Survival of the Smallest: Scientists Predict Results of Coming Extinction Event

A pair of black rhinoceros. (Robert Cooke)

(CN) – Survival will favor small birds and mammals who can live on insects and thrive in a wide range of changing habitats even as larger animals die off over the next hundred years, according to a team of researchers who predict future extinctions will not be random.

The study published Thursday in the journal Nature Communications says there will be winners and losers when it comes to adaptation – and smaller animals will be left standing.

Researchers at the University of Southampton forecast a worldwide move towards smaller birds and mammals over the next 100 years. Traits found in smaller animals like the dwarf gerbil and the white-browed sparrow-weaver songbird will give them an advantage over larger animals like the tawny eagle and black rhinoceros, who are less adaptable and require special environmental conditions.

Over the next century, the average body size of mammals will shrink down by 25%. This is a big leap when compared with the 14% reduction in species from 130,000 years ago until today, according to the study authors.

Postgraduate researcher Rob Cooke from the University of Southampton in England says this projected “downsizing” could lead to further negative effects for the long-term sustainability of how species influence evolution within the environment.

“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, urbanization and the effects of global warming,” said Cooke, lead author on the study.

“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.”

Researchers studied five characteristics of 15,484 land mammals and birds currently in existence. The five traits include body mass, the number of offspring produced at birth, habitat range, diet and the length of time between generations.

A white-browed sparrow-weaver. (Robert Cooke)

With those traits in mind, the researchers conclude survival will come easier for smaller animals. Researchers used their data range and compared it to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, which includes 27,000 species that are close to extinction. The study estimates how the loss of one species affects biodiversity and plays out in a chain reaction for larger animals.

Felix Eigenbrod, professor at the University of Southampton, says this next extinction event for mammals and birds will not be ecologically random, but play out in a process where animals die off depending on traits and vulnerability to ecological change.

Amanda Bates with the Memorial University in Canada says the research could provide a head start on where to focus resources and stave off extinction.

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

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