Mammal population losses and the extinction crisis
Gerardo Ceballos from the Universidad Nacional Autonoma de Mexico and Paul R. Ehrlich from Stanford University, United States, compared mammal population data from the 19th century and today.
They found that 173 species have collectively lost more than half of their historic range area, mostly where human activities are intensive. The authors estimate that approximately two per cent of all mammal populations have been lost, which is about double the proportion of continental mammal species that have disappeared.
A species isn't officially extinct until every last individual is gone, which is why the extinction of populations better reflects the plight of the Earth's endangered biota, say the authors.
"The loss of species diversity has correctly attracted much attention from the general public and decision-makers," they write in the conclusion to their study, which appears in the 3 May issue of Science.
"It is now the job of the community of environmental scientists to give equal prominence to the issue of the loss of population diversity."
Reference: Science 296, 904 (2002)