Session 2: Theory Behind Evolution II
Transcript of Part 3: Loss of Biodiversity in a Human-dominated World
00:07.3 Hi. I'm Liz Hadly. 00:09.2 I'm a professor at Stanford University, 00:11.2 and I'm here to tell you about some of the work 00:13.1 that my lab and I have been working on 00:16.2 for the last several decades. 00:18.1 So, by training, I'm a paleontologist, 00:20.2 which means that I go back in time 00:22.2 and study how different animals have been affected 00:25.2 by changing environments of the past. 00:28.1 Those environmental changes include climate change, 00:30.1 they include volcanic eruptions, 00:31.3 and they include dispersal between continents. 00:34.2 What I'm here to tell you about today is that, 00:36.1 increasingly, 00:37.2 I've learned that what's happening on the planet now 00:40.0 is essentially equivalent 00:42.1 to the kinds of changes that I've been looking at 00:44.1 in the fossil record. 00:46.2 The biggest reason why these things are happening 00:48.3 is that the world population is enormous, 00:51.3 and it's continuing to grow. 00:54.3 If we manage somehow to hold our population 00:58.1 to just replacing every man and woman 01:00.3 with another man and woman, 01:02.2 we will still reach 9 billion people 01:06.2 by the year 2045, 01:08.3 and that means trouble for other animals 01:11.2 on the planet. 01:13.0 As a matter of fact, world population growth 01:15.0 has really contributed to our colonization of the planet. 01:19.1 As humans expanded out of Africa 01:21.2 somewhere between 100 and 200 thousand years ago, 01:24.1 they colonized Australia, 01:26.2 they colonized Asia, 01:28.0 they colonized Europe, 01:29.1 and, last of all, they colonized the Americas. 01:32.0 So, by about 13 thousand years ago, 01:34.1 humans had reached every continent 01:38.1 except Antarctica. 01:40.3 So, this expansion was also tied to 01:44.1 extinctions of large animals, 01:46.2 so we call this the late Pleistocene megafaunal extinction, 01:49.3 and in addition to the loss of these animals, for example, 01:53.1 all of which were present in North America 01:56.1 until about 10 thousand years ago, 01:59.0 there was also a climate warming event. 02:01.2 So, not only the expansion of humans, 02:03.2 but also this climate change 02:05.2 that happened at the same time... 02:07.2 it turns out those are exactly the same two features 02:10.0 that are affecting the planet today. 02:13.1 Humans, in fact, have been killing, 02:14.3 deliberately killing, wildlife for thousands of years, 02:19.2 and through that and the expansion out of Africa, 02:22.3 it turns out that every continent 02:24.2 lost their large animals, not just North America. 02:27.2 What you see here are bar graphs of just the number of species 02:30.0 in different size categories 02:31.2 #NAME? 02:34.1 and over here are the larger animals -- 02:36.2 and Africa is really the only continent that has maintained 02:39.1 most of the large animals, like we see these elephants today, 02:41.2 whereas in North America and the other continents 02:44.1 lost their megafauna, lost their large animals. 02:47.2 These elephants now are threatened with extinction as well. 02:51.2 They have a gestation time of 22 months 02:54.0 and, on average, 02:56.1 one elephant is killed every 15 minutes. 02:58.2 There is no way that this large, 03:01.1 slow metabolism animal 03:03.1 could actually keep up with the deliberate 03:06.1 slaughter of these animals. 03:08.2 We're much, much better 03:10.2 at killing wildlife. As a matter of fact, we specialize in going after the very last 03:16.1 of some of these exquisite animals. 03:19.2 So, among about 5500 mammal species, 03:22.2 almost a quarter of them are threatened, 03:25.1 and most of them are threatened deliberately with hunting, 03:28.2 but there's more than that. 03:30.2 Humans, it turns out, have commensal animals 03:33.3 -- our cows, horses, and sheep -- 03:35.3 are actually... 03:37.2 they dominate the biomass of the planet. 