In its most general use, mortality refers to the death of an individual or the absolute number of deaths in a population. Mortality is more commonly expressed as a proportion (number of deaths relative to population size) or a rate (the proportion of deaths in a given time period), and either measure can be reported as a function of life stage to describe age-specific mortality.
On a large scale, patterns in mortality can strongly influence ecosystem, community, and evolutionary processes. The unidirectional flow of energy and the cycling of nutrients, two fundamental concepts in ecology, are closely tied to regular mortality events, where consumers transfer energy to higher trophic levels and decomposition perpetuates biogeochemical cycles. Mortality events are associated with ecological succession when they allow for a directional change in community composition. Within a species, the differential mortality of individuals with a given genotype is important in the evolutionary mechanisms of natural selection (to the degree to which mortality affects differential reproduction) and genetic drift (when mortality events are random). The most common application of mortality and all of its measures, however, is to studies in population dynamics of species and communities.
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