Stephen F. Austin State University SFA ScholarWorks

Faculty Publications Biology

2007

Population Responses of Wood Frog (Rana Sylvatica) Tadpoles to Overwintered Bullfrog (Rana Catesbeiana) Tadpoles

Leroy J. Walston

Stephen J. Mullin Stephen F Austin State University, [email protected]

Follow this and additional works at: https://scholarworks.sfasu.edu/biology

Part of the Biology Commons Tell us how this article helped you.

Repository Citation Walston, Leroy J. and Mullin, Stephen J., "Population Responses of Wood Frog (Rana Sylvatica) Tadpoles to Overwintered Bullfrog (Rana Catesbeiana) Tadpoles" (2007). Faculty Publications. 106. https://scholarworks.sfasu.edu/biology/106

This Article is brought to you for free and open access by the Biology at SFA ScholarWorks. It has been accepted for inclusion in Faculty Publications by an authorized administrator of SFA ScholarWorks. For more information, please contact [email protected]. Journal of Herpetology, Vol. 41, No. 1, pp. 24-31, 2007 Copyright 2007 Society for the Study of Amphibians and Reptiles

Population Responses of Wood Frog (Rana sylvatica) Tadpoles to Overwintered Bullfrog (Rana catesbeiana)Tadpoles

1 LEROY J. WALSTON AND STEPHEN J. MULLIN

Department of Biology, Eastern Illinois University, Charleston, Illinois 61920, USA

ABSTRACT.-A fundamental goal in ecology is to understand how environmental variation influences the distribution of individuals within a population. In this study, we used laboratory experiments to examine the population responses of sympatric Wood Frog (Rana sylvatica) tadpoles to native overwintered Bullfrog (Ranacatesbeiana) tadpoles. For periods of up to two weeks, we measured growth, activity, and refuge use of Wood Frog tadpoles in small mesocosms with and without an overwintered Bullfrog tadpole present. Bullfrog tadpoles had a negative effect on the growth of Wood Frog tadpoles allotopic (naive) to Bullfrogs, whereas the presence of Bullfrogs had no effect on growth of syntopic (experienced) Wood Frog tadpoles. There were also differential behavioral responses of the Wood Frog populations to overwintered Bullfrog tadpole visual and chemical cues. Only allotopic Wood Frog tadpoles decreased activity levels and increased use of refugia in the presence of overwintered Bullfrog tadpoles. These observations indicate overwintered Bullfrog tadpoles might exert a selective pressure on sympatric Wood Frog tadpoles, and that experience might allow for the development of strategies to maximize performance for species coexisting with overwintered Bullfrog tadpoles.

A fundamental goal in ecology is to un- the field may be influenced by the presence of derstand how organisms respond to their predators (Werner, 1991). The effects of Bull- environment and how environmental variation frogs on sympatric amphibians are often medi- influences the distribution of individuals within ated by pond hydroperiod. In the Midwest, a population. Amphibian larvae developing in Bullfrogs typically require two years for tad- ephemeral aquatic habitats often experience poles to complete metamorphosis (Phillips et a different suite of competitors and predators al., 1999) and are, thus, restricted to permanent than those larvae developing in permanent wetlands where fish may also occur. Native fish aquatic habitats (Semlitsch, 1988; Werner and species are predators of most amphibians McPeek, 1994). To persist in these environ- (Semlitsch, 1988; Werner and McPeek, 1994), ments, amphibians must have adaptations to capable of eliminating many amphibian popu- tolerate not only variation in pond hydroperiod lations from permanent ponds. Bullfrog tad- but also to tolerate different suites of competi- poles, however, are usually unpalatable to fish tors and predators. One possible adaptation to (Kruse and Francis, 1977; Werner and McPeek, environmental variation is for a species to be 1994) and are capable of persisting in these phenotypically plastic (Van Buskirk and Relyea, environments. Although ephemeral ponds do 1998). In response to competitors and predators, not typically support Bullfrog tadpole popula- many larval anurans exhibit competitor- and tions in the Midwest, ephemeral ponds may predator-induced plasticity in behavior, growth become semipermanent after receiving high rate, and morphology (Van Buskirk and Relyea, levels of precipitation or after human landscape 1998; Relyea, 2002, 2004). alterations. In these situations, Bullfrog tadpoles Throughout their native range, Bullfrogs are may be capable of surviving for over one year, considered important agents of amphibian allowing overwintered Bullfrog tadpoles to community structure (Werner et al., 1995; interact with other sympatric amphibian larvae. Hecnar and M'Closkey, 1997; Boone et al., Boone et al. (2004) observed that, within its 2004). Laboratory experiments have demon- native range, the presence of overwintered strated that Bullfrogs are competitively superior Bullfrog tadpoles resulted in decreased growth to other amphibian species (Werner and Anholt, and survival of larval amphibians allotopic 1996), although the outcome of competition in (naive) to Bullfrogs, presumably via interspecif- ic competition. Thus, the exploitation of histor- ically ephemeral aquatic habitats by Bullfrogs 'Corresponding Author. Present address: United might present a novel competition threat to States Environmental Protection Agency, 77 West resident amphibian species. Jackson Boulevard, Chicago, Illinois 60604, USA; Wood Frog (Rana sylvatica) tadpoles common- E-mail: [email protected] ly exhibit behavioral and morphological plas- 25 RESPONSES OF WOOD FROG TADPOLES

