This dissertation explored a series of such tests in one fairly typical terrestrial vertebrate predator-prey system: eastern garter snakes and newly-metamorphosed American toads. The work presented herein represents a series of predictions from natural selection theory about the evolutionary influence of predation on observed traits of an organism. Endler (1986) described 10 general methods for studying natural selection in wild species. The first method, the correlation of traits with environmental factors, was that used in this study. The results of the various chapters showed that toads used a variety of behavioral strategies to lower predation risk imposed by garter snakes, the main environmental factor under consideration. These behaviors included substrate choice, differential postures and motions when snake predators are present, and color matching to substrates. In all cases, detailed predation trials generally gave support to the hypothesis that the observed behaviors were in response to predation, and that all these behaviors lowered the risk of predation. Such behaviors, observed in a wide variety of organisms, have been assumed to have evolved in the context of predation pressure, but there are extremely few actual tests in the literature that give support to this argument.