2018-12-05     18:57 来源: 原创
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预测文章1- Foundational and Keystone Species

The harmony present in any ecological system relies on the inclusion of different types of species, each with a specific role or set of roles. Although to some extent all species contribute in important ways, scientists are now learning about the pivotal parts played by, what are being called foundational and keystone species. Interestingly, the latter represent only a small fraction of the overall animal population within an ecosystem while the former can make up a significant portion of it. In both cases, though, their removal often results in massive changes to, if not the complete destruction of, their ecosystems. Efforts to conserve these species are currently based on the new idea that they prevent the start of a domino effect that would, once started, be unstoppable. 

Foundational species are the backbones of the systems they inhabit. These species are referred to as primary producers, which means that they generate a large amount of the abundance other species require to survive. In most cases, they are a type of vegetation or stationary animal. Coral, which tends to grow in large colonies, is often pointed to as an example. Eventually a group of colonies will form a coral reef, which can sustain a complete ecosystem around it. The reef contains the skeletal remains of coral at its bottom and living coral on the top. Numerous animals, including zooplankton and sponges, live in the small crevices located in the rock-like bottom. At the top, the coral interacts with seaweed and other forms of vegetation to regulate the levels of nutrients and gases in the water. There are also more than four thousand types of fish that live on or around most coral reefs. Fish rely on the holes in the reef for protection. The more colorful species of coral provide excellent camouflage for fish, as well. Obviously, without its foundational species, an ecosystem would collapse. 

Keystone species play less apparent but equally important roles. The name comes from the keystones used in the building of stone archways. The keystone receives the smallest amount of pressure of all the stones in the arch, but, if it is removed, the arch will collapse. In the same way, research is now showing, certain species within ecosystems, although they are smaller in numbers and biomass than most of the other species present, act like keystones. These species are being categorized as either predators or engineers, depending on their relationships with the various species around them. These categories are not absolute, though, and animals are moved from one to the other as new facts come to light. 

In the case of predator keystone species, there are four carnivores that prey on herbivores and other animals. Also, the herbivores usually have no other natural predator in the ecosystem. The sea otter is now considered by many scientists to be a keystone species, because it controls the number of sea urchins, which have few other predators. Both species can be found around kelp forests, which are in the warm parts of the world's oceans. Because kelp is an underwater plant, its roots are not used for the collection of nutrients. Instead, they are there to anchor the plant. As soon as enough sea urchins chewed on the roots, which are fragile, the kelp would be removed from the ecosystem. If the sea otter were to disappear, the urchins would quickly grow in number and destroy all the kelp. 

■Engineer keystone species maintain the balance in ecosystems in different ways. ■Although bears tend to live in forests, they bring in important sources of nutrients from ocean and sea-based ecosystems. ■ The bears capture large salmon from the water and take them into the forest to eat them. ■ This distributes large amounts of protein in the form of bear waste matter as well as uneaten portions of salmon. The protein eventually supports life in the forest, either as a food source for smaller animals or the vegetation. Another species that plays a part similar to that of bears is the beaver. Through the construction of dams, beavers convert small rivers into ponds and marshes. The new landscape in turn supports a variety of fish, which in turn provides a dependable source of food for the beavers. The removal of beavers from an ecosystem would also remove the landscape it depends on.




in the same way=similarly

预测文章2- Three Theories about Origin of Life

Oxygen and nitrogen are major components of our current atmosphere. But the kinds of hydrogen reactions with other gases that are required to transform simple organic molecules into complex ones are interrupted by oxygen, which combines with hydrogen atoms from other compounds. Therefore, life on Earth must have originated when there was very little oxygen in Earth’s atmosphere. The modern scientific theory of life’s origin was first formulated in the 1920s by Russian scientist Aleksandr  Oparin and independently by British scientist J. B. S. Haldane. The assumption that life sprang up from chemical reactions that were initiated in the early atmosphere(oxygen-poor/hydrogen-rich) and came to completion in the early oceans was posited by the Oparin-Haldane hypothesis, as it came to be called. Oparin and Haldane suggested that the hydrogen-containing gases caused to react with each other to form organic compounds by energy sources such as sunlight and lightning.

With regard to the view that these complex organic compounds could have begun to shape in Earth’s oceans, some researchers remain skeptical. The probability that the fundamental building blocks of life, formaldehyde (H2CO) and hydrogen cyanide(HCN), even though they were probably available, would have been concentrated sufficiently to allow further reactions to occur was likely small. And the more complex organic compounds that might have formed in this way would not have lasted long in the surface-ocean environment, because photochemical and thermal reactions would have destroyed them. Therefore, researchers have sought alternative explanations for how complex organic compounds formed.

There is one possibility that the relevant organic compounds were created in space, and asteroids or comets brought them to Earth, probably as tiny dust particles. Recovered from the stratosphere (an upper region of Earth’s atmosphere), interplanetary dust particles (IDPs) is tiny particles that are known to be extraterrestrial origin. From various researches, we know that organic compounds, including amino acids, exist in IDPs as well as in some meteorite. Now, we actually have identified the fact that amino acids and many other complex organic compounds in interstellar dust clouds. It is believed that they form from reactions between charged particles and neutral molecules. Those atoms appear in interstellar dust clouds at very low temperatures-on the order of 200 or more degrees below zero on the Celsius scale. It may seem surprising that organic chemistry could occur in the interstellar environment, but it is precisely the extremely low temperatures involved that allow complex organic molecules to exist because temperatures are too cold to allow them to decompose.

