Competition in organisms, Biology tutorial


Competition is the interaction between organisms or species, in which fitness of one is lowered by presence of another. Limited supply of at least one resource (like food, water, and territory) utilized by both is needed. Competition both within and between species is the significant topic in ecology, particularly community ecology. Competition is one of numerous interacting biotic and abiotic factors which affect community structure. Competition among members of same species is called as intraspecific competition, whereas competition between individuals of different species is called as interspecific competition. Competition is not always simple, and can occur in both direct and indirect fashion. According to competitive exclusion principle, species less suited to struggle for resources must either adapt or die out. According to evolutionary theory, this competition inside and between species for resources plays the critical role in natural selection, though, competition may play less of role than expansion among larger groups like families.

Kinds of competition:

1) By mechanism:

The given terms explains mechanisms by which competition takes place that can usually be divided in direct and indirect. These mechanisms apply evenly to intraspecific and interspecific competition. Male-male competition in red deer during rut is example of interference competition inside a species.

i) Interference competition:

Takes place directly between individuals using aggression etc. When individuals interfere with foraging, survival, reproduction of others, or by directly preventing physical establishment in the portion of habitat.

ii) Exploitation competition:

Takes place indirectly through common limiting resource that acts as the intermediate. For instance, use of resources depletes amount available to others, or they struggle for space. Also called as exploitative competition.

iii) Apparent competition:

Takes place indirectly between two species that are both preyed on by same predator. For instance, species A and species B are both prey of predator C. Increase of species A will cause decrease of species B as increase of As would increase number of predator Cs which in turn will hunt more of species B.

2) By species:

i) Intraspecific competition:

Intraspecific competition takes place when members of same species vie for same resources in ecosystem. For instance, two trees growing close together will struggle for light above ground, and water and nutrients in soil. Thus, getting less resource, they will generally carry out less well than if they grew by themselves. Though, in this condition it may really be more helpful to think in terms of resource availability than competition. Adaptations to such environment comprise growing taller, (where specific prediction given by competition model is that all species in such situation will grow as tall as possible). Or developing larger root system (where specific prediction is that all species in system will grow very deep root systems).

ii) Interspecific competition:

Interspecific competition may take place when individuals of two different species share limiting resource in same area. If resource can't support both populations, then lowered fecundity, growth, or survival may result in at least one species. Interspecific competition has potential to modify populations, communities and evolution of interacting species. The example among animals could be case of cheetahs and lions; as both species feed on comparable prey, they are negatively impacted by presence of other as they will have less food, though they still persist together, despite prediction which under competition one will displace other. In fact, lions at times steal prey items killed by cheetahs. Potential competitors can also kill each other, and this event is known as intraguild predation. For instance, in southern California coyotes frequently kill and eat gray foxes and bobcats, all three carnivores sharing same stable prey (small mammals).

Competition has been seen between individuals, populations and species, but there is little proof that competition has been driving force in evolution of large groups. For instance between reptiles and mammals, mammals lived beside reptiles for several millions of years of time but were not capable to gain competitive edge until dinosaurs were devastated by K-T Extinction.

Evolutionary strategies:

i) r/K selection theory:

In evolutionary contexts, competition is associated to concept of r/K selection theory that associates to selection of traits that promote success in specific environments. Theory originates from work on island biogeography by ecologists Robert MacArthur and E. O. Wilson, 1967. In r/K selection theory, selective pressures are hypothesized to drive evolution in one of two stereotyped directions: r- or K-selection. Such terms, r and K, are derived from standard ecological algebra, as shown in simple Verhulst equation of population dynamics:

dN/dt= rN(1-N/K)

Where r is growth rate of population (N), and K is carrying capacity of local environmental setting. Usually, r-selected species exploit empty niches, and generate numerous offspring, each of whom has comparatively low probability of surviving to adulthood. On the contrary, K-selected species are strong competitors in crowded niches, and invest more heavily in much fewer offspring, each of whom has comparatively high probability of surviving to adulthood.

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