DOI: 10.5063/f1qz28d2
title: Data on the freshwater mollusk communities (historical and present-day data), environmental parameters, functional traits, niche and spatial coordinates, from the middle Olt River (Romania)

description: This dataset includes historical and recent information on the freshwater mollusk communities from the middle Olt River (Romania), along with the environmental parameters in the sampling sites and their spatial coordinates, as well as the species' functional traits and niche measures. The historical information dates back to the XIXth century, and comes from old literature and museum collections, the more recent data (1995-2000) and was derived from original research or literature, while the present-day data was collected during a field survey in May 2020. The study area is an 83 km section along the middle Olt River, between the town of Făgăraș (45.8512° N, 24.9733° E) and the Carpathian gorges (45.5317° N, 24.2721° E), in the region of Transylvania, Romania. Parts of this dataset were used in two papers, one currently under consideration for publication in Scientific Reports: Sîrbu, I., Benedek, A.M., Brown, B.L., Sîrbu, M. - Native versus alien communities: canonical ordination and variation partitioning with multiple response and predictor matrices disentangle structural and functional responses (2022),and the other published in 2021:Sîrbu, I., Benedek, A.M. & Sîrbu, M. Variation partitioning in double-constrained multivariate analyses: linking communities, environment, space, functional traits, and ecological niches. Oecologia 197, 43-59 (2021).In Sîrbu et al. (2022), using both historical and recent data, we aimed to:- disentangle and test the effects of hydrotechnical works - especially building of reservoirs (dams for hydroenergetic power) - environment, space, time, and non-native mollusk species on structural and functional dynamics of native freshwater mollusk communities; - investigate the differences in responses of native and alien species to the same predictors, and characterize the reversed effects of predictor ability of communities on external variables;- test effects of non-native species and communities on structural and functional diversity of natives, and - develop a novel approach and method for analyzing and expressing relationships between native and alien communities while accounting also for their responses to environment and space. In Sîrbu et al. (2021), based only on the present-day data, we defined, measured, and partitioned the CENTS space, the acronym coming from Community - Environment - Niche - (functional) Traits - Space. We proposed an algorithm to disentangle and quantify the overlapping effects of E-S (environment and space) and T-N (traits and ecological niche) variable groups on the community, which can be also used for other predictor data tables, such as a table with ecological indicator values or with phylogenetical relationships, and it also may be extended to include more than two data tables for sites or species. Our second objective was to summarize how species relate to resources and their availability in the environment, synthesize this information in a standardized way, and use these novel measures to apply the algorithm mentioned above, including an N data table, measuring the ecological niche features of the species. For this goal, we proposed a new standardized metric of niche complementarity (dissimilarity) for both categorical and continuous resources, which also account for the availability of resources in the environment. We used this metric to define and measure the species' uniqueness and one more aspect of the community diversity, the niche-based diversity (ND). We explored relationships between diversity measures and environment predictors, highlighting the use of ND in impact assessment.