Practice question

“Colonization and extinction” for the equilibrium number of species on an island is a balance between. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. At equilibrium, species identities can continue to turn over even when richness is approximately stable. The model predicts a balance of rates, not an absence of colonization or extinction. The remaining alternatives—“Immigration and reproduction”, “Competition and predation”, “Mutation and genetic drift”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Island biogeography explains species richness as a dynamic balance between immigration and extinction. Immigration generally declines as an island fills with species, whereas extinction rises as more species divide finite area and maintain smaller populations. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.