Understanding the pattern of life-history strategies in animals has long been a goal in comparative biology. Animals show an extreme range of life history strategies ranging from clonal corals that can live for millennia to the rapidly reproducing seven-figure pygmy goby which survives no longer than 59 days. While trade-offs and constraints, such as imposed by body size and energy allocation, are known to be important in determining species life-history strategies, the overall pattern of these strategies across animals is still unclear. For example, it is not known whether certain taxonomic groups or modes-of-life (i.e. arboreal, aquatic etc.), are associated with particular combinations of life-history traits. Here we use demographic data from the COMADRE database for a diverse range of animal species, spanning from sponges to birds, to calculate measures of reproduction, survival and growth components of life-history strategies. Using a phylogenetic comparative approach we test; (1) whether life-history components scale with body mass as theoretically expected; (2) whether animal life-history strategies follow a classic fast-slow continuum or are more complex; (3) whether certain life-history strategies are associated with particular taxonomic groups or ecological modes of life.
Results/Conclusions
We calculated the age at sexual maturity; reproductive life expectancy; generation time; survival curve-type; degree of iteroparity; and mean reproductive and progressive growth rates for over one hundred animal species. We found that each of these life-history components generally scaled with mass as predicted, with positive scaling for biological times (i.e. generation time), and negative scaling for rates (i.e. mean reproductive rate). After correcting for mass we show that life-history strategies are predominantly explained by two demographic axes, one relating to the fast-slow continuum and another relating to the timing of survival and reproduction as defined by survival curve-type and degree of iteroparity. We also find that certain modes-of-life are associated with particular life-history strategies, such as between arboreal lifestyles and a slow pace of life. However, while life-history strategies are constrained by body mass, the fast-slow trade-off and ecological mode-of-life, the timing within a species’ lifespan of survival and reproduction is independent of these constraints. Our results highlight that animal life-history strategies are far more flexible than previously thought. We provide a common framework for comparisons of animal life-histories across the widest phylogenetic range yet analysed and show that life-history strategy is evolutionarily labile.