Competition (biology)

If living things use the same limited resources and by limiting them compete with each other. On an individual level over competing populations or species, few experts believe that biological communities or ecosystems as well as a whole.

A distinction is made between

• Intraspecific competition, which is competition within a species or population and
• Interspecific competition, which is competition between individuals of different species.

Competition applies in the population biology widely but not without controversy, as an important factor density -dependent regulation of population densities in evolutionary biology and theory of ecological societies as a selection factor.

The ecological competitive exclusion principle postulates that species with identical or very similar ecological niche can not coexist permanently.

Mathematical modeling of the competition

The most widely used mathematical model of Lotka - Volterra competition is the model ( set up by Vito Volterra in 1926 and Alfred J. Lotka 1932). It is a further development of the logistic function. The model takes into account both intra-and interspecific competition.

The combination of both situations with type 1 and type 2 = x = y usually formulated as:

These constants define ranked: intrinsic growth rates, interaction constants and capacities.

For motivation and interpretation of the system of equations, it is helpful to think of the case of an isolated population runs their growth according to the logistic differential equation to recall: For x = 0 or y = 0 is obtained in the present model again the well-known case of intraspecific competition, as described by the logistic equation. The case of two species thus obtained by direct generalization of the one-dimensional case.

With the model, there is little elegant expect. Transition to dimensionless variables leads to

On:

In this way the properties of the model emerge clearly visible. In addition to the three trivial fixed points are obtained at a fixed point:

This fixed point represents a stable balance between type x and type y. In other cases, dies ( according to the model ) either type x or type y ( or both) from. Unlike the one-dimensional case, the fixed point of the system is not asymptotically stable in all parameter ranges. It is possible to prove stability conditions that amount to the acts which intraspecific competition stronger than interspecific competition. Only in this case, therefore, two types coexist ( the validity of the model assumed). This is the abstract basis of the known competitive exclusion principle. More details about this can be found in the below linked introduction by John Maynard Smith.

Competitive exclusion and coexistence of species

Following the Lotka - Volterra model, two types can coexist with each other only when the competition effect on individuals of the same species ( intraspecific ) is stronger than that of individuals of other species ( interspecific). Is the competition asymmetrically, so that individuals of one species more on individuals of other species act as on animals, the weaker competitor would inevitably displaced. For example, a plant species displace another from a location because it grows higher and the other ausschattet, ie it is competitive on place in the competition for light. Translated into the language of the niche Theory: The fundamental nature of the second recess is completely overlapped with that of the first type. The weak competitor ( the second type ) In the presence of strong competitors ( the first type ) no longer realized niche and therefore dies out. This means exclusion of competitors.

In the ecological field research, the absence of a realized niche and thus complete exclusion of competition is ultimately not provable. It can always be that with the inclusion of a hitherto neglected or unknown factor either a competitive free space (ie for example a location of the inferior species, which the superior competitor physiologically related may not colonize ) exists or that it is the weaker species ( fully or partially ) gaining competitive ability, so that the assumptions of the Lotka - Volterra model existing under these conditions no longer apply (Example: the weaker vigorous species can in water or nutrient deficiency more vigorous and thus be competitive on set here).

In general, there seems to be in the ecology very many cases in which two types coexist, although one of them ( perceived or real ) is competitive over lay. These cases are each a challenge to the ecological theory, as an explanatory factor must be found. Possible events include the following factors:

• The two types are actually not or only hardly in competition with each other, because they ( Habitat ) capacity K can not exploit both their, ie remain too rare.
• The competitive inferior species is faster at colonizing new, vacant habitats ( strategy a " pioneer species ").
• The environmental conditions fluctuate in a way that both types are alternately competitive on set ( in which case the time for competitive exclusion may not be sufficient ).
• Both types " go out of the way ." Mathematically, this means that: they have aggregated (or clumped ) distribution pattern across different microhabitats (often engl as " patches " means. ). Thus, the effective competition intensity is decisively reduced.

Almost all of these cases, and strategies have in common that the equilibrium case, the model is not achieved. Most the time it would take for the competitive superior way to displace its competitors, is not sufficient.

In addition to the cases above, however, it may happen that two species are in competition with each other, even though they have no contact and occupy very different niches in certain circumstances. This is for example the case when both species are hunted by the same robber. The robber has in principle free to choose between his prey objects. But maybe he prefers a kind, or one of the types has a strategy or adaptation, in order to avoid predators. Figuratively speaking now compete for prey species to " enemy free space ". This case is referred to as " apparent competition".

Example of co-existence

In the intertidal zone of rocky shores animals come with severely overlapping niche: chiton, limpet, barnacle, goose barnacle. This grazing and filtering types serve the starfish ( Pisaster ) as food. If one removes the experiment, all specimens of the starfish in an area, the number of original species reduced to one or two. The explanation for this is that a robber holding the density of the superior competitor low and thereby reduces the competition for the inferior species and thereby sichtert their existence.

Competitive situations

• Competition for food → competition over the earth for example to light; under the earth to water and ions.
• Habitat competition → competition for habitat ( areas, nesting sites, caves, ...)
• Mating partner (usually the males compete for the females, only intra -specific)