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Community ecology: Feel the love

Hank explores community ecology, the competitive exclusion principle, and how different species can coexist by occupying different niches. Created by EcoGeek.

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  • primosaur ultimate style avatar for user T-TAS
    I know what mutualism is but what I don't get is obligate mutualism. Could someone please define obligate mutualism for me?
    (5 votes)
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    • piceratops ultimate style avatar for user Just Keith
      Obligate mutualism occurs when one or both of the partner species is absolutely dependent on the other species for survival. Sometimes both partners are obligate, sometimes only one.

      For example, some plants provide nectar to bees and in return get pollinated. The plant species is absolutely dependent on the bees in order to reproduce and thus for the species to continue to survive. Depending on the species involved, the bee may or may not be obligate to that specific species of plant for their survival.
      (13 votes)
  • primosaur ultimate style avatar for user T-TAS
    Is there any difference between SYMBIOSIS and MUTUALISM or, are they both the same?
    (6 votes)
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  • male robot hal style avatar for user richmasterninja
    How have such a diversity of species emerged out of just 1? What caused them to be different and why doesn't diversity still occur, or does it?
    (1 vote)
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    • leafers ultimate style avatar for user Donovan King
      First, anybody who says "only a theory" or tries to explain that theories aren't observed or repeatable has no science education.

      Evolution has been observed and does continue today. This is why you need a flu shot every year, but not only viruses have been seen to evolve. Anole lizards in the Southern US are evolving to cope with the introduction of fire ants, for instance. The observations are hard to notice, though. It's like growing up. You were a baby, now you're an adult, but you looked the same each morning as you did the night before. You couldn't "observe" your own aging, but it obviously happened. The same goes for species evolution. Each individual will look just like its parent(s), like you look like the you from yesterday, but at some point, minute and undetectable changes build to become very noticeable.

      But how do many species come from one? A barrier of some sort prevents two groups of the same species from mating. Each group continues to evolve, but on separate paths. Think of cake and bread. They both have the same basic ingredients, but how much is used and how makes a huge difference in the end product. So each group has the same body plan and the same DNA, they went to different environments (bakeries) and adapted to become a cake or a bread.

      After this split, each one of the new species can undergo a split and so on. One species can become 2, then each can split again for 4, then 8, then 16... Of course, extinctions and geologic events will alter the rates. Always keep in mind that each branch continues to evolve. Just like your cousin is as related to your grandmother as you are, we are as related to our "grandspecies" as chimps are.
      (19 votes)
  • piceratops seedling style avatar for user maritza
    What does Biodiversity mean? it does not explain it here in this video.
    (3 votes)
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    • orange juice squid orange style avatar for user laiba khurram
      Biological diversity – or biodiversity – is the term given to the variety of life on Earth. It is the variety within and between all species of plants, animals and micro-organisms and the ecosystems within which they live and interact.

      Biodiversity comprises all the millions of different species that live on our planet, as well as the genetic differences within species. It also refers to the multitude of different ecosystems in which species form unique communities, interacting with one another and the air, water and soil.
      (4 votes)
  • aqualine sapling style avatar for user Isaak
    Where do symbiotic relationships come in?
    (1 vote)
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    • aqualine ultimate style avatar for user gaiki.amruta
      Symbiotic relationships just means two organisms living together. This includes mutualism, commensalism and parasitism.

      Mutualism is where both the organisms benefit.

      Commensalism is where one organism benefits but the other is not affected.

      Parasitism is where one organism harms the other.

      Hope this helps :)
      (3 votes)
  • winston baby style avatar for user Coolkid Awesome
    I thought a cymbiotic relationship was what they described mutualism to be. Is this true? if not then what is a cymbiotic relationship in more detail?
    (2 votes)
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  • starky ultimate style avatar for user sirus
    What does Ecolo-graphy mean?
    (1 vote)
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  • leafers seed style avatar for user tubbythehat
    Paramecium Aurelia? What is that?
    (1 vote)
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  • hopper cool style avatar for user George Cai
    At , what does Hank mean by Renal Cancer?
    (1 vote)
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  • stelly blue style avatar for user bruh
    Why are there 3 marks on the book for the ecolography?
    (1 vote)
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    • mr pants teal style avatar for user Running Chuck
      Look at the page Hank reads from. It is the first of the book. Most likely he has printed out a note and attached it to the first page of any book he could find that fitted his equally printed out (and "branded") book cover.

