The Australian Megafauna Extinctions
Many of the species of large animals (megafauna) such as mammoths, mastodons, ground sloths, and giant deer that roamed the Earth tens of thousands of years ago are now extinct. A major question is what caused these relatively sudden extinctions. In Australia, where giant kangaroos and other local megafauna species disappeared in the Late Pleistocene era (probably around 46,000 B.C.E.), some scholars have suggested that the arrival of humans on the continent had something to do with it. Others point to climate changes.
In the interval leading up to the coldest and driest phase of the last glacial cycle, environmental pressures on large mammals presumably increased as Australia became more arid. Many people have suggested that this change at least contributed to the Late Pleistocene extinctions. The effects of the deteriorating ice-age climate on megafauna have been conceived in two major ways. First, the major impact could have come from an increase in climate variability, as might well have accompanied the transition from one climate pattern to another. The biologist A. R. Main suggested that an unstable climate would have been to the disadvantage of large-bodied species because of their generally low rates of population growth. A population of a small-bodied species knocked down by an extreme climate event, like a severe drought, might be able to recover before the next one hit; populations of large-bodied species, unable to rebound so quickly, could be driven down to very small numbers and ultimately to extinction by a series of extreme events. Main saw dwarfing (the evolutionary process by which a species’ average body size decreases) as an adaptation to climate variability, because reduction in body size would be associated with earlier maturity and therefore a shorter generation time and faster recovery of populations. He suggested that the megafauna species that went extinct either lacked the evolutionary potential or were simply too large to reduce body size far enough to allow them to ride out the environmental variability of the Late Pleistocene.
Second, a general reduction in rainfall would have reduced the availability of drinking water and the productivity and nutritional quality of vegetation. Supporters of climate- driven extinction see large mammals as being most vulnerable tn those changes because of their large requirements for food and water. The archaeologist Josephine Flood noted of the megafauna that”The one thing they all had in common was large size and a gigantic thirst,” and J. M. Bowler remarked that “The progressive deterioration of climate in approach to the Last Glacial Maximum.. . would have imposed nearly impossible stresses on animals with large energy requirements.”
The biologist D. R. Horton has provided the most detailed account of just how these stresses might have caused extinction of large mammals. He argued that most of the extinct megafauna were species of woodland rather than truly arid habitats. Arid conditions expanded from the center of the continent toward the coasts in the last glacial cycle, and in this process woodland habitats were compressed and fragmented around the margins of the continent. As a result, formerly large and widespread populations of megafauna were confined to small isolated refuges where they were vulnerable to local extinctions. Within these refuges declining rainfall meant fewer sites had permanent surface water, essential for large-bodied species that needed to drink regularly. As some water points dried up, the distances separating remaining water points increased until animals that depended on access to free water were unable to travel between them. Populations of megafauna thus became tied to restricted zones of habitat within range of water holes. These zones of habitat were degraded, food supplies were exhausted by animals who for lack of water could not move away to use other areas, and populations died out. The repetition of these events at many locations eventually resulted in the total extinction of species. If the intensity of seasonality or between-year variability in rainfall also increased under the harsh conditions of the period known as the Last Glacial Maximum, occasional very deep droughts would have increased the pressures on small isolated populations of large mammals.
1
In the interval leading up to the coldest and driest phase of the last glacial cycle, environmental pressures on large mammals presumably increased as Australia became more arid. Many people have suggested that this change at least contributed to the Late Pleistocene extinctions. The effects of the deteriorating ice-age climate on megafauna have been conceived in two major ways. First, the major impact could have come from an increase in climate variability, as might well have accompanied the transition from one climate pattern to another. The biologist A. R. Main suggested that an unstable climate would have been to the disadvantage of large-bodied species because of their generally low rates of population growth. A population of a small-bodied species knocked down by an extreme climate event, like a severe drought, might be able to recover before the next one hit; populations of large-bodied species, unable to rebound so quickly, could be driven down to very small numbers and ultimately to extinction by a series of extreme events. Main saw dwarfing (the evolutionary process by which a species’ average body size decreases) as an adaptation to climate variability, because reduction in body size would be associated with earlier maturity and therefore a shorter generation time and faster recovery of populations. He suggested that the megafauna species that went extinct either lacked the evolutionary potential or were simply too large to reduce body size far enough to allow them to ride out the environmental variability of the Late Pleistocene.