■It is thought that some of the molecules created in the interstellar environment have survived the collapse of the gas and dust cloud that formed our solar nebula and Sun. ■They would have been incorporated into solid materials that condensed out of the nebula and formed asteroids and comets. ■Such materials might have been delivered to Earth in great quantities during the heavy bombardment period of solar system history, between 4.5 and 3.8 billion years ago. ■The hypothesis that life took place in or around hydrothermal vents (hot springs), where new seafloor is being created along mid-ocean ridges (underwater mountain chains) at the ocean’s bottom is the third theory of life’s origin. By seawater that flows a kilometer or more down through crevices in the rock, is heated, and then rises rapidly back to the surface, the ridges are cooled. During the process, the water gathers substances such as hydrogen, hydrogen sulfide, and dissolved ferrous iron. When it meets the cold water, the extremely hot (350°C) vent water generates a dark plume comprised mostly of iron sulfide, a compound produced by the reaction between ferrous iron and hydrogen sulfide.

Still, the explanation that submarine hydrothermal vents a likely place for life to have originated is controversial. In vent systems, there are various types of materials from which organic molecules can be synthesized. However, complex organic molecules are not stable at the high temperatures observed in vents positioned directly on the axis of a ridge. If life did originate at the mid-ocean ridges, it probably did so in cooler, off-axis vents. Some researchers claim that perfect place for life to have begun would be in some near-freezing surface environment because even the off-axis vents are too warm. The dispute as to whether life originated in a hot or cold environment is unlikely to stop.


skeptical = doubtful

sufficiently = adequately

sought = looked for

been incorporated into = become part of

预测文章3- Comets

Comets are among the most interesting and unpredictable bodies in the solar system. They are made of frozen gases (water vapor, ammonia, methane, carbon dioxide, and carbon monoxide) that hold together small pieces of rocky and metallic materials. Many comets travel in very elongated orbits that carry them far beyond Pluto. These long-period comets take hundreds of thousands of years to complete a single orbit around the Sun. However, a few short-period comets (those having an orbital period of less than 200 years), such as Halley’s Comet, make a regular encounters with the inner solar system.

When a comet first becomes visible from Earth, it appears very small, but as it approaches the Sun, solar energy begins to vaporize the frozen gases, producing a glowing head called the coma. The size of the coma varies greatly from one comet to another. Extremely rare ones exceed the size of the Sun, but most approximate the size of Jupiter. Within the coma, a small glowing nucleus with a diameter of only a few kilometers can sometimes be detected. As comets approach the Sun, some develop a tail that extends for millions of kilometers. Despite the enormous size of their tails and comas, comets are relatively small members of the solar system.

The observation that the tail of a comet points away from the Sun in a slightly curved manner led early astronomers to propose that the Sun has a repulsive force that pushes the particles of the coma away, thereby forming the tail. Today, two solar forces are known to contribute to this formation. One, radiation pressure, pushes dust particles away from the coma. The second, known as solar wind, is responsible for moving the ionized gases, particularly carbon monoxide. Sometimes a single tail composed of both dust and ionized gases is produced, but often two tails—one of dust, the other, a blue streak of ionized gases—are observed.

As a comet moves away from the Sun, the gases forming the coma recondense, the tail disappears, and the comet returns to distant space. Material that was blown from the coma to form the tail is lost from the comet forever. Consequently, it is believed that most comets cannot survive more than a few hundred close orbits of the Sun. Once all the gases are expelled, the remaining material—a swarm of tiny metallic and stony particles—continues the orbit without a coma or a tail.

Comets apparently originate in two regions of the outer solar system. Most short-period comets are thought to orbit beyond Neptune in a region called the Kuiper belt, in honor of the astronomer Gerald Kuiper. During the past decade over a hundred of these icy bodies have been discovered. Most Kuiper belt comets move in nearly circular orbits that lie roughly in the same plane as the planets. A chance collision between two comets, or the gravitational influence of one of the Jovian planets—Jupiter, Saturn, Uranus, and Neptune—may occasionally alter the orbit of a comet in these regions enough to send it to the inner solar system and into our view.

Unlike short-period comets, long-period comets have elliptical orbits that are not confined to the plane of the solar system. These comets appear to be distributed in all directions from the Sun, forming a spherical shell around the solar system, called the Oort cloud, after the Dutch astronomer Jan Oort. Millions of comets are believed to orbit the Sun at distances greater than 10,000 times the Earth-Sun distance. The gravitational effect of a distant passing star is thought to send an occasional Oort cloud comet into a highly eccentric orbit that carries it toward the Sun. However, only a tiny portion of the Oort cloud comets have orbits that bring them into the inner solar system.

