Species richness, species incidence and turnover of amphibians in Northwestern Ontario : assessing the role of habitat characteristics

Abstract

There has been recent global concern over the decline of some amphibian populations. The loss of amphibian species is of concern because they play a crucial role in ecosystem structure and are indicators of ecosystem health. Amphibians within the boreal forest, especially in Northern Ontario, have not been studied as extensively as in other parts of the world. The lack of knowledge concerning amphibians within the boreal forest is troubling because the boreal forest contains half of the world’s wetlands and is facing increasing pressure from human activities such as forest harvesting. Therefore by investigating the patterns and distribution of amphibian species richness, species incidence and turnover and the effect habitat has on each of these, we can infer the status of a species, determine how communities and species’ populations are structured and have a better understanding of how to manage and protect them. My goals were to investigate the patterns of amphibian species richness, turnover, and incidence over a 4-year period and compare these communities between northern and southern Ontario; to assess the role local habitat and landscape characteristics have on amphibian species richness and turnover; and to develop single-species habitat models for amphibian species of Northwestern Ontario. I surveyed pond sites around the Thunder Bay region of Northwestern Ontario from 1999 to 2002. Multiple day and night surveys were used to generate species lists at all study sites. I mapped out each pond along with the surrounding habitat characteristics and estimated local habitat variables. Landscape variables were collected using a GIS (Geographical Information System). I found that ten amphibian species made up the pond communities in Northwestern Ontario. There was higher immigration than extinction among the pond sites and species incidence differed over time. Species incidence was significantly different between northern and southern Ontario. These differences were related to where northern and southern Ontario were located within each species’ geographic range. Those species with high incidence were located near to the core of their range while those with a low incidence were near the periphery. Species richness was positively associated with distance to the closest stream, pH, area of agriculture and percentage of shrubs surrounding a pond site, and was negatively associated with conductivity. Turnover was positively associated with the proportion of substrate around the edge of a pond and negatively associated with bank slope. Thus richer amphibian communities occur at pond sites with high pH, a mosaic of complementary habitat surrounding the breeding site, gentle sloping banks and open areas which may promote juvenile recruitment. Species’ habitat models depended on each species’ natural history, and its distribution. As a result, each species was associated with different habitat variables. From this study, we can see that there are many factors to consider when trying to conserve an amphibian community or population. When conserving a single species, we need to take into account each habitat component on both a local and regional scale and consider each species habitat requirements. From a community perspective, we can select a mosaic of habitats that are complementary to all species. Another very important point to keep in mind is where species are within their geographic range. Depending on the where a species is located within its range can determine whether is it common or rare. Because species habitat requirements appear to vary so greatly among species, I recommend including individual species habitat models in amphibian conservation strategies and not limiting our efforts to habitat restoration/creation.