used by Anderson (1975) to s tudy h e r i t a b i l i t y of t r a i t s such as growth and b r e e d i n g s u c c e s s in M i c r o t u s . The r e s u l t s c f my and o ther s t u d i e s have i n d i c a t e d tha t homozygous female fe romyscus tend t o be s e l e c t e d a g a i n s t i n the s p r i n g . I t would t h e r e f o r e be of a d d i t i o n a l i n t e r e s t t o determine i f h o m o z y g o s i t y , p a r t i c u l a r l y at the t r a n s f e r r i n l o c u s , i s a s s o c i a t e d with the e a r l y onset c f b r e e d i n g . One of the most s i g n i f i c a n t r e s u l t s of my e x p e r i m e n t a l a n a l y s e s i s the f i n d i n g tha t removal a reas do s e l e c t i v e l y sample d i s p e r s i n g i n d i v i d u a l s . I i n i t i a l l y examined d i s p e r s a l by compar ing mice which were r e s i d e n t o n . c o n t r o l a r e a s over g i v e n p e r i o d s with mice which moved onto and o f f t h e s e a r e a s 155 d u r i n g these p e r i o d s . T h u s , I had an e s t i m a t e c f both the amount of d i s p e r s a l and the t y p e s o f mice which were d i s p e r s i n g f o r each s e a s o n . The mice which c o l o n i z e d the p u l s e d removal and c o n t i n u o u s removal a reas tended to be the same t y p e s of mice which were moving onto and o f f the c o n t r o l a r e a s . F u r t h e r , h igh r a t e s of d i s p e r s a l onto the removal a reas o c c u r r e d when there was a l o t o f movement through c o n t r o l p o p u l a t i o n s . The removal a r e a s do not merely draw r e s i d e n t mice from s u r r o u n d i n g a r e a s : they do sample main ly mice which would have been d i s p e r s i n g even i f the empty a rea were not p r e s e n t . ghen males are b r e e d i n g , m a l e d i s p e r s e r s tend to be l i g h t -we igh t , n o n - b r e e d i n g , and s u b o r d i n a t e . I have suggested tha t these are males which were unable to s e c u r e space to breed i n u n d i s t u r b e d p o p u l a t i o n s , and a re thus e n v i r o n m e n t a l d i s p e r s e r s . whi le the re may be some c o m p e t i t i o n among females f o r b r e e d i n g s p a c e , my data suggest tha t a l l females which s u r v i v e through the w i n t e r can s e t t l e and b r e e d : the onset of b r e e d i n g i n the s p r i n g i s not a s s o c i a t e d with h igh d i s p e r s a l r a t e or s p a c i n g o u t . However, some females d i s p e r s e d u r i n g the b r e e d i n g s e a s o n , and there i s some d i s p e r s a l c f both sexes d u r i n g the f a l l i n c r e a s e p e r i o d and over the w i n t e r , when r e c r u i t m e n t does not appear t c be r e s t r i c t e d i n c o n t r o l p o p u l a t i o n s . F u r t h e r , d i s p e r s i n g i n d i v i d u a l s of both sexes tend t c be more s p o n t a n e o u s l y a c t i v e , i n the absence of o ther m i c e , than are r e s i d e n t s from c o n t r o l a r e a s , a l t h o u g h a c t i v i t y 156 i s not c o r r e l a t e d w i t h any i n d i c e s c f dominance, such as weight or b r e e d i n g c o n d i t i o n . I s u g g e s t , from t h i s e v i d e n c e , t h a t some of the mice i n my sample of d i s p e r s e r s a r e not moving i n response t o s o c i a l p r e s s u r e from r e s i d e n t a n i m a l s : t h ey a re d i s p e r s i n g i n d e p e n d e n t l y of i n t e r a c t i o n s w i t h e t h e r members of the p o p u l a t i o n . S i n c e g e n e r a l a c t i v i t y i s r e l a t e d t o genotype i n f e m a l e s , a D d s i n c e d i s p e r s e r s do d i f f e r g e n e t i c a l l y from r e s i d e n t mice, i t may be t h a t t h e s e i n d i v i d u a l s a re i n n a t e d i s p e r s e r s . I n any c a s e , the d i s p e r s a l which I observed appears t o have two components: one a movement of s u b o r d i n a t e i n d i v i d u a l s i n response t o a g g r e s s i o n of r e s i d e n t s , and the o t h e r a movement of more s p o n t a n e o u s l y a c t i v e i n d i v i d u a l s , which i s independent of c o n d i t i o n s i n r e s i d e n t p o p u l a t i o n s . I t would be o f i n t e r e s t , i n a f u t u r e s t u d y , t o examine the h e r i t a b i l i t y of spontaneous a c t i v i t y , t h e ' i n n a t e ' component c f d i s p e r s a l , i n f i e l d s i t u a t i o n s . 