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

The 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/alpha 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/alpha > 0.60) were characterized by early maturity, short lifespans, low survival. rates, and high fertility and projected population growth rate (lambda) compared to "slow" (F/alpha < 0.15) mammals. In "fast" populations, lambda was overwhelmingly most sensitive to changes in reproductive parameters (age at first reproduction and fertility rates) and relativety insensitive to changes in survival rates. In "slow" populations, lambda 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/alpha ratio and (life-history variables, lambda, and elasticity of lambda, 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/alpha 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. (C) 2004 Elsevier GmbH. All rights reserved.