[請益] TPO27 閱讀第三篇 Predator Prey Cycles

看板TOEFL_iBT (TOEFL_iBT托福)作者saucy (Elevator)時間10年前 (2016/05/24 10:43)推噓1(1推 0噓 1→)

留言2則, 2人參與討論串1/1

第10題目 According to paragraph 6, which of the following was true of the hare population cycle in Krebs’s experiment? A. The effects of providing food while at the same time introducing predators cancelled each other, so there was no cycle. B. The cycle existed when either the food supply was limited or there were predators. C. There was a cycle when there were no predators and food was supplied. D. If the hares had places to hide from the lynx, the hare population increased tenfold and then remained at that level. ♦What causes the predator-prey oscillations? Do increasing number of hares lead to overharvesting of plants, which in turn results in reduced hare populations, or do increasing numbers of lynx lead to overharvesting hares? Field experiments carried out by Charles Krebs and coworkers in 1992 provide an answer. Krebs investigated experimental plots in Canada’s Yukon territory that contained hare populations. When food was added to those plots (no food effect) and predators were excluded (no predator effect) from an experimental area, hare numbers increased tenfold and stayed there—the cycle was lost. However, the cycle was retained if either of the factors was allowed to operate alone: if predators were excluded but food was not added (food effect alone), or if food was added in the presence of predators (predator effect alone). Thus both factors can affect the cycle, which, in practice, seems to be generated by conjunction of the two factors. 答案是A 但我選B 看到考滿分有人說答案應該是B 但也有人說A可以想請問這題該怎麼思考? -- ※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 140.109.26.45 ※ 文章網址: https://www.ptt.cc/bbs/TOEFL_iBT/M.1464057825.A.76C.html