Experimental analysis of predation on the diel vertical migrations of a larval salamander

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Abstract
The effects of a predatory fish on diel vertical migrations of aquatic larvae of the salamander Ambystoma talpoideum were tested in artificial ponds. Associations between larval activity and water temperature and resource abundance were also examined. In the absence of fish, larval activity was associated with the onset of darkness and decreasing water temperature. Peak larval activity occurred at 2130, about 3.5 h after peak summer water temperatures. Resource abundance (zooplankton density) in the water column did not differ from day to night. Larvae were more active during the day in spring than in summer. The presence of a visually orienting fish predator restricted larval activity to the benthic layer. Our results suggest that the presence of a visually orienting predator can be a major factor affecting patterns of diel vertical migrations. Daily and seasonal changes in water temperatures may affect thermoregulatory behavior, thereby influencing diel vertical migration patterns.