Effects of Cover and Predator Identity on Predation of Hyla squirella Tadpoles

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Habitat structural complexity can strongly affect biotic interactions. In particular, the intensity of predator-prey interactions can be mediated by habitat complexity because the effectiveness of predators often decreases in structurally complex habitats (Werner et al., 1983; Diehl, 1988; Babbitt and Jordan, 1996). Typically, increased habitat complexity reduces predation rates by providing refuges for prey or by decreasing predator efficiency (Crowder and Cooper, 1982; Savino and Stein, 1982; Werner et al., 1983). The role of habitat structure in mediating predatortadpole interactions is potentially important because predation is a significant source of mortality of anuran tadpoles (Calef, 1973; Heyer et al., 1975; Smith, 1983). Species breeding in permanent ponds display a wide array of anti-predator defenses for avoiding predation by fish (Formanowicz and Brodie, 1982; Kats et al., 1988; Lawler, 1989). In general, such defenses are lacking in species that breed in ephemeral ponds (Kats et al., 1988). In addition, activity rates of tadpoles in temporary ponds often are higher compared to species in permanent ponds (Woodward, 1983). Because many predators of tadpoles are gape-limited, rapid growth to a size refuge is an important mechanism for escaping predation (Crump, 1984; Travis et al., 1985; Richards and Bull, 1990; but see Crump and Vaira, 1991). For species breeding in ephemeral environments, rapid growth is also important for decreasing risk of desiccation (Wilbur, 1987; Newman, 1989). However, trade-offs exist between rapid growth and predator avoidance because actively foraging tadpoles are more likely to be detected by predators (Woodward, 1983; Werner and Anholt, 1993; Skelly, 1994). Although ephemeral ponds lack fish predators, these sites often contain aquatic insect predators that also are significant mortality agents (Smith, 1983; Wilbur and Fauth, 1990). Therefore, any mechanism that can reduce predator efficiency without decreasing foraging activity could enhance tadpole survival, particularly in ephemeral environments. Because structurally complex habitats can reduce predator foraging efficiency, complex environments may provide tadpoles with partial protection from predators, even when tadpoles are actively foraging. In this study we examine how habitat structure affects predation rates on squirrel treefrog (Hyla squirella) tadpoles. Hyla squirella is a common anuran in Florida, and is often numerically dominant in the ephemeral sites in which it breeds (Babbitt, unpubl. data). Hyla squirella tadpoles are active foragers even