the Monteverde Reserve Complex becomes increas-
ingly isolated from the country's other lower montane
forests (Fig. 12.1). Costa Rica's highland forests are
already separated from highland forests elsewhere
in Central America and Mexico (LaBastille and Pool
1978, Hamilton et al. 1994).
Climate change, ozone depletion, acid rain, and the
alteration of hydrological cycles are examples of dis-
ruptions of biogeochemical cycles and atmospheric
chemistry that can affect biodiversity. Many species,
particularly in the tropics, exist within a relatively
narrow range of physical conditions. If temperatures
rise, ultraviolet radiation increases, or droughts be-
come more frequent, prolonged, or severe, certain
species may no longer be able to survive or reproduce,
as appears to be the case with Monteverde's amphib-
ian fauna (see Chap. 5, Amphibians and Reptiles).
Such perturbations are often caused by human activi-
ties far from the area they impact, which emphasizes
that conservation biologists must think and work
globally as well as locally (Orians and Wheelwright
1997). Another example of a major conservation prob-
lem whose solution must be found outside the local
area is the introduction of pest species and disease
organisms (Mooney and Drake 1986).
12.3. The Status of Biodiversity
in Monteverde: What Is at Stake?
Conservation begins with an assessment of biodiver-
sity and a clear set of values and objectives. What is
the current status of populations, communities, and
ecosystems? What will be lost if conditions remain as
they are, or if they change? How will the disappear-
ance of species, interactions, or ecosystems affect hu-
mans and other species? Nowhere in the tropics do
we have a complete inventory of all species, let alone
their population sizes, dynamics, or genetic structure.
The demography of populations and the spatial re-
lationships of populations to one another within a
"metapopulation" (a group of populations; Levins
1969, Hanski and Gilpin 1996) are virtually unknown.
This section briefly reviews what we currently know
about the number of species in Monteverde.
For a few taxa in Monteverde, particularly terres-
trial vertebrates, species inventories are nearly com-
plete (see Chaps. 5—7). Thirty years of observations by
residents of Monteverde and by visiting ornitholo-
gists, students, and bird-watchers have produced an
accurate list of the area's bird species, their habitat
preferences, their basic life histories, and their sea-
sonal movements (Young et al. 1998). When a new
bird species is spotted in Monteverde, we can be con-
fident that it only recently arrived; when a species can
no longer be found, we can be reasonably certain that
it has become locally extinct. As a result, we know
that the Atlantic slope of Monteverde supports the
greatest bird diversity in Costa Rica. The area's high
species richness is caused by the intersection of three
biogeographically distinct avifaunas (South Ameri-
can, Mesoamerican, and North American) in Monte-
verde, and six distinct life zones occurring within an
area the size of a standard 24-km radius Christmas
Bird Count (see Chaps. 3 and 6). Ten of Monteverde's
bird species are listed as "at risk" by the International
Union for the Conservation of Nature (see Table 6.8).
Mammals in Monteverde have also been well inven-
toried (see Chap. 7, Mammals), and like birds they are
exceedingly diverse. More than 40% of all of Central
America's mammal species are found in Monteverde.
Reptiles and amphibians are also diverse in Monte-
verde. Amphibians, perhaps because of their limited
dispersal abilities, show greater endemism than rep-
tiles: 40% of Monteverde's amphibians are restricted
to the highlands of Costa Rica, compared to only 15%
of the area's reptiles. For both groups, there is high
beta diversity. Unfortunately, the opportunity to un-
derstand Monteverde's complete fauna of amphibians
and reptiles has passed. The stupefying declines and
disappearances of many amphibian and several rep-
tile species in Monteverde may be the most alarming
conservation problem in the region (see Chap. 5, Am-
phibians and Reptiles).
It will be many decades before we have a detailed
inventory of insects in Monteverde comparable to that
of birds, mammals, amphibians, and reptiles (see
Chap. 4, Insects and Spiders). Butterflies maybe an ex-
ception, because their biology is well known for many
of the same reasons as birds: they are diurnal, distinctly
colored, and identifiable with available field guides.
So far, 250 species of butterflies have been listed for
Monteverde. Approximately 50% of Monteverde's
butterfly species are elevational migrants, which makes
them vulnerable to local extinction if their lowland
habitats are disrupted. Monteverde is rich in other in-
sect taxa. For example, Monteverde has as many spe-
cies of cercopoid hoppers (order Homoptera) as all of
Canada, and three times as many species as Great Brit-
ain. As with other taxa, endemism in insects is much
greater in highland regions such as Monteverde than
in lowland regions. Dragonflies and damselflies (order
Odonata) and bees, wasps, and ants (order Hymeno-
ptera) are examples of taxa whose geographical ranges
are more restricted at higher elevations. For most in-
sects, however, we know little more than their names,
if that. For example, the host plants of nearly three-
quarters of Monteverde's leaf beetle species (family
Chrysomelidae) have not been determined. The popu-
lation status and interactions of other invertebrates and
423 Conservation Biology