How biodiversity affects ecosystem processes: implications for ecological revolutions and benthic ecosystem function

Current and projected rates of extinction provide impetus to investigate the conse- quences of biodiversity loss for ecosystem processes. Yet our understanding of present day biodiver- sity–ecosystem functioning relations contrasts markedly with our understanding of the responses of species to changes that have occurred in the geological record. Of the experiments that have explic- itly tested the relationship between biodiversity and ecosystem functioning, few have attempted to reconcile whether the underlying process that gives rise to the observed response is affected by bio- diversity in the same way as the observed response. In the present study, we use benthic macrofau- nal invertebrates to examine and distinguish the effects of species richness and species identity on bioturbation intensity, a key mechanism that has been important on evolutionary timescales regulat- ing ecosystem functioning in the marine benthos. Our study identifies significant effects of species richness that reflect species-specific impacts on particle reworking that, in turn, lead to elevated lev- els of nutrient generation. However, our findings also suggest that the consideration of only bioturba- tion intensity forms an incomplete evaluation of bioturbation effects because the way in which spe- cies interact with the benthic environment does not necessarily reflect organism traits only associated with particle transport. Our study emphasises the need for caution when extrapolating from assumed knowledge of organism traits to how changes in species composition associated with ecological crises may impact ecosystem function. Nonetheless, the empirically derived mechanistic effects of bioturba- tion on ecosystem functioning documented here are sufficiently general to seek correlations between diversity and function in natural systems, including those from the palaeoecological record.

Current and projected rates of extinction provide impetus to investigate the conse-
quences of biodiversity loss for ecosystem processes. Yet our understanding of present day biodiver-
sity–ecosystem functioning relations contrasts markedly with our understanding of the responses of
species to changes that have occurred in the geological record. Of the experiments that have explic-
itly tested the relationship between biodiversity and ecosystem functioning, few have attempted to
reconcile whether the underlying process that gives rise to the observed response is affected by bio-
diversity in the same way as the observed response. In the present study, we use benthic macrofau-
nal invertebrates to examine and distinguish the effects of species richness and species identity on
bioturbation intensity, a key mechanism that has been important on evolutionary timescales regulat-
ing ecosystem functioning in the marine benthos. Our study identifies significant effects of species
richness that reflect species-specific impacts on particle reworking that, in turn, lead to elevated lev-
els of nutrient generation. However, our findings also suggest that the consideration of only bioturba-
tion intensity forms an incomplete evaluation of bioturbation effects because the way in which spe-
cies interact with the benthic environment does not necessarily reflect organism traits only associated
with particle transport. Our study emphasises the need for caution when extrapolating from assumed
knowledge of organism traits to how changes in species composition associated with ecological crises
may impact ecosystem function. Nonetheless, the empirically derived mechanistic effects of bioturba-
tion on ecosystem functioning documented here are sufficiently general to seek correlations between
diversity and function in natural systems, including those from the palaeoecological record.

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