The use of the term “vacant niches” (unused but potentially usable resources) has recently increased in ecological literature. According to some studies, vacant niches are quite numerous in nature, especially, but not exclusively, in disturbed ecosystems. However, the concept of “vacant niche” is still controversial in ecology because of the failure to reach an agreement on how to define a situation when an ecosystem is devoid of such niches. In evolutionary biology, as distinct from ecology, this concept arouses fewer controversies and has contributed to the creation of the ecological theory of adaptive radiation. Still other evolutionists have used this concept to describe the course and mechanisms of the evolutionary assembly of ecosystems (nutrient cycles and ecological pyramids). These evolutionists attempt to prove that in the course of diversifi cation, vacant niches are not only occupied but are also created by newly evolved organisms.

Keywords: saturated communities, ecosystem evolution, succession, assembly