Mitigating anthropogenic barriers to facilitate distributional shifts helps reduce vulnerability of a large herbivore to climate change

Abstract

Climate change is among the greatest threats to biodiversity conservation worldwide. Understanding which species are vulnerable to climate change and in what ways is essential for adaptation planning and mitigation. We used the NatureServe Climate Change Vulnerability Index (CCVI) to conduct a range-wide assessment of tule elk (Cervus canadensis nannodes)a California-endemic ungulate with low genetic diversity, occupying highly fragmented landscapesto climate change. Using results from the CCVI, we tested the hypothesis that increasing connectivity among populations, by mitigating anthropogenic barriers to movement and dispersal, decreases vulnerability of tule elk to climate change. We compared CCVI scores given predicted conditions within current ranges with CCVI scores as if anthropogenic barriers were mitigated, with and without allowing elk to shift distributions up to 50 km to areas predicted to experience less warming, drying, or overall exposure to climate change (indicated by an interaction between warming and drying). Vulnerability of tule elk to climate change varied among populations; from most to least vulnerable rankings in the CCVI, 1 population was ranked extremely vulnerable, 1 was highly vulnerable, 12 were moderately vulnerable, and 4 were less vulnerable. Mitigating anthropogenic barriers alone did not have a significant effect on vulnerability to climate change compared to original CCVI estimates, nor did mitigation of anthropogenic barriers and shifts in distribution to areas expected to experience the least amount of warming. Mitigation of anthropogenic barriers coupled with elk shifting distributions to areas predicted to experience less drying than current ranges or less overall exposure to climate change significantly reduced climate change vulnerability. Our findings illustrate the need to prioritize increasing landscape connectivity for tule elk across California as part of climate change mitigation measures, but also may apply to non-migratory ungulates more generally, particularly where drying and warming are predicted to increase under climate change.

Habitat suitability assessment for tule elk in the San Francisco Bay and Monterey Bay areas

“…Changing habitat conditions and continued human alterations across landscapes pose a threat to elk population persistence, thus necessitating an assessment of existing unoccupied and potentially suitable habitat. For example, an aerial survey of the eastern Santa Clara County elk herds found an unexpectedly meager growth rate over the last 40 years, consistent with other studies suggesting that linkages to unoccupied but more mesic regions may be critical to future tule elk resilience (Denryter and Fischer 2022;Lanman et al 2022a). Where unoccupied suitable habitat exists, it presents an opportunity for wildlife and land managers to identify potential sites for highway crossings, promote natural or artificial landscape connectivity, and reexamine translocation as a tool to restore elk on the landscape.…”

“…In particular, the Santa Clara-Mt. Hamilton and Alameda Elk Management Units (EMUs) in the Central Diablo Range are expected to be moderately vulnerable (i.e., likely to experience a decrease in abundance or range extent) to climate change by mid-century (Denryter and Fischer 2022). Tule elk were historically common in the more coastal San Francisco Bay and Monterey Bay regions during pristine conditions but were extirpated by the 1850s (Evermann 1915;McCullough 1969).…”