The most famous short-period comet is Halley’s Comet, named after English astronomer Edmond Halley. Its orbital period averages 76 years, and every one of its 30 appearances since 240 B.C. has been recorded by Chinese astronomers. When seen in 1910, Halley’s Comet had developed a tail nearly 1.6 million kilometers (1 million miles) long and was visible during daylight hours. Its most recent approach occurred in 1986.


exceed=go beyond


propose=offer the theory


预测文章4- Agricultural Society in Eighteenth-Century British America

In the northern American colonies, especially New England, tight-knit farming families, organized in communities of several thousand people, dotted the landscape by the mid-eighteenth century. New Englanders staked their future on a mixed economy. They cleared forests for timber used in barrels, ships, houses, and barns. They plumbed the offshore waters for fish to feed local populations. And they cultivated and grazed as much of the thin-soiled, rocky hills and bottomlands as they could recover from the forest.

The farmers of the middle colonies-Pennsylvania, Delaware, New Jersey, and New York-set their wooden plows to much richer soils than New Englanders did. They enjoyed the additional advantage of setting an area already partly cleared by Native Americans who had relied more on agriculture than had New England tribes. Thus favored, mid-Atlantic farm families produced modest surpluses of corn, wheat, beef, and pork. By the mid-eighteenth century, ships from New York and Philadelphia were carrying these foodstuffs not only to the West Indies, always  a primary market, but also to areas that could no longer feed themselves-England, Spain, Portugal, and even New England.

In the North, the broad ownership of land distinguished farming society from every other agricultural region of the Western world. Although differences in circumstances and ability led gradually toward greater social stratification, in most communities, the truly rich and terribly poor were few and the gap between them small compared with European society. Most men other than indentured servants (servants contracted to work for a specific number of years) lived to purchase or inherit a farm of at least 50 acres. With their family’s labor, they earned a decent existence and provided a small inheritance for each of their children. Settlers valued land highly, for owning land ordinarily guaranteed both economic independence and political rights.

By the eighteenth century, amid widespread property ownership, a rising population pressed against a limited land supply, especially in New England. Family farms could not be divided and subdivided indefinitely, for it took at least fifty acres(of which only a quarter could usually be cropped) to support a single family. In Concurd, Massachusetts, for example, the founders had worked farms averaging about 250 acres. A century later, in the 1730s, the average farm had shrunk by two thirds, as farm owners struggled to provide an inheritance for the three or four sons that the average marriage produced.

The decreasing fertility of the soil compounded the problem of dwindling farm size in New England. When land had been plentiful, farmers planted crops in the same field for three years and then let it lie fallow (unplanted) in pasture seven years or more until it regained its fertility. But on the smaller farms of the eighteenth century, farmers had reduced fallow time to only a year or two. Such intense use of the soil reduced crop yields, forcing farmers to plow marginal land or shift to livestock production.

The diminishing size and productivity of family farms forced many New Englanders to move to the frontier or out of the area altogether in the eighteen century. "Many of our old towns are too full of inhabitants for husbandry, many of them living on small shares of land, " complained one writer. In Concurd, one of every four adult males migrated from town every decade from the 1740s on, and in many towns migration out was even greater. Some drifted south to New York and Pennsylvania. Others sought opportunities as artisans in the coastal towns or took to the sea. More headed for the colonies, western frontier or north into New Hampshire and the eastern frontier of Maine. Several thousand New England families migrated even farther north to the Annapolis Valley of Nova Scotia. Throughout New England after the early eighteenth century, most farmers' sons knew that their destiny lay elsewhere.

Wherever they took up farming, northern cultivators engaged in agricultural work routines that were far less intense than in the south. The growing season was much shorter, and the cultivation of cereal crops required incessant labor only during spring planting and autumn harvesting. This less burdensome work rhythm let many northern cultivators to fill out their calendars with intermittent work as clockmakers, shoemakers, carpenters, and weavers.



indefinitely=without limit

compounded=added to


预测文章5- The British Economy Under the Roman Empire

Following the Roman Empire conquering the area in the first century A.D., there is a great deal of archaeological evidence for the economic growth of the British Isles. Prior to this event, the economy of the British Isles, which was based on manufacturing, was centered mainly on the household and on craft skills, and where the best quality and greatest range of goods were largely a monopoly of the tribal aristocracies. This was the nature of the economy which lasted in regions of Britain that were unconquered by the Roman Empire, even though some Roman products were utilized in such areas. The majority of these Roman artifacts were glass vessels, pots, as well as small metal objects that were dispersed over a vast region. They perhaps held a symbolic value and were not necessarily used for their originally designed purposes. The spread of Roman objects beyond Roman Britain does not seem to have happened on an enormous scale. In areas where artifacts are more numerous, it is likely due to gift giving during close interactions between the Roman government and the tribes.

In regions that experienced direct economic control under the Romans, however, economic growth is clearly notable. There was an enormous increase in the number and variety of goods in circulation and the range of settlements in which they were found. This is clearly true in the overwhelming majority of excavated sites in Roman Britain, with the only exceptions being some rural regions that continued the pre-Roman, Iron Age pattern. The majority of sites resulted in the discovery of an abundance of iron, glass, and pottery, and good quantities of copper alloys, lead, tin, silver, and occasionally gold. For example, the humble iron nail is found in numbers not repeated until the Industrial Revolution.

