Introduction of non native plant and animal species often cause problems for the native populations. For plants, exotic species often become invasive and destroy habitats by out competing through crowding and superior recruitment. In successive generations the introduced species will dominant the landscape, species which may have inferior foraging and nesting characteristics. Also, the introduced species will not have the specific attributes that facilitate pollination, attributes that the native species have adapted in conjunction with their native pollinators over time.
Introduction of non native animal species can have a detrimental effect in the form of direct foraging competition, competition for nesting sites, and also the possibility that the introduced species may become predator of the native population.
Case Study: Alliara petiolata, the plant that is a double threat to The West Virginia white Butterfly.
The West Virginia white butterfly has a specific link with a native plant species from the mustard family known as “toothwort”. This plant is the only host species for the caterpillar and has recently come under threat by an introduced invasive known as garlic mustard (Alliaria petiolata). Once introduced to an area, garlic mustard out competes native plants by aggressively monopolizing light, moisture, nutrients, soil, and space. In some areas the garlic mustard has totally out competed the toothwort to the level of extirpation.
In addition to the fact that this plant is invasive, there are other physical properties of the plant that make it a much bigger threat .The garlic mustard also contains a chemical which has a toxic effect on the West Virginia white butterfly’s eggs, causing death.
The garlic mustard plant has also effected other native spring wildflowers like spring beauty (Claytonia virginica), wild ginger (Asarum canadense), bloodroot (Sanguinaria canadensis), and trilliums (Trillium species). Two other native butterfly species, the falcate orange-tip (Anthocharis midea annicka) and the mustard white butterfly (Pieris oleracea), are also at risk when garlic mustard replaces their host plants.