The word “deteriorating” in the passage is closest in meaning to
Vocabulary Questions词汇题
Aresulting
Bsuddenly occurring
Ccontinuing
Dworsening
2
In the interval leading up to the coldest and driest phase of the last glacial cycle, environmental pressures on large mammals presumably increased as Australia became more arid. Many people have suggested that this change at least contributed to the Late Pleistocene extinctions. The effects of the deteriorating ice-age climate on megafauna have been conceived in two major ways. First, the major impact could have come from an increase in climate variability, as might well have accompanied the transition from one climate pattern to another. The biologist A. R. Main suggested that an unstable climate would have been to the disadvantage of large-bodied species because of their generally low rates of population growth. A population of a small-bodied species knocked down by an extreme climate event, like a severe drought, might be able to recover before the next one hit; populations of large-bodied species, unable to rebound so quickly, could be driven down to very small numbers and ultimately to extinction by a series of extreme events. Main saw dwarfing (the evolutionary process by which a species’ average body size decreases) as an adaptation to climate variability, because reduction in body size would be associated with earlier maturity and therefore a shorter generation time and faster recovery of populations. He suggested that the megafauna species that went extinct either lacked the evolutionary potential or were simply too large to reduce body size far enough to allow them to ride out the environmental variability of the Late Pleistocene.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information
Sentence Simplification Questions句子简化题
ASmall-bodied species might be able to rebuild their populations between extreme climate events, such as droughts, whereas large-bodied species might not.
BLarge-bodied species might be reduced to very small numbers after a single extreme climate event, but it would take a series of extreme events to drive them to extinction.
CThe decline of a population of small-bodied species could have a huge and rapid effect on large-bodied species that already have difficulty in extreme climate events
DIn general, small-bodied species, unlike large-bodied species are not usually impacted by climate events due to their extremely large population size.
3
In the interval leading up to the coldest and driest phase of the last glacial cycle, environmental pressures on large mammals presumably increased as Australia became more arid. Many people have suggested that this change at least contributed to the Late Pleistocene extinctions. The effects of the deteriorating ice-age climate on megafauna have been conceived in two major ways. First, the major impact could have come from an increase in climate variability, as might well have accompanied the transition from one climate pattern to another. The biologist A. R. Main suggested that an unstable climate would have been to the disadvantage of large-bodied species because of their generally low rates of population growth. A population of a small-bodied species knocked down by an extreme climate event, like a severe drought, might be able to recover before the next one hit; populations of large-bodied species, unable to rebound so quickly, could be driven down to very small numbers and ultimately to extinction by a series of extreme events. Main saw dwarfing (the evolutionary process by which a species’ average body size decreases) as an adaptation to climate variability, because reduction in body size would be associated with earlier maturity and therefore a shorter generation time and faster recovery of populations. He suggested that the megafauna species that went extinct either lacked the evolutionary potential or were simply too large to reduce body size far enough to allow them to ride out the environmental variability of the Late Pleistocene.
Paragraph 2 suggests which of the following about megafauna species that did not go extinct during the Late Pleistocene?
Factual Information Questions事实信息题
ATheir populations grew in size during this period as they filled in zones left empty by the species that did go extinct
BTheir average body size became smaller over the course of the Late Pleistocene.
CThey tended to have a longer average life span than species that did go extinct.
DThey may have started out even larger-bodied than species that did go extinct
4
In the interval leading up to the coldest and driest phase of the last glacial cycle, environmental pressures on large mammals presumably increased as Australia became more arid. Many people have suggested that this change at least contributed to the Late Pleistocene extinctions. The effects of the deteriorating ice-age climate on megafauna have been conceived in two major ways. First, the major impact could have come from an increase in climate variability, as might well have accompanied the transition from one climate pattern to another. The biologist A. R. Main suggested that an unstable climate would have been to the disadvantage of large-bodied species because of their generally low rates of population growth. A population of a small-bodied species knocked down by an extreme climate event, like a severe drought, might be able to recover before the next one hit; populations of large-bodied species, unable to rebound so quickly, could be driven down to very small numbers and ultimately to extinction by a series of extreme events. Main saw dwarfing (the evolutionary process by which a species’ average body size decreases) as an adaptation to climate variability, because reduction in body size would be associated with earlier maturity and therefore a shorter generation time and faster recovery of populations. He suggested that the megafauna species that went extinct either lacked the evolutionary potential or were simply too large to reduce body size far enough to allow them to ride out the environmental variability of the Late Pleistocene.
