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  3. Ants Have Big Impact on Environment as "Ecosystem Engineers" Research by the University of Exeter has revealed that ants hav

Ants Have Big Impact on Environment as "Ecosystem Engineers" Research by the University of Exeter has revealed that ants hav

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问题             Ants Have Big Impact on Environment as "Ecosystem Engineers"
    Research by the University of Exeter has revealed that ants have a big impact on their local environment as a result of their activity as "ecosystem engineers" and predators. The study, published in the Journal of Animal Ecology , found that ants have two distinct effects on their local environment.
    Firstly, through moving the soil by nest building activity and by collecting food they affect the level of nutrients in the soil. This can indirectly impact the local populations of many animal groups, from decomposers 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 university’ s Centre for Ecology and Conservation, said, "Ants are very effective predators which thrive in huge numbers. They’ re also very territorial 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 groups. 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 of which can be found across Europe, including 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, the predation 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 the ecosystem not only because they constitute a great part of the animal biomass but also because they act as ecosystem engineers. Ant biodiversity is incredibly high and these organisms are highly responsive to human impact, which obviously reduces its richness. However, it is not clear how such disturbance damages the maintenance of ant services to the ecosystem. Ants are important in below ground processes through the alteration of the physical and chemical environment and through their effects on plants, microorganisms, and other soil organisms.
What does Paragraph 6 tell us?
选项 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.
答案B
解析 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)，就会没有影响或者有相反的影响。
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