The technology levels and range of the manufacturing of these objects also developed alongside the sheer increase in their quantity. During the Iron Age, the typical household objects were usually manufactured using a low technology of craft manufacture. Later, this changed to more specialized and larger-scale production methods. During this time, specialized workers could utilize equipment manufactured through'time and resource investments. In these regions, small-scale workshops used by specialized craftsmen betoken full-time employment in this work. Regardless of the large increase in the scale of manufacturing, there is little evidence of major growth in the size of productive units. We are left with the impression of an economy still based on small-scale craft production.

Where we do see an important change is in the removal of any exclusive association between the best traditional craftsmen and the governing elite. The powerful could show off their status in new ways, particularly by using Roman architecture and domestic decoration, but the traditional classes of decorative metalwork manufacture no longer seem to have been under the control of the tribal leaders. Rich objects from a wide range of archaeological sites imply the deterioration of this monopoly. There are a number of contributing factors. The control of precious metals moved to the imperial government immediately after the conquest, and gold and silver were also removed from circulation when captured as booty during the invasion. Similarly, changes in taste and the fashions of wealth and status display were stimulated by the arrival of new things like Roman dress, architecture, and sculpture.

These changes in manufacture were accompanied by increased distances over which many goods were transported to their consumers. ■ The bulk of pottery and other items originated locally, during the Iron Age; but after the Roman invasion, these objects had been produced over a far greater range of distances. ■ In this way, vast regions of the Roman province were incorporated into a society where there was wide access to material wealth. _ New changes in manufacturing production were coupled with huge increase in the importation of goods from elsewhere in the empire. ■ These commodities, which included Mediterranean foodstuffs such as olive oil as well as comparatively low-value objects such as decorated pottery, also achieved a wide distribution and are found in many different types of site.



dispersed = spread



预测文章6- Controversy about Causing Emotion

The fact that we react to certain experiences with “Emotion” is obvious. For example, the feeling of embarrassment, which triggers a physiological response that may cause blushing, is caused by a foolish act committed in the company of friends. Although this description of an embarrassed reaction seems logical, the American psychologist William James, in 1884,believed that the course of an emotional experience follows another sequence of events.

Following the argument of James, what subjective experience tells us is completely opposite that the sequence of events in an emotional experience. First, he insisted that both physiological excitement and physical reaction are generated by an incident. Only then does the individual perceive or interpret the physical response as an emotion. That is, we associate blushing that caused by physical reaction with embarrassment, such as saying something silly may cause us to blush. In 1890, James went on to claim that "people feel sorry because they cry, furious because they strike, afraid because they shudder." Simultaneously with James' proposition, Carl Lange, a Danish physiologist and psychologist, independently formulated virtually similar theory. The James-Lange theory of emotion (Lange and James, 1922) suggests that different patterns of arousal in the autonomic nervous system create the different emotions people feel, and that physiological arousal occurs prior to the emotion is perceived.

In 1927, Another early theory of emotion that challenged the James-Lange theory was proposed by Walter Cannon. He claimed that physical changes caused by the diverse emotions are not sufficiently distinct to allow people to distinguish one emotion from another. _ After Cannon stated his original theory, in 1934, it was further developed by physiologist Philip Bard.

■The Cannon-Bard theory suggests that the following chain of events takes place when an emotion is felt. ■ Stimuli which trigger emotion are received by the senses and then are relayed simultaneously to the cerebral cortex, which imparts the conscious mental experience of the emotion, and to the sympathetic nervous system, which generates the physiological state of arousal. ■ In other words, the feeling of emotion occurs roughly the same time when the physiological arousal is experienced. One does not cause the other.

In 1962, Schachter and Singer proposed a two-factor theory. Stanley Schachter thought that the early theories of emotion excluded a critical component that the subjective cognitive interpretation of why a state of arousal has occurred. According to this theory, two things must happen in order for a person to feel an emotion. At first, the person must experience physiological arousal. Then, for the person can label it as specific emotion, there must be a cognitive interpretation or explanation. Thus, Schachter delivered the conclusion that a true emotion can appear only if a person is physically aroused and can find the reason for it. When people are in a state of physiological arousal but do not know why they are aroused, they tend to label the state as an emotion that is appropriate to their situation at the time. There were several attempts to replicate the findings of this theory, but they have not been successful.

