More species = more resilience

8 01 2014

reef fishWhile still ostensibly ‘on leave’ (side note: Does any scientist really ever take a proper holiday? Perhaps a subject for a future blog post), I cannot resist the temptation to blog about our lab’s latest paper that just came online today. In particular, I am particularly proud of Dr Camille Mellin, lead author of the study and all-round kick-arse quantitative ecologist, who has outdone herself on this one.

Today’s subject is one I’ve touched on before, but to my knowledge, the relationship between ‘diversity’ (simply put, ‘more species’) and ecosystem resilience (i.e., resisting extinction) has never been demonstrated so elegantly. Not only is the study elegant (admission: I am a co-author and therefore my opinion is likely to be biased toward the positive), it demonstrates the biodiversity-stability hypothesis in a natural setting (not experimental) over a range of thousands of kilometres. Finally, there’s an interesting little twist at the end demonstrating yet again that ecology is more complex than rocket science.

Despite a legacy of debate, the so-called diversity-stability hypothesis is now a widely used rule of thumb, and its even implicit in most conservation planning tools (i.e., set aside areas with more species because we assume more is better). Why should ‘more’ be ‘better’? Well, when a lot of species are interacting and competing in an ecosystem, the ‘average’ interactions that any one species experiences are likely to be weaker than in a simpler, less diverse system. When there are a lot of different niches occupied by different species, we also expect different responses to environmental fluctuations among the community, meaning that some species inherently do better than others depending on the specific disturbance. Species-rich systems also tend to have more of what we call ‘functional redundancy‘, meaning that if one species providing an essential ecosystem function (e.g., like predation) goes extinct, there’s another, similar species ready to take its place. Read the rest of this entry »





Cleaning up the rubbish: Australian megafauna extinctions

15 11 2013

diprotodonA few weeks ago I wrote a post about how to run the perfect scientific workshop, which most of you thought was a good set of tips (bizarrely, one person was quite upset with the message; I saved him the embarrassment of looking stupid online and refrained from publishing his comment).

As I mentioned at the end of post, the stimulus for the topic was a particularly wonderful workshop 12 of us attended at beautiful Linnaeus Estate on the northern coast of New South Wales (see Point 5 in the ‘workshop tips’ post).

But why did a group of ecological modellers (me, Barry Brook, Salvador Herrando-Pérez, Fréd Saltré, Chris Johnson, Nick Beeton), ancient DNA specialists (Alan Cooper), palaeontologists (Gav Prideaux), fossil dating specialists (Dizzy Gillespie, Bert Roberts, Zenobia Jacobs) and palaeo-climatologists (Michael Bird, Chris Turney [in absentia]) get together in the first place? Hint: it wasn’t just the for the beautiful beach and good wine.

I hate to say it – mainly because it deserves as little attention as possible – but the main reason is that we needed to clean up a bit of rubbish. The rubbish in question being the latest bit of excrescence growing on that accumulating heap produced by a certain team of palaeontologists promulgating their ‘it’s all about the climate or nothing’ broken record.

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 »





Saving world’s most threatened cat requires climate adaptation

23 07 2013
© CSIC Andalusia Audiovisual Bank/H. Garrido

© CSIC Andalusia Audiovisual Bank/H. Garrido

The Iberian lynx is the world’s most threatened cat, with recent counts estimating only 250 individuals surviving in the wild. Recent declines of Iberian lynx have been associated with sharp regional reductions in the abundance of its main prey, the European rabbit, caused mainly by myxomatosis virus and rabbit haemorrhagic disease. At present, only two Iberian lynx populations persist in the wild compared with nine in the 1990s.

Over €90 million has been spent since 1994 to mitigate the extinction risk of this charismatic animal, mainly through habitat management, reduction of human-caused mortality and, more recently, translocation. Although lynx abundance might have increased in the last ten years in response to intensive management, a new study published in Nature Climate Change warns that the ongoing conservation strategies could buy just a few decades before the species goes extinct.

