1 . Biologists who study evolution (进化) have always been interested in animals that developed on islands. In some situations, animals on islands changed over time and came to look very different from the same species that lived on the mainland.
The experts point to animals such as the dwarf elephant that once lived on the Mediterranean island of Cyprus. The animal is now extinct. When it lived, however, it was only the size of a small horse. Elephants that live today in Africa and Asia are much larger than that. In the West Indies, researchers found a giant rodent (啮齿动物) that looked like a rat. However, it was about the same size as an American black bear. Rats are, of course, many times smaller than bears.
Evolutionary experts came to call this phenomenon “island effect”. They used this term to describe the fact that animals who normally have small bodies “upsize” on an island, while the opposite is true for animals who usually have large bodies.
The “island effect” produces strange-sized animals because large animals require more food than small animals. On an island, there is a limited amount of food. As a result, larger animals become smaller over generations in order to survive with lower food intake. For small animals, there is not as much risk from predators on an island, so they often grow larger.
Recently, researchers released their findings about 1,231 existing animals and 350 extinct ones that represent 23 million years of life. They found that animals on islands were more at risk of extinction compared to their relatives on the mainland. The arrival of human settlers increased the extinction risk for these strange animals.
Roberto Rozzi, a paleoecologist at Martin Luther University Halle-Wittenberg in Germany said that the extinction line has become even sharper in recent decades.
The researchers call the islands “biodiversity hotspots”. Even though they only make up 7 percent of the Earth’s land mass, they account for 20 percent of the land species.
1. Why are the animals introduced in paragraph 2?| A．To compare the two species. | B．To lead in the “island effect”. |
| C．To show two kinds of rare animals. | D．To stress the change of surroundings. |
| A．Animals of normal small bodies “upsize” on an island. |
| B．Animals of normal small bodies “downsize” on an island. |
| C．Animals of normal large size have small bodies on an island. |
| D．Animals of normal large size have larger bodies on an island. |
| A．Some things never change. | B．The gain outweighs the loss. |
| C．Humans live in harmony with nature. | D．The fittest animals survive in natural selection. |
| A．The History of Unique Island Animals | B．The Benefits of Saving Island Animals |
| C．Unique Island Animals at Greater Changes | D．Biological Diversity Threatened by Humans |
