SPATIAL AND TEMPORAL PATTERNS OF GIANT GARTERSNAKE (THAMNOPHIS GIGAS) DECLINE AND EXTINCTION IN CALIFORNIA'S CENTRAL VALLEY: PRIORITIZING RECOVERY IN A STATE.
Eric C. Hansen; Consulting Environmental Biologist; 4200 North Freeway Boulevard, Suite 4, Sacramento, CA, 95835; (916) 214-7848; echansen@sbcglobal.net; Rick D. Scherar
Endemic to the low-gradient streams, wetlands and marshes of California's Great Central Valley, giant gartersnake (Thamnophis gigas) populations have long been associated with declines corresponding with deteriorating habitat quality and perennial wetland loss. Now absent from more than half of their former range, T. gigas have been extirpated from the once-expansive wetlands of Tulare and Buena Vista lakes and presently occupy only a small number of localities in the central San Joaquin Valley associated with rapid declines. Recovery strategies address this loss by emphasizing the more robust T. gigas populations associated with rice agriculture in the Sacramento Valley, which in turn may be used to reestablish populations and genetic variation where extinctions have occurred. However, recent work suggests genetic variation is low for T. gigas throughout its range and that alarming and unexpected declines are occurring even in localities intended to serve as anchors for repatriation and recovery. While recent work provides new insights on vital rates such as growth, survival, and fecundity that will be key to managing extant populations, acting quickly to describe and preserve genetic diversity and adaptive traits may be crucial to maintaining the species under scenarios of increasing water scarcity and projected climate change.
Ecology and Conservation of Amphibians and Reptiles III