Experimental Studies of Asymmetric Competition among Anurans

Abstract

Experimental manipulations of the densities of two larval anurans, Hyla crucifer and Rana sylvatica, show that they compete asymmetrically in artificial ponds. The competitive superiority of R. sylvatica was correlated with its larger body size, faster growth, greater per capita competitive impact on conspecifics, and greater reduction in the availability of a trophic resource, periphyton. Laboratory experiments where Hyla tadpoles were grown in water conditioned by different densities and species of tadpoles provided no evidence that the observed asymmetric competition involves interference via growth inhibitors. Instead, the asymmetric interspecific competition is consistent with different impacts of species on resource availability, and these differences are predictable from patterns of intraspecific competition. Previous studies of competition among larval anurans indicate a preponderance of asymmetric competitive outcomes, which are either associated with the allopatric distributions of competitors, or with conditions that reduce the impact of competition.