An ecosystem is localized group of interdependent organisms together
with the environment that they inhabit and depend on. The natural
world is in a constant state of flux. Changes can be seen at all
time-scales, from the shortest to the longest. Short-term changes,
which are observable by people, are often cyclical and predictable:
night and day, the monthly cycle of the tides, the annual change of
the seasons, and the growth, reproduction, and death of individuals.
Viewed at this level many ecosystems, when not disturbed by humans,
appear superficially to be stable and unchanging, maintained in
equilibrium by the “balance of nature”. The sun is the original source
of energy in an ecosystem. Producers (plants) convert the light energy
into chemical energy, storing it in their cells. When primary
consumers (herbivores) eat the producers, the energy changes into a
form that can be stored in animal cells. Secondary consumers
(carnivores) transform the energy once again. Decomposers may occupy
several positions in the pyramid, both receiving energy from decaying
plants and animals and supplying it to detrivores and fungus-eaters.
Since energy is lost in each step, populations are necessarily smaller
at each higher level of the pyramid.
The effects of foreign species introduction into an ecosystem are very
profound. From small microorganisms to species of large mammals, many foreign
species introductions occur every day. New implications of their introduction
are found just as often.
When a foreign species is introduced into an ecosystem, often the
ecosystem contains no natural predators for the new species. This lack of
predators sometimes leads to; in conjunction with a supply of food suitable for
the new species, a period of exponential growth of the species. This growth and
severe increase in the size of the population can cause a shortage of food for
native species. When this occurs, the native...