Consumers and Invasive Species
Consumers are organisms (animals, bacteria, fungi) that receive energy by consuming other organisms through predation, parasitization and/or degredation, Consumers that alter the ecosystem are not
limited by resource utilization requirements of producers. By destroying biomass, consumers create an
ecosystem disturbance that can later be exploited by another producer, often
times allowing an invasive species to become established. Examples of non-indigenous consumers
affecting the ecosystem include plant pathogens and animals occupying a new
habitat with few predators (Ecology of Biological Invasions of North America and Hawaii 1984).
The American chestnut (Castanea dentata) at one time composed almost forty percent of the forests of southern
Appalachia. Beginning in the 1920’s, the fungal parasite, chestnut blight
(Cryphonectria parasitica), invaded and destroyed most of the American chestnut
trees by causing a typical canker, with splitting of bark in the process. The fungus is thought to have been accidentally introduced to North America on imported Japanese nursery stock. Since then the ecosystem has changed; after
successional changes, the chestnut-oak forests became an oak complex and later
a hickory-oak forest for a short-term effect (McCormick 1980).
Dutch elm disease, first reported in the U.S. in
1928, is caused by an elm bark beetle, Scolytus multistriatus, depositing the fungus, Ophiostoma
ulmi, when it lays eggs. Over the next forty years, the disease spread
from New England to most of the U.S. and affected the forest ecosystem by
destroying 75% of the 77 million trees (NY Times, 1989).
Rooting by feral pigs (originally introduced from Eurasia as a wild game species) at higher elevations of the
Great Smokey Mountain National Park has altered the soil characteristics such
as causing thinner forest floors, mixed organic and mineral soil horizons, and
an increase in bare ground. As a result,
there are large concentrations of nitrogen and potassium in the soil, and
nitrogen in the streams (Ecology
of Biological Invasions of North America and Hawaii 1984).
The forestry
industry loses about $2 billion of forestry products annually due to
non-indigenous insects (Pimental 2000). The
gypsy moth (Lymantria dispar dispar),
imported to start a silkworm industry, escaped and has caused great ecological
and economical damage to the American forests.
Moth larva feed on tree foliage, especially leaves of oaks and birches.
Another consumer
pathogen causing ecologic and economic damage to oak forests in California and
Oregon is the fungus, Phytophthora ramorum, which causes sudden oak death. The disease is spreading rapidly to other
parts of the country where it will destroy dominant tree species and alter the
ecosystem (Chornesky).
Black zone lines of P. ramorum Death of an oak stand from P. ramorum
Changes to the ecosystem by invasive species acting as consumers alter the keystone and/or dominant species which in turn alters the ecosystem's flora and fauna.
References
1. Chornesky, Elizabeth A. et al.
(2005). Science Priorities for Reducing the Threat of Invasive Species to
Sustainable Forestry. Bioscience. Vol
55:335-348.
2. Ecology of Biological Invasions of North America and Hawaii. (1984).
Springer-Verlag: New York. p 163-173.
3. McCormick, J. Frank, Platt, Robert B. (1980). Recovery of an Appalachian Forest Following the Chestnut Blight or Catherine Keever-You Were Right!. American Midland Naturalist. Vol104:264-273.
4. New York Times (12-5-89). [Web]. New Varieties of Elm Raise Hope of Rebirth for Devastated Tree.
5. Pimentel, David et al. (2000). Environmental and Economic Costs of Nonindigenous Species in the United States. BioScience. Vol. 50. No. 1:53-65.
No comments:
Post a Comment