Data collected from records dating back to 1500 A.D. indicate that at least 35 per cent of mammals weighing over 20 kg. have had their range cut by more than half. The researchers compared the current ranges of the world's largest 263 land mammals with their distribution 500 years ago. The findings have been published in the Journal of Mammalogy, and include a call for urgent action to protect remaining large mammals that are being hunted or suffering habitat loss.
The team's research is being described as the first “measurement of human impacts on biodiversity based on the absence of native, large mammals." Lead author, John Morrison, WWF's Director of conservation measures said, “Perhaps the most striking result of our study is that the 109 places that still retain the same roster of large mammals as in 1500 A.D. are either small, intensively managed reserves, or places of extremes - remote areas either too hot, dry, wet, frozen or swampy to support intensive [human] activities." Species that are habitat “generalists" - tigers, leopards, lions, American bison, elk and wolves - have suffered the greatest losses. Southeast Asia has just one per cent of the megafauna that roamed the region in 1500 A.D., while Australasia is faring better geographically, with 68 per cent of its large mammals holding on.
Explaining why large mammals are so important for maintaining ecological equilibrium, the scientists wrote, “Large carnivores frequently shape the number, distribution and behaviour of their prey. 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."
Eric Dinerstein, chief scientist for WWF, hopes the findings will help focus conservation efforts: “We can now pinpoint places where large mammal assemblages still play important roles in terrestrial ecosystems. 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."
February 2008
