The New Neotropical Companion

(Elliott) #1

Elimination of large animals by hunting affects forest
function, as first described by Kent Redford in a paper
with the evocative title “The Empty Forest” (1992). An
“empty” forest may appear normal, but it is not, due
to lack of key animal species that disperse seeds, for
example. Large animals are often disproportionally
depleted. At Manú National Park in the Peruvian
Amazon, the loss of large and medium primates due to
hunting negatively affected seed dispersal. Local hunting
exterminated large primates (such as spider and woolly
monkeys) and reduced medium- size primates (such as
capuchins), many of which are critical seed dispersers,
by up to 80%. As a consequence, tree species richness
was 55% lower on the hunted sites than on sites where
monkeys were not hunted. In a carefully controlled series
of experiments done in Veracruz, Mexico, Rodolfo Dirzo
and Eduardo Mendoza documented that in areas subject
to strong hunting, the mammalian fauna is altered as the
large animals are largely eliminated, the balance shifting
in favor of small animals such as rodents. These small
mammals preferentially devoured small- seeded species
of plants, providing an advantage for large- seeded species
whose seed predators had been eliminated by hunting.
Hunting pressure is clearly sufficient to change the plant
species composition of a tropical forest.
Hunting will likely continue to be a problem throughout
the tropics. Whatever balance there may have been
between indigenous peoples and the animals they hunted
is no longer equal, at least not in places where guns have
replaced traditional forms of hunting (plates 18- 7– 8).


Forest Fragmentation


Fragmentation, which is increasing throughout the
Neotropics, occurs when forests are cut and divided into
parcels of varying sizes, separated by non- forest habitat.
A patchwork of semi- isolated forest fragments results.
Fragmentation results in numerous ecological effects
and in some cases may lead to eventual loss of species.
Some of those effects come about as fragmentation
increases the proportion of edge habitat in relation to
total forest volume. Furthermore, isolation of forest
fragments inhibits dispersal of many plant and animal
species, a critical component of tropical ecology.
Millions of hectares of tropical forest (ranging from
lowland rain forest to tropical dry forest) are cleared
annually and converted to pastures, agriculture, or
some other use (plate 18- 9). In many cases, forest


clearance leaves behind scattered remnant forest
“islands.” That is fragmentation. Ecologists have
investigated how fragmentation affects complex food
webs typical of closed tropical forests. One of the most
insightful projects has been the Biological Dynamics of
Forest Fragments Project.

The Biological Dynamics of Forest
Fragments Project
Approximately 70– 90 km north of Manaus, Brazil,
on terra firme forest, there is an ongoing study that
was established to evaluate the ecological effects of
forest fragmentation, with the associated objective of
learning how best to structure biological preserves
(plate 18- 10). The project was formerly known as the
Minimum Critical Size of Ecosystems Project but has
since been renamed the Biological Dynamics of Forest
Fragments Project (BDFFP). It was initiated in 1979
with the support of INPA, the Brazil National Institute
for Research in Amazonia, and the World Wildlife
Fund. In 1989 the US National Museum of Natural
History at the Smithsonian Institution assumed the
administration of the project, and has worked in
cooperation with INPA ever since. The study has had
more than 25 principal investigators working with
such groups as woody plants, birds, primates, bats,
nonflying mammals, ants, butterflies, euglossine bees,
and various beetles. As would be expected from such
a comprehensive study, there have been numerous
publications; general reviews can be found in Lovejoy et
al. (1986); Lovejoy and Bierregaard (1990); Bierregaard
et al. (1992); and Bierregaard et al. (2001a and 2001b).
Researchers worked with cattle ranchers in designing
the project. The ranchers were persuaded to clear forest
in such a way as to create forest fragments of different
sizes and distances from an undisturbed, protected
1,000 ha (2,470 ac) forest area that served as a control
(analogous to the “mainland” or source). Fragments
varied in area as follows:


  • 1 ha/2.47 ac (5 fragments)

  • 10 ha/24.7 ac (4 fragments)

  • 100 ha/247 ac (3 fragments)

  • 200 ha/494 ac (1 fragment)
    Fragments were separated by varying distances (100–
    900 m/328– 2,953 ft) from the 1,000 ha control forest.
    The researchers posed various questions: What, for
    instance, would be the differences in biodiversity
    between two 10 ha plots, one of which was 500 m


380 chapter 18 the future of the neotropics

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