pond completely dried before 1 ticity in response to predators and competitors ponds; each in each of the previous six years (S. (Van Buskirk and Relyea, 1998; Relyea, 2002, August Mullin, pers. obs.) such that larval Bullfrogs 2004). Wood Frogs and Bullfrogs are sympatric development. Although throughout much of the United States and could not complete adult Bullfrogs have been observed along the Canada. Although their distributions are usual- of these ephemeral ponds during the ly allotopic with respect to pond hydroperiod banks months, we have not observed any (Phillips et al., 1999; Paton and Crouch, 2002), summer Bullfrog reproductive activity at these ponds in tadpoles of the two species may be able to any of the previous six years. Thus, allotopic coexist in permanent aquatic environments that Wood Frog tadpoles were considered naive to lack fish. Overwintered Bullfrog tadpoles pos- overwintered Bullfrog tadpoles. All Wood Frog sess a size advantage over Wood Frog tadpoles collected were of similar developmen- and have been observed to depredate tadpoles embryos tal stage (Gosner stage 10; Gosner, 1960). of other ranids (Ehrlich, 1979; Kiesecker and collection, each egg mass was brought Blaustein, 1997). Therefore, overwintered Bull- Upon to the laboratory and incubated in isolated frog tadpoles might have adverse effects on back glass aquaria in 25 liters of natal pond water. Wood Frog populations through an interaction All tadpoles hatched within seven days of of interspecific competition and predation. collection. Upon hatching, tadpoles were trans- There is additional evidence suggesting that ferred to population-specific aquaria (allotopic larval amphibians with prior experience to or syntopic) filled with 25 liters of aged tap competitors and predators exhibit contrasting water, where they were raised until the com- responses to the presence of the competitor or mencement of this study. Water was changed predator than inexperienced larval anurans every 5-7 days and tadpoles were fed pow- (Kiesecker and Blaustein, 1997; Van Buskirk dered rodent chow ad libitum. On 22 March and Relyea, 1998; Gomez-Mestre and Tejedo, 2005, we returned to the two permanent ponds 2002). Thus, we believe that syntopic (experi- where the syntopic Wood Frogs were originally enced) Wood Frog tadpoles from semiperma- collected and seined each pond for Bullfrog nent fishless ponds will respond differently to tadpoles. These tadpoles were 7.32 ± 1.84 g the presence of overwintered Bullfrog tadpoles (mean ± 1 SE), too large to have hatched in 2005 than allotopic Wood Frog tadpoles from ephem- stage 32-36; Gosner, 1960) and were eral ponds. (Gosner considered to have overwintered from the Herein, we present results of laboratory previous year. Those Bullfrog tadpoles not experiments addressing the responses of Wood immediately added to experimental aquaria populations to native overwintered Bull- Frog were kept in a separate aquarium filled with frog tadpoles. We used natural populations of aged tap water. Bullfrog tadpoles were fed and Frogs and Bullfrogs to test two hypoth- Wood their water was changed in the same manner as (1) overwintered Bullfrog tadpoles induce eses: the Wood Frog tadpoles. All aquaria were in behavior, growth, and survival of changes maintained on a 12:12 L:D photoperiod in Wood Frog tadpoles; and (2) Wood sympatric a temperature-controlled environment (20'C). tadpoles from populations syntopic to Frog Experiment 1: Wood Frog Growth and Survival.- respond differently than allotopic Bullfrogs used a randomized block design to test for when in the presence of overwin- We populations the effects of overwintered Bullfrog tadpoles on tered Bullfrog tadpoles. the growth and survival of Wood Frog tadpoles. The two independent variables each had two MATERIALS AND METHODS levels-the Wood Frog population type was allotopic or syntopic, and Bullfrog tadpoles Study Organisms.-We collected eight Wood were present or absent. We randomly assigned Frog egg masses on 7 March 2005 from four glass aquaria (38-liter volume) to the four ponds in Coles County, Illinois. Four egg combinations of these variables, each of which each were collected from populations masses was replicated five times. syntopic and allotopic to Bullfrogs. Syntopic On 23 March 2005, we filled each aquarium Wood Frog egg masses were collected from two with 25 liters of aged tap water. We then added permanent fishless ponds that also contained 2 g of leaf litter and 1 g of ground rodent chow a breeding population of Bullfrogs. Successful each enclosure to serve as a refuge and food recruitment of Bullfrog and Wood Frog juve- to resource. For the Bullfrog treatments, we added niles has been observed at both ponds in each single Bullfrog tadpole to an aquarium of the previous six years (S. Mullin, unpubl. a containing either 20 allotopic or syntopic Wood data). Syntopic Wood Frog tadpoles, therefore, Frog tadpoles. In treatments in which Bullfrog were considered experienced to overwintered tadpoles were absent, we added 20 Wood Frog Bullfrog tadpoles. Allotopic Wood Frog egg tadpoles from either population. We placed masses were collected from two ephemeral 26 L. J. WALSTON AND S. J. MULLIN

