Community interactions  (Page 4/21)

Competition

Resources are often limited within a habitat and multiple species may compete to obtain them. All species have an ecological niche in the ecosystem, which describes how they acquire the resources they need and how they interact with other species in the community. So, the plants in a garden are competing with each other for soil nutrients, and water. This competition between the different species is called interspecific competition. The overall effect on both species is negative because either one of the species would do better if the other species is not present. So, how do species reduce the overall negative effects of direct competition?

Competitive exclusion principle

The competitive exclusion principle    states that two species cannot occupy the same niche in a habitat. In other words, different species cannot coexist in a community if they are competing for all the same resources. An example of this principle is shown in [link] , with two protozoan species, Paramecium aurelia and Paramecium caudatum . When grown individually in the laboratory, they both thrive. But when they are placed together in the same test tube (habitat), P. aurelia outcompetes P. caudatum for food, leading to the latter’s eventual extinction.

Resource patitioning

Symbiosis

Symbiotic relationships, or symbioses (plural), are close interactions between individuals of different species over an extended period of time which impact the abundance and distribution of the associating populations. Most scientists accept this definition, but some restrict the term to only those species that are mutualistic, where both individuals benefit from the interaction. In this discussion, the broader definition will be used.

Commensalism

A commensal relationship occurs when one species benefits (+) from the close, prolonged interaction, while the other neither benefits nor is harmed (0). Birds nesting in trees provide an example of a commensal relationship ( [link] ). The tree is not harmed by the presence of the nest among its branches. The nests are light and produce little strain on the structural integrity of the branch, and most of the leaves, which the tree uses to get energy by photosynthesis, are above the nest so they are unaffected. The bird, on the other hand, benefits greatly. If the bird had to nest in the open, its eggs and young would be vulnerable to predators. Another example of a commensal relationship is the clown fish and the sea anemone. The sea anemone is not harmed by the fish, and the fish benefits with protection from predators who would be stung upon nearing the sea anemone.