Pollination
Tree reproduction exploits wind, water, or animals as intermediaries to get pollen from one tree to another. A large animal-pollinated tree, however, faces distinct problems. It needs to produce enough edible reward- nectar and pollen-in its flowers to attract the pollinators to visit but runs the risk of producing so much within one canopy(the upper portion of the tree) that the pollinators linger rather than move to the next tree. Moreover, if all other individuals of a species are in flower (which is needed for cross-pollination-the transfer of pollen from the flower of one plant to a genetically different plant) there may not be enough pollinators for the huge number of flowers produced.
One solution to these problems is to be in flower when other species are not, so that you have the pollinators to yourself. In temperate regions this is constrained by having to work around winter; nevertheless, flowering of insect- pollinated trees is indeed spread over a large part of the summer, but this still does not solve the problem of encouraging pollinators to leave the abundant food of one tree to go to another. Some large tropical trees get around this by having some parts of the tree in flower others in bud and others in fruit, giving pollinators the impression of a series of small trees. A more extreme answer, used by other tropical trees, is to produce just a few flowers at a time over a long period, possibly all year. Hawkmoths, hummingbirds, bats, bees, and other pollinators exploit these extended-blooming trees by the equivalent of “trap-lining,”where they fly over complex feeding routes, repeatedly visiting widely spread flowers, just like a trapper in the Arctic visiting his spread-out line of traps. Bees can travel more than 20 kilometers during these daily excursions.
At the other extreme, however, are mass-blooming trees producing huge numbers of flowers. This is especially seen in the aseasonal (no regular dry period) tropical evergreen forests of Borneo and Malaysia where the tallest canopy trees, mostly species of dipterocarp, may all flower and fruit simultaneously at intervals of two to ten years. Over a period lasting a few weeks to a few months, nearly all dipterocarps and up to 88 percent of all canopy species flower after years of little or no reproductive activity. The region over which such a mass-flowering event occurs can be as small as a single river valley or as large as northeastern Borneo or peninsular Malaysia. With individual dipterocarp trees presenting up to four million flowers, this mass flowering seems to ignore the above problems. But as is often the case, the solutions are subtle and not immediately obvious. Firstly, within the concentrated period during which all dipterocarp species flower, individual species flower sequentially, in the same order of species each time, thereby reducing competition for pollinators. Secondly, although an individual tree can flower over two to three weeks, individual flowers may last only a day. The main pollinators are small thrips, an insect attracted by the overpowering scent of the opening flower to spend the night moving around inside a flower eating it and the pollen. In the morning the flower falls, complete with its happy thrips, leaving the ovary on the tree to develop into a fruit. As the next wave of flowers opens the following evening the thrips fly up for their next feed, blown by even light winds to, hopefully, land in the flower of a different tree from the night before. Once there they deliver their load of pollen as they wander around feeding. This works only because, unlike most tropical trees, the dipterocarps tend to grow clumped together (the heavy winged seeds of dipterocarps spin like “helicopters” but do not go far). The thrips persist at low levels between mass flowerings and explode in numbers as the trees come into flower.
In general, mass-blooming trees use relatively unspecialized pollinators(pollinators that do not restrict themselves to certain tree types), and this gives them a greater number of pollinators to go around. Their strong visual image, created by mass flowering, can attract pollinators in large numbers from great distances. High rivalry among insects can benefit the tree if in the battle for flowers, some insects end up being ejected and going to the next tree.
1
One solution to these problems is to be in flower when other species are not, so that you have the pollinators to yourself. In temperate regions this is constrained by having to work around winter; nevertheless, flowering of insect- pollinated trees is indeed spread over a large part of the summer, but this still does not solve the problem of encouraging pollinators to leave the abundant food of one tree to go to another. Some large tropical trees get around this by having some parts of the tree in flower others in bud and others in fruit, giving pollinators the impression of a series of small trees. A more extreme answer, used by other tropical trees, is to produce just a few flowers at a time over a long period, possibly all year. Hawkmoths, hummingbirds, bats, bees, and other pollinators exploit these extended-blooming trees by the equivalent of “trap-lining,”where they fly over complex feeding routes, repeatedly visiting widely spread flowers, just like a trapper in the Arctic visiting his spread-out line of traps. Bees can travel more than 20 kilometers during these daily excursions.