brown construction paper between each aquar- chemical cues could disperse into the water ium to prevent the potentially confounding column occupied by the Wood Frog tadpoles. effects of Bullfrog visual stimuli on Wood Frogs For the Bullfrog treatments, we randomly in adjacent aquaria. We measured the mass (± selected one Bullfrog tadpole from a stock and 1.0 mg) of all tadpoles before adding them to all placed it in the cage. To mimic the same amount aquaria. The mean (±-1 SE) mass of all Wood of disturbance that the Bullfrog cages Frog tadpoles added to the aquaria was create, 35.40 ± empty Bullfrog cages were suspended in all 0.51 mg and there was no difference in mass control aquaria. For all treatments, 20 randomly between populations ( = 0.39; 1 8 P = 0.70). All selected Wood Frog tadpoles were added from Wood Frog tadpoles were of similar develop- either an allotopic or syntopic stock population. mental stage (Gosner stage 24-27; Gosner, 1960), The order in which trials occurred was ran- and all Bullfrog tadpoles used in this experi- domly determined. ment were within the same size distribution After a 12-h habituation (7.27 ± 2.05 g; Kolmogorov-Smirnov period, we quantified test; P - tadpole activity and microhabitat use. 0.20). To reduce bias, only one of us (LJW) quantified tadpole On 5 April, we terminated the experiment activity, using a method of scan sampling (from and measured Wood Frog tadpole growth and Altmann, 1974) by cautiously approaching each survival. To quantify growth, we measured the aquarium and counting the number of Wood mass (± 1.0 mg) of each Wood Frog tadpole and Frog tadpoles actively moving during a 30-60- calculated the mean for each aquarium. We then sec period. We divided this number by the subtracted the mean initial mass from the mean number of total tadpoles present to provide an final mass to determine Wood Frog growth estimate of tadpole activity. So as not to disturb within each aquarium. Bullfrog tadpole growth the leaf-litter substrate and any tadpoles that was calculated in a similar manner. We quan- might be using it, we quantified refuge use by tified survival in each aquarium as the pro- counting the number of tadpoles present in the portion of Wood Frog tadpoles that were alive side of the aquarium that lacked the leaf-litter to the total number initially stocked (N = 20). refuge. Subtracting the number observed in this Experiment 2: Wood Frog Activity and Refuge side from the number of tadpoles present Use.-We tested for chemically and visually provided the number of tadpoles located on mediated avoidance of Bullfrogs by Wood Frog the side containing the leaf-litter refuge. We tadpoles through activity and use of microhab- divided this number by the total number of itat refugia. For this experiment, we used a 2 X tadpoles present to provide an estimate of 2 factorial design using 38-liter glass aquaria, refuge use. We assumed that tadpoles on the different from those used in the previous side of the aquarium containing the leaf-litter experiment. We partitioned each aquarium into were using the refuge, regardless of the tad- equal lengthwise sections by attaching a 1-cm pole's position in the water column. For each high aluminum screen to the bottom of the replicate, we recorded activity and refuge use aquarium with silicone sealant. We then placed three times, each measurement separated by 1- 2 g (2-3 layers) of leaf litter (primarily oak, 2 h, and we calculated the mean of the three Quercus spp.) on one side of each aquarium. The observations as the metric of tadpole activity leaf litter served as refugia, and the aluminum and refuge use. After the final measurement screening served as a partition between the two was recorded for each replicate, aquaria were microhabitats (with refugia and without). Ad- drained and tadpoles were placed in separate ditionally, the 1-cm high screen partitioning containers. Tadpoles were never used in more was low enough to allow tadpoles to swim than one treatment. We terminated all freely experi- between both sides. ments on 6 April, after five replicates To determine had been the effects of Bullfrog chemical completed for each treatment. and visual cues on Wood Frog activity and Statistical Analyses.-We tested for the effects refuge use, we conducted trials once per day, of population source, Bullfrog presence, and beginning on 24 March 2005. Prior to each trial their interaction on the growth and survival of we added 20 liters of aged tap water to all Wood Frogs using a multivariate analysis of aquaria. Bullfrog cages, made of perforated variance (MANOVA), followed by univariate clear 20-cm tall plastic cups, were submerged analyses of variance (ANOVA). Spatial blocks 12 cm beneath the water surface such that the were not significant and were pooled with the opening of the cup was above the water surface, error term to increase the power of the test. We preventing Bullfrog tadpoles from escaping. We performed a multivariate analysis of variance suspended one Bullfrog cage (using monofila- (MANOVA) to test for the effects of population ment) perpendicular to the 1-cm high screen source, Bullfrog presence, and their interaction partitioning. Bullfrog tadpoles placed into these on activity and refuge use of Wood Frogs, cages were visible to Wood Frog tadpoles and followed by univariate analyses of variance RESPONSES OF WOOD FROG TADPOLES 27

