Practice question

The fixed key is scientifically inconsistent. Loss of any species reducing total function is the defining expectation of complementarity, because every species contributes a distinct role. Keystone theory instead predicts disproportionately large effects from losing particular influential species, not equivalent reductions after every species loss. 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, Keystone, 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.