03:39.2 So, these are to scale in terms of the number of individuals 03:42.2 and their body mass, 03:44.1 so you see humans here and our livestock and pets. 03:47.0 Wild animals, on the other hand, 03:48.3 have just a tiny proportion of the total biomass 03:52.1 that dominates the planet today, 03:55.1 so that means there's little room for these wild animals, 03:58.1 because we consume most of the energy 04:01.3 on the planet. 04:03.3 The other thing that's happening is climate is changing. 04:06.2 So, this is a diagram of climate change 04:09.2 over the last 5 million years, 04:11.2 and you'll not they're changing scales as we go here 04:13.1 -- this is in millions of years and then thousands of years, 04:16.2 and then just the number of years before the present, 04:18.2 and then we finally move into the future over here. 04:21.0 So, what you'll see is that, in the last 5 million years, 04:23.3 the climates we're about ready to experience, 04:26.2 within the next 50-100 years, 04:28.3 are warmer than anything we've experienced 04:32.0 in our lifetime as a species, 04:34.1 and that any of the mammal species, for example, 04:37.0 that we're used to interacting with on the planet 04:39.0 have experienced in their lifetimes. 04:41.2 As a matter of fact, in the western US alone, 04:44.0 wildfires have doubled in frequency since 1988, 04:48.1 putting many people at risk for losing their homes. 04:55.1 Climate is also contributing to actual biome shifts. 04:57.3 This is a particular X-ray image 05:00.2 of the area around Pinnacles National Park, 05:02.3 showing that the trees that are standing there right now 05:06.2 are threatened with death in the near future 05:10.0 #NAME? 05:12.3 and blue, here, are the only healthy trees in this particular environment. 05:16.1 So in just a few years, 05:18.2 we're seeing a major shift 05:20.3 in where trees are present 05:22.2 and where trees are not present on the landscape, 05:24.2 simply because of climate, 05:26.3 and then the interaction between climate and things like 05:30.0 beetles, in particular, for trees. 05:32.2 We've lost a tremendous amount of forest cover. 05:36.2 The rate of loss has slowed down, 05:38.2 but that really doesn't matter in some ways, 05:41.2 because we've lost 05:44.3 a vast amount of many of these forests 05:47.1 in just the last 14 years 05:51.0 around the world. 05:54.0 Humans, in fact, are really good at causing habitat loss. 05:57.1 We can do this... 05:58.2 basically go out... 06:00.0 this is like hunting for trees... 06:01.1 we go out and we just take them down. 06:04.2 We transform ecosystems in radical ways. 06:07.2 This is an image of what 06:09.3 New York used to look like before we actually 06:12.2 built up the city 06:14.2 next to what the place looks like now. 06:15.2 And clearly there's no way for biodiversity, 06:18.1 at least most biodiversity, 06:20.1 to thrive in an environment that's so human-dominated. 06:24.1 In fact, if you look at the sum total of the terrestrial land on the planet, 06:28.2 we have used and coopted about 51% of the land 06:32.2 area just for our use, 06:34.1 mostly for production of food for ourselves 06:36.2 and our commensal animals. 06:38.3 If you look at this, you'll see that the only places 06:41.1 that we haven't really occupied 06:44.1 and we haven't transformed 06:46.0 are the hard to reach places 06:47.2 -- the Sahara Desert, the Congo, 06:49.2 the Amazon, 06:51.0 two of the places that have the largest 06:54.2 tropical forests left in the planet -- 06:56.1 and the boreal forests and the tundra region. 06:59.2 So we've taken all the easily farmable land in the world. 07:03.2 Now, we need to basically farm this land we already have co-opted 07:08.0 more efficiently 07:10.1 in order to feed the coming mouths. 07:13.2 One of the things that matters a lot 07:15.2 when you think about how much of the land 07:17.3 we've actually changed on the planet 07:20.2 is that just by this simple rule, 07:22.2 this is one of the fundamental rules in ecology, 07:25.2 is that the number of species 07:28.1 is a function of the size of the place they occupy. 07:31.3 This is a rule of island biogeography, 07:34.2 and so here what we see across the x axis 07:36.2 is the size of the island, 07:38.1 these are the islands in the Caribbean, 07:40.2 and then number of species on the y axis, 07:43.0 and so the larger the island is 07:45.3 the more species are found on the island. 