title: Biodiversity inhibits parasites: Broad evidence for the dilution effect.
abstract: Infectious diseases of humans, wildlife, and domesticated species are increasing worldwide, driving the need to understand the mechanisms that shape outbreaks. Simultaneously, human activities are drastically reducing biodiversity. These concurrent patterns have prompted repeated suggestions that biodiversity and disease are linked. For example, the dilution effect hypothesis posits that these patterns are causally related; diverse host communities inhibit the spread of parasites via several mechanisms, such as by regulating populations of susceptible hosts or interfering with parasite transmission. However, the generality of the dilution effect hypothesis remains controversial, especially for zoonotic diseases of humans. Here we provide broad evidence that host diversity inhibits parasite abundance using a meta-analysis of 202 effect sizes on 61 parasite species. The magnitude of these effects was independent of host density, study design, and type and specialization of parasites, indicating that dilution was robust across all ecological contexts examined. However, the magnitude of dilution was more closely related to the frequency, rather than density, of focal host species. Importantly, observational studies overwhelmingly documented dilution effects, and there was also significant evidence for dilution effects of zoonotic parasites of humans. Thus, dilution effects occur commonly in nature, and they may modulate human disease risk. A second analysis identified similar effects of diversity in plant-herbivore systems. Thus, although there can be exceptions, our results indicate that biodiversity generally decreases parasitism and herbivory. Consequently, anthropogenic declines in biodiversity could increase human and wildlife diseases and decrease crop and forest production.
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620 civitello@usf.edu.
authors.forename: David J
authors.initials: DJ
authors.lastname: Civitello
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Cohen
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Hiba
authors.initials: H
authors.lastname: Fatima
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Neal T
authors.initials: NT
authors.lastname: Halstead
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Josue
authors.initials: J
authors.lastname: Liriano
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Taegan A
authors.initials: TA
authors.lastname: McMahon
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: C Nicole
authors.initials: CN
authors.lastname: Ortega
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Erin Louise
authors.initials: EL
authors.lastname: Sauer
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Tanya
authors.initials: T
authors.lastname: Sehgal
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Young
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, FL 33620.
authors.forename: Jason R
authors.initials: JR
authors.lastname: Rohr
mesh_terms: D000818:Animals; D044822:Biodiversity; D004198:Disease Susceptibility; D006790:Host-Parasite Interactions; D006801:Humans; D010272:Parasitic Diseases / Q000517:prevention & control*
keywords: associational resistance; biodiversity; dilution effect; meta-analysis; parasitism