157 FIGURES 1 5 8 . I L Time Cl ) SPRING REORGANIZATION: Increasing aggression of breeding, adult males, and dispersal of" over-wintered juveniles, result in a reorganization of the population and a decline in numbers. (2) WON BREEDING SEASON: The population is composed mainly of breeding adults. Resident adult males restrict both the recruitment of juveniles and the settling of transient adults. (3) FALL INCREASE: Adult aggression declines as breeding stops, and this results in rapid recruitment of juveniles. The population increases to jiBximum density, and is composed mainly of juveniles born late in the summer. (4) OVTRWINTER PERIOD: Survival is good, and the population declines slowly until the start of the spring reorganization. FIGURE 1: General model of seasonal fluctuations in a population of deermice. 159 FIGURE 2: Locations of the four trapping grids on the U n i v e r s i t y of B r i t i s h Columbia Endowment Lands, Vancouver, B r i t i s h Columbi 160 1972 1973 1974 FIGURE 3: Minimum number known t o be a l i v e , and p r o p o r t i o n b r e e d i n g , on c o n t r o l g r i d 1. 161 1 G R I D "3 females J A S O N DJ F M A M J J A S O N D J F M A M J I fall lover^ main I fall 'increasdwmt^vs'breeding liner. 1972 1973 overly w i n t h v J A S O N 'fall incr. 1974 main breed FIGURE 4: Minimum number known to be alive, and proportion breeding on control grid 3. 162 FEMALES MALES 1-0 JC UJ " UJ ? .5 CM CC i f z cc 2 In -5 mean •823 m^an •810 2 3 4 a: LU UJ UJ < CC z. UJ cc CJ UJ cc .3 •2 •1 mean "•169 .4 ,3 •2J .1 - mean 207 2 3 4 Q. < -1 ^ ft LU O 5 ol < cc .3 • 2 • 1 mean • 219 - m e a n •124 1 2 3 SEASON 1 - 2 . 3 SEASON FIGURE 5: Seasonal es t i m a t e s o f s u r v i v a l r a t e , r e c r u i t m e n t r a t e and t r a p - o v e r l a p i n d i c e s f o r c o n t r o l p o p u l a t i o n s . S u r v i v a l and r e c r u i t m e n t e s t i m a t e s were o b t a i n e d from the r e g r e s s i o n models d e s c r i b e d in.jthe t e x t . SPRING REORGANIZATION I 4 d W 9x9 d"x9 MAIN BREEDING PERIOD 163 Expected Observed n = 52 I n = 94 J l dxo* 9x9 A d u l t s CJx 9 Adult (j» Adult 9 Juvenile J u v e n i l e s FALL INCREASE PERIOD • 1 n = 98 cJxcy 9x9 A d u l t s dx9 Adult o" Adult 9 Juvenile 0 J u v e n i l e s OVERWINTER PERIOD 1 i n = 96 dxo" 9x9* rfx^ FIGURE 6: Observed and expected p r o p o r t i o n s o f v a r i o u s p a i r - t y p e s i n the t o t a l t r a p - o v e r l a p sample f o r each season. ^ 30 t D ) c (TJ 2 20 10 + 0 ?1 H — H H 1 1—* • grid 1 o—o grid 3 * grid 2 before remoj/al grid 2 after remov|al H 1 1 1—-< 1 1—I 1 •- -I 1 »- H 1 1-S N J M M J I over IAV] main •winter ^breeding 1972 1973 S N J M M J S fall I over ^ m a i n fall incr. Iwinter^^Mbreed, incn 1974 N FIGURE 7: Mean weights of males from control areas (grids 1 and 3) and the pulsed removal area (grid 2). w H—V-1 •—• grid 1 o—o gr id 3 grid 2 before remova grid 2 af ter removal t > i i» i — t H 1 1 1—I 1 1 1 1—I- H 1 • 1 1 1 1-N J M M J over b ^ r main 'winter breeding 1972 1973 S fa l l incr N J M over K M J w i n t e r ^ main breed, 1974 S fal l incr. N FIGURE 8: Mean weights of non-pregnant females from control areas (grids 1 and 3) and the pulsed removal area (grid 2). 166 if) OC e UJ o 2 p z g i— or o OL O or o. SPRING REORGANIZATION 5 ^ i i 2 n-5 adult adult 5 MAIN BREEDING PERIOD I -EZ2L ^ 0 •5 1 adult adult juvenile juvenile FALL INCREASE PERIOD 1 I 0 adult adult juvenile juvenile *r ?? dv ?