Competition is not always a straightforward, direct interaction either, and can occur in both a direct and indirect fashion. According to the competitive exclusion principle , species less suited to compete for resources should either adapt or die out. According to evolutionary theory , this competition within and between species for resources plays a critical role in natural selection. The following terms describe mechanisms by which competition occurs, which can generally be divided into direct and indirect.
These mechanisms apply equally to intraspecific and interspecific competition. Intraspecific competition occurs when members of the same species vie for the same resources in an ecosystem e.
For example, two trees growing close together will compete for light above ground, and water and nutrients in the soil. Therefore, getting less resources, they will usually perform less well than if they grew by themselves.
Adaptations to such an environment include growing taller especially in forests , or developing a larger root system. Interspecific competition may occur when individuals of two separate species share a limiting resource in the same area.
If the resource cannot support both populations, then lowered fecundity , growth, or survival may result in at least one species.
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Student Voices. Creature Cast. Does this mean neither can live in the zone occupied by the other? Chthamalus Figure 3. This study helped to pioneer the approach of field experiments. Using cages to exclude one or the other species, and by transferring slabs of rock from one region to the other, it was established that Chthamalus could thrive in the lower zone if protected from Balanus. Otherwise, Balanus, which is a larger and more robust species, crushed neighboring Chthamalus as it grew in size.
Chthamalus was competitively excluded from the lower inter-tidal. At the upper limit, however, both species were limited by their ability to withstand desiccation. Chthamalus, the inferior competitor, was better adapted to desiccation and so occupied the higher portion of the inter-tidal zone. Mechanisms of Competition Competition often takes place via the using up or depleting of resources by members of one species, making those resources unavailable to members of the second species.
Resources would include nest sites, food items, water or minerals in the soil. This is called indirect competition. It is likely to be most severe between individuals with similar needs for example, two species occupying the same trophic level, and with similar ecological roles or niches.
Direct competition occurs when members of one species interfere with or directly harm members of a second species. Examples include fights over space among animals, release of chemicals by plants e. Competition and Evolutionary Specialization Competition is likely to result in evolutionary divergence and specialization among closely related species. Consider the process of speciation , which is thought often to be gradual and include a period of selection for reproductive isolation once geographic isolation no longer separates the two diverging populations.
We should expect those two species to occupy very similar ecological niches, hence to be likely to compete. Quite possibly, one species will eliminate the other. It also is possible, however, that the two species will diverge ecologically, perhaps via divergence in traits such as bill size that affects the size of food items consumed. This is known as character divergence. The Galapagos Finches The Galapagos finches appear to be good examples of character divergence.
Three species of ground finches make a particularly strong case. If we assume there are seeds of different sizes -- small to large -- it makes sense that beaks of different sizes -- also small to large -- permit efficient handling and cracking of seeds in a specific size range. If only one species of finch exists, perhaps it will occupy the "middle ground" of beak and seed size.
However, once speciation occurs, should one species be slightly smaller and one slightly larger, natural selection should favor individuals that are smaller than average within one species, larger than average within the other.
Over time, beak size the character that determines which portion of the resource spectrum is consumed will diverge.
There is a complication, however. Suppose our large and small finches arose independently somewhere else, and happened to colonize various islands in one's, two's and three's. In the absence of competition, both a small and a large species might evolve towards an intermediate size. This is known as ecological release. Whether one is observing character displacement or ecological release then depends on the order and independence of speciation events.
This is hard to know, but a good cladogram would resolve the issue. Summary - The Consequences of Competition Competition can be a powerful force affecting the growth, distribution, and abundance of populations in nature.
This is supported by evidence from laboratory "bottle' experiments, field observations, and field experiments. Laboratory studies lead to the formation of the competitive exclusion principle no two species can long occupy the same niche , while field observations suggest that niche differences, while sometimes subtle, are invariably found between co-existing species. Field experiments provide strong evidence of competition in nature. Often, one species is the superior competitor, the other is better able to withstand certain environmental extremes.
Competition is a powerful force of natural selection. There are many examples of closely related species that differ "just enough" to reduce niche overlap and permit coexistence.
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