According to paragraph 2, what does Main argue would have happened to animals during dwarfing, aside from the reduction of body size?
Factual Information Questions事实信息题
AThe animals would become more sensitive to climate variability
BThe animals would form smaller populations
CThe animals would reach reproductive age sooner.
DThe animals would produce stronger offspring in each generation.
5
Second, a general reduction in rainfall would have reduced the availability of drinking water and the productivity and nutritional quality of vegetation. Supporters of climate- driven extinction see large mammals as being most vulnerable tn those changes because of their large requirements for food and water. The archaeologist Josephine Flood noted of the megafauna that”The one thing they all had in common was large size and a gigantic thirst,” and J. M. Bowler remarked that “The progressive deterioration of climate in approach to the Last Glacial Maximum.. . would have imposed nearly impossible stresses on animals with large energy requirements.”
The quotation by archaeologist Josephine Flood, “The one thing they all had in common was large size and a gigantic thirst,” is included in the discussion about megafauna in order to
Sentence Simplification Questions句子简化题
Acompare Flood’s theories about megafaunal extinctions with the theories of J. M. Bowler
Bprovide evidence that there were many different types of megafauna in Australia before the extinctions
Csupport the claim of some experts that climate change most affected large mammals because of their substantial food and water requirements
Dintroduce an argument against the idea that a single common cause could have produced the extinctions of so many different species
6
The biologist D. R. Horton has provided the most detailed account of just how these stresses might have caused extinction of large mammals. He argued that most of the extinct megafauna were species of woodland rather than truly arid habitats. Arid conditions expanded from the center of the continent toward the coasts in the last glacial cycle, and in this process woodland habitats were compressed and fragmented around the margins of the continent. As a result, formerly large and widespread populations of megafauna were confined to small isolated refuges where they were vulnerable to local extinctions. Within these refuges declining rainfall meant fewer sites had permanent surface water, essential for large-bodied species that needed to drink regularly. As some water points dried up, the distances separating remaining water points increased until animals that depended on access to free water were unable to travel between them. Populations of megafauna thus became tied to restricted zones of habitat within range of water holes. These zones of habitat were degraded, food supplies were exhausted by animals who for lack of water could not move away to use other areas, and populations died out. The repetition of these events at many locations eventually resulted in the total extinction of species. If the intensity of seasonality or between-year variability in rainfall also increased under the harsh conditions of the period known as the Last Glacial Maximum, occasional very deep droughts would have increased the pressures on small isolated populations of large mammals.
According to paragraph 4, which of the following changes may have happened during the Last Glacial Maximum?
Factual Information Questions事实信息题
AThe climate became drier overall, with greater variation in rainfall lat different times of year.
BWoodland habitats became concentrated in the center of the continent where they were protected from coastal conditions
CArid conditions slowly retreated, reversing the changes that had caused the extinctions
DClimate differences between the coasts and the interior of the continent became more extreme.
7
The biologist D. R. Horton has provided the most detailed account of just how these stresses might have caused extinction of large mammals. He argued that most of the extinct megafauna were species of woodland rather than truly arid habitats. Arid conditions expanded from the center of the continent toward the coasts in the last glacial cycle, and in this process woodland habitats were compressed and fragmented around the margins of the continent. As a result, formerly large and widespread populations of megafauna were confined to small isolated refuges where they were vulnerable to local extinctions. Within these refuges declining rainfall meant fewer sites had permanent surface water, essential for large-bodied species that needed to drink regularly. As some water points dried up, the distances separating remaining water points increased until animals that depended on access to free water were unable to travel between them. Populations of megafauna thus became tied to restricted zones of habitat within range of water holes. These zones of habitat were degraded, food supplies were exhausted by animals who for lack of water could not move away to use other areas, and populations died out. The repetition of these events at many locations eventually resulted in the total extinction of species. If the intensity of seasonality or between-year variability in rainfall also increased under the harsh conditions of the period known as the Last Glacial Maximum, occasional very deep droughts would have increased the pressures on small isolated populations of large mammals.
