It has long been appreciated that certain species play a disproportionate role in influencing community structure and ecosystem processes. Keystone species, foundation species and ecosystem engineers were all named as such precisely because of this recognition of their distinctive role. That said, species are not homogenous entities. Variation within species in key traits is common, and such variation may play an analogous role to trait diversity across species in more speciose systems. Genotype richness (analogous to species richness), Genetic relatedness (analogous to phylogenetic similarity, and trait differentiation (analogous to functional diversity) can vary semi-independently but relative importance of these for driving ecosystems processes are not clear. In this talk I synthesize existing research, and present new experimental results testing the relative and interactive importance of different dimensions of intraspecific diversity in eelgrass, Zostera marina. Eelgrass is a marine angiosperm that is the sole or dominant plant found in shallow estuaries throughout the temperate northern hemisphere, providing habitat for many species and an array of coastal ecosystem services.
Results/Conclusions
A growing body of literature emphasizes the effects of intraspecific variation on plant production, nutrient cycling, species interactions, or community structure, but mechanisms underlying these effects remain elusive. We find considerable phenotypic variation occurs among eelgrass genotypes that co-occur in northern California, but this functional diversity is uncorrelated with measures of genetic relatedness among individuals, suggesting independent dimensions of diversity. In field experiments eelgrass assemblages with a higher number and evenness of genotypes (genotypic diversity) attained higher plot level biomass. We found that more genotypically diverse plots had higher trait diversity, suggesting niche differentiation among genotypes and more efficient use of available resources at the plot level leads to greater eelgrass biomass accumulation. The relatedness of eelgrass genotypes was not a reliable proxy for trait differentiation, however relatedness did influence biomass independently of genotypic diversity or trait differentiation, such that eelgrass assemblages containing genotypes that were more closely related accumulated less biomass. We found a pronounced shift in allocation of resources to above vs. belowground biomass in genotypic monocultures, and suggest that self vs. non-self recognition may result in allocation shifts in eelgrass, with cascading effects on sediment communities and ecosystem functioning. Our findings suggest that eelgrass genetic relatedness and genotypic diversity captured fundamentally different components of intraspecific variation and should be treated as complementary rather than competing dimensions of biodiversity that can contribute independently to ecosystem functioning.