Oecologia (2003) 136:289–295 DOI 10.1007/s00442-003-1251-2

COMMUNITY ECOLOGY

Matthew J. Baber · Kimberly J. Babbitt The relative impacts of native and introduced predatory fish on a temporary wetland tadpole assemblage

Received: 18 October 2002 / Accepted: 7 March 2003 / Published online: 24 April 2003 Springer-Verlag 2003

Abstract Understanding the relative impacts of predators tor-prey encounter rates, and thus predation rate. In on prey may improve the ability to predict the effects of combination with a related field study, our results suggest predator composition changes on prey assemblages. We that native predatory fish play a stronger role than C. experimentally examined the relative impact of native and batrachus in influencing the spatial distribution and introduced predatory fish on a temporary wetland am- abundance of temporary wetland amphibians in the phibian assemblage to determine whether these predators landscape. exert distinct (unique or non-substitutable) or equivalent (similar) impacts on prey. Predatory fish included the Keywords Fish assemblages · Functional relationships · eastern mosquitofish (Gambusia holbrooki), golden top- Larval anurans · Predation · Temporary wetlands minnow (Fundulus chrysotus), flagfish (Jordanella flori- dae), and the introduced walking catfish (Clarias batrachus). The tadpole assemblage included four com- Introduction mon species known to co-occur in temporary wetlands in south-central Florida, USA: the oak toad (Bufo querci- Predators that occupy similar trophic positions may have cus), pinewoods treefrog (Hyla femoralis), squirrel distinct or equivalent effects on prey community dynam- treefrog (Hyla squirella), and eastern narrowmouth toad ics (Lawton and Brown 1993; Morin 1995; Kurzava and (Gastrophryne carolinensis). Tadpoles were exposed to Morin 1998). Predators that have distinct impacts on prey different predators in wading pools under conditions communities exert unique or non-substitutable roles on similar to those found in surrounding temporary wetlands communities, whereas predators that have equivalent (particularly in terms of substrate type, the degree of impacts affect prey communities in similar ways (Lawton habitat complexity, and temperature). Native predators and Brown 1993). This has important implications in were similar with respect to predation rate and prey community ecology because changes in the composition selectivity, suggesting similar energy requirements and of predators may not necessarily influence prey assem- foraging behavior. Conversely, native fish predators, blages if different predators exert similar impacts (Morin especially G. holbrooki, were distinct from the introduced 1995; Kurzava and Morin 1998). Understanding the C. batrachus. In contrast to expectations, C. batrachus relative impact of predators may therefore improve the were less voracious predators than native fish, particularly ability to predict prey response to changes in predator G. holbrooki. Moreover, survival of G. carolinensis and composition (Persson et al. 1991; Tonn et al. 1991). H. femoralis were higher in the presence of C. batrachus The relative impact of predators is likely to depend on than G. holbrooki. We suggest that C. batrachus was a the degree of similarity in autecological characteristics, less efficient predator than native fish because the including morphology, behavior, population biology, foraging behavior of this species resulted in low preda- trophic status, habitat use, and taxonomy (Harris 1995), and may be measured as a function of both predation rate M. J. Baber and prey selectivity (Kurzava and Morin 1998). Within Department of Biological Sciences, guilds, predation rate may be indicated by the similarity Florida International University, Miami, FL 33199, USA in body size of predators because consumption rates are M. J. Baber ()) · K. J. Babbitt expected to reflect size-dependent energy requirements Department of Natural Resources, within metabolically similar groups of organisms (Pacala University of New Hampshire, Durham, NH 03824, USA and Roughgarden 1982; Ebenman and Persson 1988). e-mail: [email protected] Prey selectivity also serves as an indicator and may be Tel.: +1-603-8624284 largely dependent on the similarity in foraging behavior Fax: +1-603-8621496 290 among predators, because this influences prey-specific 1989; Bradford et al. 1993; Fellers and Drost 