Biodiversity increases functional and compositional resistance, but decreases resilience in phytoplankton communities

Biodiversity increases the stability of ecosystem functions in fluctuating environments. Only recently, parts of the underlying processes have been uncovered. A meta-analysis of biodiversity experiments manipulating primary producer richness revealed that the increased stability in more diverse systems was driven by an increased resistance (i.e. reduced changes), rather that an increased resilience (i.e. a rapid recovery) following environmental changes. As many ecosystem functions, such as primary production, comprise the joint functional contribution of the species in the system, the stability of these ecosystem functions should inherently depend on changes in the system’s composition.

Theoretical models predict that an increased number of species interactions should slow down compositional changes. By consequence, biodiversity is expected to increase both compositional and functional resistance, but these predictions have never been put to the test. In this article, Baert et al. use marine diatom microcosms to demonstrate this tight link between compositional and functional stability. Microcosms were exposed to the herbicide atrazine for 4 weeks, after which they were let to recover for 3 more weeks in atrazine-free conditions. Primary production and species composition were indeed more resistant to atrazine stress. However, slower compositional changes also simultaneously reduced resilience, causing more diverse systems to recover more slowly. By establishing the link between functional and compositional stability, these finding reveal how biodiversity changes can be expected to become increasingly important when systems are exposed to multiple stressors.

Scientific abstract

There is now ample evidence that biodiversity stabilizes aggregated ecosystem functions, such as primary production, in changing environments. In primary producer systems, this stabilizing effect is found to be driven by higher functional resistance (i.e., reduced changes in functions by environmental changes) rather than through higher functional resilience (i.e., rapid recovery following environmental changes) in more diverse systems. The stability of aggregated ecosystem functions directly depends on changes in species composition and by consequence their functional contributions to ecosystem functions. Still, it remains only theoretically explored how biodiversity can stabilize ecosystem functions by affecting compositional stability. Here, we demonstrate how biodiversity effects on compositional stability drive biodiversity effects on functional stability in diatom communities. In a microcosm experiment, we exposed 39 communities of five different levels of species richness (1, 2, 4, 6, and 8 species) to three concentrations of a chemical stressor (0, 25, and 250 μg/L atrazine) for four weeks, after which all communities were transferred to atrazine-free medium for three more weeks. Biodiversity simultaneously increased, increasing functional and compositional resistance, but decreased functional and compositional resilience. These results confirm the theoretically proposed link between biodiversity effects on functional and compositional stability in primary producer systems, and provide a mechanistic underpinning for observed biodiversity–stability relationships. Finally, we discuss how higher compositional stability can be expected to become increasingly important in stabilizing ecosystem functions under field conditions when multiple environmental stressors fluctuate simultaneously.

Full reference (link)

Baert JM, De Laender F, Sabbe K, Janssen CR. 2016. Biodiversity increases functional and compositional resistance, but decreases resilience in phytoplankton communities. Ecology 97 (12), 3433–3440.