Studies of Interspecific Predation within an Amphibian Community

Abstract

Amphibian eggs and larvae were offered as food to adult Notophthalmus viridescens and to larval Ambystoma opacum, A. maculatum, and A. jeffersonianum. Maximum feeding rates in the laboratory were estimated for some predators. Relative palatability of small larval prey was determined through sequential choices. Prey palatability was relatively uniform for all predators: eggs and larvae of Hyla versicolor, Pseudacris triseriata, Rana pipiens and R. sylvatica, Ambystoma maculatum, A. jeffersonianum and A. opacum were readily eaten; R. clamitans and R. catesbeiana were frequently rejected; and Bufo americanus and N. viridescens (larvae) were intermediate in palatability. Limited tests with other predators (Sternotherus odoratus, Chrysemys picta and Lepomis gibbosus) confirmed these relative palatibilities. Field observations included intense predation on some prey and negative correlation between predator presence and prey abundances. Conditions at one pond varied between years: a species sometimes reproduced successfully one year and failed completely the next. In some cases field evidence is compatible with an interpretation of total failure due to predation. Synchronized breeding by palatible species may increase survival through predator satiation. Some protection from predators is also achieved by unpalatible eggs, tough outer jellies on egg clumps, and singly laid eggs. The field observations on predation and the laboratory data on palatability are compatible with theoretical analyses of predator behavior.