A higher taxonomic richness does not ensure the functional resilience of saproxylic beetle communities in evergreenQuercusforests

Diana Pérez‐Sánchez,Norman W H Mason,Estefanía Micó,Eduardo Galante,Hervé Brustel

doi:10.1111/een.13069

Abstract

1. Despite the fact that insects are suffering a global decline, little is known about the extent to which species loss affects functional diversity. Thus, to understand the relationship between taxonomic and functional diversity metrics, we focused on saproxylic beetles, which perform vital functions in forest ecosystems.2. Beetles were collected monthly for a year using flight interception traps placed in three protected areas of mature evergreen MediterraneanQuercusforests. Five morphological traits, one phenological trait, and one physiological surrogate trait were measured, and trophic guild identities were determined. Two taxonomic and six functional metrics were assessed to determine their relationships.3. Taxonomic and functional diversity patterns, as well as trait patterns, differed depending on the protected areas, as they were influenced by habitat and microhabitat characteristics. Generally, a high number of species tended to support high values of functional richness, but did not ensure high values of functional redundancy, thus affecting the resilience of communities.4. A 5% of species loss strongly affected the functional redundancy of communities, making them more vulnerable. Functional richness, however, was not affected, since it was associated with a high number of redundant species. Thus, the way species loss affected communities is highly dependent on the presence of rare or redundant species.5. Taxonomic and functional diversity metrics should be used as complementary tools for conservation purposes. In this way, the comparative analysis of taxonomic and functional patterns may help to predict the vulnerability of saproxylic assemblages to changes or disturbances.

Highlights

Insects are facing a significant decline at a planetary level (Homburg et al, 2019; Sánchez-Bayo & Wyckhuys, 2019)
It is worth highlighting that higher taxonomic diversity values generally support higher functional richness values, they can come with low functional redundancy values
The comparison of the taxonomic and functional diversity patterns of each protected area showed that communities with small numbers of species (i.e. Font Roja) can present high functional diversity, whereas communities with large numbers of species (i.e. Espadán) may be less resilient because functionally rare species predominate

Summary

Introduction

Insects are facing a significant decline at a planetary level (Homburg et al, 2019; Sánchez-Bayo & Wyckhuys, 2019). The current state of knowledge of the functional diversity of insects seems to be still insufficient to fulfil such purposes This has resulted in a poor understanding of the relationship between taxonomic diversity and functional diversity, which may be key to defining the consequences of species loss for ecosystems, an issue that is yet to be resolved (Cadotte et al, 2011). Species loss in natural communities is not random; it can depend on a range of factors such as population size or sensitivity to environmental stress (Mouillot et al, 2013; Engel et al, 2017) All this makes it necessary first to analyse the relationship between different biodiversity metrics, such as taxonomic and functional measurements, so as to help calibrate the extent to which a large number of species may ensure ecosystem functions or a small number may jeopardise them. We need to understand how species loss (both random or directed) can affect functional metrics, in order to determine how ecosystem functioning may react to future perturbations or changes (Engel et al, 2017; Leclerc et al, 2020)

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Conclusion