Straw men don't get Lyme disease: response to Wood and Lafferty.

Wood and Lafferty [1] (hereafter WL) attempt a synthesis of two views of the ecological factors underlying variable Lyme disease (LD) risk. LD emerged during the 1970s following the post-agricultural reforestation of the northeastern USA, which provided the habitat required by the blacklegged tick vector (Ixodes scapularis) and many of its hosts [2]. However, within the large and growing North American LD zone, risk and incidence vary enormously. To explain LD risk, WL contrast a ‘traditional’ perspective, in which forestation is associated with high risk, and a ‘dilution effect’ perspective, in which loss of vertebrate diversity is associated with high risk. Unfortunately, this dialectic confuses the objectives of each perspective and distorts relevant evidence. WL conflate ‘forestation’ and ‘biodiversity’, epitomized by their repeated use of the term ‘forestation and/or biodiversity’ ([1] pp. 240 and 244). Although forest is required for blacklegged tick populations, host diversity within these forests and associated landscapes varies dramatically. Reforestation during the 20th century of agricultural land has been linked to LD emergence, but more recent forest fragmentation has been linked to increased LD risk (reviewed in [2]). WL engage in fallacious reasoning, arguing that, because LD would disappear if all biodiversity were eliminated, increasing biodiversity amplifies LD. Indeed, their characterization of the ‘traditional’ approach leads them to the untenable position that the most effective means of reducing LD risk is to deforest the landscape, an option that they find ‘inadvisable’ ([1] p. 246). It also leads them to state ([1] p. 246) that, ‘most evidence currently available points to a monotonic increase in disease risk with increasing biodiversity’, a statement utterly devoid of support (and unreferenced). WL are critical of the ‘dilution effect’ perspective, contending that it ‘is part of a growing effort to market conservation actions based on the utilitarian services that biodiversity can provide for human society’ ([1] p. 246). We disagree that efforts to use scientific understanding to inform policy should be considered ‘marketing’. WL’s discomfort with the dilution effect stems from a series of mischaracterizations. First, they contend that the dilution effect ‘is premised on the unreasonable belief that biodiversity must always benefit human society’ ([1] p. 243). On the contrary, the dilution effect literature clearly shows that biodiversity can either dilute or amplify disease risk, specifying the conditions under which each would be