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The ecology of coexistence in two closely related species of frogs (rana) Licht, Lawrence Edward 1971

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11137 THE ECOLOGY OF COEXISTENCE IN TWO CLOSELY RELATED SPECIES OF FROGS (RANA) by LAWRENCE EDWARD LICHT B.A., Washington University, 1963 M.A., Un i v e r s i t y of Texas, Austin, 1967 A. THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of Zoology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1971 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission fo r extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by h i s representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of *t? O O L 0  The University of B r i t i s h Columbia Vancouver 8 , Canada i i ABSTRACT The red-legged f r o g , Rana aurora aurora and the western spotted f r o g , Rana p r e t i o s a p r e t i o s a , were found co-e x i s t i n g i n southwestern B r i t i s h Columbia. The l o c a l i t y - the upper L i t t l e Campbell River near White Rock - i s the only area i n the P a c i f i c Northwest i n which the two species are known to be sympatric. L i t t l e was known about the biology of the frogs, which are c l o s e l y r e l a t e d and resemble each other i n habits; f i n d i n g a sympatric l o c a l i t y provided a unique opportunity to study how they manage to coexist and avoid competitive ex-c l u s i o n . The study involved f i n d i n g the e c o l o g i c a l requirements during the nonbreeding season and f i n d i n g the reproductive i s o l a t i n g mechanisms. The study revealed that R. p r e t i o s a i s much more aquatic than R. aurora. The a f f i n i t y of R> aurora f o r land and R. p r e t i o s a f o r water i s the basic e c o l o g i c a l difference permitting them to c o e x i s t . The morphology, ecology, and behavior of the frogs are adapted to t h e i r preference f o r land or water. R. aurora has r e l a t i v e l y longer hind limbs than R. p r e t i o s a ; but the f e e t of R. p r e t i o s a are more extensively webbed. The eyes of R. aurora face l a t e r a l l y ; those of R. p r e t i o s a face upwards. The skin of R. p r e t i o s a i s covered with a thick mucous coating; that of R. aurora i s smooth. There i s much overlap i n the d i e t of these species; they share as much as 88% of the kinds of foods most commonly eaten, and 75% of the food items most abundantly eaten. At i i i times they feed within close proximity of each other; however, R. aurora feeds predominantly on land, whereas R. p r e t i o s a feeds predominantly from water. Body temperatures of wild frogs i n the f i e l d were s i g n i f i c a n t l y d i f f e r e n t , R. p r e t i o s a attains higher body temper-atures than R. aurora, i n d i c a t i n g divergent preferences i n habitat requirements. R. pr e t i o s a has a higher temperature tolerance than R. aurora. R. p r e t i o s a uses water to thermo-regulate, while R. aurora uses shade and sun on land. The rate of evaporative water loss and water loss leading to l e t h a l desiccation were the same i n both species, i n d i c a t i n g no obvious p h y s i o l o g i c a l basis f o r t h e i r water or land preferences. To escape from predators, R. aurora uses land and R. p r e t i o s a uses water. R. aurora i s a strong jumper, and jumps i n a nearly s t r a i g h t path at an angle of 45°; R. p r e t i o s a i s a weaker jumper and jumps i n a c i r c l e at an angle of about 10° to the ground, but normally escapes by submerging to the bottom of the nearest water. Both species breed during the same two to four weeks i n February and March within a few feet of one another i n the same bodies of water. They avoid interbreeding, however, by means of such premating i s o l a t i n g mechanisms as differences i n mating c a l l , male c a l l i n g behavior, and microgeographic choice of spawning s i t e s . Embryos of each species have d i f f e r e n t thermal adapta-t i o n s and requirements which are corr e l a t e d with adult breeding h a b i t s • For example, R. p r e t i o s a females deposit eggs i n very shallow water exposing them to r e l a t i v e l y high daytime temper-atures. R. aurora deposits eggs beneath several feet of water bu f f e r i n g them from heat stress and wide thermal f l u c t u a t i o n s . Factors underlying t h e i r rare occurrence i n sympatry and observed geographic d i s t r i b u t i o n s are discussed i n terms of t h e i r habitat requirements and the present existence of other species of ranid frogs i n the P a c i f i c Northwest. V TABLE OF CONTENTS PAGE. TITLE PAGE: i ABSTRACT. i i TABLE OF CONTENTS V LIST OF TABLES v i i i LIST OF FIGURES x ACKNOWLEDGEMENT x i i i INTRODUCTION 1 STUDY AREA. 5 MATERIALS AND METHODS 13 A. Morphology 13 B. Ecology 13 a. Habitat Preference 13 b. Food and Feeding Behavior 14 1) Natural feeding behavior observations 17 2) Laboratory feeding t e s t s 18 3) Starvation t e s t s 19 c. Environmental Physiology - Temperature 19 1) F i e l d and frog temperatures 19 2) Frog temperature tolerance 20 d. Water Balance 21 1) Dehydration 21 2) Submergence tests 2 3 e. Predators and Predator Avoidance 2 3 1) F i e l d t e s t s 2 3 2) Laboratory escape behavior 24 3) Frog jumping a b i l i t y 25 4) Predators 25 C. Comparative Reproductive Behavior 25 v i PAGE D. Embryonic Thermal Requirements and Environmental Temperatures 27 a. E f f e c t s of Temperature on Egg Development 27 b. E f f e c t s of Acute Cold Exposure on Survival 30 c. Embryonic Oxygen Consumption 31 RESULTS 32 A. Morphology 32 B. Ecology 38 a. Habitat Preferences 38 b. Pood 39 1) Feeding behavior i n the f i e l d 39 2) Analysis of stomach contents 42 3) Laboratory feeding t e s t s 45 4) Starvation experiments 62 c. Temperature 63 1) F i e l d and frog temperature 63 2) Frog temperature tolerance 71 d. Water Balance 75 1) Dehydration 75 2) Submergence t e s t s 84 e. Predator Avoidance 84 1) F i e l d 84 2) Escape behavior a f t e r release 86 3) Jumping a b i l i t y 88 4) Laboratory t e s t s with snakes 91 5) Anuran predators i n the LCR study area 94 C. Comparative Reproductive Behavior 97 a. Prebreeding and Breeding Behavior of Rana aurora 97 1) Emergence from hibernation and migration to breeding s i t e s 97 2) Prespawning a c t i v i t y at breeding s i t e s 99 3) Vocalizations at breeding s i t e s 100 4) Behavior of amplectic p a i r s 104 5) Spawning Behavior 106 v i i PAGE b. Prebreeding and Breeding Behavior of Rana p r e t i o s a 109 1) Emergence from hibernation and migration to breeding s i t e s 109 2) Vocalizations and male behavior at breeding s i t e s 110 3) Behavior i n amplexus and spawning 113 D:e Embryonic Thermal Requirements and Environmental Temperature 117 a. Rana aurora 117 b. Rana p r e t i o s a 122 c. Adult Spawning Behavior and Environmental Temperature 12 3 DISCUSSION 128 A. Morphology 128 B. Ecology 130 a. Food and Behavior 130 b. Temperature Requirements and Adaptations 132 c. Water Requirements and Adaptations 134 d. Escape Behavior 137 C. Comparative Reproductive Behavior 140 a. Reproductive I s o l a t i o n 140 D. Embryonic Thermal Requirements 142 E:. Coexistence of Ranid Frogs i n the P a c i f i c Northwest 148 LITERATURE CITED 15 3 LIST OF TABLES Analysis of food items i n gut contents of 104 newly metamorphosed and j u v e n i l e - a d u l t Rana aurora. Analysis of food items i n gut contents of 41 newly metamorphosed and j u v e n i l e - a d u l t Rana p r e t i o s a . Analysis of food items i n gut contents of 78 newly metamorphosed Rana aurora. Analysis of gut contents of 26 j u v e n i l e -adult Rana aurora. Analysis of gut contents of 18 newly meta-morphosed Rana p r e t i o s a . Analysis of gut contents of 2 3 j u v e n i l e -adult Rana p r e t i o s a . Percentage overlap of t o t a l food c l a s s i f i c a -tions between species and age groups within species. Percentage overlap of dominant eight food items (those food items occurring i n most frog stomachs). Percentage overlap of dominant eight food items (those food items most abundant i n a l l stomachs). T o t a l number of s t r i k e s , percentage of s t r i k e s , which were successful, and number of f l i e s a c t u a l l y eaten i n wet and dry conditions by Rana aurora and Rana p r e t i o s a . P r o b a b i l i t i e s associated with d i f f e r e n c e s i n feeding e f f i c i e n c y of Rana aurora and Rana  p r e t i o s a under wet and dry conditions. Comparisons of frog c l o a c a l temperatures (C) with temperatures of a i r and water where caught. Degrees centigrade d i f f e r e n c e between frog c l o a c a l temperatures and a i r or water. A b i l i t y of frogs to survive high temperatures. Rate of evaporative water loss of Rana aurora and Rana p r e t i o s a at 15 C and 60% humidity. i x TABLE XVI XVII XVIII XIX XX XXI XXII XXIII XXIV XXV PAGE Time t i l l C r i t i c a l A c t i v i t y Point (CAP) and percentage weight loss at CAP f o r small Rana  aurora and Rana p r e t i o s a at 15 C and 60% humidity. 77 Rate of evaporative water loss of Rana aurora and Rana p r e t i o s a at 28 C and 25% humidity. 79 Time t i l l C r i t i c a l A c t i v i t y Point (CAP) and percentage weight loss at CAP f o r Rana aurora and Rana p r e t i o s a at 28 C and 25% humidity. 80 Escape responses of Rana aurora and Rana p r e t i o s a released p a r a l l e l to r i v e r bank. 87 Summary of differences i n morphology, ecology, and behavior between Rana aurora and Rana p r e t i o s a . 96 Numbers of new Rana aurora egg masses found on each search at the L i t t l e Campbell River during the 1968 and 1969 breeding seasons. 108 Numbers of new Rana p r e t i o s a egg masses found on each search at the L i t t l e Campbell River during the 1968 and 1969 breeding seasons. 114 Summary of main s i m i l a r i t i e s and differences i n the prebreeding and breeding behavior of Rana aurora and Rana p r e t i o s a at the L i t t l e Campbell River study area. 116 Percentage s u r v i v a l of eggs to stage 20 at constant temperatures. 118 0.10 v a ^ - u e s f o r embryonic development. 121 X LIST OF FIGURES FIGURE PAGE 1 Geographic d i s t r i b u t i o n of Rana aurora and Rana p r e t i o s a . 2 2 Map of study area where Rana aurora and Rana  p r e t i o s a are sympatric. 8 3 L i t t l e Campbell River at time of spring over-flow. View looking south i n study area. 9 4 Main channel of L i t t l e Campbell River. View looking south i n study area. 10 5 L i t t l e Campbell River i n foreground and breeding pond i n background. View looking west i n study area. 11 6 Breeding pond nearly dry i n June. 12 7 Top view of p l a s t i c swimming pool used as t e s t i n g arena f o r predation t e s t s with snakes. 15 8 Male Rana aurora (top) and Rana p r e t i o s a . 33 9 Male Rana aurora ( l e f t ) and Rana p r e t i o s a . Note eyes of Rana p r e t i o s a face upwards. 34 10 Relative s i z e of hind limbs of Rana aurora and Rana p r e t i o s a . Lines f i t t e d to l e a s t squares regression where y = hind limb length (mm) and x = snout-vent length (mm). For Rana aurora, y = -7.8 + 2.02x, and f o r Rana p r e t i o s a , y = 3.9 +1.5Ox. 36 11 Dorsal view of r i g h t hind foot of Rana aurora and Rana p r e t i o s a , based on foot of female 60 mm snout-vent length. 37 12 Overlap of dominant food items of a l l Rana  aurora and a l l Rana p r e t i o s a , and percentage of t o t a l stomachs which contained the food. Top eight food items are those appearing i n most stomachs. Number i n parentheses i s t o t a l number of stomachs f o r each group. 55 13 Overlap of dominant food items of a l l Rana  aurora and a l l Rana p r e t i o s a and percentage of t o t a l food intake each food item comprises. Top eight food items are those most abundant i n a l l stomachs of each species. Number i n parentheses i s t o t a l number of food items i n a l l samples. 56 x i FIGURE PAGE 14 Overlap of dominant food items of frogs of d i f f e r e n t age c l a s s e s . Top eight items f o r each age c l a s s are those appearing i n most stomachs within each c l a s s . Number i n parentheses i s t o t a l number of stomachs f o r each age c l a s s . 57 15 Overlap of dominant food items of frogs of d i f f e r e n t age c l a s s e s . Top eight items are those most abundant i n a l l stomachs of each age c l a s s . Number i n parentheses i s t o t a l number of food items of a l l kinds found i n stomachs of each group. 58 16 Temperature tolerance of j u v e n i l e and adult Rana aurora and Rana p r e t i o s a . 73 17 Rate of water loss to a i r of 15 C and 60% humidity as a function of body weight. Lines f i t t e d to l e a s t squares regression where y = log rate of loss (g/hr) and x = log body weight (g). For Rana. aurora, y = -1.435 + 0.61x and f o r Rana p r e t i o s a , y = -1.429 + 0.57x. 78 18 Rate of water loss to a i r of 28 C and 2 5% humidity as a function of body weight. Lines f i t t e d to least squares regression where y = log rate of loss (g/hr) and x = log body weight (g). For Rana aurora, y = -0.495 + 0.47x, and f o r Rana p r e t i o s a , y = -0.498 + 0.51x. 81 19 Time t i l l C r i t i c a l A c t i v i t y Point (CAP) at 28 C and 25% humidity as a function of body weight. 82 20 Jumping distance as a function of frog snout-vent length. Lines f i t t e d to l e a s t squares regression where y = distance jumped (cm) and x = snout-vent length (mm). For R. aurora, y = 2.56 + 0.70x, and f o r Rana pr e t i o s a , y = 8.95 + 0.25x. 89 21 Jumping distance as a function of hind limb length. Lines f i t t e d to least squares regression where y = distance jumped (cm) and x = hind limb length (mm). For Rana  aurora, y = 8.79 + 0.31x, and f o r Rana pr e t i o s a , y = 10.1 + 0.14x. 90 FIGURE 22 A i r and water temperatures and p r e c i p i t a -t i o n data f o r 1968 and 1969, pertinant to the breeding behavior of Rana aurora and Rana p r e t i o s a at the L i t t l e Campbell River study area. Single arrows i n d i c a t e dates on which Rana aurora males began c a l l i n g ; double arrows i n d i c a t e the same f o r Rana  pr e t i o s a males. ~~ 2 3a,b Sonagrams of male Rana aurora v o c a l i z a t i o n s , a. Mating c a l l of an unpaired male submerged i n water 9 C. b. Single note emitted once a second by a male clasped with a female. 24 The mating c a l l of an unpaired male Rana  pr e t i o s a f l o a t i n g i n water 12.4 C. 25 Rate of development of eggs of Rana aurora and Rana p r e t i o s a . ~~ x i i PAGE 98 103 112 119 x i i i ACKNOWLEDGEMENT I thank Dr. J.D. McPhail f o r h i s considerate supervision throughout t h i s study. He, Dr. D.H. Ch i t t y , Dr. N.R. L i l e y , and Dr. G.G. Scudder b e n e f i c i a l l y c r i t i c i z e d rough d r a f t s of t h i s t h e s i s . Douglas Hay accompanied me on many t r i p s to the f i e l d ; I appreciate his assistance and fr i e n d s h i p . I thank Vinnie McQueen f o r taking s p e c i a l care i n typing the t h e s i s . The Fraser Valley Parks Board allowed me to use park land as a study area. Above a l l , my wife G i l l i a n deserves s p e c i a l acknowledgement f o r her constant and expert aid i n the f i e l d and laboratory; she also did i l l u s t r a t i o n s . I am g r a t e f u l to her. This research was supported by the National Research Council of Canada through a grant to Dr. J.D. McPhail and a Postgraduate Scholarship to me. 1 INTRODUCTION In northwestern North America, there are seven species of frogs belonging to the genus Rana. Within t h i s Rana species group are two c l o s e l y r e l a t e d species: the red-legged frog, Rana aurora aurora Baird and Girard, and the western spotted f r o g , Rana p r e t i o s a p r e t i o s a Baird and Girard. The d i s t r i b u t i o n of R. aurora i s i n coastal areas from southwestern B r i t i s h Columbia, southwards through Washington, Oregon, and C a l i f o r n i a . The d i s t r i b u t i o n of R. p r e t i o s a i s more extensive, and t h i s species ranges from southeastern Alaska, south through B r i t i s h Columbia, Washington, and Oregon, to northern Nevada and Utah, and eastward through Saskatchewan, Idaho, western Montana, and Wyoming (Stebbins 1951). The d i s t r i b u t i o n s of the two species are seen i n F i g . 1. One s t r i k i n g feature of the d i s t r i b u t i o n s of the two frogs i s that, except f o r a few i s o l a t e d l o c a l i t i e s i n western Washington and Oregon, t h e i r ranges are e n t i r e l y complementary (the ranges do not overlap). Moreover, the present existence of R. p r e t i o s a i n western Washington l o c a l i t i e s , where the species are sai d to be sympatric, i s doubtful (Dumas 1966). In B r i t i s h Columbia, R. p r e t i o s a i s reported to occur only east of the Coast Range mountains, while R. aurora i s r e s t r i c t e d to the coastal areas west of these mountains (Carl and Cowan 1945). (Two specimens of R. p r e t i o s a were c o l l e c t e d i n 1941 on Nicomen Island, an area which i s west of the Coast mountains (Carl and Cowan 1945), but t h i s population has not been rediscovered). However, i n 1967 I discovered a l o c a l i t y i n southwestern B.C. where R. aurora and R. p r e t i o s a occur Geographic d i s t r i b u t i o n of Rana aurora and Rana p r e t i o s 3 sympatrically. This l o c a l i t y , the upper L i t t l e Campbell River, represents the only known area where the species c o e x i s t . L i t t l e i s known about the biology of e i t h e r species. Storm (1960) studied aspects of the breeding biology of R. aurora i n Oregon, and Turner (1958, 1960) studied R. p r e t i o s a at 7800 f t i n Wyoming. Almost nothing i s known about the biology of these species i n B r i t i s h Columbia (Carl 1966). Stebbins (1954), however, ind i c a t e s that both species are very c l o s e l y r e l a t e d and resemble each other i n h a b i t s ; n a t u r a l i s t s often confused the two species. I f r e l a t e d species' e c o l o g i c a l requirements are s u f f i c i e n t l y s i m i l a r , the existence of one species may c o n t r o l the presence or absence of another. Competitive exclusion may r e s u l t i f r e l a t e d species* requirements g r e a t l y overlap (Gause 19 34). The discovery of these c l o s e l y r e l a t e d species i n sympatry provides a nearly unique opportunity to study how they achieve successful coexistence and avoid competitive exclusion. Many other studies have been c a r r i e d out on niche d i v e r s i t y and coexistence i n other vertebrate groups, e s p e c i a l l y mammals and b i r d s (Lack 1945, MacArthur 1958), but anuran vertebrates have not been c l o s e l y investigated i n t h i s regard. The a b i l i t y of r e l a t e d species to coexist must be attained i n both breeding and nonbreeding a c t i v i t i e s , and the question of how R. aurora and R. p r e t i o s a succeed has been divided i n t o two components: what are t h e i r e c o l o g i c a l r e q uire-ments and how do these permit coexistence, and how does each species remain as an independent breeding population, i . e . , what are the reproductive i s o l a t i n g mechanisms that prevent 4 interbreeding between the species? Observations and experiments throughout the study revealed that R. p r e t i o s a i s more aquatic than R. aurora. The a f f i n i t y of R. aurora f o r land and R. p r e t i o s a f o r water i s a basi c e c o l o g i c a l d i f f e r e n c e , and the water-land boundary i s c r u c i a l . This d i f f e r e n c e underlies most aspects of t h e i r comparative ecology and behavior, and provides the basis f o r understanding the mechanisms by which they c o e x i s t . The morphology, ecology, and behavior of the frogs are adapted to t h e i r preference or r e s t r i c t i o n to water or land. How these adaptations allow coexistence of the two species i s the topic studied i n t h i s t h e s i s . 5 STUDY AREA Both species, R. aurora and R. p r e t i o s a , occur i n marshes about 5 miles east of White Rock, B.C. A 7-acre f i e l d , about 220 f t above sea l e v e l , and near the junction of North B l u f f and Carvolth Roads i n Langley E l e c t o r a l D i s t r i c t , was used as the s i t e of f i e l d s tudies. Research began i n October 1967 and ended i n July 1970. The area i s wet f l a t lowland, covered predominantly by bulrushes (Juncus e f f u s u s ) , sedges (Carex sp.), and buttercups (Ranunculus repens). Ranunculus forms almost a complete carpet throughout the f i e l d . The other two plant types are abundant but scattered throughout the whole area. The eastern and western borders of the f i e l d are alder, b i r c h , and coniferous woods, the southern border i s more lowland marsh, and the northern side i s interrupted by an asphalt road, across which i s more lowland. The woods along the eastern edge of the study area l i e on a h i l l with an i n c l i n e of about 40°• This steep h i l l terminates above the f i e l d i n pasture. A permanent slow-moving stream, the L i t t l e Campbell River, flows through the centre of the f i e l d . The study s i t e i s r e f e r r e d to as the LCR study area. The r i v e r margins f l u c t u a t e considerably during the spring r a i n s , from February through A p r i l , and the width may vary from 5 to 100 f t i n a few days. In wet periods during the spring, the shallow overflow i s u s u a l l y not more than 1-3 f t deep, and a f t e r several days without r a i n t h i s overflow subsides, leaving the main channel about 5-15 f t wide. The channel depth varies from 2-6 f t i n the center, to 6-18 inches on the gradually sloping edges. There i s l i t t l e 6 current i n the r i v e r except a f t e r heavy spring r a i n s . The r i v e r bottom i s s o f t mud covered by r o t t i n g vege-t a t i o n . During the summer the r i v e r i s low and i s f i l l e d with a dense growth of Nuphar, Lemna, Potamoqeton, and Myriophyllum. Carex, Juncus, Typha, and Ranunculus grow profusely along the banks, but the c o n t i n u a l l y f l u c t u a t i n g r i v e r l e v e l u s u a l l y leaves a s t r i p of exposed mud along the r i v e r course. A temporary pond, about 40 by 200 f t , and 6-36 inches deep, l i e s 90 f t west of the r i v e r where i t flows beneath a bridge. The south h a l f of the pond i s dry by May or June, but the northern h a l f remains f i l l e d u n t i l J u ly, and then r e f i l l s again i n September. The pond i s thick with water purslane (Ludwiqia), and Potamoqeton. The bottom i s covered with dead macrophytes, and a thick cover of Juncus surrounds the pond perimeter. A map of the study area i s seen i n F i g . 2, and views of the r i v e r , f i e l d , and pond are seen i n F i g s . 3-6. A f t e r a day or more of r a i n during the spring, numerous rainpools dot the f i e l d . These pools vary i n area, from small puddles to la r g e r pools about 2-3 f t square. At times, channels form from the large pools to the r i v e r . The pools are u s u a l l y 2-4 inches deep with a s o f t mud bottom. They tend to reform i n the same places within the f i e l d , where the ground i s depressed and low. They remain f i l l e d f o r several weeks during the spring, but by June, with warm weather and less r a i n , they dry. With heavy summer r a i n s they may r e f i l l , but dry again a f t e r a few days. By September, the pools are again f i l l e d with the onset 7 of autumn r a i n s , and they p e r s i s t throughout the winter. Other amphibians l i v e i n the f i e l d i n addition to R. aurora and R. p r e t i o s a . They include the anurans, Hyla  r e g i l l a and Bufo boreas, and the urodeles, Ambystoma q r a c i l e , Ambystoma macrodactylum, and Taricha granulosa. In June 1970, the f i r s t b u l l f r o g s , Rana catesbeiana, were seen and caught i n the LCR study area. During the summers of 1968 and 1969, the f i e l d was used s p o r a d i c a l l y as pasture f o r 30-40 head of c a t t l e . They cropped the vegetation, mainly the Ranunculus. The study area was closed to the p u b l i c , and consequently, there was minimal disturbance by humans to the frogs or t h e i r h a b i t a t . Figure 2 Map of study area where Rana aurora and Rana p r e t i o s a are sympatric. 0 Figure 3 L i t t l e Campbell River at time of spring overflow. View looking south i n study area. Figure 4 Main channel of L i t t l e Campbell River. View looking south i n study area. Figure 5 L i t t l e Campbell River i n foreground and breeding pool i n back-ground. View looking west i n study area. Figure 6 Breeding pond nearly dry i n June. 13 MATERIALS AND METHODS I used a combination of f i e l d and laboratory observa-t i o n s and experiments to compare the ecology and behavior of the frogs. A. Morphology As part of a concurrent study on the population dynamics and growth of the two species of frogs, I measured the body siz e and limb length of several hundred frogs caught i n the f i e l d . Information on maximum body s i z e , age and s i z e at sexual maturity, and several morphological c h a r a c t e r i s t i c s were gathered at t h i s time. The body s i z e (snout-vent.length) of each frog was measured by holding a frog by i t s hind limbs, stretched out venter down on my knee. A measurement was made by placing a c l e a r p l a s t i c r u l e r on the back of the frog and taking the read-ing (to the nearest millimeter) from the t i p of the snout to the c l o a c a l opening. The s i z e of the r i g h t hind limb of a frog was measured by holding a p l a s t i c r u l e r alongside the limb and the measurement was taken from the middle of the c l o a c a l aperature to the t i p of the outstretched 4th d i g i t on the hind f o o t . Usually two or three measurements were made of both body and leg s i z e to reduce e r r o r i n measurements. B. Ecology a. Habitat Preference During v i s i t s to the study area, I took s p e c i a l notice of where frogs were captured. The type of substrate on which the frog was found - land or water - was recorded f o r most captures throughout the study. 14 Laboratory t e s t s on habitat preference were conducted. Frogs used had been ra i s e d from eggs i n the laboratory and a f t e r metamorphosis were kept i n glass stacking dishes. The frogs had metamorphosed from the tadpole stage one week before being used i n t e s t s . A p l a s t i c swimming pool was used f o r these t e s t s . The pool (8» x 4' x 1') was h a l f f i l l e d with d i r t (6 inches deep). A moat 3 f t long and 6 inches deep was dug out i n the center of the pool and f i l l e d with water and water purslane (Ludwigia). This t e s t i n g arena i s pictured i n F i g . 7. I t was placed on the f l o o r of the laboratory, and a plywood p a r t i t i o n b u i l t around i t to screen the observer from the animals. Temperature of the room during t h i s study was 20 C. Frogs were placed i n t h i s pool i n the same spot on each t e s t (see x i n F i g . 