EEB 122: Principles of Evolution, Ecology and Behavior?

Lecture?31. Why So Many Species? The Factors Affecting Biodiversity

https://oyc.yale.edu/ecology-and-evolutionary-biology/eeb-122/lecture-31

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.?I'm going to discuss?extinctions?from ecological, economical, evolutionary and personal points of view.?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.?

• 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. 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.?What do we actually know experimentally about what species diversity does to ecosystems??

• The?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.

• As?you increase the number of plant species, the net?primary productivity, in terms of kilograms of carbon fixed per square meter per year goes up and then levels off; so there's diminishing returns.

• 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.

• Recently there was a very nice paper shows?that more diverse pollinator communities provide more reliable service.?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.

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.

• There is a real problem 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.?

Let's now go through the economic argument.?It costs 9 million per person to?replace the earth?54 thousand-trillion?to support everybody on earth?to get them to another galaxy,?which?is basically a comment on externalization.?Externalization is?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.?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.?

• The kinds of things that people identify as ecosystem services, and certainly among them nutrient cycling, waste management, water supply, food, the regulation of the atmosphere, the regulation of water on the landscape, flooding.

• The oceans are actually doing about twice as much as the land, and the estuaries are providing a tremendous amount of ecosystem services. People?concentrate their living right around estuaries.

• If you look at what are the important parts of the continental land masses, the wetlands and the forests are extremely important parts; although you can't really say that the grasslands are unimportant, they're still providing about a trillion a year in ecosystem services.

Back in 1997, the marginal value of total planetary ecosystem services was about 33 trillion. That was about four times the U.S. GDP at that time. Of course the U.S. GDP is greater now, but I'll bet you that the replacement costs for what Nature gives us for free are bigger now too.?

And that's an estimate of how much the global economy is essentially externalizing the costs of environmental impact, and environmental services. It's an estimate of the global magnitude of the tragedy of the commons, which is that we all individually want to take and use services, but our individual behavior is eroding the environment for the community.?

This economic view has been criticized; it's been criticized for bad economics and it's been criticized for bad ecology. Mother Nature is still providing us with goods and services of enormous value, which would be impossible for us to replace if we had to.?

What would an evolutionary biologist say??

• Every tip on the Tree of Life has been on the planet for 3.5 billion years, and they've all managed to make it this far. You can't really derive any kind of morality about who has the right to dominate and who has the right to take over the resources of the world from that.?It's just a neutral pattern.

• Because it is increasing our quality of life, and our gross domestic products, and our gross planetary product, it gets spun as being necessary for standard of living and economic growth. So that would be an evolutionary point of view.

• And if we can ever actually behave nicely to other species, then that would be a profound victory of culture over biology. The extinction crisis, and the meaning of biodiversity on the planet, is an interesting probe into our own nature and our own priorities.?

Now the personal point of view, it was captured in this book that my wife and I wrote, and I'd like to tell you a little bit about why we wrote it and the sort of lessons that we've learned from it. So that's the name of the book, and this picture is in it. Peter Raven and Ed Wilson had managed to move the biodiversity crisis up to a fairly high level.?

• The causes of biodiversity crisis aren't in Nature, they're in human economic and reproductive behaviors.?And biological research isn't going to change human behavior. Human behavior can only be changed by education, economic, demographic policy, and by shared values that determine policy.

• The long-term solution requires a reduction in birthrates and radical changes in consumption. However, starving, insecure and repressed people kill each other, they destroy the environment, they drive species to extinction.

• So the political challenge is to figure out a way to make people comfortable, secure and free. And that is a necessary precondition for long-term biodiversity stability.

• Scientists often claim they need more money for research, and they'll accept it if you make it available. Politicians can avoid unpleasant decisions by saying that more research is needed.?The research must not be used as an excuse for not taking action. Because we already know this: there are too many people. Some of them, mostly in the developed world, consume too much, and both conditions must change.?

So, because of this, there are lots of conflicts; we can't reach agreement and we don't agree in that. So how do you change value systems? How do you get people to agree? How do you shift balance? And I thought at that point that it might be good just to show how people emotionally react to the process of watching a species go extinct. And Bev and I got together.?

So to summarize these different points of view.?

• If you just take the scientific point of view. There are some advantages in some experiments that show biodiversity is a good thing, but results are mixed, and if you just review all of the biodiversity stuff, on ecosystem function, you have to come away honestly and say, "Well, it's a mixed bag."

• The economic view is that the services would be very costly to replace, but how they depend on diversity is not clear; so that's because we don't know the redundancy in the system and we don't know when we hit the critical point.

• The evolutionary view is that all living things are related, but there isn't any natural value in diversity. The evolutionary or purely scientific point of view would be that there is no value in Nature; so, you know, whether the planet's dead or alive actually doesn't make any difference.

If we then place a human value on diversity, for cultural reasons, as we saw with the gibbons, or in our own culture. Basically what that does is we are placing a human value on something, and we've won the battle, and now our value system, which is our own homo sapiens value system of one kind or another?is being placed on the rest of the planet. So some people spend to exploit the planet; some people spend to conserve it.?

So what is the origin and justification of values? This interesting case of the biodiversity crisis causes us to confront that rather deep and personal question. And when you encounter people who are actively engaged in the conservation movement and environmentalism, I think you actually have to ask, "Are the values that they're deploying really something that is general and that you can derive for all people at all times, or is it simply an expression of their personal taste?" I happen to love orchids and porpoises and so forth. Other people like to eat porpoises. We're both human beings.?