Practice question

The keystone hypothesis predicts that ecosystem or community function depends disproportionately on one or a few influential species. Removing such a species can trigger an abrupt functional decline even when total richness changes only slightly, because numerous interactions or regulatory effects depend on that species. 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, Immediately after key species loss, 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.