7). During the following 30 min the po s i t i o n s of the frogs were recorded twice - each 15 min i n t e r -v a l . A frog was recorded as being e i t h e r i n land or water. (After p r e c i s e l y 30 min a snake was introduced i n t o the arena f o r studies on predation to be described l a t e r ) . b. Food and Feeding Behavior In 1968, from May to October, frogs were c o l l e c t e d from adjacent marshes f o r analysis of t h e i r stomach contents. Frogs were c o l l e c t e d i n habitats l i k e those i n the LCR study area, so that conclusions about feeding could be applied to the undisturbed study area populations. Within each month, frogs of both species were caught on the same days. They were us u a l l y taken i n the same v i c i n i t y , only a few feet apart, so that the food i n t h e i r i n t e s t i n a l t r a c t s represented prey items that Figure 7 Top view of p l a s t i c swimming pool used as t e s t i n g arena f o r predation t e s t s with snakes. CD were probably a v a i l a b l e to both species, I walked along the r i v e r margins and through the vegetation and attempted to catch a l l frogs seen on those days set aside f o r the purpose of food a n a l y s i s . A f t e r capture, each frog was k i l l e d and preserved i n a 5% formalin s o l u t i o n . At a l a t e r date, the e n t i r e i n t e s t i n a l t r a c t was removed from each specimen, and a l l animal remains were i d e n t i f i e d . A l l i n s e c t remains were i d e n t i f i e d when pos s i b l e , to family l e v e l (with the exception of Plecoptera and Trichoptera), and to growth stage (adults or l a r v a e ) . A l l spiders were l i s t e d as arachnids and not c l a s s i f i e d f u r t h e r . Only two kinds of molluscs were eaten: slugs and s n a i l s . They are l i s t e d as such. I d i d the analysis of food to obtain two kinds of data the t o t a l number of food items of each kind found i n a l l stomach and the number of stomachs containing a p a r t i c u l a r kind of food items. These data were compiled f o r R. aurora and R. p r e t i o s a separately. Moreover, each species was divided i n t o two group-ings:: newly metamorphosed frogs of the season, and frogs 1 year o l d and older. Each grouping was treated separately. The primary aim of stomach analysis was to determine the degree of overlap i n food items taken by the species. The amount of overlap i n d i e t s might provide an i n d i c a t i o n of competition f o r c e r t a i n food items. S i m i l a r i t y i n diets was determined by comparing the kinds and numbers of prey eaten by each species, and the subgroup within each species. A l l food items were tabulated, and the r a t i o of the number of food items shared between the two species, over the t o t a l number of food items f o r each species, y i e l d e d the percentage overlap i n d i e t . 17 For example, R. aurora (both subgroups) exploited 53 food items; R. p r e t i o s a exploited 49 food items. T h i r t y of these food items were common to both species. Therefore, R. aurora shares 30/53 or 56.6% of the food items i t e x p l o i t s with R. p r e t i o s a , and R. p r e t i o s a shares 30/49 or 61.2% of i t s food items with R. aurora. This method of determining percentage overlap i n d i e t i s used to compare sympatric b i r d species and was j u s t i f i e d by Holmes and P i t e l k a (1968). The dominant food items i n the d i e t of each species are l i s t e d . These were c a l c u l a t e d i n two ways: the eight most abundant items i n a l l stomachs within each species group; and the eight food items that appeared most frequently i n the frogs' stomachs regardless of t h e i r abundance i n the stomachs. For both newly metamorphosed i n d i v i d u a l s and frogs 1 year and older of each species, the top eight items make up over 50% of a l l food eaten. The remaining items were represented only infrequent-l y . 1) Natural feeding behavior observations Occasionally during the study, I used binoculars or my unaided eye to observe the natural feeding behavior of frogs that were unaware or at l e a s t , not obviously frightened by my presence. I watched t h e i r movements and o r i e n t a t i o n response to p o t e n t i a l nearby prey. Of s p e c i a l importance was the type of substrate that feeding a c t i v i t i e s occurred on and the general hunting patterns of the frogs. At times I threw c e r t a i n food items to frogs and watched t h e i r behavior. These casual and d e t a i l e d feeding observations of feeding behavior only allow q u a l i t a t i v e d e s c r i p t i o n of t h e i r feeding a c t i v i t i e s . 18 2) Laboratory feeding tests In the laboratory, an attempt was made to determine the feeding e f f i c i e n c i e s of both species under d i f f e r e n t habitat conditions. A, supply of laboratory-raised frogs was kept f o r use i n behavioral experiments. These animals were r a i s e d from eggs i n the laboratory and maintained under known conditions. Thus, f o r the behavioral studies, most of the compared t r a i t s probably had a genetic rather than environmental b a s i s . Frogs used i n feeding t e s t s were laboratory-reared and were tested j u s t s h o r t l y a f t e r metamorphosis. A l l of the frogs used were 25-29 mm sv length, and weighed 1-1.8 g. The frogs were tested under wet and dry conditions. Three glass stacking dishes (18 cm i n diameter) were f i l l e d with 1 cm of water. Three other dishes were l e f t dry. Two R. aurora and two R. p r e t i o s a were placed i n each d i s h . On a t e s t i n g day, 20-30 f r u i t f l i e s (Drosophila) were introduced i n t o the d i s h . For the follow-ing 10 min, the number of times each frog made a snap at a f l y and the number of snaps that were successful (a f l y captured) were recorded. This procedure was repeated every two days, f o r both wet and dry bowls, u n t i l f i v e t r i a l s were completed f o r each bowl. The frogs were not fed between t r i a l s as an attempt to maintain t h e i r hunger at the same l e v e l f o r each t e s t i n g day. These t e s t s yielded some information on the feeding c a p a b i l i t i e s of frogs i n wet and dry conditions, but unfortunate-l y , the e f f e c t of i n t r a s p e c i f i c and i n t e r s p e c i f i c competition among the four i n d i v i d u a l s i n each dish i s a confusing f a c t o r . Chi square t e s t s were used to t e s t the s i g n i f i c a n c e of r e s u l t s . 19 The r e s u l t s f o r a l l wet tests and a l l dry te s t s were pooled and treated separately. A c t u a l l y the analysis of variance i s the co r r e c t s t a t i s t i c a l t e s t f o r t h i s experiment, but because the t e s t s were not r i g i d l y c o n t r o l l e d , Chi square t e s t s on pooled data are s u f f i c i e n t to y i e l d meaningful p r o b a b i l i t i e s . 3) Starvation t e s t s The a b i l i t y of small frogs to survive without food was i n v e s t i g a t e d . Newly transformed laboratory-reared frogs were kept i n glass stacking dishes with a layer of moist s t e r i l e d i r t on the bottom. Temperatures with the bowls were 17-20 C. Ten frogs of each species, 5 per bowl, were maintained without food u n t i l 5 of each species had died. The number of days u n t i l each death was recorded. A f t e r h a l f of each species had died, the survivors at that time were given f r u i t f l i e s i n abundance. Further mortality and s u r v i v a l were recorded. c. Environmental Physiology - Temperature 1) F i e l d and frog temperatures The e f f e c t of temperature on the comparative ecology of the frogs was examined i n several ways. Upon a r r i v a l at the LCR study area, I recorded the a i r and water temperatures. On many days I recorded the c l o a c a l temperature, that i s , the i n t e r n a l body temperature, of every frog I caught. This was done immediately upon capture with a r a p i d reading Schulteis c l o a c a l thermometer. After the frog's temperature was taken, I recorded the a i r or water temperature i n the place where the frog was caught. The a i r temperature (dry bulb) was that at the l e v e l of the frog's body, a few cm o f f the ground. Water temperatures were measured at the water surface. Cloacal temperatures were measured on days of varying c l i m a t i c conditions (from bright sun to heavy rain) i n an attempt to e s t a b l i s h the upper and lower thermal regimes of wild frogs. 2) Frog temperature tolerance A common method of e s t a b l i s h i n g anuran temperature tolerances i s to f i n d the ' c r i t i c a l thermal maxima' (CTM). This i s defined as "the thermal point at which locomotory a c t i v i t y becomes disorganized and the animal loses i t s a b i l i t y to escape from conditions that w i l l promptly lead to i t s death" (Cowles and Bogart 1944). Hutchison (1961) provided a standard method-ology f o r t e s t s of CTM. B a s i c a l l y i t involves slowly r a i s i n g the temperature u n t i l the animal shows stress symptoms. The temperature at which the animal shows stress symptoms i s the c r i t i c a l thermal maximum. In t h i s study I followed a s l i g h t l y d i f f e r e n t procedure, but one that appears more e c o l o g i c a l l y r e l e v a n t . Instead of c o n t i n u a l l y r a i s i n g the temperature u n t i l a frog showed stress symptoms I ra i s e d the temperature to a f i x e d l i m i t and allowed the animal to remain at that temperature f o r three hours. I f a frog survived f o r at l e a s t three hours at a given high temperature (without showing signs of s t r e s s ) , i t i s l i k e l y that temperatures below that l e v e l are within the range allowing normal a c t i v i t i e s . Subjecting assay animals f o r a length of time to one temperature gives a better i n d i c a t i o n of how that animal responds, than does watching i t s behavior with a b r i e f exposure to a very high and changing temperature l e v e l . In standard CTM t e s t s , temperatures below the CTM may not be l e t h a l , but may cause stress symptoms that only develop 21 a f t e r a long exposure of time, that i s , a f t e r the temperature has already been increased to another higher point. Thus the l i m i t e d time allowed at temperatures s l i g h t l y below the CTM may be more harmful than CTM t e s t s show, because there was i n s u f f i -c i e n t time f o r the symptoms to become manifest. Frogs were tested i n the following manner. A 10-gallon aquarium was divided i n t o two with a wire mesh. A Bronwill water c i r c u l a t o r i n one h a l f heated the water of the e n t i r e aquarium. The aquarium was f i l l e d to capacity and wire mesh placed on top. Frogs to be tested were placed i n one side of the tank. They were covered e n t i r e l y by water, but could extend t h e i r n o s t r i l s out at the top. Frogs were introduced i n t o the aquarium at 18 C, and the temperature was r a i s e d to the preset l i m i t i n 15-30 min. The desired temperature was maintained f o r three hours and the behavior of the frogs recorded. Death was defined as that point when frogs sank to the bottom of the tank and ho longer responded to a pinch by tweezers; the time t i l l death was recorded. Frogs used were both laboratory-reared and wild-caught. A l l frogs were maintained from 18-20 C f o r about 5 days p r i o r to t e s t i n g . Frogs were tested i n temperatures from 27-35 C. d. Water Balance 1) Dehydration A. v i t a l problem confronting anurans i s that of proper water balance and the avoidance of de s i c c a t i o n ; paramount to t h e i r s u r v i v a l i s the maintenance of a moist s k i n . The diff e r e n c e i n habitat preference of the two frogs may r e s u l t from divergent problems i n water balance, and a comparison of the rates of evaporative water loss was made with both species. Frogs of a l l sizes (laboratory-reared and wild -caught) were used. A l l frogs tested were maintained f o r one week at 18 C before t e s t i n g ; they were held i n tanks and provided with water and no food. Wire mesh boxes, e i t h e r 4 or 6 inches square, were made to hold the fro g s . A cage with a si n g l e frog enclosed was suspended by a s t r i n g so that a l l sides of the cage were exposed to a i r . Before being enclosed, the frog was forced to release a l l bladder water by having a small rubber tube put int o i t s cloaca and pressure being applied to the bladder. At the beginning of each t e s t , frogs were weighed to the nearest .05 g. The cage and frog were weighed together to avoid d i r e c t l y handling the f r o g . Every hour thereafter, the frog was again weighed. Frogs were exposed to s t i l l a i r at two d i f f e r e n t temperatures and humidities: 15 C and 60% humidity, and 28 C and 25% humidity. At 15 C, the tes t s with the large frogs were terminated a f t e r 6 hours, but small frogs were desiccated u n t i l the l e t h a l l i m i t was reached. These frogs were considered dead when they could no longer r i g h t themselves i f turned onto t h e i r backs. This endpoint i s a standard one f o r te s t s of desiccation l i m i t s with anurans (Heatwole et a l 1969). When the l e t h a l l i m i t was reached, the frog was reweighed, and the percentage of body weight l o s t was determined. The s u r v i v a l time was recorded. At 28 C, a l l frogs were desiccated u n t i l death occurred. Again the time t i l l death and percentage weight l o s t were 23 determined. For a l l frogs tested at 15 and 28 C, the rate of evaporative water loss per hour was cal c u l a t e d and the hourly average determined. Healthy frogs of each species that were not used i n des i c c a t i o n t e s t s were s a c r i f i c e d and placed i n an oven of 110 C f o r 48 hours. The percentage of t h e i r i n i t i a l body weight comprised of water was ascertained by comparing t h e i r wet and dry weights. 2) Submergence t e s t s The a b i l i t y of frogs to withstand submergence under water was in v e s t i g a t e d . Ten frogs of each species, a l l 28-33 mm sv length, and 1.5 - 3.2 g, were kept submerged i n a tank through which water 10 C was flowing. Frogs were kept submerged f o r eight hours and t h e i r behavior and s u r v i v a l recorded. e. Predators and Predator Avoidance 1) F i e l d t e s t s Throughout the study, as I searched f o r frogs i n the f i e l d , I took s p e c i a l notice of t h e i r escape responses. On some days, when I was ass i s t e d i n my searches f o r frogs, I performed t e s t s to gain i n s i g h t i n t o the frogs' escape responses. A f t e r a frog was caught and then ready f o r release, I placed i t p a r a l l e l to the r i v e r bank, 1-2 f t from water, between me and my companion. I then scored i t s escape behavior as being e i t h e r d i r e c t l y to land or to the water. I f i t went i n t o the water, i t was scored as e i t h e r immediately submerging or remaining on the water surface. 24 2) Laboratory escape behavior One of the major predators of frogs i n the LCR study area i s the garter snake, Thamnophis s i r t a l i s . Shakes c o l l e c t e d from the study area were used as predators i n laboratory studies of frog escape behavior. Naive laboratory-reared frogs were used as the prey. Since these frogs had never encountered natural predators of any kind, learning was not an important aspect of t h e i r i n i t i a l escape responses. Predation t e s t s with snakes and frogs were conducted i n the p l a s t i c swimming pool previously described and pictured i n P i g . 7. E i t h e r one or two frogs of each species ( a l l 26-32 mm sv length) were placed midway along one side of the pool (see x i n P i g . 7). They were undisturbed f o r 30 minutes. Afte r the 30 minutes had passed, I placed a garter snake i n the pool at the same place where the frogs were introduced, regardless of the p o s i t i o n of the frogs i n the pool. The p o s i t i o n of the frogs and notes of t h e i r movements r e l a t i v e to the movements of the snake were recorded. T r i a l s were continued f o r a maximum of 2 hours, or u n t i l a frog was caught by a snake. The snakes used were caught i n marshes adjacent to the LCR study area and had probably had experience with both R. aurora and R. p r e t i o s a as prey. The snakes were kept f o r 10 days i n the laboratory with only water and no food so as to increase t h e i r hunger l e v e l and hunting behavior before being used as predators. The confines of the pool probably affected the snakes' chances of catching frogs. However, the aim of these t e s t s was to study the frogs * behavior and pattern of escape rather than 25 the number eaten and time t i l l capture. Each t e s t was run with naive frogs so that s p e c i f i c differences i n escape patterns between R. aurora and R. p r e t i o s a were apparent. 3) Frog jumping a b i l i t y Laboratory-reared and wild-caught frogs were used f o r making comparisons of jumping a b i l i t i e s . Frogs of varying body lengths were used and the sv length and hind limb length were measured on a l l i n d i v i d u a l s . An i n d i v i d u a l frog was placed on the mud of the p l a s t i c swimming pool ( F i g . 7), (the moat i n the center was f i l l e d i n ) , and allowed to jump spontaneously. The distance between jumps was measured to the nearest cm. Over a period of s i x days, each frog had 30-45 jumps measured, and the longest 10 jumps f o r each animal were selected f o r comparison. 4) Predators Known vertebrate and invertebrate predators of anurans which occurred i n the LCR study area were recorded throughout the study. C. Comparative Reproductive Behavior How the frogs are reproductively i s o l a t e d i s an import ant aspect of how they s u c c e s s f u l l y coexist during breeding a c t i v i t i e s . Information has accumulated on both species during the breeding seasons of 1968 and 1969. M a t e r i a l , unless other-wise s p e c i f i e d , i s based on data from the LCR study area, where both species are sympatric. However, two other areas, where only R. aurora i s found, were also observed, as a means of determining i f t h i s species d i f f e r e d because of sympatry with 26 R. p r e t i o s a . One l o c a l i t y i s a small pond at sea l e v e l adjacent to Beaver Lake i n Stanley Park, Vancouver, B.C. The pond, formed by overflow from a large lake, i s about 15 by 40 f t , and 6-18 inches deep. The water i s c l e a r and allows good v i s i b i l i t y of the frogs that breed i n i t . Most breeding occurs i n the deeper muddy lake nearby. The second area i s Marion Lake i n the Unive r s i t y of B r i t i s h Columbia Forestry Reserve, about 1000 f t i n elevation near Haney, B.C. The lake i s 32 acres i n area, with a mean depth of 8 f t . The water i s very c l e a r and allows good v i s i o n of the several hundred R. aurora that breed i n i t . A thick coniferous f o r e s t extends to the lake on a l l sides. In both years, continuously recording thermographs (Ryan Model D) were submerged i n the center of the LCR study area pond, at a depth of 2 f t . In 1969, continuous a i r temper-atures were taken near the pond. In 1969, recorders did not measure below 0 C. The thermograph i n a i r was not exposed to d i r e c t sunlight and thus provided the maximum temperatures i n the shade throughout the day. For 1968, a i r temperatures are from the Vancouver a i r p o r t , about 20 miles to the north of the LCR study area, and the data are corrected f o r known differences between the two l o c a l i t i e s . P r e c i p i t a t i o n records f o r both years are from the a i r p o r t s t a t i o n . Frog v o c a l i z a t i o n s were recorded with a Uher M514 microphone, and an LC-10 hydrophone ( A t l a n t i c Research Co.), and a Uher 4000 Report-L tape recorder. C a l l s were analyzed on a Sonagraph (Kay E l e c t r i c ) , adequate tests being made to ensure 27 that c a l l s were not d i s t o r t e d i f recorded with d i f f e r e n t equipment. The i n t e n s i t y of the c a l l s as they occur i n the natural environment, were measured with a Scott Type 45G sound l e v e l meter. D « Embryonic Thermal Requirements and Environmental Temperatures In addition to the breeding behavior of the sympatric fro g s , what i s important to know i s how each species faces s i m i l a r s e l e c t i v e pressures with regard to other aspects of t h e i r breeding biology. One major component of the environment, impinging on almost a l l aspects of an anuran's l i f e h i s t o r y , i s temperature. The frog embryo i s e s p e c i a l l y susceptible to thermal s t r e s s since i t i s l e f t to develop i n the place where eggs were deposited, and i s unable to escape from adverse conditions. In large part, the s u r v i v a l of embryos w i l l depend on t h e i r thermal requirements and adaptations. Moreover, Moore (1949) has pointed out that embryonic thermal requirements are a major f a c t o r i n governing the geographic d i s t r i b u t i o n s of f r o g s . Determination of the thermal requirements of embryos of both species may provide f u r t h e r evidence on the mechanisms by which R. aurora and R. p r e t i o s a have achieved reproductive success i n sympatry. a. E f f e c t s of Temperature on Egg Development The basic experimental design f o r studying the eggs was to maintain eggs at constant temperatures, examine them 28 p e r i o d i c a l l y with a d i s s e c t i n g microscope, and note t h e i r pro-gress i n development. E f f o r t s were made to examine the eggs at approximately 6-hour i n t e r v a l s , but more frequent examinations provided more precise data on the time between successive stages and endpoints f o r eggs tested near l e t h a l thermal l i m i t s . C r i t e r i a f o r a l l stages were based on the staging system f o r Rana s y l v a t i c a ( P o l l i s t e r and Moore 1937). Since the temperature tolerance of embryos increases with age (Brown 1967), a b e t t e r analysis of l e t h a l l i m i t s i s obtained i f eggs i n very e a r l y stages are used i n tolerance t e s t s ; the most r e s t r i c t i v e thermal l i m i t s are those of young embryos. A l l spawn used were only a few hours o l d ; the S» aurora eggs were i n stage 4 ( 4 - c e l l ) and the R. p r e t i o s a eggs were i n stage 3 ( 2 - c e l l ) when most tolerance experiments were i n i t i a t e d . The temperatures at which the young eggs of each species were maintained and examined f o r development varied within 2 C or l e s s , except i n the 15 C f o r R. aurora. Here the temperature varied almost 4 C. The high temperatures (> 20 C) were established i n 10-gallon aquaria with use of Bronwill water c i r c u l a t o r s . The eggs were placed i n well perforated p l a s t i c containers and submerged i n constantly c i r c u l a t e d and aerated water. The 15 C t e s t f o r R:. aurora was done i n an aquarium held at room temperature. A Porta-Temp regulator kept the water of a 50-gallon tank at 10.8 C, and another tank was held at 7 C by adjusting the flow rate of declorinated water. For the lowest temperatures, eggs were kept i n glass stacking dishes i n a c o l d room at 4.5 C, and dishes containing other eggs were 29 kept on i c e i n the co l d room. This provided temperatures of 1-3 C. At l e a s t 50 eggs of each species were tested at each temperature. The e f f e c t of temperature on the rate of development was determined by examining 15-20 eggs i n each group, and c a l c u -l a t i n g the time between successive stages. When these eggs were found to have progressed i n stage, the number of hours between observation periods was taken to be the actual i n t e r v a l between the observed stages. In some instances i t was apparent that the eggs had been i n the new stage f o r several hours, and thus there are s l i g h t errors i n estimating time between some stages. More frequent examination of eggs at high temperatures reduced these e r r o r s . However, the estimate of primary concern i s the t o t a l number of hours f o r the embryos to reach a designated endpoint (described below). A, comparison, r e l a t i v e l y free of e r r o r , of the e f f e c t of temperature on the rate of development i s obtained when the t o t a l number of hours f o r the embryos to reach the standard endpoint i s c a l c u l a t e d . Stage 20 ( g i l l c i r c u l a t i o n ) was chosen to i n d i c a t e completion of development. Since embryos of d i f f e r e n t species of Rana hatch, ( i . e . , emerge from the j e l l y coats) at d i f f e r e n t stages, f o r example, 19, 20, or 21, the time to hatching may not be as good an endpoint f o r comparative purposes as a s p e c i f i c stage i n development. Consequently, when embryos reached stage 20 without obvious developmental abnormalities, they were considered completely developed. Embryos that reached t h i s stage i n apparently normal condition subsequently survived. The actual stage f o r hatching (emergence from j e l l y ) , was 30 ascertained f o r both species. The l e t h a l temperatures f o r bo±h species were defined as those at which e i t h e r l e s s than 50% of a l l the embryos i n each group f a i l e d to reach stage 20, or they did so with obvious developmental abnormalities that resulted i n subsequent m o r t a l i t y . Some data on changes i n temperature tolerance of embryos beyond stages 3 or 4 were obtained f o r both species. R. aurora eggs i n stage 9 ( l a t e b l a s t u l a ) were held at 20, 21.5, 2.6, and 28 C ( a l l - .1 C) f o r the duration of t h e i r development. Another group of R. aurora eggs i n stage 11 (gastrula) was maintained at 2 3 - .1 C. A set of R. p r e t i o s a eggs i n stage 5 ( 8 - c e l l ) was held at 30 i .1 C and examined f o r developmental success. These eggs as well as a l l others used, were c o l l e c t e d i n the f i e l d . b. E f f e c t s of Acute Cold Exposure on Survival A ser i e s of t e s t s was performed to determine i f the embryos of both species were able to withstand short-term ex-posure to cold temperatures that were normally l e t h a l to embryos i n chronic exposure. Embryos of both species were c o l l e c t e d i n the f i e l d and maintained f o r short periods i n water of 1 and 3.5 C (both - .5 C). Groups of R. p r e t i o s a embryos i n e a r l y stage 5 ( 8 - c e l l ) were kept i n e i t h e r 1 or 3.5 C f o r 4 hours. D i f f e r e n t groups of R. p r e t i o s a embryos i n stage 7 ( 3 2 - c e l l and morula) were placed i n e i t h e r 1 or 3.5 C f o r 2.5, 4, or 8 hours. Embryos of R. aurora i n stage 9 ( l a t e b l a s t u l a ) were placed i n 1 C 31 water f o r 2.5, 4, or 8 hours. Af t e r exposure to low temperatures f o r the varying time i n t e r v a l s , each group of embryos (at l e a s t 50 f o r each group) was returned to room temperature (16-18 C) and allowed to continue development. The e f f e c t of the short-term c o l d exposure was determined by comparing the s u r v i v a l of t e s t eggs with those of the controls (embryos from the same egg mass as t e s t eggs but not subjected to cold shock). Control eggs were kept at room temperature at a l l times. The low temperatures were s i m i l a r to those occurring at night where the species breed, and the time i n t e r v a l s chosen approximated durations of c o l d exposure i n the f i e l d . c. Embryonic Oxygen Consumption Embryos of both species i n the same developmental stages were used f o r measuring 0£ consumption. T h i r t y embryos i n e a r l y stage 12 (disappearing yolk plug) were placed i n a 250 ml Erlenmeyer f l a s k kept at 18.5 - .1 C. There were 6 r e p l i c a t e s (6 f l a s k s each with 30 embryos) f o r each species. Some j e l l y was l e f t attached to the eggs. The f l a s k s were i n i t i a l l y f i l l e d with air-saturated water and then sealed. A f t e r a period of 15 hours f o r R. aurora, and 18 hours f o r R. p r e t i o s a , the O2 consumption of the embryos within the f l a s k was determined by analyzing a sample of water from each f l a s k with use of a PO2 Radiometer. Measurement of embryonic r e s p i r a t i o n i s based on embryos progressing from stage 12 to e a r l y stage 15. 