      As for the marks, I don't think they tell us anything, as the book in question probably hasn't much to do with Robert MacArthur. Except for the inlay note Hank reads from.
      (1 vote)

Video transcript

- I wouldn't be much of a teacher if I didn't tell you that life is tough and that everyone's looking out for themselves in this world. That's just the way it is, people. You know how I always say that biology is ultimately about sex and not dying. Well, both of those things are more difficult than we'd like them to be because of competition. There's a finite amount of resources on the planet, so evolution drives us to compete for them, so that we can survive long enough to spread our genes all over the place. And naturally, competition is a really important part of how different species interact when their habitats overlap. These interactions between species are what define ecological communities. So it makes sense that community ecology studies these interactions anywhere they take place. From a tide pool, to the whole ocean. From a rotting log to an entire forest. But just because interspecies interaction is mostly competitive, doesn't necessarily mean that community ecology is all about big, bloody tooth and claw scenes like from cable TV nature shows. Actually, a lot of it is, but we're not gonna get there until next week. For now, let's just note that competition, while prevalent and important, is also pretty dangerous, kind of a hassle and kind like really hurt. So a lot of interspecies interaction is actually about sidestepping direct competition and instead, finding ways to divvy up resources or otherwise let species just get along. Can you feel the love? (upbeat music) Careful guys, 'cause right now we are surrounded by potentially lethal interspecific competition going on all over the place. Since we're animals, we usually think of competition as going on between animals, but really, it happens between almost all members of the four kingdoms of life. Whenever species compete, they're going after the same resources that they need for their survival and continued population growth. In this garden the weeds are competing with the sunflower and the corn and the dill for the nutrients and water in the soil. So these resources, because they're finite in this area, are the limiting factors that we've talked about. The population can only get as big as these factors will allow. Now, a particularly nasty weed could, over time, eliminate the veggies entirely. Such elimination is known as Competitive Exclusion and it's one of the most fundamental properties in community ecology and also like life. Because the fact is, when two species are competing for the same resources, one of them is eventually gonna be more successful and eliminate the other. This bitter truth is known as the Competitive Exclusion principle and it was first identified in 1934 by Russian ecologist, G.F. Gauze, in a study of two closely related species of microscopic protists. When he was only 22 years old, Gauze made a name for himself by conducting experiments that pitted one species of protists, Paramecium Aurelia, against another, Paramecium Caudatum. First, Gauze grew each species separately with the exact same resources and found that each developed rapidly and established stable populations. But, when he grew them in the same container, P Caudatum was soon driven to extinction by P Aurelia. Paramecium Aurelia gained a competitive advantage because its population grew slightly faster than P Caudatum's. So Gauze's experiment showed that in the absence of another disturbance, two species that require the same resources can not live indefinitely in the same habitat. The inferior competitor will be eliminated. Makes sense, but, if Competitive Exclusion is the natural law of the land, then why isn't all of Earth just a crazy crap circus of constant competition, predation and ultimately extinction of all of those losers? Well, for a couple of reasons. First, not all resources are limiting. Two species of shark may compete for water in the ocean, but the ocean is, you know, gigantic. So that's not what limits their population growth. Rather, the amount of food, like a specific fish that they both eat could be limiting, while other resources are plentiful. Second, as the overwhelming diversity of life in almost any community shows us, most species, even ones that are almost identical to each other, are adaptable enough to find a way to survive in the face of competition. They do this by finding an ecological niche. The sum of all resources, both biotic and abiotic, that a species uses in it's environment. You can think of an organism's niche as it's job in the community that provides it with a certain lifestyle. We tend to keep jobs that we can do better than anyone else in our community and if we're desperate, we do a job that nobody else wants to do. But, no matter what job we have, what it pays in terms of resources, dictates our lifestyle. So finding a nice, comfy niche that you have pretty much to yourself, not only provides a steady income of food and other stuff, it also allows a species to avoid Competitive Exclusion. And this, in turn, helps create a more stable ecological community. It's an elegant and peaceful solution that I wish we humans could figure out something as good. But as with anything in life, this relative security and stability comes at a price. The bummer is that it prevents some species from living the lifestyle that they could have if nobody else competed with them at all. This ideal situation is called a Fundamental Niche and it's just that, an ideal. Few, if any, species ever get to live that way. Instead, because of the need to avoid Competitive Exclusion in order survive, many species end up with a different job and hence, lifestyle. It's not necessarily the job that they studied for in college, but it makes a decent living and that's called a Realized Niche. This my friends, is how nature does conflict management. But it sounds kind of unnatural, doesn't it? I mean, Gauze taught us that competition and winning the competition was the natural order of things. So how could it be that part of the natural order actually involves letting everyone compete and win just a little bit? And how did we ever come to discover that things actually work this way? Well, it took a special kind of person and to tell you about him, I'm gonna need a special kind of