Morphology reflects differently the various facets of species traits in stream fish

Biodiversity is a multifaceted concept for which the functional component, that influences many aspects of ecosystem functioning, remains difficult to characterise. In several taxa, many studies rely on morphological traits as proxies of species ecological attributes. However, the extent to which morphology provides a good surrogate of ecological traits has rarely been acknowledged. Here, we used morphological and ecological trait databases to test whether morphological traits are linked to ecological traits and can be used to assess various biodiversity facets in 254 stream fish communities across France. We firstly computed co-inertia analyses to test the association between morphological and ecological traits related to either habitat use, feeding or life-history strategies. We then computed a suite of diversity indices to investigate the relationship between morphological and ecological indices. We found a strong association between morphological and ecological traits, and significant relationships between diversity indices computed on morphological and ecological traits. However, these relationships varied according to the index and type of ecological traits, with the strongest relationship observed with traits related to habitat use. Although these results highlight that the use of morphological data is a promising way to understand ecological diversity, they also reveal that the choice of diversity index and the type of ecological traits targeted are particularly important and need to be taken into consideration.