近期发布 编辑：环球教育 浏览：(28次)
参考阅读TPO 17-2 Animal Signals in the Rain Forest
The daytime quality of light in forests varies with the density of the vegetation, the
angle of the Sun, and the amount of cloud in the sky. Both animals and plants have
different appearances in these various lighting conditions. A color or pattern that is
relatively indistinct in one kind of light may be quite conspicuous in another. In the varied and constantly changing light environment of the forest, an animal must be able to send visual signals to members of its own species and at the same time avoid being detected by predators. An animal can hide from predators by choosing the light environment in which its pattern is least visible. This may require moving to different parts of the forest at different times of the day or under different weather conditions, or it may be achieved by changing color according to the changing light conditions. Many species of amphibians (frogs and toads) and reptiles (lizards and snakes) are able to change their color patterns to camouflage themselves. Some also signal by changing color. The chameleon lizard has the most striking ability to do this. Some chameleon species can change from a rather dull appearance to a full riot of carnival colors in seconds. By this means, they signal their level of aggression or readiness to mate.
Other species take into account the changing conditions of light by performing their visual displays only when the light is favorable. A male bird of paradise may put himself in the limelight by displaying his spectacular plumage in the best stage setting to attract a female. Certain butterflies move into spots of sunlight that have penetrated to the forest floor and display by opening and closing their beautifully patterned wings in the bright spotlights. They also compete with each other for the best spot of sunlight.
Very little light filters through the canopy of leaves and branches in a rain forest to reach ground level — or close to the ground — and at those levels the yellow-to-green wavelengths predominate. A signal might be most easily seen if it is maximally bright. In the green-to-yellow lighting conditions of the lowest levels of the forest, yellow and green would be the brightest colors, but when an animal is signaling, these colors would not be very visible if the animal was sitting in an area with a yellowish or greenish background.
The best signal depends not only on its brightness but also on how well it contrasts with the background against which it must be seen. In this part of the rain forest, therefore, red and orange are the best colors for signaling, and they are the colors used in signals by the ground-walking Australian brush turkey. This species, which lives in the rain forests and scrublands of the east coast of Australia, has a brown-to-black plumage with bare, bright-red skin on the head and neck and a neck collar of orange-yellow loosely hanging skin. During courtship and aggressive displays, the turkey enlarges its colored neck collar by inflating sacs in the neck region and then flings about a pendulous part of the colored signaling apparatus as it utters calls designed to attract or repel. This impressive display is clearly visible in the light spectrum illuminating the forest floor.
Less colorful birds and animals that inhabit the rain forest tend to rely on other forms of signaling other than the visual, particularly over long distances. The piercing cries of the rhinoceros hornbill characterize the Southeast Asian rain forest, as do the unmistakable calls of the gibbons. In densely wooded environments, sound is the best means of communication over distance because in comparison with light, it travels with little impediment from trees and other vegetation. In forests, visual signals can be seen only at short distances, where they are not obstructed by trees. The male riflebird exploits both of these modes of signaling simultaneously in his courtship display. The sounds made as each wing is opened carry extremely well over distance and advertise his presence widely. The ritualized visual display communicates in close quarters when a female has approached.
(1 )红色松果含更多t, t很苦
参考阅读TPO 42-1 Geographic Isolation of Species
Biologist Ernst Mayr defined a species as "an actually or potentially interbreeding
population that does not interbreed with other such populations when there is
opportunity to do so." A key event in the origin of many species is the separation of a
population with its gene pool (all of the genes in a population at any one time) from other
populations of the same species, thereby preventing population interbreeding. With its
gene pool isolated, a separate population can follow its own evolutionary course. In the
formation of many species, the initial isolation of a population seems to have been a
geographic barrier. This mode of evolving new species is called allopatric speciation.
Many factors can isolate a population geographically. A mountain range may emerge
and gradually split a population of organisms that can inhabit only lowland lakes, certain
fish populations might become isolated in this way. Similarly, a creeping glacier may
gradually divide a population, or a land bridge such as the Isthmus of Panama may form
and separate the marine life in the ocean waters on either side.