32 RESULTS A. Morphology In Amphibians of Western North America, Stebbins (1951, 331-332) provides a key and contrasting d e s c r i p t i o n s of R. aurora and R. pretios a* Stebbins' descriptions are s u f f i c i e n t to d i s t i n g u i s h i n d i v i d u a l s of each species found i n the LCR study area. Photographs of R. aurora and R. p r e t i o s a from the LCR are seen i n E i g s . 8-9. R. aurora tadpoles metamorphose at a body s i z e of 2 3-27 mm. Males become sexually mature at 45 mm sv length, a si z e reached during t h e i r f i r s t f u l l year a f t e r transformation. They breed at the s t a r t of t h e i r second f u l l year. Males reach a maximum of 64 mm sv length. R. aurora females are mature at 62 mm sv length which they achieve i n about 4 years. They f i r s t breed at the s t a r t of t h e i r 4th or 5th f u l l year a f t e r trans-formation. Females grow to a maximum s i z e of 77-80 mm sv length. Tadpoles of R. p r e t i o s a transform at a sv length of 33-37 mm. Males are mature at 45 mm sv length, and they breed at the s t a r t of t h e i r second year. Females f i r s t breed at the s t a r t of t h e i r t h i r d year, and are mature at 62 mm sv length. Male R. p r e t i o s a grow to a maximum of 64 mm and females to 80-82 mm sv length. Several features of the morphology of the frogs are important i n that the differences between the two species are r e l a t e d to t h e i r divergent behavior. The hind limbs of R. aurora are r e l a t i v e l y longer than are those of R. p r e t i o s a . A com-parison of t h e i r hind limb lengths r e l a t i v e to body siz e i s seen Figure 8 Male Rana aurora (top) and Rana p r e t i o s a . Figure 9 Male Rana aurora ( l e f t ) and Rana p r e t i o s a . Note eyes of Rana p r e t i o s a face upwards. 35 i n F i g . 10. The outstretched hind limb of R. aurora i s about twice as long as i t s body length, while that of R. p r e t i o s a i s only about 1^ times as long as i t s body. An inspection of the skeletons and i s o l a t e d limb bones of specimens of each species reveals that the t i b i o - f i b u l a bone i n the limb of R. aurora i s r e l a t i v e l y longer than the corresponding bone i n the limb of R. p r e t i o s a . Another feature of the limbs that d i f f e r s between the species i s the degree of webbing on the hind f e e t . In R. p r e t i o s a , the webbing i s more extensive and extends nearly to the t i p of the d i g i t s of the hind f e e t . In R'. aurora, the d i g i t s extend beyond the webbing f o r at l e a s t several mm. A l l d i g i t s of R. p r e t i o s a are nearly completely joined by webbing, except f o r the 4th and longest d i g i t . Moreover, the actual d i g i t s of R. p r e t i o s a do not seem as muscular and thick as those of R. aurora. The c a l l o s i t i e s on the j o i n t s of the d i g i t s are more pronounced i n the feet of R. aurora. A representation of the hind feet of both species showing the d i f f e r e n c e i n webbing and d i g i t development i s seen i n F i g . 11. A. very important d i s t i n c t i o n between the species i s the p o s i t i o n of t h e i r eyes. Those of R. aurora face l a t e r a l l y , while those of R. p r e t i o s a face upwards. This d i f f e r e n c e can be seen i n F i g . 9. The skin of R. p r e t i o s a i s covered with a mucus coat-in g which i s absent from R. aurora. The mucus secretion becomes very copious when the frog i s handled, and because the frog i s normally wet from immersion i n water, i t becomes very s l i p p e r y and d i f f i c u l t to hold. Figure 10 Relative s i z e of hind limbs of Rana aurora and Rana p r e t i o s a . Lines f i t t e d to le a s t squares regression where y = hind limb length (mm) and x = snout-vent length (mm). For Rana' aurora, y = -7.8 + 2.02x, and f o r R'ana p r e t i o s a , y = 3.9 + 1.50x. Snout-vent Length (mm) Figure 11 Dorsal view of r i g h t hind foot of Rana aurora and Rana p r e t i o s a . ' based on foot of female 60 mm snout-vent length. Rang pretiosa Rana aurora 38 B. Ecology a* Habitat Preferences In the f i e l d , R. p r e t i o s a i s usually found i n the water, and r a r e l y more than a foot away from water. When r a i n -pools are present i n the spring, i n d i v i d u a l s s i t e i t h e r i n the pools or along the margins. When the rainpools dry, R. p r e t i o s a moves to the r i v e r , and none are found active i n the f i e l d away from the standing water. In the r i v e r , they s i t i n the shallows, h a l f submerged or they f l o a t i n deeper water, c l i n g i n g to aquatic vegetation, often with only t h e i r head v i s i b l e above water. At times they w i l l be on the banks of the r i v e r , only a few inches from the water. Only on wet, rainy days does £• p r e t i o s a move away from the v i c i n i t y of standing water. In contrast, R. aurora i s nearly always found on land. They may be near standing water, but they remain on land, and move within tangles of vegetation near the water. They also move many feet away from water i n both dry and wet conditions. When rainpools dry, R. aurora moves ei t h e r to the woods or to the v i c i n i t y of the r i v e r . They are found on and i n the vegeta-t i o n along the r i v e r edge and several f e e t away. They do not move i n t o the water as do R. p r e t i o s a . During the summer of 1969, I caught 98 R. p r e t i o s a . Of these, 86 were taken i n water and 12 on land only inches away from water. Of 74 R. aurora caught on the same days, 72 were on land and 2 were i n water. The t e s t s on habitat preferences with frogs placed i n 39 the p l a s t i c swimming pool y i e l d e d c l e a r r e s u l t s . During 15 t r i a l s of 30 minutes each (before snakes were introduced) 30 observa-tions were made on the frogs. R. aurora was on land 27 times and i n the water 3 times; R. p r e t i o s a was on land 7 times and i n water 23 times. Those R. p r e t i o s a on land had sometimes not found water f o r 15-20 minutes, but once they d i d , they did not leave i t to return to land. b. Food 1) Feeding behavior i n the f i e l d Adult and juv e n i l e R. aurora were r a r e l y sighted u n t i l they began jumping as I neared them i n my searches of the f i e l d . I was unable to make meaningful observations of t h e i r natural feeding behavior. The feeding behavior of newly transformed R. aurora was more e a s i l y observed. A f t e r metamorphosis i n July, the small frogs remain along the r i v e r banks. They are us u a l l y found a few feet from the r i v e r edge i n patches of Ranunculus that grows along the shore. On warm dry days during the summer, they feed at the water margin, catching small i n s e c t s along the banks, i n the vegetation, and occ a s i o n a l l y swimming a few inches i n t o the r i v e r to take an in s e c t on the water surface or on an aquatic p l a n t . In the e a r l y part of the day when there i s s t i l l moisture l e f t on the vegetation, the small R. aurora move i n t o the vege-t a t i o n and feed i n the undergrowth. During or af t e r a r a i n , small R. aurora move many feet from the r i v e r , on the carpet of Ranunculus and near Carex, t r y -i n g to catch spiders and other small i n s e c t s . I f rainpools 40 form i n the f i e l d , the frogs feed along the margins, s t a l k i n g small prey i n and out of the water. They often remain i n the v i c i n i t y of the rainpools as long as they contain water, but once these dry, they again return to the r i v e r margins. Although I did not observe feeding behavior i n adult R. aurora, i n d i v i d u a l s were often scared up as I walked along the r i v e r i n the vegetation during the summer months. Presumab-l y they were feeding i n the vegetation along the r i v e r margins, as were the young-of-the-year i n d i v i d u a l s . £• p r e t i o s a (young and adult) are e a s i l y observed i n t h e i r natural feeding behavior. Individuals were us u a l l y seen from f a r enough away that I was able to observe them without disturbing them. Throughout the year, R. p r e t i o s a feeds i n or along bodies of water, e i t h e r the r i v e r , pond, or rainpools when present. During May and e a r l y June, when rainpools are present i n the f i e l d , R. p r e t i o s a feeds along the sides of these pools, or while f l o a t i n g on the water surface. During the summer, the frogs f l o a t i n the r i v e r , hanging onto stems or other vegetation, e i t h e r i n mid-stream or at the r i v e r margins. Usually they are completely submerged except f o r t h e i r heads that protruded above the water. They often remain h a l f concealed i n thick beds of Potamoqeton or Myriophyllum. Depending on the temperature of the day, they also s i t on exposed mud along the r i v e r margins, and as the temperature r i s e s they move i n t o the water. p r e t i o s a remains motionless f o r long periods, some-times f o r an hour or more. Any su i t a b l e item that moves near them evokes an o r i e n t a t i o n response, and i f the prey i s cl o s e , 41 the frog s t r i k e s at i t . Usually a prey i s located on the water surface, and the frog swims towards i t , k i c k i n g with the hind limbs and making l i t t l e disturbance. Usually only the frog's head and eyes protrude above the water. A f t e r s t a l k i n g the prey i n t h i s manner, R. p r e t i o s a s t r i k e s from close range. On dry days, R. p r e t i o s a i s r a r e l y found out of water. At most i t i s within a foot of the water. On dry days, I saw no feeding a c t i v i t y on land i n the vegetation; a l l feeding a c t i v i t y was i n the water. However, during and a f t e r r a i n , these frogs move i n t o the wet undergrowth and feed i n and among the vegetation, sometimes many feet from the r i v e r . They quick-l y move i n t o rainpools when these form i n the f i e l d and feed from the water surface or margins. Newly transformed frogs of both species are often seen feeding within inches of each other, u s u a l l y along the r i v e r edge or near rainpools. On hot summer days, when R. aurora i s r e s t r i c t e d to the r i v e r margins, the two species often feed i n c l o s e proximity. However, on such occasions, R. p r e t i o s a i s almost always i n the water, while R. aurora i s on the nearby land. R. aurora i s more active i n seeking food and moves i n and out of the vegetation; R. p r e t i o s a spends more time waiting f o r prey to move near. Both species are p r i m a r i l y d i u r n a l i n feeding habits, but may feed at night during warm summer nights. I d i d not observe nocturnal a c t i v i t i e s . I threw various food items to adult R. p r e t i o s a to note t h e i r responses. Small grasshoppers and other small prey were r e a d i l y taken i f the prey were thrown near the frogs i n the 42 water. On many occasions, a frog would seize a prey item and then quickly submerge i t s head to swallow. Occasionally, a frog came onto the r i v e r bank to take a prey item I had thrown, but always immediately returned to water and often submerged to swallow the food. These frogs seemed reluctant to move onto land to take food, although they often swam to shore and i n v e s t -igated food items thrown onto shore. Adult R. p r e t i o s a seized and ate adult treefrogs, Hyla  r e q i l l a (30-35 mm sv length), and small R. aurora and R. p r e t i o s a (25-35 mm sv length). Three times, without any manipulation on my part, I saw adult R. p r e t i o s a grab and attempt to swallow newly metamorphosed R. aurora. In two of these cases, the R. p r e t i o s a swallowed the prey, the t h i r d frog escaped by strugg-l i n g v i o l e n t l y . Adult R. p r e t i o s a often oriented to small R. aurora moving on land, but they did not leave the water. In laboratory t e r r a r i a , adult R. aurora d i f f e r from adult R. p r e t i o s a i n an obvious way. R. aurora r e a d i l y jumps a foot or more i n attempting to grab a prey item; i t i s usually accurate i n i t s jumps. R. p r e t i o s a seldom jumps, but moves slow-l y towards a prey item and grabs i t d i r e c t l y , or jumps from a few inches away. I t sometimes jumps many times i n succession at a prey, and often tripped over i t s own feet i n i t s awkward jumping motions. 2) Analysis of stomach contents Prom May to October 1968, 104 R. aurora and 41 R. p r e t i o s a were c o l l e c t e d and t h e i r gut contents analyzed f o r food items. The sample of each was separated i n t o 2 categories: 43 78 newly transformed R. aurora; 26 juvenile-adult R. aurora; 18 newly transformed R. p r e t i o s a ; 23 j u v e n i l e - a d u l t R. p r e t i o s a . Newly metamorphosed frogs f i r s t appear i n samples taken i n J u l y and August. This i s the time that they f i r s t begin transforming from tadpoles to frogs. The stomach and i n t e s t i n a l t r a c t of every frog i n a l l samples contained some food item; there were no empty stomachs. Because I d i d not survey the invertebrates i n the marshes where the frogs were caught, I have no estimates of a v a i l a b i l i t y and abundance of prey. Therefore no data are a v a i l a b l e on whether the frogs show food preferences. However, other studies of ranid feeding behavior (Turner 1958, Jenssen and Klimstra 1966) i n d i c a t e frogs feed on what i s a v a i l a b l e at any s p e c i f i c time, and d e f i n i t e food preferences are unknown. For example, arachnids are a v a i l a b l e i n a l l months from May to October, and appear i n the guts of both species during each monthly c o l l e c t i o n . But syrphid f l i e s and larvae f i r s t become abundant i n the guts i n J u l y and August, the time period when they are e s p e c i a l l y abundant i n the marshes. The food taken by a l l R. aurora i s l i s t e d i n Table I, and the food eaten by a l l R. p r e t i o s a i n Table I I . Food items found i n the guts of newly metamorphosed R. aurora and j u v e n i l e -adult R. aurora are l i s t e d i n Tables I I I and IV. Tables V and VI l i s t the same data f o r newly metamorphosed R. p r e t i o s a and j u v e n i l e - a d u l t R. p r e t i o s a . The data presented i n these tables are the percentage of a l l stomachs within the sample containing a p a r t i c u l a r food item, and the percentage of a l l the food eaten made up by that p a r t i c u l a r food item. 44 The number of food c l a s s i f i c a t i o n s and the percentage overlap of these food c l a s s i f i c a t i o n s between and within the samples of each species i s seen i n Table VTI. Of s p e c i a l i n t e r -est i s that the newly metamorphosed frogs of both species have the highest percentage overlap with other samples. Newly meta-morphosed R. p r e t i o s a share as much as 73.1% of the food they e x p l o i t with newly metamorphosed R. aurora and j u v e n i l e - a d u l t R. p r e t i o s a . Another means of judging the degree to which both species, and age groups within species, share the same resources i s to examine the dominant foods appearing i n t h e i r gut contents. I f foods that are used frequently by each species are shared, then food overlap may be an important aspect of possible competi-t i o n between the species. The dominant foods were determined i n two fashions. F i r s t , the top food classes were selected on the basis of frequency i n the stomach samples. Second, the top food classes were selected on the basis of t h e i r abundance i n the stomach samples. The top eight food items f o r each sample were compiled by both techniques. The top eight foods based on t h e i r abundance i n the guts of frogs i n the d i f f e r e n t samples make up most of the food eaten. For a l l R. aurora, the top eight foods comprise 71.4% of a l l the food, and f o r a l l R. p r e t i o s a . the top eight comprise 57.3% of a l l the food items. For s i z e classes within species, the dominant eight foods make up- the following percentages of a l l food eaten: newly metamorphosed R. aurora - 72%, J u v e n i l e -adult R. aurora - 76%, newly metamorphosed R. p r e t i o s a - 74%, j u v e n i l e - a d u l t R. p r e t i o s a - 55.5%. 45 A comparison of the percentage overlap of the dominant eight food classes based on t h e i r frequency occurrence i s l i s t e d i n Table VIII. Table IX compares the percentage overlap of the dominant eight foods based on t h e i r abundance i n a l l the stomachs within a sample. The value 75% i n Table VIII i s s t r i k i n g . This means that newly metamorphosed frogs of both species share 75% of t h e i r most commonly eaten foods. Furthermore, they share 60.2% of the prey items that they eat i n greatest numbers (Table IX). I f the samples within each species are combined, then the species share 87.5% of the dominant foods occurring i n most stomachs (Table VIII), and 75% of the foods eaten i n most abundance (Table IX). The overlap i n d i e t between the combined samples of each species, based on the dominant eight foods, i s i l l u s t r a t e d i n F i g s . 12 and 13. F i g s . 14 and 15 i l l u s t r a t e the overlap i n dominant foods of d i f f e r e n t age classes of frogs. (Note that the actual food items, c l a s s i f i e d to family f o r most, are l i s t e d i n F i g s . 12-15). The food items among the dominant prey taken which are not shared reveal important differences i n the d i e t and feeding behavior of the two species, e s p e c i a l l y between the newly trans-formed i n d i v i d u a l s . R. aurora feed heavily on land slugs that are a v a i l a b l e away from the water i n the vegetation and mud. These slugs appear only sparsely i n the stomachs of R. p r e t i o s a . In contrast, small R. p r e t i o s a eat large numbers of Dolichopodidae, an aquatic dipteran. This aquatic prey i s not taken by R. aurora. 3) Laboratory feeding t e s t s The r e s u l t s of feeding t e s t s with newly metamorphosed TABLE I Analysis of food items i n gut contents of 104 newly metamorphosed and j u v e n i l e - a d u l t Rana aurora Pood items % o f a 1 1 % ° f t o t a l Food items % of a l l % of t o t a l roua item& stomachs food items stomachs food items Mollusca S n a i l 3.8 1.5 Slug 18.3 4.0 Arachnida 51.0 15.6 Insecta Orthoptera Locustidae 1.0 .1 Plecoptera 1.0 .1 Hemiptera Gerridae 2.9 .4 Nabidae 6.7 1.1 Saldidae 6.7 1.1 Miridae 1.0 .1 Cercopidae 41.3 17.6 C i c a d e l l i d a e 17.3 6.6 Aphididae 13.5 4.6 Coleoptera Carabidae 26.0 7.5 Carabidae larvae 4.8 1.2 D y t i s i c i d a e 1.0 .1 Limnebiidae 4.8 .8 Staphylinidae 26.9 8.0 Staphylinidae larvae 1.9 .4 Phalacridae 1.9 .3 C o c c i n e l l i d a e 1.0 .1 Lampyridae larvae 1.0 .1 E l a t e r i d a e larvae 1.0 .1 Scarabaeidae 1.9 .4 Chrysomelidae 8.7 1.8 Mylabridae 1.0 .1 Curculionidae 5.8 1.1 Insecta Trichoptera 3.8 .6 Trichoptera larvae 1.9 .4 Lepidoptera Geometridae larvae 1.0 .1 Noctuidae larvae 2.9 .4 Diptera Tipulidae 2.9 .4 Tipulidae larvae 2.9 .6 Chironomidae larvae 8.7 2.4 Ceci domyi i dae 1.0 .1 Mysetopliidae 1.9 .3 O t i t i d a e 1.0 .1 Stratiomyidae larvae 1.0 .1 Dolichopodidae 5.8 1.9 Ephydridae 3.8 .8 Syrphidae larvae 25.0 7.5 Canopidae 1.0 .1 Bibionidae 1.0 .1 Trupaneidae 1.9 .4 Muscidae 1.9 1.0 Borboridae 2.9 .4 Hymenoptera Tenthredinidae 1.9 .3 Tenthredinidae larvae 2.9 .4 Ichneumonidae 12.5 3.6 Braconidae 1.0 .1 Chalcididae 1.9 .6 Cynipidae 2.9 .4 Trichogrammatidae 1.0 .1 Formicidae 8.7 1.2 T o t a l 100 TABLE II Analysis of food items i n gut contents of 41 newly metamorphosed and j u v e n i l e - a d u l t Rana p r e t i o s a . _ . % of a l l % Of t o t a l _ . % of a l l % of t o t a l Food items stomachs food items F o o d i t e m s stomachs food items Mollusca Coleoptera S n a i l 4.9 1.3 N i t l d u l i d a e 2.4 .7 Slug 2.4 .3 Scarabaeidae 2.4 .3 .rachnida 22.0 8.5 Chrysomelidae 12.2 9.1 nsecta Chrysomelidae larvae 2.4 2.3 Orthoptera Curculionidae 12.2 1,6 Locustidae 2.4 .3 Trichoptera adult 2.4 .3 Odonata Trichoptera larvae 2.4 .3 Coenagrionidae 4.9 .7 Lepidoptera Hemiptera Hepialidae larvae 2.4 .3 Corixidae 2.4 .3 Noctuidae larvae 2.4 .3 Corixidae nymphus 2.4 .3 Pieridae larvae 2.4 .3 Gerridae 9.8 2.6 Diptera Nabidae 9.8 1.6 Tipulidae 4.9 1.0 Saldidae 9.8 1.3 Chironomidae larvae 2.4 .3 Cercopidae 17.1 6.2 Cecidomyiidae 4.9 .7 C i c a d e l l i d a e 12.2 5.5 Lauxaniidae 4.9 .7 Aphididae 17.1 3.3 Dolichopdidae 22.0 7.8 Coleoptera Ephydridae 7.3 1.3 Carabidae 19.5 7.8 Syrphidae adult 2.4 .7 Carabidae larvae 2.4 .7 Syrphidae larvae 17.1 6.5 Dytiscidae 12.2 1.6 Bibionidae 4.9 1.6 Staphylinidae 17.1 5.9 Tachnidae 7.3 1.6 Hydrophilidae larvae 2.4 .3 Hymenoptera Co c c i n e l l i d a e 4.9 .7 Ichneumonidae 4.9 .7 Coc c i n e l l i d a e l a r v a r 4.9 1.0 Vespidae 14.6 2.3 Cantharidae 2.4 .3 Formicidae 22.0 4.6 Heteroceridae 2.4 .7 Bombidae 2.4 .3 Buprestidae 7.3 1.3 Apidae 7.3 1.6 H a l i p l i d a e 2.4 .3 Total 100 Meloidae 2.4 .-7 TABLE I I I Analysis of food items i n gut contents of 78 newly metamorphosed Rana aurora Food items % of a l l stomachs % of t o t a l food items Food items % of a l l stomachs % of t o t a l food items Mollusca S n a i l Slug Arachnida Insecta 3.8 23.1 48.7 1.8 5.2 12.0 Diptera Orthoptera .2 Locustidae 1.3 Plecoptera 1.3 .2 Hemiptera .2 Gerridae 1.3 Nabidae 5.1 .7 Saldidae 6.4 1.1 Cercopidae 52.6 22.9 C i c a d e l l i d a e 17.9 7.7 Aphididae 16.7 5.7 Coleoptera 16.7 Carabidae adult 4.1 Carabidae larvae 3.8 1.3 Dytiscidae ~. 1.3 .2 Staphylinidae 20.5 6.5 Staphylinidae larvae 2.6 ..6 Phalacridae 2.6 .4 Elateridae larvae 1.3 .2 Scarabaeidae 2.6 .6 Chrysomelidae 7.7 1.8 Curculionidae 2.,6 .4 Trichoptera adult 2.6 .4 Trichoptera larvae 1.3 .2 Lepidoptera .2 Noctuidae larvae 1.3 Tipulidae adult 1.3 .2 T i p u l i d a e larvae 3.8 .7 Chironomidae larvae 11.5 3.1 Cecidomyiidae 1.3 .2 Mysetopliidae 2.6 .4 O t i t i d a e 1.3 .2 Stratiomyiidae larvae 1.3 .2 Dolichopodidae 6.4 2.3 Ephydridae 5.1 1.4 Syrphidae larvae 32.1 7.5 Trupaneidae 2.6 .6 Muscidae 1.3 .2 Borboridae 3.8 .6 Hymenoptera Tenthredinidae 1.3 .2 Tenthredinidae larvae 3.8 .6 Ichneumonidae 14.1 4.1 Braconidae 1.3 .2 Chalcididae 2.6 .7 Cynipidae 3.8 .6 Formicidae 10.3 1.5 T o t a l 100 TABLE IV Analysis of gut contents of 26 j u v e n i l e - a d u l t Rana aurora. » », % of a l l % of t o t a l , . m e. % of a l l % of t o t a l Food items stomachs food items F o o d i t e m s stomachs food items Mollusca S n a i l 3.8 .6 Slug 3.8 .6 Arachnida 57.7 26.7 Insecta Hemiptera Gerridae 7.7 1.1 Nabidae 11.5 2.2 Saldidae 7.7 1.1 Miridae 3.8 .6 Cercopidae 7.7 1.7 Gic a d e l l i d a e 15.4 3.3 Aphididae 3.8 1.1 Coleoptera Carabidae adult 53.8 17.8 Carabidae larvae 7.7 1.1 Limnebiidae 19.2 3.3 Staphylinidae 46.2 12.8 Co c c i n e l l i d a e 3.8 0.6 Lampyridae larvae 3.8 0.6 Coleoptera Chrysomelidae 11.5 1.7 Mylabridae 3.8 0.6 Curculionidae 15.4 3.3 T r i c o p t e r a adult 7.7 1.1 T r i c o p t e r a larvae 3.8 1.1 Lepidoptera Geometridae larvae 3.8 0.6 Noctuidae larvae 7.7 1.1 Diptera Tipulidae 7.7 1.1 Dolichopodidae 3.8 1.1 Syrphidae larvae 3.8 6.1 Ganopidae 3.8 0.6 Bibionidae 3.8 0.6 Muscidae 3.8 3.3 Hymenoptera 0.6 Tenthredinidae 3.8 Ichneumpnidae 7.7 1.1 Trichogrammatidae 3.8 0.6 Formicidae 3.8 0.6 T o t a l 100 4* TABLE V Analysis of gut contents of 18 newly metamorphosed Rana p r e t i o s a _ . % of a l l % of t o t a l , , . o m e % of a l l % of t o t a l Food xtems stomachs food items F o o d l t e m s stomachs food items Arachnida 77.8 14.7 Insecta Hemiptera Gerridae 5.6 .9 Nabidae 11.1 1.7 Saldidae 11.1 1.7 Cercopidae 27.8 14.7 C i c a d e l l i d a e 16.7 12.9 Aphididae 22.2 4.3 Coleoptera Carabidae 11.1 4.3 D y t i s i c i d a e 11.1 1.7 Staphylinidae 16.7 3.4 Co c c i n e l l i d a e 11.1 1.7 Co c c i n e l l i d a e larvae 5.6 .9 Heteroceridae 5.6 1.7 N i t i d u l i d a e 5.6 1.7 Chrysomelidae 5.6 1.7 Curculionidae 5.6 .9 Lepidoptera Noctuidae larvae 5.6 .9 Diptera Chironomidae larvae 5.6 .9 Cecidomyiidae 11.1 1.7 Dolichopodidae 22.2 13.8 Ephydridae 5.6 1.7 Syrphidae larvae 22.2 3.4 Tachnidae 5.6 .9 Hymenoptera Ichneumonidae 5.6 .9 Vespidae 5.6 .9 Formicidae 16.7 6.0 T o t a l 100 o TABLE VI Analysis of gut contents of 2 3 juvenile-adult Rana p r e t i o s a . « ^ % of a l l % of t o t a l 4*.ama % o f a 1 1 % o f t o t a l Food items stomachs food items F o o d i t e m s stomachs food items Mollusca S n a i l 18.7 2.1 Slug 4.3 .5 Arachnida 21.7 4.7 Insecta Orthoptera Locustidae 4.3 .5 Odonata Coenagrionidae 8.7 1.0 Hemiptera Corixidae adults 4.3 .5 Corixidae nymphs 4.3 .5 Gerridae 13.0 3.7 Nabidae 8.7 1-6 Saldidae 8.7 1.0 Cercopidae 8.7 1.0 C i c a d e l l i d a e 8.7 1.0 Aphididae 13.0 2.6 Coleoptera Carabidae adult 26.1 9.9 Carabidae larvae 4.3 1.0 Dytiscidae 13.0 1-6 Staphylinidae 17.4 7.3 Hydrophilidae larvae 4.3 .5 Co c c i n e l l i d a e larvae 4.3 1.0 Cantharidae 4.3 .5 Coleoptera Buprestidae 13.0 2.1 H a l i p l i d a e 4.3 .5 Meloidae 4.3 1.0 Scarabaeidae 4.3 .5 Chrysomelidae adult 17.4 13.6 Chrysomelidae larvae 4.3 3.7 Curculionidae 17.4 2.1 Tric o p t e r a adult 4.3 .5 Tr i c o p t e r a larvae 4.3 .5 Lepidoptera Hepialidae larvae 4.3 .5 Pieridae larvae 4.3 .5 Diptera Tipulidae 8.7 1.6 Lauxaniidae 4.3 1.0 Dolichopodidae 21.7 4.2 Ephydridae 8.7 1.0 Syrphidae adult 4.3 1.0 Syrphidae larvae 13.0 8.4 Bibionidae 8.7 2.6 Tachnidae 8.7 2.1 Hymenoptera Ichneumonidae 4.3 .5 Vespidae 21.7 3.1 Formicidae 26.1 3.7 Bombidae 4.3 .5 Apidae 13.0 2.6 T o t a l 100 52 TABLE VII Percentage overlap of t o t a l food c l a s s i f i c a t i o n s between species and age groups within species. Rana aurora Rana p r e t i o s a Newly meta- J u v e n i l e - Newly meta- Juvenile-morphosed adult morphosed adult rt u o u rt rt c rt « ! £ U to o 2 £ rt 01 O •H -P 0) rt c rt 45 33 26 43 Number of food classes Percentage overlap of food classes of group above with group below i rt -P xi E w O - 69.7 73.1 55.8 51.1 - 65.4 48.8 > 3 3 TJ i-) rt I rt 0) <U e co >,J§ 42.2 51.5 - 44.2 •H a <u o 2 e i •H 53.3 63/6 73.1 > 3 t-j rt 53 TABLE V I I I Percentage overlap of dominant eight food items (those food items occurring i n most frog stomachs). Group on * Rana aurora »Rana p r e t i o s a r i g h t over-laps with Newly meta- Juvenile- Newly raeta- J u v e n i l e -group below morphosed adult morphosed adult 1 (0 +> n E to 0 U •H a 0 u 4) 0 P a £ (0 fO i c 0) (0 rH •H C -P (U rH > P P XJ 1 (0 -P -a 0) 0) E ro w O 0 •H rH a -p <u <u o u £ E a (0 1 c 0) rH DC •H c -P 01 rH > P P -0 t"5 «5 37.5 75 37.5 50 50 60.2 75 50 50 37.5 60.2 60.2 • A l l Rana aurora combined and a l l Rana p r e t i o s a combined share 87.5% of dominant eight foods. 54 TABLE IX Percentage overlap of dominant eight food items (those food items most abundant i n a l l stomachs). Group on *Rana aurora »Rana p r e t i o s a r i g h t over-laps with Newly meta- Juv e n i l e - Newly meta- Juvenile-group below morphosed adult morphosed adult I m -P TJ CD <0 E W 0 >iJC a u <u o 0 2 E u 3 <3 1 <d CD •H OS C -P CD rH > 3 3 TJ 1 (d -P TJ 0) CD E w <d 0 10 f-l fX o •H <u o -P 2 E CD M a 1 rd a> C rH <d •H « C -P 0) rH > 3 3 TJ 1-3 (d 60.2 60.2 50 60.2 60.2 50 60.2 37.5 50 50 50 50 * A l l Rana aurora combined and a l l Rana p r e t i o s a combined share 75% of dominant eight foods. Figure 12 Overlap of dominant food items of a l l Rana aurora and a l l Rana  p r e t i o s a , and percentage of t o t a l stomachs which contained the food. Top eight food items are those appearing i n most stomachs. Number i n parentheses i s t o t a l number of stomachs f o r each group. Per Cent of Stomachs Containing Item _ r \ j w 01 o> ~g ao to o o o o o o o o o o o _J I I I I I I I I I Arachnida Oercopidae Staphylinidae Carabidae o o °- Syrphidae larvae C D 3 Aphididae Cicadellidae Slugs Dolichopodidae 1 Formicidae T3 ct> — « -o' 18 = > 3 n _H_ 4> O — 4k Figure 13 Overlap of dominant food items of a l l Rana aurora and a l l Rana  p r e t i o s a and percentage of t o t a l food intake each food item comprises. Top eight food items are those most abundant i n a l l stomachs of each species. Number i n parentheses i s t o t a l number of food items i n a l l samples. lOOn E TJ O O LL D O c a> 90 80 70-60 50-40" 30 20-R. aurora (722 items) R. pretiosa (307items) o o o z 0) o T J a. o e E l o o *-CO Z <u o T J 5 O o u 0) .c l . 