Modeling critical breeding habitat and body size variation in the federally endangered spotted turtle (Clemmys guttata).

摘要

Spotted turtles (Clemmys guttata) are declining throughout their range in eastern North America due to habitat loss and fragmentation as well as collection for the pet trade, and are classified as endangered in Canada. Knowledge of a species' critical habitat requirements are vital for conservation and management purposes, particularly for endangered species. I conducted surveys for spotted turtles along the eastern coast of Georgian Bay, Ontario to identify new populations, study sexual size dimorphism, size differences among populations, to create predictive habitat models as well as to indentify potential breeding aggregation wetlands. I found a total of 43 new individuals in 4 previously unknown or unstudied populations. Known breeding aggregation wetlands were small, shallow, close to large water bodies, far from maintained roads, had low pH, total calcium and magnesium with relatively low dissolved oxygen and high dissolved organic carbon. I created models based on quantification of ecological variables to predict the presence/absence of spotted turtles in spring aggregation wetland sites along the eastern coast of Georgian Bay, Ontario and used these models to create a field-based guide for use by the Ontario Ministry of Natural Resources and other Species at Risk decision-making agencies. Models including water chemistry variables discriminated between sites that contained breeding aggregations of spotted turtles and sites that did not. Spotted turtles exhibit sexual size and shape dimorphism in several body size traits. Females were the larger sex in body size traits that increased their potential for reproductive output, supporting the fecundity advantage hypothesis in which selective pressures favor larger females. A mainland population was significantly larger than an island population in every body size trait measured. Because of the spotted turtle's long generation time, these differences are suspected to be caused by founder effects in the island population. The island population had a highly skewed sex ratio (1 male: 4.4 females) and was estimated to contain 31 adults at a density of 1.3 turtles/ha across the entire island, with 21.4 turtles/ha in a spring aggregation wetland. My study provides valuable life-history and demographic information on a federally endangered species in Canada and provides recommendations for future studies.