Invasive and Exotic Species
Since early colonization of North America, new species have been introduced at an ever increasing rate. These species have arrived through a variety of pathways, including through the ballast of ships, in the packing material of imported goods, and through deliberate import for various uses. While most of these introduced species are beneficial or benign, about 15% become invasive.
An invasive species:
shows a tremendous capacity for reproduction and distribution throughout its new home; and,
also has a negative impact on environmental, economic, or public welfare priorities.
Many introduced species do not show a propensity to become invasive for several generations; so species we once thought were beneficial, such as grass carp, European starlings, mute swans, and nutria have demonstrated the characteristics of invasiveness long after their original introduction. These and other species are proving difficult to control in their competition against native species for food, shelter, water, or other resources and their impacts on economic interests and human welfare. Without the disease and predators that they contend with in their native lands, the spread of these species can be epic in proportion and the effort to control them can reach billions of dollars. The U.S. Fish and Wildlife Service estimates a potential economic impact of $5 billion in the Great Lakes attributed to impacts of the zebra mussel and attempts to mitigate those impacts. Zebra mussels have virtually eliminated native mussels from the Great Lakes and altered the basic food chain, threatening the availability of microscopic food for native fish.
What do we mean by native species? Generally, we mean species of plants and animals that have evolved in the Chesapeake Bay watershed and have developed mutually-sustaining relationships to each other over geologic time. Certainly, some native species can become invasive when habitat is altered and their particular needs are met on a much broader scale.
When ecologists talk about the impact of introduced species on native species and habitats, they mean that the introduced species is reproducing and distributing itself so efficiently that it is out competing native species' use of the same habitats. Nature is in a very delicate balance, much altered by humans, and the protection of remaining natural interactions between native species and their habitats are responsibility of local, state, and federal agencies and all citizens.
With their highly efficient reproduction and use of new habitats, introduced invasive species can and have quickly eliminated native species from the landscape. In fact, over 45% of species federally listed as endangered, rare, or threatened are being impacted by introduced species in the United States. On Pacific Rim islands, Madagascar off the coast of Africa, Australia, and Puerto Rico, introduced species are wreaking havoc on native species and severely altering their habitats.
Introduced invasive species can include creatures such as viruses as well as large mammals and everything in between, including amphibians, reptiles, birds, insects, plants, fish, shellfish, even jelly fish. In Maryland, one of our primary concerns is the impacts of invasive plants on habitats that support rare, native plants and plant communities. These communities include shale barrens, vernal pools, and peat bogs.
We are also concerned about:
mute swans (Cygnus olor)
nutria (Myocaster coypus)
zebra mussels (Dreissena polymorpha)
water chestnut (Trapa patens)
phragmites (Phragmites australis)
purple loosestrife (Lythrum salicaria)
wavyleaf basketgrass (Oplismenus hirtellus ssp. undulatifolius)
Also, included among species of concern are over 200 introduced species that have viable, wild populations in the Chesapeake Bay watershed, recorded by the Smithsonian Environmental Research Center.
Purple Loosestrife is Invading Our Wetlands
Can You Help Us Find It
and Remove It?
All of us can help to preserve and enhance opportunities for native species to continue to thrive in Maryland and beyond.
Find out what you can do to help
stop the spread of invasive species.
What YOU Can do to Help
Federal, Regional and State Support for Invasive Species Management
Economic Threats Posed by
Read the Report
The Effect of Nutria (myocastor coypus) on Marsh Loss in the Lower Eastern Shore of Maryland: An Exclosure Study
Mute Swans’ Impact on Submerged Aquatic Vegetation in Chesapeake Bay
Journal of Wildlife Management 2007
Predictive Modeling for Submerged Aquatic Vegetation (SAV) Decline Due to Mute Swans in the Chesapeake Bay
Proceedings of the 20th Trumpeter Swan Society Conference 2005
Mute Swan Population Dynamics
Using a stochastic model to examine the ecological, economic and ethical consequences of population control in a charismatic invasive species: mute swans in North America.
Journal of Applied Ecology 2007
Maryland's Mute Swan Management Plan - April 2003
Purple Loosestrife is Invading Our Wetlands
Can You Help Us Find It and Remove It?
A comprehensive list of invasive species (animals, plants, insects and diseases) in managed and natural aquatic and terrestrial habitats in Maryland, compiled by the Maryland Invasive Species Council. This list changes as conditions and knowledge change.
Fisheries Invasive Species - Technical Memo No. 20
For Information, contact:
Associate Director, Habitat Conservation
Wildlife & Heritage Service
Maryland Dept. of Natural Resources
580 Taylor Ave., E-1
Annapolis, MD 21401
Toll-free in Maryland:
1-877-620-8DNR, Ext. 8539
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