Impact of mortality on predator population size in systems with stage-structured prey.
ABSTRACT- The relationship between a predator population's mortality rate and its population size is investigated for several simple predator-prey models with stage-structured prey populations. Alternative models are considered; these differ in their assumptions about the nature of density dependence in the prey's population growth, and the stage-selectivity of the predator. The stability of the predator-prey system is also investigated. Instability occurs at high, rather than low predator mortality rates in most models with highly stage-selective predation; this is the opposite of the effect of mortality on stability in models with homogeneous prey populations. The results suggest that it may be common for a stable predator population to increase in abundance as its own mortality rate increases, provided that the predator has a saturating functional response. Sufficiently strong density dependence in the prey generally reverses this outcome, and results in a decrease in predator population size with increasing predator mortality rate. This raises two coupled questions; (1) do such increases in population with higher mortality actually occur in nature; and (2) if not, what prevents them from occurring?
Key words: size structure, predation, harvesting, stability
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