How formidable must a geographic barrier be to keep populations apart? It depends
on the ability of the organisms to move across barriers. Birds and coyotes can easily cross
mountains and rivers. The passage of wind-blown tree pollen is also not hindered by such
barriers, and the seeds of many plants may be carried back and forth on animals In contrast, small rodents may find a deep canyon or a wide river an effective barrier. For example, the Grand Canyon, in the southwestern United States, separate the range of the while-tailed antelope squirrel from that of the closely related Harris* antelope squirrel. Smaller, with a shorter tail that is white underneath, the white-tailed antelope squirrel inhabits deserts north of the canyon and west of the Colorado River in southern California Hams' antelope squirrel has a more limited range in deserts south of the Grand Canyon.
Geographic isolation creates opportunities for new species to develop, but it does not necessarily lead to new species because speciation occurs only when the gene pool undergoes enough changes to establish reproductive barriers between the isolated population and its parent population. The likelihood of allopatric speciation increases when a population is small as well as isolated, making it more likely than a large population to have its gene pool changed substantially. For example, in less than two million years, small populations of stray animals and plants from the South American mainland that managed to colonize the Galapagos Islands gave rise to all the species that now inhabit the islands.
When oceanic islands are far enough apart to permit populations to evolve in isolation, but close enough to allow occasional dispersions to occur, they are effectively outdoor laboratories of evolution. The Galapagos island chain is one of the world’s greatest showcases of evolution. Each island was born from underwater volcanoes and was gradually covered by organisms derived from strays that rode the ocean currents and winds from other islands and continents. Organisms can also be carried to islands by other
organisms, such as sea birds that travel long distances with seeds clinging to their feathers.
白垩纪(The cretaceous period )
(3 )含氧置非常高导致很容易出现山火，山火会消耗氧气放出二氧化碳，这可以劇氏大气中的氧 气含置。
The Cretaceous Period
The Cretaceous is usually noted for being the last portion of the 'Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants.
The breakup of the world-continent Pangea, which began to disperse during the Jurassic, continued. This led to increased regional differences in floras and faunas between the northern and southern continents.
The end of the Cretaceous brought the end of many previously successful and diverse
such as non-avian dinosaurs and ammonites. This laid open the
stage for those groups which had previously taken secondary roles to come to the
forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together.
No great extinction or burst of diversity separated the Cretaceous from the Jurassic Period that had preceded it. In some ways, things went on as they had. Dinosaurs both great and small moved through forests of ferns, cycads, and conifers. Ammonites, belemnites, other molluscs, and fish were hunted by great 'marine reptiles," and pterosaurs and birds flapped and soared in the air above. Yet the Cretaceous saw the first appearance of many lifeforms that would go on to play key roles in the coming Cenozoic world
Perhaps the most important of these events, at least for terrestrial life, was the first appearance of the flowering plants, also called the angiosperms or Anthophyta. First appearing in the Lower Cretaceous around 125 million years ago, the flowering plants first radiated in the middle Cretaceous, about 100 million years ago. Early angiosperms did not develop shrub- or tree-like morphologies, but by the close of the Cretaceous, a number of forms had evolved that any modern botanist would recognize. The angiosperms thrived in a variety of environments such as areas with damper climates, habitats favored by cycads and cycadeoids, and riparian zones. High southern latitudes were not invaded by angiosperms until the end of the Cretaceous. Ferns dominated open, dry and/or low-nutrient lands. Typical Jurassic vegetation, including conifers, cycads, and other gymnosperms, continued on into the Lower Cretaceous without significant changes. At the beginning of this period, conifer diversity was fairly low in the higher latitudes of the
Northern Hemisphere, but by the middle of the period, species diversification was
increasing exponentially. Swamps were dominated by conifers and angiosperm dicots.
At about the same time, many modern groups of insects were beginning to diversify, and
we find the oldest known ants and butterflies. Aphids, grasshoppers, and gall wasps
appear in the Cretaceous, as well as termites and ants in the later part of this period.
Another important insect to evolve was the eusocial bee, which was integral to the ecology
and evolution of flowering plants.
参考阅读TPO 33-2 Railroads and Commercial Agriculture in Nineteenth-Century United States
By 1850 the United States possessed roughly 9,000 miles of railroad track; then years
later it had over 30,000 miles, more than the rest of the world combined. Much of the new
construction during the 1850s occurred west of the Appalachian Mountains - over 2,000
miles in the states of Ohio and Illinois alone.
