Density-Dependent Effects on Microhabitat Selection and Activity of Two Species of Larval Ambystoma Salamanders

To be able to distinguish unnatural amphibian declines from natural population fluctuations we need a better understanding of the mechanisms that affect amphibian community structure. Larval pond-breeding salamanders exhibit density-dependent effects on population parameters, but little is known of the effect of density on behaviors that mediate interactions. Two species, Amby1toma tigrinum (tiger salamander) and A. laterale (blue-spotted salamander), were evaluated in laboratory aquaria for intraspecific and interspecific interactions that affect microhabitat selection and activity. Microhabitat selection was studied by partitioning containers into microhabitats that either contained or lacked refuges, and movement was recorded over a hexagonal grid to determine activity during periods of observation. Both species altered microhabitat preferences and activity levels when they shared tanks with con- or heterospecifics. These density-dependent behavioral changes may indicate that fluctuations in population densities result in behavioral responses that may contribute to coexistence