1993). For encounter rates (Morin 1995; Kurzava and Morin 1998). example, G. affinis has been introduced to the western Predatory fish are known to have dramatic effects on United States and other regions where it has had amphibian populations and several studies have demon- devastating impacts on several native amphibians, in- strated direct negative effects of fish on amphibians (Sih cluding the red-legged frog (Rana aurora), pacific 1992; Gamradt and Kats 1996; Smith et al. 1999). treefrog (Hyla regilla), and the California newt (Taricha However, because the relative impact of these predators torosa) (Gamtradt and Kats 1996; Goodsell and Kats remains unclear, it is difficult to predict the effects of 1999; Lawler et al. 1999). Thus, from a conservation predatory fish composition on larval anuran prey com- standpoint, the impact of C. batrachus on temporary munities. A better understanding requires concordance wetland tadpole assemblages warrants special concern between patterns seen in the field and controlled exper- and will be discussed. iments. Therefore, to help explain observed patterns of larval amphibian distribution and abundance in temporary wetlands of south-central Florida (Babbitt and Tanner Materials and Methods 2000; Baber 2001), we experimentally investigated the relative impact of predatory fish on a temporary wetland Study site amphibian assemblage. Specifically, we determined We conducted our study at the MacArthur Agro-Ecology Research whether four predatory fish species had distinct or Center (MAERC), a 4,086-ha cattle ranch affiliated with Archbold equivalent impacts on a tadpole prey assemblage based Biological Station and located approximately 22 km southeast of on relative predation rates (predator voracity) and prey Lake Placid, Highlands County, in south-central Florida, USA selectivity. We generated predictions derived from sim- (27200N, 81200W). ilarities in species autecology and relative size to determine if these measures were suitable predictors with Experimental setup respect to the relative impact of predators. In south-central Florida, fish readily colonize tempo- The intent of the experimental design was to simulate natural rary wetlands due to the ubiquity of wetlands in the conditions in temporary wetlands to the extent possible. Experi- ments were conducted in 20 artificial ponds (1.94 m diameter x landscape, lack of topographic relief, and dispersal 46 cm deep wading pools). We used wading pools because smaller abilities of several fish species in the region (Hart and mesocosms (e.g., plastic containers) are known to more strongly Newman 1995; Baber et al. 2002); as many as 70% of influence a variety of ecological variables, including organism temporary wetlands in the region may contain fish (Baber behavior and predator-prey relationships (Peterson et al. 1999). The ponds were enclosed within a 10x25-m area electric fence to et al. 2002). Based on a survey of 24 temporary wetlands, exclude raccoons and other species that might damage the Baber et al. (unpublished manuscript) found that species experimental setup. Each wading pool was filled to 15 cm deep richness and abundances of most tadpoles in temporary (440 l) with well water 72 h prior to running the experiment. Each wetlands declined significantly after colonization by fish. pool received a 1-l inoculum of algae and microinvertebrates that consisted of mixed plankton collections from several temporary Moreover, subsequent palatability trials in the lab indi- wetlands at MAERC. To provide habitat structure, we added 30 kg cated that predatory fish readily consumed most tempo- of sand substrate (approximately 3 cm deep) collected from a dry rary wetland anurans found in the region (Baber 2001). temporary wetland at MAERC and 5 kg of Hydrochloa carolinensis The predatory fish most common in these wetlands, and collected from local wetlands and ditches. H. carolinensis is therefore used in this study, were three native species, the common aquatic plant found in temporary wetlands at MAERC and provides structure throughout the water column. To remove aquatic eastern mosquitofish (Gambusia holbrooki), goldentop predatory invertebrates (e.g., odonates), we dried the H. carolinen- minnow (Fundulus chrysotus), and flagfish (Jordanella sis for 24 h before adding it to wading pools. Previous attempts to floridae), and the introduced walking catfish (Clarias run