The More the Merrier

“The more species in an area, the better”  is not always true.  It must be the correct species as balances within systems are very delicate.  Systems work best with native species, or those plant and animal species that occur naturally in a given area.  Each native species has acquired a set of specific  adaptations to ensure its survival in the given community.  When other species are introduced into the system, problems can occur.  Introduced species (also called exotic, nonnative, and alien) can destroy the habitat for existing species or out-compete against the native species.  If a native species is endemic, or only occurring in one area (the Nene goose of Hawaii, lemurs of Madagascar, and the Galapagos turtle of the Galapagos Islands are a few examples), the result can be extinction of a species.

How Species Get Introduced

             Accidental Travelers - As people travel across the state and around the world, they sometimes carry uninvited guests.  As boats crossed the Atlantic Ocean, zebra mussel larva were in the water filling the ships ballast tanks.  When the tanks were dumped  to take on cargo, the larva entered the Great Lakes.  Now the zebra mussels grow on top of native clams and kill them.  Norway rats rode ships to America in the holds.  These rats are now common in barns and are known to carry diseases to humans.  As people move horses and other livestock around the country, they take hay along for food.  Or times of drought in one part of the country can force buying hay from other parts of the country.  Many times this hay contained seeds from plants native to the area where the hay was cut, but not native to where the hay was going.  As the livestock ate the seeds with they hay, the undigested seeds were “planted”  when the animal when to the bathroom later in the fields.  California is one of several states that requires only certain hays which have been treated to make seeds infertile be allowed into the state.

            Reminders of “home”  - Some travelers are intentional.  As people moved to western states in the United States, the absence of large green plants was obvious.  People would water their lawns and bring plants from the east along with them.  Since the plants were not adapted to the low rainfall, extensive watering was/is needed to keep the plants alive.  This water use causes other hardships in  areas of low rainfall.  European starlings (birds) are another example.  In 1890, these birds were released into New York City’ s Central Park by people who thought it would be a good idea to stock the United States with all the different birds mentioned in Shakespeare’ s plays.  Now starlings are everywhere throughout the United States, competing with native bird species for food and nesting sites.

            Pest  Control - Balanced systems can become unbalanced allowing a species to become too abundant.  Sometimes a natural predator can be found, brought in, and released in hopes of controlling the out of control species.  Sometimes this works and other times the result is two out of control, out-competing species.  It is better to try to use native species when possible.

            Soil Erosion Control - Anyone visiting the southeast part of the United States will notice a large-leafed vine blanketing trees and fences along the roads.  Kudzu is a fast-growing vine that is native to Asia.  In the 1930’ s, is was planted to help  control soil erosion and to provide food for cattle.  Unfortunately, cattle did not like the plant and the only roots the plant had were at the beginning.  It did not put out roots along the vine and roots are what hold soil in place.  Kudzu did not accomplish any of the purposes it was brought over for but it sure liked the climate of the south and grew everywhere.  As it grows up over trees and carpets the crown, the large leaves shade the sun from the tree, eventually killing it.

            Feral Pets - Irresponsible pet owners also contribute to non-native species.  Dogs and cats which are not wanted or not prevented from reproducing revert to wilder ways and kill native species for food.  Some even mix with wild species for breeding and sleeping.  These habits disturb genetic diversity and encourage the spread of disease between wild animals and people.  Domestic cats let to run free in Hawaii killed the Nene goose which had no defense against the previously unknown predator.

Vocabulary

            domestic -  to train or adapt an animal or a plant to live in a human environment and be of use to human beings.

            endemic - an animal or plant species that naturally occurs in only one area.

            feral - domesticated animals that are now wild.

            introduced - an organism that has been brought into an area where it does not naturally occur.

            native - a species that occurs naturally in an area.

            wild - not tamed or domesticated, living in a basically free condition.

Fun Fact

Hawaii has more introduced plant species than endemic ones.

Other Resources

Local State Division of Wildlife

Local State Forest Service

Local Animal Control

Project WILD

ACTIVITY ONE