Biological invasions undermine the functional diversity of fish community in a large subtropical river

Abstract

Biological invasions are considered to be one of the main threats to biodiversity. Invasions lead to a loss of native species, changes to species composition, and a shift in the functioning and stability of ecosystems. In this study, derived from nine consecutive years of monitoring data and based on morphological functional trait values measured at the individual-level, we quantified the functional differences between native and non-native fish species and further assessed how biological invasions impact on species richness and functional diversity in the large subtropical Pearl River in southern China. Specifically, we differentiated intraspecific functional variability by separating individuals of a species according to their different life stages. Our results provided strong evidence that native and non-native fish were significantly different in their functional attributes. Invasion caused no obvious change in species richness; however, the yearly increase in non-native populations was accompanied by a significant decrease in functional niches of native species and change in several aspects of functional diversity in the fish community. Decreasing functional richness, and increasing functional divergence and specialization, indicated that most native species had been replaced by non-native species with different specific functional traits, which may affect ecosystem stability. Notably, this study provided empirical evidence that functional diversity was more sensitive to biological invasions than species richness. Our results show that control of non-native aquatic species is both necessary and urgent in the Pearl River. An understanding of the processes described in this study can form the basis of conservation in fish community, which is critical to sustainable and successful fisheries.