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

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 extinctionwere simulated to determine whether the loss of vulnerable species(with high propensity of extinctionwhen 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 speciesin rivers and estuariessupport singular functionsnot shared by dominant species, iii) the loss of vulnerable speciescan induce greater functional alteration in rivers than in lakes and estuaries. Overall, the functional structureof fish assemblages in rivers is weakly buffered against species extinctionbecause vulnerable speciessupport 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.