HOMECOMING OR NEW PAD: HISTORICAL EVIDENCE FOR CALIFORNIA RED-LEGGED FROGS AND OTHER AMPHIBIANS IN THE YOSEMITE REGION, CALIFORNIA

Abstract

Establishing historical species distributions can assist conservation translocations for threatened species, and yet, ecological changes necessitate developing restoration targets that are not analogous to historical baselines. Despite its recent conservation translocation to Yosemite Valley in Yosemite National Park, Sierra Nevada Mountains, USA, the historical distribution of the federally threatened California Red-legged Frog (Rana draytonii) in the valley remains unclear. Using archival records, interviews, and museum specimens, we examined the historical evidence for California Red-legged Frogs and sympatric amphibian species in the Yosemite region. We found a paucity of reliable amphibian records for Yosemite Valley since the 19th century, one of the most-visited sites in the US National Park System, and conclude that this is the result of historically low collecting and survey effort prior to the introduction of invasive American Bullfrogs (Lithobates catesbeianus; also Rana catesbeiana after Yuan and others 2016) in concert with a bird and mammal study bias from largely diurnal collecting that occurred when California Red-legged Frogs were extant regionally. We found previously undocumented records for individuals of the genus Rana for Yosemite Valley, consistent with a dominant historical hydrology more compatible for Foothill Yellow-legged Frogs (Rana boylii), though none could be definitively identified as California Red-legged Frogs. We conclude that extensive anthropogenic impacts, including acute ecosystem alteration and American Bullfrog introduction, contributed to the failure to detect California Red-legged Frogs in many places regionally once amphibians became a research priority in the latter 20th century. The conservation translocation of California Red-legged Frogs to Yosemite Valley illustrates the integration of historical baselines with contemporary realities, allowing for the complexities of change over time rather than focusing on restoration to an imagined, ideal environment in the past.