Trophic interactions and dynamic herbivore responses to snowpack

Abstract

Background: Trophic interactions and population structure can shape how climate change influences ecosystems by modifying herbivore responses to environmental conditions. Predation can influence herbivore behaviour and demography, but how changes in predation and population structure affect herbivore distribution across abiotic gradients remains little known. We assessed whether predators altered the response of different age and sex classes of a dominant ungulate herbivore to changing abiotic conditions. Results: Elk (Cervus elaphus) presence declined with increasing snowpack, particularly in late winter when their body condition had deteriorated. Females and juveniles exhibited strong but constant negative responses to snowpack throughout the winter, although their mean occurrence declined over time likely due to sex-biased movement to lower elevations. Mature male occurrence responded only very slightly to snowpack and in a temporally invariant manner. Neither temporal nor spatial variation in wolf (Canis lupus) occurrence affected elk occurrence or elk responses to snowpack. Conclusions: Climate change impacts on herbivore distribution in this system are driven by spatially and temporally dynamic interactions between winter conditions and population structure, but the influence of predation risk appears weak.