Crowding effect
The crowding effect (Engl.) Or Überfülleffekt describes an ecological intraspecific regulatory effect of the self-limitation (self-limitation) takes effect, and thus to the number of individuals of a type in a habitat has (habitat). It describes the regulation of the number of individuals to a level that ensures the survival of the species or the mutual regulation, for example of predator and prey.
Examples
Pork tapeworm
Due to the crowding effect, in larger tapeworm species ( pork tapeworm - Taenia solium ) only one individual lives in the intestine of a host . Mass infestation would lead to intestinal obstruction and thus to death of the host. In this case, regulation takes place chemically via messenger substances.
Tadpoles
The effect is also observed in amphibian larvae , especially in tadpoles . Here the crowding effect results in a development delay and a developmental disorder of some of the larvae . This regulation takes place via the secretion of chemical substances. Depending on the concentration in the organism, this triggers increased eating behavior up to cannibalism, or the inhibition of the entire metabolism. Overall, this ensures the survival of some of the larvae, for example when the spawning waters dry out.
Ground squirrel
The self-limitation of ground squirrel populations can also be explained by the crowding effect . The ground squirrel populations (Arctic, herbivor living rodents ) are characterized by remarkable consistency over the years from. This is due to the high level of self-limitation of the animals, which can be seen as a result of the aggressive building defense. In contrast, there are other herbivorous rodents that occur in the same arctic habitat and that exhibit extreme population fluctuations. Examples of this are representatives of the voles, the lemmings , which show a correspondingly different behavior pattern.
Crowding and the impact on the predator-prey relationship
The predator-prey relationships are affected by crowding or self-limitation, which has an effect on one or both populations. This happens through intraspecific competition or mutual interference. Due to the crowding effect, the zero-growth isoclines run differently than in the Lotka-Volterra model , which was established by Alfred J. Lotka and Vito Volterra . The effect also records the predator-predator interactions, for example. Overall, crowding has a stabilizing effect on the populations, most of all when the influence of the predators is low and these are already subject to strong self-limitation. In summary, two trends in crowding can be described:
- the frequency patterns are stable as long as the predator density is low and the prey population is little influenced by them, as well as in contrast
- a frequency pattern that is not very stable because there is a higher density of predators, which results in a greater reduction in prey.
See also
swell
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- ME Begon, JL Harper, CR Townsend, Ecology, 1st edition, Spektrum Akademischer Verlag, Berlin, 1998.
- GO Batzli, Responses of arctic rodent populations to nutritonal factors, in Oikos 40, 1983.
- A. Watson, RA Moss, A current model of population dynamics in red grouse, in Voous (Ed.), Proceedings of the XVth International Ornithological Congress, 1972.
- G. Caughley, JH Lawton, Plant-herbivore systems, in May (Eds.) Theoretical Ecology: Principles and Applications, 2nd Edition, Oxford, 1981.