Of even more significance is that the matrix strongly influences fragment
connectivity. Several species of Amazonian primates (Gilbert and Setz 2001),
antbirds, obligate flocking birds (Stouffer and Bierregaard 1995b), and euglos-
sine bees (Becker et al. 1991) that disappeared soon after fragment isolation
recolonized fragments when regrowth regenerated in the surrounding land-
scape. Among small mammals, bats, birds, and frogs in tropical Australia and
Amazonia, matrix-avoiding species are much more likely to decline or disap-
pear in fragments than are those that use the matrix (Laurance 1991a; Offer-
man et al. 1995; Stouffer and Bierregaard 1995b; Kalko 1998; Borges and
Stouffer 1999; Gascon et al. 1999; Stratford and Stouffer 1999).
Some matrix habitats are more suitable for rainforest fauna than others. In
the Amazon, regrowth dominated by Cecropiatrees, which tends to be tall and
floristically diverse with a closed canopy (Williamson et al. 1998), is used by
more rainforest bird, frog, and ant species than more open Vismia-dominated
regrowth, and almost any kind of regrowth is better than cattle pastures (Table
2.1). Forest-dependent dung and carrion beetles are also far more likely to
cross a matrix of regrowth than one that has been completely clearcut (Klein
1989). In general, the more closely the matrix approximates the structure and
microclimate of primary forest, the more likely fragmentation-sensitive species
are to be able to use it.
Synergistic Effects
In tropical anthropogenic landscapes, forests are rarely just fragmented; they
are also subjected to logging, overhunting, incursions of fire, and other human
disturbances. Such simultaneous environmental changes can interact addi-
tively or synergistically, leading to even greater impacts on fragmented popu-
lations (Laurance and Cochrane 2001).
For example, recent studies demonstrate that forest fragmentation dramat-
ically increases the vulnerability of Amazonian forests to fire (Cochrane et al.
1999; Nepstad et al. 1999). Farmers burn their cattle pastures at 1- to 2-year
- Ecological Effects of Habitat Fragmentation in the Tropics 41
Table 2.1. Total number of species recorded and percentage of species
shared with mature forest (in parentheses) in three types of matrix habi-
tat surrounding Amazonian forest fragments.
Ta x o nMatrix Habitat Antsa Birdsb Frogsc
Pasture 36 (19.4–33.3%) No data 25 (76.0%)
Vismia-dominated regrowth 62 (43.5–51.6%) 123 (86.2%) 40 (90.0%)
Cecropia-dominated regrowth 83 (48.2–51.8%) 141 (97.2%) 43 (81.4%)
Sources:aVasconcelos (1999); bBorges and Stouffer (1999); cTocher (1998).