Eukaryotes have occupied the planet only during the latter half of its existence. Continental drift has shaped the course of evolution. Mass extinction may lead to the evolutionary radiation of the survivors. Few species are abundant. Many species are rare.
Diversity indexes refer to the number of species present and their relative abundances.
Succession results from facilitation, inhibition, and tolerance of later seral species. Climax communities may vary in composition even within one environment. Terrestrial succession is accompanied by changes in soil structure, biomass, mineral cycling, species abundance, and productivity. Succession may be degradative, constructive, or cyclic. Multiple factors may act synergistically to regulate populations.