An Interview with Dr. Peter Raven, director of the Missouri Botanical Garden:
Biodiversity extinction crisis looms says renowned biologist
Rhett A. Butler, mongabay.com
March 12, 2007
Biodiversity is the basis for ecological services that range from water filtration to food production to carbon cycling, and are worth tens of trillions of dollars per year. However, despite this importance, biodiversity is increasingly threatened. Human activities are fast diminishing the hotbeds of biological richness—rainforests, wetlands, coral reefs, and grasslands—and risk turning the planet into a biologically impoverished place. The implications for mankind could be quite serious. Ecologists warn that by extinguishing biodiversity, we risk our own quality of life, gamble with the stability of climate and local weather, threaten the existence of other species, and undermine the valuable services provided by biological diversity.
For these reasons biodiversity loss ranks among the top concerns of biologists. While there is considerable debate over the scale at which biodiversity extinction is occurring, there is little doubt we are presently in an age where species loss is well above the established biological norm. Extinction has certainly occurred in the past, and in fact, it is the fate of all species, but today the rate appears to be at least 100 times the background rate of one species per million per year and may be headed towards a magnitude thousands of times greater.
Dr. Peter H. Raven at the Missouri Botanical Garden. Photo by M. Jacob.
Raven says that we have already seen exceptionally high rates of species loss starting around 40,000 years ago when modern humans first started expanding into previously uninhabited parts of the world. In a paper  co-authored with Rodolfo Dirzo of the Universidad Nacional Autónoma de México, Raven noted that all of Australia's megafauna went extinct shortly after the arrival of mankind on that continent some 40,000 years ago, while in North America about 71 percent of mammalian genera were lost within 2,000-3,000 years of man's setting foot in the New World. Raven and Dirzo observed that in both North America and Australia the species that disappeared had previously survived worse episodes of climate change and "the selective loss of large animals, in what is geologically and evolutionarily a very short period, strongly suggests the causal role of humans in this wave of extinctions." In this and other papers, Raven has also pointed to the disappearance of more than 1,000 species of birds in a 1,000-year period following the colonization of Pacific islands by humans. He says that ongoing research, which is identifying additional extinct species, is pushing the toll even higher. Places like Hawaii and modern-day French Polynesia lost more than 80 percent of their endemic species. Raven adds that "first contact" extinction is a common theme throughout the world in locations ranging from Madagascar to New Zealand.
Current IUCN data show that habitat loss is the leading threat to most endangered species, followed by direct exploitation (hunting and collecting), then the introduction of alien invasive species. To date, IUCN data do not reflect the impact of climate change, although this factor is expected to be an increasingly important source of biological stress to ecosystems and species. Raven suggests that climate change could "rival or exceed" habitat loss in its impact on biodiversity.
Future Extinction Projections.
Predicting the future is difficult, and forecasts for species loss are particularly contentious due to the large number of unknowns. How much habitat will remain in 50 years? How many humans will inhabit the Earth this century and how will their affluence affect per capita resource consumption? What will be the impact of climate change? The questions continue ad infinitum. Even such basic questions such as "How many species exist today?" remain unanswered.
Species area math
The species-area curve is a power function that is used to calculate the number of species in a given area, which can then be applied to estimate how many species go extinct when habitat is lost. Since the relationship is logarithmic, a 10 percent reduction in habitat does not result in a 10 percent extinction of species. Depending on the types of organisms involved, the model forecasts roughly a 10 percent to 20 percent extinction of species for a 50 percent reduction in habitat, whereas a 90 percent reduction in habitat would produce a 50 percent extinction rate.
Globally, there has been roughly a 50 percent decline in tropical forest cover since its recent maximum extent. This suggests an 18-20 percent rate of extinction among species. While our knowledge is still spotty, scientists have not yet been observed this loss of species. Why is this?
First, we know very little about the vast majority of species on Earth. Raven says that we have basic information on probably less than one-sixth of the world's species, so most of the species that are disappearing have never been documented. This doesn't mean they are not important.
