Figure 12.4. Distribution of the 30 forest remnants with respect to altitude and the continuous forest of
the Monteverde Reserve Complex.tions, and Guindon, "Importance of Pacific Slope Forest,"
p. 435). What happens to plants isolated in pastures,
windbreaks, or small forest patches when their avian
seed dispersers can easily cross open habitats but their
insect pollinators cannot? What are the implications of
long-distance seed dispersal but short-distance pollina-
tion for plant population genetic structure and for sexual
or natural selection on plant reproductive traits?
The isolation of spatially separated habitat patches
can be mitigated, at least in part, if the patches are
connected by habitat corridors. Research on insect
migrations over the Continental Divide emphasizes
the importance of maintaining contiguous forest (see
Williamson and Darling, "La Ventana," p. 438). With-
out adequate cover, weakly flying insects cannot
make headway against Monteverde's powerful pre-
vailing northeast trade winds during the insects' dry
season migration from the leafless Pacific slope for-
ests to the moister Atlantic slope forests. Just as Black
Guans may be reluctant to cross open areas to reach
isolated forest patches, flying insects may be deterred
by exposed windy areas. Many flying insects are para-
sitic wasps and flies, which control populations of
insect pests and contribute to biodiversity. The loss
of parasitoids or pollinators due to disruption of mi-
gration corridors could have a substantial impact on
the nature of insect and plant communities in
Monteverde. Paradoxically, roads may make it easier
for some insects to migrate, although an unexplored
question is whether they also increase the insects'
conspicuousness to predators or facilitate migration
of their parasitoids. The matrix of cleared land in
which Monteverde's forest fragments are embedded
can take on the attributes of a habitat corridor for taxa
that are effective dispersers, and even for ineffective
dispersers if pasture trees are not too distantly spaced.
Habitat linkages and migration corridors are also
important on a regional scale. Many species of fruit- and
nectar-feeding birds migrate altitudinally in rhythm
with seasonal changes in rainfall and food availability
(see Chap. 6, Birds). Radio-tracking studies provide cru-
cial details about how Resplendent Quetzals move in
complex sequences between Pacific and Atlantic slope
habitats (see Powell et al., "Altitudinal Migrations," pp.
439-442). Among vertebrates, Three-wattled Bellbirds,
hummingbirds, and fruit bats also migrate altitudinally,
but the details of their movements are poorly known (see
Chaps. 6 and 7).
Adequate linkages and migration corridors appro-
priate for different taxa must be maintained among427 Conservation Biology