their best to avoid.) Every single group had tripped over his tent.
Eventually he’d gotten so annoyed, he’d yelled at the cocaleros, which, he
had to admit, probably hadn’t been the wisest idea.
IN ecology, rules are hard to come by. One of the few that’s universally
accepted is the “species-area relationship,” or SAR, which has been called
the closest thing the discipline has to a periodic table. In its broadest
formulation, the species-area relationship seems so simple as to be almost
self-evident. The larger the area you sample, the greater the number of
species you will encounter. This pattern was noted all the way back in the
seventeen-seventies by Johann Reinhold Forster, a naturalist who sailed
with Captain Cook on his second voyage, the one after his unfortunate
collision with the Great Barrier Reef. In the nineteen-twenties, it was
codified mathematically by a Swedish botanist, Olof Arrhenius. (As it
happens, Olof was the son of the chemist Svante Arrhenius, who, in the
eighteen-nineties, showed that burning fossil fuels would lead to a
warmer planet.) And it was further refined and elaborated by E. O. Wilson
and his colleague Robert MacArthur in the nineteen-sixties.
The correlation between the number of species and the size of the area
is not linear. Rather, it’s a curve that slopes in a predictable way. Usually,
the relationship is expressed by the formula S = cAz, where S is the number
of species, A is the size of the area, and c and z are constants that vary
according to the region and taxonomic group under consideration (and
hence are not really constants in the usual sense of the term). The
relationship counts as a rule because the ratio holds no matter what the
terrain. You could be studying a chain of islands or a rainforest or a
nearby state park, and you’d find that the number of species varies
according to the same insistent equation: S = cAz.*