the experiment were abandoned because we failed to remove all batrachus). G. holbrooki is the most abundant and invertebrate predators from vegetation. Lids of fiberglass window screening attached to square wooden frames excluded breeding frequently occurring fish species in temporary wetlands adult amphibians and colonizing insects from ponds. of south-central Florida, with densities averaging 0.55/m2 (Baber et al. 2002). The native fish predators are similar with respect to both body size and foraging behavior. That Predatory fish is, they are diurnal, visual, predators that forage through- Fish were collected from local ditches at MAERC 1 week prior to out the water column. Conversely, C. batrachus, which is running the experiment, and were separated by species into native to Southeast Asia, is a benthic, nocturnal, tactile vegetated wading pools and fed Tetra Min fish flakes daily. forager and is larger than the native predators. Forty-eight hours before the experiment we collected fish from We hypothesized that similarities in size and foraging wading pools, took length measurements, and placed four similar sized individuals of each species (16 total) in separate plastic behavior among native fish lead to similarities in containers without food. Predator sizes differed among species predation rate and prey selectivity, whereas differences (F3,15=5.2, P=0.011). Tukey’s tests indicated that there was no in size and foraging behavior between native predators significant interspecific difference in the length among native and the introduced C. batrachus lead to differences in predatory fish used; however, C. batrachus were significantly larger than all native predatory fish; G. holbrooki (P<0.001), F. predation rate and prey selectivity. Moreover, introduced chrysotus (P=0.012), and J. floridae (P<0.001) (Table 1). The sizes predatory fish have been linked to the decline and local of predators used were within the range of individuals captured extinction of several amphibian populations (Bradford 291 during a related study conducted in temporary wetlands at MAERC Data analyses (Baber et al., unpublished manuscript). We performed a GLM procedure, blocked, one-way multiple analysis of variance (MANOVA) using predator identity as a factor, Prey species (tadpoles) and anuran species survival as the dependent variables. MANOVA provided a conservative test of the null hypothesis that predator The tadpole assemblage included 4 common species that co-occur treatments had no effect on the structure of the anuran assemblage in temporary wetlands at MAERC: B. quercicus, H. femoralis, H. by simultaneously considering multiple correlated responses. squirella, and G. carolinensis. We collected several adult male and Univariate ANOVAs were then used to analyze the individual females of each species of H. femoralis, H. squirella, and B. response variables of each larval anuran species, to test whether quercicus during breeding choruses at night (after heavy rains). We there were differences among predators in their selectivity of each placed females and males of each species in separate 64-l aquaria prey species. We also conducted a one-way ANOVA using the total with 20 l aged well water and sparse vegetation to induce breeding. number of surviving anurans in each replicate as the dependent Aquaria were fitted with tight screen lids to prevent frogs escaping. variable to determine if predators differed in their rate of tadpole All females laid clutches by the following morning. Eggs of G. consumption (predation rate). Finally, we performed an ANOVA carolinensis were collected the day after breeding events because using tadpole survivorship as the dependent variable and tadpole this species lays floating egg masses that are easy to collect. species as the factor to test whether tadpoles differed in their Tadpoles were reared to stage 25 (Gosner 1960) and were similar in vulnerability (survivorship) to predatory fish. We used Tukey’s size at the start of the experiment (Table 1). HSD post hoc pairwise comparisons for all analyses to determine if (1) tadpole assemblage structure, (2) predator selectivity, and (3) predation rate differed between predators, and to determine if prey Experimental design vulnerability differed between tadpole species. Tadpole survival was angularly transformed to meet the We conducted a randomized complete block experiment to assumptions of