Different Approaches to Measuring Diversity Affect the Strength of the Relationship Between Biodiversity and Ecosystem Function in Freshwater Studies: A Meta‐Analysis

ABSTRACT The notion that biodiversity begets greater ecosystem functioning is an enduring paradigm in ecology, supported by a growing body of research demonstrating the significant effects of biodiversity on ecosystem functioning (BEF). These studies use several diversity metrics, which can be estimated through taxonomic, functional and molecular approaches. Here we aim to investigate the performance of different approaches (taxonomic, functional and molecular), considering the different biodiversity metrics in each approach (e.g., richness, composition, among others). Additionally, we assess the individual response of ecosystem processes (e.g., productivity, decomposition, among others) to biodiversity in each approach. To this end, we perform a review and meta‐analysis of studies that assessed BEF relationship in continental aquatic environments, encompassing 94 studies and 322 effect sizes. Our data set includes diverse contexts, with different organisms, environments and ecosystem processes. We found an overall positive association between biodiversity and the functioning of continental aquatic ecosystems (Effect size = 0.37). We also found differences in the proportions of biodiversity metrics applied in the studies between the different approaches, as well as some geographic bias, with a predominance of studies conducted in the northern hemisphere. Additionally, lakes were the most commonly studied systems, and productivity functions were frequently analysed. We found that the molecular approach, applied exclusively in microbial studies in our dataset, showed better performance in evaluating the BEF relationship. Despite the strengths of the molecular approach, it is not without limitations. Some challenges such as high costs of sequencing and maintaining database infrastructure, can hinder its application. In light of these limitations, we understand that applying functional approaches, specifically functional richness and functional evenness metrics, in the study of the BEF relationship in continental aquatic ecosystems is promising. This can be an alternative for the continuity and advancement of studies of the BEF relationship in these environments. We also highlighted the need for studies in the southern hemisphere, covering the different freshwater ecosystem and multiple functions.