2013年5月26日托福阅读机经解析

　　词汇题：

　　negligible = minor, constraint = limit, commence = begin,

　　unexpectedly = surprisingly, enormous = huge, cluster = group

　　第一篇

　　TOPIC Distribution of Plants and Animals

　　讲地球上植物之间的相似性要远大于动物。以下阐明原因。原因一是植物很早以前就开始大范围传播，在大陆板块分开之前就分布到各处，而动物出现得较晚；原因二是动物曾经历了多次大灭绝，且之后出现的新物种代替了旧物种与原来很不相同，而植物则很长寿；原因三是动物群不如植物群一样分散广，每一个地方都有特定的动物种类，只有当大陆相连接的时候，动物才能进行传播。植物群分散比较广，并且即便是由于大陆漂移，植物也可以越过海洋进行种子的传播。所以人们能看到各个地方相似的植物群出现。最后转折，在亚洲和非洲两地的动物相似性却很高，是因为当时一度亚非板块相连。

　　解析：

　　本文属于生物学中的生物地理学biogeography范畴，从文章结构来看是典型的因果类文章，先说明结果，下面分别写几个原因，最后一段则是极具托福特色的转折。其中，关于大灭绝的部分可以参照TPO阅读文章Meteorite Impact and Dinosaur Extinction，关于植物传播的部分可以参照TPO阅读文章The Arrival of Plant Life in Hawaii。以下是与物种分布有关的内容扩展。

　　Species distribution

　　Species distribution is the manner in which a biological taxon is spatially arranged. Species distribution is not to be confused with dispersal, which is the movement of individuals away from their area of origin or from centers of high population density. A similar concept is the species range. A species range is often represented with a species range map. Biogeographers try to understand the factors determining a species’’ distribution. The pattern of distribution is not permanent for each species. Distribution patterns can change seasonally, in response to the availability of resources, and also depending on the scale at which they are viewed. Dispersion usually takes place at the time of reproduction. Populations within a species are translocated through many methods, including dispersal by people, wind, water and animals. Humans are one of the largest distributors due to the current trends in globalization and the expanse of the transportation industry. For example, large tankers often fill their ballasts with water at one port and empty them in another, causing a wider distribution of aquatic species.

　　There are three basic types of population distribution within an area. From top to bottom: uniform, random and clumped. Biogeography is the study of the distribution of biodiversity over space and time. It is very useful in understanding species distribution through factors such as speciation, extinction, continental drift, glaciation, variation of sea levels, river capture and available resources. This branch of study not only gives a description of the species distribution, but also a geographical explanation for the distribution of particular species. The traditional biogeographic regions were first modeled by Alfred Wallace in The Geographical Distribution of Animals (1876). These were based on the work of Sclater’’s terrestrial biogeographic regions. Wallace’’s system was based on both birds and vertebrates, including non-flying mammals, which better reflect the natural divisions of the Earth due to their limited dispersal abilities.