Integrating community assembly and biodiversity to better understand ecosystem function: the Community Assembly and the Functioning of Ecosystems (CAFE) approach

Abstract

The research of a generation of ecologists was catalysed by the recognition that the number and identity of species in communities influences the functioning of ecosystems. The relationship between biodiversity and ecosystem functioning (BEF) is most often examined by controlling species richness and randomising community composition. In natural systems, biodiversity changes are often part of a bigger community assembly dynamic. Therefore, focusing on community assembly and the functioning of ecosystems (CAFE), by integrating both species richness and composition through species gains, losses and changes in abundance, will better reveal how community changes affect ecosystem function. We synthesise the BEF and CAFE perspectives using an ecological application of the Price equation, which partitions the contributions of richness and composition to function. Using empirical examples, we show how the CAFE approach reveals important contributions of composition to function. These examples show how changes in species richness and composition driven by environmental perturbations can work in concert or antagonistically to influence ecosystem function. Considering how communities change in an integrative fashion, rather than focusing on one axis of community structure at a time, will improve our ability to anticipate and predict changes in ecosystem function.

A cross-scale assessment of productivity-diversity relationships

“…In our study, the strong local effect of demographic stochasticity appears plausible given the small area of the forest plots (672m 2 ) and small population sizes (12.24 ± 0.02 trees per plot; range = 1-157 trees per plot) therein. This would suggest that temporal changes in local scale biodiversity (Dornelas et al, 2014;Magurran et al, 2018) may have underappreciated effects on ecosystem function (Bannar-Martin et al, 2018).…”

Modeling How Community Assembly Alters the Functioning of Ecosystems

“…Several methods are available (e.g. Kirwan et al 2009, Bell et al 2009, Hector et al 2009, Bannar-Martin et al 2018); in this paper we focus on two of these. The first, which we call the Complementarity-Selection Effects method (originally called the ‘additive partitioning method’), is based on comparing the contributions of species to ecosystem function when they are in monocultures to those that emerge due to species interactions in polycultures (Loreau and Hector 2001).…”

“…Another approach for linking community assembly effects with ecosystem function is based on pairwise comparisons of communities and quantifies how differences in total function relate to changes in composition and individual species’ functions by calculating ‘Price components’ (Fox 2006, Fox and Kerr 2012, Bannar-Martin et al 2018). Although this approach is constrained to ecosystem functions that can be calculated as the sum of contributions of their constituent species (Fox 2006), it has the advantage that it can be more generally used to look how any change in community structure (i.e., species richness, taxonomic turnover, changes in resident abundances or function) alters ecosystem functioning.…”

“…Although this approach is constrained to ecosystem functions that can be calculated as the sum of contributions of their constituent species (Fox 2006), it has the advantage that it can be more generally used to look how any change in community structure (i.e., species richness, taxonomic turnover, changes in resident abundances or function) alters ecosystem functioning. Calculating Price components can be used flexibly to make inferences based on complex pairwise comparisons (Bannar-Martin et al 2018) or on temporal effects related to environmental change (Kremer et al in prep). Here we will focus on comparisons between the communities with the most diverse species pool and those with lower levels of richness.…”

“…Here we will focus on comparisons between the communities with the most diverse species pool and those with lower levels of richness. There are many different ways the Price components can be configured (Bannar-Martin et al 2018), but we employ a three-part arrangement that separately evaluate the functional effects of species gains (‘SG’), species losses (‘SL’) and the differences in density/function among species present in both communities being compared (the Context Dependent Effect or ‘CDE’). In Bannar-Martin et al (2018) these are called the Community Assembly components; we use this terminology in the rest of this paper.…”