What to let go
Not all species can be saved from extinction. Emma Marris talks to
conservation biologists about prioritization and triage.
Richard Cowling was playing with
maps of South Africa on a computer
screen when he had his epiphany. He
was designing a conservation plan for
the Cape Floristic Region, or fynbos, an arid
landscape of shrubs and flowers that contains
some 9,000 species, many unique to the area.
Some of these, such as the mandala-like sunset
blooms of the protea flowers, are spectacular.
Some — like the geometric tortoises, whose
fetching shells help them hide from baboons
and secretary birds — are seriously endangered.
Cowling, a conservation biologist at
Nelson Mandela Metropolitan University in
Port Elizabeth, was working on defining a set
of reserves that would maximize the chances
of conserving all those species. The project
was so large that it would end up as a series of
16 papers by 36 authors that occupied all 297
pages of Biological Conservation’s July–August
2003 issue. And it was also, Cowling realized as
he stared at the screen, “sheer nonsense”.
“I had to click on a couple of grid squares and
the project would be complete,” Cowling says.
“And it dawned on me: complete for whom?
There was no way that this reserve would ever
happen. It had to be linked to some social realities
on the ground.”
In the preface to his 1981 book, Extinction1,
Paul Ehrlich, a biologist at Stanford University
in California, provided a powerful parable for
conservation biology: the story of the rivet
popper. A passenger inspecting the plane he
is about to fly in notices someone popping
rivets out of the wings. When challenged, the
rivet popper says that the passenger shouldn’t
worry because not all the rivets are necessary.
For Ehrlich the rivets represent species and the
rivet popper represents humanity, indifferent
to the looming danger of ecosystem collapse
and the end of the natural processes that supply
raw materials of life such as clean water,
wild food, carbon sequestration and climate
regulation. In the apocalyptic style for which
he has become famous, Ehrlich predicted that
continuing to pop the rivets of ecosystems
would lead to “a crumbling of post-industrial
society”. He demanded that the rivet popping
be stopped.
There aren’t many, if any, conservation
biologists who would disagree with that conclusion.
In principle. The problem is that they
don’t have the resources to back up such ambition
in practice. Spending on conservation by
major international and non-governmental
organizations has been estimated at around
US$2 billion a year2. Given constrained
resources, the biologists have to set priorities.
‘Triage’ is a dirty word in some conservation
circles, but like many dirty words, it describes
something common. Whether they admit it or
not, conservationists have long had to make
decisions about what to save.
As more and more admit it, open discussion
about how the decisions are best made — by
concentrating on particular species, or particular
places, or absolute costs, or any other criterion
— becomes possible. Whichever criteria
come into play, one thing remains constant.
The decisions have to be made quickly. In the
bloody business of conservation biology, the
longer you pause to reorder your list, the more
species will become extinct.
Superfluous species
Perhaps the most controversial basis for triage
is redundancy — prioritizing those species that
provide a unique and necessary function to the
ecosystem they live in and letting go of those
that are functionally redundant. It might seem
sensible to lose a few rivets around the plane’s
over-engineered windows if that saves the rivets
actually holding the wings to the fuselage.
This idea was raised in the early 1990s by Brian
Walker of the Australian Commonwealth
Scientific and Industrial Research Organization3.
“Regrettable as it might be,” he wrote,
“it is most likely that global biodiversity concerns
will ultimately reduce to a cost–benefit
analysis. Without knowledge of redundancy,
or more broadly, the relationship between
the levels of biodiversity and ecosystem function,
we cannot estimate either the costs
or the benefits.”
The majority opinion among conservation
biologists today is that they still understand too
little about ecosystem functions to say for sure
which species are the ‘load-bearing’ ones whose
presence keeps a complex, multi-tiered ecosystem
from collapsing into some worst
case dull scenario of rats, roaches
and invasive grass. “We are so
fundamentally ignorant,”
says Norman Myers, a fellow
of the University of Oxford,
UK, and adjunct professor
at Duke University in Durham,
North Carolina. “We
cannot afford, by a long, long
way, to say which species are
dispensable.” Andrew Balmford,
a conservation biologist at the University
of Cambridge, UK, tends to agree:
spotting key species is “an interesting exercise
intellectually ... but by the time we’ve figured it
out the forest will have gone anyway”.
Save the genes
Not everyone is quite so convinced the problem
is ineluctable. “I think there are a lot of
systems where we know more than we think,”
says Reed Noss, a conservation biologist at
the University of Central Florida in Orlando.