Richard Lazarus, in the 1990, proposed the emotion theory that most heavily emphasizes the cognitive aspect. According to his theory, the first step in an emotional response is cognitive appraisal, and all other aspects of emotion, including physiological arousal, rely on the cognitive appraisal. This theory is most compatible with the subjective experience of an emotion’s sequence of events-the sequence that William James reversed long ago. People first appraise a stimulus, or an event, when they encounter it. This cognitive appraisal determines whether the person will have an emotional response, and, if so, what type of response. From this appraisal, the physiological arousal and all other aspects of the emotion arise. In brief, Lazarus contends that emotions are roused when cognitive appraisals of events or circumstances are positive or negative-but not neutral.


formulated = developed

component = element

replicate = replicate

contends = argues

预测文章7- Agriculture in Medieval Japan

A rapid population of Japan occurred during its medieval times. Japan’s population was around 7 million but it rose keenly to 12 million from year 1200 to 1600. In this period, numerous hamlets formed throughout the country. They were mostly formed in the lands listed as ”unsettled” or as a ”wasteland” before 1300. There were many facets in increase in number of new hamlets,but by far the most significant characteristic of newly formed hamlets were that they were much bigger in terms of size compared to that of the hamlets built before 1300. There are many factors for forming of such large towns that contributed to increase in population mass. Some factors that can be considered are people’s demand for local authority, voluntarily, to defend themselves against outside threats or to form religious communities. Whatever the impetus, such formation of large villages was due to improvements in the agricultural technologies. Some improvements in technologies involved turning over of fields, irrigation methods, and usage of waterwheels, iron tools and diversification of crop output.

Among many improvements in agriculture, field leveling was the most basic practice used to optimize the land for farming. The farmers would create flat land for farming by leveling a field. They then would use the surfeit soil from the field to level the slightly slanted field. As a result, two fields of difference in altitude would be formed. Such difference in elevation allowed farmers to use the lower for rice paddy and the higher for dry crops. Practice of field leveling allowed a paddy culture to settle and allowed vast variety in dry crops to be produced due to the formation of drop crop field. Though the labor involved in formation of fields was enormous, the field preparation enabled marshlands alongside the rivers to be used for husbandry even if the rivers were uncontrolled.

Rice crops require ample water for growth and it takes much time until they are ready to be harvested. So farmers naturally worked by places where they had access to ample supply of water, such as riverbanks, streams and ponds. However, natural water supply was inefficient for the growth of rice, especially in sweltering summers. This led to the usage and development of ditches and dikes. Development in drawing the water from the distant locations led number of dams to increase and directed them to wherever they needed them. This was most evident in Yamato Basin where famers built permanent dams. The water detained in the pools was kept for times when they needed water for farming in droughty seasons. Such development led to keen proliferation of crop output as the heated water metabolized the germination of crops and caused crops to mature even faster.

By mid 1500s,one quarter of all paddy land were used to double crop. The farmers not only used fields to grow two crops in a year, but they even grew three in a single annual cycle. ■ An envoy from Korea stated that Japanese farmers from Hyogo region would grow barley and sow in winter and harvest them in summer. ■ Followed by rice cropping in summer and fall, buckwheat was harvested in winter. ■ As time went on agriculture advanced, such technique progressed from generation to generation. ■ Farming became more consistent and the crop output became even greater. A greater sense of discipline in land tilling and wide range of crops being planted in the same piece of land broadened the understanding of agriculture in farmers.

Crops harvested were used for farmers themselves. In many cases, one hectare of decent land was enough to sustain their entire family. They would only plow enough land for food to cater families for several reasons. Much of the medieval Japanese reclamation of land was due to the search for enough arable land to meet the food needed for just a single household. In case a farmer having enough fields for crop output required for his family, he would expand his fields no that one had to put into farming for his crops to grow. This was further compounded by the scarcity of land for fanning as well as limiting capacity for water and fertilizer supplies, not to mention the likelihood of antagonizing neighbors. Taking these variable factors into consideration, farmers of this period persisted with single hectare or less of arable land, just enough to sustain their families.



optimize= make the best use of



预测文章9- Plant and Animal Life of the Pacific Islands

There are both great similarities and considerable diversity in the ecosystems that evolved on the islands of Oceania in and around the Pacific Ocean. The islands, such as New Zealand, that were originally parts of continents still carry some small plant and animal remnants of their earlier biota(animal and plant life),and they also have been extensively modified by evolution, adaptation, and the arrival of new species. By contrast, the other islands, which emerged via geological processes such as volcanism, possessed no terrestrial life, but over long periods, winds, ocean currents, and the feet, feathers, and digestive tracts of birds brought the seeds of plants and a few species of animals. Only those species with ways of spreading to these islands were able to undertake the long journeys, and the various factors at play resulted in diverse combinations of new colonists on the islands. One estimate is that the distribution of plants was 75 percent by birds, 23 percent by floating, and 2 percent by wind.

The migration of Oceanic biota was generally from west to east, with four major factors influencing their distribution and establishment. The first was the size and fertility of the islands on which they landed, with larger islands able to provide hospitality for a wider range of species. Second, the further east the islands, generally the less the species diversity, largely because of the distance that had to be crossed and because the eastern islands tended to be smaller, more scattered, and remote. This easterly decline in species diversity is well demonstrated by birds and coral fish. It is estimated that there were over 550 species of birds in New Guinea, 127 in the Solomon Islands, 54 in Fiji, and 17 in the Society Islands. From the west across the Pacific, the Bismarck Archipelago and the Solomon Islands have more than 90 families of shore fish(with many species within the families),Fiji has 50 families, and the Society Islands have 30. Third, the latitude of the islands also influenced the biotic mix, as those islands in relatively cooler latitudes, notably New Zealand, were unsuited to supporting some of the tropical plants with which Pacific islands are generally associated.

