Behavioural responses to predators and predation risk in four species of larval anurans

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Tadpoles of four anuran species show interspecific behavioural differences that could explain differential predation on these species in artificial ponds. Replicated observations of tadpoles in aquaria revealed that the spring peeper, Hyla crucifer, is quiescent and benthic; Fowler's toad, Bufo woodhousei, is active and benthic; the grey treefrog, Hyla versicolor, is active and pelagic; and the Pine Barrens tree frog, Hyla andersonii, is intermediate in activity and microhabitat position. Species with high activity levels survived poorly in independent artificial pond predation studies, relative to less active species. Costs of low activity level may include poor competitive ability, and/or slow development with increased risk of death from pond drying. Comparisons of tadpole behaviour in aquaria with and without predators present demonstrate that all four species decrease activity with a salamander, the red-spotted newt, Notophthalmus viridescens, and a fish, the black-banded sunfish, Enneacanthus obesus. Hyla andersonii became more benthic with these predators. Hyla versicolor and H. andersonii decreased conspicuous activities in response to a dragonfly naiad, Pantala. Bufo woodhousei responded to E. obesus even though B. woodhousei tadpoles are unpalatable to fish. Inactive H. crucifer responded less to predators than other species but survived well with predators. Baseline prey activity levels (observed in the absence of predators) may be more important than shifts in activity levels in response to predators in determining differential predation.