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.
AIn temperate regions, trees may spread out their flowering over the summer, but this does not solve the problem of pollinators that fail to move on to other trees.
BAlthough pollination poses a problem in the winter in temperate regions, species have solved the problem by remaining in trees with abundant food sources.
CEncouraging pollinators to move on from one tree to another is a common solution for trees in temperate regions where pollination is nevertheless constrained by winter.
DPollinators in temperate regions need to leave abundant food sources in one tree to go to another, but if trees flower over a large part of the summer, this solves their problem.
2
One solution to these problems is to be in flower when other species are not, so that you have the pollinators to yourself. In temperate regions this is constrained by having to work around winter; nevertheless, flowering of insect- pollinated trees is indeed spread over a large part of the summer, but this still does not solve the problem of encouraging pollinators to leave the abundant food of one tree to go to another. Some large tropical trees get around this by having some parts of the tree in flower others in bud and others in fruit, giving pollinators the impression of a series of small trees. A more extreme answer, used by other tropical trees, is to produce just a few flowers at a time over a long period, possibly all year. Hawkmoths, hummingbirds, bats, bees, and other pollinators exploit these extended-blooming trees by the equivalent of “trap-lining,”where they fly over complex feeding routes, repeatedly visiting widely spread flowers, just like a trapper in the Arctic visiting his spread-out line of traps. Bees can travel more than 20 kilometers during these daily excursions.
The word “exploit” in the passage is closest in meaning to
Arespond to
Bare affected by
Ctake advantage of
Dreturn to
3
One solution to these problems is to be in flower when other species are not, so that you have the pollinators to yourself. In temperate regions this is constrained by having to work around winter; nevertheless, flowering of insect- pollinated trees is indeed spread over a large part of the summer, but this still does not solve the problem of encouraging pollinators to leave the abundant food of one tree to go to another. Some large tropical trees get around this by having some parts of the tree in flower others in bud and others in fruit, giving pollinators the impression of a series of small trees. A more extreme answer, used by other tropical trees, is to produce just a few flowers at a time over a long period, possibly all year. Hawkmoths, hummingbirds, bats, bees, and other pollinators exploit these extended-blooming trees by the equivalent of “trap-lining,”where they fly over complex feeding routes, repeatedly visiting widely spread flowers, just like a trapper in the Arctic visiting his spread-out line of traps. Bees can travel more than 20 kilometers during these daily excursions.
According to paragraph 2, why might large trees benefit from spreading out their flowering over a period of time rather than having all species in flower at the same time?
AIt allows time for all species in temperate regions to complete their flowering before winter.
BIt encourages pollinators to remain only a short time in the flowers of any one tree species.
CIt makes it more likely that there will be enough pollinators to meet the needs of tree species that are currently in flower.
DIt makes trees appear healthier for a longer period of time and therefore more attractive to pollinators.
4
At the other extreme, however, are mass-blooming trees producing huge numbers of flowers. This is especially seen in the aseasonal (no regular dry period) tropical evergreen forests of Borneo and Malaysia where the tallest canopy trees, mostly species of dipterocarp, may all flower and fruit simultaneously at intervals of two to ten years. Over a period lasting a few weeks to a few months, nearly all dipterocarps and up to 88 percent of all canopy species flower after years of little or no reproductive activity. The region over which such a mass-flowering event occurs can be as small as a single river valley or as large as northeastern Borneo or peninsular Malaysia. With individual dipterocarp trees presenting up to four million flowers, this mass flowering seems to ignore the above problems. But as is often the case, the solutions are subtle and not immediately obvious. Firstly, within the concentrated period during which all dipterocarp species flower, individual species flower sequentially, in the same order of species each time, thereby reducing competition for pollinators. Secondly, although an individual tree can flower over two to three weeks, individual flowers may last only a day. The main pollinators are small thrips, an insect attracted by the overpowering scent of the opening flower to spend the night moving around inside a flower eating it and the pollen. In the morning the flower falls, complete with its happy thrips, leaving the ovary on the tree to develop into a fruit. As the next wave of flowers opens the following evening the thrips fly up for their next feed, blown by even light winds to, hopefully, land in the flower of a different tree from the night before. Once there they deliver their load of pollen as they wander around feeding. This works only because, unlike most tropical trees, the dipterocarps tend to grow clumped together (the heavy winged seeds of dipterocarps spin like “helicopters” but do not go far). The thrips persist at low levels between mass flowerings and explode in numbers as the trees come into flower.
