Classics: Invasion Meltdown

26 10 2008

One for the Classics page…

melting_rat_by_xenatalhaoui-d71xr1yDaniel Simberloff is probably best known for his work on the implications of invasive (non-indigenous) species for biodiversity, although he has contributed to a wide range of conservation disciplines.

A seminal paper that he co-wrote with Betsy Von Holle is one I consider to be a conservation Classic: their 1999 paper in the inaugural issue of Biological Invasions entitled Positive interactions of nonindigenous species: Invasional meltdown?

The establishment of non-indigenous species can have severe negative impacts on ecosystems. Introduced species that become invasive (widespread and locally dominant) transform habitats, degrade ecosystem services, reduce biodiversity and are some of the greatest threats to ecosystems today (perhaps nearly as important as habitat loss and over-exploitation).

The so-called ‘invasion meltdown‘ describes the process by which the negative impacts induced on native ecosystems by one invading non-indigenous species are exacerbated by interactions with another exotic species.

Although there isn’t a lot of information on invasion meltdowns, one good example comes from Christmas Island in tropical Australia. The introduced yellow crazy ant (Anoplolepis gracilipes) exploded in numbers when another exotic species, a scale insect, was introduced about the same time that a native scale insect species also had a local outbreak.  Because ants protect scale insects from predators and parasites in return for scale honeydew, the crazy ant suddenly had a much more abundant food source, leading to the huge increase in the ant population. This large ant population devastated the population of native red crab (Gecarcoidea natalis) and resulted in massive increase in forest undergrowth due to reduced herbivory by crabs (see O’Dowd et al. 2003). The great decline in red crabs may also make the island more vulnerable to other plant invasions.

What did Simberloff & Van Holle’s idea and subsequent examples of invasion meltdowns teach us? I believe their paper really hit home the idea that invasive species were not only a threat to biodiversity, but the self-reinforcing mutualisms of invasive species could rival other forms of human-induced biodiversity decline. Indeed, many of the effects of invasive species will be reinforced by global climate change through increasing temperatures, rising sea levels and changing rainfall patterns that increase the potential range and spread of invading species, so the problem is only going to get worse. This is why the U.N. began the Global Invasive Species Programme (GISP), and world-wide, countries are attempting to restrict the flow of invasive species so that their negative effects are lessened. Identifying the extent of the problem has stimulated a lot of people to act accordingly.

CJA Bradshaw

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Remove, Flog and Dump: The Story of Stuff

18 10 2008
© Tides Foundation & Funders Workgroup for Sustainable Production and Consumption

© Tides Foundation & Funders Workgroup for Sustainable Production and Consumption

Related to a recent post on the idiocy of anthropogenically induced climate change, the lunacy of our current economic system and the complete lack of valuing undervaluing of ecosystem services on which our lives depend, I invite you to watch the highly entertaining Story of Stuff. Although terribly American (well, I guess that’s excusable given it is made by an American and targets other Americans, the greatest per capita resource consumers in the world), it applies to everyone, everywhere.

From its extraction through sale, use and disposal, all the stuff in our lives affects communities at home and abroad, yet most of this is hidden from view. The Story of Stuff is a 20-minute, fast-paced, fact-filled look at the underside of our production and consumption patterns. The Story of Stuff exposes the connections between a huge number of environmental and social issues, and calls us together to create a more sustainable and just world. It’ll teach you something, it’ll make you laugh, and it just may change the way you look at all the stuff in your life forever.





Moving forward with extinction risk predictions from climate change

15 10 2008

A little belated, but I thought this was worth mentioning for the Potential list…

182kydeee9pyxjpgOne from Keith and colleagues in Biology Letters entitled Predicting extinction risks under climate change: coupling stochastic population models with dynamic bioclimatic habitat models is a nice example of a way forward to predict the extremely complex array of ecological processes and patterns that may arise from rapid climate change.