* n = 11 n = 22 OVERWINTER PERIOD adult 6<f fA n = 40 adult ?? FIGURE .9; P r o p o r t i o n o f m a l e s a n d f e m a l e s , a d u l t s a n d j u v e n i l e s i n t h e t o t a l t r a p - o v e r l a p s a m p l e f o r each s e a s o n : p u l s e d r e m o v a l g r i d o n l y . Minimum No. Known to be Alive -» ro IA) ^ o o o o o £91 it>a FEMALES MALES 1-0 XL UJ UJ > =>or UJ i— < or XL UJ»-U J Z CM — =) or CJ UJ or •4 .3 •2 • 1 - mean.838 1 2 3 SEASON .5 •4 3-J mean -220 • 2 •1 mean • 207 1 2 3 SEASON 1 2 3 SEASON FIGURE 11:: Seasonal estimates o f s u r v i v a l r a t e and r e c r u i t m e n t r a t e f o r the p u l s e d removal g r i d . These e s t i m a t e s were o b t a i n e d from the r e g r e s s i o n models d e s c r i b e d i n the t e x t . 169 P r o p o r t i o n of Males  in Breeding C o n d i t i o n \ \ \ V WW WW WW WW WW WW WW WW \ \ w w w WW N J M M J CD 20} Proport ion of Females w i t h  Medium o r L a r g e Nipples J S fall increase'wint 1972 N . J M M Jover|J\wj main ' creeding 1973 S N fall incr. J over wint. M gqmain S N breed. S fall incr 1973 gr id 1 o—o g r i d 2 V—JQ g r i d 3 g r i d 2 post removal W.V.V.SV.* FIGURE 1 2 : Proportions of scrotal males, and lactating females i n populations on the control and pulsed removal grids. |Main breeding period 1973 [Fall increase "winter period period 1973 1974 Main reorgani-'breeding 'increase zation period period 1974 1974 1974 FIGURE 13: Mean weight ( + 2 standard errors) of males c o l o n i z i n g the continuous removal g r i d , and of r e s i d e n t males from c o n t r o l g r i d s . 171 (A e 20 18 16 . cr ,14 12 (A •MM* a o 8 6* 2 3 -t—• c E "E e o o u u U) o c o o 1 I 2 c o u o E o e: o o a 6* E Main breeding period 1973 Fall increase period 1973 Over -winter period 1974 Spring reorgani -zation 1974 Main breeding period 1974 Fall increase period 1974 F IGURE 1 4 : Mean w e i g h t ( ± 2 standard errors) of females c o l o n i z i n g t h e c o n t i n u o u s r e m o v a l g r i d , a n d of r e s i d e n t females from c o n t r o l "grids'. 172 > n c o c 6 z E 3 E T O T A L ; ^ r f 9 r i d 3 ^Ji 6 g r i d 1 g r i d 4 'breeding 1973 J lover Iwint. F\\>^main I fal l jdJ incr. 1974 FIGURE 15: Minimum numbers known to be al ive on the control grids (grids 1 and 3) and the continuous removal grid (grid 4). 173 FEMALES MALES 174-.20 -101 n = 55 •20 10 n = 57 2 Overwinter 20 •10 z o J — or o Q_ o or Q_ 0 •201 •10 n = 66 n = 98 -20 -10 n = 47 Breeding Peak •20 • 10 n=H8 «— C M JTJ i— C M T— C M C M C M T - C M C M C M o 1 1 1 * - » - C M £ = £ : C M C M C M j £ GENOTYPE Fall Peak FIGURE 17: Genotypic p r o p o r t i o n s i n the o v e r w i n t e r , b r e e d i n g peak, and f a l l peak samples from c o n t r o l p o p u l a t i o n s . FEMALES 1 MALES 175 n=53 •5 n=57 0 1 2 3 0 1 2 3 Overwinter n = 66 n=47 • 5. o »— cr 2 O CL 0 1 2 3 0 1 2 3 Breeding Peak n = 98 •5 n=116 0 1 2 3 0 1 2 3 Fall Peak FIGURE 18: P r o p o r t i o n o f mice heterozygous a t 0, 1, 2, and 3 l o c i , a t ov e r w i n t e r , b r e e d i n g peak, and f a l l peak samples. 176 -20 s > i o . cr o CL o tr OL 1 control grid (n=88) grid A (n= 213) i I ft 113 123 213 112 122 212 222 223 331 GENOTYPE FIGURE 19: Genotypic p r o p o r t i o n s o f males on c o n t r o l areas and continuous removal g r i d ( g r i d 4 ) . 50 40 30J g.20 cr o CL O cr CL 10 ^control grid (n=88) _Jgnd4 (n=213) v 0 1 2 3 NUMBER OF HETEROZYGOUS LOCI FIGURE 20: P r o p o r t i o n o f males from the c o n t r o l g r i d and the continuous removal g r i d ( g r i d 4) h e t e r o -zygous a t 0, 1, 2, and 3 l o c i . 177 home cage cotton bedding t i p f l o o r •microswitch -ink pad • p a r t i t i o n -mouse •paper -strange cage FIGURE 21: Horizontal maze designed f o r studying the tendency of a mouse to leave a f a m i l i a r area and explore an unfamiliar one. (Scale: 1 cm = 10.2 cm) 178 REDUCTION IN DENSITY FIGURE 22: Schematic representation of seasonal changes i n populations of Peromyscus maniculatus. 