题目内容：
回答题：A Dog's Dilemma
Finding a babysitter while you go out to work is, for example,an inconvenience. For the African wild dog, one of the continent's mostendangered carnivores, it's a matter of life and death. New research shows thatonce packs fall below a certain size, there are not enough animals to both huntfood and stay at home protecting the young.
The African wild dog has declined drastically over the pastcentury. Habitual loss, persecution and unexplained outbreaks of disease haveall been blameD．Only 3, 000 to 5, 000 animals remain, and the species isexpected to go extinct within decades if the trend continues.
Other large carnivores such as the spotted hyena face similarpressures, yet are not declining. Now Franck Courchamp of Cambridge Universityhas found a reason why. The dog's weakness lies in its social organisation.
Within each pack of up to 20 adults and pups, only the dominantmale and female breeD．The remaining animals help raise the pups, cooperatingto hunt prey and defend the kill from other carnivores.
Because pups can't keep up on a hunt, large packs leave anadult behind to protect them from predators, which include lions and hyenas.But leaving a babysitter also carries costs. A smaller hunting party is lessable to tackle large prey and to defend the kill. There is also one lessstomach in which to carry food hack to the den, and one more mouth to feed whenthey get there.
Courchamp investigated this awkward trade-off by modelling howthe costs of a babysitter change with decreasing pack size. This showed thatpacks of more than five adults should be able to feed all the pups and stillspare a babysitter. But with smaller packs, either the hunting or thebabysitting suffers, or the animals have to compensate by increasing the numberof hunting excursions- which itself
carries a cost to the pack.
Field observations in Zimbabwe supported the model. Packs offive animals or fewer left pups unguarded more frequently than larger packsdiD．There was also evidence that when they did leave a babysitter, they wereforced to hunt more often.
A pack which drops below a critical size becomes caught in avicious circle, says Courchamp, who is now at Paris-Sud University. "Poorreproduction and low survival further reduces pack size, culminating in failureof the whole pack. " And deaths caused by human activity, says Courchamp,may be what reduces pack numbers to below the sustainable thresholD．Mammalecologist Chris Carbone at London's Institute of Zoology agrees. Maintainingthe integrity of wild dog packs will be vital in pre
serving the species, he says.
The African wild dog has been endangered. A．Right
B．Wrong
C．Not mentioned
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