Separating the influence of resource ‘availability’ from resource ‘imbalance’ on productivity–diversity relationships

Abstract

One of the oldest and richest questions in biology is that of how species diversity is related to the availability of resources that limit the productivity of ecosystems. Researchers from a variety of disciplines have pursued this question from at least three different theoretical perspectives. Species energy theory has argued that the summed quantities of all resources influence species richness by controlling population sizes and the probability of stochastic extinction. Resource ratio theory has argued that the imbalance in the supply of two or more resources, relative to the stoichiometric needs of the competitors, can dictate the strength of competition and, in turn, the diversity of coexisting species. In contrast to these, the field of Biodiversity and Ecosystem Functioning has argued that species diversity acts as an independent variable that controls how efficiently limited resources are utilized and converted into new tissue. Here we propose that all three of these fields give necessary, but not sufficient, conditions to explain productivity-diversity relationships (PDR) in nature. However, when taken collectively, these three paradigms suggest that PDR can be explained by interactions among four distinct, non-interchangeable variables: (i) the overall quantity of limiting resources, (ii) the stoichiometric ratios of different limiting resources, (iii) the summed biomass produced by a group of potential competitors and (iv) the richness of co-occurring species in a local competitive community. We detail a new multivariate hypothesis that outlines one way in which these four variables are directly and indirectly related to one another. We show how the predictions of this model can be fit to patterns of covariation relating the richness and biomass of lake phytoplankton to three biologically essential resources (N, P and light) in a large number of Norwegian lakes.

The role of phytoplankton diversity metrics in shallow lake and river quality assessment

“…There are various shapes of productivity diversity relationships published in the literature, but the most frequent examples show that diversity is either concave-down, or increasing function of productivity (Cardinale et al, 2009). The shape of the relationship depends on the scale of investigations (Chase and Leibold, 2002), and on whether plants or animals are studied (Mittelbach et al, 2001).…”

Biodiversity and ecosystem functioning in dynamic landscapes

“…Another article of this special issue, a metaanalysis of 78 structural equation models, provides evidence that biodiversity is a strong driver of productivity [49]. Using an existing template [50] to disentangle the effects of potential productivity (resource availability and stoichiometric imbalance) on biodiversity and realized productivity (biomass production), they use standardized path coefficients as effect sizes across ecosystem types and find that, on average, the direct effect of resource availability on biomass is as strong as the effect of biodiversity change. Resource imbalance, however, plays a minor role in these datasets [49].…”

“…few generations) in BEF experiments is providing the critically important information on the consequences of extinctions in real-world ecosystems. Globally, species are going extinct at such a high rate that the current era has qualified as a period of mass extinction [50]. However, whether this global extinction also reduces biodiversity at the local level, where functional consequences occur, is an open question.…”

Food webs: reconciling the structure and function of biodiversity

“…Early studies relating biodiversity to functions such as primary productivity, decomposition, pollination, and fisheries production were necessarily simple and primarily focused on single trophic levels ( [9] for a review). The limitations of this approach have been widely described [9,10], and there is a growing recognition that BEF studies would benefit from a framework that considers effects of changes in biodiversity across trophic levels on multiple ecosystem processes [9][10][11].…”