07:49.3 More area means more species. 07:52.2 Here you see an image 07:55.0 for different continents on the planet 07:56.3 and the number of amphibians. 07:58.1 So, even on a continental scale, 08:00.3 we're finding that larger areas 08:03.2 mean more species. 08:06.2 So, when you look at the amount of land 08:09.1 we've actually set aside to be protected on the planet, 08:12.3 it amounts to only 13% of our land surface. 08:15.2 So, even though we've co-opted 08:18.2 the function of 51%, 08:20.1 we've only actively set aside 13% of this to be protected, 08:24.1 and areas like Yellowstone National Park, 08:26.1 the world's first national park, 08:28.1 as you can see, 08:30.1 are isolated from all the other protected areas in North America. 08:35.2 So what these patches mean 08:38.0 is that we don't have a lot of connectivity 08:40.2 between our protected areas. 08:43.2 That exacerbates our attempts at conservation, 08:46.3 because animals like to move 08:49.1 to deal with different environments. 08:51.1 As the climates change, 08:52.2 they like to move to novel environments. 08:54.2 This is Yellowstone National Park, 08:57.1 seen from Earth Observatory, 08:59.1 and what you see is a nice long line there 09:02.1 showing you the division between 09:04.1 the forest service land on the west 09:06.2 and national park land on the east. 09:09.3 And what you'll see is clear-cutting 09:15.2 defines, now, the western border of Yellowstone National Park. 09:17.1 This is true for many of the protected areas of the world. 09:20.3 There's not a lot of buffer 09:23.1 for the animals that want to move away from Yellowstone 09:25.2 to a part of the landscape 09:28.1 that they can adjust to. 09:31.1 It's not just the transformation of habitat 09:34.0 that matters either; 09:35.2 it's that our transportation system itself 09:38.2 has disrupted a lot of these corridors of connection. 09:41.2 This slide, which is really spectacular 09:44.1 at showing how much of the landscape 09:46.3 we cut up with our transportation, 09:49.2 shows that... 09:51.2 in green you see the global roads, 09:53.3 you see in yellow our urban areas, 09:56.0 in blue you see our shipping routes, 09:58.2 and in white you see our air networks. 10:01.1 So it's not just on land, 10:03.0 it's not just what we've kind of transformed in terms of deforestation... 10:06.1 it's the roads we've built, 10:07.2 it's the number of ships we send across the ocean, 10:10.2 and it's the number of planes that fly in the sky, 10:12.3 all of which interrupt and threaten 10:16.2 animals that need to move across this landscape. 10:20.0 Species move to follow their habitats 10:22.2 and they've done this in the past. 10:24.1 This is in fact one of the first signs 10:26.2 of adjusting to climate that we see, 10:28.3 and the black dots, here, you see, 10:30.3 are data from the Pleistocene, 10:32.2 showing that these animals used to be present 10:36.2 greater than 10 thousand years ago, 10:38.0 somewhere between 10 and 20 thousand years ago, 10:39.2 at these parts of North America, 10:41.3 and as climates warmed 10:44.2 at the end of the Pleistocene 10:46.3 into what we call the Holocene, 10:48.1 which is the last 10 thousand years, 10:49.2 this species, the Northern Bog Lemming, 10:51.2 moved to the north, 10:53.3 and now you see its range occupying 10:56.2 the orange part of this figure. 10:58.2 So these species just responded 11:01.0 by moving pole-ward as climates changed. 11:03.2 This is a very typical response 11:06.0 among animals of the world, 11:07.2 that they move pole-ward as climates warm 11:10.0 and they move equator-ward as climates cool. 11:13.3 In fact, species are already moving north today. 11:16.3 There are examples of species 11:19.2 interacting with species that they don't normally see, 11:22.2 so southern species 11:24.2 are now starting to encounter species 11:27.1 from northern boreal forest or tundra regions, 11:29.1 and there are really interesting 11:32.1 and sometimes not very positive interactions 11:35.1 that result from those interactions. 11:37.1 They create new ecosystems. 