Amphibian species richness and distribution in northwestern Ontario : the importance of hydroperiod

Abstract

The preservation of biodiversity has become a fundamental ecological goal in recent years. If we wish to prevent or reverse worldwide amphibian declines it is imperative that we understand patterns of abundance and distribution and the causal factors. Virtually every aspect of the amphibian life cycle depends on water, and therefore wetland hydroperiod plays an important part in amphibian species richness and the distribution of individual species, particulary since two major perceived stresses on amphibians are desiccation stress and predation by fish. I used repeated surveys (breeding call and visual surveys) to investigate amphibian species richness and incidence of 93 wetlands (31 each of permanent, semi-permanent and temporary) in Northwestern Ontario in relation to hydroperiod and a number of other wetland characteristics. Amphibian species richness and incidence differed among hydroperiod categories. Species richness peaked in semi-permanent wetlands and was higher in permanent than temporary wetlands, despite presence of predatory fish. Some species, even those considered ‘temporary’ occurred equally among all wetland types while others were more likely to be found in one or two hydroperiod categories. Species that I found to be rare in the study region may be affected negatively by the amount of roads on the landscape. Salamanders appeared very susceptible to alterations of the landscape. Percent forest cover does not appear to be a factor in determining patterns of species richness or distribution, as it is in other areas. There may be a minimum 'threshold' of forest cover, below which amphibian species decline rapidly, that has not yet been reached in my study region. Permanent bodies of water offer suitable amphibian habitat, despite potential predation by fish. Amphibian species richness was equal among lakes with or without predatory fish present. The availability of refuge habitat significantly increased amphibian species richness in lakes. I suggest that lakes should not be overlooked as amphibian habitat and as conservation areas. Lakes are suitable habitat for wetland-dependent organisms like amphibians, and being permanent, are available for use even during times of drought when other less permanent wetlands are not.