Official 40 Passage 1


Latitude and Biodiversity


Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

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  • A
    Some biogeographers believe that the tropics have larger surface areas than they actually do because of the distortions produced by projections of Earth’s curved surface.
  • B
    High levels of diversity in the tropics are sometimes attributed to the fact that the tropics have more surface area of land than the higher latitudes do, though distortions in commonly used projections may seem to suggest otherwise.
  • C
    Because biogeographers disagree on whether or not the tropics are correctly represented in projections of Earth’s surface, it is difficult to determine the relationship their surface area has to their diversity.
  • D
    Most biogeographers agree that the tropics contain a larger surface area of land than higher latitudes do, but they disagree on whether or not the tropics’ level of diversity is a reflection of that larger surface area.
正确答案: B

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  • 原文
  • 译文
  • When we look at the way in which biodiversity (biological diversity) is distributed over the land surface of the planet, we find that it is far from even. The tropics contain many more species overall than an equivalent area at the higher latitudes. This seems to be true for many different groups of animals and plants.

    Why is it that higher latitudes have lower diversities than the tropics? Perhaps it is simply a matter of land area. The tropics contain a larger surface area of land than higher latitudes-a fact that is not always evident when we examine commonly used projections of Earth's curved surface, since this tends to exaggerate the areas of land in the higher latitudes-and some biogeographers regard the differences in diversity as a reflection of this effect. But an analysis of the data by biologist Klaus Rohde does not support this explanation. Although area may contribute to biodiversity, it is certainly not the whole story; otherwise, large landmasses would always be richer in species.

    Productivity seems to be involved instead, though perhaps its influence is indirect. Where conditions are most suitable for plant growth-that is, where temperatures are relatively high and uniform and where there is an ample supply of water-one usually finds large masses of vegetation. This leads to a complex structure in the layers of plant material. In a tropical rain forest, for example, a very large quantity of plant material builds up above the surface of the ground. There is also a large mass of material, developed below ground as root tissues, but this is less apparent. Careful analysis of the aboveground material reveals that it is arranged in a series of layers, the precise number of layers varying with age and the nature of the forest. The arrangement of the biological mass ("biomass") of the vegetation into layered forms is termed its "structure" (as opposed to its "composition," which refers to the species of organisms forming the community). Structure is essentially the architecture of vegetation, and as in the case of some tropical forests, it can be extremely complicated. In a mature floodplain tropical forest in the Amazon River basin, the canopy (the uppermost layers of a forest, formed by the crowns of trees) takes on a stratified structure. There are three clear peaks in leaf cover at heights of approximately 3, 6, and 30 meters above the ground; and the very highest layer, at 50 meters, corresponds to the very tall trees that stand free of the main canopy and form an open layer of their own. So, such a forest contains essentially four layers of canopy. Forests in temperate lands often have just two canopy layers, so they have much less complex architecture.

    Structure has a strong influence on the animal life inhabiting a site. It forms the spatial environment within which an animal feeds, moves around, shelters, lives, and breeds. It even affects the climate on a very local level (the "microclimate") by influencing light intensity, humidity, and both the range and extremes of temperature. An area of grassland vegetation with very simple structure, for example, has a very different microclimate at the ground level from that experienced in the upper canopy. Wind speeds are lower, temperatures are lower during the day (but warmer at night), and the relative humidity is much greater near the ground. The complexity of the microclimate is closely related to the complexity of structure in vegetation, and generally speaking, the more complex the structure of vegetation, the more species of animal are able to make a living there. The high plant biomass of the tropics leads to a greater spatial complexity in the environment, and this leads to a higher potential for diversity in the living things that can occupy a region. The climates of the higher latitudes are generally less favorable for the accumulation of large quantities of biomass; hence, the structure of vegetation is simpler and the animal diversity is consequently lower.

  • 当我们着眼于生物多样性在地球表面分布的方式,我们发现,它是非常不平均的。 热带地区比一个同等条件的高纬度地区包含更多的物种。 对于许多不同的动物和植物似乎都是这样。

    为什么高纬度比热带多样性要低?也许这只是一个土地面积的问题。 热带地区比高纬度地区拥有更大面积的土地一当我们检查最常用的地球曲面的投影,这个事实并不总是显而易见的,因为这往往夸大高纬度的土地面积一并且一些生物地理学家认为这种多样性的差异是这种影响的反映。 但由生物学家克劳斯罗德数据分析不支持这样的解释。 虽然面积可能有助于生物多样性,这当然不是全部的原因;不然的话,大的陆地面积会含有更丰富的物种。

    这似乎牵涉到生产率,但也许它的影响是间接的。 在最适合植物生长的地方——也就是那些温度较高较均匀的地方,有充足的水供应——通常会发现大量的植被。 这导致了植物体有一个复杂的层结构。 例如,在热带雨林中,大量的植物体聚集在地面之上。 也有大量的植物体,在地下成为根组织,但这是不太明显的。 仔细分析上述地面的植物体显示,它被布置在一系列的层中,精确的数量由于不同的层的年龄和森林的种类而有所不同。 植被的生物量(“生物量”)的排列形式被称为“结构”(和“组成”相对立,“组成”是指形成群落的生物的种类)。 结构本质上是植被的架构,在热带森林的条件下,它可以是非常复杂的。 在亚马逊流域的一个成熟的洪泛区热带森林,树冠(森林最上面的层,由树的冠构成)采取分层结构。 在地面以上大约3米、6米、和30米的高度,树冠有三个明显的峰在;50米的最高层对应着非常高大的树木,它们摆脱主冠的遮盖站立着,并且形成自己的开放层。 所以,这样的森林基本上包含四层的树冠。 温带的森林通常只有2个冠层,所以它们的结构就没有那么复杂。

    结构对动物的生活有很大的影响。 它构成了动物进食、移动、躲避、生活和繁殖的空间环境。 通过影响到光照强度、湿度以及温度的范围和极值,它甚至非常本地化地影响到当地气候(微观气候)。 例如,一个非常简单结构的草地植被区域,和那些有上层树冠的区域在地表有着非常不同的微观气候。 (后者)的风速较低,白天气温较低(但夜间气温较温暖),地面的相对湿度也更大。 小气候的复杂性与植被结构的复杂程度密切相关,一般而言,植被的结构越复杂,在那生活的动物的种类就越多。 热带植物的大生物量导致更高的环境空间复杂度,这导致了占据一个区域的更高生物多样性的可能性。 高纬度地区的气候条件一般不利于大量生物量的积累,因此,植被结构简单,动物的多样性也较低。
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    题干分析:原句句子主干是and 联系段并列结构:The tropics contain a larger surface area of land than higher latitudes, and some biogeographers regard the differences in diversity as a reflection of this effect. 中间破折号部分是一个让步结构。