Effects of Past Global Change on Life (1995)
Chapter: ABSTRACT
8
The Response of Hierarchially Structured Ecosystems to Long-Term Climatic Change: A Case Study using Tropical Peat Swamps of Pennsylvanian Age
WILLIAM A. DIMICHELE
National Museum of Natural History, Smithsonian Institution
TOM L. PHILLIPS
University of Illinois
ABSTRACT
Carboniferous coal-forming swamps are an excellent system in which to evaluate the effects of regional to global climatic changes on ecosystem structure and dynamics. Stressful physical conditions restrict the access of most species, creating semiclosed conditions in which the signal-to-noise ratio should be high. We examine patterns of change in coal-swamp systems during the Pennsylvanian at three levels: landscapes, habitats within landscapes, and species within habitats. The timing and extent of turnover at these three levels suggest a hierarchial organization, in the sense that patterns at one level emerge from interactions among elements at a lower level, and can have subsequent reciprocal effects on the dynamics at that lower level.
Changes in the species composition of coals, and in the dominance-diversity structure they define, occur continuously throughout the Pennsylvanian. However, there are distinct breakpoints that allow us to recognize five basic organizational themes. Each of these breakpoints corresponds to an independently inferred change in regional or global climate. Examination of species-level turnover patterns reveals highest values at the landscape-level breakpoints, suggesting at first that climate change may be affecting species turnover, which then scales upward directly into landscape changes. Estimation of the relationship between species turnover and habitat patterns, however, suggests an intermediate level of organization. Species turnover throughout the Westphalian occurs mostly within habitats and on strongly ecomorphic themes; species of the same or closely related and morphologically similar genera tend to replicate each other through time. It is the proportion of habitats that changes at the landscape-breakpoint boundaries, and habitats contain the ecomorphic elements that give the landscape its apparent dominance-diversity structure.
At the Westphalian-Stephanian boundary, high levels of extinction eliminated sufficient numbers of species that Westphalian ecomorphic patterns were destroyed and a new
