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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.