Too small to avoid catastrophic biodiversity meltdown

27 09 2013
Chiew Larn

Chiew Larn Reservoir is surrounded by Khlong Saeng Wildlife Sanctuary and Khao Sok National Park, which together make up part of the largest block of rainforest habitat in southern Thailand (> 3500 km2). Photo: Antony Lynam

One of the perennial and probably most controversial topics in conservation ecology is when is something “too small’. By ‘something’ I mean many things, including population abundance and patch size. We’ve certainly written about the former on many occasions (see here, here, here and here for our work on minimum viable population size), with the associated controversy it elicited.

Now I (sadly) report on the tragedy of the second issue – when is a habitat fragment too small to be of much good to biodiversity?

Published today in the journal Science, Luke Gibson (of No substitute for primary forest fame) and a group of us report disturbing results about the ecological meltdown that has occurred on islands created when the Chiew Larn Reservoir of southern Thailand was flooded nearly 30 years ago by a hydroelectric dam.

As is the case in many parts of the world (e.g., Three Gorges Dam, China), hydroelectric dams can cause major ecological problems merely by flooding vast areas. In the case of Charn Liew, co-author Tony Lynam of Wildlife Conservation Society passed along to me a bit of poignant and emotive history about the local struggle to prevent the disaster.

“As the waters behind the dam were rising in 1987, Seub Nakasathien, the Superintendent of the Khlong Saeng Wildlife Sanctuary, his staff and conservationist friends, mounted an operation to capture and release animals that were caught in the flood waters.

It turned out to be distressing experience for all involved as you can see from the clips here, with the rescuers having only nets and longtail boats, and many animals dying. Ultimately most of the larger mammals disappeared quickly from the islands, leaving just the smaller fauna.

Later Seub moved to Huai Kha Khaeng Wildlife Sanctuary and fought an unsuccessful battle with poachers and loggers, which ended in him taking his own life in despair in 1990. A sad story, and his friend, a famous folk singer called Aed Carabao, wrote a song about Seub, the music of which plays in the video. Read the rest of this entry »

Biogeography comes of age

22 08 2013

penguin biogeographyThis week has been all about biogeography for me. While I wouldn’t call myself a ‘biogeographer’, I certainly do apply a lot of the discipline’s techniques.

This week I’m attending the 2013 Association of Ecology’s (INTECOL) and British Ecological Society’s joint Congress of Ecology in London, and I have purposefully sought out more of the biogeographical talks than pretty much anything else because the speakers were engaging and the topics fascinating. As it happens, even my own presentation had a strong biogeographical flavour this year.

Although the species-area relationship (SAR) is only one small aspect of biogeography, I’ve been slightly amazed that after more than 50 years since MacArthur & Wilson’s famous book, our discipline is still obsessed with SAR.

I’ve blogged about SAR issues before – what makes it so engaging and controversial is that SAR is the principal tool to estimate overall extinction rates, even though it is perhaps one of the bluntest tools in the ecological toolbox. I suppose its popularity stems from its superficial simplicity – as the area of an (classically oceanic) island increases, so too does the total number of species it can hold. The controversies surrounding such as basic relationship centre on describing the rate of that species richness increase with area – in other words, just how nonlinear the SAR itself is.

Even a cursory understanding of maths reveals the importance of estimating this curve correctly. As the area of an ‘island’ (habitat fragment) decreases due to human disturbance, estimating how many species end up going extinct as a result depends entirely on the shape of the SAR. Get the SAR wrong, and you can over- or under-estimate the extinction rate. This was the crux of the palaver over Fangliang He (not attending INTECOL) & Stephen Hubbell’s (attending INTECOL) paper in Nature in 2011.

