The estimation of survival rates and the assessment of factors influencing variation in survival are essential to understanding population dynamics. However, in amphibians that alternate between an aquatic larval stage and a dispersing terrestrial stage, such understanding is limited due to the difficulty of estimating survival under field conditions. In this study, we obtained precise estimates of daily survival rates of tadpoles under field conditions using capture-mark-recapture (CMR) methods and assessed their temporal and spatial variation. Specifically, we assessed the effect of temperature, intra-specific density, and the presence of introduced bullfrogs (Rana catesbeiana) on the survival rate of Pacific treefrog (Pseudacris regilla) tadpoles in southern vancouver Island, British Columbia, Canada. Daily survival rates of tadpoles were relatively constant within a season and were also similar between years. Survival rates in different ponds varied from 95.4 to 87.9 %·d−1. Among-pond differences in survival were best explained by the interaction of temperature and tadpole density. At low tadpole densities, survival increased with temperature, but at high densities, survival decreased with increasing temperature. It was not possible to detect the effect of introduced bullfrogs over the variation accounted for by differences in temperature and intra-specific density. As in terrestrial vertebrates, biotic and abiotic factors interacted strongly to determine survival rates in these tadpoles.
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Vol. 13 • No. 3