Interspecific Aggression and Habitat Partitioning in Garter Snakes

Michael Edgehouse,Leigh C Latta,Edmund D Brodie,Mark Briffa

doi:10.1371/journal.pone.0086208

Michael Edgehouse, Leigh C Latta + Show 2 more

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https://doi.org/10.1371/journal.pone.0086208

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Abstract

Defense of a limited resource, such as space or food, has recently been discovered in snakes and has been widely documented in lizards. Garter snakes (Thamnophis spp.) are historically considered generalist predators such that food is not a limiting resource. However, in this study we show that the common garter snake (Thamnophis sirtalis) and the aquatic garter snake (Thamnophis atratus) show a strong preference for amphibians as their primary food source at the Santa Lucia Preserve (SLP), Monterey County, California. This food preference forces these snake species at SLP to exploit aquatic habitats. Our principle goal was to investigate the aggressive behavior of T. sirtalis and the potential that this aggression displaces T. atratus from its preferred habitat. We found that when individuals from either species are alone, a 100% preference for aquatic or near aquatic habitat is observed. In contrast, when these species are together, T. sirtalis occupy the aquatic habitat and T. atratus occupy an area far removed from water. Thamnophis sirtalis often physically force T. atratus from the aquatic habitat through repeated biting and other displays of aggression.

Highlights

Aggressive interactions within or between species that arise from competition for a limited resource are an important ecological mechanism structuring communities [1]
Each of the two prey types recovered from the snake species were analyzed separately. Habitat preference Both T. sirtalis and T. atratus occupied the aquatic portion of the test chamber when in the chamber alone (Fig. 2)
There was a significant difference in the spatial occupation of T. atratus and T. sirtalis (x2 = 10.33; p = 0.006) when in the test chamber together

Summary

Introduction

Aggressive interactions within or between species that arise from competition for a limited resource are an important ecological mechanism structuring communities [1]. Diet data are informative for other aspects of an organism such as growth, resource utilization, and potential competition between closely related species [20]. Another mechanism that shapes snake communities is pre-emptive competition. Sympatric Thamnophis spp. may have increased competition based on similarities in body size, diet, and general habits [15] Often this pre-emptive competition for space or food can lead to segregation or local extinction [4], [5], [13], [16], [17]

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