(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 per cent 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 PlumptreHowever 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 elephants natural range The usual technique of monitoring only small,protected areas distorts numbers because elephants move in and out of these regions,he saysIf the elephant population increases within the protected area,you can not determine whether 1t 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)
36 The wordthreatenedin the first sentence of the first paragraph could be best replaced by
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