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This week’s claim that the species extinction crisis is overblown is a sham

Headlines in newspapers and websites blared out the headlines this week: “IPCC wrong again: species loss far less severe than feared.” (IPCC is the Nobel Prize winning international group that assesses climate change and its consequences.) “IPCC’s species extinction hype fundamental flawed” it continued.

“Species extinction rates wildly overstated” went other headlines.

“The International Union for the Conservation of Nature (IUCN) “Red List” of endangered species — a benchmark for policy makers — is now also subject to review” went another, quoting the two authors of a paper that appeared in this week’s journal of Nature.

The paper’s title was emphatic enough: “species-area relationships always overestimate extinction rates.”  With modesty, they told the media that it had taken eight years of hard work to come to that stunning conclusion.

It took me eight seconds to know the paper was a sham — and I am slow reader. So let me explain why this paper fails so obviously to get at the truth. Along the way, I’ll tell you about those “species-area relationships.”

“Species-area relationships” are about predicting how many species will survive in “forest islands” like these in the coastal forests of Brazil. When forest is cleared, some species will be killed off immediately because they lived only in places that now lack trees.  But many more will die slowly, because the patches of forest that remain are too small to hold populations viable in the long term.  Photo:  Stuart Pimm

 

First, the Red List. The Red List compiles a list of species that are threatened with extinction. Some species are already extinct and some survive only in zoos. Others range from being critically endangered — often meaning only  a handful of individuals — though “endangered,” “vulnerable,” “near-threatened,” to those “of least concern.”

Go to your nearest zoo and look at the labels on the exhibits to see examples!

There are rigorous criteria for deciding into which category a species should fall. Many thousands of experts around the world evaluate the species they know and decide into which class each species should fall.

What do this have to do with those, species-area relationships?”

Absolutely nothing. The authors’ remark was entirely gratuitous.

The authors didn’t present any estimates of how many species are likely to go extinct, making their media claims particularly egregious in other ways.

Scientists have long studied why endangered species got that way. There are very many causes, but a very important one is the loss of habitat.

The less area of habitat, the fewer species it will contain. That’s the “species-area relationship” at the core of the problem.

To see that there’s more than one relationship, imagine your favourite patch of woodland. I’ve selected Rock Creek Park, just outside of Washington, DC, for my example. It was the site of the first National Geographic — National Park Service bioblitz a few years back.

How many bird species live there? Well, download the checklist from the National Park Service! It’s a large list, with four species of woodpecker, three species of owls, and many others.

Imagine this nightmare scenario. Suppose all the forest in eastern North America was cut — except Rock Creek Park. How many species would go extinct? There are several answers.

Suppose all those forests were cut within months — metaphorically “overnight.”  If you think that’s unlikely, consider how fast the world’s tropical forests are being cut!

How many species would be extinct “the following morning?” The answer is “not many” — because Rock Creek has many species.  That’s the number that the Nature paper calculates.  It does so with complex, mathematical formulas, and with considerable elegance.  That’s why it took the authors eight years.

It’s not the relevant answer, however.

How many species would eventually become extinct? The answer is very much higher.  The populations of the species that survived the initial deforestation elsewhere would eventually die out.

Those species are part of what scientists call the “extinction debt.”  They are the species that are fatally wounded, taking a while to die.  The populations are too small to be viable in the long-term.

One pair of (say) pileated woodpeckers or great-horned owls may have plenty of food in the Park. But, if one pair produces just one pair of young that survive to adulthood then you don’t need elegant mathematics to work out the answer.  There’s a 50-50 chance that both those young will be the same sex — both female or both male.

Even if they are different sexes, they will be brother and sister.

Simply, small populations suffer from the vagaries of sex and death and, on top of that inbreeding, that doom them in the long term.

 

The Florida panther became seriously inbreed when isolated from panther populations elsewhere.  It was in a slow decline toward extinction until rescued by the introduction of panthers from Texas.  Many endangered species have no such chances of being rescued.  Photo:  Stuart Pimm

 

Do we know how many species will die this slow death?  Well, yes!

Islands provide a model of small populations that get few, if any, immigrants that might rescue a foundering population.  There’s a species — area relationship for islands.  Many studies of the numbers of species on islands show that, for example, that if island “A” has half the area of island “B” then the former will have only about 85% of the species that A does.

