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Ecological adaptations in two species of shrews Hawes, Myrnal Leong 1975

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ECOLOGICAL ADAPTATIONS IN TWO SPECIES OF SHREWS fay Myrnal Leong Hawes B. A., U n i v e r s i t y o f C a l i f o r n i a , Berkeley, 1969 A t h e s i s submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of Doctor of Philosophy i n the Department of Zoology We accept t h i s t h e s i s as conforming to the r e q u i r e d standard The U n i v e r s i t y of B r i t i s h Columbia January, 1975 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver 8, Canada Date A ABSTRACT L i f e h i s t o r y s t r a t e g i e s and e c o l o g i c a l a d a p t a t i o n s of two s i m i l a r s p e c i e s cf shrews (Sorex va^rans vagjrans and Sorex obscurus setosus) were examined i n southwestern B r i t i s h Columbia i n an attempt to understand 1) how they are able to c o e x i s t i n sympatry, 2) what kinds and degrees o f i n t e r s p e c i f i c c o m p e t i t i o n are ev i d e n t , and 3) how s t r a t e g i c responses to s e l e c t i v e p r e s s u r e s d i f f e r between s p e c i e s and among h a b i t a t s . A t r a p and rec a p t u r e program allowed the study of p o p u l a t i o n dynamics and i n d i v i d u a l l i f e h i s t o r i e s of the two s p e c i e s i n a f o r e s t s i t u a t i o n where they were sympa t r i c . Standardized snap-trap l i n e s were s e t through s e v e r a l h a b i t a t types t o a s c e r t a i n b a s i c d i s t r i b u t i o n a l p a t t e r n s and h a b i t a t p r e f e r e n c e s of each s p e c i e s . F i n a l l y , the c o l l e c t i o n and specimen p r e p a r a t i o n of ext e n s i v e s e r i e s °f Sorex from lowland grassy f i e l d s f a c i l i t a t e d examination - o f . seasonal and geographic v a r i a t i o n i n morphology a n d . r e p r o d u c t i v e . s t r a t e g y . Sorex v a j r a n s and Sorex obscurus share a common l i f e h i s t o r y p a t t e r n , s e v e r a l f e a t u r e s of which were examined i n d e t a i l with r e f e r e n c e to t h e i r a d a p t i v e . s i g n i f i c a n c e . Many adaptations were co n s i d e r e d i n terms of energy l i m i t a t i o n s . Both i n t r a - and i n t e r s p e c i f i c t e r r i t o r i a l i t y were evident i n non-breeding ( f i r s t y e a r ) . i n d i v i d u a l s of each s p e c i e s . Home range a n a l y s i s , u s i n g an. e l l i p t i c a l model, r e f l e c t e d the abandonment of t e r r i t o r i a l i t y i n breeding a d u l t s as home I l l range s i z e i n c r e a s e d . Hy c o n c l u s i o n s are t h a t s t r o n g s i t e attachment and the establishment of t e r r i t o r i e s during the non-breeding time of l i f e serve to ensure the t e r r i t o r y h o lder s u f f i c i e n t food f o r o v e r w i n t e r i n g . Species d i s t r i b u t i o n s and h a b i t a t analyses show t h a t , although the two s p e c i e s o v e r l a p g e o g r a p h i c a l l y , competition i s m i t i g a t e d through, h a b i t a t s e g r e g a t i o n at the microgeographic l e v e l , with s o i l type and the a s s o c i a t e d s o i l fauna appearing. to be s i g n i f i c a n t f a c t o r s . Sorex vacjrans i s c o m p e t i t i v e l y s u p e r i o r i n the r e l a t i v e l y r i c h e r s o i l s , while Sorex obscurus has the advantage i n the more a c i d i c s o i l s . I n t r a s p e c i f i c comparison of f o r e s t - and g r a s s l a n d -i n h a b i t i n g . Sorex vacjrans r e v e a l b a s i c d i f f e r e n c e s i n r e p r o d u c t i v e s t r a t e g y . The attainment of sexual maturity i n f i r s t year females i s r e l a t i v e l y common i n lowland g r a s s l a n d h a b i t a t , whereas no such case i s documented i n f o r e s t h a b i t a t . The s h o r t e r g e n e r a t i o n , time appears to.be an a d a p t i v e response to a s i t u a t i o n where f o o d - i s l e s s l i m i t i n g and the r e p r o d u c t i v e season i s longer. -E c o l o g i c a l s t r a t e g i e s and t h e i r e v o l u t i o n i n f c r e s t and g r a s s l a n d p o p u l a t i o n s , and the s i g n i f i c a n c e o f e v o l u t i o n a r y ecology to shrew s y s t e m a t i c s are d i s c u s s e d i n l i g h t c f the f i n d i n g s . i v TABLE OF CONTENTS A b s t r a c t i i L i s t of Tables ., .. v i i L i s t of F i g u r e s i x Acknowledgements x i i I n t r o d u c t i o n 1 Methods and R a t i o n a l e 6 1. L i v e - t r a p p i n g 6 1.1. The study area and g r i d 7 1.2. Trapping procedure 9 2. Snap-trapping.................... 14 2.1. Snap-trapping areas 14 2.2. Trapping technigue 15 3. P o p u l a t i o n sampling 16 R e s u l t s and D i s c u s s i o n 20 P a r t I: The Ecology of Sorex vagjcans and S. obscurus .. 20 1. Background 20 2. Height changes 21 3. Molt .... 21 3.1. F a l l molt 24 3.2. S p r i n g molt 25 3.3. A d v e n t i t i o u s molt 26 3.4. Adaptation and the p a t t e r n and timing cf molt 26 4. Timing of molt and r e p r o d u c t i o n ................. 28 5. Side glands 33 5.1. The adaptive s i g n i f i c a n c e of s i d e gland odor 35 V 6. Home range 39 6.1. Background 39 6.1.1. S t a t i s t i c a l methods of home range c a l c u l a t i o n 40 6.2. The e l l i p t i c a l model 41 6.3. Home range s i z e 42 6.3.1. Sample s i z e 42 6.3.2. Seasonal change i n home range s i z e and l o c a t i o n . 47 6.3.3. Sexual d i f f e r e n c e s i n home range s i z e 63 7. T e r r i t o r i a l i t y 65 7.1. R e l a t i v e d i s t r i b u t i o n of ncn-breeding home ranges 65 7.2. S i g n i f i c a n c e o f t e r r i t o r i a l i t y 70 7.3. Mechanism of t e r r i t o r i a l i t y 73 7.4. i n t e r s p e c i f i c t e r r i t o r i a l i t y 76 8. Population, dynamics 80 8.1. P o p u l a t i o n numbers 80 8.2. S u r v i v o r s h i p and m o r t a l i t y 83 8.2.1. L i f e t a b l e s and s u r v i v o r s h i p curves .. 83 8.2.2. A d u l t . m o r t a l i t y 92 8.3. Recruitment ............................... 94 8.4. F e c u n d i t y 103 9. Species d i s t r i b u t i o n i n t h e . l i v e - t r a p p i n g area .. 109 9.1. C o r r e l a t i o n with h a b i t a t 109 9.2. Seasonal changes i n h a b i t a t c o r r e l a t i o n ... 112 10. Geographical d i s t r i b u t i o n of shrews ............. 116 v i 10.1. Background 116 10.2. D e s c r i p t i o n of h a b i t a t s 117 10.3. Trapping r e s u l t s 119 11. H a b i t a t d i f f e r e n c e s and the t i m i n g of events .... 123 12. Summary 125 P a r t I I : Seasonal and G e o g r a p h i c . V a r i a t i o n 129 1. Seasonal v a r i a t i o n 130 1.1. S k u l l height 130 1.2. Weight 134 1.3. Body l e n g t h . 137 1.4. The adap t i v e s i g n i f i c a n c e of seasonal v a r i a t i o n i n shrews ..... 140 2. Geographic v a r i a t i o n ............................ 143 2.1. Toothwear and t a i l length ,. 143 2.2. Seasonal onset of re p r o d u c t i o n ............ 147 2.3. Age at f i r s t r e p r o d u c t i o n 149 3. A d a p t a b i l i t y of , shrews 166 General D i s c u s s i o n 168 1. I n t e r - and i n t r a s p e c i f i c comparisons 168 2. The e v o l u t i o n of l i f e h i s t o r y s t r a t e g i e s i n shrews 170 2.1. Energy as a l i m i t i n g f a c t o r . 172 3. E c o l o g i c a l s t r a t e g y o f . f o r e s t - i n h a b i t i n g shrews . 181 4. E c o l o g i c a l s t r a t e g y of g r a s s l a n d - i n h a b i t i n g shrews 185 5. E v o l u t i o n a r y ecology and.shrew.systematics....... 189 Con c l u s i o n s 194 L i t e r a t u r e C i t e d 198 V l l LIST OF TABLES I. L i v e - t r a p p i n g e f f o r t : dates and number c f rounds 11 I I . Home range s i z e and l o c a t i o n f o r Sorex vajr a n s and Sorex obscurus i n d i v i d u a l s captured ten cr more times both when non-breeding and breeding ......... 48 I I I . Comparison of breeding p o p u l a t i o n s by generation 71 IVA. L i f e t a b l e s f o r Sorex v a j r a n s , .1971 g e n e r a t i o n , based on the disappearances from cohorts of marked i n d i v i d u a l s .......... 84 IVB. L i f e t a b l e s f o r Sorex obscurus, 1971 g e n e r a t i o n , based on the disappearances . from coho r t s of marked i n d i v i d u a l s .......... 85 VA. L i f e t a b l e s f o r Sorex v a j r a n s , 1972 g e n e r a t i o n , based on the disappearances from cohorts of marked i n d i v i d u a l s .......... 86 VB. L i f e t a b l e s f o r Sorex obscurus, 197 2 g e n e r a t i o n , based on the disappearances from cohorts of marked i n d i v i d u a l s 87 VIA. Fate of v a r i o u s c o h o r t s of the generation born i n 1971 96 VIB. Fate of v a r i o u s c o h o r t s of the generation born i n 1972 97 VII. Average oxygen consumption i n two s p e c i e s c f shrews a t three p o p u l a t i o n l e v e l s 102 VIII. Fates of v a r i o u s c o h o r t s of the generation born i n 1973 104 IX. P r o d u c t i v i t y of breeding l i v e - t r a p p e d females, 1972 and 1973 107 X. Freguency o f capture of Sorex obscurus and Sorex vajr a n s i n the two major s o i l types i n the Research F o r e s t p l o t . 113 XI. Percentage cap t u r e s of s p e c i e s c a t e g o r i e s i n h a b i t a t types represented i n l i v e -t r a p p i n g p l o t 114 XII. Snap-trapping e f f o r t and r e s u l t s f o r each v i i i h a b i t a t 120 X I I I . Summary of snap-trapping catch of Sorex obscurus and Sorex vaarans 121 XIV. Comparison of onset of molt and r e p r o d u c t i o n i n sympatric Sorex vacjrans and Sorex obscurus 124 XV. Body l e n g t h comparisons of female Sorex vagrans from S e r p e n t i n e R i v e r and Westhai I s l a n d 141 XVI. Incidence of f i r s t year females breeding i n g r a s s l a n d h a b i t a t 152 LIST OF FIGURES i x 1. General s o i l map of l i v e - t r a p p i n g p l o t , 1 mile on Road K, U.B.C. Research F o r e s t , Maple Ridge, B.C. 8 2. Grassland sampling l o c a l i t i e s 17 3 A. Monthly weight s t a t i s t i c s , Sorex va^rans 22 3B. Monthly weight s t a t i s t i c s , Sorex obscurus 23 4. Timing of molt and pregnancy f o r i n d i v i d u a l females 29 5A. Timing of molt and r e p r o d u c t i o n i n l i v e -trapped shrews, 1972 31 5B. Timing o f molt and rep r o d u c t i o n i n l i v e -trapped shrews, 1973 32 6AB. Estimated home range s i z e as a f u n c t i o n of number of captures (Sorex vaarans) 44 6C. Estimated home range s i z e as a f u n c t i o n of number of captures (Sorex obscurus) 46 7A-G. Uon-breeding and breeding home range comparisons f o r i n d i v i d u a l s captured ten or more times i n each c o n d i t i o n (Sorex vacjrans) 50 8A-D. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l s captured ten or more times i n each c o n d i t i o n (Sorex obscurus) 57 9. Home range s i z e comparisons between breeding and non-breeding i n d i v i d u a l s 62 10. Home range s i z e as a f u n c t i o n of s p e c i e s , sex, and r e p r o d u c t i v e c o n d i t i o n . . . . . . . . . . . . . . 64 IIA. R e l a t i v e d i s t r i b u t i o n of non-breeding Sorex vaarans and Sorex obscurus at two time p e r i o d s (1971 generation) ................... 67 IIB. R e l a t i v e d i s t r i b u t i o n of non-breeding Sorex vagrans and Sorex obscurus a t two time pe r i o d s (1972 generation) 68 IIC. R e l a t i v e d i s t r i b u t i o n o f non-breeding Sorex v a j r a n s and Sorex obscurus at two time p e r i o d s (1973 generation) 69 12. Minimum known po p u l a t i o n per trap p e r i o d f o r l i v e - t r a p p e d shrews, by g e n e r a t i o n 81 13A. S u r v i v o r s h i p curves f o r May/June c o h o r t s , Sorex vagjrans 89 13B. S u r v i v o r s h i p curves f o r Hay/June c o h o r t s , Sorex obscurus 90 14A. Percent t o t a l r e c r u i t m e n t f o r the 1971 g e n e r a t i o n o f Sorex vacjrans and Sorex obscurus .................................... 98 14B. Percent t o t a l r e c r u i t m e n t f o r the 1972 g e n e r a t i o n of Sorex vajrans and Sorex obscurus 99 15. R e l a t i v e d i s t r i b u t i o n of s p e c i e s (based on frequency of capture) and s o i l types i n l i v e - t r a p p i n g p l o t 110 16. Seasonal v a r i a t i o n i n s k u l l h eight on age c l a s s : Sorex vagrans from Ladner A i r Base and S e r p e n t i n e River 132 17. Regression of s k u l l height cn age c l a s s , Sorex vagrans from Ladner A i r Base and Se r p e n t i n e R i v e r 133 18. Age c l a s s r e g r e s s i o n on time: Sorex vacjrans from Ladner A i r Base, 1971 c o h o r t 135 19A. Seasonal v a r i a t i o n i n body l e n g t h of westham I s l a n d female Sorex vacjrans 13 8 19B. Seasonal v a r i a t i o n i n body length c f S e r p e n t i n e R i v e r female Sorex-vajrans 139 20. Diagrammatic r e p r e s e n t a t i o n of morphological changes o c c u r r i n g s e a s o n a l l y i n Sorex ....... 142 21. Comparison of age c l a s s r e g r e s s i o n s on time f o r t h r e e g r a s s l a n d l o c a l i t i e s 145 22. Comparison of t a i l l e n g t h v a r i a t i o n f o r three g r a s s l a n d l o c a l i t i e s 146 23. Onset of events i n two h a b i t a t s of S2E§x vacjrans 150 x i 24A. Reproduction of f i r s t and second year females at Westham I s l a n d , 1972 154 24B. Reproduction of f i r s t and second year females at Se r p e n t i n e R i v e r , 1972 155 25. Reproduction of f i r s t and second year females at Westham I s l a n d , 1973 156 26. Reproduction of f i r s t and second year females at Ladner A i r Base, 1972 158 27. Age c l a s s e s of breeding and non-breeding Westham I s l a n d females during t h e i r f i r s t summer of l i f e 160 28. Summary of l i f e h i s t o r y t a c t i c s i n r e l a t i o n to e c o l o g i c a l f a c t o r s i n three h a b i t a t s of Sorex obscurus and Sorex vacjrans 180 29. R e l a t i o n s h i p between number of young and a d u l t s produced 182 x i i ACKNOWLEDGEMENTS F i r s t of a l l , I wish t o thank my parents f o r the understanding, encouragement, freedom, and l o v e they have always given me. Dr. Seth B. Benson and Dr. 0. P. Pearson were most i n f l u e n t i a l i n my d e c i s i o n to do graduate work, and I am g r a t e f u l , f o r t h e i r encouragement. My s u p e r v i s o r , Dr. J . Mary T a y l o r , , showed i n t e r e s t and enthusiasm i n my r e s e a r c h , and provided.. many h e l p f u l s u ggestions and g u i d e l i n e s . She c o n s c i e n t i o u s l y read the manuscript and I am t h a n k f u l f o r her. many _ comments, c r i t i c i s m s , and a d v i c e . -The other members of my committee, Drs. H. D. F i s h e r , W. S. Hoar, C. S. H e l l i n g , R. J . Hudson, and G. G. S. Scudder a l s o read and commented on the manuscript, and f o r t h i s I am a p p r e c i a t i v e . I am deeply indebted to Dr. C. J. Krebs and h i s students and workers f o r : c o n s c i e n t i o u s l y . s a v i n g f o r me the many, many shrews which were i n a d v e r t e n t l y caught i n t h e i r t r a p s . The s t a f f at the Museum of Ve r t e b r a t e -Zoology a t the Berkeley campus.of the U n i v e r s i t y of C a l i f o r n i a cleaned and catalogued the long s e r i e s of s k i n s a n d . s k u l l s prepared i n the course of t h i s research,.and I am a p p r e c i a t i v e of both t h e i r i n t e r e s t and thoroughness. I g r a t e f u l l y acknowledge the c o o p e r a t i o n . o f the s t a f f a t the U.B.C. Research Fo r e s t , where the m a j o r i t y of my f i e l d work was done. For t h e i r i n t e r e s t and f o r h e l p f u l . a n d s t i m u l a t i n g d i s c u s s i o n s on shrews I wish to thank Dr. 0. P. Pearson, x i i i Dr. S. B. Benson, and Mr. Darwen N. Hennings. Data a n a l y s i s was f a c i l i t a t e d by help from-the s t a f f o f the Biology Data Center at U. B. c._. I am p a r t i c u l a r l y indebted to Mrs. Dolores L a u r i e n t e and. Mr. Steve Eorden f o r t h e i r time and help i n programming. I am g r a t e f u l t c Dr. R. S. Hoffman f o r sending the manuscript and program output f o r the e l l i p t i c a l model. I g r a t e f u l l y acknowledge - the N a t i o n a l Research C o u n c i l of Canada f o r support and funding of t h i s research through grant No. A-3462 to Dr. J. - M. T a y l o r and through post-graduate s c h o l a r s h i p s t o myself. Most of a l l , I wish to.acknowledge here the help of my husband Dave, who was u n f a i l i n g l y , generous.with h i s time, energy, and t a l e n t s through a l l phases of t h i s p r o j e c t . The l i v e - t r a p p i n g program as i t was would.not have been p o s s i b l e were i t not f o r t h i s , .help; l i k e w i s e , the. snap-trapping program was shared by the two of us.... Dave adapted the e l l i p t i c a l model program to run on the . l o c a l computer i n s t a l l a t i o n , a n d . w r o t e the. p l o t t i n g program as well as s e v e r a l of the other data a n a l y z i n g programs. I am indebted to him f o r h i s p a t i e n c e , enthusiasm and ad v i c e , -and f o r the many f r u i t f u l d i s c u s s i o n s we had . concerning my p r o j e c t . During the w r i t i n g stage he f r e q u e n t l y served as b a b y s i t t e r , f o r which I am t r u l y t h a n k f u l . . He a l s o read the manuscript and provided many h e l p f u l comments. L a s t , but not l e a s t , I-wish to thank our son Carwin f o r h e l p i n g me keep my p e r s p e c t i v e while w r i t i n g t h i s t h e s i s . 1 INTRODUCTION The e v o l u t i o n of s p e c i e s i s e s s e n t i a l l y the e v o l u t i o n of t a c t i c s by which c e r t a i n genes or gene combinations are perpetuated through time. The s t r a t e g y i s d i r e c t e d towards s u c c e s s f u l maintenance and r e p r o d u c t i o n . o f . the i n d i v i d u a l and hence of the g e n e t i c components i t . houses.. The s p e c i f i c t a c t i c s used depend upon, and are the r e s u l t o f , the i n t e r a c t i o n s of f o u r primary f a c t o r s : .. . .. 1 ) the g e n e t i c i n f o r m a t i o n a v a i l a b l e to an organism by v i r t u e of i t s e v o l u t i o n a r y h i s t o r y 2) the sensory i n f o r m a t i o n a v a i l a b l e to an organism by v i r t u e of i t s i n d i v i d u a l experience 3) the energy, space, and.other resource c o n s t r a i n t s . 4) the p a r t i c u l a r environment i n which i t f u n c t i o n s . The study.of a d a p t a t i o n s and s t r a t e g i e s of s p e c i e s i s the r e s o l u t i o n of t h e s e . f a c t o r s and t h e i r r e l a t i v e r o l e s . In c o n s i d e r a t i o n of. the. above f a c t o r s , t h i s t h e s i s examines the b i o l o g y and p o p u l a t i o n dynamics of two s i m i l a r s p e c i e s o f shrews, Sorex vacjrans vacjrans Eaird.and Sorex obscurus setosus E l l i o t , i n southwestern- B r i t i s h Columbia. I t i s an attempt t o determine i n a comparative sense both the nature and v a r i a b i l i t y of t h e i r a d a p t a t i o n s and. l i f e h i s t o r y s t r a t e g i e s i n . order to deal. with.the questions o f how they are able t o c o e x i s t s y m p a t r i c a l l y , what kinds and degrees of i n t e r s p e c i f i c , c o m p e t i t i o n are e v i d e n t , and how s t r a t e g i c responses t o s e l e c t i v e pressures d i f f e r from 2 s p e c i e s to s p e c i e s and from h a b i t a t to h a b i t a t . Much of the l i f e h i s t o r y s t r a t e g y . o f s p e c i e s concerns a l l e v i a t i o n of the long- or short-term e f f e c t s of l i m i t i n g f a c t o r s which a c t t o r e s t r i c t e i t h e r , t h e s u r v i v o r s h i p or the r e p r o d u c t i v e success of i n d i v i d u a l s . . I d e a l l y , the study of l i m i t i n g f a c t o r s r e q u i r e s changing one f a c t o r ..alone i n order to observe how the p o p u l a t i o n s i z e i s a f f e c t e d . More o f t e n than not, however, t h i s d i r e c t a p p r o a c h . i s . i m p o s s i b l e - to c a r r y out and monitor i n . nature. ..Changing the food supply of s m a l l insectivorous.mammals such as shrews, f o r i n s t a n c e , i s u n f e a s i b l e . I n s t e a d , I used a comparative approach and looked at i n t r a s p e c i f i c . d i f f e r e n c e s i n adaptive s t r a t e g i e s between, p o p u l a t i o n s i n h a b i t i n g widely d i v e r g e n t h a b i t a t types. I a l s o made i n t e r s p e c i f i c comparisons.. of sympatric p o p u l a t i o n s to - l o o k . f o r . , d i f f e r e n c e s . i n _ s t r a t e g i e s a t t r i b u t a b l e to fundamental s p e c i e s c h a r a c t e r i s t i c s . From the types of p o p u l a t i o n c h a r a c t e r i s t i c s , i n d i v i d u a l s t r a t e g i e s , and a d a p t a t i o n s observed i n v a r y i n g s i t u a t i o n s the r e l a t i v e r o l e s of v a r i o u s p o s s i b l e l i m i t i n g f a c t o r s may be i n f e r r e d . . . _ .. . . . Shrews are p a r t i c u l a r l y s u i t a b l e animals f o r use i n examining the kinds of q u e s t i o n s I,am a s k i n g . I n d i v i d u a l s have r e s t r i c t e d . powers of long-range... d i s p e r s a l , - t u t p o p u l a t i o n s are g e o g r a p h i c a l l y widespread over a v a r i e t y of environmental c o n d i t i o n s , I assume that s e l e c t i o n , operates to produce p o p u l a t i o n s of i n d i v i d u a l s with a d a p t a t i o n s and co-adapted t r a i t s ( i . e . s t r a t e g i e s ) compatible . with t h e i r 3 p a r t i c u l a r h a b i t a t and the s p e c i f i c types, of l i m i t i n g f a c t o r s encountered t h e r e . H e n c e , . . c o r r e l a t i o n between v a r i a t i o n . , i n l i f e h i s t o r y s t r a t e g i e s and- environmental d i f f e r e n c e s between p o p u l a t i o n s may be made. I n t e r s p e c i f i c comparisons of t h i s s o r t are of i n t e r e s t , p a r t i c u l a r l y i n the sympatric s i t u a t i o n , because of the e c o l o g i c a l , b e h a v i o r a l and mo r p h o l o g i c a l s i m i l a r i t i e s between S. vaojrans and S. obscurus. Presumably, they need to be l i m i t e d by d i f f e r i n g . f a c t o r s i n order to c o e x i s t (Levin, 1973), yet both are e x c e e d i n g l y s m a l l mammals.specialized f o r preying upon a v a r i e t y of s o i l i n v e r t e b r a t e s . T h e i r morphological s i m i l a r i t i e s have l e d to .systematic d i f f i c u l t i e s (H. Jackson, 1928) and c o n t r o v e r s i e s concerning t h e i r s t a t u s as s p e c i e s . ( F i n d l e y , 1955). I t . i s hoped t h a t examination of the e c o l o g i c a l s t r a t e g i e s . a n d i n t e r r e l a t i o n s h i p s , o f po p u l a t i o n s i n t h i s geographic area, as well - a s the study of morph o l o g i c a l c h a r a c t e r i s t i c s and t h e i r v a r i a t i o n , w i l l a l s o serve to .shed some l i g h t on s y s t e m a t i c r e l a t i o n s h i p s . I f the two are indeed separate s p e c i e s , , t h e i r niches should d i f f e r as a r e s u l t ...of . t h e i r g e o g r a p h i c a l l y and r e p r o d u c t i v e l y d i s t i n c t e v o l u t i o n a r y h i s t o r i e s . ... F i n a l l y , an e c o l o g i c a l study of s h r e w s h a s p o t e n t i a l a p p l i c a t i o n to a d a p t a t i o n and l i f e h i s t o r y s t r a t e g y theory i n g e n e r a l . fill l i f e i s u l t i m a t e l y - l i m i t e d by energy.. A broad view of. e v o l u t i o n a r y p a t t e r n s r e p e a t e d l y shows ada p t i v e r a d i a t i o n of forms and r e s u l t a n t e x p l o i t a t i o n of d i f f e r e n t energy s o u r c e s . Owing to c e r t a i n c h a r a c t e r i s t i c s 4 unique to shrews, the p o t e n t i a l l i m i t i n g e f f e c t s of energy seem a primary aspect of t h e i r b i o l o g y . - T h e i r exceedingly s m a l l s i z e and concomitant high s u r f a c e - t o r volume r a t i o put them c l o s e to the lower l i m i t set-by the energy-requirements of mammalian homeostasis (Pearson, 1948). Rates of v a r i c u s p h y s i o l o g i c a l processes r e l a t e d to metabolism are i n g e n e r a l maximal f o r mammalian systems (Morrison, Ryser, - and Da we, 1959). Shrews are p r e d a t o r s - which r e l y upon se a r c h i n g f o r and f i n d i n g prey that are not o n l y s m a l l but a l s o , have a r e l a t i v e l y high water content (Hawkins and J e w e l l , 1962). Consequent to the a c t i v e p u r s u i t of- these small "energy packets," shrews must spend, a l a r g e amount of time and energy hunting. They are a c t i v e both . day . and night and throughout a l l seasons of the year.- In c o n s i d e r a t i o n o f these p o i n t s , understanding. of -the a d a p t a t i o n s and s t r a t e g i e s which have evolved i n shrews should.be u s e f u l i n a p p l i c a t i o n to g e n e r a l theory and a l s o - i n comparison with other organisms, p a r t i c u l a r l y those with p o t e n t i a l l y s t r o n g energy l i m i t a t i o n s . . The t h e s i s p r e s e n t a t i o n i s d i v i d e d i n t o two p a r t s . Pa r t I . compares and c o n t r a s t s the general ecology.and l i f e h i s t o r i e s of S. v a j r a n s and S. -obscurus i n f o r e s t h a b i t a t . Most of the data presented i n t h i s s e c t i o n . a r e - d e r i v e d from s t u d i e s of the s p e c i e s i n .an area.- of sympatry, and- hence t h e i r a n a l y s i s i s r e l e v a n t to q u e s t i o n s o f . c o m p e t i t i o n and c o e x i s t e n c e . Results, from d i s t r i b u t i o n sampling are d i s c u s s e d i n r e l a t i o n t o s p e c i e s d i f f e r e n c e s and competitive 5 avoidance. P a r t I I g e n e r a l l y concerns s. vagrans and the seasonal and geographic v a r i a t i o n evident i n c e r t a i n of i t s morphological and l i f e h i s t o r y c h a r a c t e r i s t i c s . A f o r e s t -i n h a b i t i n g p o p u l a t i o n of S...vagrans i s compared . with g r a s s l a n d p o p u l a t i o n s to.study.the environmental i n f l u e n c e s on adaptive s t r a t e g i e s . Three g r a s s l a n d p o p u l a t i o n s of the s p e c i e s , are compared and c o n t r a s t e d i n examining the i n h e r e n t v a r i a b i l i t y of the s p e c i e s . 6 METHODS AND RATIONALE In order to make i n t e r - and i n t r a s p e c i f i c comparisons of general l i f e . h i s t o r y - a t t r i b u t e s i n a v a r i e t y of e c o l o g i c a l c o n t e x t s , three b a s i c approaches.were used,. each f o c u s s i n g on d i f f e r e n t a s p e c t s of the adaptive ecology of each s p e c i e s . 1) A t r a p and r e c a p t u r e program allowed the study, of p o p u l a t i o n dynamics and i n d i v i d u a l l i f e . h i s t o r i e s o f Sorex vacjrans and S. obscurus i n a sympatric s i t u a t i o n . 2) Standardized snap t r a p l i n e s were s e t through s e v e r a l h a b i t a t types i n order to a s c e r t a i n b a s i c d i s t r i b u t i o n a l p a t t e r n s and h a b i t a t p r e f e r e n c e s of the t w o . s p e c i e s . 3) D e t a i l e d i n f o r m a t i o n on s e a s o n a l a n d geographic v a r i a t i o n i n morphology and r e p r o d u c t i v e c o n d i t i o n s of S. vacjrans were obtained through. the c o l l e c t i o n and p r e p a r a t i o n of e x t e n s i v e specimen s e r i e s from lowland grassy f i e l d s . Accounts of each method f o l l o w . 1. l i v e - t r a p p i n g ... The purpose of. the . l i v e - t r a p p i n g program was to document the l i f e h i s t o r y and p o p u l a t i o n dynamics of both S. vagrans and S. obscurus. Choosing a s i t e of~sympatry f o r the l i v e - t r a p p i n g g r i d allowed the study of i n t e r s p e c i f i c i n t e r a c t i o n s i n a s i t u a t i o n of p o t e n t i a l c o m p e t i t i o n . From t h i s program I hoped to e x p l a i n how the two - s p e c i e s were able to c o e x i s t , and how c o m p e t i t i o n between them was manifest. 7 1.1. The study area and g r i d The study area was l o c a t e d at 1100 f e e t e l e v a t i o n , 1 mile on Road K at 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 Research F o r e s t (henceforth r e f e r r e d , t o . as the Research F o r e s t ) . The Research F o r e s t i s s i t u a t e d approximately 35 miles e a s t of Vancouver, and j u s t north of the m u n i c i p a l i t y of Maple Ridge (formerly known as Haney). I t i s an area of 20 square m i l e s , with e l e v a t i o n s ranging from a few f e e t above sea l e v e l to 3300 f e e t i n e l e v a t i o n . . According to the c l a s s i f i c a t i o n of K r a j i n a . (1965, 1969), the area, i s r e p r e s e n t a t i v e of the dry subzone ,of the C o a s t a l Western Hemlock b i o g e o c l i m a t i c zone. The l i v e - t r a p p i n g g r i d was l o c a t e d i n a 40-year-old f o r e s t s i t e , and c o n s i s t e d . o f stakes placed 30.feet apart i n a 12-by-12 a r r a y encompassing a 2.5 acre (one h e c t a r e ) , t o p o g r a p h i c a l l y v a r i e d p l o t . ..Common t r e e s were western hemlock (Tsuja .:hetero£h_y 11 a), western red cedar (Thuja E l i c a t a ) , red a l d e r (Alnus r u b r a ) , and vine maple (Acer c i r c i n a t u m ) , d i s t r i b u t e d i n a . p a t t e r n which- was c l o s e l y c o r r e l a t e d with s o i l type ( F i g . 1). A s s o c i a t e d with the r e l a t i v e l y poor, a c i d i c , and w e l l - d r a i n e d m o r . s o i l s was western hemlock, while the wetter and r i c h e r mcder s o i l s along seepage s i t e s and p e r i o d i c streams supported western red cedar.and the deciduous t r e e s . The l a t t e r a s s o c i a t i o n was edaphic i n nature, r e s u l t i n g from the seepage p a t t e r n s and a s s o c i a t e d i n f l u x of n u t r i e n t s . . The f o r e s t f l o o r of the study area was f a i r l y open. 8 Figure 1 . General s o i l map of l i v e - t r a p p i n g p l o t , 1 mile on Road K, U.B.C. Research F o r e s t , Maple Ridge, B.C. Mor s o i l , Tsuga h e t e r o p h y l l a Moder s o i l , T h u j a p l i c a t a i 1 T r a n s i t i o n Anmoor, s e a s o n a l l y wet, Blechnum s p i c a n t 9 with v e g e t a t i o n low -both i n d e n s i t y a n d . d i v e r s i t y . - S w o r d f e r n ( P o l i s t i c h u s SMfiitliS) » l a d y f e r n (Athjjrium f i l i x -femina) and s a l a l ( G a u l t h e r i a s h a l l o n ) were e v i d e n t a t . t h e herbaceous and shrub l e v e l s . Skunk cabbage..... ( L ^ s i c h i t uni aj>§£icajium) and deer f e r n (Blechnum s ^ i c a n t ) ...were a s s o c i a t e d with the . wetter .areas of the . p l o t w h e r e , the . s o i l , was s e a s o n a l l y waterlogged, r e s u l t i n g i n anmoor c o n d i t i o n s . Ground cover c o n s i s t e d . of . l e a f . . l i t t e r . . . and.. - a. -sparse occurrence of .mosses (Placjiothecium undulatum, Hjloccmium §£ lend ens, Rhy, t i d i a de l^hus . l o r e u s , Eur^nchium orecjanum, Mnium 3labreseens and Mnium i n s i ^ n e ) . 1.2. Trapping procedure — One hundred and f o r t y - f o u r Long worth ...live-; t r a p s ( C h i t t y and Kempson, 1949). were se t out, one per.stake, under l e g s or rocks or a t h o l e s . . Traps which c o n s i s t e n t l y , f a i l e d to c a t c h animals were moved, ..keeping, to within...a- seven, f o o t r a d i u s of the stake. . S u c c e s s f u l . t r a p s . w e r e not moved, .The Longworth t r a p proved t o be i d e a l f o r . c a t c h i n g , shrews. I t i s two-parted, which, a l l o w s f o r a compartment..containing food and n e s t i n g m a t e r i a l , both of .which- are... necessary to a v o i d .trap m o r t a l i t y with shrews.. Furthermore, the t r a p or tunnel s e c t i o n can be adjusted f o r high s e n s i t i v i t y , .again, a n e c e s s i t y i n order t h a t shrews, (some.of.which weigh l e s s than f o u r grams) t r i g g e r the t r a p ..mechanism.. The disadvantage I found.was .the tendency for-the.trap-mechanism to f r e e z e a f t e r i t had been wet and temperatures went below 10 0°C. For t h i s r e a s o n , t r a p p i n g during e s p e c i a l l y c o l d winters (1970-71 i n p a r t i c u l a r ) was sometimes u n s u c c e s s f u l or i m p o s s i b l e . Traps were b a i t e d with crushed oats, and c o t t o n b a t t i n g served as n e s t i n g m a t e r i a l . O r i g i n a l l y , p i e c e s of mealworm were added, but equal success occurred without them. Shrews r e a d i l y eat the oats and can be s u s t a i n e d by oats f o r at l e a s t the d u r a t i o n of the t r a p p i n g session.... Traps were set e a r l y i n the day, g e n e r a l l y a t . w e e k l y . i n t e r v a l s , and checked at one and one-half h o u r . i n t e r v a l s f o u r . t o . s i x times, from October 1970 to A p r i l 1974 (Table I ) . At t h e . l a s t round of the day, the traps.were p r e s e t (locked.open) and l e f t u n t i l the next t r a p p i n g p e r i o d . Shrews.were i n d i v i d u a l l y . m a r k e d by c l i p p i n g the f i r s t j o i n t o f . one or two toes of the hind f e e t . T h i s method allowed 55 p o s s i b l e combinations, a number adequate to cover a l l the i n d i v i d u a l s caught f o r any one.generation.of shrews. Numbers c o u l d be repeated f o r S. vacjrans and. S. obscurus, as I had no t r o u b l e d i s t i n g u i s h i n g the s p e c i e s . Eesides s l i g h t q u a l i t a t i v e . d i f f e r e n c e s . i n pelage c o l o r a t i o n and robustness of the r o s t r a l a r e a , the t a i l l e n g t h s of the two s p e c i e s d i d not o v e r l a p i n t h i s geographic area, although they may i n o t h e r r e g i o n s . Average t a i l l e n g t h f o r S. obscurus was 53.7 mm. (48-58, n=74), while t h a t of S. vacjrans. was 42.9 (39-47, n=87). I.have assumed t h a t the marking technique did not a f f e c t t r a p p i n g response or m o r t a l i t y . L i t t l e evidence of i n f e c t i o n appeared, and shrews marked i n the l a b o r a t o r y T a b l e I Live-trapping e f f o r t : Dates and number of rounds. Month 1 9 7 0 .... Date Rounds 1 9 7 1 ir Date Rounds 1 9 7 2 , ? Date Rounds 1 9 7 3 Date Rounds 1 9 7 ^ Date Rounds Jan» 2k k 3 0 »f 2 0 >+ 2 7 H-Feb. 2 0 - 2 1 5 1 0 i f 1 9 H-2 8 i f 3 ^ 1 1 I f 1 7 k 2k 5 2 2 3 March 20-21 8 2 8 3 6 i f 16 i f 3 0 5 3 ^ 1 1 i f 1 7 *+ 2k k 2k 3 A p r i l 1 2 5 2 0 1 2 ^ - 2 5 8 9 »f 16 5 2 3 4-3 0 * f 1 W 8 p 1 5 *t 2 3 k 2 9 >+ 1 2 3 May- 3-k 5 1 1 - 1 2 7 1 8 5 ' 2k k 3 1 6 1 0 5 1 7 5 2H- 3 2 8 5 7 ^ 1 5 5 2 3 3 3 0 5 June . 8 - 9 5 1 7 5 2 9 6 ^ 5 1 1 5 1 8 • 5 2 5 H-6 3 2 3 i f 2 9 k July 7 - 8 7 16 5 2 3 - 2 1 + 8 3 1 6 3 5 1 0 5 1 7 5 2 * f 5 3 1 k 6 . i f 1 3 k 2 3 3 0 k August 9 - 1 0 8 1 9 6 7 k 16 it 2 7 k 9 ^ 1 8 U-26 k Sept. 1 5 1 8 6 3 0 6 i f i f 1 0 5 2 5 V 2 ^ 2 9 k Oct. 1 c - 1 9 6 2k 3 3 1 9 10 k 1 7 5 2k k 3 1 ^ 1 k 1 0 U Jf 25 k 1? i f 2 8 ^f Nov. 1 ^ - 1 5 9 2£ 3 1 3 ' ^ 22 If . 