“If you can get naturalists to open up and talk
about what they know, we can at least generate
some testable hypothesis and do some
manipulation if we have time.” Kent Redford,
head scientist at the New York-based Wildlife
Conservation Society, agrees, up to a point.
“Our big problem is that we have been raised
to believe that unless you have complete information
you cannot make recommendations,
and I think that is something we are going to
be put on trial for by our children. It’s baloney.”
But his belief that science might make this
sort of prioritization possible doesn’t mean
he approves of it. “I don’t care if something is
redundant,” he says, “I want to save it for all
these other reasons.”
Perhaps aware of the resistance that functional
prioritization might encounter, Walker’s
forthright paper suggested a complementary
approach: taxonomic distinctiveness3. This
turns out to be less contentious; although
there are no organizations dedicated to sorting
the load-bearing species from the non-loadbearing,
there is at least one that dedicates its
resources to saving the mammals that are phylogenetically
distinct. The EDGE programme
— its intials stand for evolutionarily distinct
and globally endangered — of the Zoological
Society of London argues for giving priority to
endangered species of mammals that are far
out on their own on the tree of life, without
close relatives.
The EDGE scheme gives each species a
score derived from its position on a phylogenetic
tree. A lone species out on a long branch
gets a higher score because it is the sole bearer
of genes that represent a very long period of
evolution. Take the three-toed sloths,
which parted company with the
rest of the sloths some 15 million
years ago. “There are two
species of three-toed sloth
that only diverged 1 million
years ago. If one went
extinct, we would lose 1 million
years, but if we lose both,
we lose 15 million years,” says
Nick Isaac, a research fellow at
the Zoological Society who helps
to run the EDGE programme4.
“You could make an analogy with art,”
says Isaac. “You are in a spaceship leaving Earth
with three paintings. Do you take three Rembrandts,
or do you take one Rembrandt, one
Leonardo and one Picasso?” The group’s top
five targets for funding — which at this point
amounts to paying for a student in the countries
where the animals live to study their conservation
— are the Yangtze River dolphin (Lipotes
vexillifer), the long-beaked echidna (Zaglossus
bruijni) of New Guinea, the riverine rabbit
(Bunolagus monticularis) of the Karoo desert in
South Africa, the Cuban solenodon (Solenodon
cubanus) and its cousin, the Hispaniolan
solenodon (Solenodon paradoxus). Similar
to each other, but distinct from anything else,
the solenodons merit two slots. Conservation
favourites such as tigers, pandas and gorillas
are noticeably absent from the list.
There are variations on this theme floating
about. Redford suggests that when a species
is identified as endangered, a priority
list of populations within the species should
be drawn up based on genetic diversity. And
a biologist who considers his idea a little too
hot to put his name to suggests putting species
that have future evolutionary potential at the
top of the list. This means prioritizing current
species according to their capacity for future
speciation. Big, long-lived species face inherent
disadvantages under this idea: such a list
would have little room for elephants or whales.
Or redwoods.
Battle of the maps
A much more popular alternative to prioritizing
species is prioritizing areas. There is less
need to know how the ecosystem works — just
identify an area of interest and try to preserve
it in its entirety.
The first such scheme to gain real influence
was Myers’ hotspot map, which has been published
in several incarnations since its inception5
in 1988. The original version, which prioritized
tropical forests above all other places, was persuasive
enough for Conservation International,
headquartered in Arlington, Virginia, and the
MacArthur Foundation, based in Chicago,
“I don’t care if
something is
redundant. I want to
save it for all these
other reasons.”
— Kent Redford
Illinois, to adopt it as a framework for their
efforts. But like all prioritizing, it had its critics:
“I was told it was immoral, that all species
are equal,” Myers recalls.
The criteria he has used to define the
hotspots are, Myers freely admits, somewhat
arbitrary, and have evolved over time. In the
2000 version an area makes the grade if it
contains at least 0.5%, or 1,500, of the world’s
300,000 plant species as endemics — that is,
species that are seen nowhere else — and has
lost 70% or more of its primary vegetation6.
In this iteration the Brazilian
cerrado, the fynbos and
other mixed grasslands joined
the forests.