Why does the author provide the information that “although an individual tree can flower over two to three weeks, individual flowers may last only a day”?
ATo introduce an additional strategy that mass-blooming trees use to maximize their chances of pollination
BTo help explain why thrips are the main pollinators of mass-blooming trees
CTo provide a second reason why “mass-blooming” may not be the appropriate term for describing dipterocarp trees
DTo identify one of the major challenges faced by mass-blooming trees that produce huge numbers of flowers
5
At the other extreme, however, are mass-blooming trees producing huge numbers of flowers. This is especially seen in the aseasonal (no regular dry period) tropical evergreen forests of Borneo and Malaysia where the tallest canopy trees, mostly species of dipterocarp, may all flower and fruit simultaneously at intervals of two to ten years. Over a period lasting a few weeks to a few months, nearly all dipterocarps and up to 88 percent of all canopy species flower after years of little or no reproductive activity. The region over which such a mass-flowering event occurs can be as small as a single river valley or as large as northeastern Borneo or peninsular Malaysia. With individual dipterocarp trees presenting up to four million flowers, this mass flowering seems to ignore the above problems. But as is often the case, the solutions are subtle and not immediately obvious. Firstly, within the concentrated period during which all dipterocarp species flower, individual species flower sequentially, in the same order of species each time, thereby reducing competition for pollinators. Secondly, although an individual tree can flower over two to three weeks, individual flowers may last only a day. The main pollinators are small thrips, an insect attracted by the overpowering scent of the opening flower to spend the night moving around inside a flower eating it and the pollen. In the morning the flower falls, complete with its happy thrips, leaving the ovary on the tree to develop into a fruit. As the next wave of flowers opens the following evening the thrips fly up for their next feed, blown by even light winds to, hopefully, land in the flower of a different tree from the night before. Once there they deliver their load of pollen as they wander around feeding. This works only because, unlike most tropical trees, the dipterocarps tend to grow clumped together (the heavy winged seeds of dipterocarps spin like “helicopters” but do not go far). The thrips persist at low levels between mass flowerings and explode in numbers as the trees come into flower.
According to paragraph 3, all of the following statements are true of dipterocarps EXCEPT
AThey are tall, tropical evergreen trees.
BThey make up 88 percent of all canopy species in the forests of Borneo and Malaysia.
CSome species can go for up to ten years without any significant flowering.
DIndividual trees can produce up to four million flowers during a single period of reproductive activity.
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At the other extreme, however, are mass-blooming trees producing huge numbers of flowers. This is especially seen in the aseasonal (no regular dry period) tropical evergreen forests of Borneo and Malaysia where the tallest canopy trees, mostly species of dipterocarp, may all flower and fruit simultaneously at intervals of two to ten years. Over a period lasting a few weeks to a few months, nearly all dipterocarps and up to 88 percent of all canopy species flower after years of little or no reproductive activity. The region over which such a mass-flowering event occurs can be as small as a single river valley or as large as northeastern Borneo or peninsular Malaysia. With individual dipterocarp trees presenting up to four million flowers, this mass flowering seems to ignore the above problems. But as is often the case, the solutions are subtle and not immediately obvious. Firstly, within the concentrated period during which all dipterocarp species flower, individual species flower sequentially, in the same order of species each time, thereby reducing competition for pollinators. Secondly, although an individual tree can flower over two to three weeks, individual flowers may last only a day. The main pollinators are small thrips, an insect attracted by the overpowering scent of the opening flower to spend the night moving around inside a flower eating it and the pollen. In the morning the flower falls, complete with its happy thrips, leaving the ovary on the tree to develop into a fruit. As the next wave of flowers opens the following evening the thrips fly up for their next feed, blown by even light winds to, hopefully, land in the flower of a different tree from the night before. Once there they deliver their load of pollen as they wander around feeding. This works only because, unlike most tropical trees, the dipterocarps tend to grow clumped together (the heavy winged seeds of dipterocarps spin like “helicopters” but do not go far). The thrips persist at low levels between mass flowerings and explode in numbers as the trees come into flower.
