Conquest by Disease Carriers

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Science  28 Mar 2003:
Vol. 299, Issue 5615, pp. 1947
DOI: 10.1126/science.299.5615.1947c

Invasions by alien species are considered to be one of the greatest threats to native biodiversity and can have severe economic repercussions. The widescale replacement of the native red squirrel in the United Kingdom by the North American grey squirrel over the past century exemplifies these concerns. Until recently, the ousting of the red squirrel was thought to be a straightforward result of the invader's superiority. However, a numerical simulation had suggested that competition alone could not account for the observed decline. Tompkins et al. use a mathematical model to show that the pattern of the red squirrel's decline more closely resembles the effects of disease than those of competition. The parapoxvirus, which is carried by the grey squirrel without ill effect, is harmful to the red squirrel, suggesting that current conservation efforts to link the fragmentary habitats still harboring the red squirrel could, in fact, hasten its demise through the more rapid spread of disease. More generally, the fate of the red squirrel highlights the need for greater attention to the potential for disease to exacerbate the consequences of species invasions: another headache for conservationists. — AMS

Ecol. Lett.6, 189 (2003).

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