Characteristics of Tropical Rain Forests
Almost all the action in a rain forest (not just photosynthesis but also flowering, fruiting, predation, and herbivory) happens high in the canopy, the leafy green roof of the forest. Apart from the trees, the vegetation is largely composed of plant forms that reach up into the canopy by climbing the trees (for example, vines) or root in the damp, upper branches (epiphytes). The epiphytes depend on the sparse resources of mineral nutrients that they extract from crevices and pockets of the organic matter of soil found on the tree branches. The plants and animals of the canopy are not easy to study; even to gain access to the flowers in order to identify the species of tree is difficult without the erection of tree walks. It is a measure of the problems of doing research in rain forests that botanists have trained monkeys to collect and throw down flowers and a research team has used hot air balloons to move over the canopy and work in it.
Most species of animals and plants in tropical rain forests are active throughout the year, though the plants may flower and ripen fruit in sequence. In Trinidad, for example, the forest contains at least 18 closely related trees in the genus Miconia whose combined fruiting seasons extend throughout the year; this contrasts with the situation in temperate latitudes.
Dramatically high species richness is the norm for tropical rain forests, and communities rarely, if ever, become dominated by one or a few species-a very different situation from the low biodiversity of northern coniferous forests. This raises some fundamental questions. First, what is it about the evolutionary history of tropical rain forests that has allowed such diversity to evolve? Part of the answer relates to the comparative stability of patches of rain forest during the ice ages. It is thought that during these periods, drought forced tropical rain forests to contract into islands in a sea of savanna (flat grassland), and these expanded and coalesced again as wetter periods returned. This would have promoted genetic isolation of populations, allowing individual species to become well established before joining other species when rain forests grew again. This phenomenon of isolation is so important for a variety of species to develop. We may also ask why it is that among the diversity of species in tropical rain forests, a few have not dominated and suppressed the rest in a struggle for existence. At least part of the answer is that populations of specialized pathogens and herbivores develop near mature trees and attack new recruits of the same species nearby. Thus, the chance that a new seedling will survive can be expected to increase with its distance from a mature tree of the same species, reducing the likelihood of dominance by one or a few species in the forest.
The diversity of rain forest trees provides for a corresponding diversity of resources for herbivores. A variety of fresh, young leaves are available throughout the year, and a constant procession of seed and fruit production provides reliable food for specialists such as fruit-eating bats. Moreover, a diversity of flowers, such as epiphytic orchids with their specialized pollinating mechanisms, requires a parallel, specialized diversity of pollinating insects. Rain forests are the center of diversity for ants-43 species have been recorded on a single tree in a Peruvian rain forest. And there is even more diversity among the beetles; Erwin (1982) estimated that there are 18,000 species of beetles in 1 hectare (10,000 square meters) of Panamanian rain forest compared with only 24,000 in the whole of the United States and Canada.
There is intense biological activity in the soil of tropical rain forests. Leaves that fall to the ground decompose faster than in any other ecological community.As a result, the soil surface is almost bare. The mineral nutrients in fallen leaves in rain forests are rapidly released and are unlikely to be removed by natural processes. In other ecological communities, rains may carry nutrients well below the upper soil levels at which roots can recover them. By contrast, the mineral nutrients in a rain forest are safe from loss to the lower soil layers and almost all are in fact held by the plants themselves.
1
Almost all the action in a rain forest (not just photosynthesis but also flowering, fruiting, predation, and herbivory) happens high in the canopy, the leafy green roof of the forest. Apart from the trees, the vegetation is largely composed of plant forms that reach up into the canopy by climbing the trees (for example, vines) or root in the damp, upper branches (epiphytes). The epiphytes depend on the sparse resources of mineral nutrients that they extract from crevices and pockets of the organic matter of soil found on the tree branches. The plants and animals of the canopy are not easy to study; even to gain access to the flowers in order to identify the species of tree is difficult without the erection of tree walks. It is a measure of the problems of doing research in rain forests that botanists have trained monkeys to collect and throw down flowers and a research team has used hot air balloons to move over the canopy and work in it.
