Invasive Species

Concepts:
Environmental stability
Species Interactions

Objectives:
Students will be able to recognize the harm caused by invasive species in an area as well as explain how they alter the environment.

Background:
Invasive species are ones that are not native to an area.  These species can be introduced into an environment in several different ways.  Many species are introduced into an area by people.  When they move to a new and unfamiliar area, many people bring the plants and animals that were familiar in their previous home.  Some of these species are brought for agricultural reasons, others as pets which later escape, others are simply brought and released to make the environment feel more familiar. Other species come to an area as hitch hikers with humans.  As people started to travel and explore new lands, animals were brought along accidentally in cargo ships or planes.  The third way that animals are introduced to a new environment is through migration, whether intentional or not.  Animals may move to a new area to find food, or seeds may be carried by storms and deposited in a new habitat. 

However these species arrive in their new environment, they can often be detrimental to the health of this new habitat.  These species have evolved and developed survival techniques separate from the environment that they are now inhabiting.  Because the native species of this area have not had the opportunity to evolve with the species, they have not developed efficient defense against these new predators or competitors.  These new predators then are either able to hunt and diminish the population of their prey or they are able to out compete native species for food and other resources. Plants can out compete native plants by taking up more space, water, and soil nutrients, thus choking out any other species.  The plants also do not fill the niche of the previous plants, such as providing food or shelter for animals, causing even more problems for the ecosystem.  These species also have no natural predators because no predators have evolved along side them, learning to eat them. 

For these reasons, invasive species, if successful in a new habitat, can cause many problems and can damage the habitat and the delicate balance of the animals living there. 

There are several plant and animal species that have been introduced and have been causing problems in Arizona.  Conservation International believes that about 60% of the Sonoran Desert may be covered by invasive species rather than native plants (Phillips 2000).  Three-hundred eighty species of introduced species cover about 1,400,000 acres of this desert (Phillips 2000).  Following is a list of a few and their consequences:

Bullfrog
Crayfish
Fountaingrass
Buffelgrass

Other invasive species in the Sonoran Desert:
(list compiled from Phillips, 2000)

African lehmann lovegrass (Eragrostis lehmanniana)
Sahara or Moroccan mustard (Brassica tourneforti)
London rocket (Sisymbrium irio)
Pigweed (Amaranthus spp.)
Summer spurges (Euphorbia hyssopifolia)
Devil's claw (Proboscidea spp.)
Salt bushes (Altriplex spp.)
Russian thistle (Salsola tragus or Salsola kali)
Filaree (Erodium cicutarium)
Lehmann's lovegrass (Eragrostis lehmannii)
Mouse barley (Hordeum murinum)
Red brome (Bromus rubens)
Wild oats (Avena fatua)
Arabian grass (Schismus arabicus)
Mediterranean grass (Schismus barbatus)
Natal grass (Rhynchelytrum repens)

National Science Education Standards met by this lesson:
National Science Education Standards online: http://books.nap.edu/html/nses/html/index.html

Life Science (Content Standard C) grades 9-12
     Interdependence of Organisms:         
* Organisms both cooperate and compete in ecosystems.  The interrelationships and interdependences of these organisms may generate ecosystems that are stable for hundreds or thousands of years
     Biological Evolution:
*Species evolve over time.  Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, . . . (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.

Benchmarks for Scientific Literacy met by this lesson:

Common Themes: 
      11A Systems:  grades 9-12
*The successful operation of a designed system usually involves feedback.  The feedback of output from some parts of a system to input for other parts can be used to encourage what is going on in a system, discourage it, or reduce its discrepancy from some desired value.  The stability of a system can be greater when it includes appropriate feedback mechanisms.

Sources:
Alien Invaders: Invasive Species and the Threat to the Environment. Prod. Cambridge     Educational. Videocassette. Cleveland High School and Portland Art Museum Northwest Film Center, 1999.

Laycock, George. The Alien Animals.  New York: Natural History Press, 1996. 

National Resource Council. (1996). National Science Education Standards. Washinton DC: National Academy Press.

Phillips, Steven J. and Patricia Wentworth Comus. A Natural History of the Sonoran Desert. Arizona-Sonora Desert Museum Press: Tucson, 2000. 

Project 2061: American Association for the Advancement of Science. (1993) Benchmarks for Science Literacy. New York: Oxford University Press.

Invasive species websites:

Arizona Native Plant Society:   
     http://www.aznps.org/html/exotics.html

Environmental Protection Agency 
     OWOW Invasive Species Program --  
       http://www.epa.gov/owow/invasive_species/

US Fish and Wildlife Services:
      http://invasives.fws.gov/

United States Geologic Survey: 
        http://www.werc.usgs.gov/invasivespecies
        http://www.werc.usgs.gov/invasivespecies/sonorangrassfire.html 

The Problem with Invasive Species by Elizabeth Weaver