Practice question

Beta diversity represents species turnover among communities, habitats, or sites. It is high when local assemblages share few species and low when they are compositionally similar. Pairwise turnover can be measured with dissimilarity coefficients such as 1 minus Jaccard or Sørensen similarity, while regional multiplicative partitioning uses β = γ/α. Alpha diversity describes diversity within one local community, and gamma diversity is the pooled diversity across the wider region. Delta diversity is sometimes applied to turnover across larger geographic gradients, but beta is the standard between-community component. Turnover should be distinguished from nestedness. Two sites may differ because one contains a subset of the other, producing richness loss without true species replacement; modern beta-diversity analyses can separate these components. Environmental filtering, dispersal limitation, geographic distance, disturbance, and historical barriers all generate turnover. For conservation, high beta diversity means that protecting a single species-rich site may fail to capture many regional species, so multiple compositionally distinct habitats are needed. The concept therefore links local assemblages to regional gamma diversity by quantifying how rapidly membership changes across space or time.