Our data demonstrate substantial among family intraspecific variation in response to elevated C02. This variation is a necessary precondition to any evolutionary response to rising C02 and could lead to large shifts in average population-level responses under elevated C02 conditions. Evolutionary changes within populations could thus alter both ecosystem-level processes such as carbon storage and community-level interactions among species. It is important, therefore, to understand the magnitude and distribution of this variation as we refine our predictions of the ecological consequences of global climate change.

We remain a long way from accurately predicting rates of evolutionary change within a community context. Although this chapter documents the best studies to date of the evolutionary potential of herbaceous plants under elevated C02, much larger and more detailed studies of evolvability under field conditions are necessary. A clearer understanding of the physiological, allocational, and life-historical causal mechanisms for intraspecific variation in response to elevated C02 are needed. These can contribute to a more effective use of funds devoted to the necessarily large-scale studies of evolva-bility under elevated COa. Once the most appropriate traits for study have been clearly identified, comparisons of genotypes using both quantitative genetics and its recent hybrid with molecular genetics, quantitative trait locus (QTL) identification, can be used to describe the genetic architecture underlying this variation. Understanding the genetic architecture is a crucial step in assessing the evolvability of the traits.

Studies that include simultaneous measures of the changing genetic composition of species and the relative abundances of species within the community are especially important in predicting within-community adaptation versus successional community replacement as responses to changes in atmospheric chemistry. The integration of physiological, allocational, and genetic studies conducted in natural plant communities could contribute substantially both to our ability to predict whole-ecosystem carbon storage and to the integration of subdisciplines within the field of ecology. Integrated studies of species- and community-level responses to elevated C02 represent both a formidable challenge and an exciting opportunity for the unification of ecology.

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