year-round (i.e., keystone species) is especially important in corridors because
their small area significantly limits the availability of resources.
Corridor Width
Corridor width is also a vital feature because it helps determine the area of
available habitat, the diversity of resources for wildlife, and the vulnerability
of the corridor to potentially adverse edge effects (Janzen 1986; Lovejoy et al.
1986). Edge effects encompass a diverse array of ecological and microclimatic
changes that can occur on and near the forest-agricultural boundary (Lovejoy
et al. 1986; Chapter 2, this volume). In tropical rainforests the penetration
distance of various edge effects can be up to 200 m (Laurance et al. 1997).
Furthermore, because corridors generally are long and linear in design, they
tend to have a high ratio of edge to interior habitat.
An effective corridor will promote the survival of the most extinction-
prone species in a reserve or landscape (Newmark 1993). Forest interior
species often are targeted for corridor studies because many have declined dra-
matically in fragmented habitats (Laurance 1990; Stouffer and Bierregaard
1995). One key correlate of some extinction-prone species is avoidance of
edge-affected habitat (Laurance 2001). Therefore, wide corridors usually are
far better at supporting forest interior species than narrower corridors. Only
corridors more than 250 m wide were found to support the most sensitive of
the arboreal mammals in tropical Australia (Laurance and Laurance 1999).
Similarly, many understory rainforest birds in central Amazonia had reduced
abundances within at least 70 m of forest edges, and some probably exhibited
even stronger edge avoidance (Laurance 2001). For this bird community, a
250-m-wide corridor might provide only about 100 m of forest interior habi-
tat and could still fail to support very sensitive species.
Corridor Length
Corridor length can also be a key factor. For slow-moving species with a short
lifespan, a long corridor may be a population sink. Successful dispersal
through a corridor probably will be negatively related to corridor length. A
long corridor must contain all the habitat needs of a species. If this is not pos-
sible, then the presence of larger habitat patches serving as stepping stones
along the corridor route may help meet critical habitat needs for dispersing
individuals (Newmark 1993).
Canopy and Corridor Continuity
Closed-canopy ecosystems such as tropical forests may be more strongly
affected by habitat discontinuities than other habitats. Canopy connectivity
58 I. Conservation Biology and Landscape Ecology in the Tropics