【正确答案】●Direct competition is when a bird actively excludes others from getting resources. Examples of direct competition are stealing food, establishing territories, and fighting. ●Indirect competition is when birds simply use up a resource so that other birds cannot use that resource. An example is a flock of geese eating all the food in an area. ●Competition and population size are related because when a population increases, the likelihood of competition also increases. Competition may limit the population size because there are not enough resources for more birds.

【答案解析】[听力原文] Competition is the struggle among birds for resources. Whenever there's a limited supply of a resource—such as food, nest sites, or mates—there'll be competition. Competition can take place between birds of the same species or between birds of different species. There are a couple of forms of competition: direct and indirect. Direct competition is when a bird actively excludes others from getting resources. A common example is stealing; a bird may simply take food from another. Another example is territories. Especially during the breeding season, birds maintain and defend some sort of territory. They form territories to defend resources like food, or to maintain access to good nest sites, or to attract mates. Some birds compete directly by fighting, for example, when they compete for mates. Others fight over food; you can see this if you watch gulls feeding on the garbage at the local garbage dump. And the second type of competition is indirect competition, when birds simply use up a resource. When one species eats all the seeds or berries or grubs, this will prevent other species from using that resource. Indirect competition is less open than direct competition, but it can have just as great an influence on populations. For example, a flock of geese grazing in a field will gradually decrease the amount of food there. The larger the flock, the faster the food will be used up, and this reduces the amount of food available to other species. Competition determines the size of bird populations. As the population of a species increases in a particular area, the likelihood of competition also increases. Eventually, competition may limit the size of the population because there's simply not enough food and nest sites for more birds. Using points and examples from the talk, explain the two types of competition in bird populations. Then explain how population size and competition are related.