TABLE 1. (A) MANOVA results for Experiment 1, which tested for the effects of Wood Frog (Rana sylvatica) population source (allotopic/syntopic), presence of Bullfrog (Rana catesbeiana) tadpoles, and their interaction on Wood Frog growth and survival. Degrees of freedom equal 2,15 in all cases. (B) ANOVA results for Wood Frog growth and survival. The F-statistic is reported with the associated P-value in parentheses. Degrees of freedom equal 1,16 in all cases.

(A) MANOVA

Factor Wilks ?, F P Population 0.38 12.17 < 0.001 Bullfrog 0.20 30.90 < 0.001 Population X Bullfrog 0.42 10.29 0.002 (B) ANOVA Response Population Bullfrog Population X Bullfrog Growth 17.26 (< 0.001) 41.19 (< 0.001) 20.12 (< 0.001) Survival 5.04 (0.04) 15.04 (0.001) 0.38 (0.55)

(ANOVA). If the univariate analyses revealed similarly affected the survival of tadpoles from a significant interaction, we followed this both Wood Frog populations (i.e., no popula- analysis with Tukey-Kramer multiple compari- tion-by-Bullfrog interaction, Table 1B; Fig. 1A). in survival son tests. Preliminary analyses revealed that Overall, there was a difference the response variables conformed to all assump- between the two Wood Frog populations tions of parametric statistics; thus, no transfor- (percent survival: allotopic, 88.5 ± 2.7%; synto- mations were necessary. All analyses were pic, 94.0 + 1.8%; Table 1B). In the presence of performed using SAS 9.1 (SAS Institute, Cary, Bullfrogs, survival of allotopic and syntopic respectively NC) using a significance level of o = 0.05. larvae declined by 11.7% and 8.2%, (Fig. 1A). For all treatments, Bullfrog survival was 100%. There was a population-by-Bullfrog RESULTS interaction on Wood Frog tadpole growth Tadpole Growth and Survival.-Wood Frog (Table 1B). Only the growth of allotopic Wood tadpole growth and survival were influenced Frog tadpoles was reduced in the presence of an by population source and the presence of an overwintered Bullfrog tadpole (Tukey-Kramer overwintered Bullfrog tadpole (Table 1). The Test; P < 0.001). In the presence of the Bullfrog presence of an overwintered Bullfrog tadpole tadpole, growth of allotopic Wood Frog tad-

30 B 25

20

Alh°oji-Tadok

5 10 °'°1 *1 I-. F_1

U • Absent Present Absent Present Bullfrog Presence

FIG. 1. Survival (A) and Growth (B) of Wood Frog (Rana sylvatica) tadpoles from syntopic or allotopic populations in response to the presence of a Bullfrog (Rana catesbeiana) tadpole. Data are represented as means - 1 standard error. 28 L. J. WALSTON AND S. J. MULLIN

TABLE 2. (A) MANOVA results for Experiment 2, which tested for the effects of Wood Frog (Rana sylvatica) population source (allotopic/syntopic), presence of Bullfrog (Rana catesbeiana) tadpoles, and their interaction on Wood Frog activity and refuge use. Degrees of freedom equal 2,15 in all cases. (B) ANOVA results for Wood Frog activity and refuge use. The F-statistic is reported with the associated P-value in parentheses. Degrees of freedom equal 1,16 in all cases.

(A) MANOVA Factor Wilks X F P Population 0.42 10.52 0.001 Bullfrog 0.19 31.30 < 0.001 Population × Bullfrog 0.34 14.25 < 0.001

(B) ANOVA Response Population Bullfrog Population X Bullfrog Activity 4.21 (0.06) 34.53 (< 0.001) 9.94 (0.006) Refuge Use 19.68 (< 0.001) 38.18 (< 0.001) 22.91 (< 0.001)

poles declined by 61.9%, whereas the growth of presence of Bullfrog tadpole visual and chemi- syntopic Wood Frog tadpoles declined by 13.2% cal cues (Tukey-Kramer Test; P < 0.001). In the (Fig. 1B). The mean growth of all Bullfrog presence of Bullfrogs, allotopic Wood Frog tadpoles was 17.6 ± 0.32 mg/day and did not tadpoles increased their use of leaf-litter refugia differ between allotopic and syntopic Wood by 43.1%, whereas syntopic Wood Frog tad- Frog populations (t = 0.41; P = 0.687). poles exhibited a 5.4% increase in refuge use Tadpole Activity and Refuge Use.-Wood Frog (Fig. 2B). tadpole activity and refuge use were affected by a population-by-Bullfrog interaction (Table 2). Only allotopic Wood Frog tadpoles reduced DIscUSSION their activity in the presence of a Bullfrog To our knowledge, this study is the first to (Tukey-Kramer Test; P < 0.001). In response to compare the population-level responses of Bullfrog chemical and visual cues, allotopic a sympatric anuran species to native over- Wood Frogs reduced their activity by 57.5%, wintered Bullfrog tadpoles. For the most part, whereas syntopic Wood Frogs reduced their we observed asymetrical effects of overwintered activity by 18.8%. Only allotopic Wood Frog Bullfrog tadpoles on Wood Frog tadpoles from tadpoles altered their microhabitat use in the allotopic and syntopic populations. Although

451 75 A 4C 70

35 65 AIIotopic Tadpoles..-"

