Invasive Non-Native Species
Healthy native ecosystems are dynamic and ever-changing, but their changes occur within a range of natural variability (see the Agents of Watershed Change module). When is the `balance of nature' tipped too far? Some kinds of non-native plants and animals can cause havoc when, accidentally or intentionally, they are released outside their normal range into a new region (see the Sources of Invasive Species Release). The Gypsy Moth, Nutria, Zebra Mussel, Hydrilla, Sea Lamprey and Kudzu are examples of non-natives that have caused massive economic and ecological losses in new locations because the natural controls of their native ecosystems were not there.
Not all non-native species become pests, or even survive, in new locations (see the Ten Percent Rule). But when they do, they often displace a whole suite of native species to become dominant. They then take on new labels: invasive exotics, or non-native nuisance species, or simply, invasive species (see Definition). Their impacts are insidious (see Traits of Invasive Species) because they often invade the open space areas we have preserved for native flora and fauna, as well as farmlands, forests and suburbs. How big is the problem? Consider the following:
Damages from invasive species, including only those damages that can be expressed in monetary terms, have been estimated as high as $ 138 billion per year. These damages affect agriculture, rangeland, forests, people's homes and yards, human and animal health, food supplies, fishing and boating, outdoor recreation, and many other areas;
Invasive species are thought to have been involved in 70% of this century's extinctions of native aquatic species, and 42% of current endangered species are impacted significantly by invasive species;
In January 2003 the Director of the US Fish and Wildlife Service called invasive species "the biggest environmental threat to this country... it's something everyone needs to take very, very seriously."
It is increasingly important that watershed managers become aware of invasive species in their watersheds, in both the aquatic and terrestrial environments. Aquatic invaders are clearly of concern to a water resources manager, but invasive species in the watershed can have significant effects on water quality and aquatic ecosystem health due to the ways they affect bank stability and the volume and pollution levels in runoff (see Terrestrial Invasive Species that affect Water Quality). Below are recommended types of watershed management-related invasive species information needs, paired with links to the Aquatic Nuisance Species Task Force Web site and other web sites:
[The links below are to federal government sites including those of EPA and other agencies.]
A nationwide database with names and ranges of invasive species that may be in your watershed
Government Efforts at Control