Biomass: Earthly mammals on the scales

Unequally distributed: Human biomass exceeds that of all wild land mammals by almost 20 times, that of all marine mammals by 10 times, a global balance sheet for mammalian biomass reveals. According to this, the biomass of terrestrial wildlife is 22 million tons, led by white-tailed deer, wild boar and elephant. Marine mammals account for 39 million tons, with the top three being fin whales, sperm whales and humpback whales. But by far the largest biomass is in our livestock and domestic animals: 630 million tons.

While humans are the dominant and most influential animal species on our planet, when it comes to abundance or biomass, other animal groups come out on top. In particular, the arthropods, which include insects, arachnids, and crabs, far surpass all other animal groups in biomass and abundance. Other mammals are also numerically ahead: rodents account for more than 40 percent of all wild mammal species, bats are the most individual group of land mammals.

But what about the biomass of mammals? Researchers led by Lior Greenspoon from the Weizman Institute of Science in Israel have now drawn up a first inventory of all wild mammals on our planet. To do this, they used data from almost 400 mammal species for which detailed information on abundance and biomass is available. Using an algorithm, they then determined the biomass for the remaining 4,800 terrestrial mammal species based on body weight and estimated distribution.

Biomass of terrestrial wild animals is hardly higher than that of our dogs

The result: all wild mammal species on land together weigh around 22 million tons. Their biomass is thus far below that of humans and their livestock and domestic animals. We humans outnumber our wild fellow mammals by a factor of almost 20 with around 390 million tons of biomass. “Many domestic mammal species even outperform the wild mammal species with the highest proportion of biomass by a factor of ten to a thousand,” report Greenspoon and his team.

With a total of 20 million tons, our domestic dogs alone have almost the same biomass as all wild mammal species combined. At 40 million tons, the pigs we keep weigh almost twice as much as the researchers calculated. In total, the biomass of all livestock and domestic animals is 630 million tons – that is almost 30 times the amount of wild land mammals.

Large even-toed ungulates dominate

Among the top ten wild land mammals, three species are far ahead: the white-tailed deer (Odocoileus virginianus), which is common in North America, with 2.7 million tons, the wild boar with 1.9 million tons and the African elephant with 1.3 million tons. “40 percent of the biomass of wild land mammals is concentrated in just ten species,” report Greenspoon and his colleagues. Seven of them are even-toed ungulates, including five deer species. Our native red deer and fallow deer are seventh and eighth in the top ten.

This also means that rodents, bats and other groups of animals that are far ahead in terms of their number of species and individuals only make up a small proportion of the biomass. “Although more than 95 percent of all mammalian individuals belong to these small species with a body mass of less than one kilogram, they make up less than one-fifth of the total biomass,” the biologists explain. “Bats, for example, account for one-fifth of all mammal species and two-thirds their numbers, but they contribute less than one-tenth of the total biomass of wild land mammals.”

Ocean: Blue Whale fourth only

The situation is similar in the ocean: A few large species also make up the majority of the biomass in marine mammals. Of the total of 39 million tons of biomass from all marine mammals, 23 million tons – around 60 percent – are accounted for by whales. The top three are fin whales at eight, sperm whales at seven and humpback whales at four million tons. The largest mammal on earth, the blue whale, shares fourth place with the southern minke whale. Both weigh three million tons each.

“Our study thus sheds light on the biomass distribution of wild mammals on our planet,” write Greenspoon and his colleagues. “The results are important for recording the global status of mammals and for comparing different groups and species.” At the same time, the results also illustrate how much humans and their livestock and domestic animals now dominate the biomass distribution among mammals. (Proceedings of the National Academy of Sciences, 2023; doi:10.1073/pnas.2204892120 )