Transcript Document
Management of Exotic Species Sometimes, the introduction of a species to a new area has proven to be very beneficial. Often, however, these introduced organisms have become tremendous pests causing great damage. Four factors are primarily responsible for determining whether an introduced species will become established: 1. The suitability of the new habitat. 2. The adequacy of the introductory unit. 3. The degree of escape from diseases, parasties, and predators. 4. The competitive regime of the new environment. A suitable habitat and niche: Depends partly on abiotic conditons. Also involves biotic factors such as appropriate vegetation and the absence or presence of certain species. The Hutchinsonian niche: Many introduced species that have done well in North and South America have taken well to agricultural and urban conditions that were created with human civilization: European starling House sparrow Ring-necked pheasant The cattle egret was introduced from West Africa. Adequacy of Introductory Unit The introduced individuals must be capable of successfully starting a population. This implies that they must be healthy, of reproductive age, and sufficient in number to breed successfully. Attempts to reintroduce the red wolf in areas of North Carolina have suffered from the wolves’ inability to resist certain diseases. Certain types of plants (“weed species”) are well adapted to invading new habitats. In vertebrates, it is often important that the group be able to establish or fit into a social group. A whooping crane population could not be established at Gray’s Lake National Wildlife Refuge in Idaho because the young cranes had no established social structure to join. Often, when an organism is introduced into a new area, it finds itself free from “counteradaptive measures”. Brush-tailed possum European rabbit Rabbits at waterhole. Escape from Competitors Under some circumstances, an invading species may find itself in a situation or a niche where it has little competition. Invading species seem to do best when invading systems with few species. This is probably a function of reduced competition. This may explain why exotic species often do well on islands, or in places like Florida that have relatively few native species. Mechanisms of Introduction Some are deliberate: a. Livestock. b. Pets c. Predators imported for control d. Crop plants. Some are accidental: a. Seeds mixed with crop seeds. b. Animals carried with plant hosts. c. Animals carried accidentally on ships. What is the impact? Since urban and agricultural areas are particularly susceptible to invasion by exotics, human interests are often directly impacted. The impact of exotics in natural systems often depends on their ecological distinctiveness and their potential for competitive displacement, disease transmission or genetic swamping. Ecological distinctiveness – successful invaders are often quite different in some way from native species. This results in the absence of counteradaptation. This can lead to a species becoming a keystone exotic, one which can lead to an almost complete reorganization of the system. Kudzu Japanese honeysuckle Melaleuca “Mimosa tree” – Albizia sp. Introduced livestock have had a major effect on plant communities in many areas: Hydrilla Water hyacinth Exotic species have also played a major role in restructuring aquatic habitats. Sea lamprey Peacock bass Olympic National Park Dealing with Detrimental Exotics: 1. Prevent them from entering. 2. Control of spread. 3. Protection of pristine areas. 4. Local eradication. 5. Protection of individuals of critically reduced species. 6. General population reduction. 7. Biological control.