Alien invaders aren’t as tough as we once thought, according to a new study by U of T’s Dr. Anurag Agrawal in the Aug 2003 issue of Ecology Letters.

Over the past few centuries every corner of the planet has become interconnected due to increased trade and travel. This has allowed the migration of many plants and animals into new environments on a large scale. New species are referred to as “alien,” and “invasive” if they become successful in their new environment.

“Only a very small fraction, maybe one per cent of alien species become successful,” said Dr. Agrawal, a professor of botany. Sometimes these new species can be beneficial in their new environment. “Certain alien species have uses, for example garlic mustard was imported from Europe as a spice,” said Dr. Agrawal. More often however, new species can bring problems. “The major problem with invasive species is that they devastate native biodiversity and can become weeds.” Purple loosestrife for example has overgrown Canadian wetlands.

Until recently the common belief was that alien species become successful in new environments because their natural enemies, predators, parasites, and diseases, aren’t present. “This is the current dogma with ecologists,” said Dr. Agrawal. “The problem is that very few rigorous studies have been conducted to test this hypothesis.”

So he set out with UTM’s Dr. Peter Kotanen to test it himself at the Koffler Scientific Reserve, U of T’s field station near Newmarket, Ont. They planted seeds from 30 different species of plants in 15 pairs. Each pair contained one species native to Ontario, and one closely related alien species. They then exposed all the plants to native insects to feed on the plants. The bulk of the experiments showed that the alien plants were preyed upon just as much, if not more than, native plants.

Now Dr. Agrawal is trying to figure out why. He is currently testing all aspects of ecological interactions, such as attacks by fungi and viruses on the plants’ roots and leaves. See his research at www.herbivory.com.