The effect of the new railroad lines rippled outward through the economy. Farmers
along the tracks began to specialize in crops that they could market in distant locations.
With their profits they purchased manufactured goods that earlier they might have made
at home. Before the railroad reached Tennessee, the state produced about 25,000 bushels
(or 640 tons) of wheat, which sold for less than 50 cents a bushel. Once the railroad came,
farmers in the same counties grew 400,000 bushels (over 10,000 tons) and sold their crop
at a dollar a bushel.
The new railroad networks shifted the direction of western trade.In 1840 most northwestern grain was shipped south down the Mississippi River to the bustling port of New Orleans.But low water made steamboat travel hazardous in summer, and ice shut down traffic in winter.Products such as lard, tallow, and cheese quickly spoiled if stored in New Orleans' hot and humid warehouses. Increasingly, traffic from the Midwest flowed west to east, over the new rail lines. Chicago became the region’s hub, linking the farms of the upper Midwest to New York and other eastern cities by more than 2,000 miles of track in 1855. Thus while the value of goods shipped by river to New Orleans continued to increase, the South’s overall share of western trade dropped dramatically.
A sharp rise in demand for grain abroad also encouraged farmers in the Northeast and Midwest to become more commercially oriented. Wheat, which in 1845 commanded $1.08 a bushel in New York City, fetched $2.46 in 1855; in similar fashion the price of corn nearly doubled. Farmers responded by specializing in cash crops, borrowing to purchase more land, and investing in equipment to increase productivity.
As railroad lines fanned out from Chicago, farmers began to acquire open prairie land in Illinois and then Iowa, putting the fertile, deep black soil into production. Commercial agriculture transformed this remarkable treeless environment. To settlers accustomed to eastern woodlands, the thousands of square miles of tall grass were an awesome sight. Indian grass, Canada wild rye, and native big bluestem all grew higher than a person. Because eastern plows could not penetrate the densely tangled roots of prairie grass, the earliest settlers erected farms along the boundary separating the forest from the prairie. In 1837, however, John Deere patented a sharp-cutting steel plow that sliced through the sod
without soil sticking to the blade. Cyrus McCormick refined a mechanical reaper that harvested fourteen times more wheat with the same amount of labor. By the 1850s McCormick was selling 1,000 reapers a year and could not keep up with demand, while Deere turned out 10,000 plows annually.
The new commercial farming fundamentally altered the Midwestern landscape and the environment. Native Americans had grown corn in the region for years, but never in such large fields as did later settlers who became farmers, whose surpluses were shipped east. Prairie farmers also introduced new crops that were not part of the earlier ecological system, notably wheat, along with fruits and vegetables.
Native grasses were replaced by a small number of plants cultivated as commodities. Corn had the best yields, but it was primarily used to feed livestock. Because bread played a key role in the American and European diet, wheat became the major cash crop. Tame grasses replaced native grasses in pastures for making hay.
Western farmers altered the landscape by reducing the annual fires that had kept the prairie free from trees. In the absence of these fires, trees reappeared on land not in cultivation and, if undisturbed, eventually formed woodlots. The earlier unbroken landscape gave way to independent farms, each fenced off in a precise checkerboard pattern. It was an artificial ecosystem of animals, woodlots, and crops, whose large, uniform layout made western farms more efficient than the more-irregular farms in the
the ifferences of marsupial and other marnals their East.
competition in different continent
除了 opossum (负鼠，袋貂)。该段以opossum为例区分marsupial
参考阅读There are three qroups of mammal: placental mammals, marsupials, and monotremes.
Monotremes only include the platypus and four species of echidna. The remaininq
mammals are all placentals or marsupials. The placental mammals are clearly dominant, as
they have been for over 65 million years, with over 5,500 species on every continent except
Antarctica. The marsupials, with only 334 species, has carved out a niche for itself in
Australia, where it has largely displaced placental mammals. Marsupials are also found in
small numbers in South America and Central America, with a single species
(Virginia Opossum) in North America.
