Functional redundancy and sensitivity of fish assemblages in European rivers, lakes and estuarine ecosystems

Nils Teichert,Maria Teresa Ferreira,Guillem Chust,Rafaela Schinegger,Pedro Segurado,Angel Borja,Alban Sagouis,Stéphanie Pasquaud,Christine Argillier,Mario Lepage

doi:10.1038/s41598-017-17975-x

Abstract

The impact of species loss on ecosystems functioning depends on the amount of trait similarity between species, i.e. functional redundancy, but it is also influenced by the order in which species are lost. Here we investigated redundancy and sensitivity patterns across fish assemblages in lakes, rivers and estuaries. Several scenarios of species extinction were simulated to determine whether the loss of vulnerable species (with high propensity of extinction when facing threats) causes a greater functional alteration than random extinction. Our results indicate that the functional redundancy tended to increase with species richness in lakes and rivers, but not in estuaries. We demonstrated that i) in the three systems, some combinations of functional traits are supported by non-redundant species, ii) rare species in rivers and estuaries support singular functions not shared by dominant species, iii) the loss of vulnerable species can induce greater functional alteration in rivers than in lakes and estuaries. Overall, the functional structure of fish assemblages in rivers is weakly buffered against species extinction because vulnerable species support singular functions. More specifically, a hotspot of functional sensitivity was highlighted in the Iberian Peninsula, which emphasizes the usefulness of quantitative criteria to determine conservation priorities.

Highlights

The global ecological footprint of human activities entailed a rapid decline of biodiversity over the past decades[1], which affects functions and services delivered by ecosystems[2]
The river sites were assigned to four categories of fish assemblages, i.e. headwater streams (HWS), medium gradient rivers (MGR), lowland rivers (LLR), and Mediterranean streams (MES), that differs in their fish community and environmental characteristics[28]
Most previous studies reported a positive relationship between species richness and functional diversity in natural assemblages, including terrestrial[61,62] and aquatic environments[40], which suggests that species extinction is often associated with a severe decline in ecological functions[10]

Summary

Introduction

The global ecological footprint of human activities entailed a rapid decline of biodiversity over the past decades[1], which affects functions and services delivered by ecosystems[2]. Consistently related to intrinsic components driving specific response to disturbance, e.g. life-history traits, habitat requirements, population size etc., and depends on extrinsic factors, such as the intensity of threats[12,13] The combination of these factors influences the order of species’ extinction within an assemblage, and leads to a non-random pattern of functional diversity loss[6,14]. For several decades, monitoring programs conducted in continental aquatic ecosystems took advantage of the key role of fish assemblages to assess ecosystem health on the basis of ecological indicators[22,23] These indicators are relevant management tools, they do not provide quantitative information to evaluate the potential impact of species loss on ecosystem functioning.

Methods

Results

Conclusion