The fast–slow continuum and mammalian life-history patterns: an empirical evaluation

Summary The fast–slow continuum hypothesis has been proposed to explain the diversity of life-history patterns exhibited by biological populations, but the quantification and population-dynamic consequences of the continuum has remained unclear. I used the ratio of fertility rate to age at first reproduction ( F / α ratio) to quantify the tempo of life-history of 138 populations of mammals, and investigated the life-history and population-dynamic consequences of being “fast” or “slow”. “Fast” mammals ( F / α > 0.60 ) were characterized by early maturity, short lifespans, low survival rates, and high fertility and projected population growth rate ( λ ) compared to “slow” ( F / α 0.15 ) mammals. In “fast” populations, λ was overwhelmingly most sensitive to changes in reproductive parameters (age at first reproduction and fertility rates) and relatively insensitive to changes in survival rates. In “slow” populations, λ was very sensitive to changes in juvenile or adult survival rates, and relatively insensitive to changes in reproductive parameters. The pattern of relationships between the F / α ratio and life-history variables, λ , and elasticity of λ to changes in life-history variables persisted even after the effects of body size and phylogeny were statistically removed. These results suggest that fast–slow continuum in mammalian life-history is independent of body size or phylogeny, that the F / α ratio adequately quantifies the position of a population along a fast–slow continuum, and that the tempo of life- histories has substantial population-dynamic consequences.

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