Competition is an ecological interaction in which both participants in the interaction are potentially harmed. Competition generally results in lower survival, lower reproductive success, lower growth rates, and/or smaller population sizes. Competition can occur between members of the same species (intraspecific competition) or between members of different species (interspecific competition). Competition occurs when resources are in limited abundance. Many scientists think that competition is one of the most important biotic factors determining community structure.
Mechanisms of competition
Species compete by two mechanisms—interference competition and exploitative competition. Interference competition occurs when one species directly affects the ability of a another to consume resources. This can take on many forms. An animal may chase other individuals away from a potential food source. In some species, individuals or groups maintain and defend territories. Some plants produce allelopathic chemicals, which limit the growth and survival of competing plants. Within a reef, two species of coral are often separated by a small zone with no living corals.
Exploitative competition occurs via the consumption of resources. When an individual of one species consumes a resource (e.g., food, a nesting site, a mate, a photon of light, etc.), then it is no longer available to a member of a second species. Exploitative competition is probably the most common mechanism of competition in nature.
Effects of competition
Competition can influence population size and community structure. For example, intraspecific competition can result in plants being evenly dispersed across the landscape. Intraspecific competition also limits the population size of many species (see logistic growth). Interspecific competition can influence population size (see Lokta-Volterra competition model), as well as the number of species, or species richness, in a community . According to the Competitive Exclusion Principle, two species that share exactly the same environmental requirements, or niche, will not be able to coexist indefinitely. Thus, niche differentiation (e.g., feeding on different resources, in different places, or at different times) will allow more species to coexist in an area when competitive exclusion is an important factor.