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Corridors of uncertainty
OPINION
Corridors of uncertainty Strips of land linking wildlife reserves are one of the most widely used tools in conservation. Shame nobody checked that they work, says Fred Pearce WILD elephants roam across the crowded plains of India; forested river banks wind through cattle ranches in Brazil; a ribbon of green stretches across Europe where the Iron Curtain used to be. Such wildlife corridors linking up larger but isolated protected areas are the most widely adopted strategy for halting biodiversity decline, with tens of millions of dollars spent creating and protecting them every year. But do they work? Has enthusiasm for a neat idea got ahead of the science? Might corridors sometimes do more harm than good? The principle is simple. As wildlife habitat is broken into isolated fragments by farms, roads and settlements, we need to link them up with corridors of green. That way, even if the entire habitat cannot be recreated, old migration patterns can be revived, escape routes created ahead of climate change and – perhaps most crucially – isolated populations can interbreed, enhancing their genetic diversity and their resilience to encroaching threats. The idea started with one of the icons of conservation science, E. O. Wilson of Harvard University. His 1960s work on islands revealed how isolated ecosystems were threatened by their isolation. Corridors were the obvious answer and, half a century on, they are all the rage in national conservation plans from Australia to Zambia. Many are cross-border, such as the Selous-Niassa Corridor linking Tanzania and Mozambique, and the Lower Danube Green Corridor 26 | NewScientist | 4 February 2012
across Romania, Bulgaria, Ukraine them. But that’s not the case. and Moldova. When the Iron Recently, Paul Beier, a veteran Curtain fell two decades ago, conservation biologist from North governments from both sides Arizona University at Flagstaff, rushed to convert the border zone and his colleague Andrew into a corridor for the wildlife that Gregory, warned that “despite had prospered amid the land much research, there is little mines, barbed wire and gun evidence that conservation placements. All seven countries corridors work as intended”. of Central America and Mexico There is, they say, plenty of have agreed to join together their evidence that wild animals will many small protected areas in a move through corridors. But MesoAmerican Biological advocates of the corridors want, Corridor that will ultimately link and claim, much more than this. North and South America. They say that animals don’t just After several decades of activity “If corridors do not work, you might expect good research much of our wildlife evidence on the advantages of conservation efforts both newly created corridors and will come to nought” the natural corridors that mimic
go for a walk in their conservation woods, but that they move permanently and interbreed with neighbouring populations. In this way corridors supposedly unite isolated, threatened populations into an interbreeding – and much more resilient – whole. Such claims sometimes hold up. In the UK, the expansion of Kielder Forest in Northumberland in the 1950s and 60s provided a link between isolated populations of threatened red squirrel. Genes from isolated populations have now “leapfrogged through hundreds of forest fragments” across 100 kilometres and more (Science, vol 293, p 2246). But the Kielder Forest is much wider than a conventional corridor. Few studies have looked for gene flow in genuine corridors; even fewer have found it. One study investigated the genetic diversity of small marsupials in a narrow forest corridor traversing 4.5 kilometres of grazed grasslands in Queensland, Australia. It found that genetically distinct populations had persisted at either end. Mixing was a myth (Landscape Ecology, vol 21, p 641). Other studies have shown that conservation corridors work. But most have looked at short corridors of a hundred metres or so through largely natural landscape. “Just because species can use and travel along short corridors in a natural setting does not mean that they will be successful dispersing along much longer corridors embedded in a large, heavily impacted landscape,” says Gregory. “Still
Comment on these stories at newscientist.com/opinion
Fred Pearce is a consultant for New Scientist. For more information on the Do Corridors Work? project visit docorridorswork.org
One minute with...
