Practice question

The species–area relationship shows that larger sampled or habitat areas generally contain more species. It is often represented as S = cAᶻ, where S is species richness, A is area, c depends on the taxonomic group and region, and z is the slope on logarithmic axes. Several mechanisms contribute. Larger areas contain more individuals, increasing the chance of encountering rare species; they usually encompass more habitat types and environmental gradients, creating additional niches; and larger populations have lower stochastic extinction risk. On islands or isolated habitat fragments, area also affects extinction rates and interacts with distance-dependent colonization. Competition, predation, and mortality can strongly alter local composition, but their effects on richness vary with intensity, trophic structure, and environmental context. Area has a broad, repeatedly observed scaling relationship with richness across taxa and regions, making it the strongest general predictor among these alternatives. Sampling design still matters: simply surveying more area detects more species even without ecological change, whereas genuine habitat-area effects operate through population persistence and heterogeneity. Log-transforming the relation yields log S = log c + z log A, allowing comparisons of slopes.