Density-dependent habitat selection alters drivers of population distribution in northern Yellowstone elk

Smith, Brian J.; MacNulty, Daniel R.; Stahler, Daniel R.; Smith, Douglas W.; Avgar, Tal

doi:10.1101/2022.07.12.499670

Cited by 2 publications

(1 citation statement)

References 86 publications

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“…However this seasonal bias is likely to be much smaller for bison than for elk. The elk counts were corrected for sightability to prevent underestimation of true population size as a result of animals that were present but not observed (Smith & MacNulty, 2023). Bison counts were not corrected for sightability.…”

Section: Methodsmentioning

confidence: 99%

Does restoring apex predators to food webs restore ecosystems? Large carnivores in Yellowstone as a model system

Hobbs,

Johnston,

Marshall

et al. 2024

Ecological Monographs

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Modification of food webs is a frequent cause of shifts in ecosystem states that resist reversal when the food web is restored to its original condition. We used the restoration of the large carnivore guild including gray wolves (Canis lupis), cougars (Felis concolor), and grizzly bears (Ursus arctos horribilis) to the northern range of Yellowstone National Park as a model system to understand how ecosystems might resist reconfiguration after the restoration of apex predators to the food web. The absence of wolves, cougars, and grizzly bears for nearly a century from the northern range was the primary cause of dramatic changes in riparian plant communities. Willows (Salix spp.) were suppressed in height by intense browsing by the dominant herbivore, elk (Cervus canadensis). The loss of activity by beavers (Castor canadensis) coincided with the loss of tall willows. We hypothesized that intense elk browsing interrupted the mutualism between willow and beavers: ecosystem engineering by beavers was a critical component of willow habitat and tall willows were a critical component of habitat for beavers. This interruption made riparian communities resilient to the disturbance caused by the restoration of apex predators. We hypothesized further that reductions in elk browsing attributable to reductions in elk population size were not sufficient to prevent the suppression of willow growth. To test these hypotheses, we conducted a 20‐year, factorial experiment that crossed simulated beaver dams with the exclusion of browsing. We found that willows grew to heights expected for restored communities only in the presence of dams and reduced browsing. Willows experiencing ambient conditions remained well below this expectation. We found no difference in heights or growth rates of willows in experimental controls and willows in 21 randomly chosen sites, confirming that the results of the experiment were representative of range‐wide conditions. A reorganized community of large herbivores was implicated in the suppression of willow growth. We conclude that the restoration of large carnivores to the food web failed to restore riparian plant communities on Yellowstone's northern range, supporting the hypothesis that this ecosystem is in an alternative stable state caused primarily by the extirpation of apex predators during the early 20th century.

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Section: Methodsmentioning

confidence: 99%

Does restoring apex predators to food webs restore ecosystems? Large carnivores in Yellowstone as a model system

Hobbs,

Johnston,

Marshall

et al. 2024

Ecological Monographs

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Movement ecology of endangered caribou during a COVID‐19 mediated pause in winter recreation

Gill,

Serrouya,

Calvert

et al. 2023

Animal Conservation

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The long‐term conservation of species at risk relies on numerous, and often concurrent, management actions to support their recovery. Generally, these actions are habitat‐based while others are focused on a species' position within its ecological community. Less studied are the impacts from human presence, despite evidence that human activity may reduce the area functionally available for occupancy or resource acquisition. In the winter of 2020/2021, COVID‐19‐related travel restrictions led to a reduction in helicopter‐assisted back‐country skiing (heli‐skiing). We examined how these reductions in heli‐skiing (termed the anthropause) affected the movement ecology and resource selection of southern mountain caribou (Rangifer tarandus caribou) as compared to two prior years (2018/2019 and 2019/2020) and the following year when heli‐skiing resumed (2021/2022). We found that home‐range size was on average 80–120% larger during the anthropause than in years of normal heli‐ski operations. Movement rates also varied among periods, with movement during the anthropause (11.9 km2/day) being higher than in 2019/2020 (7.8 km2/day) and 2021/2022 (8.7 km2/day), though similar to 2018/2019 (12.2 km2/day). Resource selection among periods did not differ, with caribou consistently selecting old forests, high elevations and gentle terrain. These results suggest that back‐country recreation, specifically heli‐skiing, may be limiting access to resources for southern mountain caribou. This limitation arises through reduced home‐range size within suitable late‐winter habitat, relative to when heli‐skiing is reduced or not occurring – consistent with Encounter Theory. While the demographic effects of reduced home‐range size and movement were not examined here, reduced access to resources likely compounds other stressors known to affect population viability of caribou. The results of this study demonstrate the impact that recreation can have on wildlife and highlight the need to consider heli‐skiing and other forms of recreation when developing recovery plans.

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Density-dependent habitat selection alters drivers of population distribution in northern Yellowstone elk

Cited by 2 publications

References 86 publications

Does restoring apex predators to food webs restore ecosystems? Large carnivores in Yellowstone as a model system

Does restoring apex predators to food webs restore ecosystems? Large carnivores in Yellowstone as a model system

Movement ecology of endangered caribou during a COVID‐19 mediated pause in winter recreation

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