Box 9: Differences in environmental heterogeneity and biodiversity within and between regions provide a foundation for formulating biodiversity research questions on the patterns of diversity and why diversity matters.

POLAR, PELAGIC, AND TEMPERATE-SHELF ECOSYSTEMS: CONTRASTS IN DIVERSITY AND ENVIRONMENTAL HETEROGENEITY

Three regional systems—representing polar, pelagic, and temperate-shelf environments—offer tantalizing contrasts in their relative diversity and ecosystem structure. They serve as examples of the types of systems within and between which compelling research questions on the patterns of and the processes controlling diversity could be formulated:

  • One of the most interesting contrasts in polar marine ecology is between the Antarctic and Arctic, with the former having a much higher species richness (for example, four times the number of mollusks) than the latter. Yet the Antarctic lacks the ecological (habitat and physical) diversity of the Arctic. Historical processes have led to some of the observed differences—the Arctic is heavily disturbed and has a younger fauna—but explanations for many differences in diversity and ecosystem function remain illusory.
  • The Baltic Sea has far lower diversity than the adjacent North Sea, due primarily to differences in salinity. Despite this contrast, there appear to be few if any striking differences in energy production and flow in the water column and benthos. Both seas have similar major functional types of organisms (such as benthic macrophytes, phytoplankton, and suspension-feeding clams and mussels). What role does this level of similarity play in apparently reducing the role of diversity in energy dynamics?
  • In the central Pacific Ocean pelagic ecosystem, the western and eastern portions appear to be comparable in species composition and structure. However, there is a significant increase in nutrient input in the eastern portion. This difference in frequency of nutrient injection may provide an excellent opportunity to determine how one scale of environmental heterogeneity does—or does not—influence biodiversity dynamics.
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    Key References: Elmgren (1984, 1989); McGowan and Walker (1993); Dayton et al., (1994).

cesses that generate or alter these patterns, and natural processes that historically generated a given pattern; and (3) consequences to ecosystem function of biodiversity change (e.g., Box 9).

Patterns

Adequate knowledge of patterns of biodiversity is basic to understanding and predicting the processes responsible for these patterns. Patterns include



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