Biology Reference
In-Depth Information
Buried within the species extinction crisis is another, less publicized calamity: the increas-
ing rarity of species populations. These losses of populations, as well as in some cases en-
tire species, have led biologists to sound warning after warning. The eminent biologist E. O.
Wilson, for example, pronounced in a speech in early 2000 that “biodiversity cannot afford
another century like the last one. We are about to lose thousands of species a year, especially
in rainforests.” Wilson could have extended the depth of the problem, if risking the simpli-
city of his message, by adding a phrase whose meaning has gone unnoticed by the general
public: we have been losing populations of species faster than we have been losing species
themselves.
These two concerns—rarity of species and paucity of particular populations—merge when
it comes to those species whose entire earthly existence is represented by a single population,
as a result of either natural forces or human encroachment. Who are these singleton species,
and how many of them are now close to the abyss of extinction?
In 2003, several colleagues and I put together a paper for the ProceedingsoftheNational
AcademyofSciences to address this question, name those species, and suggest how their im-
minent extinction might be prevented. Our work on the paper, which was published in 2005,
sparked the scientific basis for this topic, an interpretation of the evolutionary and contem-
porary aspects of rarity. We focused our effort on a subgroup of relatively well known but
threatened vertebrates, our fellow creatures with backbones—birds, mammals, reptiles, am-
phibians (fishes are yet to be analyzed). We postulated that certain of these species were
already so uncommon that they would be extinction's next dodo birds unless action were
taken to prevent their disappearance.
To begin, we turned to the gold standard for evaluating rarity of wild species, the Interna-
tional Union for Conservation of Nature and Natural Resources (IUCN) and its famed Red
List of Threatened Species, which ranks species on the basis of sizes of remaining popu-
lations. The IUCN assigns the category “endangered” or “critically endangered” to species
whose numbers have plummeted toward extinction. We then went a step further. “Let's name
the rarest of the rare, those species whose entire global range is limited to one population at
a single site,” my colleague John Lamoreux suggested. He was proposing that we limit our
survey to such species as the Bloody Bay poison frog, which hails from the last patches of
rain forest on the island of Trinidad, the only place on Earth where it can be found.
Once a species such as the Bloody Bay poison frog is restricted to a single dot on the
map, if one or another of several catastrophes strikes—if the spot is plowed, burned, flooded,
drained, paved, polluted, or overrun with pigs, rats, or other invasive species—the threatened
species that lived in that dot is gone: vanished forever. Rarity then becomes the precursor to
extinction or, at least, its preexisting condition. Alternatively, if you save the place, you save
the rare species—conservation in black-and-white.
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