Habitat-specific distribution and abundance of arctic ground squirrels (Urocitellus parryii plesius) in southwest Yukon

Abstract

Arctic ground squirrels ( Urocitellus parryii plesius (Osgood, 1900); formerly Spermophilus parryii plesius Osgood, 1900) were studied in three distinct habitat types (boreal forest, low-elevation meadows, and alpine meadows) in the Kluane region of the southwest Yukon Territory, Canada, from 2008 to 2010 to determine if populations in these different habitats provide evidence for habitat-specific distribution and abundance. Abundance in the boreal forest has been shown to be synchronous with the cycle of snowshoe hares ( Lepus americanus Erxleben, 1777) in the region owing to shared predators. We predicted that populations in the boreal forest would be low because of the current low phase in the cycle of snowshoe hares, and that in low-altitude meadows and alpine meadows, ground squirrels would be relatively abundant. Late-summer densities differed significantly between habitat types with 0.38 ± 0.13 squirrel/ha (mean ± 1 SE) in boreal-forest habitat, 1.25 ± 0.22 squirrel/ha in low-altitude-meadow habitat, and 5.7 ± 0.22 squirrels/ha in alpine-meadow habitat. In 2009, populations were extirpated from boreal-forest habitat, while densities in low-elevation meadows and alpine meadows were 1.6 ± 0.34 squirrel/ha and 6.1 ± 0.7 squirrels/ha, respectively. The current absence of squirrels from the boreal forest and the persistence of populations in low-elevation-meadow and alpine-meadow habitat suggest that source–sink dynamics may exist between boreal-forest and meadow habitat types.

Forest or meadow: the consequences of habitat for the condition of female arctic ground squirrels (Urocitellus parryii plesius)

“…These grids were dominated by a white spruce (Picea glauca (Moench) Voss) forest, small clearings, and willow (genus Salix L.) thickets with occasional aspen (genus Populus L.) stands (described by Krebs et al 2001 andGillis et al 2005). In the low meadow (ϳ10 ha in size), data were collected from 2008 to 2009 on one grid dominated by grasses and surrounded by boreal forest (described by Green 1977;Donker and Krebs 2011). On the boreal forest grids, AGS population density was 0.38 ± 0.13 squirrels/ha (all age and sex classes combined) in 2000 and declined to extirpation by 2009; in the low meadows, AGS density was stable between 2008 and 2009 at 1.25 ± 0.22 squirrels/ha (Donker and Krebs 2011).…”

“…However, following the 1998 snowshoe hare peak in the Kluane region of southwestern Yukon, boreal forest populations failed to recover and since 2000 have remained near zero (Werner et al 2015). In contrast to this dramatic disappearance, AGS in nearby low-and high-elevation meadows are common (Green 1977;Gillis et al 2005;Werner et al 2015) and populations appear stable in these meadow habitats (Donker and Krebs 2011). We evaluate two broad hypotheses to explain the observed habitat-specific dynamics:…”

How will the greening of the Arctic affect an important prey species and disturbance agent? Vegetation effects on arctic ground squirrels

“…Predation can contribute substantially to active season mortality [e.g. of juveniles (Byrom and Krebs 1999)] and differences in predation risk may explain some of the temporal and spatial variation in active season survival and reproduction (Gillis et al 2005a;Donker and Krebs 2011). Winter survival has been found to vary between boreal forest and alpine tundra sites (Gillis et al 2005a), but did not differ between sites across a shrub to alpine tundra ecotone (Wheeler 2012).…”

Factors Governing the Distribution and Abundance of Arctic Ground Squirrels

“…These surveys measured colony characteristics considered to reflect levels of food availability (e.g., richness and abundance of food plants, soil composition) and predation risk (distance-specific visibilities, slope angle, distance to predator cover). To estimate population density, I used a powder tracking method developed by Boonstra et al (1992) for lemmings and voles, but adapted for ground squirrels (Hubbs et al, 2000;Donker and Krebs, 2011;Werner et al, 2015b). Small (5 × 7 cm) black plastic tiles, covered in mineral oil and unscented talcum powder, were placed in all burrows within a specified area (minimum size 0.5 ha) and left for six hours.…”