Ecology introduction | Ecology | Khan Academy

We're now going to start looking at ecology, which is just a study of how life interacts with other life or how living things interact with each other and their environment. So you could think of it as, well, how is life interacting with living things?

So that's the technical term often given as biotic factors. Biotic factors, you have the word bio in there, signaling life. Non-living things are called abiotic factors. "A" is the prefix often for "not," so abiotic is "not living." A lot of living factors are just the technical terms, but if you even think about yourself as you watch this video, you are in an environment; you are interacting with it.

There are many abiotic factors around you that you might notice: the air that you are breathing, the temperature, your access to water. But there's also biotic factors. Even if you think you're in a room alone, you're not fully in; you're not completely alone. There is bacteria around you that you might not see. There might be other forms of life; you might have a plant in the room.

Those are the biotic factors that you are interacting with. That plant in that room might be producing oxygen that you are then breathing, or you're producing carbon dioxide, which that plant is able to fix and grow. It might be interacting with abiotic factors like sunlight, which it uses in photosynthesis to fix the carbon. We study all of that in some depth in biology, and really, ecology is a bit of a synthesis of a lot of what we—or if anything, all of what we learn in biology—because it's taking life up; it's studying life at another level.

It's not just the individual organism anymore, and it's not even just the population or the community. We're talking about an even bigger system that is incredibly complex, and that's why it's a really interesting thing to study. Now, all of these images here are things that folks would associate with an ecosystem. Over here, you have a coral reef, and some of the life is obvious: you see the coral, you see the fish.

But there's also life that you're not seeing. There are going to be bacteria in this water that's not visible, at least in this picture. The abiotic factors are going to be things like the water temperature or, frankly, just even the existence of water, or the salt content of the water, or other minerals that are in the water. These pictures, over here, you don't necessarily see the animal life, but there is for sure going to be—if you were to dig into this grass or look through these bushes—you will find animal life.

You will find insects; you'll find other animals. The trees are life, so that's going to be part of the ecosystem. If we're studying ecology, we would think about, well, how do these trees interact with the water? How do they interact with the other species? How do they provide shelter for them or food, or how are they dependent on the other life in some way to grow?

Same thing for, in this case, the mushrooms. How is this fungus living on this tree branch or in conjunction with the moss and whatever else? All of this is a study of ecology, the study of ecosystems. Now, when folks are talking about ecology, they like to talk about different scales, and so let's now think about the different scales within an ecosystem or even beyond an ecosystem.

I have some pictures that, if you watch a wildlife show, you typically see some images like this. Since we at least are familiar with it, at least on TV—hopefully we get to visit this at some point in our life—let's just think about the different characters here on the different ecological scales. At the most basic scale is the individual.

So let me write this down: you have the individual. If we were talking about these elephants, the individual would be one individual elephant right over there. Now, the next scale is the population. The next scale is the population, and if we were to stick with our African savannah theme right over here, the population—you have an individual elephant. The population would be the members of that same species that live in that area.

So in this case, the population would at least include these elephants that we see in the picture. There might be a couple of elephants that are off the picture, and I should say in particular these are going to be the African elephants. So it's the members of the same species that are living in the same place, and it's up for the classifier or the scientist, whoever is studying it, to define what we mean by living in the same place.

We might define it as the elephants that live within a few miles of this watering hole; you might define it as the elephants that live within a broader area. It could be, you know, that live in East Africa or South Africa, or whatever it might be. Defining the population is all the members of the species that live in an area, but that area is up for definition.

Now, the next level up is the community. That is all the living things that might live in that area, however we define the area. For example, if this lion and this giraffe live in the area that we used to define the population, they would be members of the community. So let me circle them; they would be members of the community.

It wouldn't even just be the big animals that you see here; it would include all the life that is in that area. It would include the vegetation that is in the area; it would include the bacteria, it would include the fungus, it would include any animals that are living inside of this water that you see there.

Now, if you go even one more level of kind of inclusion, then we go to the ecosystem. Then we go—I'll go down here—then you go to an ecosystem. What an ecosystem is, it's all of the living things in that community, so all of the living things in an area. Then you're also adding the non-living things, the abiotic factors.

So you're including the rock and the air and the weather and the clouds and the water itself that is part of that watering hole. A lot of times, you might think that the abiotic factors affect the biotic factors. If you don't have water, or if the temperature is too cold or too hot, it might be hard for a certain type of life to thrive.

But it goes both ways; the biotic factors affect the abiotic factors. We have oxygen in our environment due to life on Earth. They might also affect the various chemical composition of certain parts of the abiotic factors, say the water or the soil or whatever else. If you want to get a level above an ecosystem, then sometimes you'll hear people talk about a biosphere. Biosphere—it's you can think of it as a meta-ecosystem, or oftentimes, in my head, I view it as a fully enclosed, fully contained ecosystem.

Biospheres are actually, well, I guess the most famous biospheres or the one that we're typically referring to is—we could refer to the whole Earth as a biosphere. It has multiple ecosystems, and once again, the ecosystems—it depends what the researcher wants to define as an ecosystem. They could define it as something around a certain river in a certain area, just like that, or they might define the ecosystem as a broader region.

But all of the ecosystems in the world are part of the biosphere that we know as part of Earth. It's self-contained because we don't think that there are that many influences from outside of the Earth, although even there we have to give some credit to the Sun, that is providing abiotic factors. For sure, we wouldn't have life on Earth as we know it without the Sun.

There's also things like the moon; the gravitational effects—you could consider that an abiotic factor. Without the tides, we would not have life as we know it. But one thing that's really fun, as many of you all know, I enjoy science fiction, is to think about, well, what kind of biospheres could you have?

Even if you think about beyond the Earth, this is a depiction here—this is actually from NASA's website—of how humans could create biospheres outside of the planet. It's this interesting thing where, you know, that's "land," quote-unquote, up here; it would be artificially created and then you would rotate it so that there's the perception of gravity.

But anyway, the study of ecosystems, the study of biospheres, the study of ecology in general is incredibly fascinating. Because when you have all of this complexity, each living thing is incredibly complex. In fact, if you want, you could even sometimes consider part of a living thing as an ecosystem in and of itself.

If you were to look even on the surface of your hand, you have bacteria living there that's dependent on you in some way, and you might actually benefit from the bacteria or actually get hurt from the bacteria in some way. So there's all sorts of different scales, but once you start factoring everything in together, it becomes these incredibly beautiful, complex, often balanced—sometimes imbalanced—systems that have emergent properties that start to have behaviors, or that—and I want to use that word very loosely—that somehow describe the ecosystem as a whole.