Competition and Interdependence

Organisms within an ecosystem do not exist in isolation. They interact with one another in ways that determine their survival and reproduction. This lesson explores the two key ecological relationships you need to understand for AQA GCSE Biology: competition (both interspecific and intraspecific) and interdependence between species.

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What Is Competition?

Competition occurs when two or more organisms require the same resource that is in limited supply. Resources are anything organisms need to survive and reproduce. Competition is one of the most important factors controlling population size.

There are two types of competition:

Type	Definition	Example
Intraspecific competition	Competition between organisms of the same species	Two robin males fighting over territory in the same garden
Interspecific competition	Competition between organisms of different species	Grey squirrels outcompeting red squirrels for food in UK woodlands

Intraspecific competition is often more intense because organisms of the same species have identical resource requirements.