Only small animals might stand a chance in a manmade world

Smaller animals tend to have several advantages over large-bodied ones. They need less food and less space. They also tend to breed much faster, producing far more offspring. It’s not for nothing that rodents like mice and rats and birds like pigeons and sparrows have colonized most of the planet.

These competitive advantages will continue to serve smaller animals well in a world remade by humans, says a team of researchers at the University of Southampton in the United Kingdom.

In coming decades small animals that live fast, bear lots of offspring, and can thrive in various habitat while dining scraps and insects will come to predominate at the expense of larger creatures, which need lots of space and food, reach full maturity slowly and have few offspring. Animals that can adopt to urbanized habitats with greater ease will also fare better in an fast-urbanizing world.

The “winners” of this evolutionary race will include dwarf gerbils and songbirds in the wild while the “losers” will include species like the tawny eagle and black rhinoceros.

“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,” says Rob Cooke, a postgraduate researcher at the University of Southampton who was the lead author of a study published in the journal Nature Communications.

On average the body mass of mammals will shrink by 25% over the next century, the researchers posit, as creatures large and small will seek to adapt to environmental changes brought on by extensive habitat loss and other stressors as a result of human activities. “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 (the last interglacial period) until today,” the scientists write.

Downsizing happens naturally in larger land animal species when they find themselves on islands where limited resources force them to grow smaller over succeeding generations. Take elephants on the island of Borneo, known as pygmy elephants, which have come to be considerably smaller than Asian elephants on the mainland, from which they split off tens of thousands of years ago.

To see which animals will fare well or not so well in coming decades, the researchers examined a total of 15,484 land mammals and birds according to five characteristics that define their roles in nature: body mass, litter/clutch size, breadth of habitat, diet and length of time between generations. They then looked at a global list of endangered and threaten species to see which animals are most likely to go extinct within 100 years as habitats continue to shrink.

“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,” notes Felix Eigenbrod, a professor of applied spatial ecology at the university.

Having said that, the future has yet to come to pass. Stepped-up conservation efforts could go a long way towards saving rhinos, elephants, tigers and other large animals in their natural habitats.