One of the major problems with predicting how biodiversity might respond to climate change is the typical simplicity of single-species ‘envelope’ models – these models basically use tolerance limits (generally, physiological) or optimum conditions to predict how a species’ distribution might change. Unfortunately, this usually negates the complex dynamics of populations, the dispersal capacity of individuals, and interactions with other species that may all dominate possible responses. In other words, climatic envelope models may be way, way off (and probably vastly optimistic).

Keith and colleagues have brought us a step closer to better predictions of (and hopefully, better responses to) climate change effects on species. They linked a time series of habitat suitability models with spatially explicit stochastic population models to explore factors that influence the viability of plant species populations in South African fynbos, a global biodiversity hotspot. They discovered that complex interactions between life history, disturbance regimes and distribution patterns mediate species extinction risks under climate change.

Well done! Our next challenge is to incorporate multiple species’ interactions into such models (just to make them as mind-bogglingly complex as possible) to give us better approaches for managing our depauperate future.

CJA Bradshaw

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Loss of nature’s value makes bank crisis look ridiculous

13 10 2008

Thanks for pointing this one out, Tim (see ConsBlog.org). In the theme of demonstrating (how many different ways do we need to show this before it bloody well sinks in?) the value of ecosystem services currently being degraded by habitat loss, invasive species, over-exploitation and climate change, some people in power are starting to take notice.

All you investors, bankers, share brokers and buyers – beware! Without a large upheaval of the current economic system that promotes absolute consumption and growth in a finite and dwindling resource base, you will lose a lot more that the value of a few shares.

The global economy is losing more money from the disappearance of forests than through the current banking crisis, according to an EU-commissioned study.

It puts the annual cost of forest loss at between $2 trillion and $5 trillion… (read on)






Poor media coverage promotes environmental apathy and untruths

11 10 2008

I just came across this excellent opinion piece by James Fahn on how climate change is covered by the media.

Poor countries’ media must tackle climate change

Paraphrasing briefly, the article laments the ill-equipped, uninformed and lowly stature of reporters covering climate change issues. The corollary is that simple junk, badly researched stances and plain untruths are rife throughout the media. For many, many examples of such plainly misinformed ‘journalism’ on climate change issues, just visit BraveNewClimate.com for a taste of the worst.

My comments on Fahn’s piece touch on several issues. First, it’s not just the ‘poor’ country that has problems with respect to ill-equipped reporters – the developed world (and Australia could easily be one of the leaders here) has some particulary terrible coverage of climate change impacts. Second, this problem extends to all environmental issues, not just climate change. Indeed, for some of the most important issues facing humanity today (loss of biodiversity and the ecosystem services they provide), should not the best people be put onto the job? Finally, whatever happened to journalism? Isn’t this supposed to be well-researched, cross-examining, hard-hitting and plain investigation into the affairs affecting everyday life? Instead, too many so-called ‘journalists’ are nothing more than blindly parrotting reporters who wouldn’t know what research was if it came up and bit them on the arse.

Addendum 16 October: I’ve added a little poll below directed toward Australian blog readers:

CJA Bradshaw

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Wake Up, Freak Out

9 10 2008
© Leo Murray

© Leo Murray

An excellent, short animated film about the perils of climate change and its implications for biodiversity (including humans). Highly recommended.

This really isn’t about polar bears any more. At this very moment, the fate of civilization itself hangs in the balance.

It turns out that the way we have been calculating the future impacts of climate change up to now has been missing a really important piece of the picture. It seems we are now dangerously close to the tipping point in the world’s climate system; this is the point of no return, after which truly catastrophic changes become inevitable.

Wake Up, Freak Out – then Get a Grip is a short, animated film about climate change by Leo Murray.





Classics: Fragmentation

3 10 2008
Figure 2 from Brook et al. (2008): Synergies among threatening processes relative to habitat loss and fragmentation. a) A large population within unmodified, contiguous habitat occupies all available niches so that long-term abundance fluctuates near full carrying capacity (K). b) When habitat is reduced (e.g. 50 % area loss), total abundance declines accordingly. c) However, this simple habitat-abundance relationship is complicated by the spatial configuration of habitat loss. In this example, all remaining fragmented subpopulations might fall below their minimum viable population (MVP) sizes even though total abundance is the same proportion of K as in panel B. As such, limited connectivity between subpopulations implies much greater extinction risk than that predicted for the same habitat loss in less fragmented landscapes. Further synergies (positive feedbacks among threatening processes; black arrows) might accompany high fragmentation, such as enhanced penetration of predators, invasive species or wildfire, micro-habitat edge effects, and reduced resistance to drought with climate change.

