Practice question

Community species richness is directly shaped by ecological variables such as area, productivity, habitat heterogeneity, disturbance, colonization, extinction, and biotic interactions. Larger areas tend to hold more individuals and habitat types. Productivity affects resource supply, although its relationship with richness can be positive, negative, or hump-shaped. Competition can reduce richness through exclusion or, under some conditions, promote niche differentiation. A DNA sequence is information at the molecular level and is not used as a direct ecological predictor of how many species occur in a sampled community. Genetic variation and evolutionary history ultimately influence traits, speciation, and adaptation, so DNA is not irrelevant to biodiversity in the broadest causal sense. However, merely specifying “DNA sequence” does not define an environmental or community process comparable to area, productivity, or competition. It may be used methodologically to identify cryptic species or estimate phylogenetic diversity, which can change measured richness if taxonomy improves, but that is a measurement issue rather than a direct determinant in this comparison. The intended distinction is between proximal ecological controls of community richness and underlying hereditary information within organisms.