[Alex Linder]

[same WW article]

"officials think an angler, determined to pull something big out of Yellowstone Lake, a decade or more ago tossed in some non-native lake trout. Unfortunately, those voracious eaters now threaten the lake's native, and much smaller, Yellowstone cutthroat population. As for tamarisk, it came along in the 1800s with settlers who wanted more trees for fuel and shelter. Russian olive trees, meanwhile, arrived in the West as an ornamental. ...

Purple loosestrife, a colorful wetlands perennial that reached New England from Europe in the early 1800s as an ornamental, is blamed for overrunning both native vegetation and open water habitat. On rangelands, leafy spurge, another Eurasian native, is thought capable of cutting the productivity of grazing lands by three-quarters as it displaces native grasses.

You can find exotics overhead, too, in the shape of English sparrows and starlings that are booming in numbers. They live year-round in Wyoming and are hard on native bird species that migrate back and forth with the seasons becase they take over the prime nesting spots.

"Starlings and English sparrows are very aggressive, by comparison, to a lot of native birds," says Rothwell. "So even if a (native) bird does get a foothold, the starlings and English sparrows will hassle them until they leave and then take over."