analysis of variance. We performed a Box’s M examine the effect of five predator treatments, which included test for the assumption of homoscedasticity, and a Levene’s test for four predatory fish species, and one control (no predators) on a the assumption of equal variances among dependent variables. tadpole prey assemblage consisting of four species. Ponds were Wilks’ l was used to determine statistical significance in MANO- placed in four spatial blocks to account for unknown physical VA (Morrison 1976). Controls were not included in analyses gradients at the site. All treatments were randomly assigned to because 99% of tadpoles survived in the control pools, and thus positions within the blocks. Prey assemblages consisted of 50 stage mortality in treatment pools could be attributed to predation. All 25 (Gosner 1960) individuals of each species (200 tadpoles total) statistical analyses were performed using SPSS 11.0 (SPSS 2002). and treatments with predators consisted of one individual. Tadpole prey assemblages were placed in wading pools 3 days after setup and a single predatory fish was placed in each wading pool (except control pools) 24 h after prey assemblages were added. The Results experiment began at 0800 hours on 16 July 2000 and was terminated at 0800 hours on 17 July 2000. Based on previous Larval anuran assemblage structure differed with respect attempts, running the experiment for only 24 h ensured that many, to predator treatment (Table 2, Fig. 1). Specifically, but not all, tadpoles were likely to be consumed. Moreover, running such a short experiment negated the impacts of competition and predators differed significantly in their selectivity of G. developing intra- and inter-specific size differences, which influ- carolinensis and H. femoralis (Table 2. Fig. 1). All native ence susceptibility to predators. Water temperature during the fish consumed significantly more G. carolinensis tadpoles experiment ranged from 33 to 27C. The densities of all species than the introduced C. batrachus (P<0.005), but there used were within the range of densities that occur in natural ponds. G. All experimental protocols were approved by the Animal Care and were no differences among native fish in the number of Use committee of Florida International University (protocol 99– carolinensis consumed (Fig. 1). G. holbrooki consumed 04). more H. femoralis tadpoles than C. batrachus (P=0.033) but there were no differences in the consumption of H. femoralis tadpoles between any other predators (Fig. 1). There were no differences among predators in their

Table 1 Mean length of predators (standard length) and prey (snout–vent) used in the experiment. Prey and predator lengths are Table 2 Results of a multivariate analysis of variance (MANOVA) means (mm) € standard deviation (SD) to determine if anuran assemblage structure differs among predator treatments and if individual anuran survival differs among predator Experimental organisms Mean lengths treatments. of experimental individuals Source of variation df Wilks’ l FP Predators MANOVA (dependent variables: anuran species survival) G. holbrooki (mosquitofish) 44€2 Predatory fish species 3, 15 0.105 2.404 0.037* J. floridae (flagfish) 42€3 F. chrysotus (goldentop minnow) 46€4 Source of variation df Type III ss FP a C. batrachus (walking catfish) 57€3 ANOVA (between subjects) Prey H. femoralis 3, 15 3,481 3.975 0.038* H. femoralis (pinewoods treefrog) 3.0€0.2 H. squirella 3, 15 333 1.861 0.195 H. squirella (squirrel treefrog) 2.9€0.3 G. carolinensis 3, 15 2081 20.767 0.000*** B. quercicus (oak toad) 2.6€0.2 B. quercicus 3, 15 71.4 0.152 0.926 G. carolinensis (eastern narrowmouth toad) 2.7€0.2 * significant at alpha <0.05 a C. batrachus was significantly longer than other fish predators *** significant at alpha <0.0001 292 selectivity of B. quercicus or H. squirella. (Table 2, Fig. 1). Predation rate (total number of tadpoles consumed) differed among fish predators (F3,15=5.06, P=0.019). G. holbrooki consumed significantly more tadpoles than C. batrachus (Fig. 2A). Numerically, G. holbrooki also consumed more tadpoles than F. chrysotus and J. floridae, although this was not significant (Fig. 2A). Anuran species differed in their vulnerability to fish predation (F3,15=19.88, P<0.0001) (Fig. 2B). Specifically, B. quercicus was less vulnerable than H. squirella, H. femoralis, and G. carolinensis tadpoles (Fig. 2B).

