THE MICHIGAN BOTANIST
Hansen and di Castri 1992, Holland et al. 1993, Risser 1995, and Ward and
Wiens In Press). These functions include serving as frontiers for successional
change (Rusek 1992), governing ecological flows and patterns (Wiens 1997),
and preservation of biodiversity (Yoon 1997).
It is important to understand how and why the tension zone concept developed because it is part of one of the major themes in ecology-the search for pattern or distribution in space of species and individuals and understanding their
relationships with other organisms and the environment (McIntosh 1976), and
understanding change and uniformity within ecosystems (Hagen 1992). This
search has been going on since the time of Darwin. In On the Origin of Species
(1859), Darwin presented the contrasting views of change brought about by the
struggle of competition and "a high degree of uniformity, stability, and interdependence" (Hagen 1992) that nature's complex web sometimes produces.
The author gratefully acknowledges the comments provided by A. A. Reznicek and two anonymous referees on earlier drafts of this work.
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