Practice question

Alternative prey can maintain or increase predator numbers even while the principal prey declines because the predator’s energy intake depends on the total accessible resource base. Generalists may switch toward the alternative, and reproduction or survival supported by that food can offset losses caused by scarcity of the main prey. In a multispecies growth equation, positive contributions from alternative prey can keep predator per-capita growth above mortality. Predator abundance is therefore neither necessarily constant nor unaffected by the main prey’s decline. This subsidy can have an important indirect effect: sustained predators may continue attacking the depleted focal prey, creating apparent competition between prey species and potentially preventing recovery. If predators switch strongly away from rare prey, however, alternative food can stabilize coexistence. Outcomes depend on prey profitability, encounter rates, switching behavior, and whether prey abundances covary. The central prediction is energetic rather than categorical—when alternative prey contribute enough food, predator carrying capacity and population growth need not track the main prey alone.