Predator Avoidance and Diel Patterns of Microhabitat Use by Larval Tiger Salamanders

Diel patterns of microhabitat use of larval tiger salamanders, Ambystoma tigrinum nebulosum, were studied in three permanent ponds in the White Mountains of east—central Arizona during the summers of 1982—1984. Variation in the importance of risk of predation, distribution of food resources, and temperature gradients caused patterns of microhabitat use to vary among populations. Microhabitat use of larvae at Big Meadows Tanks (BMT) 1 and 2 was strongly influenced by risk of predation from adult predaceous diving beetles, Dytiscus dauricus. Adult beetles were active at night and moved almost exclusively in vegetated littoral areas, while larval salamanders occupied vegetated shallows during the day and moved to open, deeper areas at night. Field and laboratory experiments with larvae in the presence and absence of beetles demonstrated that larvae were responsive to changes in predation risk and altered their patterns of microhabitat use to minimize encounter rates with beetles. Dytiscus was essentially absent from the third study pond, Lower Cottonwood Tank (LCT), and in contrast to the Big Meadows populations, salamanders at LCT used littoral areas both day and night. Food densities and temperatures were monitored in different microhabitats of study ponds to determine microhabitats likely to be used by salamanders. Densities of zooplankton and macroinvertebrate prey were higher in vegetated shallows than in open, deeper areas at all times of day, throughout the summer sampling periods at all ponds. Larvae at Big Meadows used vegetated shallows by day, apparently because food densities and temperatures were higher than in pelagic areas, but avoided vegetated shallows at night when risk of beetle predation increased. Comparisons of dry masses of flushed stomach contents showed that feeding chronologies varied among populations and years. Salamanders balance conflicting demands of resource acquisition and risk of predation by altering their daily pattern of microhabitat use in response to periodic change in predation risk.