Extinction

Two teams of British scientists have produced the best evidence yet that our planet is experiencing a mass extinction.

Two separate papers, published in Science 19 March and funded largely by the Natural Environment Research Council (NERC) highlight the serious concerns that have been growing among the world’s scientists for over ten years.

John Lawton, chief executive of NERC and co-author of one of the papers said, ’Fossil records show five major extinctions. Current extinction rates are approaching these magnitudes. The difference is that this extinction is caused by one species – us.’

Both teams based their findings on surveys carried out on species diversity in plants and animals in Britain.

The first team, led by Dr Jeremy Thomas from the Centre for Ecology and Hydrology Dorset, looked at the drop in the numbers of bird, butterfly and plant species over a 40-year period here in Britain.

They analysed three surveys produced between twenty and forty years ago covering nearly all the UK’s native bird, plant and butterfly populations. Thousands of volunteers collected the data by scrutinising 10km squares of countryside on the Ordnance Survey national.

The surveys were recently repeated providing the chance to compare changes in species number and abundance of birds, plants and butterflies in Britain.

Jeremy said, ’In the last ten years there has been an enormous interest in global extinction rates but it has always been difficult to quantify. These are the most detailed surveys in the world, and, for the first time, we have good data on one group of insects – butterflies. The reason this is important is because insects make up 54% of all known species on this planet.

’Past assumptions about extinction were based on just a small number of species studied; mainly birds. But birds make up only 0.6% of all species on Earth.’

He went on to say, ’The results are appalling. In Britain 71% of all butterfly species have declined in the last 20 years. For the first time we can say, that in the UK, one group of insects has suffered as badly as birds or plants – this adds enormous strength to hypothesis that the world is approaching its sixth major extinction event.’

The second paper, led Carly Stevens of the Open University, points the finger at mankind as the cause for this loss of biodiversity.

Carly and colleagues at the Centre for Ecology and Hydrology Monks Wood, and Villanova University in the USA, studied the effects of pollution on the number of plant species on 68 grassland sites throughout Britain. In particular they looked at nitrogen pollution from industry, traffic, and agricultural emissions such as fertilisers and animal waste.

They discovered that as nitrogen levels increased the number of plant species decreased.

Carly, 25, an Open University and NERC-funded PhD student, said, ’I studied the same type of grassland in different sites. Plants that were particularly sensitive were heather, harebell, eyebright, purple moor grass, mountain fern moss and ribwort plantain.

’The average levels of nitrogen pollution in the UK and Europe may be resulting in over 20% loss of species richness. This is a very strong argument for the need to reduce pollution.’

EU legislation has set a maximum level for nitrogen emissions of 25kg per hectare per year. Below this, legislators say, nitrogen levels do not cause noticeable damage to the grasslands. Carly’s research suggests this limit is too high and that any level of pollution reduces the number of plant species, thus affecting biodiversity.

Co-author Nancy Dise said, ’The data suggests that it has taken around 40 years of high nitrogen deposition to get to this state, so it may take some time for species to return. And some of the changes may be irreversible”