"• 30 ) 60

-- °-oO.-'°° . 25

20 C.- [-- 20 50 - Stpic; Tadpoles 15 45

In An Absent Present Absent Present Bullfrog Presence Fic. 2. Activity (A) and refuge use (B) of Wood Frog (Rana sylvatica) tadpoles from syntopic or allotopic populations in response to the presence of Bullfrog (Rana catesbeiana) tadpole visual and chemical cues. Data are represented as means ± 1 standard error. RESPONSES OF WOOD FROG TADPOLES 29 both Wood Frog populations exhibited similar (Werner and Anholt, 1996), and researchers survival rates, only the growth and behavior have observed declines in larval growth of other of allotopic Wood Frog tadpoles was affected amphibians resulting from depleted food re- by the presence of a Bullfrog tadpole. The sources attributed to the presence of Bullfrog experiments in this study examined two differ- tadpoles (Lawler et al., 1999; Adams, 2000; ent paradigms of species interaction. In Exper- Boone et al., 2004). Therefore, resource de- iment 1, changes in Wood Frog growth and pletion resulting from interspecific competition survival in response to the physical presence might have resulted in decreased larval growth of Bullfrog tadpoles might be the result of of allotopic Wood Frogs. This effect might also exploitative or interference interspecific compe- be a result of the antipredator behaviors, as tition or predation. In Experiment 2, however, larval growth is often associated with activity we observed changes in Wood Frog activity and refuge use (Petranka and Hayes, 1998; and refuge use in response to chemical and Relyea, 2002, 2004). Although these behavioral visual cues from caged Bullfrog tadpoles. These responses decrease the likelihood of being responses are the result of interference me- detected by predators (Werner and Anholt, chanisms only. 1996), this benefit often comes at a cost of Overall, Wood Frog tadpole survival declined slower growth (Relyea, 2002, 2004). by 9.9% when an overwintered Bullfrog tadpole Organisms exhibiting phenotypic plasticity in was present. Although Bullfrog tadpoles are variable environments are often at a selective capable of consuming congeneric tadpoles advantage compared to organisms that do not (Ehrlich, 1979; Kiesecker and Blaustein, 1997), exhibit plastic responses (Van Buskirk and we did not directly quantify predation in this Relyea, 1998; Relyea, 2002, 2004). For instance, study. Overwintered Bullfrog tadpoles often Kiesecker and Blaustein (1997) reported that, in reduce the survival of other larval anurans response to nonnative overwintered Bullfrog through exploitative competition (Kupferberg, tadpoles, only syntopic Red-Legged Frogs (Rana 1997; Adams, 2000; Boone et al., 2004), and the aurora)exhibited behavioral plasticity in activity relatively large size of overwintered Bullfrog and refuge use. As a result, syntopic Red- tadpoles suggests that interference competition Legged Frogs experienced