Spatial processes (e.g., dispersal, landscape structure) are increasingly recognized as important drivers of patterns of community structure, and may be particularly important to organisms with complex life cycles (CLC). Amphibians, for example, typically utilize aquatic habitats for larval development and terrestrial habitats for adult development, with anthropogenic factors altering the availability of both habitat types across a landscape. The availability of suitable terrestrial or aquatic habitat for amphibians could have varying impacts on the abundances of different species depending upon the demographic importance of different life stages (larvae vs. adult). We hypothesized that species that spend a greater proportion of their lives on land (e.g., long-lived adults) would be less influenced by the amount of aquatic breeding habitat available, and thus be more abundant per isolated pond than would shorter lived species. Shorter lived species spend a greater proportion of their time in the aquatic habitat, and would likely be more abundant in landscapes with higher proportions of aquatic habitat. Using a combination of call, visual, and egg mass surveys of focal ponds varying in proximity to aquatic habitat, we found support for this hypothesis.
Results/Conclusions
Long-lived species, including Ambystoma maculatum (spotted salamander) and Hyla versicolor-chrysoscelis complex (grey tree frog) were more abundant in isolated ponds and less abundant where ponds were numerous in a given area. Shorter lived species, including Acris crepitans (cricket frog) and Pseudacris crucifer (spring peeper), abundances per pond were not influenced by pond isolation. Additionally, preliminary evidence suggests an inverse relationship between the abundance of larval A. maculatum, which are aquatic predators, and the abundance of the larvae of several frog species. In all, these results emphasize the importance of considering demography and the relative significance of different life stages when examining the responses of species with CLC to spatial processes and the structure of metacommunities.
