We used analyses based on surveys of > 1700 water bodies in a 100,000-ha area in the John Muir Wilderness (JMW) and Kings Canyon National Park (KCNP) to determine the influence of nonnative trout on the distribution and abundance of Hyla regilla in the High Sierra Nevada. At the landscape scale (JMW compared to KCNP), a negative relationship between trout and frogs in lakes was evident. In the JMW study area where trout are more abundant, only 7.2% of all water bodies contained H. regilla versus 26.6% in the KCNP study area. Also, the percentage of the total water body surface area containing H. regilla was 19.4 times higher in the KCNP study area than in the JMW study area. Hyla regilla were most abundant in portions of KCNP where the probability of finding lakes with trout is lowest and least abundant in the northern part of the JMW where the probability of finding lakes with trout is highest. At the water body scale, after accounting for the effects of all significant habitat and isolation variables, the odds of finding H. regilla in water bodies with no trout was 2.4 times greater than in water bodies with trout, and the expected number of H. regilla in water bodies with H. regilla and without trout was 3.7 times greater than in water bodies with both H. regilla and trout. Hyla regilla were significantly more likely to be found at the lower elevations (3000-3400 m) compared to higher elevations (3400-3800 m) and in shallow water bodies with high percentages of silt in near-shore habitats. Our study demonstrates a negative relationship between fish presence and H. regilla distribution and abundance in lakes and suggests that H. regilla has declined in portions of the High Sierra with high numbers of trout-containing lakes. It adds an additional native species to the mounting evidence of landscape-scale declines of native species resulting from the introduction of predatory fish.
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