29 ^ 2 If 1 3 ^ 25 3 1 8 i f Dec. 1 1 k 5 l f .,„•—— , 1^, . .... _„ 12 recovered r a p i d l y with l i t t l e l o s s of blood. Of 111 S. .vagrans marked from 1970 ,through 1973, 80* (89) were re c a p t u r e d at l e a s t once. Of the 83 S. obscurus marked i n the same p e r i o d , 88% (72) were recaptured a t l e a s t once. Since most of the animals marked were young animals j u s t e n t e r i n g the p o p u l a t i o n , d i s p e r s a l probably accounts f o r many of the cases i n which no rec a p t u r e s were made. At each capture, the f o l l o w i n g . d a t a were taken: g r i d l o c a t i o n , s p e c i e s , i n d i v i d u a l number, sex, weight, t a i l l e n g t h , breeding c o n d i t i o n , odor, s t a t e of pelage (melt), and e c t o p a r a s i t e s , i f any. Sexing of . l i v e shrews was p o s s i b l e o n l y i n mature i n d i v i d u a l s , as males and females i n t h e i r f i r s t c a l e n d a r year are v i r t u a l l y i d e n t i c a l e x t e r n a l l y . O c c a s i o n a l l y young females have s l i g h t l y darker f u r surrounding each n i p p l e , and these so c a l l e d " t e a t -s p o t s " may sometimes be a c l u e t o t h e i r sex. Breeding males have swollen i n g u i n a l areas from the enlarged t e s t e s , and at times the penis e v e r t s . , They are a l s o d i s t i n g u i s h e d by the development of l a t e r a l glands which emit a str o n g and d i s t i n c t odor. Females i n t h e i r second calendar year are d i s t i n g u i s h a b l e by. t h e i r l a c k of male c h a r a c t e r i s t i c s and, l a t e r on, by the evidence o f pregnancy and l a c t a t i o n . Shrews were weighed with Pesola s c a l e s a c c u r a t e to 0.1 grams ( p r i o r t o J u l y 1971, weighing was dene with a P e s c l a a c c u r a t e t o 0,5 grams) i n a small p l a s t i c bag, the weight of which was l a t e r s u b t r a c t e d . I measured length cf t a i l , both as an a i d i n i d e n t i f i c a t i o n and t o assess v a r i a t i o n , by 13 p l a c i n g a s m a l l m i l l i m e t e r r u l e from -the,.base along the d o r s a l l e n g t h of the t a i l , h o l d i n g the shrew.by the nape. During the months when two generations of shrews overlapped, the r e l a t i v e age of newly captured animals could be a s c e r t a i n e d . a d u l t shrews, i . e . Those born the previous year, were l a r g e r , had a s l i g h t l y darker.pelage, with f e e t and. t a i l , p r a c t i c a l l y - h a i r l e s s . I could e a s i l y check the amount of wear on the t e e t h as I hel d a shrew and allowed i t to b i t e my f i n g e r ( i t c o u l d not break- s k i n ) . A d u l t s had o b v i o u s l y worn t e e t h , with v a r y i n g amounts of pigmentation remaining. Young shrews were c h a r a c t e r i z e d by smaller body weight,, s l i g h t l y l i g h t e r c o l o r e d pelage, with w e l l - h a i r e d f e e t , (which.appeared darker i n c o l o r ) and t a i l . The te e t h were g e n e r a l l y unworn and w e l l pigmented. I found both s p e c i e s t o be e x c e l l e n t animals f o r t h i s type of study. In the course of search f o r prey, shrews a c t i v e l y e x p l o r e nooks and c r a n n i e s t h r o u g h o u t . t h e i r range, and they r e a d i l y entered .the l i v e - t r a p s . T h e i r high r a t e of metabolism r e q u i r e s a concomitantly high degree of f o r a g i n g a c t i v i t y , so not only were m u l t i p l e captures made of s i n g l e i n d i v i d u a l s over a s h o r t time, but t r a p p i n g was e a s i l y done at s h o r t i n t e r v a l s during the day, a v o i d i n g the d i f f i c u l t i e s both of walking through dense f o r e s t i n the dark, and of the u b i q u i t o u s . and n o c t u r n a l 2 § J 2 I I s c u s f i l l i n g . u p the t r a p s . More i m p o r t a n t l y , t r a p m o r t a l i t y was e l i m i n a t e d with f r e q u e n t checks. As w i l l be d i s c u s s e d , the home ranges.of these shrews tended t o be q u i t e s t a t i o n a r y and small enough 14 so t h a t s e v e r a l were i n c l u d e d i n the g r i d . I n d i v i d u a l s c o u l d thus be f o l l o w e d from weaning, to senescence, the l e n g t h of l i f e being s h o r t enough t h a t s e v e r a l g e n e r a t i o n s were encompassed. 2. Snap-trapping Trap l i n e s were s e t out i n v a r i o u s h a b i t a t s during the s p r i n g and summers of 1970 through 1973. For t h i s study, the purpose of these l i n e s was to e s t a b l i s h d i s t r i b u t i o n a l p a t t e r n s and h a b i t a t p r e f e r e n c e s of the shrew s p e c i e s as they occur i n t h i s r e g i o n . 2.1. Snap-trapping areas B a s i c a l l y , snap-trap, l i n e s were , .confined t o the two D n i v e r s i t y o f B r i t i s h Columbia f o r e s t s : the U n i v e r s i t y Endowment Lands and the U. B. C. Research F o r e s t . The U n i v e r s i t y Endowment.Lands i s . a p e n i n s u l a r area o f 1670 a c r e s bordered by the ocean to the north and south, the c i t y of Vancouver to the east,-and t h e - U n i v e r s i t y at the western t i p . I t c o n s i s t s of both young and o l d growth, and v e g e t a t i o n t y p i c a l of the l o w l a n d , . w e t .subzone of the C o a s t a l D o u g l a s - F i r Zone - - ( K r a j i n a , . 1965,- 1969). C h a r a c t e r i s t i c are dense,- mixed stands o f -the - dominant s p e c i e s , d o u g l a s - f i r (Eseudotsuga. . m e n z i e s i i ) , and subdominants, western r e d cedar (Thuja £ l i e a t a ) g r a n d f i r (Abies grandes), western hemlock (Tsucfa heterophylla) , and b r o a d - l e a f maple (Acer macrgphy llunt). Red a l d e r (Alnus 15 r u b r a ) , vine maple. (Acer cireinaturn) and. b i t t e r c h e r r y (El^SiJs emarcjinata) are also, f r e q u e n t . T y p i c a l u n d e r s t o r y elements are Mnium i n s i g n e , Eurhynchium ..sp., Polystichum munitum, and T i a r e l l a t r i f o l i a t a . ( K r a j i n a , 1969). , Although t r a p l i n e s were s e t i n areas of the Endowment Lands f o r e s t and i n s m a l l f i e l d s , between .the f o r e s t and campus, the p r i n c i p l e area. f o r . snap-strapping was the D.B.C. Research F o r e s t . Trap l i n e s were s e t through, the s e v e r a l h a b i t a t types and biogeocoenoses .... (the p l a n t and s o i l a s s o c i a t i o n s , . a c c o r d i n g to Krajina,-1965, 1969) r e p r e s e n t e d w i t h i n the Research F o r e s t . These have been described.and analyzed i n d e t a i l (Lesko, 1961; O r l o c i , -1961; La c a t e , 1962), and I w i l l l a t e r d i s c u s s only g e n e r a l aspects of the v a r i o u s h a b i t a t s i n v o l v e d . 2.2. Trapping technique Museum S p e c i a l snap t r a p s , . b a i t e d .with peanut b u t t e r , were used f o r t h i s p a r t of the..study. . I n i t i a l l y , l i n e s of 40 to 50 t r a p s were spaced approximately .ten . f e e t a p a r t . Beginning, i n 1971, l i n e s of up to.400 Museum S p e c i a l s were s e t . a t two-meter i n t e r v a l s . T h i s technigue . proved more p r o d u c t i v e and r e s u l t e d i n what appeared to be a more r e p r e s e n t a t i v e catch.. S a t u r a t i o n t r a p p i n g such as t h i s r e s u l t e d i n g r e a t e r s e n s i t i v i t y to c l u m p p d . d i s t r i b u t i o n s and a l s o was more e f f e c t i v e i n c a t c h i n g shrews. Some e f f o r t was made t o p l a c e i n d i v i d u a l , t r a p s i n . what seemed .to..be promising s e t t i n g s , but t h i s was not always p r a c t i c a b l e when 16 p u t t i n g out so many t r a p s . s o c l o s e t o g e t h e r . A t o t a l of 51 l i n e s was s e t during., the. p e r i o d from January, 1971 to August, 1973. They were u s u a l l y checked twice a day. Museum s k i n s were, made of specimens with i n t a c t s k u l l s , and the standard measurements, weight, t o t a l l e n g t h , t a i l l e n g t h , hind f o o t l e n g t h and e a r l e n g t h , were taken along with notes on breeding c o n d i t i o n , molt, and p a r a s i t e s . 3. Population-Sampling Through the years 1972 and 1973 I . prepared e x t e n s i v e biweekly specimen s e r i e s . of Sorex vacjrans c o l l e c t e d from t h r e e g r a s s l a n d , l o c a l i t i e s . T h i s . was f a c i l i t a t e d -by Dr. C h a r l e s Krebs and h i s s t u d e n t s , who have a l i v e - t r a p p i n g program f o r Mic r o t u s . Shrews which entered t h e i r t r a p s and di e d o v e r n i g h t were saved .and- frozen, for- me. ... The. three l o c a l i t i e s , . Ladner . A i r Base, S e r p e n t i n e - R i v e r , and Westham I s l a n d , are c l o s e t o sea l e v e l , and .located about 15 miles south of . Vancouver, approximately seven miles .from one another ( F i g . 2). A l l - t h r e e are ...diked,., f o r m e r l y c u l t i v a t e d f i e l d s predominated by grasses and o c c a s i o n a l l y mown. T h i s h a b i t a t w i l l h e n c e f o r t h be r e f e r r e d to as g r a s s l a n d . The c o l l e c t i o n of e x t e n s i v e s e r i e s of S. vagrans from these g r a s s l a n d p o p u l a t i o n s served to provide m a t e r i a l . by which both seasonal and g e o g r a p h i c v a r i a t i o n i n morphological and r e p r o d u c t i v e c h a r a c t e r i s t i c s could be 17 F i g u r e 2. Grassland sampling l o c a l i t i e s . 18 made. E n e r g e t i c a l l y s i g n i f i c a n t events such as molting and re p r o d u c t i o n were s t u d i e d i n d e t a i l through a u t o p s i e s . The timing and nature of these events i n g r a s s l a n d p o p u l a t i o n s , compared with s i m i l a r o b s e r v a t i o n s made on the l i v e - t r a p p e d p o p u l a t i o n from, f o r e s t h a b i t a t , provided a means by which the environmental, i n f l u e n c e s on r e p r o d u c t i v e s t r a t e g i e s c o u l d be s t u d i e d . M o r p h o l o g i c a l c h a r a c t e r i s t i c s such as body s i z e and s k u l l height, were examined-in order to t e s t the hypothesis t h a t v a r i a t i o n occurs s e a s o n a l l y as an ada p t i v e response to unf a v o r a b l e environmental c o n d i t i o n s (Dehnel, 1949; Pucek, 1963). A t o t a l , of 1947 S. v a j r a n s from the three g r a s s l a n d l o c a l i t i e s was examined, 1174.of them prepared and measured as standard museum s k i n s and s k u l l s . . . Reproductive data, i n c l u d i n g t e s t e s s i z e , number and crown-rump length of embryos, and evidence of l a c t a t i o n , were taken. Pelage was examined f o r evidence o f molt and c a t e g o r i z e d as j u v e n i l e , w i n t e r , or a d u l t pelage. , S k u l l s were cleaned by the Museum of Vertebrate Zoology at t h e . U n i v e r s i t y of C a l i f o r n i a , Berkeley, - and much of the c o l l e c t i o n i s housed and catalogued there (Accession 11352, catalogue numbers 142276-143691). S k u l l h e i g h t measurements were made on the g r a s s l a n d s e r i e s by p l a c i n g the s k u l l on a g l a s s s l i d e such t h a t i t re s t e d on the f r o n t i n c i s o r s and o c c i p i t a l b u l l a e . Maximum heig h t to 0.05 mm. was obtained with d i a l c a l i p e r s zeroed with r e s p e c t to the s l i d e . , 19 R e l a t i v e aging of shrews was p o s s i b l e by measuring the amount of t o o t h wear on i n c i s o r s . a n d molars. E a s i c a l l y f o l l o w i n g Pearson's (1945) . method, I. s e l e c t e d a standard s e r i e s of f i v e s k u l l s r e p r e s e n t i n g p r o g r e s s i v e l y .greater degrees of wear. These wereMVZ specimen . numbers 143503, 14 3533, 143516, 14348 9, ..and 14 3463, i n order of wear, and they were given toothwear index numbers of 2, . 4 , 6 , 8, and 10, r e s p e c t i v e l y . Upper- t e e t h of specimens were compared with the standard s e r i e s under a d i s s e c t i n g scope, and an index number from .1 , to 11.was assigned, depending on the degree of toothwear r e l a t i v e to the s e r i e s . 20 RESULTS AND DISCUSSION PART I THE ECOLOGY OF SOREX VAGRANS AND SOREX OBSCURUS The l i v e - t r a p p i n g program permitted the examination and a n a l y s i s of i n d i v i d u a l l i f e h i s t o r i e s and t h e i r p o p u l a t i o n consequences. In t h i s s e c t i o n , I w i l l present and d i s c u s s the r e s u l t s of t h i s program, beginning with . i n t e r p r e t a t i o n s of the adaptive s i g n i f i c a n c e of v a r i o u s l i f e h i s t o r y phenomena observed, f o l l o w e d by d i s c u s s i o n s of p o p u l a t i o n dynamics and co m p e t i t i v e i n t e r a c t i o n s , between s p e c i e s . R e s u l t s of the snap-trapping program w i l l be presented i n r e l a t i o n t o the problem of c o e x i s t e n c e . .During the l i v e - t r a p p i n g p e r i o d , October 1970 to A p r i l 1974,.a t o t a l of 116 S. vagrans and. 86 S. obscurus were marked. T h i s i n v o l v e d 3361 captures of S. vagrans, f o r an average of 29 capt u r e s . p e r i n d i v i d u a l , and 1843 captures of S. obscurus, averaging 21.4 captures per i n d i v i d u a l . 1. Background B a s i c a l l y , S. vagrans and s. obscurus share a common l i f e h i s t o r y p a t t e r n . Young are born i n s p r i n g , and by f a l l t h e . breeding, a d u l t g e n e r a t i o n (animals i n t h e i r second calendar year) have v i r t u a l l y disappeared, completing the y e a r l y p o p u l a t i o n turnover.. The young, or f i r s t year animals, o v e r - w i n t e r , the males showing s i g n s of 21 r e p r o d u c t i v e a c t i v i t y by mid-winter. The t i m i n g of breeding v a r i e s g e o g r a p h i c a l l y , but i n -the area .of the . Research F o r e s t , females become r e c e p t i v e i n March. A f t e r a t h r e e week g e s t a t i o n (Johnston and Rudd, .1957), young are born and females can undergo a postpartum e s t r u s , . as suggested . . f o r Sorex fumeus , (Hamilton, .1940),- Sorex araneus (Erambell, 1935; Dehnel, 1952; Brambell and H a l l , . 1957) and.the s h o r t -t a i l e d shrew, B l a r i n a brevicauda (Pearson, 1944). 2. Weight Changes Weight . changes o c c u r r i n g over the l i f e t i m e of i n d i v i d u a l shrews r e f l e c t the b a s i c l i f e h i s t o r y p a t t e r n . F i g u r e s . 3A and 3B show weight changes o c c u r r i n g i n the 1971 and 1972 c o h o r t s of S. vagrans and S. obscurus. The weights of breeding females f l u c t u a t e to a l a r g e - e xtent - with pregnancy and l a c t a t i o n and are omitted. The g e n e r a l p a t t e r n of weight changes i s s i m i l a r i n both s p e c i e s . A summer constant i s reached i n t h e f i r s t year, f o l l o w e d by.a sharp i n c r e a s e i n the f a l l , . concomitant with the molting p r o c e s s . Weight then drops to a winter c o n s t a n t , somewhat lower than t h a t of summer, and . r i s e s s h a r p l y with sexual m a t u r i t y . 3. Molt Both Sorex vagrans and S..obscurus undergo two p e r i o d s of molt. In the f a l l , f i r s t year animals molt the s h o r t , brown j u v e n i l e pelage to the long dark major from plush 22 Figure 3A. Monthly weight s t a t i s t i c s , Sorex vagrans. This represents average changes which occur over the l i f e t i m e of i n d i v i d u a l s . S t a t i s t i c s are based on weights of l i v e -trapped i n d i v i d u a l s . ro ro 23 Figure 3B. Monthly weight s t a t i s t i c s , Sorex obscurus. This represents average changes which occur over the l i f e t i m e o f i n d i v i d u a l s . S t a t i s t i c s are based on weights of l i v e -trapped i n d i v i d u a l s . MONTHLY WEIGHT STATISTICS - SOREX OBSCURUS M A S 1971 O N D » i 1 -i M A M J 6 1972 H 1 A S ro 24 pelage of winter. In S. vagrans, the long, winter pelage i s a c h a r c o a l c o l o r , while t h a t of S. obscurus i s a g r e y e r , smokier shade of brown. The. a d u l t summer ... pelage, seen i n second year animals, i s again s h o r t , and.browner.than winter pelages but a darker shade than j u v e n i l e , pelages. The beginning of f a l l molt i s m a r k e d . i n . i n d i v i d u a l s by a sudden i n c r e a s e i n weight i n September.and October and a n o t i c e a b l e t h i c k e n i n g and b l a c k e n i n g of the s k i n . 3.1. F a l l molt J u v e n i l e s , of S. vagrans and S. obscurus d i d not, as a r u l e , undergo a p o s t - j u v e n i l e molt i n t h e i r f i r s t summer, as does the s h o r t - t a i l e d shrew, B l a r i n a b r e v i c a u d a . ( F i n d l e y and Jones, 1956). The f a l l molt occurred synchronously f o r both sexes, but a t the Research F o r e s t , S. obscurus lagged about two weeks b e h i n d S . vagrans. Sorex.vagrans i n d i v i d u a l s began showing the f i r s t s i g n s of molt (weight. g a i n , t h i c k e n i n g and darkening of the skin) at.mid-September. The molt began .as a d o r s a l patch on the rump.and progressed forward towards the head. As.the molt was completed-on the dorsum, i t began at the p o s t e r i o r , on, the s i d e s and venter, and worked up towards the neck.. The f a l l molt, f o r Sorex araneus i n Europe (Crowcroft, 1955) i s s i m i l a r . t o t h a t of S. vagrans and S. obscurus. .An i n d i v i d u a l -S. vagrans.or §• obscurus took approximately three weeks to complete the f a l l molt. 25 3.2. Spring molt The s p r i n g molt, i n which the long,. i n s u l a t i v e winter f u r i s r e p l a c e d by the sh o r t .summer pelage, had e s s e n t i a l l y the r e v e r s e p a t t e r n of t h a t o f - t h e f a l l . m o l t . Molt-began a t the a n t e r i o r venter and q u i c k l y moved p o s t e r i o r l y , as-the head r e g i o n began to molt. L a s t to. be. molted . was the p o s t e r i o r dorsum. : Females completed t h e i r s p r i n g molt q u i c k l y i n March, S. vagrans u s u a l l y during the f i r s t h a l f of March and S. obscurus during the l a t t e r h a l f . . In three years of o b s e r v a t i o n , m o l t . f o r females was.completed by the f i r s t .week of A p r i l . I n d i v i d u a l .molts were completed i n about two weeks, and females of one s p e c i e s tended to molt synchronously. U n l i k e the f a l l . m o l t , s e xual d i f f e r e n c e s were e v i d e n t i n t h e . s p r i n g molt. Spring molt i n males-was.less r e g u l a r , p a r t i c u l a r l y f o r male S. obscurus, which-sometimes molted i n patches a l l over the body, or d i d not molt at a l l . The molt g e n e r a l l y occurred synchronously f o r a l l - m a l e s of a s p e c i e s , but was delayed by s e v e r a l weeks r e l a t i v e to the s p r i n g molt of females. r . Dalquest (1944). had d i f f i c u l t y . i n d i s t i n g u i s h i n g , the spri n g . m o l t of Sorex vagrans, remarking t h a t - t h e worn winter f u r and f r e s h summer f u r are s i m i l a r i n c o l o r . I found no d i f f i c u l t y i n d i s t i n g u i s h i n g the two because, although.the a d u l t summer pelage i s .darker than the. brown j u v e n i l e pelage, i t i s about h a l f . a s long and.of a browner shade than the winter pelage. Dalquest a p p a r e n t l y d i d not take i n t o 26 account s e x u a l d i f f e r e n c e s i n specimens simply a c c o r d i n g f o r trends on that b a s i s . t i m i n g of molt, a r r a n g i n g h i s to date of capture and l o o k i n g 3.3. A d v e n t i t i o u s molt .... Besides the r e g u l a r f a l l and s p r i n g molts, a d v e n t i t i o u s molts were observed-in i n d i v i d u a l S. vagrans and S. cbscurus at other times. T h i s o c c u r r e d . i n several-female.shrews t h a t had weaned one or.more l i t t e r s . u s u a l l y the. area a f f e c t e d was the v e n t r a l r e g i o n , where . nursing no doubt l e d ..to ..wear and t e a r of the f u r surrounding the n i p p l e s . T h i s type of molt g e n e r a l l y o c c u r r e d only when the female was a p p a r e n t l y anoestrous. ...... In January or e a r l y February, as males became r e p r o d u c t i v e l y a c t i v e , t h e i r odor-producing s i d e glands developed. T h i s occurrence was . marked by a s m a l l (approximately 3 x 6 mm.) molt patch a t the s i t e of each gl a n d , l o c a t e d l a t e r a l l y behind the f o r e l i m b s . - The r e s u l t of t h i s molt was the replacement of normal h a i r . w i t h s h o r t , coarse, and sparse h a i r s on the gland, which appeared e x t e r n a l l y as a moist, r e d d i s h yellow patch. 3.4. Adaptation and the p a t t e r n and t i m i n g of molt The molting p a t t e r n of any species, i s s u b j e c t to n a t u r a l s e l e c t i o n . . One may expect t h e . s p e c i f i c p a t t e r n , as w e l l as t h e . t i m i n g , of this.energy-demanding process to be of an adap t i v e nature, p a r t i c u l a r l y i n shrews, the minimal 27 s i z e of which p l a c e s them i n an e n e r g e t i c a l l y p r e c a r i o u s p o s i t i o n (Pearson, 1948).. It has been shown .that i n order . to maintain the homeothermic s t a t e , the metabolism of shrews, must be e x c e e d i n g l y high because of heat l o s s due to the l a r g e surface-to-volume r a t i o (Morrison and Pearson, 1947; Pearson, 1947; M o r r i s o n , Ryser, and Dawe, 1959; Hemmingsen, 1960; Buckner, 1964)., Sorex vagrans and S. obscurus have l i t t l e s e a sonal storage of . f a t . : European s p e c i e s a l s o undergo i n s i g n i f i c a n t s easonal body, fat.. v a r i a t i o n (Myrcha, 1969). Although some suggestion has been made that the use of i n t e r s c a p u l a r brown f a t a i d s i n heat p r o d u c t i o n d u r i n g p e r i o d s when shrews a r e — e x p e r i e n c i n g low temperatures (Buchalczyk and Korybska, 1964; Hissa and Jarkhonen, 1969; Pasanen, 1971), the. problem ...of... i n s u l a t i o n s t i l l remains foremost i n thermoregulatory e f f i c i e n c y when the s u r f a c e - t o -volume r a t i o i s high. , The p a t t e r n of molt, p r o g r e s s i o n i n S. vagrans and S. obscurus i s such t h a t the long.... i n s u l a t i v e winter f u r comes i n . f i r s t on the ,dorsum duri n g the f a l l molt, and t h i s s i t e i s l a s t to be r e p l a c e d d u r i n g the s p r i n g molt. The a d a p t i v e nature of t h i s p a t t e r n may well.be c o r r e l a t e d with the huddled posture assumed by i n a c t i v e shrews. Longer pelage o f f e r s g r e a t e r i n s u l a t i o n (Herrington, 1951; Hart, 1964). T h a t . p a r t . o f the body most exposed to c o l d thus r e t a i n s the more . i n s u l a t i v e h a i r s . f o r the l o n g e s t - time. The a d a p t i v e value of the molt p a t t e r n may a l s o be seen 28 from another viewpoint. During the process o f . m o l t , growing new h a i r s push out and r e p l a c e the o l d . For a s h o r t p e r i o d of time, these new h a i r s o f f e r l i t t l e . i n the way of i n s u l a t i o n . The molt on the p o s t e r i o r dorsum takes place e a r l i e s t i n the f a l l . a n d l a t e s t i n . the . s p r i n g , when temperatures are l i k e l y to be the warmest.during the molt p e r i o d . 4. Timing of Molt and Reproduction The two most energy-demanding events i n the l i f e of a shrew, are probably molt and r e p r o d u c t i o n . For shrews, molt can be p a r t i c u l a r l y t a x i n g s i n c e t h e i r high s u r f a c e - tor-volume r a t i o means a p r o p o r t i o n a t e l y . g r e a t e r area.must.be molted than f o r l a r g e r mammals. .Also, the energy demands of r e p r o d u c t i o n are h i g h , p a r t i c u l a r l y f o r females. The postpartum e s t r u s permits a female to become .pregnant with a second i n c i p i e n t l i t t e r while n u r s i n g . the f i r s t . The f i r s t l i t t e r i s weaned, with each o f f s p r i n g almost as l a r g e as,the female, and a t t h a t time the second l i t t e r i s born. I t would t h e r e f o r e be expected t h a t a d a p t i v e . s t r a t e g y i s r e f l e c t e d i n . t h e r e l a t i v e t i ming of the s p r i n g molt and r e p r o d u c t i o n . , . .. . . . Females of both s p e c i e s , molted i n e a r l y s p r i n g and became pregnant s h o r t l y upon completion of molt. P o s s i b l y the t r i g g e r i n g of e s t r u s i s somehow r e l a t e d to the molting process, because f o r an i n d i v i d u a l female, pregnancy u s u a l l y f o l l o w e d d i r e c t l y upon completion of the molt ( F i g . 4). Figure k. Timing of molt and pregnancy for i n d i v i d u a l females. 29a Ind . number 1 0 1 9 1 0 2 6 1 2 1 0 1 3 5 8 1 7 1 0 2 0 2 7 2 0 3 4 2 0 4 5 2 0 4 6 2 0 4 8 2 0 6 7 • 1 9 7 2 • 1 9 7 3 T T 1 0 0 4 1 0 1 0 1 0 12 T 0 2 7 1 0 3 8 16 1 0 2 0 0 5 21 1 0 2 0 8 9 • • M A R C H Duration of molt Onset of pregnancy A P R I L 30 Thus, females avoided o v e r l a p of the two energy-demanding p r o c e s s e s . The males had j u s t the o p p o s i t e seguence. They became r e p r o d u c t i v e l y a c t i v e i n l a t e winter, almost a month before the females began t h e i r s p r i n g molt. The males kept t h e i r long winter pelage u n t i l May, when they f i n a l l y underwent t h e i r s p r i n g molt.. The r e l a t i v e t i m i n g of .melt „ and r e p r o d u c t i o n f o r both sexes and s p e c i e s i s represented, i n F i g s . 5A and 5B. f o r 1972 and 1973. The seguence and timing of molt and r e p r o d u c t i o n i n males has s e v e r a l p o s s i b l e a d a p t i v e advantages. Since the females.determine the onset of breeding, and s i n c e the onset may d i f f e r from year, to year and from l o c a l i t y t o l o c a l i t y , i t pays f o r . t h e males to be ready e a r l y . , C l i m a t i c a l l y , i t i s s t i l l winter.when males a t t a i n s e x u a l maturity, so keeping the winter pelage appears a d a p t i v e f o r thermoregulatory.purposes. When-they f i n a l l y molt, the t i m i n g i s such t h a t most, females will... have completed t h e i r postpartum e s t r u s a n d . w i l l have.been bred a second time. S i g n i f i c a n t l y , the males.molt at j u s t about the time the f i r s t l i t t e r s a r e . l e a v i n g the nest. T h e o r e t i c a l l y , t h i s i s the time of most.abundant food (Lack, 1954, 1966) The major g u a l i t a t i v e d i f f e r e n c e in., the timing, and nature of the molt between .the s p e c i e s appeared i n . t h e males. The s p r i n g molt i n S. vagrans males was u s u a l l y s w i f t and r e g u l a r and completed f o r a l l m a l e s w i t h i n a couple of weeks. For i n d i v i d u a l S. obscurus, however, the 31 F i g u r e 5"A. Timing o f molt and r e p r o d u c t i o n i n l i v e -trapped shrews, 1972. I • 8 I • f Feb March Apr i l May June Ju ly Aug S e p t 1972 32 Figure 5"B. Timing of molt and reproduction i n l i v e -trapped shrews, 1973• X 0 o CD C O c CO 1_ U) CO > X CD o GO Males become reproduct ive Females reproduct ive First young appear in traps Males become reproduc t ive Females I r ep roduc t i ve F i r s t y o u n g a p p e a r in t raps | | no mo l t m o l t i n g m o l t e d Feb March Apr i I • May June 1973 Ju ly Aug Sept so 33 molt was o f t e n patchy, i r r e g u l a r , and p r o t r a c t e d . P o s s i b l y these d i f f e r e n c e s are r e l a t e d to the e v i d e n t l y s h o r t e r breeding season of S. obscurus (see Sect. 8.5), at l e a s t i n t h i s a r e a . Male S. obscurus would have l e s s s e l e c t i v e pressure to maintain a . s w i f t r e g u l a r molt s i n c e breeding females tend to d i e out s h o r t l y a f t e r weaning one l i t t e r . I n §• vagrjjns, however, r e p r o d u c t i o n i s extended through the summer months, and females o f t e n have two or three s u c c e s s i v e l i t t e r s . Assuming t h a t the summer pelage enhances s u r v i v a l , and hence r e p r o d u c t i v e success to.some extent, s e l e c t i o n would f a v o r S. vagrants males which completed the molt q u i c k l y . 5. Side Glands Dermal s i d e glands i n s e v e r a l s p e c i e s of.shrews have long been r e c o g n i z e d , and h i s t o l o g i c a l d e s c r i p t i o n s and c o n j e c t u r e s as t o p o s s i b l e f u n c t i o n based on experimentation and o b s e r v a t i o n have been made. Although dermal glands are common and widespread i n the f a m i l y S o r i c i d a e , v a r i a t i o n i n occurrence, season of a c t i v i t y , and h i s t o l o g y among s p e c i e s i s evident from the l i t e r a t u r e . The a p p a r e n t l y more p r i m i t i v e shrews shew g r e a t e r numbers of glands which are a l s o h i s t o l o g i c a l l y d i s t i n c t . In a d d i t i o n to s i d e glands, f o r instance,.„the s h o r t - t a i l e d shrew ( B l a r i n a brevicauda) has a v e n t r a l gland (Coues, 1896) which i s e n t i r e l y sebaceous i n nature, while the s i d e glands are h a l f sebaceous and h a l f sweat t u b u l e s (Eadie, 1938; 34 Pearson, 1946). The shrew Suncus murinus has c o n c e n t r a t i o n s of sweat glands on the t h r o a t and behind the ea r s , as w e l l as sebaceous s i d e glands with a surrounding r i n g . o f sweat tu b u l e s (Dryden and Conaway, 1967). I t i s suggested t h a t the sweat glands are r e s p o n s i b l e f o r production of the musky odor and t h a t the o i l y s e c r e t i o n s of the s p e c i a l i z e d sebaceous t u b u l e s of the s i d e glands f u n c t i o n to tr a p the odor (Dryden and Conaway, op. c i t . ) . Reports on the dermal glands of Sorex s p e c i e s i n d i c a t e the e x i s t e n c e o n l y o f s i d e glands (Jackson, 1928). The glands of Sorex araneus are. h i g h l y v a s c u l a r i z e d sweat tu b u l e s surrounded by a p e r i p h e r a l r i n g of . l a r g e , sebaceous glands i n breeding males, and only moderately v a s c u l a r i z e d sweat glands i n females (Johnsen, 1914).. The s i d e glands i n Sorex vagrans and S. obscurus are a l s o probably a mixture o f sweat and sebaceous gla n d s . ... . The o b s e r v a t i o n s I have made on the s i d e glands of S. vagrans and S. obscurus are as f o l l o w s : 1) The glands are well-developed i n breeding males. When the t e s t e s begin t c enlarge, a molt takes place i n the s i d e gland area, c o r r e l a t e d with development of the gland i t s e l f and i t s appearance e x t e r n a l l y , on the f l e s h s i d e the patches are h i g h l y v a s c u l a r i z e d red o v a l s with a p e r i p h e r a l r i n g of l i g h t e r r ed. 2) The glands i n females and immatures are at best rudimentary. They can be de t e c t e d i n breeding females only on the f l e s h s i d e of the s k i n , as s m a l l o v a l areas of 35 s l i g h t l y rougher t e x t u r e , and are only s l i g h t l y , i f at a l l , more v a s c u l a r i z e d . I could not d e t e c t a change in.odor i n breeding females. Examination under a. d i s s e c t i n g scope f a i l e d t o r e v e a l any t r a c e of s i d e gland i n immatures of e i t h e r sex. T h i s i s i n agreement with the o b s e r v a t i o n s of C l o t h i e r (1955). 3) The odor from the s i d e glands of breeding males.was d i s t i n c t i v e and d i f f e r e n t i n S. vagrans and S. obscurus. The s m e l l of a breeding S. vagrans male can be d e s c r i b e d , as musky, while t h a t of a breeding S. obscurus male i s . a mere pungent, a c r i d odor, The d i f f e r e n c e i n odors was se obvious t h a t I was a b l e to p r e d i c t with confidence t h e . . s p e c i e s , of breeding male i n a t r a p before opening the t r a p t c r e l e a s e the animal. . . . . . . . . 4) Odor seemed to i n c r e a s e with excitement. P l a c i n g two breeding males together i n a cage r e s u l t e d i n a wave of odor emission from them. 5.1. The adaptive s i g n i f i c a n c e of s i d e gland odor Se v e r a l i n t e r p r e t a t i o n s of the f u n c t i o n of the odor produced by s i d e glands have been made i n . t h e l i t e r a t u r e . Johnsen (1914), working with Sorex araneus, suggested t h a t the odor f u n c t i o n s t o a t t r a c t the sexes during the breeding season. Hamilton (1940) found.the s i d e glands of S. fumeus to enlarge with the onset of r e p r o d u c t i v e a c t i v i t y i n males and s l i g h t l y i n females, and concluded t h a t the.odor served as a s e x u a l a t t r a c t a n t . Both M i c h i e l s e n (1966) and 36 Crowcroft (1957) noted t h a t breeding male and anoestrous female Sorex araneus had the most h i g h l y developed s i d e glands; the l a t t e r suggested t h a t the males used the scent to make t h e i r paths u n a t t r a c t i v e to other males, while o d i f e r o u s , anoestrous females d e t e r r e d males. Pearson (1946), i n h i s study of B l a r i n a brevicauda, a l s o concluded t h a t the odors, present i n both males and females, f a c i l i t a t e d mutual avoidance. Skaren (1964) noted a constant and d i s t i n c t d i f f e r e n c e between the s m e l l s of Sorex araneus and S. u n g u i c u l a t u s i n Europe and suggested a p o s s i b l e s p e c i e s r e c o g n i t i o n f u n c t i o n . The emission of odor from the s i d e glands of shrews i s i n essence an act of communication: i t has the e f f e c t of t e l l i n g the r e c e i v e r something about the s t a t e of the sender. As such, i t may f u n c t i o n e i t h e r i n t e r - or i n t r a s p e c i f i c a l l y . C o n c e i v a b l y , odor-producing glands may have begun as an aposematic c h a r a c t e r . I t i s well known t h a t mammalian p r e d a t o r s f i n d shrews d i s t a s t e f u l ; I have found s e v e r a l shrews a p p a r e n t l y . k i l l e d and then abandoned by p r e d a t o r s . I f , however, odor served p r i m a r i l y to warn pred a t o r s of the u n p a l a t a b i l i t y of shrews, one would expect the c h a r a c t e r to be more widespread i n the p o p u l a t i o n r a t h e r than c o n f i n e d mainly to breeding i n d i v i d u a l s , as i s the case with most s p e c i e s s t u d i e d . More l i k e l y , the odor emitted a c t s as a pheromone, a chemical s i g n a l exchanged between members of the same s p e c i e s . ...... I s h a l l review the s i x b a s i c f u n c t i o n s of pheromones 37 (Marler and Hamilton, 1967) , each i n terms of my o b s e r v a t i o n s on Sorex vagrans and S. obscurus. 1) D i s p e r s a l and aggregation. Except f o r the n e s t l i n g p e r i o d , shrews are s o l i t a r y , a s o c i a l animals. T e r r i t o r i a l i t y i n s e v e r a l s p e c i e s ( M i c h i e l s e n , 1966) suggests t h a t odor i s used i n marking out and maint a i n i n g t e r r i t o r i e s . In S. vagrans and S. obscurus, however, . the p e r i o d of s t r i c t e s t avoidance and non-overlap i s during the f i r s t summer, when animals are immature and have no developed s i d e glands. Thus, f o r these s p e c i e s , cdor from s i d e glands does not appear to serve i n p o p u l a t i o n d i s p e r s i o n . 2) Alarm substances. The s o l i t a r y nature of shrews pre c l u d e s the p o s s i b i l i t y of use of pheromones as danger s i g n a l s . 3) Parent-young r e l a t i o n s h i p s . Although I have evidence t h a t young may f o l l o w t h e i r mothers about i n the e a r l y stages of weaning, the l a c k of development of prominent s i d e glands i n e i t h e r young or mothers i n d i c a t e s . a n e g l i g i b l e r o l e f o r pheromones. However, odors I cannot dete c t may be used i n t h i s regard. I have.evidence t h a t young r e t u r n to the nest a f t e r i n i t i a l e x c u r s i o n s . Having marked by t o e - c l i p p i n g the f i r s t j u v e n i l e . o f . t h e year t o enter a t r a p , I captured a l a c t a t i n g female i n . the same v i c i n i t y one and a h a l f hours l a t e r with blood.on her b e l l y f u r , presumably from the toes of the f r e s h l y c l i p p e d young. Odors may play a r o l e i n the o r i e n t a t i o n of young at t h i s 38 e a r l y stage. 4) T r a i l - l a y i n g . C o n c e i v a b l y , breeding males can leave scent markers duri n g t h e i r expanded wanderings, e i t h e r to announce t h e i r presence to r e c e p t i v e females or t o help them r e t u r n to t h e i r home ranges. I have found males to expand a p p r e c i a b l y t h e i r home ranges upon reachin g s e x u a l maturity. Some maintain these expanded home ranges, whereas o t h e r s seem to abandon them a l t o g e t h e r (as i s a l s o evidenced by i n g r e s s of new breeding males). ...... 