Second, species extinction, like climate change, has a lag time. Species continue to persist in forest fragments, often for decades, but prior habitat loss has sealed their fate. Small populations are at particular risk of extinction due to a number of factors including reduced genetic variability from inbreeding and vulnerability to catastrophic events. For a species living in a single isolated habitat, all it takes is a single disease outbreak, fire, or bad winter to wipe it off the face of the planet. Raven notes that research indicates an average species half life of 50 years (range: 25-75 years), meaning forest fragments can be expected to lose half their species in 50 years and around three-quarters within a century. These "living dead" may include long-lived species, like some species of primates and trees, where habitat perturbation might not be evident for tens or even hundreds of years. This phenomenon suggests that protection of remaining forests in such areas might not be enough to prevent extinctions caused by past habitat loss.
The bulk of future extinctions are forecast to occur in the world's so-called biodiversity hotspots, areas with high numbers of endemic species that have already suffered large-scale habitat loss and are threatened by burgeoning population growth. Norman Myers, an Oxford University biologist who has figured prominently in conservation literature over the past 20 years, pioneered the concept of biodiversity hotspots when he identified 25 such places covering 12 percent of Earth's land surface . He found that these were home to 44 percent of vascular plants and 35 percent of terrestrial vertebrates—a discovery that provided leverage for conservation initiatives. The 16 of these hotspots characterized by tropical forest have already lost an average of 90 percent of their forest cover. Species-area math predicts that this depletion alone would result in the eventual extinction of 50 percent of the endemic species in these areas.
If present rates of forest loss continue, Raven projects that extinction rates from habitat loss alone will reach 1,500 extinctions per million species per year, a significant increase from today's rate of around 150, and nearly a 60-fold increase from the rate of roughly 26 between the years 1500 and 2000 . Assuming there are 10 million species on the planet, this translates to an annual loss of 15,000 species, most of which will be small and poorly known. Among better known organisms, notably plants and mammals, Raven forecasts a heavy toll. He estimates that 565 species of mammals and at least 500 species of birds will go extinct within the next 50 years; he also notes that these are conservative numbers and that individual populations are at even greater risk.
Not without hope
Despite the bleak outlook, there is still time to save biodiversity, Raven says. In fact, he argues, now is the best time to act, since global biodiversity is further reduced with each passing moment.
Dr. Peter H. Raven at the Missouri Botanical Garden. Photo by M. Jacob.
As director of one of the world's leading botanical institutions, the Missouri Botanical Garden, Raven also argues that promoting interest in nature among children is absolutely critical for a future where ecological issues will be of increasing importance. He speaks from experience; as a 15-year-old, he discovered an unknown species of tree growing in San Francisco's Presidio area, which amazingly was a species represented by only a single plant. He went on to join the California of Sciences at a time when environmental issues consisted of whether or not to throw trash out the window, and the Sierra Club was oriented towards recreation rather than conservation and environmental issues. He says environmental problems—from climate change to biodiversity loss—will provide unparalleled challenges and opportunities for today's youths.
In March, 2007, Raven elaborated on his research and his thoughts on the extinction crisis in an interview with Rhett A. Butler of mongabay.com.
QUESTIONS & ANSWERS WITH DR. PETER RAVEN
- What do you see as the greatest threat to biodiversity?
- What about the impact of climate change in the tropics?
- Are we any closer to knowing whether we're losing hundreds of species per year or hundreds of thousands?
- What are your thoughts on the Wright and Muller-Landau paper?
- What is your outlook for biodiversity?
- What can be done to help poor farmers in developing countries help protect biodiversity?
- How can conservation efforts be improved?
- What about preserving biodiversity in human-dominated landscapes?
- Could "market mechanisms" make a big difference in conserving the world around us?
- What is the role of the Missouri Botanical Garden in conservation and environmental education?
- Have you seen much progress in biodiversity research efforts in recent years?
- How can the next generation of scientists be to address some of Earth's problems?
- Do you have any advice for students interested in pursing careers in science and/or conservation?
