Apparently, you need to kiss a lot of frogs before you find a prince.
Turns out you also need to examine a lot of piles of elephant dung before you find a frog. 48.33, to be precise.
Now, if someone could be a bit more quantitative about the frog/prince ratio, we could work out princes per pile of elephant dung.
Showing posts with label elephants. Show all posts
Showing posts with label elephants. Show all posts
Thursday, May 28, 2009
Wednesday, May 27, 2009
No animals, no trees
A couple of recent papers show how seed dispersal is harmed when forest vertebrates disappear - it's not just bees and microbes that provide ecosystem services, we need the big stuff too.
In Biotropica, Stephen Blake of the WCS and colleagues look at seeds in the dung of forest elephants in the Congo. There are a lot:
And in Ecological Applications a US/Thai team look at the impact of bushmeat hunting on the dispersal of the hog plum, Choerospondias axillaris which, as the name suggests needs mammals (although not just pigs) to move it about. The clue is in the paper's title 'Bushmeat poaching reduces the seed dispersal and population growth rate of a mammal-dispersed tree.' "Extinction of C. axillaris is a real possibility, but may take many decades," they add. "Recent and ongoing extirpations of vertebrates in many tropical forests could be creating an extinction debt for zoochorous trees whose vulnerability is belied by their current abundance."
In Guanacaste, Costa Rica, they (especially Dan Janzen) got round this problem by introducing cattle, replacing the large herbivores that had gone extinct in prehistory. The trees thrived as a result. But Guanacaste is a dry forest. To paraphrase the music hall song about the horse and the lighthouse, I imagine it'd be harder to keep a cow in a jungle.
In Biotropica, Stephen Blake of the WCS and colleagues look at seeds in the dung of forest elephants in the Congo. There are a lot:
Analysis of 855 elephant dung piles suggested that forest elephants disperse more intact seeds than any other species or genus of large vertebrate in African forests, while GPS telemetry data showed that forest elephants regularly disperse seeds over unprecedented distances compared to other dispersers. ... Our results suggest that the loss of forest elephants (and other large-bodied dispersers) may lead to a wave of recruitment failure among animal-dispersed tree species, and favor regeneration of the species-poor abiotically dispersed guild of trees.
And in Ecological Applications a US/Thai team look at the impact of bushmeat hunting on the dispersal of the hog plum, Choerospondias axillaris which, as the name suggests needs mammals (although not just pigs) to move it about. The clue is in the paper's title 'Bushmeat poaching reduces the seed dispersal and population growth rate of a mammal-dispersed tree.' "Extinction of C. axillaris is a real possibility, but may take many decades," they add. "Recent and ongoing extirpations of vertebrates in many tropical forests could be creating an extinction debt for zoochorous trees whose vulnerability is belied by their current abundance."
In Guanacaste, Costa Rica, they (especially Dan Janzen) got round this problem by introducing cattle, replacing the large herbivores that had gone extinct in prehistory. The trees thrived as a result. But Guanacaste is a dry forest. To paraphrase the music hall song about the horse and the lighthouse, I imagine it'd be harder to keep a cow in a jungle.
Friday, February 09, 2007
Just Science day 5: Kill and cure?
The best way to protect an endangered species might be to ... cull it.
That's the conclusion reached by Michael Bode and Hugh Possingham in a theoretical analysis published recently in Ecological Modelling. The problem that they address is the tendency of some species to show boom-and-bust population dynamics. This seems a particular feature of tightly linked predator-prey systems: if predator is rare, prey booms, predator has lots of food, predator booms, prey crashes, predator starves, predator crashes, and so on. The Canadian lynx-hare system is the most famous example.
At the bottom of the cycles, population sizes might be so small that either predator or prey is highly vulnerable to extinction - by some other event, such as disease or disaster.
