Fine-scale community and genetic structure are tightly linked in species-rich grasslands

Abstract

Recent evidence indicates that grassland community structure and species diversity are influenced by genetic variation within species. We review what is known regarding the impact of intraspecific diversity on grassland community structure, using an ancient limestone pasture as a focal example. Two genotype-dependent effects appear to modify community structure in this system. First, the abundance of individual constituent species can depend upon the combined influence of direct genetic effects stemming from individuals within the population. Second, the outcome of localized interspecific interactions occurring within the community can depend on the genotypes of participating individuals (indicating indirect genetic effects). Only genotypic interactions are thought to be capable of allowing the long-term coexistence of both genotypes and species. We discuss the implications of these effects for the maintenance of diversity in grasslands. Next, we present new observations indicating that losses of genotypic diversity from each of two species can be predicted by the abundance of other coexisting species within experimental grassland communities. These results suggest genotype-specific responses to abundance in other coexisting species. We conclude that both direct and indirect genetic effects are likely to shape community structure and species coexistence in grasslands, implying tight linkage between fine-scale genetic and community structure.

Figure 1.

Traits measured in genotype monoculture predict genotype performance and species abundance in communities that possess both genetic and species diversity. Trait score relates to the score of a genotype on the ‘size’ principal component from principal components analysis of monoculture trait data [17]. More negative trait scores indicate greater plant size. Plots (a)–(c) show the correspondence between the trait score of each genotype and its performance in the Booth and Grime communities (16-genotype treatment). Each point in plots (d)–(f) refers to a community with unique genotypic composition in the Booth and Grime experiment [10]. A single randomly selected community replicate represented the 16-genotype communities as these possessed identical initial genotypic composition. Population trait score is the sum of trait scores of all genotypes composing a species' population that were included initially in that community. Species abundance is the pin-quadrat abundance observed in year 5 of the Booth and Grime communities. Regression lines are shown where the regression is significant at p < 0.05. The dashed regression line and the R² value in (a) omit the outlier visible at the top of this plot [17]. Plus symbols, 16-genotype; open triangles, 4-genotype; filled circles, 1-genotype.

Figure 2.

Performance of individuals of C. rotundifolia when grown in competition with three different genotypes of the sedge C. caryophyllea. (a) Percentage survival of individuals of C. rotundifolia on a log-odds scale (logit of 0 = 50% on the probability scale) and (b) biomass of surviving individuals of C. rotundifolia. Data are from the clipped, unfertilized treatment of the pot experiment conducted by Fridley et al. [15]. Error bars are standard errors of the mean.