A lifestyle view of life-history evolution

The evolution of life cycles or life histories is one of the most important topics in behavioral and population ecology and in evolutionary biology. There is inherent interest in explaining the diversity of life cycles among species: These span a range from rapidly multiplying but short-lived bacteria and yeast to the long life and slow breeding of the wandering albatross (1). However, when we look closely at the characteristics of a life history, we see traits that reflect the evolutionary fitness of organisms: survival of individuals from young to old and the onset, magnitude, and duration of reproduction. When advantages in life-history characteristics are associated with heritable organismal traits, the essence of natural selection is born (2).

During the past two decades, a paradigm surrounding the evolution of life histories has developed. This paradigm has grown from two research traditions: studies of the diversity of life histories among species and experimental research within a few model species. The first part of the current paradigm is that life histories vary with the body size of species. This is the well known mouse-to-elephant relationship in many traits, and mammals have played a central role in extending this idea from initial physiological traits, such as metabolism, to more ecological traits, such as population densities and life histories (3–5). On the mouse-end of this continuum, we have short life spans and rapid reproduction, and on the elephant-end, we have long lives and slow breeding. However, a change in the tempo of life is not solely reflected by size. When the influence of body size of species is held statistically invariant, a new continuum of faster lives to slower lives can be seen, although the placement of species along …

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