179 TABLES Table 1 Mean Number Caught/Minimum Number Al i v e on Control Grids Total March-October November-February Grid 1 males .84 .87 .76 females .78 .83 .64 Grid 3 males .83 .85 ! .77 females .82 .89 .63 Table 2 Observed Rates of Su r v i v a l , Recruitment and Trap-Overlap Indices i n Control Populations  Sex: Males Females Season: Spring re-organization Main breeding F a l l i n -crease Over-winter Spring re-organization Main breeding F a l l i n -crease Over-winter Mean Minimum 2-week survival rate: .74 .85 .79 .77 .77 .87 .81 .80 Mean 2-week recruitment rate: .21 .13 .35 .15 .11 .16 .32 .14 ^lean number of rec r u i t s per 2 weeks: 2.1 .9 3.4 1.8 .9 1.1 2.9 1.2 Number of Double Captures: 12 13 77 83 40 59 119 109 Trap-Overlap Index:** .08 .03 .16 .20 .26 .14 .240 .268 * A double-capture consists of two di f f e r e n t mice being **Trap-Overlap Index i s the observed number of 'double captured at the same trap st a t i o n within one 2-night captures' divided by the maximum which could be ex-trapping period. pected. Calculation of expected numbers i s described i n the text. 181 Table 3 Number of Residents, Disappearing Mice, Recruits and Transients with Weights Greater and Less Than the Weekly Mean Weights, i n A l l Seasons (Males Only). Season Glass Numbet of males with Weights: Above the Mean Below the Mean Ch.i2 Spring re-organiza-tion residents disappearing mice 14 7 recr u i t s transients 5 4 rec r u i t s § transients 5 12 6 7 13 3.832 NS Main breeding residents disappearing mice 7 12 recr u i t s transients 4 10 re c r u i t s § transients 14 residents § disappearing mice 19 5 9 16 16 32 14 NS NS 4.757 p< .05 F a l l Increase residents disappearing mice 5 12 recr u i t s transients 14 23 re c r u i t s § transients 37 residents § disappearing mice 17 4 10 53 35 88 14 NS 4.388 ,10> p>.05| 5.920 ,025>p >.01p Over-winter residents disappearing mice 14 14 rec r u i t s transients 5 9 10 21. 18 18 1.904 ^ • - I O -NS 182 Table 4 Number of Residents, Disappearing Mice, Recruits, and Transients Having Weights Above and Below the Weekly-Means, i n a l l Seasons (Females Only). Season Class Number of Females with Weights C h i 2 Above the Mean Below the Mean Spring re-organiza-t i o n residents 11 11 disappearing mice 9 10 NS rec r u i t s 2 3 transients 1 6 NS recr u i t s § transients 3 9 Main Breeding residents 7 5 disappearing mice 9 9 NS rec r u i t s 6 18 transients 10 20 NS recruit s § transients 16 38 residents § disappearing mice 16 14 3.644 J0>p>.05 F a l l Increase residents 11 7 disappearing mice 17 6 NS recr u i t s 11 45 transients 14 32 NS recr u i t s § transients 25 77 residents 5 disappearing mice 28 13 22.193 p<.001 Over-winter residents 17 8 disappearing mice 6 15 5.608. p <-02 rec r u i t s 5 12 transients 5 9 NS 1 3 3 Table 5 Capture Frequencies of Breeding and Non-Breeding Mice on Control Areas During the Spring Reorganization Sex Class Number of Captures Breeding Not Breeding males residents disappearing mice 5 18 4 15 NS re c r u i t s transients 3 9 2 10 NS females residents disappearing- mice 3 21 10 6 x 2 = 8.780 p < .001 re c r u i t s transients 1 4 2 4 Table 6 Observed and Expected Numbers of Juvenile Recruits on Control Areas During the Main Breeding Season Grid Year Males Females Observed Expected Observed Expected 1 '73 1 23.8 10 23.8 •74 2 8.7 4 8.7 3 •73 3 8.7 6 8.7 •74 6 2.2 5 2,2 Total 12 43.4 25 43.4 184 Table 7 Number of Adult Residents, Disappearing Mice, Recruits, and Tran-sients with Weights Greater and Less Than the Weekly Mean Weights In a l l Seasons. A l l Juveniles Have Been Removed From the Sample. Sex Class Number of mice with weights: C h i 2 Above the Mean Below the Mean males resident § disappearing mice re c r u i t s § transients 19 14 14 25 2.567 p<..20 females residents § disappearing mice rec r u i t s § transients 16 14 13 27 2.268 p< .20 Table 8 Capture Frequencies of Breeding and Non-Breeding Mice on Control Areas, During the Main Breeding and F a l l Increase Periods.  