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  3. Marine ecosystems certainly have less permanence than terrestrial ecosystems

Marine ecosystems certainly have less permanence than terrestrial ecosystems

游客2025-02-19  41
问题     Marine ecosystems certainly have less permanence than terrestrial ecosystems. Ashore, ecologists are not confronted with shifting ecological discontinuities, or with changes in the characteristic conditions of individual ecosystems, because, unless man intervenes, the tree line on a mountain or the passage between grassland and savannah remains approximately static over a human lifetime. It is only on the millennial scale that such boundaries migrate significantly, or that characteristic regional ecosystems disappear. Urban sprawl, deforestation, overgrazing, and intensive agriculture are accomplishing in a few decades what nature cannily do in centuries, but that sad fact does not alter the argument. Although the human population explosion can produce pressures that rapidly shift ecological boundaries and modify ecosystems ashore, it is paradoxically more difficult directly to modify the average locations of the ephemeral and shifting ecological boundaries of the sea. We can accomplish this only indirectly by atmospheric modification, resulting in a changed global climate and a shifted ocean circulation. [br] The passage indicates which of the following about the “ecological boundaries of the sea?”
选项 A、They have become increasingly sensitive to changes in global climate.
B、They are not significantly impacted by changes in Earth’s atmosphere.
C、Their stability is essential to the health of marine ecosystems.
D、They are more closely tied to surrounding physical conditions than are analogous boundaries on land.
E、They are less susceptible to direct human intervention than are analogous boundaries on land.
答案 E
解析 根据五六两句，人类可以直接改变陆地生态界限，但是要想改变海洋生态界限，只能通过改变大气来间接产生影响。A项海洋生态界限确实受到大气影响，但是看不出increasingly。B项表述相反。C项文中未提及。D项文中未提及。
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