Populations, communities, and ecosystems | Middle school biology | Khan Academy

In biology, it's useful to have some shared language so we can communicate and describe the world around us in ways that we can all understand together.

So here, we're going to talk about populations, communities, and ecosystems, and as we'll see, these are all related ideas.

So first of all, a population is talking about the members of a specific species in an area. For example, in this picture, we have a population of zebra. I have one zebra there, one zebra there. There might be some others that we can't see; in fact, there are likely to be. So these are each members of a population of zebra.

Now we have other populations in this picture. We have a population of buffalo. These three are members of that population. We have a population of antelope; in fact, there is a bunch of antelope in this picture. So we have many members of that population. We even see some animals here in the background. I can't quite make out what they are, but that could be a different population. Let's say if those are elephants, they might be elephants the way I see them, but that could be members of a population of elephants.

So if that is a population, what is a community? Well, a community is all of the living species that live in the same area. So we have a community of animals that is made up of populations of buffalo, of zebra, and of antelope.

And I want to make clear that the populations, or when we're talking about the communities, we're not necessarily just talking about large animals like this. We could be talking about populations of mosquitoes. We could be talking about populations of fish in this pond if there are any fish. We could have a population of a certain species of plant. Likewise, when we're talking about communities, we're talking about collectively all of the living organisms together.

Now last but not least, what would be an ecosystem then? Well, an ecosystem is all of the living organisms plus all of the non-living things. So the ecosystem that we see here would also include the water; it would also include the dirt; it would also include the air. Organisms like those that we see right here are constantly interacting with both the living and non-living parts of their environment.

These interactions are how organisms get food, shelter, water, and warmth. These interactions are how organisms survive and produce offspring.

So let's get a little bit more practice with this idea of populations, communities, and ecosystems. We will do that by looking at this picture right over here. Pause this video and think about what are the populations here.

Well, you might not know the name of all these different types of fish, but you can see that there's a population of this gold-colored fish right over here. There's also another population of this blue-colored fish. We could keep looking for other populations. Looks like there's a population of this silver-colored, or I guess longish silver fish, right over here.

But once again, it's not just the fish. There's a population of coral. There are populations of microorganisms that we can't see here. The community would be all of these living organisms that live close to each other.

And we'll see sometimes they compete with each other, sometimes they eat each other, but sometimes they help each other, or sometimes they don't matter that much to each other. We'll study that into a lot more detail.

And then the ecosystem includes all of the above plus the water, plus the oxygen that is in the water, plus the sand at the bottom of the ocean.

So I'll leave you there. Hopefully, you now have a sense of what biologists are talking about when they talk about populations, communities, and ecosystems.