The hypothesis of convergence takes the deterministic view that community (or assemblage) structure can be predicted from the environment, and that the environment is expected to drive evolution in a predictable direction. Here we present results of a comparative study of freshwater fish assemblages from headwater streams in four continents (Europe, North America, Africa and South America), with the general objective of testing whether these assemblages display convergent structures under comparable environmental conditions (i.e. assemblage position in the stream longitudinal continuum). We tested this hypothesis by comparing species richness and trophic guilds of those stream fish assemblages represented in available data from multiple sites on each continent. Independent of phylogenetic and historical constraints, fish assemblage richness and trophic structure in the four continents converged along the stream continua to a substantial degree. For the four continents, assemblage richness increased, the proportion of invertivorous species decreased, and the proportion of omnivorous species increased from upstream to downstream, supporting theoretical predictions of the river continuum concept. However, the herbivore/detritivore and piscivore guilds were virtually absent from our small European and North American stream sites, unlike our African and South American stream sites. This divergence can be linked to differences in energy availability between temperate and tropical systems.3

No abstract

RATIONALE: Dorsal white muscle is the standard tissue analysed in fish trophic studies using stable isotope analyses. However, sampling white muscle often implies the sacrifice of fish. Thus, we examined whether the non-lethal sampling of fin tissue can substitute muscle sampling in food web studies. METHODS: Analysing muscle and fin d15N and d13C values of 466 European freshwater fish (14 species) with an elemental analyser coupled with an isotope ratio mass spectrometer, we compared the isotope values of the two tissues. Correlations between fin and muscle isotope ratios were examined for all fish together and specifically for 12 species. We further proposed four methods of assessing muscle from fin isotope ratios and estimated the errors made using these muscle surrogates. RESULTS: Despite significant differences between isotope values of the two tissues, fin and muscle isotopic signals are strongly correlated. Muscle values, estimated with raw fin isotope ratios (1st method), induce an error of ca. 1% for both isotopes. In comparison, specific (2nd method) or general (3rd method) correlations provide meaningful corrections of fin isotope ratios (errors <0.6%). On the other hand, relationships, established for Australian tropical fish, only give poor muscle estimates (errors >0.8%). CONCLUSIONS: There is little chance that a global model can be created. However, the 2nd and 3rd methods of estimating muscle values from fin isotope ratios should provide an acceptable level of error for the studies of European freshwater food web. We thus recommend that future studies use fin tissue as a non-lethal surrogate for muscle

Aim To estimate population extinction rates within freshwater fish communities since the fragmentation of palaeo-rivers due to sea level rise at the end of the Pleistocene; to combine this information with rates estimated by other approaches (population surveys, fossil records); and to build an empirical extinction-area relationship.Location Temperate rivers from the Northern Hemisphere, with a special focus on rivers discharging into the English Channel, in north-western France. Methods(1) French rivers. We used a faunal relaxation approach to estimate extinction rates in coastal rivers after they became isolated by the sea level rise. Tributaries within the Seine were used to build a species-area relationship for a non-fragmented river system to predict species richness in coastal rivers before their fragmentation. (2) Other rivers. Extinction rates obtained for four other Holarctic river systems fragmented at the end of the Pleistocene, the fragmented populations of one salmonid species (Japan) and the fossil records from the Mississippi Basin were included in the study. Results(1) French rivers. Within strictly freshwater fish species, rare and/or habitat specialist species were the most affected by fragmentation. In contrast, euryhaline species were not affected. A negative relationship between extinction rate and river basin size was observed. (2) Other rivers. Our study established a common scaling relationship for freshwater fish population extinction rates that spans seven orders of magnitude in river basin size. Main conclusionsThis study strongly suggests that extinctions of fish populations occurred within French coastal rivers after they became isolated 8000 years ago. The patterns observed at regional and inter-continental scales are consistent with the expectation that large populations are less prone to extinction than small ones, resulting in a strong extinction-area relationship coherent over a large spatiotemporal scale. Our study is the first multi-scale quantitative assessment of background extinction patterns for freshwater fishes.

The restoration of previously extinct salmon populations is usually achieved with stocking programmes, but natural recolonization can also occur through the straying of individuals from nearby populations. Here we investigated the origin of Atlantic salmon (Salmo salar) that recently recolonized the Seine River (France). The degradation of this river had led to the extinction of the population, but since the 1990s, the water quality has greatly improved. Although no stocking was performed, 162 individual salmon were recently observed by video-counting. Seven fish were sampled for morphological and genetic analyses. These individuals were genotyped at 17 microsatellites markers and their probable source populations were identified using baseline samples from regional and distant populations. Four of the sampled individuals were grilse and three were multi-sea-winter fish. Genetic analyses revealed that the fish partly originated from a nearby stock but also from distant populations, suggesting long-distance straying. This natural recolonization of a large river by strayers from several origins is discussed in terms of population sustainability and management. / La restauration de populations antérieurement éradiquées de saumons se fait ordinairement par des programmes d'empoissonnement, mais il peut aussi exister une recolonisation naturelle par les individus errants des populations avoisinantes. Nous examinons ici l'origine des saumons atlantiques (Salmo salar) qui ont récemment recolonisé la Seine(France). La dégradation du fleuve avait entraıné l'extinction de la population, mais depuis les années 1990, la qualité de l'eau s'est grandement améliorée. Bien qu'aucun empoissonnement n'ait été effectué, 162 saumons individuels ont récemment été observés par comptage vidéo. Sept poissons ont été prélevés pour des analyses morphologiques et génétiques.Nous avons déterminé leur génotype à 17 marqueurs microsatellites et identifié leur population d'origine probable au moyen d'échantillons de référence provenant de populations régionales et éloignées. Quatre des individus prélevés étaient des madeleineaux et trois avait passé plusieurs hivers en mer. Les analyses génétiques montrent que les poissons proviennent en partie d'un stock voisin et en partie de populations lointaines, ce qui indique une errance sur de longues distances. Nous discutons de la recolonisation d'une grande rivière par des poissons errants d'origines diverses, en particulier de la durabilité et de la gestion de la population