What Limits Tailed Frog Tadpole Density and Distribution in Western Montana Streams?

We explored the possible limitation of temperature and other habitat features on tailed frog tadpole populations in northwestern Montana. We sampled densities and habitat features in two regions with different climatic regimes and in streams with and without tadpoles, expecting larger density and size in the warmer region. We also expected habitat conditons to be more optimal (higher gradient, swifter velocity, and less canopy cover) in streams with tadpoles. Temperature appeared to positively influence tadpole size, though both tadpole size and density were strongly correlated with other variables. Density was correlated with gradient, canopy, depth, and elevation, whereas length was correlated with width and density. Contrary to expectations, we found lower densities in the warmer region. Streams in the warmer region were lower in elevation and gradient than the colder region streams. These lower gradient streams are optimal habitat for sculpin, which prey on tadpoles. The presence of sculpin in these warmer-region lower-gradient streams suggests predation could explain the lower densities. In comparing habitat features of streams with and without tadpoles, only gradient varied significantly, which also supports the idea of predation limiting densities