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Comment and Earth

Humans decimating the diversity of life should worry us all

A global limit set for safe biodiversity loss may be a blunt tool, but we still need to worry about breaching it far and wide says Georgina Mace

By Georgina Mace

19 July 2016

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Sun sets on Damaraland, Namibia

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As Earth’s population grows, so too does our use of the land, converted from its natural, prehuman state to farms, roads, quarries and more with an inevitable loss of species.

At what point does this threaten the sustainability of society?

Scientists have speculated about this for decades, but finally it is possible to start answering that question. A major study published last week shed much needed light on how we are doing. The outcome should worry us all.

It analysed more than 2 million records on around 39,000 species. Researchers were able to work out changes at the local scale as a result of human impact, and relate them to a revised planetary biosphere boundary proposed last year. It turns out that 10 per cent of native species have gone from over 58 per cent of all land.

Why worry about species loss? There are moral and aesthetic reasons, but here the focus was species’ functional role, sustaining plant growth rates, for example, or nutrient cycling and decomposition.

We know that many of these roles are best maintained with greater diversity of species, and the global extinction rate is estimated to be at least 100-fold that of pre-human times. These metrics underpinned the first biodiversity boundary set in 2009.

That was revised last year to reflect several factors: that the global extinction rate does not translate straightforwardly to the local scale (it is local diversity that is important), and that variety of functional types of species may be more vital than the total number.

How definitive is the new snapshot? The findings are slightly improved if non-native species are included, while a less precautionary approach suggests biodiversity could dip more than 10 per cent before being unsafe.

On the other hand, the situation may be worse, as some of the most vital ecosystem functions are in biomes where data is sparse but sensitivity to species loss may be very high, such as tundra.

Clearly, we need to refine this planetary boundary. But even if it is not perfect, it is all we have, and we should worry deeply about breaching it so widely.

Journal: Science, DOI: DOI: 10.1126/science.aaf2201

Georgina Mace is professor of biodiversity and ecosystems at University College London

 

 

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