UC Santa Barbara

Mountain yellow-legged frogs (Rana muscosa and Rana sierrae) of California's Sierra Nevada have been extirpated from over 90% of their historic range, initially by introduced trout predators, and more recently by the emergence of the lethal amphibian chytrid fungus (Batrachochytrium dendrobatidis). Formerly widespread and abundant, mountain yellow-legged frogs are grazers and highly connected high level predators, living in low diversity, low productivity high elevation lakes. Here, I examine the extent to which frog extinctions impact Sierra Nevada lake communities. First, in a study that combined surveys of benthic macroinvertebrates in 22 lakes over 5 years with a reanalysis of benthic macroinvertebrate community data from over 150 lakes, I found no strong differences in benthic macroinvertebrate community diversity or composition between lakes with frogs vs. lakes without frogs. I also conducted experiments to evaluate the impact of tadpoles as grazers on benthic algae, and found that tadpoles do reduce algal biomass in artificial habitats, but that the effect can be small and may not outweigh the influence that abiotic variability has on algal biomass in lakes. Lastly, while I documented that large and periodic tadpole aggregations create biogeochemical hotspots of dissolved nitrogen, the phenomena may not be widespread enough to drive differences in diatom diversity in lakes with vs. without tadpoles. Within lakes, I found little indication that diatom community diversity and composition were responding to tadpole generated nitrogen hotspots as a fluctuation-dependent mechanism with potential to enhance diatom coexistence. While none of the ecological effects of mountain yellow-legged frogs and tadpoles that I observed suggests that their extinctions are having large impacts on Sierra Nevada lake communities, they should not be discounted as expendable, because there are many other ways in which these amphibians could be important in their communities.