Conserving amphibians in the face of land development: integrating field experiments as a planning tool

Abstract

Regulations designed to guide development practices inadequately reflect ecological understanding and fall short of preserving viable habitats. Environmental consultants use rapid assessments and monitoring on individual ponds to rank pond habitat quality, relying on coarse proxies, including vegetative indicators, soil characteristics, hydroperiod, and breeding evidence in obligate species. Planners incorporate these rankings to inform the layout of neighborhoods, roadways, infrastructure and housing. However, important drivers of amphibian survival and fecundity--including metapopulation dynamics, habitat connectivity, watershed health, terrestrial density dependence, and environmental gradients--are often poorly measured and regulated. Given that development proceeds regardless, what options exists improve land development practices?\n\nIntegrating experimentation into the planning process can inform land development and improve amphibian conservation. Working as part of the design team we employed an adaptive approach called designed experiment to inform development practices. We manipulated Ambystoma opacum larvae within enclosures to test the effects of inter-pond conditions (versus intra-pond density dependence) on the survival and fecundity of conspecifics, Rana sylvatica and Ambystoma maculatum. While the A. maculatum populations were decimated with only 1.5 % survival. For A. opacum and R. sylvatica results indicate habitat variation between ponds accounted for 63.7% and 50.3% of the variance in survival rates of larvae, respectively, and are not predicted by the presence and abundance of egg masses, while density effects accounted for 3.5% and 2.8% of the variation in survival. The results suggest that ponds ranked as high value based on egg mass counts may actually function as habitat sinks. This study illustrates the potential value of assessment approaches that emphasize habitat quality across pond clusters to guide mitigation, conservation, regulations, and to establish sites and funding for ecological research.