Marsupials and placental mammals are both mammals, that is, warm-blooded tetrapods
with sweat glands that provide milk for young and are covered in a layer of fur or hair.
What distinguishes the two from each other are 1) their mode of reproduction, 2) genitalia,
and 3) their blood temperature, which is slightly less than that of placental mammals. For
many centuries, marsupials were considered "primitive" mammals, but there is little real
evidence for this outside of cultural bias. Because marsupials mainly occupy Australia and
remote areas of South America, they v/ere poorly characterized by scientists until the
Instead of staying in a womb like placental mammals, marsupials leave the mother's body
at a very early stage, climbing from the genital opening to a special pouch with nipples for
milk. This evolutionary strateqy avoids the need for a complex placenta to protect a
qrowinq fetus from the immune system of its mother. Marsupials and placental mammals
both evolved around the same time; about 125 million years ago, and despite evolving
separately since that time, have displayed significant parallel evolution as they have
radiated from shrew-like ancestors. For the casual observer without prior knowledge of the
species, the only way to distinguish a marsupial from a placental mammal is to examine
Some well-known marsupials include the koala, kanqaroo, opossums, possums, wombats,
the Tasmanian Devil, marsupial mice, bandicoot, and less well-known species such as the
marsupial mole, numbat, bilbv, and Musky Rat-kanqaroo. Placental mammals
include rodents, whales, elephants, otters, horses, cats, dogs, humans, and many more.
生物-动物the reason of the explosion of starfish
TPO 5-3 The Cambrian Explosion
The geologic timescale is marked by significant geologic and biological events, including the origin of Earth about 4.6 billion years ago, the origin of life about 3.5 billion years ago, the origin of eukaryotic life-forms (living things that have cells with true nuclei) about 1.5 billion years ago, and the origin of animals about 0.6 billion years ago. The last event marks the beginning of the Cambrian period. Animals originated relatively late in the history of Earth — in only the last 10 percent of Earth's history. During a geologically brief 100-million-year period, all modern animal groups (along with other animals that are now extinct) evolved. This rapid origin and diversification of animals is often referred to as "the Cambrian explosion."
Scientists have asked important questions about this explosion for more than a century. Why did it occur so late in the history of Earth? The origin of multicellular forms of life seems a relatively simple step compared to the origin of life itself. Why does the fossil record not document the series of evolutionary changes during the evolution of animals? Why did animal life evolve so quickly? Paleontologists continue to search the fossil record for answers to these questions.
One interpretation regarding the absence of fossils during this important 100-million-year period is that early animals were soft bodied and simply did not fossilize. Fossilization of soft-bodied animals is less likely than fossilization of hard-bodied animals, but it does occur. Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition. In fact, fossil beds containing soft-bodied animals have been known for many years.
The Ediacara fossil formation, which contains the oldest known animal fossils, consists
exclusively of soft-bodied forms. Although named after a site in Australia, the Ediacara formation is worldwide in distribution and dates to Precambrian times. This 700-million-year-old formation gives few clues to the origins of modern animals, however, because paleontologists believe it represents an evolutionary experiment that failed. It contains no ancestors of modern animal groups.
A slightly younger fossil formation containing animal remains is the Tommotian formation, named after a locale in Russia. It dates to the very early Cambrian period, and it also contains only soft-bodied forms. At one time, the animals present in these fossil beds were assigned to various modern animal groups, but most paleontologists now agree that all Tommotian fossils represent unique body forms that arose in the early Cambrian period and disappeared before the end of the period, leaving no descendants in modern animal groups.
A third fossil formation containing both soft-bodied and hard-bodied animals provides evidence of the result of the Cambrian explosion. This fossil formation, called the Burgess Shale, is in Yoho National Park in the Canadian Rocky Mountains of British Columbia. Shortly after the Cambrian explosion, mud slides rapidly buried thousands of marine animals under conditions that favored fossilization. These fossil beds provide evidence of about 32 modern animal groups, plus about 20 other animal body forms that are so different from any modern animals that they cannot be assigned to any one of the modern groups. These unassignable animals include a large swimming predator called Anomalocaris and a soft-bodied animal called Wiwaxia, which ate detritus or algae. The Burgess Shale formation also has fossils of many extinct representatives of modern animal groups. For example, a well-known Burgess Shale animal called Sidneyia is a representative
of a previously unknown group of arthropods (a category of animals that includes insects, spiders, mites, and crabs).
