523 Ecology, 82(2), 2001, pp. 523–540  2001 by the Ecological Society of America MORPHOLOGICAL AND BEHAVIORAL PLASTICITY OF LARVAL ANURANS IN RESPONSE TO DIFFERENT PREDATORS RICK A. RELYEA 1 Department of Biology, University of Michigan, Ann Arbor, Michigan 48109 USA Abstract. Many organisms can adjust to a changing environment by developing alter- native phenotypes that improve their fitness. Our understanding of phenotypic plasticity is largely based upon observations from single species responding to two different environ- ments and measuring a single plastic trait. In this study, I examine predator-induced phe- notypic plasticity in tadpoles by observing how six species of larval anurans respond to five different predator environments in 11 different traits (seven morphological traits, two behavioral traits, growth, and development). The results demonstrate that behavioral and morphological plasticity may be ubiquitous in larval anurans. The six prey species exhibited different responses to the same predator species, and each prey exhibited different responses to different predator species. This suggests that responses to a particular predator may not serve as general defense against all predators; rather, prey express predator-specific suites of responses. I also compared relative differences in plasticity among species and among traits. In contrast to earlier findings using only two predator environments, I found that different anurans possess similar degrees of plasticity for most of their traits when reared in a large number of environments. In addition, behavioral traits were always more plastic than morphological traits. Finally, I examined trait integration to address whether there were apparent trade-offs among traits and limits imposed by the abiotic environment. Trait integration, or the degree of correlated responses among traits across predator environments within a prey species, was very low. This further suggests that the suites of responses are predator specific and may be under independent directions of selection in different predator environments. Trait correlations across prey species indicated that there is an apparent trade-off between tail fin depth and body size. This relationship is supported by selection studies within prey species. Relating the responses to the pond permanence habitat gradient over which the amphibians exist, I found that species inhabiting more temporary ponds possess higher general activity levels, shallower tail fins, and larger bodies; these traits are known to result in more rapid growth. In a companion paper, I quantify the predation risk of the 30 predator– prey combinations and examine the relationships between prey response and predation risk. Key words: behavior; Bufo americanus; Hyla versicolor; morphology; phenotypic plasticity; Rana catesbeiana; Rana clamitans; Rana pipiens; Rana sylvatica; tadpoles. INTRODUCTION Organisms that experience environmental variability must either avoid it or adjust to it. Those organisms that adjust to environmental variability by producing environment-specific phenotypes are said to be phe- notypically plastic. The evolution and ecological con- sequences of adaptive plasticity have been receiving increased attention (Bradshaw 1965, Schlichting 1986, Sultan 1987, West-Eberhard 1989, Via et al. 1995) be- cause ecologists and evolutionary biologists are real- izing that phenotypic plasticity is not merely uninter- esting developmental noise. Rather, plastic responses are often adaptive responses of organisms in multiple environments. Further, they are often maintained by 1 Present address: Department of Biological Sciences, Uni- versity of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA. E-mail: relyea+@pitt.edu natural selection (Kingsolver 1995a, Dudley and Schmitt 1996, Van Buskirk and Relyea 1998) and have important implications to the structure of ecological communities (Turner and Mittlebach 1990, Werner and Anholt 1996, Schmitz et al. 1997). The current state of our knowledge concerning phe- notypic plasticity is that many species exhibit the phe- nomenon and it often appears to be adaptive. Plastic responses are induced by numerous environmental con- ditions, including abiotic factors such as flooding, tem- perature, light, and nutrients (Clausen et al. 1941, Hie- sey 1953, Cook and Johnson 1968, Scheiner and Good- night 1984) and biotic factors such as the presence of competitors (Marshall and Jain 1969, Werner and Hall 1976, Moran 1991, Pfennig 1992), herbivores (Mc- Naughton and Chapin 1985, Belsky 1986, Paige and Whitham 1987), and predators (Havel 1987, Harvell 1990, Bro ¨nmark and Miner 1992, Smith and Van Bus- kirk 1995). Likewise, there are numerous possible re- sponses to these environmental factors including