Masters Thesis

Habitat differentiation and resource use among different age classes of post metamorphic Rana boylii on Red Bank Creek, Tehama County, California

To obtain the most complete understanding of a species' life history requirements, one must know what habitat characteristics and resources are critical to each life history stage. Rana boylii are known to associate with various stream habitats throughout their life cycle, and these habitat associations may vary based on changes in age, season or both. In this study I looked at meso-scale habitat use and resource use among adult, sub-adult, and metamorph R. boylii on Red Bank Creek, Tehama County, California during three seasons using visual encounter surveys. For each age class the proportion of habitat used was compared to the proportion of habitat available to see if habitat selection existed. The proportions of each age class observed in each of the four habitat types over time were also compared, to determine if habitat differentiation existed between age classes or seasonally. The results indicated that adults and sub-adults generally used different habitat than metamorphs, but metamorph habitat use changed seasonally. Adults and sub-adults showed a preference for pool and riffle habitat, whereas young of the year metamorphs selected for slower moving glides and runs. However, after metamorphs had overwintered they selected for riffles. These results suggest R. boylii exhibit natal site fidelity. Diet data were obtained using a procedure known as gastric lavage. The results of the diet analysis indicated that all age classes of R. boylii consume terrestrial insects. There were no significant differences in the taxonomic groups of insects found in the diet samples of different age classes. There was also no significant difference in mean prey size for different age classes. However, the results suggest that R. boylii are gape limited predators, since larger frogs consumed a greater proportion of large prey items. This lack of a significant result could be due to sample size.

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