and whether the species can use the modified landscape and find resources.
For instance, nocturnal species may be better able to survive fragmentation
than their diurnal counterparts because of the greater similarity of ambient
conditions between forest fragments and the surrounding matrix at night
(Daily and Ehrlich 1996). Fragmentation has also been shown to decrease
aboveground biomass, especially on the fragment edges (Laurance et al. 1997).
A study in Brazil showed that large canopy trees in tropical rainforests experi-
ence a higher mortality rate when they are in a heavily fragmented system
(Laurance et al. 2000). Fragmentation also affects the reproduction of species
that remain in the forest patches. For example, species of dipterocarp trees that
inhabit lowland forests of Borneo exhibit seed dispersal events that coincide
with El Niño–Southern Oscillation events. Because these dipterocarp species
are dominant canopy species, their dispersal and reproduction are strongly
affected by local and regional logging, which can disrupt their timed repro-
duction (Curran et al. 1999).
Finally, tropical forest fragmentation can differentially affect species disper-
sal mechanisms on a landscape scale (Aldrich and Hamrick 1999; see also
Chapter 3, this volume). Metapopulation dynamics between habitat patches
result in local population extinctions, causing diversity losses in patches that
are often unrecoverable in large expanses of degraded areas. Genetic isolation
between widely isolated or dispersal-limited populations leads to loss of over-
all genetic diversity between populations and increasing vulnerability to dele-
terious genetic effects, such as susceptibility to pathogens. Landscape-scale
strategies must use research on a broad base of ecosystems, species, and popu-
lations. For example, Madagascar, which holds a high amount of unique bio-
diversity, has lost more than 90 percent of its primary forest. Threats on the
island have not abated, and forest losses continue in the few remaining frag-
ments. The medium-term existence of many tropical forest species is threat-
ened by widespread forest loss and fragmentation.
Introduced Species
A biodiversity concern related to fragmentation is that of introduced species.
Tr opical regions have a large number of endemic species that are unique to a
particular area or region, usually because of genetic isolation created by phys-
ical barriers (e.g., water in the case of island species). Often in the case of dis-
turbed areas, such as in fragmented systems, local endemic species are replaced
by wide-ranging species, including those tolerant of disturbed habitats
(Tocher et al. 2001). Successful nonnative species often are ones that range
over wide areas and tolerate disturbance well. Globally, almost all areas are
affected by these introduced species, with island biota being especially vulner-
able. Changes in complex ecological systems, such as introduction of prey
species, can have cascading effects on fauna (Roemer et al. 2002). Invasive
20 I. Conservation Biology and Landscape Ecology in the Tropics