Figure 2 from Brook et al. (2008): Synergies among threatening processes relative to habitat loss and fragmentation. a) A large population within unmodified, contiguous habitat occupies all available niches so that long-term abundance fluctuates near full carrying capacity (K). b) When habitat is reduced (e.g., 50 % area loss), total abundance declines accordingly. c) However, this simple habitat-abundance relationship is complicated by the spatial configuration of habitat loss. In this example, all remaining fragmented subpopulations might fall below their minimum viable population (MVP) sizes even though total abundance is the same proportion of K as in panel B. As such, limited connectivity between subpopulations implies much greater extinction risk than that predicted for the same habitat loss in less fragmented landscapes. Further synergies (positive feedbacks among threatening processes; black arrows) might accompany high fragmentation, such as enhanced penetration of predators, invasive species or wildfire, micro-habitat edge effects, and reduced resistance to drought with climate change.

This is, perhaps, one of the most important concepts that the field of conservation biology has identified as a major driver of extinction. It may appear on the surface a rather simple notion that the more ‘habitat’ you remove, the fewer species (and individuals) there will be (see MacArthur & Wilson’s Classic contribution: The Theory of Island Biogeography), but it took us decades (yes, embarrassingly – decades) to work out that fragmentation is bad (very, very bad).

Habitat fragmentation occurs when a large expanse of a particular, broadly defined habitat ‘type’ is reduced to smaller patches that are isolated by surrounding, but different habitats. The surrounding habitat is typically defined a ‘matrix’, and in the case of forest fragmentation, generally means ‘degraded’ habitat (fewer native species, urban/rural/agricultural development, etc.).

Fragmentation is bad for many reasons: it (1) reduces patch area, (2) increases isolation among populations associated with fragments, and (3) creates ‘edges’ where unmodified habitat abuts matrix habitat. Each of these has dire implications for species, for we now know that (1) the smaller an area, the fewer individuals and species in can contain, (2) the more isolated a population, the less chance immigrants will ‘rescue’ it from catastrophes, and (3) edges allow the invasion of alien species, make the microclimate intolerable, increase access to bad humans and lead to cascading ecological events (e.g., fire penetration). Make no mistake, the more fragmented an environment, the worse will be the extinction rates of species therein.

What’s particularly sad about all this is that fragmentation was actually seen as a potentially GOOD thing by conservation biologists for many long years. The so-called SLOSS (Single Large or Several Small) debate pervaded the early days of conservation literature. The debate was basically the argument that several small reserves would provide more types of habitat juxtapositions and more different species complexes, making overall diversity (species richness) higher, than one large reserve. It was an interesting, if not deluded, intellectual debate because both sides presented some rather clever theoretical and empirical arguments. Part of the attraction of the ‘Several Small’ idea was that it was generally easier to find series of small habitat fragments to preserve than one giant no-go area.

However, we now know that the ‘Several Small’ idea is completely inferior because of the myriad synergistic effects of fragmentation. It actually took Bruce Wilcox and Dennis Murphy until 1985 to bring this to everyone’s attention in their classic paper The effects of fragmentation on extinction to show how silly the SLOSS debate really was. It wasn’t, however, until the mid- to late 1990s that people finally started to accept the idea that fragmentation really was one of the biggest conservation evils. Subsequent work (that I’ll showcase soon on ConservationBytes.com) finally put the nail in the SLOSS debate coffin, and indeed, we haven’t heard a whisper of it for over a decade.

For more general information, I invite you to read the third chapter in our book Tropical Conservation Biology entitled Broken homes: tropical biotas in fragmented landscapes, and our recent paper in Trends in Ecology and Evolution entitled Synergies among extinction drivers under global change.

CJA Bradshaw

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