Activity 5: Background Information

Competition
Competition occurs between two or more organisms. It occurs when the use of a resource by one organism results in a reduced availability of the resource for other organisms. This limits the potential growth and reproduction of the other organisms. A resource is any factor or material that is required for survival, growth, and reproduction. Although competition occurs at the individual level, the repercussions are felt by the entire population. There are two types of competition. When competition occurs among organisms that belong to the same species it is referred to as intraspecific competition. When it occurs between individuals of different species it is interspecific competition.

Intraspecies competition varies as the density of the population of organisms changes. For example, as the size or density of a opulation increases, so does the intensity of the competition. As the size or density of a population decreases the strength of the intraspecies competition decreases as well. This acts to stabilize a population.

Interspecific competition, on the other hand, can destabilize a population. This can occur if one species is less capable of competing for the limiting resource. The strength of the competition in this situation is determined by the stronger competitor and may eventually lead to the extinction of the weaker competitor. Two species with very similar resource requirements cannot exist in the same place at the same time if one competitor is stronger than another.

There are two ways in which species can compete. One is through exploitation. (Also referred to as scramble competition.) In this type of competition the two species differ in their abilities to use or extract the resource. One is more efficient than the other. For example, the feeding rates in animals might differ, or the ability of one plant to extract water from the soil may differ from that of other plants. The other way is through interference competition or contest competition. In this type of competition one organism directly affects the ability of the other organism to obtain a resource by physical contact. This is done by guarding or defending the resource by displays or fighting. It can also be accomplished by chemical means like allelopathy.