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The Relative Impacts of Native and Introduced Predatory Fish on a Temporary Wetland Tadpole Assemblage

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The Relative Impacts of Native and Introduced Predatory Fish on a Temporary Wetland Tadpole Assemblage 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
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