11:39.1 So, these are animals just doing what they need to do 11:43.0 and challenging us, too, 11:44.2 in thinking about what is natural, what is pristine, 11:47.2 and what we should expect in the future. 11:50.1 So, I already said that animals are on the move 11:53.1 and what that means is that 11:55.2 they need to find areas that they can colonize, 11:57.3 where they can live. 12:00.1 And it turns out that this fundamental rule of island biogeography, 12:03.2 that includes more... 12:05.2 larger area means larger number of species... 12:08.1 it also includes a concept of connectivity. 12:11.2 So, the closer these islands or these populations 12:15.0 are to each other, 12:16.1 the more likely they are to maintain more species. 12:18.3 So, what you see across the x axis 12:20.3 is the number of species present, 12:22.3 and this is the rate of extinction shown in red 12:26.3 and immigration, shown in blue. 12:28.1 And so when the populations 12:31.3 are far from the mainland, 12:33.1 there are many fewer species 12:35.1 that can be maintained, 12:36.1 and when they're close to another population 12:40.0 they can maintain more species. 12:41.3 Likewise, when the island area is small, 12:44.1 it maintains very few species 12:46.2 compared to when the islands are large. 12:48.3 So it's this equilibrium, 12:51.0 it's this balance between these rates 12:52.2 that really matters, 12:54.3 and we have to think about this in moving into the future. 12:58.1 So really what that means is biodiversity 13:01.1 is threatened even in protected areas, 13:03.2 and it's threatened surely by overexploitation, 13:05.2 by hunting, deliberate poaching, 13:08.0 but it is also threatened by ecosystem transformation. 13:11.2 Protected areas don't preserve entire ecosystems, 13:15.0 and so the transformation of what's happening outside the protected areas 13:18.1 matters to the species that live within it. 13:21.1 Novel species are interacting with disease 13:25.0 and bringing new diseases into places 13:27.1 that they haven't yet been because they are responding to climate change 13:30.2 and other sources of environmental transformation, 13:33.3 and that means that the connectivity between these protected areas 13:39.0 is very important. 13:40.1 So, finally, the thing that's really pushing all of this is climate change, 13:43.3 and that's what's very important 13:46.1 to consider going into the future. 13:48.2 Now, one of the things that happens as populations 13:51.1 get fragmented 13:53.1 is that their population size, the animals' population size, 13:56.2 starts to decline. 13:58.3 And extinction, the loss of a species forever on the plant, 14:01.2 is just when population size goes to zero. 14:04.2 So, here we see amphibians, birds, mammals, 14:07.2 and many other species, 14:09.2 and these are all animals that are threatened somehow with extinction. 14:13.0 There are animals shown in black 14:14.2 that are completely extinct in the wild. 14:16.3 There are animals shown in these warmer colors 14:19.2 that show different kinds of threats to their systems, 14:23.0 whether they're facing eminent extinction 14:25.1 or whether their populations are threatened. 14:28.2 And so, all this is to show is that 14:31.3 there are many animals, many... over... 14:34.2 you know, thousands of animals that are threatened with extinction 14:37.3 because of population demise. 14:41.0 In fact, global population numbers of wildlife 14:45.0 are 50% of what they were 14:47.1 just in 1970, 14:49.1 so animals of all types 14:51.1 -- birds, fish, reptiles, and mammals -- 14:54.0 are showing really large declines 14:56.2 in the number of populations 14:58.2 that are on the planet, 15:00.2 just the number of individuals of these species 15:03.1 have declined by half. 15:06.0 I want to give you an example of what this means. 15:08.1 So, this is the Iberian lynx, 15:10.1 it's found in Spain, and this animal, in 1900, 15:13.1 was occupying most of Spain. 15:15.2 And you can see its demise through the '60s, the '80s, 15:18.1 and in 2010 there are two populations remaining, 15:24.0 one with 73 individuals and the other with 173 individuals. 