Land cover alteration shifts ecological assembly processes in floodplain lakes: Consequences for fish community dynamics

Drivers of interspecific synchrony and diversity-stability relationships in floodplain fish communities

Diversity and interspecific synchrony are among the main drivers behind the temporal stability of community abundance. Diversity can increase stability through the portfolio effect, while higher synchrony generally decreases stability. In turn, species interactions and similar responses to environmental variation are considered the main factors underlying the strength of interspecific synchrony, despite the challenges in determining their relative roles. The analysis of the relationship between interspecific synchrony and the trait (or phylogenetic) distance between species can increase the robustness of inferences about these factors. Here, we used pairwise interspecific and community-wide analyses to investigate, respectively, the drivers of interspecific synchrony and the influence of trait and phylogenetic diversity on the stability of fish communities. For that, we used 18 years of fish abundance data from the Upper Paraná River floodplain. At the interspecific level, we used quantile regressions to test within-guild relationships between interspecific synchrony and trait and phylogenetic distance between species. At the community level, we tested the relationships between community-wide synchrony, stability, and (trait and phylogenetic) diversity. We found that interspecific synchrony decreased with trait and phylogenetic distances. In the community-level analysis, we found that more synchronous fish communities were less stable, but the relationship between diversity and stability was in general weak. At the interspecific level, our study highlights the role of similar responses to environmental variation in driving species' temporal dynamics. At the community level, the strength of the relationships between trait or phylogenetic diversity and community stability depended on the feeding guild. On the other hand, we found strong relationships between synchrony and stability. These results suggest that increased synchrony levels in response to regional environmental changes could decrease the stability of fish communities in this floodplain.

Environmental filtering in the dry season and spatial structuring in the wet: different fish community assembly rules revealed in a large subtropical floodplain lake

Although environmental filtering and spatial structuring are commonly regarded as two key factors shaping community dynamics, their relative contribution remains unknown for numerous aquatic ecosystems, particularly highly dynamic floodplain lakes. This issue is here addressed by examining the seasonal metacommunity dynamics of freshwater fishes in Lake Dongting, a large subtropical lake of the middle Chang-Jiang basin in southern China. Physicochemical variables and fish assemblages were recorded at 20 sampling sites during the wet, normal, and dry seasons. Distance-based redundancy analysis and associated variation partitioning were used to examine the relative role of environmental variables and spatial factors in fish community assembly in each season. Analysis results demonstrated that the relative contribution of environmental filtering and spatial structuring varied depending on environmental features and the extent of hydrological connectivity in different seasons. Intensified physicochemical parameters in the dry season convinced the enhanced environmental filtering, whereas high hydrological connectivity in the wet season favored the stronger spatial process. Specifically, the community assembly processes were temporally dynamic; spatial structuring (or mass effects), resulting from excessively high dispersal rates, was dominant during the flooding season, and environmental filtering was stronger than spatial structuring (or dispersal limitation) during the non-flooding season. These findings highlight the importance of conserving local habitats of Lake Dongting during the dry and normal seasons, and maintaining of the flood pulse of the lake and its natural variability during the wet season. Apparently, the construction of a water-level regulation project at the Chenglingji Channel, the outlet watercourse of Lake Dongting, is not supported because it will change the flood pulse of this lake and thus impact habitat heterogeneity or variability.

Spatial Variation in the Composition and Diversity of Fishes Inhabiting an Artificial Water Supply Lake, Eastern China

With the intensification of eutrophication, many artificial water supply lakes that act as a biological filter for water diverted from rivers have been built to alleviate water scarcity in Eastern China. In this study, we selected Lake Yanlong, a representative artificial water supply lake in Yancheng City, as our experimental lake to explore how the community composition of fishes changed among different habitat types and assess potential consequences for effective water treatment. From October 2015 to October 2020, we conducted quarterly surveys of fish communities and environmental factors in the Mangshe River (MR; water for lake) compared to four different water treatment zones of Lake Yanlong (PZ, the pretreatment zone with inlet from the MR; EZ, the emergent macrophyte zone; SZ, the submerged macrophyte zone; DZ, the deep purification zone with outlet to urban waterworks). A total of 16,339 individual fish belonging to 11 families and 49 species were collected. Six of the eight dominant species observed across zones were small-bodied fishes. Despite reduced fish species richness, the relative abundance and biomass of fishes tended to be higher in Lake Yanlong relative to the MR. The Shannon-Wiener diversity index, Pielou evenness index, Simpson’s diversity index all decreased from the MR to the DZ in the following sequence: MR < PZ < EZ < SZ < DZ. Analysis of similarities and similarity percentage analysis confirmed that fish communities differed significantly among zones and Coilia ectenes, Carassius auratus, Pseudobrama simony, Hemiculter leucisculus, and Hemiculter bleekeri were the major differentiating species. Mantel’s test and redundancy analysis revealed that water depth, aquatic vegetation coverage, and phytoplankton concentrations were the major factors determining the spatial distribution of fishes when moving from the MR to the DZ of Lake Yanlong. Stocking piscivorous fish can be used as an effective measure to control the abundance of prolific small-bodied fishes in Lake Yanlong. The details backing these findings are important for understanding how the community composition of fishes among habitat types in Lake Yanlong influence water quality, and to develop suitable biomanipulation strategies for the management of fish resources and maintaining proper function of these artificial water supply lakes.