5) Sex pheromones. The strong c o r r e l a t i o n between t e s t e s growth and development of s i d e g l a n d s . i s evidence of a r e p r o d u c t i v e r o l e f o r the odor emitted. The len g t h of the female e s t r u s i s onl y f o u r hours (Dehnel, 1952; Crowcroft, 1957), and c o n s i d e r i n g the s o l i t a r y h a b i t s , of shrews, pheromones from the male would presumably be. e f f e c t i v e i n a c t i n g over long d i s t a n c e s (perhaps by s c e n t . g r a d i e n t s o f t r a i l markers) to e l i c i t approach and c o p u l a t o r y behavior by the female. 6) I n d i v i d u a l and group r e c o g n i t i o n . As shrews are not known t o form any long l a s t i n g s o c i a l bonds, pheromones probably do not serve i n i n d i v i d u a l r e c o g n i t i o n beyond sex. As a s p e c i e s r e c o g n i t i o n s i g n a l , however, the chemical system has almost u n l i m i t e d p o t e n t i a l owing to the v e r s a t i l i t y of p o s s i b l e combinations and p r o p o r t i o n s . The g r e a t e s t demand f o r s p e c i e s s p e c i f i c i t y i n s i g n a l s occurs when r e p r o d u c t i o n i s i n v o l v e d . The . development of s i d e glands s o l e l y i n breeding males, coupled with the 39 d i s t i n c t i v e odors f o r sympatric S. vagrans and S. obscurus, s t r o n g l y i n d i c a t e a s p e c i e s r e c o g n i t i o n and sex r o l e f o r the pheromones i n these shrews. The use of odor as a taxonomic c h a r a c t e r i s s e v e r e l y l i m i t e d , s i n c e the s m e l l s are r e t a i n e d only i n l i v e i n d i v i d u a l s . A q u a n t i t a t i v e study of shrew pheromones co u l d provide v a l u a b l e i n f o r m a t i o n regarding t h e i r nature and v a r i a b i l i t y as we l l as provide i n s i g h t i n t o taxonomic problems. 6. Home Range 6,1. Background The home range of an animal provides the p h y s i c a l boundaries w i t h i n which i t s niche i s r e a l i z e d . Home range i s g e n e r a l l y accepted as being t h a t area over which an animal moves i n p u r s u i t of i t s normal v i t a l a c t i v i t i e s (Burt, 1943; J e w e l l , 1966). S h i l l i t o (1963) made a p r a c t i c a l m o d i f i c a t i o n to the d e f i n i t i o n by i n c l u d i n g the time dimension, a l l o w i n g f o r the c o n s i d e r a t i o n c f home range changes over the course of an animal's l i f e . The s i z e and nature of the home range has long been recognized as a s p e c i e s s p e c i f i c c h a r a c t e r (e.g. Seton, 1910), and as such, i t has adapt i v e value i n r e l a t i o n to o t h e r . l i f e h i s t o r y c h a r a c t e r i s t i c s . The heme range s i z e , shape, i t s v a r i a t i o n with sex and season, and the r e l a t i v e d i s t r i b u t i o n of home ranges w i t h i n a p o p u l a t i o n are a l l aspects s u b j e c t t o s e l e c t i o n and m o d i f i c a t i o n . Understandably, home range as an e c o l o g i c a l parameter has r e c e i v e d a great deal of uo a t t e n t i o n . Home range s t u d i e s o f s m a l l mammals are g e n e r a l l y based on mark and recapture techniques s i n c e d i r e c t o b s e r v a t i o n i s v i r t u a l l y i m p o s s i b l e . Notable exceptions i n v o l v e the use of i s o t o p e s (e.g. Godfrey, 1954a, 1954b; M i l l e r , 1957; Kaye, 1961) or t r a c k i n g ( J u s t i c e , 1961; Scheppe, 1965, 1967; Wise, 1967; L. E. Brown, 1969). Methods used f o r the a n a l y s i s of animal movements i n terms of home range s i z e f a l l i n t o two b a s i c c a t e g o r i e s : c a r t o g r a p h i c a l and s t a t i s t i c a l . C a r t o g r a p h i c a l technigues i n v o l v e d e f i n i n g an area which covers a l l of the capture s i t e s of an i n d i v i d u a l . S e v e r a l methods, based on minimum area, boundary s t r i p , or range l e n g t h , may be used i n a c t u a l d e termination of the area (Hayne, 1948 ; S t i c k e l , 1954). 6.1.1. S t a t i s t i c a l methods of home range c a l c u l a t i o n The s t a t i s t i c a l method of home range s i z e d etermination e s t a b l i s h e s an area t o which i s attached a c e r t a i n p r o b a b i l i t y of the animal's presence. T h i s method i s g e n e r a l l y based on data r e s u l t i n g from mark.and recapture i n a p o p u l a t i o n . Hayne (1949) f i r s t suggested that home range could be def i n e d on the b a s i s o f the degree of p r o b a b i l i t y of capture away from the c e n t e r of a c t i v i t y , i . e . the ge o g r a p h i c a l c e n t e r , or a r i t h m e t i c mean of a l l p o i n t s of captu r e . Using t h i s concept. Dice and Clark (1953) and Calhoun and Casby (1958) presented c i r c u l a r , heme range models, assuming the average d e v i a t i o n i n d i s t a n c e from the 41 g e o m e t r i c a l c e n t e r of the home range to be uniform i n a l l d i r e c t i o n s . The i m p l i c a t i o n s of t h i s assumption are e i t h e r t h a t the e x t e r n a l environment has no. i n f l u e n c e on the animals's movements, cr t h a t the i n f l u e n c e i s exerted with equal s t r e n g t h from a l l d i r e c t i o n s , both of which are u n l i k e l y (Tanaka, 1963; Hohr, 1965). Mazurkiewicz (1969, 1971) g e n e r a l i z e d the b a s i c model of Calhoun and Casby (1958) and proposed the e l l i p t i c a l home range.model, which i n c l u d e s an added parameter of d i r e c t i o n . . R e s u l t s . o f other s t u d i e s (Howard, 1949; Davis, 1953; Kaye, 1961; Mchr, 1965) support Mazurkiewicz*s suggestion that most home.ranges are elongated because animals tend t o p r e f e r c e r t a i n d i r e c t i o n s , 6.2. The e l l i p t i c a l model For the home range c a l c u l a t i o n s of Sorex.vagrans and §2£§2 2^§£]S£SS 1 have used an e l l i p t i c a l model based on the m o d i f i c a t i o n s of the concepts of Mazurkiewicz (op. c i t . ) and J e n n r i c h and Turner (1969) put f o r t h . b y Koeppl, S l a d e , and Hoffmann (1975). a l l c a l c u l a t i o n s were made on a D i g i t a l PDP-11 computer. I w i l l b r i e f l y o u t l i n e here.the b a s i c parameters i n v o l v e d i n c a l c u l a t i o n of. the. e l l i p t i c a l home range. For more d e t a i l s , see Koeppl, Slade, and Hoffmann (op. c i t . ) . Assuming a b i v a r i a t e normal d i s t r i b u t i o n , a l l capture s i t e s f o r each i n d i v i d u a l are d e s c r i b e d by f i v e s t a t i s t i c a l parameters: the mean X, the mean Y, the v a r i a n c e . o f X, the v a r i a n c e of Y, and the c o v a r i a n c e of X and Y, The means 42 d e s c r i b e the g e o m e t r i c a l c e n t e r , while the va r i a n c e s and covari a n c e d e s c r i b e the d i s t r i b u t i o n of p o i n t s around the ce n t e r . These parameters thus d e f i n e the shape and l o c a t i o n of the home range. The s i z e of the e l l i p s e , depends upon what percentage of a l l c a p t u r e s i t i s to c o n t a i n . . I have chosen the 95% l e v e l f o r d e f i n i n g the ab s o l u t e s i z e of the e l l i p s e and the home range area. The len g t h s of the major and minor axes are t h e r e f o r e determined as 1.96 times the r e s p e c t i v e standard d e v i a t i o n s from the mean, and the boundary of the home range i s a c l o s e d curve connecting c a l c u l a t e d p o i n t s of egual p r o b a b i l i t y of capture. Although the above f i v e b a s i c s t a t i s t i c s d e s c r i b e the d i s p e r s i o n and c e n t e r of the home range, an e l l i p t i c a l model a l s o i n v o l v e s o r i e n t a t i o n . I t i s i n t u i t i v e l y c l e a r that the v a r i a n c e of X and Y, upon which the s i z e and shape of the home range are based, depends upon the o r i e n t a t i o n of the e l l i p t i c a l a x i s w i t h i n the s c a t t e r of p o i n t s . In t h i s model, the axes are computed on the b a s i s of the eig e n v a l u e s , which i n tu r n are computed, from the, b a s i c s t a t i s t i c s and p r o v i d e a measure of the i n t r i n s i c v a r i a b i l i t y of the s c a t t e r of l o c a t i o n s along two orthogonal axes passing through the a c t i v i t y c e n t e r . 6.3. Home range s i z e 6.3.1. Sample s i z e Good e s t i m a t i o n of home range s i z e based, on mark and reca p t u r e techniques r e q u i r e s t h a t an adequate number of 43 r e c a p t u r e s be made, The capture s i t e s should r e p r e s e n t not on l y the range o f the animal but a l s o i t s frequency o f a c t i v i t y w i t h i n t h a t range. Mazurkiewicz. (1971), working with the European v o l e Clethrionomys g l a r e o l u s , c a l c u l a t e d the average s h i f t i n the g e o m e t r i c a l center cf the home range f o r cumulative c a p t u r e s and found i t d i d not s t a b i l i z e u n t i l the 19th capture. However, s i n c e the standard d e v i a t i o n s of d i s t a n c e of capture from the.center began t o l e v e l o f f a f t e r o n l y three captures, Mazurkiewicz decided t h a t a minimum o f f i v e captures would give r e l i a b l e home range s t a t i s t i c s . Others working with small, mammals ( B l a i r , 1942; Hayne, 1950; S t i c k e l , 1954; Calhoun and Casby, 1958) con s i d e r e d ten captu r e s t o be minimal. Sample s i z e f o r home range estimates g e n e r a l l y presented no problem i n t h i s study. Shrews which s e t t l e d i n the area entered t r a p s r e a d i l y ; o t hers tended to disappear a f t e r very few c a p t u r e s . In order to determine how many captures were needed before a r e l a t i v e l y constant home range s i z e was c a l c u l a t e d , I chose s e v e r a l i n d i v i d u a l s having high f r e q u e n c i e s of r e c a p t u r e and p l o t t e d the home range s i z e . a s a f u n c t i o n of the number of cumulative captures. The r e s u l t s are shown i n F i g u r e s 6A-C. A f t e r a sharp i n i t i a l i n c r e a s e , home range s i z e g u i c k l y l e v e l l e d o f f . . The i n c r e a s e with l a t e r captures i s owing t o . the onset of breeding a c t i v i t y . On b a s i s of these graphs, I have s e t ten captures as the minimum f o r i n c l u s i o n , i n my heme range a n a l y s e s . C o n s i d e r i n g t o t a l c a p t u r e s , 52.5? of the Figure 6A. Estimated home range s i z e as a funct o f number of captures (Sorex vagrans). 44a S vagrans 13SS 9 A ±5 Figure 6B. Estimated home range size as a function of number of captures (Sorex vagrans). S. vagrans 2045 ? B 1+6 F i g u r e 6C. Estimated home range s i z e as a f u n c t i o n o f number of captures (Sorex o b s c u r u s ) . S. obscurus 1012 9 CO 00 • 40 60 60 100 120 140 ISO Number of captures S. obscurus 1036 O* Number of captures 47 S. vagrans (61 out of 116 animals) were captured at l e a s t ten times and up to. 160 times; 4495 (38 out of a t o t a l o f 86) of the S. obscurus were captured from 10 to a maximum of 121 times. Of these t o t a l c a p t u r e s , however,.only .20 S. vagrans and 10 S. obscurus i n d i v i d u a l s were captured 10 or mere times both as non-breeders and breeders. These. r e p r e s e n t e d the 1971 and 1972 g e n e r a t i o n s , which were f o l l o w e d i n t h e i r e n t i r e t y . 6.3.2., Seasonal change i n home range s i z e and l o c a t i o n . ... The s i z e of an animal's home range i s i n t r i c a t e l y r e l a t e d t o the e n e r g e t i c requirements and r e s e r v e s of the animal. In a broad sense, s i z e of home range has.been shown to be c o r r e l a t e d with body weight, food type, and.the way.in which food i s obt a i n e d (McHab, .1963). Within , one. s p e c i e s , one might expect changes, i n e n e r g e t i c requirements or r e p r o d u c t i v e s t a t e s t o b e . r e f l e c t e d i n the.movements.of. the animal, p a r t i c u l a r l y i n s o l i t a r y animals such as.shrews. Using the e l l i p t i c a l model, s i z e s of i n d i v i d u a l home ranges were c a l c u l a t e d on the b a s i s o f t o t a l captures, c a p t u r e s while non-breeding,..and captures while breeding. Home range s i z e and l o c a t i o n (mean X-and Y) are. l i s t e d i n Table I I f o r the i n d i v i d u a l s which were captured a t l e a s t ten times i n both c o n d i t i o n s . These are.animals-which were captured as young animals, . e s t a b l i s h e d . t h e m s e l v e s i n the area of the p l o t , s u r v i v e d the . winter, ..and. formed the r e s i d e n t breeding p o p u l a t i o n the f o l l o w i n g s p r i n g . J Non-breeding Breeding Home Home Ind. Sex n range Mean Mean n range Mean Mean # size (m^) X y size (m^) X y S. vagrans 2 F 29 1390 9 . 0 8 . 5 1+1 1811 9 . 8 8.1+ 5 F 19 593 1+.8 2 . 9 27 2821 3 . 3 1006 M 20 1372 2 . 7 1.3 56 3980 M 3 . 5 1013 F 1*+ 1316 9 . 3 1.1+ 51 11+26 1 0 . 3 1.6 1019 F 100 981+ 5 .9 3 . 9 13 2589 1026 F 29 1735 h.5 1.9 59 1577 2.1+ 1037 M 26 935 1 .5 1+.8 31 2525 2.1+ 1210 F 19 702 1 1 . 7 3 . 7 50 5261 1 0 . 6 1+.1+ 1358 F 105 1187 5 A 6 . 7 22 11+87 3 . 0 6 . 0 1710 F 81 811 1 1 . 0 7 . 7 59 3667 9 . 7 8 . 3 2002 M 108 l5*+0 3 . 0 5 . 3 19 1908 3 . 9 h.f 2003 M 55 790 11 .6 3.1 87 1+1+6O 8 . 5 2 . 9 2027 F 59 1986 1 0 . 8 9 . 8 11+ 1703 7 A 8.1 2 0 3 ^ F 61 6 58 1 .8 7 . 5 27 1318 1 .8 6.1 2038 M 10 8^ +6 6 . 3 2 . 2 33 3079 5.1 1.8 20^5 F 125 1610 7 . 2 7 . 2 3 5 318U 5 . 6 6 . 3 201+6 F 50 1850 7 . 8 1 .5 21+ 1980 7.1 1 .5 20^8 F 86 12*+1 1 0 . 6 7 . 6 ^5 261+7 10.1 7 . 6 2067 F 1+2 510 11 .7 ^ . 5 12 732 11 .8 1+.0 2310 M 1+1 553 1 . 3 3 . 6 ^5 2160 2 . 2 5.1 S. obscurus 100tf F 70 115^ 9 . 2 11 .3 21+ 1+1+25 8 . 7 1 0 . 0 1010 F ^3 1057 2.1+ 2 . 8 15 981 1.6 3 . 0 1019 F 10 338 3 .1 1.1 21+ 2191+ 1+.1 1.8 1027 F 61 1951 6.1 11 .3 12 1873 5 .3 1 0 . 6 1036 M 92 1387 10 .2 1+.2 29 3^15 9 . 0 1038 F 55 472 11.3 1 .5 20 2338 1 0 . 7 3 . ^ 1610 F 13 566 1.8 1 0 . 2 21 891 1.9 1 0 . 9 2 0 0 5 F 50 791 2 . 6 1 0 . 9 18 1101 2 . 2 1 0 . 2 2089 F 73 679 11 .2 11 .6 10 605 11 .2 11 .6 2110 F 57 160*+ 7 . 3 11 .3 21+ 3861 6.1+ 1 0 . 5 Table I I . Home range size and lo c a t i o n for S. vagrans and obscurus indivi d u a l s captured ten or more times both when non-breeding and breeding. Mean x and y are references to grid coordinates of the 12-by-12 l i v e - t r a p p i n g p l o t . 49 F i g u r e s 7 and 8 g r a p h i c a l l y i l l u s t r a t e the e l l i p t i c a l home range data given i n Table I I . . f o r . non-breeding and breeding captures of i n d i v i d u a l s of each s p e c i e s , r e s p e c t i v e l y . The number of captures a t each capture s i t e f o r an i n d i v i d u a l are g i v e n . In the gre a t m a j o r i t y of cases, the breeding heme range s i z e was s i g n i f i c a n t l y l a r g e r than non-breeding ranges. The one S. vagrans which showed a s l i g h t decrease i n home range s i z e (#2027) was an unexplainable. case i n which a c t i v i t y a l t e r n a t e d between two s m a l l , widely separated areas of the p l o t , with no captures connecting them,. The S. obscurus data i n c l u d e d three with s l i g h t l y decreased estimated breeding home range s i z e s (#1010, 1027,. . 2089), but are u n f o r t u n a t e l y l e s s r e l i a b l e than the S. vagrans data because of the tendency f o r S. obscurus i n d i v i d u a l s to be lo c a t e d a t the edges of the p l o t . Although the home range area of most shrews i n c r e a s e d s i g n i f i c a n t l y when the animal reached s e x u a l maturity, i t s a c t u a l l o c a t i o n i n the p l o t tended to remain s t a t i o n a r y , p a r t i c u l a r l y f o r females. To t e s t the v a l i d i t y of using home ranges which were c a l c u l a t e d to extend s i g n i f i c a n t l y beyond the c o n f i n e s . o f the p l o t , I s u b d i v i d e d non-breeding S. vagrans home ranges i n t o those which were c a l c u l a t e d to be more than 95% with i n the p l o t and l e s s than 95% w i t h i n the p l o t . Student's . t -t e s t showed no s i g n i f i c a n t d i f f e r e n c e i n s i z e . 50 Figure ?A. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sprex vagrans captured ten or more times i n each c o n d i t i o n . G r i d l o c a t i o n s and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95$ of p o i n t s . Sorex vagrans 50a IND. NO. NON —BREEDING BREEDING AND SEX HOME RANGE HOME RANGE 51 Figure 7B. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sorex vagrans captured ten or more times i n each c o n d i t i o n . G r i d l o c a t i o n s and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95% of p o i n t s . B 52 Figure 7C. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sorex vagrans captured ten or more times i n each c o n d i t i o n . Grid l o c a t i o n s and number o f captures per...locality are shown. E l l i p s e s are drawn to i n c l u d e 95$ of p o i n t s . Sorex vagrans 52a I N D . N O . N O N — B R E E D I N G B R E E D I N G A N D S E X H O M E R A N G E H O M E R A N G E 53 Figure 7D. Non-breeding and.breeding home range comparisons for i n d i v i d u a l Sorex vaerans captured ten-or more times i n each c o n d i t i o n . G r i d l o c a t i o n s and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95% of p o i n t s . D 5^  Figure 7E. Non-breeding and breeding home range comparisons for i n d i v i d u a l Sorex vagrans captured ten or more times i n each condition. Grid locations and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to include 95% of points. Sorex vagrans 54a IND. NO. NON-BREEDING BREEDING E 55 Figure 7F. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sorex vagrans captured ten or more times i n each c o n d i t i o n . G r i d l o c a t i o n s and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95% of p o i n t s . 56 Figure 7G. Non-breeding and breeding home range comparisons for i n d i v i d u a l Sorex vagrans captured ten or more times i n each condition. Grid locations and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to include 95% of points. 56a Sorex vagrans IND. NO. NON —BREEDING BREEDING AND SEX HOME RANGE HOME RANGE G 57 Figure 8A. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sorex obscurus captured ten or more times i n each c o n d i t i o n . G r i d l o c a t i o n s -and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95$ of p o i n t s . Sorex obscurus I N U . N O . NON —BREEDING BREEDING AND SEX HOME RANGE HOME RANGE 1019 58 Figure 8B. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sorex obscurus captured ten or more times i n each c o n d i t i o n . Grid l o c a t i o n s and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95% of p o i n t s . Sorex obscurus 58a IND. NO. NON-BREEDING BREEDING AND SEX HOME RANGE HOME RANGE B 59 Figure 8C. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sorex obscurus captured ten or more times i n each c o n d i t i o n . G r i d l o c a t i o n s and number o f captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95$ of p o i n t s . 59a Sorex obscurus IND. NO. AND SEX NON —BREEDING HOME RANGE BREEDING HOME RANGE 1610 C 60 Figure 8D. Non-breeding and breeding home range comparisons f o r i n d i v i d u a l Sorex obscurus captured ten or more times i n each c o n d i t i o n . Grid l o c a t i o n s and number of captures per l o c a l i t y are shown. E l l i p s e s are drawn to i n c l u d e 95$ of p o i n t s . 60a Sorex obscurus IND. NO. AND SEX NON-BREEDING HOME RANGE BREEDING HOME RANGE 2089 2110 ? D 61 Most of the i n d i v i d u a l s remaining i n the p l o t f o r t h e i r e n t i r e l i f e s p a n were females. T h i s , coupled with the l a r g e i n g r e s s of unmarked breeding males i n the s p r i n g (to be d i s c u s s e d i n more d e t a i l l a t e r ) , i n d i c a t e s t hat some males, at l e a s t , may s h i f t or abandon.their home ranges a l t o g e t h e r when s e x u a l l y mature. Perhaps the degree of."wanderlust" depends on the p r o x i m i t y of r e c e p t i v e females. I t i s of obvious s e l e c t i v e advantage f o r males to f i n d as many r e c e p t i v e females as p o s s i b l e , i n l i g h t of the f a c t t h a t shrews do not form p a i r bonds (Crowcroft, 1955b). Furthermore, s i n c e the e s t r u s of females l a s t s no more than f o u r hours (Dehnel, 1952; Crowcroft, . 1957), s u c c e s s f u l males must c o n t a c t females f r e g u e n t l y and c o n t i n u o u s l y . I t was o f t e n the case t h a t breeding males g r a d u a l l y wandered f u r t h e r and f u r t h e r from t h e i r winter r a n g e s . u n t i l f i n a l l y they l e f t the area a l t o g e t h e r . T h i s i s r e f l e c t e d i n some of the graphs a l r e a d y r e f e r r e d to i n F i g . 6, where l a t e r c a p t u r e s s h a r p l y i n c r e a s e d the o v e r a l l estimates of home range s i z e . From the i n f o r m a t i o n gathered on seasonal changes i n home range s i z e of S. vagrans and S. obscurus, i t i s obvious t h a t a s i n g l e o v e r a l l estimate f o r a s p e c i e s i s inadeguate. Home range s i z e s t a t i s t i c s f o r non-breeding and breeding S. vagrans and S. obscurus are shown, r e s p e c t i v e l y , i n F i g . 9. D i f f e r e n c e s between non-breeding and breeding range s i z e f o r each s p e c i e s are s t a t i s t i c a l l y s i g n i f i c a n t , a c c ording t o Student's t - t e s t . S i m i l a r expansion of range d u r i n g 62 F i g u r e ^. Home range s i z e comparisons between breeding and non-breeding i n d i v i d u a l s . Student's t - t e s t showed s i g n i f i c a n t d i f f e r e n c e s between breeding and non-breeding home range s i z e s , but no d i f f e r e n c e s between s p e c i e s . o o o X CN E a) N 0) C O c C O rr E o I . 12-11-10-9; 8-7-6H 5-4-3-2-1 • 40 22 35 S.V. 23 So. S.V. S.O. Non-breeding Breeding X (m 2) Non-breeding Breeding S. vagrans 1039 3258 S. obscurus 1227 ^020 63 r e p r o d u c t i v e a c t i v i t y was a l s o found f o r . S. vagrans by I n g l e s (1961) and f o r Sorex araneus . ( S h i l l i t o , . . . . 1963 ; M i c h i e l s e n , 1966; Buckner, 1969), although.the home ranges of Sorex araneus tend t o be s m a l l e r i n an abs o l u t e sense than those of North American shrews. 6.3.3. Sexual d i f f e r e n c e s i n home range s i z e F u r t h e r a n a l y s i s o f the home range .data was done f o r each sex, using Student's t - t e s t f o r a l l comparisons t o be d i s c u s s e d (Fig. 10). For non-breeding animals of. both. s p e c i e s , no s i g n i f i c a n t d i f f e r e n c e s were found between the home range s i z e o f males and females. As.shown i n the p r e v i o u s s e c t i o n f o r the p o p u l a t i o n as a whole,.both sexes expand t h e i r range s i g n i f i c a n t l y upon reachin g sexual m a t u r i t y . Comparison between breeding ranges of males and those of. females, however, shows t h a t f o r both S.,vagrans and S. „obscurus, the breeding range of males i s s i g n i f i c a n t l y l a r g e r . For both s p e c i e s , the breeding heme range .of females. averaged two times the s i z e of t h e i r non-breeding ranges, while male S. vagrans and S. obscurus home.ranges i n c r e a s e d an average of f i v e times upon se x u a l m a t u r i t y . Comparisons between s p e c i e s showed .the average home range area f o r each o f the v a r i o u s c a t e g o r i e s ..to. be s i m i l a r . C o n ceivably, however, the ranges f o r _S. obscurus are underestimated, because so many i n d i v i d u a l s were c o n t i n u a l l y captured along the p e r i p h e r a l rows of the p l o t . 6k Figure 10. Home range s i z e (mean, standard d e v i a t i o n , and 95% confidence l i m i t s ) as a f u n c t i o n of s p e c i e s , sex, and r e p r o d u c t i v e c o n d i t i o n . Student's t - t e s t showed no s i g n i f i c a n t d i f f e r e n c e s between species or non-breeding sexes, but ranges of breeding animals were s i g n i f i c a n t l y l a r g e r than those of non-breeding, and ranges of breeding males s i g n i f i c a n t l y l a r g e r than those of breeding females. Home Range Size (m 2) •b. Cn o 00 ~o o O o o O o o o o o o o o o o o o o o o o o o o o o o o o o o o o o ^ 1 1 1 1 1 1 H 1 1 1 o I CT - \ CD CD Q. ZJ' CQ > -J 3 SB 05 CO CD CD Q. Zi' CO > 73 3 EL < ICQ —\ w w o cr </> a cz cz I f < 03 ICQ 03 CT) 100 o CT W O c •o •o •o •o O 65 The i n c r e a s e i n home range area, c o r r e l a t e d with r e p r o d u c t i v e a c t i v i t y may be seen as a . l i f e h i s t o r y s t r a t e g y r e l a t e d to s e v e r a l , p o s s i b l e f a c t o r s , , Expansion of-home ranges r e s u l t s i n i n c r e a s e d o v e r l a p and thus f a c i l i t a t e s b r i n g i n g the sexes together. The apparent nomadism e x h i b i t e d by some males would serve to encourage g e n e t i c mixing i f they are s u c c e s s f u l i n mating. Increased energy requirements may account f o r a degree of home range expansion, p a r t i c u l a r l y f o r males t h a t . enter the breeding c o n d i t i o n i n mid-winter. L i k e w i s e , r e p r o d u c t i v e females no doubt have much i n c r e a s e d energy demands.. Competition with the next g e n e r a t i o n may a l s o play a pa r t i n home range expansion when the f i r s t l i t t e r becomes weaned. 7. T e r r i t o r i a l i t y 7.1. R e l a t i v e d i s t r i b u t i o n of non-breeding home ranges .. .. The evidence o f i n c r e a s e i n home range s i z e -with... the onset of s e x u a l m a t u r i t y i n s h r e w s , r a i s e s t h e . q u e s t i o n of what determines the home range s i z e of non-breeding animals. In s t u d i e s of Sorex araneus i n the Netherlands, . M i c h i e l s e n (1966) found immature animals to have contiguous, non-ov e r l a p p i n g home ranges, and i n t e r p r e t e d t h i s , as s t r o n g evidence of t e r r i t o r i a l i t y . For .the same, s p e c i e s i n B r i t a i n , Buckner (1969) concluded that:mature females h e l d t e r r i t o r i e s a g a i n s t other females, but t o l e r a t e d o v e r l a p with males. The same author (1966) a l s o r e p o r t e d home range 66 s i z e to be determined by p o p u l a t i o n d e n s i t y and avoidance.of o v e r l a p i n Manitoba Sorex c i n e r e u s . Although the e l l i p s e model i s a v a l u a b l e , t o o l f o r a n a l y s i s of s i z e and l o c a t i o n of home ranges, . i t . n e c e s s a r i l y obscures d e t a i l s of the home range boundaries, thus.making i t d i f f i c u l t to analyze the i n f l u e n c e of one range on i t s n e i g h b o r i n g ranges. T h e r e f o r e , i n order to_determine.the r e l a t i v e , d i s t r i b u t i o n of. . S. vagrans and . S. obscurus i n d i v i d u a l s , I mapped the capture s i t e s of the.immature animals of the 1971, 1972, and 1973 g e n e r a t i o n s ( F i g s . 11A-C). The areas are enclosed by l i n e s drawn.connecting.the outermost s i t e s . In order to show. changes which occur between the summer and f a l l months, mapping .was.done_for two time p e r i o d s each year, from June through August, and from September through December. I i n c l u d e d , o n l y those i n d i v i d u a l s t h a t were captured at t h r e e . o r more . d i f f e r e n t s i t e s . I n d i v i d u a l s which disappeared_ before they reached sexual m a t u r i t y have t h e i r i d e n t i f y i n g numbers i n parentheses. In the f a l l months, one of the most s t r i k i n g a s p e c t s common to a l l t h r e e g e n e r a t i o n s i s the v i r t u a l absence o f s u b s t a n t i a l o v e r l a p of ranges. What o v e r l a p e x i s t s . t e n d s to i n v o l v e animals which a p p a r e n t l y do not make i t to the breeding season. During;the summer months, a.higher.degree of o v e r l a p i s e v i d e n t , but again the o v e r l a p s tend, to i n v o l v e animals which emigrate or die by the end of summer, or, at best, before winter. 67 F i g u r e 11 A. R e l a t i v e d i s t r i b u t i o n o f non-breeding Sorex  vagrans and S. obscurus at two time p e r i o d s , 1971 generation. I n d i v i d u a l numbers i n parentheses represent animals which disappeared before reaching sexual m a t u r i t y . 1971 GENERATION S. obscurus S. vagrans 68 F i g u r e 11B . R e l a t i v e d i s t r i b u t i o n of non-breeding Sorex vagrans and S. obscurus at two time p e r i o d s , 1 9 7 2 generation. I n d i v i d u a l numbers i n parentheses represent animals which disappeared before reaching sexual m a t u r i t y . 1972 GENERATION S. o b s c u r u s S. v a g r a n s 6 9 Figure 11C. R e l a t i v e d i s t r i b u t i o n o f non-breeding Sorex  vagrans and S. obscurus at two time p e r i o d s , 1973 generation. I n d i v i d u a l numbers i n parentheses represent animals which disappeared bef.ore reaching sexual m a t u r i t y . 1973 GENERATION S. obscurus S. vagrans 70 S l i g h t home range s h i f t s or. extensions i n t o vacated areas were e v i d e n t throughout, summer. The disappearance o f S. vagrans #1410 from the 1971 g e n e r a t i o n r e s u l t e d i n numbers 1510, 1358, and 1019 extending t h e i r ranges, f i l l i n g the vacated area ( F i g . 1 T A ) . ^ S i m i l a r l y , . the extensions o f the ranges of S. obscurus #2110 and . 2005-....{ 1972.....generation), f o l l o w e d the disappearance of #2002 ( F i g . . 11B) . .Of note i s the f a c t t h a t those animals which w i l l e v e n t u a l l y breed, i n the p l o t tend to have e s t a b l i s h e d non-overlapping ranges e a r l y i n the summer. . . ... I i n t e r p r e t these f i n d i n g s as i n d i c a t i v e of a t e r r i t o r i a l system among the shrews. B y . f a l l , . c o n t i g u o u s , v i r t u a l l y non-overlapping ranges have been e s t a b l i s h e d , e s s e n t i a l l y as a r e s u l t of the dropping out of i n d i v i d u a l s which overlapped i n the summer,.along with some..expansion and s h i f t i n g of the remaining i n d i v i d u a l s t o f i l l vacant areas. Almost a l l the animals present i n the s t a b l e f a l l months s u r v i v e the winter .to reach .sexual .maturity. E v i d e n t l y , most m o r t a l i t y and p o p u l a t i o n changes .occur dur i n g the summer, when t e r r i t o r i e s are being e s t a b l i s h e d . 7.2. S i g n i f i c a n c e of t e r r i t o r i a l i t y For a l l three g e n e r a t i o n s , success i n overwintering.and r e a c h i n g s e x u a l maturity i s h i g h l y c o r r e l a t e d with the a b i l i t y to hol d and maintain a t e r r i t o r y . b y f a l l . . In Table I I I , I have c a t e g o r i z e d the breeding p o p u l a t i o n s of the S. vagrans S. obscurus 1971 Generation Cf t o t a l Native: 7 3 10 Immigrant: 1 5 6 Transient: 1 i+ 5 Total breeding i n 1972: 9 12 21 1972 Generation Native: 6 5 11 Immigrant: 0 k k Transient: 0 1 1 ? Cf t o t a l 8 5 *>3 0 2 2 2 6 8 10 13 23 Total breeding i n 1973s 10 16 If 1 5 0 6 6 0 1 1 If 8 12 1+ 2 6 0 3 3 If 5 9 1973 Generation Native.: Non-native: Total breeding i n 197*+: 5 1 6 3 11 if 15 Table I I I . Composition of breeding populations, by generation. "Native" r e f e r s to i n d i v i d u a l s that were established on the area as immatures. "Immigrants" arri v e d a f t e r sexual maturity and remained i n the area at l e a s t 30 days. The l a t t e r two categories are lumped as "Non-native" for the 1973 generation. 72 1971, 1972, and 1973 g e n e r a t i o n s . The. term " n a t i v e " . r e f e r s to a l l the breeders which had e s t a b l i s h e d t e r r i t o r i e s . i n the area before the onset of r e p r o d u c t i v e a c t i v i t y . .Immigrants are those which were f i r s t marked as. breeding. a d u l t s . and remained f o r more than 30 days of a r r i v a l as breeding a d u l t s (these two c a t e g o r i e s are lumped for.:the 1973 g e n e r a t i o n as "non-native" s i n c e t r a p p i n g was d i s c o n t i n u e d s h o r t l y a f t e r the onset of breeding i n 1974). The .great m a j o r i t y of both S. vagrans and S. obscurus breeding females were n a t i v e s , suggesting t h a t s e l e c t i o n s t r o n g l y . favors..females . which remain i n one area. The large.number.of male immigrants.and male t r a n s i e n t s of both s p e c i e s r e f l e c t s the expansion or abandonment of the o r i g i n a l defended .home range i n , s e a r c h of females. . .:.... . U n l i k e the s i t u a t i o n i n some t e r r i t o r i a l b i r d s (Kendeigh, 1941; Nice, 1941; Herisley and Cope, . 1951 ; Stewart and a i d r i c h , 1951; Hinde,.1956; Orians,.1961; Tompa, . 1962 ; Wynne-Edwards, 1962; J. L. Brown, .1969) the e x i s t e n c e of n o n - t e r r i t o r i a l s u r p l u s shrews ( i . e . f l o a t e r s ) . i s not apparent. In three g e n e r a t i o n s , a l l but one female t h a t s u c c e s s f u l l y bred had a l s o been present i n a t e r r i t o r y the p r e v i o u s f a l l . The high i n c i d e n c e ;of new.breeding males e n t e r i n g the area a f t e r the onset of r e p r o d u c t i v e a c t i v i t y i s matched by the egress of f o r m e r l y t e r r i t o r i a l males, and can be e x p l a i n e d simply by nomadism. Happing of breeding ranges, shows . t h a t t e r r i t o r i a l i t y r a p i d l y breaks down with the onset of s e x u a l a c t i v i t y . 73 Student's t - t e s t on home range s i z e of non-breeding males and females showed no s i g n i f i c a n t d i f f e r e n c e . I t t h e r e f o r e seems evident t h a t t e r r i t o r i a l i t y i s . o n l y i n d i r e c t l y r e l a t e d to r e p r o d u c t i o n : * i t serves to allow winter s u r v i v a l t o . the breeding season. . For t h i s reason, I would not expect s u r p l u s , n o n - t e r r i t o r i a l i n d i v i d u a l s to e x i s t a f t e r f a l l . . . . . . H o l l i n g (1959) found.that the d e n s i t y ..of Sorex c i n e r g u s p o p u l a t i o n s i n c r e a s e d , markedly with i n c r e a s i n g prey d e n s i t i e s , s u p p o r t i n g t h e . h y p o t h e s i s that food most.strongly l i m i t s Sorex numbers. The .high d e n s i t i e s supportable.by summer food a v a i l a b i l i t y c o u l d t h e r e f o r e r e s u l t ; i n . l i t t l e o v e r a l l s u r v i v a l i f winter. food a v a i l a b i l i t y , were s i g n i f i c a n t l y lower. T e r r i t o r i a l behavior on the part of an i n d i v i d u a l shrew would act to.ensure s u f f i c i e n t space f o r i t s own winter s u r v i v a l . . . .; . _ The h y p o t h e s i s t h a t energy l i m i t a t i o n d u r i n g . w i n t e r . i s the f o r c e which g i v e s s e l e c t i v e advantage to t e r r i t o r i a l behavior i s supported by Randolph (1973), i n a study o f . t h e e c o l o g i c a l e n e r g e t i c s of ..the s h o r t - t a i l e d . shrew, b£§Zic.auda. , He estimated t h a t „ the. . winter .food reguirement of the shrew exceeds the summer food ..reguirement of H3%, and that while o n l y 358 of the t o t a l prey energy base i s needed during summer, t h i s percentage i n c r e a s e s , to .373? i n wint e r . The actu a l . e n e r g y a v a i l a b l e to shrews on,the f o r e s t f l o o r was e i g h t times as great i n summer as i n winter. 