15:28.2 So, not only have we lost populations, 15:31.1 and clearly we've lost individuals, 15:33.0 we're just down to a couple hundred of these lynx. 15:36.2 And what does that mean? 15:38.1 It means that they've gone through what we call a population bottleneck, 15:42.1 and I'll explain what that means to the species in just a second. 15:46.1 In particular, what we see is that as population size declines, 15:50.2 so, as we decrease population size, 15:53.2 we actually decrease genetic diversity as well, 15:56.2 and so in general the larger the population is 16:00.0 the more genetic diversity will be maintained in that population. 16:03.2 And why do we care about population diversity? 16:06.3 We care about population diversity 16:08.2 because that's the toolkit that species have 16:11.2 to move into the future. 16:13.2 So, if we... you know, 16:15.1 if we kind of look at this in a little simulated model, here, 16:18.3 if you think of every one of these marbles, 16:20.2 these different colored marbles, 16:22.2 as some sort of a... 16:24.2 different kinds of a... 16:26.1 a genotype of some sort, 16:28.2 we start with a lot of genetic diversity 16:30.1 and then you just grab a few of these marbles, 16:32.3 you're going to get a bottleneck. 16:35.2 There's no way you can get all of this diversity 16:37.2 if you decrease the number of marbles 16:39.1 that you've pulled out of the system. 16:40.2 That's called a bottleneck. 16:42.3 You can recover, you can recover in numbers. 16:45.1 You can actually start reproduction 16:47.1 of this particular hypothetical species, 16:51.0 but you can't recover the initial genetic diversity, 16:53.1 because it takes so long, 16:55.1 in evolutionary time, 16:56.2 to accumulate. 16:58.0 So not only are numbers of individuals important, 17:00.3 but it's important to retain those individuals 17:02.3 as long as possible 17:05.1 to maintain genetic diversity. 17:07.1 Genetic diversity is a toolkit for adaptation. 17:11.2 Here's a great example. 17:13.1 These are the wolves of Isle Royale. 17:15.1 They've been studied for over 50 years, 17:17.1 it's the longest study of a predator-prey system 17:20.1 that we know about. 17:22.0 Wolves colonized this island 17:24.2 in Lake Superior in the 1940s 17:27.2 and they bounced around, 17:28.2 there's a pretty close relationship 17:30.2 between wolves and their moose prey, 17:32.3 where there's kind of a dynamic between the two of them. 17:37.2 There's been some severe winter declines in moose 17:41.1 and then that affects the wolves in some way. 17:44.1 There's been a particular canine parvovirus 17:47.1 that caused a large crash in the number of wolves, 17:49.2 and every one of these diamonds 17:51.2 shows you that there was a winter bridge to the mainland 17:55.1 that wolves could colonize across, 17:57.2 and so the population 18:00.3 was continually being rescued. 18:02.3 You see now that there aren't very many of these colonization events 18:06.3 and in fact the wolves are in decline. 18:11.2 And not only are they in decline, 18:13.1 but because they are losing their genetic diversity, 18:17.2 abnormalities in this population 18:20.0 have increased dramatically. 18:22.0 So, for example, these particular abnormalities 18:25.1 in their spinal column... 18:27.0 in Isle Royale, their incidence is about 1 in every 3, 18:31.2 and in a normal population 18:34.0 it would just be about 1%. 18:36.1 What this means is... 18:38.1 you can see in this last wolf here, of these three... 18:41.0 these are the last three wolves remaining on Isle Royale as of 2015, 18:46.1 and this last wolf has a shortened tail, 18:49.1 it's slightly twisted, 18:51.1 and his back... he looks like he has scoliosis. 18:53.2 They think that this is the pup of these two, this pair, 18:56.3 but these are the last three left, 18:58.3 and clearly this wolf has been affected by inbreeding. 19:04.2 So, there is this possibility 19:08.2 to rescue populations 19:10.2 by bringing in some kind of new individuals 19:13.2 to a population, 19:15.0 and that indeed is what happened to the Florida puma. 19:16.2 So, in the mid-1990s, 19:20.3 puma were brought in from Texas, 19:23.3 and what you see in terms of the population size, 19:25.2 which was on decline, 19:27.2 is that they basically started breeding more frequently, 19:30.2 and so the population really bounced up in individuals, 19:34.1 but there was also a rescue of genetic variation. 