英语听力文摘 种群动态进化
Rapid Evolution and Population Dynamics
种群(population)指在一定时间内占据一定空间的同种生物的所有个体。种群中的个体并不是机械地集合在一起，而是彼此可以交配，并通过繁殖将各自的基因传给后代。种群是进化的基本单位，同一种群的所有生物共用一个基因库。对种群的研究主要是其数量变化与种内关系，种间关系的内容已属于生物群落的研究范畴。
A recent study suggests that adaptive evolution might actually play a role in the dynamics of the predator-prey relationship.
Until recently, many ecologists didn’t study the effect of evolution on population dynamics because evolution is much slower than the predator-prey cycle. But a study suggests that (1)adaptive evolution might actually play a role in the dynamics of the predator-prey relationship.
Cornell University biologists studied the population dynamics of (2)green algae and (3)rotifers, the (4)microscopic (5)aquatic animals that feed on them. They expected that the rotifers would eat the algae and multiply until the algae population crashed. This would then cause the rotifer population to crash, which would allow the algae population to recover, and the whole cycle to begin again.
What they observed, however, was that there was some lag between the time the algae population reached a certain (6)density and the time the rotifer population began its recovery. Why? And how does evolution fit into all this?
Well, it turns that some algal cells are resistant to digestion, although this resistance (7)comes at a cost: they reproduce more slowly. As the more dominant, non-resistant strains of algae crashed, the resistant algal cells began cloning themselves more rapidly, and this temporarily stabilized the algae population.
In the meantime, the rotifer population crashed because the rotifers had less to eat, allowing the non-resistant strains of algae to recover. Once the non-resistant algae became common again, the rotifer population increased, completing the cycle. So basically, adaptive evolution enabled the algae population to reestablish itself by delaying the time it took the predator population to recover.
Understanding the effects of adaptive evolution may help scientists to better understand the behavior of (8)drug-resistant bacteria and outbreaks of disease.
译文：
直到最近，许多生态学家都没有研究种群动态进化所带来的影响，因为进化的速度远远慢于捕食的周期。但是研究表明，适应性进化可能影响着掠食者与被掠食者之间的动态。
康乃尔大学的生物学家研究了以绿藻为食的轮虫的种群动态。他们预测，轮虫将会吃掉绿藻并繁衍后代直到绿藻的种群锐减。由于绿藻的减少，轮虫的种群也会锐减，这时绿藻种群便开始恢复，整个循环周期便又开始了。
但是他们观察到在绿藻种群到达一定的密度之后，轮虫种群并没有立刻开始恢复。为什么呢?进化过程是如何与之一致的呢?
实际上，有些藻类细胞会对消化产生抵抗性。尽管这些抵抗也是有代价的：它们的繁殖更加缓慢。由于处于优势，不抗消化的绿藻品种数量减少，抗消化的绿藻细胞开始更加快速的繁殖，这就暂时稳定了绿藻种群。
同时，轮虫种群随着它们食物的减少而减少，这就让不抗消化的绿藻品种开始恢复。一旦不抗消化的绿藻又变得普遍了，轮虫种群就开始增长，完成整个循环周期。因此，适应性进化使得绿藻种群能够通过拖延捕食者种群恢复的时间来重建自己。
对适应性进化影响的了解将会帮助科学家更好的明白抗药菌的行为以及疾病的爆发。
Notes:
(1)adaptive evolution 适应进化
(2)green algae n.绿藻类
(3)rotifer n.轮虫类
(4)microscopic[,maikr?'sk?pik] adj.微观的;用显微镜可见的
Prison guard: Microscopic implants will restrain convicts from engaging in criminal activity. The sensors will require lots of fine-tuning.
监狱看守：微小的植入片将阻止囚犯从事犯罪活动。这种传感器需要进行大量的微调。
(5)aquatic animals 水生动物;水栖动物
God has made devices to keep fish and other aquatic animals alive in cold regions.
神设定了装置，让鱼和其他水生动物生活在寒冷的区域。
(6)density ['dens?ti] n.密度
This wave of excess density is sound.
这种过剩密度的波就是声波。
(7)come at 攻击，袭击;达到;得到
Put the food where the cat can't come at it.
把食物放在猫够不着的地方。
(8)drug-resistant adj.耐药的;抗药性的
One of the most important things is to identify cases quickly -- especially drug-resistant cases, which are increasing.
最重要的事情之一是尽快辨认出这些病例——尤其是那些逐渐增长的抗药性病例。
