Comparative Ecology of Thamnophis elegans, T. cyrtopsis, and T. rufipunctatus in New Mexico

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A field and laboratory investigation was pursued to determine what ecological differences, if any, exist among three species of garter snakes, Thamnophis elegans vagrans (Baird and Girard), T. cyrtopsis cyrtopsis (Kennicott), and T. rufipunctatus (Cope), allowing them to coexist. Of the 157 garter snakes captured, 83 were T. elegans, 45 were T. cyrtopsis, and 29 were T. rufipunctatus. From the field studies it was noted that there was a definite food preference; T. rufipunctatus fed only on fish, T. cyrtopsis on amphibians, and T. elegans on amphibians, fish, and worms. Some segregation of species was indicated as to habitat. Thamnophis rufipunctatus occurred in rocky areas near still water; T. elegans were found in vegetation of various types; and T. cyrtopsis lived in both well vege- tated and rocky areas. The preferred temperature range was lower for T. rufipunc- tatus than for T. elegans and T. cyrtopsis. Thamnophis rufipunctatus and some T. cyrtopsis used refugia in rocky areas, but few T. elegans were found in rocky situ- ations and probably sought shelter in areas of logs and vegetation. Thamnophis rufipunctatus spent much of their time in water, whereas T. elegans were the most terrestrial, and T. cyrtopsis were immediate in this respect. From the laboratory experiments it was determined that body density differed between T. cyrtopsis and T. elegans with the difference reflected in the method of swimming-T. cyrtopsis swam on the surface and T. elegans below it. This behavior may have been a result of the animals ability to retain or not retain air within its lung. The differences among the species studied indicate that although the three species live in the same geographical area they do indeed live in different ecological niches. Because of these differences that allow sympatry the three species-T. elegans, T. cyrtopsis, and T. rufipunctatus-coexist. INTRODUCTION. Three species of garter snake, western garter snake, Thamophis elegans vagrans (Baird and Girard), black-necked garter snake, T. cyrtopsis cyrtopsis (Kennicott), and narrow-headed garter snake, T. rufipunctatus (Cope), occur in the same area around Wall Lake, Catron County, New Mexico. During the summers of 1959-1962 a field and laboratory investigation was pursued to de- termine the specific ecological requirements of each species that allow them to coexist.