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Q: Tell us about your research.
A: What we're doing in our large research project is
actually testing different ideas about how new species arise.
We're asking whether new species arise because of geographic
isolation, or whether perhaps they arise across habitat transitions.
For instance, in transitions from rain forest to savannah, from
lowland rain forest to cloud forest and grasslands high on the east
slope of the Andes. [We're asking] whether these ecological gradients
are important in generating new species.
In South America, one of the most striking habitat transitions
is from the lowland forest to the uplands on the east slope of the
Andes, and it's been known for a long time that this is one of the
most diverse areas of the world. Traveling over a few hundred kilometers,
you go from steamy tropical lowland forest to high Andean alpine meadows.…
It's a stark and dramatic transition that involves changes between
habitats over relatively short distances … of a few tens of kilometers.
Q: Why are you studying these transitional areas?
A: We think that areas that are very complex geographically --
like the east slope of the Andes, where you have complex habitats
and differences in habitats in very close proximity -- really are the
pumps that generate new species. They're really the areas of active
diversification.… We're testing that idea by analyzing populations of
birds, bats, rats, frogs, lizards across that habitat transition, across
that gradient from lowland tropical forests all the way up to the high
Andes.
What we're really interested in is the role of adaptation to novel
environments in generating new species. And what we're trying to
investigate is how populations become adapted to new environments,
and whether or not that actually translates into speciation, into
the formation of new species.
So we're really testing a very old idea: that new species come about
through adaptation to local environments. We're also asking whether
geographic isolation is necessary for this, and in fact what we've
found to date suggests geographic isolation isn't particularly important,
but that the overriding process is really one of adaptation to novel
environments.
This is part of the reason that the east slope of the Andes seems
to be such an important area for generating new species. As the Andes
were uplifted, the lowland species would have had the opportunity to
invade new sorts of habitats, novel habitats. And as they did so they
would have adapted to these new conditions.
They may or may not have been geographically isolated. But the
real question is whether adaptation to these new environments can
lead to the formation of new species, and then whether those new
species then can come back -- for instance, into the lowlands to
increase the diversity of lowland rain forests. And what we've found
to date suggests that adaptation across ecological gradients is really
a fundamentally important process in creating new species.
If we're right about the importance of habitat transitions in
generating diversity, then those edges, those transitions between
habitats, become incredibly important, because it's across those
transitional zones that new species can form.… [They] provide the
opportunity for species to adapt to a novel environment, for populations
to diverge and become adapted to new environments, and ultimately, that
may be the engine that drives speciation.
Q: Where do habitat transitions occur?
A: You know, these habitat transitions are everywhere.
They occur over different sorts of geographical scales. They can
occur over a few hundred meters, or a few kilometers, or hundreds or
thousands of kilometers. But the important point is that … there's
the opportunity for species that exist in one of those habitats to
adapt across that transition to a novel habitat. And that may be what
may be fundamentally important in generating new species.
Q: What about the role of geographic isolation?
A: For the last 40 years or so, 50 years, really, biologists
have thought that geographic isolation was fundamentally important for
the formation of new species. And the reason that idea was so widely
accepted is because it's intuitively obvious: If things are isolated
on an island or on separate islands, then it's easy for them to evolve
reproductive isolation where they become different. But recently I
think we've found that geographic isolation may not be as important
as we thought. We're finding that populations can adapt to different
selective pressures over very short geographic distances and without
geographic isolation, and that this local adaptation could be critically
important in generating new species.
Q: Will your research help us make better decisions about
conservation?
A: I think it's important to understand how new species
arise and what the evolutionary and ecological processes are that
generate and maintain diversity for long-term conservation. Currently,
we tend to be a little bit shortsighted, and we tend to try and preserve
areas that have high numbers of species without much concern for the
process that generated those species or the processes that maintain
that diversity.
Without understanding the processes that generate diversity and that
maintain diversity, we have very little hope of preserving it. We're in
for some enormous changes in the next few decades, changes in the climate
that exceed anything that's happened in the last million years.
We have no idea whether or not evolutionary processes are going to be
able to keep pace with this rate of change in the environment. And a
fundamental part of species' persistence is their ability to adjust to
new environments. And a fundamental part of new species coming into
existence is their ability to adapt to new situations.
If our goal in conservation is to try and preserve the evolutionary
and the ecological processes that generate diversity and that sustain
diversity over the long term, then our finding that habitat gradients
are important in generating new species really changes the way we do
conservation biology. It changes the way we plan reserves.
Q: How should conservation efforts change?
A: Traditionally, conservation biology aims to preserve
species diversity, and that's an approach that preserves the patterns
produced by evolutionary history.… Reserves are most often placed in
areas of contiguous habitats. So you get a reserve in a big block of
lowland rain forest and you get a reserve in the grasslands in the
mountains. But you rarely get reserves that capture the transition
between those habitats. What we're finding suggests that those
transitions are incredibly important in generating new species and
generating novelty, and that it's selection across those habitat
differences that's critically important in generating diversity. So
if we take that into consideration, then it changes the way we design
reserves.
We think that conservation biology needs to change the focus
slightly and emphasize more the processes that generate and sustain
diversity. How do new species come into existence? What ecological
conditions favor new species? What we're finding is that geographic
complexity, changes in elevation and vegetation type and soils and
things, are probably very, very important. That is, these things
result in changes in habitats, and it's the differences in selection
across those habitats that seems to be critically important for
generating new species and for generating diversity.
So if we take the view that it's important to preserve evolutionary
and ecological processes, then the focus of conservation shifts from
trying to preserve areas of high species diversity to trying to
preserve those areas that are important for generating diversity.
And that is areas that have high geographic complexity, high habitat
complexity, and transitions between habitats.
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