According to paragraph 3, one way in which mass-flowering trees reduce competition for pollinators is by
Alimiting the mass-lowering event to a relatively small area, such as a single river valley
Blimiting the period during which the mass-flowering takes place to a few weeks
Chaving individual species flower one after the other within the period in which the mass-flowering occurs
Dallowing some flowers to fall to the ground, where other noncompeting pollinators are present
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In general, mass-blooming trees use relatively unspecialized pollinators(pollinators that do not restrict themselves to certain tree types), and this gives them a greater number of pollinators to go around. Their strong visual image, created by mass flowering, can attract pollinators in large numbers from great distances. High rivalry among insects can benefit the tree if in the battle for flowers, some insects end up being ejected and going to the next tree.
The word “ejected” in the passage is closest in meaning to
Atoo late
Btoo slow
Cpushed out
Dkept away
8
In general, mass-blooming trees use relatively unspecialized pollinators(pollinators that do not restrict themselves to certain tree types), and this gives them a greater number of pollinators to go around. Their strong visual image, created by mass flowering, can attract pollinators in large numbers from great distances. High rivalry among insects can benefit the tree if in the battle for flowers, some insects end up being ejected and going to the next tree.
Paragraph 4 suggests which of the following ideas about mass-blooming trees?
AThey depend on a special type of pollinator that can quickly go around to many trees.
BTheir flowers have very little scent because they attract pollinators through visual signals.
CTheir survival depends on their growing next to one another.
DTheir chance of pollination increases when there is competition for flowers among pollinators.
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Tree reproduction exploits wind, water, or animals as intermediaries to get pollen from one tree to another. A large animal-pollinated tree, however, faces distinct problems.[■] It needs to produce enough edible reward- nectar and pollen-in its flowers to attract the pollinators to visit but runs the risk of producing so much within one canopy(the upper portion of the tree) that the pollinators linger rather than move to the next tree. [■]Moreover, if all other individuals of a species are in flower (which is needed for cross-pollination-the transfer of pollen from the flower of one plant to a genetically different plant) there may not be enough pollinators for the huge number of flowers produced.[■]
One solution to these problems is to be in flower when other species are not, so that you have the pollinators to yourself. In temperate regions this is constrained by having to work around winter; nevertheless, flowering of insect- pollinated trees is indeed spread over a large part of the summer, but this still does not solve the problem of encouraging pollinators to leave the abundant food of one tree to go to another.[■] Some large tropical trees get around this by having some parts of the tree in flower others in bud and others in fruit, giving pollinators the impression of a series of small trees. A more extreme answer, used by other tropical trees, is to produce just a few flowers at a time over a long period, possibly all year. Hawkmoths, hummingbirds, bats, bees, and other pollinators exploit these extended-blooming trees by the equivalent of “trap-lining,”where they fly over complex feeding routes, repeatedly visiting widely spread flowers, just like a trapper in the Arctic visiting his spread-out line of traps. Bees can travel more than 20 kilometers during these daily excursions.
Look at the four squaresthat indicate where the following sentence could be added to the passage
Large animal-pollinated trees must overcome these challenges to reproduce successfully.
Where would the sentence best fit？Click on a square sentence to the passage.
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For trees to reproduce, pollen from flowers of one individual of a species must be transferred to the flowers of another.
ASmall tree species are able to get pollen from one individual to another using wind or water, but most large species must also depend on animal pollinators, typically insects.
BTemperate and tropical trees differ in the strategies they use to ensure adequate pollination: temperate trees produce only a few flowers in a year, while tropical trees rely on mass blooming.
CIf many trees flower at once, there may not be enough local pollinators, so mass-blooming trees may flower in sequence or attract pollinators from great distances with their strong visual image.
DLarge animal-pollinated trees must produce enough pollen and nectar in their flowers to attract pollinators but not so much that pollinators have no reason to move on to flowers of other trees.
EDipterocarps do not seem to face the same problems as other trees because their primary pollinators are thrips that are easily blown from tree to tree by strong tropical winds.
FStrategies to encourage pollinators to move to other trees include producing just a few flowers over extended periods, dropping opened flowers quickly, and having only parts of the tree flower at once.
