Right now, ants are scurrying across every continent except Antarctica, doing the hard work of tech ecosystems. They scatter seeds, churning the soil and accelerate decomposition. They forage and hunt and are eaten. You may not know how much you rely on them.
“Ants are the movers and shakers of ecosystems,” said Nate Sanders, an ecologist at the University of Michigan. “If we know something about it, we can understand how ecosystems are set up and how they work.”
“I would argue that without ants, most ecosystems would just collapse,” said Patrick Schultheiss, an ecologist at the University of Hong Kong. While some naturalists worry about an insect apocalypse, scientists are rushing to keep track of what’s at stake. But they didn’t know how many ants there are or where they live.
dr. Schultheiss and colleagues have a new ant count: 20 quadrillion – 20 with 15 zeros on it. Ants outnumber humans at least 2.5 million to 1. Ant biomass is about 20 percent of human biomass, or the mass of carbon of the nearly 8 billion people now living on Earth. The ant biomass also weighs about 12 megatons, which is about the equivalent of two Giza pyramids on one scale.
Their estimate, published Monday in the Proceedings of the National Academy of Sciences, collected counts of ants living or foraging on the surface that scientists had previously produced around the world. At more than 1,300 sites, ants were collected from leaf litter samples or in pits, where they fall while foraging. The researchers used those counts to estimate ant abundance for a variety of environments, including tropical forests and arid scrub.
The study used a logical, solid approach, said Dr. Sanders, who was not involved in the study, but it hadn’t been done before.
Previous measurements of global ant population and biomass were either approximations based on the planet’s total insect population or extrapolated from certain parts of the world. Estimates for the total biomass of ants ranged from 2.5 megatons of carbon to 70 megatons. The new study instead took a bottom-up approach, collecting all existing ant counts the authors could find and working from there.
dr. Sanders said the study’s approach is “something you can really look at and logically get to the same point as the authors.”
The actual number of ants is almost certainly higher than 20 quadrillion because the new calculations only include a conservative estimate for arboreal ants and ruled out underground ants altogether, said Dr. schultheiss. There were also fewer studies with the necessary methods from some parts of the world such as Central Africa and regions of Southeast Asia, while regions such as North America and Europe had more studies. As more research is done in geographic areas with ant holes, as well as treetops and soils, the number of ants will increase.
“I wouldn’t be surprised if it turns out to be an order of magnitude higher in reality,” said Sabine Nooten, an ecologist at the University of Hong Kong and co-author of the study. “We’re just scratching the surface.”
Tropical areas are biodiversity hotspots for a large number of plants and animals, and ants are no exception. Nearly 70 percent of surface-foraging ants reside in low-latitude biomes, such as tropical forests and grasslands, the study found. A study in this year’s journal Science Advances found that the subtropics have some of the highest ant biodiversity in the world, and the new findings match that. With the sizable canopies of tropical forests and known tree ant densities, there are likely many more tropical ants in the tropics than current counts.
Obtaining an updated ant count has been an essential step for scientists to monitor any changes in insect ecology as they monitor global insect populations for decline. They need to know what’s there to know if it’s missing.
“It’s a great foundation that I hope will improve with time,” said Dr. Sanders. “It’s a real call to action for biodiversity scientists around the world, not only to fill these gaps, but also to start monitoring potential changes.”
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