INVASIVE SPECIES AS JUNK FOOD FOR PREDATORS.

If there is an upshot to the appearance of invasive species, it is that they might provide an additional food source for the native animals whose territory they are invading. However, an analysis of scientific studies spanning more than two decades has revealed that predators benefit most from eating invasive prey only if their traditional food sources remain intact--that is, if they are able to maintain their usual diet and eat invaders merely as an occasional snack.

For a study in the journal Ecology Letters, researchers reviewed 109 studies covering the interactions of 47 different prey species and 93 predator species. They discovered that predator populations increased as much as 57% after an invasion of new prey--but only when native prey remained abundant.

Lauren Pintor, study coauthor and assistant professor of aquatic ecology at Ohio State University, suspects that invasive prey do not provide predators with the best nourishment. "Eating non-native prey isn't as good for predators as eating native prey. It may be that the new prey isn't as nutritious, or that the predator hasn't evolved the ability to eat or digest it well." In all of these studies, whenever predators' diets were restricted to non-native prey, the predators did not perform as well as they did on native prey. 'We only saw a benefit to the predator when the non-native prey provided a supplemental food source."

She and coauthor James Byers, Distinguished Professor of Ecology at the University of Georgia, hope that the results will help environmental agencies identify where invasive species may have the greatest impact. "To me," says Byers, "the most interesting finding is that non-native species seem to really aid native predators when they serve as a supplemental food source...