Wesley Stevenson
speaker
1,470 appearances
54 recordings
1 series
first heard Sep 2010
last heard May 2015
Wesley Stevenson’s voice in public audio — every appearance, attributed to the second.
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Appearances
Let's take a trip into the jungle.
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And if the WWF and the Zoological Society of London are right, there are now fewer animals here than there were 40 years ago, and they've fallen by an average rate of 50%.
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In fact, it's not just in the jungles, but all over the world.
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This news prompted startling headlines and it also got the more or less inbox buzzing.
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We've had a lot of emails like this one from Steve Welsh.
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More or less listeners are a sceptical lot, so let's have a look at what the figure means and how it was arrived at.
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It came from the recently released Living Planet Index, and the project manager is Louise McRae from the Zoological Society of London.
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So does it mean that if you counted all the vertebrates in 1970 and counted them all in 2010, the number is 50% less?
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Let's imagine a scenario.
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You have two populations, one of frogs and one of birds.
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And let's say in 1970, there were 10 frogs and 100 birds, giving a total of 110 animals.
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By 2010, the frogs had declined by 80% and the birds by 20%, leaving two frogs and 80 birds, a total of 82 animals.
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The average decline of these two populations is 50%, but the total number of animals hasn't halved, which is probably not what most people would have understood from the headlines.
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Another thing about the index, as loyal listener Steve points out, is this is just an index of vertebrates and doesn't include insects or plants, and it's not as if either the WWF or the Zoological Society of London have actually been out to count the animals themselves.
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This is a figure modelled using available data.
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some of which is patchy.
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But also you're placing more weight on those areas where the data isn't as rich as it is, for example, in Europe and other parts of the world.
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Now there's nothing wrong with modelling the figures, and Louise and her colleagues feel confident that the way they've extrapolated the data has given them a pretty solid figure, with a margin of error of 10 percentage points either way.
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But there are some who aren't so confident that the figure really tells us what they think it's telling us.
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The weighting in favour of tropical areas, where there's less data, has caused concern for people like Professor Steve Buckland, Professor of Biostatistics at St Andrews University in Scotland, and whose models are used in calculating the figure.
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Showing 141–160 of 1,470 · page 8 of 74
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