There is much stress in communities, and it is this stress
that continues to push better adapted species to be successful in the community.
There are many factors that govern competition between species which may
result in extinction or separation of that species from its original areas.
Species are associated with a particular and unique set of biological and
physical influences which are known as niches. The term "niche" is
used in ecology with a variety of meanings, but all of them have to do
with a habitat that is filled by species within an entire ecosystem.
Students will take a closer look at how populations can become
stressed in an ecosystem by interpreting scientific data. There are
many chemical interactions between populations. It is known that there
are many chemical secretions released by a particular plant population
that will prevent other plants to grow around them. A classic experiment
deals with the California chaparral. It had been known for many years
that chaparral plants have a characteristic pungent and aromatic odor,
and that this is due to the presence of volatile substances released from
the shoots of the plants. These chemicals (known as terpenes and
phenolic compounds) are absorbed onto surrounding soil surfaces and in
turn suppress the growth of the seedlings of many species in the area.
This chemical interaction may provide clues on how ecosystems
evolve through time. Chemicals are used to prevent predators from
attacking a plant. Chemicals are emitted from plants and are used
to protect the plants from their "enemies." However, it is known
that insects can develop mutants that can successfully attack these plants,
and if a plant cannot develop a stronger plant, than it will go extinct
because the insects will eat the plant into extinction.
- The worksheet asks students questions on what
happens when there is competition between various populations. This
graph illustrates the "Rule of Gause." If two species are utilizing
the same resource, one will most probably reach this position where its
growth rate is zero before the other. The graph illustrates competition
between two species population of Paramecium in a closed culture.
One species, Paramecium caudatum (B), declines to extinction as the result
of its inability to compete with Paramecium aurelia (A) for the same food
sources. This exercise helps students to interpret data.
1. time in days;
2. population density
5. rapidly increases until
about 9-10th day in which it levels off, decreases slightly after 18th
6. increase at about same rate as A until the 4th day, then
it slowly decreases until the population dies at 18;
7. A and B are
competing, B begins to lose on 4th day until it dies, A continues to survive.