higher survival rates might also occur (Wilbur, 1984). In response to in the presence of Bullfrog tadpoles than overwintered Bullfrog chemical and visual cues, allotopic Red-Legged Frogs (which did not the decrease in activity and increase in refuge exhibit behavioral plasticity). Our results are use exhibited only by allotopic Wood Frog interesting in that we discovered that only tadpoles are characteristic of predator-induced allotopic Wood Frog tadpoles exhibited behav- responses (Van Buskirk and Relyea, 1998; ioral plasticity in the presence of overwintered Relyea, 2002, 2004). Although antipredator Bullfrog tadpole chemical- and visual cues. responses were exhibited only by allotopic Thus, we were surprised to find that the Wood Frogs, competition is the most plausible performance of allotopic Wood Frog tadpoles mechanism for our observations of Wood Frog did not improve as a result of the expression of growth and survival because survival rates of these behaviors. In fact, allotopic Wood Frog both Wood Frog populations to the presence of tadpoles suffered from slower growth in the overwintered Bullfrog tadpoles were similar. presence of overwintered Bullfrog tadpoles. We cannot rule out, however, the likelihood that These observations contrast previous studies predation occurred during this study. that have found that, when in the presence of Only allotopic Wood Frog tadpoles grew a competitor or predator, larval anurans that slower when in the presence of an overwintered exhibiting phenotypic plasticity experience Bullfrog tadpole. In a similar study using greater fitness (Kiesecker and Blaustein, 1997; outdoor mesocosms, Boone et al. (2004) found Van Buskirk and Relyea, 1998). that other allotopic larval amphibians (Spotted Our results indicate that the syntopic Wood Salamanders, Ambystoma maculatum and South- Frog tadpoles in our study do not perceive ern Leopard Frogs, Rana sphenocephala) grew overwintered Bullfrog tadpoles as a predation more slowly when in the presence of sympatric threat. Consequently, syntopic Wood Frog tad- overwintered Bullfrog tadpoles. Amphibian poles might use food resources more efficiently larval growth carries important population- than allotopic Wood Frog tadpoles. Experience level implications, as larger size at metamor- is the most plausible explanation for the phosis confers greater adult fitness in terms of performance of Wood Frog tadpoles. Related survival and fecundity (Semlitsch, 1985; Berven, studies have shown that the performance of 1990; but see Boone, 2005). Two mechanisms organisms experienced to a competitor or may be responsible for the reduced growth of predator is greater than the performance of allotopic Wood Frog tadpoles in our study. those with no prior experience (Chivers and Bullfrog tadpoles are superior competitors Smith, 1994; Kiesecker and Blaustein, 1997; Van 30 L. J. WALSTON AND S. J. MULLIN

