Research Topics Wildlife & Fish
Foothill Yellow-legged Frog (Rana boylii)
Ecology, River Regulation, and Conservation
adult. (Photo: R. Peek)
The stream-breeding foothill yellow-legged frog (Rana boylii) is experiencing range-wide population declines. R. boylii historically occurred in foothill and mountain streams from northern Baja California to southern Oregon west of the Sierra-Cascade crest. Because R. boylii inhabits streams in the foothills of California, a suite of anthropogenic impacts, including river regulation, habitat alteration, aerial drift of pesticides, and invasive species, directly and indirectly affect these frogs. Among these multiple stressors, changes to flow regimes and downstream habitat alteration resulting from hydroelectric power generation and other water management projects have the greatest impact because of R. boylii's dependence on riverine environments. In unregulated rivers, R. boylii avoids winter and early spring flood-induced mortality by synchronizing reproduction and rearing of vulnerable aquatic lifestages (eggs and larvae) with predictable receding late spring flows and summer low flows. In California, the major development of hydroelectric dams and large reservoirs that occurred 40-50 years ago resulted in the destruction and fragmentation of many riverine habitats. Populations of R. boylii that have survived below hydroelectric dams are typically small and research has demonstrated that they are negatively affected by aseasonal water releases and other alterations to natural flow regimes.
North Fork American River. (Photo: R. Peek)
Recent research has repeatedly shown that R. boylii are adversely affected by aseasonal pulse flows, which create stressful or fatal velocity conditions for early life stages. However, within regulated rivers, there are opportunities to improve flow management to meet the ecological requirements of this species.
The primary objective of this website is to provide summarize and provide links to current information on R. boylii, with special attention on the impacts and risks associated with river regulation. The information is organized by topic and geographic region in order to facilitate quick access to relevant data, and to help watershed managers, researchers, biologists, and river enthusiasts develop effective conservation approaches for R. boylii.
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