The Relative Importance of Life‐History Variables to Population Growth Rate in Mammals: Cole’s Prediction Revisited

TLDR

The relative importance of life‑history variables to population growth rate (λ) has substantial consequences for the study of life‑history evolution and for the dynamics of biological populations. The study examines how perturbations in life‑history variables affect population dynamics and predicts age‑structured population responses based on the F/α ratio. The authors estimated λ elasticities for age at maturity, age at last reproduction, juvenile survival, adult survival, and fertility across 142 mammalian populations, then used these elasticities to assess relative importance and test theoretical predictions. Across most mammalian populations, no single life‑history variable dominated λ, and this held after accounting for phylogeny and body size; empirical support for theoretical predictions was weak, but when F/α > 0.60, age at maturity and fertility were most influential, whereas when F/α < 0.15, survival rates dominated.

Abstract

The relative importance of life‐history variables to population growth rate (λ) has substantial consequences for the study of life‐history evolution and for the dynamics of biological populations. Using life‐history data for 142 natural populations of mammals, we estimated the elasticity of λ to changes in age at maturity (α), age at last reproduction (ω), juvenile survival (Pj), adult survival (Pa), and fertility (F). Elasticities were then used to quantify the relative importance of α, ω, Pj, Pa, and F to λ and to test theoretical predictions regarding the relative influence on λ of changes in life‐history variables. Neither α nor any other single life‐history variable had the largest relative influence on λ in the majority of the populations, and this pattern did not change substantially when effects of phylogeny and body size were statistically removed. Empirical support for theoretical predictions was poor at best. However, analyses of elasticities on the basis of the magnitude (F) and onset (α) of reproduction revealed that α, followed by F, had the largest relative influence on λ in populations characterized by early maturity and high reproductive rates, or when $$F/ \alpha &gt; 0.60$$ . When maturity was delayed and reproductive rates were low, or when $$F/ \alpha &lt; 0.15$$ , survival rates were overwhelmingly most influential, and reproductive parameters (α and F) had little relative influence on λ. Population dynamic consequences of likely responses of biological populations to perturbations in life‐history variables are examined, and predictions are made regarding the numerical dynamics of age‐structured populations on the basis of values of the F/α ratio.