Introduction: In the wild, organisms are always working to survive. This may mean a plant is bending around another in order to get a better light source, or two lions fighting over a recently killed antelope. Organisms compete for all kinds of things - shelter, food, mates - and how they do it and with whom determines the type of competition occurring.

Interspecific competition happens between two different species. Using plants as a an example (since most people are more familiar with animals), imagine that in the tropical rainforest a large tree has just fallen down in a windstorm. As a result, a space has opened up in the canopy that is flooding a lot of sunlight onto the forest floor. Since light is usually quite limited in this part of the biome, there would be an instant charge of plants to try and take advantage of this new situation. Many plants are able to bend towards or away from light sources. When this spot in the canopy opens, the plant that is able to get there the fastest and be able to retain its position would be able to take full advantage of the Sun.

Intraspecific competition happens between organisms of the same species. In the tropical rainforest a species known as a weaver bird builds a very elaborate nest in which its eggs will be laid (see image right). The male is the one that builds the nest. The female, on the other hand, is the one who selects which male with whom she wants to mate. There may be many males building nests all in the same area. The female comes around and inspects each one and ultimately chooses to mate with, and lay her eggs, in the nest built by the male she thinks is the best. Since there is only one female and multiple males, they are competing for her attention.

Another factor that plays into the principle of competition is that of an organism's niche. A niche is the actual "job" of the organism within the ecosystem and specifically where it lives. When two organisms have the same or similar niches, competition is likely to occur. This happens because resources are often limited and both species cannot exist in the same area at the same time. Many times (but not always) when two species are trying to exist in the same space at the same time, something called competitive exclusion occurs. This basically means that one species out competes the other for the limited resource, forcing it to either move or die.

Directions for this Lesson: Answer the practice questions and then watch the video to learn more about how organisms compete with each other and interact.