Narrator: Listen to a part of lecture in en ecology class. Professor:Now we've said that animal behavior patterns involve an interplay between an animal and its environment.

旁白：请听一段生态学课堂讲座. 教授：我们已经说过动物的行为模式涉及到动物和它的环境之间的相互作用。

In particular, behavior patterns can change as an animal becomes adapted to its environment.

特别是，动物的行为模式会随着其适应环境而改变。

We can see the results of this in the way that animals have developed different types of feeding behavior.

我们可以从动物发展出不同类型的进食行为的方式中看到结果。

Animals are generally classified as a generalist feeders and specialist feeders.

动物一般分为一般饲养者和专门饲养者。

Now, um, these terms are used in a variety of ways.

现在，这些术语被用在很多方面。

At times, they're used to refer to an animal's range of habitats.

有时，它们被用来指动物的栖息地范围。

I've also seen them used to describe the number of foraging techniques that are used by an individual or species.

我也见过它们被用来描述个体或物种使用的觅食技术的数量。

Um, but for our purposes, we're going to use them to refer to the range of food items that are eaten by a species.

但就我们的目的而言，我们将用它们来指代一个物种所吃的食物种类。

So a generalist feeder is a species that eats a wide variety of foods during its lifetime.

所以多面手是指在其一生中吃各种各样的食物的物种。

And a specialist is a species that feeds on a highly restricted number of foods.

专家是一种以数量非常有限的食物为食的物种。

A good example of a generalist would be a rat.

多面手的一个很好的例子就是老鼠。

Rats are notorious for eating just about anything that's available, whether it's a plant or an animal.

老鼠以吃任何能吃的东西而臭名昭著，无论是植物还是动物。

At the other end of the spectrum, we have the koala which eats only the leaves of eucalyptus trees.

另一方面，考拉只吃桉树的叶子。

Okay, now there are advantages to each.

每一种都有好处。

For a generalist, If 1 type of food isn't around, it can feed on another that's more abundant.

对多面手来说，如果一种食物不在周围，它可以吃另一种更丰富的食物。

On the other hand, the advantage of being a specialist is that the animal is well adapted to its food.

另一方面，成为专家的好处是动物能很好地适应食物。

You could say that specialists are feeding masters, their consumption, even their digestive system is just so finely tuned. For instance, take the koala.

你可以说专家是觅食的大师，他们的能量消耗，甚至他们的消化系统都做到了很好的适应。以考拉为例。

The eucalyptus leaves that it feeds on, don't contain much protein.

它赖以为生的桉树叶，蛋白质含量并不高。

What's more, the leaves contain compounds that are poisonous to most species.

更重要的是，叶子中含有的化合物对大多数物种都有毒。

But the koalas digestive system has adapted to handle this.

但考拉的消化系统已经适应了这种情况。

It's liver deactivates, the poisonous compounds, and its digestive system is designed to extract the maximum amount of nutrients from the leaves.

这是肝失活。有毒化合物和它的消化系统的设计是为了从叶子中提取最大数量的营养物质。

So it's not a question of which strategy is better.

所以问题不是哪个策略更好。

The real question is, what determines how selective animal species are in what they eat?

真正的问题是，是什么决定了动物物种在食物选择上的选择性?

Well, the answer may lie in a concept called optimal foraging.

答案可能在于一个叫做最佳觅食的概念。

The idea is that natural selection favors animals whose feeding behavior has the lowest cost to benefit ratio.

这个理论认为，自然选择倾向于那些饲养行为成本效益比最低的动物。

That is you want to get the best healthiest food you can.

那就是你想要得到你所能得到的最健康的食物。

And you want to do it as quickly as possible. And as easily as possible.

你想要尽快完成。而且尽可能容易。

Now, in a natural environment, no animal forage in an absolutely optimal manner.

现在，在自然环境中，没有动物以绝对最佳的方式觅食。

But, well, I read some research on a little rat called the kangaroo rat, which lives in deserts in North America.

但是，嗯，我读过一些关于一种叫袋鼠鼠的小老鼠的研究，这种老鼠生活在北美的沙漠里。

The kangaroo rat is a generalist which eats plant matter like seeds and fruit.

袋鼠鼠是吃植物物质如种子和水果的多面手。

It lives in deep burrows which provide protection from the desert heat and from predators like hawks or snakes.

它们生活在深深的洞穴中，这些洞穴可以保护它们免受沙漠的炎热和鹰、蛇等捕食者的伤害。

And it goes foraging at night for food，for plant matter, under the protection of darkness.

它晚上出去觅食, 为了找植物吃，在黑暗的保护下。

Even though it's a generalist，

即使它是一个多面手，

If the only thing available is seed, if a choice of seeds is available to it, it picks up seeds that provide more energy than those it leaves behind.

如果唯一可用的是种子，如果可以选择的种子可供它选择，它会捡到比它留下的种子提供更多能量的种子。

And it carries them back to its burrow.

然后把它们带回洞穴。

Once it's there, it might eat only the richest seeds from the ones that brought back.

一旦它到了那里，它可能只吃那些带回来的最丰富的种子。

So it selects seeds outside in a way that lets it spend as little time as possible foraging in that risky environment,

所以它在外面选择种子，让它在危险的环境中花尽可能少的时间觅食，

and then sorts out its food later when it's safely in its burrow.

等它安全回到洞穴后再挑选食物。

Oh, yes, Kenneth. You have a question?

哦,是的,肯尼斯。你有问题吗?

Male student:But what about the koala? It gets by uh, by being even more selective, you'd think you would be really risky to rely completely on eucalyptus leaves.

男学生: 那考拉呢?通过更严格的筛选，你会认为完全依赖桉树叶是非常危险的。

Wouldn't it be better to diversify like the kangaroo rat, and eat, at least one or two other things?

像袋鼠鼠那样多样化，至少吃一两样别的东西不是更好吗?

Professor:Well, what do you think the koala would say? What do I gain by being so selective?

教授: 你觉得考拉会怎么说?我这么挑剔有什么好处?

In terms of optimal foraging, it's clear that eucalyptus trees provide an abundant source of food.

在最佳觅食方面，很明显，桉树提供了丰富的食物来源。

Other animals can't eat the leaves and think of how little energy the koala uses.

其他动物不能吃树叶，想想考拉消耗的能量是多么的少。

It spends only about 3 hours each day eating to get the energy it needs.

它每天只花3个小时进食来获得所需的能量。

So being a specialist allows it to get the nutrients it needs with minimal expenditure of energy.

因此，作为一名专家，它可以以最少的能量消耗获得所需的营养。