Neutral Theory

Abstract

Neutral theory in ecology explores the properties and dynamics of model ecological communities whose species are assumed to be symmetric, or identical, in their per capita vital rates. Contemporary neutral theory, known as the unified neutral theory (UNT), is constructed on the foundation of the theory of island biogeography, to which a process of speciation has been added. The theory describes how populations and communities would be expected to change if they were influenced solely by ecological drift (demographic stochasticity), random dispersal, and random speciation. The UNT generates a rich array of predictions about patterns of relative species abundance, species–area relationships, and phylogeny, and it provides a biological explanation for Fisher’s α, a widely used measure of species diversity. There have been many recent advancements in the UNT that improve its generality and provide it with a full sampling theory, increasing utility of neutral theory for testing hypotheses about the assembly of ecological communities. Neutral theory has been controversial because of its symmetry assumption. This assumption is only a first approximation, and it is violated to a greater or lesser degree by real demographic differences among species in natural communities. Neutral theory provides the theoretical tools and null hypotheses for assessing the significance of these differences. Neutral theory in ecology has many parallels to neutral theory in population genetics, but it is a much younger area of theoretical inquiry and is therefore less well developed.