Community Interactions

hi in this lesson will be talking about community ecology and the interactions in communities. Now a community is all the populations of different organisms that live in the same area, and these different species in a community are going to interact with one another. We call this inter specific interactions, and these interactions can be beneficial or harmful to the survival and reproduction of the organisms involved. Now, this idea of being beneficial for survival and reproduction gets at the idea of fitness, which is the ability of an organism to survive and reproduce compared to the average member of their population. Because these interactions affect fitness and because fitness is a strong driver of evolution, we're going to see co evolution where species influence each others and evolution due to the either harmful or beneficial interactions they have. So a common example is something like this bird which can feed on these flowers because it's Bill has evolved to be, you know, just the right shape to get in there. And you know the bird is gonna get food. The flower is going to get to use. The bird is a pollinator, pretty common example. But the point I want to make to you guys is that this goes beyond, you know, making two parts that fit together. Look at this interaction. Rabbits air fast, right? Rabbits aren't fast just because it's fun to be fast or their fans of the flash there fast because there are predators hunting them. They need to be fast to get away. So I want you to think about the evolution that takes place. Due to these interactions, almost is like an evolutionary arms race between these organisms in the battle for survival. Let's actually take a look at the different types of interactions. First one I wanna look at is called Commence Soliz, Um, and this is an interaction where one organism benefits and the other is just unaffected. So here you can see an example of that. These fish hang around the shark, basically waiting for some scraps to come their way. It's a good way to get a free meal, and you know, the shark is basically unaffected. They're just kind of freeloaders, but he's going to get his meal anyways. Now it's worth noting that, as with everything in biology, you know, these aren't super well defined boundaries so to speak. I mean, we call this relationship between the shark and these fish. Commence Soliz. Um but it's not uncommon to see a shark eat one of the fish that's trailing it happens regularly. So, you know, commence Soliz. Um yes, but just know that there's always exceptions. So the next type of interaction I wanna look at his competition. This is negative for both of the organisms involved. This is when individuals compete for the same resource is and it's not gonna work out well for either of them. And here you can see an example of that where two males are competing for mates and you know, this could result in a fatal injury, for example, or something like that. At worst, it's going to mean one of them doesn't get to mate. I'm sorry at best. It's gonna mean one of them doesn't get to make. At worst, one of them could tie, um, the next interaction. I wanna talk about our type of interaction on Talk About is positive for one organism and negative for the other. And this is like what we saw going on with the hair and links right? That was an example of predation. But you can also have herbivorous, which you see here, which is good for the cow. Not so good for the plant. It's eating and parasitism, which will talk more about later. Now. Lastly, you have mutual is, um which is positive for both organisms. And you can see an example of that here between these clownfish and see an enemy. Hi, Nemo. All right, let's flip the page.

the role that an organism or a population plays in its environment is called its ecological niche. Now not every niche is going to be glamorous. As you can see with this dung beetle right here, however, the point is Maura, about finding a niche that isn't occupied by anyone else so that you can best exploit the resource is available there now organisms. They're gonna have a range of conditions that they can survive in, and we call this an organism's fundamental niche. This is just all the environmental conditions suitable to the organism ignoring the inter specific interactions. Now the realized niche is going to be the part of the fundamental niche that an organism will actually occupy due to the limiting factors imposed upon it. So this outer ring represents the fundamental niche and this inner ring. It's the organisms realized. Niche or, I should say, inner area. Now. Species in a community are going to compete. Both individuals within a species are going to compete and specie individuals from different species are going to compete with each other in trust. Specific competition is going to occur between individuals of the same species and because these individuals are of the same species, they're gonna have the same niche, which means they're going to compete for the same resource. Is which is why this is a density dependent competition. As density goes up, so does competition. Now inter specific competition is when individuals of different species have overlapping niches. And this can result in either symmetric competition where both species air negatively affected by the competition or a symmetric competition where one is much more negatively affected than the other. Now it's common for one species to out compete, another due to certain fitness tradeoffs. For example, organisms might have, you know, uh, develop certain traits that make it really efficient at gathering some type of food. For example, uhh. However, there is a trade off for this, you know, by gaining that skill, they're sacrificing an opportunity elsewhere. So it should note that species that excel a competing for certain resource is will be lacking in other areas. And here you can just see a really cool type of inter specific interaction. I mean, that's a bear. Fighting a tiger does not get much cooler than that. And this, of course, is just ridiculous. E mean that poor prairie dog. Anyhow, let's flip the page