8-2 P 7 : o T J ttJ T J O U 0) O T J a. < 3 2 a> o T J "ai E o 10 T J O CL O Food Item Figure 14 Overlap of dominant food items of frogs of d i f f e r e n t age c l a s s e s . Top eight items f o r each age c l a s s are those appearing i n most stomachs within each c l a s s . Number i n parentheses i s t o t a l number of stomachs f o r each age c l a s s . 100 6 CO C. C D C O C J V) o D E o CO c C O o • Juvenile-Adult B- aurora (n=26) H Juvenile-Adult R. pretiosa (n=23) • Newly Metamorphosed R. aurora (n°78) 0 Newly Metamorphosed R pretiosa (n= 18) 40 pi <u o T J c £ CD o T J o -Or o T J T J o CL o XT o o Q 7] / / / / Z QJ O T J "3 a> o T J 8-2 / / / / / / / / 0) o T J '5. o o l _ a> O / / / / XS 0 SZ L_ a. a k. — >» to O T J T J F o o d Item Figure 15 Overlap of dominant food items of frogs of d i f f e r e n t age c l a s s e s . Top eight items are those most abundant i n a l l stomachs of each age c l a s s . Number i n parentheses i s t o t a l number of food items of a l l kinds found i n stomachs of each group. Percent of Total Food Items -n o o a . a> U l 0") 0 0 1 0 o o o o o o —I 1 1 I ' I o o Muscidae Dolichopodidae Formicidae S 3 Gerrfdae Cercopidde Aphididae Slugs Chrysomelidae m E3 • a> to 5 1 << ^ 2 2 fl> rj> -* -+ Q a 3 3 o o -\ -1 •o T J 3T ZX o o CA CA a> <x> Q. O. c _ C . c c < < ft) CD 3 2. 5" «> > > a. a. c c = * = ; Q C 3 -« Q o' a 3 3 tA (A T J - I a> ;+ o' CD 0 0 2 CD (0 3 3 (A (A 59 frogs under wet and dry conditions are seen i n Table X. The t o t a l number of s t r i k e s , the percentage of successful s t r i k e s , and the actual numbers of f l i e s eaten, are l i s t e d . The r e s u l t s under each of the two conditions were pooled, and the d i f f e r -ences between species tested by Chi squares; the l e v e l s of s i g n i f i c a n c e f o r differences observed are seen i n Table XI. In both wet and dry conditions, R. p r e t i o s a attempted to capture f l i e s more frequently than did R. aurora. R. p r e t i o s a o r i e n t s and s t r i k e s as long as f l i e s are present. When they see a f l y , they move to within an inch or les s and s t r i k e at i t . R. p r e t i o s a usually misses the f i r s t s t r i k e , and may s t r i k e many times i n succession u n t i l the f l y i s ei t h e r caught or moves away. In wet bowls, R. p r e t i o s a ate and struck almost exclusive-l y at f l i e s on the water surface, and seldom attempted to eat f l i e s on the walls of the bowls. In contrast, R. aurora r a r e l y s t r i k e s at f l i e s on the water surface i n wet bowls, but t r i e s f o r those prey that are moving on the walls and cover of the bowls. R. aurora jumps at the f l i e s from several inches away, and i s us u a l l y s u c c e s s f u l . I f not, they jump two or three times i n quick succession, but not repeatedly as did R. p r e t i o s a . In the dry bowls, R. aurora i s very accurate and usually catches the f l i e s on t h e i r f i r s t attempt. Although R. pr e t i o s a i s more active at s t r i k i n g at f l i e s , and does so without h e s i t a t i n g before each s t r i k e (R. aurora c h a r a c t e r i s t i c a l l y hesitates before s t r i k i n g ) , they are no more successful at capturing f l i e s than R. aurora. The percentage of successful s t r i k e s f o r both species does not d i f f e r under each of the conditions, although R. p r e t i o s a spends much 60 TABLE X T o t a l number of s t r i k e s , percentage of s t r i k e s , which were suc c e s s f u l , and number of f l i e s a c t u a l l y eaten i n wet and dry conditions by Rana aurora and Rana p r e t i o s a . Wet Dry Rana aurora Rana p r e t i o s a Rana aurora Rana pr e t i o s a T o t a l number of 171 476 268 428 s t r i k e s Percentage of s t r i k e s 25.6 25.1 38.6 42.1 successful Number of f l i e s a c t u a l l y eaten 39 118 102 178 61 TABLE XI P r o b a b i l i t i e s associated with differences i n feeding e f f i c i e n c y o f R a n a aurora and Rana pr e t i o s a under wet and dry conditions. T o t a l number of s t r i k e s Percentage of s t r i k e s successful Number of f l i e s a c t u a l l y eaten R . R . aurora wet -p r e t i o s a wet* R . R o aurora wet -p r e t i o s a wet R . R . aurora wet -p r e t i o s a wet* R . R . aurora dry -p r e t i o s a dry* R . R o aurora dry -p r e t i o s a dry R . R. aurora dry -pr e t i o s a dry* R . R . aurora wet -aurora dry* R . R . aurora wet -aurora dry R . R . aurora wet -aurora dry* R . R. p r e t i o s a wet -p r e t i o s a dry* R. R . p r e t i o s a wet p r e t i o s a dry* R . R o p_retiosa wet -pr e t i o s a dry* * i n d i c a t e s P -£.05 f o r differences observed. 62 more e f f o r t at feeding than does R. aurora. However, R. p r e t i o s a eats more f l i e s since i t s t r i k e s more often than R. aurora. Both species are more successful at capturing f l i e s i n dry conditions than i n wet, but they do not d i f f e r i n t h e i r a b i l i t i e s i n dry conditions. In the wet bowls, R. p r e t i o s a attempts to capture f l i e s that are water bound, but with each lunge toward a f l y , the frog pushes the water and thus moves the f l y . However, they s t r i k e repeatedly, and are usually ultimate ly s u c c e s s f u l . R. aurora i s less accurate i n i t s jumping a b i l i t y i n wet bowls, since i t s t i l l attempts to capture f l i e s on the walls and not those i n the water. 4) Starvation experiments Starvation t e s t s with newly metamorphosed frogs showed that they are able to l i v e f o r many days on the energy source retained from t h e i r l i f e as tadpoles. Of the i n i t i a l ten newly transformed R. aurora, s i x l i v e d from 38-45 days (mean of 42 days) before s t a r v i n g . The remaining four were given food a f t e r 45 days, but three of them died from three to f i v e days l a t e r . One surviving frog l i v e d well and grew although i t had been starved f o r 45 days. Fiv e of the i n i t i a l ten R. p r e t i o s a l i v e d from 31-35 days (mean of 33.8 days) before dying. A f t e r 35 days the re-maining f i v e were fed f l i e s i n abundance, but four died from one to four days l a t e r . The lone survivor regained a normal healthy appearance and fed well t h e r e a f t e r . Individuals of both species that survived without food u n t i l food was given to them were weak and emaciated. How-63 ever, when f l i e s were added to the bowls with the frogs, a l l i n d i v i d u a l s attempted to feed. A l l except one of each species was too weak to feed e f f i c i e n t l y , and although some did catch food, they were beyond the point of s u r v i v a l . c. Temperature 1) F i e l d and frog temperatures In the Lower Fraser Valley and the LCR study area, weather conditions i n early spring of 1969 were very d i f f e r e n t from those of the same period i n 1968. A. prolonged c o l d wave (s e t t i n g a 50-year record) i n 1969 kept the r i v e r and f i e l d under i c e u n t i l l a t e February, and freezing temperatures occurred almost n i g h t l y u n t i l the second week of March. The a i r and water temperatures which existed during the l a s t week of February i n 1968 were not encountered u n t i l the second week of March i n 1969. The onset of breeding by both species was delayed f o r almost two weeks i n 1969, a f a c t which provides evidence that there e x i s t s temperature thresholds necessary f o r i n i t i a l breeding a c t i v i t y . As soon as the i c e and snow melt from the spawning s i t e s , during February and March, both R. aurora and R. p r e t i o s a breed. During breeding a c t i v i t i e s , R. aurora had c l o a c a l temperatures as low as 6 C, but the lowest recorded f o r R. p r e t i o s a was 8.1 C. On near fr e e z i n g nights, R. aurora may remain active because they spawn while completely submerged under water. R. p r e t i o s a spawn at the water surface, and t h e i r breeding a c t i v i t y i s r e s t r i c t e d to warmer nights when temper-atures are above 7 C. Most R. p r e t i o s a spawn during the day-64 l i g h t hours, u s u a l l y i n f u l l sunshine when a i r temperatures are at l e a s t 10 C. No j u v e n i l e frogs of e i t h e r species were seen active during the breeding season. Young frogs were f i r s t found about 2-3 weeks a f t e r breeding ended. By t h i s time a i r temperatures had r i s e n considerably and there were no longer freezing nights. Lowest temperatures were us u a l l y above 7 C at night, and daytime recordings began to reach 15-20 C. On days below 8-10 C, frogs were i n a c t i v e . A f t e r breeding f i n i s h e d , adult frogs disappeared and were not seen f o r about 3 weeks. The reappeared about the same time that the j u v e n i l e s became active (when d a i l y temperatures were above 10 C). By mid-April i n a l l years, frogs of both species and a l l sizes had commenced regular non-breeding a c t i v i t i e s . C loacal temperatures of frogs were recorded at i n -d e f i n i t e i n t e r v a l s from mid-April to November (the time when frogs went i n t o hibernations). Their body temperatures were measured under a v a r i e t y of c l i m a t i c conditions. Both species were i n a c t i v e at temperatures below 8-10 C. In A p r i l , by dusk, a i r temperatures were at t h i s minimum and frogs were i n a c t i v e as I searched f o r them. E a r l y morning searches i n A p r i l were successful only a f t e r the a i r had warmed to about 10 C. The onset of hibernation seems to be governed i n part, by the low temperatures p r e v a i l i n g i n November. In a l l years, frogs were not e a s i l y found i n November, a f t e r a period of low temperatures. In 1968, during the l a s t days of October, night 65 temperatures had dropped to 3-4 C f o r about 3 days, and daytime temperatures barely reached 10 C After t h i s cold s p e l l , frogs were not found. An occasional frog was active on sunny days i n November, but the population as a whole had hibernated. Throughout the study, I recorded the c l o a c a l temper-atures of 115 R. aurora. These averaged 19.5 (range 9.6-28.5, SD=4.9). The c l o a c a l temperatures of 133 R. p r e t i o s a averaged 20.8 C (range 9.6-29.0. SD=5.0). (These temperatures are of nonbreeding frogs o n l y ) . The diff e r e n c e between t h e i r temper-atures i s s i g n i f i c a n t (P>.01). On many occasions i t appeared that the frogs used behavioral t r a i t s (moving i n t o or out of d i r e c t sun, or in t o or out of water) as a means of c o n t r o l l i n g t h e i r body temperatures. For example, on a warm morning i n June 1968, an adult female R. p r e t i o s a was s i t t i n g on a log along the r i v e r bank. The sunshine was d i r e c t l y on the frog when the a i r temperature was 24.6 C; the frog's body temperature was undoubtedly higher. Soon the frog moved along the log u n t i l i t was i n the shade created by overhanging vegetation. In 10 minutes i t was again i n d i r e c t sunshine, and a f t e r about 5 minutes, i t again moved to shade on the l o g . This happened three times u n t i l eventually the frog jumped i n t o the r i v e r . I immediately caught the frog and i t s temperature was 27.6 C. The a i r temperature 2 cm above the log where the frog had been was 29.7 C, and had the frog remained i n f u l l sunshine, i t s temperature may have been higher. During mid-summer, i n the mornings, when the sun i s shining and the a i r about 20 C, R. p r e t i o s a i s most often found along the r i v e r margin, at the water edge or on the mud bank, 66 basking i n the sun. The water i n the shallows i s usually 3-6 C higher than i n mid-stream. By afternoon, when the a i r r i s e s to 25 C or more, and the r i v e r shallows reach the same temperature, R. p r e t i o s a moves int o the depths and i s almost completely sub-merged i n the cooler waters. R. aurora uses the shade offered by vegetation i n the f i e l d or along the r i v e r margin, to behaviorally thermoregulate. In the mornings, during the summer, R. aurora occurs i n the open grass areas or along the exposed r i v e r banks i n f u l l sun-l i g h t . As the temperature r i s e s to above 25 C, R. aurora i s no longer found exposed to d i r e c t sun, but moves int o the shade under vegetation. The temperatures i n such vegetational areas i s often 5 C or more lower than the exposed a i r . During mid-summer, i n J u l y and August, on days with high a i r and water: temperatures, the frogs had an opportunity to a t t a i n high body temperatures. On these days, the c l o a c a l temperatures of the frogs are good i n d i c a t o r s of the body temper-atures they n a t u r a l l y prefer during t h e i r d a i l y a c t i v i t i e s . The temperatures a v a i l a b l e i n the f i e l d may be considered as a gradient, and frogs can a t t a i n t h e i r preferred temperatures by moving int o the most suitable conditions. The frogs used the a v a i l a b l e heat only to a given l i m i t . For example, on 22 May 1969, at 1000 hrs, the a i r i n d i r e c t sunlight was 26.2 C, and the shallow water of the r i v e r was 21.4 C. Four R. pr e t i o s a on the r i v e r bank had body temperatures of 27.3 C, and four others i n the r i v e r shallows were at 24-25 C. By 1400 hrs, the a i r was 31.8 C i n the sun, and the water was 28.2 C. Five R. p r e t i o s a had body temperatures of 28.5 C, and three others 67 were from 26-2 7.2 G. A l l were i n the water and not on land where they could have achieved much higher body temperatures. Eight other R. p r e t i o s a were seen i n water; none were seen on land i n d i r e c t s u n l i g h t . S i m i l a r behavior (avoidance of high temperatures) was also demonstrated by R. aurora. However, t h i s species uses the shade within tangles of vegetation on land rather than water to regulate t h e i r body temperatures. On 9 June 1969, the a i r i n open sun was 33.5 C. Nine R. aurora were caught i n tangles of vegetation with temperatures of 24-27.5 C. No R. aurora were seen exposed i n d i r e c t sunlight that day. A c l e a r demonstration of behavioral thermoregulation by R. aurora occurred on 2 J u l y 1968. Only scattered pools remained from the r a p i d l y drying pond. In these pools there were newly metamorphosed frogs as well as tadpoles about to transform. The area around the pools was open and exposed to d i r e c t s u n l i g h t . At 0900 hrs, the water temperature on the surface of the pools was 27.5 C, and about 4 inches below the surface i t was 21 C, i n the vegetation that choked the pool. Many R. aurora about to transform were on the water surface on the vegetation; some were at the margins of the pools. I l e f t these frogs undisturbed and returned at 1400 hrs. This time the water surface was 34.5 C, and 4 inches below i t was 26.7 C. No R. aurora were seen on the water surface or along the margins of the pools. As I sat and watched, i n d i v i d u a l R. aurora would suddenly emerge from the depths of the pools, swallow a i r and soon submerge again i n t o the pools. They were staying i n the c o o l e r water i n the bottom of the pools i n the vegetation. As 68 i n d i c a t e d below, they could t o l e r a t e the surface temperatures only b r i e f l y , f o r 34.5 C i s within t h e i r l e t h a l temperature range. At the time I measured the c l o a c a l temperatures of frogs i n the f i e l d , I also recorded the a i r and water temper-atures, depending on where the frog was caught. The f i e l d and frog temperatures were taken within seconds of each other i n an attempt to record even a small dif f e r e n c e i f i t ex i s t e d . Compar-isons of c l o a c a l and substrate ( a i r or water) temperatures are made i n Table XII. Table XIII l i s t s the number of degrees d i f f e r e n c e between frog and a i r or water temperature. The highest recording f o r R. p r e t i o s a i n a i r (that i s , when the frog i s on land and not i n water) was 28.8 C. However, t h i s maximum may be somewhat lower than the true upper l i m i t because i t i s d i f f i c u l t to catch R. p r e t i o s a on land on very hot days when i t i s usually i n the water. When I did catch i t on land, I often was not able to quickly record i t s temperature. The frogs were very active and movements lowered t h e i r temper-atures by evaporative c o o l i n g . Table XII c l e a r l y demonstrates that the body temper-atures of both species are, on the average, higher than the medium ( a i r or water) they are taken from. However, i n some instances l i s t e d i n Table XIII, the c l o a c a l temperature was below that of the a i r or the water. This happened when the frog was i n wet grasses on land. As the frog moved to escape, a i r cool i n g of i t s skin probably lowered i t s i n t e r n a l temperature. I f a frog was caught i n the shade, the body temperature was 69 TABLE XII Comparisons of frog c l o a c a l temperature (C) with temperatures of a i r and water where caught. Rana aurora N Cloacal A i r Water P r o b a b i l i t y 75 18.6 (SD=4.4) 17.2 (SD=4.9) P < .01 37 21.1 (SD=5.2) - 21.0 (SD=6.3) P > .05 48 18.8 (SD=4.7) 77 21.9 (SD=5.0) Rana p r e t i o s a 17.1 (SD=4.5) - P <.05 21.1 (SD=5.5) P :=> .01 70 TABLE XIII Degrees centigrade diff e r e n c e between frog c l o a c a l temperatures and a i r or water. Rana aurora Cloacal 1.4 C more than a i r Range: -2.9 to 4.6 Cloacal 0.1 C more than water Range: -4.5 to 2.2 Rana p r e t i o s a Cloacal 1.6 C more than a i r Range: -1.0 to 5.5 Cloacal 0.8 C more than water Range: -2.2 to 6.0 71 u s u a l l y the same as the a i r , or lower, i f the vegetation was wet. The greatest divergence i n frog and environmental temper-autes r e s u l t e d i f the frog was i n d i r e c t sunshine and motionless. This basking behavior allows much heat to be absorbed by the f r o g . Occasionally, a frog caught i n water has a temperature lower than the water. This happened when the frog submerged as I caught i t . The water below the surface was i n v a r i a b l y cooler than that at the surface. I only recorded the warmer surface water i n compar-ing frog and water temperatures. R. p r e t i o s a used both a i r and water to r a i s e i t s body temperature above i t s surroundings. R. aurora does not bask i n the sun while h a l f submerged i n the water as does R. p r e t i o s a . The divergence between R'. aurora body temperature and that of the water i s minimal. 2) F^og temperature tolerance Frogs of both species can t o l e r a t e temperatures of 2 7-31 C f o r at l e a s t 3 hours, and they show no adverse e f f e c t s from exposure to these temperatures. Their a b i l i t y to survive at higher temperatures i s summarized i n Table XIV, and presented g r a p h i c a l l y i n F i g . 16. No c o r r e l a t i o n s existed between heat res i s t a n c e and sex or s i z e of the f r o g . The onset of heat stres s produced d i f f e r e n t symptoms i n each species. Heat stres s i n R. aurora d r a s t i c a l l y increases the frogs' l e v e l s of a c t i v i t y and swimming. At temperatures below 31 C, R. aurora i s r e l a t i v e l y i n a c t i v e , and only infrequent-l y swims r a p i d l y and f o r long periods. They normally remain motionless at the bottom or sides of the aquarium. At 31 C, they begin swimming very r a p i d l y through the water and t r y to emerge TABLE XIV A b i l i t y of frogs to survive high temperatures 72 A l l frogs survived 180 min at 27-31 C Rana aurora Rana p r e t i o s a Min t i l l Min t i l l Min t i l l Min t i l l N C p a r a l y s i s death N C p a r a l y s i s death mean (SD) mean (SD) mean (SD) mean (SD) 10 32 145.7 (59.0) 151.9 (48.9) 10 21 33 30.2 (22.2) 49.9 (40.5) 10 5 34 7.8 ( 7.6) 16.0 ( 4.8) 5 - - _ 5 32 171.0 (28.5) 171.5 (26.9) 33 164.8 (48.1) 165.2 (46.8) 34 149.4 (25.5) 157.2 (23.8) 35 77.6 (64.6) 83.6 (27.5) Figure 16 Temperature tolerance of juv e n i l e and adult Rana aurora and Rana p r e t i o s a . Temperature (C) 74 by pushing t h e i r heads out. No frogs died at 31 C, but through-out the 3 hours they were i n constant motion. At tests with higher temperatures, a f t e r 31 G was reached, the R. aurora became hyperactive as before, and then, a f t e r varying i n t e r v a l s of time at the higher temperatures (see Table XIV), p a r a l y s i s of the limbs set i t . P a r a l y s i s of hind limbs i s f i r s t , and a f t e r a b r i e f period t h e i r forelimbs become f u n c t i o n l e s s . Soon the frog i s unable to move i t s back or head, and sinks to the bottom of the aquarium. A f t e r a few minutes they died. Death i s sometimes preceded by a se r i e s of muscular spasms. Fewer than 50% of R:. aurora died at 32 G, but 100% died at 33 C. The upper tolerance l i m i t f o r R. aurora i s between 32-33 C. P a r a l y s i s and death occur r a p i d l y above 33 C. R. p r e t i o s a i s able to t o l e r a t e higher temperatures than R. aurora. The behavior of R. p r e t i o s a i s not obviously affected at temperatures below 33 C. The frogs are not excess-i v e l y active at 31 or 32 C, but by 33 C, they begin more active swimming and make frequent attempts to leave the water. In R. p r e t i o s a heat stress before death i s not l i k e that of R. aurora. The limbs of R. p r e t i o s a keep moving and p a r a l y s i s i s not marked even above 33 C. Instead, the frogs become uncoordinated i n o v e r a l l swimming motions, and swimming becomes slow and d i f f i c u l t . They begin r o l l i n g onto t h e i r sides as they swim, and soon swimming becomes slower and i s attempted at only i r r e g u l a r i n t e r v a l s . A f t e r f i n a l attempts to swim, a se r i e s of spasms from back to head ends i n t h e i r death. At t h i s point they sink i n the water. As seen i n Table XIV the upper l e t h a l l i m i t , f o r R. p r e t i o s a i s between 34-35 C. 75 d. Water Balance 1) Dehydration The rate of water loss by evaporation to s t i l l a i r i s a function of the i n i t i a l body size of a f r o g ; large frogs lose water at a slower rate than do small i n d i v i d u a l s . The rate of water loss r e f l e c t s , i n part, the surface to volume r a t i o of the animal being desiccated (Spight 1968). The r e s u l t s of dehydration tests with frogs at 15 C and 60% humidity are seen i n Tables XV and XVT. As expected, small frogs lose water more r a p i d l y than do larger ones. The r e l a t i o n -ship between the body weight and rate of water loss i s expressed by the le a s t squares regressions p l o t t e d i n P i g . 17. R. aurora and R. p r e t i o s a do not d i f f e r i n the rate of evaporative water loss to s t i l l a i r of 15 C (F - 3.40, P^.05). At 15 C, several small i n d i v i d u a l s of each species were exposed to drying conditions u n t i l they succumbed from d e s i c c a t i o n . At the point when they were no longer able to r i g h t themselves i f turned on t h e i r backs ( c r i t i c a l a c t i v i t y point -CAP), they were s a c r i f i c e d and weighed again. The percentage weight loss of s i x small R. aurora at CAP was 34.1% (range 32.3-37.0%). For s i x small R. p r e t i o s a , the percentage weight l o s t at CAP was 33.2% (range 31.8-34.8). I t took from 9-12 hours f o r a l l frogs to die of water l o s s . The r e s u l t s of t e s t s at 28 and 25% humidity are summarized i n Tables XVII and XVIII. As was found at the lower temperature, frogs lose water as a function of t h e i r i n i t i a l body weight, and t h i s r e l a t i o n s h i p i s seen g r a p h i c a l l y i n F i g . 18. 76 TABLE XV Rate of evaporative water loss of Rana aurora and Rana pr e t i o s a at 15 C and 60% humidity. Rana aurora Body weight of frog (g) g water loss/hr mean (SD) g water l o s s / g body weight/hr mean (SD) .98 1.27 1.41 1.68 1.76 1.78 21.75 22.48 24.14 27.22 28.27 34.29 .048 .040 .043 .062 .052 .053 .212 .241 .318 .277 .345 .312 (.027) (.022) (.015) (.035) (.020) (.015) (.041) (.029) (.037) (.036) (.027) (.063) .054 .034 .033 .041 .031 .032 .010 .012 .013 .010 .013 .009 (.030) (.019) (.012) (.026) (.014) (.008) (.002) (.003) (.002) (.001) (.001) (.002) Rana p r e t i o s a 2.63 2.74 2.81 3.01 3.07 3.11 18.29 22.00 22.73 24.87 27.20 31.80 .060 .058 .104 .075 .067 .070 .207 .188 .237 .285 .2 33 .258 (.027) (.029) (.033) (.023) (.031) (.019) (.056) (.050) (.039) (.021) (.036) (.040) .024 .022 .040 .028 .023 .025 .012 .009 .011 .012 .009 .008 (.009) (.010) (.011) (.007) (.010) (.006) (.003) (.002) (.002) (.001) (.001) (.001) 77 TABLE XVT Time t i l l C r i t i c a l A c t i v i t y Point (CAP) and percentage weight lo s s at CAP f o r small Rana aurora and Rana p r e t i o s a at 15 C and 60% humidity. ~" Rana aurora Body weight Min t i l l Percentage body (g) CAP weight loss at CAP 0.98 564 32.7 1.27 552 32.3 1.41 578 34.7 1.68 663 35.1 1.76 635 32.9 1.78 615 37.0 Mean = 34.1 Rana p r e t i o s a 2.63 672 34.6 2.74 688 32.8 3.01 915 34.8 3.05 750 34.1 3.07 650 31.5 3.11 962 31.8 Mean = 33.2 Figure 17 Rate of water loss to a i r of 15 G and 60% humidity as a function of body weight. Lines f i t t e d to l e a s t squares regression where y = log rate of loss (g/hr) and x <= log body weight (g). For Rana aurora, y = -1.435 + 0.61x and f o r Rana p r e t i o s a , y = -1.429 + 0.57x. 79 TABLE XVII Rate of evaporative water loss of Rana aurora and Rana p r e t i o s a at 28 C and 25% humidity. Rana aurora Body weight g water loss/hr g water l o s s / of f r o g (g) mean (SD) g body weight/hr mean (SD) 4.70 .66 .139 5.70 .75 .142 16.95 1.24 (.173) .092 (.008) 21.41 1.35 (.135) .075 (.004) 26.37 1.42 (.136) .060 (.008) 34.02 1.57 (.046) .051 (.003) Rana p r e t i o s a 7.74 .92 .126 12.46 1.19 .107 15.06 1.27 (.079) .096 (.014) 16.14 1.27 (.108) .088 (.013) 16.93 1.22 (.389) .081 (.017) 21.21 1.55 (.486) .083 (.016) 28.90 1.83 (.220) .069 (.004) 80 TABLE XVIII Time t i l l C r i t i c a l A c t i v i t y Point (CAP) and percentage weight loss at CAP f o r Rana aurora and Rana p r e t i o s a at 28 C and 25% humidity. Rana aurora Body weight Min t i l l Percentage body (g) CAP weight loss at CAP 4.70 120 28.1 5.70 140 28.9 16.95 255 32.2 21.41 290 30.7 26.37 345 32.7 34.02 330 25.3 Mean « 29.7 Rana p r e t i o s a 7.74 170 31.5 12.46 185 28.8 15.06 300 32.7 16.14 310 39.5 16.93 255 32.7 21.21 257 31.4 28.90 345 33.2 Mean = 32.8 Figure 18 Rate of water loss to a i r of 28 C and 25% humidity as a function of body weight. Lines f i t t e d to l e a s t squares regression where y = log rate of loss (g/hr) and x = log body weight (g). For Rana aurora, y = -.0495 + 0.47x, and f o r Rana p r e t i o s a , y = -0.498 + 0.51x. Body Weight (gm) Figure 19 Time t i l l C r i t i c a l A c t i v i t y Point (CAP) at 28 C and 25% humidity as a function of body weight. 5 0 0 i © R. aurora O R. pretiosa ^ 4 0 0 1 c £ o_ < 3 0 0 1 © o 6 0 ) E i - 200H °9 O 1001 0 5 i — 20 - r -25 —I— 30 35 Body Weight (gm) 83 The rate of water loss of the two species does not d i f f e r s i g -n i f i c a n t l y (F = 2.05, P>.05). At 28 C, a l l frogs were dehydrated u n t i l CAP was reached, and the percentage weight l o s t at death did not d i f f e r s i g n i f i c a n t l y between the two species (Table XVTII). The actual time t i l l CAP was reached was also c o r r e l a t e d with body s i z e of the f r o gs. As seen i n F i g . 