by chance, small patches of forest inevitably sample fewer species than do
larger forest patches. In the tropics this phenomenon tends to be amplified by
the fact that many forest organisms have patchy distributions and complex
patterns of endemism (Gentry 1986; Zimmerman and Bierregaard 1986; Vas-
concelos 1988; Rankin-de Merona et al. 1992; Laurance et al. 1998c).
Another key attribute of tropical rainforests is that many species are locally
rare throughout all or much of their geographic range (Hubbell and Foster
1986; Pittman et al. 1999). For example, predators and large-bodied animals
generally are rarer than herbivores and small-bodied species; a single jaguar
(P anthera onca), for instance, can have a home range spanning hundreds of
square kilometers (Rabinowitz 2000). In fragmented landscapes, rarity can
have a strong influence on whether species ultimately persist. Even if a rare
species is present when a fragment is isolated, its population size may be so
tiny that it has little chance of surviving in the long term (Laurance et al.
1998c).
Second, large fragments usually support a wider range of habitats than
smaller fragments, and this generally means more species will be present.
Habitat diversity is important in the tropics, where many species need special-
ized food resources or microhabitats (Zimmerman and Bierregaard 1986;
Brown and Hutchings 1997). For example, many herbivorous insects feed on
only one or a few closely related plant species, and numerous birds have
unique foraging specializations, such as following swarms of army ants to
- Ecological Effects of Habitat Fragmentation in the Tropics 35
Figure 2.1. Species-area relationships for nine species of terrestrial insectivorous
birds (mean ±SE) in central Amazonia, illustrating that large forest fragments
typically sustain greater species richness than do smaller fragments and that forest
fragments have fewer species than do equal-sized tracts of intact forest (controls)
(after Stratford and Stouffer 1999).