XX.3.6.2 If the phenotypic cohesion of a population is maintained by normalizing selection by the environment, we speak of an ecological species

It is assumed that the existence of species in organisms without sexual reproduction is frequently maintained through the action of normalizing selection by the environment.If it is assumed, with some simplification, that only a limited number of ecological niches exist in nature, to the use of which organisms can adapt evolutionarily, then the integrity and simultaneously distinctness of a species can be maintained by natural selection, which regularly eliminates from nature all the individuals that substantially deviate from the optimal phenotype.Individuals that deviate only a little from the optimal phenotype or that differ in properties that do not substantially affect the effectiveness of utilization of the particular niche, are removed regularly from the population by genetic drift and, from time to time, by genetic draft.Groups of mutually similar organisms optimally adapted to utilization of the individual niches can be considered to be ecological species (van Valen 1976), where the ecological species conceptis basically again a subtype of the cohesion species concept.

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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.