Is Disease Increasing or Decreasing, and Does It Impact or Maintain Biodiversity?

,\KSTRI\CT: Disease is a growing concern in conservation biology. Alteration to habitats can favor intermediate ho.sts such as mosquitoes. Stress may increasc susceptibility to infectious diseasc. Alterations to trophic cascades can indirectly favor the cmergence of diseases on Ihose spccies tiwi increase in abundance. Most notably. pathogen pollution. by introduced species. can expose hosts to diseaSes for which thcy have no coevolved resistance. Thcse effects can impair conservation by making formerly common spccies rare or inhibiting rare specics from recovering. In addition. managing wildlife diseases can havc undesirable environmental impacts. Because conservation biology focuses on thrcats. Itss attention has been paid to the conccpt thar envi­ ronmcntal changc will lead to declincs in disease. Because thc spread. persistence. and impact of infectious diSeases tcnd to incrcase with host densit)'. rare specics of concern should suffer less from host-specific infectious disease than COllll11Un spccies. Parasites may themselves be sensitive to environmental change and suffer direct mortality or interruption of life cycles. This loss of disease may be of concern in instances where diseases arc important for biodiversity. A lack of disease may allow common specics (and particularly introduced species) to exclude rarc species. A loss of trophically transmitrcd parasites may impair predators. In conclusion. environmental change will hamper some diseases and favor others in ways that may be of substantial concern for conservation biology.