Population Interactions

Populations do not live in isolation. Instead, they interact with other populations living in the same area. In some cases, populations compete for resources such as food, water, or shelter.

Competition Between Species

INTERSPECIFIC COMPETITIONis (competition between species) takes place when two or more species rely on the same limited resource.

Competitive Exclusion

If two species are so similar in their requirements that the same resource limits both species' growth, one species may win and survive over the other. This process is referred to as COMPETITIVE EXCLUSION.

In nature, there are many things that affect weather two species can require the same resources and still coexist depends on other factors in the ecosystem. For example, predators may keep competing populations below the levels at which resources such as foodwould become limiting factors.

Niches

Within a community, each species has a unique living arrangement called its NICHE. Think of a niche as the organism’s “job”.

A niche includes an organism's living place (habitat), its food sources, the time of day it is most active, and many other factors specific to that organism's way of life.

Predation

PREDATION is the act of one organism eating another organism.

Because eating and avoiding being eaten are so important to survival, it is not surprising that many effective adaptations have evolved in both predators and prey.

Predator Adaptations

Many predators have coloring that hides, or camouflages, them in their surroundings.

Some predators, such as wolves and killer whales, may team up in packs to capture their prey.

Most predators have sharpsenses that enable them to find prey.

Adaptations such as claws, teeth, fangs, and stingers help many predators catch prey.

Prey Adaptations

Several adaptations help prey avoid being eaten.

Prey may use camouflage to hide from predators.

Another type of defensive coloring has the opposite effect—it makes the organism stand out. Such "warning coloration" serves as a caution to predators.

Some organisms aren't poisonous or dangerous themselves, but they look like organisms that are. This type of defense is called MIMICRY.

-Milk snake vs. Coral snake

Plants cannot run away from predators, but they have other defenses that include poisonous chemicals and other structures such as spines and thorns.

Symbiotic Relationships

A SYMBIOTIC RELATIONSHIPis a close interaction between species in which one of the species lives in or on the other.

There are three main types of symbiotic relationships:

1. PARASITISM, 2. MUTUALISM, and 3. COMMENSALISM.

PARASITISMis a relationship in which one organism, the parasite, obtains its food at the expense of another organism, the host, hurting the host species.

Usually the parasite is smaller than the host. Both mosquitoes and tapeworms (that live and feed in the intestines of larger animals), are examples of parasites.

MUTUALISM, both organisms benefit from the symbiotic relationship.

One example of mutualism occurs inside your own body. Your large intestine has millions of bacteria. The bacteria benefit by having a warm, moist home with a constant stream of nourishment, your food.

In turn, some intestinal bacteria produce vitamin K. Vitamin K is essential for blood clotting. Both you and the bacteria benefit from this relationship.

COMMENSALISM, is a relationship in which one organism benefits, while the other organism is neither harmed nor helped.

One example of a commensalism relationship is when a spider crab may place seaweed on its back. The crab benefits by being camouflaged from its predators. The seaweed does not seem to be significantly affected.

True commensalism in nature is rare, since most interactions harm one species (parasitism) or help both species (mutualism) to some degree.