Dietary overlap and potential competition in a dynamic ungulate community in Northwestern Canada

Abstract

The potential for interspecific competition for food resources is a key consideration when newly introduced ungulates occupy a shared range with resident native species. Management plans in Yukon, Canada, for reintroduced bison (Bison bison) and introduced elk (Cervus canadensis) called for an assessment of competition for food resources between these species and resident populations of caribou (Rangifer tarandus), thinhorn sheep (Ovis dalli), and moose (Alces americanus). To assess potential competition among ungulates, we examined dietary overlap of 7 ungulate species in southwestern Yukon, Canada. We compared diet composition at the forage class level and composite diet indices (diversity, evenness, and niche breadth) among species found at 2 elevation classes (high [!1,200 m ASL] and low [<1,200 m ASL]) during summer and winter, using data derived from microhistological analyses of feces. Composite indices and percent of key forage classes in diets differed among ungulates during summer and winter and at both high and low elevations. Potential dietary overlap for most species pairs was low to moderate (0.07-0.60). However, for bison and thinhorn sheep at high elevations, and bison and semi-feral horses (Equus ferus caballus) at low elevations, it was high (0.82-0.97) during both summer and winter, indicating potential for food competition. Dietary overlap between species appeared to be based primarily on morphophysiological classification (i.e., browser-intermediate-grazer), rather than body size. Bison, horses, and sheep were all grazers. Intermediate species, such as introduced elk, had only moderate dietary overlap with several species. We concluded that the potential for competition for food resources based on dietary overlap between bison and sheep and bison and horses may be high in our study area, depending on forage availability, but for all other species pairs in our study area the potential for forage competition is low to moderate. Ó 2015 The Wildlife Society.

Impact of rewilding, species introductions and climate change on the structure and function of the Yukon boreal forest ecosystem

“…Grizzly bears survived the Last Glacial Maximum (LGM) in coastal and Beringian refugium, and the black bear moved northward as the ice retreated at the end of the LGM (Slough & Jung 2007). The ungulate community in the region has been dynamic (Beach & Clark 2015;Jung et al 2015a), with species naturally colonizing from the south of the LGM, and species introduced or reduced by humans. Caribou, thinhorn sheep and mountain goats have occurred in Yukon for at least the past 200 years.…”

“…The cow harvest has declined recently and moose numbers have risen since 2009. Moose feed large-ly on shrubs in winter and summer, and they are the only ungulate species in the area with a predominate intake of shrubs (Jung et al 2015a). Their most likely competitor for food is the snowshoe hare (Wolff 1980;Belovsky 1984).…”

“…The critical questions regarding reintroduced bison is whether they will compete for food with other ungulates, and whether the abundance of wolves and other carnivores will increase in response to reintroduced bison, allowing increased predation pressure on caribou, moose and other herbivores, through apparent competition induced by reintroduced bison (Larter et al 1993;Jung 2011). Jung et al (2015a) calculated dietary overlap in winter and summer between 7 species of ungulates in the Yukon and found that for most pairs of species overlap was relatively minor except for thinhorn sheep and bison, which prefer sedges and grasses in both winter and summer. However, forage resources were unlikely to be limiting so that potential competition between bison and moose or caribou has been of little concern.…”

“…forage quantity and quality, and environmental conditions) for elk in southwestern Yukon are comparatively poor (Strong et al 2013). Elk eat both shrubs and grasses/ sedges (Jung et al 2015a), particularly sage (Artemisia frigida), and at current densities are unlikely to compete with other mammals in the Yukon area because of their reliance on boreal grasslands and aspen parklands (Strong et al 2013).…”

Winter diets of reintroduced bison (Bison bison) in northwestern Canada

“…In 1988, wood bison were reintroduced to southwestern Yukon, Canada, as part of a national recovery program (Government of Yukon 2012; Jung et al 2015). Their range is topographically diverse, with a complex mix of vegetation communities, but contains relatively few wet sedge meadows, a preferred foraging habitat for bison in lowland boreal regions (Reynolds et al 1978;Campbell and Hinkes 1983;Larter and Gates 1991).…”