We are all familiar with the process of competition as we ourselves face it in various ways in our day-to-day life. Competition occurs in nature generally, but not necessarily, when resources like food, space, mates are limited.
Resource limitation leading to competition is implicit in Darwin’s ideas on struggle for existence and survival of the fittest. Though not implicit in Darwin’s ideas on struggle for existence and survival of the fittest. Though not widely recognized competition could occur even when resources are not limiting.
For example, consider species A that does not require a certain resource for its existence, but it prevents species B from acquiring that resource which the latter needs. The consequence is that the growth and reproduction of species B are reduced because of the presence of species A in the same habitat. This is called ‘interference competition’ and appears to be rather common among the higher animal groups.
Although competition is most intense when the competing species are closely related, because their requirements are similar, competition between taxonomically unrelated species is not uncommon. For instance, in certain South American lakes, shore birds such as flamingoes compete with fish in the lake for a common resource – Lake Zooplankton which serves as food for both fish and birds. It has been observed that in lakes with large resident populations of flamingoes, fish populations are comparatively small.
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What happens when two related species compete for the same resource needed by both? The outcome usually depends on how ‘competitive’ the species are. If one species is competitively superior, it will eventually exclude the other species from the habitat, a phenomenon referred to as Gause’s Principle of Competitive Exclusion, named after the Soviet biologist G.F. Gause. If both are equally strong competitors, the outcome depends on the initial conditions; an uncertain and unstable coexistence is possible. If however, both species are weak competitors, both could co-exist peacefully indefinitely in the same habitat.
Experiments conducted by many ecologists under laboratory conditions demonstrate the competitive exclusion of the weaker competing species. Gause showed this using two species of the familiar microorganism Paramecium. When P .caudatum and P .auraelia are cultured together, the former is eventually eliminated. Do such experiments prove that competition and competitive exclusion occur regularly in nature? In general, the evidence for competitive exclusion, if any, in nature is rather circumstantial. Because the conditions in nature are much more complex than in a laboratory, the outcome of competition between the two species of Paramecium could be entirely different from what Gause found in the laboratory. Nevertheless, there are a few recorded cases of competitive exclusion in nature. For example, the disappearance of the native red squirrel from England was believed to be due to is replacement by the American grey squirrel, which was introduced earlier in England. Even in this case, the evidence is still only circumstantial.
While reverse competition at the intraspecific level might lead to population regulation, establishment of social hierarchy “peck order” and territoriality, at the interspecific level competition may lead to extinction of the inferior species, narrow specialization to avoid competition, and to evolution of new species.