The study led by Damien Fordham from The Environment Institute (The University of Adelaide) and Miguel Araújo from the Integrative Biogeography and Global Change Group (Spanish Research Council) shows that climate change could lead to a rapid and severe decrease in lynx abundance in coming decades, and probably result in its extinction in the wild within 50 years. Current management efforts could be futile if they do not take into account the combined effects of climate change, land use and prey abundance on population dynamics of the Iberian Lynx.

Read the rest of this entry »





Software tools for conservation biologists

8 04 2013

computer-programmingGiven the popularity of certain prescriptive posts on ConservationBytes.com, I thought it prudent to compile a list of software that my lab and I have found particularly useful over the years. This list is not meant to be comprehensive, but it will give you a taste for what’s out there. I don’t list the plethora of conservation genetics software that is available (generally given my lack of experience with it), but if this is your chosen area, I’d suggest starting with Dick Frankham‘s excellent book, An Introduction to Conservation Genetics.

1. R: If you haven’t yet loaded the open-source R programming language on your machine, do it now. It is the single-most-useful bit of statistical and programming software available to anyone anywhere in the sciences. Don’t worry if you’re not a fully fledged programmer – there are now enough people using and developing sophisticated ‘libraries’ (packages of functions) that there’s pretty much an application for everything these days. We tend to use R to the exclusion of almost any other statistical software because it makes you learn the technique rather than just blindly pressing the ‘go’ button. You could also stop right here – with R, you can do pretty much everything else that the software listed below does; however, you have to be an exceedingly clever programmer and have a lot of spare time. R can also sometimes get bogged down with too much filled RAM, in which case other, compiled languages such as PYTHON and C# are useful.

2. VORTEX/OUTBREAK/META-MODEL MANAGER, etc.: This suite of individual-based projection software was designed by Bob Lacy & Phil Miller initially to determine the viability of small (usually captive) populations. The original VORTEX has grown into a multi-purpose, powerful and sophisticated population viability analysis package that now links to its cousin applications like OUTBREAK (the only off-the-shelf epidemiological software in existence) via the ‘command centre’ META-MODEL MANAGER (see an examples here and here from our lab). There are other add-ons that make almost any population projection and hindcasting application possible. And it’s all free! (warning: currently unavailable for Mac, although I’ve been pestering Bob to do a Mac version).

3. RAMAS: RAMAS is the go-to application for spatial population modelling. Developed by the extremely clever Resit Akçakaya, this is one of the only tools that incorporates spatial meta-population aspects with formal, cohort-based demographic models. It’s also very useful in a climate-change context when you have projections of changing habitat suitability as the base layer onto which meta-population dynamics can be modelled. It’s not free, but it’s worth purchasing. Read the rest of this entry »





Translocations: the genetic rescue paradox

14 01 2013

helphindranceHarvesting and habitat alteration reduce many populations to just a few individuals, and then often extinction. A widely recommended conservation action is to supplement those populations with new individuals translocated from other regions. However, crossing local and foreign genes can worsen the prospects of recovery.

We are all hybrids or combinations of other people, experiences and things. Let’s think of teams (e.g., engineers, athletes, mushroom collectors). In team work, isolation from other team members might limit the appearance of innovative ideas, but the arrival of new (conflictive) individuals might in fact destroy group dynamics altogether. Chromosomes work much like this – too little or too much genetic variability among parents can break down the fitness of their descendants. These pernicious effects are known as ‘inbreeding depression‘ when they result from reproduction among related individuals, and ‘outbreeding depression‘ when parents are too genetically distant.

CB_OutbreedingDepression Photo
Location of the two USA sites providing spawners of largemouth bass for the experiments by Goldberg et al. (3): the Kaskaskia River (Mississipi Basin, Illinois) and the Big Cedar Lake (Great Lakes Basin, Wisconsin). Next to the map is shown an array of three of the 72-litre aquaria in an indoor environment under constant ambient temperature (25 ◦C), humidity (60%), and photoperiod (alternate 12 hours of light and darkness). Photo courtesy of T. Goldberg.

