Does lemming winter grazing impact vegetation in the Canadian Arctic?
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In low-productivity environments such as the tundra, it has been proposed that regular, multi-annual population cycles of lemmings could be driven by winter food depletion in years of peak abundance. If lemming population dynamics is controlled by food resources, we predict that (1) winter grazing should negatively impact the abundance of food plants, (2) this impact should be proportional to lemming density and (3) high lemming winter grazing pressure should result in reduced plant growth during the following summer. We tested these predictions on Bylot Island, Nunavut, Canada, where two species of lemmings are present: the brown (Lemmus trimucronatus) and collared lemming (Dicrostonyx groenlandicus). We installed 16 exclosures in their preferred wintering habitat (snowbeds) and annually sampled plant biomass inside and outside exclosures at snow melt and at peak growth during the summers of 2009–2012, covering a full population cycle. Winter grazing had no impact on total vascular plant or moss biomass at snow melt in all years. Among plant families, only Caryophyllaceae, which was uncommon, showed a decline. In moss taxa, a negative effect was found on Polytrichum in only 1 year out of three. Overall, plant regrowth during the subsequent summer showed annual variation and tended to be reduced in the 2 years of high lemming abundance. However, this could be a consequence of summer grazing. Overall, the impact of lemming winter grazing on plants was weak and short-lived, even in years of high lemming abundance. Therefore, our results are not consistent with the hypothesis that food depletion during winter was the cause of the lemming decline following peak abundance at our study site. Other factors may limit lemming populations and prevent them from reaching densities high enough to exhaust their food resources.
KeywordsBottom-up Exclosures Herbivory Lemmus Plant biomass
We thank S. Pellerin, H. Mailhot-Couture, P. Morissette, V. Lamarre, N. Perreault and E. Lévesque for help in identifying, sampling and sorting plants. We also thank R. Pouliot for help in identifying mosses. The research relied on the logistic assistance of the staff of the Polar Continental Shelf Program (PCSP, Natural Resources Canada) and of Sirmilik National Parks, Nunavut. The research was funded by the Natural Sciences and Engineering Research Council of Canada, the Canadian federal government’s International Polar Year program (project MD-021) and the Northern Student Training Program, both administered by Indian and Northern Affairs Canada, the Canadian Network of Centres of Excellence ArcticNet, PCSP and the Fonds Richard-Bernard of the department of biology of Université Laval.
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