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Winners and losers

Study predicts 'downsizing' to smaller animals over next century


By Kelly Foss

Researchers, including one from Memorial University, are forecasting a worldwide move towards smaller birds and mammals over the next 100 years.

Dr. Amanda Bates, Canada Research Chair in Marine Physiological Ecology, and associate professor, Department of Ocean Sciences, Faculty of Science, joined with geographers, biologists and oceanographers at the University of Southampton on a paper published recently in the journal Nature Communications.

Top row: dwarf gerbil and white-browed sparrow-weaver. Bottom row: tawny eagle and black rhinoceros.
Top row: dwarf gerbil and white-browed sparrow-weaver. Bottom row: tawny eagle and black rhinoceros.
Photo: Robert Cooke

It argues that, in the future, small, fast-lived, highly fertile, insect-eating animals will thrive in a wide-variety of habitats and predominate.

The “winners” include rodents, such as dwarf gerbils and songbirds, such as the white-browed sparrow-weaver. Less adaptable, slow-lived species, requiring specialist environmental conditions, will likely fall victim of extinction.

The “losers” include animals like the tawny eagle and black rhinoceros.

Humans biggest threat

“We predict the average, or median, body mass of mammals will decline by 25 per cent over the next century,” said Dr. Bates. “This decline represents a large, accelerated change when compared with a mere 14 per cent body size reduction from the present day in comparison to species from 130,000 years ago during the last interglacial period.”

Dr. Amanda Bates
Dr. Amanda Bates at the Ocean Sciences Centre in Logy Bay, N.L.
Photo: Rich Blenkinsopp

Dr. Rob Cooke is lead author and a postgraduate researcher at the University of Southampton.

He says by far the biggest threat to birds and mammals is humankind – due to the organisms’ ongoing habitat destruction by way of deforestation, hunting, intensive farming, urbanization and the effects of global warming.

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

“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.”

Opportunity for targeted conservation

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.

“As long as a species that is projected to become extinct persists, there is time for conservation action.” — Dr. Amanda Bates

They used these traits to understand the role of different animals within the environment around them. In addition, the researchers used the International Union for Conservation of Nature Red List of Threatened Species to determine which animals are most likely to become extinct in the next century. They then used modern statistical tools to combine this data to make their projections and evaluate the loss of biodiversity.

The researchers believe their findings demonstrate that the projected loss of mammals and birds will not be ecologically random, but rather a selective process where certain creatures will be filtered out, depending on their traits and vulnerability to ecological change.

“Extinctions were previously viewed as tragic, deterministic inevitabilities, but they can also be seen as opportunities for targeted conservation actions,” said Dr. Bates. “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.”

The research team hopes further studies can be carried out to look in more detail at the longer-term effect of species becoming extinct on habitats and ecosystems.

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