Stuart Pimm couldn't imagine studying nature without being involved in saving it. Now a professor of conservation biology at Duke University, he is an expert in mass extinction.

As a teenager, he loved watching birds. To pursue his passion for ornithology, he went to Oxford, and later to New Mexico State University, where he earned his Ph.D. Then he went to Hawaii in the late 1970s, for a six-month period of fieldwork, where he wanted to see all the bird species that were supposed to be there at that time. The bird species became by then so rare that he could not find them. Some were already extinct. An enormous sense of loss enveloped him.

Although Pimm was publishing papers in esteemed journals such as Science and Nature, he was haunted by the nightmare of what would happen 40 years later—that is, now. He wanted to make sure that other parts of the world didn't go the same way.

It also became a profound spiritual issue for him: “What kind of stewards (of nature) are we going to be?”

He determined to use his science to prevent further extinctions and went from being an academic ecologist to an active conservation professional. He felt nothing is more important that handing the planet off to our children and grandchildren in at least as good a state as we inherited it.

Possibilities for his work opened up with a chance phone call from Michael Soulé in the early 1980s and invite for a meeting on conservation biology. Michael Soulé is a professor emeritus of environmental studies at the University of California at Santa Cruz, and the founder of Society for Conservation Biology. “Michael really brought everyone together on this,” says Pimm.

During his travels and work, Pimm once spent a summer in Kashmir, and also heard tigers in India, but hasn’t seen them yet. “Wouldn’t it be an awful tragedy for India, if the only images of tigers were the photos of the dead bodies laid out in front of Victorian Englishmen?”

All along, he has spent his life understanding the process of extinction—the what, where, why, when, and how of extinction of species. Not only that, but also how to protect species in the face of extinction.

As an academic ecologist, he has been involved, for the last 20 years, in studying the distribution, extinction, and ways of protecting plant and animal species. He and his colleagues published a paper on that in the journal Science in 2014. The paper, an advanced study of the work that had begun much earlier, states that “current rates of extinction are about 1,000 times the background rate of extinction.” He says human actions are driving species to extinction about one thousand time faster than normal.

He is not a fan of the phrase “sixth mass extinction” for “it suggests it’s like the previous five mass extinctions—and it isn't. Most importantly, there are things we can do to prevent it.”

The five mass extinctions are end-Ordovician, end-Devonian, end-Permian, Triassic-Jurassic, and end-Cretaceous. The normal background rate—the rate of extinction in the earth's history before humans came along—does not take this big five “episodic” events into account.

As an active conservation professional, Pimm started an NGO called SavingSpecies that works with local NGOs to stop the extinction of endangered species, raises funds for them, and launches restoration projects. The organisation has projects in the Florida everglades, Brazil, Madagascar and Columbia.

Pimm says by knowing what species are endangered and where they are, the conservation community can intervene and save species. In an email conservation, he lays out the grim details of extinction, and how conservation can help ward off the extinction. He offers hope in the face of continuing loss of species.

How did you arrive at the normal background rate? What was your methodology?
We have three types of data. The fossil record provides direct, but limited, evidence. By tracking when species first appeared and disappeared in the fossils, the average ‘life span’ of species and its chance of extinction can be calculated. Unfortunately, fossils are often only identifiable to the genus level, so it is only known how long a group of species existed, rather than the individual species that make up the group.

We also analysed molecular phylogenies: evolutionary trees inferred from DNA sequence data. Such information is now increasingly accurate and available for many groups of species. The pattern of the lengths of branches in the trees contain information about the rate of extinction. Since relatively young species have had less time to go extinct, a disproportionately small number of deep branches compared to the younger branches indicates that a substantial number of extinctions have occurred.

Finally, we analysed information how fast groups of species are diversifying—how much faster is speciation than extinction.

Combined, these sources suggest an extinction rate of one species per 10 million species per year. And, it’s against that number that we compare the present rates and find they are 1,000 times higher.

We still don’t know all the species on earth; all are not documented yet. How did you take that into consideration?
Simply put: we really have no idea how many species there are. Birds, mammals, yes, plants, we have a pretty good guess, but insects and fungi? Not a clue.