Eastern North America tests exactly that prediction for “forest islands”.  By about 1870, it had about half the forest cover it had in 1620.  (Most of the forest had been cut, but not all at once.)  So, we expect 100 – 85% = 15% of the species to have become extinct according to this island species-area curve.  Apply that to the roughly 30 species of bird that live only in the forests of Eastern North America and one predicts 4.5 species will go extinct.

Four have.  And another one is endangered, which is in strikingly good agreement.

It was when the Nature paper used that as an example to hype its own results, by asserting that species area methods always failed that I knew it was sham.  The eastern North America example, in fact, is only one of a dozen or more studies from around the world that show how well the island species –area relationship works.

Wording matters. It always does.

In writing to me about the fuss his paper had caused, author Fangliang He, an ecologist at Sun Yat-sen University in China, said:

“I have followed up some of the media and felt there is a danger of misinterpreting our work, which I would like to clarify here. … All we have said is that the backward SAR is flawed and overestimates extinction rates, not anything more than that.”

Well, of course, that wasn’t what the paper said and it wasn’t what the authors said to the media. If the paper had had “backward SAR” in the title, the media wouldn’t have commented. And one wonders whether Nature would have published it.

I checked the websites that carried this story.  Most allow comment, except the ones in China.  Professor He had not bothered to provide them with the clarification he provided me.

 

 

 

Comments

  1. Roger Kitching
    Brisbane, Australia
    June 7, 2011, 5:56 am

    Well done, Stuart!
    Once again we see how seemingly innocuous and, presumably, well intentioned pieces of more or less fundamental scientific research can be picked up and misused by those looking for a wedge to drive into an environmental debate.

    What struck me on reading the paper – and trying to interpret it for my research group – is that the whole species-area business – which has a respectable lineage and important place within conservation ecology – is based on axioms of an equilibrium world and species that are neutral players. In other words given time from the formation of ‘islands’ (by whatever means) there will be a process of settling down, and interaction with a supposedly static world around them, then the forces of immigration and extinction will come into a dynamic equilibrium – this is the essence of the throry of island biogeography – BUT the theory says nothing about which species will be involved – like the much debated Neutral Theory of Hubbell, all species involved are entirely interchangeable. Any field biologist (perhaps any zoologist) knows this cannot be true. Particular species interact with others in non-random ways. Experiencing, with Stuart, the tigers of Nagarhole National Park, some years ago, it was obvious to me that the huge numbers of ungulates which had been allowed to recover since the Park’s establishment some years ago, were in turn supporting the healthy population of large predators in the area. Species are hostages to their own natural history – they do not and cannot exist in isolation. Whether this is true for rainforest trees remains moot – but the idea of neutrality cannot in my view be generalized. Returning to extinction, current islands (fragments) do not exist in a fixed world. The heterogenous environment of which they are a part is ever changing – in no small part through on going anthropogenic change. Add to that the sometimes very slow demography-driven processes that underpin ‘extinction debt’ and the very idea that we should interpret extinctions and extinction threats as if we were observing the equilibrium point of a process that had stopped, is clearly nonsense. Species-area curves remain an important idea in ecology. Within conservation biology they are a useful but essentially heuristic notion. As a guide to explanation for the current parlous state of the worlds biota, and potentially a guide to policy formulation, they are sadly lacking – as this latest paper has shown.

  2. [...] from the overestimation problem, for example Stuart Pimm who has responed quite strongly in a blog article. Also Chris Thomas, whose 2004 Nature paper was also among the culprits identified by He and [...]

  3. Barbara Livoreil
    Bangor University, UK
    June 4, 2011, 4:11 am

    Dear all

    First many thanks for reacting, fast and clearly. This is not always the case when inappropriate or biased papers are published by popular media… I wish scientists always had time to provide more information, clear and well argumented, to the general public…
    What is of paramount importance is our ability to get a “reply to” posted in Nature or whatever journal it is. And to do it as fact as possible.

