Invasive Plants and AnimalsEssential Knowledge for Naturalists
No, we are not prejudiced agaist plants and animals of foreign origin. We are however, wary of human-caused damage that results from bringing certain non-native organisms into an ecosytem that is not adapted to handle the impact of that species. These species, known as invasive species, can cause untold ecological harm if allowed to dominate in an ecosystem where they have no natural enemies.
Invasive animals, such as the zebra mussel, cause widespread ecological and economic problems. This mussel, the size of your finger-tip, is native to the Caspian Sea. Discovered in the Great lakes in 1988, this pest has spread to all of the Great Lakes. The mussel is eaten by some waterfowl, and the freshwater drum, but not in enough quantity to control its proliferation. Formerly sandy beaches on the Lake Erie Islands are now covered with the shells of dead zebra mussels.
The zebra mussel is a filter-feeder that takes naturally occuring levels of algae and other suspended items out of the water, thereby allowing sunlight further penetration into the weater, which in turn can cause harmful algal blooms. These algal blooms threaten drinking water supplies. Perhaps worse, when the algae die, they decompose, which uses oxygen from the water. This may be a leading cause, along with increased phosphates, for the "dead-zone," an oxygen deprived portion of Lake Erie where nothing can live.
Another invasive animal species is the Gypsy Moth. This winged invader was brought to the U.S. in the mid-to-late 1800's in an ill-fated attempt to bring the silk production trade to the country. The caterpillars of this species attack oak and other broad-leaved trees. Defoliated trees can survive, but if other stressors such as drought, other insects, or repeated defoliations his, tree mortality results. In Ohio, infestation of gyspsy moths has resulted in oak forests transitioning to beach-maple-tulip forests in some areas.
Invasive PlantsPerhaps 25% of the plant species known in Ohio are introduced from other regions of the world. Most of these cause no problems. they fill niches in plant communities without domininating. These do not cause widespread, apparent harm to the environment. However, a small contingent of introduced plants are able to out-compete the native plants in Ohio. These non-native invasvie species have several characteristics in comon.
Invasive plants create seeds or propagules prolifically. They grow fast. Their seeds stay viable in the seedbank for a long time. They do not have natural enemies in the new ecosystem. An interesting factor that can create an invasive plant where a non-native previously existed. If a generally harmless non-native plant is not palatable to the herbivores of an ecoregion, but its competitors are, at high herbivore populations, the non-native plant may become invasive and spread rapidly. In effect, the herbivores, such as deer, reduce competition by weeding the natives out in favor of the non-native.