The Role of Grazers in Controlling the Amount of P.docx

1、The Role of Grazers in Controlling the Amount of PThe Role of Grazers in Controlling the Amount of Planktonic Algae in Lakes食草动物在控制湖泊中浮游藻类数量的作用Many theories have been formulated to explain the role of grazers such as zooplankton浮游动物 in controlling the amount of planktonic algae 浮游藻类(phytoplankton浮游植

2、物或群落) in lakes. The first theories of such grazer control were merely based on observations of negative correlations between algal海藻的 and zooplankton浮游动物 numbers. A low number of algal cells in the presence of a high number of grazers suggested, but did not prove, that the grazers had removed most o

3、f the algae。The converse相反的 observation, of the absence of grazers in areas of high phytoplankton浮游植物 concentration, led Hardy 哈迪to propose his principle of animal exclusion排斥，排除, which hypothesized that phytoplankton浮游植物 produced a repellent 杀虫剂that excluded grazers from regions of high phytoplankt

4、on concentration.This was the first suggestion of algal defenses against grazing.Perhaps the fact that many of these first studies considered only algae of a size that could be collected in a net (net phytoplankton), a practice that overlooked the smaller phytoplankton (nannoplankton微型浮游生物) that we

5、now know grazers are most likely to feed on, led to a de-emphasis降低重要性，不予强调 of the role of grazers in subsequent research. Increasingly, as in the individual studies of Lund伦德, Round, and Reynolds雷诺兹, researchers began to stress the importance of environmental factors such as temperature, light, and

6、 water movements in controlling algal numbers.These environmental factors were amenable 有责任的，应服从的，经得起检验的to field monitoring 实地检测and to simulation模拟 in the laboratory. Grazing was believed to have some effect on algal numbers, especially after phytoplankton growth rates declined at the end of bloom p

7、eriods, but grazing was considered a minor component of models that predicted algal population dynamics.The potential magnitude of grazing pressure on freshwater phytoplankton has only recently been determined empirically. Studies by Hargrave哈格雷夫 and Geen基恩 estimated natural community grazing rates

8、by measuring feeding rates of individual zoo-plankton species in the laboratory and then computing community grazing rates for field conditions using the known population density of grazers. The high estimates of grazing pressure postulated假定，要求，视。为理所当然 by these researchers were not fully accepted,

9、however, until the grazing rates of zooplankton were determined directly in the field, by means of new experimental techniques. Using a specially prepared feeding chamber室，堂. Haney was able to record zooplankton grazing rates in natural field conditions. In the periods of peak zooplankton abundance,

10、 that is, in the late spring and in the summer. Haney recorded maximum daily community grazing rates, for nutrient-poor lakes and bog沼泽，泥塘 lakes, respectively, of 66 percent and 114 percent of daily phytoplankton production. Cladocerans had higher grazing rates than copepods，usually accounting for 8

11、0 percent of the community grazing rate. These rates varied seasonally, reaching the lowest point in the winter and early spring. Haneys thorough research provides convincing field evidence that grazers can exert significant pressure on phytoplankton population.很多理论已经被建立，来解释包括浮游动物在内的食草动物在控制湖泊中浮游藻类数量

12、的作用。有关食草动物控制说的第一批理论仅仅只是建立在某些观察上面，结果显示海藻数量和浮游动物数量之间存在负相关的相互关系：食草动物数量越多，海藻细胞数量越少，这表明但是还不足以证明食草动物压抑了大多数藻类的生长。相反性观察显示，在高密度浮游植物的区域中，食草植物几乎消失。据此哈迪提出了动物相互排斥的理论，假设浮游植物能制造出杀虫剂，驱除食草动物，防止其出现在高密度的食草动物区域。这首次表明藻类对食草动物的对抗性。许多最初的研究只考虑到了能聚集成为网状浮游植物的相同大小的海藻，忽视了更小的浮游植物即微型浮游生物，也就是我们现在都知道的，食草动物最有可能捕食的对象。这一事实也许降低了食草动物在后续

13、研究中的重要性。渐渐地，研究者们根据伦德、朗徳、雷诺兹的个体研究，开始强调温度、光照、水体运动等环境因素在控制藻类数量的重要性。这些环境因素能够在实地检测以及实验室里的模拟实验中得到检验。研究者们认为食草动物能够影响藻类数量，尤其是在浮游植物生长率自高峰期末期开始下降后的一段时间，但是，在预测藻群动态的模型中，食草动物仅被看作是一个较小的组成部分。直到最近，有关淡水浮游植物的潜在摄食压力才被确定下来，而且还只是从经验上判断。由哈格雷夫和基恩进行的研究，对自然条件下的群落捕食速率进行了估计，其手段是通过测量出实验室内单个浮游动植物种类的捕食速率，然后利用已知的食草动物群落密度，计算实际条件下的群

