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题目内容
题目材料：
In European lowland heathlands, heather bushes, grasses, and bracken compete with one another for the sandy soil's scarce nutrients, with none acquiring permanent dominance. In Dutch heathlands, however, atmospheric nitrogen pollution produced by intensive animal farming has turned heathlands into grassland, the result of an interaction between nitrogen pollution and heather-eating beetles. Additional nitrogen usually increases growth of both grass and heather, and at first heather usually thrives because the grasses cannot penetrate the canopy of its bushes. Heather beetle population size, like that of many herbivorous insects, varies from year to year. When heather beetles are abundant, their larvae grow particularly well on the nitrogen-enriched heather shoots. Voraciously feeding larvae and adults then defoliate the bushes, tipping the competitive balance between heather and grasses irrevocably.
以上解析由 考满分老师提供。
