Generalizing wolf effects across the Greater Yellowstone Area: a cautionary note

Abstract

Although numerous authors are investigating indirect effects of wolf recovery, the most fundamental ecological impact of the Greater Yellowstone Area wolf reintroduction, the effects of wolf predation on ungulate populations, remains unclear. We report on a 5‐year comparative study of wolf (Canis lupus)‐elk (Cervus elaphus) dynamics on an elk herd in the headwaters of the Madison River within Yellowstone National Park and the lower Madison elk herd that winters 40 km downriver outside the Park. A resident pack became established on the Madison headwaters area in 1997 and grew to multiple packs totaling 30–40 animals by 2002. During winter 1999 emigrates from Yellowstone established a pack on the lower Madison area. However, poor recruitment and low adult survival limited wolf population growth, with the area supporting a single pack, never exceeding 5 animals. Wolf kill rates on the lower Madison area were approximately double that documented for the Madison headwaters area. Moderate kill rates in the Madison headwaters, combined with high wolf densities and modest elk densities, resulted in an estimated 20% of the elk population being killed during winter and projections for a declining elk population. In contrast, high kill rates on the lower Madison area, combined with low wolf densities and high elk densities, resulted in winter predation estimates not exceeding 4% of the elk population. We suspect this level of mortality will be of little biological significance with respect to elk population trajectory. These results suggest that the effects of wolf predation on elk populations differ substantially over relatively small spatial scales, depending on a complex suite of interacting factors. Thus, we caution against generalizing the effects of wolf restoration on elk dynamics from any single study and encourage collaborations to develop comparative predator‐prey studies that improve our understanding of wolf‐ungulate interactions and enhance conservation.

Elk migration patterns and human activity influence wolf habitat use in the Greater Yellowstone Ecosystem

“…Thus, when prey migrate away during summer (as in other systems), wolves may be forced to travel long distances from the den to locate prey (Walton et al 2001), whereas wolves with resident prey can access an abundance of prey close to their den (Fig. Such patterns, whereby migratory elk depart for high-elevation summer range, have been hypothesized to decouple wolves from the distribution of elk in summer in much of the GYE (Garrott et al 2005). Such patterns, whereby migratory elk depart for high-elevation summer range, have been hypothesized to decouple wolves from the distribution of elk in summer in much of the GYE (Garrott et al 2005).…”

“…Outside the core protected area of Yellowstone National Park (YNP), however, the low-elevation valleys where many ungulates winter are typically dominated by private lands and livestock grazing. The coincidence of summer livestock grazing and the departure of migratory elk (i.e., the ''replacement'' of native with domestic prey) has been hypothesized as a key driver of wolf-livestock conflict in the GYE (Garrott et al 2005), but this notion has not been empirically evaluated. The coincidence of summer livestock grazing and the departure of migratory elk (i.e., the ''replacement'' of native with domestic prey) has been hypothesized as a key driver of wolf-livestock conflict in the GYE (Garrott et al 2005), but this notion has not been empirically evaluated.…”

Intraguild relationships between sympatric predators exposed to lethal control: predator manipulation experiments

“…Perhaps the most widely-known example of positive ecological outcomes arising from the restoration of top-predators is the reintroduction of gray wolves Canis lupus to the Greater Yellowstone Ecosystem in North America. Wolf restoration has coincided with remarkable changes to faunal and floral communities there ([4]; but see [5-7]), but has also increased conflict between humans and wolves [8-10]. …”

Changing migratory patterns in the Jackson elk herd

“…Wolves can affect recruitment in 2 ways—directly and indirectly. Wolves directly predate calves but also may increase anti‐predator behavior in cow elk (see Garrott et al ) that results in reduced pregnancy rates (Creel and Winnie , Christianson and Creel ). In 2006–2007, only 70% (53/76) of adult female elk sampled during January–March in Buffalo Valley, within the LDM summer range of the Jackson herd unit, were pregnant (S. Fairbanks, Iowa State University, unpublished data), and 71% of migratory elk in Clark's Fork herd unit were pregnant when sampled during winters of 2008–2010 (Middleton et al a ).…”