Spatial distribution and survival rate of waterfrog tadpoles in relation to biotic and abiotic factors: a field experiment

Predictions about population and community dynamics are usually based on la b experiments. Because the results are difficult to transfer to natural con ditions, the major purpose of this study was to test the effects of biotic and abiotic factors on tadpole populations in a natural environment. We sto cked six ponds, created the previous year, with known numbers of Rana escul enta and R. lessonae tadpoles and followed their development over several m onths. When compared among ponds, tadpole density correlated positively wit h the nitrate:phosphate ratio. This suggests that water chemistry may have affected survival, either directly or indirectly via productivity. Within p onds, both species showed a clear preference for the shallow zone. This beh avior probably reflects a preference for warm water close to the surface, r ather than avoidance of predators, because relative densities of odonates a lso increased from deep to shallow zones. This study is one of few that not only considers the distribution of the anuran tadpoles but the distributio n of their predators as well.