14、落摄食速率。然而，这些研究者们在假定摄食压力的前提下得出的大胆估计，一开始并没有得到广泛的认可。后来人们又采用新的试验方法，直接测定出了实际条件下的浮游动物的食草速率，直到这个时候，人们才开始广泛接受他们的观点。哈尼专门准备了一个喂养室，记录浮游动物在实地的自然条件下的捕食速率。在浮游动物生长的高峰期，也就是春末和夏季，哈尼记录下了一天之中群落捕食速率的最大值。其中对于低营养的湖泊来说，浮游动物的日生产量是66%；对于沼泽湖泊来说，其日生产量是114%。与桡足动物相比，水蚤类动物捕食速率更高，通常要占到群落捕食速率的80%。 捕食速率随着季节的变化而变化，在冬季和早春时节速率最低。哈尼的整个研

15、究提供了有力的实地证据，证明食草动物能够对浮游植物群落产生巨大的压力。I. Words and Phrasesgrazer greiz n. 吃草的动物，食草动物planktonic algae ,plktnk ldi: 浮游藻类zooplankton zu:(),pl(k)t()n n. 浮游动物phytoplankton fat,pl(k)t()n n. 植 浮游植物（群落）correlation ,krle()n n. 数 相关，关联；相互关系hypothesize hapsaz v. 假设，假定repellent rpel()nt n. 驱虫剂deemphasis di:emfsis

16、n. 降低重要性；不予强调amenable mi:nb()l adj. 有责任的，应服从的；有义务的；经得起检验的magnitude mgntju:d n. 大小；量级empirically mprkli adv. 以经验为主地cladoceran klds()r()n n. 水蚤类动物；枝角目动物copepod kupipd n. 桡足动物II. Notes1. grazer: 食草动物，是以植物为主要食物来源的动物，如牛，羊，马等。但作为肉食性动物的对应词，也常用以泛指食取植物的动物。2. zooplankton: 浮游动物，一类经常在水中浮游，本身不能制造有机物的异养型无脊椎动物和脊索动

17、物幼体的总称。3. negative correlations: 负相关,在回归与相关分析中，因变量值随自变量值的增大(减小)而减小(增大)的现象。在这种情况下，表示相关程度的相关系数为负值。4. repellent: 驱避剂，可使害虫逃离的药剂。这些药剂本身虽无毒杀害虫的作用，但由于其具有某种特殊的气味，能使害虫忌避，或能驱散害虫。如樟脑能驱避衣蛾。5. phytoplankton: 浮游植物，是一个生态学概念，是指在水中营浮游生活的微小植物。通常浮游植物就是指浮游藻类，主要包括蓝藻门Cyanophyta、硅藻门Bacillariophyta、金藻门Chrysophyta、黄藻门Xantho

18、phyta、甲藻门Pyrrophyta、隐藻。淡水浮游植物包括蓝藻、隐藻、甲藻、金藻、黄藻硅藻、裸藻、和绿藻八个种类。6. copepods: 桡足类，隶属于节肢动物门、甲壳纲、桡足亚纲。为小型甲壳动物，体长3mm，营浮游与寄生生活，分布于海洋、淡水或半咸水中。桡足类活动迅速、世代周期相对较长，在水产养殖上的饵料意义不如轮虫和枝角类。Reading Comprehension Questions阅读理解Choose the best answer on the basis of the Text 根据文章选择最佳答案1. The author most likely mentions Hard

19、ys principle of animal exclusion in order to 1.文中作者提到哈迪的动物排斥原理，最有可能是为了A. give an example of one theory about the interaction of grazers and phytoplankton A. 举例说明食草动物和浮游植物的互动理论 B. defend the first theory of algal defenses against grazingB. 支撑第一个理论：藻类对食草动物具有防御功能C. support the contention that phytoplan

20、kton numbers are controlled primarily by environmental factorsC. 支持一下争论：浮游植物的数量主要受环境因素控制D. demonstrate the superiority of laboratory studies of zooplankton feeding rates to other kinds of studies of such ratesD. 表明实验室形式下的对浮游动物捕食速率研究相对于其它类型的研究具有优越性E. refute researchers who believed that low numbers o

21、f phytoplankton indicated the grazing effect of low numbers of zooplanktonE. 反驳那些认为浮游植物数量少与少数量的浮游动物的捕食效应有关的研究者2. It can be inferred from the passage that the “first theories” of grazer control would have been more convincing if researchers had been able to2. 根据本文可以推断出，有关食草动物的控制作用的“首批理论”将会更加令人信服，如果研究

