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(捕食) 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 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(微妙) 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(食草动物) 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 (生物量) 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?

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