- What can the general public do at home to help?
- Can you explain what originally lead you to pursue your remarkable career in biology?
- What's your favorite place to visit?
- What's your outlook for Madagascar?
Mongabay: What do you see as the greatest threat to biodiversity?
Extinction projections are a serious question. Recently I've been looking at birds, since they are relatively well-documented compared to other groups of organisms. Logically 25 percent of birds could be extinct by the end of the century, although being birds we estimate that half of those may not actually become extinct because people will undertake extreme measures to try to save them.
The 25 percent extinction forecast for birds is a lot lower than the half to two-thirds of all species on Earth that we've predicted are either likely to be extinct or will be reduced to populations so small that they will be on the way to extinction by the end of the century.
Birds, in general have wider ranges and are more mobile that other species, allowing many of them to escape some forms of habitat destruction. However we do know that large numbers have gone extinct in the past. For example in the islands of the Pacific, more than 1000 species went extinct over the last 1000 to 1500 hundred years. We discuss this in detail in papers (2000 , 2006 ) I co-authored with Stuart Pimm of Duke University and others.
My feeling, which we haven't really had the chance to rework and review, is our forecast that half of all species becoming extinct or being on the way to becoming extinct by the end of this century is still a modest and quite reasonable projection.
Most of the projections that have been made about extinction have been made on the basis of habitat loss and island biogeography relationships alone. It's obvious now that there are three other factors that are helping to drive species toward extinction.
First would be alien invasive species, including disease and pests that may be introduced. For example, of the plant species in the United States thought to be on edge of extinction 40% of are so threatened because of invasives.
Second there's selective hunting and gathering of species. Bushmeat hunting in Africa is one of the better known manifestations of this, but it really goes on all over the world. The targeting of plants with medicinal properties has been augmented in recent years by rising demand for herbal medicines and supplements in China, Japan, Europe and the United States. Demand for these plants is driving exploitation in distant countries.
Third is climate change, which is potentially as devastating or more devastating than habitat destruction. One article in Nature^ estimates that climate change could drive a million of the world's species to extinction as soon as 2050. On a local level, specific papers have been written about South Africa and Australia, indicating very clearly that habitats here today won't exist after further climate change.
We've already warmed the climate an estimated 0.8 degrees Celsius since pre 1750 levels, and the existing buildup of carbon dioxide and other greenhouse gases will pull that up to 1.5 degrees Celsius even if no further burning of fossil fuels occurs. At 2-2.5 degrees Celsius it is anticipated that we will hit great tipping points that we haven't had to contend with yet but will make warming all the more worse.
In the United States, climate models predict that alpine and sub-alpine habitats will be exhausted in the lower 48 states during the course of this century. While you can't logically project the outcome for every species whose habitat is disappearing, it seems likely that many will have a very tough time adjusting to temperature change. Further, if you factor in shifts in precipitation patterns and potential inundation of coastal areas the outlook is not promising for biodiversity.
Mongabay: What about the impact of climate change in the tropics?
Raven: Climate change is the tropics is a big concern since that's where the bulk of biodiversity resides. Tropical moist forests are especially at risk since changes in rainfall distribution could fuel drier conditions that leave them susceptible to forests fires. We are already seeing this in the Amazon and Indonesia, particularly on the island of Borneo.
Mongabay: This era, characterized by mounting biodiversity loss, has been widely cited as the "Sixth Great Extinction" and some big numbers, in terms of annual species loss, have been put forward based on species-area math, but do we have any better idea of the magnitude of current species loss? Are we any closer to knowing whether we're losing hundreds of species per year or hundreds of thousands?
In a paper published in Nature (2000), Pimm and Raven draw up three scenarios of how species extinctions in tropical forests may unfold due to forest clearance. Curve a is the extinction curve on based current estimates, not taking into account biodiversity hotspots. Curve b assumes that biodiversity hotspots are cleared in the next decade to the point where only currently protected areas are saved. Curve c shows species loss if all remaining habitat in hotspots is saved.
