Invasive species not more troublesome than in home ranges

Many birders chafe at any species labeled "invasive" or nonnative. We point to House Sparrows or kudzu (below) as species that compete with natives, often to the detriment of the latter. We often think of the invasives as out-of-control marauders that run rampant after finding new territories to exploit.


A recent worldwide study organized by Stan Harpole, assistant professor of ecology, evolution and organismal biology at Iowa State University, found somewhat mollifying results:

"There is this assumption that when plants invade a new area that they become much more abundant in the new area than they were in the native areas," said Harpole. "It turns out that, on average, they aren't any more abundant away from home than they are at home."

The 70 researchers at 65 sites around the globe found that a "rule of 10s" can apply to invasive species, Harpole said.

"Of, say, 100 plants that arrive in a new area, only about 10 percent of those will survive without being in a greenhouse or some other controlled area," he said. "Of those 10 that can survive, only about 10 percent of those really cause problems.

"When you think about all the species we've brought over from other areas, relatively few have become serious pest species. The problem is we've brought over so many that quite a few have become major problems and they get a lot of attention."