So, rather than trying to estimate how many species are going extinct per day—which depends on wildly uncertain estimates of how many species there are—we express things as a rate.  That’s a fraction of the species we do know per year. For example, background rates are one extinction per 10 million species per year.  Current rates are hundreds of species per million species per year.

What was the conventional wisdom years ago when you started looking into the this, and in what way does your work advance the knowledge of mass extinctions?
There seemed to be two schools of thought before. One was that 'all ecology is conservation'—well, clearly it isn't and conservation is much more than just ecology.

First, there are a lot of deeply interesting ecological questions. Some—how abundant species are, and what factors determine abundance—often have great importance when applied to rare species. But, a lot of ecological questions have far more tenuous application to real conservation problems.

Second, consider for example the work of Krithi Karanth, who did her Ph.D with me.  (She is now getting a lot of attention from the Indian media, for good reasons!) Krithi worked, in part, on looking at resettlement of people in Bhadra Wildlife Sanctuary. Resettlement is very controversial and has been done very badly in the past. Yes, we need people out of sanctuaries, whenever possible, so how can we do it in a way that is good for both people and tigers? Conservation, yes. Ecology, no.

The second was that conservation was a second class profession, not scientific enough, with poorly-defined problems, and mostly a matter of become an advocate. My international awards (Heineken, Tyler) have come from bringing rigorous scientific analysis to the topic of extinctions and how to prevent them.

What are the crucial elements of extinction going on now? Is it different from all the big five in the past, and in what way? What do past extinctions say about the present one?
In my Science paper last year and in a supporting article in Conservation Biology, my colleagues and I calculate two sets of numbers: how fast are species going extinct, and how fast should they would normally go extinct. We measure extinction rates as extinctions per one million species, per year. The numbers for birds, mammals and amphibians—the groups we know best—run 100 to several hundred extinctions per million species, per year. The normal background rate is close to one extinction per 10 million species per year.

So, human actions are driving species to extinction about 1,000  times faster than normal.

In what ways are humans contributing to the higher extinction rates?
In particular, we are destroying habitats, introducing species into places where they do not belong, hunting species, changing the climate.

You said this kind of loss of biological diversity hasn’t been seen in the last 60 million years, that is, end-Cretaceous. Could you give details of how and in what ways, this present extinction is similar to the end-Cretaceous one. In what ways is it different?
Well, if current trends continue for this century, then the total loss of species will be comparable to what happened at the end of the Cretaceous. Of course, unlike then, we do have the ability to prevent these mass extinctions. Incidentally, when we talk about the normal background rate of extinction, we exclude these episodic mass extinctions.

What is the role of climate change and global warming extinction?
I prefer the term ‘climate disruption’ for it’s more complex than just warming. Warming causes species to move to higher elevations. They may be able to do that, if there’s enough space, but they may not be and species' ranges may shrink. But, warming causes the sea level to rise—with catastrophic consequences for people and environments in low-lying areas, such as Bangladesh. And glaciers are melting, changing river flows and causing a lot of complex ecological changes.

Could you describe ecological changes that you have seen or experienced?
Well, there are species that I’ve seen that are now extinct, or in some cases, now survive only in zoos. When it comes to climate, I know from my own fieldwork that I’m seeing species higher up mountains and further north than they were 50 years ago.  And migrant birds arrive earlier in the spring—and flowers bloom earlier.

You have projects in the Florida everglades, Brazil, and Columbia. Could you talk about India: the extinction, loss of species and biodiversity, and what could be in store for India?
There are two classes of species that are on the verge of extinction. The well-known ones are species like the tiger: large-bodied species that take up a lot of space, have large geographical ranges, and which are often hunted or killed when they come into conflict with us. The great majority are species with very small geographical ranges. They are very vulnerable to habitat destruction. One of the most important places for such species is the Western Ghats.

What should we do to stop mass extinction?
For the wide ranging species, such as the tiger, we need to find ways to prevent human-wildlife conflict. I’m not involved in this in India, but I know many people who are. My friend Ullas Karanth and Krithi Karanth, who is also his daughter, are good sources.

