An organism's niche | Ecology and natural systems | High school biology | Khan Academy

In this video, we're going to talk about an organism's niche, and all a niche is, it's a fancy way of saying where you will actually see an organism: the environmental conditions where you are going to actually see organisms of a certain kind.

To understand an organism's niche, let's talk about an organism's tolerance. In everyday language, a tolerance is how well can you tolerate something. In general, for a given type of organism, we can describe what conditions we are likely to find them in and describe it in terms of tolerance.

So, in this diagram right over here, we're thinking about a certain type of fish, and maybe these conditions are the water temperature. But it doesn't have to be water temperature; it could be the salinity—how much salt is there in the water. It could be the acidity of the water; it could be some other factor. But let's just say that we're talking about temperature.

So, there's going to be some optimal conditions for this type of fish, and under those optimal conditions, you're going to have a lot of abundance of that fish. This dimension right over here is the organism's abundance. You're going to see a lot of them.

Now, let's say the warmer the water got, warmer and warmer, and for various reasons, it just becomes less and less comfortable for that type of fish. We go from optimal to stressful conditions, and in those stressful conditions, you have fewer of those fish. Now, it might be the water temperature itself, or maybe the water temperature is creating other factors in the environment that are making it harder for that fish to live.

If you got super hot, extreme conditions, you're not going to get any of those fish. You could go the other way; let's say it gets colder and colder. We're getting to the lower end of the tolerance limit. Those are again stressful conditions, but if you get cold enough, you just cannot see fish in that environment.

So, when we think about abiotic factors—non-living factors like temperature, like acidity—where we're thinking about where an organism can and cannot live, this is known as a fundamental niche. But the fundamental niche is just where you could possibly find an organism.

We're also going to talk about something known as a realized niche, which takes into consideration the abiotic and biotic factors—non-living and living factors—to determine where you are actually likely to see the organism.

On the left here, we're looking at the fundamental niche for this type of fish along two dimensions. We're looking at temperature on this horizontal dimension and we're looking at dissolved oxygen tolerance on this vertical dimension. So, one way to think about this, this point right over here would be an environment that is very cold and does not have much oxygen dissolved in the water. Well, that is going to be an extreme condition for this species of fish, so you will not find it there.

Likewise, if it's really warm and you have a lot of oxygen dissolved in the water, it's also an extreme condition where you won't find the fish. This fish needs a certain oxygen range, and someplace in the middle is probably going to be optimal for it. Down here would be stressful, up here would be stressful, and similarly for the temperature, it has a temperature range, and someplace in the middle is probably going to be optimal.

So, if you have this dissolved oxygen and this temperature around here, you're probably going to have a high abundance of that fish, and as you get further and further from this point, you're going to have a lower and lower abundance when you look at just these two dimensions. But we know that environments are much more complex than just two dimensions.

It's not just about the temperature, and it's not just about the amount of oxygen; there might be the amount of light that's available, the amount of food that's available, the other organisms that eat this fish. So, for you to factor in all of the abiotic and biotic factors, you might have a realized niche that is a subset of this fundamental niche.

The fundamental niche is where you could possibly find them, while the realized niche is where you actually do find them. For example, this point right over here might be pretty optimal temperature, but because there's so much oxygen dissolved in the water, there maybe there's some large predators there that are likely to eat that fish that need a lot of oxygen.

Likewise, at a high-temperature range right over here, maybe there's a lot of other species of fish that can live there, and so there's more competition for food. Once again, you're less likely to find this species at these points over here. So, its realized niche is more of all of this, and when most people are talking about an organism's niche, they're usually talking about the realized niche.

They're thinking about all of the factors, both abiotic (non-living) and biotic things like predators and competition with other organisms. Now, the last thing I’ll talk about is some organisms have a pretty broad niche; they can live in many different types of environments, and some are more specialized.

Think about a cockroach versus, say, a koala. A cockroach can live in many, many, many different places with many different food sources. You see them all over the world, while koalas, you only see them in roughly one part of the world because they only eat leaves from one type of tree.

So, they have a very specialized niche, or you could think of them as a specialist species, while a cockroach is more of a generalist species.