High biodiversity generally limits outbreaks of disease among humans and wildlife, University of South Florida researchers write in the Proceedings of the National Academy of Sciences. The new research is the first to quantitatively support the controversial “dilution effect hypothesis,” which warns that human-driven biodiversity losses can exacerbate parasite outbreaks. Much of the debate surrounding this idea concerns whether it applies generally or only to a few select parasites. After reviewing more than 200 published scientific assessments, the USF team found “overwhelming” evidence that the dilution effect applies broadly to many parasitic species in humans and wildlife. They also found that plant biodiversity reduces the abundance of herbivore pests. The results have implications for public health efforts, the researchers say, and make a case for better management of forests, croplands, and other ecosystems.