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  • Prof: Now today I am going to talk about biodiversity

  • and whether or not it's something we should be worried

  • about, and how to think about things

  • like the extinction crisis which is being caused by human

  • activity.

  • And I don't want you to forget this extremely simple idea here,

  • that the impact of humans on the environment basically is a

  • function of how many people there are on the planet,

  • times the average amount that each of those people consumes,

  • multiplied perhaps by some fudge factor to express good or

  • bad behavior on the part of the humans.

  • And I think that the Greeks probably could have written that

  • down 2500 years ago.

  • It's pretty straightforward.

  • It's nothing that is particularly surprising.

  • Nevertheless it is striking to me that this half of the

  • equation, the upper half of the equation,

  • which is the population problem,

  • has pretty much disappeared from public discourse on this

  • issue, and I think it's a result of

  • pushback from various groups that see any discussion of the

  • population problem as inevitably involving contraception or

  • abortion, which for some groups has

  • religious issues.

  • And it's also a pushback from the poor countries of the world,

  • against the rich countries, saying,

  • "You can't come down here and tell us what to do after

  • you've all gone and screwed up your own environment.

  • Let us get on with our own lives, and that's not our

  • priority."

  • Nevertheless, in the long-term,

  • that's true.

  • The impact of humans on the environment of the planet is

  • basically a function of how many people there are on the planet

  • times how much they're using.

  • And we can't get away from that.

  • You will find in the literature on things about biodiversity

  • problems, extinction problems, an awful lot of fairly refined,

  • scientific analysis.

  • You will find people applying cutting edge ecological theory

  • to the issue.

  • But, by way of introduction, I never want you to forget that

  • the problem of human impact on the other species on the planet

  • is not a problem that we can really solve with scientific

  • research.

  • We can only solve it by understanding the incentives

  • that people encounter to have more babies,

  • or fewer babies, and the incentives that they

  • encounter to consume more or to consume less.

  • This is a really tough nut.

  • If any of you think this is simple, just think of what's

  • going on in the global financial crisis.

  • The people of the world are trying to stimulate consumption.

  • They're desperate not to be poor.

  • And that flies right in the face of the environmental

  • catastrophe.

  • I don't think there's any easy answer on that.

  • Yes Blake?

  • Student: People are interested in

  • >.

  • Prof: Right, Bob Wyman teaches a class on

  • population growth.

  • By the way, let me just take one of Bob's slides,

  • which he shared with me recently.

  • If you go around the planet and you ask people how many babies

  • do they want, good sociological research

  • indicates that they want about two-thirds of what they actually

  • get.

  • And that suggests that the easiest way to solve the

  • population problem is not to do anything Draconian,

  • but just to give every woman on the planet control of her own

  • reproductive fate; by whatever means.

  • Okay, I just wanted to make sure I got that message across

  • up front.

  • Now today I'm going to discuss extinctions, and I am going to

  • do it from ecological, economical, evolutionary and

  • personal points of view.

  • And within the ecological literature this is an old

  • chestnut, and basically back oh say about

  • thirty to fifty years ago there was intuition that suggested

  • that the more diverse an ecosystem was the more stable it

  • would be.

  • And people like stability, they don't like to be hit by

  • surprises, and so diversity would be good because it

  • conferred stability.

  • Then Bob May showed that more diverse communities can be less

  • stable.

  • That's not a necessary logical connection, that more diverse

  • things are more stable; sometimes more diverse

  • communities are less stable.

  • Since then there have been a lot of experiments.

  • There isn't a convincing clear pattern.

  • More recent theory shows that sometimes diversity can increase

  • stability.

  • This one seems to be a moving target,

  • and I think it's one where we have to be modest and say that,

  • "You know, in any particular circumstance

  • we don't really know what would happen."

  • Stability itself is a fairly abstract term,

  • and it can either refer to resistance,

  • which means ability to remain in the same state,

  • or to resilience, which means ability to return

  • to the same state following a perturbation;

  • so bending without breaking.

  • And that is probably more important in the real world.

  • Okay?

  • Now, what do we actually know experimentally about what

  • species diversity does to ecosystems?

  • Well there's some evidence, by the way, that most of this

  • data has to do with plants, or plants and insects.

  • A richer community appears better able to survive a

  • drought.

  • That is probably because the plants in interaction with each

  • other are actually conserving water locally.

  • If you look at net primary productivity,

  • as you increase the number of plant species,

  • the productivity, in terms of kilograms of carbon

  • fixed per square meter per year goes up and then levels off;

  • so there's diminishing returns.

  • But the more different kinds of things,

  • at least at the beginning, that you pack into a given

  • space, because they're partitioning

  • the environment differently the more they're going to be able to

  • take out of the sunlight and the C02 and the water that's in the

  • system, and convert it into

  • biologically useful materials.

  • There's some evidence that as you increase the number of

  • species in the community, the harder it is for an

  • invasive species to get into that community.

  • So these kinds of things are done usually in fairly simple

  • experimental gardens.

