Effects of Species Diversity on Communities and Ecosystems

Understanding the causes and consequences of variation in biodiversity has long been a central theme in ecology.  We have worked on three fronts in this research area: documenting patterns of change in biodiversity in real systems, performing experiments to demonstrate the mechanisms by which diversity does and does not affect communities and ecosystems, and collaborating with other ecologists, conservation biologists and economists to test links between the loss of biodiversity and the provision of goods and services to humans by natural ecosystems.

One ongoing research project in this area consists of a long-term manipulation of seaweed diversity in intertidal communities.  This experiment (ran from 2004 to 2011) and found that diversity has strong effects on plant biomass and production, as well as on invertebrate diversity and abundance, but these effects emerge only in experiments that are long term and conducted in the field on natural substrate that includes significant environmental heterogeneity that allows niche differences among species to be expressed (Stachowicz et al. 2008a, b).  This suggests that many current experiments conducted for short periods of time or under environmentally homogenous conditions may have underestimated the effects of diversity.  We have followed this up with experiments that show the effects of seaweed diversity are comparable in magnitude to other known drivers of community structure and function such as the presence of grazers (Aquilino and Stachowicz 2012).  Further the diversity of grazing gastropods affects algal ecosystems in complex ways that depends on the presence of substratum heterogeneity as grazers in differ their efficiency on substrates of different rugosity.  Finally, the abundance and diversity of grazers themselves also depend on seaweed diversity (Best et al. 2014) suggesting a complex feedback between diversity and ecosystem processes that may contribute to the maintenance of diversity in the long run.

We are currently using this experiment to examine how environmental heterogeneity not only causes diversity to influence ecosystem functioning, but also to examine the role of this same heterogeneity in maintaining diversity in the first place.  This involves both monitoring the recovery of experimentally maintained monocultures since 2011 and small scale experimental manipulation of substrate heterogeneity under field conditions.

Predictions of the consequences of diversity loss are complicated by the fact that we often do not know exactly how diversity is changing, and that it may be changing in different ways at different scales. At the global scale, diversity is undoubtedly declining due to extinctions, many caused directly or indirectly by the activities of humans. At the regional scale diversity may often increase due to introduction of new species, although our work comparing invasions and extinctions in coastal ecosystems has shown that despite little change or even increases in total diversity, the composition of the biota has changed in important qualitative ways. Specifically, we find that extinctions occur mainly at the level of high-order predators and other carnivores, whereas invasions are dominated by species at lower trophic levels like suspension feeders and detritivores. A major focus of our lab’s work is examining the consequences of these changes in diversity for the structure and function of local communities and the services they provide to humans.  An applied component of this examines the consequences of variation in diversity and variation in native vs invasive species dominance in suspension feeding fouling communities for the filtration of estuarine water and the maintenance of water quality.  Early work on this (Byrnes and Stachowicz 2009) is being enhanced by the use of more realistic flow regimes and a greater diversity of phytoplankton to test the effects of different kinds of environmental variation on the effects of suspension feeder diversity on marine communities.

Selected relevant papers

Duffy J.E., Reynolds P.L., Boström C., Coyer, J.A, Cusson M., Donadi S., Douglass J.G., Eklof, J., Engelen A., Eriksson B.K., Fredriksen S., Gamfeldt L., Gustafsson C., Hoarau G, Hori M., Hovel K., Iken K., Lefcheck J.S., Moksnes P-O, Nakaoka M., O’Connor M.I., Olsen J.L., Richardson J.P., Ruesink J.L., Sotka E.E., Thormar J., Whalen M.A., and Stachowicz J.J. 2015. Biodiversity and top-down control in eelgrass ecosystems: A global comparative experiment. Ecology Letters 18:696-705 [-pdf-]

Best, R.J., A. Chaudoin, M.E. Bracken, M.H. Graham and J.J. Stachowicz. 2014. Plant-animal diversity relationships in a rocky intertidal system depend on invertebrate body size and algal cover. Ecology 95:1308-1322 [-pdf-]

Aquilino, K.M., M. Coulbourne, and J. J. Stachowicz. 2012. Mixed species diets enhance the growth of two rocky intertidal herbivores. Marine Ecology Progress Series 468:179-189.[-pdf-]

Aquilino, K.M. and J.J. Stachowicz. 2012. Seaweed richness and herbivory increase rate of community recovery from disturbance. Ecology 93:879-890.[-pdf-]

Byrnes, J.E. and J.J. Stachowicz. 2009. Short and Long Term Consequences of Increases in Exotic Species Richness on Water Filtration by Marine Invertebrates. Ecology Letters 12:830-841.[-pdf-]

Palumbi, S.R., P.A. Sandifer, J.D. Allan, M.W. Beck, D.G. Fautin, M.J. Fogarty, B.S. Halpern, L.S. Incze, Jo-Ann Leong, E. Norse, J.J. Stachowicz, and D.H. Wall. 2009. Managing for ocean biodiversity to sustain marine ecosystem services. Frontiers in Ecology and the Environment 4: 204-211.[-pdf-]

Stachowicz, J.J., R.J. Best, M.E.S. Bracken, and M. H. Graham. 2008. Complementarity in marine biodiversity manipulations: reconciling divergent evidence from field and mesocosm experiments. Proceedings of the National Academy of Sciences USA 105:18842-18847.[-pdf-]

Stachowicz, J.J, M. Graham, M.E.S. Bracken, A.I. Szoboszlai. 2008. Diversity enhances cover and stability of seaweed assemblages: the importance of environmental heterogeneity and experimental duration. Ecology 89:3008-3019. [-pdf-]

Worm, B., E. B. Barbier, N. Beaumont, J. E. Duffy, C. Folke, B. S. Halpern, J. B. C. Jackson, H. K. Lotze, F. Micheli, S. R. Palumbi, E. Sala, K. A. Selkoe, J. J. Stachowicz, and R. Watson. 2006. Impacts of Biodiversity Loss on Ocean Ecosystem Services. Science 314:787-790. [-pdf-]

Stachowicz, J. J., J. F. Bruno, and J. E. Duffy. 2007. Understanding the effects of marine biodiversity on communities and ecosystems. Annual Review Of Ecology Evolution And Systematics 38:739-766. [-pdf-]

Byrnes, J. E. 2007, P. L. Reynolds, and J. J. Stachowicz. Invasions and Extinctions Reshape Coastal Marine Food Webs. PLoS One 2:e295. [-pdf-]

Byrnes, J. E., J. J. Stachowicz, K. M. Hultgren, A. R. Hughes, S. V. Olyarnik, and C. S. Thornber. 2006. Predator diversity strengthens trophic cascades in kelp forests by modifying herbivore behavior. Ecology Letters 9:61-71. [-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-]

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