Humans are remarkably good at moving species around: We unwittingly carry stowaway organisms in our luggage when we fly, in our cars when we take a road trip, and on our bodies when we're simply taking a stroll.

But what happens to the parasites of native species when a new species shows up, and could knowing what happens help us predict the effects of an invasive species on disease? A new study has found something unexpected – that invasive species may actually help prevent disease from spreading.

To figure out if such predictions are possible – and what information is needed to make those predictions – a team of researchers from the University of Michigan, Purdue University and Utah State University carried out a study on an invasive water flea, Daphnia, that has begun to spread in freshwater areas throughout the United States.

Their experiment asked how the invasive water flea is affecting the dominant native water flea and the fungal parasite that the two species share. Results of the study were published online in the American Naturalist on Sept. 20, 2016.

The study has broader implications for predicting how an invasive species will affect disease prevalence. Scientists must take into account the ecological characteristics of invasive species, including the ways in which the invasive species affect the number of other organisms in a community.

The first author is Catherine Searle, who performed the research as a postdoctoral fellow in the lab of Professor Meghan Duffy of the U-M Department of Ecology and Evolutionary Biology. Searle is currently an assistant professor at Purdue University. The research team included an expert in mathematical biology, Michael Cortez of Utah State University, Duffy, and current or former members of her lab including technicians Katherine Hunsberger and Isabella Oleksy, graduate students Dylan Grippi (MS 2014) and Clara Shaw, and undergraduates Solanus de la Serna, Chloe Lash and Kailash Dhir.

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