The total global biomass of a group of organisms can be a useful metric for their ecological impact and complements measures of species diversity or individual abundance. Writing in Proceedings of the National Academy of Sciences USA in February 2023, Greenspoon et al. used global data on mammalian population sizes to estimate the biomass of wild mammals. Starting with terrestrial species, they applied a machine-learning approach to the 6% of species for which data are available to infer biomass estimates for the remaining 94%. This showed that the available 6% of species actually account for 55% of the total biomass. Overall, 50% of the biomass was Artiodactyla; Rodentia and Proboscidea constitute the next-largest fractions. Just 10 species (including white-tailed deer, wild boar and African elephants) accounted for 40% of the total biomass. A similar exercise for marine mammals showed that their total biomass is greater than that of wild terrestrial mammals, but their species number is much lower. Baleen whales account for the largest fraction of marine mammal biomass. Finally, the authors used a simpler methodology to estimate the biomass of humans, livestock and domestic pets, to put the wild estimates into perspective. There are 22 Mt of wild terrestrial mammals and 38 Mt of marine mammals, but an estimated 390 Mt of humans and 630 Mt of domesticated animals (of which 420 Mt are cattle, 40 Mt are pigs and 20 Mt are dogs). We chose this study for our Year in Review for its stark indication of the effects of human land use on the natural world, and the imbalance between wild and domesticated species.
Original reference: Proc. Natl Acad. Sci. USA 120, e2204892120 (2023)
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