    Then we have another problem. Readers get lost and confused, they see that scientists disagree among themselvles and do not speak one voice. DG Environment (Europe) told us several years ago how it made his life difficult when having to face pressure groups or people not eager to take nature into account.. So the question is, how coudl we improve this? Who made the decision in Nature to accept this paper? Was it peer-reviewed before publication, in which case this may have increased the chance of detecting the problem (by what %, this is another question).

    What is also interesting is the reply He sent to Stuart Pimm as he acknowledges the problem. This shoudl be published.. because at the end, you guys agree! there is a consensus rather than a controversy and actually.. things are rather clear. for everybody.

  4. Vicki Breazeale, Ph.D.
    pt reyes station, CA
    June 1, 2011, 2:42 pm

    I am so sorry that the editors of Nature decided to publish this study. However, academic freedom is a necessity. I published in Nature many years ago.

    The UN has declared that this the decade of biodiversity. We all need to help our inter-species friends as much as possible. They have lost habitat and the ability to travel to a new habitat due to corridor disruption. It is the time for all humans to become “Mother Nature” in whatever way they can in their local environment.

    Best regards,

    Vicki Breazeale

  5. Vicki Breazeale, Ph.D.
    pt reyes station, CA
    June 1, 2011, 2:39 pm

    Hello Stuart,

    Thanks for you work on behalf of biodiversity on Earth. I love nature and have kissed many species, including sharks, monkeys, slugs and tarantulas; they are all very gracious.

    Regards,

    Vicki

  6. Mark Thompson
    Prince George
    May 26, 2011, 12:52 pm

    My comment re-appeared on the nature site today. Perhaps it was a technical glitch? Nonetheless, I think that the ‘catchy’ title of the He & Hubbell paper is sensationalist rather than scientific. I take no issue with the stats presented by He & Hubbell – beyond the facts as Stuart points out that their publication used a simplified version of the species-area relationship that does not hold to the observed predictions. The paper blows everything out of proportion in its outlandish claim that the SAR methods ‘always overestimate’ extinction rates. I’m a measly grad student ecologists and I knew immediately that the statement was false. I’ve enjoyed reading Hubbell’s theories on the neutral theory of biodiversity, but what a mistake in this paper and the Nature editors should not have published it as it was worded.

  7. Mark Thompson
    Prince George
    May 26, 2011, 2:03 am

    I completely agree with you Stuart and there are other problems with the article. The publication in Journal of Herpetology by Malcom McCallum (2007) Vol. 41, No. 3, pp. 483–491 estimated extinction rates 211X background extinction rates and 25,039–45,474 times the background extinction rate if the threatened red list was used.

    Interestingly, I managed to log in and place a comment on the Nature news and article page related to this story. My comment was approved and appeared on Nature for a few hours. However, it has been removed since and they are not taking comments. It seems very strange. Here is what I posted:

    Dear Mark Thompson,

    The following post you wrote on the Nature website has been approved by the moderator:

