A dome-shaped net recruitment curve is due to:
A dome-shaped net recruitment curve rises at low abundance because more potential parents can produce more recruits, reaches a maximum, and then falls when crowding becomes severe. Intraspecific competition for food, space, or other resources reduces survival or reproduction at high density. The descending limb therefore records overcompensating density dependence rather than constant mortality or an absence of density effects. Population regulation concerns feedback, not mere limitation. A drought may sharply reduce numbers yet fail to push the population toward a repeatable equilibrium. Competition, disease, territoriality, and some predator responses can strengthen with crowding, changing births or deaths in a direction that opposes the density change and thereby producing regulation. Reading the terms biologically, rather than memorizing labels, shows how individual survival and reproduction scale up to population change. Ecological predictions remain conditional on the stated environment, because changing resources, mortality, or interactions can alter the observed demographic pattern. This interpretation connects individual-level processes with measurable changes in survival, reproduction, recruitment, or abundance across the population.
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 5