The primary questions for the understanding of dominance is: what keeps most species rare and makes few species dominant? Even in neutral communities consisting of ecologically equivalent species, overall biomass or abundance are dominated by few species. Neutral theory predicts that even in the absence of any trait differences between species, stochastic events will create dominance for some and rarity of many species. The identity of the dominant species and the degree of dominance follows not from any ecological interactions or environmental conditions, but depends on ecological drift, dispersal success, and timing of colonization. However, most realized communities deviate from neutrality and the primary question posed above requires mechanistic answers. These answers will strongly differ with the scale of the analysis, for example, on the local scale of interacting populations (i.e., communities) and on the regional scale of species pools. Within communities, the main mechanisms creating dominance are interactions within and between species as well as the abiotic factors constraining these interactions. Between communities, dispersal and spatial niche differentiation are strong forces regulating how the regional species pool transfers into local community structure. Addressing the regional species pool itself, the evolution and descent of certain lineages is the major driver of regional dominance.
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