PRUDENT investors learned long ago that putting your eggs into lots of baskets reduces risk. Conservationists have now hit on a similar idea: a population of endangered animals will have a better chance of survival if it is divided into interconnected groups. The prospects of the species will be better because the chance that all the constituent subpopulations will die out at the same time is low. And, in the long term, it matters little if one or two groups do disappear, because immigrants from better-faring patches will eventually re-establish the species' old haunts.
谨慎的投资者很早以前就学会通过分散投资来降低风险。自然资源保护者最近偶然得出一个相似的想法：将濒危物种的种群划入几个互相联系的亚种群将增加它们的存活率。此举将为该物种带来更好的前景，因为各亚种群的成员同时灭亡的可能性较低。而且，从长期看来，就算物种的一两个亚种群消失了也无关紧要，因为那些来自食物充沛之"斑块"[1]的“新移民”最终将重建物种原有的生境。
One endangered species divided in just this way is the world's rarest carnivore, the Ethiopian wolf, which lives high in the meadows of the Bale Mountains. Just 350 exist in three pockets of meadow connected by narrow valleys in the Bale Mountains National Park, with a further 150 outside this area.
埃塞俄比亚狼（Ethiopian wolf）就是根据此种方式分群而居的濒危物种之一。它们是世界上最珍稀的食肉动物，居住在贝尔山脉（Bale Mountains）的高地草场之上。在贝尔山国家公园的三块由狭窄峡谷相联接的袖珍草场之上，仅存活着350余只埃塞俄比亚狼，另有150余只生存在其他地区。
Two of the main threats to the Ethiopian wolf come from diseases carried by domestic dogs. One of these, rabies, is of particular concern because it is endemic in the dog population. At first blush, vaccinating the wolves against rabies seems a simple solution. It would be ambitious, because the prevailing thinking—that all individuals matter and therefore all outbreaks of disease should be completely halted—implies that a large proportion of wolves would need to be vaccinated.
埃塞俄比亚狼群所面临的主要威胁有两类来自于家犬所携带的疾病。其中之一为狂犬病，尤为令人担忧，因为这是家犬种群的常见疾病。乍一看来，为狼群注射防狂犬病疫苗是一种简单的办法。不过这个想法未免脱离实际，因为人们普遍认为，每一匹狼都很紧要，因此应当避免狂犬病在任何一匹狼体内爆发，而这意味着将要为大量狼群注射疫苗。
Dan Haydon, of the University of Glasgow, and his colleagues believe that conservation biologists should think differently. With the exception of humans, species are important but individuals are not. Some outbreaks of disease can be tolerated. In a paper published this week in Nature, they recast the mathematics of vaccination with this in mind.
格拉斯哥大学（University of Glasgow）的丹.何顿（Dan Haydon）及其同事认为，保育生物学家（conservation biologist）们的想法应该不同。除人类以外，种群比个体来得重要。疾病在某些个体中爆发是可以接受的。本周刊登于《自然（Nature）》杂志的一篇论文称，他们基于上述想法，重新提出了计算疫苗接种数的数学方法。
On epidemiologists' standard assumption that every individual counts, vaccination programmes are intended to prevent epidemics by ensuring that each infected animal, on average, passes the disease on to less than one healthy animal. This implies that around two-thirds of all the wolves would need to be vaccinated. A programme that sought to save a species rather than individuals would allow each infected wolf to pass the disease on to more than one healthy animal and hence require fewer vaccinations. Dr Haydon and his colleagues have calculated, using data from a rabies outbreak in 2003, that vaccinating between 10% and 25% would suffice, provided veterinarians gave jabs to those wolves living in the narrow valleys that connect the subpopulations.
根据流行病学的标准假设：以个体来计算，要阻止流行病的爆发，疫苗接种方案要确保平均每个受感染的动物将疾病传播给其他健康的动物的数量少于一。这就意味着约有三分之二的狼群需要接受疫苗。但若某方案目的是拯救某个物种而非该物种中所有个体，它将允许上述疾病传播数量多于一，从而减少需要接受疫苗的狼群数量。何顿博士和他的同事曾采用2003年狂犬病爆发的数据进行计算，结果表明，如果兽医为那些居住在连接各分部狼群的峡谷中的狼注射疫苗，那么大约10%到25%的狼群接受疫苗就足够了。
If the threat of rabies arose every five years, targeting all the wolves in the corridors would cut the risk of extinction over a 20-year period by fourfold. If this were backed up by vaccinating a mere 10% of the wolves in the three connected meadows, the chance of extinction would drop to less than one in 1,000. Saving a few seems to be an efficient way of protecting the many.
如果对居住于峡谷内的所有狼群每五年开展一次狂犬病治疗，在20年内，埃塞俄比亚狼种灭亡的可能性将降低四倍。如果，在这一做法的基础之上，再加上对三个相互联结的草场内仅10%的狼群注射疫苗，埃塞俄比亚狼种灭亡的可能性将减至低于千分之一。拯救某物种的少量个体看来是保护该物种大部分个体的有效之道。
注1：斑块(patch)，景观生态学的专有名词，指外观上不同于周围环境的区域，例如海洋中的岛屿、草地上的小片森林等，不同于周围整个大环境的局部环境。翻译 by icetea
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