The word “sparse” in the passage is closest in meaning to
Ahighly varied
Bnatural
Cprotected
Dthinly distributed
2
Almost all the action in a rain forest (not just photosynthesis but also flowering, fruiting, predation, and herbivory) happens high in the canopy, the leafy green roof of the forest. Apart from the trees, the vegetation is largely composed of plant forms that reach up into the canopy by climbing the trees (for example, vines) or root in the damp, upper branches (epiphytes). The epiphytes depend on the sparse resources of mineral nutrients that they extract from crevices and pockets of the organic matter of soil found on the tree branches. The plants and animals of the canopy are not easy to study; even to gain access to the flowers in order to identify the species of tree is difficult without the erection of tree walks. It is a measure of the problems of doing research in rain forests that botanists have trained monkeys to collect and throw down flowers and a research team has used hot air balloons to move over the canopy and work in it.
The author mentions monkeys and hot air balloons in paragraph 1 in order to
Aemphasize how difficult it is to do research in tropical rain forests
Bcompare the tools used by different researchers working in rain forests
Cexplain why tree walks are still the preferred way of gaining access to flower samples for research
Dillustrate that most of the activity in a tropical rain forest happens in the canopy
3
Almost all the action in a rain forest (not just photosynthesis but also flowering, fruiting, predation, and herbivory) happens high in the canopy, the leafy green roof of the forest. Apart from the trees, the vegetation is largely composed of plant forms that reach up into the canopy by climbing the trees (for example, vines) or root in the damp, upper branches (epiphytes). The epiphytes depend on the sparse resources of mineral nutrients that they extract from crevices and pockets of the organic matter of soil found on the tree branches. The plants and animals of the canopy are not easy to study; even to gain access to the flowers in order to identify the species of tree is difficult without the erection of tree walks. It is a measure of the problems of doing research in rain forests that botanists have trained monkeys to collect and throw down flowers and a research team has used hot air balloons to move over the canopy and work in it.
Select TWO answer choices that describe characteristics of epiphytes discussed in paragraph 1. To receive credit, you must select TWO answers.
AEpiphytes live in the rain forest canopy.
BEpiphytes are a source of food for monkeys.
CEpiphytes flower and fruit seasonally.
DEpiphytes obtain their food from mineral deposits on tree branches.
4
Most species of animals and plants in tropical rain forests are active throughout the year, though the plants may flower and ripen fruit in sequence. In Trinidad, for example, the forest contains at least 18 closely related trees in the genus Miconia whose combined fruiting seasons extend throughout the year; this contrasts with the situation in temperate latitudes.
In paragraph 2, why does the author discuss the fruiting habits of closely related trees in the genus Miconia in Trinidad?
ATo indicate that rain forests in Trinidad are the best environment for the growth of trees in the genus Miconia
BTo illustrate that flowing and fruiting activity happens year-round in tropical rain forests.
CTo argue that activity in forests in temperate latitudes is similar to that of Trinidad
DTo explain why some tropical rain forests may be inactive at certain times of the year.
5
Dramatically high species richness is the norm for tropical rain forests, and communities rarely, if ever, become dominated by one or a few species-a very different situation from the low biodiversity of northern coniferous forests. This raises some fundamental questions. First, what is it about the evolutionary history of tropical rain forests that has allowed such diversity to evolve? Part of the answer relates to the comparative stability of patches of rain forest during the ice ages. It is thought that during these periods, drought forced tropical rain forests to contract into islands in a sea of savanna (flat grassland), and these expanded and coalesced again as wetter periods returned. This would have promoted genetic isolation of populations, allowing individual species to become well established before joining other species when rain forests grew again. This phenomenon of isolation is so important for a variety of species to develop. We may also ask why it is that among the diversity of species in tropical rain forests, a few have not dominated and suppressed the rest in a struggle for existence. At least part of the answer is that populations of specialized pathogens and herbivores develop near mature trees and attack new recruits of the same species nearby. Thus, the chance that a new seedling will survive can be expected to increase with its distance from a mature tree of the same species, reducing the likelihood of dominance by one or a few species in the forest.
The phrase “promoted” in the passage is closest in meaning to
Aencouraged
Bexplained
Cspeeded up
Dprevented
6
Dramatically high species richness is the norm for tropical rain forests, and communities rarely, if ever, become dominated by one or a few species-a very different situation from the low biodiversity of northern coniferous forests. This raises some fundamental questions. First, what is it about the evolutionary history of tropical rain forests that has allowed such diversity to evolve? Part of the answer relates to the comparative stability of patches of rain forest during the ice ages. It is thought that during these periods, drought forced tropical rain forests to contract into islands in a sea of savanna (flat grassland), and these expanded and coalesced again as wetter periods returned. This would have promoted genetic isolation of populations, allowing individual species to become well established before joining other species when rain forests grew again. This phenomenon of isolation is so important for a variety of species to develop. We may also ask why it is that among the diversity of species in tropical rain forests, a few have not dominated and suppressed the rest in a struggle for existence. At least part of the answer is that populations of specialized pathogens and herbivores develop near mature trees and attack new recruits of the same species nearby. Thus, the chance that a new seedling will survive can be expected to increase with its distance from a mature tree of the same species, reducing the likelihood of dominance by one or a few species in the forest.
