Abstract
The study of the interrelationship between productivity and biodiversity is a major research field in ecology. Theory predicts that if essential resources are heterogeneously distributed across a metacommunity, single species may dominate productivity in individual metacommunity patches, but a mixture of species will maximize productivity across the whole metacommunity. It also predicts that a balanced supply of resources within local patches should favor species coexistence, whereas resource imbalance would favor the dominance of one species. We performed an experiment with five freshwater algal species to study the effects of total supply of resources, their ratios, and species richness on biovolume production and evenness at the scale of both local patches and metacommunities. Generally, algal biovolume increased, whereas algal resource use efficiency (RUE) and evenness decreased with increasing total supply of resources in mixed communities containing all five species. In contrast to predictions for biovolume production, the species mixtures did not outperform all monocultures at the scale of metacommunities. In other words, we observed no general transgressive overyielding. However, RUE was always higher in mixtures than predicted from monocultures, and analyses indicate that resource partitioning or facilitation in mixtures resulted in higher-than-expected productivity at high resource supply. Contrasting our predictions for the local scale, balanced supply of resources did not generally favor higher local evenness, however lowest evenness was confined to patches with the most imbalanced supply. Thus, our study provides mixed support for recent theoretical advancements to understand biodiversity-productivity relationships.
Highlights
The relationship between productivity and biodiversity of ecosystems has been, and continues to be, a major focus of ecological research [1,2,3]
The general patterns on the local scale matched those on the metacommunity scale (Fig. 2), and there were significant and interactive effects of Psup and N:P ratio on algal biovolume (Table 1B)
Algal biovolume generally increased with Psup and there were no differences among N:P ratios at low and high levels of Psup (Fig. 2A)
Summary
The relationship between productivity and biodiversity of ecosystems has been, and continues to be, a major focus of ecological research [1,2,3]. It has often been implicitly assumed that these estimates are interchangeable [5], whereas they are most often not [2] Another issue that limits our understanding of the productivity-diversity relationship is the direction of causality. While ecologists have traditionally viewed biodiversity as a function of productivity [2,5,8], recent work has explored the relationship from a fundamentally differing perspective, where productivity is viewed as a function of changes in biodiversity [9] This has spurred a lively debate about whether biodiversity is the cause or consequence of the productivity of ecosystems The mean effect of increasing richness in these studies is to increase both biomass production and depletion of resources [13,14]
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