Myers’ hotspot map set a
trend: it is now practically compulsory
for every conservation
organization to have its own priority
map. The Cape Floristic Region
received its journal-filling loving-care
from Cowling and his peers in part because
it had made it onto so many of these prioritization
lists. As well as being an accredited
hotspot under Myers’s scheme it had also made
it into conservation group WWF’s ‘Global 200’
scheme. Birds found nowhere else, such as the
protea canary and the orange-breasted sunbird,
had propelled the area onto Birdlife International’s
Endemic Bird Areas list7.
Priority actions
The fynbos demonstrates the extent to which
maps will agree about things, which raises the
question of why there should be so many. “It
has been a not terribly profitable exercise over
the last ten years to have such a proliferation
of schemes that are basically very similar,”
says Georgina Mace, who runs the
Centre for Population Biology at Imperial
College in London, UK. “They act
as sort of branding for the organizations.
It still surprises me that the big conservation
organizations have not gotten together
under a single banner, like Make PovertyHistory.”
At the same time, partisans can detect —
and defend, debate and disparage — various
differences in approach. “We have
been arguing, or certainly jockeying,
to present one piece of science as
more legitimate or stronger than
another,” says Jon Hoekstra, a
senior scientist at the Nature
Conservancy in Seattle,
Washington. These squabbles
are framed to suggest
that there is one right
answer — one most valid
way to prioritize areas.
But different starting assumptions and different
goals mean that many of the schemes are
not directly comparable. “We have to remember
that they reflect the philosophical decisions
made at the beginning,” says Hoekstra.
The approach that currently enjoys perhaps
the highest level of acclaim, at least scientifically,
is that taken by Hugh Possingham of the
University of Queensland, in Brisbane, Australia.
His one goal is maximizing number of
species conserved, and he loathes scoring
systems. Instead he uses algorithms
that measure real-world costs
against benefits in terms of species
number, and the resulting
papers, colleagues say, are in a
league of their own8.
In his latest work he compares
different actions in different
places with each other, which
is more complex than one might
think. Land prices vary around the
world, as does species richness. Many investments
have diminishing returns over time:
once a large chunk of one ecosystem is protected,
turning a bit more into a park won’t save
many additional species. On the other hand,
some interventions begin to pay off seriously
only after a certain investment threshold is
reached. “If you were trying to get all the rats
off an island, unless you invest enough to get
them all off, you might as well not even bother,”
explains Possingham. On top of all this is the
problem that data on costs are infamously
scanty — so much so that many earlier
analyses just used land area as a proxy, an astonishing simplification.
“In a sense, it is just about good problem
definition,” says Possingham. “If you don’t do
that right, you head down these scoring paths.
The people who make them just have a feeling
of which facts are important, and they throw
them in.” Possingham tries to be as rigorous
as possible, and sometimes that means not
everything gets saved. “A lot of people get upset
with that. It basically says some regions aren’t
working at all. They are too expensive, the
threats are too huge, or there are not enough
species in them.”
Mount Lofty’s short straw
Consider, for example, the Mount Lofty woodlands
of Australia, where eucalyptus trees shelter
rare orchids (pictured), spiny echidnas and
cockatoos. Surely it is worth preserving them
from the invasive predators such as foxes and
cats that threaten them? But in a trade-off
between spending on the Mount Lofty ranges
and on the montane regions of the fynbos,
Possingham’s algorithms give the money to
the fynbos — among other regional investments.
The Australian woodlands get nothing,
despite the fact the fact that Possingham, an
avid birder, would bitterly regret losing part
of the original range of the endangered regent
honeyeater (Xanthomyza phrygia); he’s particularly
keen on honeyeaters.
Putting this sort of insight into practice is
not simple. Most Australian money isn’t transferable
to South Africa, any more than money
given to preserve pandas can be spent on solenodons.
But some of those who administer the
sliver that is fungible — people at the World
Bank, the Global Environmental Facility and
other large foundations — are taking an interest
in Possingham’s approach. Peter Kareiva,
the head scientist of the Nature Conservancy, is
one of many researchers who has
been co-authoring papers with Possingham
on such return-on-investment
models of conservation9; a few years ago,
as it happens, he rubbished the whole idea of
hotspots in American Scientist10.
Balmford, too, is excited about these approaches. “Possingham’s new techniques
on setting priorities dynamically, allowing
you to shift from one to another, are really
exciting,” he says. The difficulty is getting
them adopted by managers and decisionmakers
on the ground. “We have got to get
away from conservation scientists handing
down ideas from on-high to practitioners
and expecting them to be received gratefully.