Finally, a fourth major factor in species distribution, and indeed in the shaping of Pacific ecosystems, was wind. It takes little experience on Pacific islands to be aware that there are prevailing winds. To the north of the equator these are called north-easterlies, while to the south they are called south-easterlies. Further south, from about 30°south, the winds are generally from the west. As a result on nearly every island of significant size there is an ecological difference between its windward and leeward(away from the wind)sides. Apart from the wind action itself on plants and soils, wind has a major effect on rain distribution. The Big Island of Hawaii offers a prime example; one can leave Kona on the leeward side in brilliant sunshine and drive across to the windward side where the city of Hilo is blanketed in mist and rain.

While such localized plant life and climatic conditions are very noticeable, over Oceania as a whole there is relatively little biodiversity, and the smaller the island and the further east it lies, the less there is likely to be. When humans moved beyond the islands of Near Oceania (Australia, New Guinea, and the Solomon Islands), they encountered no indigenous mammals except for flying foxes, fruit bats, and seals on some islands. Other vertebrate species were restricted to flying animals and a few small reptiles.

However, local adaptations and evolution over long periods of isolation promoted fascinating species adaptations to local conditions. Perhaps most notable, in the absence of mammals and other predators, are the many species of flightless and ground-nesting birds. Another consequence of evolution was that many small environments boasted their own endemic(native)species, often small in number, unused to serious predation, limited in range, and therefore vulnerable to disruption. In Hawaii, for example, the highly adapted 39 species and subspecies of honeycreepers, several hundred species of fruit flies, and more than 750 species of tree snails are often cited to epitomize the extent of localized Oceanic endemism(species being native to the area)。





预测文章8- Sea Turtle Hatchling Strategies for Navigation

Sea turtles’ eggs are laid at night to minimize the likelihood of their discovery by predators, and the offspring, when ready to emerge from their eggshells and dig their way out of the sand, hatch at night for the same reason. Since the offspring are especially vulnerable immediately after hatching,it is vital for them to get to the sea as soon as possible. Turtle hatchlings use a number of cues to tell them where the sea is.

The most important cue seems to be light. The night sky is usually brightest over the sea. Cover a turtle hatchling’s eyes, and it cannot find the sea even if there is other information available, such as a downward slope of the sand toward the water’s edge. The hatchlings respond to light cues covering a vertical range of only about 30°above the horizon or, depending on the species, even less. Responding only to lights that are close to the horizon decreases the risk that hatchlings will become confused. They seem less attracted to yellow light than to other colors—loggerhead turtles show an aversion to yellow light—and this preference may keep them from becoming disoriented by the rising Sun.

It is usually safest to have more than one internal compass, and hatchlings seem to be guided by more than light alone. They steer away from sand dunes and vegetation. Possibly these objects merely block light behind them that might mislead turtle hatchlings about where the sea is, but it is also possible that turtles are sensitive to the shape of such objects and process  these shapes as signals that the sea is located in some other direction. Such reinforcing cues, however, are not enough to guide hatchlings away from the artificial lights that now burn on many a beach environment. Artificial lighting is often strong enough to completely overcome the signals a hatchling sea turtle is programmed to recognize. Artificial light, if it is bright enough, becomes a stimulus so powerful that the hatchlings respond to nothing else, crawling toward it from hundreds of meters away.

If all goes well and the hatchlings scramble over the sand in the right direction, avoid their enemies, and reach the surf, a new set of orienting mechanisms takes over. As soon as they are afloat, the hatchlings begin to swim at something over 1.5 kilometers per hour. They dive into the path of the wave undertow, where the receding waters sweep them outward, away from the beach. When they surface again, the head for open sea. This time, they are guided not by sight but apparently exclusively by the direction of the incoming waves. Experiments with loggerheads, greens, and leatherbacks have shown that hatchlings swim toward approaching waves; but if the sea is calm, they swim randomly or in circles. Under experimental conditions, hatchlings will swim into the waves even if doing so sends them back to the beach again.

The farther a hatchling gets from shore, the less reliable wave direction becomes as a pointer to the open sea. Researchers have shown that hatchling green sea turtles released from a hatchery in Borneo, East Malaysia, are able to navigate around small islands and keep swimming offshore, even when there are few waves to guide them. They may be relying on yet another internal compass this time oriented to Earth’s magnetic field. Recent experiments suggest that leatherback and olive ridley hatchlings “switch on” their geomagnetic compass almost as soon as they are out of the nest. Though the hatchlings position themselves geomagnetically as soon as they leave the nest and appear to be able to use that position as a reference point, they will not follow it automatically if other cues, such as light and sound, are available. Hatchlings find their geomagnetic compass useful only after they have already been able to determine the direction they should swim. A simple directional compass—one that always sent the turtles westward, for instance—would be useless if the open sea lay in some other direction. Therefore, a magnetic compass does not so much tell a hatchling turtle which way to go as keep it on course once it has determined the direction it should swim from some other cue.


reinforcing= supporting


experimental=trial switch on= activate

预测文章10- Determining the Ages of the Planets and the Universe

The planets of our solar system all revolve around the Sun in the same direction and in orbits that lie in nearly the same plane. This is strong evidence that the planets formed simultaneously from a single disk of material that rotated in the same direction as the modern planets.

