托福阅读真题第191篇Habitat Selection
Habitat Selection
Paragraph 1：Researchers who study habitat selection have proposed various models for the process. Marine biologist Peter F. Sale hypothesized the existence of a simple mechanism of habitat selection in fish that is based on levels of exploratory behavior. Sense organs monitor specific stimuli in the environment and send a summation of pertinent stimuli back to central-nervous-system centers, which regulate the amount of exploration. As the constellation of cues approaches some optimum level, exploratory behavior ceases and the animal stays where it is.
1. According to paragraph 1, all of the following are processes that occur during exploratory behavior EXCEPT:
O A favorable combination of cues are gathered.
O Sense organs detect and record stimuli in the surrounding area.
O Sense organs receive further directions from the central nervous system.
O The central nervous system receives a summary of stimuli from the sense organs.
Paragraph 2：An alternative hypothesis is that an animal has a cognitive map of the ideal habitat and that its behavior is goal directed. However, working with a species of surgeonfish, Sale tested juveniles in laboratory tanks with various water depths and bottom covers under which fish could hide. Exploration time was least in the tank with shallow water and bottom cover and highest in the tank with shallow water and no bottom cover. In choice tests and field observations, most fish preferred shallow areas with bottom cover. Thus, Sale concluded, there is no need to suggest the inheritance of complex cognitive maps and goal-directed behaviors; rather, the animal simply moves around more in an unsuitable habitat and less in a suitable one.
2. In paragraph 2, why does the author discuss Sale’s research with a species of surgeonfish?
O To demonstrate how animals distinguish suitable habitats from unsuitable ones
O To give an example of an animal that shows little or no exploratory behavior during habitat selection
O To challenge the hypothesis that animals have complex cognitive maps of their ideal habitat that guide their habitat selection
O To provide evidence that fish prefer areas that are shallow and have covering under which to hide
Paragraph 3：Sale’s model still does not explain how the animal “knows” what is suitable and what is not, or how stimuli from multiple cues are integrated. Nor does it explain the role of photoperiod (the duration of the animal’s daily exposure to sunlight) in the response of dark-eyed juncos to photographs of their natural habitat. These wild-caught birds were presented a choice of viewing one of two 35-millimeter color slides showing different habitats. Birds kept in the lab under a winter photoperiod of nine hours of light and fifteen hours of darkness preferred (spent more time in front of) slides of their southern winter habitat. After day length was increased to fifteen hours of light and nine hours of darkness, the birds’ viewing preferences shifted to the northern summer habitat.
3. According to paragraph 3, Sale’s model of habitat selection is unable to explain which of the following?
O Why dark-eyed juncos’ interest in a particular habitat changes with the duration of daylight they are exposed to
O Why the environment suitable for dark-eyed juncos in the winter differs from the environment suitable for them in the summer
O Why only some species of animals respond to photographs of their natural habitats
O Why birds studied in the lab behave differently than birds in the wild do
4. Paragraph 3 supports which of the following statements about dark-eyed juncos?
O The habitat preference of dark-eyed juncos changes with the amount of daylight present.
O Wild-caught dark-eyed juncos do not recognize photographs of their own habitat.
O Dark-eyed juncos choose their habitat based on seasonal temperatures.
O Artificial light affects dark-eyed juncos’ choice of habitat differently than does natural sunlight.
Paragraph 4： Social cues may also affect choice of habitat. Large juncos (usually males) dominate smaller individuals (usually females and juveniles) in wintering flocks. Biologist Ellen Ketterson explained the finding that females usually migrate farther south than males by hypothesizing that subordinate birds are forced to migrate farther to avoid competing with dominants. In their lab study, researchers E. Roberts and Peter Weigl found that during the short days (stimulating winter), small subordinate juncos showed the strongest preference for winter scenes.
5. According to paragraph 4, what reason has been suggested for why female juncos often migrate farther south than do male juncos?
