California Invasive Species

Ecological impacts

Biological species invasions alter ecological systems in a multitude of ways. Worldwide an estimated 80% of endangered species could suffer losses due to competition with or predation by invasive species.^[28] Pimentel also reports that introduced species, such as corn, wheat, rice, and other food crops, and cattle, poultry, and other livestock, now provide more than 98% of the U.S. food system at a value of approximately $800 billion per year."^[28] As highly adaptable and generalized species are introduced to environments already impacted by human activities, some native species may be put at a disadvantage to survive while other species survival is enhanced.

Genetic pollution

Purebred naturally evolved region specific wild species can be threatened with extinction in a big way through the process of Genetic Pollution i.e. uncontrolled hybridization, introgression and Genetic swamping which leads to homogenization or replacement of local genotypes as a result of either a numerical and/or fitness advantage of introduced plant or animal^[35]. Nonnative species can bring about a form of extinction of native plants and animals by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially detrimental for rare species coming into contact with more abundant ones where the abundant ones can interbreed with them swamping the entire rarer gene pool creating hybrids thus driving the entire original purebred native stock to complete extinction. Attention has to be focused on the extent of this under appreciated problem that is not always apparent from morphological (outward appearance) observations alone. Some degree of gene flow may be a normal, evolutionarily constructive process, and all constellations of genes and genotypes cannot be preserved however, hybridization with or without introgression may, nevertheless, threaten a rare species' existence^.

Health impacts

An increasing threat of exotic diseases exists due to increased transportation and encroachment of humans into previously remote ecosystems that can lead to new associations between a disease and a human host (e.g., AIDS virus in human host. Introduced birds (e.g. pigeons), rodents and insects (e.g. mosquitoes, fleas, lice and tsetse fly) can serve as vectors and reservoirs of human diseases. Throughout recorded history epidemics of human diseases such as malaria, yellow fever, typhus, and plague have been associated with these vectors. A recent example of an introduced disease is the spread of the West Nile virus across North America resulting in human deaths and in the deaths of many birds, mammals, and reptiles.  Waterborne disease agents, such as Cholera bacteria (Vibrio cholerae), and causative agents of harmful algal blooms are often transported via ballast water. The full range of impacts of invasive species and their control goes beyond immediate effects and can have long term public health implications. For instance, pesticides applied to treat a particular pest species could pollute soil and surface water.

Source http://en.wikipedia.org/wiki/Invasive_species All of the above text is available under the terms of the GNU Free Documentation License

^{Of course many of the invasive species in the Bay Area are not listed online due to the forces of political correctness, you can learn more about some invasive species in California by visiting the California Invasive Plant Council at http://www.cal-ipc.org/}