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Marine ecosystems are experiencing rapid and pervasive loss of species. Understanding the consequences of species loss is critical to effectively managing these systems. Over the last several years, numerous experimental manipulations of species richness have been performed, yet existing quantitative syntheses have focused on a just a subset of processes measured in experiments and, as such, have not summarized the full data available from marine systems. Here, we present the results of a meta-analysis of 174 marine experiments from 42 studies that have manipulated the species richness of organisms across a range of taxa and trophic levels and analysed the consequences for various ecosystem processes (categorised as production, consumption or biogeochemical fluxes). Our results show that, generally, mixtures of species tend to enhance levels of ecosystem function relative to the average component species in monoculture, but have no or negative effect on functioning relative to the ‘highest-performing' species. These results are largely consistent with those from other syntheses, and extend conclusions to ecological functions that are most commonly measured in the marine realm (e.g. nutrient release from sediment bioturbation). For experiments that manipulated three or more levels of richness, we attempted to discern the functional form of the BEF relationship. We found that, for response variables categorised as consumption, a power-function best described the relationship, which is also consistent with previous findings. However, we identified a linear relationship between richness and production. Combined, our results suggest that losses of species will, on average, tend to alter the functioning of marine ecosystems. We outline several research frontiers that will allow us to more fully understand how, why, and when diversity may drive the functioning of marine ecosystems.
R code for data handling, analyses, and figure plotting.
Supplementary figures/results. Including Fig. A1 (comparing response variables when measured at the focal [within] trophic level or at adjacent [bottom-up and top-down] trophic levels; Fig. A2 (jacknife simulations of removing individual studies from the effect of producer richness on consumption); Fig. A3 (state vs. rate variables).
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