India has exceptional numbers of people living in or near national parks. Can we encourage them to live elsewhere? That’s a hugely difficult and controversial topic, but where India has both examples of doing it well and doing it badly! Through National Geographic’s Big Cats Initiative, I’m involved in funding lots of successful approaches to minimise big cat-human conflict.

Second, there’s the problem of poaching. Tigers are worth far more to India living—for people to watch—than ground up as traditional medicines. Poaching is not easy to stop.

For species with narrow ranges, it’s very much a matter of protecting habitats. Much of the Western Ghats has been deforested. We need to protect these areas. Importantly, we need to connect isolated patches of remaining habitats, because such patches lose their species quickly. This is what my group does: we fund local conservation groups to connect, protect and restore (CPR) land. We’ve done projects in four countries now, but not yet in India.

What are the biggest challenges now?
I think the biggest challenge is to find out what works and what doesn’t. The answers may not be the same in all places. All conservation in local and— from my visits to India, I know about the extraordinary cultural diversity there—what works in one place may not work in another. SavingSpecies has an excellent model that is very effective in the places where we’ve applied it. We haven’t tried it everywhere! And our most important insight is that it's always a matter of helping local groups do what they can. I can’t come to India to tell Indians how to conserve biodiversity.  But I can help colleagues who live in these places with ideas and money.

Why should people care—busy and harried as they are with day-to-day life and so on—about mass extinctions that happened so far back and even the present one? Most people in developing and poor countries need food first, and they don’t care for loss of biodiversity.
It’s never as simple as food versus biodiversity. The poorest people in the world live amid biodiversity—they often depend on it in a much more direct way that rich people do. The question then is can we find ways to give people an alternative, more sustainable future than one which destroys the world around them?

I’ve scores of experiences in South America, Africa, Madagascar, where by carefully discussing the issues with local communities, we can find solutions. Tigers are worth a lot to India; so are the forests in which they live; so are the medical plants that can be collected from them, and so on.  How can we best manage the conflicting needs?

Why is biodiversity important to our everyday life? What does it do for us whether one is rich or poor?
There are three reasons to care about biodiversity: spiritual (or ethical, or religious), aesthetic, and economic. Most societies care—we do not wantonly destroy nature and often revere the natural world. Second, species are essential icons in our culture; elephants and tigers in India are obvious examples. And third, biodiversity has both direct and indirect benefits.

So yes, people gather resources from nature both on land and from the water, a direct benefit. By keeping hillsides forested, one protects the land against erosion. Less directly, the burning of tropical forests worldwide puts as much carbon dioxide into the atmosphere as all cars and trucks. That causes the loss of land in Bangladesh and elsewhere that is so alarming.

Often people, especially politicians, talk about development and environment as opposed binaries. It’s a kind of zero-sum game. Could you please talk about development, and what you think it is? Politicians and others nearly always talk like this in isolation from practical examples or, when they do quote case studies, manage to botch what they teach.

The Incredible India advertising campaign shows the great importance of ecotourism in the minds of those who develop it. (And this is in a country that has unrivalled cultural appeal to travellers.) Ecotourism is not only important in terms of the money itself, but because it often helps the poorest sector of many tropical countries—the rural poor. It’s money that goes (or should go) to the right places.

Second, when, for example, India dams the rivers in the Himalayas, as obvious an example of development as one can imagine, whom does it benefit? Does it help the people who live in the area?

Perhaps, but close inspection of many ‘developments’ often show their costs and benefits to be decidedly complex. All too often it’s the rich that benefit and the poor who do not.

A lot of deforestation worldwide (though I cannot talk of India) displaces the people who have lived there traditionally often benefitting only corrupt large landowners who then acquire title to land. My work often has to do with making sure people benefit, or at least are not harmed, by having biodiversity nearby.

Finally, the work we do at SavingSpecies often finds that the best use for land can often be to protect for nature. Around the world, a lot of land is simply bad land—cleared for bad reasons, too poor for grazing—and the best economic use of it is to soak up carbon dioxide from the atmosphere.