Regulations guiding land development around seasonal isolated wetlands disregard habitat requirements for breeding amphibians. Given the complex aquatic-terrestrial lifecycle of amphibians, this deficiency needs to be addressed at multiple scales, including the pond, migration corridor, upland habitat, watershed and regional levels. Amphibians are susceptibility to water quality, temperature, hydrology, and watershed impacts, and already suffer declines. Global warming is likely to exacerbate these pressures. Variation in hydroperiod within ponds overtime and varied hydrology across ponds within a landscape produce a stochastic system. Amphibians in these systems likely function as metapopulations, relying on juvenile dispersal and rescue effects to counter local extinction. Yet amphibians are a critical link in the food chain as nutrient vectors connecting aquatic and terrestrial ecosystems. Furthermore, the latitudinal distribution of pond clusters and the local responsiveness of organisms to hydrology and climate, positions vernal pools as useful monitors for global warming impacts. Traditionally, research has focused on one or a few breeding populations with limited long-term assessment or cross-pond analysis. Most studies have identified larval densities as a driver of survival and fecundity over time. I chose to study habitat quality across ponds in contrast to larval densities within ponds. Larval densities of the predatory salamander Ambystoma opacum were experimentally manipulated using field enclosures across eight ponds to test the impact of density versus pond habitat on the survival and growth of conspecifics and the prey species, Rana sylvatica. Ponds were selected based on presence of egg masses and larvae for comparability.
Results/Conclusions
Pond-scale factors had a far greater effect on survival and fecundity than manipulated predator densities. Pond effects were significant for survivorship and fecundity for both A. opacum and R. sylvatica when evaluated across ponds regardless of densities. The pond effects for A. opacum survival accounted for 63.7% of the variation and 50.3% of the variation for R. sylvatica, while the density effects accounted for 3.5% and 2.8% respectively. The results indicate that the variation in pond habitat within a cluster is significant even for ponds that appear, based on current rapid assessment practices, to be productive. The rapid assessment approach, which includes egg mass counts and larval diversity evaluation, may be lumping ponds with low survival with source ponds. Such ponds may actually be functioning as habitat sinks with low amphibian survival. Furthermore, findings based on individual habitat analysis may not scale up to the metascale conditions of a site.
