Title：Sociality in Animals

　　Social insects represent the high point of invertebrate evolution. Some specieslive 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.

　　We know, or think we know, that social groups are good. Wolves are better predators when they hunt in packs, and pigeons escape from falcons far more often when feeding in flocks. Group building projects—the dams beavers build to block a body of water that provides them with relative safety from predators and the lodges they build for shelter, for instance—can provide a high level of protection and comfort. Why, then, are social species so very rare? 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.

　　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.

　　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.

　　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 antelope 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 noisyherds.

　　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 feed 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

　　Paragraph 1

　　Social insects represent the high point of invertebrate evolution. Some specieslive 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.

　　1. According to paragraph 1, which of the following is true of sociality among animal species?

　　 Sociality is much more common among invertebrates than among vertebrates.

　　 Very few animals are considered social because most spend the majority of their lives alone.

　　 An animal group must contain more than one family unit for the species tobe considered social.

　　 All animals that rear their young are considered to be social.

　　Paragraph 2

　　We know, or think we know, that social groups are good. Wolves are better predators when they hunt in packs, and pigeons escape from falcons far more often when feeding in flocks. Group building projects—the dams beavers build to block a body of water that provides them with relative safety from predators and the lodges they build for shelter, for instance—can provide a high level of protection and comfort. Why, then, are social species so very rare? 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.

　　2. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

　　 Group living allows some animals to transcend problems of habitat.

　　 Group living is only advantageous when benefits outweigh inevitable problems.

　　 Problems resulting from living socially extend beyond the habitat.

　　 It is difficult to determine whether the benefits of social living offset its costs

　　Paragraph 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 speciesspecific 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 potentiallyhuge.

　　3. What does paragraph 3 say about the relationship between natural selection and animals that live apart from other members of their species?

　　 Natural selection does not favor living apart because individuals are unable to obtain resources equal to those of group members.

　　 Natural selection does not favor living apart because of the intense competition for resources among individuals apart from a group.

　　 Natural selection favors living apart because individuals are unlikely to attract the attention of predators.

　　 Natural selection favors living apart because group living increases competition for limited resources of food and nesting sites.

　　4. The word "devastate " in the passage is closest in meaning to

　　 alter

　　 spread to

　　 destroy

　　 involve

　　5. In paragraph 3, why does the author mention distemper and its effect on seals?

　　 To explain why sociality is now relatively rare in seals 

　　To prove that parasites prevent animals from growing healthy and strong

　　 To show how easily social animals transmit potentially deadly diseases

　　 To provide an example of a species-specific disease that affects solitary animals

　　標(biāo)題:社會性的動物

　　群居昆蟲代表了無脊椎動物進(jìn)化的高潮。一些物種生活在數(shù)以百萬計的群體中，協(xié)調(diào)它們的建筑和覓食、繁殖和后代的照料。然而，只有少數(shù)種類的昆蟲存在社會性，而且在脊椎動物中也很罕見:羚羊(大羚羊)和獅子是例外，而不是規(guī)則。幾乎所有的魚、兩棲動物、爬行動物、鳥類和哺乳動物都是孤獨(dú)的，除非是在求愛和交配的時候。鳥類和哺乳動物通常會養(yǎng)育它們的幼仔，但一年四季的家庭幾乎是不為人知的，盡管它們的研究對象確實(shí)存在。昆蟲也是如此。

　　我們知道，或者認(rèn)為我們知道，社會群體是好的。狼是更好的捕食者，當(dāng)它們成群獵食時，鴿子會從獵鷹中逃脫，更多時候是成群覓食。團(tuán)體建筑工程——筑壩者建造水壩來阻擋水體，使它們相對安全，免受掠食者和他們?yōu)楸幼o(hù)所所建的小屋的保護(hù)，例如，可以提供高水平的保護(hù)和舒適。那么，為什么社會物種如此稀有呢?事實(shí)上，在社會生活中，生活中必然會出現(xiàn)超越生境需求的問題，因此只有當(dāng)這些成本被相應(yīng)的利益抵消時，才會有一群人活得更久。

