2019年10月26日雅思阅读考试真题及答案
雅思的最新一期考试，在上周末进行，大家对自己的考试有信心吗？跟着店铺来一起看看2019年10月26日雅思阅读考试真题及答案。
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gripsA THERE’S no animal that symbolis rainforest diversity quite as spectacularly as the tropical butterfly. Anyone lucky enough to e the creatures flitting between patches of sunlight cannot fail to be impresd by the variety of their patterns. But why do they display such colourful exuberance？ Until recently， this was almost as pertinent a question as it had been when the 19th-century naturalists， armed only with butterfly nets and insatiable curiosity， battled through the rainforests. The early explorers soon realid that although some of the butterflies’ bright colours are there to attract a mate， others are warning signals. They nd out a message to any predators： “Keep off， we’re poisonous.
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” And becau wearing certain patterns affords protection， other species copy them. Biologists u the term “mimicry rings” for the clusters of impostors and their evolutionary idol.
B But here’s the conundrum. “Classical mimicry theory says that only a single ring should be found in any one area，” explains George Beccaloni of the Natural History Muum， London. The idea is that in each locality there should be just the one pattern that best protects its wearers. Predators would quickly learn to avoid it and eventually all mimetic species in a region should converge upon it. “The fact that this is patently not the ca has been one of the major problems in mimicry rearch，” says Beccaloni. In pursuit of a solution to the mystery of mimetic exuberance， Beccaloni t off for one of the megacentres for butterfly diversity， the point where the western edge of the Amazon basin meets the foothills of the Andes in Ecuador. “It’s exceptionally rich， but comparatively well collected， so I pretty much knew what was there， says Beccaloni.” The trick was to work out how all the butterflies were organid and how this related to mimicry.”
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shrinktofitC Working at the Jatun Sacha Biological Rearch Station on the banks of the Rio Napo， Beccaloni focud his attention on a group of butterflies called ithomiines. The distant relatives of Britain’s Camberwell Beauty are abundant throughout Central and South America and the Caribbean. They are famous for their bright colours， toxic bodies and complex mimetic relationships. “They can compri up to 85 per cent of the individuals in a mimicry ring and their patterns are mimicked not just by butterflies， but by other incts as diver as damlflies and true bugs，” says Philip DeVries of the Milwaukee Public Muum’s Center for Biodiversity Studies.
D Even though all ithomiines are poisonous， it is in their interests to evolve to look like one another becau predators that learn to avoid one species will also avoid others that remble it. This is known as Miillerian mimicry. Mimicry rings may also contain incts that are not toxic， but gain protection by looking likes a model species that is： an adaptation called Batesian mimicry. So strong is an experienced predator’s avoidance respon that even quite inept remblance gives some protection. “Often there will be a whole ries of species that mimic， with varying degrees of verisimilitude， a focal or m
odel species，” says John Turner from the University of Leeds. “The results of the deceptions are some of the most exquisite examples of evolution known to science.” In addition to colour， many mimics copy behaviours and even the flight pattern of their model species.
E But why are there so many different mimicry rings？ One idea is that species flying at the same height in the forest canopy evolve to look like one another. “It had been suggested since the 1970s that mimicry complexes were stratified by flight height，” says DeVries. The idea is that wing colour patterns are camouflaged against the different patterns of light and shadow at each level in the canopy， providing a first line of defence against predators.” But the light patterns and wing patterns don’t match very well，” he says. And obrvations show that the incts do not shift in height as the day progress and the light patterns change. Wor still， according to DeVries， this theory doesn’t explain why the model species is flying at that particular height in the first place.
F “When I first went out to Ecuador， I didn’t believe the flight height hypothesis and t 金妍儿冬奥会
out to test it，” says Beccaloni.”A few weeks with the collecting net convinced me otherwi. They really flew that way.” What he didn’t accept， however， was the explanation about light patterns. “I thought， if this idea really is true， and I can work out why， it could help explain why there are so many different warning patterns in any one place. Then we might finally understand how they could evolve in such a complex way.” The job was complicated by the sheer diversity of species involved at Jatun Sacha. Not only were there 56 ithomiine butterfly species divided among eight mimicry rings， there were also 69 other inct species， including 34 day-flying moths and a damlfly， all in a 200-hectare study area. Like many entomologists before him， Beccaloni ud a large bag-like net to capture his prey. This allowed him to sample the 2.5 metres immediately above the forest floor. Unlike many previous workers， he kept very preci notes on exactly where he caught his specimens.退出的英文
G The attention to detail paid off. Beccaloni found that the mimicry rings were flying at two quite parate altitudes. “Their u of the forest was quite distinctive，” he recalls. “For example， most members of the clear-winged mimicry ring would fly clo to the for
kiddyest floor， while the majority of the 12 species in the tiger-winged ring fly high up.” Each mimicry ring had its own characteristic flight height.
respiratory system在线翻译英文翻译汉字H However， this being practice rather than theory， things were a bit fuzzy. “They’d spend the majority of their time flying at a certain height. But they’d also spend a smaller proportion of their time flying at other heights，” Beccaloni admits. Species weren’t stacked rigidly like pasnger jets waiting to land， but they did appear to have a preferred airspace in the forest. So far， so good， but he still hadn’t explained what caus the various groups of ithomiines and their chromatic consorts to fly in formations at the particular heights.
