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Interactions between populations

Video transcript
- [Voiceover] In the introduction to ecology, we introduce the idea of a community, which is all about different populations that are in the same habitat, that share the same area or that are in the same area. So populations, and if we're thinking in terms of water or in the air, it could be to share a similar volume even, populations sharing a habitat. Sharing a habitat. And in particular in this video, we're going to focus on the interactions between those populations, the interactions between the different species. The technical term for that is interspecific interactions. I like to just say interactions between species. Now the first one that is often thought about is the notion of competition. And this is when different populations, different species, are competing for the same resources. You can imagine a forest, where you have different populations of plants that are competing for sunlight, that are competing for water, that are competing for nutrients in the soil. Even in this picture right over here, this is a picture of a community. All of these different populations of fish, and other things, sea anemones and coral, they are sharing this same region, and many of them could be in competition with each other. They might be going after the same food, or they might be going after the same shelter someplace. And oftentimes, when people are talking about these inter-species or interspecific interactions, you'll see something like this, a minus slash minus, or a negative sign slash a negative sign. And that means that this type of interaction, when you have two species or two populations that are in competition with each other, the more that you have of one, it's going to have a negative effect on the other, and vice versa. If I'm a plant, and if I'm in competition with another plant, and that one's taking my light, and if there's more of it taking my light, that's gonna have a negative impact on me and vice versa. If I'm in competition with you, and we eat the same thing, the more of me that there's around eating your food, that's gonna have a negative impact on you, and vice versa. So the next form of interspecific interaction, or interaction between species, is predation. This is when one population likes to eat another population. And you might often associate predation with pictures like this that you see on television shows, on documentaries, you see a cheetah hunting, it looks like a cheetah hunting a gazelle or a deer of some kind. Actually it says right here it's a young bushback. And this is predation. But this is not the only form of predation. This picture here of the goat eating grass, this is also predation. It's not quite as bloody and as violent, but it is still predation, because you have one species eating another species. In this case you have this animal, the goat, that is eating the grass. And this type of predation, this specific type of predation, is called herbivory. But it is a type of predation. So we could say, predation, slash herbivory. Let me do a little slash here. Slash herbivory, which is a special case of predation. And you'll often see a plus slash minus. The more of, let's say this species that you have, the species that is being eaten, it's going to benefit the predator, but the more of the predator that you have, it's going to have a negative effect on the actual prey. The next types of interactions are ones where you have long-term, fairly intimate interactions, where you have organisms that oftentime live with each other, or often on each other. And this general term of organisms that have these long-term intimate interactions is symbiosis. Now, in every day language, when people talk about symbiosis, they're often talking about organisms that really benefit each other. But technically, symbiosis isn't just about benefiting each other. It could be that they're even hurting each other in some way, or that maybe one benefits while the other one really doesn't care. And so there're several types of symbiosis. The first that we could talk about is parasitism. Parasitism. And this looks a lot like predation, where the more that the parasite benefits, the most of the host that there is, but the host is actually hurt by the parasite. And there's all sorts of examples of parasitism. We have, right over here, a zoomed in picture of a louse. So why is this parasitism? Well if this lice, if this louse, I should say, so this is parasitism. And we would call the louse here a parasite, parasitism. And this benefits by living in your hair because that's where it gets its food from, it can lay, or living on your scalp, it gets your food by sucking your blood, it can also lay eggs in your hair. In some ways you could view it as almost a shelter from the rest of the environment. But it's negative for you. It will make you itchy, it is taking your blood, it is uncomfortable. And so, parasitism, once again, it's good for the parasite, just like predation is good for the predator, but not so good for the host in the case of parasitism. Now you have another situation, where it is benefiting both sides. And that is called mutualism. Mutualism, let me do that in a different color. So mutualism. This is where both sides benefit. And oftentimes when people talk about symbiosis, they're really talking about mutualism, which is a specific type of symbiosis, where both species, or both animals, organisms, benefit. They don't have to just be animals. This is an example of mutualism right here. Let me do that in a color you can see. So this is mutualism, where you have a clownfish living within a sea anemone. The sea anemone is providing the clownfish shelter, while the clownfish is keeping away other fish that might eat that sea anemone. So they are both benefiting from that interaction, and so that is mutualism. Now you have another category, where one species is benefiting, and the other one is maybe a little bit more indifferent. So one species is benefiting, and then the other one, well, maybe it is a little bit indifferent. And we call that commensalism. Commensalism. And once again, there's many examples of commensalism. This right over here is a picture of bacteria living on your skin, and you do have bacteria living on your skin right now. Accept it. And actually, well oftentimes it's a good thing. Sometimes it's mutualism, that it's providing protection from harmful bacteria. But sometimes it, the bacteria are surely benefiting, it's living off of nutrients on your skin. The skin is its habitat. But oftentimes, it doesn't really have an impact on you. Now, commensalism, let me write this down. Commensalism, oftentimes the more that we study it and the more that we understand it, we realize that actually maybe the host actually is benefiting, which it is mutualism, or maybe the host actually is getting hurt, in which case it is parasitism. So oftentimes commensalism isn't completely neutral for the host. It could go either way. And so these are all the different types of interactions. So I encourage you to look around you, look at the world around you, and don't just limit yourself to animals, think about bacteria, think about plants. And think about within a habitat, what're all of the different interspecies interactions, and how you might wanna classify them.