Spatial patterns and determinants of trait dispersion in freshwater fish assemblages across Europe

Abstract

Aim Understanding how species assemble into assemblages and identifying the determinants of assembly processes remains a key challenge in ecology. Within assemblages, functional trait dispersion can be used to infer assembly processes, but this inference could depend on the trait considered. Here, using both single and multiple trait‐based approaches, we analysed dispersion patterns for alpha (i.e., related to niche partitioning) and beta (i.e., related to environmental tolerance) traits in freshwater fish assemblages and characterized how trait dispersion patterns vary along environmental gradients at large spatial scale. Location Western Palaearctic, 290 river catchments. Time period Contemporary. Major taxa studied Freshwater fish. Methods Based on freshwater fish occurrence records in 290 European river catchments, we computed dispersion indices (mean pairwise distance) using standardized effect sizes for each single trait and multiple traits. We then used linear models including climatic, geo‐morphological, biotic and human‐related factors to determine the key drivers shaping freshwater fish dispersion patterns across Europe. Results We highlighted spatial variation in trait dispersion, with both underdispersion and overdispersion simultaneously observed for a given trait, but also distinct patterns of trait dispersion, even within beta and alpha traits. We provided evidence that elevation range and current and past climatic conditions mainly structured trait dispersion patterns. Finally, our results revealed that spatial patterns in trait dispersion based on multiple traits were less pronounced than those based on individual traits. Main conclusions Our results highlighted that traits showed different spatial and environmental patterns, reflecting different ecological patterns. This could lead to potential problems when using functional indices computed on multiple traits and challenges their relevance to describe diversity patterns and to infer the assembly processes shaping community structure.

Can ancestry and morphology be used as surrogates for species niche relationships?

“…etary overlap (hypothesis 4). Together, these findings lend some support for approaches in community ecology that rely on species traits to infer niche relationships (e.g., Côte et al, 2019;Kraft et al, 2008).…”

“…This challenges the traditional view that local community structure derives mainly from niche-partitioning and opens the possibility for alternative hypotheses that metapopulational dynamics (e.g., mass effects) and regional species extinction probabilities (e.g., Lottery Competition and Neutral Theory) are strong determinants of the structure and diversity of local communities (Bell, 2001;Chesson & Warner, 1981;Hubbell, 2001;Sale, 1977). Either way, the relationships between phylogeny, morphological similarity and indicators of ecological performance (e.g., diet) remain poorly documented, this in spite of the fact that numerous studies have assumed morphological traits and/ or phylogeny are effective surrogates for species niches when analyzing patterns of community structure (e.g., Cooper, Rodríguez, & Purvis, 2008;Côte, Kuczynski, & Grenouillet, 2019;Kraft, Valencia, & Ackerly, 2008).…”

Environmental filters of freshwater fish community assembly along elevation and latitudinal gradients

“…Such differences in trait databases could produce different conclusions. For example, two studies had disparate results when describing latitudinal patterns of European freshwater fish community assembly (Côte et al, 2019;Schleuter et al, 2012). Those discrepancies were attributed to the choice of functional traits (morphological vs. ecological) and whether functional traits were organized into single or multiple trait categories (i.e., distinguishing between alpha and beta traits; Saito et al, 2016).…”

“…Alpha traits are defined by behaviour, feeding strategies and resource use that predominantly explain species co-existence (i.e., limiting similarity), whereas beta traits are defined by tolerance of abiotic conditions that are associated with environmental filters (Ackerly & Cornwell, 2007;Ingram & Shurin, 2009). Previous studies recommend that these two trait distinctions be analysed independently to elucidate better whether similar traits are associated with similar assembly processes (Côte et al, 2019;Saito et al, 2016).…”

TOFF, a database of traits of fish to promote advances in fish aquaculture

“…However, an overview of broad-scale insights is poorly available because useful datasets are scattered over several decades of literature in many languages. Some trait compilations have already been proposed (e.g., 15–18 ) but most of them focus on particular set of traits to address specific questions, fail to ensure homogeneity of data (e.g., no standardized definitions of traits making comparison from different sources doubtful), gather information for a limited geographic area/taxonomic range, and/or has restricted availability. Although original citations are provided, the largest available comprehensive compilations of fish traits (i.e.…”