The first real engagement of SAR happened with John Harte’s maximum entropy talk in the process macroecology session on Tuesday. What was notable to me was his adamant claim that the power-law form of SAR should never be used, despite its commonness in the literature. I took this with a grain of salt because I know all about how messy area-richness data can be, and why one needs to consider alternate models (see an example here). But then yesterday I listened to one of the greats of biogeography – Robert Whittaker – who said pretty much the complete opposite of Harte’s contention. Whittaker showed results from one of his papers last year that the power law was in fact the most commonly supported SAR among many datasets (granted, there was substantial variability in overall model performance). My conclusion remains firm – make sure you use multiple models for each individual dataset and try to infer the SAR from model-averaging. Read the rest of this entry »

Ghost extinctions

5 07 2012

The Philippine bare-backed fruit bat (Dobsonia chapmani; body size = < 220 mm, < 150 g; IUCN status: ‘Critically Endangered A2cd’) is endemic to lowland rain forests [top habitat image] from Negros and Cebu islands. This species of flying fox had been missing from the 1970s and was declared extinct in 2002 (34). In May 2003, five specimens [one shown in the picture above] were trapped in night nets in the Calatong forest (Negros Island), a ~ 1,000-ha fragment of secondary rain forest and agricultural lands [bottom habitat image] (35). The species is reliant on fruit-bearing vegetation and caves for feeding and roosting, respectively. As with many other Philippine bats, it suffers from habitat degradation and hunting. The family Pteropodidae comprises > 150 species. Despite their Draculian look, they all feed on fruits and nectar, and act as important plant pollinators (36), as well as disease vectors such as Ebola virus (37). Flying foxes are distributed in the tropics and subtropics from the Eastern Mediterranean, through the Arabian Peninsula, Asia, Australia, and many islands of the Indian Ocean. Photos courtesy of Ely L. Alcala.

Jared Diamond (1) coined the expression ‘evil quartet’ for the four main human causes of species extinctions: habitat loss/fragmentation, overkill, introduced species and extinction chains [with climate change and extinction synergies (2), the updated expression would be ‘evil sextet”]. However, one third of ‘extinct’ mammal species has been ‘found’ again. Recent studies reveal that the probability of rediscovery depends on the cause of extinction.

Arriving in a city to search for an old friend, I would first look in the suburb where he lived, the pub where we enjoyed a drink and some music, or the park where we used to play football. But if my friend was an outlaw, or had recently gone through a traumatic experience, my chances of finding him at his favourite spots would shrink.

If, instead of a friend, we are searching for the last survivors of an extinct-declared species, surveys also tend to take place in the habitat in which the species was previously found. Such a strategy rests on the classical hypothesis that, given the spatial distribution of a species, its gradual decline must occur from the periphery to the core of its distribution (‘range collapse’) where, in theory, the habitat should be of better quality and the number of individuals higher (3). In contrast, recent work supports that the trajectory of demise of threatened vertebrates progresses from the core to the periphery (‘range eclipse’) (4), because many perturbations make their way as a progressive wave, e.g, fire, logging or urbanisation.

Diana Fisher (5) supports the ‘range eclipse’ hypothesis for ‘extinct’ mammals which have been rediscovered. She quantifies that 60% of the new records are made from peripheral habitats, mainly when the principal cause of extirpation is habitat loss. Not only that, on average species are rediscovered at altitudes 35 % higher than historical records, and only in 5 % of the cases at the locality where it had been last seen.

Read the rest of this entry »

Over-estimating extinction rates

19 05 2011

I meant to get this out yesterday, but was too hamstrung with other commitments. Now the media circus has beat me to the punch. Despite the lateness (in news-time) of my post, my familiarity with the analysis and the people involved gives me a unique insight, I believe.

So a couple of months ago, Fangliang He and I were talking about some new analysis he was working on where he was testing the assumption that back-casted species-area relationships (SAR) gave reasonable estimates of inferred extinction rates. Well, that paper has just been published in today’s issue of Nature  by Fangliang He and Stephen Hubbell entitled: Species–area relationships always overestimate extinction rates from habitat loss (see also the News & Views piece by Carsten Rahbek and Rob Colwell).

The paper has already stirred up something of a controversy before the ink has barely had time to dry. Predictably, noted conservation biologists like Stuart Pimm and Michael Rosenzweig have already jumped down Fangliang’s throat.

Extinction rates of modern biota in the current biodiversity crisis (Ehrlich & Pringle 2008) are wildly imprecise. Indeed, it has been proposed that extinction rates exceed the deep-time average background rate by 100- to 10000-fold (Lawton & May 2008; May et al. 1995; Pimm & Raven 2000), and no rigorously quantification of these rates globally has ever been accomplished (although there are several taxon- and region-specific estimates of localised extinction rates (Brook et al. 2003; Regan et al. 2001; Hambler et al. 2011; Shaw 2005).

