Trait-based mechanistic approach highlights global patterns and losses of herbivore biomass functional diversity

Abstract

Terrestrial mammalian herbivores strongly shape ecosystems and influence Earth system processes. Herbivorous mammals can alter vegetation structure, accelerate nutrient distribution, and modify carbon cycling. The Late Pleistocene megafauna extinctions triggered significant changes in ecosystems and climate, and current extinctions are having similarly pervasive consequences. A lack of global dynamic models of mammal populations limits our understanding of the ecological role of wild mammals and the consequences of their past and future extinctions. Here we present a global model of herbivore mammal populations defined by their ecological role based on a classification of all extant herbivores (n = 2599) in 24 functional groups. The eco-physiological model predicts present-day mammal biomass in natural conditions. Biomass hotspots occur in areas today dominated by humans, which account for 30% of biomass loss and limit future rewilding potentials. Large herbivore (body mass > 5 kg) biomass is higher in hot and wet areas with high evapotranspiration. Conversely, small herbivore biomass is more evenly distributed, particularly in colder climates. Thus, energy-water dependency is higher in large herbivores than smaller ones. Negative deviations from the biomass and water-energy relationship unveil past extinction patterns. Late Pleistocene extinctions may have triggered a collapse of biomass in Australia and South America and heavy losses in North America and northern Asia. The herbivore biomass estimates provide a quantitative benchmark for conservation and management actions. The herbivore model and the functional classification create new opportunities to integrate mammals into Earth system science.