Mammal Population Losses and the Extinction Crisis

To: Birding Aus <>
Subject: Mammal Population Losses and the Extinction Crisis
From: Laurie&Leanne Knight <>
Date: Fri, 03 May 2002 21:41:57 +1000
Those you with access to today's edition of Science might like to have a look at
the following item - I have appended an news item from the Independent.

Mammal Population Losses and the Extinction Crisis
Gerardo Ceballos and Paul R. Ehrlich
Science May 3 2002: 904-907.
Species under threat as their habitats are cut in half
By Steve Connor, Science Editor
03 May 2002
Life on Earth is facing an extinction crisis that could be far worse than 
previously thought, according to two leading ecologists who have studied 
the rate at which animal populations are being lost.
The scientists have found that the geographical ranges of 173 species of 
mammals have declined, collectively, by more than 50 per cent over several 
decades, indicating a severe constriction of the animals' breeding 
Paul Ehrlich of Stanford University in California and Gerardo Ceballos of 
Mexico University believe that the loss of viable breeding populations is a 
critical factor that has often been overlooked.
"The loss of species diversity has correctly attracted much attention from 
the general public and decision makers. It is now the job of the community 
of environmental scientists to give equal prominence to the issue of the 
loss of population diversity," Professor Ehrlich said. "We are talking 
about nothing less than the preservation of human life-support systems. We 
neglect the issue at our peril."
Studies of biodiversity should take into account the number of endangered 
populations of breeding animals in a species, and not rely on identifying 
extinct species, the scientists said. In the journal Science they write: 
"Most analyses of the current loss of biodiversity emphasise species 
extinctions and patterns of species decline and do not convey the true 
extent of the depletion of humanity's natural capital ... We need to 
analyse extinctions of both populations and species," they say.
Professor Ehrlich and Dr Ceballos compared the territories of existing 
breeding populations of 173 mammals living on five continents with 
historical records of the known distribution of the same species. They 
estimated, conservatively, that about 2 per cent of all populations of 
mammals had been lost compared with a global extinction rate of about 1.8 
per cent. "But according to our data, the loss of mammal populations 
actually may be much more severe, perhaps 10 per cent or higher," said 
Professor Ehrlich. "While distribution maps often showed species occurring 
over wide areas, it turns out that many of them actually have lost most of 
their populations in these areas and have been reduced to scattered remnant 
The North American brown bear and grey wolf, and the Asian tiger are 
examples of animals whose ranges may be far smaller than suggested by 
official maps. "We suspect that many less prominent species ... have lost 
portions of their ranges but without detection because they have not been 
subject to intensive mapping attempts," the scientists said.
The study reveals wide differences between how species resist human 
interference. All wild populations of Pere David's deer from China, for 
instance, have gone extinct, whereas the spotted hyena has lost only 14 per 
cent of its populations despite large loss of its natural habitat caused by 
man. There were striking differences in the demise of breeding populations 
of wild animals between continents, with Africa and South-east Asia 
suffering some of the largest losses.
"Population extinctions today seem to be concentrated either where there 
are high human population densities, or where other human impacts ... have 
been severe," the scientists said. "Australia, which is the continent with 
the largest number of mammal species extinctions, is also a continent 
showing a widespread severe reduction of populations."
Some species are threatened further because most or all of their breeding 
populations are in one country and are, therefore, vulnerable to the 
vagaries of a single political system. "A combination of political endemism 
and political instability has certainly made the fates of the black and 
Sumatran rhinos much more uncertain. In both of these conservation cases, a 
high priority would be to re-establish populations not only over a broader 
geographic range but also within a greater variety of countries," they said.
At risk: How the world's rare animals have declined
Black rhinoceros
One of the most endangered animals on the planet, numbers have fallen from 
about 65,000 individuals 20 years ago to less than 2,500 today. Widely 
hunted and now poached in sub-Saharan Africa for its ivory.
The largest predator in Asia needs extensive territories to maintain a 
viable breeding population. Habitat loss, forest logging and hunting have 
reduced its numbers to precariously low levels.
Hunted for its meat and threatened by habitat encroachment, the largest of 
the great apes is suffering a gradual decline, made worse by the isolation 
of once fully interbreeding populations.
Spotted hyena
Even this resourceful predator-cum-scavenger has suffered at the hands of 
man. Scientists estimate that its wild populations have diminished by 14 
per cent over the past few decades.
Pere David's deer
Hunted to extinction in the wild but preserved for centuries in the huge 
deer parks built by the Chinese emperors. Brought to Europe to grace the 
deer parks of the aristocracy.

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