Practice question

Alpha, beta, and gamma diversity refer to different spatial scales. Alpha diversity is measured within a relatively homogeneous local habitat or community and may be represented by species richness or an index combining richness and evenness. Beta diversity quantifies differentiation among habitats, often as species turnover or as a multiplicative relation such as β = γ/α. Gamma diversity is the total diversity of the larger landscape or region containing those local communities. Consequently, describing alpha diversity as regional diversity reverses the established scale terminology. A forest quadrat’s species diversity is alpha diversity; the change from forest to grassland is beta diversity; and the pooled diversity of the full landscape is gamma diversity. These levels are linked but not interchangeable. High gamma diversity can arise from high local richness, high turnover among sites, or both. Likewise, a landscape whose sites are individually rich may still have low beta diversity if their species lists are nearly identical. The scale-based definitions make “Alpha = regional diversity” the incorrect statement, while within-community alpha, between-community beta, and regional gamma are mutually consistent.