The adult female on the top right is an invasive species from Africa. Daphnia lumholtzi has become increasingly prevalent in the lakes of the Midwest. Daphnia dentifera is a native water flea species found throughout North America. Photo by A. Oleksy/University of Michigan

ANN ARBOR, Mich., Sept. 22 (UPI) -- Invasive species may not be all bad. New research suggests the introduction of non-native species can reduce the spread of disease.

Initially, scientists were interested to find out how invasive species affect parasite populations in a given ecosystem. To find out, researchers analyzed the effects of an invasive water flea from Africa, Daphnia lumholtzi, on the native water flea species Daphnia dentifera.


Experiments showed the invasive species became more easily infected by the fungal parasite the two water flea species share. The discovery suggested the introduction of an invasive species would spread parasites and accompanying diseases more readily.

To test their hypothesis in the lab, researchers created a series of miniature ponds in buckets. Scientists populated each bucket with different combinations of native and invasive water fleas. To their surprise, the researchers found buckets with fewer or no invasive water fleas featured increased disease concentrations. More invasive water fleas yielded less diseased environs.

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Researchers built a mathematical model to help them understand what was going in. The simulation suggests the invasive water fleas drive down total water flea population by competing for resources. With fewer hosts, the fungal disease was less able to propagate.

Researchers published the new findings in the journal The American Naturalist.

The findings are forcing ecologists and infectious diseases scientists to rethink how they account for invasive species.

"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," researchers explained in a University of Michigan news release.