Changes in demography, distribution, and diet in garter snakes following eradication of a non-native prey subsidy

Interactions between non-native and native consumers are often complex and cryptic. I shed light on relationships between non-native brook trout (Salvelinus fontinalis), native amphibians, their shared predator (aquatic garter snake; Thamnophis atratus) and a sympatric amphibian specialist (common garter snake; T. sirtalis) using a treatment-control removal experiment in a sub-alpine system of northern California. Eradication of non-native S. fontinalis resulted in an immediate decrease in T. atratus abundance and survival, whereas their abundance increased in concert with T. sirtalis in an adjacent control basin. Additionally, T. atratus body condition decreased substantially during this time, despite their increased use of lentic breeding ponds and increased predation on native amphibians, including the first documented predation on coastal tailed frog (Ascaphus truei). My findings corroborate and strengthen previous research suggesting T. atratus abundance, and the resulting hyperpredation experienced by native amphibians, is likely linked with the presence of salmonids stocked for recreational angling in historically fishless waters. Additionally, there appears to be some degree of negative association between the two sympatric species of garter snake, but my study was not designed to fully investigate this relationship and the evidence provided herein is merely correlative. These results not only demonstrate how a single introduced species can have drastic and unintended consequences in seemingly pristine wilderness settings, they also illustrate how restoration-based management via removal of a single non-native species can aid in reshaping native food webs