Each year, invasive exotic species cause an estimated $120 billion in damage in the United States, not to mention the untold amount of harm they do to the structure and function of native ecosystems. In this latest study, researchers found that exotic herbivores, including cattle, rabbits and goats introduced by Old World explorers, can encourage the spread of invasive exotic plants increasing their relative abundance by nearly 70 percent over native plants.
"Exotic herbivores may facilitate the growth of exotic plants by selectively consuming native plants, potentially freeing resources for exotic plants that can resist these herbivores," said John Parker, graduate researcher in the School of Biology at the Georgia Institute of Technology.
Parker, along with Professor Mark Hay and fellow graduate student Deron Burkepile, analyzed 63 published studies of more than 100 exotic and 400 native plant species. In addition to finding that exotic plant eaters increased the percentage of exotic plants in a community, they found that exotic plant eaters also increased the richness and variety of exotic plants.
They also found that native herbivores, once thought to have little effect on exotic plants, are far more effective in reducing their number. They decreased the relative abundance of exotics by 28 percent and the absolute abundance by 15 percent.