Interactions on the Arctic tundra between endemics, migrants, and northward expanding rodent populations
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Lemmings are key herbivores in the Arctic and an integral part of the food web. Rising temperatures are decreasing snow quality and making the environment more hospitable for southern invaders. Consequently, southern species have expanded onto the tundra, including the meadow vole (Microtus pennsylvanicus). Voles and lemmings play a similar functional role in the Arctic ecosystem and thus may compete for resources. In addition to expanding boreal species, lemmings may also compete for resources with migratory species. Lesser snow geese (Chen caerulescens caerulescens) breed in the Arctic and their population has increased exponentially due to land-use changes in their winter range. Snow goose grazing reduces graminoid abundance, leaving large patches of unvegetated land. Therefore, geese may indirectly impact lemming populations through habitat degradation. The objectives of this thesis were to (1) determine lemming and vole dietary overlap using stable isotope analysis and (2) analyze lemming winter habitat selection in an area impacted by snow geese. Our results suggest dietary overlap between vole and lemming populations is minimal. We also found that lemmings avoid goose-affected areas, suggesting geese may be indirectly impacting lemming habitat selection through habitat destruction. Thus, while lemming populations are declining in Arctic regions where they are sympatric with voles, habitat degradation by geese may be an additive factor contributing to lemming population declines. Ultimately, changes in lemming population abundance or distribution has the potential to disrupt the entire Arctic food web through changes in prey availability and predation risk.
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