7.3. Mechanism of t e r r i t o r i a l i t y D i s c u s s i o n of t e r r i t o r i a l i t y should i n c l u d e some 74 c o n s i d e r a t i o n of the mechanism by which t e r r i t o r i e s . , are maintained. T e r r i t o r i a l i t y , by d e f i n i t i o n , . i n c l u d e s the i m p l i c i t assumption of p u r p o s e f u l ."defense,", be i t by f i g h t i n g , marking, s i n g i n g , or other means. Although I have not a c t u a l l y observed . t e r r i t o r i a l b ehavior i n the w i l d , I kept S. vagrans i n . t e r r a r i a . a n d was a b l e t o observe b e h a v i o r a l i n t e r a c t i o n s . When two shrews were kept i n the same t e r r a r i u m , . t h e y . c o n s i s t e n t l y made t h e i r nests i n o p p o s i t e c o r n e r s . Invaders o f . t h e . n e s t area of another shrew were d r i v e n out. with. ..squeaking... and sometimes f i g h t i n g . S i g n i f i c a n t l y , .. I . noted , d i s t i n c t b e h a v i o r a l d i f f e r e n c e s between nonbreeding and. breeding i n d i v i d u a l s . Young non-breeders were . more..wary and s e c r e t i v e , but were a l s o more a g g r e s s i v e when.handled.or when another shrew invaded the nest s i t e . . The o l d breeding males I observed were, on the c o n t r a r y , l e s s . c a u t i o u s , l e s s a g g r e s s i v e , and l e s s s i t e - a t t a c h e d , being prone.to c o n s t a n t wandering about the t e r r a r i u m . Often they w e r e . s u f f i c i e n t l y b o l d to take a mealworm from my. hand. , I f a t e r r i t o r y i s thought of as an a r e a . i n which the a g g r e s s i v e s t a t e of an animal increases... (Emlen, 1957) , my o b s e r v a t i o n s on d i f f e r e n c e s i n behavior between f i r s t and second year animals are w e l l c o r r e l a t e d with, the evidence.of t e r r i t o r i a l i t y i n f i r s t year shrews. . H i c h i e l s e n (1966) concluded t h a t a g g r e s s i o n and f i g h t i n g , played ..the .major r o l e i n maintenance o f t e r r i t o r i e s . o f Sorex araneus, based on .the a g g r e s s i v e behavior of the s p e c i e s as noted by Crowcroft 75 (1955b). E i s e n b e r g (1964) s t u d i e d , the behavior of §2£§2 y.a.2rans taken from the f i e l d s and second growth woodlots of the U. B. C. Endowment Lands .and. found t h a t animals l i v i n g i n the same t e r r a r i u m l e a r n e d to avoid.one another and e s t a b l i s h e d themselves i n ..dif f e r e n t nest boxes where, i n i t i a l l y , r e s i d e n t s would chase away. intruders..,... He found, however, t h a t a g o n i s t i c behavior i n c r e a s e d as . shrews went from immature to su b a d u l t , and i n f e r r e d . t h a t mutual avoidance served to d i s p e r s e a d u l t s without the need to f i g h t . I found l i t t l e evidence of wounding i n l i v e - t r a p p e d shrews, and I i n f e r from t h i s that t e r r i t o r i a l encounters d i d not o f t e n r e s u l t i n s e r i o u s f i g h t s , .Indeed, i t would be h i g h l y disadvantageous were con s t a n t f i g h t i n g necessary i n t e r r i t o r y maintenance. Threat behavior i n .posturing, and v o c a l i z a t i o n has been noted i n shrews, .however, and.no.doubt must p l a y an important p a r t . i n defending, t e r r i t o r i e s . , The f u n c t i o n of scent i n shrews has a l r e a d y . been d i s c u s s e d t o some exten t , and while I cannot ..exclude .the p o s s i b i l i t y of the use of odor i n marking t e r r i t o r i e s , the f a c t .that, s i d e glands are developed i n the.animals which a r e . l e a s t s i t e a t t a c h e d ( i . e . breeding males) i n d i c a t e s a separate f u n c t i o n . Pearson (1946), working, with the s h o r t - t a i l e d shrew, B l a r i n a b r e v i c a u d a , concluded that the.glands, served to keep the animals a p a r t . U n l i k e S. vagrans and S. obscurus, however, both male and ..female . B l a r i n a . have well-developed glands when non-breeding. They disappear 76 only i n es t r o u s females. 7.4. I n t e r s p e c i f i c t e r r i t o r i a l i t y I n t e r s p e c i f i c t e r r i t o r i a l i t y has been, shown t c e x i s t among s p e c i e s of b i r d s ( P i t e l k a , 1951; Simmons, 1951; Dixon, 1954; Legg and P i t e l k a , 1956; Emlen, 1957; Sealander and G i l l e n , 1959 ; R i p l e y , 1961; Orians and . C o l l i e r , 1963; Ori a n s and W i l l s o n , 1964; Orians and Horn, 1969), but.... owing, -to d i f f i c u l t y i n o b s e r v a t i o n , i n t e r s p e c i f i c t e r r i t o r i a l behavior of s m a l l mammals i n . the wild, cannot often..be documented. Some exce p t i o n s are the s t u d i e s of H e l l e r (1970, 1971), Brown (1971), and Sheppard (1971), working with s p e c i e s of chipmunks. .' ~ With Sorex vagrans and Sorex obscurus, a s i g n i f i c a n t o b s e r v a t i o n to be made from F i g . 11 i s t h a t very l i t t l e i n t e r s p e c i f i c o v e r l a p occurs i n home ranges.of non-breeders. While i n t r a s p e c i f i c . t e r r i t o r i a l i t y i n .mammals i s . r e l a t i v e l y easy to document by the evidence of mutually . e x c l u s i v e and contiguous home ranges, the same, evidence does not n e c e s s a r i l y i n d i c a t e the presence of i n t e r s p e c i f i c t e r r i t o r i a l i t y . — The concept of t e r r i t o r i a l i t y , v i e w e d from an e v o l u t i o n a r y sense, assumes t h a t t h e. .time and. energy an animal i n v e s t s i n m a i n t a i n i n g a t e r r i t o r y u l t i m a t e l y r e s u l t s i n g r e a t e r r e p r o d u c t i v e success. Presumably,.... the " t e r r i t o r y " i s a s s o c i a t e d with, some l i m i t i n g . f a c t o r , ....or f a c t o r s , e.g. food, space, or p o t e n t i a l mate. I t i s l o g i c a l 77 t h a t c o n s p e c i f i c s have the most i n common and i n t r a s p e c i f i c c o m p e t i t i o n i s t h e r e f o r e the g r e a t e s t . ; .Therefore, the occurrence of i n t e r s p e c i f i c t e r r i t o r i a l i t y . w o u l d i n d i c a t e t h a t the nic h e s of the s p e c i e s .involved o v e r l a p p e d . t o an extent t h a t the added energy used i n . d e f e n d i n g the t e r r i t o r y a g a i n s t members of another s p e c i e s was . worthwhile. -. .. Assuming i n t r a - s p e c i f i c t e r r i t o r i a l i t y e x i s t s in.each of the two s p e c i e s , . t h e . . q u e s t i o n which .remains i s , are h a b i t a t d i f f e r e n c e s alone enough to e x p l a i n t h e . d i s t r i b u t i o n of home ranges between s p e c i e s , o r . does i n t e r s p e c i f i c t e r r i t o r i a l i t y a l s o p l a y a p a r t ? R e f e r r i n g back to the the vegetation.and s o i l map of the p l o t , ( Fig. ,1) and comparing i t with the.home.ranges shown i n F i g . 11, i t may be seen t h a t S. ,obscurus . home ranges tend to f a l l , f o r the most, p a r t , i n areas c h a r a c t e r i z e d by mor s o i l and i t s . accompanying.... v e g e t a t i o n , while those of S. vagrans are g e n e r a l l y i n . t h e moder s o i l . The s i g n i f i c a n c e of h a b i t a t type i n determining the s p e c i e s d i s t r i b u t i o n s i n the p l o t i s apparent from t h r e e o b s e r v a t i o n s : , , ,... 1) Year a f t e r y e a r , . i n s p i t e of c o n s i d e r a b l e , i n g r e s s of young of both s p e c i e s , S. obscurus and.S. vagrans s e t t l e i n b a s i c a l l y the same areas on the g r i d . These areas r e p r e s e n t d i f f e r e n t h a b i t a t t y p e s . ... . . 2) As w i l l be seen i n Sect. 10.3, the h a b i t a t types used by each s p e c i e s i n the study g r i d , correspond to the b a s i c h a b i t a t p r e f e r e n c e s shown by the geographic 7 8 l d i s t r i b u t i o n of the two s p e c i e s elsewhere i n t h i s r e g i o n . , 3) Occurrence of shrews i n the ''wrong" h a b i t a t o f t e n r e s u l t e d i n the disappearance of t h o s e . i n d i v i d u a l s b e f o r e the onset of breeding (e.g. S. obscurus #1008 and 1128 from the 1971 g e n e r a t i o n , S. vagrans #2008 from the 1972 g e n e r a t i o n ) . _. . While these p o i n t s i n d i c a t e a d i f f e r e n t i a l preference f o r h a b i t a t types, they do not exclude the p o s s i b i l i t y of c o m p e t i t i v e e x c l u s i o n by means. of i n t e r s p e c i f i c t e r r i t o r i a l i t y . One way to t e s t f o r c o m p e t i t i v e . e x c l u s i o n i s removal of one s p e c i e s t o see i f an invasion_.of the other s p e c i e s r e s u l t s . Although I d i d not. do t h i s , I. do -have i n d i r e c t evidence t h a t i n t e r s p e c i f i c t e r r i t o r i a l i t y o c curs i n c o n j u n c t i o n with h a b i t a t p r eference. The f o l l o w i n g p o i n t s are p e r t i n e n t here: -1) The exact boundaries of.. the. home, ranges of neighboring S, vagrans and S. obscurus f o l l o w more, the l i n e s of the neighbor's home range than those o f . the h a b i t a t l i m i t s . . One would expect more o v e r l a p , p a r t i c u l a r l y i n t r a n s i t i o n a l areas, i f the animals were responding s c l e l y to h a b i t a t . -2) I have seen l i t t l e evidence of a mechanism- f o r s p e c i e s r e c o g n i t i o n i n immature animals.. I f I.am corr e c t . . i n c o n c l u d i n g t h a t t h e . d i s t i n c t i v e . o d o r s of breeding S. vagrans and S. obscurus males serve f o r s p e c i e s r e c o g n i t i o n , then i t i s l i k e l y t h a t immature shrews t r e a t c ongenerics as eguals r e g a r d l e s s of s p e c i e s . 79 3) B e h a v i o r a l l y , shrews are s o l i t a r y animals, p a r t i c u l a r l y when non-breeding (Crowcroft,. 1975; my own o b s e r v a t i o n s ) . T e r r i t o r i e s are l i k e l y maintained, by border f i g h t i n g ( M i c h i e l s e n , 1966), and because of t h e i r a s o c i a l n a ture, i t i s u n l i k e l y t h a t they would d i s t i n g u i s h s p e c i e s . 4) Shrews of most. s p e c i e s are , i n s e c t i v o r o u s and c a r n i v o r o u s , e a t i n g a l a r g e range . of a v a i l a b l e food (Hamilton, 1930). Hence, com p e t i t i o n may. e x i s t between sympatric s p e c i e s , and no l e s s b e n e f i t . would come from defending t e r r i t o r y a g a i n s t i n d i v i d u a l s of another s p e c i e s . , 5) During the breeding season, i n d i v i d u a l s , p a r t i c u l a r l y males, wander t o . a great .extent, r e g a r d l e s s . o f h a b i t a t , i n d i c a t i n g ..that i n previous months, l i m i t i n g , of i n d i v i d u a l s to c e r t a i n h a b i t a t types was f a c i l i t a t e d by t e r r i t o r i a l i t y . . . -; Co n s i d e r i n g a l l o b s e r v a t i o n s , i t seems l i k e l y t h a t .the l i v e - t r a p p e d S. vagrans and S. obscurus d e f e n d . t e r r i t o r i e s independent and i r r e s p e c t i v e of sex or. s p e c i e s during the non-breeding p e r i o d . The data support.the hypothesis t h a t r e l a t i v e c o m p e t i t i v e success i s determined by h a b i t a t : Sorex obscurus i s a b l e to maintain t e r r i t o r i e s a g a i n s t S. vagrans i n a c i d i c , western hemlock h a b i t a t , while S. vagrans has the c o m p e t i t i v e advantage.in d o u g l a s - f i r and red cedar h a b i t a t s . The apparent s t a b i l i t y . of the ..system i n d i c a t e s a b a s i c , ; ...if s u b t l e , d i f f e r e n c e . i n . the niches, of the two s p e c i e s . In h i s study of competition and 80 i n t e r s p e c i f i c a g g r e s s i o n i n .chipmunks, J . H. Brown (1971) came to much the same c o n c l u s i o n s i n noting how two s p e c i e s were able to exclude each other from t h e i r r e s p e c t i v e p r e f e r r e d h a b i t a t s . 8. P o p u l a t i o n Dynamics 8.1. P o p u l a t i o n numbers The minimum known p o p u l a t i o n s i z e s f o r S. vagrans .and S. obscurus were c a l c u l a t e d . f o r each t r a p period, as the number of shrews captured on t h a t date, plus a l l others not captured then, but captured both before and a f t e r t h a t date ( F i g . 12). The minimum known p o p u l a t i o n of each g e n e r a t i o n , along with the o v e r l a p of g e n e r a t i o n s , are e v i d e n t . C o n c e n t r a t i n g on the g e n e r a t i o n s born i n .1971 and. 1972, which were fo l l o w e d i n t h e i r e n t i r e t y , s e v e r a l o b s e r v a t i o n s can be made. The year 1971 seems to have been a p r o d u c t i v e year f o r both s p e c i e s , and i s c h a r a c t e r i z e d by a .. l a r g e ... ingress... of young animals. However,while the 1972 numbers, of S. yji^rans remained comparable t o the 1971 l e v e l s , those of S. obscurus f e l l s h a r p l y . The drop i n p o p u l a t i o n s i z e f o r S. obscurus i n 1972 i s a t t r i b u t a b l e t o a combination of low r e c r u i t m e n t and reduced s u r v i v a l of young. :•- .. P o p u l a t i o n highs f o r both s p e c i e s were recorded c o n s i s t e n t l y during t h e . months of.. J u l y and August. P o p u l a t i o n s i z e s t a b i l i z e d , beginning i n September, and l a s t e d through the winter, g i v i n g 1971 and 1972 p o p u l a t i o n 81 Figure 1 2 . Minimum known p o p u l a t i o n per t r a p p e r i o d f o r l i v e - t r a p p e d shrews, by generation. Minimum known p o p u l a t i o n represents a t a l l y of a l l i n d i v i d u a l s caught i n a p a r t i c u l a r trap p e r i o d plus those not caught then, but captured both before and a f t e r that date. The generations overlap f o r s e v e r a l months each year. 82 d e n s i t i e s of about 12 per hectare f o r S. vagrans, and 12 and f i v e per he c t a r e , r e s p e c t i v e l y , f o r 1971 and. 1972 gen e r a t i o n s of S. obscurus. I t should b e . n o t e d t h a t while these d e n s i t y e s t i m a t e s are given per h e c t a r e , i . e . the area of the p l o t , the e f f e c t i v e t r a p p i n g area i s g r e a t e r owing,to the presence o f home ranges.which j u s t border on the . p l o t . L i t t l e comparable i n f o r m a t i o n on p o p u l a t i o n d e n s i t i e s f o r these s p e c i e s i s a v a i l a b l e . Using an e l e c t r i c fence method, Vaughan (1969) found d e n s i t i e s of one to f o u r Sorex.vagrans per acre i n s u b a l p i n e p o p u l a t i o n s . Per h e c t a r e , t h i s .would amount to 2.5 to 10, numbers comparable t o those i n my l i v e -t r a p p i n g area. Density e s t i m a t e s . g i v e n . f o r other s p e c i e s (per hectare) a re: B l a r i n a b r e v i c a u d a , .5.5 and 2.0 ( B l a i r , 1940, 1941), 7.4 ..(Eadie, 1944) , 11.4 (Quay, . 1 948); Sorex c i n e r e u s , 7.4-9. 9 (Manville, 1949); C r y j r t o t i s . l a r v a , . .4. 9 (Howell, 1954); Sorex minutus, 9 . ( M i c h i e l s e n , 1966) ; and §21§x araneus, 18 ( M i c h i e l s e n , 1 9 6 6 ) C a u t i o n should .be used i n a t t a c h i n g too much s i g n i f i c a n c e . t o . c o m p a r i s o n o f these estimates, however, as they i n v o l v e . v a r y i n g techniques and r e p r e s e n t p o p u l a t i o n s a t d i f f e r e n t times of the year and from d i f f e r e n t h a b i t a t types. Numerical i n c r e a s e s f o r both S, vagrans and S. obscurus tend to occur i n February, with the i n f l u x of breeding males. T h i s l a s t s u n t i l the f i r s t appearance of the young of the year, i n May, when the a d u l t . p o p u l a t i o n s begin, a steady d e c l i n e . The l a s t s u r v i v o r s of the pre v i o u s year.'s g e n e r a t i o n disappear by the end of September. 83 8.2. S u r v i v o r s h i p and m o r t a l i t y 8.2.1. L i f e t a b l e s and s u r v i v o r s h i p curves . Continued o b s e r v a t i o n of s i n g l e p o p u l a t i o n s through time a l l o w s the c o n s t r u c t i o n of l i f e t a b l e s . . .that_ _can f a c i l i t a t e understanding of what f a c t o r s r e g u l a t e p o p u l a t i o n s i z e and when they operate. B a s i c a l l y , . l i f e t a b l e s r e p r e s e n t p o p u l a t i o n s i z e through time. In s p i t e o f . t h e s m a l l sample s i z e s , a g e n e r a l .idea can .. be gained of., the p o p u l a t i o n dynamics of the two ge n e r a t i o n s (1971. and 1972). of S. vagrans and S. obscurus which were fo l l o w e d e n t i r e l y . For the r e s u l t i n g a g e - s p e c i f i c l i f e t a b l e (Tables IVA,B and VA,B) , I d i v i d e d each g e n e r a t i o n i n t o three c o h o r t s , depending on time of f i r s t appearance i n the „pcpulation: .. the May/June c o h o r t , July/August, and September/October c o h o r t s . Thus, the May/June cohort r e p r e s e n t s the e a r l i e s t d e t e c t a b l e beginnings of the l i f e h i s t o r y p r e - w e a n i n g m o r t a l i t y not being r e p r e s e n t e d . H o r i z o n t a l . l i f e t a b l e s such as these assume the v a r i o u s c o h o r t s , t o . be . r e a l e n t i t i e s ; i n t h i s case, t h e . c o h o r t s are.based on the t i m e o f f i r s t c apture, so some e r r o r , may occur .as a r e s u l t of immigration i n l a t e r months of animals born, e a r l y i n .the season. In any event, a n a l y s i s w i l l b a s i c a l l y be r e s t r i c t e d to the f i r s t c o h o r t s , where e r r o r s of t h i s . k i n d are not a problem. . . . Comparison of cohort s i z e s .. of..... S. vagrans. . ..and S. obscurus f o r 1971 and 1972 r e v e a l s t h a t approximately 803? of S. vagrans young entered the p o p u l a t i o n as the May/June 8k Table IVA. Life tables for. Sorex vagrans, 1971 generation, based on the disappearances from cohorts of marked individuals. Cohort;size May-June; 26 Not recaught Died Number Percent Percent Month i n subsequent i n surviving disappeared surviving i months trap at i during i at i M/J 12 0 26 lf6 100 J 1 0 ^k 7 5k A 2 0 1 3 1 5 5 0 S 1 0 11 10 k2 0 0 0 10 0 39 N 0 0 10 0 3 9 D 0 0 10 0 3 9 J 0 0 10 0 39 F 0 1 10 0 39 M 1 0 9 11 35 A 1 0 8 13 31 M 3 0 7 3^ 27 J 0 0 if 0 1 5 J 1 0 if 25 1 5 A 3 0 y 100 12 S 0 0 0 0 July-Aug; k J/A S 0 N D J F M A M J J 2 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 If 2 2 5 0 0 0 5 0 0 0 0 0 0 0 100 100 50 50 25 25 25 25 25 25 25 25 0 Sept-Oct; 1 S/0 N D 0 1 0 0 0 0 1 1 0 0 100 100 100 0 85 Table IVB. Life tables for Sorex obscurus, 1971 generation, based on the disappearances from cohorts of narked individuals. Cohort;size Kay-June;11 July-Aug; 5 Sept-Oct; h Month Not recaught Died Number Percent Percent i n subsequent i n surviving disappeared surviving i months trap at i during i at i M/J h 0 11 36 100 J 0 0 7 0 6k A 0 0 7 0 6k S 0 0 7 0 6h 0 0 0 7 0 6k N 0 0 7 0 6k D 0 0 7 0 6k J 0 0 7 0 6k F 0 0 7 0 6k M 0 0 7 0 6k A 3 0 7 ^3 6h M 3 0 if 75 37 J 0 0 1 0 9 J 0 0 1 0 9 A 1 0 1 100 9 S 0 0 0 0 J/A 1 0 5 20 100 S 1 0 if 25 80 0 0 0 3 0 60 N 0 0 3 0 60 D 0 0 3 0 60 J 1 0 3 33 60 F 0 0 2 0 WO M 1 0 2 50 ko A 0 0 1 0 20 M 1 0 1 100 20 J 0 0 0 0 S/0 0 0 5 0 100 N 1 0 5 " 20 100 D 0 0 0 80 J 0 0 if 0 80 F 0 0 it 0 80 M 0 0 if 0 80 A 1 0 if 25 80 M 0 0 3 0 60 J 2 0 3 67 60 J 1 0 1 100 20 A 0 0 0 0 Table VA. L i f e t a b l e s f o r Sorex vagrans, 1972 generation, based on the disappearances from cohorts of marked i n d i v i d u a l s . Not recaught Died Cohort; s i z e Month i n subsequent i n i months trap May-June; 16 M/J 5 0 J 1 0 A 1 0 S 0 0 0 0 0 N 1 0 D 0 0 J O 0 F 0 0 M 1 0 A 0 0 M O O J If 0 J 0 0 A 0 0 S 3 0 0 0 0 July-Aug; 3 J/A 1 0 S 0 0 0 0 0 N 0 0 D 0 0 J O 0 F 0 0 M O O A 0 0 M 1 0 J 0 0 J 0 0 A 1 0 S 0 0 Number Percent Percent s u r v i v i n g disappeared s u r v i v i n at i during i at i 16 31 100 11 9 69 10 10 63 9 0 56 9 0 56 9 11 56 8 0 50 8 0 50 8 0 50 8 12 50 7 0 hk 7 0 hh 7 56 hh 3 0 19 3 0 19 3 100 19 0 .0 3 33 100 2 0 67 2 0 67 2 0 67 2 0 67 2 0 67 2 0 67 2 0 67 2 0 67 2 50 67 1 0 33 1 0 33 1 100 33 0 0 Table VB. L i f e t a b l e s f o r Sorex obscurus. 1972 generation, based on the disappearances from cohorts of marked i n d i v i d u a l s . Cohort; s i z e May-June; 5 July-Aug; 6 Not recaught Died Number Percent Percent Month i n subsequent i n s u r v i v i n g disappeared s u r v i v i n i months trap at i during i at i M/J 2 0 5 ho 100 J 0 0 3 0 60 A 1 0 3 33 60 S 0 1 2 50 ho 0 0 0 1 0 20 N 0 0 1 0 20 D 0 0 1 0 20 J 0 0 1 0 20 F 0 0 1 0 20 M 0 0 1 0 20 A 0 0 1 0 20 M 1 0 1 100 20 J 0 0 0 0 J/A 2 0 6 33 100 S 0 0 5 0 67 0 1 0 5 25 67 N 0 0 3 0 50 D 0 0 3 0 50 J 0 0 3 0 50 F 0 0 3 0 50 M 0 0 3 0 50 A 0 0 3 0 5o M 1 0 2 33 ho J 2 0 2 100 33 J 0 0 0 0 co 88 c o h o r t of each r e p r o d u c t i v e season, while, f o r . the same p e r i o d only 50% of the S. obscurus j o i n e d the p o p u l a t i o n . A p o s s i b l e a r t i f a c t here i s the a r b i t r a r y d i v i s i o n of c o h o r t s by two calendar month i n t e r v a l s , c o n s i d e r i n g the evidence t h a t S. obscurus tends t o breed . s l i g h t l y . l a t e r .than S. vagrans. The 1973 g e n e r a t i o n showed the. r e v e r s e , t r e n d , however, with a l l the young S. obscurus ( n i n e . i n d i v i d u a l s ) being r e p r e s e n t e d i n the May/June cohort and the . S. vagrans d i v i d e d almost evenly, with .14 animals i n .the May/June coh o r t , 12 animals i n the July/August cohort, and two i n the l a s t c o h o r t . When the data f o r both years and the f i r s t two c o h o r t s are combined, s u r v i v a l from f i r s t summer to . t h e . f o l l o w i n g summer (July) i s about 17% f o r S. vagrans and only 4%. f o r S. obscurus. The r a t e f o r S. v a g r a n s - i s comparable to t h a t given f o r Sorex araneus by M i c h i e l s e n . (.1966) while . the lower r a t e f o r S. obscurus i s c l o s e r t o t h e . r a t e s found-by Pearson (1945) f o r B l a r i n a brevicauda and by M i c h i e l s e n f o r Sorex f i n u t u s . . S u r v i v o r s h i p curves taken from . the . l i f e t a b l e s and r e p r e s e n t i n g the f i r s t c o h o r t s are shown i n F i g u r e s 13A.... and 13B. Because of the p a r t i c u l a r l y s m a l l sample s i z e s from the 1972 g e n e r a t i o n of S. obscurus, the M/J and.J/A c o h o r t s are combined. The graphs f o r both s p e c i e s are c h a r a c t e r i z e d by a sharp i n i t i a l d e c l i n e and subsequent s t a b i l i t y (with s l i g h t d e c l i n e ) over the f a l l and winter months, followed.by another dropoff d u r i n g the breeding season. In both Figure 13A. S u r v i v o r s h i p curves f o r May/June cohorts, Sorex vagrans. 89a 90 Figure 1 3B . Survivorship curves for May/June cohorts, Sorex obscurus. 90a o 1971 g e n e r a t i o n 100 - * H/J J A S 0 N D J F M A M J A S 0 91 s p e c i e s , the i n i t i a l drop r e p r e s e n t s somewhat more than 50% of the i n d i v i d u a l s . While much of t h i s i s a r e s u l t o f j u v e n i l e m o r t a l i t y , no doubt d i s p e r s a l a l s o p l a y s a p a r t . , Except f o r the high i n i t i a l m o r t a l i t y , the g e n e r a l s u r v i v o r s h i p curve of shrews approximates the h y p o t h e t i c a l "Type I " curve ( P e a r l , . 1928; Deevey, 1917; Slobodkin, 1962), i n which m o r t a l i t y i s represented as a n e g a t i v e l y skewed r e c t a n g l e . , I m p l i c i t i n t h i s type o f , curve. are . o p t i m a l c o n d i t i o n s f o r l i f e and . t h e occurrence, .of s e n i l e d e t e r i o r a t i o n . Under n a t u r a l c o n d i t i o n s , few. animals a c t u a l l y e x h i b i t t h i s type of s u r v i v o r s h i p , and_in mammals, the i d e a l i s o f t e n a l t e r e d by a p e r i o d of high j u v e n i l e . l o s s (Caughley, 1966), as seen.in shrews. What are the b a s i c i m p l i c a t i o n s of. the.„survivorship curves of S. vagrans and S. obscurus? T h e . f a c t t h a t more than h a l f the o r i g i n a l cohort d i s a p p e a r s w i t h i n the f i r s t f i v e months of l i f e i n d i c a t e s t h a t t h i s i s the time during which s e l e c t i o n operates at a premium. ...Evidence from, home range data suggests t h a t s u c c e s s f u l defense.of a t e r r i t o r y d u r i n g t h i s p e r i o d i s of s t r o n g s e l e c t i v e advantage. P o s s i b l e f a c t o r s a s s o c i a t e d with the i n a b i l i t y to maintain.a t e r r i t o r y are exposure to unfavorable environmental c o n d i t i o n s , p r e d a t i o n , and g e n e r a l harassment from, more ag g r e s s i v e t e r r i t o r y h o l d e r s . Although p r e d a t o r s . c f small mammals may f i n d shrews u n p a l a t a b l e , .wandering or d i s o r i e n t e d i n d i v i d u a l s may . s t i l l b e . k i l l e d , even though l a t e r r e j e c t e d . Avian predators may be l e s s d i s c r i m i n a t i n g 92 i n t a s t e , f o r s o r i c i d remains have been found i n owl p e l l e t s (D. Hawes, p e r s . comm.; D. G. Smith, et. a l . , 1972). The high e n e r g e t i c demands on shrews r e g u i r e s that, a l a r g e p r o p o r t i o n of the d a i l y energy budget.of i n d i v i d u a l s . b e devoted to s e a r c h i n g f o r prey. Conceivably, m o r t a l i t y .of young shrews with no t e r r i t o r i e s can. r e s u l t , from, the i n a b i l i t y to f i n d s u f f i c i e n t food before being d r i v e n away by the l o c a l t e r r i t o r y holder. 8.2.2. Adult m o r t a l i t y .. S e v e r a l t h e o r i e s have been .advanced on the cause.and nature of a d u l t m o r t a l i t y i n shrews. In p r e p a r i n g museum specimens, I have encountered an exceptional.... g r a s s l a n d S. vagrans i n d i v i d u a l (MVZ #143463, from. Serpe n t i n e River) which e v i d e n t l y had not o n l y s u r v i v e d two w i n t e r s , but.was pregnant with three embryos; hence, ...the p o t e n t i a l p h y s i o l o g i c a l l i f e s p a n i s probably longer than the 16. or .1.7 months maximum I have observed i n the Research F o r e s t shrews. Shrews kept under i d e a l c o n d i t i o n s . i n .the l a b o r a t o r y can a l s o f a r exceed the maximal . . l i f e s p a n s observed i n the w i l d (Pearson, 1945)., Crowcroft (1957) advances the theory t h a t g e n e r a l food shortage, i n l a t e summer and autumn becomes too much of a s t r e s s f o r a d u l t s a l r e a d y exhausted from the r e p r o d u c t i v e effort..... M i c h i e l s e n (1966) c i t e s other p o s s i b l e m o r t a l i t y f a c t o r s : l a c k o f . a winter molt i n second year shrews and subseguent,. inadegiiacy of i n s u l a t i o n ( S t e i n , 1954) ; p a r a s i t i c l o a d (Borowski and 93 Dehnel, 1952); and e x c e s s i v e toothwear (Spannhcf,. 1952). M i c h i e l s e n puts f o r t h the theory that.young of the year, being t e r r i t o r y - h o l d e r s , are s o c i a l l y dominant . ever... the parent g e n e r a t i o n , the. i n d i v i d u a l s . .of. which are thus homeless as w e l l as worn out p h y s i o l o g i c a l l y . I have found, i n d i c a t i o n s .that some, of the above p o s s i b i l i t i e s can p l a y a r o l e i n a d u l t m o r t a l i t y . A u t o p s i e s of hundreds of g r a s s l a n d S. vagrans r e v e a l e d heavy i n f e s t a t i o n s of ring-shaped nematodes under the.skin i n . the shoulder and head r e g i o n s of a d u l t ..shrews.,. Few of these p a r a s i t e s were found i n young animals. E c t o p a r a s i t e s on.the l i v e - t r a p p e d shrews seemed ..to i n f e s t , .young, and o l d i n d i s c r i m i n a n t l y , however. ,. These p a r a s i t e s , i n c l u d e d . t i c k s , mites, and f u r b e e t l e s (Isptinus americanus, f a m i l y L e p t i n i d a e ) . P o s s i b l y the p a r a s i t e .load, i n . c o n j u n c t i o n with other f a c t o r s , pushes o l d . a d u l t s beyond t h e i r . e n e r g e t i c l i m i t s , p a r t i c u l a r l y i f food becomes s c a r c e . . Granted the l a c k of winter.molt can be. d e t r i m e n t a l to s u r v i v a l , I see no reason to a t t r i b u t e . . m o r t a l i t y , d i r e c t l y , or i n d i r e c t l y to i t . Parent g e n e r a t i o n shrews,.in f a c t , are u s u a l l y a l r e a d y gone by the.time f i r s t year animals, undergo the winter molt. L i k e w i s e , .although toothwear c e r t a i n l y o c c u r s , e a t i n g i s a p p a r e n t l y not s e r i o u s l y impeded;. I. have seen second year S. o b s c u r u s . s u r v i v e . f o r months with one .or both upper i n c i s o r s m i ssing. A l s o , the t e e t h . o f s. .obscurus are more robust and wear .more slowly, than, those of S. vagrans, yet S.,obscurus a d u l t s disappear much sc c n e r . Both toothwear and l a c k of winter molt appear to be merely i n d i c a t i v e of the f a c t that l i t t l e s e l e c t i v e , pressure e x i s t s f o r p r o l o n g i n g s u r v i v a l i n adult... shrews .once the r e p r o d u c t i v e e f f o r t i s made. Assuming t e r r i t o r i a l i t y to be a r e a l i t y and an. investment.of energy by young shrews.in exchange f o r g r e a t e r assurance of . .winter s u r v i v a l , the chances t h a t the h y p o t h e t i c a l l o n g r l i v e d , t e r r i t o r y - l e s s a d u l t has of competing s u c c e s s f u l l y . a g a i n s t . f i r s t .year shrews, s u r v i v i n g the winter, and breeding, again, must indeed be s m a l l . . The l a c k of t e r r i t o r y may well add to the demise, of r e p r o d u c t i v e a d u l t s , although I .do. not . b e l i e v e , as M i c h i e l s e n (1966:146) s u g g e s t s , . t h a t a d u l t s are " f o r c e d t o roam v a i n l y i n search of a t e r r i t o r y , " and are.thus exposed to weather and p r e d a t i o n . As shown i n the e l l i p s e p l o t s , most a d u l t s remain . i n the area f a m i l i a r to.them, thereby r e t a i n i n g some advantages, of. having .a. t e r r i t o r y , .but probably cannot a f f o r d the energy t o d e f e n d . i t . a n y l o n g e r . The presence of presumably aggressive.young shrews, i n .the same area and the r e s u l t i n g i n t e r a c t i o n .and harassment c o u l d very w e l l add to the a l r e a d y high energy demands of the a d u l t s , however. 8.3. Recruitment A q u e s t i o n to be asked i n regard.to cohort, s i z e s and i n g r e s s of shrews i s how the t i m i n g of.an i n d i v i d u a l ' s b i r t h a f f e c t s i t s r e l a t i v e breeding sucess. Since o n l y the f a t e s 95 of i n d i v i d u a l s which remain i n my study area can be f o l l o w e d , a c e r t a i n b i a s a g a i n s t d i s p e r s i n g animals i s i n e v i t a b l e . In l i g h t o f the t e r r i t o r i a l system. e s t a b l i s h e d by young shrews, however, chances are .that d i s p e r s i n g animals tend to s u f f e r h i g h e r m o r t a l i t y , so my .bias i s somewhat a l l e v i a t e d . The c h a r t s i n Table VI(A .and B) attempt to c a t e g o r i z e the f a t e s of a l l f i r s t year shrews marked i n 1971 and 1972, r e s p e c t i v e l y . T h e . f i r s t column i n c l u d e s a l l i n d i v i d u a l s marked each month. T h e . a n i m a l s marked i n the e a r l y months most l i k e l y have been.born in. or beside the p l o t ; . immigration undoubtedly .plays, a .mere important r o l e i n l a t e r months. The next column. , i s e s s e n t i a l l y a measure of l o s s , e i t h e r through m o r t a l i t y or e m i g r a t i o n . Column t h r e e accounts f o r those r e c a p t u r e d o v e r a p e r i o d exceeding 30 days, but which.did not e v e n t u a l l y breed i n the area. The f o u r t h and l a s t column i s a .measure of the number found i n breeding c o n d i t i o n the f o l l o w i n g y ear. . The numbers i n the f o u r t h column show. t h a t .young S. vagrans born e a r l y i n the season, i n Hay, make up.a s u b s t a n t i a l l y higher p r o p o r t i o n of the animals which breed the f o l l o w i n g year than do e i t h e r those b o r n . l a t e r c r those immigrating to the area l a t e r . . . For those years, no ..such b i a s seems to e x i s t f o r the S. obscurus groups.. : P o s s i b l y t h i s i s a s p u r i o u s c o r r e l a t i o n . F i g u r e s 14A and. 14E are d e r i v e d from the f i r s t columns, and they show.the percent t o t a l r e c r u i t m e n t through time. The curve f o r S. vagrans Sorex obscurus Sorex vagrans 1971 Generation 1971 Generation Total: Oct. Sept. August July June May Total; Sept. August July June May Month vO ro LO -r V A -r Lo —k —k 0 vO _k -0 Monthly total Newly < O ON ro V A ro ON ro LO 0 Lo ro vO V A V A 1-3 O 05 M naught 0 0 k O 0 ro Lo O Not r after 0 0 ro k O O ro 0 ro V A O 0 V A 0 Lo Lo V A vO # Monthly total ecaptured 30 days 0 k k O 0 O —k 0 -r O Settled but dis-appeared before breeding Subtotal: 0 Lo LO ro V A O 0 O Subtotal O O 0 ro V A -r -r O ^ Monthly total Settled but dis-appeared before breeding _k OJ ro ro ro O -r LO • * 0 O 0 ro Settled and bred in 1972 0 0 ON -0 V A O O 00 0 V A O 0 ro V A ro ro -r % Monthly total Settled and bred in 1972 ON OO a 0 • V A k 0 . V A —k O • V A O ro k ON Lo k O 0 Lo • LO ON • V A ro K3 O 05 I—' Settled and bred in 1972 Sorex obscurus 1972 Generation Sorex vagrans 1972 Generation C O > CD P O • d TO 1—' p *<! ct c t «<! CD P • w c t k -r ro ro ro O J _^  —k L \0 ON co C O C O O ro O ro O V A 0 O 0 O 0 O O O 0 1 C O ro V A & O O 0 O c t O " c t P ro 0 —k O ro 0 V A O V A O 0 O -r V A vO \o 00 0 v O o c t P r - 1 ro C O c t o c t p \-> V A ro o o ct CO CD c t > c t ro C-H CD p -* -T ro V A V A V A V A v O o o ro O J V A O J o ro o o o ro V A o o ro o o ro O N V A o VA o V A v O V A v O V A ro v O 0 ts ct tr ct O O t$ c t r+ P tr •-3 O P H c t 3 ; O O c t t5 P c t H tr ct K O O c t P p c t M tr <s-4 O o P c t H tr H t-3 O P 25 CD O P tr c t p 3 H+> O c t c t CD CD O J O O P f i c t P £ 4 M CD C L P CO *rj CD c t c t (—1 CD 'd cr CD CD 4 CD CD C L C L C L H- cr ts cr c (KJ CD c t O C L CD M cr co *-i CD CD c t CL c t M H - CD v O tS V ] C L O J Figure 1M-A. Percent t o t a l recruitment for the 1971 generation of Sorex vagrans and Sorex obscurus. 1 9 7 1 G E N E R A T I O N 98a 1 9 7 1 31 19 99 Figure 1W-B. Percent total recruitment for the 1972 generation of Sorex vagrans and Sorex obscurus. 99a n = n = 21 11 100 approaches 100% a s y m p t o t i c a l l y as a i n v e r s e e x p o n e n t i a l f u n c t i o n , while that of S. obscurus i s n e a r l y l i n e a r . The apparent success of e a r l y - b o r n S. vagjcans may simply be a t t r i b u t a b l e to the f a c t t h a t most young are.born then^ I f , however, S. vagrans born e a r l y i n the year have a true s e l e c t i v e advantage, then the r e c r u i t m e n t curves may be i n t e r p r e t e d as r e f l e c t i n g a s t r a t e g i c response i n r e p r o d u c t i v e e f f o r t . A mechanism by which e a r l y - b o r n shrews are a t a s e l e c t i v e advantage i s t e r r i t o r i a l i t y . . T h i s would.apply i f a g g r e s s i o n l e v e l s of young shrews begin at high l e v e l s from the time of weaning. L a t e r a r r i v a l s would.thereby.be at ,a d i s t i n c t disadvantage. However, i f a g g r e s s i o n _ l e v e l s are.a f u n c t i o n of age, time of year, or c e r t a i n . . e n v i r o n m e n t a l c o n d i t i o n s , the i n f l u e n c e of t e r r i t o r i a l i t y jger se. wculd; not so s t r o n g l y f a v o r the e a r l y - b o r n . E i s e n b e r g . (1964), i n h i s b e h a v i o r a l s t u d i e s of Sorex vagrans.. from the Endowment Lands, found t h a t under l a b o r a t o r y c o n d i t i o n s immature shrews denned together u n t i l approximately .seven weeks of age. At three months, agg r e s s i o n l e v e l s were notabl y higher and animals denned s e p a r a t e l y , defending the nest s i t e . f r o m i n t r u d e r s . I f these r e s u l t s can be a p p l i e d to the s i t u a t i o n i n nature, the b e h a v i o r a l b a s i s of t e r r i t o r i a l i t y would not come i n t o p l a y u n t i l l a t e summer. T e r r i t o r y maps ( F i g s . 11A-C) , do i n f a c t , show much . higher degrees o f o v e r l a p f o r June through August d i s t r i b u t i o n s than f o r September through November d i s t r i b u t i o n s . 