What can be inferred from paragraph 3 about northern coniferous forests?
AThey experienced stability during the ice ages, leading to established species today.
BTheir evolutionary history differs significantly from that of tropical rain forests.
CThe level of species dominance is similar to that of tropical rain forests.
DTheir species experienced the phenomenon of genetic isolation.
7
Dramatically high species richness is the norm for tropical rain forests, and communities rarely, if ever, become dominated by one or a few species-a very different situation from the low biodiversity of northern coniferous forests. This raises some fundamental questions. First, what is it about the evolutionary history of tropical rain forests that has allowed such diversity to evolve? Part of the answer relates to the comparative stability of patches of rain forest during the ice ages. It is thought that during these periods, drought forced tropical rain forests to contract into islands in a sea of savanna (flat grassland), and these expanded and coalesced again as wetter periods returned. This would have promoted genetic isolation of populations, allowing individual species to become well established before joining other species when rain forests grew again. This phenomenon of isolation is so important for a variety of species to develop. We may also ask why it is that among the diversity of species in tropical rain forests, a few have not dominated and suppressed the rest in a struggle for existence. At least part of the answer is that populations of specialized pathogens and herbivores develop near mature trees and attack new recruits of the same species nearby. Thus, the chance that a new seedling will survive can be expected to increase with its distance from a mature tree of the same species, reducing the likelihood of dominance by one or a few species in the forest.
According to paragraph 3, pathogens and herbivores affect plant-species diversity in rain forests by
Aspecializing their feeding on only a few species of trees
Bdominating and suppressing organisms that feed on young trees
Cfeeding mainly on mature trees
Dlimiting the number of new trees growing near mature trees of the same species
8
The diversity of rain forest trees provides for a corresponding diversity of resources for herbivores. A variety of fresh, young leaves are available throughout the year, and a constant procession of seed and fruit production provides reliable food for specialists such as fruit-eating bats. Moreover, a diversity of flowers, such as epiphytic orchids with their specialized pollinating mechanisms, requires a parallel, specialized diversity of pollinating insects. Rain forests are the center of diversity for ants-43 species have been recorded on a single tree in a Peruvian rain forest. And there is even more diversity among the beetles; Erwin (1982) estimated that there are 18,000 species of beetles in 1 hectare (10,000 square meters) of Panamanian rain forest compared with only 24,000 in the whole of the United States and Canada.
According to paragraph 4, which of the following statements about species diversity in rain forests is NOT true?
AHerbivores can rely on a variety of species as food sources.
BA diversity of tree species results in a corresponding diversity of plant-eating animals.
CSpecialization of the pollination mechanisms of species results in a relatively low number of pollinators.
DA large number of species can live within a relatively small area.
9
There is intense biological activity in the soil of tropical rain forests. Leaves that fall to the ground decompose faster than in any other ecological community. [■] As a result, the soil surface is almost bare. [■]The mineral nutrients in fallen leaves in rain forests are rapidly released and are unlikely to be removed by natural processes. [■] In other ecological communities, rains may carry nutrients well below the upper soil levels at which roots can recover them. [■] By contrast, the mineral nutrients in a rain forest are safe from loss to the lower soil layers and almost all are in fact held by the plants themselves.
Look at the four squaresthat indicate where the following sentence could be added to the passage
One reason for this is that little rainfall reaches the forest floor directly so minerals are not washed away.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Activity in tropical rain forests happens primarily in the canopy.
ATropical rain forests are difficult to access due to large numbers of plants and animals on the forest floor.
BDuring the ice ages tropical rain forests did not vary in size, which led to an increase in species richness.
CAll closely related rainforest species flower at the same time and then rest while non-related species flower.
DTropical rain forests contain many diverse species and little domination of a few species over others.
EGreat plant diversity in tropical rain forests supports a similar diversity in the animal species that inhabit them.
FThe quick decomposition of leaves releases a large amount of nutrients that are accessible to plant roots and easily recovered.
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