Age Structure and Population Dynamics

Abstract

Age structure in populations can take a variety of forms and thus have a variety of effects on population dynamics. Species can be comprised of multiple age classes in a single-stage life cycle (age-class structuring) or show multistage life cycles, where different stages in the life cycle are analogous to age classes (stage structuring). Species can also show both types of age structuring. Stage-structured populations are commonly an adaptation to habitats that show extreme temporal or spatial heterogeneity in resource availability. Such species are usually defined by very high fecundity, display typical r-oriented ‘boom or bust’ population dynamics in one or more life stages, and have the ability to persist through long periods of dormancy in response to unfavorable environmental condition. Age structure in age-class-structured species generally affects population dynamics through more subtle changes in annual population growth rate in response to annual variation in habitat quality and population density. Because this variation affects different age classes unequally, age-structured populations typically show a greater variety of responses to subtle changes in environmental conditions and are thus much more strongly regulated than are stage-structured populations. Regardless of type of age structuring, the effects of age structuring on population dynamics are extremely varied and numerous, and go well beyond simply differences in age-specific survival or fecundity.