Less than twenty-one percent of the earth's terrestrial surface still contains all of the large mammals that used to occur there 500 years ago, according to a new study. Authored by a team of scientists from the World Wildlife Fund (WWF) and Princeton University, the study is the first of its kind to offer an ecologically based measurement of human impacts on biodiversity based on the absence of native, large mammals.
Large mammals are top predators and serve as landscape engineers, so their loss has long-term effects on the health of an ecosystem. The study also points out the vulnerability of large mammals to extinction, and the importance of protected areas where large mammals still occur. The study ultimately provides further guidance to large international conservation organizations, governments and other stakeholders on prioritizing their long-term conservation efforts.
"Perhaps the most striking result of our study is that those 109 places that still retain the same roster of large mammals as in 1500AD are either small, intensively managed reserves or places of extremes," says John Morrison, WWF's Director of Conservation Measures and lead author of the study. "Remote areas are either too hot, dry, wet, frozen or swampy to support intensive human activities."
Scientists compared current ranges of the largest 263 terrestrial mammals with their distributions in 1500 AD. Large mammals were defined as those with a body mass of over 20 kilograms (44 pounds), the mass at which carnivores typically switch from invertebrates to larger prey. The year 1500 AD was chosen as the baseline date because colonization began to increase significantly around this year, and with the Industrial Revolution, the most profound influences of human beings on nature started. Additionally, as only seven large mammal species have become extinct since 1500 AD, there have been and are opportunities for active conservation of the remaining species.
The number of species which have suffered the greatest range contraction are habitat generalists and include tigers (Panthera tigris), elk (Cervus elaphus) American bison (Bison bison), leopards (Panthera pardus), lions (Panthera leo) and wolves (Canis lupus). The species that has undergone the greatest loss of habitat is, rather surprisingly, the elk; the elk's range is historically greater than any other species. In terms of percentage of reduction, the largest impact of human settlement and agriculture has been on the range of the horse (Equus caballuas).
Geographically, Australasia fares best, holding 68 percent of the large mammals it once held, while Indomalaya - including such countries as Vietnam, Laos, Cambodia, and Thailand - fares the poorest with only 1 percent. Range collapse in a previously widely occurring species is often associated with species now listed as vulnerable or threatened by the IUCN, but not always - as indicated by the elk.
Eric Dinerstein, WWF's Chief Scientist and Vice-President of Conservation Science, notes:: "The obvious question we always ask ourselves is: How does this information help us? First, we can now pinpoint places where large mammal assemblages still play important roles in terrestrial ecosystems Second, we now have targets where through strategic reintroductions - such as returning wolves to Yellowstone - we can restore intactness in places missing one or two species and recover the ecological fabric of these important conservation landscapes."
"A number of key geographic areas identified by this study. such as North America's Northern Great Plains, the Eastern Himalayas, and Namibia - many of which are World Wildlife Fund priorities - deserve continued long-term conservation support to not just restore the roster of species found there but to bring back the sizes of their populations to play their important ecological roles," Dinerstein says.
The study, entitled "Persistence of Large Mammal Faunas As Indicators of Global Human Impact," is published in the December 2007 issue of the Journal of Mammalogy, Volume 88, Issue 6.
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