Interspecific competition occurs when individuals of different species use the same limited resource, such as food, light, water, nesting space, or soil nutrients. It matters because competition can shape population sizes, species distributions, and the structure of entire ecosystems. When two species depend on the same resource in the same place, each can reduce the other's growth, survival, or reproduction.
This interaction is a major reason why ecological communities change over time.
Key Facts
- Interspecific competition is competition between different species for the same limited resource.
- Competition reduces fitness when it lowers survival, growth, or reproduction.
- Competitive exclusion principle: two species cannot coexist indefinitely if they occupy exactly the same niche and resources are limiting.
- Resource partitioning occurs when species reduce competition by using resources in different ways, places, or times.
- Character displacement is an evolutionary change in traits that reduces competition between similar species.
- Lotka-Volterra competition model: dN1/dt = r1N1[(K1 - N1 - alpha12N2)/K1].
Vocabulary
- Interspecific competition
- An ecological interaction in which individuals of different species compete for the same limited resource.
- Niche
- The role of a species in its environment, including the resources it uses and the conditions it can tolerate.
- Competitive exclusion
- The process in which one species outcompetes another when both require the same limiting resources in the same niche.
- Resource partitioning
- The division of resources among species in ways that reduce direct competition.
- Character displacement
- An evolutionary shift in traits between competing species that makes their niches less overlapping.
Common Mistakes to Avoid
- Calling all negative species interactions competition is wrong because predation, parasitism, and disease also harm organisms but do not require shared use of the same limited resource.
- Assuming competition always causes extinction is wrong because species can coexist if they partition resources, use different habitats, or compete weakly.
- Confusing interspecific with intraspecific competition is wrong because interspecific means different species, while intraspecific means members of the same species competing with each other.
- Ignoring resource limitation is wrong because competition is strongest when a needed resource is scarce, not when it is abundant enough for all individuals.
Practice Questions
- 1 Two bird species feed on the same insects in a tree. Species A eats 120 insects per day when alone, but 75 per day when Species B is present. By what percent did Species A's insect intake decrease?
- 2 A habitat has 300 seed patches. Species X uses 180 patches, Species Y uses 150 patches, and 90 patches are used by both species. How many patches are used by only one of the two species?
- 3 Two plant species grow in the same field and both need sunlight and nitrogen. Over several generations, one species evolves taller stems while the other grows wider roots. Explain how this could be an example of character displacement and how it may reduce competition.