Diversity Dimensions of Freshwater Fish Species around the World

摘要

The quality and coverage of the available taxonomical and geographical information and the recognition that diversity is multi-faceted are two main factors that hinder to understand the spatial and temporal variations of biodiversity. In this study, we aim to quantify the global distribution of five diversity components used to assess freshwater fish diversity in river basins around the world. The multidimensional character of these diversity components was estimated and the so obtained diversity dimensions mapped. This was done taking into account those well-surveyed basins discriminated by considering collector’s curves, and additionally by controlling for the effect of survey effort on all considered diversity components. A total of 1,472,109 occurrence records were analysed, corresponding to 17,292 species of freshwater fishes. Five diversity components were considered: functional richness, species richness, taxonomic diversity, and two rarity measures. Well-surveyed river basins were discriminated using accumulation curves. The effects of survey biases and knowledge gaps were minimized by determining the relationship of each component with the completeness values calculated for each river basin. The geographical pattern derived from raw data is skewed by the unequal knowledge available, and all diversity components were positively correlated with completeness values. The first dimension described the association between species richness and functional diversity. The second dimension represented rarity and taxonomic diversity. The congruence between species richness and functional diversity suggests that ecosystem functions increase with the number of fish species present in river basins and that a decrease in species richness may involve a loss of functionality. The levels of rarity and taxonomic diversity of many species-poor basins found in arid and cold regions suggest that the distinctiveness of their freshwater fishes is primarily a consequence of how isolated these basins are.