Evidence of Intraguild Predation in a Snake Assemblage: Bigger Seems Better

Abstract

Intraguild predation can play a significant role in structuring species composition with intraguild prey under both competitive and predatory pressure from intraguild predators. How intraguild prey are able to persist at sites with their predators is a complex issue with empirical evidence not always supporting theoretical models, indicating a need for more in situ research. A prominent grassland predator in the south central region of Pennsylvania, Coluber constrictor constrictor (Northern Black Racer), co-occurs with potential prey snakes including Lampropeltis triangulum (Eastern Milksnake) and Thamnophis sirtalis sirtalis (Eastern Gartersnake). Starting in 2008, this 7-year study examined how intraguild predation may differentially influence the body size and demographic traits of prey species in south-central Pennsylvania at sites with and without Northern Black Racers. The body size of adult Eastern Milksnakes was unaffected by the presence of racers. Eastern Milksnakes were more abundant, but with fewer juveniles, at racer-present sites. Adult female Eastern Gartersnakes were larger in body size, and adult males were less frequently encountered, in racer-present sites. These results indicate that intraguild predation in a snake community may affect the body size and demographic traits of prey species differentially, likely through predatory exclusion. However, the exact mechanisms behind our findings, and the resulting dynamics of snake diversity, are unclear and require further analyses.