World will shift to smaller animals over next century: Study

Smaller birds and mammals, which can thrive in a wide-variety of habitats, are more likely to avoid becoming extinct over the next 100 years, scientists say.

Researchers at the University of Southampton in the UK predict a worldwide move towards smaller birds and mammals in the next century.

In the future, small, fast-lived, highly-fertile, insect-eating animals, which can thrive in a wide-variety of habitats, will predominate. 

These 'winners' include rodents, such as dwarf gerbil -- and songbirds, such as the white-browed sparrow-weaver, they said.

Less adaptable, slow-lived species, requiring specialist environmental conditions, will likely fall victim of extinction. These 'losers' include the tawny eagle and black rhinoceros.

The study, published in the journal Nature Communications, predict the average body mass of mammals specifically will collectively reduce by 25 per cent over the next century. 

This decline represents a large, accelerated change when compared with the 14 per cent body size reduction observed in species from 130,000 years ago until today.

"By far the biggest threat to birds and mammals is humankind -- with habitats being destroyed due to our impact on the planet, such as deforestation, hunting, intensive farming, urbanisation and the effects of global warming," said Rob Cooke, a postgraduate researcher at the University of Southampton.

"The substantial 'downsizing' of species which we forecast could incur further negative impacts for the long-term sustainability of ecology and evolution," said Cooke.

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"This downsizing may be happening due to the effects of ecological change but, ironically, with the loss of species which perform unique functions within our global ecosystem, it could also end up as a driver of change too," he said.

The research team focussed on 15,484 living land mammals and birds and considered five characteristics that relate to the role of each species in nature: body mass, litter/clutch size, breadth of habitat, diet and length of time between generations. 

In addition, the researchers used the International Union for Conservation of Nature (IUCN) Red List of Threatened Species to determine which animals are most likely to become extinct in the next century. 

They used modern statistical tools to combine all this data to make their projections and evaluate the loss of biodiversity.

"We have demonstrated that the projected loss of mammals and birds will not be ecologically random -- rather a selective process where certain creatures will be filtered out, depending on their traits and vulnerability to ecological change," said Felix Eigenbrod, a professor at the University of Southampton.

"Extinctions were previously viewed as tragic, deterministic inevitabilities, but they can also be seen as opportunities for targeted conservation actions," said Amanda Bates, Research Chair at Memorial University in Canada.

"As long as a species that is projected to become extinct persists, there is time for conservation action and we hope research such as ours can help guide this," Bates said. 

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