The Role of Temperature on the Behavioral and Ecological Associations of Sympatric Water Snakes

Abstract

Several aspects of the thermal ecology of five sympatric water snake species were explored quantitatively. Body temperatures of captured snakes are compared to ambient temperatures at the capture site and evaluated in terms of daily and seasonal activity patterns. Three species of water snakes, Nerodia rhombifera, N. cyclopion and N. fasciata, account for 86% of this snake community. Each species has a relatively distinctive usage of the arboreal and aquatic habitats and each has a characteristic activity pattern. A fourth congener, Nerodia erythrogaster is uniformly nocturnal (77% of census data) and aquatic (88%). The fifth species, Regina grahamii was seasonally asynchronous with Nerodia spp. and was the most arboreal member of the community (84%). N. cyclopion was the only species active in all months of the year. During the cool months (Nov.-March) it was primarily a diurnal perching snake (70-90% of census), and during the summer N. cyclopion was nocturnal and aquatic (82100%). The trend toward becoming nocturnally active in the summer was characteristic of all Nerodia spp. N. rhombifera, however, became much more arboreal during the summer months. N. fasciata was uniform in habitat usage for most of the year (60% aquatic) but did not become nocturnal until June a month or two after congeners. Observed year to year variations in mean body temperature of each species reflected climatic fluctuations over the four years of study. The data indicate that only one species, N. cyclopion, makes seasonal adjustments of daily activity periods and arboreal tendencies that maintain fairly uniform body temperatures even through the cool months. When the thermal axis of the fundamental niche is considered in light of available data on the food, time, and space axes, the influence of temperature on this ectothermic community appears to be significant. In summary, we maintain that the underlying mechanism for the asynchronous daily and seasonal patterns of habitat use is specific differences in thermal niches. The two most ecologically similar species do not appear to be in competition for thermal niche space, but rather partition the thermal resource to reduce interference competition.