Questions 1–5.

Questions 6–10. Select the TWO correct answer choices.

Questions 11–15 are based on the passage below.

For much of the twentieth century, ecologists assumed that the most important species in any ecosystem were the most abundant ones — the dominant trees of a forest or the grasses of a prairie. In 1969, however, the ecologist Robert Paine introduced the concept of the "keystone species" after a series of experiments on the rocky shores of the Pacific Northwest. When Paine removed a single predator, the ochre starfish, from sections of shoreline, the mussels it normally ate multiplied rapidly and crowded out dozens of other species. Within a few years, the diversity of the community had collapsed.

Paine's insight was that a species' ecological importance may be wildly disproportionate to its numbers. The concept has since been applied to sea otters, which control sea urchins that would otherwise devour kelp forests, and to wolves, whose return to Yellowstone National Park has been linked to changes in elk behaviour and the recovery of streamside vegetation. Some ecologists caution, however, that the keystone label has been applied too loosely, and that in many ecosystems influence is spread across several interacting species rather than concentrated in one.

Questions 16–20 are based on the passage below.

Debates about how to protect biodiversity have often been framed as a choice between "land sparing" and "land sharing". Advocates of land sparing argue that farming should be made as intensive and productive as possible on a limited area, so that large tracts of land can be set aside as untouched reserves. Advocates of land sharing counter that farms themselves should be made hospitable to wildlife, through hedgerows, reduced pesticide use and patches of natural habitat, even if this lowers yields and requires more total land for agriculture.

Field studies have produced no simple verdict. In some tropical regions, many forest species cannot survive on even wildlife-friendly farmland, which seems to favour sparing. In long-farmed European landscapes, by contrast, a number of species have come to depend on traditional agricultural habitats and would decline if those were replaced by intensive fields. Increasingly, researchers suggest that the best strategy depends on local conditions and that a mixture of both approaches may be more realistic than either in its pure form.