Seasonal trends in aggression among sympatric larval salamanders: the roles of habitat-mediation and behavioural conservatism

Abstract

The behaviours of sympatric congeners are influenced by the competing forces of behavioural conservatism, or the retention of similar behaviour among closely related species, and species-specific environments that promote behavioural divergence. Species inhabiting ephemeral ponds represent an ideal system for examining the net effect of these opposing factors, as pond assemblages consist of closely related species exhibiting varying degrees of temporal partitioning, such that congeners experience widely differing pond conditions. We observed intraspecific larval aggression among the salamanders Ambystoma opacum , A. tigrinum and A. maculatum to quantify species differences in responses to temperature, prey availability, and predation risk and to determine if responses could be attributed to relatedness or temporal variation in habitat conditions. Despite their fundamental similarities, focal species displayed divergent responses to habitat variables in laboratory trials, and these patterns contributed to dissimilar ontogenetic trends in intraspecific agonistic behaviour in situ. Ontogenetic trends in aggression for spring-breeding species supported a priori predictions regarding the influences of temporal variation in predation and pond drying. Overall, species-specific influences of habitat conditions appeared to supersede behavioural similarities predicted by phylogenetic inertia, and our results also indicate the potential for variance in ecological function among species regarded as functionally equivalent.