Competition (biology)
（重定向自Biological competition）
![Sea anemones compete for the territory in tide pools](/Images/godic/202412/24/Clone_war_of_sea_anemones_2-17-08-20505.jpg")
![Male-male competition in red deer during rut is an example of interference competition within a species.](/Images/godic/202412/24/Hirschkampf0505.jpg")
![The Competitive Exclusion Principle states that two species aren't able to coexist at constant population values competing for the same resource. In this example, stage 1 shows a smaller (yellow) species of bird originally foraging for insects across the whole tree. In stage 2, a larger, invasive (red) species of bird is introduced into the environment and competes with the yellow bird for resources. As time goes on, the invasive red species dominates the yellow species in competition for the middle part of the tree and for the more abundant resources, as shown in stage 3. The yellow species then adapts to its new niche and both birds thrive without competition.](/Images/godic/202412/24/Competitive-20Exclusion-20Principle.svg0505.png")
![Medium ground finch (Geospiza fortis) on Santa Cruz Island in the Galapagos](/Images/godic/202412/24/Geospiza_fortis0505.jpg")
Competition is an interaction between organisms or species in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource (such as food, water, and territory) used by both can be a factor. Competition both within and between species is an important topic in ecology, especially community ecology. Competition is one of many interacting biotic and abiotic factors that affect community structure. Competition among members of the same species is known as intraspecific competition, while competition between individuals of different species is known as interspecific competition. Competition is not always straightforward, and can occur in both a direct and indirect fashion.