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题目材料：
This passage is adopted from material published in 2005
Given that ants and aphids are both abundant insect groups that often share the same habitats, that aphids excrete energy-rich honeydew, and that ants aggressively defend resources, it is difficult to understand why so few species of aphid have evolved a close relationship with ants. For example, only a quarter of the aphid species in the Rocky Mountain region are attended by ants, and in Central Europe, about one third are obligate myrmecophile [animals that closely associate with ants]. More than a dozen hypotheses have been proposed to account for the variability in aphid-ant relationships and the low proportion of attended species. First among them is the plant permissive hypothesis, which suggests that host-plant quality plays a critical role in determining the attractiveness of aphids for ants. Both variation in the quality of different hosts or different parts of the same host plant may affect the quality of honeydew, which is either more or less attractive to ants. However, this hypothesis ignores the fact that several species of aphids may feed on the same host plant or even plant organ but have very different degrees of associations with ants and assumes that the quality of phloem sap determines that of the honeydew. Recent studies have found that feeding on woody plant parts is positively associated with ant attendance, whereas mobility, feeding in isolation, and having winged adults are negatively associated with ant attendance.
Given that ants and aphids are both abundant insect groups that often share the same habitats, that aphids excrete energy-rich honeydew, and that ants aggressively defend resources, it is difficult to understand why so few species of aphid have evolved a close relationship with ants. For example, only a quarter of the aphid species in the Rocky Mountain region are attended by ants, and in Central Europe, about one third are obligate myrmecophile [animals that closely associate with ants]. More than a dozen hypotheses have been proposed to account for the variability in aphid-ant relationships and the low proportion of attended species. First among them is the plant permissive hypothesis, which suggests that host-plant quality plays a critical role in determining the attractiveness of aphids for ants. Both variation in the quality of different hosts or different parts of the same host plant may affect the quality of honeydew, which is either more or less attractive to ants. However, this hypothesis ignores the fact that several species of aphids may feed on the same host plant or even plant organ but have very different degrees of associations with ants and assumes that the quality of phloem sap determines that of the honeydew. Recent studies have found that feeding on woody plant parts is positively associated with ant attendance, whereas mobility, feeding in isolation, and having winged adults are negatively associated with ant attendance.
以上解析由 考满分老师提供。