101 Another p o s s i b l e e x p l a n a t i o n of the r e l a t i o n between r e c r u i t m e n t r a t e and breeding success i s t h a t . t h e l e v e l . o f a g g r e s s i o n i s p r o p o r t i o n a l to the... p o p u l a t i o n d e n s i t y . Buckner (1964) s t u d i e d the metabolism... of shrews.sampled .from known p o p u l a t i o n d e n s i t i e s and found.the.metabolic r a t e s . o f S. c i n e r e u s and S. a r c t i c u s from high d e n s i t i e s to be s i g n i f i c a n t l y g r e a t e r (at the 5 1 l e v e l ) than.those from low p o p u l a t i o n d e n s i t i e s (Table V I I ) . He a t t r i b u t e d t h i s to more freguent c o n t a c t and c o m p e t i t i o n f o r s p a c e . , . I f such i s the case with the .Research Fores t _ shrews, . and h i g h e r metabolic r a t e can be i n t e r p r e t e d i n .terms of. a g o n i s t i c t e n d e n c i e s , one would expect t h a t a h i g h . i n i t i a l . r e c r u i t m e n t lowers the chances of success f o r l a t e r . a r r i v a l s , but.a constant r e c r u i t m e n t r a t e through the«summer.results i n more e g u i t a b l e success among a l l i n d i v i d u a l s , r e g a r d l e s s of time of e n t r y . . . :.. .. My data seem to support the above, h y p o t h e s i s . Regardless of r e c r u i t m e n t numbers, t h e . number, of animals which s e t t l e and breed i n the area v a r i e s l i t t l e from year to year (with the e x c e p t i o n of a p a r t i c u l a r l y high.number of S. obscurus breeding i n 1972). r P o s s i b l y , as.this.number i s reached i n the p o p u l a t i o n during ; the first._summer, a g g r e s s i v e . l e v e l s i n c r e a s e a n d . t e r r i t o r i a l . b e h a v i o r b e g i n s . Thus, S. obscurus, with i t s c o n s t a n t low r e c r u i t m e n t r a t e i n 1971 and 1972, shows comparable .degrees of r e p r o d u c t i v e success f o r a l l c o h o r t s . In S. vagrans, high d e n s i t i e s were Less than 2 per acre 2 to k per acre More than h per acre Species # t r i a l s ml .0 2/g-hr. # t r i a l s ml.02/g-hr. # t r i a l s ml .0 2/g-hr. Sorex cinereus Sorex a r c t i c u s 8 13 15.3 t 1 A 10.9 i 1.1 5 11 15.5 i 1.9 10.9 i 1.3 5 9 19.6 t 2.1 13.3 ± 2.6 Table V I I . Average 0 2 consumption i n two species of shrews at three population l e v e l s (from Buckner, ^^6h). o ro 103 reached e a r l y i n the 1971 and 1972 seasons, and success was p r o p o r t i o n a t e l y lower f o r ensuing a r r i v a l s . . . The data f o r breeding success of the 1973 g e n e r a t i o n are l i m i t e d , s i n c e o n l y three t r a p p e r i o d s r e p r e s e n t the breeding.season.in 1974. Assuming the animals caught i n F e b r u a r y , M a r c h , and A p r i l of 1974 a c c u r a t e l y r e p r e s e n t the s u c c e s s f u l breeders of t h e i r g e n e r a t i o n , however, the r e s u l t s . .show a r e v e r s e t r e n d from previous years. A c h a r t . o f the f a t e . o f v a r i o u s c o h o r t s of the 1973. g e n e r a t i o n i s .shown ...in. ..Table V I I I . Recruitment f o r S. vagrans was. spread through.May, ..June, and J u l y , with high i n g r e s s . f o r , . the . l a t t e r , month. Concomitantly, the breeding success r a t e s a r e . h i g h e r f o r a l l these months. Sorex obscurus, on the other ..hand, showed high i n i t i a l i n g r e s s i n the f i r s t two. months along ..with r e l a t i v e l y high s u r v i v a l . These r e s u l t s may a l s o , be e x p l a i n e d i n terms of a r e l a t i o n , between d e n s i t y and a g g r e s s i v e tendencies i n young animals. The r a t e . o f i n g r e s s i t s e l f may be determined by v a r i o u s environmental v a r i a b l e s such as the g u a l i t y , g u a n t i t y , and a v a i l a b i l i t y of food. 8.4. F e c u n d i t y A l l l i f e h i s t o r y phenomena are u l t i m a t e l y r e l a t e d t o s u c c e s s f u l r e p r o d u c t i o n . I t i s almost a t a u t o l o g y to say t h a t s e l e c t i o n f a v o r s those i n d i v i d u a I s . . w h i c h . mcst s u c c e s s f u l l y i n t r o d u c e t h e i r genes i n t o .future g e n e r a t i o n s . F e c u n d i t y , i n v o l v i n g s i z e , number, and spacing of l i t t e r s , i s only one of many f a c t o r s concerned i n the r e p r o d u c t i v e Sorex obscurus 1973 Generation Sorex vagrans 1973 Generation t-3 P cr CD < l-H I—I M 113 ct CD O Ms <! P hi H-O P t/1 o o t r o hi ct W o •-*> C T t r CD CTO CD !3 CD hi P ct H* O P cr o hi 3 vO V ] O J H3 O ct P I—1 vO CD p CJ\ OJ ON OJ •va OJ o ro ON o -a t-9 O ct P M ro co o o ct CO CD ct > P 0Q P w ct P CD s; P ON CO OJ ON OJ ON OJ ON OJ ro ro -»• oo » vn ro co P a* ct o ct P. ON ON NJT. 00 O J • O J OJ OJ ON V I NJ"l # VJT. OJ ON OJ OJ V A O ro ro co P cr ct o ct P H ro o o — i OJ co OJ ro o ct tr ct O . O t i ct ct P tr t-3 O cf^, P ct S O O ct p p ct M tr £ 5 CD o p p t r ct I ts —' o — 1 NJ\ ro OJ o o o o -r v n OJ OJ OJ V J \ OJ OJ ON OJ ON CO ~o o ct K O O ctD p ct M-tr P H> O ct ct CD hi hi CD O J O O p CL c+ p p «<! hi cn CD P. P CO W CD ct ct ct S O O ct p 03 ct H tr i—1 i-3 O cfJA P Cf CD hi p H CD hi CD CD CD CL CL CL ti crP CM CD ct M> O CL hi H-CD W I cr co ht CD CD ct CL ct y-> H- CD p Pi — i fo vO ts - O CL -r 10 5 s t r a t e g y of a s p e c i e s . . S p e c i e s r e c o g n i t i o n . a n d t i m i n g . o f r e p r o d u c t i o n have a l r e a d y been d i s c u s s e d ; . the . i m p l i c a t i o n s of the age at f i r s t r e p r o d u c t i o n w i l l be d i s c u s s e d l a t e r (Part I I , Sect. 2.3) . Of the specimens snap-trapped from the f o r e s t h a b i t a t , o n l y seven S. obscurus and. ten S..vagrans were pregnant females. L i t t e r s i z e s , i n utero,.based on . these specimens were 4.1 f o r S. obscurus (range 2 to 6) and 5.4 f o r S. vagrans (range 3 to 8 ) , the d i f f e r e n c e s . net .being s i g n i f i c a n t (566 S. vagrans from g r a s s l a n d h a b i t a t had.an average of 5.8 embryos). L i t t e r s i z e s . c f other, subspecies of S. vagrans have been determined to. be . 5 . 5 5 f o r S. y. h a l i c o e t e s (Johnston and Rudd, 1957) and 6.4 f o r S. v. monticola ( C l o t h i e r , 1955). I t has been suggested (Johnston and Rudd, op. c i t . ) that l i t t e r , s i z e may vary g e o g r a p h i c a l l y , as does c l u t c h s i z e of many b i r d s (Lack, 1947). The proximate f a c t o r s determining l i t t e r s i z e are unknown, but are l i k e l y t o be a combination of g e n e t i c and environmental i n f l u e n c e s . By l i v e - t r a p p i n g i n d i v i d u a l s . throughout . t h e i r l i f e t i m e s , I was able t o determine the number .of..pregnancies of i n d i v i d u a l females remaining i n . . the... p l o t . Assuming l i t t e r s i z e to be e s s e n t i a l l y e q u a l . f o r . S. vagrans and S. obscurus, d i f f e r e n c e s i n f e c u n d i t y would depend.on.the number of l i t t e r s produced by i n d i v i d u a l s of each s p e c i e s . Since the success of a pregnancy i n terms of l i t t e r size.was not o b t a i n a b l e , the only other measure of r e l a t i v e f e c u n d i t y 106 I have i s the number of s u c c e s s i v e p r e g n a n c i e s . o c c u r r i n g f o r each female. Data from the 1970.generation-of breeding females are omitted; i n the f o l l o w i n g years, . I was more experienced and c o u l d score with . reasonable accuracy pregnancies (small t e a t s , i n c r e a s i n g , weight,..evidence of b u l g e s ) , l a c t a t i o n (constant.high.weight, l a r g e t e a t s with e x t e n s i v e milk glands v i s i b l e under .the s k i n ) , or both s i m u l t a n e o u s l y ( i n l a t t e r stages, . high weight, s m a l l e r t e a t s ) . weight data from .successive t r a p p i n g p e r i o d s f a c i l i t a t e d d e t e r m i n a t i o n s . ~ . . . Table IX i s a summary o f . - d a t a r e l a t e d .to the p r o d u c t i v i t y of females breeding i n the years.1972 and 1973. A l l but one female were n a t i v e to the p l o t , ...having. been e s t a b l i s h e d i n the area as non-breeders. .For each year, the r e s p e c t i v e number of i n d i v i d u a l s with one, two,.and t h r e e recorded pregnancies was . counted. . . T h e . — t o t a l number . ~of l i t t e r s was c a l c u l a t e d on the assumption that.each pregnancy was s u c c e s s f u l l y c a r r i e d t o term, s c i t i s a. maximal ..figure. The number of r e c r u i t s , however, being determined.by the t o t a l number of young animals marked i n a p a r t i c u l a r c a lendar year, i s a minimal e s t i m a t e . ..It a l s o assumes t h a t immigration and emigration balance each other out. While. ..I r e a l i z e the f i g u r e s are s u b j e c t , to l a r g e e r r o r s i n e s t i m a t i o n , r e l a t i v e values f o r comparison between s p e c i e s can s t i l l be of s i g n i f i c a n c e . In a l l r e s p e c t s , S. vagrans e x h i b i t s g r e a t e r r e p r o d u c t i v e success. In 1972, when the number of breeding cn X a CD ca M M O W CQ cd > X U CD U o O w CO , Q o Breeding Year No. Females with n observed pregnancies Total no. breeding females Total no. observed pregnancies No. r e c r u i t s (= # marked) 1 pregnancies per female X r e c r u i t s per female 1972 1973 n=1 n=2 n=3 2 1 5 8 19 22 2.If 2.75 2 If 1 6 13 29 2.16 i f . 8 1972 1973 7 1 0 8 9 12 1.1 1.5 2 2 0 if 6 10 " 1.5 2.5 Table IX. Productivity of breeding live-trapped females, 1972 and 1973. o 108 females was the same f o r both s p e c i e s , S. vacjrans had almost t w i c e . t h e recruitment t h a t S. obscurus a t t a i n e d . . I n d i v i d u a l female S. vagrans a l s o experienced more pregnancies; in.no year d i d I f i n d a female S. obscurus breeding three times. I t i s d i f f i c u l t , however, to e s t a b l i s h the r e l a t i o n s h i p between r e p r o d u c t i v e success and parameters ..such, as the number of breeding females or number of times.bred. In 1972, r e l a t i v e l y high numbers of breeding females d i d not r e s u l t i n concomitantly high r e p r o d u c t i v e , success, p a r t i c u l a r l y f o r S. obscurus. ; The..majority of ..S. vagrans females were observed to go through three pregnancies, ... but the apparent r e c r u i t m e n t d i d not exceed.. , that of . the f o l l o w i n g year when not only were fewer females p r e s e n t , but most became pregnant only twice. E v i d e n t l y , v a r i a t i o n s from year t o year are g r e a t , and no s i n g l e f a c t o r w i l l determine breeding success. The number of l i t t e r s up to three produced by a female of e i t h e r s p e c i e s seems to be determined, mainly by how long she s u r v i v e s d u r i n g the breeding season. In other words, females tend to remain r e p r o d u c t i v e u n t i l . e i t h e r , they. d i e , or complete three pregnancies, . a f t e r which they e n t e r . a s t a t e of anoestrus. T h i s .became evident, when, the . month. ..of l a s t capture was examined f o r females,having.one, two, and three pregnancies, r e s p e c t i v e l y . I n d i v i d u a l s /having, only one pregnancy a l l disappeared between A p r i l and.late May. Those pregnant twice g e n e r a l l y disappeared during June, and those with three recorded pregnancies remained u n t i l J u l y or 109 August. On t h i s b a s i s , the d i f f e r e n c e s i n f e c u n d i t y between S. vagrans and S. obscurus females appear to.be due l a r g e l y to the f a c t t h a t the l a t t e r a r e . r e l a t i v e l y s h o r t - l i v e d . Of the 12 breeding . female S. obscurus i n v o l v e d , i n t h i s a n a l y s i s , . e i g h t disappeared before June, t h r e e . d u r i n g . June, and one remained u n t i l J u l y . Of 14.female S. vagrans, o n l y f o u r disappeared before June, t h r e e during J u n e t w o . dur i n g J u l y , t h r e e during August, and.two l a s t e d .until-September.-,. The e a r l y disappearance of S. obscurus a d u l t s may be i n d i c a t i v e of sub-optimal h a b i t a t c o n d i t i o n s and-.ccmpeti.tion from the new g e n e r a t i o n . .. As r e f e r r e d to p r e v i o u s l y ( F i g s . 141 and 14B),.the r e c r u i t m e n t curve f o r 1972 and. 1673 S. .obscurus shows, almost a constant . rate.throughout the summer. The l a t e r a r r i v a l s , at l e a s t , .... , are.. . probably d i s p e r s e r s from more optimal h a b i t a t s . The young e n t e r i n g the p l o t l a t e r i n the summer have, v i r t u a l l y . , unworn.. t e e t h , and presumably were weaned s h o r t l y before a r r i v a l a t the p l o t . 9. S p e c i e s D i s t r i b u t i o n i n the L i v e - t r a p p i n g Area 9 .1. C o r r e l a t i o n with h a b i t a t In order to g u a n t i f y the d i s t r i b u t i o n of shrews i n the l i v e - t r a p p i n g a r e a , the t o t a l number of c a p t u r e s per stake was c a l c u l a t e d f o r each s p e c i e s . A v i s u a l r e p r e s e n t a t i o n .of the r e s u l t s i s g i v e n i n p e r s p e c t i v e p l o t s . o f the g r i d , with number of captures t r a n s l a t e d i n t o h e i g h t . f o r . e a c h . s t a k e ( F i g . 15). Comparison of the p l o t s f o r S. vagrans and 110 Figure 15. Relative d i s t r i b u t i o n of species (based on frequency of capture) and s o i l types i n live-trapping p l o t . OBCURUS DISTRIBUTION n = 1807 captures 111 §» obscurus shows t h a t on the whole they are d i s t r i b u t e d i n d i f f e r e n t areas of the p l o t , e x c l u s i v e . o f one.another. , .. . Notably, the s p e c i e s d i s t r i b u t i o n s .are c o r r e l a t e d ... wit h the h a b i t a t types, based on s o i l and v e g e t a t i o n , represented i n the study g r i d , , A s o i l map of the area,.done from.the same p e r s p e c t i v e as the s p e c i e s d i s t r i b u t i o n . p l o t s , is.shown f o r ease of comparison. Four, b a s i c . . s o i l . ... types are rep r e s e n t e d : 1) mor 2) moder 3) intermediate...4).anmocr. Mor and moder resemble one another. - i n . having . a sharp d i s t i n c t i o n between o r g a n i c and m i n e r a l . l a y e r s , but moder s o i l s are r i c h e r and have a higher.. „pH, ..thus s u p p o r t i n g b a c t e r i a l growth (as opposed to the predominance,cf fungus i n mor s o i l s ) and an i n c r e a s e d . proportion... of.. l a r g e r arthropods (Wallwork, 1970)., Intermediate zones . r e f e r ..to h a b i t a t t r a n s i t i o n a l between mor and moder. ...Anmoor h a b i t a t s are those which are p e r i o d i c a l l y waterlogged:., seasonal p o o l s , streams and seepage s i t e s . The p a t t e r n of S. obscurus d i s t r i b u t i o n s can be seen to f o l l o w . the d i s t r i b u t i o n of mor type h a b i t a t s , along the upper rows.and i n the lower l e f t c o r n e r and lower r i g h t a rea.of the p l o t . Captures of S. vagrans, however, are co n c e n t r a t e d i n the moder h a b i t a t s along a c e n t r a l s t r i p , running d i a g o n a l l y across the p l o t and i n the lower rows... For s t a t i s t i c a l purposes, _each.stake.was.categorized a c c o r d i n g to the s o i l . , type i n i t s ..location. For both s p e c i e s , the t o t a l number of ..captures per. stake was t a b u l a t e d f o r : 1) a l l i n d i v i d u a l s , 2) non-breeders c n l y , 3) 112 breeding males, and .4) breeding females. The captures were then t o t a l l e d a c c o r d i n g to h a b i t a t type f o r each of these c a t e g o r i e s . In order to make s p e c i e s comparisons of the frequency of occurrence i n each of the two main s o i l types, moder and mor, two-by -two contingency ..tables were s e t .up f o r c h i - s q u a r e a n a l y s i s . . These t a b l e s and t h e i r c h i - s g u a r e v a l u e s are given i n Table X. H a b i t a t . d i f f e r e n c e s between. s p e c i e s e x i s t at a high l e v e l c f s i g n i f i c a n c e f o r comparisons o f a l l l i k e c a t e g o r i e s ( c h i - s q u a r e . . v a l u e s are even higher when a l l f o u r h a b i t a t s are compared). 9.2. Seasonal changes i n h a b i t a t c o r r e l a t i o n s The a c t u a l percentage of c a p t u r e s i n every h a b i t a t type i s used to compare changes which occur with .reproductive a c t i v i t y w i t h i n one s p e c i e s (Table. XI) . ,. The . l a r g e s t d i f f e r e n c e s o c c u r . i n S. obscurus,.between.non-breeders and breeding males, with breeding males l e s s , d i s c r i m i n a t i n g . i n t h e i r c h o i c e of s o i l type. Chi-square t e s t s on.the number of captures i n mor and moder between any two c a t e g o r i e s w i t h i n a s p e c i e s show t h a t no s i g n i f i c a n t . d i f f e r e n c e s occur between S. vagrans p a i r s , but that with S. obscurus the h a b i t a t d i s t r i b u t i o n of. breeding males w a s . s i g n i f i c a n t l y d i f f e r e n t from that of e i t h e r non-breeders or .breeding females (X 2=89.1 and 27.2, r e s p e c t i v e l y ) . ,.  Sorex vagrans i n d i v i d u a l s tend to keep to the same h a b i t a t s r e g a r d l e s s of r e p r o d u c t i v e s t a t e and concomitant changes . i n . home .range...... The reason f o r the change i n h a b i t a t d i s t r i b u t i o n of 113 MODER MOR A l l captures: S. obscurus *f13 1175 2 X = 1125 S. vagrans 1906 ^90 Non-breeder captures: S. obscurus 182 772 S. vagrans 1309 295 Breeding male captures: S. obscurus 182 S. vagrans *+30 Breeding female captures: S. obscurus ^9 169 S. vagrans 376 9h H = Species are d i s t r i b u t e d e q u a l l y w i t h respect to s o i l type. Rejected at <.001 l e v e l f o r a l l c a t e g o r i e s . Table X. Frequency of capture of S. obscurus and S. vagrans i n the two major s o i l types i n the Research Forest p l o t . X 2 = 962 23^ 101 X = 1M X 2 = 209 SOIL TYPE Low moor Moder Transition Mor n= Sorex obscurus Non-breeders 0 17 11 72 1077 Breeding males 2 37 12 ^9 lf82 Breeding females 0 20 12 68 2kS Sorex vagrans Non-breeders 2 66 17 15 1997 Breeding males If 62 19 15 697 Breeding females 3 63 18 16 597 Table XI. Percentage captures of species categories i n habitat types represented i n live-trapping plot. 115 breeding male S. obscurus can only .be. surmised. Conceivably, the e x p l a n a t i o n f o r the., i n v a s i o n , of .breeding S. obscurus males i n t o h a b i t a t occupied.mainly by S. vagrans d u r i n g the non-breeding season i s r e l a t e d t o . t h e r e l a x a t i o n of t e r r i t o r i a l defense by breeding S. vagrans i n d i v i d u a l s . I f S. obscurus i n d i v i d u a l s are being excluded, from the presumably r i c h e r S. vagrans h a b i t a t , and i f assuming the mechansism. of t h i s e x c l u s i o n . i s . , . i n t e r s p e c i f i c t e r r i t o r i a l i t y , then one would expect a hig h e r .incidence o f ( S..obscurus t r a n s g r e s s i o n s i n t o S. vagrans h a b i t a t . w i t h the onset of r e p r o d u c t i v e a c t i v i t y . However, only the breeding S. obscurus males are captured with i n c r e a s e d .frequency i n moder s o i l s ; S. obscurus females show the same..distribution whether or not they are s e x u a l l y a c t i v e . . T h i s . . f a c t . alone suggests t h a t the r e l a x a t i o n of t e r r i t o r i a l i t y i n i t s e l f . i s i n s u f f i c i e n t to e x p l a i n the d i s t r i b u t i o n a l , p a t t e r n s o f breeding S. obscurus. , To go one step .furt h e r , ..inference can a l s o be made t h a t . t e r r i t o r i a l i t y a l o n e , i s i n s u f f i c i e n t t o account f o r the d i s t r i b u t i o n a l p a t t e r n s seen i n non-breeding animals of both s p e c i e s . . . ... The d i s t r i b u t i o n , o f b r e eding, and ..non-breeding shrews may i n s t e a d be e x p l a i n e d i n terms of a d a p t i v e s t r a t e g i e s r e l a t e d t o the p a t t e r n . c f the h a b i t a t i t s e l f . . The. h a b i t a t i n which S. vagrans i s e s t a b l i s h e d i s , as d i s c u s s e d e a r l i e r , an edaphic b i o g e o c e n o s i s based on topography.and seepage p a t t e r n s . The moder s o i l i s , , i n g e n e r a l terms, a .result-.. o f the moisture and e n r i c h i n g supply of n u t r i e n t s brought i n by 116 the seepage ( K r a j i n a , 1969). Because of the r e l i a n c e on seepage s i t e s , the d e n d r i t i c p a t t e r n of t h i s type of h a b i t a t i s continuous, f o l l o w i n g water, courses. The. S. obscurus h a b i t a t , on the other hand, i s disjunct,.. being, i n t e r s e c t e d by the l i n e s of seepage. Hence, during the.breeding season, S. obscurus males wandering i n se a r c h . o f .females..are. more l i k e l y t o c r o s s S. vagrans h a b i t a t , whereas S, vagrans males need only f o l l o w the seepage p a t t e r n s . ,. The r e l a x a t i o n of t e r r i t o r i a l a g g r e s s i v e n e s s at t h i s time no doubt c o n t r i b u t e s to the extensive m o b i l i t y of S. obscurus males..... P o p u l a t i o n numbers i n my study area suggest t h a t the.mor h a b i t a t of S. obscurus supports a lower d e n s i t y of shrews, i n which case i t i s more to the advantage of breeding.males to ream e x t e n s i v e l y , 10, G e o g r a p h i c a l D i s t r i b u t i o n of Shrews . .. , 10.1, Background, I n v e s t i g a t o r s have s t u d i e d . t h e . g e o g r a p h i c a l .and e c o l o g i c a l d i s t r i b u t i o n s o f . S, vagrans and S. obscurus through snap-trapping and, although p o p u l a t i o n s from d i f f e r e n t regions. may. vary, .in some regards, s e v e r a l o b s e r v a t i o n s have been made. Sorex vagrans has been found mainly i n damp h a b i t a t s : marshes, bogs,. meadows, by streams, and i n wet f o r e s t (H.,Jackson, 1928; .Dalguest, 1948; C l o t h i e r , 1955; I n g l e s , 1961;. Spencer and Pettus, 1966; Hennings, 1970)., The s p e c i e s as .a .whole . . i s independent of l i f e zones and has a wide e c o l o g i c a l 1 1 7 t o l e r a n c e l i m i t e d only by moisture (Dalquest, 1948; Durrant, 1952; L. N.Brown, 1967), although i t i s found with, g r e a t e r r e l a t i v e f r e q u e n c i e s i n d r i e r h a b i t a t s d u r i n g - p e r i o d s of high p o p u l a t i o n numbers (Spencer .and Pe t t u s , ..1966). Sorex obscurus appears t o have a yet wider, e c o l o g i c a l t o l e r a n c e , o c c u r r i n g i n marsh h a b i t a t , dry c o n i f e r o u s f o r e s t , a l p i n e heather, along streams, t a l u s slopes,_and dense r a i n - f o r e s t t h i c k e t s , but i t . i s . ..common, .only., l o c a l l y (Dalquest, 1948).,. Some researchers-have f o u n d . i t only at higher a l t i t u d e s , above t i m b e r l i n e (Rand, 1948), or i n . high mountain country (Durrant, 1952). Hennings (1970) has suggested that S.,vagrans .and §• obscurus i n Montana are separated, a l l o t o p i c a l l y . . even where they are g e o g r a p h i c a l l y sympatric. Sorex.obscurus..did not appear i n streamside t r a p s u n t i l the l o c a l e s , vagrans numbers were somewhat reduced.by t r a p p i n g , i n d i c a t i n g t h a t S. vagrans may outcompete S. obscurus f o r . f a v o r a b l e moist h a b i t a t s . In a s i m i l a r s i t u a t i o n , Dalquest (1941) concludes t h a t S. vagrans i s a b l e t o outcompete the l a r g e r Sorex ^£owbridgii, r e s t r i c t i n g the l a t t e r t o suboptimal dry f o r e s t h a b i t a t . 10.2. D e s c r i p t i o n of h a b i t a t s . Snap-trapping was c o n f i n e d to the .extreme southwestern c o r n e r of B r i t i s h Columbia, p r i m a r i l y . i n the.Research.Forest and Endowment Lands. Habitats, through which lines..were ...set were c a t e g o r i z e d i n t o f i v e types which I f e l t were not only 118 convenient i n terms of c o m p a r a b i l i t y with those .described i n the l i t e r a t u r e , but were a l s o , on the whole,, d i s c r e t e and r e c o g n i z a b l e . The two f o r e s t types were.less homogeneous, being s u b j e c t to edaphic c o n d i t i o n s and mosaicism. The v a r i o u s biogeocoenoses comprising each. f o r e s t type are d e s c r i b e d i n f u l l d e t a i l by K r a j i n a (1969). The f i v e h a b i t a t types, with b r i e f . d e s c r i p t i o n s , a r e : 1) F i e l d s : open areas where the v e g e t a t i o n i s . low, being comprised of mixed grasses,.sedges,.weeds,.and other s h o r t , herbaceous p l a n t s . T h i s h a b i t a t i s s e a s o n a l l y wet, and has an abundance of s u r f a c e l i t t e r c o v e r i n g a w e l l melanized s o i l . ......... 2) HiLter-edge: l a k e - and stream-edge h a b i t a t s , char-a c t e r i z e d by shrubby v e g e t a t i o n . . (e.g. C a r e x s p , , Rubus s p e c t a b i l i s , S a l i x sp.) and gleyed (waterlogged), o f t e n rocky s o i l . -3) D i s t u r b e d h a b i t a t : toad- edge and areas logged w i t h i n the l a s t 15 years, with, young c o n i f e r o u s regrcwth and pioneer s p e c i e s of p l a n t s , p a r t i c u l a r l y , fireweed .E£ilobium a n g u s t i f o l i u m ) , red a l d e r (alnus r u b r a ) , bracken f e r n (Pterygium S3ililiiJiJS) # ISl-llS SPP» * and ..mixed g r a s s e s . , 4) D o u g l a s - f i r f o r e s t : Pseudotsuga m e n z i e s i i the dominant t r e e , g e n e r a l l y i n f a i r l y r i c h s i t e s with moder humus; sword f e r n (Polystichum munitum), s a l a l ( g a u l t h e r i a s h a l l o n ) , or moss the predominant growth i n the.understory... 5) Western hemlock f o r e s t : Tsuga hetejrojDhv.ll a the dominant t r e e , u s u a l l y i n mor humus, with s a l a l or moss i n 119 the understory. 10.3. Trapping r e s u l t s The t r a p p i n g e f f o r t and r e s u l t s f o r each h a b i t a t are presented (Table XII) , along with a summary of the S. vagrans and S. obscurus c a t c h and t o t a l t r a p . n i g h t s per h a b i t a t (Table X I I I ) . . Comparisons between . h a b i t a t s cannot be made owing to unequal t r a p p i n g e f f o r t s , but. i n t e r s p e c i f i c comparisons can be made w i t h i n each h a b i t a t type. .. . — Both s p e c i e s tend to.be cosmopolitan i n . d i s t r i b u t i o n . In t h i s r e g i o n , S. obscurus i s present at e l e v a t i o n s d o w n t o sea l e v e l , and i n a l l the h a b i t a t s ^ s a m p l e d e x c e p t . f o r g r a s s l a n d . Sorex vagrans was.present.in. a l l . h a b i t a t s , but became s c a r c e at higher e l e v a t i o n s ( i . e . ;above ,.,about .1300 f e e t ) , where S. c i n e r e u s , a shrew of e q u i v a l e n t s i z e , became pre v a l e n t . . . . . . . The major d i f f e r e n c e s . i n h a b i t a t . d i s t r i b u t i o n between S. vagrans and S. obscurus are the abundance, of S. vagrans and absence of S. obscurus i n . ..grassland, .and the predominance of S. obscurus i n Western .,Hemlock, h a b i t a t . These d i f f e r e n c e s p a r a l l e l the type of h a b i t a t . s e g r e g a t i o n e v i d e n t i n the l i v e - t r a p p i n g p l o t , „ where S. obscurus p r e v a i l s i n the mor s o i l s and S. vagrans i n the moder s o i l s . In g r a s s l a n d , where S. vagrans reaches-high d e n s i t i e s i n the absence of S. obscurus, the s o i l i s yet r i c h e r . m u l l - l i k e moder (Wallwork, 1970). Although I cannot say. f o r c e r t a i n what the proximal f a c t o r s are which determine the r e l a t i v e r 120 Feet Trap Sorex Sorex Habitat Trapping Dates Elev. nights obscurus vagrans F i e l d July 1 , 1971 0 100 0 6 July 12-13 100 >+60 0 5 Aug 8-10 500 600 0 1 Nov 15-20 100 750 0 h June 12-1*f, 1972 100 300 0 8 July 2-3 3 7 5 1+00 0 1 Mar 31-Ap 2 , 1973 350 1170 0 2 Apr 7-10 500 300 0 0 Water Feb 2 0 , 1971 900 50 0 1 edge May 30-31 1025 100 0 0 July 7-8 1670 500 3 0 Aug 17-19 1125 315 0 1 May 26 - 2 7 , 1972 1580 200 0 0 July 15-17 1250 ^00 0 0 Aug 3 - 5 , 1971 1175 1200 1 0 Disturbed Jan 3 1 , 1971 850 80 0 0 areas March 13 875 50 1 1 March 20 1200 50 0 0 Aug 17-19 1125 120 0 0 Oct 9 -10 1300 360 2 2 May 5 - 7 , 1972 1580 600 1 0 May 26-28 390 0 0 July 2-3 3 7 5 hOO 0 0 A p r i l 7 - 9 , 1973 500 570 0 0 A p r i l 7-9 500 300 0 0 July 11-13 1^75 600 1 0 Douglas- Jan 31', 1971 ho 0 0 f i r Nov 15-20 100 750 2 0 Nov 2 7 - 2 9 750 750 3 0 May 2-h, 1972 600 0 1 June 12-1 100 . 600 h 9 May 1-3, .197,1 100 1200 1 0 Western July 15-16, 1971 1350 500 2 0 hemlock July 2 2 - 2 3 1350 500 0 0 Aug 8-10 700 750 6 1 Aug 17-19 1125 150 0 0 Aug 25 1660 250 1 0 Oct 9-10 1200 750 1 0 Nov 2 7 - 3 0 1250 150 1 0 May 26 - 2 8 , 1972 1580 270 0 0 A p r i l 21-23 900 1050 1 1 May 1^-16 1100 675 0 0 May 29-31 1000 1200 5 h Table XII. Snap-trapping e f f o r t and r e s u l t s for each habitat. 121 T o t a l T o t a l T o t a l H a b i t a t Trap n i g h t s S. obscurus S. vagrans F i e l d * f l80 0 27 Water edge 2865 h ' 2 Disturbed areas 3520 5 3 D o u g l a s - f i r f o r e s t 39LK) 10 10 Western hemlock f o r e s t 62^5 17 6 Table XIII. Summary of snap-trapping catch of S. obscurus and S. vagrans. 122 success of s p e c i e s i n d i f f e r e n t h a b i t a t s , i t i s clear., t h a t the hygrotopes, edatopes, and i n v e r t e b r a t e p r e y . c o r r e l a t e d with c e r t a i n h a b i t a t s must i n t e r a c t to determine.. the s u i t a b i l i t y of t h a t h a b i t a t f o r a given s p e c i e s . Since the range of s u i t a b i l i t y o v e r l a p s a c o n s i d e r a b l e degree f o r both s p e c i e s , c o m p e t i t i v e i n t e r a c t i o n s probably... play ...a s i g n i f i c a n t r o l e i n l i m i t i n g the numbers and d i s t r i b u t i o n . o f each s p e c i e s . . In g e n e r a l , i t appears.that S. obscurus i s b a s i c a l l y a f o r e s t shrew, and t h a t S. vagrans succeeds best i n r i c h e r . s o i l s proximal to water. . . ~ The i s o l a t e d , remnant stand of d o u g l a s - f i r .which comprises the U. B. C. Endowment Lands, i s s i t u a t e d , cn ..a s m a l l peninsula at about 100 f e e t e l e v a t i o n , and s e p a r a t e s the campus from t h e . c i t y of Vancouver. In. the .Endowment Lands f o r e s t , both S. obscurus and S. vagrans were captured.. However, l i n e s s e t s i m u l t a n e o u s l y i n small..fields..and i n . the f o r e s t immediately ad j a c e n t t o . them, r e v e a l e d , t h a t o n l y S. vagrans i n h a b i t e d the grassy areas.and only.. S. obscurus the adjacent f o r e s t e d area. P o p u l a t i o n sampling.from.other lowland l o c a l i t i e s (Part II) also. ...show . that .. g r a s s l a n d h a b i t a t i n t h i s r e g i o n i s able to support h i g h . d e n s i t i e s . o f v§3£an§» a n < * i s p r e f e r r e d by t h i s . ..species over, f o r e s t h a b i t a t . The absence of S. obscurus. from g r a s s l a n d , combined with i t s apparent broad, e c o l o g i c a l - t o l e r a n c e (Dalquest, 1948), suggests i t i s ... unable to compete with S. vagrans i n t h a t h a b i t a t , at l e a s t at lower e l e v a t i o n s . 123 11. H a b i t a t D i f f e r e n c e s and the Timing of Events The i n t e r r e l a t i o n s h i p i n the timing, of. melt ..and r e p r o d u c t i o n has a l r e a d y been d i s c u s s e d ..in. g eneral. terms f o r both s p e c i e s . One would reason t h a t a c t u a l o n s e t . c f these events would be synchronous i n the area .of sympatry i f . the same mechanisms were i n v o l v e d ; however, such i s net the case (Table XIV) . Of a l l events c o n s i d e r e d , the f a l l molt a l o n e . i s c h a r a c t e r i z e d by c o n s i s t e n t synchrony between s p e c i e s , and among years. Experiments with Sorex araneus.. (Bcrowski, 1961) have shown t h a t summer shrews respond to . a r t i f i c i a l l y shortened d a y l i g h t by undergoing an e a r l y . f a 11 molt, r e g a r d l e s s of temperature.. The evidence from .my. .data a l s o suggests photoperiodism i s r e s p o n s i b l e f o r . i n i t i a t i n g melt i n p r e p a r a t i o n f o r winter, i n which case i t i s not s u r p r i s i n g t h at two s p e c i e s of s i m i l a r s i z e and.in .the same geographic area would undergo t h i s temperature adapted molt at the same time. The asynchronous events are b a s i c a l l y . t h e s e which are somehow r e l a t e d to the time.at which young are. born and f i r s t appear as independent members of the p o p u l a t i o n . . I n these cases, S. obscurus c o n s i s t e n t l y , l a g s „a„. few.. ..weeks behind S. vagrans ......in . onset. . as discussed, e a r l i e r , . s p r i n g molt i n females i s completed immediately p r i o r to..estrus and p o s s i b l y i s p h y s i o l o g i c a l l y r e l a t e d . .to t h e . .onset of r e p r o d u c t i v e a c t i v i t y i n females. , Assuming t h i s to.be c o r r e c t , the c h a i n of events f o l l o w i n g the s p r i n g molt, Event Year Onse Sorex vagrans t Sorex obscurus F a l l molt 1971 1972 1973 M i d - l a t e Sept. M i d - l a t e Sept. M i d - l a t e Sept. M i d - l a t e Sept. M i d - l a t e Sept. M i d - l a t e Sept. Spring molt of females 1972 1973 Mid-March E a r l y March Mid-March Mid-March Spring molt of males 1972 1973 E a r l y May E a r l y May Late May M i d - l a t e May Males breed 1972 1973 Mid-Feb. Late Jan. Mid-Feb. Mid-Feb. Females breed 1972 1973 E a r l y A p r i l Late March M i d - A p r i l E a r l y A p r i l Young appear 1972 1973 Early-mid May E a r l y May M i d - l a t e May Mid-May Table XIV. Comparison of onset of molt and re p r o d u c t i o n i n sympatric Sorex vagrans and Sorex obscurus. 125 pregnancy, l a c t a t i o n , and the weaning.of young, i s d i r e c t l y r e l a t e d t o , and temporally determined by, the onset of the molt. The s i g n i f i c a n c e of the . d i f f e r e n c e . i n . timing ..between s p e c i e s may be viewed i n l i g h t , of . the h y p o t h e s i s , t h a t s p e c i e s which reproduce s e a s o n a l l y are adapted, such t h a t the young are born at. the time o f . o p t i m a l food a v a i l a b i l i t y (Lack, 1954, 1966). Sorex vagrans and. S. obscurus occupy d i f f e r e n t h a b i t a t s based on s o i l type, and t h e . i n v e r t e b r a t e fauna of the r e s p e c t i v e s o i l types d i f f e r s i n .composition and a l s o i n se a s o n a l abundance and a c t i v i t y . I t i s not unreasonable to view,the t i m i n g of events as o p t i m i z i n g s t r a t e g y and to assume t h a t each ..species r e a c t s to the dynamics of i t s prey p o p u l a t i o n s , whether d i r e c t l y or i n an e v o l u t i o n a r y sense. The t i m i n g of the .spring molt,cf, males of both s p e c i e s c o i n c i d e s r e s p e c t i v e l y . w i t h the. appearance of young, and may a l s o be r e l a t e d t o the t i m i n g , o f peak food abundance. 12. Summary . . In the l i v e - t r a p p e d area of sympatry, the breeding p o p u l a t i o n of any one year i s comprised only o f . i n d i v i d u a l s born the previous year, Young are.born from mid-spring through the summer, d u r i n g which time . they e s t a b l i s h both i n t r a - and i n t e r s p e c i f i c t e r r i t o r i e s . The s u c c e s s f u l maintenance of t e r r i t o r i e s i s p o s i t i v e l y c o r r e l a t e d with o v e r w i n t e r i n g and breeding the f o l l o w i n g season. I n d i v i d u a l 126 young of the year f o l l o w a g e n e r a l p a t t e r n c f e i t h e r d i s a p p e a r i n g a f t e r t h e . f i r s t few r e c a p t u r e s , or.remaining i n f a i r l y s t a b l e home ranges, which become i n c r e a s i n g l y non-o v e r l a p p i n g . Summer po p u l a t i o n s a r e . high, but decrease r a p i d l y with a d u l t m o r t a l i t y and j u v e n i l e d i s p e r s a l or m o r t a l i t y . L i t t l e or no i n g r e s s occurs by. the end of summer, and the p o p u l a t i o n s t a b i l i z e s . The g r e a t e s t s e l e c t i v e pressure on f i r s t year animals. seems. ..to. be s u r v i v a l of the summer and f a l l months; ..overwintering animals s u f f e r low m o r t a l i t y . By early.autumn the a d u l t s , born the previous year, have disappeared,.and the young of the year molt i n t o a darker, l o n g e r and more plush, pelage..