Interaction between Species

No organism exists independently of other organisms. The producers, consumers, and decomposers of an ecosystem interact with one another in a variety of complex ways, and each forms association with other organisms. There are four basic kinds of interaction between species: competition, in which the outcome is negative for both groups; symbiosis, which benefits both groups; and  predation  and parasitism, in which the outcome benefits one and is detrimental to the other (Table T).
Each type of interaction affects evolution, the persistence of species, and the overall diversity of life. It is important to understand that organisms have evolved together so that predator, parasite, prey, competitor, and symbiont have adjusted to one another. Human interventions frequently upset these adjustments.

Competition
Competition occurs when two or more individuals attempt to use an essential common resource such as food, water, shelter, living space, or sunlight. When this type of competition occurs, the more fit species will win out and persist, and the less fit will lose, must evolve into a slightly different niche, and migrate to a different geographic area or become extinct. This is known as the competitive exclusion principle, which states that two species that have exactly the same requirements cannot coexist in exactly the same habitat; one will always exclude the other.