Much of the information used to infer past extinction rate estimates is based on  the species-area relationship (e.g., Brook et al. 2003); this method estimates extinction rates by reversing the species-area accumulation curve, extrapolating backward to smaller areas to calculate expected species loss. The concept is relatively simple, even though the underlying mathematics might not be. Read the rest of this entry »

How fast are we losing species anyway?

28 03 2011

© W. Laurance

I’ve indicated over the last few weeks on Twitter that a group of us were recently awarded funding from the Australian Centre for Ecological Synthesis and Analysis – ACEAS – (much like the US version of the same thing – NCEAS) to run a series of analytical workshops to estimate, with a little more precision and less bias than has been done previously, the extinction rates of today’s biota relative to deep-time extinctions.

So what’s the issue? The Earth’s impressive diversity of life has experienced at least five mass extinction events over geological time. Species’ extinctions have kept pace with evolution, with more than 99 % of all species that have ever existed now gone (Bradshaw & Brook 2009). Despite general consensus that biodiversity has entered the sixth mass extinction event because of human-driven degradation of the planet, estimated extinction rates remain highly imprecise (from 100s to 10000s times background rates). This arises partly because the total number of species is unknown for many groups, and most extinctions go unnoticed.

So how are we going to improve on our highly imprecise estimates? One way is to look at the species-area relationship (SAR), which to estimate extinction requires one to extrapolate back to the origin in taxon- and region-specific SARs (e.g., with a time series of deforestation, one can estimate how many species would have been lost if we know how species diversity changes in relation to habitat area). Read the rest of this entry »

Where in the world to invest in plant conservation

31 05 2010


It’s been a good few weeks with many of our papers coming out online early – for example, I highlighted one last week on ecosystem function breakdown from global warming.

Although this has been out for a few weeks, our new paper lead by PhD candidate Xingli Giam (formerly of National University of Singapore, recently completed Australian Endeavour Scholar, now at Princeton University and all-round up-and-coming research star), and with contributions from Hugh “Vascular” Tan and Navjot Sodhi of National University of Singapore and me, is entitled Future habitat loss and the conservation of plant biodiversity (just published online in Biological Conservation).

This one is a bit of a complicated one, so let me walk you through it.

Plants not only represent a huge component of global biodiversity (~320 000 species), they represent the ‘habitats’ in which animals live and provide the major source of nutrients to food webs. They also provide most of our food and other materials essential for human existence. Basically we’d be screwed without them.

Because so many of the world’s biomes are severely threatened now because of massive habitat loss, degradation, over-exploitation, invasive species, extinction synergies and climate change, we need to maximise our efficiency in protecting what’s left. While global prioritisation schemes have a fruitful scientific history since Myers & colleagues’ classic paper (see Biodiversity Hotspots), there are a number of problems that plague the concept and its implementation. Read the rest of this entry »

The biodiversity extinction numbers game

4 01 2010

© Ferahgo the Assassin

Not an easy task, measuring extinction. For the most part, we must use techniques to estimate extinction rates because, well, it’s just bloody difficult to observe when (and where) the last few individuals in a population finally kark it. Even Fagan & Holmes’ exhaustive search of extinction time series only came up with 12 populations – not really a lot to go on. It’s also nearly impossible to observe species going extinct if they haven’t even been identified yet (and yes, probably still the majority of the world’s species – mainly small, microscopic or subsurface species – have yet to be identified).

So conservation biologists do other things to get a handle on the rates, relying mainly on the species-area relationship (SAR), projecting from threatened species lists, modelling co-extinctions (if a ‘host’ species goes extinct, then its obligate symbiont must also) or projecting declining species distributions from climate envelope models.

But of course, these are all estimates and difficult to validate. Enter a nice little review article recently published online in Biodiversity and Conservation by Nigel Stork entitled Re-assessing current extinction rates which looks at the state of the art and how the predictions mesh with the empirical data. Suffice it to say, there is a mismatch.