Mongabay: Have you seen the Wright and Muller-Landau paper which argued that deforestation will slow mid-century, resulting in more moderate rates of species extinction? What are your thoughts?
Raven: The vast majority of people in the field pretty well discount what they said. Wright and Muller-Landau  argue that population growth will slow down and cutting will be alleviated, but if you consider the fact that the global footprint of humans is rising then this is a tough argument to swallow. Globalfootprint.org does a good job of explaining this. It estimates that we are currently using 120% of Earth's productivity, meaning that we're using more than what Earth can sustainably produce. This has climbed from about 70% in 1970, so it's risen rapidly.
|Wright and Muller-Landau projections||
Forest cover in Africa (2000): 31-35%
Projected cover in Africa (2030): 18-28%
Projected extinction in Africa (2030): 16-35%
Forest cover in Indo-Malaya (2000): 39%
Projected cover in Indo-Malaya (2030): 33-39%
Projected extinction in Indo-Malaya (2030): 21-24%
I see it as sort of conventional nay saying and I don't think there's any real factual basis for their assertions, which are pretty optimistic. We certainly hope their forecasts are true, but we need to work under the assumption that it's not since biodiversity loss is irreplaceable. There's never anything wrong to saving as much as you can.
Mongabay: What is your outlook for biodiversity? Are there reasons to be hopeful? Is the situation improving or are we only hastening the demise of other species?
Raven: The reason to be hopeful is that people are paying more attention to biodiversity for a variety of different reasons. One is that people know that biodiversity is the primary way we capture energy from the sun, so anything said about biomass or productivity of that kind will somehow tie into biodiversity even if we don't fully understand how at this time. All of our food, with very small exceptions, comes from plants in one form or another. A great proportion of our medicines come from natural products -- about one quarter of all drugs in the United States are derived from plants.
As all of those matters become more evident, I think more people will see the critical importance of biodiversity. It is already evident in the targets set for by the U.N. Millennium Development Goals and we are even seeing religions getting involved as they realize that impoverished biodiversity is bad for the poor. Both Evangelical Christian and Jewish leaders, for example, issued statements that last time the Endangered Species Act in the United States was up for grabs, while various religious groups have called for action on climate change.
The blue anole, a threatened species on Isla Gorgona. Photo by Thomas Marent
One point I like to emphasize is that now is the best opportunity we have to take action. The longer we wait, the fewer choices we have and the more we lose. The sooner we act, the better, because we'll be able to preserve more for enjoyment, use and the ecological services afforded by biodiversity. There's everything to be gained by saving as much as possible and nothing to be gained by ignoring the problem. The sheer logic of the situation will drive people to increasingly reasonable behavior.
Mongabay: OK, so it's clear what we have to do in places like the United States, but what about the poor farmer in Brazil, Ghana, or India? What can they do if they are struggling just to feed their family?
Raven: People are seeing natural communities as being more valuable than they once did for the services they provide and because of the relationship to traditional lifestyles. But from economic standpoint, a positive outcome hinges on our ability to become a kind of global society.
Threatened species in the United States according to IUCN 2006
Another positive development is the apparent jump in philanthropic interest in dealing with the world's problems. The Gates and Buffet gifts are spectacular examples of this. The more people realize the impact of individual action, the more likely we will be able to preserve the world in a relatively rich and diverse, rather than a completely depleted, condition.
Mongabay: Since the 1970s tropical deforestation and loss of other important ecosystems has only increased despite increasing prominence and more funding for conservation efforts. Using that narrow definition, one could say that conservation has failed. Going forward, how can conservation efforts be improved and what can be done to protect biodiversity globally?
Raven: The traditional approach to preserving biodiversity by conserving still holds because by protecting land in the face of knowing so little about most kinds organisms, you're preserving many more kinds of organisms than you could if you were just working with specific ones, like birds for instance. Protected areas are still probably the best and most comprehensive strategy. However the problem is that none of the three factors that I see as driving the demise of global biodiversity - namely global heating, alien invasives, or hunting and gathering of specific kinds of plants and animals -- really respect protected areas. Further, as the climate changes protected areas will not be able to shift due to surrounding urban areas and agricultural zones. This makes them all the more susceptible to the impact of climate change, whether it is rising sea levels, a dip in precipitation levels, or warmer temperatures.
