Seasonal and Ontogenetic Variation in the Diet of the Mexican Garter Snake, Thamnophis eques, in Lake Tecocomulco, Hidalgo

Abstract

Stomach contents of Thamnophis eques at Lake Tecocomulco, Mexico, were recorded, and prey populations sampled. Results indicate significant differences in diet between large (>44.0 cm SVL) and small (<44.0 cm SVL) snakes. Large snakes fed mainly on aquatic vertebrates (fishes, frogs, and salamander larvae) and leeches, small snakes on earthworms and leeches. Lack of a correlation between snake size and size of prey (leech or earthworm) indicates that the ontogenetic change in diet is not just a result of predator growth progressively diminishing the availability and/or ability to handle small prey. There was also seasonal variation in prey which was associated with fluctuations in prey availability. Birth season seems associated with annelid abundance. Differences in local distribution of large and small snakes were found and may reflect differences in foraging patterns. Possible effects of allopatry on the diet of this population are discussed.