Stork writes that the ‘average’ estimate of losing about 100 species per day has hardly any empirical support (not surprising); only about 1200 extinctions have been recorded in the last 400 years. So why is this the case?

As mentioned above, it’s difficult to observe true extinction because of the sampling issue (the rarer the individuals, the more difficult it is to find them). He does cite some other problems too – the ‘living dead‘ concept where species linger on for decades, perhaps longer, even though their essential habitat has been destroyed, forest regrowth buffering some species that would have otherwise been predicted to go extinct under SAR models, and differing extinction proneness among species (I’ve blogged on this before).

Of course, we could just all be just a pack of doomsday wankers vainly predicting the end of the world ;-)

Well, I think not – if anything, Stork concludes that it’s all probably worse than we currently predict because of extinction synergies (see previous post about this concept) and the mounting impact of rapid global climate change. If anything, the “100 species/day” estimate could look like a utopian ideal in a few hundred years. I do disagree with Stork on one issue though – he claims that deforestation isn’t probably as bad as we make it out. I’d say the opposite (see here, here & here) – we know so little of how tropical forests in particular function that I dare say we’ve only just started measuring the tip of the iceberg.

CJA Bradshaw

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This post was chosen as an Editor's Selection for

ResearchBlogging.orgStork, N. (2009). Re-assessing current extinction rates Biodiversity and Conservation DOI: 10.1007/s10531-009-9761-9

Conservation Scholars: Barry Brook

7 04 2009

The Conservation Scholars series continues with conservation biologists that were not highlighted in our book Tropical Conservation Biology (where we produced a series of ‘Spotlights’ describing the contributions of great thinkers in conservation science). Each highlight of a Conservation Scholar includes a small biography, a list of major scientific publications and a Q & A on the person’s particular area of expertise.

Another good friend and colleague, Barry Brook, is our twelfth Conservation Scholar…


Barry Brook (right) talking with Frank Fenner at the Australian Academy of Science.

Barry Brook (right) talking with Frank Fenner at the Australian Academy of Science.

Professor Barry W. Brook holds the Foundation Sir Hubert Wilkins Chair of Climate Change and is Director of Climate Science at the University of Adelaide‘s Environment Institute. He has published two books and over 140 peer-reviewed scientific papers, and regularly writes opinion pieces and popular articles for the media. In 2006, he was awarded the Australian Academy of Science Fenner Medal for distinguished research in biology and the Edgeworth David Medal by the Royal Society of New South Wales, and in 2007, the H.G. Andrewartha Medal by the Royal Society of South Australia and was listed by Cosmos as one of Australia’s top 10 young scientists. His area of expertise is climate change, global change biology, and the synergies between different human impacts on biodiversity. Specific topics include analytical and computer simulation modelling for risk assessment of climate change impacts, understanding the relevance of past extinctions to the present biodiversity crisis, tropical conservation, and wildlife population management. His research methods focus primarily on the statistical analysis, interpretation and computational modelling of long-term data, and meta-analysis of large-scale databases. Scenarios for future impacts are modelled at global, regional and local scales, to provide a robust scientific underpinning for scientific management and government policy. His current work is aimed at determining the extent to which climate change might amplify other major anthropogenic threats to biodiversity (e.g., demographic and genetic stress, habitat degradation, introduced predator and competitor species), and developing new modelling systems which realistically captures this information and so can be used for the purposes of prediction, adaptation and ecosystem management and restoration. Effective communication of the science of climate change is fundamental to providing policy makers with the type of evidence required to institute meaningful mitigation policy and to understand available adaptation options. It is this imperative that has motivated Barry to take an active leadership role in the communication of the science of global change to government, industry and the community (directly, via public lectures and workshops and advisory committees, and indirectly via television, radio, the print media and popular science articles). It is his strong belief that presenting hard-won technical scientific evidence to a broad audience in an intelligible way is the surest path to provoking meaningful societal change towards long-term sustainability.

