As ecological systems are altered with cascading changes in diversity, the oft-asked question is: does diversity matter for ecosystem function? This question has been tested a multitude of times, with the results often supporting the idea that more diverse assemblages provide greater functioning (such as productivity, nutrient cycling, supporting greater pollinator abundance, etc.). Besides greater functioning, scientists have hypothesized that more diverse systems are inherently more stable. That is, the functions communities provide remain more constant over time compared with less diverse systems, which may be less reliable.
While the relationship between diversity and stability has been tested for some functions, Proulx and colleagues examined the stability of 42 variables over 7 years across 82 experimental plots planted with either 1, 2, 4, 8, 16 or 60 plant species in Jena, Germany. They examined patterns of variation (and covariation) in the functions and found that many show lower variation over time in plots with more plant species. Greater stability was found at many different trophic levels including plant biomass production, the abundance and diversity of invertebrates and the abundance of parasitic wasps -which indicate more complex food webs. They also found greater stability in gas flux, such as carbon dioxide. Despite the greater stability in these measures of above-ground functions, below ground processes, such as earthworm abundance and soil nutrients, were not less variable in high diversity plots.
How ecosystems function is of great concern; these results show that more diverse plant communities function more stably and reliably than less diverse ones. The next step for this type of research should be to address what kind of diversity matters. A greater number of species means more different kinds of species, with differing traits and functions. What aspect of such functional differences determine stability of ecosystem function?
This is an exciting paper that continues to highlight the need to understand how community diversity drives ecosystem function.
Proulx, R., Wirth, C., Voigt, W., Weigelt, A., Roscher, C., Attinger, S., Baade, J., Barnard, R., Buchmann, N., Buscot, F., Eisenhauer, N., Fischer, M., Gleixner, G., Halle, S., Hildebrandt, A., Kowalski, E., Kuu, A., Lange, M., Milcu, A., Niklaus, P., Oelmann, Y., Rosenkranz, S., Sabais, A., Scherber, C., Scherer-Lorenzen, M., Scheu, S., Schulze, E., Schumacher, J., Schwichtenberg, G., Soussana, J., Temperton, V., Weisser, W., Wilcke, W., & Schmid, B. (2010). Diversity Promotes Temporal Stability across Levels of Ecosystem Organization in Experimental Grasslands PLoS ONE, 5 (10) DOI: 10.1371/journal.pone.0013382