On 30th November 2 Reading Passages were from our book, 6 Reading Passage 3 Volume 1 and 29th Reading Passage 3 Volume 2.
MIMIC YOUR NEIGHBOR
A. There’s no animal that symbolises rainforest diversity quite as spectacularly as the tropical
butterfly. Anyone lucky enough to see these creatures flitting between patches of sunlight cannot
fail to be impressed 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 19thcentury
naturalists, armed only with butterfly nets and insatiable curiosity, battled through the
rainforests. These early explorers soon realised that although some of the butterflies’ bright
colours are there to attract a mate, others are warning signals. They send out a message to any
predators: “Keep off, we’re predicting poisonous.” And because wearing certain patterns affords
protection, other species copy them. Biologists use the term mimicry rings for these 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 Museum, 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 case has been one of the major problems in mimicry
research,” says Beccaloni. In pursuit of a solution to the mystery of mimetic exuberance, Beccaloni
set 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 organised and how this related to mimicry.”
C. Working at the Jatun Sacha Biological Research Station on the banks of the Rio Napo, Beccaloni
focused his attention on a group of butterflies called ithomiines. These 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 comprise up to 85 per cent of the individuals in a mimicry ring and their
patterns are mimicked not just by butterflies, but by other insects as diverse as damselflies and
true bugs,” says Philip DeVries of the Milwaukee Public Museum’s Center for Biodiversity Studies.
D. Even though all ithomiines are poisonous, it is in their interests to evolve to look like one another
because predators that learn to avoid one species will also avoid others that resemble it. This is
known as Mullerian mimicry. Mimicry rings may also contain insects that are not toxic, but gain
protection by looking like a model species that is: an adaptation called Batesian mimicry. So strong
is an experienced predator’s avoidance response that even quite inept resemblance gives some
protection. “Often there will be a whole series of species that mimic, with varying degrees of
verisimilitude, a focal or model species,” says John Turner from the University of Leeds. “The
results of these 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
IELTS Academic Readings For Exam Practice – Volume 2 – Dr. Kiranpreet Kaur Makkar
www.makkarielts.com 87
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 observations show that the insects do not shift in
height as the day progresses and the light patterns change. Worse 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 set out to test
it,” says Beccaloni.”A few weeks with the collecting net convinced me otherwise. 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 insect species, including 34 day-flying moths and a damselfly, all
in a 200-hectare study area. Like many entomologists before him, Beccaloni used 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 precise notes on exactly where he caught his
specimens
G. The attention to detail paid off. Beccaloni found that the mimicry rings were flying at two quite
separate altitudes. “Their use of the forest was quite distinctive,” he recalls. “For example, most
members of the clear-winged mimicry ring would fly close to the forest 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.
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 passenger 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 causes the various groups of ithomiines and their chromatic
consorts to fly in formations at these particular heights.
I. Then Beccaloni had a bright idea. “I started looking at the distribution of ithomiine larval food
plants within the canopy,” he says. “For each one I’d record the height to which the host plant
grew and the height above the ground at which the eggs or larvae were found. Once I got them
back to the field station’s lab, it was just a matter of keeping them alive until they pupated and
then hatched into adults which I could identify.”
IELTS Academic Readings For Exam Practice – Volume 2 – Dr. Kiranpreet Kaur Makkar
www.makkarielts.com 88
Questions 28-32
The Reading Passage 3 has seven paragraphs A-I. Which paragraph contains the following
information? Write the correct letter A-I, in boxes 28-32 on your answer sheet. NB You may use
any letter more than once.
28. Criticism against flight height theory of butterfly.
29. Explained why Beccaloni carried out research in Ecuador.
30. Different mimicry ring flies at different height.
31. The method of catching butterfly by Beccaloni.
32. Not all Mimicry patterns are toxic information sent out from insects.
Questions 33-38
Do the following statements agree with the Information given In Reading Passage 1
In boxes 33-38 on your answer sheet, write
TRUE If the statement is true
FALSE If the statement is false
NOT GIVEN If the Information is not given in the passage
33. All butterflies’ colour of wing reflect the sense of warning to other predator.
34. Insects may imitate butterflies’ wing pattern as well.
35. Flying Altitude of butterfly is determined by their food.
36. Beccaloni agreed with flight height hypothesis and decide to reassure its validity.
37. Jatun Sacha has the riches diversity of breeds in the world.
38. Beecaloni has more detailed records on the location of butterfly collection than others.
Questions 39-40
Choose the correct letter, A, B, C or D. Write your answers in boxes 39-40 on your answer sheet.
39. Which is correct about butterflies flight altitude?
A) Flight height theory already established.
B) Butterfly always flies at a certain height
C) It is like the airplane’s flying phenomenon
D) Each butterfly has its own favorable height
40. Which is correct about Beccaloni next investigation after flight height?
A) Some certain statistics have already been collected
B) Try to find connections between larval height and adult ones
C) It’s very difficult to raise butterfly larval
D) Different larval favors different kinds of trees