Major Publications

Questions and Answers

1. What do you believe is the most pressing biodiversity conservation problem we need to address as a society today?

Active intervention and triage. Global factors (climate warming, land use change, invasive species, environmental pollution) are the primary drivers of the current biodiversity crisis, and as such, solutions that don’t see ‘the big picture’ are doomed to fail. In the past, we’ve taken a ‘reserve-and-isolate’ approach to conservation (e.g., create protected areas and then exclude people). We’ve also focused predominantly on the problems facing individual threatened species. This will not work on the scales required for 21st century conservation biology. As species distributions shift and whole communities of interacting organisms are damaged by these overarching threats, we are going to have to face two challenging prospects: (i) we’ll need to move many species ourselves rather than simply hoping for them to disperse to new areas of their own accord, and (ii) we’ll need to give up on many of the most-vulnerable species in order to save most of the rest. We are not going to avoid extinctions – but can possibly still avoid a mass extinction.

2. How did you make the change from pure theoretical ecologist to climate change specialist?

I’m not sure I ever really made a change (certainly not a switch). Scientific careers naturally evolve as one’s research interests take different directions. I’ve always been interested in numerical modelling, synergies in complex systems and the emergent properties that result, and treatment of risk and uncertainty. Whether it be theoretical ecology, palaeobiology, or contemporary climate change impacts – it’s all ‘systems science’. Certainly climate change is an overarching threat, potentially the most damaging of all, and so is always in the mix when considering future scenarios of biodiversity and societal responses. Energy, land use, human values – they’re all intrinsic parts of the big picture in which conservation must operate.

3. You’ve done a lot of work predicting species extinction trends – what are some of the principal take-home messages about extinctions and how to prevent (reduce) them?

Species start out rare, and end their existence rare – it’s fundamental to evolution [I guess phyletic transformations are the exception to the former, but the latter is universal]. In between – during most of a species’ lifetime (of typically 1 to 10 million years) – most species are fairly abundant (locally or regionally). So extinction dynamics is the science of understanding how abundant things become rare. There are interesting theoretical properties of small populations that are close to extinction, which make them fun to study, but the business end of conservation is on the decline phase. More abundant populations and those species with populations in multiple locations are harder to knock out. As are genetically diverse populations, and those with wide ranges. ‘Geographical insurance’ should not be underestimated as a conservation tool. If you want to prevent extinctions, you must work hardest at preventing excessive and widespread declines in abundance, and in maintaining viable populations that are resilient to short-term environmental variation. The rest is detail – and much of it theoretically interesting but not particularly relevant to preventing mass extinction.

4. What skill(s) do you believe is(are) most important for burgeoning conservation biologists to master?

Pragmatism, numerical aptitude, and literacy. Pragmatism because you must realise that not everything can be saved (or studied) and that natural laws are not up for negotiation. Numerical skills because all scientists should be modellers (a hypothesis is a verbal model), and sensible integration of data streams into a meaningful ‘signal’ (whilst acknowledging uncertainty) is the most fundamental step in driving scientific progress. We’re all jigsaw builders, but we haven’t got the final picture to look at and haven’t got the time or resources  just to jam pieces together randomly. Literacy because if scientists can’t communicate their work, then it is of no practical value. There are a lot of embedded traditions in scientific writing that have no place in modern communication.

5. What’s your philosophy on statistical support for ‘evidence’ of effects in conservation biology?

From a holistic perspective, full reality is, and always will be, unknowable. For reasons of convenience and practicality, we leave most minor things out. Science is about identifying the main factors required to summarise a system of interest, whilst looking out for unusual boundary effects. Evidence is therefore about quantifying effect size, especially the relative important of different effects. Statistics is all about getting a handle on the uncertainty in your estimates of effect size. Issues of power and variability are important considerations here, as are appropriate methods of model construction, selection, simplification and inference. Binary concepts such as whether a result is ‘significant’ (or not), or methods of multivariate ‘data dredging’ in which an investigator is led by the data rather than being driven by a priori hypotheses, are ultimately pretty meaningless.

CJA Bradshaw

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Conservation Scholars: Navjot Sodhi

3 02 2009

The Conservation Scholars series continues now with conservation biologists that were not highlighted in our book Tropical Conservation Biology (where we produced a series of ‘Spotlights’ describing the contributions of great thinkers in conservation science). Each highlight of a Conservation Scholar includes a small biography, a list of major scientific publications and a Q & A on the person’s particular area of expertise.