Precisely when the planets came into being has been a difficult issue to resolve. While Earth’s water is necessary for life, its abundance near the planet’s surface makes rapid erosion inevitable. Continuous alteration of the crust by erosion and also by igneous (volcanic) and metamorphic (pressure and heat within Earth) processes makes unlikely any discovery of rocks nearly as old as Earth. Thus geologists have had to look beyond this planet in their efforts to date Earth’s origin. Fortunately, we do have samples of rock that appear to represent the primitive material of the solar system. These samples are meteorites, which originate as extraterrestrial objects, called meteors, that have been captured in Earth’s gravitational field and have then crashed into our planet.

Some meteorites consist of rocky material and, accordingly, are called stony meteorites. Others are metallic and have been designated iron meteorites even though they contain lesser amounts of elements other than iron. Still others consist of mixtures of rocky and metallic material and thus are called stony-iron meteorites. Meteors come in all sizes, from small particles to the small planets known as asteroids; no asteroid, however, has struck Earth during recorded human history. Many meteorites appear to be fragments of larger bodies that have undergone collisions and broken into pieces. Iron meteorites are fragments of the interiors of these bodies, comparable to Earth’s core, and stony meteorites are from outer portions of these bodies, comparable to Earth’s mantle (the layer between the core and outer crust)。

Meteorites have been radiometrically dated by means of several decay systems, including rubidium-strontium, potassium-argon, and uranium-thorium. The dates thus derived tend to cluster around 4.6 billion years, which suggests that this is the approximate age of the solar system. After many meteorites had been dated, it was gratifying to find that the oldest ages obtained for rocks gathered on the surface of the Moon also were approximately 4.6 billion years. This must, indeed, be the age of the solar system. Ancient rocks can be found on the Moon because the lunar surface, unlike that of Earth, has no water to weather and erode rocks and is characterized by only weak movements of its crust.

Determining the age of the universe has been more complicated. Most stars in the universe are clustered into enormous disk-like galaxies. The distance between our galaxy, known as the Milky Way, and all others is increasing. In fact, all galaxies are moving away from one another, evidence that the universe is expanding. It is not the galaxies themselves that are expanding but the space between them. What is happening is analogous to inflating a balloon with small coins attached to its surface. The coins behave like galaxies: although they do not expand, the space between them does. Before the galaxies formed, matter that they contain was concentrated with infinite density at a single point from which it exploded in an event called the big bang. Even after it assembled into galaxies, matter continued to spread in all directions from the site of the big bang.

The evidence that the universe is expanding makes it possible to estimate its age. This evidence, called the redshift, is an increase in the wavelengths of light waves traveling through space—a shift toward the red end of the visible spectrum of wavelengths. Expansion of the space between galaxies causes this shift by stretching light waves as they pass through it. The farther these light waves have traveled through space, the greater the redshift they have undergone. For this reason, light waves that reach Earth from distant galaxies have larger redshifts than those from nearby galaxies. Calculations based on these redshifts indicate that about 13.7 billion years ago all of the galaxies would have been at one spot, the site of the big bang. This, then, is the approximate date of the big bang and the age of the universe.






预测文章11- The Role of the Ocean in Controlling Climate

To predict what the climate will be like in the future, scientists must rely on sophisticated computer models. These models use mathematical equations to represent physical processes and interactions in the atmosphere, ocean,  and on land. A starting point is usually based on current measurements or estimates of past conditions. Then, using a spherical grid laid out over the entire globe, thousands of calculations are performed at grid intersections to represent and assess how conditions in the air, in the sea, and on land will change over time. Because of their complexity and size, supercomputers are used to run full-scale climate models. Much of the uncertainty in their outputs comes from the way that various aspects of the climate are represented by different models, and even more so, because there are aspects of climate that are not well understood—one of which is how the ocean impacts climate.

The ocean’s role in global warming stems principally from its huge capacity to absorb carbon dioxide and to store and transport heat. In the sea, photosynthesis by marine plants and algae, especially phytoplankton, removes great quantities of carbon dioxide from the atmosphere. Hence, the greater  the growth (productivity) of phytoplankton in the sea, the greater the removal of carbon dioxide. But what controls the ocean’s productivity? There are several limiting factors, but results from a recent experiment suggest that in areas of the ocean where other nutrients are plentiful, iron may be one of the most important and, until recently, unrecognized variables controlling phytoplankton production. Some have proposed a radical, highly controversial and uncertain means to counteract global warming—adding iron to the oceans to induce phytoplankton blooms. Perhaps increased phytoplankton growth would use up a significant amount of carbon dioxide in the atmosphere, but perhaps not, and there might well be side effects that could be detrimental to the ocean ecosystem.