Recent studies have revised outbreeding depression in a variety of plants, invertebrates and vertebrates (1, 2). An example is Tony Goldberg’s experiments on largemouth bass (Micropterus salmoides), a freshwater fish native to North America. Since the 1990s, the USA populations have been hit by disease from a Ranavirus. Goldberg et al. (3) sampled healthy individuals from two freshwater bodies: the Mississipi River and the Great Lakes, and created two genetic lineages by having both populations isolated and reproducing in experimental ponds. Then, they inoculated the Ranavirus in a group of parents from each freshwater basin (generation P), and in the first (G1) and second (G2) generations of hybrids crossed from both basins. After 3 weeks in experimental aquaria, the proportion of survivors declined to nearly 30% in G2, and exceeded 80% in G1 and P. Clearly, crossing of different genetic lineages increased the susceptibility of this species to a pathogen, and the impact was most deleterious in G2. This investigation indicates that translocation of foreign individuals into a self-reproducing population can not only import diseases, but also weaken its descendants’ resistance to future epidemics.

A mechanism causing outbreeding depression occurs when hybridisation alters a gene that is only functional in combination with other genes. Immune systems are often regulated by these complexes of co-adapted genes (‘supergenes’) and their disruption is a potential candidate for the outbreeding depression reported by Goldberg et al. (3). Along with accentuating susceptibility to disease, outbreeding depression in animals and plants can cause a variety of deleterious effects such as dwarfism, low fertility, or shortened life span. Dick Frankham (one of our collaborators) has quantified that the probability of outbreeding depression increases when mixing takes place between (i) different species, (ii) conspecifics adapted to different habitats, (iii) conspecifics with fixed chromosomal differences, and (iv) populations free of genetic flow with other populations for more than 500 years (2).

A striking example supporting (some of) those criteria is the pink salmon (Oncorhynchus gorbuscha) from Auke Creek near Juneau (Alaska). The adults migrate from the Pacific to their native river where they spawn two years after birth, with the particularity that there are two strict broodlines that spawn in either even or odd year – that is, the same species in the same river, but with a lack of genetic flow between populations. In vitro mixture of the two broodlines and later release of hybrids in the wild have shown that the second generation of hybrids had nearly 50% higher mortality rates (i.e., failure to return to spawn following release) when born from crossings of parents from different broodlines than when broodlines were not mixed (4).

Read the rest of this entry »





To corridor, or not to corridor: size is the question

24 04 2012

I’ve just read a really interesting post by David Pannell from the University of Western Australia discussing the benefits (or lack thereof) of wildlife ‘corridors’. I’d like to elaborate on a few key issues, and introduce the most important aspect that really hasn’t been mentioned.

Some of you might be aware that the Australian Commonwealth Government has just released its Draft National Wildlife Corridors Plan for public comment, but many of you might not really know what a ‘corridor’ constitutes.

Wildlife or biodiversity ‘corridors’ have been around for a long time, at least in terms of proposals. The idea is fairly simple to conceive, but very difficult to implement in practice.

At least for as long as I’ve been in the conservation biology biz, ‘corridors’ have been proffered as one really good way to make broad-scale landscape restoration plausible and effective for (mainly) forest-dwelling species which have copped the worst of deforestation trends around Australia and the world. The idea is that because of intense habitat fragmentation, isolated patches of primary (or at least, reasonably intact secondary) forest can be linked by planting some sort of long corridor of similar habitat between them. Then, all the little creatures can merrily make their way back and forth between the patches, thus rescuing each other from extinction via migration. Read the rest of this entry »





Species’ Ability to Forestall Extinction – AudioBoo

8 04 2011

Here’s a little interview I just did on the SAFE index with ABC AM:

Not a bad job, really.

