Norman Owen-Smith, University of Witwatersrand
Q: How would you convince a skeptic that
extinction rates are high nowadays?
NS: Looking outwards from Africa, where we
still have a wide diversity of large mammals, I would note the
disappearance of those very large mammals elsewhere in the world.
Around the end of the Pleistocene -- perhaps 10,000 years ago,
or earlier than that -- these species, which were once formerly
abundant, no longer occurred.
Q: What are the chief kinds of things people
do to cause extinctions?
NS: There are two main effects that humans
have. The one that was very prevalent in the past was, of
course, as hunters; people depended upon those animals as food sources.
Humans also have many other effects -- modifying
habitats through use of fire, changing fire effects, and recently
by occupying habitats formerly available to species, land that was once
available for wildlife.
Q: What is the relevance of understanding
prehistoric extinctions to our current biodiversity crisis?
NS: It's really important for us, in trying
to explain what's happening now and in the future, to explain
what has happened in the past.
Q: Did you hear anything
at the symposium that you thought was interesting new data or interpretation?
NS: I think what the meeting has reinforced
is the awareness of the central role of humans in the extinctions,
particularly as supported by the timing of when those extinctions
occurred in different parts of the world. In Australia, they now appreciate
that the extinctions occurred
at an earlier period in time, and therefore much closer to the
first arrival of humans in Australia. But in looking at the role of humans in
those extinctions, I think of
the very large mammals -- the so-called "megaherbivores,"
weighing more than a metric ton, the elephants, rhinos, species
of that size -- while their role as predators of those species seems
uncontestable. Those species were not able to sustain hunting
pressure from a predator, when in the past they had not had a
predator preying upon adult animals. Those species were vulnerable.
Nevertheless, there were other factors involved,
particularly in the timing of the extinctions, which occurred
at a time of rapid climatic change at the end of the last glacial.
Of course, that transition, the climatic transition, doesn't
seem to have been any different from that of previous changes
from glacial, interglacial, conditions. And, therefore, the climatic
change alone doesn't seem a sufficient argument. That's why
I felt one also had to look at some other consequences of what
might have followed the elimination of the megaherbivores by human
hunting. In particular, awareness of how great an impact those species can have on habitat
conditions for other species. They are these species that can
function as ecosystem engineers and change woodland conditions,
change grasslands, in a way that may actually have been beneficial
to other species in creating a mosaic diversity of habitats.
In fact, the paleontological record does seem to suggest that
habitats in the past were more diverse than they are at present,
and it's difficult to ascribe that change in diversity to climatic
Q: What reasons are there to hope to stem the current
NS: That's actually a major challenge, largely
because of the preemption of habitats by human population growth.
To the extent to which that population growth remains unchecked,
and people spread out across the landscape, we face a major problem.
I think the only way of really attacking that problem is to draw
people out of rural areas into city environments, where they exert less direct pressure on habitats of other
species, and they also are open to education and awareness of
problems that they would not be aware of living in remote rural