Aggression by Non-Native Crayfish Deters Breeding in California Newts

Abstract

Adaptations used to defend against native predators may not be effective against introduced predators. For this reason perturbations caused by introduced species often affect the distribution and abundance of native prey organisms (Diamond & Case 1986). Predation is a strong selection pressure over time and results in antipredator adaptations in prey. Many adaptations are behavioral; these adaptations allow prey to exist in an environment where predation risk varies during ecological time (Lima & Dill 1990). The behavior of an organism reflects a complex of adaptations that have evolved in response to selection pressures from native predators (see Dill 1987; Lima & Dill 1990). When a nonnative organism is introduced, the interactions between the native and introduced species are often unpredictable. Introduced species can affect native organisms in a variety of ways. Resource exploitation, competition, and predation by nonnative species are well studied topics (see Diamond & Case 1986; Simberloff 1981). The current issues surrounding amphibian decline have prompted researchers to examine the effects of introduced predators on native amphibians (Hayes & Jennings 1986; Pechmann & Wilbur 1994). In most studies direct predation on larvae and/or eggs was found to be the primary detrimental effect on native amphibians (Cory 1963; Hayes & Jennings 1986; Bradford 1991; Bradford et al. 1993; Bronmark & Edenhamn 1994; Gamradt & Kats 1996). In southern California, California newts (Taricha torosa) have been declining and have recently been listed as a species of special concern (Jennings & Hayes 1994). In a previous study (Gamradt & Kats 1996), we observed an inverse relationship between the distribution of Cali-