Classics: The Living Dead

30 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 ConservationBytes.com

Zombie_ElephantTilman, D., May, R.M., Lehman, C.L., Nowak, M.A. (1994) Habitat destruction and the extinction debt. Nature 371, 65-66

In my opinion, this is truly a conservation classic because it shatters optimistic notions that extinction is something only rarely the consequence of human activities (see relevant post here). The concept of ‘extinction debt‘ is pretty simple – as habitats become increasingly fragmented, long-lived species that are reproductively isolated from conspecifics may take generations to die off (e.g., large trees in forest fragments). This gives rise to a higher number of species than would be otherwise expected for the size of the fragment, and the false impression that many species can persist in habitat patches that are too small to sustain minimum viable populations.

These ‘living dead‘ or ‘zombie‘ species are therefore committed to extinction regardless of whether habitat loss is arrested or reversed. Only by assisted dispersal and/or reproduction can such species survive (an extremely rare event).

Why has this been important? Well, neglecting the extinction debt is one reason why some people have over-estimated the value of fragmented and secondary forests in guarding species against extinction (see relevant example here for the tropics and Brook et al. 2006). It basically means that biological communities are much less resilient to fragmentation than would otherwise be expected given data on species presence collected shortly after the main habitat degradation or destruction event. To appreciate fully the extent of expected extinctions may take generations (e.g., hundreds of years) to come to light, giving us yet another tool in the quest to minimise habitat loss and fragmentation.

CJA Bradshaw

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Show me the (conservation) evidence

29 08 2008

Guest post from Professor William J. Sutherland, Miriam Rothschild Chair in Conservation Biology, Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom:

We carry out research in conservation largely under the belief that this is making a difference to the planet. However, research (e.g., Sutherland et al. 2004) shows that little of this research is used in practice. There are many good reasons why practitioners only use a small fraction of the available science: most do not have access to the scientific search engines, they usually have very limited access to scientific journals and most importantly, they usually do not have the time or training to search the literature. Another important problem is that the most important source of information is the experience of practitioners, but this is rarely quantified or documented.

To help overcome these problems the website ConservationEvidence.com has been established. It has two main objectives: (1) providing a means for practitioners to document their experience through the online journal Conservation Evidence and (2) summarising the global literature including unpublished report and papers in languages other than English. Currently (August 2008), this has details of over 1200 interventions but the aim is to increase this to 10,000 interventions. The next stage, which is currently being worked on, is then to provide summaries of the consequences of different interventions.

The ambitious objective is to change the way in which global conservation practice is carried out so that practitioners have ready access to information on the effectiveness of interventions including the experience of other practitioners.

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Australian Wet Tropics Biosequestration Project

28 08 2008

Guest post from Penny van Oosterzee, Degree Celsius:

© P. van Oosterzee
© P. van Oosterzee

The Wet Tropics Regional Biosequestration Project Development Document was launched last week on the global stage, for public scrutiny, via the Climate Community and Biodiversity (CCB) website. There are only a dozen other cases in the world that have managed to reach this level of scrutiny.

The CCB standards are used in both the voluntary global markets and also for CDM (clean development mechanism) projects (only afforestation and reforestation) that have significant biodiversity outcomes. It is well known that land use, land use change, and forestry provides the most cost-effective means of reducing greenhouse gas emissions globally, and we believe the Wet Tropics project is at the leading edge of showing how.

The Wet Tropics Project is the world’s first regional biocarbon verification case based on community NRM (Natural Resource Management) activities, aggregating different bio-sequestration activities (reforestation, assisted natural regeneration, avoided deforestation, grazing land management, reduced use of fertiliser in agriculture) of myriad landholders in one verification case.

The initiative of using NRM Regional Plan’s as a basis for biosequestration project design is an innovation that can be rolled out across the state and nationally. Using Regional Plans ensures scientifically robust monitoring outcomes because of the adoption of systems already in place for monitoring. Economically the approach allows trading to occur at the regional and landholder level, and sets the stage for new livelihoods in regional Australia in a climate constrained world.

The Wet Tropics Project is itself a pilot for the NRM regions comprising the catchments of the Great Barrier Reef which are pivotal for its the survival. The Wet Tropics Project also helps to inform national policy debates since both Garnaut and the Federal Government’s Green Paper point out the importance of forestry and agriculture but fail to provide any way forward, and are on a watching brief for solutions.

The Wet Tropics initiative with its link to regional plans immediately enables entry into other global developments such as water quality credits and biodiversity credits.

See also the Degree Celsius website for more information.

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Cost, not biodiversity, dictates decision to conserve

26 08 2008

One for the Potential list:

originalEuroGreen_LogoI’ve just read a great new paper by Bode et al. (2008) entitled Cost-effective global conservation spending is robust to taxonomic group.

After the hugely influential biodiversity ‘hotspot concept hit the global stage, there was a series of subsequent research papers examining just how we should measure the ‘biodiversity’ component of areas needing to be conserved (and invested in). The problem was that depending on which taxa you looked at, and what measure of ‘biodiversity’ you used (e.g., species richness, endemism, latent threat, evolutionary potential, functional redundancy), the priority list of where, how much and when to invest in conservation differed quite a lot. In other words, the congruency among listed areas was rather low (summarised nicely in Thomas Brooks‘ paper in Science Global biodiversity conservation priorities and examined also by Orme et al. 2005). This causes all sorts of problems for conservation investment planners – what to invest in and where?

Bode and colleagues’ newest paper demonstrates at least for endemism, the taxon on which you base your assessment is much less important for maximising species conservation than factors such as land cost and the degree of threat (e.g., as measured by the IUCN Red List).

