Landscape Complementation and Metapopulation Effects on Leopard Frog Populations

For many species, not all required resources are contained in breeding habitat. Such species depend on landscape complementation, i.e., linking together different landscape elements through movement, to complete their life cycles. We suggest that the dichotomous habitat classification of many metapopulation analyses (habitat vs. nonhabitat) masks our ability to detect metapopulation effects for such species. We tested this using a species for which landscape complementation is obligate and metapopulation structure is likely: Rana pipiens, the northern leopard frog. We used breeding chorus survey data to index relative abundance of leopard frogs in 34 “core” ponds and conducted Poisson regression analysis to determine the effects on frog density of local pond habitat, availability of summer habitat (landscape complementation), and number of occupied ponds in the surrounding landscapes (metapopulation structure). All of these factors had statistically significant effects on frog density. However, when summer habitat was not included in the statistical model, the metapopulation structure was no longer significant; i.e., its effect was masked. Our results suggest that one must be cautious in applying the results of metapopulation analyses to species for which the habitat vs. nonhabitat categorization of the landscape is not appropriate. The potential for rescue and recolonization to maintain a regional population must be assessed within the constraints of the entire landscape.