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(see, e.g., Tucker et al., 1991). Barry et al. (1995) document a
shift in the community structure of invertebrate fauna in a
California rocky intertidal zone consistent with observations of
warming sea surface temperature between 1932 and 1993. In addition
to these regional changes, the observed increase in the
intra-annual amplitude of atmospheric CO2 concentration may indicate that the
cycle of net primary production and respiration is increasing in
vigor on a hemispheric scale (Keeling et al., 1996a).
Natural and anthropogenic habitat destruction and fragmentation
are the greatest contributors to the extinction of species.
Consider the entirely new ''ecosystem'' that has recently grown to
occupy several percent of the land area of the United States. It is
composed of a patchwork of asphalt, concrete, and structures, with
some accompanying reforestation; all of these influence and are
influenced by other ecosystems, society, and climate. Fire and
other disasters such as floods and storms are part of a naturally
varying environment to which ecosystems will adapt, but this new
"ecosystem" will be more challenging.