19 large frogs survived longer than small animals, but there appears to be no r e a l d i f f e r e n c e between the species. There i s obvious v a r i a b i l i t y i n the time t i l l death. For example, a 34 g R. aurora died sooner than a 26 g R. aurora, and a 28 g R. p r e t i o s a . However, when i n t e r s p e c i f i c comparisons are made, frogs of equal s i z e survived equally long durations. The t o t a l water content of frogs was determined by k i l l i n g frogs and drying them i n an oven f o r 48 hours at 110 C. Eleven R. aurora averaged 81.3% (SD = .04) of t h e i r body weight as water, and eleven R. p r e t i o s a averaged 82.9% (SD = .05). The body water content of i n t a c t , healthy frogs of each species does not d i f f e r . The behavior of frogs within the enclosures as they were being dehydrated d i f f e r e d between species, e s p e c i a l l y at 15 C. From the onset of t e s t i n g , R. aurora was more active and moved around more than R. p r e t i o s a . Many minutes during each hour of t e s t i n g , R. aurora t r i e d escaping and crawling within the cages. A f t e r these bursts of movement, a frog would s e t t l e down, with i t s limbs tucked beneath i t s body, i n a water-con-serving p o s i t i o n (Heatwole et a l 1969). As an i n d i v i d u a l R. aurora l o s t about 20% of i t s body weight to evaporative water l o s s , i t began showing stress e f f e c t s and again moving energetic-84 a l l y i n presumed escape attempts. R. p r e t i o s a was less active than R. aurora, and assumed a water-conserving p o s i t i o n almost from the s t a r t of dehydration t e s t s . For several hours, R. p r e t i o s a d i d not move. When i n d i v i d u a l s had l o s t about 25% of t h e i r body weight from water l o s s , they became much more active and sought to escape from the cages. A f t e r f r a n t i c e f f o r t s of several minutes, they again s e t t l e d i n t o a less exposed p o s i t i o n , that i s , with legs tucked completely beneath t h e i r bodies. 2) Submergence t e s t s Frogs of both species are able to remain completely submerged i n water of 10 C, f o r eight hours, without showing adverse e f f e c t s . The frogs remain completely motionless a f t e r the f i r s t hour, and breathing rates are much reduced. When released from under water and a f t e r a few minutes i n a i r , they are able to move and jump without d i f f i c u l t y . e. Predator Avoidance 1) F i e l d In searching f o r frogs i n the LCR study area, I usually saw R. p r e t i o s a i n the r i v e r , the pond, or rainpools. From A p r i l to June, rainpools were abundant i n the f i e l d , and R. p r e t i o s a was found i n or along the margins of the water. As the rainpools disappeared during the summer, the frogs moved to the r i v e r and stayed there throughout the summer. The behavior of R. p r e t i o s a , as I approached them, was to remain motionless, e i t h e r s i t t i n g on the bank, or f l o a t i n g i n the water within the r i v e r . I f I moved slowly, I could approach 85 them within a foot or l e s s , but as I reached f o r them they would r a p i d l y submerge i n t o the bottom of the r i v e r , or rainpool, and disappear i n t o the mud. They remained submerged f o r many minutes (the maximum recorded was 17 i n water of 18 C). They then slowly swim to the surface and reappear exposing only t h e i r heads or eyes, usually from beneath cover of aquatic vegetation. Any sudden movement causes them to immediately submerge again. During rains i n the summer, R. p r e t i o s a leaves the r i v e r and wanders onto land, at times many feet from the r i v e r and i n t o the vegetation. When I approached these frogs on land, they immediately hopped toward the nearest body of water ( i n summer the r i v e r ) . They did not he s i t a t e , but began jumping towards the r i v e r . No frog ever hopped away from the r i v e r on these occasions. When at the r i v e r they immediately submerged i n t o the mud below. During a l l months, from A p r i l to October, almost with-out exception, I encountered R. aurora on land moving among the plant cover. Often they were near rainpools, or near the r i v e r i n summer, but during r a i n , they move some distance away from standing water. As I approached these frogs, they hopped quick-l y i n the opposite d i r e c t i o n , with strong, lengthy jumps. Many times they sought cover i n the thick sedges or bulrushes that were widespread throughout the f i e l d . A f t e r several long jumps, they frequently stopped and remained motionless beneath cover. When near water and frightened, they jump towards water but do not always enter and often seek cover i n the vegetation along the bank. I f they enter water, they r a r e l y submerge, but swim quic k l y on the water surface, staying close to the bank and 86 plant cover along i t . They do not r e a d i l y submerge, but often swim up or down the r i v e r and again seek escape on land. 2) Escape behavior a f t e r release Throughout the study I released R. p r e t i o s a along the r i v e r bank and scored t h e i r escape behavior 194 times. The same was done 121 times f o r R. aurora. Their escape responses are seen i n Table XIX. Immediately upon release, most R. p r e t i o s a jumped into the r i v e r and immediately submerged. Only eleven i n d i v i d u a l s remained on the water surface, p a r t i a l l y hidden by cover. Those frogs that jumped towards land e x h i b i t p e c u l i a r jumping behavior. T h e i r jumps became e r r a t i c and took a c i r c u l a r course. They jumped very low to the ground, at an angle of about 20°, with a few jumps i n one d i r e c t i o n and immediately began c i r c l i n g . A f t e r f i v e to eight jumps, they had t r a v e l l e d i n a small c i r c l e and reached the point where they had been released. They did not jump i n a s t r a i g h t d i r e c t i o n more than two or three times. Some frogs continued making these c i r c u l a r routes three or four times, u n t i l they f i n a l l y found the water and entered i t and submerged. Some i n d i v i d u a l s never found the water and instead, t r i e d to bury beneath the cover of plants on the mud. They hes i t a t e d to hop a f t e r three or four c i r c l e s , and indeed, seemed to grow clumsy and t r i p on t h e i r f e e t . They were e a s i l y captured and d i d not seek further escape. Most of the R. aurora released on land p a r a l l e l to the r i v e r t r i e d to escape on land (Table XIX). They jumped i n a s t r a i g h t d i r e c t i o n , at an angle of 45° or more o f f the ground 87 TABLE XIX Escape responses of Rana aurora and Rana p r e t i o s a released p a r a l l e l to r i v e r bank. Rana aurora Rana p r e t i o s a to water to land to water to land 42 79 163 31 submerged remained on submerged remained on surface surface 9 33 152 11 88 and went a good distance with each jump. They often sought cover i n the vegetation a f t e r f i v e to eight quick hops away from the r i v e r , or along the bank. Those frogs that entered the water stayed on the surface (except f o r 9 of the 42 i n d i v i d u a l s ) and swam r a p i d l y away along the banks. A f t e r swimming several f e e t , they often turned and faced me, keeping themselves p a r t i a l l y concealed by vegetation. A f t e r a while some i n d i v i d u a l s again moved to land and remained motionless on the bank.. 3) Jumping a b i l i t y The comparative jumping a b i l i t y of frogs i s seen i n F i g . 20. The distance jumped i s a function i n part, of the sv length of the frogs, with bigger frogs able to jump f a r t h e r . However, as seen i n F i g . 20, R. aurora jump fa r t h e r than R. p r e t i o s a of equal body length. As pointed out i n F i g . 10, aurora have longer hind limbs than do R. p r e t i o s a , and as Rand (1956) has noted, anurans with long limbs jump fa r t h e r than those with shorter limbs. The distance jumped by R. aurora and R;. p r e t i o s a as a function of t h e i r hind limb lengths i s seen i n F i g . 21, and as expected, R. aurora jumps f a r t h e r . The jumping behavior of the two species d i f f e r s i n a way not indicated by distance alone. R. aurora jumps at an angle of about 45°, and R. p r e t i o s a jumps at an angle of about 20°. R. aurora makes three to s i x jumps i n rapid succession, i n nearly a s t r a i g h t path. R. p r e t i o s a hops r a p i d l y i n small jumps, usually i n a c i r c u l a r d i r e c t i o n , so that i t ends where i t had s t a r t e d . They r a r e l y hop i n the same d i r e c t i o n more than two to four times, but tend to move i n a c i r c u l a r d i r e c t i o n . Figure 20 Jumping distance as a function of frog snout-vent length. Lines f i t t e d to l e a s t squares regression where y = distance jumped (cm) and x = snout-vent length (mm). For Rana aurora, y = 2.56 + 0.70x, and f o r Rana p r e t i o s a , y = 8.95 + 0.25x. O R. pretioso Snout-vent Length (mm) Figure 21 Jumping distance as a function of hind limb length. Lines f i t t e d to l e a s t squares regression where y = distance jumped (cm) and x = hind limb length (mm). For Rana aurora, y = 8.79 + 0.31x, and f o r Rana p r e t i o s a , y = 10.1 + 0.14x. 4) Laboratory t e s t s with snakes The innate escape behavior of laboratory-reared newly metamorphosed frogs was studied by exposing them to t h e i r n a t u r a l predator, the garter snake, Thamnophis s i r t a l i s . To seek escape from a hunting snake, the frogs could use the moat f i l l e d with water purslane, or remain on the mud of the p l a s t i c swimming pool used as the t e s t i n g arena. While the snake was searching f o r , or chasing frogs, I noted the p o s i t i o n of the frogs every 20 minutes. I recorded whether the frogs were on land or i n the water. In a serie s of ten t r i a l s l a s t i n g two hours each, the p o s i t i o n of the frogs was recorded 60 times (three times per hour f o r 20 hours). R. aurora was on land 50 times and i n the water 10 times; R. p r e t i o s a was on land 6 times and i n the water 54 times. Each species obviously used a d i f f e r e n t habitat to escape from the hunting snake. However, the c o n t r o l i n t h i s experiment i s the behavior of the frogs with-out a snake present. These r e s u l t s were described i n the section on habitat preference and showed that, even without snakes, £• aurora chooses land and R. p r e t i o s a uses water. The object of these t e s t s was to learn about the general escape patterns of the frogs when confronted with a natural predator. Almost 30 hours were spent watching the frogs' behavior when confined with a hungry, hunting snake. Rather than attempt to quantify t h e i r movements, I believe i t i s s u f f i c i e n t to describe t h e i r general patterns of escape responses and means of concealment. Differences were apparent between the species. A note about the hunting behavior of the snakes i s 92 h e l p f u l . A snake gave chase and seemed to be d i r e c t l y aware of the frogs only when they moved. I f a frog did not move, the snake would pass within inches and not s t r i k e at i t . Only when a frog moved did a snake become o v e r t l y e x c i t e d . The smell of the frogs produced searching behavior i n the hungry snakes, as judged by the excessive tongue f l i c k i n g of the snakes i n the t e s t i n g arena, but smell alone, without movements by the frogs did not cause the snakes to pursue the frogs. R. aurora r e l i e d alomst e n t i r e l y on i t s jumping a b i l i t y to escape. Individual R. aurora remained f l a t t e n e d on the ground and motionless whenever the snake approached even as close as two inches. I f the snake moved c l o s e r , the frog quickly jumped, i n r e l a t i v e l y long leaps, to the opposite side of the arena. The snake was usually surprised by the jumping fr o g , but often gave chase several seconds l a t e r . The frog had u s u a l l y jumped f a s t enough so that i t was again able to f l a t t e n out on the ground at the f a r end of the arena, several f e e t from the snake. I f an R. aurora jumped i n t o the moat while f l e e i n g , i t quickly l e f t the water i f the snake began searching f o r i t there. I t sometimes clung to the sides of the moat and slowly crawled out on to the land during the time the snake was searching i n the water. Most R. aurora were caught because they jumped from one end of the tank and then back again to where the snake was. However, t h i s i s an a r t i f a c t of the small s i z e of the t e s t i n g arena rather than i n e f f i c i e n t escape behavior under natural circumstances. When caught, almost a l l R. aurora emitted d i s t r e s s c a l l s , v o c a l i z a t i o n s l i k e screams, with t h e i r mouth wide open (Bogart 1960). 93 As in d i c a t e d by the positions recorded f o r R. pr e t i o s a as they attempted to escape, t h i s species almost always sought refuge i n the water. Shortly a f t e r t h e i r i n i t i a l i n troduction i n t o the t e s t i n g arena, R. p r e t i o s a entered the moat and stayed there. When a snake began searching the moat, the frog sub-merged to the bottom, or remained h a l f concealed with the t h i c k -ness of the water purslane i n the moat, showing only i t s eyes above the water.. Only r a r e l y did R. pr e t i o s a leave the water and seek escape on land. When on land, R. p r e t i o s a remained f l a t t e n e d complete-l y against the mud of the arena. Even when a snake approached within an inch, the frog did not jump. I t did so only when the snake crawled over the frog or nudged i t with i t s snout. The fro g then began jumping i n small, e r r a t i c leaps, often i n a c i r c u l a r d i r e c t i o n . I t was e a s i l y caught by a pursuing snake, unless i t found the moat. Of seven R. p r e t i o s a eaten by snakes, f i v e were caught on land and two i n water. Three of the f i v e had not yet found the moat, but had remained on land since t h e i r i n t r o d u c t i o n i n t o the t e s t i n g arena. Only one i n d i v i d u a l gave a d i s t r e s s c a l l when caught by the snake. For both species, the main t a c t i c to avoid detection was to f l a t t e n onto the mud when on land. They both stayed motionless f o r an hour or more i f they were not detected or disturbed by the moving snake. In water, R. p r e t i o s a r e l i e d on submergence and concealment i n the vegetation and R. aurora used ra p i d swimming to escape the pursuing snake, u n t i l i t could hide. 5) Anuran predators i n the LCR study area 94 In the LCR study area, there occur numerous vertebrate and invertebrate predators of anuran tadpoles and frogs. The following vertebrates were a c t u a l l y seen i n the f i e l d or are known to occur i n the Lower Fraser V a l l e y . Raccoon (Procyon I o t o r ) . Raccoons were never seen feeding i n the f i e l d , but t h e i r tracks were numerous a l l along the course of the r i v e r . During a l l seasons of the year, new tracks were seen, i n d i c a t i n g raccoons fed along the r i v e r i n the f i e l d . Great blue heron (Ardea herodias). On v i r t u a l l y every v i s i t to the f i e l d i n spring and summer, I saw e i t h e r one or two herons feeding i n or along the r i v e r i n the f i e l d . Herons were usually seen i n p r e c i s e l y those places where newly metamorphosed frogs were most abundant. I saw a heron catch two adult R. pr e t i o s a , but I was never able to i d e n t i f y other prey. Frogs were c e r t a i n -l y a major part of t h e i r d i e t , as they are i n other parts of the Lower Fraser Valley (D. Short, per. comm.). Belted k i n g f i s h e r (Megaceryle alcyon). During the spring and summer when tadpoles are s t i l l i n the r i v e r , on numerous v i s i t s I saw k i n g f i s h e r s diving i n t o the r i v e r . Garter snake (Thamnophis s i r t a l i s ) . This snake i s a major frog predator throughout i t s range. I t i s very abundant i n the LCR study area, and I caught 30 d i f f e r e n t i n d i v i d u a l s (none were removed). When made to regurgitate t h e i r food, eight snakes had remains of frogs or tadpoles. One snake was caught eating a newly metamorphosed marked R. aurora, and another j u s t eating a 47 mm male R. p r e t i o s a . Many snakes escaped capture, and 95 almost a l l were seen along the pond and r i v e r where tadpoles and frogs l i v e . Northwestern salamander (Ambystoma g r a c i l e ) and Rough skinned newt (Taricha granulosa). The larvae of the urodeles are voracious tadpole predators, and the neotenic form of A. g r a c i l e also eats tadpoles. The larvae and neotenic adults of A. g r a c i l e are very numerous i n the r i v e r . They w i l l consume hundreds of tadpoles i n a week as I observed i n the laboratory. The above vertebrates are probably major predators l i v i n g i n the LCR study area. They normally eat anurans and are very abundant. The following predators may add to the general predation pressure on R. aurora and R. p r e t i o s a : cutthroat trout (Salmo c l a r k i i ) , r e d - t a i l e d hawk (Buteo jamaicensis), marsh hawk (Cireus cyaneus), great horned owl (Bubo birginianus)» red fox (Vulpes f u l v a ) , s t r i p e d skunk (Mephitus mephitus), mink (Mustela v i s o n ) , f e r a l housecat ( F e l i s domesticus). A wide v a r i e t y of invertebrates found i n the LCR area prey e s p e c i a l l y on tadpoles. However, the giant water bug (Lethocerus americanus) i s capable of eating small f r o g s . In June 1968, I caught 83 Lethocerus nymphs and adults from the pond. In the r i v e r they are very numerous and are probably a threat to small R. p r e t i o s a . The leech (Batrachobdella picta) i s extremely abundant i n the pond and r i v e r . They were found attached to about 75% of a l l R. p r e t i o s a captured, and i n June some frogs had as many as 2 0 small leeches attached. They occur on R. aurora to a much l e s s e r extent, because of R. aurora's preference f o r land as a h a b i t a t . TABLE XX Summary of differences i n morphology, ecology, and behavior between Rana aurora and Rana pretio s a* Rana aurora - t e r r e s t r i a l Morphology longer legs eyes l a t e r a l l i t t l e mucous bold pattern Ecology a c t i v e l y searches f o r food feeds on land upper thermal tolerance 33 C Behavior jumping good long s t r a i g h t jumps uses land to escape from predators i n water, c l i n g s to vegeta-t i o n and swims on surface i n escape behavior Rana p r e t i o s a - aquatic Morphology shorter legs eyes dorsal copious mucous more uniform i n co l o r Ecology waits to ambush prey feeds from water tol e r a t e s 35 C Behavior jumping poor c i r c u l a r jumps uses water to escape from predators i n water, submerges to bottom to escape 97 A summary of the main differences i n the morphology, ecology and behavior between R. aurora and R. p r e t i o s a i s seen i n Table XX. G. Comparative Reproductive Behavior a. Prebreeding and Breeding Behavior of Rana aurora 1) Emergence from hibernation and migration to breeding s i t e s The f i r s t R. aurora appear as soon as i c e and snow begin melting from the r i v e r and f i e l d . Frogs have been found overwintering i n both r i v e r and woods, and the duration of i c e cover p r i m a r i l y a f f e c t s the time of emergence. In 1968, the l a s t i c e melted about 14 February, and d a i l y searches were f i r s t s uccessful on 24 February when several males were caught. In 1969, frogs were f i r s t caught on 3 March, the unusually pro-longed i c e and c o l d having delayed emergence. The temperature data f o r both years ( F i g . 22) i n d i c a t e that R. aurora f i r s t become active when the a i r has been at l e a s t 5 C f o r several days. I f temperatures f a l l below t h i s a f t e r emergence, the frogs apparently become i n a c t i v e . (Subadult frogs did not appear f o r the f i r s t time u n t i l several weeks a f t e r breeding terminated, and a i r temperatures were d a i l y above 10 C. Very soon a f t e r emergence, R. aurora begins to move to breeding s i t e s . Most movements occur at night and seem to be stimulated by cloud and p r e c i p i t a t i o n , conditions under which higher temperatures p r e v a i l . On c l e a r days, some frogs were caught active during daylight hours, but most were found during dusk, before the r a p i d drop i n temperature accompanying the Figure 22 A i r and water; temperatures and p r e c i p i t a t i o n data f o r 1968 and 1969, pertinent to the breeding behavior of Rana aurora and Rana p r e t i o s a at the L i t t l e Campbell River study area. Single arrows i n d i c a t e dates on which Rana aurora males began c a l l i n g ; double arrows i n d i c a t e the same f o r Rana p r e t i o s a males. 1968 1969 5 10 15 20 25 I 6 II 16 21 26 25 2 7 12 17 22 27 I 6 II February March February March April 99 onset of darkness. In both years, by about one week af t e r emergence, several dozen males had arrived at the breeding s i t e s . The breeding s i t e s were i n the northern ends of the pond and adjacent portions of the r i v e r . 2) Prespawning a c t i v i t y at breeding s i t e s Males arri v e d f i r s t at the pond and r i v e r breeding s i t e s and remained concealed, often i n f u l l sunlight, near sedges and bulrushes. No feeding a c t i v i t y was noticed at t h i s time, and the frogs quickly entered the water when approached. In the f i r s t week a f t e r emergence, no female R. aurora were found at the breeding s i t e s , but several were found 150-300 f t away i n the f i e l d . Males were at the breeding s i t e s at l e a s t one week before they began to v o c a l i z e . Not a single c a l l was heard i n a f u l l week of almost round-the-clock observations, yet more males were found at each search. This suggests that the males f i n d these s i t e s and o r i e n t to them without use of vocal cues from other males already at the s i t e s . Although the males are not vocal when f i r s t gathered at the s i t e s , experiments show that they w i l l p e r s i s t e n t l y and tenaciously clasp a female R. aurora, or any other animal of sui t a b l e s i z e , i f given a chance. Male R. aurora, c o l l e c t e d from breeding s i t e s before c a l l i n g had started and placed with female R. aurora (or R. pretiosa) i n aquaria, quickly assumed amplexus. At Stanley Park, about 1900 hr on 19 February 1968, a p a i r of R. aurora was caught i n amplexus, and on 20 February, about 2000 hr i n Stanley Park, a male R. aurora was seen t i g h t l y 100 clasped with a male salamander, Ambystoma g r a c i l e , which f i n a l l y broke free a f t e r a 10-minute struggle. Thus c a l l i n g and i n i t i a -t i o n of a chorus i s not a necessary p r e r e q u i s i t e f o r sexual arousal i n male R. aurora. 3) V o c a l i z a t i o n s at breeding s i t e s Male R. aurora began c a l l i n g a f t e r about one week at the breeding s i t e s . In 1968, a f t e r several days of l i s t e n i n g with no i n d i c a t i o n of vocal a c t i v i t y , I f i r s t heard the c a l l s on the afternoon of 28 February, and i n 1969, on the afternoon of 8 March. Stimuli responsible f o r i n i t i a t i n g the c a l l i n g are uncertain, but r i s i n g temperatures seem e s p e c i a l l y important. In both years, the water and a i r temperatures were above 6 C f o r several days before c a l l i n g s t a r t e d . Temperatures i n the pond where frogs had gathered had not f a l l e n below 6 C f o r f i v e to seven days before i n i t i a l vocal a c t i v i t y ( F i g . 22). Unpaired male R. aurora, at every breeding s i t e ob-served, emit t h e i r mating c a l l while completely submerged under water seven inches to three f t i n depth (up to 15 f t i n Marion Lake). They normally remain stationary on the bottom or concealed i n t u f t s of submerged vegetation. Of numerous males observed i n d a i l y and n i g h t l y recording sessions, only two were observed to c a l l above water, which they did only b r i e f l y before submerging again. Males c a l l several feet apart and remain motionless on the substrate or i n vegetation. At i n d e f i n i t e i n t e r v a l s they surface f o r a i r , and may swim a few inches above water, u s u a l l y returning and submerging very near the spot from which they surfaced. 101 The mating c a l l of R. aurora i s very low i n volume and has l i t t l e carrying power. The c a l l s , given underwater, as they normally are, are barely audible i n a i r ; i f the frog i s c a l l i n g i n several feet of water, no sound at a l l can be detected i n a i r , and a hydrophone i s necessary to detect the c a l l s . Frogs c a l l i n g near the surface i n shallow water produce c a l l s heard, at most, 2 0-30 f t away i n a i r . Mating c a l l s given above the water cannot be heard beyond 50 f t . Males c a l l i n g i n about two fe e t of water at 12.8 C emit c a l l s which carry about 30 f t underwater, as v e r i f i e d by use of a hydrophone. The i n t e n s i t y of c a l l s given above water by a male two feet away from the sound meter reached a maximum of only 3 db. The c a l l i s less intense i f given underwater and measured d i r e c t -l y above the c a l l i n g male at the water surface. The c a l l s have a d e f i n i t e v e n t r i l o q u i a l e f f e c t and f i r s t appear to emanate from frogs v o c a l i z i n g some distance away. They are almost completely masked by the loud "chorus" of the P a c i f i c t r e e f r o g (Hyla r e q i l l a , which often c a l l s simultaneously. (For comparison, note that a single Hyla c a l l i n g 15 f t away from the sound meter gives c a l l s having a maximum i n t e n s i t y of 10 db.) Observations at Marion Lake emphasize the unusual behavior of c a l l i n g male R. aurora. On 8 A p r i l 1969, at 2100 hr, I l i s t e n e d i n a i r f o r sounds of male R. aurora I knew to be present i n the lake. Not a single c a l l was heard from any p o s i t i o n around the lake or from a boat i n the center of the lake. However, on l i s t e n i n g beneath the water with a hydrophone, I heard the mating c a l l s of several hundred R. aurora. The 102 e n t i r e lake, beneath the water, resounded with the c a l l s of frogs submerged at depths up to 15 f t . The same series of events was repeated the next day. At the LCR study area, R. aurora males were found to c a l l during the day, but most were vocal during the night and ea r l y morning. When c a l l i n g has begun f o r a season, i t may continue n i g h t l y u n t i l breeding has terminated. Low a i r temper-atures at night do not seem to a f f e c t the males c a l l i n g sub-merged i n the warmer water. Mating c a l l s are emitted at i n d e f i n i t e i n t e r v a l s , but there seem to be cycles of maximum i n t e n s i t y i n a "chorus" throughout the night. Males c a l l more frequently when other males move near them. When two males approach, they r a p i d l y repeat t h e i r mating c a l l s i n quick succession, doing so u n t i l they attempt mutual amplexus, emit release c a l l s , and swim away. Any movement near a c a l l i n g male stimulates him to c a l l more often, at times up to 30 seconds without cessation. The mating c a l l of unpaired R. aurora has not been described previously by analysis with the sound spectrograph. The c a l l c o n s i s t s of e i t h e r two, three, four, or f i v e notes, but almost a l l c a l l s are three or four notes. A sonagram f o r a t y p i c a l mating c a l l given by a male 58 mm (sv length) c a l l i n g submerged i n water 9 C i s seen i n F i g . 