  • And I think that the application of that to the real

  • world I have to remain agnostic on;

  • it might work, it might not.

  • Recently there was a very nice paper--

  • this in the Proceedings of the Royal Society this year--

  • showing that more diverse pollinator communities provide

  • more reliable service.

  • So this X axis here is proportion of native vegetation,

  • and this is the number of pollinator individuals,

  • and this is again proportion of native vegetation and number of

  • visits.

  • And basically what it's showing is that the more diverse the

  • pollinator community, the more likely it is that the

  • plants in it are going to get pollinated,

  • because the different kinds of pollinators are complementary,

  • they're trading services as they come in.

  • And this connects a bit to ecosystem function,

  • because after all one of the things that Mother Nature gives

  • us in agriculture is the services of the pollinators.

  • And if we didn't have them, the almond industry and the

  • apple industry of the world would collapse.

  • So if we do things that wipe out the pollinator community,

  • or radically simplify it, this paper suggests we can

  • expect that we're going to have a decrease in our fruit and our

  • nut crops.

  • So a few ecological points about diversity is that it does

  • seem to improve some ecosystem properties.

  • There's some evidence that connects species diversity to

  • resilience and to resistance to invasion.

  • Not too many people who have been working in the ecosystem

  • function end of science have been terribly worried about the

  • diversity of individuals in genes;

  • they've been looking mostly at species diversity.

  • But it may very well be that if you have say a group of

  • pollinators and you look within a single species and you compare

  • very genetically diverse species of pollinators with very

  • genetically homogenous species of pollinators that the genetic

  • diversity may also have a significant impact.

  • So there are a whole series of levels at which one can ask the

  • diversity question, and not all of them are equally

  • well researched.

  • Now let me just go back to the ecological view of diversity

  • here and make a general comment on it.

  • One of the arguments that conservation advocates use is

  • that biodiversity is important for ecosystem function.

  • And I'm now about to go into an argument on ecosystem function.

  • Okay?

  • And it's about how much it's going to cost us to replace

  • those services.

  • And I'm just setting a pointer here,

  • because I'll come back in a few minutes and point out that if

  • you claim that you need a lot of biodiversity to maintain clean

  • air, clean water,

  • pollination services, everything that Nature gives us

  • for free, but if Nature is really

  • redundant, so that you could actually get rid of 90% of the

  • species on the earth before you even noticed any decrease in

  • ecosystem function, that you are then involving

  • yourself in a political argument which is quite dangerous;

  • and that is that you appear not to know what you're talking

  • about.

  • Because your critics could come back year after year saying,

  • "Oh, we've lost another 10% of the species on the planet

  • and the ecosystems are still functioning just fine.

  • You're just crying wolf."

  • Until, of course, you get down to the point where

  • you've trimmed away so many that the next ones really do make a

  • difference to ecosystem function,

  • and then we're all in deep water.

  • So there is a real problem here of being able to communicate to

  • the general public, and the politicians,

  • the issue that you could have a lot of ecosystem redundancy,

  • which is buffering you from the extinctions that might otherwise

  • be affecting ecosystem function, but at some point,

  • if you've eliminated a lot of species,

  • you will hit a limit at which there's no redundancy left,

  • and at that point ecosystems start to collapse.

  • So let's now go through the economic argument,

  • and you'll see how much it might cost to replace things.

  • So there have been attempts, mainly by Bob Costanza and his

  • group-- he's now at the University of

  • Vermont-- to estimate what is the value

  • of ecosystem function.

  • And before we get into Costanza's, we can look at

  • something like Habitat II.

  • So Ed Bass decides twenty years ago or so to build a very

  • futuristic architectural piece out in the Arizona desert,

  • which is an attempt to see whether or not you could

  • actually build an interstellar spacecraft with a self-enclosed,

  • completely recycling ecosystem, such that people could go in it

  • and there would be everything in it that people would need to

  • live forever.

  • So if you just make one of those things and put it out into

  • space, potentially humans could colonize other galaxies.

  • It's a very bold idea, right?

  • So it costs 9 million per person, and if we wanted to

  • replace the earth with that, you could figure that it's

  • about 54 thousand-trillion to replace- to support everybody on

  • earth, to get them to another galaxy.

  • Unfortunately Habitat II didn't work.

  • >

  • So it wasn't complete, and the people who went in it

  • and tried to live in it had to bail out after about six months.

  • So this line of reasoning, which by the way is always

  • going to end up with very big numbers, is basically a comment

  • on externalization; and externalization is

  • economics talk for things which are not my problem,

  • thank you.

  • So they are basically what we define,

  • in our approach to the problem, as being outside the scope of

  • the problem and outside the scope of our ability to come up

  • with a solution.

  • And I think you'll see that some of these things need to be

  • internalized.

  • So the issue of externalization is that in economics it means

  • it's not captured by the market.

  • So it's not something whose consequences,

  • whose costs, are reckoned into market

  • calculations.

  • So what Costanza and his crew did was they tried to calculate

  • the marginal value of ecosystem services,

  • and they just took the present value of the service and then