According to paragraph 4, what happened to megafauna populations as the type of available habitat changed during the last glacial cycle?
Factual Information Questions事实信息题
AThey were forced to adapt to an unfamiliar woodland environment.
BThey became scattered over larger and larger areas
CThey were forced to move farther and farther into the interior of the continent
DThey were trapped in smaller and smaller areas of the continent
8
The biologist D. R. Horton has provided the most detailed account of just how these stresses might have caused extinction of large mammals. He argued that most of the extinct megafauna were species of woodland rather than truly arid habitats. Arid conditions expanded from the center of the continent toward the coasts in the last glacial cycle, and in this process woodland habitats were compressed and fragmented around the margins of the continent. As a result, formerly large and widespread populations of megafauna were confined to small isolated refuges where they were vulnerable to local extinctions. Within these refuges declining rainfall meant fewer sites had permanent surface water, essential for large-bodied species that needed to drink regularly. As some water points dried up, the distances separating remaining water points increased until animals that depended on access to free water were unable to travel between them. Populations of megafauna thus became tied to restricted zones of habitat within range of water holes. These zones of habitat were degraded, food supplies were exhausted by animals who for lack of water could not move away to use other areas, and populations died out. The repetition of these events at many locations eventually resulted in the total extinction of species. If the intensity of seasonality or between-year variability in rainfall also increased under the harsh conditions of the period known as the Last Glacial Maximum, occasional very deep droughts would have increased the pressures on small isolated populations of large mammals.
According to paragraph 4, what happened to the megafauna when some of the permanent sources of surface water dried up?
Factual Information Questions事实信息题
AThey had to follow the rain to new areas of the continent.
BThey were pushed out of their territory by other thirsty species.
CThey had to get their water primarily from vegetation.
DThey could no longer travel between water holes.
9
In the interval leading up to the coldest and driest phase of the last glacial cycle, environmental pressures on large mammals presumably increased as Australia became more arid. Many people have suggested that this change at least contributed to the Late Pleistocene extinctions. The effects of the deteriorating ice-age climate on megafauna have been conceived in two major ways. First, the major impact could have come from an increase in climate variability, as might well have accompanied the transition from one climate pattern to another. The biologist A. R. Main suggested that an unstable climate would have been to the disadvantage of large-bodied species because of their generally low rates of population growth. [■] A population of a small-bodied species knocked down by an extreme climate event, like a severe drought, might be able to recover before the next one hit; populations of large-bodied species, unable to rebound so quickly, could be driven down to very small numbers and ultimately to extinction by a series of extreme events. [■] Main saw dwarfing (the evolutionary process by which a species’ average body size decreases) as an adaptation to climate variability, because reduction in body size would be associated with earlier maturity and therefore a shorter generation time and faster recovery of populations. [■] He suggested that the megafauna species that went extinct either lacked the evolutionary potential or were simply too large to reduce body size far enough to allow them to ride out the environmental variability of the Late Pleistocene. [■]
Look at the four squaresthat indicate where the following sentence could be added to the passage
But, for many species, this adaptation was not a solution.
Insert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
10
The extinctions of many Australian megafauna in the Late Pleistocene may have been due to climate change.
Prose Summary Questions概要小结题
Select 3 answers
ABecause of their slow rates of population growth, large-bodied species may have been unable to survive a series of extreme climate events, such as periodic droughts
BLarge mammals require large amounts of food and water, and both surface water and nutritious vegetation were disappearing as the climate became drier
CDuring the Last Glacial Maximum, the climate in the continent’s interior became more like that of the coasts, with periods of deep drought alternating with periods of excessive rainfall
DUnlike in other parts of the world, human hunting is not a possible explanation for the extinction of Australian megafauna since humans were not yet present on the continent.
EAs woodland habitats became smaller and more isolated, local populations may have used up their food supply and died out because they could not reach distant water sources
FAlthough many archaeologists accept the idea of extinctions caused by climate change, others question how it was possible in so many different kinds of locations.