Fossil formations like the Burgess Shale show that evolution cannot always be thought of as a slow progression. The Cambrian explosion involved rapid evolutionary diversification, followed by the extinction of many unique animals. Why was this evolution so rapid? No one really knows. Many zoologists believe that it was because so many ecological niches were available with virtually no competition from existing species. Will zoologists ever know the evolutionary sequences in the Cambrian explosion? Perhaps another ancient fossil bed of soft-bodied animals from 600-million-year-old seas is awaiting discovery.
Passage 辑斗分类 题目
社会科学类-历史 newspaper development in Western Europe
真题原文：By the eighteenth century, newspapers had become firmly established as a means of spreading news of European and world affairs, as well as of local concerns; within European society. One of the first true newspapers was the Dutch paper Nieuwe Tidingen It began publication in the early seventeenth century at about the same time that the overseas trading company called the Dutch East India Company was formed The same ships that brought goods back from abroad brought news of the world, too.
Dutch publishers had an advantage over many other publishers around Europe because the Netherlands' highly decentralized political system made its censorship laws very difficult to enforce Throughout Europe in the seventeenth century, governments
began recognizing the revolutionary potential of the free press and began requiring licenses of newspapers—to control who was able to publish news Another tactic, in France and elsewhere on the continent from the 1630s onward, was for governments to sponsor official newspapers. These state publications met the increasing demand for news but always supported the government’s views of the events of the day
By the eighteenth century, new conditions allowed newspapers to flourish as never before First,demand for news increased as Europe's commercial and political interests spread around the globe—merchants in London, Liverpool ,or Glasgow, for example, came to depend on early news of Caribbean harvests and gains and losses in colonial wars Europe's growing commercial strength also increased distribution networks for newspapers. There were more and better roads, and more vehicles could deliver newspapers in cities and convey them to outlying towns Newspaper publishers made use of the many new sites where the public expected to read, as newspapers were delivered to cafes and sold or delivered by booksellers.
Second, many European states had established effective postal systems by the eighteenth century.lt was through the mail that readers outside major cities and their environs—and virtually all readers in areas where press censorship was exercised firmly— received their newspapers. One of the most successful newspapers in Europe was a French-language paper (one of the many known as La Gazette,) published in Leiden, in the Netherlands, which boasted a wide readership in France and among elites throughout Europe.
Finally, press censorship faltered in one of the most important markets for news— England— at the turn of the eighteenth century after 1688. debate raged about whether
the Parliament or the Crown had the right to control the press, and in the confusion the press flourished. The emergence of political parties further hampered control of the press because political decisions in Parliament now always involved compromise, and many members believed that an active press was useful to that process. British government's control of the press was reduced to taxing newspapers, a tactic that drove some papers out of business.
Eighteenth-century newspapers were modest products by modern Western standards. Many were published only once or twice a week instead of every day, in editions of only a few thousand copies. Each newspaper was generally only four pages long. Illustrations were rare , and headlines had not yet been invented. Hand-operated wooden presses were used to print the papers, just as they had been used to print pamphlets and books since the invention of printing in the fifteenth century.
Yet these newspapers had a dramatic impact on their reading public Regular production of newspapers (especially of many competing newspapers) meant that news was presented to the public at regular intervals and in manageable amounts. Even strange and threatening news from around the world became increasingly easy for readers to absorb and interpret Newspaper readers also felt themselves part of the public life about which they were reading This was true partly because newspapers, available in public reading rooms and in cafes, were one kind of reading that occupied an increasing self-aware and literate audience. Newspapers also were uniquely responsive to their readers. They began to carry advertisements, which both produced revenue for papers and widened readers' exposure to their own communities. Even more important was the inauguration of letters to the editor in which readers expressed their opinions about
happened to the water on Venus?
The answer to the first question is that carbon dioxide is still found in abundance on Earth, but now, instead of being in the form of atmospheric carbon dioxide, it is either dissolved in the oceans or chemically bound into carbonate rocks, such as the limestone and marble that formed in the oceans. If Earth became as hot as Venus, much of its carbon dioxide would be boiled out of the oceans and baked out of the crust. Our planet would soon develop a thick, oppressive carbon dioxide atmosphere much like that of Venus.
