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鏇存柊鏅�(sh铆)闁擄細2015-12-10 11:50:58 渚嗘簮锛殀0

鐎忚

鏀惰棌

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銆€銆€A Dog鈥檚 Dilemma

銆€銆€Finding a babysitter while you go out to work is, for example, an inconvenience. For the African wild dog, one of the continents鈥檚 most endangered carnivores, it鈥檚 a matter of life and death. New research shows that once packs fall below a certain size, they are not enough animals to both hunt food and stay at home protecting the young.

銆€銆€The African wild dog has declined drastically over the past century. Habitual loss, persecution and unexplained outbreaks of disease have all been blamed. Only 3,000 to 5,000 animals remain, and the species is expected to go extinct within decades if the trend continues.

銆€銆€Other large carnivores such as the spotted hyena face similar pressures, yet are not declining. Now Franck Courchamp of Cambridge University has found a reason why. The dog鈥檚 weakness lies in its social organization.

銆€銆€Within each pack of up to 20 adults and pups, only he dominant male and female bread. The remaining animals help raise the pups, cooperating to hunt prey and defend the kill from other carnivores.

銆€銆€Because pups can鈥檛 keep up on a hunt, large packs leave an adult behind to protect them from predators, which include lions and hyenas. But leaving a babysitter also carries costs. A smaller hunting party is less able to tackle large prey and to defend the kill. There is also one less stomach in which to carry food back to the den, and one more mouth to feed when they get there.

銆€銆€Courchamp investigated this awkward trade-off by modeling how the costs of a babysitter change with decreasing pack size. This showed that packs of more than five adults should be able to feed all the pups and still spare a babysitter. But with smaller packs, either the hunting or the babysitting suffers, or the animals have to compensate by increasing he number of hunting excursions鈥晈hich itself carries a cost to the pack.

銆€銆€Field observations in Zimbabwe supported the model. Packs of five animals or fewer left pups unguarded more frequently than larger packs did. There was also evidence that when they did leave a babysitter, they were forced to hunt more often.

銆€銆€A pack which drops below a critical size becomes caught in a vicious circle, says Courchamp, who is now at Paris-Sud University. 鈥淧oor reproduction and low survival further reduces pack size, culminating in failure of the whole pack.鈥� And deaths caused by human activity, says Courchamp, may be what reduces pack numbers to below the sustainable threshold. Mammal ecologist Chris Carbone at London鈥檚 Institute of Zoology agrees. Maintaining the integrity of wild dog packs will be vital in preserving the species, he says.

銆€銆€瑭炲尟锛�

銆€銆€carnivore 椋熻倝鍕�(d貌ng)鐗� hyena 楝ｇ嫍

銆€銆€pup 灏忕嫍 prey 琚崟椋熺殑鍕�(d貌ng)鐗�

銆€銆€predator 鎹曢鑰� culminate 鍛婄祩锛岄仈(d谩)鍒伴爞榛�(di菐n)

銆€銆€integrity 瀹屾暣 Zimbabwe 娲ュ反甯冮煁

銆€銆€娉ㄩ噵锛�

銆€銆€1.A smaller hunting party is less able to tackle large prey and to defend the kill.锛氫竴鍊�(g猫)杓冨皬鐨勬崟鐛电兢楂斾笉澶鏄撴崟鎹夊ぇ鍕�(d貌ng)鐗�锛屼篃涓嶅お瀹规槗淇濊(w猫i)鐛电嵅鐗�銆�

銆€銆€2. A pack which drops below a critical size becomes caught in a vicious circle, says Courchamp锛欳ourchamp瑾�锛屸€滀竴鍊�(g猫)缇ら珨鐨勮(gu墨)妯￠檷鍒拌鎴掔窔浠ヤ笅鏅�(sh铆)灏辨渻(hu矛)闄峰叆鎯℃€у惊鐠�(hu谩n)銆傗€�

銆€銆€绶寸繏(x铆)

銆€銆€1.The African wild dog has been endangered.