And here’s another one from Radio New Zealand:

CJA Bradshaw





S.A.F.E. = Species Ability to Forestall Extinction

8 01 2011

Note: I’ve just rehashed this post (30/03/2011) because the paper is now available online (see comment stream). Stay tuned for the media release next week. – CJAB

I’ve been more or less underground for the last 3 weeks. It has been a wonderful break (mostly) from the normally hectic pace of academic life. Thanks for all those who remain despite the recent silence.

© Ezprezzo.com

But I’m back now with a post about a paper we’ve just had accepted in Frontiers in Ecology and Environment. In my opinion it’s a leap forward in how we measure relative threat risk among species, despite some criticism.

I’ve written in past posts about the ‘magic’ minimum number of individuals that should be in a population to reduce the chance of extinction from random events. The so-called ‘minimum viable population (MVP) size’ is basically the abundance of a (connected) population below which random events take over from factors causing sustained declines (Caughley’s distinction between the ‘declining’ and ‘small’ population paradigms).

Up until the last few years, the MVP size was considered to be a population- or species-specific value, and it required very detailed demographic, genetic and biogeographical data to estimate – not something that biologists tend to have at their fingertips for most high-risk species. However, several papers published by our group (Minimum viable population size and global extinction risk are unrelated, Minimum viable population size: a meta-analysis of 30 years of published estimates and Pragmatic population viability targets in a rapidly changing world) have shown that there is in fact little variation in this number among the best-studied species; both demographic and genetic data support a number of around 5000 to avoid crossing the deadly threshold.

Now the fourth paper in this series has just been accepted (sorry, no link yet, but I’ll let you all know as soon as it is available), and it was organised and led by Reuben Clements, and co-written by me, Barry Brook and Bill Laurance.

The idea is fairly simple and it somewhat amazes me that it hasn’t been implemented before. The SAFE (Species Ability to Forestall Extinction) index is simply the distance a population is (in terms of abundance) from its MVP. In the absence of a species-specific value, we used the 5000-individual threshold. Thus, Read the rest of this entry »





Linking disease, demography and climate

1 08 2010

Last week I mentioned that a group of us from Australia were travelling to Chicago to work with Bob Lacy, Phil Miller, JP Pollak and Resit Akcakaya to make some pretty exciting developments in next-generation conservation ecology and management software. Also attending were Barry Brook, our postdocs: Damien Fordham, Thomas Prowse and Mike Watts, our colleague (and former postdoc) Clive McMahon, and a student of Phil’s, Michelle Verant. At the closing of the week-long workshop, I thought I’d share my thoughts on how it all went.

In a word, it was ‘productive’. It’s not often that you can spend 1 week locked in a tiny room with 10 other geeks and produce so many good and state-of-the-art models, but we certainly achieved more than we had anticipated.

Let me explain in brief why it’s so exciting. First, I must say that even the semi-quantitative among you should be ready for the appearance of ‘Meta-Model Manager (MMM)’ in the coming months. This clever piece of software was devised by JP, Bob and Phil to make disparate models ‘talk’ to each other during a population projection run. We had dabbled with MMM a little last year, but its value really came to light this week.

We used MMM to combine several different models that individually fail to capture the full behaviour of a population. Most of you will be familiar with the individual-based population viability (PVA) software Vortex that allows relatively easy PVA model building and is particular useful for predicting extinction risk of small populations. What you most likely don’t know exists is what Phil, Bob and JP call Outbreak – an epidemiological modelling software based on the classic susceptible-exposed-infectious-recovered framework. Outbreak is also an individual-based model that can talk directly to Vortex, but only through MMM. Read the rest of this entry »





Mega-meta-model manager

24 07 2010

As Barry Brook just mentioned over at BraveNewClimate.com, I’ll be travelling with him and several of our lab to Chicago tomorrow to work on some new aspects of linked climate, disease, meta-population, demographic and vegetation modelling. Barry has this to say, so I won’t bother re-inventing the wheel:

