Stachowicz Lab University of California, Davis

Ecological Consequences of Genetic Diversity

Some communities, such as coral reefs, kelp forests, and seagrass beds may be comprised of a single dominant species, and genetic diversity within these species may play an analogous role to species diversity in more speciose systems.

Through manipulative field experiments and laboratory mesocosms, we have been examining the effects of genetic diversity in the eelgrass Zostera marina on community function and stability. Field experiments show that genetic diversity enhances community resistance to natural disturbances by grazing geese and algal blooms as well as experimentally imposed disturbances. These differences in disturbance response affect the abundance of epifaunal grazers such as amphipods and other small crustaceans on seagrasses.

Top: A field experiment in the Bodega Harbor Eelgrass beds. Left: Brandt Geese moving in to graze on eelgrass. Bottom: Measuring nutrient uptake in seagrass in the lab.

In laboratory experiments we have been measuring the physiological performance of individual seagrass clones grown in common gardens. We find strong physiological differences in nutrient uptake as well as allocation to shoot vs. root biomass in which no single clone maximizes all aspects of clonal performance. This suggests there are phenotypic differences among clones that may underlie observed diversity effects in the field.

Current work in this area focuses on understanding the influence of genetic relatedness, trait differences, and genotypic identity on seagrass ecosystem functioning. This is a collaboration with Susan Williams and Rick Grosberg. Our previous work used only the number of genotypes as a measure of genetic diversity. Recent analyses of species diversity experiments show that phylogenetic diversity may be a more reliable predictor of ecosystem functioning than simply the number of species. However, such approaches have not yet been applied to understanding the effects of genetic on ecosystem functioning. We are building on our own previous work to ask whether genotypic richness, or genetic relatedness/distance better predicts ecosystem functioning? If genetic relatedness measures are better predictors, then what mechanisms underlie this relationship? Can genetic relatedness predict ecological relatedness? We are assessing the relationship between genetic relatedness and phenotypic distinctiveness of eelgrass and using manipulative experiments to test the relative importance of the number of genotypes in an assemblage vs. their genetic relatedness and trait diversity for ecosystem functioning.

Relevant Papers

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Stachowicz, J.J., S.J. Kamel, A.R. Hughes, and R.K. Grosberg. 2013. Genetic relatedness influences plant biomass accumulation in eelgrass (Zostera marina). American Naturalist. In Press.[-pdf-]

Best, R.J. and J.J. Stachowicz. 2013. Phylogeny as a proxy for ecology in seagrass amphipods: which traits are most conserved? PLoS ONE.

Best R.J., N.C. Caulk, and J.J. Stachowicz. 2013. Trait versus phylogenetic diversity as predictors of competition and community composition in herbivorous marine amphipods. Ecology Letters 16:72-80.[-pdf-]

Best, R.J. and J.J. Stachowicz. 2012. Trophic cascades in seagrass meadows depend on mesograzer variation in feeding rates, predation susceptibility, and abundance. Marine Ecology Progress Series 456:29-42.[-pdf-]

Kamel, S.J., A.R. Hughes, R.K. Grosberg, and J.J. Stachowicz. 2012. Fine-scale genetic structure and relatedness in the eelgrass Zostera marina. Marine Ecology Progress Series 447:127-137[-pdf-]

Tomas F., J.M. Abbott, M. Balk, C. Steinberg, S.L. Williams, and J.J. Stachowicz. 2011. Plant genotype and nitrogen loading influence seagrass productivity, biochemistry, and plant-herbivore interactions. Ecology 92:1807-1817[-pdf-]

Hughes, A.R. and J.J. Stachowicz. 2011. Seagrass genotypic diversity increases disturbance response via complementarity and dominance. Journal of Ecology 99:445-453.[-pdf-]

Hughes, A.R., R.J. Best, and J.J. Stachowicz. 2010. Genotypic diversity and grazer identity interactively influence seagrass and grazer biomass. Marine Ecology Progress Series 403: 43-51. [-pdf-]

Hughes, A.R., J.J. Stachowicz, and S.L. Williams. 2009. Morphological and physiological variation among seagrass (Zostera marina) genotypes. Oecologia 159:725-733.[-pdf-]

Hughes, A.R. and J.J. Stachowicz. 2009. Ecological impacts of genotypic diversity in the clonal seagrass, Zostera marina. Ecology 90: 1412-1419.[-pdf-]

Hughes, A. R., and J. J. Stachowicz. 2004. Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance. Proceedings of the National Academy of Sciences of the United States of America 101:8998-9002. [-pdf-]

Hughes, A. R., J. E. Byrnes, D. L. Kimbro, and J. J. Stachowicz. 2007. Reciprocal relationships and potential feedbacks between biodiversity and disturbance. Ecology Letters 10:849-864. [-pdf-]