23. Each i n d i v i d u a l note consists of f i v e to six separate pulses. There i s a r i s e i n p i t c h and i n t e n s i t y on the l a s t notes within a series°. The dominant frequencies of the notes l i e between 450 and 1300 Hz, and the notes may extend to 7.5 kHz. Figure 23a,b Sonagrams of male Rana aurora v o c a l i z a t i o n s , a. Mating c a l l of an unpaired male submerged i n water 9 C. b. Single note emitted once a second by a male clasped with a female. SECONDS 104 A. c a l l with four notes l a s t s about 1 sec (0.90-1.00 f o r 12 c a l l s from three males i n water at 9 C). A five-note c a l l l a s t s about 1.25 sec. The c a l l can be compared to a repeating s e r i e s of the sound 'uh', with more emphasis placed at the end of the s e r i e s : uh uh uH UH. 4) Behavior of amplectic p a i r s Male R. aurora clasp females i n an a x i l l a r y p o s i t i o n as described by Storm (1960) and pictured i n L i c h t (1969a), and as seen i n other ranids. The male holds very t i g h t l y and i t requires some e f f o r t to remove him from a female. While c l a s p -i n g , the male emits a singl e c a l l note, about once every second. As the male gives t h i s note, h i s throat pulses and h i s abdomen contracts, causing him to p u l l s l i g h t l y backwards as he grips the female. He makes t h i s sound with h i s mouth d i r e c t l y behind the female•s tympanum. This s i n g l e note i s very constant i n structure and i s e s s e n t i a l l y a burst of energy between 750 and 1500 Hz ( F i g . 23). The s p e c t r a l c h a r a c t e r i s t i c s of the note f a l l within the range of dominant frequencies of the mating c a l l . The note i s un-pulsed and l a s t s only .05 seconds. I t i s extremely low i n volume and cannot be heard beyond one to two feet from the amplectic male i n a quiet room. I t i s at most 1 dB i n i n t e n s i t y when measured six inches away. However, t h i s note i s emitted d i r e c t l y i n t o the female's ear and consequently may be more intense f o r her. Males clasped with receptive females emitted t h i s sound c o n t i n u a l l y . Without cessation, a male c o n t i n u a l l y repeat-ed t h i s note almost every second f o r a f u l l hour during which 105 he was observed. I t i s given both underwater and i n a i r , i f the amplectic p a i r i s placed out of water. Males also give t h i s c a l l when clasped with females which are unreceptive and attempt-ing to gain t h e i r release, but when the female becomes very-a c t i v e , the male ceases and emits a d i f f e r e n t kind of c a l l as described by L i c h t (1969a). Males from a l l populations studied gave the single note when clasped, and i t seems to be a normal part of t h e i r vocal r e p e r t o i r e during breeding. The second type of c a l l amplectic males emit i s a s e r i e s of one to eight notes which d i f f e r i n temporal and s t r u c t u r a l pattern from the mating c a l l of unpaired males (see F i g s . 7, 8 i n L i c h t 1969a, and F i g . 23 i n t h i s r e p o r t ) . This amplectic c a l l has been recorded from males clasped with un-receptive females both i n the f i e l d and laboratory, but i t i s not yet c e r t a i n that t h i s c a l l i s given by males clasped with receptive females. However, there i s some preliminary evidence that i t may. A hydrophone was held near a p a i r of R. aurora i n 2 f t of water at Marion Lake. The male did not give t h i s amplectic c a l l as the female remained s t i l l , but as she began to swim a few inches, the male began v o c a l i z i n g . When she stopped swimming, he stopped c a l l i n g . On another occasion, i n the laboratory, a male R. aurora was clasped with a female £• p r e t i o s a which remained quiet and did not struggle. She was thus a 'simulated' receptive female R. aurora. They were l e f t alone i n a darkened room and not disturbed, but recordings were made of a l l v o c a l i z a t i o n s . The male spontaneously emitted amplectic c a l l s (series of one to eight) at i n t e r v a l s . Subsequent observations i n d i c a t e d that the male c a l l e d whenever the female R. p r e t i o s a began to swim. 106 Sonagraph analyses of male R. aurora release c a l l s (those c a l l s given by males when they come p h y s i c a l l y i n contact with other males, and i d e n t i f y i n g the c a l l e r as male) and male amplectic c a l l s reveal much s i m i l a r i t y . The release c a l l s are hig h l y v a r i a b l e i n both s p e c t r a l and temporal pattern and are not e a s i l y q u a n t i f i e d . Males are i n varying states of e x c i t e -ment when they emit the release c a l l s , but i n general c a l l s are more intense (more energy) and more r a p i d l y repeated than the amplectic c a l l s . Although they cannot be considered the same c a l l types, the amplectic c a l l seems to be a modified version of the male release c a l l . A male R. aurora i s quickly forced to release an un-receptive female R. aurora which undergoes elaborate and ex-tensive behavior to gain her release. When placed i n aquaria with two inches of water, an unreceptive female can secure her release i n less than one minute (Licht 1969a). Further t e s t s were conducted with unreceptive females placed i n tanks contain-ing water one or two f t deep. Under these circumstances, when clasped by a p e r s i s t e n t male R. aurora, the female attempts to gain her release by c o n t i n u a l l y r o l l i n g over i n the water and is s u i n g release c a l l s . P e r s i s t e n t males w i l l maintain t h e i r g r i p f o r as long as 15 minutes, but eventually relax t h e i r c l a sp on the female. The same females, when placed i n only two inches of water, can gain t h e i r release within a minute, owing to t h e i r a b i l i t y to use the substrate to maneuver more e a s i l y . 5) Spawning Behavior During both years at the LCR, the i n i t i a t i o n and termination of egg laying was p r e c i s e l y determined. Egg laying 107 started on the night of 28 February and ended on 13 March i n 1968, and i n 1969, i t began on the evening of 15 March and stopped on 3 A p r i l . Once egg laying began i t was i n t e n s i v e , and most females spawned within two weeks a f t e r the f i r s t egg was found (Table XXI). Weather data seen i n F i g . 22 i n d i c a t e that water: temperature of 7 C i s s u f f i c i e n t f o r spawning and that once t h i s minimum i s reached, most eggs are deposited. In 1969, only one egg mass was deposited before the pond reached at l e a s t 7 C. In both seasons, a l l eggs were deposited overnight as determined by dusk and dawn v i s i t s to the LCR s i t e . Although males may v o c a l i z e during the daylight hours, the females apparently spawn only during the dark ( i t i s unknown whether they respond to the male c a l l during the night or day). Egg masses were attached to s t a l k s of submerged vegeta-t i o n (Typha. Carex. and Potomageton) at minimum depths of 12 inches and as deep as 3 f t (up to 15 f t i n Marion Lake). The eggs are placed i n quiet water with l i t t l e or no flow, and i n areas exposed to sunlight f o r most of the day. Masses were us u a l l y 2 f t or more apart from each other, but at each d i s t i n c t s i t e at the LCR, the eggs are l a i d i n the same general v i c i n i t y . For example, ten masses were deposited within 20 s q . f t . i n the r i v e r . The eggs often become covered with a f i l m of debris and may be d i f f i c u l t to d i s t i n g u i s h , but i f one mass i s found, a c a r e f u l search w i l l reveal others nearby. In the LCR pond, R. aurora deposits i t s eggs i n the center where water i s deepest (2 - 3 f t ), and about 108 TABLE XXI Numbers of new Rana aurora egg masses found on each search at the L i t t l e Campbell River during the 1968 and 1969 breeding seasons. 1968 1969 Date No. masses Date No. masses February 26 0 March 12 0 27 0 13 0 28 1 14 0 29 5 15 1 March 1 2 16-22 0 2-- 5 2 23 3 6 0 24 0 7 4 25 5 8 1 26 3 9 0 27 10 10 8 28-31 0 11 0 A p r i l 1 0 12 8 2 0 13 5 3 11 14 0 4 0 15 0 5 0 109 3-15 f t from the pond edge. In the r i v e r , the eggs are l a i d i n water two to four f t deep, close to the main channel at the deepest part of the overflow. No R. aurora mass was found within four f t of the shoreline and submerged less than 18 inches deep. The o v i p o s i t i o n s i t e s are those at which males v o c a l i z e . In the LCR l o c a l i t y i n 1968, the f i r s t R. aurora mating c a l l s were heard on 28 February and the l a s t egg mass l a i d on 13 March. In 1969, these dates are 8 March and 3 A p r i l . Thus the e f f e c t i v e breeding season lasted 15 days i n 1968 and 27 days i n 1969. b. Prebreedinq and Breeding Behavior of R. p r e t i o s a 1) Emergence from hibernation and migration to breeding s i t e s Emergence from overwintering s i t e s begins as e a r l y i n the year as the winter thaw permits. Frogs were f i r s t caught on 21 February 1968, and 3 March 1969. A i r temperatures of 5 C i s evidently the minimum necessary f o r i n i t i a l a c t i v i t y , but several males seen basking i n the sun probably had higher body temper-atures. The males a r r i v e f i r s t at breeding s i t e s and on a r r i v a l they remain i n shallow water at the edges of the pond and along the margins of the r i v e r overflow. From 3 to 9 March 1969, about 18 or more males gathered i n t o two separate areas. About eight males were within a 3 f t square area at the edge of the pond where bulrushes provided cover. Ten or more males were within a s i m i l a r area along the shallows of the r i v e r , about 65 f t away from the pond. A few s o l i t a r y males were caught scattered along the r i v e r and pond borders about 10-20 f t from 110 the main groupings, and they remained apart from the aggregations before c a l l i n g s t a r t e d . A l l males were basking i n the sun or f l o a t i n g on the water surface. 2) Vocalizations and male behavior at breeding s i t e s C a l l i n g by unpaired males at breeding s i t e s began on 29 February 1968, and on 9 March 1969. The f i r s t c a l l s were noted i n the afternoon when the a i r temperatures were about 12 C i n d i r e c t sunlight at the c a l l i n g s i t e s . C a l l i n g continued throughout the afternoon and i n t o the evening, but ceased on some nights when temperatures were near f r e e z i n g . Within a day or two a f t e r c a l l i n g began, s o l i t a r y males i n i t i a l l y found away from the main aggregations, and i n d i v i d u a l l y marked by toe c l i p p i n g , were recaptured within the groups of males. Males c a l l e d from w i t h i n one f t of each other, and as many as six may c l u s t e r i n t o an area two f t square. They c a l l e d while f l o a t i n g on the water surface with t h e i r heads up, or s i t t i n g above the water on mats of vegetation: they were not observed to c a l l underwater. They remained i n the shallows of the pond or r i v e r overflow i n water only two to six inches deep, and v i r t u a l l y a l l males faced toward shore as they c a l l e d . On the f i r s t few days a f t e r c a l l i n g began, the males i n close proximity constantly clasped each other. Whenever a male moved, i t attracted the attention of a nearby male which swam towards i t and attempted amplexus. A f t e r breaking apart, both males would remain s t i l l f o r many minutes u n t i l they would again attempt amplexus or move apart. A f t e r several days of t h i s behavior, these bouts of mutual amplexus were no longer I l l seen, and thereafter the males remained within inches of each other, v o c a l i z e d , but did not c l a s p . The mating c a l l of R. p r e t i o s a males i s usually a s e r i e s of short bass notes from s i x to nine i n number, but notes of four to 26 i n a series are also given. About noon, on 26 March 1969, when the water was 13 C, I counted the notes of 163 c a l l s given by seven males. Twenty-seven had s i x notes, 48 had seven notes, 47 were eight notes, and 23 had nine; the r e s t were e i t h e r four, f i v e , ten or twelve notes. However, i t was observed that as a male approached another frog, the number of notes increased, and reached as many as 26 before that c a l l ceased. Playback of recorded c a l l s on tape loops to nearby males c o n t i n u a l l y evoked prolonged c a l l s from them. The c a l l of R. p r e t i o s a i s low i n volume and c a r r i e s only 50-100 f t at most. The f i r s t two or three notes i n a c a l l are barely audible, but the i n t e n s i t y increases with each succeeding one. A male c a l l i n g four f t away from the sound meter gave mating c a l l s which were 4-5 db. The c a l l of Hyla  r e g i l l a completely masks the low bass notes of R. p r e t i o s a . A sonogram of a t y p i c a l c a l l with ten notes i s seen i n E i g . 24. Each note i s unpulsed and l a s t s about 0.03 sec. At 11.4 C the i n t e r v a l between notes within a c a l l i s 0.11-0.14 sec, and a c a l l of seven notes l a s t s 1.10-1.22 sec. Each note contains dominant frequencies between 0.5 and 1.5 kHz, and the l a s t notes within a c a l l extend, with reduced energy, to about 5.5 kHz. Figure 24 The mating c a l l of an unpaired male Rana p r e t i o s a f l o a t i n g i n water 12.4 C. 5H LU U 3 -O o -L t . i J . U l .2 A 6 .8 I 1.2 1 4 1.6 1.8 2 22 SECONDS 113 3) Behavior i n amplexus and spawning Before amplexus, females f i n d t h e i r way to the breed-ing s i t e s and there remain within range of the males' mating c a l l s . They remain apart from the males u n t i l ready to spawn. For example, i n 1969, four females were found about 75 f t from the pond several days before the males began to give mating c a l l s , and three were recaptured i n the same area on successive days. One female f i r s t caught on 3 March was caught again i n amplexus on 12 March, i n the pond 60 f t from where she was o r i g -i n a l l y found. During both years, eight amplectic pairs of R. p r e t i o s a were encountered, and a l l but one p a i r were found i n bri g h t sun-shine i n raid-afternoon, with a i r temperatures about 15-16 C. Pairs remained very s t i l l i n shallow water only two to f i v e inches i n depth, with the male's back often three-quarters out of water. No c a l l s from amplectic male R. p r e t i o s a were detected, although two males gave ra p i d ' t r i l l s ' when f i r s t grasping a female and assuming amplexus; the clasp i s a x i l l a r y as i n other ra n i d s . Unreceptive female R. p r e t i o s a secure t h e i r release by use of release c a l l s and abdominal v i b r a t i o n s . The f i r s t egg masses i n 1968 were deposited on 1 March, and i n 1969 on 13 March. Subsequent egg masses appeared within several days as seen i n Table XXII. The eggs were mostly deposited during mid-afternoon, but during the night as w e l l . In each area where males c a l l e d , the eggs were deposited i n one spot. The masses were us u a l l y deposited on top of, or immediately touching, a mass already present. For example, c l u s t e r s of 26, 19, and 11 masses were found i n areas le s s than 114 TABLE XXII Numbers of new Rana p r e t i o s a egg masses found on each search at L i t t l e Campbell River during 1968 and 1969 breeding seasons. 1968 1969 Date No. masses Date No. masses February 26 0 March 12 0 27 0 13 15 28 0 14 0 29 0 15 0 March 1 3 16 1 2-5 10 17 0 6 0 18 0 7 15 19 9 8 0 20 1 9 0 21 18 . 10 2 22 0 11 0 23 10 12 0 24 0 13 0 25 0 14 0 26 0 115 two f t square. The smallest number found together was f i v e . The masses are not attached to any vegetation and are deposited i n such shallow water that only the bottom h a l f of each i s sub-merged while the tops are exposed d i r e c t l y to the a i r . This c l u s t e r i n g phenomenon i s d i r e c t l y due to the behavior of both the male and female. On four d i f f e r e n t days, males were observed c a l l i n g from the surface of the egg j e l l y , while other males were c a l l i n g only inches away. More s t r i k i n g evidence i s that females may a c t u a l l y seek out egg masses a l -ready present on which to deposit new ones. On 20 March 1969, a female was observed depositing the f i r s t eggs i n an area where males had been c a l l i n g f o r several days. The next day there were 18 new masses surrounding or touching that one. I moved a l l 19 masses to an i d e n t i c a l spot four f t away. On 2 3 March, two other masses had been added to the surface of the others and a t h i r d mass was deposited only three inches away. No new masses were added to the new or o r i g i n a l s i t e s on subsequent days, but these preliminary mani-pulations suggest that there are i n female R. p r e t i o s a s p e c i f i c behavioral adaptations f o r grouping of egg masses. Si t e s used f o r egg-laying i n 1969 were within one f t of those used i n 1968. A t h i r d new s i t e i n the r i v e r was also used i n 1969. As w i l l be discussed, two s i t e s were within 10 f t of those used by R. aurora, although the s p e c i f i c area chosen d i f f e r e d i n several respects. In 1968, the e f f e c t i v e breeding season was 11 days, and 15 days i n 1969, as determined by the f i r s t day of c a l l i n g and l a s t day of egg l a y i n g . 116 TABLE XXIII Summary of main s i m i l a r i t i e s and differences i n the prebreeding and breeding behavior of Rana aurora and Rana p r e t i o s a at the L i t t l e Campbell River study area. Rana aurora (1) Emerge from hibernation i n February and March (2) Move to breeding s i t e s when a i r i s minimum of 5-6 C. (3) Use the northern portions of pond and r i v e r f o r breeding. (4) Males v o c a l i z e several f e e t apart (5) Males vo c a l i z e under several f e e t of water at l e a s t 3 f t from shoreline. (6) C a l l s given mainly at night but may occur during the day. (7) Females spawn during the night. (8) Eggs l a i d several feet apart attached to vegetation i n depths of 12 inches or more and 3 f t or more from margins of pond and r i v e r . (9) In 1968 c a l l i n g began 28 February and spawning ended 13 March; 8 March and 3 A p r i l i n 1969. Rana p r e t i o s a (1) Same (2) Same (3) Same (4) Males v o c a l i z e inches apart i n small groups. (5) Males vo c a l i z e i n a i r from shallow margins of pond and r i v e r . (6) C a l l i n g occurs during day-l i g h t and on nights above 5-6 C. (7) Females spawn during the day, often i n f u l l sunshine. (8) Eggs l a i d i n groups un-attached i n only a few inches of water at r i v e r and pond margins. (9) C a l l i n g began 29 February and spawning ended 10 March i n 1968; 9 March and 2 3 March i n 1969. 117 A summary of the main s i m i l a r i t i e s and differences i n the prebreeding and breeding behavior of R. aurora and R. p r e t i o s a i s seen i n Table XXIII. D. Embryonic Thermal Requirements and Environmental Temperature a. Rana aurora The eggs of R. aurora are loosely enclosed i n a compact oval j e l l y mass attached to vegetation at l e a s t 18 inches below the water surface. The eggs are large. The diameter of 186 i n d i v i d u a l eggs from nine egg masses averaged 3.03 mm (SD = .29). The percentage s u r v i v a l of stage 20 from stage 4 at d i f f e r e n t temperatures i s shown i n Table XXIV. No eggs at 1-3 C survived beyond stage 11. Although mortality i s s l i g h t l y greater than 50% at 4.5 C, t h i s temperature i s not believed to be l e t h a l . Eggs that were s t i l l a l i v e at stage 18 were attacked by a fungus, and apparently died as a r e s u l t of t h i s i n f e c t i o n . (Embryos were seen moving within the fungus-coated j e l l y capsules, but were dead by stage 20). Consequently, the lower l e t h a l temper-ature i s probably s l i g h t l y lower than 4.5 C. Between 4.5 C and 20 C, development proceeds normally, and these temperatures are considered to represent t o l e r a b l e l i m i t s . At 2 3 C, the embryos underwent abnormal g a s t r u l a t i o n (stage 11), and were deformed i n successive stages. About 10% of these reached stage 20, but a l l were badly misshapen and soon died. At 24 C and 25 C, a l l embryos died s h o r t l y a f t e r abnormal g a s t r u l a t i o n . The f a c t that most embryos survived at 20 C whereas at 23 C a l l f a i l e d r e l a t i v e l y e a r l y (at stage 11), in d i c a t e s that 118 TABLE XXIV Percentage s u r v i v a l of eggs to stage 20 at constant temperatures. Incubation temperature % s u r v i v a l C Rana aurora Rana p r e t i o s a 1 _ 3 0 0 4.5 + .5 47 0 7.0 + 1.0 84 76 10.8 + 1.0 93 87 15.0 + 2.0 90 -20.0 + .1 86 86 23.0 + .1 0 -24.0 + .1 0 93 25.0 + .1 0 -26.0 + .1 - 90 28.0 + .1 - 94 - in d i c a t e s eggs not tested at that temperature. Figure 25 Rate of development of eggs of Rana aurora and Rana p r e t i o s a . 28° 20° I0fl° 7° o> 100 200 300 400 500 600 70 0 800 900 1000 > CO Q Time since Stage 3 (in Hrs) c 100 200 300 400 500 600 700 800 900 1000 1100 1200 13001400 Time since Stage 4 (in Hrs) 120 the upper l i m i t i s probably nearer 20 than 23 C. Thus the over-a l l l i m i t s f o r R. aurora embryos i n e a r l y stages are approximate-l y 4-21 C. Greater tolerance to temperature increase i s gained as development proceeds. Eggs f i r s t placed i n 2 3 C at stage 11 were able to reach stage 20 s u c c e s s f u l l y , although they did not i f maintained at t h i s high temperature from an e a r l i e r stage. Eggs i n stage 9 could t o l e r a t e 21.5 C, but died i n stage 17 at both 26 and 28 C. Embryos of R. aurora i n stage 9 that were exposed to 1 G f o r e i t h e r 2.5, 4, or 8 hours and subsequently kept i n room temperatures survived as well as c o n t r o l embryos. S u r v i v a l was over 80% f o r a l l groups. The e f f e c t of temperature (within t o l e r a b l e l i m i t s ) on the rate of development i s seen i n F i g . 25a. The biggest increase i n rates occur with only small increments of heat at the lower end of the thermal l i m i t s , as can be seen by comparing the slopes of the curves i n F i g . 25a. This can be i l l u s t r a t e d another way by comparing the time f o r the eggs to reach stage 20 at each temperature. Based on the number of hours to reach stage 20, the Q ^ Q values can be c a l c u l a t e d f o r various temper-ature i n t e r v a l s (Table XXV). As seen i n F i g . 25a, the maximum delays i n development occurred between stages 11 and 12. Eggs at 1-3 C did not proceed beyond stage 11, and at 4.5 C i t took 210 hours f o r development to proceed from stage 11 to stage 12. This delay was s t i l l apparent at higher temperatures, although much diminished. Embryos do not emerge from the j e l l y capsule u n t i l 121 TABLE XXV 0.10 v a l u e s f ° r embryonic development. Temperature range Rana aurora 4.5 - 7.0 19.5 7.0 - 10.8 4.0 10.8 - 15.0 3.2 15.0 - 20.0 3.1 (10.8 - 20.0) (3.1) Rana p r e t i o s a 7.0 - 10.8 4.7 10.8 - 20.0 4.3 20 - 24 1.9 24 - 26 1.5 26 - 28 1.6 (20 28) (1.7) 122 stage 21. They hatch with well developed g i l l s and are capable of swimming, although they generally do not do so a c t i v e l y u n t i l a f t e r a few days. The C>2 consumption by R. aurora embryos between stages 12-25 at 18.5 C averaged 0.59 cmm 0 2/egg/hour (SD > .10), with a range of 0.51 to 0.77 cmm 02/egg/hour, f o r the six r e p l i c a t e s . b. Rana p r e t i o s a The eggs of R. p r e t i o s a are deposited i n j e l l y masses that are rounded and globular, but less f i r m than those of R. aurora. Masses are l a i d i n groups on top of or next to each other, unattached to vegetation and i n only a few inches of water at the margins of the breeding s i t e s . The diameter of 292 eggs from 12 masses averaged 2.31 (SD = .18) mm. The percentage s u r v i v a l of embryos that s u c c e s s f u l l y developed from stage 3 to stage 20 at each temperature i s l i s t e d i n Table XXIV. No development beyond stage 7 or 8 was noted f o r eggs at 1-3 C, and those at 4.5 C d i d not progress beyond stage 10 or 11. At 7 C, the s u r v i v a l was 76%. This may i n d i c a t e that the l e t h a l l i m i t i s at or not f a r below 6 C. Between 7 and 28 C, the embryos developed normally to stage 20. The upper l i m i t f o r development was determined by placing embryos at stage 5 i n 30 C. They began showing abnorm-a l i t i e s at stage 11, and most appeared as deformed neurulae i n stage 14. About 55% reached stage 20, but a l l had warped backs and t a i l s . Since these eggs were already i n stage 5 when introduced to 30 C, and s t i l l did not survive, eggs i n e a r l i e r stages would be expected to be even le s s t o l e r a n t . Hence, the 12 3 l e t h a l l i m i t f o r newly f e r t i l i z e d eggs (or those i n stage 3) i s probably close to 28 C. The maximum and minimum l i m i t s may be considered 6-28 C. Embryos i n stages 5 or 7 that were exposed to 1 or 3.5 C f o r e i t h e r 2.5, 4, or 8 hours survived as well as did the c o n t r o l s . The developmental rates at t o l e r a b l e temperatures are seen i n F i g . 