… working for a week with Dr Robert LacyProf Resit Akcakaya and collaborators, on integrating spatial-demographic ecological models with climate change forecasts, and implementing multi-species projections (with the aim of improving estimates of extinction risk and provide better ranking of management and adaptation options). This work builds on a major research theme at the global ecology lab, and consequently, a whole bunch of my team are going with me — Prof Corey Bradshaw (lab co-director), my postdocs Dr Damien FordhamDr Mike Watts and Dr Thomas Prowse and Corey’s and my ex-postdoc, Dr Clive McMahon. This builds on earlier work that Corey and I had been pursuing, which he described on ConservationBytes last year.

The ‘mega-meta-model manager’ part is a clever piece of control-centre software that integrates these disparate ecological, climate and disease dynamic inputs. Should be some good papers coming out of the work soon.

Of course, I’ll continue to blog over the coming week. I’m not looking forward to the 30-hour travel tomorrow to Chicago, but it should be fun and productive once I get there.

CJA Bradshaw

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Fanciful mathematics and ecological fantasy

3 05 2010

© flickr/themadlolscientist

Bear with me here, dear reader – this one’s a bit of a stretch for conservation relevance at first glance, but it is important. Also, it’s one of my own papers so I have the prerogative :-)

As some of you probably know, I dabble quite a bit in population dynamics theory, which basically means examining the mathematics people use to decipher ecological patterns. Why is this important? Well, most models predicting extinction risk, estimating optimal harvest rates, determining minimum viable population size and metapopulation dynamics for species’ persistence rely on good mathematical abstraction to be realistic. Get the maths wrong, and you could end up overharvesting a species (e.g., 99.99 % of fisheries management), underestimating extinction risk from habitat degradation, and getting your predictions wrong about the effects of invasive species. Expressed as an equation itself, (conservation) ecology = mathematics.

A long-standing family of models known as ‘phenomenological’ models (i.e., because they deal with the phenomenon of population size which is an emergent property of the mechanisms of birth, death and immigration) has been used to estimate everything from maximum sustainable yield targets, temporal abundance patterns, wildlife management interventions, extinction risk to epidemiological patterns. The basic form of the model describes the growth response, or the relationship between the population’s rate of change (growth) and its size. The simplest form (known as the Ricker), assumes a linear decline in population growth rate (r) as the number of individuals increases, which basically means that populations can’t grow indefinitely (i.e., they fluctuate around some carrying capacity if unperturbed). Read the rest of this entry »





Life and death on Earth: the Cronus hypothesis

13 10 2009
Cronus

Cronus

Bit of a strange one for you today, but here’s a post I hope you’ll enjoy.

My colleague, Barry Brook, and I recently published a paper in the very new and perhaps controversial online journal , the Journal of Cosmology. Cosmology? According to the journal, ‘cosmology’ is:

“the study and understanding of existence in its totality, encompassing the infinite and eternal, and the origins and evolution of the cosmos, galaxies, stars, planets, earth, life, woman and man”.

The journal publishes papers dealing with ‘cosmology’ and is a vehicle for those who wish to publish on subjects devoted to the study of existence in its totality.

Ok. Quite an aim.

Our paper is part of the November (second ever) issue of the journal entitled Asteroids, Meteors, Comets, Climate and Mass Extinctions, and because we were the first to submit, we managed to secure the first paper in the issue.

Our paper, entitled The Cronus hypothesis – extinction as a necessary and dynamic balance to evolutionary diversification, introduces a new idea in the quest to find that perfect analogy for understanding the mechanisms dictating how life on our planet has waxed and waned over the billions of years since it first appeared.

