Competition is an interaction between organisms or species in which both require a resource that is in limited supply. Competition lowers the fitness of both organisms involved since the presence of one of the organisms always reduces the amount of the resource available to the other.
Great egret and neotropic cormorant competing over territory
Male-male competition in red deer during rut is an example of interference competition within a species.
Sea anemones compete for the territory in tide pools
Medium ground finch (Geospiza fortis) on Santa Cruz Island in the Galapagos
In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species, or of different species. These effects may be short-term, or long-term, both often strongly influence the adaptation and evolution of the species involved. Biological interactions range from mutualism, beneficial to both partners, to competition, harmful to both partners. Interactions can be direct when physical contact is established or indirect, through intermediaries such as shared resources, territories, ecological services, metabolic waste, toxins or growth inhibitors. This type of relationship can be shown by net effect based on individual effects on both organisms arising out of relationship.
The black walnut secretes a chemical from its roots that harms neighboring plants, an example of competitive antagonism.
Predation is a short-term interaction, in which the predator, here an osprey, kills and eats its prey.
Pollination has driven the coevolution of flowering plants and their animal pollinators for over 100 million years.
Male-male interference competition in red deer