The role of environmental vs. biotic filtering in the structure of European ant communities: A matter of trait type and spatial scale.

Olga Boet,Xavier Arnan,Javier Retana,Judi Hewitt

doi:10.1371/journal.pone.0228625

Abstract

Functional trait-based approaches are increasingly used for studying the processes underlying community assembly. The relative influence of different assembly rules might depend on the spatial scale of analysis, the environmental context and the type of functional traits considered. By using a functional trait-based approach, we aim to disentangle the relative role of environmental filtering and interspecific competition on the structure of European ant communities according to the spatial scale and the type of trait considered. We used a large database on ant species composition that encompasses 361 ant communities distributed across the five biogeographic regions of Europe; these communities were composed of 155 ant species, which were characterized by 6 functional traits. We then analysed the relationship between functional divergence and co-occurrence between species pairs across different spatial scales (European, biogeographic region and local) and considering different types of traits (ecological tolerance and niche traits). Three different patterns emerged: negative, positive and non-significant regression coefficients suggest that environmental filtering, competition and neutrality are at work, respectively. We found that environmental filtering is important for structuring European ant communities at large spatial scales, particularly at the scale of Europe and most biogeographic regions. Competition could play a certain role at intermediate spatial scales where temperatures are more favourable for ant productivity (i.e. the Mediterranean region), while neutrality might be especially relevant in spatially discontinuous regions (i.e. the Alpine region). We found that no ecological mechanism (environmental filtering or competition) prevails at the local scale. The type of trait is especially important when looking for different assembly rules, and multi-trait grouping works well for traits associated with environmental responses (tolerance traits), but not for traits related to resource exploitation (niche traits). The spatial scale of analysis, the environmental context and the chosen traits merit special attention in trait-based analyses of community assembly mechanisms.

Highlights

A central goal in ecology is to understand the processes underlying community assembly [1,2,3,4]
Our first objective was to analyse the relative role of environmental filtering and competition on the structure of European ant communities at different spatial scales
The role of environmental vs. biotic filtering in the structure of European ant communities corroborated our first hypothesis, because our results suggest that environmental filtering is the main mechanism influencing ant community structure at the largest spatial scale (European)

Summary

Introduction

A central goal in ecology is to understand the processes underlying community assembly [1,2,3,4]. A plethora of processes (e.g. evolutionary history, environmental constraints, biotic interactions) operating at different spatial and temporal scales contribute to community assembly patterns [5]. Species interactions (i.e. biotic filtering) can exert a strong influence on the final number of species that co-occur in a community, mainly through competitive exclusion [9]. On those taxa where interspecific competition might be an important process structuring local assemblages, it is useful to understand the relative contribution of environmental filtering vs competition [2,10]. Environmental filtering is expected to dominate during early succession [18] and high elevations [12,19,20] where environmental conditions are harshest, with biotic filtering becoming increasingly important in the later stages of succession [21]

Objectives

Methods

Results

Conclusion