Dan Marrone Images of a black hole could test general relativity, says the man hoping to take the first photo of one A black hole, by definition, is black. So how are you going to take a picture of one? If you look right at the black hole it should look quite dark, as very little light escapes. But just around the edge of it you see a bright ring, which is due to the photons that barely missed going into the black hole and skimmed around the edge of it a couple of times. This light is what we think we will be able to detect with the Event Horizon Telescope (EHT). The EHT is a “whole Earth telescope”. How does it work? In radio astronomy, to get a higher resolution than you can from a single telescope, you record signals from many telescopes around the world and multiply them together with a special computer. It is as if you have a single telescope almost the size of the Earth. Which black holes are you targeting? Sagittarius A*, which is the supermassive black hole at the centre of our galaxy, and the black hole at the centre of M87, the biggest galaxy in the Virgo cluster of galaxies. With a telescope the size of the Earth and at the frequencies we are observing, we can just make out black holes of this size. Every image of a black hole so far has been an artist’s impression. Will the real thing match expectations? The question of creating an image from what we measure is a tricky one. We will most likely represent it as a false colour image, using colours to represent how bright the light is. This image will not be as pretty as an artist’s impression. The galaxy blurs the light between us and the black hole, so there are a lot of sharp features we can’t possibly see. But any image we get shouldn’t disappoint – we are looking at something no one has ever seen before. What about capturing a moving image – “black hole, the movie” as it were? We can, if there is something orbiting the black
Profile Dan Marrone is an astronomer at the University of Arizona Steward Observatory. He is part of the Event Horizon Telescope programme, inaugurated last month, which aims to take the first picture of a black hole in 2015
hole, as we expect there will be. If there is gas orbiting before it falls into the black hole, this takes between 4 and 27 minutes, depending on the spin of the black hole. If we look for several days and see changes in the structure, we can represent that as a movie as well. What are you hoping to learn from this image? Just being able to take a picture of a black hole, and show this shadow that we expect to be there because the light is not escaping, will be important. Beyond that we have a lot to learn about the structure of our galaxy’s black hole, and what happens to a black hole when it is being starved of material, as Sagittarius A* appears to be. We also expect to be able to test general relativity, which tells us that the ring of light around the edge of the back hole needs to be perfectly circular. If general relativity is breaking in this very strong field regime, where gravity is at the limits of its power, then this ring of light won’t be perfectly circular. Interview by Jon White
4 February 2012 | NewScientist | 27
jorge vieira
less that such movements occur frequently enough to allow enough gene flow to occur so that the connected habitat blocks function as one population.” Many corridors are useless. Developers in the Brazilian Amazon are required by the national Forest Code to leave 60-metre-wide forest strips along river banks. But a study of birds and animals in those corridors found that anything with a width less than 400 metres had no benefit on the numbers of species along the banks, let alone on promoting gene transfer (Conservation Biology, vol 22, p 439). Yet, far from widening the corridors, the Brazilian parliament recently voted to relax the Forest Code. This all matters because big claims are made for conservation corridors. The suggestion is that they can minimise the impact of development by substituting for wild habitat. If that is wrong, much of our conservation efforts will come to nought. Gregory and Beier have set up a project, Do Corridors Work?, to work out what makes a successful corridor, and have issued a plea for help finding ones to investigate. Perhaps we should not make the perfect the enemy of the good. Surely any corridor is better than none? But consider this. The edges of wild areas are known danger zones for wildlife, where predators and diseases may invade. Linking two existing protected areas with a long narrow corridor may expose it to greater danger along these edges. Unless the benefit exceeds the threat, then there is serious potential to do harm. Gregory and Beier do not dismiss corridors altogether. They believe they can still work, if designed properly. The problem is, we don’t really know what that means. n
Corridors of uncertainty Strips of land linking wildlife reserves are one of the most widely used tools in conservation. Shame nobody checked that they work, says Fred Pearce WILD elephants roam across the crowded plains of India; forested river banks wind through cattle ranches in Brazil; a ribbon of green stretches across Europe where the Iron Curtain used to be. Such wildlife corridors linking up larger but isolated protected areas are the most widely adopted strategy for halting biodiversity decline, with tens of millions of dollars spent creating and protecting them every year. But do they work? Has enthusiasm for a neat idea got ahead of the science? Might corridors sometimes do more harm than good? The principle is simple. As wildlife habitat is broken into isolated fragments by farms, roads and settlements, we need to link them up with corridors of green. That way, even if the entire habitat cannot be recreated, old migration patterns can be revived, escape routes created ahead of climate change and – perhaps most crucially – isolated populations can interbreed, enhancing their genetic diversity and their resilience to encroaching threats. The idea started with one of the icons of conservation science, E. O. Wilson of Harvard University. His 1960s work on islands revealed how isolated ecosystems were threatened by their isolation. Corridors were the obvious answer and, half a century on, they are all the rage in national conservation plans from Australia to Zambia. Many are cross-border, such as the Selous-Niassa Corridor linking Tanzania and Mozambique, and the Lower Danube Green Corridor 26 | NewScientist | 4 February 2012
across Romania, Bulgaria, Ukraine them. But that’s not the case. and Moldova. When the Iron Recently, Paul Beier, a veteran Curtain fell two decades ago, conservation biologist from North governments from both sides Arizona University at Flagstaff, rushed to convert the border zone and his colleague Andrew into a corridor for the wildlife that Gregory, warned that “despite had prospered amid the land much research, there is little mines, barbed wire and gun evidence that conservation placements. All seven countries corridors work as intended”. of Central America and Mexico There is, they say, plenty of have agreed to join together their evidence that wild animals will many small protected areas in a move through corridors. But MesoAmerican Biological advocates of the corridors want, Corridor that will ultimately link and claim, much more than this. North and South America. They say that animals don’t just After several decades of activity “If corridors do not work, you might expect good research much of our wildlife evidence on the advantages of conservation efforts both newly created corridors and will come to nought” the natural corridors that mimic
go for a walk in their conservation woods, but that they move permanently and interbreed with neighbouring populations. In this way corridors supposedly unite isolated, threatened populations into an interbreeding – and much more resilient – whole. Such claims sometimes hold up. In the UK, the expansion of Kielder Forest in Northumberland in the 1950s and 60s provided a link between isolated populations of threatened red squirrel. Genes from isolated populations have now “leapfrogged through hundreds of forest fragments” across 100 kilometres and more (Science, vol 293, p 2246). But the Kielder Forest is much wider than a conventional corridor. Few studies have looked for gene flow in genuine corridors; even fewer have found it. One study investigated the genetic diversity of small marsupials in a narrow forest corridor traversing 4.5 kilometres of grazed grasslands in Queensland, Australia. It found that genetically distinct populations had persisted at either end. Mixing was a myth (Landscape Ecology, vol 21, p 641). Other studies have shown that conservation corridors work. But most have looked at short corridors of a hundred metres or so through largely natural landscape. “Just because species can use and travel along short corridors in a natural setting does not mean that they will be successful dispersing along much longer corridors embedded in a large, heavily impacted landscape,” says Gregory. “Still
Comment on these stories at newscientist.com/opinion
Fred Pearce is a consultant for New Scientist. For more information on the Do Corridors Work? project visit docorridorswork.org
One minute with...
