Reading Exercise: Finches on Islands

Today, the pursuit continues. On Daphne Major, among the most barren of the Galápagos Islands, an uninhabited volcanic peak where cacti and shrubs rarely grow taller than a researcher’s knee, Peter and Rosemary Grant have dedicated more than three decades observing Darwin’s finch respond to challenges posed by storms, drought, and competition for food. As biologists at Princeton University, the Grants are familiar with many individual birds on the island and can trace the lineage of these birds through generations. They have repeatedly witnessed Darwin's theory in action across numerous generations of finches.

B

The Grants’ most profound insights have arisen from observing the changing beak shapes of the medium ground finch. The plumage of this bird, about the size of a sparrow, varies from drab brown to deep black. At first glance, it might not appear remarkable, but within the scientific community studying evolutionary biology, the medium ground finch is a standout. Its beak represents a middle ground among the various shapes and sizes found among Galápagos finches: larger than that of the small ground finch, which specializes in consuming small, soft seeds, yet smaller than that of the large ground finch, which excels in cracking and consuming large, hard seeds.

C

When the Grants commenced their research in the 1970s, only two finch species inhabited Daphne Major: the medium ground finch and the cactus finch. The island is so compact that researchers were able to count and categorize every bird. When a severe drought struck in 1977, the birds quickly consumed the last of the easily accessible small seeds. The smaller members of the medium ground finch population, lacking the bill strength required to crack large seeds, perished.

D

Bill and body size are inherited characteristics, and the subsequent generation had a high percentage of individuals with large bills. The Grants had documented natural selection in action—the same process that, over many millennia, guided the evolution of the Galápagos’ 14 distinct finch species, all descended from a common ancestor that arrived on the islands several million years ago.

E

Eight years later, intense rains brought by an El Niño event transformed the typically sparse vegetation on Daphne Major. Vines and other plants that normally struggle for survival suddenly thrived, outcompeting the plants that produce large seeds for the finches. Small seeds became predominant in the food supply, and larger birds with larger bills experienced higher mortality rates compared to smaller ones. ‘We can observe natural selection,’ remarks Rosemary Grant. ‘It occurs when the environment changes. When local conditions reverse, so too does the direction of adaptation.’

F

Recently, the Grants observed another form of natural selection impacting the medium ground finch: competition from larger, stronger relatives. In 1982, a third finch, the large ground finch, arrived on Daphne Major. These birds have stout bills resembling the business end of a crescent wrench. Their arrival marked the first such colonization documented in the Galápagos in nearly a century of scientific observation. ‘We realized,’ says Peter Grant, ‘we had a very unusual and potentially significant event to monitor.’ For 20 years, the large ground finch coexisted with the medium ground finch, sharing the supply of large seeds with its larger-billed relative. Then, in 2002 and 2003, another drought struck. No birds nested that year, and many perished. Medium ground finches with larger bills, displaced from feeding areas by the more dominant large ground finches, suffered particularly high losses.

G

When wetter weather returned in 2004 and the finches resumed nesting, the new generation of medium ground finches was dominated by smaller birds with smaller bills, capable of surviving on smaller seeds. According to Peter Grant, this event marked the first time that biologists were able to observe the complete process of evolutionary change due to interspecies competition and the strongest response to natural selection that he had witnessed in 33 years of studying Galápagos finches.

H

On the inhabited island of Santa Cruz, just south of Daphne Major, Andrew Hendry from McGill University and Jeffrey Podos from the University of Massachusetts at Amherst have uncovered a new, human-induced twist in finch evolution. Their research focused on birds living near the Academy Bay research station, on the outskirts of Puerto Ayora town. The human population in the area has grown rapidly—from 900 people in 1974 to 9,582 in 2001. Today, Puerto Ayora is filled with hotels and beachside bars,’ says Hendry. ‘People have transformed this extremely arid place in an attempt to create a Caribbean-style resort.’

