Alien Nation

Some ecologists are saying that not all alien species are bad and that some fit into ecosystems just fine. They believe that efforts to rid ecosystems of all exotics are impractical. Michael Rosenzweig, a professor of evolutionary biology at the University of Arizona, says, "You can't roll back the clock and remove all exotics or fix habitats." He argues that alien species don't actually reduce biodiversity. Daniel Simberloff, a professor of ecology and evolutionary biology at the University of Tennessee, says only a small percentage of alien species cause problems in their new habitats.