I thought I’d start this new batch with one of my good friends and colleagues, Navjot Sodhi. He is our eleventh Conservation Scholar…


I am currently Professor of Conservation Ecology at the National University of Singapore. I received my PhD from the University of Saskatchewan (Canada), and I have been studying the effects of rain forest loss and degradation on Southeast Asian fauna and flora for over the last 13 years. I have published over 100 scientific papers in international and regional scientific journals such as Nature, Science, Trends in Ecology and Evolution, Annual Review of Ecology, Evolution and Systematics, Auk, Current Biology, BioScience, Ecological Applications, Journal of Applied Ecology, Conservation Biology, Biological Conservation, and Biodiversity and Conservation. I have written/edited several books/monographs such as Southeast Asian Biodiversity in Crisis (2006, Cambridge University Press), Winged Invaders: ‘Pest’ birds of Asia-Pacific (2006, SNP, Singapore), Tropical Conservation Biology (2007, Blackwell) and Biodiversity and Human Livelihoods in Protected Areas: case studies from the Malay Archipelago (2008, Cambridge University Press), and I am currently co-editing a textbook called Conservation Biology  for All (2009, Oxford University Press).  I have also spent time at Harvard University as a Bullard Fellow (2001-02) and Hrdy Fellow (2008-09) where I now hold an adjunct associate position. I am (or have been) an Associate Editor/Editor of prestigious journals such as Conservation Biology, Biological Conservation, Animal Conservation, the Auk and Biotropica. Read the rest of this entry »

Conservation Scholars: Stuart Pimm

5 01 2009

This series on takes a page out of our book Tropical Conservation Biology (Sodhi, Brook & Bradshaw) – therein we produced a series of ‘Spotlights’ describing the contributions of great thinkers to conservation science. Each highlight of a Conservation Scholar includes a small biography, a list of major scientific publications and a Q & A on the person’s particular area of expertise.

Our ninth Conservation Scholar is Stuart Pimm


I am the Doris Duke Professor of Conservation Ecology at the School of the Environment at Duke University and have a secondary appointment of Extraordinary Professor at the Conservation Ecology Research Unit at the University of Pretoria, South Africa. My interests are endangered species conservation, biodiversity, species extinction, and habitat loss. I’m the author of over 200 scientific publications, many of them in Nature and Science, and have written four books, the most recent being the critically acclaimed World According to Pimm: a Scientist Audits the Earth. In 2006, Prince Willem-Alexander presented me the Dr. A.H. Heineken Prize for Environmental Sciences on behalf of the Royal Netherlands Academy of Arts and Sciences. How did all this happen?

Like many peers, I started out as a naturalist during my adolescence, read zoology at university, and then did a PhD in ecology. Unlike others, I worked in Hawai’i soon afterwards where I was deeply shaken by the total absence of many of the birds I expected to see – they were either extinct or close to it. I was curious about why some species succumbed while other survived. Importantly, these losses were an outrage. Scientists, I realized, could help prevent extinctions. Vitally, they had an obligation to do so. Thereafter, my research group has sought out the species and ecosystems that are in most urgent need of protection. That work takes us to the Everglades, the Amazon and the coastal forests of Brazil, to southern Africa, and to Madagascar. We work with local organisations and governments to provide the best possible advice to solving conservation problems. We’re problem driven and that means we develop whatever skills are needed to their solution. We’ve always had good quantitative skills, but in addition, my group members all use geographic information system and analyses of satellite imagery – skills we developed only in the last decade. And yes, some of the solutions come from sharing our knowledge with politicians and advising on policy issues.

Major Publications

Questions and Answers

1. The current biodiversity crisis has been termed the “sixth extinction”; an allusion to the five largest mass die-offs in Earth’s past. Is this comparison justified?

In the previous five die-offs – the last killed off the dinosaurs – more than half the variety of life disappeared. It took roughly ten million years to recover the former numbers of species. Human actions in the last thousand years have probably wiped out about 10 % of species, while actions in the last century have threatened at least 10 % of the remainder. By threatened, I mean that expert opinion judges that these species will become extinct in the next few decades if we do nothing to protect them. It gets worse. Tropical forests hold perhaps two-thirds of all species on land and tropical oceans, especially coral reefs, the great majority of marine species. If current trends continue, human actions will so massively reduce these ecosystems that a third or more of the remaining species will be on a path to extinction within a few decades.

