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.