Wild mammals are not only our closest animal relatives, they are often among the best-studied animal species in the world. Nevertheless, it was previously unclear how large the biomass of land and sea mammals is on our planet. A comprehensive balance sheet now shows that the biomass of all terrestrial, non-domesticated mammals is 22 million tons, and that of marine mammals is 39 million tons. This means that the biomass of humans exceeds that of all wild land mammals by a factor of almost 20 and that of all marine mammals by a factor of ten. However, by far the largest biomass is in our livestock and domestic animals: their mass adds up to around 630 million tons, as the researchers report.
In view of the rapid loss of species, it is all the more important to know the existing species as well as possible and also to keep an eye on their number and their share in the earth’s ecosystems. But there are significant gaps in our knowledge of the animal world on our planet. Even for mammals, which are some of the best-studied and most iconic animals, the data is incomplete. Many studies have examined the distribution, diversity and number of species of terrestrial and marine mammals. So far, however, there have only been very rough estimates for the biomass of mammals. “But biomass is a good complement to species richness and other indicators of biodiversity,” explain Lior Greenspoon from the Weizman Institute of Science in Israel and his colleagues. Because the biomass also provides information about the ecological footprint and abundance on a global level.
Deer, wild boar and elephant among the top three
That’s why Greenspoon and his team have now created a comprehensive 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. The evaluation showed that the biomass of all wild mammal species on land is around 22 million tons. Compared to the biomass of our own species, this is little: At around 390 million tons, we humans exceed our wild fellow mammals by almost 20 times. The discrepancy with livestock and domestic animals is even clearer: Their biomass is 630 million tons – that’s almost 30 times more than wild land mammals, as the researchers report. 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.
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 10 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. Rodents, bats and other animal groups that are far ahead in terms of their number of species and individuals, on the other hand, 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,” explain the biologists. “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.”
Whales dominate the biomass in the sea
A few large species also make up the majority of the biomass of marine mammals. Of the total 39 million tons of biomass from all marine mammals, 23 million tons – about 60 percent – are accounted for by whales, as Greenspoon and his colleagues have determined. 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, each weighing three million tons. “Our study thus sheds light on the biomass distribution of wild mammals on our planet,” the scientists write. “The results are important for understanding the global status of mammals and for comparing different groups and species.”
Source: Lior Greenspoon (Weizman Institute of Science, Rehovot) et al., Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2204892120)