Interspecific aggression and habitat partitioning in garter snakes

Area of Science:

• Ecology
• Behavioral Ecology
• Herpetology

Background:

• Resource defense and territoriality are documented in lizards and some snakes.
• Garter snakes (Thamnophis spp.) are typically generalist predators, with food not usually a limiting factor.
• Previous research has not extensively explored resource competition or aggressive displacement among garter snake species.

Purpose of the Study:

• To investigate the aggressive interactions between the common garter snake (Thamnophis sirtalis) and the aquatic garter snake (Thamnophis atratus).
• To determine if T. sirtalis aggression displaces T. atratus from preferred aquatic habitats at the Santa Lucia Preserve (SLP).
• To understand the role of food preference in driving habitat selection and interspecific conflict.

Main Methods:

• Observational study at the Santa Lucia Preserve, Monterey County, California.
• Documenting habitat preference and use by T. sirtalis and T. atratus, both alone and together.
• Quantifying aggressive behaviors, including biting and physical displacement, by T. sirtalis towards T. atratus.

Main Results:

• Both T. sirtalis and T. atratus show a 100% preference for aquatic habitats when alone.
• When together, T. sirtalis exclusively occupies aquatic habitats, while T. atratus retreats to terrestrial areas.
• T. sirtalis actively and aggressively displaces T. atratus from aquatic environments through physical means.

Conclusions:

• Interspecific aggression in garter snakes can lead to significant habitat displacement.
• Resource limitation, specifically a preference for amphibians, drives competition and aggressive interactions between T. sirtalis and T. atratus.
• Aggressive behavior by T. sirtalis shapes the habitat use and niche partitioning of T. atratus in this ecosystem.