of individuals in and out of the corridor and by their movements and repro-
duction within the corridor (Figure 3.1; Bennett 1990). In addition to
dispersing animals, reproduction in corridors, as detected in the rainforest cor-
ridors of northern Australia and the central Amazon (Laurance 1996; de Lima
1998), also provides an additional source of individuals for the corridor pop-
ulation. For some Nearctic migrant birds, shade coffee and cocoa plantations
in Central America provide useful and even crucial habitats (Robbins et al.
1992; Perfecto et al. 1996; Greenberg et al. 1997).
Aiding Ecosystem Processes
Habitat corridors can also provide additional landscape services by aiding
ecosystem processes by protecting watersheds (Karr and Schlosser 1978) and
providing windbreaks, for example. Riparian vegetation along streams can
reduce soil erosion and maintain water quality and stream flows by shading
streams and thereby reducing the excessive growth of aquatic plants, includ-
ing exotics (Parendes and Jones 2000; Chapter 18, this volume). Furthermore,
adequate streamside vegetation can reduce the inflow of agrochemicals and
nutrients, thereby helping to maintain water quality and inhibit the growth of
aquatic algae. Windbreaks and fencerows can reduce windspeeds and conse-
quently help protect pastures, crops, livestock, and natural habitats from expo-
sure.
Costs of Corridors
Wildlife corridors have their critics. A number of potential detrimental effects
have been suggested (Simberloff and Cox 1987; Simberloff et al. 1992; Hess
1994) that should be considered when recommending corridors as a compo-
nent of a regional conservation strategy (see also Figure 3.1).
Spread of Biotic and Abiotic Disturbances
First, as a result of increased immigration, wildlife corridors could facilitate the
spread of diseases, exotic species, weeds, and undesirable species (Simberloff
and Cox 1987; Hess 1994). Increased immigration might also disrupt local
adaptations of species and even decrease the level of genetic variation by caus-
ing outbreeding depression, which occurs with the mating of highly dissimi-
lar individuals (Simberloff and Cox 1987). However, such events are unlikely
to occur when corridors are being used to reconnect habitats that have been
isolated by human land uses rather than connecting naturally unconnected
habitats (Noss 1987).
Second, corridors might facilitate the spread of abiotic disturbances such
as fire (Simberloff and Cox 1987). In tropical landscapes, ignition sources of
54 I. Conservation Biology and Landscape Ecology in the Tropics