Countries with the highest percentage of threatened species [(extinct+endangered+vulnerable)/(total assessed species-data deficient species)] derived from IUCN 2006 data. The United States ranks sixth at 41 percent, New Zeland ninth (34%), Madagascar tenth (34%), Australia fourteenth (32%), and Japan 31st (23%).
We need to figure out social justice and how to take care of people all over the world -- alleviating poverty, providing clean water and combating disease -- all the things that go into improving the state of human beings or there won't be any room to preserve biodiversity.
Mongabay: What about preserving biodiversity in human-dominated landscapes, so-called "countryside biodiversity"?
Raven: Michael L. Rosenzweig, Professor of Ecology & Evolutionary Biology at the University of Arizona, pointed this out well in "Win Win Ecology". He argues that only a small part of biodiversity can be preserved in parks but a lot more can be preserved in degraded landscapes if we make some special provisions. Gretchen C. Daily at Stanford University has also done a lot of work in this area. This is not a perfect answer but a peccary answer to conservation in the face of human dominance of the planet. It is certainly part of what we need to do. We have to realistic and opportunistic.
We also have to remember that the situation now is better than it will ever be in the future. By definition there is more biodiversity today than there will be tomorrow, a year from now or 10 years from now. The sooner we act the better.
I continually argue that opportunities for preserving biodiversity are very tightly linked with achieving global sustainability. You really can't save biodiversity without attending to the needs of people.
Mongabay: Could market mechanisms like carbon trading, better methodologies for valuing ecosystem services and biodiversity, and the elimination of market-distorting subsidies that reduce the true costs of logging and fossil fuel use make a big difference in conserving the world around us?
Raven: Absolutely. Not only carbon trading but higher taxes on fuel. We need leaderships from governments, though they themselves will never have the money to effect change all themselves. Their polices provide a context in which the private sector and individual people operate. Today corporations control far more money than governments and face less constraints in implementing policies. Actually in the U.S. we're see a lot of positive signs from corporations on these issues.
Mongabay: What is the role of the Missouri Botanical Garden in conservation and environmental education?
The Japanese Gardens at the Missouri Botanical Garden in springtime. Photo by J. Jennings
The Missouri Botanical Garden's Climatron with water lilies and Carl Milles sculptures in the foreground. Photo by J. Monken
Mongabay: You have long called for more research into biodiversity and then the development of mechanisms to manage it. Have you seen much progress?
Raven: We know a lot more than we did back when I really first called for increased funding for biodiversity research as Chairman for the Committee on Research Priorities in Tropical Biology at the National Research Council in 1979. There's been a lot of progress in understanding how forests and other natural communities work. Of course we only know a tiny fraction what could be known.
Mongabay: Among the generation of students just now embarking on careers, do you see much interest in science or are potential scientists being lost to more "commercial" pursuits like technology and complex finance? How can the next generation of scientists be inspired to begin to address some of Earth's significant problems looming in the immediate future?
Hands-on learning for the next generation of conservationists
Mongabay: Do you have any advice for students interested in pursing careers in science and/or conservation? What about people who don't have science backgrounds? How can they get involved?
Raven: In order to achieve global sustainability, we must all work together. Recycling, energy conservation, and all of the efforts that we hear about will help. People who pursue careers in science and technology in relation to conservation will be able to help a lot, but it is basically conservation practiced by everyone throughout the world that is going to get us where we want to go.
Students should know that there are wonderful efforts in conservation and science related to conservation, where huge contributions will be made, and where there's a great deal of room for innovative people, whether on the theoretical or scientific end of matters, or on the application of what we know: just getting "out there" and doing good things building towards sustainability.
Mongabay: What can the general public do at home to help?
