Practice question

The complementarity hypothesis assumes that species contribute distinct traits or ecological functions. Differences in resource use, phenology, spatial occupation, or facilitation allow mixtures to capture resources more completely and perform better than would be expected if all species were functionally interchangeable. Ecosystem function can respond to diversity through niche partitioning, facilitation, insurance, or a sampling effect. Niche differences allow more complete resource use, asynchronous responses stabilize aggregate output, and high richness increases the chance of including a strongly productive species. Functional redundancy can buffer initial losses, but compensation is rarely unlimited because species differ in response traits and performance under stress. Consequently, both response shape and species identity are needed to distinguish among competing biodiversity hypotheses. In this context, the keyed term, Each species adds unique function, 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.