Spatial and Temporal Heterogeneity of Selection in an Early Successional Field: Patterns and Processes

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9307202 Stratton Environmental heterogeneity is often invoked in theories of microevolution but little is known of the spatial or temporal scale of variation in selection. The evolutionary outcome of natural selection depends critically on whether variation in fitness is fine grained or course grained. For example, dispersal of offspring in microsites with similar fitness effects will promote local adaptation, while heterogeneity within the dispersal radius favors the evolution of generalists. Variation in selection is defined by reversals in the relative fitness of genotypes (genotype x environmental interactions for fitness). My previous work has shown that soil nutrients and vegetation patterns vary on scale of meters and affect the absolute fitness of Drigeron, but changes in rank fitness among genotypes occur on a scale of centimeters. Selective heterogeneity may thus qualitatively different from easily observed ecological heterogeneity. %%% Spacial autocorrelation analysis will be used to measure spatial and temporal variation in the relative fitness of 12 genotypes of Erigeron annuus over two years. I will compare the magnitude of pure spatial and temporal variation in selection with second order changes in the location of fitness peake among years. Simultaneous measurements of soil nutrients, light, water, and background vegetation will identify factors correlate with the relative fitness in the field; greenhouse experiments will then be used to confirm the casual relationships. Furthermore, I will test whether variation in selection is caused by frequency dependent, genotype genotype interactions at several spatial scales. This research will be among the first studi es of temporal variation in selection in natural plant populations, and the first to test the stability of spatial patterns of selection through time.