To answer the question about Venus' lack of water, we must return to the early history of the planet. Just as on present-day Earth, the oceans of Venus limited the amount of atmospheric carbon dioxide by dissolving it in the oceans and binding it up in carbonate rocks. But being closer to the Sun than Earth is, enough of the liquid water on Venus would have vaporized to create a thick cover of water vapor clouds. Since water vapor is a greenhouse gas, this humid atmosphere — perhaps denser than Earth ' s present-day atmosphere, but far less dense than the atmosphere that envelops Venus today—would have efficiently trapped heat from the Sun. At first, this would have had little effect on the oceans of Venus. Although the temperature would have climbed above 100° C, the boiling point of water at sea level on Earth, the added atmospheric pressure from water vapor would have kept the water in Venus' oceans in the liquid state.
This hot and humid state of affairs may have persisted for several hundred million years. But as the Sun’s energy output slowly increased over time, the temperature at the surface would eventually have risen above 374°C. ■ Above this temperature, no matter what the atmospheric pressure, Venus* oceans would have begun to evaporate, and the added water vapor in the atmosphere would have increased the greenhouse effect. _This would
have made the temperature even higher and caused the oceans to evaporate faster,
producing more water vapor. _That, in turn, would have further intensified the greenhouse
effect and made the temperature climb higher still.■
Once Venus' oceans disappeared, so did the mechanism for removing carbon dioxide from
the atmosphere. With no oceans to dissolve it, outgassed carbon dioxide began to
accumulate in the atmosphere, intensifying the greenhouse effect even more.
Temperatures eventually became high enough to "bake out" any carbon dioxide that was
trapped in carbonate rocks. This liberated carbon dioxide formed the thick atmosphere of
present-day Venus. Over time, the rising temperatures would have leveled off, solar
ultraviolet radiation having broken down atmospheric water vapor molecules into
hydrogen and oxygen. With all the water vapor gone, the greenhouse effect would no
longer have accelerated.
Nine生物-_The mating of cichild
詩阅读Cichlids mate either monogamously or polygamously. The mating system of a given cichlid
species is not consistently associated with its brooding system. For example, although
most monogamous cichlids are not mouthbrooders, Chromidotilapia, Gymnogeophagus,
Spathodus and Tanganicodus all include - or consist entirely of - monogamous
mouthbrooders. In contrast, numerous open- or cave-spawning cichlids are polygamous;
examples include many Apistogramma, Lamprologus, Nannacara, and Pelvicachromis
Most adult male cichlids, specifically in the Haplochromini tribe of cichlids, exhibit a unique pattern of oval-shaped, color dots on their anal fins. These phenomena are known as egg-spots and aid in the mouthbrooding mechanisms of cichlids. The egg-spots consist of carotenoid based pigment cells, which indicates a high cost to the organism, when considering that fish are not able to synthesize their own carotenoids.
The mimicry of egg-spots is utilized by males for the fertilization process. Mouthbrooding females lay eggs and immediately snatch them up with their mouths. Over millions of years, male cichlids have evolved egg-spots to initiate the fertilization process more efficiently. When the females are snatching up the eggs into their mouth, the males gyrate their anal fins, which illuminates the egg-spots on his tail. Afterwards, the female, believing these are her eggs, places her mouth to the anal fin (specifically the genital papilla) of the male, which is when he discharges sperm into her mouth and fertilizes the eggs.
The genuine color of egg spots is a yellow, red or orange inner circle with a colorless ring surrounding the shape. Through phylogenetic analysis, using the mitochondrial ND2 gene, it was hypothesized that the true egg spots evolved in the common ancestor of the Astatoreochromis-lineage and the modern Haplochrominis. This ancestor was most likely riverine in origin, based upon the most parsimonious representation of habitat type in the cichlid family. The presence of egg-spots in a turbid riverine environment, would seem particularly beneficial and necessary for intra-species communication.
