Realized natality occurs:
Realized natality is the actual production of new individuals under the environmental and demographic conditions experienced by a population. It incorporates constraints such as limited food, unavailable mates, unfavorable weather, disease, competition, age structure, and failure of embryos or propagules. Consequently, realized natality is usually below absolute or physiological natality, the maximum reproductive rate possible under ideal conditions. Measuring realized natality requires field or experimental observation over a defined interval and population boundary. It should also be disting
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 11