if species occupy the same niche or have overlapping niches, something's gonna have to change. Now. If two species occupy the same niche and there's no disturbance in their environment, one will out compete, the other says the competitive exclusion principle. You can see this represented in this chart here where, you know, assuming that there's no disturbance species, one is going to weigh out, compete, species to and species to is gonna go extinct or that population is gonna go extinct, I should say now, if competing species have overlapping niches, they can do what's, uh oh are. They can experience what's called niche differentiation where they'll actually use the environment differently to better coexist. And this could be achieved through resource partitioning, where similar species will differentiate their niches to better use. The resource is available and you know, mostly to use different resource is to lower the competition between them. So you can see that happening here where we have these three species that are all overlapping in their niches and they're going to have a niche differentiation, and that's going to lower the competition between them Now, over time, what you can see happening from this competition. His character displacement and very famous example of that are the finches on the Galapagos Islands that Darwin characterized. Now this is when similar species have distributions that overlap, and so they developed differences to reduce their competition. Now this example right here is super arbitrary. But I just want to use it for illustrative purposes. I'm gonna jump out of the way here, So let's say that the yellow birds and the red birds overlap. They all want the bugs off this tree, but the red birds are going to you know, they're bigger than the yellow birds, so they're going to crowd them out, and they're going to get the bugs from the middle of the tree because I don't know. That's where they want the bugs from something like that. As I said, this is arbitrary. So if that's the case, then the yellow birds could still get the bugs from the top of the tree or the bottom of the tree. So they're going to differentiate their niche to reduce competition. And over time, let's say that these birds evolved to specialize in, you know, eating the bugs at the middle of the tree versus the top of the tree. I don't know what trait that would be, but, you know, assuming that, you know, like their beaks, for example, started out kind of similar and then got more different based on the fact that these guys air eating off the top of the tree and these guys air eating off the middle of the tree, then we'd have character displacement. So essentially, this is when species developed differences to reduce competition. And you can see that again with the Galapagos finches, who all had, uh, you know, these different differences develop so that they could take advantage of different types of food. Resource is available. All right with that, let's flip the page.

predation is when one organism consumes another organism. The organism that consumes is the predator, and the organism that gets consumed is the prey. Now, often predators air gonna be carnivores or meat eaters animals that feed on flesh. A special case of predation is herbivorous, which is predation when an animal consumes plant tissue. And often this is going to be done by herbivores for plant eaters, animals that feed on plant matter. Now predators can actually help play a role in keeping prey populations below carrying capacity, which can be very important for communities. Likewise, herbivore populations could be balanced by predation also disease. And it should be noted that plants have evolved defenses against herbivores. Now we can see some examples of predation right here and some examples of meat eating. And I just got to say, Really kudos to this heron, which speared the crap out of that fish. I mean, I couldn't believe it when I saw this image. Now predators and prey, herbivores and plants. They're all part of this evolutionary arms race, right? You know, it's like we were talking about with the rabbit. It runs fast to get away from a predator not just because running fast is cool. So we're going to take a look at some defenses that organisms have and we're gonna kind of categorize them as constitutive defenses and induce a ble defenses. So constitutive defenses, air always present, regardless of predators being around or not, this stick bug is a great example. Always looks like a stick, Always gonna be hard to see. Another example in the case of plants would be thorns. Thorns are grown on the plant there just there. That's sort of a constitutive defense for it Now induce a ble Defenses are physical, behavioral or chemical traits that are induced in response to the presence of predators. And you can see here that this cat is about to get it from this skunk which has an induce a ble defense that is chemical. It will spray it. Nasty stuff. All right with that, let's go ahead and flip the page

