91av

WHEN animals become extinct, it is likely that whole groups of species will
disappear at once, biologists have warned. This makes extinctions a much greater
threat to biodiversity than was previously thought, and adds weight to a
proposal by Californian biologists that tissue samples and genetic material from
threatened species should be preserved.

Most attempts to quantify the effect of extinctions assume that species of
mammals and birds disappear at random. This would mean that losing a particular
bird, for instance, would not be too serious because a number of similar,
related species would survive. Now Andy Purvis of Imperial College, London, is
warning that this picture is too optimistic, because threatened species tend to
be related.

Whole groups such as chimpanzees, golden-lion tamarins, manatees and rhinos
are all threatened, Purvis and colleagues at the University of Virginia in
Charlottesville and the Institute of Zoology in London found, after analysing
lists of endangered species. If all these species became extinct, we would lose
85 genera of mammals and 38 genera of birds. For mammals alone, this is
equivalent to the destruction of 850 million years of evolutionary history,
Purvis says.

Past extinctions support this view, he says. Time and again mass extinctions
have devastated whole groups of closely related animals, such as reef-building
organisms and the dinosaurs.

Extinction strikes in groups because related species tend to be vulnerable to
the same hazards, such as introduced species or habitat loss. “Any time you
prune based on characteristics of organisms, you will prune non-randomly,”
Purvis told 91av. “If you’re slow, fat, tender and edible, the
chances are that your relatives are slow, fat, tender and edible.”

Meanwhile, a group of biologists is trying to organise international DNA
banks for endangered species that would ultimately expand to include all
animals. The group is led by Oliver Ryder of the Center for Reproduction of
Endangered Species at the Zoological Society of San Diego, in California.

“I don’t believe it will be possible to recreate species from purified DNA,”
admits Ryder. But he does believe that data banks could aid conservation efforts
and foresees the possibility of transferring DNA between organisms, carrying
useful traits such as disease resistance. He will outline his plans at a
conference next month sponsored by San Diego Zoo.