Competition
Competition is one of the major interactions that shapes ecological communities. Learn how organisms compete for limited resources, how competition occurs within and between species, and how resource partitioning can allow species to coexist.
A conceptual model for understanding competition in ecological communities.
In This Article
What Is Competition?
Competition is an ecological interaction in which organisms use the same limited resource. When a resource cannot fully satisfy all organisms that need it, individuals may interfere with one another directly or may simply reduce the amount available to others.
Competition can occur among members of the same species or between different species. The resource might be food, water, light, space, nesting sites, nutrients, or another requirement for survival and reproduction.
Competition is strongest when organisms have overlapping resource needs and those resources are limited.
Intraspecific vs. Interspecific Competition
Intraspecific competition occurs between individuals of the same species. Because members of a species often have very similar resource requirements, competition within a species can be intense.
Interspecific competition occurs between individuals of different species. The species may overlap in their use of a resource even though they occupy different ecological niches.
Intraspecific
Two deer compete for the same food or two seedlings compete for sunlight.
Interspecific
Two bird species compete for similar nesting sites or food.
What Do Organisms Compete For?
Competition only matters when something is limited relative to demand. If food, water, light, or space is abundant, organisms may need the same resource without experiencing much competition.
For plants, light, water, minerals, and space can be important limiting resources. Animals may compete for food, territories, mates, shelter, or nesting sites. The limiting resource depends on the environment and the species involved.
Competition and the Ecological Niche
An organism’s niche includes how it uses resources and interacts with its environment. When two species rely heavily on the same limited resources, their niches overlap.
This is one reason ecologists distinguish between a species’ fundamental niche and its realized niche. Competition can restrict where or how a species actually lives, making its realized niche smaller than the range of conditions it could use in the absence of competitors.
Competition is not simply “animals fighting.” It is an interaction caused by overlapping use of limited resources.
Competitive Exclusion
The competitive exclusion principle states that two species with exactly the same niche cannot stably coexist indefinitely when they compete for the same limiting resources. One species may eventually outcompete the other in that environment.
In real ecosystems, however, species often avoid complete overlap. They may use different resources, feed at different times, occupy different microhabitats, or specialize on different parts of the same resource. This is called resource partitioning.
Competitive Exclusion
If two species require exactly the same limiting resources in the same way, long-term coexistence is unlikely.
Resource Partitioning
Species may divide resources by space, time, food type, or other dimensions of the niche.
Common Misconceptions
If You See This on a Test, Think This
Quick Practice
1. What makes a resource capable of causing competition?
2. What is the difference between intraspecific and interspecific competition?
3. Why can resource partitioning allow species to coexist?
4. How can competition affect a species’ realized niche?
5. Does competition require direct physical contact?
Key Takeaways
- Competition occurs when organisms use the same limited resource.
- Intraspecific competition occurs within a species; interspecific competition occurs between species.
- Competition can involve food, water, light, space, shelter, territories, or other resources.
- Competition can influence population growth, survival, and reproduction.
- Resource partitioning can reduce competition and allow species to coexist.
- Competitive exclusion is associated with complete overlap in limiting resource use.
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