Energy Use, Life Histories, and the Evaluation of Potential Competition in Two Species of Garter Snake

Abstract

The energy flow in syntopic populations of the greater snakes Thamnophis radix and T. sirtalis in Ohio ranged from 74,676 to 144,041/kJ/ha/yr. Important factors affecting this quantity were the high densities of the snakes (114 to 212 snakes/ha), the high annual reproductive rate (approximately 15 to 19 young/female), and the high growth rates of the newborn snakes prior to their first hibernation period. This large intake of energy was channeled primarily into secondary productivity, with calculated tissue production/assimilation ratios (P/A) averaging 74% for new- born snakes prior to their first hibernation period and then dropping to a yearly average of 14% for the adults of both species. The factors that allow for high P/A values were the low metabolic rates, the circadian oscillations in metabolic rates, the winter period of low temperatures, voluntary hypothermia during the day, and generally low activity levels. The garter snakes' impact upon the food resources at the study site appeared to be minimal during the three years of this study. A 1 to 4 predator/prey biomass ratio was estimated to be sufficient for maintenance, growth, and reproduction. Since the calculated predator/prey ratios were much smaller than this value, interspecific exploitative competition for food resources is unlikely to be a major factor in the population dynamics of either species of garter snake at the site studied.