22、者们能够A. observe high phytoplankton numbers under natural lake conditionsA. 观察在自然湖泊条件下的浮游植物数量B. discover negative correlations between algae and zooplankton numbers from their field researchB. 从他们的实地研究中发现藻类同浮游动物之间的负相关关系C. understand the central importance of environmental factors in controlling the gr

23、owth rates of phytoplanktonC. 明白环境因素在控制浮游植物增长率的核心重要性D. make verifiable correlations of cause and effect between zooplankton and phytoplankton numbers D. 在浮游动物数量和浮游植物数量之间做出可检验的因果相互关系E. invent laboratory techniques that would have allowed them to bypass their field research concerning grazer controlE.

24、 创新试验方法，使之绕过他们有关食草动物控制作用的实地研究3. Which of the following, if true, would call into question Hardys principle of animal exclusion?3. 假设它们都是正确的，下列哪一个能够质疑哈迪的动物排斥理论？A. Zooplankton are not the only organisms that are affected by phytoplankton repellents.A. 浮游动物不是唯一一个被浮游植物杀虫剂影响的生物B. Zooplankton exclusion is

25、 unrelated to phytoplankton population density. B. 浮游动物排斥与浮游植物群落的密度无关C. Zooplankton population density is higher during some parts of the year than during others.C. 浮游动物群落密度在某些年份高于其他年份D. Net phytoplankton are more likely to exclude zooplankton than are nannoplankton.D. 网状浮游植物比微型浮游植物更有可能排斥浮游动物E. Phyt

26、oplankton numbers can be strongly affected by environmental factors.E. 环境因素能够对浮游植物数量产生很大的影响4. The author would be likely to agree with which of the following statements regarding the pressure of grazers on phytoplankton numbers?4. 有关食草动物对浮游植物数量的压力，作者更有可能赞同一下哪个观点I. Grazing pressure can vary according

27、 to the individual type of zooplankton.I. 根据单个浮游动物的类型的不同，摄食压力会有所不同II. Grazing pressure can be lower in nutrient-poor lakes than in bog lakes.II. 摄食压力在低营养的湖泊中可能低于在沼泽湖泊中的压力III. Grazing tends to exert about the same pressure as does temperature.III. 摄食能够产生和温度一样的压力 A. I only B. III only C. I and II only

28、 D. II and III only E. I, II, and IIIA. 只有I是正确的 B. 只有III正确 C. 只有I 、II正确D. 只有 II 、III正确 E. I,、II、III都正确5. The passage supplies information to indicate that Hargrave and Geens conclusion regarding the grazing pressure exerted by zooplankton on phytoplankton numbers was most similar to the conclusion r

29、egarding grazing pressure reached by which of the following researchers? 5. 根据文中提供的信息表明，哈格雷夫和吉恩有关浮游动物对浮游植物数量具有摄食压力的结论，与下列那位研究者得出的有关摄食压力的结论最相似？A. 哈迪 B. 伦德 C. 朗徳 D. 雷诺兹 E. 哈尼 A. Hardy B. Lund C. Round D. Reynolds E. Haney 6. It can be inferred from the passage that one way in which many of the early r

30、esearchers on grazer control could have improved their data would have been to 6. 根据本文可以推断出，早期的许多研究者用来改善他们有关食草动物控制作用的研究数据的方法可能是A. emphasize the effects of temperature, rather than of light, on phytoplanktonA. 强调温度而不是光照对于浮游植物的影响B. disregard nannoplankton in their analysis of phytoplankton numbersB. 忽

31、视微型浮游生物在他们分析浮游植物数量中的重要性C. collect phytoplankton of all sizes before analyzing the extent of phytoplankton concentration C. 在分析浮游植物密度之前收集不同大小的浮游植物 D. recognize that phytoplankton other than net phytoplankton could be collected in a netD. 认识到，除网状浮游植物外的浮游植物能够在网状中聚集E. understand the crucial significance

32、 of net phytoplankton in the diet of zooplanktonE. 明白网状浮游植物在浮游动物饮食中的决定性作用7. According to the passage, Hargrave and Geen did which of the following in their experiments?7. 根据这篇文章， 哈格雷夫和吉恩在实验中做了以下哪个？A. They compared the grazing rates of individual zooplankton species in the laboratory with the natural grazing rates of these species.A. 他们比较了单个浮游动物物种在实验条件下的摄食速率和他们在自然条件下的摄食速率B. They hyp