Which of these contributes to predator’s carrying capacity besides victim abundance?
Alternative prey can raise a predator population’s effective carrying capacity because they provide energy when the principal victim is scarce. A generalist predator may switch its foraging effort, maintain survival and reproduction, and persist at densities that the focal prey alone could not support. In population models, predator growth depends on the summed contributions of consumable prey, so an additional positive term can keep net growth above mortality. Refuge space generally protects prey and may lower predator intake rather than support more predators. Mutualism and migration can influence abundance in particular systems, but neither is the direct additional food resource specified. Alternative prey can also produce apparent competition: one prey species supports more predators, increasing predation on another species even though the prey do not compete for resources. Whether alternative prey stabilize dynamics depends on predator switching, prey synchrony, and functional responses. The central carrying-capacity mechanism is energetic subsidy—more total accessible prey biomass permits a larger equilibrium predator population than the main prey population could sustain alone.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 14