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Levels of Biological Organization Biological systems can be considered to be organized into a number of hierarchical levels (Figure 1). There is variation within each organizational level (e.g., com- Imunity) considered, as well as among different units at the particular level (e.g., upland versus bottom land hardwood communities) being considered. Accordingly, for the genetic measures of diversity, there is an average value for multilocus het- erozygosity, proportion of polymorphic loci and alleles per locus for each community, species group, species, population or individual. There also would be a genetic difference among the organizational units at each hierarchical level (e.g., different species groups within a community). Diversity among units may be more important gt times than the diversity within the units. The best management strategy for con- gerving among-unit diversity may be to manage the units as separate entities, whereas the within-units diversity might require a management strategy of exchange among wits. Communities and Species Groups Species assemblages are the highest hierarchical level yet studied for genetic diversity. Johnson (1973) studied genetic diversity in Hawaiian Drosophila. As the ,IY,tmber of species in an assemblage increase, the allelic diversity also increases. A Similar relationship has been found for assemblages of southeastern freshwater fish dominated primarily by sunfish (Centrachidae). Although Johnson (1973) did not Study the relationship between genetic and species evenness in Drosophila, there is evidence for a relationship between these components of diversity in a set of 11 Species assemblages of southeastern freshwater fish (Figure 2). Genetic diversity Southeastern Fish Assemblages 1.00r 0.95 W LP N 0.90 N a? 0.85 ty U 0.80 m C c9 0.75 0.5 0.6 0.7 0.8 0.9 1.0 Species Evenness (SE) Figure 2. Genetic and species evenness are plotted for 11 fish assemblages from South Carolina and Florida. The linear relationship between the variables and coefficient of determination (r') are given. Genetics and Biodiversity ? 245 GE = 0.66 + 0.28 SE r2 = 0.80