Community Ecology

What is an Ecological Community?

community consists of all the interacting populations (different species) that live in a defined area. Community interactions, such as competition, predation, and various forms of symbiosis, can powerfully affect an ecosystem. A community is defined by biotic factors, or living things.

Community Interactions


Competition occurs between organisms that attempt to use the same resource in the same place at the same time. This resource could be food, space, water or even mates. There are two types of competition:

Type of Competition Explanation Example
Intraspecific Competition Competition among individuals in the same species; Intraspecific competition is the basis for natural selection and can lead to a species developing adaptations over time.



Two hartebeests competing for territory

Interspecific Competition Competition among individuals is different species. Usually this is because they occupy the same niche. Interspecific competition can lead to specialization among species or can lead to extinction.



Both the leopard and the lion feed on the same animals


Predation is an interaction in which one organism captures and feeds on another organism. The organism doing the capturing is called the predator and the organism being captured is called the prey. The predator and prey have a close relationship, where they depend upon each other closely. Take a look at the following graph that describes a typical predator/prey relationship:


Did you notice that the predator and prey oscillate (cycle up and down) with each other in population size? There is a slight lag in time between the increase and decrease of their numbers because one is directly affecting the other.



Symbiosis is any close association between two species that share some sort of relationship. The three types of symbiosis are mutualism, commensalism, and parasitism. Do you remember those?