Toward a loss of functional diversity in stream fish assemblages under climate change

Abstract

The assessment of climate change impacts on biodiversity has so far been biased toward the taxonomic identification of the species likely either to benefit from climate modifications or to experience overall declines. There have still been few studies intended to correlate the characteristics of species to their sensitivity to climate change, even though it is now recognized that functional trait-based approaches are promising tools for addressing challenges related to global changes. In this study, two functional indices (originality and uniqueness) were first measured for 35 fish species occurring in French streams. They were then combined to projections of range shifts in response to climate change derived from species distribution models. We set out to investigate: (1) the relationship between the degrees of originality and uniqueness of fish species, and their projected response to future climate change; and (2) the consequences of individual responses of species for the functional diversity of fish assemblages. After accounting for phylogenetic relatedness among species, we have demonstrated that the two indices used measure two complementary facets of the position of fish species in a functional space. We have also rejected the hypothesis that the most original and/or less redundant species would necessarily experience the greatest declines in habitat suitability as a result of climate change. However, individual species range shifts could lead simultaneously both to a severe decline in the functional diversity of fish assemblages, and to an increase in the functional similarity among assemblages, supporting the hypothesis that disturbance favors communities with combination of common traits and biotic homogenization as well. Our findings therefore emphasize the importance of going beyond the simple taxonomic description of diversity to provide a better assessment of the likely future effects of environmental changes on biodiversity, thus helping to design more effective conservation and management measures.

Functional Rarity: The Ecology of Outliers

“…At the local scale, functional distinctiveness takes into account all species within the community to measure whether species i is more or less functionally close to the rest of the community [40]. At the regional scale, functional uniqueness relies on the functionally nearest species to measure the extent to which species i has no functional equivalent (or redundancy) in the pool [90]. These two indices simply correspond to the Mean Pairwise Distance (MPD) and the Mean Nearest Taxon Distance (MNTD) measuring the isolation (based on phylogenetic relationships) of each species from all the others and to its closest relative, respectively [91].…”

Morphology predicts species' functional roles and their degree of specialization in plant–frugivore interactions

“…mammals and birds in seed-dispersal networks or several vertebrate and invertebrate taxa in pollination networks) [49][50][51]. Analyses of functional diversity calculated from morphological traits have therefore been restricted to analyses within a single taxon [5,16,33,39,52]. If species from different taxa fulfil similar, converging functional roles in different regions, then this might result in incomplete and misleading patterns of functional diversity.…”

Linking changes in community composition and function under climate change

“…A substantial body of research has also focused on understanding the relationships between functional traits and community compositional change along environmental gradients (Diaz et al 1998, Weiher et al 1998, Thuiller et al 2004, Shipley et al 2006, Suding et al 2008, Cornwell and Ackerly 2009, Laughlin et al 2012 A relatively small number of studies have attempted to meet this challenge by predicting concomitant change in biodiversity outcomes and ecosystem functioning under climate change scenarios. A simple approach to achieving this objective has been to link projected changes in the distributions of individual species with information on the functional attributes of those species, to inform potential changes in the functional composition and diversity of the assemblages obtained when the species-level predictions are ''stacked'' (Thuiller et al 2006, Buisson et al 2013, Gallagher et al 2013, Terrier et al 2013). Alternatively, current community-level functional attributes have been modeled in response to key environmental variables and projected into the future (Dubuis et al 2013).…”