Morphological diversity of freshwater fishes differs between realms, but morphologically extreme species are widespread

Abstract

Aim The aim was to analyse the morphological diversity of the world freshwater fish fauna. We tested to which extent the distributions of morphological traits are supported by extreme morphologies and how those extreme morphologies are distributed among realms and affect the functional vulnerability. We also analysed the contribution of between‐ and within‐order morphological variability to the morphological differences between realms. Major taxa studied Freshwater fish. Location Global. Time period 1960s–2010s. Methods We used a global database of freshwater fishes from the six realms. Ten morphological traits were measured on 9,150 species, that is, 75% of the ca. 13,000 freshwater fish species. A principal components analysis was conducted to combine the 10 traits into a multidimensional space. We used Kolmogorov–Smirnov tests to compare the difference in morphological diversity between the six realms and between and within the major fish orders. We then identified the morphologically extreme species and quantified their contributions to the morphological range to assess the functional vulnerability and redundancy of fish faunas in the six biogeographical realms for freshwater ecosystems. Results We report a strong morphological variability among freshwater fishes of the world, with significant morphological differences among realm fish faunas, caused by an interplay between taxonomic composition of the realm faunas and morphological differences within orders among the realms. Morphologically extreme species accounted for a large percentage of the filling of the global morphological space and are distributed throughout the world. Main conclusions Fish morphological diversity is largely supported by a few species with extreme trait combinations, indicating that functional vulnerability exists throughout the world. Our results suggest that more attention should be paid to these morphologically extreme species and that they should be protected to ensure the sustainability of functions they support.

Morphological sorting of introduced freshwater fish species within and between donor realms

“…Among the 14,953 species present in the occurrence database, 9,150 species were morphologically described using pictures and drawings from textbooks and scientific websites (Su et al, 2019).…”

“…The 10 morphological traits (nine unitless ratios and body size) selected are commonly used in assessment of fish functional diversity (e.g. Bellwood, Goatley, Brandl, & Bellwood, 2014;Su et al, 2019;Toussaint et al, 2016;Villéger, Miranda, Hernandez, & Mouillot, 2010) and are linked to the feeding and locomotion functions of fish that determine their contribution to key ecosystem processes, such as controlling food webs and nutrient cycles (Villéger et al, 2017) (Supporting Information Figure S1b). Functional traits not measurable on side pictures, such as gut length, oral gape area and shape, were not included because they are currently only available for a few species in public databases.…”

“…Fish maximum body lengths were downloaded from FishBase (http://www.fishb ase.org). Information about the 9,150 species with combined trait values (PC1-PC5) used in this study are available in Su et al (2019).…”

“…Established species tend to be larger, with deeper bodies, and to have more piscivorous or detritivorous diets (Cucherousset, Blanchet, & Olden, 2012;Toussaint et al, 2018). However, functional diversity of fishes markedly varies between the six biogeographic realms, namely the Afrotropical, Australian, Neotropical, Nearctic, Oriental and Palaearctic realms (Su, Villéger, & Brosse, 2019;Toussaint, Charpin, Brosse, & Villéger, 2016). Therefore, to work towards a better understanding of the causes and consequences of the invasion process in the world's rivers, it is important to disentangle the relative importance of the natural functional differences between donor zones, the human preference for some functional characteristics and the capacity of each introduced species to establish (or not) in a new environment.…”

Mapping extinction risk in the global functional spectra across the tree of life

“…We used the last updated version of the most comprehensive database to get morphological traits, available for 10,705 species of strictly freshwater fishes (19,42). Morphological measures and conventions are detailed in previous studies (19,42,43). All morphological traits have been measured on side view picture, using one specimen per species and applying conventional rules for unusual morphologies (e.g.…”