Practice question

“Both species are strong competitors” for which of the following reflects unstable coexistence. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Species interactions are classified by their net effects on the fitness of each participant, but those effects can change with density, resource supply, life stage, and environmental stress. Competition reduces access to shared limiting factors, whereas predation and parasitism transfer resources from victim to consumer. The remaining alternatives—“Both species are weak competitors”, “α12 and α21 < 1”, “Species interact independently”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Coexistence requires stabilizing differences that make each species limit itself more strongly than it limits its competitor, or an equalizing process that keeps fitness differences small. Without such mechanisms, persistent competitive asymmetry tends toward exclusion. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.