Discussion

Relative impacts of predators Fig. 1 Differences in the number of tadpoles consumed (predation rate) by predatory fish species; n=50 tadpoles per species Lawton and Brown (1993) suggest that communities may contain species that play very similar roles. Although the number of studies examining predator relationships is small, the emerging pattern is that taxonomically similar predators with similar autecological characteristics can have equivalent impacts on prey species composition (e.g., Morin 1995; Kurzava and Morin 1998). Our results also point to this redundancy in the case of native predatory fish (G. holbrooki, F. chrysotus, and J. floridae) that colonize temporary wetlands in Florida. These predators appear to play very similar roles in the organization of larval anuran prey assemblages, both in terms of their predation rate and prey selectivity. Simi- larities in predation rate may be attributed to the comparable body sizes and close taxonomic relationship among these native predators, which may result in similar energetic requirements (Ebenman and Persson 1988; Harris 1995; Kurzava and Morin 1998). The observed similarities among native predators in prey selectivity may be attributed to foraging behavior, which in turn, influences prey encounter rates. That is, the native predatory fish are all diurnal, visual predators and forage throughout the water column. Our study demonstrates differences and similarities in the impact of these predators on a temporary wetland tadpole assemblage. However, to better understand the relative impact of predators in this system, it is also necessary to investigate the influence of predator or prey size (Travis et al. 1985; Babbitt and Tanner 1998), the presence of alternative prey (Blouin 1990), variations in abiotic characteristics e.g., habitat size (Pearman 1993), and the presence of multiple predators (Sih et al. 1998; Eklv and Werner 2000). Perhaps most importantly, a series of recent papers has demonstrated that multiple Fig. 2 A Differences in predation rate (proportion of tadpoles predators often have non-additive impacts on prey (e.g., consumed) among predators; n=200 tadpoles per fish treatment. B Eklv and Werner 2000). That is, the effects of multiple Differences in prey vulnerability (proportion of each tadpole predators cannot be predicted simply by summing the species consumed) to predatory fish species; n=50 tadpoles per species. Bar letters (a, b) represent significant differences in effects of single predator types (Sih et al. 1998). Two predator rate among predators (A) and prey vulnerability (B) main types of non-additive effects are risk reduction, which is caused by predator-predator interactions, and risk enhancement, which is caused by conflicting prey 293 responses to more than one predator (Sih et al. 1998). selection for deflection of invertebrate predator strikes Moreover, an important factor potentially influencing the away from the body when odonates are common preda- outcome of this experiment was the selection of water tors (Caldwell 1982). depth. This experiment was conducted in water depths of only 15 cm, which is in the shallow range of depths found in natural temporary wetland habitats in the region (Baber Conservation implications et al. 2002). In deeper aquatic habitats, predators and prey may forage in more defined regions of the water column. Many species of fish have been accidentally or deliber- For example, in deeper wetlands, J. floridae forage ately introduced into freshwater ecosystems throughout predominately in or near the substrate in deeper wetlands, the world. The impact of introduced predatory fish whereas F. chrysotus and G. holbrooki forage in the warrants concern given the general catastrophic impacts middle to the top of the water column (Jordan, personal that these predators have had on native tadpole assem- communication, Baber, personal observation). As such, blages in other regions, such as Australia (Richards and the vertical positioning of J. floridae may be more similar Bull 1990) and the western United States (e.g. Bradford et to C. batrachus in deeper aquatic environments. Other al. 1993; Gamradt and Kats 1996; Knapp and Matthews studies have documented the influence of vertical posi- 2000). Native prey species may lack the defensive tioning on prey encounter rates (Power 1984; Wang and adaptations necessary to coexist with introduced predators Appenzeller 1998; Saint et al 2000). For example, Saint et because prey are exposed to new selection pressures when al. (2000) found that the depth distribution of the white non-native predators are introduced (Lima and Dill 1990). sucker (Catostomus commersoni) was largely influenced For example, Gamradt and Kats (1996) suggest that by the abundance and type of zoobenthos and zooplank- California newts (Taricha torosa) of the Santa Monica ton. Mountains are not adapted to coexist with introduced mosquitofish (G. affinis). Our results indicate that C. batrachus may have a Relative impact of C. batrachus relatively small impact on the abundance and distribution of temporary wetland amphibians compared to G. As hypothesized, there were distinct differences between holbrooki, F. chrysotus, and J. floridae. C. batrachus the effects of the introduced C. batrachus and native consumed less tadpoles than the native fish used in this predators, particularly G. holbrooki. We expected that C. study (particularly G. holbrooki), although, C. batrachus batrachus would consume more tadpoles than native did readily consume temporary wetland tadpole species. species due to its larger size. The average size of walking Moreover, native predatory fish in this study are able to catfish fish used in this experiment was 5.7 cm, which is prey on larger (later stage) tadpoles by repeatedly biting close to the mean size found in south-central Florida the tail or visceral regions until prey are immobilized and temporary wetlands (9.1 cm, Baber 2001), and 1–2 cm can easily be consumed at all sizes up to metamorphosis larger than the average size of native predators. This (Baber 2001). Conversely, C. batrachus is gape-limited, species can grow to 22.5–30 cm, standard length and because this species rarely attains large sizes in (Courtenay et al.1974), though larger fish are more temporary wetland systems, it may not be an effective common in permanent water bodies (Baber, personal predator of larger sized temporary-wetland tadpoles. observation). In contrast to expectations, C. batrachus Baber (2001) found that averaged sized C. batrachus in consumed significantly less tadpoles than native predato- south-central Florida temporary wetlands did not con- ry fish. We attributed the general differences in predation sume large tadpoles (Gosner Stage 31, SVL range 10– rate between C. batrachus and G. holbrooki to differences 22 mm) of any species occurring in temporary wetlands. in foraging behavior. C. batrachus is a nocturnal, benthic, As such, the relative impact of C. batrachus may depend tactile forager that only ventures near the water surface to largely on the timing of wetland colonization. Specifical- gulp air. Conversely, G. holbrooki is a diurnal, visual ly, tadpole assemblages in wetlands colonized by C. predator that is morphologically adapted to forage at the batrachus late in the anuran breeding season (e.g., July/ water surface (Moyle and Cech 2000). Likewise, G. August) may suffer less drastic changes than tadpole carolinensis tadpoles also filter feed near the water assemblages in wetlands colonized earlier in the breeding surface. Moreover, this species is dorso-ventrally flat- season. tened with a dark dorsum and a light venter to minimize Native predatory fish used in this experiment colonize detection by predators foraging lower in the water a larger proportion of temporary wetlands and are column. Similar vertical positioning of G. holbrooki and generally more abundant than C. batrachus. Baber et al. G. carolinensis in the water column is likely to result in (2002) found no instances where wetlands at MAERC higher encounter rates than for C. batrachus and G. were colonized by C. batrachus but not native predatory carolinensis. Survival of H. femoralis was also signifi- fish and that the mean density of C. batrachus was only cantly higher in the presence of C. batrachus than G. 0.025 m2, which was much lower than the mean density holbrooki. H. femoralis may be more easily detected by of G. holbrooki (0.55 m2), J. floridae (0.108 m2), and the visual foragers (native predators) due the species red slightly lower than F. chrysotus (0.029 m2). tail coloration. Tail coloration may result from natural 294 Relative vulnerability of larval anurans to predatory fish Baber MJ, Childers DL, Babbitt KJ, Anderson DL (2002) Controls on the distribution and abundance of fish in temporary wetlands. Can J Fish Aquat Sci 59:441–450 Hyla squirella was readily consumed by all predators and Blouin MS (1990) Evolution of palatability differences between the species relative vulnerability did not differ among closely related treefrogs. J Herpetol 24:309–311 predator treatments. H. squirella is highly active and Bradford DF (1989) Allotopic distribution of native frogs and forages throughout the water column. It is likely that introduced fishes in high Sierra Nevada lakes of California: Implications of the negative effect of fish introductions. Copeia encounter rates among predators were similar despite 1989:775–778 foraging