Season Sex Breeding Class C h i 2 Condition Resi- Disappear- Tran- Recruits dents ing mice sients Main Breeding males Breeding(B) Not-breed-ing (NB) 80 31 9 41 30 59 24 28 39.555 p< .005 B/NB 2.67 .53 .38 1.08 fern. Breeding Not-breed-ing 42 33 15 55 55 67 32 31 21.618 p<.005 B/NB .76 .49 .47 1.77 F a l l Increase males Breeding Not-breed-ing 13 24 11 9 38 24 72 205 72.597 p< .0005 B/NB .342 1.00 .153 .044 fem. Breeding Not-breed-ing 42 19 30 15 61 39 140 38 18.161 p< .0005 B/NB .688 .487 - .214 .395 185 Table 9 Breeding Condition on F i r s t Capture of Recruits and Transients, i n the Main Breeding and F a l l Increase Periods Season Sex Breeding Condition When F i r s t Captured Class Recruits Transients C h i 2 1 Main breeding males Breeding Not Breeding 10 5 9 20 3.767 P .10 females Breeding Not Breeding 6 7 16 23 NS F a l l Increase males Breeding Not Breeding 2 8 65 51 (Fisher) p =.06 females Breeding Not Breeding 7 9 49 37 .494 NS Table 10 Observed and Expected Trap-Overlap Frequencies, by Sex and Age, In the F a l l Increase Period Adult Adult Juvenile Juvenile Males Females Males Females Observed 41 55 36 64 x2=24.902 Expected 65.0 62.8 25.9 42.3 p< .005 * see text f o r d e f i n i t i o n 186 Table 11 Observed and Expected Numbers of Juvenile Recruits on Control Areas i n the F a l l Increase Period Grid Year Males Females Observed Expected Observed Expected 1 '72 12 8.7 11 8.7 '73 20 19.5 22 19.5 •74 3 15.2 6 15.2 .3 '72 18 13.0 16 13.0 •73 15 •15.2 20 15.2 •74 12 15.2 12 15.2 Total 80 86.8 87 86.8 Table 12 Comparison of Juvenile Recruitment i n the Main Breeding and F a l l Increase Periods  Sex Main F a l l Breeding Increase Inales observed 12 80 x2=11.857 expected 43.4 86.8 p < .001 females observed 25 87 x2=3.603 expected 43.4 86.8 .10>10>.05 13:7 Table 13 Loss of Potential Juvenile Recruits Between Pregnancy arid Recruitment Season loss bei Fore nursing loss a f t e r nursing tota! L loss number proportion number proportion number proportion Main Breeding 39.00 .310 49.80 .396 : 88.80 .707 F a l l Increase 108.25 .385 6.60 .023 114.85 .408 Table 14 Trap-Overlap Frequencies i n the Overwinter Period Number of Double Captures Males Females Observed 83 109 \ x 2 = 12.713 Expected 107.4 84.4 p < .0005 Table 15 Distributions of Durations of L i f e of Females Before the Start of the Overwinter Period Class Number of Females with Durations of L i f e : residents disappearing mice above the mean below the mean x 2 = 1.097 .3 > p > .2 15 16 7 16 188 Table 16 Sex Ratios (Males per Female) of Mice Moving Onto Removal Areas, and of Residents on Control Areas, During the Spring Reorganization  Grid Year # Males # Females Sex Ratio Pulsed Removal Continuous Removal 1973 1974 1974 8 11 18 4 5 8 2.0 2.2 2.3 Total Removal 37 17 2.2 Controls 25 25 1.0 Table 17 Number of Residents on Control Areas and Colonists To Removal Areas with Weights Greater and Less Than the Weekly Mean Weights on Control Areas Sex Grid Number of Mice With Weights: Above the Mean Below the Meat Males Control Removal 14 5 10 26 x2= 8.871 p <.005 Females Control Removal 11 11 1 17 x2= 7.310 p < .01 189 Table 18 Proportions of Resident Control Mice, and Removal Colonists Caught i n Breeding Condition at Least Once During the Spring Reorganization  Sex Grid # Breeding at #Not Breeding Proportion least once Breeding Males Control 5 18 .22 Removal 4 33 • 11 Females Control 3 21 .13 Removal 2 15 .12 Table 19 Trap-overlap frequencies on the Pulsed Removal and Control Areas (Sexes Combined).  Season Grid Observed # double captures Maximum ex-pected dou-ble captures Index of Trap-Over-lap (0/E) P Spring Reorganiza-t i o n Controls Pulsed removal 40 5 156 24 .26 .21 > .5 Main breeding Controls 59 437 .14 > .5 Pulsed removal 11 86 .13 F a l l increase Controls 119 495 .24 > . 2 Pulsed removal 22 119 .18 Over-winter Controls 109 407 .27 > .5 Pulsed removal 40 116 .34 Table 20 Observed and Expected Numbers of Juvenile Recruits on the Control and Pulsed Removal Grids Sex Season Grid Number of Recruits 0/E C h i 2 P Observed Expected males • Main Controls 12 43.4. .28 Breeding Pulsed Removal 3 4.3 .70 F a l l Controls 80 86,8 .92 3.128 10>P>05 Increase Pulsed Removal 24 17.3 1.39 females Main Controls 25 43.4 .58 Breeding Pulsed Removal 4 4.3 .93 F a l l Controls 87 86.8 1.00 NS Increase Pulsed Removal 16 17.3 ,92 Table 21 Capture Frequencies of Breeding and Non-Breeding Mice; Control Residents, Total Control Population, and Colonists _' to the Continuous Removal