2. How reliable are biogeographic proxies such as the species-area relationship for inferring extinction rates?

Our ability to predict future trends on land comes from the species-area relationship. It’s one of the great ecological laws – that is, a commonly observed pattern across different species groups in different areas. An oceanic island, half the size of larger island, will have about 15 % fewer species according to this law. Imagine we convert what was once a continuous forest – say, eastern North America – into islands of about half the forest cover. There are about 30 species of bird endemic to the forests of the region, so we’d expect to lose 4.5 species. And, indeed, four species of bird became extinct as eastern North America lost its forests in the four centuries since European colonisation – and another species in threatened with extinction! Detailed calculations like this one have now been done on many areas of tropical forest, which often contain hundreds of endemic species. The numbers of species the model predicts to go extinct and those that have done so are very similar (or are presently in danger of doing so, for extinctions take time to happen.). These excellent calibrations of the law mean that we can predict how many species will go extinct if we reduce tropical forests further.

3. How can scientists most effectively engage the often pseudo-scientific arguments posed by environmental ‘sceptics’, who claim global hazards, such as the large-scale death of species and climate change, are illusory or inconsequential?

The most effective strategy is not to engage the sceptics. I’m for honest scientific debate – it’s what I do every day. The evidence for global change and massive loss of species is unassailable, however. Sceptics ignore the evidence, usually in my experience, because they are paid to do so. There is nothing honest in the debate, indeed, it usually isn’t a debate. Would you debate someone who thought the world was flat? If you were so foolish as to do so, what would happen? You’d present all the familiar observations -Earth’s shadow on the Moon, for example, – and demolish your opponent. Would he continue with his foolish ideas? You bet! He would loudly trumpet that he’d debated a competent, thoughtful scientist at the University of Somewhere. To outsiders, his pathetically ignorant ideas would gain credibility and his sponsors would continue to pay him. Lots of good people work hard to address ways to reverse global change and reduce species loss. Get on with solving problems and don’t waste time with fools.

4. What is the future of tropical biodiversity… ‘according to Pimm’?

The important message is that we can stem the loss of tropical biodiversity – its future is not yet written. We can slow the rate of deforestation and we know enough about the patterns of where the most vulnerable species live to make their protection a priority.

CJA Bradshaw

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(with thanks to Navjot Sodhi, Barry Brook, Ward Cooper, Wiley-Blackwell and Stuart Pimm for permission to reproduce the text – buy your copy of Tropical Conservation Biology here)

Save the biggest (and closest) ones

12 11 2008

© somapsychedelica

© somapsychedelica

A paper we recently wrote and published in Biological Conservation entitled Using biogeographical patterns of endemic land snails to improve conservation planning for limestone karsts lead by my colleague Reuben Clements of WWF has recently been highlighted at Our main result was that following the basic tenets of the theory of island biogeography, the largest, least-isolated limestone karsts in South East Asia (biologically rich limestone outcrops formed millions of years ago by the deposition of calcareous marine organisms) have the greatest proportion of endemic land snails (a surrogate taxon for uniqueness among other species). I’ll let Rhett at do the rest (see original post):

Researchers have devised a scientific methodology for prioritizing conservation of limestone karsts, biologically-rich outcroppings found in Southeast Asia and other parts of the world. The findings are significant because karsts – formed millions of years ago by sea life – are increasingly threatened by mining and other development.

Using data from 43 karsts across Peninsular Malaysia and Sabah, authors led by Reuben Clements of WWF-Malaysia reported that larger karsts support greater numbers of endemic snails – a proxy for biological uniqueness among other species – making them a priority for protection.

“Larger areas tend to have greater habitat diversity, which enables them so support a higher number of unique species.” said Clements, species conservation manager for WWF-Malaysia.