    This is a highly unfortunate outcome for conservation science and not because of the great research that He and Hubbell just published. It is unfortunate because there is undue focus and attention on species loss as the core of our problems. Scientists have a responsibility to fix a mistake that has plagued conservationists for too long – our psychological myopia that overemphasizes priority toward unique species units over the common regularity that is inherent in biodiversity. The biodiversity crisis is not just about species, but the loss of ecosystems services via homogenization and ecological transformations stemming from human niche constructing behaviour and the ecologically destructive feedback loops this generates.
    It doesn’t take a grand calculation or an elegant formula to look at the evidence and conclude that there is a biodiversity crisis going on. An experiment in its most general sense is any measurement. Taking a moment to browse through G oogleEarth you can immediately gather data on the human footprint – you can measure the spatial extent of our land conversion from roads and other pieces of infrastructure that acts as an ecological sealant plus the added impact of forestry clear-cuts and agricultural lands. The species that lived in these spaces may very well remain in adjacent patches – in fact most species outside of the tropics are widely distributed and highly unlikely to go extinct under these circumstances. Still, however, this does not mean that there is no effect on the biodiversity. Biomass is diminished, trophic states are altered, and ecological services are diminished in scale. Perhaps researchers like He and Hubbell are so fixated on the complexity of the species problem that they are missing the obvious point to this biodiversity crisis?
    The problem is simple. If you have several billion salamanders of a single species regulating soil and wetland communities that are responsi ble for the recycling of nutrients through these ecosystems, for example, it matters if you reduce that species down to a few thousand individuals in scattered populations. The species still exists, but the functional regulations are diminished. Trophic cascades can in turn can lead to such things as reduced forestry yields or climate change via the decreased rates of nutrient flow and increased rates of heterotrophic decay releasing CO2 into the atmosphere. What difference does it make if the species still exists or not? It makes a huge difference social-ecologically to have diminished biodiversity in our human constructed environments. School grounds, for example, lack the complexity of nature and are most often stripped down to grass, pavement, and a few metal bars for kids to swing on. How on Earth can these children receive proper mental development without being inundated by the complexity of life? Where will their conservation ethics develop? This process of ecologica l apartheid separating communities from wild nature takes the wealth and capital of ecology out of the common wealth economy. This problem has very little to do with species extinctions and almost everything to do with population loss, not to mention the mass extinction of migration routes (http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0060188).
    The resilience of the system is what matters and we know that ecosystems have multi-dimensional and dynamic states that can fluctuate in the face of disturbance but shift once criticality has been exceeded. These ecologically resilient ‘phase-shifts’ tend to homogenize ecosystems, reduce global net or scalar levels of productivity, and diminish future resilience capacity as levels of human disturbance will not let up. I am firmly convinced that the notion of an endangered species as a conservation tool has had a devastating effect on conservation efforts – because it puts way too muc h emphasis on one piece of the biodiversity puzzle. Peter Kareiva and Michelle Marvier called attention to this in their 2003 article in American Scientist on “Conserving biodiversity coldspots” (http://www.bren.ucsb.edu/academics/courses/297-2S/Readings/Coldspots.pdf) and have followed up on the economic prioritization myth surrounding biodiversity hotspots. The mass of research and conservation funds are being directed toward the conservation and preservation of endangered species, which makes no sense in light of prioritizing the ecology of this problem. Ceballos and Ehrlich (2002) touched on this in their article in Science on “Mammal population losses and the extinction crisis”, where they stated:
    “Most analyses of the current loss of biodiversity emphasize species extinctions (3?5) and patterns of species decline (6?8) and do not convey the true extent of the depletion of humanity’s natural capital. To measure that dep letion, we need to analyze extinctions of both populations and species.”
    I would add that we also need to put the extinctions of migration and evolutionary potential into this equation as well. It is time for researchers who report on these issues to de-emphasize the species level connection. He and Hubbell attempt to do this by raising the importance of habitat loss. However, their statements on this seem inadequate because the underlying emphasis is still geared toward species loss. Researchers have a responsibility to properly report on the Anthropocene extinction by including the dynamic and hierarchical fabric of life into their reports. Extinction is more complicated and more rampant than is being reported herein and this is highly unfortunate.

    Thank you for contributing,

    -Nature editors
    >>>>

  8. Sorana Tarmu
    Jersey City, NJ, USA
    May 25, 2011, 2:03 pm

    I am an ecologist with experience in wildlife conservation policies. I have enthusiastically subscribed to Nature’s newsletters immediately after I have graduated, at the dawn of the Internet era. I realized eventually that the Nature publication doesn’t have any reverence to nature. This paper is a dire confirmation of my hunch.

  9. Greg Laden
    Twin Cities, USA
    May 23, 2011, 2:08 pm

    Nice analysis of the analysis, and I agree. They may have touched on an interesting statistical issue but not one that changes overall estimates of extinction rates. I blogged the paper here: http://tinyurl.com/3ehg8tv

  10. Roger Harris
    U S A
    May 23, 2011, 1:14 pm

    An incisive and well-thought out, and may I say, impassioned rebuttal of He and Hubbell’s Nature paper.

    When is it acceptable for scientists to abdicate scientific integrity and social responsibility to garner attention? Never, in my opinion. Already, the anti-conservationists and climate-deniers are busy citing He and Hubbell to dismiss any evidence of the dire consequences of “business as usual” for humankind.

    I believe this paper is the beginning of a new mindset, analogous to those of climate deniers but now applied to denying there is a problem with the decline of abundance and variety of species. I wonder if He and Hubbell are ready to defend that consequence of their work?