— In mid-winter, , males begin , t o . . show. . signs. ..of r e p r o d u c t i v e a c t i v i t y : weight gain, enlarged and. descended t e s t e s , enlarged penis .which o c c a s i o n a l l y e v e r t s , and s i d e g l a n d areas which molt and.become, h a i r l e s s , moist and s c e n t - p r o d u c i n g . O v e r a l l a c t i v i t y of the m a l e s . i n c r e a s e s , r e s u l t i n g i n extended home ranges and the abandonment..of s t r i c t t e r r i t o r i a l i t y . Females remain .non-reproductive and i n s t e a d undergo a s p r i n g molt i n which s h o r t , brown...fur s i m i l a r t o the j u v e n i l e pelage r e p l a c e s the. more i n s u l a t i v e dark winter f u r . In l a t e March the r e c e p t i v i t y , of females determines the onset of r e p r o d u c t i o n . The .. f i r s t . young appear i n t r a p s the.second week of May, and i t . i s . . n e t . u n t i l then t h a t a d u l t males molt f rom ... winter pelage. The synchrony of the f i r s t appearance of young and..the s p r i n g molt of males suggests t h a t t h i s i s a p e r i o d of o p t i m a l food 1 2 7 a v a i l a b i l i t y . Female shrews can undergo a postpartum e s t r u s and may have up to three s u c c e s s i v e l i t t e r s . .Females were o f t e n both pregnant and l a c t a t i n g . No l i v e - t r a p p e d , animals a t t a i n e d s e x u a l maturity i n t h e i r f i r s t summer, . nor .did. I c o l l e c t any breeding f i r s t year shrews from the Research F o r e s t . , . .. I n t e r s p e c i f i c d i f f e r e n c e s i n S. vagrans and S. obscurus became e v i d e n t from the . l i v e - t r a p p i n g . . study. D i s t i n c t d i f f e r e n c e s i n s c e n t s produced by . the .side glands of breeding males probably serve .to f a c i l i t a t e r e p r o d u c t i v e i s o l a t i o n as w e l l as b r i n g the sexes of a s p e c i e s t o g e t h e r . The s p e c i e s are f u r t h e r separated by. s i g n i f i c a n t and c o n s i s t e n t h a b i t a t d i f f e r e n c e s : S. vagrans i s c o n f i n e d to the area fed by seepage waters and c h a r a c t e r i z e d by.moister, r i c h e r s o i l s , and S. obscurus o c c u r s . on. the. w e l l - d r a i n e d s l o p e s where a c i d i c mor s o i l s and . t h e i r , r e l a t e d p l a n t a s s o c i a t i o n s p r e v a i l . D i s t r i b u t i o n sampling at the geographic l e v e l supports t h e s e . b a s i c h a b i t a t . d i f f e r e n c e s . , ... The onset of v a r i o u s . l i f e history.phenomena (e.g. molt and breeding) was g e n e r a l l y l a t e r i n S. obscurus than i n S. vagrans. T h i s d i f f e r e n c e i s p r o b a b l y . a t t r i b u t a b l e to the r e l a t i o n s h i p between predator and .prey,., assuming the i n v e r t e b r a t e s upon which the shrews p r e y d i f f e r i n composition and hence i n timing of seasonal abundance i n the r e s p e c t i v e s o i l types. .Reproductive . e f f o r t . w a s . g r e a t e r . i n S. vagrans than i n S. obscurus, p r i m a r i l y because S. vagrans 128 females averaged a g r e a t e r number of l i t t e r s , while, on. the whole, S. obscurus females disappeared s h o r t l y a f t e r appearance of f i r s t l i t t e r s . - . The p o p u l a t i o n conseguence of t e r r i t o r i a l i t y i s d e n s i t y r e g u l a t i o n a t l e v e l s which per m i t , the s u r v i v a l : of the p o p u l a t i o n through winter c o n d i t i o n s of low temperatures and decreased food a v a i l a b i l i t y . The evidence suggests t h a t t e r r i t o r i a l behavior.on the p a r t of f i r s t .year i n d i v i d u a l s i n c r e a s e s through the summer with i n c r e a s i n g . p o p u l a t i o n d e n s i t y . . In g e n e r a l , members of e a r l y cohorts.comprise .the breeding p o p u l a t i o n cf the. f o l l o w i n g ... y e a r s u g g e s t i n g s e l e c t i v e advantage f o r members of f i r s t l i t t e r s . 129 PART II SEASONAL AND GEOGRAPHIC VARIATION The n a t u r a l v a r i a b i l i t y of s p e c i e s l i e s a t the heart o f e v o l u t i o n a r y theory., Study of s p e c i e s v a r i a t i o n , and i t s s i g n i f i c a n c e has been the b a s i s of most e v o l u t i o n a r y s t u d i e s and hypotheses of s p e c i a t i o n . In t h i s s e c t i o n I w i l l c o n s i d e r two types of v a r i a t i o n observed i n shrews, s e a s o n a l v a r i a t i o n and geographic v a r i a t i o n . . . Seasonal v a r i a t i o n ..is the adap t i v e response . i n i n d i v i d u a l s to changes i n environmental demands.and i n t h e i r own l i f e c y c l e s . As such, i t i s g e n e r a l l y c o n s i d e r e d nongenetic v a r i a t i o n (Mayr, . 1966), i . e . a. m o d i f i c a t i o n . . o f the i n d i v i d u a l phenotype.or behavior which .does-not.involve g e n e t i c changes, although c e r t a i n l y genetic, . f a c t o r s determine the amount, and d i r e c t i o n of the ...permissible f l e x i b i l i t y . Geographic v a r i a t i o n , of a s p e c i e s i s a p o p u l a t i o n phenomenon, the consequence of the.geographic v a r i a t i o n of the . environment, . i n v o l v i n g . . . phenotypic, b e h a v i o r a l , e c o l o g i c a l , and l i f e h i s t o r i c a l v a r i a t i o n at the p o p u l a t i o n l e v e l . ,Although i t i s not p o s s i b l e t c determine by simple o b s e r v a t i o n how much.of the v a r i a b i l i t y . s h o u l d . . b e a s c r i b e d to nongenetic m o d i f i c a t i o n and how much to g e n e t i c f a c t o r s , I w i l l present s e v e r a l examples of observed geographic v a r i a t i o n and d i s c u s s t h e i r p o t e n t i a l s i g n i f i c a n c e . 130 1,. Seasonal V a r i a t i o n 1.1. S k u l l height Numerous workers have noted a gradual f l a t t e n i n g of the br a i n c a s e of North American Sorex _(Merriam, 1895; H. Jackson, 1928; P r u i t t , 1954; Rudd, 1955),.. and t h i s decrease i n s k u l l h eight has commonly . .been ...attributed . .to age. Dehnel (1949) found that i n the. European shrew, Sorex araneus, f l a t t e n i n g of the s k u l l over the. f a l l and winter months was,, however, f o l l o w e d by a p e r i o d i n the s p r i n g when s k u l l h eight a g a i n i n c r e a s e d . In.a h i s t o l o g i c a l study of t h i s phenomenon, Z. Pucek .(1963) showed,that winter decrease i n s k u l l height was due to r e s o r p t i o n , o f bone, a t the c r a n i a l sutures,- and t h a t new bone t i s s u e grew at these s i t e s the f o l l o w i n g s p r i n g . . Dapson (1968) i n v e s t i g a t e d the s k u l l h eight phenomenon i n the s h o r t - t a i l e d shrew, B l a r i n a breyicauda..... He po i n t e d out t h a t B l a r i n a a l s o showed a decrease i n . s k u l l h e i g h t i n winter followed by an i n c r e a s e i n s p r i n g , but only " i f the data were grouped by month of captu r e . ... Grouping h i s specimens by age c l a s s , based on toothwear,.he noted.no s i g n i f i c a n t i n c r e a s e . His c o n c l u s i o n was th a t the. i n c r e a s e shown when a n a l y s i s i s done by date of . .capture i s an a r t i f a c t due to the disappearance of o l d e r c o h o r t s .and..the emergence of new weanlings . t h a t provided.the bulk c f the p o p u l a t i o n i n l a t e , winter and s p r i n g . Countering t h i s argument, z. Pucek (1970). s t a t e d that no shrews are born a f t e r September, and t h a t the most i n t e n s i v e changes i n 131 s k u l l height occur between October and February. Working on North American Sorex (S. vagrans and S. obscurus), Hennings ( 1 9 7 0 ) found s e a s o n a l , v a r i a t i o n i n c r a n i a l h e i g h t to be s i m i l a r to t h a t found.by Z...Pucek (op. c i t . ) , though the magnitude of f l u c t u a t i o n . w a s . s m a l l e r than i n Sorex araneus.. He t e s t e d Bapson*s i d e a s by grouping the s k u l l s by age c l a s s , and found t h a t the-changes were indeed dampened and showed no s p r i n g i n c r e a s e . . . ._ My own data are l e s s c o n c l u s i v e . ., average s k u l l h e i g h t s f o r S. vagrans from Ladner A i r Base and . from. .Serpentine R i v e r are analyzed by month ( F i g . 1 6 ) . The s k u l l d e c l i n e s i n height during the f i r s t months of l i f e ( 8 . 7 9 L decrease from A p r i l to January), but the h y p o t h e s i z e d . s p r i n g jump, though apparent i n the f i g u r e , 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 . P o s s i b l y , by European standards,.the winter c o n d i t i o n s i n t h i s area are s i g n i f i c a n t l y m ilder ,... or food i s l e s s l i m i t i n g . By grouping the s k u l l s i n t o age c l a s s e s ( F i g . 1 7 ) , the r e s u l t s are s i m i l a r t o those of Dapson (1968). and Hennings ( 1 9 7 0 ) . However, the s i g n i f i c a n c e of t h i s , and,of DapsonAs c r i t i c i s m s of the P o l i s h work, are q u e s t i o n a b l e . European workers have hypothesized t h a t decrease .in. s k u l l height..is r e l a t e d to v a r i o u s a d a p t a t i o n s . f o r s u r v i v i n g , c o l d winters and food s c a r c i t y . The. f a c t t h a t , the amplitude o f . t h e response i s i n c r e a s e d where winters, are more severe (Mezhzherin, 1 9 6 4 ) supports.the i d e a t h a t . t h e s e . s k u l l h e i g h t changes are i n response to environmental c o n d i t i o n s , not 132 Figure 16. Seasonal v a r i a t i o n i n s k u l l h e i g h t : Sorex  vagrans from Ladner A i r Base and Serpentine R i v e r (mean and standard e r r o r ) . S K U L L HEIGHT (mm.) 133 Figure 17. Regression o f s k u l l height on age c l a s s : Sorex vagrans from Ladner A i r Base and Serpentine R i v e r (mean and standard e r r o r ) . SKULL HEIGHT (mm.) 4*. > O m o ro > CO Oi CO -J - r -00 co-f-CO o OI ro .O) Ol CO to rO rO CO CO VI 00 to cn ro co co 134 age. Thus, Dapson's grouping of the s k u l l s by age c l a s s i s not the a p p r o p r i a t e t e s t . In. f a c t , assuming the winter p o p u l a t i o n of shrews t o be comprised of animals which d i f f e r up t o four months i n age, one would expect.the l e v e l i n g o f f seen i n s k u l l height f o r c e r t a i n age c l a s s e s , i f these age c l a s s e s correspond to the ages of animals o v e r w i n t e r i n g . Comparisons of F i g u r e s 16 and 17 w i l l show.that such i s the case. Furthermore, Dapson's theory assumes a change i n age c l a s s composition i n time, i . e . during the winter, a g r e a t e r p r o p o r t i o n of younger animals should be found. Age c l a s s , however, i n c r e a s e s evenly with time f o r g r a s s l a n d shrews (Fig 18). Hence, while my data do not c o n c l u s i v e l y support the r e s u l t s found by the European workers, they do at l e a s t i n d i c a t e t h a t the r e l a t i o n s h i p between s k u l l height.and age i s not a simple l i n e a r decrease with age, as.suggested by Dapson. 1.2. Height The low winter weight i n shrews (see F i g . 4, Sect.2.2, Part I) has been a t t r i b u t e d to p h y s i o l o g i c a l changes i n the a d r e n a l cortex r e s u l t i n g i n a marked decrease. i n i n t r a c e l l u l a r water content (Hyvarinen, 1968). European r e s e a r c h e r s have documented the decrease i n c e l l u l a r water (Suida, 1964 ; M. Pucek, 1965; Myrcha, .. 1969) . and have hypothesized t h a t i t i s p h y s i o l o g i c a l l y r e l a t e d t o ..a lowering of metabolic a c t i v i t y . T h i s . . lowering of the metabolic s t a t e a l l o w s the shrew to s u r v i v e the winter with 135 Figure 18. Age c l a s s r e g r e s s i o n on time: S. vagrans from Ladner A i r Base, 1971 cohort. Age c l a s s i s determined on the bas i s of toothwear. AGE C L A S S CO CD Q v ^ / v > - c o * . c n o N N « D C D o P H 1 r - 1 ( 1 1 CO ro CO 0^-- O - + - — i — i L X X 1 to (1) ro 25 ro 136 on l y a s l i g h t l y i n c r e a s e d a b s o l u t e amount of food, while the r e l a t i v e amount i s g r e a t l y i n c r e a s e d owing to. the ..animal's s m a l l e r s i z e (Mezhzherin, 1964; Gebczynski, 1965; Z. Pucek, 1970). Other work supports the.theory t h a t .metabolism.and water content are r e l a t e d . (Skujina and.. McLaren, 1967) . European shrews a p p a r e n t l y have an. i n c r e a s e d , response ( i . e. . g r e a t e r weight l o s s owing to water) i n regions.. . where winters are more.severe (Mezhzherin, 1964). . The.decrease i n weight f o r S. vagrans averages 6.8%.from summer l e v e l s . t o winter low, while t h a t f o r S. obscurus. i s 11. 2%(Fig.... 3, Sect. 2,Part I ) . The comparable d e c r e a s e . f o r Sorex araneus i n Poland i s 24.455 (Z. Pucek, 1965). „ wolk.. (1969) kept Sorex araneus i n outdoor cages with u n l i m i t e d . f o o d through the year and found a decrease i n weight, of only.. 16.7% . i n winter with temperature lows of -169C; no.change a t . a l l was shown with animals kept i n the l a b o r a t o r y with u n l i m i t e d food and c o n s t a n t temperatures (Z. Pucek, .1964). . The c o n c l u s i o n s from these experiments.are t h a t the winter weight l o s s shown by w i l d shrews ,is_not a. response to e i t h e r food or temperature a l o n e , but to a^.combination, of these f a c t o r s . The f a c t t h a t S. vagrans and S. obscurus show a s i g n i f i c a n t l y l e s s e r response may. t h e r e f o r e . b e due. to one or a combination of t h r e e f a c t o r s : , . food, temperature, and g e n e t i c d i f f e r e n c e s . , I t should be remembered t h a t , b o t h S. vagrans and S. obscurus are s m a l l e r than Serex araneus, which average 8.5 g. as young a d u l t s (Wolk, . 1969), so the response may be tempered by the e n e r g e t i c l i m i t a t i o n s of 137 may a l s o e x p l a i n the d i f f e r e n c e i n between S. vagrans and the l a r g e r 1.3. Body length . Dehnel (1949) noted t h a t body length, a s . w e l l as weight and s k u l l h e i g h t , decreased with the approach.of.winter i n Sorex lE^neus i n Poland. I n v e s t i g a t i o n .of. the mechanism, by which body,length v a r i e d r e v e a l e d t h a t . t h e s i z e . a n d shape.of the i n t e r v e r t e b r a l d i s c s changed, ..the nucleus, pulposus f l a t t e n i n g l o n g i t u d i n a l l y d u r i n g the autumn..and e a r l y w inter, and s w e l l i n g again d u r i n g , s p r i n g (Saure. and Hyvarinen, 1965 ; Hyvarinen, 1969a). Studying s e x u a l maturation i n f i r s t year Sorex araneus,. Z. Pucek. (1960) concluded t h a t body length .did not change ... as a . r e s u l t of r e p r o d u c t i v e a c t i v i t y i n young females, but was a f u n c t i o n of age and s e a s o n a l i t y . Body l e n g t h s of female S. vagrans from the Serpentine R i v e r and Westham.. I s l a n d l o c a l i t i e s were analyzed f o r seasonal v a r i a t i o n as w e l l as f o r v a r i a t i o n as a f u n c t i o n . o f r e p r o d u c t i v e a c t i v i t y . Monthly body length.averages f o r a l l females e x c l u d i n g those breeding i n t h e i r f i r s t .year ( F i g s . 19A,B), support the o b s e r v a t i o n s , o f . European r e s e a r c h e r s t h a t body l e n g t h . decreases.,over. the winter season and i n c r e a s e s markedly.in the s p r i n g . ..Analyses were separated by l o c a l i t y , . a s Westham I s l a n d shrews proved to be s i g n i f i c a n t l y l a r g e r on the average than Serpentine River s m a l l s i z e . T h i s percentage decrease S. obscurus. 138 Figure 19A. Seasonal v a r i a t i o n i n body length of Westham Island female Sorex vagrans. BODY LENGTH (MM.) o «x> > »i c (A o -fife-139 Figure 19B. Seasonal v a r i a t i o n i n body length of Serpentine R i v e r female Sorex vagrans. BODY LENGTH (MM.) *6£T o -4 C ro CA 5J o 8 o -+--EE o 03 rO O IV) 4^  140 shrews (see a l s o Sect. 2.1, P a r t I I ) . Contrary t o the f i n d i n g s of Z. Pucek (1960), however, the average body l e n g t h of f i r s t year breeding, females, though s m a l l e r than that of second year breeding females, was a l s o s i g n i f i c a n t l y l a r g e r than t h a t of . t h e i r .ncn-breeding c o u n t e r p a r t s (Table XV)... E v i d e n t l y , age, season, and r e p r o d u c t i v e a c t i v i t y a l l i n f l u e n c e the body l e n g t h of shrews. 1.4. The a d a p t i v e s i g n i f i c a n c e of seasonal v a r i a t i o n i n shrews Seasonal changes i n s k u l l h e ight, body weight, and body l e n g t h i n S..vagrans have been shown to p a r a l l e l , t o some degree, the changes shown i n Sorex araneus and are represented d i a g r a m m a t i c a l l y i n F i g u r e 20. The p a t t e r n of changes, p a r t i c u l a r l y the r e g r e s s i v e p r o c e s s e s . i n l a t e . f a l l and e a r l y winter, .has.been i n t e r p r e t e d as.being p r i m a r i l y a s t r u c t u r a l a d a p t a t i o n to l i v i n g i n northern areas (Z. Pucek, 1970). Reduction i n o v e r a l l s i z e d u r i n g the .winter months r e s u l t s i n a l e s s f a v o r a b l e body surface-to-volume r a t i o , but the g r e a t e r i n s u l a t i o n a f f o r d e d by the longer winter pelage i s a p p a r e n t l y e f f i c i e n t to the. e x t e n t t h a t . t h e average d a i l y metabolic r a t e i n c r e a s e s by. only. 5.6% ...over t h a t of f i r s t year summer l e v e l s (Gebczynski,.1965, 1969). While the a b s o l u t e amount of food, necessary i n winter i n c r e a s e s by o n l y 10% of the l e v e l s f o r the p r e v i o u s summer, the r e l a t i v e food i n t a k e i n c r e a s e s by 25% (Wolk, 1969). Non-breeding 1st year females Breeding 1st year females Breeding 2nd year females Serpentine R i v e r 57.67 -^t=6.52 df=1 59 p<.001 y *\ t=5.7 df= =219 P< .001 60.75 J t=9.l8 df= =137 P< .001 t=6.l+1 df=129 p<.001 6*f.l8 t=5.l5 df= = 114-p< .001 Westham I s l a n d 59.87 t=i3.05 < df=197 y p<.001 65.1^ t=4-.l df=122 p<.001 -> 67.52 Table XV. Body length (mm.) comparisons of female S. vagrans from Serpentine Riv e r and Westham I s l a n d . Results of Student's t - t e s t are shov/n f o r comparisons made. Body length d i f f e r e n c e s for a l l comparisons were h i g h l y s i g n i f i c a n t . 1^2 Figure 20. Diagrammatic r e p r e s e n t a t i o n of morphological changes o c c u r r i n g s e a s o n a l l y i n Sorex (from Z. Pucek, 1970). 142a 143 The most important l i f e processes are r e s t r i c t e d to the two p e r i o d s i n a shrew's l i f e when e n v i r o n m e n t a l . c o n d i t i o n s , e.g. weather and food a v a i l a b i l i t y , are..favorable. (Z. Pucek, 1970). F u l l p h y s i c a l d e v e l o p m e n t , s u f f i c i e n t f o r maintenance of the . i n d i v i d u a l , . i s a t t a i n e d . u p o n . l e a v i n g the nest, but the growth which i s concomitant. with s e x u a l maturity i s d e l a y e d . u n t i l t h e . f o l l o w i n g s p r i n g . The body l e n g t h of female S. vagrans t h a t become.sexually m a t u r e . i n t h e i r f i r s t year i s i n t e r m e d i a t e between that, of non-breeding f i r s t year females and second y e a r . a d u l t . f e m a l e s . Perhaps t h i s r e p r e s e n t s a compromise. between, the optimal s i z e s f o r r e p r o d u c t i o n and f o r o v e r w i n t e r i n g . . The^degree t o which s i z e parameters of o v e r w i n t e r i n g parous females can r e g r e s s i s unknown. 2. Geographic V a r i a t i o n 2.1. Toothwear and t a i l l e n g t h The major purpose f o r l o o k i n g at the degree, c f tooth wear was to get a measure of the r e l a t i v e ages of the g r a s s l a n d s e r i e s of shrew specimens....... Figure... 18, showing r a t e of toothwear, has already.been d i s c u s s e d . . However, analyses of l a r g e sample s i z e s (417 from • L a d n e r . . A i r . Base, 366 from Serpen t i n e S i v e r , and 391 from.Westham Island) showed t o o t h wear d i f f e r e n c e s among . l o c a l i t i e s to be s i g n i f i c a n t . The r a t e of t o o t h wear was determined f o r each l o c a l i t y by sampling animals from November of t h e i r f i r s t 144 year t o October of t h e i r second year and. by p l o t t i n g age c l a s s r e g r e s s i o n s based on the month of capture* Shrews i n t h e i r f i r s t summer and f a l l were omitted because... p o p u l a t i o n r e c r u i t m e n t a t t h a t time would a f f e c t t h e . s l o p e s c a l c u l a t e d . The l i n e a r r e g r e s s i o n s f o r the three l o c a l i t i e s . a r e shown i n F i g u r e 21. A n a l y s i s of c o v a r i a n c e gave the f o l l o w i n g r e s u l t s : 1) Between Ladner A i r Base and Serpent i n e River,., no s i g n i f i c a n t d i f f e r e n c e s were found i n e i t h e r the s l o p e s or the Y - i n t e r c e p t . 2) When Ladner A i r Base ..and S e r p e n t i n e . R i v e r , were compared with Westham I s l a n d , the toothwear s l o p e s were again the same, but the d i f f e r e n c e s i n the Y - i n t e r c e p t s were h i g h l y s i g n i f i c a n t . These f i n d i n g s i n d i c a t e t h a t , while the r a t e c f tooth wear i s comparable f o r a l l three populations,.Westham I s l a n d shrews possess l a r g e r t e e t h . The s i g n i f i c a n c e of - t h i s | e r se, i s not c l e a r . The d i f f e r e n c e . .may. r e f l e c t some ad a p t a t i o n f o r c e r t a i n environmental c h a r a c t e r i s t i c s o f . t h a t p a r t i c u l a r l o c a l i t y , o r . i t may r e f l e c t some a d a p t a t i o n f o r c e r t a i n environmental c h a r a c t e r i s t i c s o f . t h a t . p a r t i c u l a r l o c a l i t y , or i t may be a r e s u l t of p l e i o t r o p y or the founder e f f e c t , s i n c e Westham I s l a n d shrews.are g e o g r a p h i c a l l y , and hence r e p r o d u c t i v e l y , i s o l a t e d from the. other. lowland g r a s s l a n d shrews. The t a i l l e n g t h of Westham.Island shrews i s a l s o s i g n i f i c a n t l y g r e a t e r than t h a t of other p o p u l a t i o n s ( F i g . 22) . Figure 21. Comparison of age class regressions on time for three grassland l o c a l i t i e s . Serpentine R i v e r : y = 5.293 + 0.5031x n = 163 Ladner A i r Base: y = 6.07^  + OA789X n = 175 Westham I s l a n d : y = 3.689 + 0.^ 317x n = 102 14-6 F i g u r e 22. Comparison of t a i l l e n g t h v a r i a t i o n f o r three g r a s s l a n d l o c a l i t i e s . Tail length (mm.) CO O Ladner A i r Base Serpentine River Westham Island CO cn - t — o cn -4— cn o co CO CO CO 147 2.2. Seasonal onset of r e p r o d u c t i o n I f s u c c e s s f u l r e p r o d u c t i o n i s the u l t i m a t e goal (in a Darwinian sense) of the i n d i v i d u a l s o f . a s p e c i e s , then study of the geographic v a r i a t i o n . i n r e p r o d u c t i v e biology.and s t r a t e g y of that s p e c i e s . s h o u l d reveal.some of..the s e l e c t i v e p r e s s u r e s t h a t have operated i n . i t s ..evolutionary . h i s t o r y . The c o l l e c t i o n and p r e p a r a t i o n of the s e r i e s . o f . shrews from g r a s s l a n d h a b i t a t p r o v i d e s abundant m a t e r i a l f o r .comparison with S. vagrans from the a l t i t u d i n a l l y higher, f o r e s t l i v e -t r a p p i n g p l o t at the Research F o r e s t . . .. In 1972, a n a l y s i s of a s e r i e s of g r a s s l a n d S. vagrans was made while a l s o l i v e - t r a p p i n g the. Research. F o r e s t shrews. Recapturing the same i n d i v i d u a l s at weekly i n t e r v a l s i n the Research F o r e s t l i v e - t r a p p i n g p l o t r e s u l t e d i n accurate d a t i n g of the onset of r e p r o d u c t i o n . ... Ei-weekly specimen,sampling from the g r a s s l a n d plots.was l e s s a c c u r a t e s i n c e a longer i n t e r v a l occurred between, sampling dates. A l s o , not a l l age and r e p r o d u c t i v e c l a s s e s of t h e . p o p u l a t i o n were always represented i n the sample. In.some i n s t a n c e s , t h e r e f o r e , I r e s o r t e d to. i n f e r r i n g the . time, of .onset...of r e p r o d u c t i o n i n females ..from the assumption t h a t g e s t a t i o n l a s t e d three weeks and weaning took, place another three weeks a f t e r b i r t h . (Johnston and Rudd, 1957). In t h i s manner, onset of r e p r o d u c t i o n i n females could.be c a l c u l a t e d on the b a s i s of whichever_of three events.gave the e a r l i e s t date: the appearance of. females i n e a r l y . pregnancy,. the appearance of l a c t a t i n g females ( l e s s three weeks), or the 148 a c t u a l appearance of young ( l e s s six.weeks) . The t i m i n g of an i n d i v i d u a l ' s r e p r o d u c t i v e e f f o r t can be c r i t i c a l to i t s . s u c c e s s . Temperate mammals, f o r the.most p a r t , reproduce s e a s o n a l l y because only at c e r t a i n times o f the year are f a c t o r s such as food and weather.optimal f o r s u c c e s s f u l r e a r i n g of young (Cohen, 1971 ; Negus.and .Berger, 1972). L i k e p r e d a t o r s i n g e n e r a l (Hairston,. Smith and Slobo d k i n , 1960), shrews appear to be l i m i t e d most by. food a v a i l a b i l i t y . They are ap p a r e n t l y not p r e d a t o r - l i m i t e d , nor do adverse winter c o n d i t i o n s l e a d t o . h i g h . m o r t a l i t y where.a t e r r i t o r i a l system i s e s t a b l i s h e d . .Concomitant, with, .the s t r o n g s e a s o n a l i t y a s s o c i a t e d with v e r t i c a l m i g r a t i o n , r e p r o d u c t i o n , a c t i v i t y , and l i f e .. stages .. of . s o i l i n v e r t e b r a t e s i s a l a r g e degree, of f l u c t u a t i o n i n a v a i l a b i l i t y of the.prey .animals f o r . shrews. T h e r e f o r e , though i t appears t h a t shrews are b a s i c a l l y w e l l , a d a p t e d , f o r s u r v i v i n g the c o l d , they are i n d i r e c t l y . . d e p e n d e n t . on temperature as i t a f f e c t s . t h e l i f e h i s t o r i e s . o f t h e i r . prey. I f the onset of r e p r o d u c t i o n , p a r t i c u l a r l y i n : f e m a l e s , i s t r i g g e r e d d i r e c t l y by.temperature or by t h e . a c t i v i t y of s o i l i n v e r t e b r a t e s , (which i n . turn i s . .dependent on temperature), then g e o g r a p h i c a l d i f f e r e n c e s . i n average maximum temperatures i n the s p r i n g s h o u l d . c o r r e l a t e with.the onset of s e x u a l a c t i v i t y . For., both years, the onset of r e p r o d u c t i v e a c t i v i t y was notably .. e a r l i e r . . i n . the. lowland g r a s s l a n d S. vagrans. The appearance of .young. i n the Research F o r e s t l i k e w i s e lagged about fo u r weeks behind the 149 f i r s t appearance of lowland, g r a s s l a n d young.. However, a s s o c i a t e d with the time l a g i s a temperature l a g as ..well ( F i g . 23). Comparing the mean monthly .maximum. temperatures f o r the area of the l i v e - t r a p p i n g p lot.and.the lowland g r a s s l a n d s , i t can be seen t h a t during the, f i r s t , .months ...of the year the Research F o r e s t .temperature curve.lagged.a month or more behind t h a t of . the. .. lowlands, . suggesting ..a r e l a t i o n s h i p , be i t d i r e c t or indirect,.between.temperature and the onset of r e p r o d u c t i v e a c t i v i t y . , Reproductive onset was c o r r e l a t e d with, the ... attainment.... of e g u i v a l e n t temperatures i n both areas. T h i s r e l a t i o n s h i p i s . no doubt i n f l u e n c e d by the f a u n a l composition.of the r e s p e c t i v e s o i l types and t h e . e f f e c t of temperature on the v a r i o u s s p e c i e s comprising the s o i l fauna. 2.3. Age at f i r s t r e p r o d u c t i o n . The most s t r i k i n g d i f f e r e n c e between Research.Forest and lowland g r a s s l a n d S. vagrans i s the. occurrence . i n the g r a s s l a n d s of females breeding i n t h e i r . . f i r s t summer and. the absence of t h i s phenomenon i n . .forest... h a b i t a t . . By determining the g e n e r a t i o n time, .the age a t f i r s t r e p r o d u c t i o n s t r o n g l y i n f l u e n c e s the growth r a t e of a p o p u l a t i o n (Lewontin, 1965)., In s e a s o n a l l y breeding animals, each female born. ..can., . h y p o t h e t i c a l l y . breed immediately or remain n o n - r e p r o d u c t i v e . u n t i l , the s p r i n g of the f o l l o w i n g y e a r . T h e . l i f e . h i s t o r y s t r a t e g y . u s e d depends upon the e v o l u t i o n a r y past of the animal, i . e . i t s g e n e t i c 150 F i g u r e 23. Onset of events i n two h a b i t a t s of Sorex vagrans. Onset of events in two habitats of Sorex vagrans 7 0 + 6 0 + F » | 4 0 4 3 0 f Mean monthly maximum temperatures Lowland field Forest Onset of events O males become reproductive © females molt • females become reproductive © field young appear •& forest young appear M O 151 p o t e n t i a l , and the environmental cues, which t r i g g e r the p h y s i o l o g i c a l response. In t h i s s e c t i o n ..the r e s u l t s of a u t o p s i e s and aging of lowland g r a s s l a n d shrews, are presented i n c o n j u n c t i o n with examination of. ..factors which may determine f i r s t y e ar.breeding, i n an attempt to analyze the s e l e c t i v e advantages and disadvantages of t h i s l i f e h i s t o r y s t r a t e g y . Young shrews are those i n t h e i r . f i r s t c a l e n d a r year of l i f e , while r e f e r e n c e s to e l d shrews i n d i c a t e they are i n t h e i r second.year. Although the occurrence of f i r s t year breeding was common to a l l three g r a s s l a n d l o c a l i t i e s , the a c t u a l percentages of f i r s t year females breeding were net always c o n s i s t e n t from l o c a l i t y to l o c a l i t y nor, with.the.exception of Serpentine R i v e r , from year t o . year. (Table XVI).,. The data do not r e v e a l why such v a r i a t i o n e x i s t s . . P o s s i b l y the low percentage of young females.breeding.at the L a d n e r . . A i r Base l o c a l i t y i n 1972 was because.of the a p p a r e n t l y l a t e s t a r t i n onset of breeding of o l d females .that year ( F i g . 23). Another p o s s i b l e e x p l a n a t i o n ,concerns the food a v a i l a b i l i t y at the v a r i o u s l o c a t i o n s , which, . as I , have alre a d y s t a t e d , are g e o g r a p h i c a l l y i s o l a t e d from one another.. Inherent g e n e t i c d i f f e r e n c e s , between p o p u l a t i o n s i s yet another p o s s i b l e e x p l a n a t i o n ; I have shown s i g n i f i c a n t morphological d i f f e r e n c e s , e.g. t a i l l e n g t h , body l e n g t h , and the s i z e of t e e t h , t o . e x i s t . The r e s u l t s i n regard to f i r s t .year... breeding ... are... not. s u f f i c i e n t l y c o n s i s t e n t to g i v e t h i s p o s s i b i l i t y more than p a s s i n g No. 1st year females sampled 1972 No. breeding Percent breeding No. 1st year females sampled 1973 No. breeding Percent breeding Westham Island 110 27 25 87 9^ 56 Ladner A i r Base 97 2 2 92 18 20 Serpentine River 108 25 23 1*1 10 2l+ Table XVI. Incidence of f i r s t year females breeding i n grassland habitat. ro 153 c o n s i d e r a t i o n , however. Although the e f f e c t s of. removal sampling from the same areas biweekly cannot.be.discounted, one would expect the i n f l u e n c e t o be comparable..for a l l l o c a l i t i e s , s i n c e the t r a p p i n g pressure.was.equivalent. . . The r e p r o d u c t i v e h i s t o r i e s of a l l 1972 young and o l d females from Westham I s l a n d and Serpentine Biv e r r e v e a l t h a t most pregnancies are c o n f i n e d t o the period... before . J u l y ( F i g . 24A,B) . Young, females which breed are,.sexually a c t i v e s h o r t l y a f t e r becoming independent. Late summer.pregnancies i n young females are v i r t u a l l y absent, .but.the.occurrence of l a c t a t i o n and the presence of enlarged u t e r i are s i g n s of p r e v i o u s r e p r o d u c t i v e a c t i v i t y . L a c t a t i o n a l . . .anoestrus commonly oc c u r s . i n shrews (Brambell, .1935) and i s p a r t i c u l a r l y e v i d e n t i n second year females d u r i n g the . l a t e r p a r t of summer. As the breeding season progresses, an i n c r e a s i n g percentage of females captured a r e . f i r s t year animals while a d e c r e a s i n g percentage ..of these, are r e p r o d u c t i v e . At Westham I s l a n d , .young breeding.females r e p l a c e the o l d very e a r l y i n the season, p a r t i c u l a r l y i n 1973, when more than h a l f the young .females.sampled.were r e p r o d u c t i v e (Fig. 25). Pregnancies i n 1973 occurred throughout the summer months i n young Westham I s l a n d females, i n d i c a t i n g r e l a t i v e l y . f a v o r a b l e c o n d i t i o n s . P o s s i b l y the second year females, having overwintered, are at a p h y s i o l o g i c a l and c o m p e t i t i v e disadvantage when such.... a high p r o p o r t i o n of young females become r e p r o d u c t i v e . . At Ladner A i r Base, i n 1972, when onl y 2% of f i r s t year females Figure 2^ -A. Reproduction of f i r s t and second year females at Westham Island, 1972 KEY I | N o n - b r e e d i n g [fli U terus enlarged H Pregnant V/\ Lac ta t i ng Pregnant & lac ta t ing i c N 1st year females 2nd year females CD c_ ro o 3 3 s o co > - z * D Cn O 155 Figure 2*fB. Reproduction of f i r s t and second year females at Serpentine R i v e r , 1972. (Key as on p. 15I+) 156 F i g u r e 25. Reproduction o f f i r s t and second year females at Westham I s l a n d , 1973 (key as on p. 15M-) 157 bred, many more second year females remained r e p r o d u c t i v e throughout the season ( F i g . 26). Comparison of the seasonal onset . of r e p r o d u c t i v e a c t i v i t y i n g r a s s l a n d and.Research F o r e s t females.shows t h a t the animals from the f o r e s t h a b i t a t have a - s i g n i f i c a n t l y l a t e r s t a r t ( F i g . 23). T h i s and the absence of f i r s t year breeding i n the f o r e s t h a b i t a t suggest. a r e l a t i o n s h i p between the t i m i n g of the commencement of t h e . r e p r o d u c t i v e season and the breeding or l a c k t h e r e o f , i n young. .females, i . e . perhaps only, females born very e a r l y i n the year are a b l e to breed t h a t same season. In s t u d i e s of three European . Sorex (Sorex minutus, Sorex araneus, and S. c a e c u t i e n s ) , Z . P u c e k (1960) concluded t h a t o n l y females from the f i r s t l i t t e r s of the seascn.could become s e x u a l l y mature. The evidence ..given .to.support t h i s c o n c l u s i o n i n c l u d e d the f a c t t h a t the .. majority., .of. young pregnant females were caught e a r l y i n the .season._ He .stated t h a t the animals were aged by tooth a n a l y s i s (though no .data or evidence were presented) and.by the s i z e of the thymus, the i n v o l u t i o n of which was claimed to be c o r r e l a t e d with age. Using the lowland g r a s s l a n d , shrew data, i t was p o s s i b l e , by examining age c l a s s e s of a l l young breeding females, t o t e s t the h y p o t h e s i s . t h a t only .females from . e a r l y l i t t e r s became s e x u a l l y mature i n t h e i r f i r s t . y e a r . The age c l a s s e s of a l l f i r s t year females from . Westham.. I s l a n d . are represented by date of capture, with r e p r o d u c t i v e and non-158 Figure 26. Reproduction o f f i r s t and second year females at Ladner A i r Base, 1972 (key as on p. I5 * f ) . 