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Habitat fragmentation increases Lyme disease risk.
Keesing, Felicia1,2, Allan, Brian3, Ostfeld, Richard2, 1 2 3
ABSTRACT- Forest fragmentation has recently been shown to reduce mammalian species diversity and to elevate population densities of white-footed mice. One potential consequence of reduced diversity and high mouse density in small fragments is an increase in human exposure to Lyme disease. Such an increased risk would be expected because of the role of white-footed mice as the principal natural reservoir for Lyme bacteria. Ticks feeding on mice have a higher probability of acquiring the bacterium than do ticks feeding on any other host species. We hypothesized that small forest patches (<2 ha) would have higher density of infected nymphal ticks, which is the primary risk factor for Lyme disease, than would larger patches (2-8 ha). In summer 2000, we sampled tick density and Lyme infection prevalence in 14 maple-dominated forest patches, ranging in size from 0.6-7.4 ha, in Dutchess County, NY. We found a significant linear decline in nymphal infection prevalence with increasing patch area, and a significant exponential decline in nymphal density with increasing patch area. The consequence was a dramatic decrease in the density of infected nymphs, and therefore in Lyme disease risk, with increasing forest patch size. We did not observe a similar relationship between density of larval ticks and patch size. These results demonstrate that, by influencing population density and community composition of vertebrate hosts for disease-bearing vectors, habitat fragmentation can influence human health.
KEY WORDS: biodiversity, habitat fragmentation, disease, eastern deciduous forest