Global Diversity in Mammalian Life Histories: Environmental Realms and Evolutionary Adaptations

Abstract

Mammalian investments in survival, development, and reproduction are constrained by physiological and evolutionary factors, so their life history strategies can be characterized by a few axes of variation. These axes conform a space in which species are positioned according to which life history strategies are favoured in the environment they exploit. Yet, a global synthesis quantifying the realized mammalian life history diversity is lacking, and exploring how the environment shapes mammalian life history strategies is missing. Here, we used six life history traits to build a global life history space and explored how major environmental realms (land, air, water) influence mammalian life history strategies. We demonstrate that realms are tightly linked to distinct life history strategies. Predominantly, aquatic and aerial species adhere to slower life history strategies, while terrestrial species tend to exhibit faster life histories. Highly encephalized terrestrial species, like monkeys, are a notable exception to these patterns. In addition, species transitioning between the terrestrial and aquatic realms, such as seals and otters, show intermediate life history strategies. Furthermore, time since evolutionary divergence from land is a strong predictor of aquatic life history strategies. Our results provide compelling evidence linking environmental realms to the diversity of life history strategies among mammals, potentially informing assessments of species viability.