Biology Reference
In-Depth Information
While George was tracking jaguars and pumas, Sue and her field team were searching in the
same area for the elusive bald-faced saki monkey. Sakis are seed-eating primates, so the “big,
fierce animals are rare” theory makes no sense as a descriptor of density. Moreover, sakis
live in small family groups of fewer than ten individuals, typically including a single adult
male, one to three adult females, and one or more young. At first, Sue figured that the trees
whose seeds they eat must dictate the monkeys' locales and limit their range. But careful ob-
servation of their behavior and a bit of tree climbing led to a novel hypothesis to explain their
rarity.
The answer lay in the architecture of the forest itself. Sue collaborated with Greg Asner,
a tropical ecologist with the Carnegie Institution for Science who, together with George, had
mapped the aboveground biomass, and estimated from that, carbon density of the Madre de
Dios rain forest. The tool they used to collect the biomass data was a laser scanner mounted
on a small aircraft. What this innovative technology and revolutionary study showed is that
a forest that looks uniform to an untrained eye from the air and even from the ground, look-
ing up at the canopy, is actually quite variable in its three-dimensional structure and biomass.
And the sakis saw the forest in a unique way: Sue and Greg found that they could predict
where to find these rare canopy-dwelling primates by knowing the forest's biomass—data
provided by the laser sensor. The densest branches in the canopy provided aerial concourses
for these tree-running primates. In essence, Sue's work showed that the saki monkey was an
Amazon old-growth forest equivalent of the famed northern spotted owl of western North
America's coastal conifer forests. That nocturnal predator is a habitat specialist, persisting
only where the high but open forest canopy still enables it to hunt its preferred prey (flying
squirrels) and breed successfully. The main difference in habitat restrictions of the northern
spotted owl and the saki monkey is that the patchy distribution of coastal old-growth conifer
forests is due to logging. The distribution of sakis in unlogged Amazon forests is a natur-
al pattern of rarity, it seems, because the structure that permits troop movement, the canopy
runways of dense, wide branches, is scarce. Sakis may be very common in suitable patches
but overall are rare because preferred patches, with the aerial superhighways they require,
are rare. The advent of airborne laser scanning in the tropical rain forests of Colombia, Peru,
Panama, and Brazil will surely enhance prediction of where rare, dense-canopy primates and
other vertebrates might live over vast scales.
When we sat down to breakfast the next morning, we disturbed a clump of fruit flies camped
in the bowl of bananas. These shortlived insects feasted on the ripe flesh and skin of fruit.
They might spend a fruit fly eternity, measured in days, in a home range no larger than a
serving bowl. Across the river, scarlet macaws preened their lustrous feathers in the bright
sunshine. Fruit flies and scarlet macaws lead lives that are polar opposites in range, age span,