Buskirk and Relyea, 1998; Gomez-Mestre and EHRLICH, D. 1979. Predation by bullfrog tadpoles (Rana Tejedo, 2002). Therefore, prolonged exposure to catesbeiana) on eggs and newly hatched larvae of Bullfrog tadpoles may condition sympatric the planes Leopard Frog (Rana blairi). Bulletin of Wood Frogs and allow them to recognize the Maryland Herpetological Society 15:25-26. Bullfrog tadpoles as less of a potential compe- GOMEZ-MESTRE, I., AND M. TEJEDO. 2002. Geographic tition or predation threat. Our results suggest variation in asymmetric competition: a case study with that there is a genetic two larval anuran species. Ecology 83: basis for the development 2102-2111. of this strategy because we observed the GOSNER, N. 1960. A simplified table for staging anuran differential population responses of Wood embryos and larvae with notes on identification. Frogs to overwintered Bullfrog tadpoles with- Herpetologica 16:183-190. out any conditioning of Wood Frog tadpoles to HECNAR, S. J., AND R. T. M'CLOSKEY. 1997. Changes in Bullfrog tadpoles. the composition of a ranid frog community Although the distributions of native Bullfrogs following bullfrog extinction. American Midland and Wood Frogs are usually allotopic, fishless Naturalist 137:145-150. aquatic habitats that fail to dry between years KIESECKER, J. M., AND A. R. BLAUSTEIN. 1997. Population may permit Bullfrogs to exploit these habitats differences in responses of Red-Legged Frogs where they may (Rana aurora) to introduced Bullfrogs. Ecology have adverse effects on 78:1752-1760. allotopic amphibian populations. Evolutionary KRUSE, K. C., AND M. G. FRANCIS. 1977. A predation experience might play an important role in the deterrent in larvae of the Bullfrog, Rana catesbeiana. adaptation of strategies that promote coexis- Transactions of the American Fisheries Society tence with Bullfrog tadpoles. Therefore, in areas 106:248-252. where Bullfrogs have been introduced, native KUPFERBERG, S. 1997. Bullfrog (Rana cateseiana) invasion larval amphibians might perceive overwintered of a California river: the role of larval competition. Bullfrogs differently than amphibians that have Ecology 78:1736-1751. evolved with Bullfrogs. LAWLER, S. P., D. DRffz, T. STRANGE, AND M. HOLYOAK. 1999. Effects of introduced mosquitofish and bullfrogs Acknowledgments.-This on the threatened California Red-Legged study was conducted Frog. Conservation Biology 13:613-622. in accordance with Institutional Animal Care PATON, P. W. C., AND W. B. CROUCH. 2002. Using the and Use Committee guidelines (protocol 04- phenology of pond-breeding amphibians to de- 008). We thank D. Mott and the Illinois De- velop conservation strategies. Conservation Bi- partment of Natural Resources for permission ology 16:194-204. to collect egg masses (IDNR Scientific Collection PETRANKA, J., AND L. HAYES. 