Gaia

Gaia

In the 1960s, James Lovelock conceived the novel idea of Gaia – that the Earth functions like a single, self-regulating organism where life itself interacts with the physical environment to maintain conditions favourable for life (Gaia was the ancient Greeks’ Earth mother goddess). Embraced, contested, denounced and recently re-invigorated, the idea has evolved substantially since it first appeared. More recently (this year, in fact), Peter Ward countered the Gaia hypothesis with his own Greek metaphor – the Medea hypothesis. Essentially this view holds that life instead ‘seeks’ to destroy itself in an anti-Gaia manner (Medea was the siblicidal wife of Jason of the Argonauts). Ward described his Medea hypothesis as “Gaia’s evil twin”.

One can marvel at the incredible diversity of life on Earth (e.g., conservatively, > 4 million protists, 16600 protozoa, 75000-300000 helminth parasites, 1.5 million fungi, 320000 plants, 4-6 million arthropods, > 6500 amphibians, 10000 birds and > 5000 mammals) and wonder that there might be something in the ‘life makes it easier for life’ idea underlying Gaia. However, when one considers that over 99 % of all species that have ever existed are today extinct, then a Medea perspective might dominate.

Medea

Medea

Enter Cronus. Here we posit a new way of looking at the tumultuous history of life and death on Earth that effectively relegates Gaia and Medea to opposite ends of a spectrum. Cronus (patricidal son of Gaia overthrown by his own son, Zeus, and banished to Hades) treats speciation and extinction as birth and death in a ‘metapopulation’ of species assemblages split into biogeographic realms. Catastrophic extinction events can be brought about via species engineering their surroundings by passively modifying the delicate balance of oxygen, carbon dioxide and methane – indeed, humans might be the next species to fall victim to our own Medean tendencies. But extinction opens up new niches that eventually elicit speciation, and under conditions of relative environmental stability, specialists evolve because they are (at least temporarily) competitive under those conditions. When conditions change again, extinction ensues because not all can adapt quickly enough. Just as all individuals born in a population must eventually die, extinction is a necessary termination.

We think the Cronus metaphor has a lot of advantages over Gaia and Medea. The notion of a community of species as a population of selfish individuals retains the Darwinian view of contestation; self-regulation in Cronus occurs naturally as a result of extinction modifying the course of future evolution. Cronus also makes existing mathematical tools developed for metapopulation theory amenable to broader lines of inquiry.

For example, species as individuals with particular ‘mortality’ (extinction) rates, and lineages with particular ‘birth’ (speciation) rates, could interact and disperse among ‘habitats’ (biogeographical realms). ‘Density’ feedback could be represented as competitive exclusion or symbioses. As species dwindle, feedbacks such as reduced community resilience that further exacerbate extinction risk (Medea-like phase), and stochastic fluctuation around a ‘carrying capacity’ (niche saturation) arising when environmental conditions are relatively stable is the Gaia-like phase. Our Cronus framework is also scale-invariant – it could be applied to microbial diversity on another organism right up to inter-planetary exchange of life (panspermia).

What’s the relevance to conservation? We’re struggling to prevent extinction, so understanding how it works is an essential first step. Without the realisation that extinction is necessary (albeit, at rates preferably slower than they are currently), we cannot properly implement conservation triage, i.e., where do we invest in conservation and why?

We had fun with this, and I hope you enjoy it too.

CJA Bradshaw

ResearchBlogging.orgBradshaw, C.J.A., & Brook, B.W. (2009). The Cronus Hypothesis – extinction as a necessary and dynamic balance to evolutionary diversification Journal of Cosmology, 2, 201-209 Other: http://journalofcosmology.com/Extinction100.html

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Connectivity paradigm in extinction biology

6 10 2009

networkI’m going to do a double review here of two papers currently online in Proceedings of the Royal Society B: Biological Sciences. I’m lumping them together because they both more or less challenge the pervasive conservation/restoration paradigm that connectivity is the key to reducing extinction risk. It’s just interesting (and slightly amusing) that the two were published in the same journal and at about the same time, but by two different groups.

