【OG24-526题】According to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti_mofa留学圈mofaGRE在线题库系统_GRE在线搜题_GRE题库解析_GRE真题机经_GRE课程_GRE培训机构

最新题目

题目内容

纠错

In the Sonoran Desert of northwestern Mexico and southern Arizona, the flowers of several species of columnar cacti-cardon, saguaro, and organ pipe-were once exclusively pollinated at night by nectar-feeding bats, as their close relatives in arid tropical regions of southern Mexico still are. In these tropical regions, diurnal (daytime) visitors to columnar cactus flowers are ineffective pollinators because, by sunrise, the flowers' stigmas become unreceptive or the flowers close. Yet the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise, allowing pollination by such diurnal visitors as bees and birds. Why have these cacti expanded their range of pollinators by remaining open and receptive in daylight?

This development at the northernmost range of columnar cacti may be due to a yearly variation in the abundance-and hence the reliability-of migratory nectar-feeding bats. Pollinators can be unreliable for several reasons. They can be dietary generalists whose fidelity to a particular species depends on the availability of alternative food sources. Or, they can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species. Finally, they may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.

Recent data reveals that during spring in the Sonoran Desert, the nectar-feeding bats are specialists feeding on cardon, saguaro, and organpipe flowers.However, whereas cactus-flower abundance tends to be high during spring, bat population densities tend to be low except near maternity roosts. Moreover, in spring, diurnal cactus-pollinating birds are significantly more abundant in this region than are the nocturnal bats. Thus, with bats being unreliable cactus-flower pollinators, and daytime pollinators more abundant and therefore more reliable, selection favors the cactus flowers with traits that increase their range of pollinators. While data suggest that population densities of nectar-feeding bats are also low in tropical areas of southern Mexico, where bats are the exclusive pollinators of many species of columnar cacti, cactus-flower density and bat population density appear to be much more evenly balanced there:compared with the Sonoran Deses cardon and saguaro, columnar cacti in southern Mexico produce far fewer flowers per night. Accordingly, despite their low population density, bats are able to pollinate nearly 100 percent of the available flowers.

According to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti

have flowers that remain open after sunset are pollinated primarily by dietary specialists can be pollinated by nectar-feeding bats have stigmas that are unreceptive to pollination at night are sometimes pollinated by diurnal pollinator

正确答案： E

参考解析

提交我的解析

文章大意逻辑
在墨西哥西北部和亚利桑那州南部的索诺兰沙漠，柱状仙人掌（如刺木仙人掌、巨人柱和管风琴仙人掌）的花曾经只在夜间由吸食花蜜的蝙蝠授粉，其在墨西哥南部干旱热带地区的近亲仍保持如此。在热带地区，白天的访客不是有效的授粉者，因为日出时花的柱头不再接受花粉或花已闭合。但索诺兰沙漠的仙人掌花在日出后仍开放，能被蜜蜂和鸟类等白天访客授粉。这种发展可能是因为吸食花蜜的迁徙蝙蝠数量每年有变化。授粉者不可靠有多种原因：可能是杂食性，对特定物种的忠诚度取决于替代食物来源；可能是专食性，但数量每年变化大；也可能是专食性，但数量长期相对花的数量低。最近数据显示索诺兰沙漠春季时，吸食花蜜的蝙蝠是专食这些仙人掌花的，但仙人掌花在春季数量多，蝙蝠种群密度除了在育幼栖息地附近较低。而且春季白天授粉的鸟类比夜间蝙蝠数量多。 文章类型及逻辑简图
文章类型为现象解释型。逻辑简图： Phenomenon: Sonoran Desert columnar cacti can be pollinated by diurnal visitors while their southern Mexico relatives can't.（现象：索诺兰沙漠柱状仙人掌能被白天访客授粉，而其墨西哥南部近亲不能） Explanation 1: Variation in abundance of migratory nectar feeding bats.（解释1：迁徙吸食花蜜蝙蝠数量的变化） Explanation 2: Reasons for pollinators' unreliability (generalists, variable abundance of specialists, chronically low abundance of specialists).（解释2：授粉者不可靠的原因（杂食性、专食性数量变化、专食性数量长期低）） Data support: Bat population density is low in spring except near maternity roosts, and diurnal pollinating birds are more abundant.（数据支持：春季蝙蝠种群密度除育幼栖息地附近低，且白天授粉鸟类更丰富） 做题方法及问题类型
问题类型为细节题，做题方法是通过题干中“Sonoran cacti differ from their close relatives in southern Mexico”定位到文章开头部分关于两者对比的描述。 选项分析
A选项：“have flowers that remain open after sunset”。文章重点强调的是索诺兰仙人掌日出后花仍开放，而非日落后，该选项不符合原文描述，排除。 B选项：“are pollinated primarily by dietary specialists”。原文未提及索诺兰仙人掌主要由专食性授粉者授粉，排除。 C选项：“can be pollinated by nectar feeding bats”。其墨西哥南部近亲也能被吸食花蜜的蝙蝠授粉，这不是两者的区别，排除。 D选项：“have stigmas that are unreceptive to pollination at night”。与原文不符，原文未提及索诺兰仙人掌柱头夜间不接受授粉，排除。 E选项：“are sometimes pollinated by diurnal pollinator”。符合原文中索诺兰沙漠仙人掌花能被白天访客（如蜜蜂和鸟类等）授粉这一描述，当选。

题目讨论 (如果对题目有任何的疑惑，欢迎在这里提出来，大家会帮你解答的哦~)

还没有人评论,赶快抢个沙发~

做题笔记

参考解析

题目讨论 (如果对题目有任何的疑惑，欢迎在这里提出来，大家会帮你解答的哦~)

请选择错误类型：

请描述一下这个错误：