Responses of the macroinvertebrate taxonomic distinctness indices of lake fauna to human disturbances in the middle and lower reaches of the Yangtze river

In recent decades, floodplain lakes have been among the most endangered ecosystems in the world due to human activities, and they are experiencing severe degradation in ecological function and declines in biodiversity. Previous studies have mostly concentrated on the effects of human disturbances on the traditional taxonomic structure of aquatic communities, but little is known about the responses of other facets of biodiversity measures (e.g., phylogenetic relatedness) to anthropogenic impacts. Here, we examined the effectiveness of species richness and taxonomic distinctness (TD) indices (the average taxonomic distinctness, Delta(+), and variation in taxonomic distinctness, Lambda(+)) in determining anthropogenic effects based on four datasets of macroinvertebrate communities in 31 shallow lakes in the Yangtze floodplain. The species composition and number of entire taxa and three subsets (mollusk-, insect- and oligochaete-only taxa) were all significantly different among the five lake groups, with the highest species richness in the river-connected lakes, followed by the oxbow, macrophytic, macrophytic-algal transition and algal lakes. For the TD indices, only the Lambda(+) of entire taxa showed clear differences among lake groups, with the highest values in the algal lakes and the lowest values in the river-connected lakes. However, the TD indices based on the other three datasets showed no differences and did not clearly reveal the degree of anthropogenic disturbances as we expected. However, the spatial pattern of species richness was largely influenced by lake area rather than by water quality. In contrast, the TD indices were insensitive to lake area and responded more readily to water quality than species richness. We proposed that the TD indices provided a useful complement to traditional diversity indices (e.g., species richness) and could be considered as a potential bioassessment metric for detecting the environmental degradation level of freshwater lakes.