A team of environmental researchers has estimated the biomass of all wild mammals, finding that humans vastly outweigh all of them combined.
The team, led by Ron Milo of the Weizmann Institute of Science in Rehovot, Israel, was attempting to identify a metric that could be used to track conservation efforts on a global scale.
“Estimating the number of individual organisms is technically challenging even for a single species, due to issues such as detectability, interannual and seasonal variability, and the lack of standardization in measurement methods, especially for small-bodied species,” the team explained in their paper.
“Quantifying the biomass of all mammals allows us to compare species with very different body sizes. Biomass is, therefore, complementary to species richness and other diversity metrics, and can serve as an indicator of wild mammals’ abundance and ecological footprint on a global scale, as a benchmark to follow the temporal dynamics of the global wildlife state, and as an intuitive datasource for conservation efforts.”
The team first collected available population estimates for specific species. They were able to find estimates for 392 land mammals, which is only around 6 percent of all wild land mammal species. To make estimates for the other species, the team turned to machine learning.
“We also obtained a combination of species-specific properties influencing animal abundance, for each wild land mammal,” the team explained. “Using the species-specific properties and the global population reports, we constructed a machine learning model that infers the global populations of the remaining ≈94 percent of species, which lack global abundance estimates.”
This provided estimates for 4,805 mammal species. Though this is still short of the estimated 6,400 living land mammal species, the team didn’t include animals where data was too scarce, and given their rarity they believe the effect on the overall biomass would be negligible anyway.
Overall, the team estimated the biomass of all wild mammal species to be around 22 million tonnes. That biomass wasn’t evenly distributed, with around 40 percent of it concentrated in only 10 species.
White-tailed deer made up the most biomass by any individual species (excluding humans), with 2.7 million tonnes distributed across an estimated 45 million individuals. Wild boar were next, weighing 1.9 million tonnes in all, followed by the African savanna elephant at 1.3 tonnes.
Humans, meanwhile, have a biomass of around 390 million tonnes, while cattle bred as livestock outweigh even us at 420 million tonnes.
“The global composition of mammal biomass reflects human-induced pressures on wild mammal populations: the increasing human population, the growing global demand for animal-based products, and the related expansion of factory farms, leading for example to the result where domesticated mammals now outweigh wild land mammals 30 to one,” the team highlights in their discussion.
“While biomass is not a direct indicator of conservation status or anthropogenic pressures, we suggest that the ratio between the biomass of wild and domesticated species biomass provides further perspective on the extraordinary increase in humanity’s impact on our planet.”
The team hopes that more effort will go into creating global population estimates for other species, which would make the biomass estimate more accurate.
The study is published in the Proceedings of the National Academy of Sciences.
Source Link: Humans Weigh Far More Than All The Wild Mammals On Earth Combined
