Relative importance of biodiversity and the abiotic environment in mediating an ecosystem process

Whilst there is a wealth of empirical studies that indicate negative ecosystem consequences of biodiversity loss, much debate remains over the existence, strength and importance of the same patterns in natural systems. We used a gradient of organic enrichment as a means of defining non-random species loss in the marine benthos and, using partial linear regression, determined the relative importance of macrofaunal biodiversity and the abiotic environment in affecting a benthic ecosystem process (bioturbation intensity; indicated by sediment mixing depth), that is important in mediating benthic functioning. Of the abiotic and biotic variables tested (n = 8), species richness and sediment total organic carbon (TOC) content together explained 65%, of the variability in this ecosystem process, with more than half of this variability explained solely by species richness. Importantly, the relative importance of biodiversity decreased at low levels of species richness and/or high levels of TOC. These results have profound implications for manipulative field experiments, where environmental factors are likely to dominate ecosystem processes, because the extent and importance of biological mediation could be underestimated. Our results also revealed that a large proportion of the explained variability in the ecosystem process is explained by the underlying reciprocal relationship (shared variability) between biodiversity and sediment TOC, highlighting the importance of species-environment interactions. If we are to fully appreciate the role of biodiversity in natural systems, Our findings suggest that the intimate relationship between species and their environment. needs to be more prominently featured in future studies that consider the ecosystem consequences of biodiversity loss,