字幕表 動画を再生する 英語字幕をプリント Hi. It's Mr. Andersen and welcome to biology essentials video 55. This is on biodiversity. This is video 55 of 55 videos. So this is the last one. You made it to the end. And so if you made it the whole way from the first video on natural selection to this last video, congratulations. If not, I better get started because you want to know about biodiversity. I started with Darwin and I end with EO Wilson. EO Wilson is kind of a modern day Darwin. He's famous. And some people would call him the father of biodiversity. I got a chance to meet him last year and talk to him for just briefly. But what he was excited about was the encyclopedia of life. It was his TED wish. This idea that we could have a website where we organize all life on our planet. Each organism or each species gets its own page. And it can infinitely grow from there. And so it was fun to talk to him. He actually injured his eye when he was a child fishing. Set the hook and the fish got caught in his eye. And so he ended up having poor vision. And so instead of concentrating on the big of ecology he concentrated on the small. And he's famous for his work with ants. Understanding how they communicate using chemicals. And so we owe a lot to him. But he also studied the importance of biodiversity. The importance of life on our planet and the amount of life that we have. And so I'll leave you with a quote at the end from EO Wilson. But I better get started on biodiversity. Remember, ecosystems are large areas where the climate is the same, but they are constantly in flux with the changing environment. And as that environment changes, and environments are changing especially fast now due to human impact, it's important that you have biodiversity or variation in ecosystems. And so biodiversity is a pretty big term. We could define it in a couple of different ways. But I'm mostly going to kind of talk about ecosystem biodiversity. And then concentrate on keystone species. And so a keystone species is essentially one species in an ecosystem that is disproportionally move important than other species. In other words when you remove it the ecosystem has a tendency to fall apart. I'll talk about sea otters and jaguars as examples of keystone species. But first of all what is biodiversity? Biodiversity is essentially variation in life. And when we talk about biodiversity we could be talking about the actual species that we have. We could be talking about the genes that we have. Or we could be talking about the ecosystems that we have on our planet. But essentially it's how much variation we have in life. And so this rainforest in Australia must be balanced between all of the species that live there. And then increasingly impacts that humans are going to have as we start to change the climate and as we start to effect ecosystems. And so this is a picture of some fruit found in a forest in Panama. And so as we look in rain forests we surely have an increase in biodiversity. But humans are starting to do things that will actually decrease biodiversity. So farming is great. We need food obviously. But what we're doing with a lot of our farming is we're farming using what's called a monoculture. So we're just planting one thing. So this used to be a forest. We cut it down. We're just planting potatoes. And when we do that, we're decreasing the amount of the area of life where we can have a diversity of life. And we're replacing it with just one species of potato. So we're decreasing the species. And we're decreasing that genetic variability. And I love this graph over here. What it shows you essentially is how many species we have on our planet. And how many of those we've actually discovered. And how many scientists think we have yet to discover. So insects when they publish this table, they thought there were around maybe 9 million species of insects on our planet. But we've only identified a small portion of that. Same with plants. Arachnids. Mushrooms. We've always discovered much less than half of the species that are still found on our planet. And some scientists would push this number way out here. Maybe close to like 30 million types of insects. And we've only identified a small percentage of those. And so we're at a weird time where the amount of genetic diversity that we have on our planet is decreasing at a rate much faster than we can actually identify it. And that's why biodiversity is important. Now one thing I want to talk about in this podcast is the idea of a keystone species. A keystone is a great analogy. So if you're building an arch, an arch essentially has pedestals on either side. You're going to have series of stones that go across the top. But this one block, this one block right up here is called the keystone. In other words this whole thing you could imagine, if I were to remove this keystone, all of the weight of this side and all of the weight on this side are all placed against that keystone. So if I remove that, the whole arch falls in on itself. Now ecosystems are not built like arches but they are to a degree. And so a jaguar is an important predator in South America. And the reason why is that it feeds on cayman. It can even kill adult cayman. It feeds on turtles. It feeds on deer. It feeds on capybara and tapirs and peccaries and anacondas and sloths and armadillos and frogs. In other words it feeds on up to 87 different species. And so if the population of deer gets higher, than the jaguars that mostly feed at night are going to start to prey on that deer. Or as the whatever, capybara population goes up. And so this one jaguar is going to serve as a control on a number of different species in that area. If we remove the jaguar, we move that selective pressure. We remove that one keystone species. And so it's weird to say it's more important, but it is more important than removing just the capybara in an area. Because it's going to have a greater impact on the entire ecosystem. Sea otters also have been mentioned as a keystone species. And why is that? Well, they love to feed on sea urchins. And sea urchins themselves feed on kelp. And so we have these kelp forests in the Pacific Ocean. Sea urchins would decimate kelp forests if they weren't kept in check by the sea otters. So if we remove that sea otter, now the sea urchins are gong to go crazy and deplete the kelp. And all of these fish depend on the kelp forest. And so it can have a greater, even though if we were to measure like the weight of the sea otters in that area of the ocean. It's very small. But they actually feed on quite a bit. There were some studies that showed that orcas were preying on sea otters as they saw a decrease in the seal population. And a lot of that maybe had an impact, it was a human impact, that way actually causing that diet shift. Orcas, you know, a sea otter's not much food for an orca. But it can have huge impacts on the whole ecosystem. And so that's what a keystone species is. But I want to leave you with this one quote of EO Wilson. He was talked to in the 1980s, they were talking to him about the cold war and nuclear build up and all of these things seemed to be putting us at risk. And he said, "The one process ongoing that will take millions of years to correct is the loss of genetic and species diversity by destruction of natural habitats. This is the folley our that our descendants are least likely to forgive us." It's important that you understand that you're part of an ecosystem and you clearly are a keystone species and you can make big changes. And so without further ado, that's the end!