Abstract
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. 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. 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.
Highlights
Trophic interactions and population structure can shape how climate change influences ecosystems by modifying herbivore responses to environmental conditions
We focus on elk because of their strong roles in affecting the demography and persistence of woody shrubs [12] that provide habitat for other species [13]
We presented four predictions of how responses to snowpack conditions by elk, the dominant ungulate herbivore in the Yellowstone Ecosystem, would be mediated by predation hazard, time, and sex
Summary
Trophic interactions and population structure can shape how climate change influences ecosystems by modifying herbivore responses to environmental conditions. A more general understanding of how herbivore distribution, abundance, and foraging are affected by shifting abiotic conditions will greatly improve our knowledge of climate change impacts on natural ecosystems. While we know generally that climate can strongly affect herbivore responses, we lack knowledge about which factors mediate herbivore distribution in relation to environmental conditions. Species interactions change with abiotic conditions [4], and directly alter herbivore abundance [5] and distribution [6], and to change the way in Trophic interactions can strongly influence herbivore distribution and behavior and mediate herbivore impacts on plants. By affecting the spatial distribution of herbivores [11], predation risk has the potential to shape how plant-herbivore interactions respond to changing abiotic conditions. Climate-induced habitat deterioration in habitat patches with high predation risk could potentially have no impact on herbivore distribution if the herbivores already avoided such locales
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