behavior differences among predators. Similarly, Bradford DF, Tabatabai F, Graber DM (1993) Isolation of the relative vulnerability of B. quercicus tadpoles did not remaining populations of the native frog, Rana mucosa,by differ among predator treatments. The non-significant introduced fishes in Sequoia and Kings Canyon National Parks, impact of all predatory fish on B. quercicus tadpoles California. Cons Biol 7:882–888 Caldwell JP (1982) Disruptive selection: a tail color polymorphism reflects the species general unpalatability to predatory in Acris tadpoles in response to differential predation. Can J fish, as indicated from laboratory experiments (Baber Zool 60:2818–2827 2001). Tadpole unpalatability / toxicity has been suggest- Courtenay WR Jr, Sahlman HF, Miley II WW, Herrema DJ (1974) ed as one of the primary factors that decreases the risk of Exotic fishes in fresh and brackish waters of Florida. Biol Cons 6:292–302 predation by fishes (Formanowicz and Brodie 1982). Ebenman BL, Persson L (1988) Size structured populations. Furthermore, B. quercicus is known to breed in shallow Springer, Berlin Heidelberg New York margins of permanent aquatic habitats, indicating that this Ecklv P, Werner EE (2000) Multiple predator effects on size- species is able to breed in permanent wetlands containing dependent behavior and mortality of two species of anuran larvae. Oikos 88:250–258 predatory fish (Baber et al., unpublished manuscript). Fellers GM, Drost CA (1993) Disappearance of the cascades frog In conclusion, there were no discernable differences in (Rana cascade) at the southern end of its range, California, the impact of native predatory fish on amphibian assem- USA. Biol Cons 65:177–181 blages under the conditions of the experiment. However, Formanowicz DR Jr, Brodie ED Jr (1982) Relative palatabilities of native predators (particularly G. holbrooki) were distinct members of a larval amphibian community. Copeia 1982:91–97 Gamradt SC, Kats LB (1996) Effect of introduced crayfish and from C. batrachus with respect to their impact on prey mosquitofish on California newts. Cons Biol 9:1155–1162 species. This was attributed to foraging behavior charac- Goodsell JA, Kats LB (1999) Effect of introduced mosquitofish on teristics that lowered encounter rates with prey. C. Pacific treefrogs and the role of alternative prey. Cons Biol batrachus appears to have a relatively minor impact on 13:921–924 Gosner KL (1960) A simplified table for staging anuran embryos the distribution and abundance of temporary wetland and larvae with notes on identification. Herpetologica 16:183– amphibians compared to its native counterparts. From a 190 conservation standpoint, our results indicate that G. Harris PM (1995) Are autoecologically similar species also holbrooki, which is the most frequently occurring and functionally similar? A test in pond communities. Ecology 76:544–552 abundant fish in temporary wetlands, is also the most Hart R, Newman JR (1995) The importance of isolated wetlands to voracious predator of larval anurans. fish and wildlife in Florida: Florida Game and Freshwater Fish Commission, Nongame Wildlife Program. Project Report. NG Acknowledgments This work was part of M.J. Baber’s doctoral 88–102 dissertation at Florida International University (FIU). The authors Knapp RA, Matthews KR (2000) Non-native fish introductions and wish to thank Bradley Bennett, Daniel Childers, Maureen Donnelly, the decline of the mountain yellow-legged frog from within Joel Heinen, Sharon Lawler and Joel Trexler, the Wetland protected areas. Cons Biol 14:428–438 Ecosystem and Ecology Lab at FIU, and two anonymous reviewers Kurzava LM, Morin PJ (1998) Tests of functional equivalence: for comments on earlier drafts of this manuscript. We thank Sara complementary roles of salamanders and fish in community Tompkins for help in the field and editorial assistance. Thanks also organization. Ecology 79:477–489 to Patrick Bohlen, Gene Lollis and Mike McMillian at the Lawler SP, Dritz D, Strange T, Holyoak M (1999) Effects of MacArthur Agro-Ecology Research Center (MAERC) for housing introduced mosquitofish and bullfrogs on the threatened and logistical support. This material is based upon work supported California red-legged frog. Cons Biol 13:613–622 by the National Science Foundation under Grant No. 9910514. Lawton JH, Brown VK (1993) Redundancy in ecosystems. In: Funding was also provided by the FIU Tropical Biology Program. Schultze ED, Mooney HA (eds) Biodiversity and ecosystem This paper is contribution number 58 to the FIU Tropical Biology function. Springer, Berlin Heidelberg New York, pp 255–270 contribution series and contribution number 64 to MAERC. 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