The embarrassment of riches: agricultural food subsidies, high goose numbers, and loss of Arctic wetlands -- a continuing saga

摘要

Agriculture has provided a nutritional subsidy to the Anatidae (swans, geese, ducks), which has affected their trophic relationships and the Arctic wetlands where they breed. The Mid-Continent Population of lesser snow geese, which breeds in the Canad ian Arctic and which traditionally wintered in the coastal marshes of the Gulf States, now feeds in agricultural landscapes. The geometric growth of this population since 1970 is coincident with increased application of nitrogen to farmland and high crop yields. Widespread availability of agricultural foods allows the birds to meet much of their energy demand for migration and reproduction. Their migration conforms to a stepping stone model linked to land use, but feeding also takes place upon arrival o n the Arctic breeding grounds. High bird numbers have dramatically affected coastal marshes of the Canadian Arctic. Foraging has produced alternative stable states characterized by sward destruction and near irreversible changes in soil properties of exp osed sediments. Locally, this loss of resilience has adversely affected different groups of organisms, resulting in an apparent trophic cascade. A spring hunt was introduced in 1999 in an attempt to check population growth. The current annual cull is now thought to be higher than the replacement rate. Much of the decline of the Mid-Continent Population is probably linked to shooting, but the harassment of birds that fail to acquire sufficient food for reproduction may contribute. The agricultural food s ubsidy has led to a mismatch between this avian herbivore and its environment -- a consequence of migratory connectivity that links wintering and breeding grounds.