Evaluating mechanisms of plant‐mediated effects on herbivore persistence and occupancy across an ecoregion

Abstract

Citation: Wilkening, J. L., E. J. Cole, and E. A. Beever. 2019. Evaluating mechanisms of plant-mediated effects on herbivore persistence and occupancy across an ecoregion. Ecosphere 10(6):Abstract. Contemporary climate change is rapidly creating one of the greatest challenges for management and conservation during the 21st century. Mountain ecosystems, which have a high degree of spatial heterogeneity and contain numerous habitat specialists, have been identified as particularly vulnerable. We used data from multiple years across sites spanning a >40 million ha ecoregion to test hypotheses regarding how community-level characteristics of vegetation may affect a mammalian generalist herbivore, the American pika (Ochotona princeps). We examined patterns of pika persistence across sites in the hydrographic Great Basin, and occupancy within a subset of these sites. We used mixed-effects logistic regression models to compare evidence in support of competing explanations for each pattern within an informationtheoretic framework (using Akaike's information criterion). Models reflected four hypothesized classes of mechanisms related to nutritional ecology, ecosystem function, indirect indication of climatic effects, and (synergistic) combinations of these three classes. At the site level, models reflecting synergistic effects received the most support. At the within-site level, support appeared to be split equally among hypotheses containing predictors related to either nutritional ecology or indirect climate effects. Well-supported predictors included cover of invasive plant species, cover of more-xeric plant species, species evenness, and proportion of graminoid species. Our results both (1) identify important aspects of vegetation communities that may influence herbivore distribution in mountainous areas across a large, diverse geographic region, and (2) contribute to an improved understanding of how mountain ecosystems may be affected by ongoing climate change, more broadly.

Factors influencing distributional shifts and abundance at the range core of a climate‐sensitive mammal

“…Both variables are expected to indirectly influence forage conditions by mediating the availability of aboveground biomass and vegetation quality (Stephenson, 1998). Forage quality and composition have been documented as important for pika persistence and abundance elsewhere, including across the Southern and Central Rocky Mountains (Erb et al, 2014; Yandow et al, 2015), hydrographic Great Basin (Wilkening et al, 2019), as well as in the Pacific Northwest (Varner & Dearing, 2014). Despite the predictive abilities of these two variables, our field measurements of vegetation cover and type performed surprisingly poorly, possibly due to high, near‐patch forage availability in this ecoregion.…”

Sampling a pika's pantry: Temporal shifts in nutritional quality and winter preservation of American pika food caches

“…While these changes appear to be the most pronounced at lower elevations and/or in more-isolated mountain ranges (Beever et al, 2016), evidence of demographic decline is also evident in parts of the species' core range (Billman et al, 2021;Stewart et al, 2017). Although pika declines have been associated with microhabitat features and changing vegetation communities, particularly reduced forb cover (Wilkening et al, 2011(Wilkening et al, , 2019, no studies have examined the effects of climate change on the nutritional quality of these plants, which could provide a key mechanistic link between changes in vegetation and changes in pika distribution, density, behavior, or physiology.…”