Connecticut Water Trails Association
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Connecticut Water Trails Association |
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Connecticut Water Trails Program
Connecticut Invasive Species
What Is A Native Species?
All organisms are native to planet Earth (until
further notice) and each species of bacteria, fungi, plant, animal, and
other creature has a home somewhere on this planet where it has existed
and evolved for thousands of years. A
native or indigenous
species is one that occurs in a particular place without the help of
humans, which is not always easy to determine. Species native to North
America are generally recognized as those occurring on the continent
prior to European settlement.
An organism’s home, or native range, is determined
by a host of influences such as climate, geology, soils, hydrology,
biological interactions, and natural dispersal. Living things disperse
within their native ranges by moving around on their own or with the
help of air, water, wind, and other animals. However, beginning with
Columbus’ discovery of America in the 15th century, people
have played an increasingly significant role in moving plants, animals
and other organisms around the world, to places far beyond their likely
natural dispersal ranges. And this is where the trouble lies!
What’s An Exotic
Species?
An organism is considered
exotic (alien,
foreign, non- indigenous, non-native) when it has been introduced by
humans to a location(s) outside its native or natural range. This
designation applies to a species introduced from another continent,
another ecosystem, and even another habitat within an ecosystem.
For example, black locust (Robinia
pseudoacacia), a tree that is native to the southern Appalachian
region and portions of Indiana, Illinois and Missouri, was planted
throughout the U.S. for living fences, erosion control, and other uses
for many years. Black locust is considered exotic outside its natural
native range because it got to these new places by human introduction
rather than by natural dispersal. Another example is saltmarsh cordgrass
(Spartina alterniflora), a
wetland plant that is native to eastern North American estuaries.
Saltmarsh cordgrass was introduced intentionally to western North
American shoreline habitats, where it did not occur previously. Sadly,
it has become established and is now considered a serious invasive
species, displacing native species and adversely impacting wetland
communities and several endangered native bird and plant species.
European settlers brought hundreds of plants to
North America from their home lands for use as food and medicine, and
for ornamental, sentimental, and other purposes. Introductions of exotic
plants continue today and are increasing due to a large and
ever-expanding human population, increased international travel and
trade, and other factors.
Once An
Exotic, Always An Exotic!
An estimated 3,500 species of exotic plants
have escaped cultivation in the U.S., are able to reproduce in the wild,
and have become established, or “naturalized”. These plants, however
much a part of our current landscapes and ecosystems, are nonetheless
exotic, since they were moved here by people. For centuries,
horticulturists have imported and disseminated interesting new exotic
plants. Unfortunately, many of these have become invasive pests that are
having serious impacts to native species and ecosystems.
What Makes An Exotic
Species Invasive? (When Is A Guest A Pest?)
Many non-native species exist in apparent harmony in
environments where they were introduced. For example, a relatively small
number of exotic plants (e.g., corn, wheat, rice, oats) form the basis
of our agricultural industry and pose little to no known threat to our
natural ecosystems. The most important aspect of an alien plant is how
it responds to a new environment. An
invasive species is
one that spreads and establishes over large areas, and persists.
Invasiveness may be characterized and enhanced by robust vegetative
growth, high reproductive rate, abundant seed production, high seed
germination rate, and longevity. Some native plants exhibit invasive
tendencies in certain situations.
It may come as a surprise to many that certain animals, such as the domestic cat, are considered to be invasive species. The domestic cat, native to northeast Africa, was introduced from Egypt to countries worldwide thousands of years ago. Although it is often a much loved house pet, the domestic cat is also an avid hunter that is very detrimental to native wildlife.
The domestic cat is an invasive species so common that it inhabits all but a few islands worldwide. The domestic cat was first introduced to non-native areas of the world to control rodent populations. To this day, the cat is still beneficial in keeping other invasive species under control, as well as an important companion for many people. However, the domestic cat is capable of spreading disease to wildlife and humans, and it is responsible for the extinction of many species of birds, which is why it is now considered an invasive species.
While the domestic cat arguably provides some
benefits for humans and helps to control other invasive species
populations, many other invasive species only cause harm or destruction
to the ecosystem into which they are introduced.
How Many Invasive Species Are There
According to the Plant Conservation Alliance’s Alien Plant Working Group, about 1,050 plant species have been reported as being invasive in natural areas in the United States. This represents an astonishing one-third or so of the exotic plant species established and self-reproducing in the wild. Currently there is no exact count of how many invasive animal species are present in the United States.
It is estimated that half of all the species
on the endangered species list - 57% of animals and 39% of plants - are
declining at least in part due to invasive species. Invasive species
cost the United States an estimated 128 billion US dollars (USD)
annually and 400 billion USD worldwide due to economic losses such as
damage to crops. Much of this money is also spent on the prevention of
invasions, education about the consequences of invasive species and
control measures.
How Bad Are Invasive
Species?
Invasive species impact
native plants, animals, and natural ecosystems by: Reducing native biological diversity Altering hydrologic conditions & flooding regimes Altering soil characteristics Altering fire intensity and frequency Interfering with natural succession Competing for native pollinators Repelling or poisoning native insects Displacing rare plant or animal species Increasing predation on native birds Serving as reservoirs of plant pathogens Replacing complex communities with monocultures
Diluting the genetic composition of native species through hybridization
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