Mountain yellow-legged frogs (Rana muscosa) at high elevations of the Sierra Nevada must obtain enough food during summer to survive 7–9 winter months when their aquatic habitats are frozen and food is presumably unavailable. Adults of R. muscosa prey on a variety of organisms, including aquatic and terrestrial invertebrates and anuran larvae. To determine if anuran larvae influence the condition, distribution, and survival of adults of R. muscosa, we assessed body condition (variation from the expected mass for given length) and distribution of R. muscosa in relation to abundance and distribution of larval Hyla regilla, Bufo canorus, and Bufo boreas. Using three years of mark-recapture data, we found that abundance of larval H. regilla in a water body was positively correlated with the condition of R. muscosa. Moreover, R. muscosa had higher relative mass (Wr) values in areas with other anuran larvae than in areas with no other amphibian species. High Wr values significantly increased the probability of recapturing frogs in following years. Using surveys of over 1700 lakes and ponds in the John Muir Wilderness and Kings Canyon National Park, we also found that the presence of larval H. regilla or Bufo in a water body was a significant indicator of the presence of adults of R. muscosa after accounting for significant habitat and isolation variables. These findings taken together suggest that some adults of R. muscosa actively seek out water bodies with other anuran species during the critical summer months and that the anuran larvae provide a nutritious food source that increases the body condition and, therefore, survival of the frogs.
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Vol. 58 • No. 3