Conservationists (自然保护主义者) may be miscalculating the numbers of the
{{B}}threatened{{/B}} animals such as elephants, say African and American
researchers. The error occurs because of a flaw in the way they estimate animal
numbers from the piles of dung (粪) the creatures leave behind.
The mistake could lead researchers to think that there are twice as many
elephants as there really are in some regions according to Andrew Plumptre of
the Wildlife Conservation Society (WCS) in New York. Biologist
Katy Payne of Cornell University in Ithaca, New York, agrees. "We really need to
know elephant numbers and the evidence that we have is quite indirect," says
Payne, who electronically tracks elephants. Counting elephants
from planes is impossible in the vast rainforests of Central Africa. So
researchers often estimate elephant numbers by counting dung piles in a given
area. They also need to know the rate at which dung decays: Because it's
extremely difficult to determine these rates. However, researchers counting
elephants in one region tend to rely on standard decay rates established
elsewhere. But researchers at the WCS have found that this
decay rate varies from region to region depending on the climate and
environment. Using the wrong values can lead the census astray (离开正道), says
Plumptre. He and his colleague Anthony Chifu Nchanji studied
decaying elephant dung in the forests of Cameroon. They found that the dung
decayed between 55 and 65 percent more slowly than the dung in the rainforests
of neighbouring Gabon. If researchers use decay rates from Gabon to count
elephants in Cameroon, they would probably find more elephants than are actually
around. This could mean estimates in Cameroon are at least twice as high as
those derived from decay rates calculated locally, says Plumptre. "However
accurate your dung density estimate might be, the decay rate can severely affect
the result." Plumptre also says that the dung-pile census
should be carried out over a region similar in size to an elephant's natural
range. The usual technique of monitoring only small, protected areas
distorts numbers because elephants move in and out of these regions, he says.
"If the elephant population increases within the protected area, you can not
determine whether it is a real increase or whether it is due to elephants moving
in because they are being poached (入侵偷猎) outside." Plumptre
says that similar problems may also affect other animal census studies that rely
on indirect evidence such as nests, tracks or burrows (地洞).
单选题
The word "threatened" in the first sentence of the first paragraph
could be best replaced by ______.