Evaluating a predator–prey interaction in the field: the interaction between beetle larvae (predator) and tadpoles (prey) M. J. Rubbo, R. S. Mirza à , L. K. Belden w , J. J. Falkenbach, S. I. Storrs z & J. M. Kiesecker ‰ Department of Biology, Pennsylvania State University, PA, USA Keywords dytiscid; wood frog; predation; field experiment; chemical cue. Correspondence Michael J. Rubbo. Current address: Department of Biology, 2125 Derring Hall, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060, USA. Tel: 540-231-2715. Email: rubbo@vt.edu Current addresses: à Department of Biology, Nipissing University, North Bay, ON, Canada. w Department of Biology, Virginia Tech, Blacksburg, VA, USA. z University of Missouri, Division of Biological Sciences, Columbia, MO, USA. ‰ The Nature Conservancy, Wyoming Field Office, Lander, WY, USA. Received 16 February 2005; accepted 3 October 2005 doi:10.1111/j.1469-7998.2006.00080.x Abstract The larval amphibian community of temporary pond ecosystems has served as a model for studies in community ecology, with a majority of this work being conducted in mesocosms. Recent research has suggested that mesocosms may overestimate ecological effects; therefore, experimental studies conducted under field conditions are required to gauge the results of mesocosm studies. To assess a species interaction under more natural conditions, we conducted a series of field experiments examining the predator–prey interaction between beetle larvae (Dytiscus sp.; predator) and larval wood frogs Rana sylvatica (prey) in central Pennsylvania, USA. Quantitative sampling of woodland ponds indicated that beetle larvae of the genus Dytiscus were the most common predator of tadpoles. In a field enclosure experiment, dytiscids were effective predators of tadpoles in the pond environment. Moreover, tadpoles avoided areas in a pond containing caged dytiscids, demonstrating that tadpoles recognize the chemical stimuli of predators in complex environments. The results of this study are consistent with data from prior laboratory and mesocosm studies and suggest that these venues can produce reliable interpretations of predator–prey dynamics in this community. Introduction The food web of temporary pond ecosystems has served as a model for studies in community ecology (Wilbur, 1997). Of the taxa that utilize this environment, larval amphibians have received the most attention in terms of ecological research (see Wilbur, 1997 and references therein). Specifically, the study of predator–prey dynamics in this food web has contributed significantly to our understand- ing of this interaction. In addition to direct mortality effects, predation influences communities of larval amphi- bians by altering patterns of distribution (Smith, 1983) and species composition (Morin, 1981). In response to predation, amphibians have developed a variety of defences (Lima & Dill, 1990), including distastefulness (e.g. Kats, Petranka & Sih, 1988), morphological defences (e.g. Relyea, 2002), decreased activity (e.g. Lawler, 1989) and the avoidance of specific habitats (e.g. Petranka & Hayes, 1998). However, despite the wide-ranging signifi- cance of this work, the field of amphibian community ecology has used a rather standardized approach to ecologi- cal questions. The majority of experiments utilizing larval amphibians have been conducted in the laboratory or in mesocosms (Skelly & Kiesecker, 2001). These mesocosms (i.e. cattle tanks) are generally believed to provide a reasonable ap- proximation of the natural environment and are favored because of their ability to allow researchers to use multi- factorial experiments with high levels of replication (Wilbur, 1989, 1997). However, recent evaluations of mesocosm studies in this system suggest that they may overestimate ecological effects (Skelly & Kiesecker, 2001; Skelly, 2002). Therefore, experimental studies conducted in natural ponds are necessary to quantify species interactions in more com- plex environments, thereby providing a means to gauge the effects of mesocosm or laboratory studies. To evaluate a species interaction in a temporary pond community in the field, we first conducted a survey of the predators of larval amphibians in temporary woodland ponds in central Pennsylvania, USA. This survey was Journal of Zoology 269 (2006) 1–5 c  2006 The Authors. Journal compilation c  2006 The Zoological Society of London 1 Journal of Zoology. Print ISSN 0952-8369