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Date of Award


Document Type

Thesis: EWU Only

Degree Name

Master of Science (MS) in Biology




"There are multiple examples of Natricine snakes not only changing their diet to utilize an invasive fish, but deriving a fitness benefit from the new and often abundant prey item as well. To investigate a potentially similar scenario arising on the Turnbull National Wildlife Refuge (Spokane Co., Wash.), we analyzed the morphometrics, fitness, feeding behavior, and diet of wandering garter snakes from three study sites: invaded, historically invaded (recent but not present invasion) and uninvaded. We used mass and snout-vent length (SVL) measurements to infer fitness using a scaled mass index, recorded garter snakes feeding on brook stickleback in the lab and analyzed the presence/absence of prey DNA in their feces. While snakes from the stickleback-present site had shorter SVL and lower mass, there was not a significant difference in fitness. In the laboratory feeding analysis, number of attacks and percent successful attacks differed significantly by site. Snakes from the invaded site attacked more frequently but had fewer successful attacks than the other snakes. Prey classes were categorized as fish, amphibian, small mammal, invertebrate, avian or brook stickleback. No significant difference was found in diet composition between sites. Fish and invertebrates were the most common items, with only one stickleback-present snake having the invasive fish in its diet. We propose that in avoiding the brook stickleback, these wandering garter snakes are not only failing to act as a biotic control on the invasive organism, but are also compounding the effects of the fish by their continued utilization of native populations as prey"--Leaf iv.