With a variety of habitats including sinkholes, caves, cliffs, and underground rivers, and separated from other outcroppings by lowland areas, karsts support high levels of endemism among insects, snails, fish, plants, bats and other small mammals. Animals that inhabit karsts provide humans with important services including pest control, pollination, and a sustainable source of income (swiftlet nests used for bird nest soup, a Chinese delicacy, are found in karst caves). But karsts are increasingly under threat, especially from mining for cement and marble. An earlier study by Clements showed that limestone quarrying is increasing in Southeast Asia by 5.7 percent a year – the highest rate in the world – to fuel the region’s construction boom. The biodiversity of karsts – especially among animals that move to surrounding areas to feed – is also at risk from destruction of adjacent ecosystems, often by loggers or for agriculture.

Clements says the new study, which is published in the November issue of the journal Biological Conservation, will help set conservation priorities for karsts.

“The protection of karsts has been mainly ad hoc and they are usually spared from quarrying by virtue of being situated within state and national parks, or if they possess some form of aesthetic or cultural value,” he said. “Taking Peninsular Malaysia for example, our results suggest that we should set aside larger karsts on both sides of the Titiwangsa mountain range for protection if we want to maximize the conservation of endemic species. Protecting karsts on one side of the mountain chain is not enough.”

“With our findings, we hope that governments would reconsider issuing mining concessions for larger karsts as they tend to be more biologically important,” Clements said.

Tropical Conservation Biology

8 09 2008

An obvious personal plug – but I’m allowed to do that on my own blog ;-)

I’d like to introduce a (relatively) new textbook that my colleagues, Navjot Sodhi and Barry Brook, and I wrote and published last year with Blackwell (now Wiley-Blackwell) Scientific Publishing – Tropical Conservation Biology.

We’re rather proud of this book because it was a timely summary and assessment of the scientific evidence for the degree of devastation facing tropical biodiversity today and in the future. I’ve summarised some of the main issues in a previous post covering a paper we have ‘in press’ that was born of the text book, but obviously the book is a far more detailed account of the problems facing the tropics.

This introductory textbook examines diminishing terrestrial and aquatic habitats in the tropics, covering a broad range of topics including the fate of the coral reefs; the impact of agriculture, urbanisation, and logging on habitat depletion; and the effects of fire on plants and animal survival.

One of the highlights of the book is that each chapter (see below) Includes case studies and interviews with prominent conservation scientists to help situate key concepts in a real world context: Norman Myers (Chapter 1), Gretchen Daily (Chapter 2), William Laurance (Chapter 3), Mark Cochrane (Chapter 4), Daniel Simberloff (Chapter 5), Bruce Campbell (Chapter 6), Daniel Pauly (Chapter 7), Stephen Schneider (Chapter 8), Stuart Pimm (Chapter 9) and Peter Raven (Chapter 10). These biographies are followed by a brief set of questions and answers that focus on some of the most pertinent and pressing issues in tropical conservation biology today. It is our intention that readers of Tropical Conservation Biology will benefit from the knowledge and be inspired by the passion of these renowned conservation experts.


  1. Chapter 1: Diminishing habitats in regions of high biodiversity. We report on the loss of tropical habitats across the tropics (e.g., deforestation rates). We also highlight the drivers of habitat loss such as human population expansion. Finally, we identify the areas in immediate need of conservation action by elucidating the concept of biodiversity hotspots. Read the rest of this entry »

Classics: Island Biogeography

19 08 2008

‘Classics’ is a category of posts highlighting research that has made a real difference to biodiversity conservation. All posts in this category will be permanently displayed on the Classics page of

© Princeton University Press

© Princeton University Press

MacArthur, R.H. & Wilson, E.O. (1967). The Theory of Island Biogeography. Princeton University Press, Princeton, NJ

Although this classic book was written before the discipline of conservation biology really kicked off, it has to be one of the more influential in terms of reserve design and the estimation of extinction rates. The original theory was proposed as a determinant of total species richness on islands as a function of island size. Put (almost too) simply the bigger the island, the more species it contains. This ultimately lead to the branch of biogeography/conservation biology that applied ‘species-area’ relationships to habitat fragments to extrapolate total species number and more importantly (in the context of the extinction crisis), estimate rates of species loss. The species-area literature is a hot-bed of critique and polemic, yet no one can deny that this seminal paper really kicked off the idea that reduced and fragmented areas are bad for biodiversity. We wouldn’t have nature reserves today if it wasn’t for this simple, yet brilliant piece of work.

CJA Bradshaw

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