Bode and Possingham model various options for damping these cycles by removing some predators, prey, or both, from the system. "Remarkably," they say, "if the interventions are enacted at the appropriate time, infrequent culling of a small number of individuals significantly reduces the probability of extinction of the predator."
My first thought when I saw this, was that we probably rarely know enough about a species' population dynamics to know when the best time to cull is, and that such a move would be politically untenable. But, as Bode points out, the most likely candidates for such a move are large game-park species, such as elephants, about which we know quite a lot. It's also heartening that their (as they say, simplistic) simulation suggests that culling prey (which would be plants for elephants, I suppose) is more likely to be effective than predators, and that culling would be needed only rarely.
They conclude:
I swapped e-mails with Bode, and besides mentioning that, in parks with very high elephant densities, such as Kruger, culling elephants seems 'almost unavoidable' (the issue seems to have flared up most recently in late 2005, judging by this BBC story), he also mentioned that similar issues were arising in Australia regarding koalas and kangaroos. As he says, why is it always the cure animals?
All I can say is I'm glad I don't have to make these decisions. Culling animals is clearly a terrible business - particularly for long-lived, highly social species such as elephants. But we now effectively control the destiny of all large, slow-breeding vertebrates. If the only places they can survive is in the parks we set up, and if we take a truly utilitarian and, dread word, holistic view of conservation, then we also have to take the responsibility of 'managing' their populations. Science isn't he only thing to guide us on such decisions, but it's best ot take as informed and clever a decision as possible, towards which Bode and Possingham's ideas can only help.
That's the conclusion reached by Michael Bode and Hugh Possingham in a theoretical analysis published recently in Ecological Modelling. The problem that they address is the tendency of some species to show boom-and-bust population dynamics. This seems a particular feature of tightly linked predator-prey systems: if predator is rare, prey booms, predator has lots of food, predator booms, prey crashes, predator starves, predator crashes, and so on. The Canadian lynx-hare system is the most famous example.
At the bottom of the cycles, population sizes might be so small that either predator or prey is highly vulnerable to extinction - by some other event, such as disease or disaster.
Bode and Possingham model various options for damping these cycles by removing some predators, prey, or both, from the system. "Remarkably," they say, "if the interventions are enacted at the appropriate time, infrequent culling of a small number of individuals significantly reduces the probability of extinction of the predator."
My first thought when I saw this, was that we probably rarely know enough about a species' population dynamics to know when the best time to cull is, and that such a move would be politically untenable. But, as Bode points out, the most likely candidates for such a move are large game-park species, such as elephants, about which we know quite a lot. It's also heartening that their (as they say, simplistic) simulation suggests that culling prey (which would be plants for elephants, I suppose) is more likely to be effective than predators, and that culling would be needed only rarely.
They conclude:
Most current methods of ecosystem control attempt to keep a single species population below a certain threshold, or between fixed bounds, leading to highly inefficient management. Furthermore, unnecessarily high levels of culling can generate considerable public opposition. Given the clumsy nature of such static controls, this view may be reasonable. Our dynamic control solution has the substantial benefit of minimising the preventable culling of organisms, and being extremely cost-effective.
I swapped e-mails with Bode, and besides mentioning that, in parks with very high elephant densities, such as Kruger, culling elephants seems 'almost unavoidable' (the issue seems to have flared up most recently in late 2005, judging by this BBC story), he also mentioned that similar issues were arising in Australia regarding koalas and kangaroos. As he says, why is it always the cure animals?
All I can say is I'm glad I don't have to make these decisions. Culling animals is clearly a terrible business - particularly for long-lived, highly social species such as elephants. But we now effectively control the destiny of all large, slow-breeding vertebrates. If the only places they can survive is in the parks we set up, and if we take a truly utilitarian and, dread word, holistic view of conservation, then we also have to take the responsibility of 'managing' their populations. Science isn't he only thing to guide us on such decisions, but it's best ot take as informed and clever a decision as possible, towards which Bode and Possingham's ideas can only help.
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