Conditions for caribou persistence in the wolf-elk-caribou systems of the Canadian Rockies

Abstract

Woodland caribou populations are considered threatened in Alberta and have declined in the Canadian Rocky Mountain National Parks of Banff and Jasper despite protection from factors causing caribou populations to decline outside of parks. Recent research emphasizes the importance of the numeric response of wolves to moose in moose-caribou-wolf systems to caribou persistence. Moose are rare in the Canadian Rockies, where the dominant ungulate prey for wolves is elk. Few studies have explored wolf-elk dynamics and none have examined implications for caribou. We used data collected in Banff to estimate the numeric response of wolves to elk from 1985 to 2005. Because no caribou kill-rate data exist for the Rockies, we explore the consequences of a range of hypothetical kill-rates based on kill-rates of alternate prey collected from 1985 to 2000 in Banff. We then multiplied the numeric response of wolves by the estimated caribou kill-rates to estimate the wolf predation response on caribou as a function of elk density. Caribou predation rates were inversely density dependent because wolf numbers depend on prey species besides caribou in multiple prey species systems. We then combined this simple wolf-elk-caribou model with observed demographic and population estimates for Banff and Jasper caribou from 2003-2004 and solved for the critical kill-rate thresholds above which caribou populations would decline. Using these critical kill-rate thresholds, Jasper caribou are likely to persist when wolf densities are below 2.1 -4.3 wolves/1000km 2 and/or when elk densities are below 0.015-0.033 elk/km 2 . Thresholds for Banff caribou persistence are much lower because of inverse density dependence. Future research is needed on some of the necessary assumptions underlying our modeling including multi-prey wolf numeric responses, wolf kill-rates of caribou, caribou mortality by other predators, and spatial aspects of wolf-elk-caribou dynamics.

Seeking sanctuary: the neonatal calving period among central mountain woodland caribou (Rangifer tarandus caribou)

“…However, the fitness value of prioritizing conservation of calving habitat relative to other seasons needs to evaluated (Gaillard et al 2010). If calf mortality during the neonatal period is compensatory (Vaupel et al 1979;Tveraa et al 2003;Griffin et al 2011), then conservation of winter and migratory ranges may be of equal or greater importance in supporting long-term population persistence by contributing to adult survival and juvenile recruitment (Hebblewhite et al 2007a;DeCesare et al 2012a). Also, it should be noted that there may be no ideal calving habitat within a multiple-predator ecosystem, instead caribou may have to make a series of trade-offs between low risk from one predator and higher risk from another (Gustine et al 2006;Dussault et al 2012;Leblond et al 2016) while balancing nutritional requirements during lactation (Parker et al 2009).…”

“…Predation is the main natural cause of calf mortality (Linnell et al 1995;Gustine et al 2006). Research suggests calf predation is probably most important for population growth during the calf's first winter (6-12 months) prior to recruitment into the population as a yearling (Hebblewhite et al 2007a;Johnson et al 2010;DeCesare et al 2012a). However, the neonatal period is an especially vulnerable time for predation (Adams et al 1995;Gustine et al 2006), and there is limited information available on the neonatal period of a calf's life (0-4 weeks of age), including parturition rates, neonatal calf survival, adult female habitat selection, and calving-range fidelity (Rettie and Messier 1998;Wittmer et al 2005a;Pinard et al 2012).…”

Sea otters, kelp forests, and the extinction of Steller’s sea cow

“…Ripple et al (57) hypothesized one such chain of events, with extirpation of wolves in the northern United States causing increased coyote numbers, thus purportedly forcing snowshoe hare populations downward and forcing the hare's obligate predator, lynx, to extinction in local areas as well. Elk and moose population increases in the Canadian Rockies (caused in some cases by forest management practices) have elevated wolf densities, in turn driving caribou numbers downward (58) (Fig. 4B).…”

Interactions of wolves, mountain caribou and an increased moose-hunting quota --- Primary-prey management as an approach to caribou recovery.

“…Densities of predators, such as wolves, have increased considerably due to the increase in moose (Seip 1992, Rettie andMessier 1998, Wittmer et al 20056), and as a result, predation on caribou also has increased. Wolf numerical response, however, remains linked to the abundance of their primary prey, moose in my study area, and not to caribou abundance (Hebblewhite et al 2007). Thus, even as caribou numbers decline, there is no feedback to wolf numbers.…”

“…Across much of woodland caribou range, moose numbers have increased in the last century and a half, due mainly to human forestry practices (Peterson 1955, Spalding 1990), which has led to an increase in wolf numbers (Seip 1992, Rettie andMessier 1998, Wittmer et al 20056). As a result, predation on caribou also has increased, but the numerical response of wolves remains coupled to the abundance of their primary prey, moose, and not to caribou (Hebblewhite et al 2007). Thus, even as caribou numbers decline, there is no feedback to wolf numbers.…”