Read the following passage carefully and answer the items that...

Read the following passage carefully and answer the items that follow the passage. Your answers to these items should be based solely on the passage.

Can agricultural productivity meet human needs in the long run? Since twentieth century advances, given increasing costs, do not seem sustainable, further increases in output will not be achieved easily. Global population growth, while showing signs of slowing down, has pushed farmers and herders into areas unsuited to intensive agriculture, accelerating worldwide ecological disruptions. Reserves of arable land and fresh water have diminished alarmingly. Chemical runoffs have compounded pollution problems. Invasion of natural habitats have hastened species extinction. Desertification has been severe in the last hundred years, especially in North Africa, southern portions of Africa, Australia, northern Mexico, and the American Southwest. Tropical forests have shrunk by one-half since World War II, with agricultural pressures causing three-quarters of that loss. Government intervention has produced its share of catastrophes, ranging from a terrible famine in China between 1958-1961 that may have killed 30 million people and destroyed the Aral Sea. Taking everything into consideration, we may remain hopeful about humankind's agricultural prospects, but we can scarcely look forward optimistically at the end of the first quarter of the twenty-first century.

Which one of the following words means 'incursion'?