英語聽力文摘種群動態(tài)進化

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Rapid Evolution and Population Dynamics

種群(population)指在一定時間內占據(jù)一定空間的同種生物的所有個體。種群中的個體并不是機械地集合在一起，而是彼此可以交配，并通過繁殖將各自的基因傳給后代。種群是進化的基本單位，同一種群的所有生物共用一個基因庫。對種群的研究主要是其數(shù)量變化與種內關系，種間關系的內容已屬于生物群落的研究范疇。

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.

譯文：

直到最近，許多生態(tài)學家都沒有研究種群動態(tài)進化所帶來的影響，因為進化的速度遠遠慢于捕食的周期。但是研究表明，適應性進化可能影響著掠食者與被掠食者之間的動態(tài)。

康乃爾大學的生物學家研究了以綠藻為食的輪蟲的種群動態(tài)。他們預測，輪蟲將會吃掉綠藻并繁衍后代直到綠藻的種群銳減。由于綠藻的減少，輪蟲的種群也會銳減，這時綠藻種群便開始恢復，整個循環(huán)周期便又開始了。

但是他們觀察到在綠藻種群到達一定的密度之后，輪蟲種群并沒有立刻開始恢復。為什么呢?進化過程是如何與之一致的呢?

實際上，有些藻類細胞會對消化產生抵抗性。盡管這些抵抗也是有代價的：它們的繁殖更加緩慢。由于處于優(yōu)勢，不抗消化的綠藻品種數(shù)量減少，抗消化的綠藻細胞開始更加快速的繁殖，這就暫時穩(wěn)定了綠藻種群。

同時，輪蟲種群隨著它們食物的減少而減少，這就讓不抗消化的綠藻品種開始恢復。一旦不抗消化的綠藻又變得普遍了，輪蟲種群就開始增長，完成整個循環(huán)周期。因此，適應性進化使得綠藻種群能夠通過拖延捕食者種群恢復的時間來重建自己。

對適應性進化影響的了解將會幫助科學家更好的明白抗藥菌的行為以及疾病的爆發(fā)。

Notes:

(1)adaptive evolution 適應進化

(2)green algae n.綠藻類

(3)rotifer n.輪蟲類

(4)microscopic[,maikr?'sk?pik] adj.微觀的;用顯微鏡可見的