The planet’s wild mammals are quite literally losing weight, while one terrestrial mammal now consumes almost all the planet’s resources, a new study concludes.
All the world’s terrestrial mammals—elephants and armadillos, mice and marmosets, leopards and lemmings—would probably collectively weigh no more than 20 million tonnes, according to the new calculations.
By comparison, humankind, in mass, probably tips the scales at 390 million tonnes. Throw in all the domestic mammals that feed or serve humanity, and the pointer climbs another 630 million tonnes.
This 1000-million-tonne total of humanity and its chosen creatures is, according to another new finding from the same research laboratory, about the same as the mass of the most prolific and crowded phylum on the planet: the arthropods, a group that includes flies, spiders, termites, springtails, bees, ants, butterflies, and grasshoppers.
Both studies are signed by, among others, Prof. Ron Milo of the Weizmann Institute in Israel. The first sentence of his laboratory mission statement makes the case for him: “We love to understand and explain the world using numbers as our sixth sense,” it says. And the latest measurement of the mass of the surviving wild mammals—creatures with whom and from whom Homo sapiens evolved—simply fills in details of the bigger pictures he and his colleagues have assembled over the past decade or so.
In 2018, the same laboratory tried to calculate a gross estimate of all the carbon in all the planet’s living tissue—wood and root, leaf and mould, flesh and bone, blood, hoof, and horn and so on—to confirm what was already increasingly clear: humankind enjoyed a disproportionate share of life’s basic chemical currency.
Two years later, Milo and his team made an estimate of the mass of human artefacts—from asphalt roads to supermarket shopping bags, from castles and carparks to carts and aircraft carriers, from cities to cardigans—to warn that the mass of human manufacture was now greater than that of all living tissue on Earth.
The latest research involves a closer look at the potential survival of some of the most charismatic creatures that share the planet with humanity: because conservationists, biologists, and campaigners have been concerned about the numbers of tigers, or gorillas, or oryx, or orangutans, or whales and dugongs, many of the mammalian groups have been well–studied and closely monitored over many decades. The scientists report in the Proceedings of the National Academy of Sciences that they assembled census data and other information about 392 wild mammal species (about 6% of the total) and then used computer models and calculations to make comparable judgments about the rest, arriving at the alarming finding that human livestock weighed at least 30 times more.
They made not-quite-so-confident judgments about marine mammals—think baleen whales, seals, dugongs, and so on—that roam 70% of the planet, to arrive at an estimate of 40 million tonnes. This is twice the mass of the land-dwelling wild mammals. But it is still 15 times less than the total of the world’s farmed cattle, sheep, and pigs.
In the journal Science Advances, some of the same researchers also tackled the puzzle of the arthropods, the little jointy-legged things that exist everywhere in huge—but reportedly diminishing—numbers. They found that the possible head count of individual insects and other groups living in and on the soil alone could surpass 10 billion billion. This adds up to probably 1000 million tonnes in biomass. In numbers, most of these creatures are soil mites and springtails. In mass, 40% are termites, and 10% ants.
“Arthropods have been described as ‘the little things that run the world’ because of their central role in multiple ecological processes,” said Dr. Yuval Rosenberg, one of the leaders of the study. “We must take them into account if we’re to fully understand humanity’s impact on the planet and the possible consequences of climate change.”
The findings are not quite comparable: the arthropod study takes the measure of dry weight; the mammalian one of “wet” biomass. Even so, the estimates of insect mass cannot be so confident, nor provide the detail, as the one that some of the same team also made of the examination of the planet’s much more extensively-studied wild mammals. They found that almost half the mass of the land dwellers was made up of the artiodactyls, or even-hoofed creatures such as deer, giraffes, antelopes, and camels. Carnivores such as lions and tigers and wolves made up 3%, bats 7%, rodents 16%, marsupials 7%, elephants 8%, and the perissodactyla or odd-hoofed creatures such as horses, tapirs, and rhinos just 1%. The planet’s wild primates—humankind’s closest wild relatives—were estimated to make up 4% of the total mass.
There are huge uncertainties and the authors concede their calculations were “technically challenging”. But the message of such research is inescapable: the Anthropocene has arrived. Humans now dominate the globe, and many of the other species now depend on human protection for their survival.
“This study is an attempt to see the bigger picture,” Milo said. “The dazzling diversity of various mammal species may obscure the dramatic changes affecting our planet. But the global distribution of biomass reveals quantifiable evidence of a reality that can be difficult to grasp otherwise: it lays bare the dominance of humanity and its livestock over the far smaller populations of remaining wild mammals.”