Grid Sex Season Grid # Times Captured B/NB Breeding Not Breeding Males Main Removal 17 45 .27 Breeding Total Controls 161 151 .52 Control Resi-dents 80 30 .73 F a l l Removal 28 47 .37 Increase Total Controls 57 339 .14 Control Resi-dents 13 38 .26 Females Main Removal 15 27 .36 Breeding Total Controls 145 185 .44 Control Resi-dents 42 55 .43 F a l l Removal 18 32 .36 Increase Total Controls 106 278 .44 Control Resi-dents 42 61 .41 191 Table 22 The Proportions of Mice Weighing Less than 15 g, and Between 15 and 16 g, Which Were Breeding When Caught Oh The Continuous Removal Area and on the Control Areas Weight Class Males Females <15 g 15 g - 16 g <1S g 15 g - 16 g Removal Con-t r o l Removal Con-t r o l Removal Con-t r o l Removal Con-t r o l Breeding Not-Breeding 2 4 89 101 10 20 69 188 9 18 90 205 8 29 32 150 Proportion Breeding .022 .040 .145 .106 .100 .089 .250 .193 . P .41 .50 > P > .40 p >.50 P >.50 Table 23 Recruitment of Juveniles onto Control Areas and the Continuous Removal Area, During the Main Breeding and F a l l Increase Periods. The Calculation of Expected Values i s Explained i n the Text . Sex Season Grid Number of Recruits Observed Expected Males Main Breeding Controls 12 43.4 Removal 4 ' 17.7 F a l l Increase Controls 80 86.8 Removal 49 35.3 Females Main Breeding Controls 25 43.4 Removal 12 15.8 F a l l Increase Controls 87 86.8 Removal 35 32.2 3 192 Table 24 Characteristics of Dispersing Mice-(Mice Moving Onto and Off Control Areas, and Mice Colonizing Removal Areas) When Compared to Mice Resident on Control Areas Season Mice Moving Onto and Off Control Areas Colonists on the Continuous Removal Areas Spring Reorganization - more males - l i g h t e r mice - breeding females - more males - l i g h t e r males Main Breeding - non-breeding males - l i g h t e r mice - juveniles -non-breeding males - l i g h t e r mice -more males -juveniles F a l l Increase - breeding males - l i g h t e r mice - juveniles - breeding males - l i g h t e r mice - juveniles Overwinter - l i g h t e r mice - l i g h t e r mice Table 25 Regressions of Number Caught on the Continuous Removal Grid Against Minimum Number Known to be Al i v e on the Two Con-t r o l Areas. The Regression Model Used Was: Number Caught = Constant + A (Minimum # Alive) Regression Constant A R 2 A l l mice: Control 1 Control 3 1,48 2.14 .25 .33 .21** .35** Males: Control 1 2.33 .18 ** .19 Control 3 1.92 .33 ,23 Females: Control 1 Control 3 2.34 1.10 .09 .24 .04 .18** A l l mice: Mean Controls .60 .17 .31** Males: Mean Controls 1.39 .15 ** .27 Females: Mean Controls .71 .12 .10* * P <.05 ** P <.01 Table 26 Regressions of Number Caught on the Continuous Removal Grid Against Density and Rate of Increase on the Control . Areas. The Regression Model Used Was: Number Caughtr Constant + A (Density) + !fi (Rate of Increase) Regression Constant A B R 2 A l l mice Males Females -.40 1.60 -1.18 .18 .14 .18 37.44 8.28 21.75 ** .39 .28** .18* ** P <.01 * P< .05 Table 27 Regressions of Recovery Ratio on the Continuous Removal Area Against Density and Rate of Increase on the Control Areas. The Regression Model Used Was: Recovery Ratio = Constant + A (Density) + B (Rate of Increase) Regression Constant A B R 2 A l l mice Males Females .43 .60 .43 -.002 -.01 -.01 1.85 .77 2.04 * .15 .10 ** .23 ** P <.01 * P< .05 Table 28 The Results of Laboratory Crosses Showing The Inheritance of the Two A l l e l e s at the Transferrin Locus Phenotypes Number of Offspring Number Number 2 x P of Parents of the Phenotype of of L i t t e r s Offspring J J JM MM J x J 94 _ _ 25 94 _ J x JM 26 14 •- 14 40 3.60 .10>P>. 05 J x M - 10 - 2 10 -JM xJM 8 32 8 10 48 5.33 .10>P>. 05 M x JM - 7 3 3 10 1.60 .20>P>. 