Practice question

The redundancy hypothesis groups species with overlapping ecological roles. Loss of one member may have little immediate effect because another can compensate, but function declines after losses remove enough members—or a uniquely important member—to cross the system's effective functional threshold. Biodiversity–function hypotheses differ in how they assign ecological importance among species. Complementarity emphasizes distinct contributions, redundancy emphasizes overlap and compensation, rivet theory emphasizes cumulative weakening, keystone theory emphasizes particular influential species, and idiosyncrasy emphasizes context dependence. Real communities can display several patterns because functions differ and environmental conditions alter interactions. Richness alone therefore cannot identify mechanism; species traits, relative abundance, functional groups, and the order of species loss must also be considered. In this context, the keyed term, Critical species are lost, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.