Some people say that we should eat invasive species like lionfish and kudzu to help put the brakes on their out-of-control spread. When nonhuman predators are looking for something to eat, though, they aren’t considering the ecological impact of their choice. An invasive species is just one more option on the menu. But is it a good one?
In general, predators should have negative effects on populations of prey, and those prey should benefit predators. But the situation gets a bit more complicated — and more difficult to predict — when nonnative species enter the picture. With no shared evolutionary history, nonnative prey may lack the appropriate defenses against predators in their new territory and, thus, be more vulnerable. At the same time, the predator may not be adequately equipped to capture and consume the newcomer. And if the nonnative prey somehow displaces native species that the predator relies on, then the predator might be in big trouble.
To see what happens to predators after an invasive species arrives, Lauren Pintor of Ohio State University in Columbus and James Byers of the University of Georgia in Athens drew data from previously published studies. They tossed out several studies that looked at native Australian predators and cane toads, as the toads are toxic and not really a viable menu option. The remaining 109 studies covered both land and ocean and included insects, crustaceans and birds. The researchers then looked for trends in predator populations after the arrival of the nonnative species.
The analysis revealed that predator populations tend to increase in abundance and growth rate after the arrival of nonnative prey species, the researchers report in the November Ecology Letters. But that only occurred when native prey communities were left intact. When predators could only eat the nonnative species, the predators didn’t fare so well and fertility suffered. Invasive species, it appears, are better snacks than meals.
The authors caution against concluding that the positive population trends for predators is “evidence that nonnative species are not harmful to native biodiversity and ecosystems.” There is plenty of evidence that invasive species can do real harm. About 42 percent of threatened and endangered species are at risk because of invasive species, for example. And nonnatives can spread diseases, alter soil composition and increase wildfire risks.
The “data simply suggest that nonnative prey may not be overly impacting the native prey base for native predators,” Pintor and Byers write.
That’s a bit of good news in a field often filled with bad.