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Listen to part of a lecture in a biology class.
听一段生物学课程。
Professor, since we are going to talk about changes in animal populations in the wild, I'd like to ask about something I read in an article online, about how the population size of some animal species can affect other animal species, and how other environmental factors come into play too.
教授，既然我们讨论动物种群在自然界的变化，我想问一些关于我在网上读到的文章，一些物种的群体大小是如何影响其他物种的，而且其他环境因素是如何发挥作用的。
Right. Relationships between animal species in a given ecosystem can get pretty complex.
好的。物种关系在特定的生态系统中可能会非常的复杂。
Because in addition to predator-prey relationships, there are other variables that affect population size.
因为除了生物掠夺关系，还有其他影响种群大小的变数。
The article mentioned that populations of predators and their prey might go up rapidly and then decline all of a sudden.
文章提到捕食者的数量和它们的猎物可能很快地上升，然后突然下降。
Oh. Yeah! I read about that in my ecology class. It happens in cycles. I think that's called a boom-and-bust cycle. Right?
是的！我在生态学课上读到过，它会周期性地出现。我想这叫做繁荣与萧条交替循环，对吗？
OK. Well, hold on a second. First I want to go over some key concepts.
好的，稍等。首先我想复习一些关键概念。
Let's say there was a species that had access to plenty of food and ideal conditions.
比如说有一个物种可以获得很多食物并存在于理想的环境中。
Under those circumstances, its population would increase exponentially, meaning it would increase at an ever-accelerating pace.
在这样的环境下，它的种群会迅猛增长，意味着它将以持续加速的速度增长。
Wow! That sounds a little scary.
哇！听起来有点可怕。
Well, it doesn't usually happen. Like you said, a rapid population growth is often followed by a sudden decline.
这通常不会发生，如你所说，一个快速增长的种群随之而来的经常是突然衰退。
But we do occasionally see exponential growth in nonnative species when they are transplanted into a new environment.
但是我们偶尔会看到当非本地的物种转移到新环境时，它们会急剧增长。
Um...because they face little competition and have favorable growing conditions.
因为它们不用面对竞争，并且有良好的生长条件。
But for most species, most of the time, resources are finite.
但对于多数物种来说，更多时候资源有限。
There's only so much available...which leads me to my point.
只有一些可以利用，这将引出我要说的重点。
Every ecosystem has what we call a carrying capacity.
每个生态系统都有我们所说的容纳量。
The carrying capacity is the maximum population size of a species that can be sustained by the resources of a particular ecosystem.
容纳量是物种群体大小的最大化，可以由一个特定生态系统的资源支撑。
Resources are, of course, food, water, and just as important, space.
资源当然是食物、水和同等重要的空间。
Although every species has a maximum rate at which the population of that species could increase, assuming ideal conditions for the species in its environment.
假设物种处于理想环境，然而每个物种都有它种群增长的最大定额。
There are always going to be environmental factors that limit population growth. This is called environmental resistance.
总有环境因素限制种群增长，这叫做环境阻力。
Environmental resistance is important because it stops populations from growing out of control.
环境阻力很重要，因为它阻止种群增长失控。
Factors such food supply, predation and disease affect population size, and can change from year to year or season to season.
如食物供给、捕食和疾病因素可以影响种群大小，而且年年或每季都有变化。
