The relevance of community approaches to assess the state of biodiversity: A case study in French river fish communities

Background/Question/Methods

Biodiversity indicators are crucial management and communication tools for the conservation of biodiversity. However, their ecological meaning and relevance are still debated. It has been suggested recently that a new family of biodiversity indicators could be more relevant at the community level compared to the species level because they include a part of species interactions with other species or their habitat. Moreover, approaches based on traits, characters or evolutionary history, usually referred to as “functional indicators” are radically different from those developed historically (i.e. indicators based on expert species, focal species or reference state approaches).

The state of freshwater fish communities is usually assessed via multiparametric indices that are compared to ideal, pristine reference states. We developed functional indicators, which aim to combine several components of biodiversity, including interspecific interactions, and ultimately the processes that drive ecosystem functioning. Thanks to the French river fish database our first approach was to construct the Community Specialisation Index (CSI) of common species of fishes. Our second approach was to develop originality index of communities based on phylogeny, life history traits and eco-morphological traits. We analysed the spatial and temporal trends of these indicators across inland France between 1990 and 2009. 

Results/Conclusions

We showed that the average community specialization tended to decline over the past two decades. We show that these metrics, which can be easily used with several taxonomic groups, is sensitive to several human pressures across spatial and temporal scales. Our results, which document the ongoing process of functional biotic homogenization from local to national spatial scales much better than traditional biodiversity metrics, demonstrate the relevance of community approaches. We also showed that the phylogenetic originality of communities increased during the same period of time. We discuss the relevance of these different indicators as a function of biodiversity policies and ecological contexts (e.g. scales, biological model).