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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.
According to paragraph 4, how do lions increase their chances of successfully hunting wildebeest?
选项 A、They work together as a team to chase and capture the animals.
B、They wait until groups of the animals come close to their hiding place.
C、They follow and catch the animals that are operating alone.
D、They focus on the smallest members of the species.
答案A
解析 本题属于事实信息题，询问狮子如何提高捕捉到牛羚的机会。第4段第4句提到，为了捕获牛羚，一些狮子跟在猎物之后，一直将它们赶到其他狮子埋伏的地方。这说明狮子是通过分工合作(一部分负责追赶，一部分负责埋伏围堵)的方式捕获牛羚的，故A项符合题意。B项“狮子们一直等着，直到一群群动物靠近它们隐藏的地方”、C项“狮子们跟随并捕获单独行动的动物”和D项“狮子们把注意力放在最小的牛羚上”均无依据。
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