2.5 million ac) to assure that maximum biodiversity is
maintained. This is particularly true for top carnivore
species, each of which requires a large range.Climate Change
All ecosystems will be increasingly affected by global
climate change throughout the present century. There
is now an immense body of research ranging from
climatology to ecology that documents the reality
of ongoing and perhaps accelerating global climate
change. The driver for climate change is global warming
from additional greenhouse gases, in particular carbon
dioxide. The terrestrial tropics have been a major source
of added greenhouse gases, mostly due to deforestation,
which releases carbon dioxide when forest remnants
are burned to clear the brush. Ecologically speaking,
climate change is the proverbial elephant in the room.
Don’t think even for a minute that you can ignore it.
In the tropics, climate change is currently happening
fastest in areas such as flooded grasslands, deserts, and
mangrove forests. The rate is more moderate for tropical
and subtropical broad- leaved forests.
What climate change ultimately means is that
organisms within various ecosystems must essentially
move to keep up with changing temperature.
Distributions of organisms along various elevational
zones will change, for example, as organisms from lower
elevations will attempt to move higher, thus to remain
within their thermal comfort zone. The ecosystems
of the world are being reshuffled as organisms are
increasingly affected by climate alteration, most
particularly temperature change, a trend that will
continue indefinitely.
For species of the lowland tropics, the largest threat
from climate change is biological attrition, which
occurs when climate warms beyond a species’ thermal
tolerances and there is no region to which to migrate
(plate 18- 12). Adaptation by natural selection is, of
course, possible, but such a process is measured in
generations and may never occur. Strong selection
pressures may just as easily result in extinction as
adaptation. And without question, climate change
is likely to force the reassembly of ecological
communities as species react individualistically to the
impact of climate change. Given the intricate ecological
relationships ongoing in tropical ecosystems, where
biodiversity is the most essential attribute, it isimpossible to predict the degree to which tropical food
webs will unravel and realign.
Tropical forests are huge ecosystems that are major
centers of carbon cycling, which has an enormous
global impact. It is not clear, given the complexities of
climate change, whether tropical forests, particularly
tropical moist forests, will ultimately act as carbon sinks
or carbon sources. More years with excessive heat and
drought are forecast with climate change. It is clear
that when major events such as an El Niño/Southern
Oscillation (ENSO) occur (associated with higher than
usual temperatures as well as drought), many trees
perish and subsequent decomposition liberates CO2
to the atmosphere; in becoming a carbon source to
the atmosphere, the forest thus adds to greenhouse gas
accumulation. Climate change is expected to exacerbate
ENSO occurrences, and models of climate change
predict much reduced rainfall in parts of the Amazon.A Tipping Point?
An unsettling scenario has been suggested by D.
Nepstad and colleagues. The vast Amazon Basin to a
large degree makes its own weather. The transpiration of
water within the basin and its subsequent condensation
into rainfall is a major factor in its hydrodynamics and
ultimately its sustained productivity. With continuing
logging and land clearance throughout Amazonia,
forest degradation will continue. This trend towardPlate 18- 12. This Common Basilisk (Basiliscus basiliscus),
photographed in in Belize, is resting in the shady
undergrowth. The thermal world of lizards requires constant
adjustment to maintain a suitable body temperature, making
them susceptible to climate change. Photo by John Kricher.chapter 18 the future of the neotropics 383