I

Academy Bay archives from the early 1960s reveal that medium ground finches caught there had either small or large bills. Few had medium-sized bills. The finches seemed to be beginning a new adaptive radiation: If this trend continued, the medium ground finch on Santa Cruz might divide into two distinct subspecies, each specializing in different seed types. However, in the late 1960s and early '70s, medium ground finches with medium-sized bills began to thrive at Academy Bay alongside small and large-billed birds. The growing human population had introduced new food sources, including exotic plants and bird feeding stations supplied with rice. Bill size, once crucial for the finches' survival, no longer mattered. ‘Now an intermediate bill can suffice,’ Hendry says.

J

At a control site far from Puerto Ayora, relatively untouched by humans, the medium ground finch population remains split between large- and small-billed birds. In undisturbed areas of Santa Cruz, there's no ecological niche for a moderate medium ground finch, and the finches continue to diversify. In town, although there are still many finches, previously distinct populations are blending.

K

The finches of Santa Cruz illustrate a subtle process whereby human interference can halt evolution, stopping the formation of new species. At a time when global biodiversity continues to decline, Darwin’s finches have yet another unexpected lesson to impart. ‘To restore some of the lost diversity,’ Hendry says, ‘we must protect not only existing creatures but also the processes that drive the emergence of new species.

Questions 1-4

Now complete the table.

Choose NO MORE THAN TWO WORDS from Reading Passage 1 for each answer.

Write your answers in boxes 1-4 on your answer sheet.

Questions 5-8

Complete the following summary of paragraphs in Reading Passage 1

Using NO MORE THAN TWO WORDS from the Reading Passage for each answer.

Write your answers in boxes 5-8 on your answer sheet.

On the remote island of Santa Cruz, Andrew Hendry and Jeffrey Podos conducted a study on reversal 5………………… due to human activity. In the early 1960s medium ground finches were found to have a larger or smaller beak. But in the late 1960s and early 70s, finches with 6………………… flourished. The study speculates that it is due to the growing 7………………… who brought in alien plants with intermediate-size seeds into the area and the birds ate 8………………… sometimes.

Questions 9-13

Do the following statements align with the author's assertions in Reading Passage 1?

In boxes 9-13 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

9   Grants’ discovery has questioned Darwin’s theory.

10   The cactus finches are less affected by food than the medium ground finch.

11   In 2002 and 2003, all the birds were affected by the drought.

12   The discovery of Andrew Hendry and Jeffrey Podos was the same as that of the previous studies.

13   It is shown that the revolution in finches on Santa Cruz is likely a response to human intervention.

Answers:

1. (severe) drought (Đoạn C, “When a severe drought hit in 1977, the birds soon devoured the last of the small, easily eaten seeds.”)

2. large seeds (Đoạn C, “Smaller members of the medium ground finch population, lacking the bill strength to crack large seeds, died out.”)

3. heavy rains (Đoạn E, “Eight years later, heavy rains brought by an El Nino transformed the normally meager vegetation on Daphne Major.”)

4. small seeds (Đoạn E, “Small seeds came to dominate the food supply, and big birds with big bills died out at a higher rate than smaller ones.”)

5. finch evolution (Đoạn H, “man-made twist in finch evolution”)

6. medium-sized bills (Đoạn I, “But in the late 1960s and early 70s, medium ground finches with medium-sized bills began to thrive at Academy Bay along with small and large-billed birds.”)

7. human population (Đoạn H, “The human population of the area has been growing fast-from 900 people in 1974 to 9,582 in 2001.”)

8. Rice (Đoạn I, “…including exotic plants and bird feeding stations stocked with rice.”)

9. FALSE (Đoạn A, “Grant have spent more than three decades watching Darwin’s finch respond to the challenges of storms”)

10. NOT GIVEN (Không có thông tin)

11. TRUE (Đoạn F, “Then, in 2002 and 2003, another drought struck. None of the birds nested that year, and many died out.)