Interspecific aggression in garter snakes

The aquatic garter snake at Sibley Volcanic Regional Preserve, Oakland, CA. 
Photo credit: Sarah Stierch.

Aggressive behavior is used in many vertebrate communities to gain control of resources,  snakes, however, have been thought the exception. Some snake species use male-to-male combat for access to females, but this is intraspecies behavior.  Food partitioning usually thought to shape community structure of snake communities. A new study by Edgehouse and colleagues used two species of garter snakes at the Santa Lucia Preserve in Monterey Co. California. Both the common garter snake,Thamnophis sirtalis, the aquatic garter snake, a T. atratus and western terrestrial garter snake T. elegans coexist with their abundant, toxic prey  the California newt, Taricha torosa. At the study site,  Thamnophis sirtalis and T. atratus are aquatic and demonstrate independently evolved resistance to tetrodotoxin (TTX), a potent neurotoxin, found in the skin of the newt.

Edgehouse et al.  show that the common garter snake (Thamnophis sirtalis) and the aquatic garter snake (Thamnophis atratus) show a strong preference for amphibians and forces these snakes to exploit aquatic habitats. They investigate the aggressive behavior of T. sirtalis and the potential that this aggression displaces T. atratus from its preferred habitat. When individuals from either species were alone, they showed a complete preference for aquatic or near aquatic habitats. In contrast, when these species are together, T. sirtalis occupy the aquatic habitat and T. atratus occupy an area far removed from the water. They found Thamnophis sirtalis often physically force T. atratus from the aquatic habitat through repeated biting and other displays of aggression.

The spatial partitioning documented by the authors is likely a direct result of food availability and aggressive defense of the prey resource. The most abundant amphibian prey found in the snakes at the study site were California newt and the pacific treefrog.

Edgehouse M, Latta LC IV, Brodie ED III, Brodie ED Jr (2014) Interspecific Aggression and Habitat Partitioning in Garter Snakes. PLoS ONE 9(1): e86208. doi:10.1371/journal.pone.0086208

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