Interference Competition in Postmetamorphic Salamanders: Interspecific Differences in Aggression by Coexisting Species

Abstract

I examined whether interference competition occurred among the terrestrial juveniles of two pond—breeding salamanders, Ambystoma maculatum and A. talpoideum. In a laboratory experiment, I observed intra— and interspecific agonistic behavior between pairs of recently metamorphosed individuals by staging encounters between resident salamanders (i.e., possessors of a refugium) and (1) conspecific, (2) heterospecific, and (3) surrogate (control) intruders. Resident A. maculatum exhibited significantly more threat and submissive behavior to live intruders than to surrogates, with more agonistic behavior direct toward conspecifics than to heterospecifics. Intruders likewise exhibited significantly more threat and submissive behavior to conspecific residents than to heterospecific residents. In contrast, neither resident nor intruding A. talpoideum altered their behavior in response to differing types of opponents. These results indicate that interference competition may operate in the terrestrial environment. Further, the agonistic behavior of terrestrial Ambystoma is the antithesis of that of the larvae of these two species, which suggests an ontogenetic switch in behavior at metamorphosis. These data are the first indication of such a shift in competitive abilities in amphibians. This behavioral switch may sustain coexistence between these two species by counterbalancing the competitive advantage of one species in the aquatic stage with that of the other species in the terrestrial stage.