10 M x M - • - 4 1 4 — Total 55 206 Table 29 The Results of Laboratory Crosses Showing the Inheritance of the Two A l l e l e s at the Esterase Locus Phenotypes Number of Offspring Number Number 2 x P of Parents of the Phenotype of of L i t t e r s Offspring FF FS SS F x FS 1 3 — 1 4 -F x S - 8 - 3 8 -FS x FS 12 25 13 13 50 .04 >.50 S x FS - 55 63 35 118 .27 >.50 S x S - - 7 3 7. Total 55 187 1 9 5 Table 30 The Results of Laboratory Crosses Showing The Inheritance of the Two A l l e l e s at the Glutamate Oxalate Transaminase Locus Phenotypes Number of Offspring Number Number 2 X P of Parents of the Phenotype: of of L i t t e r s Offspring FF FS SS F x F 76 _ _ 17 • 76 _ F x FS 52 46 - 28 98 .37 P .50 F x S - 8 - 2 8 -FS x FS 3 4 1 3 8 - . S x FS — 10 2 5 12 2.67 .20>P>.10 Total 55 202 Table 31 Genotypes Used i n the Genetic Analyses Genotype Code Genotype Recorded Frequency Tf GOT ES 99 113 J J FF SS .17 .18 123 J J FS SS .15 .14 112 J J FF FS .11 .08 212 JM FF FS .10 .07 213 JM FF SS .09 .08 222 JM FS FS .07 .06 122 J J FS FS .07 .07 223 JM FS SS .06 .06 Rare Genotypes MM or SS or FF .18 .26 Table 32 Observed and Expected Genotype Frequencies on Control Areas . Sex Sample G e n o t y p e 2 113 123 213 112 122 212 222 223 Rare X P Geno-types males Winter Observed 8 11 6 4 5 ( 11 ) 12 2.126 NS Expected 8.4 7.8 4.7 6.5 5.5 ( 11.4 ) 12.6 Breed- Observed 13 6 5 6 3 ( 10 ) 4 5.646 NS ing Expected 10.0 4.3 5.7 7.7 3.8 C 7.4) 8.2 F a l l Observed 23 26 12 6 7 11 7 10 16 12.703 P>.10 Expected 22.4 17.0 11.5 12.9 9.3 7.5 5.1 10.3 21.8 females Winter Observed 8 . 10 6 2 5 c 13 ) 11 2.025 NS Expected 7.2 7,9 5.6 3.9 4.1 c 12.1 ) 12.4 Breed- Observed 4 11 14 9 5 c 7 ) 16 16.977 .01>P>.005 ing Expected 8.8 7.7 7.2 5.9 4.9 ( 14.9 ) 16.3 F a l l Observed 12 21 11 3 8 7 6 6 24 7.754 NS Expected 12.2 14.5 9.1 7.4 7.4 6.2 6.2 9.6 25.6 Table 33 Observed and Expected Numbers of Mice Having 0, 1, 2 and 3 Heterozygous Loci Sex Sample # Heterozygous Loci 2 X P 0 1 2 3 males Winter Observed 14 25 15 3 .072 NS Expected 13.3 25.2 15.3 3.3 Breeding Observed 13 19 12 3 1.102 NS Expected 13.8 21.3 10.4 1.5 (combining 2 and 3) F a l l Observed 31 49 28 8 1.164 NS Expected 31.8 51.3 27.4 5.6 Females Winter Observed 10 26 13 4 1.112 NS Expected 11.7 23.2 15.0 3.1 Breeding Observed 8 44 13 1 16.115 P< .005 Expected 15.1 28.4 18.2 4.5 F a l l Observed 21 49 21 7 3.567 NS Expected 21.7 42.5 28.0 5.0 198 Table 34 Survival Rates Estimated From Regression Models With Genotypic Frequencies Allowed to Vary (Seasons-Only Model) Or Held Constant at Their Mean Values Sex Season Estimated Minimum 2-Week Survival Rate Constant-Genotype Model Males Spring reorganization .733 .684 Main Breeding .874 .866 F a l l Increase .807 .782 Overwinter .868 .878 Females Spring reorganization .747 .225 Main Breeding .858 .745 F a l l Increase .808 .809 Overwinter .829 .666 Table 35 Proportions of Mice Heterozygous at 0, 1, 2 and 3 Lo c i : Peak Breeding, F a l l Peak and Winter Samples  Sample # Heterozy- males females gous l o c i Control Continu- Pulsed Control Continu- Pulsed grids ous re- removal grids ous re- removal moval moval n=47 n=63 n=ll n=66 n=50 n=16 Peak 0 .28 .32 .27 .12 .36 .38 Breeding 1 .40 .48 .64 .67 .40 .31 2 .26 .16 .09 ,20 .20 .31 3 .06 .04 .00 .01 .04 .00 n=116 n=71 n=30 n=98 n=50 n=26 F a l l peak 0 .27 .28 .43 .21 .30 .38 1 .42 .47 .40 .50 .56 .58 2 .24 .24 .13 .21 .10 .04 3 .07 .01 .03 .08 .04 .00 n=57 n=50 n=10 n=53 n=45 n=18 Winter 0 .25 .32 .50 .19 .36 .44 1 .44 .36 .50 .49 .40 .56 2 .26 .32 .00 .25 .22 .00 3 .05 .00 .00 .07 .02 .00 y \ •5 199 Table 36 Agonistic and Social Behaviors Recorded During the Neutral Arena Encounters Behavior Behavior Proportion of Mice Tested Which Type Showed This Behavior Agonistic attack § chase .12 upright threat .22 threat .22 submission .14 rapid avoidance .27 Social grooming opponent .29 mounting opponent .10 approach .61 upright .30 naso-anal s n i f f i n g .23 following opponent .15 avoidance .56 being groomed .33 being mounted .12 Table 37 Factor Solution for Agonistic Behavior. . Behavior Factor Loadings Factor 1(AF1) Factor 2 (AF2) attack and chase upright threat threat submission rapid avoidance .869 .829 . 