There are two pigmentation genes that are found to be associated with egg-spot
patterning and color arrangement. These are fhl2-a and fhl2-b, which are paralogs. These
genes aid in pattern formation and cell-fate determination in early embryonic
development. The highest expression of these genes was temporally correlated with
egg-spot formation. A SINE (short interspersed repetitive element) was also seen to be
associated with egg-spots. Specifically, it was evident upstream of the transcriptional start
site of fhl2 in only haplochrominis species with egg-spots
参考阅读An invasive species is a species that is not native to a specific location (an introduced
species), and that has a tendency to spread to a degree believed to cause damage to the
environment, human economy or human health.
The term as most often used applies to introduced species that adversely affect the
habitats and bioregions they invade economically, environmentally, or ecologically. Such
species may be either plants or animals and may disrupt by dominating a region,
wilderness areas, particular habitats, or wildland-urban interface land from loss of natural
controls (such as predators or herbivores). This includes plant species labeled as exotic
pest plants and invasive exotics growing in native plant communities.The European Union
defines "Invasive Alien Species" as those that are, firstly, outside their natural distribution
area, and secondly, threaten biological diversity. The term is also used by land managers,
botanists, researchers, horticulturalists, conservationists, and the public for noxious weeds.
辨阅读TPO 47-3 Coral Reefs
An important environment that is more or less totally restricted to the intertropical zone is
the coral reef. Coral reefs are found where the ocean water temperature is not less than
21 °C, where there is a firm substratum, and where the seawater is not rendered too dark
by excessive amounts of river-borne sediment. They will not grow in very deep water, so a
platform within 30 to 40 meters of the surface is a necessary prerequisite for their
development. Their physical structure is dominated by the skeletons of corals, which are
carnivorous animals living off zooplankton. However, in addition to corals there are
enormous quantities of algae, some calcareous, which help to build the reefs. The size of
reefs is variable. Some atolls are very large—Kwajelein in the Marshall Islands of the South
Pacific is 120 kilometers long and as much as 24 kilometers across-but most are very much
smaller, and rise only a few meters above the water. The 2,000 kilometer complex of reefs
known as the Great Barrier Reef, which forms a gigantic natural breakwater off the
northeast coast of Australia, is by far the greatest coral structure on Earth.
Coral reefs have fascinated scientists for almost 200 years, and some of the most pertinent
observations of them were made in the 1830s by Charles Darwin on the voyage of the
Beagle. He recognized that there were three major kinds: fringing reefs, barrier reefs, and
atolls; and he saw that they were related to each other in a logical and gradational
sequence. A fringing reef is one that lies close to the shore of some continent or island. Its
surface forms an uneven and rather rough platform around the coast, about the level of low water, and its outer edge slopes downwards into the sea. Between the fringing reef and the land there is sometimes a small channel or lagoon. When the lagoon is wide and deep and the reef lies at some distance from the shore and rises from deep water it is called a barrier reef. An atoll is a reef in the form of a ring or horseshoe with a lagoon in the center.
Darwin's theory was that the succession from one coral reef type to another could be achieved by the upward growth of coral from a sinking platform, and that there would be a progression from a fringing reef, through the barrier reef stage until, with the disappearance through subsidence (sinking) of the central island, only a reef-enclosed lagoon or atoll would survive. A long time after Darwin put forward this theory, some deep boreholes were drilled in the Pacific atolls in the 1950s. The drill holes passed through more than a thousand meters of coral before reaching the rock substratum of the ocean floor, and indicated that the coral had been growing upward for tens of millions of years as Earth's crust subsided at a rate of between 15 and 51 meters per million years. Darwin s theory was therefore proved basically correct. There are some submarine islands called guyots and seamounts, in which subsidence associated with sea-floor spreading has been too speedy for coral growth to keep up.
Like mangrove swamps, coral reefs are extremely important habitats. Their diversity of coral genera is greatest in the warm waters of the Indian Ocean and the western Pacific. ■ Indeed, they have been called the marine version of the tropical rain forest, rivaling their terrestrial counterparts in both richness of species and biological productivity. _They also
have significance because they provide coastal protection, opportunities for recreation,
and are potential sources of substances like medicinal drugs. _At present they are coming
under a variety of threats, of which two of the most important are dredging and the effects
of increased siltation brought about by accelerated erosion from neighboring land areas.
