A new freshwater biodiversity indicator based on fish community assemblages

Abstract

Biodiversity has reached a critical state. In this context, stakeholders need indicators that both provide a synthetic view of the state of biodiversity and can be used as communication tools. Using river fishes as model, we developed community indicators that aim at integrating various components of biodiversity including interactions between species and ultimately the processes influencing ecosystem functions. We developed indices at the species level based on (i) the concept of specialization directly linked to the niche theory and (ii) the concept of originality measuring the overall degree of differences between a species and all other species in the same clade. Five major types of originality indices, based on phylogeny, habitat-linked and diet-linked morphology, life history traits, and ecological niche were analyzed. In a second step, we tested the relationship between all biodiversity indices and land use as a proxy of human pressures. Fish communities showed no significant temporal trend for most of these indices, but both originality indices based on diet- and habitat- linked morphology showed a significant increase through time. From a spatial point of view, all indices clearly singled out Corsica Island as having higher average originality and specialization. Finally, we observed that the originality index based on niche traits might be used as an informative biodiversity indicator because we showed it is sensitive to different land use classes along a landscape artificialization gradient. Moreover, its response remained unchanged over two other land use classifications at the global scale and also at the regional scale.

Figure 1. Functional character measurements.

a) All measurements are standardised by the standard length. Caudal peduncle length is also standardised by body depth; caudal peduncle depth was only standardised by body depth; b) pectoral fin position: pectoral fin dorsal side distance divided by body depth at pectoral fin; c) eye position: eye–ventral side distance divided by body depth at the eye; mouth position: mouth–ventral side distance at the position of the eye divided by body depth at the position of the eye.

Figure 2. Spatial distribution of human pressures.

We used the CORINE Land Cover data set and its land use classification as an artificialization gradient from natural habitat to urban habitat. Colors from green to red represent increasing pressures.

Figure 3. Functional trees.

(a) Tree based on Life History Traits (b) Tree based on functional Niche traits (c) Tree based on functional Diet Morphological traits (d) Tree based on functional habitat-linked morphological traits.

Figure 4. Results of species values of originality and specialization in a Cleveland’s dot plots in proportions (i.e. the sum of species values is one for each index).

Figure 5. Spatial distribution of community specialization (CSI) and originality (COI) indices for 2005 (the years with the most sample stations).

Colors from green to red represent increasing index values.

Figure 6. Community indices response to land use artificialization with the CORINE Land Cover dataset.

Colors from green to blue represent increasing pressures.

Figure 7. Niche-COI response to land use artificialization across watersheds.

The Mix class is not represented because of limited sample size.