pecies in an established ecosystem have evolved to interact and be interdependent.
But what happens when a species somehow ends up somewhere different than its native
ecosystem? Its interactions can have damaging impacts on native species and on the
ecosystem as a whole.
An invasive species is any species that is introduced to a new ecosystem and causes
harm in that ecosystem. There are several ways in which an invasive species can
damage ecosystems. For example, its population size might grow rapidly due to a
lack of predators. It might outcompete existing species for ecosystem resources,
such as water, space, and food. It might disrupt food webs. It might prey on native
species or introduce diseases. It also might keep native species from successfully
reproducing. Native species can become endangered or threatened due to invasive
species. In some cases, they can be driven to extinction.
Many aquatic ecosystems have been affected by invasive species. Zebra mussels are
an example of an aquatic species that has become invasive in many places throughout
the United States. These species are native to Eastern Europe. They were carried to
the United States in ballast water—water that is carried in a ship to help it stay
balanced. In the 1980s they entered the Great Lakes ecosystems. Since then they
have spread to many states. Zebra mussels cause major damage to ecosystems. They
are filter feeders that eat plankton, an important food source for native species.
They create conditions that encourage the growth of harmful algae. They clog
waterways and pipes. And once they become a part of an ecosystem, they are
impossible to remove.
Several species of carp are called Asian carp. These species are also causing major
problems for ecosystems in the United States. These fish have no predators in US
aquatic ecosystems. They can grow up to 100 pounds in size. They upset food webs by
eating a huge amount of plankton, which then cannot be used by the native species.
These fish were originally brought to Arkansas to clean the ponds used in fish
farms. Flooding caused some of the carp to enter wild ecosystems, and now they are
found in a vast number of US waterways.
impassible for boats.
Invasive species are spread in a variety of ways. Most of these involve human
activity. In some cases, like that of water hyacinth, a species was intentionally
brought to new ecosystems because people liked the way it looks. Asian carp were
intentionally brought to the United States, but escaped their intended area. And,
as in the case of zebra mussels, species can move from one place to another in
ships’ ballast water. Canals constructed to connect waterways also allow species to
move into new habitats. Some land species are transported in wood products such as
firewood or shipping containers. People also introduce new species into ecosystems
when they release pets into their local ecosystem or when they plant nonnative
species in their gardens.
Eliminating species that have become a part of an ecosystem is often difficult.
Sometimes it is impossible. One key to controlling invasive species is to prevent
them in the first place. There are many steps that people can take to prevent
invasive species. These include not moving water or wood from one place to another,
cleaning boats and other equipment before moving to a different waterway, planting
only native species, and never releasing unwanted pets into the wild.