O To avoid the colder temperatures farther north
O To provide safer habitats for their juveniles
O To avoid having to compete with males
O To find habitats having the longest days
Paragraph 5：Risk of predation and competition are other factors that may affect habitat use. Hairy-footed gerbils live in vegetated islands in a sea of sand in the Namib Desert of southern Africa. Habitat use was determined by tracks in the sand and by how quickly they gave up feeding at stations containing seeds mixed with sand. Gerbils preferred sites around bushes or grass clumps to open areas and were more active on new-Moon nights than on full-Moon nights. They also gave up feeding at seed trays sooner in open areas and on full-Moon nights. These differences were likely caused by greater risk of predation in open areas and when the Moon was full. When striped mice, a close competitor of the gerbil, were removed, gerbils increased foraging activity, especially in the grass clumps.
6. According to paragraph 5, why do hairy-footed gerbils prefer to feed in bushes and grass clumps?
O There is more food available there.
O There is less competition there from striped mice.
O There is more shade there from the heat of the desert.
O There is less danger there of being harmed by a predator.
Paragraph 6：The immediate cues to which animals respond when selecting a habitat may not be the same as the ultimate factors that have brought about the evolution of the response. For example, the blue tit, a European bird, lives in oak woodlands where most of its preferred food is found. But the blue tit establishes its territory each year before leaves and caterpillars (its staple food) have even appeared, so it must be using some other cue, such as the shape of the trees, to select its habitat. In fact, we know little about the signals that animals respond to when choosing their habitat. And in migratory species, it is not even clear when in the life cycle a choice of habitat is made. One study found that breeding sites may be selected in late summer or fall before migration, rather than in the spring, as is usually assumed.
7. According to paragraph 6, which of the following is true about habitat selection by the blue tit?
O It selects a habitat having the tallest trees.
O It selects a habitat where there are no caterpillars to eat the leaves.
O It selects its territory each year in spring.
O It selects its habitat before its preferred food appears in the area.
8. Paragraph 6 supports which of the following statements about scientists’ knowledge of habitat selection?
O Scientists have successfully identified most of the immediate factors that animals respond to in choosing their habitats.
O Scientists have determined the seasons in which most animal species choose their habitats.
O Scientists know that evolution has led animals to ignore cues in their environment when choosing habitats.
O Scientists still have much to learn about the cues to which animals respond in choosing their habitats.
Paragraph 3：Sale’s model still does not explain how the animal “knows” what is suitable and what is not, or how stimuli from multiple cues are integrated. Nor does it explain the role of photoperiod (the duration of the animal’s daily exposure to sunlight) in the response of dark-eyed juncos to photographs of their natural habitat. These wild-caught birds were presented a choice of viewing one of two 35-millimeter color slides showing different habitats. Birds kept in the lab under a winter photoperiod of nine hours of light and fifteen hours of darkness preferred (spent more time in front of) slides of their southern winter habitat. ■After day length was increased to fifteen hours of light and nine hours of darkness, the birds’ viewing preferences shifted to the northern summer habitat.
Paragraph 4：■Social cues may also affect choice of habitat. ■Large juncos (usually males) dominate smaller individuals (usually females and juveniles) in wintering flocks. ■Biologist Ellen Ketterson explained the finding that females usually migrate farther south than males by hypothesizing that subordinate birds are forced to migrate farther to avoid competing with dominants. In their lab study, researchers E. Roberts and Peter Weigl found that during the short days (stimulating winter), small subordinate juncos showed the strongest preference for winter scenes.
9. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
However, photoperiod is not the only factor in the habitat selection of this bird species.
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.
10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your choices to the spaces where they belong. To review the passage, click on View Text.
Researchers who study habitat selection among animals have proposed various models for the process.
Answer Choices
O Peter F. Sale argued against the hypothesis that animals have cognitive maps of their ideal habitat by demonstrating that animals explore less in suitable habitats than in unsuitable ones.
O Animals kept in the lab easily recognized images of their natural habitats during different seasons of the year.
O Researchers have demonstrated that migratory species of birds select their breeding habitats at a point in their life cycle when they are ready to reproduce.
O Peter F. Sale’s model of habitat selection explained how animals distinguish suitable habitats from unsuitable ones as they integrate stimuli from multiple cues in the environment.
O Laboratory experiments and field observations showed that day length, dominance relation within species, risk of predation, and competition for food play a role in habitat selection.
O The fundamental elements that determine habitat selection may differ from the immediate cues to which the animals respond.
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