Interspecific Relationships - Negative Interactions > Competition

The rivalry between two or more organisms for the same limited resource, where the use of the resource by one reduces its availability to the other, is called competition.

Competition that occurs between individuals of the same species for limited resources is called intraspecific competition.

Competition that occurs between individuals of different species for the same limited resources is called interspecific competition.

A type of competition in which one organism directly prevents another from accessing a resource is called interference competition.

A type of competition in which organisms share a resource, but one uses it more efficiently than the other, is called exploitative competition.

• A biotic interaction where two or more organisms compete for the same limited resource
• Both species are harmed → Sign notation: (−/−)
• Resources can be: food, water, space, light, and mates.
• Resources need not be scarce for competition to occur (esp. in interference competition)

By Participants

By Mechanism

"Two closely related species competing for the same resource cannot coexist indefinitely - the competitively inferior one will be eliminated."

• Proof 1: Balanus excludes Chthamalus from lower intertidal zone (Scotland)
• Proof 2: Goats drove Abingdon tortoise to extinction in Galápagos
• Proof 3: Paramecium aurelia eliminated P. caudatum in lab cultures
• Limitation: Species escape exclusion via resource partitioning/niche shift

• Fundamental Niche = Full niche possible without competition
• Realised Niche = Actual niche when competition is present (smaller)

• Competition is an interaction (-/-) where organisms struggle for the same limited resources, resulting in a negative impact on the biological fitness of both participants.
• It is generally more intense when it occurs between members of the same species (intraspecific) rather than between members of different species (interspecific) because their resource requirements are identical.
• The struggle can occur directly, in which one organism actively prevents another from accessing a resource (interference competition), or indirectly, in which one organism rapidly consumes a shared resource (exploitative competition).
• Gause's Competitive Exclusion Principle states that two closely related species competing for the exact same resource cannot coexist indefinitely; the competitively weaker species will eventually be eliminated.
• To avoid elimination, competing species often adapt to coexist through resource partitioning (using different parts of a resource or hunting at different times) or character displacement (evolving distinct physical traits to reduce overlap).
• Competition usually restricts a species to a smaller realised niche rather than its full-potential fundamental niche; however, if the dominant competitor is removed, the restricted species will rapidly expand its range in a process called competitive release.