　　最明顯的代價就是競爭。一個物種的所有成員都有相同的棲息地;當(dāng)它們生活在一起時，它們會嘗試吃同樣的食物，并占據(jù)相同的巢穴�？偟膩碚f，一個群體的競爭要少得多，而選擇應(yīng)該有利于任何一個人(所有的事物都是平等的)自己出發(fā)，讓集團(tuán)的成員在有限的資源中相互競爭。另一個困難是個體的濃度促進(jìn)了疾病和寄生蟲的傳播�？偟膩碚f，社會動物比獨(dú)居動物攜帶更多的寄生蟲和物種特異性疾病。寄生蟲和疾病削弱了動物的力量，限制了動物的生長，在高度社會化的生物中，流行病會毀滅整個種群。犬瘟熱(一種病毒性疾病)已經(jīng)被認(rèn)為可以消滅所有的海豹群體，例如。因此，社會生活的懲罰可能是巨大的。

　　但在某些情況下，回報可能更大。其中有兩個已經(jīng)被提及:合作狩獵和防御團(tuán)體。社會狩獵很可能會進(jìn)化，因?yàn)楂C物太大而不能單獨(dú)行動。為了捕獲角馬，一些獅子跟隨它們的獵物，把它們趕到埋伏的地方。在其他物種中，個體覓食或同時捕食并分享食物。例如，那些日子過得很糟糕的吸血蝙蝠，會被更成功的社區(qū)成員喂養(yǎng)，但他們在未來會得到回報。合作甚至可以分享有關(guān)食物位置的信息。一些殖民地的鳥類，如河岸燕子，利用一個成功的覓食者(食物獵人)的離開方向來定位獵物的濃度。信息傳遞可以是無意的，盡管有些物種利用特殊的集合調(diào)用或行為。

　　集體防御的合作，如我們在麝牛或大象的圈子里看到的，在脊椎動物中很少見，但在群居昆蟲中很普遍。另一方面，用許多眼睛來觀察危險的策略在鳥類和哺乳動物中很普遍。一群瞪羚(小羚羊)更有可能發(fā)現(xiàn)潛伏的獅子或隱藏的獵豹，而不是一個單獨(dú)的個體，而且距離更遠(yuǎn)。事實(shí)上，一個群體進(jìn)入了一種分時的安排，在這種安排中，每只羚羊都在不停地咬著一口草，一段時間的直立和警惕的咀嚼。一個更大的群體每分鐘可以承受更多的叮咬，有更多的眼睛去掃描危險。然而，對于生活在森林中能見度有限的小羚羊來說，隱藏起來可能比聚集在喧鬧的羊群中要好得多。

　　在幾百萬種昆蟲中，只有幾千種是社會性昆蟲。這些稀有性一般局限于白蟻和膜翅目昆蟲。所有白蟻都是社會性的:它們的飲食(纖維素)要求每一代都為下一代提供一種特殊的細(xì)菌或真菌以幫助消化。在眾多的膜翅類動物中，有些是社會性的，包括所有的螞蟻和一些蜜蜂和黃蜂，但許多都是獨(dú)居的。

　　本條第一款

　　群居昆蟲代表了無脊椎動物進(jìn)化的高潮。一些物種生活在數(shù)以百萬計的群體中，協(xié)調(diào)它們的建筑和覓食、繁殖和后代的照料。然而，只有少數(shù)種類的昆蟲存在社會性，而且在脊椎動物中也很罕見:羚羊(大羚羊)和獅子是例外，而不是規(guī)則。幾乎所有的魚、兩棲動物、爬行動物、鳥類和哺乳動物都是孤獨(dú)的，除非是在求愛和交配的時候。鳥類和哺乳動物我們