ARE THERE ENOUGH OF US OUT THERE ALREADY?

IT’S NO SURPRISE THAT, beginning around 1950, we’re no longer living in the Holocene Epoch but the Anthropocene. It turns out that by many measures, including biomass, human beings have overrun the natural world. Indeed, Elizabeth Pennisi’s article addresses this: “Wild Mammals Add Up to a ‘Shockingly Tiny’ Total Biomass,” Science, March 3, 2023. 

Here are tidbits gleaned from Pennisi’s fascinating article, together with my usual Internet sleuthing.

An Epochal Transition. As described by the University of California, Berkeley, “The Holocene is the name given to the last 11,700 years of the Earth’s history—the time since the end of the last major glacial epoch, or ‘ice age.’ Since then there have been small-scale climate shifts—notably the ‘Little Ice Age’ between 1200 and 1700 A.D.—but in general, the Holocene has been a relatively warm period in between ice ages.” 

The word “Holocene,” according to Merriam-Webster, derives from the Greek holos, “whole,” and kainos, “recent,” as opposed to the previous Pleistocene (“most recent”) Epoch, dating from about 2,580,000 to 11,700 years ago. 

“Anthropocene” derives from the Greek ánthrōpos, “human,” in recognizing our impact on the natural world.

Biomass Totals. “Humans and domestic species far outweigh other mammals,” notes Elizabeth Pennisi. In comparing total biomass, she cites a recent study published in the Proceedings of the National Academy of Sciences concluding that wild land mammals alive now have a total biomass of 22 million tons, and marine mammals account for another 40 million tons. 

“What wild mammal treads most heavily on the land?” Pennisi asks. “Not elephants, according to a new global estimate of the total masses of mammal species. Not wild mice, despite their numbers. The heavyweight champion is that furtive denizen of parks, meadows, and forests throughout the Americas, the white-tailed deer. It accounts for almost 10% of the total biomass of wild land mammals.”

Human Impact. But, Pennisi notes, “Those numbers are relatively puny: Ants alone amount to 80 million tons, Schultheiss [a University of Würzburg behavior ecologist] has estimated. But the comparison the team hopes will capture attention is with humans, who weigh in at 390 million tons, with their livestock and other hangers-on such as urban rats adding another 630 million tons.”

Other Animal Totals. “On land,” Pennisi says, “much of the wild mammalian biomass is concentrated in a few large-bodied species, including boar, elephants, kangaroos, and several kinds of deer. The top 10 species account for 8.8 million tons—40% of the estimated global wild land mammal biomass, Milo’s team reported [quantitative biologist Ron Milo is at the Weizmann Institute of Science]. Rodents—not counting human-associated rats and mice—make up 16% and carnivores account for 3% of that biomass.”

Mass Versus Numbers. “Among marine mammals,” she continues, “baleen whales account for more than half of the biomass. But in sheer numbers, bats rule the mammalian world: They constitute two-thirds of individual wild mammals, though only 7% of the total terrestrial mass.”

Machine-learning Methodology. Pennisi recounts, “At Milo’s lab, Lior Greenspoon and Eyal Krieger were able to find detailed data on the global number, body weight, range, and other measures for 392 wild mammal species, enough to calculate their total biomass directly. To predict the total mass for less-studied mammals, they used the data for half of the 392 species to train a machine learning system.”

Having the A.I. do the work, “They then fed whatever data they could find—ranges, body sizes, abundance, diets—for each of about 4400 additional mammal species into the model to estimate their biomasses and abundance.”

On the Domestic Front. The A.I reported that cows collectively weigh 420 million tons and dogs about as much as all wild land mammals. The biomass of housecats is about double that of African elephants and four times that of moose.”

Why Bother? Some researchers say these efforts “provide a snapshot of the state of the mammalian world,” but “won’t drive conservation….”

Pennisi says, “Not true, counters Sabine Nooten, an insect ecologist and Schultheiss’s collaborator at Würzburg. ‘We can only conserve what we understand, and we can only truly understand what we can quantify.’ ”

And, quite beside all this, it certainly explains our moving from the Holocene to the Anthropocene. ds 

© Dennis Simanaitis, SimanaitisSays.com, 2023