It has got to be through examples, and from
realizing from their peers that those things
make sense.”
This is the dreaded implementation gap, in
which theory ignores practice and practice
ignores theory. In the end, it may not matter
which prioritization scheme is most scientifically
defensible. What matters is that the people
carrying out a scheme feel that it makes sense
and will save species. On this pragmatic basis,
many schemes shouldn’t even be considered
for implementation, says Hoekstra — including
some of his own work. “I wrote this crisis
eco-regions paper. It gives some real interesting
perspective on the world. It highlights the
crisis in temperate grasslands. But I don’t think
it is as useful to look at the map I generated to
decide where to work; you could end up trying
to restore something that is lost.”
Armchair scientists
“So much of this stuff is done by well-meaning
people sitting as it were in their armchairs,”
says Stuart Pimm, a conservationist at Duke
University. Pimm recently eschewed the priority
list for his own expertise and invested in
some land in the Amazon he knew was ripe for
conservation. “You have to do what you think
you can do. It is going to be based on imperfect
information and it is going to be very, very
strongly conditioned by local politics and economics
and social conditions,” he says.
Pimm aside, the armchair approach can seem
deeply entrenched. Redford points out the perennial
problem of papers that follow pages of
science with a cursory command, “that deadly
last paragraph that begins ‘managers should’ ”.
For Noss, one solution is educating those managers.
“We need a system that can provide midcareer
training to people who are going
to be working in land-management
agencies, ocean-management
institutions, and in environmental
consultancies. Otherwise
they are going to keep
using these more outdated
and less defensible approaches
to prioritization.”
For an on-the-ground
conservationist, such as Stuart
Cowell, project coordinator with
Bush Heritage Australia, the many
different schemes have been influential, but
not immediately applicable. “We haven’t taken
those approaches off the shelf,” he says. Bush
Heritage buys land with conservation value,
but unlike the ideal maps on paper, some land
is never going to come up for sale. What Cowell
and his colleagues are asking themselves,
he says, is: “Is there a benefit to an organization
spending the time and resources in doing
this sort of prioritization, which looks good in
theory but perhaps does not take us as far as
just some good expert knowledge?”
There are some small successes. Possingham
has had some luck impressing government
bureaucrats with the rigour of his analyses;
some spending decisions in Australia have been
made on the back of his work. And South Africa
has had real success in bridging the implementation
gap. “The US and European style is that
the scientists write it and hope someone picks it
up, but the South Africans are trying to get the
people who are going to implement it to help
with the priorities,” says Redford.
The messy reality
Since his conversion experience over the
digital maps of the fynbos, Cowling
has been one of those attempting
to build the input of decisionmakers
and local people into
his schemes from day one.
“The plans [I’ve worked on]
were done not because they
appealed to anyone’s curiosity
in an academic sense but
because they were needed,” he
explains. He’s more interested
in determining the possible than
mapping the ideal. “Through the
process of negotiation [with stakeholders]
you end up with a series of projects, and
funding is sought.” And sometimes that which
is sought is actually found.
Cowling says that getting all conservation
biologists to do their prioritization work with
both feet on the ground “will require a substantial
change in how researchers operate”.
“Getting involved in the slushy stuff takes time.
The kind of research is not likely to appear in
the pages of high impact journals. You might
get it into the pages of Ecology and Society,” he
says. But his work is not going unrecognized,
whatever its impact factor; Balmford singles
Cowling out for praise as someone “not just
concerned with getting the algorithm to get
the best bang for the buck, but with the more
messy, more real, more interesting reality”.
There is no reason why, in theory, one could
not include the slushy stuff of real life as inputs
in a prioritization scheme. “People say that
this mathematical approach can’t account for
anything, but it can,” says Possingham. “The
question is, can you put it in with a plausible
number?” Imagine a platonic scheme in
which one could include the intransigence of
a particular politician, the likelihood of a coup
in a certain country, the relative value of the
US dollar, the effect of eco-fatigue among the
donating public, and the looming spectre of climate
change, each quantified and slotted into
equations (along with values representing their
uncertainty, of course). Such a marvel might
give you the best tactics. But it would be no
help in setting fundamental goals for future
conservation — a subject on which unanimity
seems about as likely as a full recovery for the
Yangtze River dolphin. ■
Emma Marris writes for Nature from
Columbia, Missouri.