25b. The curves f o r 24 and 26 G are intermediate to those f o r 20 and 28 C. Whereas an 8 C increase from 20 to 28 C only decreased the developmental time by 36%, the 3.8 G r i s e from 7 to 10.8 C decreased i t by 44%, i n d i c a t i n g that the eggs are most s e n s i t i v e to small temperature changes at low temper-atures. The variations i n temperature s e n s i t i v i t y are also i n d i c a t e d by Q ^ Q values based on the number of hours to complete development (Table XXV). R. p r e t i o s a embryos hatch i n l a t e stage 19, before they have attained g i l l c i r c u l a t i o n . The consumption of embryos between stages 12 and 15 averaged 0.5 7 cram C^/egg/hour (SD = .06). The s i x r e p l i c a t e s ranged from 0.50 to 0.69 cmm C^/egg/hour. c. Adult Spawning Behavior and Environmental Temperature In the Lower Fraser V a l l e y , both species begin breed-ing a c t i v i t i e s soon a f t e r i c e melts from spawning s i t e s . In 1968, 1969, and 1970, both species began breeding within the same week each year, when water temperatures i n a temporary pond used f o r spawning reached 6 C. The egg masses of both species are deposited i n the 124 same pond or slow-moving r i v e r . However, there are important d i f f e r e n c e s i n breeding behavior. Male R. aurora are unique among a l l ranids i n that they c a l l under water. The males are submerged i n the center of the pond, about 3 f t i n depth, and up to 4 f t deep i n the r i v e r , and c a l l most a c t i v e l y at night. Female R. aurora are attracted to the males i n these s i t e s . They spawn only at night and place t h e i r eggs attached to vege-t a t i o n at minimum depths of 18 inches, and at l e a s t 2 or 3 f t from the pond and r i v e r margins. Indivi d u a l egg masses are about 2 f t apart. A f t e r a few days, some egg masses may break from t h e i r attachment and f l o a t to the surface. Male R. p r e t i o s a c a l l i n groups, with i n d i v i d u a l males only inches apart within the group. They c a l l i n a i r from the very margins of the pond and r i v e r i n water only 2-6 inches deep. Most c a l l i n g occurs i n the daylight hours, and i t i s e s p e c i a l l y intense on sunny afternoons. R. p r e t i o s a females spawn during the daylight, most often i n f u l l sunshine, and deposit t h e i r eggs at those s i t e s where males c a l l . Females tend to deposit t h e i r eggs on top of, or immediately next to, another egg mass, so that numerous masses may occur i n an area le s s than 2 f t sq. The largest groups seen deposited i n small areas were groups of 26, 19, and 11 egg masses; most others were from 5-8 masses. These egg masses are only i n a few inches of water and the top halves of most are exposed d i r e c t l y to the a i r . Male £• p r e t i o s a may c a l l from the surface of the j e l l y masses once they are deposited, and consequently, females responding to t h e i r c a l l s f i n d masses nearby on which to deposit t h e i r own. Whereas both species breed simultaneously when the 125 water temperature of the breeding pond has reached about 6 C ( i n the center at a depth of 2 f t ) , and the eggs are l a i d on the same days, the egg masses of each are subjected to very d i f f e r e n t temperatures depending on where they are l a i d . Measure-ments were made of the water temperatures a c t u a l l y surrounding the eggs during t h e i r development i n the f i e l d - water surround-ing 18 R. aurora egg masses averaged 15.4 C (SD = 1.7) and 20.7 C (SD = 2.7) around 19 R. p r e t i o s a egg masses. (The measurements were made at 1200 hr 3 cm away from each egg mass). The measure-ments made only seconds apart i n d i c a t e the divergent thermal regimes to which the eggs are subjected. The data r e f l e c t the dif f e r e n c e s that e x i s t throughout the daylight hours. Almost every day, R. p r e t i o s a embryos develop i n warmer water than R. aurora embryos. There i s less divergence at night, except when near-freezing temperatures p r e v a i l . The absorption of s o l a r r a d i a t i o n by the black ova with-i n a j e l l y mass and the retention of t h i s heat by the j e l l y (Savage 1950), may r a i s e the temperature within a mass above that of the surrounding water. In f u l l sunlight, during the l a s t week of March 1969, the temperatures within 16 R. aurora masses averaged 15.3 C (SD = 2.2), while the surrounding water averaged 13.8 C (SD = 2.1); the egg masses averaged 1.5 C (range of 0.6 - 3.6 C) higher than the water. For R. p r e t i o s a the temperatures within 20 egg masses averaged 20.4 C (SD = 3.3), while the surrounding water averaged 17.6 C (SD = 3.2). The R. p r e t i o s a egg masses averaged 2.7 C (range of 0.4 - 5.2 C) higher than the water. The measurements were made i n sunlight so that the divergence between the water and i n t e r n a l mass 126 temperature i s maximal. (A quick-reading thermometer was placed about 2 cm in t o the egg mass j e l l y , and the water reading was made about 3 cm from the mass). A f t e r dusk the j e l l y coats r e t a i n heat longer than the water does (4 R. pretiosa egg masses s t i l l had temperatures averaging 1.3 C higher than the water 1.5 hours a f t e r sunset), and only several hours a f t e r sunset do the mass and water temperatures become nearly the same. Metabolic heat from eggs may be retained by the j e l l y . The i n t e r n a l temperatures of R. p r e t i o s a egg masses diverge more from the water than do those of RJ. aurora masses. Because R. p r e t i o s a masses are h a l f exposed to the a i r by being i n such shallow water, a great amount of j e l l y i s exposed to d i r e c t sunlight, so that considerable heat i s accumulated. Moreover, the grouping of the egg masses i n one place also helps r a i s e egg temperatures by reducing the flow of water around and through the masses; ra i s e d temperatures are maintained f o r longer periods i n t h i s fashion. The R. aurora masses normally remain submerged while development proceeds, so that they are not exposed to d i r e c t s u n l i g h t . Those masses that f l o a t to the surface a f t e r break-ing from t h e i r attachment to submerged vegetation are exposed to s o l a r r a d i a t i o n on only a part of t h e i r dorsal surface. The compact, globular j e l l y mass allows only a small portion of j e l l y to become exposed to d i r e c t sunlight, but there i s s t i l l enough heat gained to r a i s e the i n t e r n a l egg mass temperature above that of water by as much as 3.6 C. The highest temperature recorded within a R. p r e t i o s a egg mass was 27,5 C, and the lowest was 4 C. However, on freezing 127 nights, which occurred on numerous occasions when eggs were s t i l l developing, the egg mass temperatures may have f a l l e n below 4 C. Indeed, a t h i n layer of i c e that had formed over the surface of the j e l l y masses overnight was seen on dawn v i s i t s to the study area i n 1968 and 1969. In 1970, night temperatures were sub-freez i n g throughout most of the days the embryos were developing, and a large proportion of egg masses a c t u a l l y froze s o l i d over-night; a l l frozen embryos died. On the other hand, almost every afternoon, the R. p r e t i o s a masses reached 20 C and higher. For R. aurora masses, the highest temperature recorded was 20.5 C, and the lowest was 4.5 C. Most daytime temperatures reached only 12-15 C within the masses, but freezing night temper atures do not a f f e c t the masses deposited a foot or mor below the water. 128 DISCUSSION U n t i l t h i s study, r e l a t i v e l y l i t t l e was known about the biology of R. aurora and R. p r e t i o s a . These frogs are c l o s e -l y r e l a t e d and throughout t h e i r ranges they are almost complete-l y a l l o p a t r i c . Consequently, the discovery of a sympatric l o c a l -i t y provided a rare opportunity to study how they were able to c o e x i s t , since they were reported to resemble each other i n h a b i t s . The mechanisms by which they achieve successful co-existence and avoid competitive exclusion were in v e s t i g a t e d . This study has revealed that a primary e c o l o g i c a l d i f f e r e n c e between the two species i s that R. aurora i s more t e r r e s t r i a l than R. p r e t i o s a . Adaptations to t h e i r habitat preferences - land f o r R. aurora and water f o r R. p r e t i o s a -provide the basis f o r a discussion of how these c l o s e l y r e l a t e d species achieve successful coexistence. A. Morphology R. aurora and R. p r e t i o s a are s i m i l a r i n general form and body s i z e , but important morphological differences do e x i s t . The length of the hind limbs d i f f e r . Those of R. aurora are longer than those of R. p r e t i o s a of equal snout-vent length. The longer limbs of R. aurora c o r r e l a t e with i t s better c a p a b i l -i t y at jumping; R. aurora can jump fa r t h e r i n distance and height than R. p r e t i o s a . Rand (1952) found the same c o r r e l a t i o n when comparing the jumping a b i l i t i e s of s i x anuran species. In normal escape behavior, R. aurora usually jumps to f l e e from predators, and t h e i r leg morphology functions to t h i s end. R. p r e t i o s a uses swimming to escape from predators, and t h e i r 129 hind feet are extensively webbed. The basic habitat preference - land f o r R. aurora and water f o r R. pr e t i o s a - are c l e a r l y r e f l e c t e d i n the divergent adaptations of t h e i r limb morphology. The p o s i t i o n of the eyes also c o r r e l a t e s with divergent behavior. R. p r e t i o s a i s more aquatic than R. aurora. The dorsal p o s i t i o n of the eyes i n R. p r e t i o s a may function i n several ways. In attempting to escape, these frogs normally submerge to the mud bottom of the r i v e r or rainpools. They remain on the bottom, usually with only t h e i r eyes exposed. The dorsal p o s i t i o n of the eyes allows R. p r e t i o s a to see while almost completely concealed i n mud or debris. Moreover, as the frogs surface, they push t h e i r heads out of water, usually only t h e i r eyes and so expose only a small portion of t h e i r body to nearby enemies. The eyes i n the dorsal p o s i t i o n may also help R. p r e t i o s a i n feeding a c t i v i t i e s , f o r frogs f l o a t i n g at the water surface, with only head and eyes showing, can remain hidden from nearby p o t e n t i a l prey. The c o l o r a t i o n of R. aurora i s adaptive i n that the dorsal spots and brown-red background provide protection through d i s r u p t i v e c o l o r a t i o n as the frog feeds and seeks escape i n vegetation and plant cover on land. I t i s much more s t r i k i n g that the c o l o r a t i o n of R. p r e t i o s a i s highly suited to i t s habitat preferences. The f a i r l y uniform greenish-brown dorsum with d i s r u p t i v e black spots makes R. p r e t i o s a very d i f f i c u l t to detect on the mud of the r i v e r banks or i n the mud and debris at the bottom of the rainpools and r i v e r . The frog blends well with i t s background at e s s e n t i a l times, during attempted escape 130 from predators, and when feeding. The mucous covering on the skin of R. pr e t i o s a becomes copious i f the frog i s handled. This r e s u l t s i n the frog becom-ing very s l i p p e r y and slimy enough to e a s i l y s l i p through one's grasp. This probably enables the frog to escape from some predators. This mucous may also function i n water balance as discussed l a t e r . B. Ecology a. Food and Behavior I f competition i s understood to be the demand f o r a resource a v a i l a b l e i n l i m i t e d q u a ntities (Tanner 1967), then there i s l i t t l e l i k e l i h o o d of competition over food i n the LCR study area. The f i e l d i s r i c h i n prey organisms su i t a b l e to both species; i t i s a r i c h area containing many diverse h a b i t a t s . The a v a i l a b i l i t y of food i s ind i c a t e d by the f a c t that not a s i n g l e frog of 145 examined was without food i n i t s stomach. Moreover, no frogs caught during the study appeared weak and emaciated (except f o r a single b l i n d R. aurora). Frogs that had never eaten external food were able to survive over one month without eating, and i n d i v i d u a l s starved that long would regain health and normal behavior when fed. Thus should a s c a r c i t y of food a r i s e , an u n l i k e l y condition i n the LCR study area, frogs of both species could withstand food l i m i t a t i o n s f o r many days. In spring and autumn, when rainpools are f i l l e d , the frogs may feed c l o s e r to each other than at other times. S i m i l a r food w i l l be encountered. As well as having d i f f e r e n t h abitat preferences, the two species have d i f f e r e n t feeding 131 behavioro R. aurora moves around more to seek out food, while R. p r e t i o s a waits to ambush i t s prey. Again, the opportunity f o r competition i s l i m i t e d because of divergent feeding t a c t i c s . As i n other aspects of t h e i r ecology, the species d i f f e r i n the habitat preferred f o r d a i l y feeding a c t i v i t i e s . R. aurora feeds predominantly on land, along the r i v e r bank or margins of rainpools, moving within the plant cover. R. pre t i o s a feeds almost e x c l u s i v e l y from water. The food eaten r e f l e c t s t h i s divergence i n feeding s i t e s i n that R. p r e t i o s a eats more aquatic prey organisms than does R. aurora. The predominance of aquatic prey i n the d i e t of R. pre t i o s a was also found i n previous food studies (Schonberger 1945, Turner 1959). Both species come i n t o contact with many of the same prey items. The percentage overlap i n t h e i r d i e t i s high, e s p e c i a l l y between newly metamorphosed i n d i v i d u a l s , which feed within inches of each other during the summer months. Although both may feed on many of the same food items, they secure t h e i r food from a d i f f e r e n t substrate. Consequently, opportunities f o r d i r e c t competition of prey organisms are reduced. During wet weather, when both species feed on land, the chances of seeking food and competing are greater, but i n most circumstances they w i l l be separated by habitat preferences. £• aurora has access to a wider v a r i e t y of food, f o r they can take aquatic, semi-aquatic, and s t r i c t l y t e r r e s t r i a l organisms during feeding sojourns. R. p r e t i o s a i s normally r e s t r i c t e d to aquatic and semi-aquatic forms during most of the days, because of the warm dry weather which p r e v a i l s during most of the summer. For example, they are not able to feed on the 132 t e r r e s t r i a l land slugs which are eaten abundantly by the R. aurora which find s them i n the vegetation i n the f i e l d . b. Temperature Requirements and Adaptations Temperature tolerance and preference of the frogs are ad d i t i o n a l f a c t o r s which reduce p o t e n t i a l competitive i n t e r a c t i o n s between the species and allow greater niche p a r t i t i o n i n g and successful coexistence. Progs can regulate t h e i r body temperature to some extent by appropriate behavioral responses. By moving i n t o or out of sun-l i g h t , or water, they can gain or lose heat accordingly. I t i s not l i k e l y that i n natural conditions frogs w i l l die from over-heating. However, depending on t h e i r upper thermal tolerance, (below which they carry out d a i l y l i f e - s u s t a i n i n g a c t i v i t i e s ) , t h e i r a c t i v i t y w i l l be modified. Progs with high temperature tolerance are les s subject to d i r e c t heat s t r e s s , and can also continue a c t i v i t i e s such as feeding, i n conditions where frogs with lower thermal tolerance would be prevented. R. p r e t i o s a t o l e r a t e s higher temperatures than does aurora. In the summer i n the LCR study area, the a i r was often above 33 C. R. p r e t i o s a can t o l e r a t e temperatures as high as 35 C, but R. aurora w i l l die quickly above 33 C. Both species avoid high temperatures by moving int o microhabitats which provide protection against heat s t r e s s . R. pre t i o s a uses water to thermoregulate, and i t maintains a body temperature of about 2 7-30 C. during very warm days. L i l l y w h i t e (1970) found that R. catesbeiana. a very aquatic frog, uses water to regulate i t s i n t e r n a l temperature also . Because R. p r e t i o s a uses water f o r 133 feeding and other needs, during very hot days i t can s t i l l remain ac t i v e by remaining i n the water. On warm days, in s e c t a c t i v i t y i s maximal and feeding behavior i s i n t e n s i v e . During hot days i n J u l y and August, R. aurora i s not a c t i v e i n mid-afternoon when temperatures are high. Frogs r e s t r i c t t h e i r movements to tangles of vegetation and shaded areas; they avoid open sunlight and increase t h e i r feeding about dusk. The few degrees dif f e r e n c e i n temperature tolerance between the two species, combined with t h e i r behavior i n achieving preferred body temperatures, allows R. p r e t i o s a to remain active when R. aurora i s not. A. few i n d i v i d u a l s of R. aurora had body temperatures of 28 C i n hot days i n July, but most were from 22-25 C. I t was more common to f i n d R. p r e t i o s a with 27-30 C on these days. The d i f f e r e n c e i n temperature tolerance and preference would reduce competitive i n t e r a c t i o n s by allowing the frogs to be active at d i f f e r e n t times and places. Heat stress i s possible i n the LCR study area f o r newly transformed R. aurora, which in h a b i t the pond. In J u l y , when R. aurora metamorphose, the frogs f i n d themselves i n only a few inches of water at temperatures which can surpass t h e i r tolerance l i m i t s . They are forced to seek the cooler depths and cannot wander onto the vegetation, because of high a i r temperatures and reduced moisture a v a i l a b l e . Although they may not succumb, they are r e s t r i c t e d to a habitat which allows maximal predation to occur. Shakes and invertebrate predators, e s p e c i a l l y Lethocerus, k i l l many of the transforming and new frogs. The tadpoles which have not yet metamorphosed probably do not escape from the many predators i n the depths and consequently, most are probably eaten. 134 c. Water Requirements and Adaptations I t i s d i f f i c u l t to say i f R. p r e t i o s a prefers the water, or i s , indeed, r e s t r i c t e d to i t . There may be a subtle p h y s i o l o g i c a l basis underlying i t s very aquatic behavior, but studies on water balance did not reveal s i g n i f i c a n t differences with R. aurora. Often R. p r e t i o s a would submerge when i t had caught a prey item, and they fed on land only i n wet weather. Perhaps they can more e a s i l y digest food when i t i s moist. How-ever, the necessity or preference f o r using water as a refuge from predators may also l i m i t t h e i r choice of feeding s i t e s . I t would be advantageous feeding i n places which leave an i n d i v i d u a l l e s s susceptible to predation. R. aurora and R. p r e t i o s a lose water by evaporation at the same rate to s t i l l a i r . The r a t e of water loss i s a func-t i o n of body s i z e , and frogs of small s i z e lose water more rap i d -l y than larger i n d i v i d u a l s . Adult body sizes of both species are about the same, with a maximum s i z e of about 80 mm recorded f o r females. Young frogs d i f f e r i n that R. aurora transform at a smaller s i z e than R. p r e t i o s a . R. aurora are 25-27 mm at metamorphosis, and at 28 C, such small animals desiccate r a p i d l y , and die a f t e r a few hours with no opportunity to replenish l o s t water. This f a c t assumes importance, because at the time £° aurora metamorphose i n the LCR study area, i n J u l y , temper-atures are often above 28 C, and the only standing water i s that of the r i v e r . R. aurora are r e s t r i c t e d to the r i v e r margins, and are not active elsewhere i n the f i e l d . This r e s t r i c t i o n to the r i v e r a f f e c t s them i n several ways. They are exposed to heavy predation by snakes and herons, which hunt along the r i v e r . 135 Also they are eaten by adult R. pr e t i o s a , which feed from the r i v e r , and eat small frogs when they can catch them. As soon as the rains come i n the f a l l , R. aurora move away from the r i v e r to the rainpools. Newly transformed R. p r e t i o s a remain i n the r i v e r where they metamorphose. They f i n d l i t t l e r e s t r i c t i o n of t h e i r movement since they prefer the aquatic h a b i t a t . The body water content i s the same f o r both species. Each i n i t i a l l y contains about 80% of body weight as water. This i s the same f o r other species of ranids studied (Thorson 1955). Thus the time t i l l death and the percentage water loss at the l e t h a l d e s i c c a t i o n l i m i t i s not due to the i n i t i a l water supply of each species. At 15 C, small frogs died when they had l o s t from 31-37% of t h e i r body weight, and the species did not d i f f e r . At 28 C, R. aurora l o s t an average of 29.7% of i t s body weight at the c r i t i c a l a c t i v i t y point, and R. p r e t i o s a l o s t 32.8%. The temperature of 28 C i s near the upper temperature tolerance l i m i t f o r R. aurora, and the heat stress may have influenced the water balance. Thorson (1955) also found that R. pipiens died a f t e r l o s i n g a smaller percentage of i t s body weight at near l e t h a l temperatures, than when desiccated at reduced thermal conditions. For other species of North America ranids, desiccated at moderate temperatures f o r each species, i n d i v i d u a l s died a f t e r l o s i n g about 30-35% of t h e i r weight, as did R. aurora and R. p r e t i o s a . R. aurora was more active i n the cages while i t was being desiccated than was R. p r e t i o s a . This may in d i c a t e that 136 R. aurora responds more quickly to water loss than does R. p r e t i o s a , and a c t i v e l y seeks to f i n d water to replenish losses. R. p r e t i o s a assumed the water conserving p o s i t i o n f o r longer periods than did R. aurora, but both species were very active when they had l o s t about 20% of t h e i r weight. The copious amounts of mucous on the body of R. p r e t i o s a should provide some defense against desiccation (Elkan 1968). In t h i s respect, one would expect R. p r e t i o s a to be more r e s i s -tant to d e s i c c a t i o n than R. aurora, which has l e s s mucoid cover-ing on i t s s k i n . C e r t a i n l y , the extensive mucous on R. p r e t i o s a would prevent body f l u i d d i l u t i o n during the long i n t e r v a l s i t remains i n water, since i t would e f f e c t i v e l y r e s t r i c t abundant water inflow through i t s binding q u a l i t y . The mucoid covering on the skin of R. p r e t i o s a i s probably adaptive i n i n h i b i t i n g water d i l u t i o n since the species i s so aquatic. ( I t also aids i n escape behavior, because the frog, wet from i t s immersion i n the r i v e r , becomes very s l i p p e r y and can quickly squeeze out of one's hand). The marked preference f o r water shown by R. p r e t i o s a cannot be ascribed to an obvious p h y s i o l o g i c a l b a s i s . Again, however, R. p r e t i o s a moves to land only when the vegetation and ground are wet, ( i n d i c a t i n g water requirements as an under-l y i n g causal f a c t o r f o r i t s behavior). Perhaps because R. p r e t i o s a i s a poor jumper on land, when compared with R. aurora, i t r e s t r i c t s i t s movements to moist l o c a t i o n s . I f i t wandered f a r overland i n dry conditions, i t would face a danger of d e s i c c a t i o n by not being able to return quickly and e f f i c i e n t l y to water. I t would be advantageous to venture onto land only 137 when the danger of dehydration i s eliminated. In contrast, R. aurora i s a good, long, strong jumper, and quickly t r a v e l s distances on land. I t would have a better chance of f i n d i n g water should the need a r i s e , and as indicated by i t s greater l e v e l of a c t i v i t y i n des i c c a t i o n experiments, i t would not wait f o r long periods before seeking to replenish l o s t water. At 10 C frogs of both species survived equally well submerged i n water f o r eight hours. I t would be i n t e r e s t i n g to in v e s t i g a t e t h e i r a b i l i t y to remain submerged at higher temper-atures, those normally found i n summer conditions. At high temperatures, the rate of water flow across the skin should be increased, and oxygen i n the water- reduced. The mucoid cover-ing on R. p r e t i o s a skin may r e s u l t i n d i f f e r e n t c a p a b i l i t i e s under these conditions, preventing body f l u i d d i l u t i o n while s t i l l allowing gas transport (Elkan 1968), while R. aurora may f i n d d i f f i c u l t i e s . d. Escape Behavior The patterns of escape e x h i b i t e d , by frogs i s species-s p e c i f i c and innate. Naive laboratory-reared frogs responded i n threat s i t u a t i o n s as d i d wild caught frogs tested i n the laboratory and observed i n the f i e l d . The c i r c u l a r jumping behavior of R. p r e t i o s a released on land i s i n t r i g u i n g . Because t h i s species i s r a r e l y more than a few fe e t from standing water, jumping i n a c i r c u l a r d i r e c t i o n brings the frog i n t o v i s u a l contact with water should i t be forced away from i t or lose i t s o r i e n t a t i o n . When R. p r e t i o s a 138 begins i t s c i r c u l a r jumping pattern, i t usually f i n d s i t s way back to water a f t e r the f i r s t or second c i r c l e s have been completed. These frogs hop low to the ground and soon t i r e i f they have not been able to enter water. They apparently r e l y on t h e i r i n i t i a l jumps to achieve t h e i r escape, and do not have the endurance to maintain s a l t a t o r y behavior f o r long. More-over, they are clumsy jumpers, and often t r i p on t h e i r webbed f e e t . When R. p r e t i o s a ventures onto land i n wet and rainy conditions, i t does not r e a d i l y show the c i r c u l a r jumping pattern when frightened. The frogs hop d i r e c t l y and quickly to the nearest water; they apparently know t h e i r surroundings and the shortest route f o r escape to the nearest rainpool or r i v e r . C i r c u l a r movements would not be advantageous, since a predator would e a s i l y capture the frog; the c i r c u l a r movement does not allow much distance to be gained. C l e a r l y R. p r e t i o s a i s vulnerable on land and dependent on standing water f o r s u r v i v a l . As Gans and Parsons (1966) noted, the important aspect of a frog's jumping a b i l i t y i s that i t carry the frog across the water-land i n t e r f a c e . In t h i s respect, R. p r e t i o s a can be considered a successful jumper. However, i t i s c l e a r that R. aurora i s more adept at jumping behavior, and indeed, depends on strong s a l t a t i o n f o r s u r v i v a l . The long, r e l a t i v e l y s t r a i g h t jumps of R. aurora carry the frog many feet i n a few seconds. Moreover, the angle of 45° at which R. aurora jumps i s l i k e l y to y i e l d the maximum f l i g h t distance f o r a given energy input (Gans and Rosenberg 1966). Another important feature of a high jump angle i s that i t allows a frog to leap over obstacles, 139 such as grasses and stems, that i t may encounter along i t s escape route. I saw t h i s as I chased R. aurora i n the f i e l d ; they moved quickly and e f f i c i e n t l y over obstacles - sedges and bulrushes - that would have blocked t h e i r path i f they had not cleared them with high jumps. The low jump angle of R. p r e t i o s a i s i n e f f i c i e n t i n t h i s respect; instead they r e l y on concealment i n grasses and plant cover, rather than jumping f o r f l i g h t , i f they are trapped on land and have not found water. Both species r e l y on concealment and freezing against the substrate f o r as long as possible before moving and ex-posing themselves. R. p r e t i o s a w i l l wait u n t i l snakes approach within inches before moving, but R. aurora jumps more r e a d i l y . This r e f l e c t s the effectiveness jumping has f o r each species. R. aurora i s good and can elude a predator with a few long hops, while R. p r e t i o s a can not. On wet days, R. p r e t i o s a was detected on land only when they began r a p i d l y jumping towards the r i v e r , gambling to reach water before being caught as they jumped on land. Of course, I cannot say how many R. p r e t i o s a did not jump as I neared them, but i t can be concluded that water i s the refuge they prefer i n t h e i r escape behavior, a l b e i t , i n almost every other aspect of t h e i r behavior as w e l l . When R. p r e t i o s a jumps i n t o the water, i t almost always submerges i n t o the mud bottom. In contrast, R. aurora u s u a l l y swam only a few inches out i n t o the channel and then clung to plants or f l o a t i n g debris. They did not remain i n the water f o r long, and r a r e l y submerged. The presence of large cutthroat trout i n the L i t t l e Campbell River may be a reason f o r t h i s , and also small R. aurora could e a s i l y be eaten by 140 adult R. p r e t i o s a which are found i n the water. C. Comparative Reproductive Behavior a. Reproductive I s o l a t i o n In the LCR study area, both species begin breeding a c t i v i t y on v i r t u a l l y the same day of the year, and as seen i n Tables XX and XXI, egg-laying may occur simultaneously. Both species breed i n the same r e s t r i c t e d portions of the pond and r i v e r . The mating c a l l of both can be heard at the same time and place. Adult males of both species are 45-64 mm (sv length), and the females are 62-77 mm. Under these circumstances, one might expect a high percentage of i n t e r s p e c i f i c matings. How-ever, during both years, I found only one i n t e r s p e c i f i c p a i r (a male R. aurora and a female R. pretiosa) i n amplexus. The