68 The Economist January 8th 2022
Science & technology
EcologySomething in the air
I
n the past, studying ecosystems for
signs of change has needed lots of boots
on the ground. Plants, being sedentary, can
be recorded easily by unleashing an infan
try of phdstudents eager to make a name
for themselves. Taking a census of an area’s
animals is, however, a different matter. It
frequently involves sitting quietly for
hours on end, noting which species walk,
flutter or slither by, and what they are up
to. Sometimes, the troops assigned to do
this see a lot. Sometimes not.
Any viewer of crime dramas might
think, though, that there is a better way.
Just as dnatraces on an unwashed glass or
a carelessly discarded cigarette butt can
place a suspect as having been in a particu
lar place, so can dnashed by a creature as it
goes about its business. Ecologists have
thought of this, and it certainly works for
things like animal droppings. But these,
too, must first be detected and collected—
and they will identify only the animal that
dropped them. What would really speed
things up would be a means of sampling an
entire habitat at one go.
Such an approach is called metagenom
ics, and it does already exist. But, at themoment, it is applied mainly to bodies of
water and to soil, rather than to openair
dryland habitats. Several groups of re
searchers would therefore like to extend it
more widely—by plucking the dnacon
cerned from thin air.Sniffing around
Two of these groups, one led by Christina
Lynggaard of the University of Copenha
gen and the other by Elizabeth Clare of
York University, in Toronto, have used zoos
to test ways of extracting dnafrom the at
mosphere. Zoos are ideal for this because
they house known animals. Both groups
have just published preliminary results in
Current Biology. Others, meanwhile, are al
ready looking in the wild.
Dr Clare’s team adapted an existing
samplecollection method by pumping airthrough filters normally employed to ex
tract dnafrom water. Dr Lynggaard’s team
tried three approaches. The first percolated
the air to be analysed through some water,
to try to dissolve any dnait was carrying
and so permit that dnato be analysed by
conventional metagenomic methods. The
second and third used fans—in one case
large, of the sort employed to cool big com
puters in data centres, and in the other
small, used to cool desktop devices. In both
instances these fans blew air through fil
ters of the type that airconditioning sys
tems use to remove particles of pollution.
Dr Lynggaard’s zoo of choice was Co
penhagen’s. She put testing stations inside
some of the animal houses and the rainfor
est house, and also near several outdoor
enclosures. She let the waterpercolation
and largefan systems run for 30 minutes.
The smallfan system was allowed a more
generous 30 hours to do its stuff.
Dr Clare, meanwhile, chose Hamerton
Zoo Park, in Britain. She, too, ran her tests
for 30 minutes at a time, and did so at a
score of sites, both indoors and out.
Both groups scored palpable hits. All
three of Dr Lynggaard’s methods detected
30 mammal species living nearby. Some,
such as white rhinos, golden lion tamarins
and Eastern grey kangaroos, were exhibits
in the zoo. But many were not. Her equip
ment also noted, for example, red squir
rels, hares, brown rats and domestic cats.
Dr Clare’s findings were similarly encour
aging. Her group not only logged 17 nearby
zoo animals, but also eight other types of
mammals and birds. These includeddnasniffers can now detect which animal species are living in an area→Alsointhissection
69 Breedingcropsinspace
70 An obituaryofE.O.Wilson
71 A palaeontological controversy