Humans ‘drive out large mammals’
Almost
80% of the Earth’s surface has experienced a sharp fall in the number
of large mammals as a result of human activities, a study suggests.By
examining records dating back to AD1500, US researchers found that at
least 35% of mammals over 20kg had seen their range cut by more than
half.They said urgent action was needed to protect the animals, which
were being hunted or suffering habitat loss.
The findings have been published in the Journal of Mammalogy.
The
research, carried out by a team of scientists from Princeton University
and conservation group WWF-US, has been described as the first
“measurement of human impacts on biodiversity based on the absence of
native, large mammals”.”Perhaps the most striking result of our study
is that [the] 109 places that still retain the same roster of large
mammals as in AD1500 are either small, intensively managed reserved or
places of extremes,” revealed lead author John Morrison, WWF-US’s
director of conservation measures.”Remote areas are either too hot,
dry, wet, frozen [or] swampy to support intensive activities.”
‘Eco-engineering’
The
researchers compared the current ranges of the world’s largest 263 land
mammals with their distribution 500 years ago.The species that suffered
the greatest loss were “habitat generalists”, including tigers,
leopards, lions, American bison, elk and wolves.Geographically,
Australasia fared best, holding on to 68% of its large mammals. At the
other end of the scale, South-East Asia only had 1% of the mega fauna
that roamed the region in AD1500.In their paper, the scientists
explained why large mammals were so important for maintaining the
ecological equilibrium.”Large carnivores frequently shape the number,
distribution and behaviour of their prey,” the researchers wrote.”Large
herbivores function as ecological engineers by changing the structure
and species composition of surrounding vegetation.”Furthermore, both
sets of mammals profoundly influence the environment beyond direct
species interactions, such as through [the food chain].”
WWF
chief scientist Eric Dinerstein said he hoped the findings would help
focus conservation efforts.”We can now pinpoint places where large
mammal assemblages still play important roles in terrestrial
ecosystems,” he explained.”Through strategic re-introductions – such as
returning wolves to Yellowstone – we can restore… places missing one
or two species and recover the ecological fabric of these important
conservation landscapes.”