According to some concepts, only a limited number of potential niches exist in each environment and thus the number of species that can adapt their phenotypes to these niches is also limited. If, through mutations, an individual deviates too much from the phenotype that is optimal for the niche of a particular species, it or its progeny will sooner or later be eliminated from the population. This theory, which became the basis for the concept of an ecological species, has the advantage that it can also be employed for species that do not reproduce sexually or for species where the frequency of sexual processes or gene flow between the individual populations within the area of occurrence of the particular species is so low that it could not suffice for ensuring species cohesion (Ehrlich & Raven 1969). On the other hand, the model of an ecological species has the disadvantage that its basic starting point, i.e. the assumption of a limited number of niches occurring in nature, does not much agree with current knowledge in ecology. Ecological data and conclusions following from other biological disciplines tend to indicate that there are an enormous number of potential niches in nature, of which only a small portion is actually occupied. Thus, it tends to seem from an evolutionary point of view that the individual species do not select their niches from a previously existing limited choice, but rather that they actively create them themselves. Until a giraffe is formed in evolution, the relevant niche basically does not exist; to be more exact, the given resources objectively existing in nature can be utilized in an almost unlimited number of ways and can become part of an enormous number of basically different niches. If a niche is formed in nature, i.e. if a species emerges in evolution that occupies it and begins to utilize its resources, a number of originally existing potential niches can simultaneously disappear and, at the same time, a number of new potential niches can, on the other hand, be formed.
- more or less1937
- not at all1900