DEMOGRAPHIC PLASTICITY IN GIANT GARTERSNAKE POPULATIONS IN MANAGED WETLANDS AND AGRICULTURAL AREAS.
Eric C. Hansen; 4200 North Freeway Boulevard, Suite 4, Sacramento, CA, 95835; (916) 214-7848; echansen@sbcglobal.net; Rick D. Scherar, Gary C. White, Barry R. Noon
Population models are a valuable tool for managing wildlife populations and estimates of demographic rates are an essential component of those models. Thamnophis gigas (giant gartersnake) has been eliminated from more than one half of its former range. Although factors such as habitat degradation and diminished water quality are attributed to these declines, the demographic trajectories of declining populations are only now emerging for T. gigas. The correlates of habitat and environment affecting demographic parameters also remain unclear. We used capture-mark-recapture data to estimate survival, growth rates and asymptotic size, and size at first reproduction in female T. gigas in populations at managed wetlands and at sites embedded in agricultural settings and evaluated the hypothesis that these vital rates varied among sites. Model-selection results indicated that T. gigas in agricultural areas grew more quickly but grew to a similar asymptotic length as those in managed wetlands and indicated lower survival and earlier age at first reproduction in agricultural areas. Central to developing management plans needed to prevent further extirpations in a variety of settings, this work contributes information needed to identify sensitive vital rates and to compare and track the status and trajectories of populations vital to the species' recovery.
Poster Session