Could Lose Thousands Of At-Risk Species: Study Indicates Extinctions
Are Not Random Events
13, 2000 -- A new study indicates that thousands
of at-risk bird and mammal species worldwide could eventually become
extinct due to the non-random nature of extinction events. The findings
will be reported in the April 14 issue of the journal Science.
findings suggest that extinction events result in a further loss
of biodiversity, possibly even the extinction or threatening of
thousands of additional species of animals, including large, charismatic
ones such as rhinos and chimpanzees," says John L. Gittleman, associate
professor of biology at the University of Virginia, one of the study's
have identified a number of characteristics that make certain species
prone to greater extinction risk
s, and we have
determined that extinctions do not occur randomly. Species that
are biologically prone to certain risk factors are far more likely
to go extinct than suggested by models of random extinction. The
resulting potential loss of biodiversity is enormous."
says the biological characteristics that make a mammal species more
likely to become extinct include living at a high trophic level,
low population density, long gestation length, and especially small
geographic range size.
we looked at 1,000 simulated phylogenies [evolutionary trees representing
the branching order of ancestral relations among species], we found
that the chances of large numbers of species going extinct were,
in real terms, much greater than in simulated models of random extinction.
We believe that the threat of extinction for many species is real
and because of a cluster effect could result very quickly in further
loss of biodiversity and genetic history," Gittleman says.
that have many close relatives are the most likely to be saved from
extinction, Gittleman says, but species that are of a unique lineage
with few relatives, such as the giant panda, are at severe risk.
Once lost, there would be a significant loss of evolutionary history
can't simply pluck species randomly from the tree of life in a computer
model and come up with a realistic account of what is happening
in nature," Gittleman says. "Many factors affect the likelihood
of extinction risk for any given species, and these factors are
not random. Our findings suggest that we must take seriously the
threat of biodiversity loss that is likely occurring in reality
because of the nonrandom nature of extinction risk."
points out that in addition to the particular biological characteristics
that make some species prone to extinction, there are several environmental
factors that also can accelerate risk.
species become endangered because of human activity such as habitat
destruction for agriculture or development purposes, and by exploitation
of species through fishing and hunting. Many species also become
threatened by the introduction of exotic species and disease. The
reality is, extinctions are not random events."
other authors of the study are Andy Purvis and Paul-Michael Agapow
of the Department of Biology, Imperial College, U.K.; and Georgina
M. Mace, Institute of Zoology, the Zoological Society of London.
John Gittleman, (804) 982-5740 or Fariss Samarrai, (804) 924-3778