Right
now, ants are scurrying around every continent except
Antarctica, doing the
hard work of engineering ecosystems. They spread seeds, churn up soil, and
speed up decomposition. They forage and hunt and get eaten. You may not know
how much you rely on them.
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“Ants are the
movers and shakers of ecosystems,” said Nate Sanders, an ecologist at the
University of Michigan. “Knowing anything about them helps us understand how
ecosystems are put together and how they work.”
“I would argue
most ecosystems would simply collapse without ants,” said Patrick Schultheiss,
an ecologist at the University of Hong Kong. As some naturalists worry about an
insect apocalypse, scientists are racing to keep track of what is at stake. But
they did not know how many ants there are or where they live.
Schultheiss and
colleagues have a new ant census count: 20 quadrillion — 20 with 15 zeros
following it. Ants outnumber humans at least 2.5 million to 1. Ant biomass is
around 20 percent of human biomass, or the mass of carbon from the nearly 8
billion humans now living on Earth. The ant biomass also weighs around 12
megatons, which is about the equivalent of two
Pyramids of Giza on a scale.
Their estimate
assembled censuses of ants living or foraging at the surface that scientists
had previously produced around the world. In more than 1,300 locations, ants
were collected from leaf litter samples or in pit traps, which they fall into
while foraging. The researchers used those counts to estimate the abundance of
ants for different environments, including tropical forests and arid
shrublands.
The study used a
logical, solid approach, said Sanders, who was not involved in the study, but
it has not been done before.
Previous measures
of global ant population and biomass have been either approximations based on
the planet’s total insect population or extrapolated from particular parts of
the world. Estimates for ants’ total biomass had a wide range, from 2.5
megatons of carbon to 70 megatons. The new study instead took a bottom-up
approach, compiling all of the existing ant counts the authors could find and
working up from there.
Sanders said the
study’s approach “is something that you can actually look at and logically get
to the same point the authors got.”
The true number of
ants is almost certainly higher than 20 quadrillion because the new
calculations only included a conservative estimate for arboreal ants and
excluded subterranean ants altogether, Schultheiss said. There were also fewer
studies with the necessary methods from some parts of the world, such as
central Africa and regions in Southeast Asia, while regions such as
North America and Europe had more studies. As more research is carried out in
geographic areas with ant gaps, as well as in treetops and soils, the ant count
will grow.
Tropical areas are
biodiversity hot spots for a large swath of plants and animals, and ants are no
exception. Nearly 70 percent of surface-foraging ants are in low-latitude
biomes, such as tropical forests and grasslands, the study found. A study in
the journal Science Advances this year found the subtropics have some of the
highest ant biodiversity in the world, and the new findings align with that.
With tropical forests’ voluminous canopies and known densities of arboreal
ants, there are likely to be far more tropical ants in the tropics than current
counts.
Getting an updated ant
census was an essential step for scientists to track any changes in the
insects’ ecology as they monitor global insect populations for declines. They
have to know what’s there to know if it’s gone missing.
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