Long-term distributional dynamics of a michigan amphibian assemblage

TLDR: The distributions of amphibian populations (1988-1992) were strongly related to two habitat characteristics: pond hydroperiod and forest canopy cover, and tendencies for ponds to experience population colonizations and extinctions also were associated with pond isolation.

Abstract: From 1988 to 1992 we surveyed the distribution of 14 amphibian species in a set of 37 ponds in southeastern Michigan, USA. Thirty-two of these ponds had been surveyed previously between 1967 and 1974. We found that the distributions of amphibian populations (1988-1992) were strongly related to two habitat characteristics: pond hydroperiod and forest canopy cover. Most species exhibited nonrandom distributions with respect to these pond characteristics. Between surveys, the distribution of each species changed, and most species experienced multiple population colonizations and extinctions. Turnover in the distribution of populations among ponds (estimated via Jaccard's similarity coefficient) averaged nearly 50% among species. The substantial number of species colonizations (40 cases) and extinc- tions (34 cases) between surveys resulted in little net change in number of breeding popu- lations for most species; just four species experienced net changes of more than two popu- lations. Historical information indicated that, for many ponds, hydroperiod and canopy cover changed between surveys. In several cases habitat changes associated with forest succession apparently had negative impacts on amphibian populations. In ponds that now dry each summer and are under closed canopies, two-thirds of the breeding populations present during 1967-1974 were extinct during the recent survey. No population colonizations occurred in these ponds between surveys, in marked contrast to other ponds, in most of which amphibian species richness either was maintained or increased. In addition, tendencies for ponds to experience population colonizations and extinctions also were associated with pond isolation. Our results highlight the volatile nature of amphibian distributions and point to forest suc- cession, via its effects on canopy and hydroperiod, as a potential force shaping the dynamics of amphibian populations.