Dan Marrone Images of a black hole could test general relativity, says the man hoping to take the first photo of one A black hole, by definition, is black. So how are you going to take a picture of one? If you look right at the black hole it should look quite dark, as very little light escapes. But just around the edge of it you see a bright ring, which is due to the photons that barely missed going into the black hole and skimmed around the edge of it a couple of times. This light is what we think we will be able to detect with the Event Horizon Telescope (EHT). The EHT is a “whole Earth telescope”. How does it work? In radio astronomy, to get a higher resolution than you can from a single telescope, you record signals from many telescopes around the world and multiply them together with a special computer. It is as if you have a single telescope almost the size of the Earth. Which black holes are you targeting? Sagittarius A*, which is the supermassive black hole at the centre of our galaxy, and the black hole at the centre of M87, the biggest galaxy in the Virgo cluster of galaxies. With a telescope the size of the Earth and at the frequencies we are observing, we can just make out black holes of this size. Every image of a black hole so far has been an artist’s impression. Will the real thing match expectations? The question of creating an image from what we measure is a tricky one. We will most likely represent it as a false colour image, using colours to represent how bright the light is. This image will not be as pretty as an artist’s impression. The galaxy blurs the light between us and the black hole, so there are a lot of sharp features we can’t possibly see. But any image we get shouldn’t disappoint – we are looking at something no one has ever seen before. What about capturing a moving image – “black hole, the movie” as it were? We can, if there is something orbiting the black
Profile Dan Marrone is an astronomer at the University of Arizona Steward Observatory. He is part of the Event Horizon Telescope programme, inaugurated last month, which aims to take the first picture of a black hole in 2015
hole, as we expect there will be. If there is gas orbiting before it falls into the black hole, this takes between 4 and 27 minutes, depending on the spin of the black hole. If we look for several days and see changes in the structure, we can represent that as a movie as well. What are you hoping to learn from this image? Just being able to take a picture of a black hole, and show this shadow that we expect to be there because the light is not escaping, will be important. Beyond that we have a lot to learn about the structure of our galaxy’s black hole, and what happens to a black hole when it is being starved of material, as Sagittarius A* appears to be. We also expect to be able to test general relativity, which tells us that the ring of light around the edge of the back hole needs to be perfectly circular. If general relativity is breaking in this very strong field regime, where gravity is at the limits of its power, then this ring of light won’t be perfectly circular. Interview by Jon White
4 February 2012 | NewScientist | 27
jorge vieira
less that such movements occur frequently enough to allow enough gene flow to occur so that the connected habitat blocks function as one population.” Many corridors are useless. Developers in the Brazilian Amazon are required by the national Forest Code to leave 60-metre-wide forest strips along river banks. But a study of birds and animals in those corridors found that anything with a width less than 400 metres had no benefit on the numbers of species along the banks, let alone on promoting gene transfer (Conservation Biology, vol 22, p 439). Yet, far from widening the corridors, the Brazilian parliament recently voted to relax the Forest Code. This all matters because big claims are made for conservation corridors. The suggestion is that they can minimise the impact of development by substituting for wild habitat. If that is wrong, much of our conservation efforts will come to nought. Gregory and Beier have set up a project, Do Corridors Work?, to work out what makes a successful corridor, and have issued a plea for help finding ones to investigate. Perhaps we should not make the perfect the enemy of the good. Surely any corridor is better than none? But consider this. The edges of wild areas are known danger zones for wildlife, where predators and diseases may invade. Linking two existing protected areas with a long narrow corridor may expose it to greater danger along these edges. Unless the benefit exceeds the threat, then there is serious potential to do harm. Gregory and Beier do not dismiss corridors altogether. They believe they can still work, if designed properly. The problem is, we don’t really know what that means. n