1998. Chemically mediated Permit NH04-0946). We are grateful to E. avoidance of a predatory odonate (Anax junius) by Bollinger, K. Kruse, M. Walston, and two American Toad (Bufo americanus) and Wood Frog anonymous reviewers for their constructive (Rana sylvatica) tadpoles. Behavioral Ecology and Sociobiology 42:263-271. comments on previous drafts of this manu- PHILLIPS, C. A., BRANDON, script. R. A. AND E. 0. MOLL. 1999. Field guide to amphibians and reptiles of Illinois. Illinois Natural History Survey Manual 8, Champaign. RELYEA, R. A. 2002. Competitor-induced LITERATURE CITED plasticity in tadpoles: consequences, cues, and connections to ADAMS, M. J. 2000. Pond permanence and the effects of predator-induced plasticity. Ecological Mono- exotic vertebrates on anurans. Ecological Applica- graphs 72:523-540. tions 10:559-568. -. 2004. Fine-tuned phenotypes: tadpole plastic- ALTMANN, J. 1974. Observational studies of behavior: ity under 16 combinations of predators and sampling methods. Behaviour 49:227-267. competitors. Ecology 85:172-179. BERVEN, K. A. 1990. Factors affecting population SEMLITSCH, R. D. 1985. Reproductive strategy of fluctuations in larval and adult stages of the Wood a facultatively paedomorphic salamander, Ambys- Frog (Rana sylvatica). Ecology 71:1599-1608. toma talpoideum. Oecologia 65:305-313. BOONE, M. D. 2005. Juvenile frogs compensate for • 1988. Allotopic distribution of two salaman- small metamorph size with terrestrial growth: ders: effects of fish predation and competitive overcoming the effects of larval density and interactions. Copeia 1988:290-298. insecticide exposure. Journal of Herpetology VAN BUSKIRK, J., AND R. A. RELYEA. 1998. Selection for 39:416-423. phenotypic plasticity in Rana sylvatica tadpoles. BOONE, M. D., E. E. LITrLE, AND R. D. SEMLrnSCH. 2004. Biological Journal of the Linnean Society 65: Overwintered bullfrog tadpoles negatively affect 301-328. salamanders and anurans in native amphibian WERNER, E. E. 1991. Nonlethal effects of a predator on communities. Copeia 2004:683-690. competitive interactions between two anuran CHIVERS, D. P., AND R. J. F. SmITH. 1994. The role of larvae. Ecology 72:1709-1720. experience and chemical alarm signaling in WERNER, E. E., AND B. R. ANHOLT. 1996. Predator- predator recognition by Fathead Minnows, Pime- induced behavioral indirect effects: consequences phales promelas. Journal of Fish Biology 44:273- to competitive interactions in anuran larvae. 285. Ecology 77:157-169. RESPONSES OF WOOD FROG TADPOLES 31

and commu- WERNER, E. E., AND M. A. MCPEEK. 1994. Direct and in- WILBUR, H. M. 1984. Complex life cycles direct effects of predators on two anuran species nity organization in amphibians. In P. W. Gaud along an environmental gradient. Ecology Price, C. N. Slobodchikoff, and W. S. 75:1368-1382. (eds.), A New Ecology: Novel Approaches to Wiley, New WERNER, E. E., G. A. WELLBORN, AND M. A. MCPEEK. Interactive Systems, pp. 195-224. 1995. Diet composition in postmetamorphic Bull- York. frogs and Green Frogs: implications for interspe- cific predation and competition. Journal of Herpe- 2006. tology 29:600-607. Accepted: 12 September COPYRIGHT INFORMATION

TITLE: Population Responses of Wood Frog (Rana sylvatica) Tadpoles to Overwint SOURCE: Journal of Herpetology 41 no1 Mr 2007 PAGE(S): 24-31

The magazine publisher is the copyright holder of this article and it is reproduced with permission. Further reproduction of this article in violation of the copyright is prohibited. To contact the publisher: http://www.ukans.edu/~ssar/