Interactions between Larval Salamanders: A Case of Competitive Equality

Abstract

We used a replicated field experiment to determine the relative intensity of intraspecific and interspecific competition between larvae of Siren intermedia and Notophthalmus viridescens. These two salamanders possess markedly different morphologies and life histories and belong to distantly related salamander families, but feed on similar prey. Each species was raised in artificial ponds, alone at either low density (3 larvae per pond, 1.95 m-2) or high density (6 larvae per pond, 3.90 m-2) or together in a 3:3 ratio for a combined density of 6 larvae per pond. These 5 treatments were each replicated 4 times in a total of 20 ponds. The experimental design allowed us to explicitly compare the relative intensities of intra- and interspecific competition under realistic conditions. Competition affected different components of fitness in each species. Both intraspecific and interspecific competition caused a decline in survival of Notophthalmus, but had no detectable effect on body size or length of larval period. Negative densitydependent mortality may regulate Notophthalmus populations in the larval stage of their complex life cycle. Intraspecific competition caused a decline in both the survival and growth of larval Siren, but interspecific competition caused only growth to decline. Decreased growth rates may increase the vulnerability of larval Siren to desiccation and to predation. We found no evidence to reject the null hypothesis that larvae of these two species are equal competitors at the densities we employed. Our results indicate that, despite dissimilarities in life history and morphology, and a distant phylogenetic relationship, larval Siren and larval Notophthalmus compete as equals. J.E. Fauth, W.J. Resetarits, Jr. and H.M. Wilbur, Dept of Zoology, Duke Univ., Durham, NC 27706, USA.