Why populations can’t be saved by a single breeding pair

3 04 2018

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© Reuters/Thomas Mukoya

I published this last week on The Conversation, and now reproducing it here for CB.com readers.

 

Two days ago, the last male northern white rhino (Ceratotherium simum cottoni) died. His passing leaves two surviving members of his subspecies: both females who are unable to bear calves.

Even though it might not be quite the end of the northern white rhino because of the possibility of implanting frozen embryos in their southern cousins (C. simum simum), in practical terms, it nevertheless represents the end of a long decline for the subspecies. It also raises the question: how many individuals does a species need to persist?

Fiction writers have enthusiastically embraced this question, most often in the post-apocalypse genre. It’s a notion with a long past; the Adam and Eve myth is of course based on a single breeding pair populating the entire world, as is the case described in the Ragnarok, the final battle of the gods in Norse mythology.

This idea dovetails neatly with the image of Noah’s animals marching “two by two” into the Ark. But the science of “minimum viable populations” tells us a different story.

No inbreeding, please

The global gold standard used to assess the extinction risk of any species is the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. Read the rest of this entry »





Our global system-of-systems

28 02 2018

Complex-systems

I’ve just read an excellent paper that succinctly, eloquently, and wisely summarised the current predicament of our highly interconnected, global, complex adaptive system (i.e., our environment).

If you are new to the discussions around state shifts, hysteresis, tipping points, and system collapse, there might be a lot in the new paper by Philip Garnett of the University of York that you could find intimidating (and not just because of the complexity of the concepts he discusses). If you are more up-to-date on these discussions, I highly recommend reading this paper for distilling some of the more pertinent questions.

The essence of the paper is that our global environment (Earth) is one giant, complex system made up of interacting sub-systems. We can think of these as a giant, interconnected network of nodes and connections (often called ‘edges’) between them. If you do ecological network theory, then you know what I’m talking about.

What’s particularly fascinating to me is that Philip Garnett is not an environmental scientist; in fact, he’s a a lecturer in Operations Management and Business Analytics (although he does have a background in genetics and biology) who specialises in complex systems theory. In fact, much of his paper uses socio-economic examples of system complexity and collapse, yet the applications to environmentalism in general, and to ecological integrity in particular, are spot on.

Read the rest of this entry »





Influential conservation ecology papers of 2017

27 12 2017

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As I have done for the last four years (20162015, 2014, 2013), here’s another retrospective list of the top 20 influential conservation papers of 2017 as assessed by experts in F1000 Prime.

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Four decades of fragmentation

27 09 2017

fragmented

I’ve recently read perhaps the most comprehensive treatise of forest fragmentation research ever compiled, and I personally view this rather readable and succinct review by Bill Laurance and colleagues as something every ecology and conservation student should read.

The ‘Biological Dynamics of Forest Fragments Project‘ (BDFFP) is unquestionably one of the most important landscape-scale experiments ever conceived and implemented, now having run 38 years since its inception in 1979. Indeed, it was way ahead of its time.

Experimental studies in ecology are comparatively rare, namely because it is difficult, expensive, and challenging in the extreme to manipulate entire ecosystems to test specific hypotheses relating to the response of biodiversity to environmental change. Thus, we ecologists tend to rely more on mensurative designs that use existing variation in the landscape (or over time) to infer mechanisms of community change. Of course, such experiments have to be large to be meaningful, which is one reason why the 1000 km2 BDFFP has been so successful as the gold standard for determining the effects of forest fragmentation on biodiversity.

And successful it has been. A quick search for ‘BDFFP’ in the Web of Knowledge database identifies > 40 peer-reviewed articles and a slew of books and book chapters arising from the project, some of which are highly cited classics in conservation ecology (e.g., doi:10.1046/j.1523-1739.2002.01025.x cited > 900 times; doi:10.1073/pnas.2336195100 cited > 200 times; doi:10.1016/j.biocon.2010.09.021 cited > 400 times; and doi:10.1111/j.1461-0248.2009.01294.x cited nearly 600 times). In fact, if we are to claim any ecological ‘laws’ at all, our understanding of fragmentation on biodiversity could be labelled as one of the few, thanks principally to the BDFFP. Read the rest of this entry »





Two new postdoctoral positions in ecological network & vegetation modelling announced

21 07 2017

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With the official start of the new ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH) in July, I am pleased to announce two new CABAH-funded postdoctoral positions (a.k.a. Research Associates) in my global ecology lab at Flinders University in Adelaide (Flinders Modelling Node).

One of these positions is a little different, and represents something of an experiment. The Research Associate in Palaeo-Vegetation Modelling is being restricted to women candidates; in other words, we’re only accepting applications from women for this one. In a quest to improve the gender balance in my lab and in universities in general, this is a step in the right direction.

The project itself is not overly prescribed, but we would like something along the following lines of inquiry: Read the rest of this entry »





Genetic Management of Fragmented Animal and Plant Populations

10 12 2016

logoThat is the title of a new textbook that will be available mid-2017.

After almost 6 years work, authors Dick Frankham, Jonathan Ballou, Katherine Ralls, Mark Eldridge, Michele Dudash, Charles Fenster, Bob Lacy & Paul Sunnucks have produced an advanced textbook/research monograph that aims to provoke a paradigm shift in the management of small, isolated population fragments of animals and plants.

One of the greatest unmet challenges in conservation biology is the genetic management of fragmented populations of threatened animal and plant species. More than a million small, isolated, population fragments of threatened species are likely suffering inbreeding depression, loss of evolutionary potential, and elevated extinction risks (genetic erosion). Re-establishing gene flow between populations is required to reverse these effects, but managers very rarely do this. On the contrary, molecular genetic methods are mainly being used to document genetic differentiation among populations, with most studies concluding that genetically differentiated populations should be managed separately (i.e., kept isolated), thereby dooming many populations to eventual extinction.

The need for a paradigm shift in genetic management of fragmented populations has been highlighted as a major issue in conservation. The rapidly advancing field of molecular genetics is continually providing new tools to measure the extent of population fragmentation and its genetic consequences. However, adequate guidance on how to use these data for effective conservation is still lacking, and many populations are going extinct principally for genetic reasons. Consequently, there is now urgent need for an authoritative textbook on the subject.

Read the rest of this entry »





Species-area & species-accumulation curves not the same

30 05 2016

IBI’ve just read an elegant little study that has identified the main determinants of differences in the slope of species-area curves and species-accumulation curves.

That’s a bit of a mouthful for the uninitiated, so if you don’t know much about species-area theory, let me give you a bit of background for why this is an important new discovery.

Perhaps one of the only ‘laws’ in ecology comes from the observation that as you sample from larger and larger areas of any habitat type, the number of species tends to increase. This of course originates from MacArthur & Wilson’s classic book, The Theory of Island Biography (1967), and while simple in basic concept, it has since developed into a multi-headed Hydra of methods, analysis, theory and jargon.

One of the most controversial aspects of generic species-area relationships is the effect of different sampling regimes, a problem I’ve blogged about before. Whether you are sampling once-contiguous forest of habitat patches in a ‘matrix’ of degraded landscape, a wetland complex, a coral reef, or an archipelago of true oceanic islands, the ‘ideal’ models and the interpretation thereof will likely differ, and in sometimes rather important ways from a predictive and/or applied perspective. Read the rest of this entry »