Biology Reference
In-Depth Information
Another important aspect of trophic rarity, or the “big, fierce animals are necessarily rare”
paradigm introduced by Paul Colinvaux, is prey density. In fact, again using South Asia as
an example, researchers have shown that tiger density in a given habitat can be predicted
by the prey density estimated for that habitat. Tigers reach highest densities in the riverine
grasslands of Asia, over 20 adults per 100 square kilometers, and an order of magnitude
lower densities in mature forests, all because large prey animals—deer, wild boars, and In-
dian bison—do likewise. Perhaps more studies of co-occurring jaguars and pumas and their
prey elsewhere in the Amazon will indicate a similar relationship between prey density and
predator numbers.
Bolstered by George's TrackTag data, an answer to the initial question, “How much is
enough to conserve rare nature as represented by the jaguar?” suddenly seemed more attain-
able, at least for this region of the Amazon. Individual jaguars in this part of Amazonian Peru
have very large home ranges, as much as 400 square kilometers, the data suggested. “If we
calculate the jaguar's use of habitat, while accounting for their apparent preference for flood-
plains and riversides,” George commented, “then maintaining genetically viable, healthy
populations of jaguars of, say, 500 breeding females will probably require well above 20,000
square kilometers—perhaps between 30,000 and 40,000 square kilometers—assuming a
good peccary population.” This also assumes that the areas being conserved incorporate ex-
tensive riverbank and floodplain habitat. How do the protected areas of the Amazon measure
up to this task? Of the more than one hundred protected areas in the Amazon, not one is large
enough, and only about a dozen are over 10,000 square kilometers; the average reserve size
is only 3,500 square kilometers. Aggregates of protected areas with open passages between
them—conservation landscapes, a topic explored in more depth in a moment—will clearly
be required.
Studying big cats that were, for the most part, out of harm's way from humans, but not
from each other, offered further insights. Each jaguar, male and female, examined by the
team provided evidence of these cats' ferocity toward one another. All showed signs of
struggle: cuts, old wounds, bitten ears. Several radio-collared jaguars had already perished in
the lethal jaws of another: hardly a children's bedtime story, but the reality show of life in the
rain forest. A visiting biologist who was familiar with California pumas had a novel view of
the violence, suggesting that the frequency of scrapes, wounds, and scars indicated a healthy
population as animals fought to maintain access to areas with high levels of prey. A basic law
of nature drives this aggression and, ultimately, the wide spacing of jaguars in the rain forest.
Perhaps the most important finding was that even where humans have less influence, as in
Tambopata, jaguars have a density of only around 4 per 100 square kilometers—rare by any
reckoning.
