Influence of forest cover on tadpole vital rates in two tropical treefrogs

The vital rates of anuran tadpoles inhabiting ephemeral pools may be influenced by the amount of forest cover. To better understand this topic in a tropical system, I compared the vital rates of tadpoles of the treefrogs Agalychnis callidryas and Dendropsophus ebraccata in pools with different extents of forest cover in the Osa Peninsula, Costa Rica. I used a randomized block design, with artificial pools in pasture, edge, and forest, to measure the growth, development, and survival of tadpoles within each habitat. I assessed abiotic conditions in each forest-cover treatment by quantifying the light environment, water temperature, and dissolved oxygen content. Pasture-light environments were open with few obstructions, whereas edge- and forest-light environments were closed, with a complex vegetation structure obstructing solar radiation. Water temperature was strongly correlated with the amount of light contacting the ground in each forest-cover treatment. Tadpoles of both species grew larger in pasture than in forest. Survival of A. callidryas was lower in pasture (42%) than in edge and forest ( 90%), whereas survival of D. ebraccata was high in all forest-cover treatments ( 87%). These results suggest that the use of pasture pools for breeding represents a trade-off for some species, such that tadpoles have reduced survival but gain fitness benefits of faster growth compared to tadpoles in edge and forest pools. Water temperature may be the primary factor responsible for interspecific and intraspecific variation in tadpole performance across tropical forest-cover gradients.