River dams and the stability of bird communities: A hierarchical Bayesian analysis in a tropical hydroelectric power plant

Flow regulation by dams impacts more than land use on water quality and benthic communities in high-gradient streams in a semi-arid region

In semi-arid regions, water policy has strongly promoted the construction of water reservoirs with little or no consideration for their ecological consequences. In order to quantify the effect induced by flow discontinuity on environmental conditions, water quality, and invertebrate communities at high-gradient streams, we investigated unregulated and regulated reaches at 13 watercourses, located in the Dry Chaco Ecoregion (South America). Dams differed in the dominant land uses (rangeland, agriculture, and urban) of the related catchment area. We assessed on-site hydro-geomorphic features, water quality and bacteriological parameters, habitat condition, chlorophyll a, macrophytes cover, and macroinvertebrate communities. Significant increases in mineral parameters and organic contamination indicators were detected at regulated reaches, such as: conductivity, total solids, turbidity, color, and phosphates. Dams negatively affected habitat condition, and macrophyte cover increased at regulated sites. Macroinvertebrates showed a diminution in most of the metrics analyzed, with a decrease of sensitive groups and an increase in the more tolerant ones. Redundancy Analysis revealed that SWQI (physicochemical based index) and the proportion of coarse gravel were stronger predictors on metrics arrangement. Variance partitioning analyses proved that regulation effects prevailed over land use in explaining metrics variation. Invertebrate community was positively related to better ecological conditions, which suggests that restitution of ecological integrity at regulated reaches should include habitat restoration. These results are relevant for the management of regulated water resources in arid and semi-arid regions in a context of climate change.

Drivers of Taxonomic, Phylogenetic, and Functional Beta Diversity of Himalayan Riverine Birds

Abiotic and biotic factors drive compositional differences among local species assemblages. Determining the influence of different drivers on beta diversity patterns can provide insights into processes governing community organization. Examining beta diversity patterns along taxonomic, phylogenetic and functional dimensions enables a nuanced understanding of underlying processes that govern community assembly and dynamics. The dynamic and complex riparian habitats in the Himalaya, and the hyper-diverse riverine bird community offer a fascinating setup to examine the role of environmental factors in influencing community structuring. Using a large dataset on river bird communities from field census across multiple drainages in the Indian Himalaya, we aimed at discerning processes that structure these communities through an understanding of pair-wise dissimilarities in species composition across sites. We determined the relative contributions of turnover and nestedness in taxonomic, phylogenetic, and functional beta diversity patterns in the Eastern and Western Himalaya that differ in species richness. Generalized Dissimilarity Modeling was used to examine the relative contributions of climatic, geographic, and anthropogenic factors toward explaining different metrics of beta diversity. The riverine bird communities in the drier and seasonal Western Himalaya were poorer in species richness, more phylogenetically and functionally clustered than that in the Eastern Himalaya. The contribution of the turnover component to the overall beta diversity was higher than the nestedness component in river bird communities, particularly in the Eastern Himalaya. Habitat and climatic factors differentially influenced the beta diversity patterns in both Eastern and Western Himalaya, with river width consistently explaining a large variation in beta diversity in the east and the west. The results show that environmental filtering plays a crucial role in structuring riverine bird communities in the Himalayan headwaters, highlighting the need to ameliorate the threats posed by the slew of hydroelectric projects and forest loss in the region.