159 r e p r o d u c t i v e i n d i v i d u a l s i n d i c a t e d ( Fig. 27). The g e n e r a l r a t e of toothwear was c a l c u l a t e d from November of t h e i r f i r s t c a l e n d a r year through September of t h e i r second year (Sect. 2.1). Females which breed i n t h e i r f i r s t year are p r i m a r i l y those born e a r l y i n the year. Most of the p o i n t s r e p r e s e n t i n g r e p r o d u c t i v e l y a c t i v e females, (based on evidence of pregnancy or l a c t a t i o n ) l i e along the tcothwear s l o p e , i n d i c a t i n g they are from a common c o h o r t . P o i n t s r e p r e s e n t i n g r e p r o d u c t i v e l y immature females show a more s c a t t e r e d d i s t r i b u t i o n which suggests t h a t they were born throughout the summer months... Although i t i s apparent from F i g u r e 27 that the young breeding females are not n e c e s s a r i l y from the very f i r s t l i t t e r s , , i t i s h i g h l y improbable t h a t t h e i r own female o f f s p r i n g a t t a i n s e x u a l m a t u r i t y i n t h e i r summer of b i r t h . In the e v o l u t i o n , of optimal r e p r o d u c t i v e s t r a t e g i e s , the age a t f i r s t r e p r o d u c t i o n i s e s s e n t i a l l y dependent on the weighing of two f a c t o r s : 1) the r e l a t i v e success r a t e of young born to e a r l y breeders ( i . e . f i r s t year shrews) _ 2) the p o s t - r e p r o d u c t i v e s u r v i v a l of f i r s t year breeders. . . . . . . I t i s s e l f - e v i d e n t t h a t the s e c o n d . f a c t o r gains i n c r e a s i n g importance as the r e l a t i v e success r a t e of young born to e a r l y breeders goes down. Although i t was not p o s s i b l e to measure the success rate, of f i r s t year breeders, I was able 160 Figure 27. Age c l a s s e s of breeding and non-breeding Westham I s l a n d females during t h e i r f i r s t summer of l i f e . The l i n e represents the r a t e o f toothwear c a l c u l a t e d f o r animals sampled a f t e r p o p u l a t i o n recruitment has ended ( f i g . 18). 161 to make some r e l e v a n t comparisons between r e p r o d u c t i o n i n f i r s t and second year females. . Autopsies of pregnant females i n c l u d e d counts of the number of embryos and t h e i r crown-rump length.... . F i r s t year females had an average of 6.16 ± .53 embryos (range 3 to 8, n=25) and second year females.averaged 5.8 ± .32 embryos (3 to 9, n=71) . Student's t - t e s t showed ..that no s i g n i f i c a n t r e s o r p t i o n of embryos occurs d u r i n g t h e.course.of pregnancy. Thus the average l i t t e r s i z e appears the same.for both f i r s t and second year females. N e s t l i n g m o r t a l i t y . a n d . j u v e n i l e s u r v i v a l were, however, i m p o s s i b l e to measure. The number Of e m b r y o s . i n second.. ... or subsequent pregnancies was measured a g a i n s t the.number in.apparent f i r s t pregnancies ( c h a r a c t e r i z e d by the absence c f ..mammary gland development),, and again no s i g n i f i c a n t d i f f e r e n c e s were found. However, of the 47 females i n 1972 and 1973 which were both l a c t a t i n g and pregnant.again, only.seven, or 15%, were f i r s t year females, whereas, o f . a t o t a l of 335 breeding females sampled, . 131,.or.39%, were i n . t h e i r f i r s t year. Hence, a d i s p r o p o r t i o n a t e l y low percentage of females bred more than once i n s u c c e s s i o n during t h e i r f i r s t . year. The tendency to have only one l i t t e r perhaps i n c r e a s e s the p o s t - r e p r o d u c t i v e s u r v i v a l . o f . b r e e d i n g f i r s t year.females, hence i n c r e a s i n g the p r o b a b i l i t y of s u c c e s s f u l o v e r w i n t e r i n g and breeding again the f o l l o w i n g . s p r i n g . , S t u d i e s of Sor^x araneus a l s o shewed t h a t r a r e l y were young females l a c t a t i n g and pregnant s i m u l t a n e o u s l y (Z. Pucek, 1960). 162 The high degree of v a r i a b i l i t y e v i d e n t i n s e v e r a l aspects r e l a t e d to age at f i r s t r e p r o d u c t i o n suggests t h a t complex p h y s i o l o g i c a l and e n v i r o n m e n t a l . f a c t o r s govern..the r e p r o d u c t i v e a c t i v i t y of shrews. V a r i a t i o n among s i m i l a r , p r o x i m a l , but mutually i s o l a t e d , lowland p l o t s , - i n d i c a t e s t h a t c l i m a t e alone does not determine .either, the seasonal or i n d i v i d u a l onset of r e p r o d u c t i v e a c t i v i t y i n females. Yearrr to-year v a r i a t i o n at one l o c a l i t y decreases.the p o t e n t i a l s i g n i f i c a n c e of g e n e t i c i n f l u e n c e s i n e x p l a i n i n g r e p r o d u c t i v e p a t t e r n s . ...„•. S e v e r a l f a c t o r s lend .support.to the h y p o t h e s i s . t h a t the onset of the r e p r o d u c t i v e season i n shrews i s . t i m e d such t h a t the f i r s t l i t t e r s are born or weaned at. an .optimal time. Within one area, r e p r o d u c t i o n i s more, cr l e s s synchronous among .second year females,; suggesting , an a d a p t i v e . response to some environmental cue.. A high p r o p o r t i o n of the r e s i d e n t female shrews breeding i n the Research For e s t l i v e - t r a p p i n g p l o t , was . b o r n , i n .an. e a r l y l i t t e r of the previous year. The c o i n c i d e n c e . o f the s p r i n g molt of males with the weaning o f . y o u n g , . . i n d i c a t e s . a f a v o r a b l e time, i n terms of energy a v a i l a b i l i t y . .... For shrews, the a v a i l a b i l i t y and q u a l i t y of food i s probably the primary e s s e n t i a l i n determining optimal, c o n d i t i o n s . ...As p r e d a t o r s , they must expend a certain.amount .of energy i n s e a r c h i n g f o r and o b t a i n i n g . f o o d ; t h e . d i f f e r e n t i a l between the energy expended and the energy obtained depends to a 163 l a r g e extent on the s i z e , a c t i v i t y , l o c a t i o n , and c a l o r i f i c content of the prey. A l l these f a c t o r s are s e a s o n a l l y v a r i a b l e , but p r e d i c t a b l e , i n the s o i l i n v e r t e b r a t e s o f any one area. I f then, f i r s t . l i t t e r s are born a t . . t h e o p t i m a l time f o r s u r v i v a l , i t f o l l o w s t h a t . l i t t e r s . born...to females from these f i r s t l i t t e r s , n e c e s s a r i l y have ... lower. r e l a t i v e success r a t e s . Of s i g n i f i c a n c e here i s . t h e p o i n t t h a t the success r a t e s f o r s u c c e s s i v e l i t t e r s . should be..; i n v e r s e l y r e l a t e d t o the degree t o which energy i s . l i m i t i n g . . Hence, v a r i a t i o n i n g u a l i t y or q u a n t i t y o f food c o u l d e x p l a i n both g e o g r a p h i c a l and y e a r l y v a r i a t i o n , i n the . r e p r o d u c t i v e p a t t e r n s seen. The a c t u a l mechanisms.involved. which allow f i r s t year breeding i n g r a s s l a n d shrews are probably r e l a t e d to e a r l i e r warming of temperatures i n .spring, and the concomitant a c t i v i t y of s o i l i n v e r t e b r a t e s . , . P o s s i b l y exposure of e a r l y l i t t e r s to c e r t a i n photoperiods i s a l s o i n v o l v e d . . . . The v i r t u a l absence of f i r s t . y e a r - b r e e d i n g i n .males deserves some comment. In Sorex araneus,.although the s i z e of t e s t e s v a r i e d with season, no sexual maturation was observed i n young males u n d e r . n a t u r a l - c o n d i t i o n s . ( Z . Pucek, 1960). Young animals captured i n the . summer . of ten showed symptoms of se x u a l maturity by their:, second month i n c a p t i v i t y , however (Z. Pucek, 1964; Crowcroft, 1964). Male shrews of the genus B l a r i n a a p p a r e n t l y do..not. breed i n t h e i r f i r s t year e i t h e r , although again, . e a r l y s e x u a l maturation can occur i n c a p t i v i t y (Pearson, 1945). 164 Of 525 f i r s t year males examined f r o m . t h e t h r e e g r a s s l a n d l o c a l i t i e s i n 1972 and 1973, 20 showed evidence of e n l a r g e d t e s t e s and s l i g h t development of s i d e . g l a n d s . Hotably, 11 of these were from Westham I s l a n d in.1973, when ex t e n s i v e r e p r o d u c t i v e a c t i v i t y was a l s o e v i d e n t i n f i r s t year females. although i t i s not known whether these males were spermatogenic,, the evidence shows that they have.at l e a s t the p o t e n t i a l f o r e a r l y sexual maturity. The... f a c t t h a t such occurrences are r a r e i n d i c a t e s t h a t a n y . s e l e c t i v e advantage a s s o c i a t e d with e a r l y breeding i n males . . . i s outweighed by other f a c t o r s , i . e . the c o s t s o f . e n t e r i n g . a n d m a i n t a i n i n g the r e p r o d u c t i v e s t a t e exceed. the r e t u r n s i n r e a l i z e d g e n e t i c r e p r e s e n t a t i o n . Perhaps young males would be unable to compete with second year.males. The a d a p t i v e s i g n i f i c a n c e of f i r s t , y e a r breeding as.-a s t r a t e g y , may be seen i n l i g h t of the..general r e p r o d u c t i v e b i o l o g y of Sorex.. The p r o l i f i c nature of, shrews, i s w e l l documented i n the l i t e r a t u r e . l i t t e r s i n g r a s s l a n d h a b i t a t s average s i x , and a postpartum e s t r u s . p e r m i t s a subsequent l i t t e r to be born a t the time the p r e v i o u s l i t t e r i s weaned. The r e p r o d u c t i v e r a t e goes, up exponentially.... i f . second g e n e r a t i o n shrews breed t h e i r f i r s t . year. ... Using . the r a t i o n a l e of Pearson (1945), i n a s t a b l e system, r e g a r d l e s s of how p r o l i f i c breeders a r e , f o r each, p a i r . of ..shrews present at the beginning of one breeding .season, c n l y ..one p a i r , on the average, w i l l remain at the beginning of the 165 next. Since the g o a l of an i n d i v i d u a l ' s r e p r o d u c t i o n i s not to perpetuate the p o p u l a t i o n or the s p e c i e s , . b u t to maximize the r e p r e s e n t a t i o n of i t s own genes r e l a t i v e , tc, that of o t h e r s i n the p o p u l a t i o n , i n t e n s e r e p r o d u c t i v e e f f o r t w i l l be s e l e c t e d f o r i f i t i n c r e a s e s the chances.of s u r v i v a l to the next breeding p e r i o d f o r that p a r t i c u l a r group of genes. Because second year females have v i r t u a l l y . n o . c h a n c e .of s u r v i v i n g another winter to breed a g a i n , maximal, f e c u n d i t y i s s e l e c t e d f o r as long as i t i s . n o t d e t r i m e n t a l to the s u r v i v a l of t h e i r n e s t l i n g s . For f i r s t year females, however, the p o t e n t i a l gains to be made from breeding have p o t e n t i a l l y heavy c o s t s . I t becomes a ..matter of .what i s o p t i m a l f o r s u r v i v a l of t h e i r . g e n e s . . Should energy be spent to maximize t h e i r own chances of s u r v i v a l , . o r to maximize t h e i r r e p r o d u c t i v e e f f o r t ? Where food i s not l i m i t i n g a n d . m o r t a l i t y . f a c t o r s tend to be density-independent, i t would, be . to.the female *s advantage to breed as scon as p o s s i b l e , p a r t i c u l a r l y i f her chances of o v e r w i n t e r i n g are s m a l l . I f density-rdependent c l i m i t i n g f a c t o r s were predominant, however, a n d . s u r v i v a l of l a t e r l i t t e r s low, then one would ..expect ...a . g r e a t e r p r o p o r t i o n of the a v a i l a b l e energy to be i n v e s t e d i n c o m p e t i t i v e and s u r v i v a l a b i l i t y . The c o n t r a s t i n g s i t u a t i o n s e x i s t i n g between Research F o r e s t and g r a s s l a n d S. vagrans can be . examined using the f o r e g o i n g r a t i o n a l e . S o i l i n v e r t e b r a t e , s t u d i e s show an i n v e r s e r e l a t i o n s h i p between the numbers of s o i l animals and 166 t h e i r biomass (Wallwork, 1970). Richer s o i l s have g r e a t e r biomass and fewer numbers of i n v e r t e b r a t e s . For i n s e c t i v o r o u s p r e d a t o r s such as shrews,. t h i s ..means l a r g e r energy packets and, hence, l e s s energy . s p e n t . i n _ c b t a i n i n g f o o d . S t u d i e s have shown t h a t . i n comparison t o . c o n i f e r o u s f o r e s t s o i l s , g r a s s l a n d s o i l s tend to.support a.,much higher r a t e of energy t u r n o v e r , with the r e s u l t t h a t f o r shrews, food would not l i k e l y be a s t r o n g limiting... f a c t o r Under c o n d i t i o n s of density-dependent, m o r t a l i t y * s p e c i f i c a l l y food l i m i t a t i o n , selection„would f a v o r s t r a t e g y which i n c r e a s e d the i n d i v i d u a l ' s chances, .of s u r v i v a l , e.g. t e r r i t o r i a l i t y i n shrews, at the Research-Forest...In the grassy lowland a r e a s , a p p a r e n t l y the p r e f e r r e d , h a b i t a t °f §. vagrans, the. most e f f e c t i v e s t r a t e g y , i n the f a c e of o v e r a l l high p r o d u c t i v i t y (and subsequent low s u r v i v o r s h i p ) i s maximizing p r o d u c t i v i t y . , I would, .expect .that t e r r i t o r i a l i t y p l a y s a s m a l l e r r o l e i n . t h e g r a s s l a n d .areas, p a r t i c u l a r l y e a r l y i n the season and under f a v o r a b l e food c o n d i t i o n s . . 3. A d a p t a b i l i t y of Shrews The a d a p t a b i l i t y of shrews i s e v i d e n t . i n t h e i r p h y s i o l o g y and morphology as w e l l as i n t h e i r l i f e h i s t o r y s t r a t e g i e s . Apparent p h y s i o l o g i c a l , a d a p t a t i o n s , as i n d i c a t e d by s e a s o n a l changes i n . w e i g h t , . s k u l l h e i g h t , and body l e n g t h , seem aimed a t conserving.energy.during p e r i o d s of d e t e r i o r a t i n g environmental c o n d i t i o n s . These 1 6 7 a d a p t a t i o n s allow shrews to i n h a b i t areas which show s t r o n g s e a s o n a l i t y . . Shrews are p r e d a t o r s s p e c i a l i z e d f o r e x p l o i t i n g s o i l i n v e r t e b r a t e s , a r e s o u r c e .which i s u b i q u i t o u s over a g r e a t v a r i e t y of environmental c o n d i t i o n s , but i s i t s e l f . v a r i a b l e , both s p a t i a l l y and t e m p o r a l l y , i n terms of d i s t r i b u t i o n , abundance, and type. The geographic . . v a r i a b i l i t y , shown . i n morphological and l i f e h i s t o r y c h a r a c t e r i s t i c s i n S. vagrans i s i n d i c a t i v e of a d a p t i v e r e s p o n s e s . t o . v a r y i n g e c o l o g i c a l c o n d i t i o n s and prey a v a i l a b i l i t y . The apparent, f l e x i b i l i t y c h a r a c t e r i s t i c of f e a t u r e s of t h e i r r e p r o d u c t i v e b i o l o g y , e.g. the t i m i n g of onset, number of l i t t e r s , and age , a t f i r s t r e p r o d u c t i o n , a l l o w s shrew .populations, to e x p l o i t o p p o r t u n i s t i c a l l y the energy : a v a i l a b l e to them under. a v a r i e t y of environmental c o n d i t i o n s . , . . S i g n i f i c a n t d i f f e r e n c e s among p o p u l a t i o n s , i n h a b i t i n g ^ g e o g r a p h i c a l l y i s o l a t e d but s i m i l a r h a b i t a t s suggest g e n e t i c d i f f e r e n c e s . o r non-genetic a d a p t i v e responses to s u b t l e environmental d i f f e r e n c e s . 168 GENERAL DISCUSSION L i f e h i s t o r y f e a t u r e s such as t o t a l f e c u n d i t y , maximum l o n g e v i t y , and s t a t i s t i c a l age schedules of r e p r o d u c t i o n and death, are d i r e c t l y r e l a t e d to the r e l a t i v e . s u c c e s s of the p o p u l a t i o n s of a s p e c i e s (Cole, 1954), ^They are, t h e r e f o r e , s u b j e c t to the i n f l u e n c e of n a t u r a l , s e l e c t i o n , as .are p h y s i o l o g i c a l and morphological a t t r i b u t e s . I t r i s apparent from the f o r e g o i n g s e c t i o n s t h a t s t r a t e g i c , morphological, and p h y s i o l o g i c a l responses to e n v i r o n m e n t a l . f a c t o r s are r e a l i z e d both at the s p e c i f i c and p o p u l a t i o n l e v e l s i n shrews. 1. I n t e r - and I n t r a s p e c f i c Comparisons Comparisons at the i n t e r s p e c i f i c l e v e l r e v e a l e d v a r i o u s d i s s i m i l a r i t i e s between b a s i c a l l y s i m i l a r , s p e c i e s , while i n t e r - p o p u l a t i o n s t u d i e s of . Sorex vagrans . i n d i c a t e d i n h e r e n t v a r i a b i l i t y i n l i f e . h i s t o r y . s t r a t e g i e s w i t h i n one s p e c i e s under d i f f e r e n t environmental .regimes,••, . : Comparison of sympatric shrew p o p u l a t i o n s i n the f o r e s t h a b i t a t of the Research F o r e s t . showed... common, .patterns. ..in g e n e r a l l i f e c y c l e ; both Sorex vagrans and Sojcex .obscurus are annual s p e c i e s having_.a r e s t r i c t e d breeding season .which i s delayed u n t i l the second c a l e n d a r . . y e a r of l i f e . D i s p e r s a l of young f o l l o w s weaning, , and t e r r i t o r i e s are e s t a b l i s h e d by autumn. The s u r v i v a l , value of t e r r i t o r y maintenance i s e v i d e n t from the f a c t t h a t a l l breeders are 169 animals t h a t s u c c e s s f u l l y maintained, t e r r i t o r i e s while immature. In both s p e c i e s , t e r r i t o r i a l i t y was seen to break down with the onset of r e p r o d u c t i v e a c t i v i t y , although s i t e attachment was s t i l l e v ident, p a r t i c u l a r l y . , f o r . females. Breeding male S. obscurus tended towards a greater-degree o f nomadism than d i d breeding male S. vagrans, a f a c t o r which may be r e l a t e d t o _ q u a l i t a t i v e d i f f e r e n c e s between s p e c i e s i n c o n t i n u i t y of t h e i r p r e f e r r e d h a b i t a t s . . D i f f e r e n c e s between, s p e c i e s were apparent i n the frequency of occurrence . i n . p a r t i c u l a r h a b i t a t s .at both microgeographic and. geographic . l e v e l s . Perhaps as a response to d i f f e r i n g s e l e c t i v e f o r c e s i n t h e i r r e s p e c t i v e h a b i t a t s , s p e c i e s showed s l i g h t . s i z e d i f f e r e n c e s i n terms of body weight and g e n e r a l robustness of . c r a n i a l . . a n d . d e n t a l f e a t u r e s , S. obscurus being, l a r g e r , i n . a l l , r e s p e c t s . The t i m i n g of seasonal events a l s o d i f f e r e d . . s l i g h t l y , . with S. obscurus g e n e r a l l y l a g g i n g up to two weeks, i n onset of molt and r e p r o d u c t i o n . S i g n i f i c a n t . . . ..variation i n r e p r o d u c t i v e s t r a t e g i e s was e v i d e n t , S. vagrans. having higher f e c u n d i t y by v i r t u e of the g r e a t e r l o n g e v i t y of females. . I n t r a s p e c i f i c comparisons .between S. vagrans p o p u l a t i o n s l i v i n g i n f o r e s t at 1100. f e e t with, those i n h a b i t i n g g r a s s l a n d s near sea l e v e l r e v e a l e d marked d i f f e r e n c e s i n r e p r o d u c t i v e s t r a t e g i e s . The breeding season i n g r a s s l a n d s was r e l a t i v e l y l onger,..with..subsequently higher p o t e n t i a l f o r repeated breeding w i t h i n a season. In 170 a d d i t i o n , the occurrence of breeding among f e m a l e s . i n t h e i r f i r s t summer was common i n g r a s s l a n d , .. implying. . a s i g n i f i c a n t l y higher growth p o t e n t i a l f o r . . . g r a s s l a n d p o p u l a t i o n s r e l a t i v e to t h e i r f o r e s t . counterparts.. Q u a n t i t a t i v e d i f f e r e n c e s i n the occurrence, of f i r s t year breeding between the grassland, p o p u l a t i o n s . a n d . w i t h i n one p o p u l a t i o n from year t o year. i n d i c a t e the. o p e r a t i o n of s u b t l e c o n t r o l l i n g f a c t o r s , perhaps a . r e l a t i o n s h i p between photothermal e f f e c t s and the a v a i l a b i l i t y and a c t i v i t y of prey items. 2. . The E v o l u t i o n of L i f e H i s t o r y S t r a t e g i e s in.Shrews With the i n f o r m a t i o n thus f a r analyzed, .. i t . i s p o s s i b l e to hypothesize c a u s a l f a c t o r s or systems. t h a t . . a f f e c t the l i f e h i s t o r y s t r a t e g i e s o f shrew p o p u l a t i o n s and, furthermore, to d i s c u s s . the . r e l a t i v e . impact..that these f a c t o r s might have on any given l i f e h i s t o r y , t r a i t . . S e v e r a l aspects qt the b i o l o g y of shrews.underline the s i g n i f i c a n t r o l e t h a t energy p l a y s i n shaping l i f e h i s t o r y a d a p t a t i o n s . P r e d a t o r s as a group are.expected to be food-l i m i t e d ( Hairston, ..Smith and Slobodkin, 1960) ;, . t h i s i s understandable from the viewpoint of..their p o s i t i o n . i n the t r o p h i c pyramid. as i n s e c t i v o r o u s p r e d a t o r s , .shrews have reached the t h e o r e t i c a l l o w e r . l i m i t of s i z e for.homeotherms (Pearson, 1948), presumably as.an a d a p t a t i o n f o r . a l l o w i n g access to and m o b i l i t y w i t h i n the m i c r o h a b i t a t of t h e i r prey. The high surface-to-volume r a t i o i m p l i c i t i n such 171 s m a l l body s i z e i s e n e r g e t i c a l l y i n e f f i c i e n t i n a p h y s i o l o g i c a l sense, but e v i d e n t l y i s . compensated f o r i n e c o l o g i c a l e f f i c i e n c y . I t . h a s a l s o been..pointed out (Morrison, Ryser, and Dawe, 1959) t h a t , the .SDA . .. ( S p e c i f i c Dynamic. Action) a s s o c i a t e d with p r o t e i n m e t a b o l i s m . r e s u l t s i n a high p r o p o r t i o n of otherwise waste heat which shrews use i n m a i n t a i n i n g homeostasis. . The d i e t .of... shrews can, t h e r e f o r e , a l s o p a r t i a l l y compensate, f o r the . e n e r g e t i c l i m i t a t i o n s of t h e i r s m a l l . s i z e . .Insects and .other s o i l i n v e r t e b r a t e s are themselves s i z e - l i m i t e d , though, so i n terms of being prey items, -they c o n s t i t u t e . s m a l l energy packets, even f o r shrews., Shrews, t h e r e f o r e , not only pay a p r i c e of e n e r g e t i c i n e f f i c i e n c y i n being small., enough .to e x p l o i t t h i s energy source, but they . must. ..alsc expend c o n s i d e r a b l e time and energy i n o b t a i n i n g i t . . Research on s e a s o n a l v a r i a t i o n , i n the p h y s i o l o g y and morphology.of shrews (Dehnel, 1949; Crowcroft and I n g l e s , 1959; ...Z. Pucek, 1963, 1965, 1970 ; Buchalczyk and Korybska, 1964;.Mezhzherin, 1964; Suida, 1 964; Gebczynski, 1965; .Saure and .Hyvarinen, 1965; Mezhzherin and Helnikova, 1966; - H y v a r i n e n , 1968, 1969a, 1969b, 1969c; H i s s a and Jarkhonen,.1969; Myrcha, 1969; Pasanen, 1971) has brought a t t e n t i o n to .the. .complex a d a p t a t i o n s t h a t . have, evolved, presumably f o r .energy c o n s e r v a t i o n during unfavorable times.of the year. My own data on the t i m i n g of r e p r o d u c t i o n . r e l a t i v e t c molt a l s o support the idea that energy i s l i m i t i n g . The degree to which food i s l i m i t i n g v a r i e s from 172 h a b i t a t t o h a b i t a t , and the e f f e c t of other f a c t o r s , such as c l i m a t e , p r e d a t i o n , and c o m p e t i t i o n , changes p r o p o r t i o n a t e l y . The f o l l o w i n g d i s c u s s i o n w i l l examine s t r a t e g i e s shown by shrews i n response to 1) s i t u a t i o n s i n which food i s the apparent.primary e f f e c t o r of l i f e h i s t o r y s t r a t e g i e s , and 2) food i s l e s s of a l i m i t i n g f a c t o r . 2.1. Energy as a l i m i t i n g f a c t o r The m a n i f e s t a t i o n s of food as a . l i m i t i n g f a c t o r may be viewed from an e v o l u t i o n a r y p e r s p e c t i v e a s . w e l l a s . i n .terms of p o p u l a t i o n b i o l o g y . as p r e d a t o r s which spend most of t h e i r time s e a r c h i n g f o r s m a l l items, shrews f i t . t h e c l a s s i c a l concept of " f i n e - g r a i n e d " s p e c i e s , as-presented.by MacArthur and L e v i n s (1964)...... They u t i l i z e , s e v e r a l , resource types i n the p r o p o r t i o n s i n which they, occur, . with l i t t l e d i s c r i m i n a t i o n or s e l e c t i o n . S p e c i e s w i t h . s u c h . f i n e - g r a i n e d d i f f e r e n c e s a v o i d competition, through ..the.development.of marked h a b i t a t p r e f e r e n c e s (e.g. Lack,.1945; H a i r s t c n , 1949, 1951; MacArthur, .1958; . Johnson, 1966; Hespenheide, 1971 ; Jaeger, 1972), with the r e s u l t t h a t , although twc s p e c i e s s t i l l e x p l o i t the same types of r e s o u r c e s , the p r o p o r t i o n . o f these r e s o u r c e types d i f f e r s . H a b i t a t . . s p e c i a l i z a t i o n s may be g e o g r a p h i c a l or m i c r o g e o g r a p h i c a l , but.the end r e s u l t i s n i c h e d i v e r s i f i c a t i o n . . M i c h i e l s e n (1966), working, with, sympatric shrews, i n Europe,, concluded t h a t the.two s p e c i e s had.about the.same h a b i t a t p r e f e r e n c e , but t h a t times of l i m i t e d food 173 a v a i l a b i l i t y ( i . e . winter) r e s u l t e d i n s e g r e g a t i o n i n t o d i f f e r i n g s t r a t a , Sorex araneus becoming e p i g e a l . and Sorex minutus, hypogeal. . I t was suggested t h a t by v i r t u e of i t s s m a l l s i z e Sorex minutus.could s u s t a i n i t s e l f with the l i m i t e d food a v a i l a b l e i n the s u p e r f i c i a l l i t t e r l a y e r s d u r i n g p e r i o d s of c o l d . Support f o r t h i s . h y p o t h e t i c a l a d a p t i v e f u n c t i o n of s m a l l s i z e c o u l d be found i n . t h e g e o g r a p h i c a l s i z e d i s t r i b u t i o n s of shrew s p e c i e s . i n Europe (Mezhzherin, 1964), with northern r e p r e s e n t a t i v e s , s m a l l e r than southern ones and with the c o l d e s t a r e a s ; i n h a b i t e d , b y the s m a l l e s t s p e c i e s . With moles, i t .was found. ..that. .only the r e l a t i v e l y s m a l l i n d i v i d u a l s . were a b l e . t o .survive a p a r t i c u l a r l y harsh winter ( S t e i n , 1951). In my study of g e o g r a p h i c a l l y s y m p a t r i c S . .vagrans . and S. obscurus, I found s i g n i f i c a n t microgeographic,.. a l l o t o p i c s e p a r a t i o n between s p e c i e s . Sorex vagrans i n h a b i t e d , the wetter, r i c h e r moder s o i l s .and a s s o c i a t e d biogeocenoses, while S. obscurus e x i s t e d predominantly .in the.poorer a c i d i c mor s o i l s . The same types of . h a b i t a t . . s p e c i a l i z a t i o n s . were seen a t a geographic l e v e l . S e v e r a l r e s e a r c h e r s . .(Ealquest, 1941; C l o t h i e r , 1955; F i n d l e y , 1955; Buckner, 1966;. Spencer and P e t t u s , 1966; L. N. Brown, 1967; Hennings, 1970) .have found S. vagrans to be. l i m i t e d .to. moist h a b i t a t s . of streamside, marshland, meadows and along r i v e r . c o u r s e s , whereas S. obscurus i s more t o l e r a n t of d r i e r . s i t e s , such as i h i l l s i d e s and dry f o r e s t . ( F i n d l e y , op. cit.;.„Spencer and P e t t u s , op. c i t . ; Brown, op. . c i t . ; Hennings, op. c i t . ) . 171 The occurrence of contiguous, a l l o p a t r y i n . the d i s t r i b u t i o n of two c l o s e l y r e l a t e d s p e c i e s i s .often taken as evidence f o r c o m p e t i t i v e e x c l u s i o n , p a r t i c u l a r l y when broadening of e c o l o g i c a l t o l e r a n c e s occurs i n areas of_ nonr o v e r l a p (Mayr, 1966). H u t c h i n s o n 1 s . (1957) i n c l u d e d niche model p r o v i d e s f o r the c o e x i s t e n c e of .potential... - competitors when the c o m p e t i t i v e l y s u p e r i o r s p e c i e s has a.narrower, or more s p e c i a l i z e d niche i n c l u d e d . i n the.niche of the other s p e c i e s . The c o m p e t i t i v e l y i n f e r i o r s p e c i e s , _ i n . t u r n , .has wider e c o l o g i c a l t o l e r a n c e . D i s t r i b u t i o n s may thus .be e x p l a i n e d by the combined i n f l u e n c e , of..competition, and p h y s i c a l aspects of the environment (e.g...moisture., .or . s o i l t y p e ) . Such has been documented f o r many.species p a i r s (e.g. pocket gophers, Dennerly, 1959; -barnacles, ..Connell, 1961; m i c r o t i n e s , M o r r i s , 1969; c r a y f i s h , Bevbjerg, 1970; salamanders, Jaeger, 1972) .... Hennings (1970) has pointed out t h a t , i n the.absence o f S. vagrans east of t h e . C o n t i n e n t a l D i v i d e , S . cbscurus occupies a wider v a r i e t y of h a b i t a t s , i n c l u d i n g hydrosere communities. He suggests :that the a l l o t b p i c d i s t r i b u t i o n o f S. obscurus and S. vagrans i s a t l e a s t _ i n . p a r t a t t r i b u t a b l e to e x c l u s i o n of S. obscurus by S. vagrans.in m o i s t . h a b i t a t s . C o n s i d e r i n g the " f i n e - g r a i n e d " c h a r a c t e r o f . d i f f e r e n c e s between the t«o s p e c i e s , i t . i s not s u r p r i s i n g . t h a t i n t e r s p e c i f i c c o m p e t i t i o n would occur., where .both, species..are sympatric, and t h a t marked h a b i t a t d i f f e r e n c e s have evolved 175 as an outcome of such c o m p e t i t i o n . My own data on i n t e r s p e c i f i c t e r r i t o r i a l i t y suggests t h a t each s p e c i e s i s b e t t e r "able to compete i n . i t s own p r e f e r r e d h a b i t a t type. Obviously, an i n t e r a c t i o n between i n t e r s p e c i f i c c o m p e t i t i o n and i n n a t e "preferences'." f o r c e r t a i n , h a b i t a t - c o n d i t i o n s determines the microgeographic d i s t r i b u t i o n s of S. vagrans and S. obscurus where they are sympatric. The .question of which f a c t o r p l a y s a l a r g e r r o l e . i s . o f g r e a t i n t e r e s t and bears on the r e l a t i o n s h i p and degree of .overlap between the fundamental and r e a l i z e d .niches of..both s p e c i e s i n t h i s area. H y p o t h e t i c a l l y , i f removal of S. obscurus. from. my l i v e - t r a p p i n g p l o t d i d not a f f e c t the. d i s t r i b u t i o n o f S. vagrans, but removal of S. vagrans. r e s u l t e d i n the expansion of S. obscurus i n t o t h e v a c a t e d . a r e a , then i t might be concluded t h a t S. vagrans excluded.S. obscurus and had both i t s fundamental and r e a l i z e d niche i n c l u d e d i n the fundamental niche of S. obscurus. I f removal of e i t h e r s p e c i e s d i d l i t t l e . t o a f f e c t the d i s t r i b u t i o n of t h e . o t h e r , the i n d i c a t i o n would be t h a t h a b i t a t preference and perhaps ..... concomitant a d a p t a t i o n s played a l a r g e r role..., One such a d a p t a t i o n might be the more robust and.slower-wearing t e e t h c h a r a c t e r i s t i c of S. obscurus, that., may r e p r e s e n t ..an a d a p t a t i o n f o r p r e y i n g upon a lower p r o p o r t i o n . of s o f t r bodied i n v e r t e b r a t e s . fiemoval experiments, done i n areas of microgeographic a l l o p a t r y , would a i d i n the understanding of the f o r c e s t h a t have operated i n . the. e v o l u t i o n and s p e c i a t i o n of the genus. At the geographic l e v e l , h a b i t a t 176 comparisons may be made i n re g i o n s where each s p e c i e s occurs a l o n e . , -The e x i s t e n c e of i n t e r s p e c i f i c t e r r i t o r i a l i t y . i m p l i e s a g g r e s s i v e resource c o m p e t i t i o n , f o r . there .would be no reward f o r the energy expended i n t e r r i t o r y maintenance i f some resource were not gained. (MacArthur, 1972).. Assuming t h a t the l i m i t i n g r e s o u r c e i n v o l v e d i s . food,..the. a d a p t a t i o n s which make one s p e c i e s c o m p e t i t i v e l y s u p e r i o r over a c l o s e l y r e l a t e d congener i n a given h a b i t a t are not. o f t e n , obvious. B e h a v i o r a l and mor p h o l o g i c a l d i f f e r e n c e s between s p e c i e s .can be compared and c o n t r a s t e d w i t h . d i f f e r e n c e s . i n . h a b i t a t . a n d resource types i n hopes of f i n d i n g c o n v i n c i n g , c o r r e l a t e s . However, I do not doubt t h a t many of t h e . b a s i c . d i f f e r e n c e s are at the l e v e l of the c e n t r a l , n e r v o u s system and.therefore not measureable. C o n s i d e r i n g the s i g n i f i c a n c e . , o f f o o d . i n the a d a p t i v e b i o l o g y of shrews, the d i s t r i b u t i o n , abundance, and composition of the , i n v e r t e b r a t e ..faunas, c h a r a c t e r i s t i c o f the s o i l types i n h a b i t e d by S. vagrans and S. obscurus r e s p e c t i v e l y may pl a y a. c r i t i c a l r o l e . . i n the r e l a t i v e s u i t a b i l i t y of the h a b i t a t f o r each s p e c i e s . To my knowledge, no a p p r o p r i a t e s t u d i e s of . . s o i l .fauna have been done i n t h i s r e g i o n . .However, because. the b a s i c s o i l types have r e l a t e d b i o l o g i c a l c h a r a c t e r i s t i c s , g e n e r a l i z a t i o n s can be made and a p p l i e d to the shrew h a b i t a t s I have s t u d i e d . A ..large p a r t of . t h e c h a r a c t e r i s t i c s Of the i n v e r t e b r a t e fauna of any given s o i l type i s determined by v a r i o u s f a c t o r s , such as c l i m a t e and 177 pH c o n d i t i o n s , which i n f l u e n c e the nature of decomposition (Wallwork, 1970). C o n d i t i o n s of low pH are c h a r a c t e r i s t i c of mor s o i l s and f a v o r decomposition by f u n g a l a c t i v i t y , which i n t u r n supports l a r g e numbers.of.microarthropods A c a r i (mites), Collembola ( s p r i n g t a i l s ) , and i n s e c t l a r v a e . Carnivorous a r t h r o p o d s , such as ce n t i p e d e s , . s p i d e r s , and s t a p h y l i n i d and c a r a b i d b e e t l e s are w e l l represented i n .mor s o i l s , along with t h e i r microarthropod prey. In the moder s o i l s , where S. vagrans occurs i n the .Research F o r e s t , . the microarthropod fauna i s supplemented..with .a g r e a t e r r e p r e s e n t a t i o n o f i n s e c t s and t h e i r l a r v a e . These, i n . t u r n , add o r g a n i c m a t e r i a l t o the s o i l and h e l p , to decrease the a c i d i t y . B a c t e r i a l decomposers have increased.importance i n moder s o i l over mor s o i l s . I t can .be.generalized from the comprehensive woodland s o i l study by Bornebusch. (1930) t h a t an i n v e r s e r e l a t i o n s h i p , b e t w e e n number and. biomass of s o i l fauna e x i s t s ; r i c h e r s o i l s support g r e a t e r biomass but fewer numbers of invertebrate's. The above r e l a t i o n s h i p has s i g n i f i c a n t . . i m p l i c a t i o n s concerning the b i o l o g y of shrews as .predators and the e v o l u t i o n of l i f e h i s t o r y s t r a t e g i e s . I f i n r i c h e r s o i l s prey i s present both i n g r e a t e r biomass a n d . i n . l a r g e r packets, energy becomes l e s s l i m i t i n g i n an ,ab s o l u t e ..sense as well as i n terms of the energy which . the,shrew must expend i n f o r a g i n g . T h e o r e t i c a l l y , one should f i n d t h a t the t o t a l energy a l l o c a t e d t o r e p r o d u c t i v e . a c t i v i t i e s , i n c r e a s e s as the l i m i t i n g e f f e c t of food decreases. As long as the 178 f a c t o r s l i m i t i n g the growth of a p o p u l a t i o n are not s t r o n g l y density-dependent, i n d i v i d u a l s . w i t h i n c r e a s e d . , r e p r o d u c t i v e e f f o r t have a s e l e c t i v e advantage.,.This i s . p a r t i c u l a r l y t r u e under c o n d i t i o n s of high d e n s i t y r i n d e p e n d e n t m o r t a l i t y . In the e c o l o g i c a l l i t e r a t u r e the t h e o r e t i c a l aspects., of these c o n s i d e r a t i o n s have been discussed._within, the concept of r and K s e l e c t i o n (MacArthur, 1962; Cody,....1966;.MacArthur and Wilson, 1967; H a i r s t o n , T i n k l e and Wilbur, .1970; Pianka, 1970; Roughgarden, 1971; Gadgil.and S o l b r i g , 1972) The concept of r and K s t r a t e g i e s , h a s meaning.only on.a comparative b a s i s (Gadgil. and S o l b r i g , 1972).. In t h i s r e gard, an r s t r a t e g i s t devotes a l a r g e r f r a c t i o n . o f the a v a i l a b l e r e s o u r c e s to r e p r o d u c t i o n than does., a r e l a t e d K s t r a t e g i s t . K s e l e c t i o n , or s e l e c t i o n . f or .non-rreprcductive a c t i v i t i e s (e.g. t e r r i t o r i a l i t y , f a t d e p o s i t i o n , or predator avoidance) a t the expense of r e p r o d u c t i v e , a c t i v i t i e s , , i s advantageous on l y i f i t maximizes , o v e r a l l . . f i t n e s s by enhancing r e p r o d u c t i o n at. some l a t e r , s t a g e . i n the. l i f e h i s t o r y . The amount of energy devoted.to. s u c h . a c t i v i t i e s depends upon the c o s t and p r o f i t , . d i f f e r e n t i a l . , Under c o n d i t i o n s of food l i m i t a t i o n s .and. densityrdependent p o p u l a t i o n r e g u l a t i o n , K s e l e c t i o n o p e r a t e s . t o . i n c r e a s e the s u r v i v a l value of the i n d i v i d u a l . . .by....improving i t s c o m p e t i t i v e a b i l i t i e s . G e n e r a l l y , K s e l e c t i o n . i s . . s e l e c t i o n f o r q u a l i t y , which i n t u r n becomes manifest i n . r e p r o d u c t i v e success. Where density-independent.. f a c t o r s have .an i n c r e a s e d e f f e c t i n p o p u l a t i o n r e g u l a t i o n , however, and 179 causes of m o r t a l i t y are l e s s d i s c r i m i n a t i n g or p r e d i c t a b l e (e.g. f l o o d i n g , f r e e z i n g , d e s s i c a t i o n ) , t h e n those i n d i v i d u a l s which put out the g r e a t e s t , r e p r o d u c t i v e e f f o r t w i l l have the edge s t a t i s t i c a l l y . As with , the., terms r and K s e l e c t i o n , density-dependent and.density independent a r e . n o t a b s o l u t e terms. They r e f e r to a continuum o f . e f f e c t s and are u s e f u l mainly i n . a comparative context. Because the concept of r a n d K s e l e c t i o n . i s . . a . f a i r l y n a t u r a l c a t e g o r i z a t i o n of a l l n a t u r a l s e l e c t i o n , i t . i s convenient to use i t i n a n a l y z i n g the r e l a t i o n s h i p , between a s s o c i a t i o n s of i n t e r r e l a t e d b i o l o g i c a l _ t r a i t s . . and e c o l o g i c a l f a c t o r s i n shrew p o p u l a t i o n s . V a r i o u s a d a p t a t i o n s may be s e e n . i n the c o n t e x t . o f how they a f f e c t the t o t a l f i t n e s s of the i n d i v i d u a l and why they,might be o f s e l e c t i v e advantage. Assuming the g e n e r a l i z a t i o n s on freguency, abundance and d i s t r i b u t i o n o f . s o i l i n v e r t e b r a t e s may be a p p l i e d to the h a b i t a t s the shrews used.in.my study, we have the s i t u a t i o n where, t h e o r e t i c a l l y , food becomes l e s s l i m i t i n g as we go from the ..forest . h a b i t a t of S. obscurus, to the f o r e s t h a b i t a t of S. vagrans, and f i n a l l y t o the g r a s s l a n d h a b i t a t of S. vagrans, where a much g r e a t e r f a u n a l biomass and higher r a t e of energy, turnover are c h a r a c t e r i s t i c of the m u l l - l i k e , moder s o i l s t h e r e (Wallwork, 1970). The r e l a t i o n s h i p between v a r i o u s l i f e h i s t o r y t a c t i c s of shrews and the e c o l o g i c a l parameters a s s o c i a t e d with t h e s e . t h r e e h a b i t a t . t y p e s i s diagrammatically represented i n F i g u r e 28. The f o l l o w i n g 180 Figure 28. Summary of l i f e h i s t o r y t a c t i c s i n r e l a t i o n to e c o l o g i c a l f a c t o r s i n three h a b i t a t s of Sorex vagrans and Sorex obscurus. S o i l type: Increasing r selection (Increasing e f f e c t of density-independent mortality factors) . • — . : ». ' Increasing length of breeding season Increasing s o i l pH —• — • Mor Moder Forest: S. obscurus habitat Forest: S. vagrans habitat M u l l - l i k e moder Grassland: S. vagrans habitat a. generally one, but sometimes two l i t t e r s . a. generally two, up to three l i t t e r s . a. up to three, maybe four l i t t e r s . b. t e r r i t o r i a l during f i r s t year b. t e r r i t o r i a l during f i r s t year b. s t r i c t t e r r i t o r i a l i t y doubtful. c. breed only i n second year c. breed only i n second year c. up to 50% of f i r s t year females breed. w >* o M -H O - P •P W OJ -H •H U JQ <U •P Q) O <H a •ri t-t Increasing prey size and biomass Increasing food a v a i l a b i l i t y 181 s e c t i o n s d i s c u s s the r e l a t i o n s h i p s i n more d e t a i l . 