19:37.3 The eight Texas puma... 19:40.3 you see before this time, 19:43.0 there's hardly any variation, 19:45.2 and after that time there's an enormous increase 19:48.2 in the amount of genetic variation in this population, 19:51.2 suggesting that there's been genetic rescue 19:54.1 just by adding eight individuals 19:56.2 from another healthier population. 20:00.0 Small populations, then, 20:02.1 to kind of summarize this part, 20:04.1 small populations 20:06.2 tend to result in inbreeding, and so... 20:09.1 and the reason is because it brings out 20:12.0 the recessive deleterious genotypes. 20:15.3 In this case, you'll see this lineage 20:19.1 showing this recessive allele 20:21.1 that doesn't get expressed in the offspring 20:24.1 because there's always this dominant allele, 20:26.3 this large A, 20:28.2 that is overprinting it. 20:31.1 When there's inbreeding, 20:33.0 you have the opportunity to produce an individual 20:36.2 that has both of these recessive alleles, 20:39.0 and what that means is that 20:40.3 these deleterious phenotypes 20:43.0 then become expressed. 20:45.3 Okay, so what are these recessive deleterious alleles? 20:49.2 What do they result in? 20:50.2 What's the problem with inbreeding? 20:52.2 It turns out that inbreeding creates 20:56.1 a pretty typical list of problems with many animals: 21:00.0 their faces aren't symmetrical; 21:02.2 they have reduced fertility, 21:04.1 and this is true both in terms of the number of offspring that they produce 21:11.0 and also whether their sperm are even viable; 21:12.3 there are many genetic disorders, including Down's syndrome, 21:14.2 that show up in animals; 21:16.3 they have a much lower birth rate; 21:18.1 higher infant mortality; 21:20.3 and because they have a slowed growth rate, 21:23.1 they also reach a much smaller adult size; 21:26.2 and then most importantly, perhaps, 21:28.2 in this changing world 21:30.1 is that they really lose a lot of their abilities 21:33.0 to respond with their immune system. 21:36.0 So, I want to point out... 21:38.0 here is an example in tigers, 21:40.1 these are white tigers... 21:42.2 white tigers, for those of you who don't know, 21:44.1 white tigers are not Siberian 21:45.2 -- they look like they should be, 21:47.1 they have this white coat -- 21:48.2 it turns out they're completed created in zoos. 21:51.1 White tigers are actually Bengal tigers, 21:53.2 they're from India, 21:55.1 and they've been highly inbred in zoos 21:57.1 because people like white tigers. 21:59.2 But it turns out the white coat 22:01.2 is also associated with the same gene 22:06.0 that creates cross-eyes in the individuals, 22:10.0 so it crosses the optic nerve, 22:12.2 and so every white tiger that you see 22:15.1 is cross-eyed. 22:16.3 And you can see this other tiger, here, 22:18.3 with a severely misformed face and a very asymmetrical face, 22:23.0 he has a cleft palate, 22:24.3 he has a lot of problems. 22:26.1 This animal could not survive in the wild. 22:30.1 So, to conclude, 22:32.2 I just want to really underscore that 22:35.1 humans dominate the planet. 22:37.3 Populations of wild animals and species of animals 22:40.3 are threatened with extinction -- 22:43.1 they're in decline. 22:44.2 What does that matter? 22:46.1 Why does that matter? 22:48.0 Declining populations lose genetic diversity. 22:50.2 They're more likely to lose all those tools 22:53.1 that they need to adapt to whatever the future 22:56.0 is bringing to us. 22:57.2 And then, importantly, 22:59.2 the connectivity between these populations, 23:02.1 the ability for these animals to move 23:04.2 and find a new home, 23:06.2 is increasingly getting more and more difficult. 23:09.1 That's critical for their survival. 23:12.1 So, what I want to do is conclude 23:14.2 by saying thank you to all of 23:17.1 the former and current members of my lab, 23:18.3 all of my collaborators, 23:20.1 the funding agencies I've had through the years, 23:21.3 and Stanford University.