EFFECTS OF INTRAGUILD INTERACTIONS ON FITNESS AND MICROHABITAT USE OFLARVAL AMBYSTOMA SALAMANDERS

Two sympatric salamander species, Ambrystoma jeffersonianum and A. mac ulatum, were evaluated to determine the relative effects of intraguild interactions, High larval densities increased mortality, and both spe cies negatively affected the survivorship of each other. However, inte rspecific interactions did not differ significantly from the effects o f intraspecific competition. Larval growth and survival were negativel y correlated with the duration of water in the pond, and both species had similar mortality rates during two years of contrasting environmen tal extremes. Both species exhibited similar microhabitat usage when a lone, When refugia were absent, both species suffered heavy mortality. Shifts in microhabitat use when refugia were present resulted in incr eased survivorship of larvae. Behaviors resulting in habitat partition ing and the use of refugia by larvae may be important components for t he coexistence of A. maculatum and A. jeffersonianum in breeding ponds . These results indicate that A. maculatum is a more behaviorally vari able species which is hypothesized to be a factor in the success of th is widespread and common species.