作者单位:Univ Calif Davis, Dept Wildlife Fish & Conservat Biol, One Shields Ave, Davis, CA 95616 USA[1]Univ Georgia, Savannah River Ecol Lab, Aiken, SC 29802 USA[2]US Geol Survey, Western Ecol Res Ctr, Dixon Field Stn, 800 Business Pk Dr,Suite D, Dixon, CA 95620 USA[3]San Diego Zoo Inst Conservat Res, 15600 San Pasqual Valley Rd, Escondido, CA 92027 USA[4]