pollinators, were apparently reluctant to fly into
fragments isolated by 80 m (262 ft) or more from
other forest.- Primate species richness in four 10 ha fragments
combined was less than the species richness in a
single 100 ha fragment. - Small nonflying mammals such as various rodents
increased in species richness, biomass, and
abundance in 1 ha fragments compared with 10 ha
fragments and continuous forest. - In areas where forest was cut but not burned, the
rate of succession in the cut patch was faster, and the
dense vegetation supported a larger community of
butterflies than either isolated forest fragments or
continuous forest. - Three species of Phyllomedusa frogs were lost from
small fragments, probably because peccary wallows
form the breeding pools for these small frogs, and
peccaries had abandoned these areas. With the
peccaries gone, the frogs could not breed.
Fragmentation thus produces various ecological
domino effects.
Edge effects were also evident in isolated fragments.
Many injured and dead trees were found along edges,
and the overall turnover rate of trees was highest on
edges. Rates of litter accumulation accelerated near
edges. Seedling recruitment patterns varied as well.
Edge effects have been a focus of study in relation to
forest fragmentation and will be discussed in more
detail below.
Isolation is frequently problematic. Small, distantly
isolated forest fragments become ecologically
depauperate and function differently from normal
continuous forest, sometimes resulting in what
might be called ecological meltdowns. This should
come as little surprise, given that so many species of
Neotropical trees, for instance, are dependent on long-
distance pollinators or seed dispersers or both. A tree
isolated in a small fragment well over 100 m from other
forest could, in effect, be made sterile for want of seed
dispersers. Unfortunately, isolation due to the creation
of forest fragments is occurring throughout Brazil and
other tropical countries the world over. In general,
fragmentation will exert its most severe impact on
those species that require a large area but are reluctant
to cross small gaps. There are many such species.
A study directed by Gonçalo Ferraz of 55 bird
species inhabiting the forest and forest fragments of the
BDFFP demonstrated that bird species are sensitive to
varying degrees to patch area and to isolation. Many
species were strongly affected by area, while the effect
of isolation was more variable among species. For
example, the Black- throated Antshrike (Frederickena
viridis) is a typical forest- interior species. It is a poor
colonizer that virtually never leaves the interior forest
understory and is thus highly sensitive to area loss.
Another species, the White- chinned Woodcreeper
(Dendrocincla merula), is one of several species that
typically follow army ant swarms. This behavior makes
it particularly sensitive to isolation (because army ants
are confined to forest) but less sensitive to area loss.
However, bird species typically found in edge habitat
or in canopy gaps are more tolerant of fragmentation.
Because of varying ecological responses among
species, it is clear that fragmentation alters community
structure (plate 18- 11). This makes predicting the
outcome of fragmentation quite difficult.
One way to mitigate the effects of fragmentation is
to connect isolated fragments by corridors of uncut
forest. Instead of islands of forest isolated by pasture
and other hostile anthropogenic ecosystems, corridors
permit the movement of species within ecosystems
to which they are adapted. Fragments thus joined
represent an interconnected matrix in which their
respective areas are functionally additive, making for
a much greater area and therefore sustaining a higher
equilibrium point with regard to biodiversity.
Even an uncut forest of 1,000 ha may not be sufficient
to meet the ecological requirements of certain species.
John Terborgh (1986) argues that national parks must
have between 100,000 and 1 million ha (approx. 250,000–Plate 18- 11. Cecropia trees (chapter 7) are among the most
aggressive colonizers along edges and normally increase in
fragmented areas. Photo by Dennis Paulson.382 chapter 18 the future of the neotropics