Thermal niche overlap in garter snakes (Thamnophis) on Vancouver Island

Abstract

Although the three species of garter snakes (Thamnophis) on Vancouver Island have generally different diets, they overlap in food habits to some extent. Consequently, additional separation along other niche dimensions is expected. In this study, differences in thermal niches were examined in the field. Two of the three species had similar body temperatures and both were significantly different from the third. The linear relationship between body and substrate temperatures was not statistically different among species, however, allowing body temperatures to be directly related to habitat and (or) activity period differences. Extremes of habitat selection, rather than differences in diel activity periods, probably account for most of the interspecific variation in body temperature. On the other hand, the three species do coexist in some habitats and the observed differences in mean body temperature are small. Body temperature also varied slightly according to sex and reproductive condition, gravid females generally being warmer than other snakes.