3. E c o l o g i c a l Strategy of F o r e s t - i n h a b i t i n g Shrews _ S e v e r a l l i f e h i s t o r y a d a p t a t i o n s of shrews suggest the s e a s o n a l l y l i m i t i n g nature of food a v a i l a b i l i t y i n the f o r e s t . These i n c l u d e the r e l a t i v e t i m i n g of melt and r e p r o d u c t i o n , the e s s e n t i a l l y synchronous... onset o f r e p r o d u c t i o n w i t h i n each sex, and s e a s o n a l d i f f e r e n c e s i n s u r f a c e a c t i v i t y . The s t r o n g e s t i n d i c a t o r . o f the temporally l i m i t i n g e f f e c t s of food i s the intra-..and. i n t e r s p e c i f i c t e r r i t o r i a l i t y d i s p l a y e d by Sorex obscurus ..and. S.....vagrans. C l e a r l y , t e r r i t o r i a l "behavior i s .a m a n i f e s t a t i o n of c o m p e t i t i o n f o r r e s o u r c e s which are l i m i t i n g , in.... a. densityr-dependent manner. As such, it.may be viewed as a r e s u l t . o f K s e l e c t i o n , or s e l e c t i o n f o r i n c r e a s e d c o m p e t i t i v e . a b i l i t y . The establishment of t e r r i t o r i e s ..during the. f i r s t summer of l i f e and the abandonment of s t r i c t t e r r i t o r i a l i t y d u r i n g the r e p r o d u c t i v e season appear, to be. mechanisms whereby p o p u l a t i o n d e n s i t i e s are r e g u l a t e d e a r l y i n . t h e . l i f e c y c l e . C o n s i d e r i n g the p r o l i f i c nature, of shrews and. the high energy demands ..of the i n d i v i d u a l , . i t . seems . reasonable t h a t d e n s i t y r e g u l a t i o n a t . an ..early . stage prevents o v e r u t i l i z a t i o n of r e s o u r c e s . N i c h o l s o n . {1950) . h a s e x p e r i m e n t a l l y shown the e f f e c t s o f . c r o w d i n g . a n d food l i m i t a t i o n i n the b l o w f l y l u c i l i a c u ^ r i n a . His . r e s u l t s ( F i g . 29) are g e n e r a l l y a p p l i c a b l e to many animals t h a t combine high r e p r o d u c t i v e r a t e s with a delay between 182 Figure 29. Relationship between number of young and adults produced (redrawn from Nicholson, 1950). 182a Optimal density of young NUMBER OF YOUNG 183 r e p r o d u c t i o n and the a p p l i c a t i o n of the a p p r o p r i a t e d e n s i t y -dependent check. In the case of shrews,..winter .food, l e v e l s serve as the delayed density-dependent r e g u l a t i n g f a c t o r . T h e o r e t i c a l l y , an e s p e c i a l l y , high d e n s i t y .of.shrews c o u l d exhaust the nonrenewable food.supply e a r l y i n . t h e . s e a s o n so t h a t v i r t u a l l y none c f the p o p u l a t i o n .survives to the r e p r o d u c t i v e season. The p r e d i c t a b i l i t y of s e a s o n a l changes i n prey a v a i l a b i l i t y could.work e v o l u t i o n a r i l y i n s e l e c t i n g f o r t e r r i t o r i a l behavior at a time o f . f o o d abundance., The g r e a t e r the r e g u l a r i t y and p r e d i c t a b i l i t y of ~a given unfavorable environmental. ..or b i o l o g i c a l . . phenomenon,... the s t r o n g e r w i l l be the s e l e c t i v e pressure f o r an organism to i n c r e a s e i t s f i t n e s s by d i v e r t i n g some of i t s resources to the a l l e v i a t i o n of unfavorable e f f e c t s . (Gadgil.and. S o l b r i g , 1972). In the case of the. h y p o t h e t i c a l , . n o n - r t e r r i t o r i a l p o p u l a t i o n , any i n d i v i d u a l t h a t d i v e r t e d some.of.its summer energy budget i n t o t e r r i t o r y defence...would be.more...likely.to s u r v i v e an o v e r u t i l i z a t i o n of f o o d . r e s o u r c e s because.fewer shrews would be u t i l i z i n g r e s o u r c e s i n . i t s f o r a g i n g a r e a . An important e f f e c t of. t e r r i t o r i a l i t y i s . d e n s i t y r e g u l a t i o n . , Wynne-Edwards (1962, 1963), however, presents t e r r i t o r i a l i t y as an example of. a ..mechanism evolved, by p o p u l a t i o n s so t h a t the a v a i l a b l e r e s o u r c e s . are..not e x p l o i t e d beyond the c a r r y i n g c a p a c i t y . o f , the environment.. The concept of group s e l e c t i o n i s an i n h e r e n t part of t h i s hypothesis and i s a s u b j e c t of c o n t r o v e r s y i n .the e v o l u t i o n a r y l i t e r a t u r e ( J . L . Brown, 1964, 1969; 184 J . M. Smith, 1964; Crook, 1965; l a c k , .1966; Wiens, 1966; W i l l i a m s , 1966). While t e r r i t o r i a l i t y may have the e f f e c t of d e n s i t y r e g u l a t i o n i n shrew p o p u l a t i o n s , I b e l i e v e i t both unnecessary and improper.to name d e n s i t y r e g u l a t i o n as the s e l e c t i v e f o r c e ,or c a u s a l f a c t o r f o r the e v o l u t i o n .of t e r r i t o r i a l i t y . The . e v o l u t i o n a r y . . mechanism of t e r r i t o r i a l i t y i s adequately e x p l a i n e d . by . . i n d i v i d u a l s e l e c t i o n f o r c o m p e t i t i v e s u p e r i o r i t y , r e g a r d l e s s of what e f f e c t such s e l e c t i o n has a t the p o p u l a t i o n l e v e l . , . . .. A q u e s t i o n which may.be asked a t . t h i s p o i n t . i s whether t e r r i t o r i a l behavior i n shrews i s g e n e t i c a l l y determined.as a f u n c t i o n of age or as a response to c e r t a i n environmental f a c t o r s . Assuming i t i s a K s e l e c t e d mechanism.to enhance c o m p e t i t i v e a b i l i t i e s f o r the i n d i v i d u a l l i v i n g under c o n d i t i o n s of density-dependent m o r t a l i t y , . I... t h i n k i t reasonable to conclude t h a t t e r r i t o r i a l behavior would become p r o p o r t i o n a t e l y l e s s s i g n i f i c a n t as the i n f l u e n c e of density-dependent m o r t a l i t y f a c t o r s gave way t o . t h a t , of density-independent m o r t a l i t y f a c t o r s . To take an extreme example, under c o n d i t i o n s of h i g h l y u n p r e d i c t a b l e d e n s i t y r independent m o r t a l i t y and v i r t u a l l y ^ u n l i m i t e d .food a v a i l a b i l i t y , one would expect very . l i t t l e . energy to be a l l o c a t e d t o t e r r i t o r i a l i t y . Therefore,.depending on.the environmental c o n t r o l s of a given h a b i t a t . . . and t h e i r " p r e d i c t a b i l i t y " based on the p r e v i o u s . e x p e r i e n c e of the l o c a l gene p o o l , shrew p o p u l a t i o n s should.show v a r y i n g , but i n n a t e , responses to f a c t o r s such as d e n s i t y and food 185 a v a i l a b i l i t y . . In s t r o n g l y s e a s o n a l , temperate environments i n which the l i m i t i n g e f f e c t s of food are preceded by a time l a g , t e r r i t o r i a l behavior i n immature i n d i v i d u a l s during the p e r i o d of food abundance i s . l i k e l y to be an i n t r i n s i c p a r t of the dynamics of the p o p u l a t i o n . 4. E c o l o g i c a l S t r a t e g y of G r a s s l a n d - i n h a b i t i n g Shrews Grassland and Research F o r e s t shrews may be. compared with r e s p e c t to r and K . selected... a t t r i b u t e s , and t h e i r e c o l o g i c a l i m p l i c a t i o n s . That.lowland g r a s s l a n d shrews are r s e l e c t e d r e l a t i v e t o shrews.from f o r e s t .habitat i s e v i d e n t from r e p r o d u c t i v e h i s t o r i e s a l r e a d y examined. I n . s h o r t , the r e p r o d u c t i v e r a t e of grassland.shrews i s higher than t h a t of Research F o r e s t shrews., of the same s p e c i e s . 7 The breeding season i s longer i n , t h e lowland, g r a s s l a n d , ;.so. mere . . l i t t e r s per female are p o s s i b l e . The phenomenon. ..of . f i r s t .year breeding i n these g r a s s l a n d females e f f e c t i v e l y shortens the g e n e r a t i o n time. Lewcntin (1965) has shown t h a t the p o p u l a t i o n growth r a t e , r , i s h i g h l y s e n s i t i v e to a decrease i n age at f i r s t r e p r o d u c t i o n . . ... ..... I have found at most.only about 50%.of the f i r s t year females i n a p o p u l a t i o n breeding and v i r t u a l l y no f i r s t year males breeding. F i r s t year breeding was..correlated with apparent time of b i r t h (based on tooth-wear), and i f the c o r r e l a t i o n has b a s i s i n r e a l i t y , i n t e r p r e t a t i o n s cf l i f e h i s t o r y s t r a t e g i e s of g r a s s l a n d shrews becomes.complicated by the occurrence of d i f f e r e n t t a c t i c s depending upon 186 e a r l i n e s s of b i r t h . In a l l l i k e l i h o o d , breeding f i r s t year females cannot a l s o defend t e r r i t o r i e s . . The l a c k .of t e r r i t o r i e s i n f i r s t year breeding females c o u l d a d v e r s e l y a f f e c t t h e i r winter s u r v i v a l and h e n c e , t h e i r r e p r o d u c t i v e success the f o l l o w i n g year, depending.on the s i g n i f i c a n c e . o f the r o l e of t e r r i t o r i a l i t y i n g r a s s l a n d . p o p u l a t i o n s . I f the s i g n i f i c a n c e of defending.an area l i e s . i n the f o o d . v a l u e . o f t h a t a r e a , then the advantages of t e r r i t o r i a l i t y , should be p r o p o r t i o n a l to the degree to which .food . i s . l i m i t i n g . Although g e n e r a l i n v e r t e b r a t e biomass . i n g r a s s l a n d exceeds t h a t of woodland s o i l s , winter a v a i l a b i l i t y , may .also decrease to the extent t h a t food becomes l i m i t i n g . , The i n c r e a s e d abundance.of avian p r e d a t o r s i n g r a s s l a n d , h a b i t a t s c o n s t i t u t e s another source o f . density-dependen.t.mortality, although i t i s g e n e r a l l y the rodent p o p u l a t i o n s which comprise the bulk of d i e t f o r b i r d s of prey (Maser, 1965; Smith, Wilson, and Frost,:1972;.Vernon, .1972) . I f t e r r i t o r i a l i t y p l a y s a r o l e i n ..the. g r a s s l a n d h a b i t a t s , the areas apparently, a l s o support a tremendous number of t r a n s i e n t s . In.,1972 the numbers of shrews, taken from each of the g r a s s l a n d . p l o t s biweekly diminished only s l i g h t l y , r e g a r d l e s s of season (although.. l e s s ..mortality occurred i n the c o l d , wet time of y e a r ) . Over 400 have.been e x t r a c t e d from each area. In c o n t r a s t , a g r i d s i m i l a r l y trapped i n an area of the Research F o r e s t (logged,, and seeded with grasses) was v i r t u a l l y trapped cut (approximately 75 t o t a l ) w i t h i n three months. 187 Density-independent m o r t a l i t y f a c t o r s , may play a l a r g e r r o l e i n lowland f i e l d s than i n f o r e s t , h a b i t a t s . .... A l l t h r e e g r a s s l a n d s i t e s are s u b j e c t to p e r i o d i c . f l o o d i n g , d u r i n g mild, but wet, w i n t e r s . Although s h r e w s c a n . a p p a r e n t l y s u r v i v e moderate and p a r t i a l f l o o d i n g . . o f . t h e i r h a b i t a t (based on my experiences l i v e - t r a p p i n g f o r m i c r o t i n e s i n p a r t i a l l y f l o o d e d f i e l d s where the t r a p s t h a t were n e a r l y f l o a t i n g captured shrews), heavy f l o o d i n g . would. no doubt cause high m o r t a l i t y . . During severe..winters, . the. g r a s s l a n d s o i l , o f t e n unprotected by snow. or..dense v e g e t a t i o n , , can become f r o z e n to a depth of s e v e r a l i n c h e s . This.cculd.make most s o i l i n v e r t e b r a t e s i n a c c e s s i b l e t o . f o r a g i n g shrews. Hence, winter food a v a i l a b i l i t y . i s probably h i g h l y u n p r e d i c t a b l e i n the g r a s s l a n d s . .. E v i d e n t l y , both density-dependent ... and. . d e n s i t y -independent m o r t a l i t y can and do e x e r t s e l e c t i v e . p r e s s u r e on the l i f e h i s t o r y s t r a t e g i e s o f g r a s s l a n d shrews... Although. r and K s e l e c t i o n i s a u s e f u l and convenient concept,, other e g u a l l y p l a u s i b l e e x p l a n a t i o n s should not be.overlooked. Thus, the occurrence of f i r s t year breeding . i n . g r a s s l a n d shrew p o p u l a t i o n s may. not only, be i n t e r p r e t e d as. r s e l e c t i o n , i n d i c a t i v e of l e s s density-dependent m o r t a l i t y r e l a t i v e to density-independent m o r t a l i t y , but. i t may.also be e x p l a i n e d by higher temperatures r e s u l t i n g i n an e a r l i e r s t a r t to the breeding season r e l a t i v e to shrews.from f o r e s t h a b i t a t . The e a r l i e r s t a r t may allow g r a s s l a n d females from 188 f i r s t l i t t e r s to become r e p r o d u c t i v e j u s t because, they are exposed to the c o r r e c t environmental cues (e.g. photothermal e f f e c t s ) . The two e x p l a n a t i o n s are of course.not.mutually e x c l u s i v e . I f f i r s t year breeding were simply a . f u n c t i o n of p h y s i o l o g i c a l exposure to e a r l y environmental . c o n d i t i o n s , and i f i t were a d a p t i v e , one would.expect s e l e c t i o n f o r e a r l y breeding i n second year females. ..The adaptiveness .of f i r s t year breeding would i n t u r n depend o n . t h e . d e n s i t y -dependent and independent e f f e c t s of the b i o t i c and a b i o t i c environment. L i v e - t r a p p i n g s t u d i e s o f . g r a s s l a n d p o p u l a t i o n s are.now needed i n order to determine the l i f e h i s t o r y , consequences of the ways i n which v a r i o u s segments.of the p o p u l a t i o n a p p o r t i o n t h e i r energy r e s o u r c e s . A. number of ques t i o n s may be asked i n l i g h t of what we now. know. What are the r e p r o d u c t i v e h i s t o r i e s of breeding f i r s t . y e a r females, when were they born, how.many times do. they ... breed, and. how does breeding a f f e c t t h e i r s u r v i v a l and l o n g e v i t y ? What are the r e l a t i v e r o l e s o f t e r r i t o r i a l i t y among.nonrreproductive . and r e p r o d u c t i v e f i r s t year animals,, and what .types..of i n t e r a c t i o n s occur between them? What are the p o p u l a t i o n parameters i n ge n e r a l of g r a s s l a n d p o p u l a t i o n s and.how do these compare with those of f o r e s t populations?.. What .. are the apparent l i m i t i n g f a c t o r s . o f g r a s s l a n d p o p u l a t i o n s , and how are these r e f l e c t e d i n g e n e r a l l i f e . h i s t o r y , s t r a t e g i e s ? In c o n j u n c t i o n with the l a s t q u e s t i o n , s o i l i n v e r t e b r a t e surveys should be done on a se a s o n a l b a s i s t c measure 189 changes which occur i n d i s t r i b u t i o n , abundance and.type. The same i s needed f o r f o r e s t s o i l s , i n .order .to compare q u a n t i t a t i v e l y the food r e s o u r c e s of S. yjigrans and S. obscurus h a b i t a t types. 5. E v o l u t i o n a r y Ecology and Shrew Systematics In essence, an. organism i s s i m p l y . a mechanism f o r o b t a i n i n g energy and re p r o d u c i n g the g e n e t i c components which determine i t s a t t r i b u t e s . These a t t r i b u t e s ..are complex, i n t e r r e l a t e d a d a p t a t i o n s which.allow.the organism to f u n c t i o n i n i t s p h y s i c a l and b i o t i c . environment. . They are the phenotype of the organism, upon which s e l e c t i o n a c t s . The o p e r a t i o n of s e l e c t i o n through time, r e s u l t s . i n s e l e c t i o n of t h e i r g e n e t i c d e t e r m i n a n t s - r e v o l u t i o n a r y change c o n s i s t s of q u a n t i t a t i v e and q u a l i t a t i v e , c h a n g e s . i n gene pools . ..... ....... At the heart, of e v o l u t i o n l i e s t h e . e c o l o g i c a l r e l a t i o n s h i p . What i s adapt i v e o r . advantageous f o r . a n organism depends upon i t s environment, and, furthermore, the ad a p t a t i o n s an organism e x h i b i t s depend upon i t s unique environmental and g e n e t i c h i s t o r y . ... ...... In pursuing the l i f e h i s t o r y a d a p t a t i o n s of sympatric s p e c i e s and p o p u l a t i o n s of s i n g l e species, i n d i f f e r e n t h a b i t a t s , t h i s study has demonstrated the.,: p o t e n t i a l ..of environmental f o r c e s ( p h y s i c a l , extrademe, and intrademe) i n molding the b i o l o g y of shrew p o p u l a t i o n s . Comparisons of l i f e h i s t o r y phenomena between the S. vagrans and 190 S. obscurus p o p u l a t i o n s at the Research F o r e s t showed more s i m i l a r i t y than between p o p u l a t i o n s of f o r e s t and g r a s s l a n d S. vagrans. Even comparisons of... g r a s s l a n d .. p o p u l a t i o n s . of §• vagrans showed s i g n i f i c a n t v a r i a t i o n . ..Shrew p o p u l a t i o n s , r e g a r d l e s s of s p e c i e s , r e a c t . s e n s i t i v e l y to environmental f a c t o r s , and s i m i l a r responses are seen .under . s i m i l a r c o n d i t i o n s . These responses i n v o l v e . , g e n e t i c s and morphology, as w e l l as l i f e h i s t o r y s t r a t e g i e s . „.„.,..•. . . . In a study of karyotypes of some P a c i f i c . c o a s t . shrews, R. , J . Brown (1970) . found, both inter - r and i n t r a - p o p u l a t i o n d i f f e r e n c e s i n chromosome morphology... i n . Sorex vagrans. D i f f e r e n c e s g e n e r a l l y i n v o l v e d apparent, s h i f t s i n . , the p o s i t i o n of the centromere, with no change. . i n .the . d i p l o i d number of 54. Presumably, the . d i f f e r e n c e s ..shown.in chromosome morphology and fundamental number,. (number of p a i r e d arms e x c l u d i n g the sex p a i r ) are a t t r i b u t a b l e . t o p e r i c e n t r i c i n v e r s i o n s (R.;J. Brown, op. c i t . ) . . . . A c h a r a c t e r i s t i c of i n v e r s i o n h e t e r o z y g o t e s . i s t h e . i n v i a b i l i t y a s s o c i a t e d with m e i o t i c recombinations, or c r o s s i n g - o v e r (White, 1954). However, i t i s b e l i e v e d t h a t these heterozygotes can and do, i n f a c t , h a v e . i n c r e a s e d . f i t n e s s i f t h e i r i n v e r s i o n s c o n t a i n co-adapted gene complexes.which the i n v i a b i l i t y of c r o s s - o v e r products i n . e f f e c t ..maintains (Dobzhansky, 1951; Dobzhansky and Pavlovsky, .1962). Brown found k a r y o t y p i c morphology t o v a r y . i n a c l i n a l f a s h i o n along with phenotypic c h a r a c t e r s , and suggested, that .the chromosomal rearrangements i n S. vagrans represented 191 a d a p t a t i o n to changing environmental f a c t o r s . . F i n d l e y (1955), l o o k i n g at morphological c h a r a c t e r s i n Sorex, proposed t h a t , f o u r recognized North-American.Sorex s p e c i e s (S. vagran, S. obscurus, §. rjjaguinae, and §• £§cificus, based on Jackson, 1928) w e r e . i n . a c t u a l i t y one p o l y t y p i c s p e c i e s d i s t r i b u t e d g e o g r a p h i c a l l y . i n a complex, c l i n a l c h a i n which i s r e f l e x e d back.on i t s e l f . Where the ends ov e r l a p (along the northern C a l i f o r n i a .coast), the subspecies had become . s u f f i c i e n t l y d i f f e r e n t to .be r e p r o d u c t i v e l y i s o l a t e d . As e v i d e n c e . .for t h i s purported Rassenkreis, F i n d l e y gave examples . cf presumed i n t e r g r a d a t i o n i n s i z e and c o l o r between S. vagrans and S. obscurus i n areas of the Rocky Mountains and.presented t h i s as evidence f o r i n t e r b r e e d i n g . . R e c e n t l y , ..Hennings (1970), r e a n a l y z i n g the s i t u a t i o n i n western Montana .using l a r g e r sample s i z e s and more q u a l i t a t i v e - c h a r a c t e r i s t i c s , concluded that gene flow between the montane p o p u l a t i o n s was n i l , or a t most onl y s l i g h t , r e g a r d l e s s of i n t e r g r a d a t i o n . i n other m orphological c h a r a c t e r s . In h i s r e v i e w . o f . c e r t a i n H o l a r c t i c shrews, Hoffmann (1971) a l s o questioned ..the s p e c i e s concept of F i n d l e y on other ..counts,. and. s t a t e d t h a t the evidence f a v o r e d c o n s i d e r i n g .Sorex obscurus and Sorex vagrans d i s t i n c t s p e c i e s . On the b a s i s of my f i n d i n g s concerning ..S. vagrans and S. obscurus i n southwestern B r i t i s h Columbia, and i n l i g h t of t h i s d i s c u s s i o n , I concur with the o p i n i o n s c f Hennings and Hoffmann. Despite the i n t e r g r a d a t i o n of c e r t a i n 192 morphological measurements apparent . i n the l o c a l s p e c i e s (M. Jackson, 1951), other evidence i n d i c a t e s r e p r o d u c t i v e i s o l a t i n g mechanisms i n o p e r a t i o n between the s p e c i e s . : One which has thus f a r not been r e p o r t e d i n the North American shrew l i t e r a t u r e , t o my knowledge, i s the s p e c i e s - s p e c i f i c d i f f e r e n c e i n odors emanating from., the s i d e glands of breeding males. In a d d i t i o n , I found,the s t r u c t u r e and l o c a t i o n of the t i n e s on the f r o n t , . i n c i s o r s to d i f f e r q u a l i t a t i v e l y between s p e c i e s , as Hennings ..(1970) .described f o r Montana S. vagrans and S. obscurus. , H a b i t a t , s e l e c t i o n a t , the microgeographic l e v e l appears to .be a mechanism whereby i n t e r s p e c i f i c c o m p e t i t i o n i s m i t i g a t e d and c o e x i s t e n c e allowed. While F i n d l e y r e c o g n i z e d the high degree of geographic v a r i a b i l i t y i n shrews, and even.suggested . t h a t . . s m a l l , s i z e might be an a d a p t a t i o n f o r c e r t a i n environmental c o n d i t i o n s , he a p p a r e n t l y f a i l e d t o take i n t o account the f a c t t h a t . c o -e x i s t i n g s p e c i e s c o u l d r e a c t s i m i l a r l y , to f a c t o r s such ..as c l i m a t e and s o i l type. The c h a r a c t e r s he. c o n s i d e r e d t a x o n o m i c a l l y u s e f u l were s i z e , and . c o l o r , . t w o c h a r a c t e r s t h a t are p a r t i c u l a r l y s u b j e c t to geographic v a r i a b i l i t y . Thus, s p e c i e s i n h a b i t i n g coast.redwood f o r e s t s . a r e redder than those i n h a b i t i n g f i e l d s o r _ marshes. . Northern p o p u l a t i o n s are c o n s i d e r a b l y s m a l l e r than. southern. S i z e has been d i s c u s s e d as a c h a r a c t e r which i s v a r i a b l e not o n l y g e o g r a p h i c a l l y , but a l s o s e a s o n a l l y , depending on c l i m a t i c c o n d i t i o n s . 193 although c h a r a c t e r displacement i n size, o f t e n occurs.as a mechanism f o r c o m p e t i t i v e avoidance when two . c l o s e l y r e l a t e d s p e c i e s come together .(e.g. H a l l , .1951, f o r weasels), t h i s does.not seem to be the . s t r a t e g y used by the shrew s p e c i e s concerned with here. Instead, m i c r o h a b i t a t s e g r e g a t i o n o c c u r s . E v i d e n t l y , size., i n shrews i s an adapti v e c h a r a c t e r i s t i c f o r c e r t a i n ..environmental c o n d i t i o n s , and these c o n d i t i o n s can o f t e n s e l e c t f o r s i m i l a r c h a r a c t e r i s t i c s i n c o e x i s t i n g s p e c i e s . . I n ..her study of Endowment Lands S. vagrans and S. obscurus,.M. Jackson (1951) found t h a t on the average the l o c a l S. vagrans were s l i g h t l y l a r g e r than t h a t d e s c r i b e d , as t y p i c a l f o r the s p e c i e s by H. Jackson (1928), while the. .S. .obscurus. were c o n s i d e r a b l y s m a l l e r than t y p i c a l . In other words, i n t h i s area the two s p e c i e s converge i n size... Although M. Jackson a t t r i b u t e d these a b e r r a n c i e s to a degree of h y b r i d i z a t i o n , . I t h i n k they can be b e t t e r e x p l a i n e d by.character.convergence, the r e s u l t of s i m i l a r responses t o the same environmental c o n d i t i o n s . 194 CONCLUSIONS The a d a p t a t i o n s and e c o l o g i c a l - s t r a t e g i e s of Sorex vagrans and Sorex obscurus have been s t u d i e d by means of i n t e r - and i n t r a s p e c i f i c comparisons of -populations l i v i n g i n both f o r e s t and g r a s s l a n d h a b i t a t s . . In r e f e r r i n g to the s p e c i e s vagrans and obscurus, I.have - chosen not. to f o l l o w F i n d l e y ' s . (.1.955) . suggestion that they are.members of one s p e c i e s complex. In. a d d i t i o n . _ t o s p e c i e s - s p e c i f i c d i f f e r e n c e s i n morphology of the f r o n t i n c i s o r s , I . noted d i s t i n c t and s t r i k i n g , d i f f e r e n c e s i n t h e odors .emitted by breeding males. The s c e n t s were s p e c i e s - s p e c i f i c . a n d c o u l d w e l l serve as a mechanism f o r s p e c i e s r e c o g n i t i o n , thus f a c i l i t a t i n g r e p r o d u c t i v e i s o l a t i o n . . ... . . In g e n e r a l morphology and l i f e h i s t o r y p a t t e r n , S. vagrans and S. obscurus show b a s i c a l l y the . same ada p t a t i o n s f o r e x p l o i t i n g s i m i l a r r e s o u r c e s . For homeotherms, both are very . s m a l l , with ,S. obscurus approximately 15% h e a v i e r , having , a .longer t a i l and mere robust s k u l l and d e n t i t i o n . The r e l a t i v e . t i m i n g of molt.and r e p r o d u c t i o n i s such that the two energy-demanding events are non-overlapping. The seguence of these events i n the s p r i n g i s r e v e r s e d f o r males and females, a phenomenon which emphasizes the r o l e of energy i n the r e p r o d u c t i v e . s t r a t e g i e s of each sex. Strong s i t e attachment .and ..the; e s t a b l i s h m e n t of t e r r i t o r i e s d u r i n g the non-breeding, time of l i f e. serve ..to ensure the t e r r i t o r y h older s u f f i c i e n t food f o r 195 o v e r w i n t e r i n g . At the p o p u l a t i o n l e v e l , the e f f e c t of t e r r i t o r i a l i t y i s d e n s i t y r e g u l a t i o n at a time before prey r e s o u r c e s become l i m i t i n g . I t i s a x i o m a t i c t h a t s p e c i e s with i d e n t i c a l e c o l o g i c a l requirements cannot c o e x i s t a t the same l o c a l i t y ; one s p e c i e s w i l l e v e n t u a l l y out-compete the. other. . The. f i n e -g r a i n e d d i f f e r e n c e s between S. vagrans.and S.,obscurus,_a r e s u l t of t h e i r common s p e c i a l i z a t i o n f o r s o i l i n v e r t e b r a t e s and absence of s e l e c t i o n or d i s c r i m i n a t i o n , , of i n d i v i d u a l prey items, c r e a t e s a s i t u a t i o n of p o t e n t i a l . c o m p e t i t i o n when the s p e c i e s are i n sympatry. I have,shown t h a t , although these s p e c i e s o v e r l a p g e o g r a p h i c a l l y , . c o m p e t i t i o n between them i s m i t i g a t e d through h a b i t a t s e g r e g a t i o n . a t the microgeographic l e v e l . S o i l type and .the. a s s o c i a t e d s o i l fauna appear to be the most i m p o r t a n t . f a c t o r s . i n , d e t e r m i n i n g s p e c i e s d i s t r i b u t i o n s , with S. vagrans i n h a b i t i n g . m u l l . a n d moder s o i l s and S. obscurus i n h a b i t i n g the poorer, more a c i d i c mor s o i l s . The evidence f o r inter-., and w e l l as i n t r a s p e c i f i c t e r r i t o r i a l i t y i n d i c a t e s t h a t a c t i v e , c o mpetition, between s p e c i e s may s t i l l e x i s t , however. A degree of o v e r l a p o c c u r s , p a r t i c u l a r l y on i n t e r m e d i a t e s o i l s , but .continued e x i s t e n c e of the two s p e c i e s i s allowed because, i n the sense of Hutchinson (1957), each s p e c i e s has a refuge i n which i t i s the s u p e r i o r competitor. The .immediate m a n i f e s t a t i o n of s u p e r i o r i t y i n c o m p e t i t i v e i n t e r a c t i o n s i s s u c c e s s f u l defense of t e r r i t o r y i n t e r s p e c i f i c a l l y . 196 In comparing S. vagrans p o p u l a t i o n s f r o m . f o r e s t and g r a s s l a n d h a b i t a t s , I have found .that l i f e _ . h i s t o r y s t r a t e g i e s i n these shrews are .contingent..upon . t h e i r environment. S p e c i f i c a l l y , when the .role of food as a l i m i t i n g f a c t o r assumes d e c r e a s i n g ..importance, and c o n c o m i t a n t l y , density-independent l i m i t i n g f a c t o r s . g a i n . i n importance, s t r a t e g i e s appear. to be. such, t h a t - a g r e a t e r p r o p o r t i o n of a v a i l a b l e energy i s a l l o t t e d t o . r e p r o d u c t i v e a c t i v i t i e s . Thus, shrews i n the lowland g r a s s y . h a b i t a t s , where food i s a p p a r e n t l y abundant bot h . i n terms of biomass and "packaging," are r s e l e c t e d with respect, to t h e i r f o r e s t c o u n t e r p a r t s . T h e i r r e p r o d u c t i v e s t r a t e g i e s i n c l u d e .a longer breeding season and the occurrence of r e p r o d u c t i v e a c t i v i t y i n f i r s t year females. . T e r r i t o r i a l i t y appears t o play l e s s , of. a r o l e i n g r a s s l a n d h a b i t a t , where p o p u l a t i o n d e n s i t i e s are high. ,.. The d e n s i t i e s supportable by the h a b i t a t are perhaps ..too high f o r t e r r i t o r i a l a g g r e s s i v e n e s s to be e f f e c t i v e l y advantageous. Also, with density-independent... m o r t a l i t y f a c t o r s p l a y i n g a l a r g e r r o l e , t e r r i t o r i a l i t y . i n g r a s s l a n d would not be as s t r o n g l y s e l e c t e d f o r as i t seems t c be i n the f o r e s t h a b i t a t . A d a p t a b i l i t y has been.shown to be a s i g n i f i c a n t g u a l i t y of shrews. I t i s seen i n t h e i r . .genetics, ..physiology, morphology, and l i f e h i s t o r y . As p r e d a t o r s . depending ..upon s m a l l , s e a s o n a l l y v a r i a b l e prey whose numbers f l u c t u a t e from 197 year t o year, i t i s advantageous f o r shrews to have p o t e n t i a l f o r d i f f e r e n t i a l apportionment of a v a i l a b l e energy i n t o r e p r o d u c t i v e and non-reproductive, a c t i v i t i e s . . A l s o , because t h e i r o v e r a l l niche d i c t a t e s t hat shrews be s m a l l , and because i n d i v i d u a l s have no.long range m o b i l i t y , they have l i t t l e independence from,, or . c o n t r o l ..over, t h e i r immediate environment and must, . t h e r e f o r e , . be able., to cope with a v a r i e t y of both p r e d i c t a b l e . .and,.- u n p r e d i c t a b l e changes. Within the c o n f i n e s o f . t h e i r . s p e c i a l i z a t i o n , shrews show a r e l a t i v e l y h i g h , degree of. e c o l o g i c a l a d a p t a b i l i t y and opportunism, and i t i s t h i s q u a l i t y . t h a t i s no doubt r e s p o n s i b l e f o r t h e i r . w i d e d i s t r i b u t i o n i n d i v e r s e h a b i t a t s , as w e l l as t h e i r e v i d e n t p o t e n t i a l f o r s p e c i a t i c n . 198 LITERATURE CITED B l a i r , W. F. 1940. Notes on home ranges and p o p u l a t i o n s of the s h o r t - t a i l e d shrew. 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