名校最新大学英语四级阅读精讲的系列讲义：(136)

　　Research by the University of Exeter1 has revealed that ants have a big impact on their local environment as a result of their activity as ecosystem engineers and predators(食肉动物). The study, published in the Journal of Animal Ecology, found that ants have two distinct(显著的)effects on their local environment.

　　Firstly, through moving of soil by nest building2 activity and by collecting food they affect the level of nutrients(营养物)in the soil. This can indirectly impact the local populations of many animal groups, from decomposers(腐生物,分解体)to species much higher up the food chain.

　　Secondly, they prey on a wide range of other animals, including larger prey which can be attacked by vast numbers of ant workers.

　　Dirk Sanders, an author of the study from the universitys Centre for Ecology and Conservation, said: Ants are very effective predators which thrive in huge numbers. Theyre also very territorial3 and very aggressive, defending their resources and territory against other predators. All of this means they have a strong influence on their surrounding area.

　　In this research, we studied for the first time how big this impact is and the subtleties of it. What we found is that despite being predators, their presence can also lead to an increase in density and diversity of other animal groups4. They genuinely play a key role in the local environment, having a big influence on the grassland food web, Sanders said.

　　The study, carried out in Germany, studied the impact of the presence of different combinations and densities of black garden ants and common red ants, both species which can be found across Europe, including in the UK. It found that a low density of ants in an area increased the diversity and density of other animals in the local area, particularly the density of herbivores and decomposers. At higher densities ants had no or the opposite effect, showing that predation is counteracting the positive influence.

　　Dr Frank van Veen, another author on the study, said: What we find is that the impact of ants on soil nutrient levels has a positive effect on animal groups at low levels, but as the number of ants increases, their predatory impacts have the bigger effect thereby counteracting the positive influence via ecosystem engineering.

　　Ants are important components of ecosystems not only because they constitute a great part of the animal biomass5 but also because they act as ecosystem engineers. Ant biodiversity6(生物多样性)is incredibly high and these organisms are highly responsive(敏感的，易受影响的) to human impact, which obviously reduces its richness. However, it is not clear how such disturbance damages the maintenance of ant services to the ecosystem7.Ants are important in below ground processes8 through the alteration of the physical and chemical environment and through their effects on plants, microorganisms, and other soil organisms.

　　1 .Why are ants compared to ecosystem engineers?

　　A.Because they build their own nests.

　　B.Because they collect food.

　　C.Because their activity affects the environment.

　　D.Because they are predators.

　　2. As predators, ants

　　A.prey on small as well as large animals.

　　B.collect nutritious food from the soil

　　C.collect food as decomposers.

　　D.prey on species much higher up the food chain.

　　3. Dirk Sanders study centered on how ants

　　A.can manage to thrive in huge numbers.

　　B.defend their resources and territory against other predators.

　　C.attack those invading animals for survival.

　　D.produce such a big impact on the environment.

　　4. What does paragraph 6 tell us?

　　A.Ants bring about a negative influence to an area when their population is small.

　　B.Ants bring about a positive influence to an area when their population is small.

　　C.Ants predation counteracts the positive influence they may have on an area.

　　D.At higher density, ants produce a positive influence on an area.

　　5. What still remains unclear about ants, according to the last paragraph?

　　A.What roles do ants play in the ecosystem in which they live?

　　B.How do ants affect the animal diversity in a given ecosystem?

　　C.How do human activities affect ants influence on a given ecosystem?

　　D.How do ants alter the physical and chemical environment?

　　答案与解析：

　　1. C

　　短文的第一段提供了答案。A不是正确答案，因为并不是因为蚂蚁会筑巢才被誉为生态系统工程师，而是因为它们筑巢和获取食物的方式改变了土壤的营养水平，为整个食物链提供了很好的生态环境(见第二段)。

　　2.A

　　答案能够从短文的第三段直接找到。该段告诉我们，蚂蚁的掠食范围很广，甚至包括比它们体积更大的动物(larger animals)。prey 在这里的意思是 捕猎，捕食 ，作为动词，后面跟介词on或upon。

　　3.D

　　Dirk Sanders说： In this research, we studied for the first time how big this impact is and the subtleties of it. (第五段)所以，D是正确选择。句中the subtleties of it 的意思是：蚂蚁对环境影响的精妙之处。

　　4.B

　　短文第六段第二句的大概意思是，蚂蚁数量小(a low density of ants)的话，能使其他动物的品种和数量增加(increased the diversity and density of other animals)，从而给环境带来积极影响;第三句说，如果蚂蚁的数量大(At higher densities)，就不可能产生同样的影响，或者是相反的影响，这表明，蚂蚁的掠食活动会抵销蚂蚁给环境带来的积极影响。第七段Dr Frank van Veen 表达了大体相同的内容。

　　5.C

　　最后一段的第二和第三句提供了答案。第二句告诉我们，蚂蚁极易受人类的影响(these organisms are highly responsive to human impact)，第三句告诉我们，科学家还不清楚人类对蚂蚁这种干扰如何破坏蚂蚁对生态系统的维护作用( it is not clear how such disturbance damages the maintenance of ant services to the ecosystem. )。