860 -.043 .325 .082 .135 .137 .898 .566 % of t o t a l variance accounted for: 48.9 20.4 200 Table 38 Factor Solution for Social Behaviors Behavior - Factor Loadings Factor 1 (SF1) Factor 2 (SF2) Factor 3 (SF3) grooming opponent .834 .180 -.059 mounting opponent .770 -.035 .072 approach. .698 -.013 .272 upright .297 .150 .669 naso-anal s n i f f i n g .806 .097 -.088 following opponent .744 .087 .058 avoidance -.153 -.149 .823 being groomed .177 .912 -.003 being mounted -.019 .911 -.013 % of t o t a l variance account for 36.6 18.3 12.9 Table 39 Comparison of Factor Scores of Breeding arid Non-breeding Males Factor Breeding Condition N Mean Mean Square F r a t i o P (df 1,103) (1-tailed) AF1 Breeding 28 .204 .849 2.123 < 10 Not-breeding 77 .0004 .400 AF2 Breeding 28 -.356 1.245 2.327 <.10 Not-breeding 77 -.110 .535 SF1 Breeding 28 .061 .075 .211 NS Not-breeding 77 .001 .355 SF2 Breeding 28 .015 1.350 3.971 Not-breeding 77 .271 .340 < .025 SF3 Breeding 28 .222 .747 1.737 NS Not-breeding 77 .413 .430 201 Table 40 Comparison of Mean Factor Scores of Resident Males on Control Grids with .Those of Colonists on the Continuous Removal Grid ' Factor Control males fn=1051 Continuous Removal males fn=65") F df a, 169) P mean standard deviation mean standard deviation AF1 AF2 .054 -.175 .636 .736 -.128 -.154 .520 .524 3.82 .043 .04 .82 SF1 -.104 .645 -.244 .633 1.93 .16 SF2 .203 .591 -.232 .618 .09 .76 SF3 .461 .571 .514 .498 .38 .54 Table 41 C l a s s i f i c a t i o n functions Derived from Discriminant Analysis of Resident Males from Control Grids and Colonists To the Continuous Removal Grid, Using Factors AF1 and SF1. Group Residents Colonists AF1 .131 -.425 SF1 -.243 -.631 Constant -.709 -.797 202 Table 42 Summary of Analysis of Factor Scores For Agonistic arid Social Factors  Factor Influenced by: Breeding Condition Weight Grid ( r e s i -dent or colonist) Retests Genotype # Heterozy-gous l o c i AFl AF2 P < .10 P < .10 P < .05 P =<.04 _ P <.025 P < .05 SFl SF2 SF3 P <.025 P < .025 P = .16 P < .05 P <.005 P <.05 Table 43 Mean Scores i n the Maze Test for Males and Females From Control Grids (n=158): Comparisons Made With the Mann-Whitney U Test  Variable mean (standard deviation) P males females LLH 24.99 (22.06) 17.88 (19.45) .002 LES 41.44 (23.64) ' 35.40 (25.18) .018 THOM 43.01 (22.12) 41.56 (20.76) .174 TSTRNG 7.75 (15.46) 9.25 (15.27) .027 NSECT 7.64 ( 7.08) 9.19 ( 7.00) .019 203 Table 44 Comparisons of Maze Behavior of Breeding and Non-breeding Mice From the Control Grids (n=158) Comparisons Were Made With Mann-Whitney U Tests V a r i a -ble Males Females Mean (standard deviation) P (Mean (standard deviation) P Breeding Not breeding Breeding Not breeding LLH 20.15(23.29) 29.68(21.48) .042 12.25(17.27) 17.27(17.42) .042 LES 27.08(27.50) 43.14(21.44) .025 21.80(23.59) 37.88(23.80) .003 THOM 29.46(25.13) 44.55(20.35) .024 32.45(23.29) 44.54(18.63) .012 TSTRNG 15.08(23.40) 7.25(18.49) .319 18.60(21.04) 7.80(12.45) .019 NSECT 8.69( 7.15) 8.18( 7.20) .293 12.85( 5.25) 8.78( 7.12) .018 Table 45 Comparisons of Maze Behavior of Mice From Control, Pulsed Removal, and Continuous Removal Grids. Comparisons Were Made with Kruskal-Wallis Analyses of Variance Variable Breeding Males Females Condition (n=158) (n=145) means means Control Continu- Pulsed P Control Continu- Pulsed P ous re- remo- ous re- remo-moval val moval val Breeding LLH 20.15 27.71 24.80 .83 12.79 25.91 28.00 .04 LES 27.08 51.57 48.20 .13 22.47 35.91 39.00 .08 THOM 29.46 51.43 54.20 .06 31.05 43.64 42.21 .12 TSTRNG 15.08 7.86 2.80 .46 19.58 7.36 8.71 .07 NSECT 8.69 2.71 7.40 .11 12.74 9.77 9.71 .29 •Not Breeding LLH 29.68 21.66 22.67 .07 17.27 12.69 21.50 .04 LES 43.14 44.71 37.90 .41 37.88 34.44 41.30 .52 THOM 44.55 42.92 42.44 .81 44.54 39.47 48.50 .57 TSTRNG 7.25 5.47 8.85 .17 7.80 9.19 5.20 .80 NSECT 8.18 6.16 8.87 .33 8.78 8.72 7.13 .46 204 Table 46 Comparisons of General A c t i v i t y Scores of Mice From Control, Pulsed Removal, and Continuous Removal Grids Sex Grid Mean a c t i v i t y score (log transforms) Standard error N F df P Males Controls 8.470 " .062 60 6.349 2,134 <.005 Pulsed Removal 8.453 .088 30 Continuous Re-moval 8.773 .070 47 Females Controls Pulsed Removal Continuous Re-moval 8.644 8.486 8.746 .055 .092 .065 39 14 28 2.718 2,78 <.10 205 EEF EBENCES Anderson, J . 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