From our own work looking at the correlates of extinction risk (measured mainly by proxy as threat risk), the range of a population (i.e., the amount of area and number of habitats it covers) is the principal determinant of risk – the smaller your range, the greater your chance of shuffling off this mortal coil (see also here). This is, of course, because a large range usually means that you have some phenotypic plasticity in your habitat requirements, you can probably disperse well, and your not going to succumb to localised ‘catastrophes’ as often. It also probably means (but not always) that your population size increases as your range size increases; as we all know, populations must be beyond their minimum viable population size to have a good chance of persisting random demographic and environmental vagaries.

Well, the two papers in question, ‘Both population size and patch quality affect local extinctions and colonizations‘ by Franzén & Nilssen and ‘Environment, but not migration rate, influences extinction risk in experimental metapopulations‘ by Griffen & Drake, show that connectivity (i.e., the probability that populations are connected via migration) are probably the least important components in the extinction-persistence game.

Using a solitary bee (Andrena hattorfiana) metapopulation in Sweden, Franzén & Nilssen show that population size and food patch quality (measured by number of pollen-producing plants) were directly (but independently) correlated with extinction risk. Bigger populations in stable, high-quality patches persisted more readily. However, connectivity between patches was uncorrelated with risk.

Griffen & Drake took quite a different approach and stacked experimental aquaria full of daphnia (Daphnia magna) on top of one another to influence the amount of light (and hence, amount of food from algal growth) to which the populations had access (it’s interesting to note here that this was unplanned in the experiment – the different algal growth rates related to the changing exposure to light was a serendipitous discovery that allowed them to test the ‘food’ hypothesis!). They also controlled the migration rate between populations by varying the size of holes connecting the aquaria. In short, they found that environmentally influenced (i.e., food-influenced) variation was far more important at dictating population size and fluctuation than migration, showing again that conditions promoting large population size and reducing temporal variability are essential for reducing extinction risk.

So what’s the upshot for conservation? Well, many depressed populations are thought to be recoverable by making existing and fragmented habitat patches more connected via ‘corridors’ of suitable habitat. The research highlighted here suggests that more emphasis should be placed instead on building up existing population sizes and ensuring food availability is relatively constant instead of worrying about how many trickling migrants might be moving back and forth. This essentially means that a few skinny corridors connecting population fragments will probably be insufficient to save our imperilled species.

CJA Bradshaw

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ResearchBlogging.org

This post was chosen as an Editor's Selection for ResearchBlogging.org

Franzen, M., & Nilsson, S. (2009). Both population size and patch quality affect local extinctions and colonizations Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2009.1584

Griffen, B., & Drake, J. (2009). Environment, but not migration rate, influences extinction risk in experimental metapopulations Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2009.1153





Vortex of travel to RAMAStan

9 06 2009




Just a short post to say that the frequency of posts might decline somewhat over the coming weeks. I’m currently travelling in the US on a mixture of leave and work.

From the work side of things, I’ll be heading shortly to Harvard University in Boston to spend some time with colleague Navjot Sodhi of the National University of Singapore who’s finishing up a year-long Hrdy Fellowship there. We’ll be joined by my close friend and colleague, Barry Brook, and Resit Akçakaya of RAMAS fame. We’ll be working on a few ideas regarding extinction dynamics, modelling and climate change projections for species distributions and risk.

We’ll be heading next to visit Bob Lacy of VORTEX fame at the Chicago Zoological Society. We’ll be joined by Phil Miller of the IUCN‘s Species Survival Commission (SSC) Conservation Breeding Specialist Group, JP Pollak of Cornell University, and maybe Jon Ballou of the Smithsonian National Zoological Park. We’re hoping to help take the next generation of species vulnerability software into a more realistic framework that accounts for the complexities of climate change.

I’m looking forward to the trip and meeting new colleagues.

CJA Bradshaw








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