Question

1. Describe the “fast – slow” continuum for life histories of mammals. List several inter-related life history traits for mammals at each end of the continuum. Give an example of a “fast” and a “slow” mammal.
2. How does body size in mammals relate to lifespan, total length of maternal investment including gestation and lactation, litter size, and neonate size. Describe an example where something about the ecology of a mammal causes it to deviate from the typical expectations for its body size
3. How does litter size vary with latitude and why?

Answer 1

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.