Multistage life cycles generally represent an adaptation to environments that show extreme temporal or spatial heterogeneity in availability of key habitats. The r-selected dynamics, storage effect, and high dispersal potential seen in some life stages allow a very rapid population response when habitats become available. Many of the effects of age-class structuring on population dynamics detailed above are seen to some degree in at least one life stage in stage-structured species as well. However, with stage-structured populations, effects on population dynamics also result from each life stage potentially having a unique life history and therefore behaving more as distinct life forms rather than age classes. For example, different life stages of many invertebrate and amphibian species may have completely different physical forms and ecological requirements, and thus behave as distinct life forms with unique niches rather than as different age classes of the same life form. Because effects of age structure on age classes in the different life stages of multistage species can be similar to those detailed above for age-class-structured single-stage species, this article emphasizes unique aspects of population dynamics driven by the distinct stage structuring of these species.
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