some organisms use their appearance as a defense. A prismatic coloration is warning coloration, usually in the form of bright colors that signal chemical defenses. So as we can see with this poisonous frog here it is, brightly colored that bright, bright red is just gonna pop. And it's there to signal to predators that hey, I'm poisonous, E. I mean, you can see me if you want to even go for it. But not gonna be happy now. Cryptic coloration is the opposite. Instead of drawing attention to yourself, you're trying to camouflage, and this is gonna make pray hard to see Now, believe it or not, there is lizard on this tree right here. It is super well camouflaged. So I'm just gonna go ahead and trace its outline so you can see, Hopefully you can kind of get the idea. But yeah, there is a lizard hiding there. It is just incredibly well disguised. Now, speaking of disguises, Mimic Re is a really interesting evolved defense, and basically it's when one organism evolves to resemble another in some way. And this could be an appearance in smell in sound and even in behavior. And we look at two examples of mimicry here. The first is basing and mimic re, which is mimic re when a species sort of tries thio imitate the warning signs off some other harmful species. So classic example is this. We have the coral snake up top, which is poisonous, and this mimic the king snake right here, which is non poisonous. And the King snake is using Basin mimic re to fool other organisms into thinking it's a coral snake and therefore poisonous and therefore stay away. Now, malaria in Mimic Re is when two distinct species mimic each other's warning signs. So in this case, we have two types of butterflies. We have a monarch up here and what's called a vice Roy Butterfly. They look very, very similar, and they actually both have the defense mechanism of being really bad tasting. They're very unpalatable now. Why would these two species mimic each other's warning signs? Well, it actually puzzled people for a long time, and then, um, basically, someone created this mathematical model to show that bye, both species mimicking each other. They actually increase their chances of survival because it's almost like this. If you're a predator and you learn that. You know, uh, this one particular bug tastes bad. And there's another bug that looks just like it. You're not really going to tell the difference between them. So it's actually increases the fitness of both organisms to sort of have this convergence in appearance. Uh, very, very strange, interesting stuff. Now with that, let's go ahead and flip the page.

symbiosis is a close relationship between organisms of different species. In a symbiosis, the relationship can prove to be beneficial or harmful to the organisms involved. Now I want to take a look here at a great example of a beneficial symbiosis. What we're looking at our plant roots that have developed these nodes. These notes contain bacteria that perform nitrogen fixation, which allows the plant to absorb nitrogen. Basically, these bacteria provide the plant with usable nitrogen, so their relationship is one of mutual ism. Because both species benefit, the plant gets nitrogen, and it provides the bacteria with nutrition and a safe environment. Now, in this case, the plant is actually acting as a host because it's harboring the symbiont, the bacteria inside of its roots. Now it's worth noting that some relationships can be commence. Eliza's um, where one organism benefits and the other is unaffected. It's also worth noting that some interactions can occur without a symbiotic relationship. For example, facilitation is an interaction where one or both species benefit and getting back Thio uh, you know, nitrogen fixation by certain plants adding mawr nitrogen into the soil that can facilitate the growth of other species later on, so those two different types of plants wouldn't have a symbiotic relationship, but one would be benefiting the other. Now let's talk about when these relationships sour little things. Take a turn for the worst parasitism. This is a relationship where one species, the parasite, benefits at the expense of its host and, oh, parasites or parasites that live in the body of their hosts. But some parasites live on the outside of their hosts. They're called ecto parasites. Here is an example of a crazy fungal parasite which in this case, is completely taken over the body of a torrential A. This is called corgis EPS fungus and is actually the basis for a very popular zombie game that shows people getting infected with the court accepts fungus. All right, that's all I have for this lesson. I'll see you guys next time