Abstract
Tests of the biodiversity and ecosystem functioning (BEF) relationship have focused little attention on the importance of interactions between species diversity and other attributes of ecological communities such as community biomass. Moreover, BEF research has been mainly derived from studies measuring a single ecosystem process that often represents resource consumption within a given habitat. Focus on single processes has prevented us from exploring the characteristics of ecosystem processes that can be critical in helping us to identify how novel pathways throughout BEF mechanisms may operate. Here, we investigated whether and how the effects of biodiversity mediated by non-trophic interactions among benthic bioturbator species vary according to community biomass and ecosystem processes. We hypothesized that (1) bioturbator biomass and species richness interact to affect the rates of benthic nutrient regeneration [dissolved inorganic nitrogen (DIN) and total dissolved phosphorus (TDP)] and consequently bacterioplankton production (BP) and that (2) the complementarity effects of diversity will be stronger on BP than on nutrient regeneration because the former represents a more integrative process that can be mediated by multivariate nutrient complementarity. We show that the effects of bioturbator diversity on nutrient regeneration increased BP via multivariate nutrient complementarity. Consistent with our prediction, the complementarity effects were significantly stronger on BP than on DIN and TDP. The effects of the biomass-species richness interaction on complementarity varied among the individual processes, but the aggregated measures of complementarity over all ecosystem processes were significantly higher at the highest community biomass level. Our results suggest that the complementarity effects of biodiversity can be stronger on more integrative ecosystem processes, which integrate subsidiary “simpler” processes, via multivariate complementarity. In addition, reductions in community biomass may decrease the strength of interspecific interactions so that the enhanced effects of biodiversity on ecosystem processes can disappear well before species become extinct.
Highlights
A growing number of evidences in the literature have shown that biodiversity loss can affect the functioning of natural ecosystems [1,2,3,4,5,6]
Because studies have focused on single ecosystem processes, we have neglected the role of diversity in integrated and multiple ecosystem functions [6,9,21], but see [22,23,24,25]
Our results strongly suggest that the consistent complementarity effect of bioturbator diversity on bacterioplankton production (BP) was a product of multivariate nutrient complementarity
Summary
A growing number of evidences in the literature have shown that biodiversity loss can affect the functioning of natural ecosystems [1,2,3,4,5,6]. A study that analyzed the effects of seaweed diversity on the uptake of different forms of inorganic nitrogen showed that if individual species have dominant effects (i.e., sampling effects) on the uptake of particular nitrogen forms, species-rich assemblages may enhance the uptake of bulk inorganic nitrogen through multivariate nutrient complementarity [29] Such a result raises important questions germane to the BEF debate. Ecosystem processes that are dominantly governed by a particular species should be more dependent on species composition [29,30,31] It is unclear, whether multivariate complementarity effects may transcend trophic levels and habitats by connecting spatially segregated communities
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