Raven: In places like the United States where we use twice as much energy as anyone else except Australia, but don't have an improved standard of living because of it, we can both win great improvements for conservation and save a lot of money for ourselves by embracing a more sustainable lifestyle.
Anything that can help improve sustainability will help biodiversity.
Mongabay: Can you explain what originally lead you to pursue your remarkable career in biology?
Raven: Getting interested in nature and science at an early age was the key. At the age of 14 my family moved to the Presidio in San Francisco, which gave me great opportunities for exploring Golden Gate Park. I soon became involved with the student section of the California Academy of Sciences, My first real interest in conservation began on a trip to Colombia as a doctoral student at UCLA, then in 1962 the debate over the effects of DDT really opened my eyes to these issues. At Stanford University in the mid-1960s a couple of us started to worry about the impact of human population growth. Eventually, in 1968, Paul Ehrlich wrote his famous book The Population Bomb.
Mongabay: Over the course of your distinguished career you have traveled widely. Is there a particular experience or place that expresses why you feel the way you do about biodiversity?
Raven: I think in some ways South Africa has the most remarkable accumulation of plant species of anywhere in the world because so many things there have radiated so explosively and wonderfully. However, the plants in California are about as spectacular as you find anywhere in the world in the sense that their ranges are so narrow and they are so different from one place to another. California has many endemic species that are so beautifully adapted to the Mediterranean summer-dry climate
I like lots of different kind of plants and lots of kinds of nature. Madagascar is an extremely interesting place. It's about the size of California but with twice as many species -- 90 percent of which are found nowhere else
Mongabay: I completely agree with you on Madagascar. Seems like things are looking up there from a conservation standpoint.
Raven: We have about 50 people in Madagascar -- all of whom are Malagasy, with only two or three exceptions. We've trained most of them and they are doing a fantastic job.
Ranomafana National Park in Madagascar
Mongabay: Yes, It really is amazing to see how much biodiversity is left when you consider how much forest has been cut down. It kind of makes you wonder what it was like before.
Raven: We're working on a catalog of the plants of Madagascar and there are two amazing facts: one is that in every group we work with there are about 50 percent more kinds than have been recorded, all the missing ones are new species. The second point is that while many species are very restricted in range we have been able to find virtually all of them still alive even when we look back on herbarium specimen that were collected 100 or 150 years ago.
We are concerned over the potential impact of climate change. To my knowledge nobody has really done a climate model for Madagascar specifically.
More on Peter Raven
Peter Raven is currently director of the Missouri Botanical Garden in St. Louis, Missouri and an adjunct professor of biology at the University of Missouri-St. Louis. He has been bestowed at least 17 honorary degrees from various universities around the world and has been awarded over 100 other honors including the National Medal of Science presented by President Clinton. Raven has served on the President's Committee of Advisors on Science and Technology and, mostly recently, co-chaired the Scientific Expert Group on Climate Change and Sustainable Development for the United Nations Foundation (UN Foundation) and Sigma Xi, the Scientific Research Society. Raven has authored award-winning textbooks and written hundreds of peer-reviewed papers.
- Dirzo, R. and Raven, P.H. (2003). Global state of biodiversity and loss. Annual Review of Environment and Resources, November 2003, Vol. 28, Pages 137-167
- IUCN Redlist (redlist.org)
- Myers N, Mittermeier RA, Mittermeier C, da Fonseca GAB, Kent J. 2000. Biodiversity hotspots for conservation priorities. Nature 403:853—58
- Pimm, S. L. and P. Raven. 2000. Extinction by numbers. Nature 403: 843-845.
- Pimm, S., P. Raven, A. Peterson, C. H. Sekercioglu, and P. R. Ehrlich. 2006. Human impacts on the rates of recent, present, and future bird extinctions. PNAS 103, 10941-10946
- Wright, S.J. and Muller-Landau, H.C. (2006) The future of tropical forest species. Biotropica 38, 287—301
- Thomas, C.D. et al. 2004. Extinction risk from climate change. Nature 427, 145—148.
- IUCN Redlist (redlist.org)