SCOTT DETROW, HOST:
We know that Earth's biodiversity is in crisis, but it's hard to monitor lots of different species at once to know exactly how they are changing. Well, NPR's reporter Ari Daniel met a team of researchers who say they have a technique to do just that across an entire country.
(SOUNDBITE OF BIRDS CHIRPING)
ARI DANIEL, BYLINE: We'll start at the base of a colossal guanacaste tree erupting out of the ground in northern Belize. At the base of the trunk is a hole I can just peek inside.
(SOUNDBITE OF FOOTSTEPS)
NINA GARRETT: Now you can hear them chittering.
DANIEL: I follow Nina Garrett's gaze into that hole.
(SOUNDBITE OF BAT CHITTERING)
DANIEL: Oh, yeah, a little guy.
GARRETT: Yeah.
DANIEL: He's on, like, the back wall of the trunk.
GARRETT: Yeah.
DANIEL: It's a common vampire bat. Now, Garrett, who's a biology grad student at York University in Canada, knows that a whole group of these bats reside in this tree. But she's curious if there might also be white-winged vampire bats inside - a different species.
GARRETT: It's always sort of been suspected to be in the area just based on habitat type and range maps.
DANIEL: But bats are elusive and skittish. Most techniques would likely spook any animals roosting here. So how can Garrett tell what's inside this tree? Well, the bats can't hide completely. All creatures, big and small, are forever losing pieces of themselves, little fragments of DNA cast into the environment.
GARRETT: They are shedding hair. It could be little skin cells. It could be saliva, even, when they, you know, breathe out.
DANIEL: Garrett wants to collect this environmental DNA from inside the tree to deduce who's here.
(SOUNDBITE OF FILTER PAPER CRINKLING)
DANIEL: She lays a piece of filter paper atop a small fan, places the apparatus inside the tree, and flips the switch.
(SOUNDBITE OF FAN RUNNING)
DANIEL: The fan draws the internal air across the filter, trapping free-floating DNA, which Garrett can analyze later for the presence of not just bats but any mammal and, if she wanted, plants and fungi too. That's the power of this technique. It can catalog the array of living things in and around this trunk. Problem is, a single tree hollow doesn't tell you how species are doing on a grander scale. And Elizabeth Clare, a biodiversity scientist at York University, wanted to think bigger.
ELIZABETH CLARE: We wanted to see whether we could measure biodiversity on the scale of an entire country.
DANIEL: But she didn't know how to even attempt such a thing. Then, a few years ago, a team of British chemists and physicists reached out with an idea. This group monitors pollution levels across the U.K. using a network of stations that continuously draw air from the environment across little disks of filter paper, a lot like the setup in that guanacaste tree.
CLARE: Those same systems, it turns out, have been accidentally capturing this airborne DNA that we want, at the same time.
DANIEL: Clare and her colleagues took about a year's worth of these filters and analyzed them for DNA. They were astonished by what they found - hundreds of different kinds of insects and spiders, a heap of plants and fungi, and more than a hundred species of birds and mammals. Each filter disc on its own stored just a morsel of information.
CLARE: But when you have hundreds of them being collected all the time at spatially distributed scales and you step back, all of those dots coalesce into a picture.
DANIEL: A picture of the biodiversity of a nation and how that picture is changing. The results appear in a preprint article that hasn't yet been peer reviewed. Ryan Kelly studies environmental DNA at the University of Washington and wasn't involved in the research. He says that unlike a traditional census, DNA is a fuzzier representation of how various organisms are living at a specific place and time. But he finds the approach compelling, given the possibilities it might open up.
RYAN KELLY: If we have biodiversity management questions, all sorts of environmental impact questions, things that we've never really known how to do at scale before, I think this paper points the way to doing that.
DANIEL: And this may be the beginning of bigger things to come, given that these kinds of stations that monitor pollution are distributed in many places around the world, says Elizabeth Clare.
CLARE: If we can do it at the level of a country, we can do it at the level of a continent. This is something that truly could scale to huge, almost planetary measurements.
DANIEL: Imagine that - an ongoing census of global biodiversity pulled right out of thin air. For NPR News, I'm Ari Daniel. Transcript provided by NPR, Copyright NPR.
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