参考阅读TP0 52-3 Early Food Production in Sub-Saharan Africa
At the end of the Pleistocene (around 10,000 B.C.), the technologies of food production
may have already been employed on the fringes of the rain forests of western and central
Africa, where the common use of such root plants as the African yam led people to
recognize the advantages of growing their own food. The yam can easily be resprouted if
the top is replanted. This primitive form of "vegeculture" (cultivation of root and tree crops)
may have been the economic tradition onto which the cultivation of summer rainfall cereal
crops was grafted as it came into use south of the grassland areas on the Sahara's southern
As the Sahara dried up after 5000 B.C., pastoral peoples (cattle herders) moved southward along major watercourses into the savanna belt of West Africa and the Sudan. By 3000 B.C., just as ancient Egyptian civilization was coming into being along the Nile, they had settled in the heart of the East African highlands far to the south. The East African highlands are ideal cattle country and the home today of such famous cattle-herding peoples as the Masai. The highlands were inhabited by hunter-gatherers living around mountains near the plains until about 3300 B.C., when the first cattle herders appeared. These cattle people may have moved between fixed settlements during the wet and dry seasons, living off hunting in the dry months and their own livestock and agriculture during the rains.
As was the case elsewhere, cattle were demanding animals in Africa. They required water at least every 24 hours and large tracts of grazing grass if herds of any size were to be maintained. The secret was the careful selection of grazing land, especially in environments where seasonal rainfall led to marked differences in graze quality throughout the year. Even modest cattle herds required plenty of land and considerable mobility. To acquire such land often required moving herds considerable distances, even from summer to winter pastures. At the same time, the cattle owners had to graze their stock in tsetse-fly-free areas The only protection against human and animal sleeping sickness, a disease carried by the tsetse fly, was to avoid settling or farming such areas - a constraint severely limiting the movements of cattle-owning farmers in eastern and central Africa. As a result, small cattle herds spread south rapidly in areas where they could be grazed. Long
before cereal agriculture took hold far south of the Sahara, some hunter-gatherer groups in the savanna woodlands of eastern and southern Africa may have acquired cattle, and perhaps other domesticated animals, by gift exchange or through raids on herding neighbors.
Contrary to popular belief: there is no such phenomenon as "pure" pastoralists, a society that subsists on its herds alone. The Saharan herders who moved southward to escape drought were almost certainly also cultivating sorghum, millet; and other tropical rainfall crops. By 1500 B.C., cereal agriculture was widespread throughout the savanna belt south of the Sahara. Small farming communities dotted the grasslands and forest margins of eastern West Africa, all of them depending on what is called shifting agriculture. This form of agriculture involved clearing woodland, burning the felled brush over the cleared plot, mixing the ash into the soil, and then cultivating the prepared fields. After a few years, the soil was exhausted, so the farmer moved on, exploiting new woodland and leaving the abandoned fields to lie fallow. Shifting agriculture, often called slash-and-burn, was highly adaptive for savanna farmers without plows, for it allowed cereal farming with the minimal expenditure of energy.
The process of clearance and burning may have seemed haphazard to the uninformed eye, but it was not. Except in favored areas, such as regularly inundated floodplains: tropical Africa's soils were of only moderate to low fertility. The art of farming was careful soil selection, that is, knowing which soils were light and easily cultivable, could be readily turned with small hoes, and would maintain their fertility over several years' planting, for
cereal crops rapidly remove nitrogen and other nutrients from the soil. Once it had taken
hold: slash-and-burn agriculture expanded its frontiers rapidly as village after village took up new lands, moving forward so rapidly that one expert has estimated it took a mere two centuries to cover 2,000 kilometers from eastern to southern Africa, related=associated in accordance with=consistent with
ferocious=fierce boost=increase modest=small disintegrate=fall apart relatively=comparatively exercised = applied emergence = rise tactic = strategy thus = consequently undoubtedly=certainly accomplished=achieved intermediate: in-between reinforce=strengthen unambiguous
北京市海淀区环球教育培训学校 版权所有 客服信箱：Marketing@gedu.org
投诉电话：010-62125800-2572 Copyright © 1997-2017 Global Education. All rights reserved.