Feeding habits and diet overlap of three species of garter snakes (Thamnophis) on Vancouver Island

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Abstract
Closely related, sympatrtc species of organisms often show resource partitioning. In this study, diet partitioning is examined in three sympalric species of garter snakes (Thamnophis) on Vancouver Island. Thamnophis sirtalis feeds mainly on amphibians and earthworms, Thamnophis ordinoides on earthworms and slugs, and Thamnophis elegans on slugs, fish, and small mammals. Thamnophis sirtalis and T. ordinoides, which are mote widely distributed on Vancouver Island than is T. elegans, have not been shown to modify their diets in the absence of T. elegans, but it is suggested that this lack of niche shift may be due to variations in prey availability. Neither innate differences in food preferences among the species nor interspecific competition for food have been shown to explain the observed differences in diet among the three species. Certain types of prey appear more likely than others to turn up in large numbers in stomach samples and it is suggested that this may be due to variations in ease of capture and (or) abundance. Possible explanations of the observed diets are discussed.

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