INTERACTIONS WITHIN COMMUNITIES
- A community is all the populations that are in an ecosystem at a given time.
- An ecological niche is an organism role in the ecosystem; it includes its interactions with the abiotic and biotic components of the ecosystem.
- A fundamental niche is the biological characteristics and the resources the individuals can use under ideal conditions.
- A realized niche is the biological characteristics and the resources the individuals actually use. Ex. Lions compete with hyenas and vultures for similar resources.
- Interactions between organisms of two species can be classified into two groups; interspecific competition, predation and symbiosis.
- Symbiosis is when two species maintain a close relationship; includes parasitism, mutualism and commensalisms.
Competition, predation and symbiosis
- occurs between organisms of different species, and it limits population growth.
- Interference competition is when the individuals actually fight over a resource. Ex. Tree swallows and bluebirds fight over birdhouses.
- Exploitative competition is when the individuals of different species consume shared resources. Ex. Arctic foxes and snowy owls prey on the same population of arctic hares.
- The greater the niche overlap is between populations the more competition that is experienced.
- If resources are limited then two species could not remain in competition for the same niche indefinitely; Gause’s principle.
- There are three effects of interspecific competition:
2. The behaviour may change for one of the competitor, so it could survive using different resources.
3. One population may migrate to a habitat that has more resources.
- Resource partitioning involves organisms of different species occupying nonoverlapping ecological niches.
- Ex. Anolis lizards in the Caribbean occupy different perching sites so they can coexist in the same geographic range. Ex. Three species of plant can grow in the same area because they have different root lengths (fibrous vs tap root systems) that allow them to obtain nutrients at various depths in the soil.
- Due to interspecific competition populations of species have evolved adaptations to enable them to use resources so they can survive.
- Character displacement occurs when disruptive selection pressures leads two species in the same geographical range having divergent traits Ex. Three-spined sticklebacks in freshwater lakes.
- The mouth size of the species were determined by their feeding habits.