Biodiversity reduces human, wildlife diseases and crop pests

Well, I would say humans are parasites.

http://www.eurekalert.org/pub_releases/2015-06/uosf-ubb061215.php

Public Release: 15-Jun-2015
University of South Florida (USF Health)

With infectious diseases increasing worldwide, the need to understand how and why disease outbreaks occur is becoming increasingly important. Looking for answers, a team of University of South Florida (USF) biologists and colleagues found broad evidence that supports the controversial 'dilution effect hypothesis,' which suggests that biodiversity limits outbreaks of disease among humans and wildlife.

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Much of the debate about the dilution effect hypothesis has focused on whether it applies generally or only to a few select parasites. Until now, there have been no quantitative assessments to broadly support or refute it, and the lack of evidence has hampered understanding the relationship between biodiversity and disease risk.

In reaching their conclusions, the research team reviewed more than 200 assessments relating biodiversity to disease and found that the dilution effect applied broadly to many parasitic species.

'Our study found broad evidence that species-rich communities suffer less infectious disease, and the magnitude of this effect was independent of host density, study design, type and specialization of parasites, and whether the parasite infected humans or wildlife, indicating that dilution was robust across all ecological contexts examined,' stated Civitello. 'This suggests that maintaining biodiversity in nature could reduce the abundance of many parasites of humans and wildlife,' explained Civitello. 'Conversely, human-induced declines in biodiversity could contribute to increases in both human and wildlife diseases.'

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