R. p r e t i o s a was clasped on land as she moved to the breeding s i t e s . Of more than one hundred egg masses studied, only a s i n g l e egg mass may have resulted from a cross between R. p r e t i o s a and R. aurora; the eggs were the s i z e of R. p r e t i o s a eggs. However, even t h i s mass may not have been a hybrid one. I t may have been a R. p r e t i o s a egg mass destroyed i n early developmental stages by cold temperatures. I have not crossed the species to determine the l e v e l of genetic c o m p a t i b i l i t y , but i t i s u n l i k e l y that hybrid embryos w i l l develop normally. Dumas (1966) and Porter (1961) have demonstrated that hybrid crosses of P a c i f i c Northwest Rana do not produce viable o f f -spring, and they crossed both R. aurora and R. p r e t i o s a with other species. Moreover, a f t e r examining several hundred frogs i n the f i e l d , I have not found one resembling a hybrid or 141 d i f f i c u l t to i d e n t i f y as e i t h e r species. Thus there i s no c l e a r evidence f o r i n t e r s p e c i f i c matings i n these species that breed under conditions very susceptible to even chance encounters. Dozens of egg masses of each species were found within several feet of each other. The following f a c t o r s seem important f o r t h e i r success-f u l reproductive i s o l a t i o n : (1) The mating c a l l of each i s d i s t i n c t i v e and as i n other anurans ( L i t t l e J o h n and Michaud 1959) the females are l i k e l y to respond to c a l l s emitted by c o n s p e c i f i c males. (2) There are microgeographic differences i n breeding s i t e s . In the pond and r i v e r R. aurora breeds i n water at l e a s t 3 f t from shore and i n depth 12 inches and greater, while p r e t i o s a breeds at the very edges of the r i v e r overflow and pond border i n water only a few inches deep. (3) R. aurora c a l l s underwater, and R. p r e t i o s a c a l l s i n the a i r . (4) R. aurora c a l l s mainly at night, and R. p r e t i o s a c a l l s mainly i n the afternoon and evening, and r a r e l y on warmer nights• (5) R. aurora females probably respond to male c a l l s only during the night and e a r l y mornings as they spawn only during the night. They spawn i n deep water i n areas where male R. aurora c a l l . R. p r e t i o s a spawn mainly during morning and mid-afternoon hours and i n very shallow water i n those spots where males have congregated. (6) The e f f e c t of the s i n g l e note uttered by amplectic 142 male R. aurora on the spawning behavior of the female i s unknown. I f i t i s a necessary part of the courtship behavior leading to successful egg-laying, a female R. aurora may be i n h i b i t e d from re l e a s i n g her eggs i f clasped by a s i l e n t male R. p r e t i o s a . These f a c t o r s work to reduce gamete wastage by r e s t r i c t -ing i n t e r s p e c i f i c matings. Mayr (1963) has noted that e t h o l o g i c a l premating i s o l a t i n g mechanisms may be reinforced i n the area of sympatry i f compared to a l l o p a t r i c populations of each species-. B l a i r (1955) has reported on such a f i n d i n g i n frogs of the genus Microhyla i n the southwestern United States. However, r e f e r r i n g to the reports of Storm (1960) f o r R. aurora i n Oregon, and Turner (1958) f o r R. p r e t i o s a i n Wyoming, and the present work on populations of R. aurora i n Stanley Park and Marion Lake, I f i n d no major differences i n behavior of these species i n a l l o p a t r i c and sympatric populations. Nevertheless, differences may be subtle, and studies should be undertaken i n t h i s d i r e c t i o n . D. Embryonic Thermal Requirements During the nonbreeding season, R. p r e t i o s a i s more aquatic than R. aurora. In almost a l l aspects of t h e i r ecology, R. p r e t i o s a uses water and R. aurora uses land. During the breeding season, however, t h e i r behavior i s reversed; R. aurora i s more aquatic than R. p r e t i o s a i n that R. aurora spawns i n the deep water of the pond and r i v e r whereas R. p r e t i o s a breeds i n water only a few inches deep at the very margin of the pond and r i v e r (Licht 1969b). This r e v e r s a l presents c e r t a i n problems, e s p e c i a l l y to the developing embryos. But i n part, the embryos 143 are adapted to cope with some of these problems. At each extreme, the thermal tolerance l i m i t s f o r R. aurora, 4-21 C, are beyond those encountered by developing embryos. R. aurora usually do not spawn u n t i l the water reaches 6 or 7 C. A f t e r t h i s temperature i s reached only an unusually prolonged c o l d s p e l l could lower the temperature at the depths the eggs are deposited to below 4 C. Moreover, the embryos can withstand short-term cold exposure as low as 1 C. The egg masses are completely submerged and so well protected from thermal extremes. Even those masses that r i s e to the surface do so only a f t e r the embryos are at stages where they can t o l e r a t e temperatures beyond 21 C. Female R. aurora spawn at night and the eggs are not exposed to sunlight and r i s i n g temper-atures u n t i l several hours a f t e r f e r t i l i z a t i o n . This means that the embryos have progressed several stages before water temper-atures r i s e , and t h e i r tolerance i s increased. For example, embryos i n stage 4 can t o l e r a t e 20 C but not 2 3 C, however, embryos i n stage 9 can survive at 2 3 C. S u r v i v a l a f t e r short-term exposure i n even higher temperatures i s l i k e l y . (A d e t a i l e d discussion of breeding habits and embryonic thermal requirements i s found i n the paper by L i c h t (1970)). For R. p r e t i o s a , the upper l i m i t of 28 C i s s u f f i c i e n t -l y high to provide safety from most natural heat s t r e s s . How-ever, freezing and subfreezing night temperatures, that often occur during February and March i n the Lower Fraser Valley, present a major problem. Although young embryos can withstand temperatures as low as 1 C f o r at le a s t up to eight hours (a longer i n t e r v a l of low temperatures than normally occurs i n the 144 f i e l d ) , subfreezing temperatures i n the f i e l d may r e s u l t i n i c e formation on the dorsal portion of the grouped egg masses. Ice destroyed whole egg masses i n 1970. Embryos of both species are responsive to small changes i n temperature at the lower end of t h e i r tolerance l i m i t s : i . e . Q ^ Q values are highest at low temperature i n t e r v a l s . This rapid acceleration i n developmental rates with only small increments of heat has the important advantage of minimizing any delay i n development due to c o l d . Both species breed i n tempor-ary ponds, and i f these dry up before the tadpoles metamorphose, the frogs are l e f t stranded. The quicker the hatching time, the sooner the tadpoles can assume growth toward metamorphosis. In add i t i o n , ranid eggs are palatable and nontoxic when eaten by possible predators (Licht 1969c). Prolonged delays i n develop-ment could r e s u l t i n more predation on the r e l a t i v e l y defense-l e s s embryos. Because of the r e l a t i v e l y exposed s i t e of the egg masses of R. p r e t i o s a , embryos of t h i s species are subjected to both higher and lower temperatures than those of R. aurora. For R. p r e t i o s a , time to complete development i s decreased by 71% between 10 and 20 C , but only by 36% between 20 and 28 G. The Q ^ Q values within any i n t e r v a l between 20 and 28 C are about the same. This means that once a minimum temperature of 20 G i s attained within the R. p r e t i o s a egg mass, there i s l i t t l e f urther gain i n developmental r a t e . The pattern of grouping the egg masses i n very shallow water r e s u l t s i n temper-atures within masses reaching 20 C or more almost d a i l y , so that development during daylight proceeds maximally. By spawning i n 145 the early morning or mid-day, often i n f u l l sunlight, females immediately provide warm temperatures f o r newly f e r t i l i z e d eggs. The shallow water warms quickly and remains so f o r several hours a f t e r dusk. Embryos can undergo several hours of rapid develop-ment before being exposed to the col d night temperatures. Apparently the R. p r e t i o s a population of the Lower Fraser Valley uses a l l possible heat sources during the daylight to achieve maximal embryonic developmental r a t e s . Although even young embryos can t o l e r a t e temperatures as low as 1 C f o r several hours, the daylight spawning of R. pr e t i o s a appears to be an adaptation f o r ensuring the embryos are at an advanced stage before exposure to possible l e t h a l cold temperatures. Although the data on consumption of embryos i n la t e g a s t r u l a t i o n (stage 11) show no s i g n i f i c a n t differences between the two species, there may be differences i n l a t e r stages of development. Since R. aurora embryos hatch at stage 21 and R. p r e t i o s a hatch i n l a t e stage 19, t h i s d i f f e r e n c e may r e f l e c t a diffe r e n c e i n C>2 requirements of the advanced embryos (Moore 1940). The cool deep waters where R. aurora embryos develop are r i c h i n oxygen. An oxygen-rich environment allows the embryos to hatch at a r e l a t i v e l y l a t e , free-swimming stage. However, R. p r e t i o s a embryos develop i n the warm, shallow, oxygen-deficient margins of the pond and r i v e r . Frog embryos consume more C>2 as they develop (Moog 1944). The C>2 present i n the warm water i s probably s u f f i c i e n t f o r the ear l y stages, but may be i n s u f f i c i e n t as the embryos near hatching. Since the j e l l y surrounding the eggs reduces the d i f f u s i o n of oxygen from the water to the embryo, i t i s advantageous under low oxygen 146 conditions f o r the embryos to hatch at an e a r l y stage. The poor embryonic s u r v i v a l of R. p r e t i o s a compared with that of R. aurora may be i n d i r e c t l y a r e s u l t of oxygen d e f i c i e n c y . There i s very l i t t l e water flow i n the places where R. p r e t i o s a embryos develop, e s p e c i a l l y i n the pond. Bacteria, algae, and fungi are not washed away and tend to coat most of the egg masses. Embryos were seen moving i n s i d e fungus-covered eggs, but were dead several days l a t e r , presumably smothered by the fungus coating. The better s u r v i v a l of £• p r e t i o s a i n the r i v e r compared with the pond i n 1968 i s probably because of better water flow over the eggs i n the r i v e r . R. aurora i s c l e a r l y a species adapted to breed i n •northern' environments. The breeding behavior, c h a r a c t e r i s t i c s of the eggs and egg masses, the low minimum and maximum temper-ature tolerance, and the l a t e stage of hatching, a l l function f o r developmental success of embryos i n cool waters. Only the developmental rates are slow when compared with those of other 'northern' species. R. p r e t i o s a i s p e c u l i a r i n several respects. Females spawn on the same dates as R. aurora females, but they do not provide a 'northern' environment f o r t h e i r eggs. Since the egg masses are i n c l u s t e r s i n a few inches of water at the margins of breeding s i t e s , heat i s trapped and the i n t e r n a l temper-atures of the egg masses are r a i s e d . As a r e s u l t development proceeds maximally during the day. However, t h i s gain i n increased rates i s o f f s e t by two major f a c t o r s . F i r s t i s the low night temperatures (already discussed), that are capable of 147 destroying many embryos , p a r t i c u l a r l y those at the surface of exposed masses. The second disadvantage may be even more important. In the Lower Fraser V a l l e y , only a few days without r a i n , r e s u l t s i n a appreciable drop i n the margins of the slow-moving streams and ponds where both species spawn. For R. aurora t h i s presents l i t t l e problem, as i t s eggs are at l e a s t several feet away from the water's edge and i n deeper water. However, the eggs of R. p r e t i o s a are often l e f t stranded by the receding water, and e n t i r e egg masses may be desiccated. The populations of R. p r e t i o s a west of the Coastal mountains, such as the study population, reached the Lower Fraser Valley p o s t g l a c i a l l y e i t h e r from Central B r i t i s h Columbia or from the east (Dumas 1966). The main continuous range of R. p r e t i o s a l i e s east of the Coast mountains. In one popula-t i o n from within the continuous range of t h i s species (7800 f t i n Wyoming), R. p r e t i o s a i s reported to lay eggs i n groups at the margins of temporary ponds (Turner 1958). Apparently the Lower Fraser Valley population of R. p r e t i o s a has not evolved new breeding habits, and has retained the same reproductive behavior as populations to the east. Their 'strategy 1 seems to be that of racing against high mortality from cold at night, and desiccation i n dry s p e l l s , by using a v a i l a b l e heat during the day to increase developmental rates and thereby decrease the time t i l l the embryos hatch. This 'strategy' appears marginal i n my study area, and R. p r e t i o s a s u f f e r s high pre-hatching m o r t a l i t y when compared with R. aurora. The only data a v a i l a b l e on temperature tolerance of 148 R. p r e t i o s a from east of the Coastal mountains i s that of Johnson (1965). He recorded thermal l i m i t s of 6-28 C f o r R. p r e t i o s a l u t i v e n t r i s embryos. I f t h i s i s t y p i c a l of eastern populations, i t appears that the reproductive 'strategy' and thermal tolerances of R. p r e t i o s a are the same throughout i t s range. This does not mean that the 'strategy' i s marginal throughout i t s range. In the Lower Fraser V a l l e y R. p r e t i o s a may be prevented from evolving better adapted breeding behavior, such as spawning i n deeper water, by the presence of R. aurora. Successful reproductive i s o l a t i o n between these two species i s due i n part to t h e i r s p e c i f i c choice of spawning s i t e s . A change to deeper water spawning by R. p r e t i o s a would probably r e s u l t i n a breakdown of the reproductive i s o l a t i n g mechanisms that separate i t from R. aurora. In such a case, the loss of reproductive e f f o r t and the r e s u l t i n g embryonic mortality would probably be greater than the m o r t a l i t i e s now due to desiccation and f r e e z i n g . E. Coexistence of Ranid Frogs i n the P a c i f i c Northwest The most important point brought out by the i n v e s t -i g a t i o n of the comparative ecology of the two species of frogs i s that R. p r e t i o s a i s more aquatic than R. aurora. In almost a l l aspects of i t s ecology, R. p r e t i o s a used water, e i t h e r by preference or r e s t r i c t i o n , while R. aurora used land. The basis of t h e i r e c o l o g i c a l separation i s the water-land boundary. This i s true whether the body of water i s a small rainpool, the pond, or the r i v e r . R. p r e t i o s a i s almost always found i n the water, f l o a t i n g on the surface i n mid-stream or at the water margins. 149 R. aurora i s found on land, perhaps at the water edge, but most often several feet i n l a n d . The obvious preference or r e s t r i c t i o n to water f o r usual d a i l y a c t i v i t i e s shown by R. p r e t i o s a i s probably the major f a c t o r allowing successful coexistence with R^ aurora. As a consequence of t h e i r divergent habitat preferences, competitive i n t e r a c t i o n s severe enough to lead to exclusion of e i t h e r species are not operating i n the LCR study area. The only adverse e f f e c t of the two species l i v i n g i n sympatry d i s -covered i n t h i s study i s the possible predation of small R. aurora by adult R. p r e t i o s a , e s p e c i a l l y during the summer when both species l i v e i n or along the r i v e r . The population s i z e of each species i s not g r e a t l y affected by the other's presence. The d i s t r i b u t i o n s of the species, and t h e i r rare occurrence i n sympatry, are not explained by competitive i n t e r -actions, a p o s s i b i l i t y which existed before t h i s study. S» p r e t i o s a can be successful and e s t a b l i s h large populations within the range of R. aurora. The Coast Range mountain Chain undoubtedly i s a b a r r i e r f o r more extensive intermingling of the species on a broad s c a l e . However, l o c a l habitat condi-t i o n s w i l l most l i k e l y determine whether e i t h e r species w i l l survive i n a p a r t i c u l a r l o c a l i t y . There are c e r t a i n requirements of a habitat should i t be occupied by e i t h e r R. aurora or R. p r e t i o s a . The embryonic requirements, those of the eggs and developing embryos, are important i n c o n t r o l l i n g t h e i r d i s t r i b u t i o n s . For R. p r e t i o s a there must be s u f f i c i e n t r a i n f a l l during the breeding season 15G so that the egg masses are not l e f t stranded on the banks of the bodies of water used as spawning s i t e s . In the Lower Fraser V a l l e y , spring r a i n s are usually abundant, but i f not, R. p r e t i o s a may lose a f u l l year's reproductive output. For R. aurora, the breeding s i t e s must be of s u f f i c i e n t depth so that the eggs are not exposed to undue heat stress as the embryos have a very low heat tolerance (Licht 1970). R. aurora deposit t h e i r eggs i n such a manner that they w i l l not be stranded under conditions of sparse r a i n f a l l . For non-breeding R. p r e t i o s a , an e s s e n t i a l habitat requirement i s the presence of standing water. The feeding and escape behavior of R. p r e t i o s a are c a r r i e d out almost e n t i r e l y i n standing water, and the species would not survive without i t . R. aurora i s able to l i v e away from standing water by moving i n t o wooded areas, which provide conditions to meet t h e i r needs during non-breeding a c t i v i t i e s . They can seek escape from high temperatures, and i n woods, high humidities p r e v a i l . However, i f standing water i s present, R. aurora also depends on i t f o r food and escape. But they are not as dependent as R. p r e t i o s a . There are no obvious reasons why R. p r e t i o s a i s so scarce west of the Gbast Range, e s p e c i a l l y i n the Lower Fraser s V a l l e y . In t h i s l o c a l i t y there e x i s t many area which meet the requirements of JR. p r e t i o s a ; indeed, R. aurora i s widespread i n these places. There i s one strong p o s s i b i l i t y to explain the s c a r c i t y of R. p r e t i o s a . B u l l f r o g s , Rana catesbeiana. were introduced i n t o the Lower Fraser V a l l e y about 100 years ago. They have since successively established large populations and are widespread throughout the Lower Fraser V a l l e y . 151 Rana catesbeiana i s a highly aquatic f r o g , and l i k e p r e t i o s a , i s r e s t r i c t e d to water or i t s immediate v i c i n i t y a l l year round. Moreover, R. catesbeiana i s a voracious predator and often feeds on other anurans; b u l l f r o g s are the largest anurans i n North America and can feed on adult frogs of most other species. I t would eat R. p r e t i o s a j u v e n i l e s , and probably even the adults ( c e r t a i n l y males) with l i t t l e t rouble. Thus i t i s h i g hly l i k e l y that R. p r e t i o s a was once more widespread i n Lower Fraser Valley before the b u l l f r o g was introduced. Dumas (1966) found that i n western Washington R. p r e t i o s a populations were threatened by enlarging R. catesbeiana populations and may now be e x t i n c t . Further evidence f o r t h i s hypothesis i s the following f i n d i n g . About three miles to the west of the LCR study area, downstream on the L i t t l e Campbell River,is a l o c a l i t y where R. catesbeiana are found i n large number They are sympatric with R. aurora. The habitat conditions i n that area are s u f f i c i e n t to meet the requirements of R. p r e t i o s a , but t h i s species i s absent from the area. I t would be only years before R. p r e t i o s a would be eliminated from such an area, having to feed i n ponds and streams side by side with the much bigger, h i g h l y predatory b u l l f r o g . In 1970, the f i r s t b u l l f r o g s were found i n the LCR study area. They probably migrated from lower portions of the r i v e r . Thus, i n a matter of years, the R. p r e t i o s a population may be i n danger of elimination from the LCR study area. I be l i e v e i t to be an unfortunate way of t e s t i n g the above hypothesis, but the changing numbers of R. p r e t i o s a i n future 152 years w i l l be worth watching c l o s e l y . The e c o l o g i c a l equivalent of R. aurora east of the Coast Range i n B r i t i s h Columbia i s the wood fro g , R. s y l v a t i c a . I t i s much l i k e R. aurora i n i t s preference f o r land over water f o r non-breeding a c t i v i t i e s (Heatwole 1965, B e l l i s 1966). R. p r e t i o s a and R. s y l v a t i c a are sympatric throughout eastern B r i t i s h Columbia. R. aurora may indeed be excluded from eastern B.C., because of competition with R. s y l v a t i c a . The red-legged frog can coexist with e i t h e r the b u l l f r o g or the western spotted f r o g , which are highly aquatic forms, and e i t h e r of these l a t t e r two frogs could coexist with the wood f r o g . But neither R. aurora and R. s y l v a t i c a or R. pr e t i o s a and R. catesbeiana species p a i r s would survive i n sympatry. 153 LITERATURE CITED B e l l i s , E.D. 1965. Home range and movement of the wood frog i n a northern bog. Ecology 46: 90-98. B l a i r , W.F. 1955. Mating c a l l and stage of speciation i n the Microhyla olivacea-M. c a r o l i n e n s i s complex. Evolution 9: 469-480. Bogart, CM. 1960. The influence of sound on the behavior of amphibians and r e p t i l e s . In Animal Sounds and Communication. Edited by W.E. Lanyon and W.N. Tavolga. Amer. Inst. B i o l . S c i . , Washington, D.C. p. 137-320. Brown, H.A. 1967. High temperature tolerance of the eggs of a desert anuran, Scaphiopus hammondi. Copeia, 1967: 365-370. C a r l , G.C. 1966. The amphibians of B r i t i s h Columbia. B r i t . Columbia Prov. Mus. Handbook No. 2: 1-62. C a r l , G.C. and I. McT. Cowan. 1945. Notes on some frogs and toads of B r i t i s h Columbia. Copeia, 1945: 52-53. Cowles, R.B. and CM. Bogart. 1944. A preliminary study of the thermal requirements of desert r e p t i l e s . B u l l . Amer. Mus. Nat. H i s t . 8: 256-296. Dumas, P.C 1966. Studies of the Rana species complex i n the P a c i f i c Northwest. Copeia, 1966: 60-74. Elkan, E. 1968. Mucopolysaccharides i n the anuran defence against d e s i c c a t i o n . J . Zool. London, 155: 19-53. Gans, C. and T.S. Parsons. 1966. On the o r i g i n of jumping mechanisms i n frogs. Evolution 20: 92-99. Gans, C. and H.I. Rosenberg. 1966. Numerical analysis of frog jumping. Herpetologica, 22: 209-213. Gause, G.F. 19 34. The struggle f o r existence. Williams and Wilkins. Baltimore. Heatwole, H. 1961. Habitat s e l e c t i o n and a c t i v i t y of the wood frog , Rana s y l v a t i c a Le Conte. Amer. Midi. Nat. 66: 301-313. Heatwole, H., F. Torres, S. B l a s i n i de Austin, and A. Heatwole. 1969. Dynamics of evaporative water - loss by the coqui, Eleutherodactylus p o r t o r i c e n s i s . Comp. Biochem. P h y s i o l . 28: 245-269. Holmes, R.T. and F.A. P i t e l k a . 1968. Food overlap among co-e x i s t i n g sandpipers on northern Alaskan tundra. System. Zool. 17: 305-318. 154 Hutchison, V.H. 1961. C r i t i c a l thermal maxima i n salamanders. P h y s i o l . Zool. 34: 92-125. Jenssen, T.A. and W.D. Klimsta. 1966. Food habits of the green frog, Rana clamitans, i n southern I l l i n o i s . Amer. Mid i . Nat. 76: 169-182. Jbhnson, O.W. 1965. Early development, embryonic temperature tolerance and rate of development i n Rana p r e t i o s a  l u t i v e n t r i s Thompson. PhD Thesis. Oregon State Univ. (Diss. Abst. 25). Lack, D. 1945. The ecology of c l o s e l y r e l a t e d species with s p e c i a l reference to cormorant (Phalacrocorax carbo) and shag (P. a r i s t o t e l i s ) . J . Anim. E c o l . 14: 12-16, L i c h t , L.E. 1969a. Unusual aspects of anuran sexual behavior as seen i n the red-legged f r o g , Rana aurora aurora. Can. J . Zool. 47: 505-509. L i c h t , L.E. 1969b. Comparative breeding behavior of the red-legged frog (Rana aurora aurora) and the western spotted frog (Rana p r e t i o s a pretiosa) i n south-western B r i t i s h Columbia. Can. J . Zool. 47: 1287-1299. L i c h t , L.E. 1969c. P a l a t a b i l i t y of Rana and Hyla eggs. Amer. Midi. Nat. 82: 296-298. L i c h t , L.E. 1970. Breeding habits and embryonic thermal requirements of the frogs, Rana aurora aurora and Rana p r e t i o s a p r e t i o s a i n the P a c i f i c Northwest. Ecology 52: 116-124. L i l l y w h i t e , H.B. 1970. Behavioral temperature regulation i n the b u l l f r o g , R. catesbeiana. Copeia 1970: 158-168. L i t t l e j o h n , M.J. and T.C. Michaud. 1959. Mating c a l l d i s -crimination by females of Strecker's chorus frog (Pseudacris s t r e c k e r i ) . Tex. J . S c i . 11: 86-92. MacArthur, R.H. 1958. Population ecology of some warblers of northern coniferous f o r e s t s . Ecology 39: 599-619. Mayr, E. 1963. Animal species and evolution. Harvard Univers-i t y Press, Cambridge. Moog, F. 1944. The chloretone s e n s i t i v i t y of frogs' eggs i n r e l a t i o n to r e s p i r a t i o n and development. J . C e l l . Gbmp. Ph y s i o l . 23: 131-155. Moore, J.A.. 1940. Adaptive differences of the egg membranes of f r o g s . Amer. N a t u r a l i s t , 74: 89-93. Moore, J.A. 1949. Pattern of evolution i n the genus Rana. In Genetics, paleontology and evolution. Edited by Jepsen, G.L.E., Mayr, E. and Simpson, G.G. Princeton Univ. Press, N.J. p. 315-338. 155 P o l l i s t e r , A.W. and J.A. Moore. 1937. Tables f o r the normal development of Rana s y l v a t i c a . Anat. Rec. 68: 489-496. Porter, K.R. 1961. Experimental crosses between Rana aurora  aurora Baird and Girard and Rana cascadae S l a t e r . Herpetologica, 17: 156-165. Rand, A.S. 1952. Jumping a b i l i t y of c e r t a i n anurans, with notes on endurance. Copeia 1952: 15-20. Schonberger, C F . 1945. Food of some amphibians and r e p t i l e s of Oregon and Washington. Copeia, 1945: 120-121. Spight, T.M. 1968. The water economy of salamanders: evaporative water l o s s . P h y s i o l . Zool. 41: 195-203. Storm, R.M. 1960. Notes on the breeding biology of the red-legged frog (Rana aurora aurora). Herpetologica, 14: 96-100. Stebbins, R.C. 1951. Amphibians of Western North America. Univ. of C a l i f . Press, Berkeley. Stebbins, R.C. 1954. Amphibians and Reptiles of Western North America. McGraw-Hill, N.Y. Tanner, J.T. 1966. E f f e c t s of population density on growth rate of animal populations. Ecology 47: 733-745. Thorson, T.B. 1955. The r e l a t i o n s h i p of water economy to t e r r e s t r i a l i s m i n amphibians. Ecology 36: 100-116. Turner, F.B. 1958. L i f e h i s t o r y of the western spotted frog i n Yellowstone National Park. Herpetologica, 14: 96-100. Turner, F.B. 1959. An analysis of the feeding habits of Rana  pr e t i o s a p r e t i o s a i n Yellowstone National Park, Wyoming. Amer. Mi d i . Nat. 61: 403-413. Turner, F.B. 1960. Population structure and dynamics of the western spotted f r o g , Rana p r e t i o s a p r e t i o s a Baird and Girard i n Yellowstone Park, Wyoming. E c o l . Monog. 30: 251-278. 

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