Relationship of road density and marsh condition to turtle assemblage characteristics in the Laurentian Great Lakes

Human-induced degradation of coastal wetlands often leads to altered trophic dynamics and species assemblages. Here we use data from 77 coastal marshes in three Laurentian Great Lakes collected between 2001 and 2007 to examine the relationship between human disturbance (road density and wetland quality) and characteristics of aquatic turtle assemblages, including species richness and abundances. Painted turtles (Chrysemys picta) were encountered disproportionately in degraded wetlands and the probability of occurrence decreased with improved site quality. Abundance of painted turtles peaked, however, at intermediate road density in surrounding 1- and 2-km buffers. Across all sites, species richness was highest and common snapping turtles (Chelydra serpentina) were most abundant in wetlands with intermediate water quality. The common musk turtle (Sternotherus odoratus) was absent from degraded wetlands in the lower lakes (Erie and Ontario) that fell within their historical range, but reached high abundances in marshes of Georgian Bay and the North Channel, a region with relatively low human disturbance. Analysis of sex ratios in painted turtles revealed a significant male bias in an area with high road density, while the sex ratio did not differ significantly from 1:1 in a less developed region, consistent with reports of high female mortality in urban areas.