chair. (upbeat music) Canadian born ecologist, Robert MacArthur was in his late 20's when he made a discovery that made him one of the most influential ecologists of the 20th century. While researching his doctoral thesis at Yale University in 1958, he was studying five species of Warblers that live in coniferous forests in the northeastern United States. At the time, because there were so many different species of Warblers that lived, fed and mated in such close quarters, many ornithologists thought that the birds occupied the exact same niche, and thus were an exception to Gauze's Competitive Exclusion principle. But, MacArthur, was not convinced. A mathematician by training, he set out to measure exactly how and where each kind of Warbler did it's foraging, nesting and mating. In order to do this, he studied each tree the birds lived in, divided them into zones, sixteen zones to be exact. From bare lichen at the base of the trunk, to new needles and buds at the tips of the branches. After many seasons of observing many birds in many trees, he found that each species of Warbler divided it's time differently among various parts of the tree. One Warbler called the Cape May, for example, spent most of it's time toward the outside of the tree at the top. Meanwhile, the Bay Breasted fed mostly around the middle interior. MacArthur also found that each of the Warblers had different hunting and foraging habits and even bred at slightly different times of the year so that their highest food requirements didn't overlap. These differences illustrated how the Warblers partitioned their limiting resources each finding it's realized niche that allowed it to escape the fate of Competitive Exclusion. The phenomenon he observed is now known as Resource Partitioning, when similar species settle into separate niches that let them coexist. Thanks in part to this discovery MacArthur became known as a pioneer of modern ecology, encouraging curiosity and hypothesis driven research, championing the use of genetics and ecological study in collaborating with biologists like E.O. Wilson and Jared Diamond. Sadly, he died of renal cancer at the age of 42, but his study of Northern Warblers remains a classic example of community ecology that is still taught today. So, if organisms can do this, if they can behave in ways that help minimize competition while increasing their odds for survival, it follows that traits associated with this behavior would start being selected favorably. After all, that's what natural selection is for. When this happens, it's known as Character Displacement. To demonstrate, let's go back to some other famous ecologists, our favorite couple of evolutionary biologists and lovebirds, Peter and Rosemary Grant. I told you before about how they observed the process of speciation among Darwin's famous Galapagos Finches. Well on the same island, Daphne Major, in 2006, they witnessed character displacement in action. For a long time, a small population of finches had the island to themselves, where they ate a variety of seeds including seeds of the Fever plant, which were bigger and more nutritious than the smaller seeds that were available, but were harder for the little finches to open. Then, in 1982 a group of much bigger finches showed up on the island and they began to commandeer the islands abundant supply of Fever Plant seeds. Within just 20 years, the Grants found that the small finches beaks shrunk to allow them to specialize in eating only the smaller, less nutritious seeds. But now the little finches have those seeds all to themselves. The traits of the two populations had actually diverged to help facilitate the partitioning of resources. See? Competition can be hard on us, but it can also make us better people. Or, you know, finches, warblers or kangaroo mice. But there are also kinds of interspecies interaction where species actually join forces in the fight for survival. This is the ultimate in conflict avoidance. In these cases, species in a community actually manage to avoid competition altogether by forming downright, tight relationships that benefit one, if not both, of the parties involved. You may have heard of both of these cases. First, Mutualism where both species benefit and Commensalism, where one species benefits and the other's kinda like, whatever. Mutualism abounds in nature and for those who've been paying attention to Crash Course you've heard me talk about it many, many times before. A prime example are Mycorrhizae, the fungal roots that we talked about a few weeks ago. Where fungi and plant roots get entangled and essentially rub each other's backs for nutritious favors. Others you may have heard about include flowering plants that produce nectars to attract pollinators and then bear fruit to attract animals to help spread the seeds inside. Often times these relationships become rather needy, like in the case of termites. They can't break down the cellulous in the wood they eat without the enzymes produced by the microorganisms that live inside their digestive system. Without the little critters, the bigger critters would die. Such a needy relationship is called Obligate Mutualism. By contrast, Commensalism is where one species definitely benefits and the other isn't really hurt or helped. Such neutrality, of course, is difficult to prove, because even a seemingly benign interaction probably has some effect. Barnacles for example, hitchhike on Gray Whales, getting a free ride through swathes of plankton rich water for feeding. While clearly a benefit to the barnacles, the relationship is often considered commensal, because the whales probably don't really care whether the barnacles are there or not. Or do they? The barnacles might slow down the whale as it swims through the water. But, on the other hand, they might also serve as a type of camouflage from predators like orcas, in which case they confer an advantage. So, it probably comes down to meh, for the whale and when you consider all the other possibilities out there when species interact, meh isn't such a bad option. Especially considering that next week, we're going for the throat. By which I mean, we'll be investigating the kill or be killed world of animal predation and all of the fantastic evolutionary changes it can trigger that lead to even greater diversity in ecological communities. There's probably gonna be a lot of blood though, so you might wanna bring your poncho.