Historically, human actions have been inconsequential on the forces of nature, however, humans are now influencing the processes of the planet. The water bodies of Canada and the world are being invaded by non-native or exotic species. An exotic species is any species intentionally or accidentally transported and released by man into an environment outside its present range. These plant and animal species are considered to be among the most severe agents of habitat alteration and degradation, and they are a major cause of the continuing loss of biological diversity throughout the world.
Not all aquatic species that are introduced into new environments are successful; in fact, ecologists predict that most will fail and those that manage to survive will fail to establish reproducing colonies. An ecosystem's resistence to exotic species depends on competition between them and native species for food and habitat. The greater the diversity in an ecosystem, the more competitors an exotic species will encounter, thereby decreasing its chances of becoming established.