226 ❯ STEP 4. Review the Knowledge You Need to Score HighType IIIindividuals have a steep downward curve for those of young age, representing a
death rate that flattens out once a certain age is reached. Examples of type III organisms
include many fishes, oysters, and other marine organisms.Community and Succession
Community
Most species exist within a community. Because they share a geographic home, they are
bound to interact. These interactions range from positive to neutral to negative.Forms of Species Interaction- Symbiosis.A symbiotic relationship is one between two different species that can be
classified as one of three main types: commensalism, mutualism, or parasitism.
A. Commensalism.One organism benefits while the other is unaffected. Commen-
salistic relationships are rare, and examples are hard to find. Cattle egrets feast on
insects that are aroused into flight by cattle grazing in the insects’ habitat. The birds
benefit because they get food, but the cattle do not appear to benefit at all.
B.Mutualism. Both organisms reap benefits from the interaction. One popular exam-
ple of a mutualistic relationship is that between acacia trees and ants. The ants are
able to feast on the yummy sugar produced by the trees, while the trees are protected
by the ants’ attack on any potentially harmful foreign insects. Another example
involves a lichen, which is a collection of photosynthetic organisms (fungus and
algae) living as one. The fungus component pulls its weight by helping to create an
environment suitable for the lichen’s survival, while the algae component supplies
the food for the fungus. Without each other’s contribution, they are doomed.
C.Parasitism.One organism benefits at the other’s expense. A popular example of a
parasitic relationship involves tapeworms, which live in the digestive tract of their
hosts. They reap the benefits of the meals that their host consumes by stealing the
nutrients and depriving the host of nutrition. Another less well-known example of
parasitism involves myself and my younger brother’s Playstation 2 console. - Competition.Both species are harmed by this kind of interaction. The two major forms
of competition are intraspecific and interspecific competition. Intraspecific competition
iswithin-species competition. This kind of competition occurs because members of the
same species rely on the same valuable resources for survival. When resources become
scarce, the most fit of the species will get more of the resource and survive. Interspecific
competitionis competition between different species. - Predation.This is one of the “negative” interactions seen in communities (well, for one
half of those involved, it is negative.) ☺ One species, the predator, hunts another
species, the prey. Not all prey give in to this without a fight, and the hunted may
develop mechanisms to defend against predatory attack. The next section describes the
various kinds of defense mechanisms developed by prey in an effort to survive.
Defense Mechanisms
Aposematic colorationis a very impressive-sounding name for this defense mechanism.
Stated simply, it is warning coloration adopted by animals that possess a chemical defense
mechanism. Predators have grown cautious of animals with bright color patterns due to
past encounters in which prey of a certain coloration have sprayed the predator with a
chemical defense. It is kind of like the blinking red light seen in cars with elaborate alarmDel (12th grade):
“Know this for
the multiple-
choice questions.
I should
have....”BIG IDEA 2.D.1
Everything from
cells to ecosystems
is affected by inter-
actions involving
the exchange of
matter and energy.
BIG IDEA 4.A.5
Communities are
composed of popu-
lations that interact
in complex ways.