Introduction
Regional intercomparisons between ecosystems on different continents
can be a powerful tool to improve understanding of the ways in which
ecosystems respond to global change. Large areas are often needed to
characterize the causal mechanisms governing interactions between ecosystems and their environments. Factors such as weather and climate
patterns and land-ocean and land-atmosphere interactions all play
important roles. Regional studies that hold as many factors constant over
as large an area as possible are likely to yield the most useful insights into
the functioning of ecosystems and their responses to outside stresses.
As a result of the strong physical north-south symmetry between the
western coasts of North and South America, many researchers have used
this area as a focus for comparative marine and terrestrial studies. The
similarities in climate, coastal oceanography , and physiography between
these two regions have been extensively documented. Examples of this
symmetry are the mountains and oceans that introduce similar west-toeast climatic gradients and the latitudinal variations in radiation inputs
that result in similar north-south changes in day length, diurnal cycles of
temperature, and ecological adaptations to climate. However, climatic
effectsarising from increasing concentrations of atmospheric carbon dioxide
are expected to occur more rapidly in the Northern Hemisphere than in
the Southern Hemisphere, due to the buffering effect of the oceans in the
south. Over time these asymmetries in the controls on ecosystems are
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