Of course, their findings could be considered too simplistic because they don’t (couldn’t) evaluate other potentially more important components of ‘biodiversity’ such as genetic history (evolutionary potential) or ecological functional redundancy (the idea that a species becomes more important to conserve if no other species provide the same ecosystem functions); however, I think this paper is something of a landmark in that it shows that ‘socio-economic’ uncertainty generally outweighs uncertainty due to biodiversity measures. The long and short of this is that planners should start investing if there is evidence of heightened threat and land is cheap.

A few other missing bits means that the paper is more heuristic than prescriptive (something the authors state right up front). There is no attempt to take biodiversity, threat or land cost changes arising from climate change into account (see relevant post here), so some of the priorities are questionable. Related to this is the idea of latent risk (see relevant paper by Cardillo et al. 2006) – what’s not necessarily threatened now but likely will be in the very near future. Also, only a small percentage of species are listed in the IUCN Red List (see relevant post here), so perhaps we’re missing some important trends. Finally, I had to note that almost all the priority areas outlined in the paper happened to be in the tropics, which stands to reason given the current and ongoing extinction crisis occurring in this realm. See a more detailed post on ‘tropical turmoil‘.

Despite the caveats, I think this could provide a way forward to the conservation planning stalemate.

CJA Bradshaw

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Classics: Biodiversity Hotspots

25 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 ConservationBytes.com

info-chap7-slide-pic03Myers, N., Mittermeier, R.A., Mittermeier, C.G., da Fonseca, G.A.B. & Kent, J. (2000). Biodiversity hotspots for conservation priorities. Nature, 403, 853-858

According to Google Scholar, this paper has over 2500 citations. Even though it was published less than a decade ago, already Myers and colleagues’ ‘hotspots’ concept has become the classic lexicon for, as they defined it, areas with high species endemism and degradation by humans. In other words, these are places on the planet (originally only terrestrial, but the concept has been extended to the marine realm) where at the current rates of habitat loss, exploitation, etc., we stand to lose far more irreplaceable species. The concept has been criticised for various incapacities to account for all types of threats – indeed, many other prioritisation criteria have been proposed (assessed nicely by Brooks et al. 2006 and Orme et al. 2005), but it’s the general idea proposed by Myers and colleagues that has set the conservation policy stage for most countries. One little gripe here – although the concept ostensibly means areas of high endemic species richness AND associated threat, people often take the term ‘hotspot’ to mean just a place with lots of species. Not so. Ah, the intangible concept of biodiversity!

CJA Bradshaw

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The extinction vortex

25 08 2008

One for the Potential list:

vortexFirst coined by Gilpin & Soulé in 1986, the extinction vortex is the term used to describe the process that declining populations undergo when”a mutual reinforcement occurs among biotic and abiotic processes that drives population size downward to extinction” (Brook, Sodhi & Bradshaw 2008).

Although several types of ‘vortices’ were labelled by Gilpin & Soulé, the concept was subsequently simplified by Caughley (1994) in his famous paper on the declining and small population paradigms, but only truly quantified for the first time by Fagan & Holmes (2006) in their Ecology Letters paper entitled Quantifying the extinction vortex.

Fagan and Holmes compiled a small time-series database of ten vertebrate species (two mammals, five birds, two reptiles and a fish) whose final extinction was witnessed via monitoring. They confirmed that the time to extinction scales to the logarithm of population size. In other words, as populations decline, the time elapsing before extinction occurs becomes rapidly (exponentially) smaller and smaller. They also found greater rates of population decline nearer to the time of extinction than earlier in the population’s history, confirming the expectation that genetic deterioration contributes to a general corrosion of individual performance (fitness). Finally, they found that the variability in abundance was also highest as populations approached extinction, irrespective of population size, thus demonstrating indirectly that random environmental fluctuations take over to cause the final extinction regardless of what caused the population to decline in the first place.

What does this mean for conservation efforts? It was fundamentally the first empirical demonstration that the theory of accelerating extinction proneness occurs as populations decline, meaning that all attempts must be made to ensure large population sizes if there is any chance of maintaining long-term persistence. This relates to the minimum viable population size concept that should underscore each and every recovery and target set or desired for any population in trouble or under conservation scrutiny.

CJA Bradshaw

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Synergies among extinction drivers

24 08 2008

Hopefully one for the Potential list:

© J. Hance

Brook, BW, NS Sodhi, CJA Bradshaw. (2008) Synergies among extinction drivers under global change. Trends in Ecology and Evolution 23, 453-460

A review my colleagues, Barry Brook and Navjot Sodhi, and I have just published in Trends in Ecology and Evolution demonstrates how separate drivers of extinction (e.g., habitat loss, over-exploitation [hunting, fishing, etc.], climate change, invasive species, etc.) tend to work together to heighten the extinction probability of the species they affect more than the simple sum of the individual effects alone.

In what we termed ‘synergies’, the review compiles evidence from observational, experimental and meta-analytic research demonstrating the positive and self-reinforcing actions of multiple drivers of population decline and eventual extinction. Examples include experimental evidence that wild radishes experiencing inbreeding depression have lower fitness than expected from simple population reduction (Elam et al. 2007), inter-tidal polychaetes succumb to pollution effects much more so at low densities than when populations are abundant (Hollows et al. 2007), and habitat fragmentation, harvest and simulated climate warming increase rotifer extinction risk up to 50 times more than expected from the additive effects of the threatening processes (Mora et al. 2007).

We argued that conservation actions only targeting single drivers will more than likely be inadequate because of the cascading effects caused by unmanaged synergies. Climate change will also interact with and accelerate ongoing threats to biodiversity, so the importance of accounting for these interactions cannot be understated.

CJA Bradshaw

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