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  3. SOCIALITY IN ANIMALS (1) Social insects represent the high point of invertebrate evolution. Some species live in communities

SOCIALITY IN ANIMALS (1) Social insects represent the high point of invertebrate evolution. Some species live in communities

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问题                                             SOCIALITY IN ANIMALS
    (1) Social insects represent the high point of invertebrate evolution. Some species live in communities of millions, coordinating their building and foraging, their reproduction, and their offspring care. Yet sociality is found in only a few species of insects, and is rare among vertebrates as well: wildebeest (large antelope) and lions are the exception rather than the rule. Nearly all fish, amphibians, reptiles, birds, and mammals are solitary, except when courting and mating. Birds and mammals usually rear their young, but year-round family groups are almost unknown, though they are intensely studied where they do exist. The same is true for insects.
    (2) We know, or think we know, that social groups are good. [A] Wolves are better predators when they hunt in packs, and pigeons escape from falcons far more often when feeding in flocks. [B] Group building projects—the dams beavers build to block a body of water provide them with relative safety from predators and the lodges they build for shelter, for instance—can provide a high level of protection and comfort. [C] Why, then, are social species so very rare? [D] In fact, living socially presents inevitable problems that transcend habitat needs so that only when these costs are offset by corresponding benefits is group living a plus.
    (3) The most obvious cost is competition. All the members of a species share the same habitat; when they live together, they are trying to eat the same food and occupy the same nesting sites. In general, there is far less competition away from a group, and selection should favor any individual who (all things being equal) sets off on its own, leaving the members of its group behind to compete among themselves for limited resources. Another difficulty is that concentrations of individuals facilitate disease and parasite transmission. On the whole, social animals carry more parasites and species-specific diseases than do solitary animals. Parasites and diseases diminish the strength and limit the growth of animals, and among highly social creatures, epidemics can devastate whole populations. Distemper (a viral disease) has been known to wipe out entire colonies of seals, for instance. So the penalty of social life is potentially huge.
    (4) But in some instances, the payoffs can be even greater. Two have already been mentioned: cooperative hunting and defensive groups. Social hunting is likely to evolve where prey is too large to be taken by individuals operating alone. To capture wildebeest some members of a group of lions follow their prey and herd them toward others lying in ambush. In other species, individuals forage or hunt simultaneously and share the food. Vampire bats that have had a bad day, for instance, are fed by more successful members of the community, but they are expected to return the favor in the future. Cooperation can even involve sharing information about the location of food. Some colonial birds, such as bank swallows, use the departure direction of a successful forager (food hunter) to locate concentrations of prey. Information transfer can be unintentional though some species make use of special assembly calls or behavior.
    (5) Cooperation in group defense, such as we see in circles of musk oxen or elephants, is quite rare among vertebrates but is prevalent among the social insects. The strategy of employing many eyes to watch for danger, on the other hand, is widespread in birds and mammals. A herd of gazelles (small antelope) is far more likely to spot a lurking lion or a concealed cheetah than is a lone individual, and at a greater distance. In fact, a group enters into a kind of time-sharing arrangement in which individual antelopes alternate biting off a mouthful of grass with a period of erect and watchful chewing. A larger group can afford more bites per individual per minute, there being more eyes to scan for danger. For a small antelope living in a forest where visibility is limited, however, remaining hidden is probably a better bet than assembling into noisy herds.
    (6) Among the millions of species of insects, only a few thousand are social. Those rarities are generally confined to termites and Hymenoptera. All termites are social: their diet (cellulose) requires that each generation feeds a special kind of bacteria or fungi to the next generation to aid in its digestion. Of the numerous hymenopterans, some are social—including all ants and a few bees and wasps—but many are solitary.
An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Some animal species demonstrate sociability, but solitary behaviors are far more typical among animals.
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Answer Choices
(A) Because birds and mammals engage in courting, mating, and establishing year-round family groups to rear young, they are most likely to be social species.
(B) Some social animals obtain food through cooperation and share food and information about food sources with each other.
(C) Social animals help each other watch for danger more effectively, and some species work together to combat predators.
(D) Living in communities presents disadvantages, such as the competition for resources and the easy transmission of diseases.
(E) Some entire species of social animals have become extinct because of disease epidemics.
(F) Although some species of ants, bees, and wasps are famous for their sociality, most social insects are not hymenopterans.
选项
答案B,C,D
解析 本题属于文章总结题，句意为“有些动物体现出社会性，但独居的行为在动物中要典型得多”。B项“某些群居动物通过合作获得食物，并互相分享食物及关于食物源的信息”是第4段整段信息的整合，而且相关信息在第2段也有提及。文章第5段倒数第2句提到，如果群体更大，每只动物每分钟咬的次数就更多，因为能有更多双眼睛盯着危险，C项前半部分“群居动物互相放哨更有效率”可找到依据；而第5段第1、2句提到，团体防御合作在群居昆虫、鸟类、哺乳动物中都很普遍，C项后半部分“某些物种团队合作抵御捕食者”可以找到依据，而且第2段海狸建坝和修建小屋都与团体防御捕食者相关。文章第3段阐述了群居带来的两大代价：竞争和疾病传播，D项“群居会造成一些不利的结果，如资源竞争、疾病的快速传播”是对第3段整段信息的整合。因此，B项和C项均是本文关于动物的社会性的主要观点，而D项则解释了群居的坏处。进而侧面说明为什么更多的动物选择独居，电是文章重要观点之一，且是能解释题干给出的总结句的主要观点。第1段倒数第2、3句指出，几乎所有的鸟类和哺乳动物都是独居的，科学家几乎没有发现它们有全年固定的家庭群居生活，故A项“因为鸟类和哺乳动物会求偶，交配，有全年固定的家庭来抚育后代，所以它们最有可能是群居动物”错误。文章第3段倒数第2、3句指出，流行病可能会毁灭整个种群，但是这只是第3段其中一个信息点，即“群居带来的其中一个代价：传播疾病”，这一段还提到了群居带来的另一个代价：资源竞争。E项“某些群居动物整个物种因为流行性疾病灭亡”对信息的概括不够全面。文章第6段最后一句只提到“在众多的膜翅目昆虫中，所有的蚂蚁、一些蜜蜂、黄蜂是群居动物，但许多都是独居动物”，但并未提及大多数群居昆虫不是膜翅目昆虫，F项“尽管蚂蚁、蜜蜂、黄蜂等一些物种以社会性著名，但大多数群居昆虫不是膜翅目昆虫”在文中找不到依据。
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