Within the ocean, the production of limestone, in the form of calcium carbonate skeletons or shells, also reduces atmospheric carbon dioxide. However, when deposits of limestone become exposed and weathered on land or are recycled in the sea, carbon dioxide is released back into the atmosphere. What is not well understood is how much carbon dioxide resides in the sea and at what rate it is taken up and recycled. Relatively new research has also discovered beneath the sea a new and potentially significant threat to skyrocketing Earth temperature: gas hydrates. Gas hydrates are a solid, crystalline form of water, like ice, except that they contain additional gas, typically methane, and are often found stored in ocean sediments. Increased ocean temperatures could cause gas hydrates to dissociate, releasing massive amounts of methane gas into the atmosphere and cause undersea landslides in the process. Consequently, hydrates may, if released, significantly increase global warming as well as create a geologic hazard to offshore drilling operations.

The ocean is also a great reservoir and transporter of heat. Heat from the ocean warms the atmosphere and fuels tropical storms. Heat is transported by currents from the equator to the poles. Ocean circulation is strongly controlled by wind and by the sea’s balance of salt and heat. Scientists think that climate warming may slow down circulation, while cooling may speed it up, but these responses are not well understood. Evaporation from the ocean also supplies the precipitation that creates fields of snow and ice at high latitudes. Snow and ice coverage change the reflectivity Earth’s surface and are an important influence on how much incoming radiation is either absorbed or reflected. Furthermore, clouds and water vapor in the atmosphere come mainly from the sea and strongly influence climate. Surprisingly, clouds are one of the least understood and most poorly modeled parts of the climate change equation. Most climate modeling grids fail to take into account common-sized cloud formations. Aerosols, tiny particles of soot, dust, and other materials, are thought to seed cloud formation scatter incoming radiation and promote cooling, but this effect, which would counteract warming, is also only superficially understood. Computer models of climate change must take into account all of the processes within the ocean, over land, and in the sky that potentially influence warming. No wonder there is such uncertainty.


principally= mainly

controversial= producing disagreement

induce= cause the formation of

fuels= provides energy for

预测文章12- The Sentinel Behavior of Meerkats

A species of small mongooses in Africa called meerkats share sentinel (guard) duties to warn other group members by repeating alarm calls if a predator is seen. This is an important job, because when meerkats are foraging, their heads are in the ground seeking prey, and they cannot see a predator coming.

The question is, why do group members take turns acting as sentinels? Kin selection, that is, being able to save the lives of family members can be one hypothesis for this type of sentinel behavior. Family members share copies of a meerkat's genes. Kin selection is achieved by helping a meerkat’s own offspring as well as non descendant kin, including sibling, nieces, nephews, aunts, and uncles. Therefore, if members of a certain group are closely related, a sentinel ensures that copies of its genes can be passed on to future generations by saving the majority of family members by alerting others, even at the expense of its own life.

Assuming this hypothesis is true, we can predict that group members have close genetic ties. Otherwise, kin selection would not work. But this prediction does hold true. A dominant, breeding female is mother to 75 percent of all the litters in a group, and one dominant male fathers 75 percent of all the pups born. Even though a typical meerkat group includes a few immigrants, most subordinate adults are siblings or half siblings. Therefore, it is likely that subordinate adults share 25 or 50 percent of their genes.

On account of most meerkat group members being family, it is possible that kin selection has favored sentinel behavior. Nonetheless, by itself, a close inherent relationship is not enough evidence to conclude that kin selection has played a role. Thus, we need further evidence, and must improve the prediction.

Based on the same hypothesis, a more specific prediction is that each mongoose should increase the frequency of sentinel behavior when they are guarding family members. This new prediction needed testing, so the group was observed to determine which members stand guard and when. The immigrants without any kin relations to other group members acted as sentinels just as much as the individuals with many relatives nearby. Therefore, the result of this test does not support the kin-selection hypothesis.

Another hypothesis that is often suggested to explain such cooperative behavior is that it results from reciprocal altruism~each individual takes turns standing guard to benefit the rest of the group, rather than itself. The reciprocal altruism theory can work only when those who cheat by avoiding guard duty can be identified and punished by the rest of the group. This hypothesis produces the prediction that there should be a regular rotation of sentry duty within the group and that the ones who neglect this duty should be chastised. However, this is not observed. In fact, the group members do take turns on sentry duty, but there is no predetermined order for this. In addition, when some members shorten their shift, other group members increase their contributions to compensate. The predictions and observations of the reciprocal-altruism hypothesis do not coincide with each other.

Yet another hypothesis for the evolution of meerkat sentinel behavior is that it results from selfish antipredator behavior. This idea stems from the fact that the meerkat watching for predators increases its personal safety, and warning others does not harbor any disadvantage. So, when a meerkat has had enough to eat, it should watch for predators. The sentinel on duty can then return to foraging. This hypothesis produces a prediction that sentinel duty is not dangerous or risky in any way. This does seem to be true. Over the course of 2,000 hours of observation, no sentinels were attacked or killed by predators. They may actually be safer because they are the first to sense the predator. Moreover, they generally stand guard within 5 meters of a burrow, and are the first underground when a predator comes close. ■ If a meerkat’s personal safety is increased with serving as a sentinel, it would be possible to predict that an individual would spend a proportion of its time guarding, whether it was solitary or part of a group. ■ As predicted, individual meerkats spend about the same time on guard duty as members of large groups. ■ Groups with more members suffer less predation because there is a sentinel for a longer portion of foraging time than in small groups. ■




in addition=futher more

come close=approaches