Practice question

Alpha diversity is the diversity within a particular local habitat or community. It may be measured simply as species richness or with indices such as Shannon or Simpson diversity that also incorporate relative abundance. For example, the diversity inside one pond, grassland plot, or forest quadrat is alpha diversity. Beta diversity compares composition among such habitats and represents species turnover, while gamma diversity pools species across the larger landscape or region. Delta diversity is sometimes used for turnover across broader geographic gradients, but it is not the standard local component. Scale must be specified because the same area can be “local” in one study and “regional” in another; alpha is defined relative to the sampling hierarchy. High alpha diversity can result from habitat complexity, resource partitioning, moderate disturbance, immigration, or reduced dominance, but a local site with many species need not have high evenness. Similarly, a region can have high gamma diversity even when each site has modest alpha diversity if different sites contain different species. The term therefore identifies both a spatial level and the diversity structure measured at that level.