Influence of harvest, climate and wolf predation on Yellowstone elk, 1961‐2004

Abstract

In the period following wolf (Canis lupus ) reintroduction to Yellowstone National Park (1995 Á/2004), the northern Yellowstone elk (Cervus elaphus ) herd declined from Â/17 000 to Â/8000 elk (8.1% yr(1 ). The extent to which wolf predation contributed to this decline is not obvious because the influence of other factors (human harvest and lower than average annual rainfall) on elk dynamics has not been quantified. To assess the contribution of wolf predation to this elk decline, we built and assessed models based on elk-related data prior to wolf reintroduction (1961 to 1995). We then used the best of these models to predict how elk dynamics might have been realized after wolf reintroduction (1995 to 2004) had wolves never been reintroduced. The best performing model predicted 64% of the variance in growth rate and included elk abundance, harvest rate, annual snowfall, and annual precipitation as predictor variables. The best performing models also suggest that harvest may be super-additive. That is, for every one percent increase in harvest rate, elk population growth rate declines by more than one percent. Harvest rate also accounted for Â/47% of the observed variation in elk growth rate. According to the best-performing model, which accounts for harvest rate and climate, the elk population would have been expected to decline by 7.9% per year, on average, between 1995 and 2004. Within the limits of uncertainty, which are not trivial, climate and harvest rate are justified explanations for most of the observed elk decline. To the extent that this is true, we suggest that between 1995 and 2004 wolf predation was primarily compensatory.

Space use and social ecology of coyotes (Canis latrans) in a high-elevation ecosystem: relative stability in a changing environment

“…In addition to vegetation impacts inside Rocky Mountain National Park, the large elk population also impacted residential areas of the nearby town of Estes Park (Schultz and Bailey 1978). In Yellowstone National Park, Wyoming, following wolf (Canis lupus) reintroduction and grizzly bear (Ursus arctos horribilis) recovery alongside a severe climate and increased harvest, elk populations have declined (Vucetich et al 2005) and elk movements and habitat use have changed (Fortin et al 2005;Mao et al 2005). Associated trophic cascades have been documented, including recovery of riparian vegetation (Beyer et al 2007) and aspen (Ripple and Beschta 2007).…”

Can we save large carnivores without losing large carnivore science?

“…Carnivores are just one of many potential causal agents operating in ecosystems (Vucetich et al, 2005;Middleton, 2014;Peterson et al, 2014;Ford and Goheen, 2015). Yet for many studies claiming support for the MRH, TCH and BMTCH, the study framework is designed to create evidence for these hypotheses rather than being designed so that evidence for plausible alternative hypotheses is both tested and compared at the same time (Winnie, 2014).…”

“…Environmental changes following the restoration of wolves to Yellowstone National Park are often given as a clear example of the beneficial effects of restoring large carnivores to ecosystems (Table 2), but there are alternative hypotheses to explain many of the observed changes (Vucetich et al, 2005;Marshall et al, 2013;Middleton et al, 2013b). There is strong evidence that wolves alone are not responsible for all the changes attributed to them (Mech, 2012;Winnie and Creel, 2017).…”

“…Many other important changes to the Yellowstone system occurred around the same time as wolf restoration, and 'when we tell the wolf story, we get the Yellowstone story wrong' (Middleton, 2014). Using data from 1961 to 2004, Vucetich et al (2005) investigated the TCH and showed that changes in climate and harvest rate are justified explanations for most of the observed decline in Yellowstone elk, rather than heightened predation by wolves. Indeed, wolf predation was determined to be compensatory to existing rates of mortality (e.g.…”

“…Indeed, several studies using strongly-inferential methods demonstrate that such top-down effects do not always occur, or if they do, they are far weaker than bottom-up processes (e.g. Gasaway et al, 1983;Boertje et al, 1996;Hayes et al, 2003;Vucetich and Peterson, 2004;Vucetich et al, 2005; Giordano, 2013;Marshall et al, 2013;Allen et al, 2014b;Ford et al, 2015a;Sivy, 2015; see also Schmitz et al, 2000;Bowyer et al, 2005;Sergio et al, 2008;McCoy et al, 2012;White, 2013;McPeek, 2014;Kuijper et al, 2017). Ford and Goheen (2015) showed that of five strongly-inferential experiments investigating large carnivores' roles, only two found evidence supporting the TCH.…”