Nonconsumptive effects of fish on stream salamanders with implications for downstream range limits

Understanding biotic and abiotic drivers of predator changes is important for predicting spatial variation in stream community composition. Transitions from ephemeral to permanent streams are paired with concurrent shifts in vertebrate communities that seemingly support the application of the predator–permanence hypothesis for low-order streams. Semiaquatic amphibians tend to decline at this transition, and one hypothesis for this decline has been the presence of their fish predators, who cannot succeed in streams that dry for part of the year. Both prey avoidance and asymmetrical competition favor fish in previous experiments, but these studies have not facilitated prey switching or access to alternative habitats that could allow for coexistence. This study sought to identify nonconsumptive effects of fish predators on stream salamander adults provided with an alternative habitat to escape the interaction. We evaluated the performance and habitat selection of 2 species of stream salamander—Desmognathus amphileucus Bishop, 1941 and Desmognathus monticola Dunn, 1916—in the presence or absence of a caged fish— Cottus carolinae (Gill, 1861)—when provided terrestrial prey. We observed that in the presence C. carolinae, both salamander species had reduced body condition and selected more terrestrial habitat. This study supports conclusions that competitive and likely predatory interactions between headwater fish and semiaquatic salamanders cause salamanders to become more terrestrial, grow more slowly, and transform at smaller sizes. Thus, stream permanence and associated environmental conditions may interact to result in a shifting predator community where fish occur. If the stream-permanence transition moves upstream as a consequence of climate change, spatial constriction of stream communities that are most successful in fishless streams will be accelerated.