GAUTHIER, G.*; GIROUX, J.-F.; BETY, J.; ROCHEFORT, L.; Universite Laval, Quebec, Qc, Canada; Universit� du Quebec a Montreal, Qc, Canada; Universite Laval, Quebec, Qc, Canada; Universite Laval, Quebec, Qc, Canada: Trophic Interactions in a High Arctic Snow Goose Colony

Overabundance of goose populations caused by the food subsidy that they benefit in the south while feeding in agriculture lands is a perturbation currently affecting several arctic ecosystems. We examined the role of trophic interactions in structuring a high arctic community characterized by a large breeding colony of Greater Snow Geese (Chen caerulescens atlanticus). According to the hypothesis of exploitation ecosystem of Oksanen, terrestrial communities are controlled by top-down interactions. However, because of the low primary productivity, herbivore populations are too low in the Arctic to support functional predator populations, and thus these communities should be dominated by the plant/herbivore interaction. Since 1990, we have been monitoring annual abundance and productivity of geese, the impact of goose grazing, predator abundance (mostly arctic foxes Alopex lagopus) and the abundance of lemmings, the other important herbivore in this community, on Bylot Island, Nunavut. Goose grazing removed a significant proportion of the standing crop (~50%) in wet meadows every year. Grazing changed plant composition and maintained the production of grasses and sedges at a low-level equilibrium. However, fox predation was also severe and generated marked annual variation in egg predation and goose productivity. Predation intensity was closely related to the lemming cycle, a consequence of an indirect trophic interaction between lemming and geese via shared predators. We conclude that, contrary to the hypothesis of exploitation ecosystems, both the plant/herbivore and the predator/prey interactions are important in this arctic community.