�@Ecologists have traditionally warned us that global trade and increasing travel have resulted in the movement of various species to new geographical areas. These ecologists say that many transplanted species fail to take hold and therefore die off. Other species, however, not only survive but even thrive in their new environments, becoming invasive and leading to the extinction of native species.

�AWhen the Panama Canal was being planned in the late nineteenth century, scientists were not even aware of the potential peril of species invasions, so there were no concerns about the linking of the Rio Chagres and Rio Grande rivers, which had formerly been separated by the Continental Divide. With the canal’s completion in 1914, freshwater fish spices from both rivers were able to mingle freely in each other’s waters.

�BResearcher Dr. Scott A. Smith recently set out to see how the ecological communities of each river had been affected. He found that several species from the Rio Chagres had successfully established themselves in the Rio Grande, and species from the Rio Grande had populated sections of the Rio Chagres. What was surprising and encouraging, though, was that none of the original species in either river had become extinct. Instead, each ecosystem had coped with the invasions and become, in a real sense, even richer, with an increased number of species.

�C”Traditional ecological theory would predict that such colonization events would result in the extinction of local species,” Smith says. Established theory sees every species as filling a niche, or role，in its environment. Proponents of this theory believe that each ecosystem is saturated, meaning that all niches are filled. In these so-called “niche-model communities,” invasive species either die out or drive out existing species.

�DSmith believes his findings show that some invasive species do neither of these things. Most species are not tightly adapted to a particular niche, and new species can often find a role to play in the new ecosystem. “When invasions do occur,” Smith says, “that should increase species richness.”

�EEven though species invasions are now progressing at a more rapid pace due to human interference, they have occurred since the beginning of time and will continue to do so. At the least, these new findings should make us hesitate to assume that spices introduced to a new environment necessarily lead to ecological disaster. The environment may be more flexible than we have been led to believe.