IV.7.1 The absence of interspecific competition must not be mistaken for the absence of intraspecific competition.

Interspecies competition and intraspecies competition are frequently confused.The conception of the vacant niche was quite popular amongst ecologists in the 1980’s and rather unpopular in the 1990’s.This term basically contains an internal contradiction.A niche is defined only by the ecological requirements of the organism that occupies it.However, the concept of a vacant (empty) niche is intuitively easy to understand, so that it seems to have become established in contemporary ecological literature.A number of field workers have pointed out that there are a great excess of unutilized resources in nature, that the environment would be capable of supporting a much greater number of species of organisms than exist at the present time.A great many species of herbivorous insects feed only one kind of plant and a great many plants remain completely unutilized by insects, i.e. they have no herbivore.In this connection, a great many biologists are of the opinion that the existence of unutilized resources is contrary to Darwin’s theory of evolution, as it indicates that there is no substantial competition in nature that would force species to evolve.

            It should be emphasized that the existence of vacant niches and unutilized resources could indicate not very intense interspecies competition, but is in no way connected with the existence of non-existence of intraspecies competition.Even in an environment with a great many unutilized resources, i.e. with a great many potential niches, the individual species of organisms each occupies its own niche, within which the members of a single species usually compete very fiercely.Simultaneously, competition need not in any way consist in a fight for nutrition.Organisms can compete for hiding places, in rates of reproduction, in the ability to resist pressure from more numerous populations of predators, etc.Even where an ecologist sees quite ideal conditions, i.e. a small population in an environment with adequate sources of all nutrients and where he would thus expect an absence of any kind of interspecies orintraspecies competition, the existence of intraspecies selection can be predicted with complete certainty.If organisms were not limited in any way, their populations would not remain at the same size, but would grow exponentially.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.