Natality and Mortality

Natality is the process by which populations gain new individuals through birth, hatching, germination or fission, and is essentially synonymous with birth rate; the two underlying biological contributors to natality are fertility (the reproductive capacity itself) and fecundity (the realised reproductive output). Natality is commonly expressed as a crude birth rate, i.e., the number of new organisms born per female per unit time, and more formally as $b = \dfrac{\text{number of births per unit time}}{\text{average population}}$. Mortality is the opposing, population-reducing process — the loss of individuals through death in a given unit of time — and is generally expressed as specific mortality (the count of members of an original population that have died after a given interval has elapsed) or as a crude death rate, $d = \dfrac{\text{number of deaths per unit time}}{\text{average population}}$. Mortality rate is itself density-dependent: it tends to rise at high population density because crowding brings greater hazards — increased predation pressure, faster disease spread, and heighten …