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Water temperature is recognized as an important driver of aquatic ecosystems and is of increasing interest because of global warming. However, to date, no studies have disentangled the contribution of annual thermal variability from the contributions of annual thermal mean and other environmental variables to spatiotemporal patterns of macroinvertebrate assemblages in mountain streams. In this study, we explored patterns of macroinvertebrate biodiversity within and among 5 mountain stream sites in the Serio watershed (Orobic Alps, Northern Italy) along a gradient of annual water thermal variability (annual range: ~1–16°C) but with similar means. At each site, macroinvertebrates were sampled; physicochemical variables, flood disturbance, and resource availability were measured monthly over a year; and water temperature was monitored continuously. The relationship between macroinvertebrate assemblages and environmental conditions was described by separating time and space through co-inertia analyses. Results showed a strong temporal co-inertia, with floods and mean monthly temperature most associated with within-site macroinvertebrate temporal patterns (70% of total variance) and with the greatest effects on the abundance of stoneflies. Synchronous floods occurred in all sites and promoted changes in macroinvertebrate community composition through a loss of taxa and individuals, whereas monthly water temperature variations were associated with the replacement of individuals among taxa. Spatial differences (30% of the total variance) were mainly linked to geographical proximity, although annual thermal variability covaried with annual temporal dissimilarity in taxonomic composition, suggesting that temporal patterns also explain spatial differences. Overall, the study indicates that even when accounting for the overall environmental setting, the thermal regime remains an important driver of macroinvertebrate spatiotemporal patterns. Mountain streams are particularly subject to thermal variation, and an increase in mean water temperature and thermal variability will substantially influence community composition, with the strongest effects on cold stenothermal taxa. Large-scale research across mountain ranges is essential to properly assess how spatiotemporal thermal heterogeneity influences the distribution of macroinvertebrates, as well as to guide conservation strategies in the context of increasing global warming. [ABSTRACT FROM AUTHOR]

The recognition of multi-causality and spatial non-stationarity in the determinants of large-scale biodiversity patterns requires to consider the role of multiple mechanisms, their interactions, and how these mechanisms vary in strength relative to each other across geographical space. Here, we challenge the view that historical climate stability primarily drives European patterns of groundwater crustacean diversity by testing also the role of spatial heterogeneity and productive energy. First, we predicted that the three mechanisms would be equally important at continental scale when analyzed separately, but that the importance of historical climate variability would weaken in joint analyses due to co-variation with the two other mechanisms. Second, we predicted that the three mechanisms would exhibit predictable latitudinal changes in their relative strength. To test these predictions, we selected predictors representing each mechanism and analyzed separately and jointly their effects and interactions using global regression models. We further mapped the independent and overlapping effects of mechanisms across Europe using partial geographically weighted regressions. When analyzed separately, the three mechanisms explained the same amount of variation in species richness, but in the joint analysis, the influence of historical climate stability became hidden in the variation shared with the other mechanisms. Topographic heterogeneity interacted synergistically with actual evapotranspiration and habitat heterogeneity on species richness. Spatial non-stationarity in the independent and overlapping effects of the three mechanisms was the most plausible explanation for the hump-shaped latitudinal pattern of crustacean species richness. Productive energy and spatial heterogeneity were important predictors at mid and southern latitudes, whereas historical climate stability overlapped with the two other mechanisms in northern Europe and productive energy in southern Europe. Multi-causality and spatial non-stationarity provide a broader perspective of groundwater biodiversity determinants that revives the importance of spatial heterogeneity and the strong dependence of subterranean communities on food supply from the surface. [ABSTRACT FROM AUTHOR]

Land use effects are considered among the main stressors on freshwater biodiversity, with up to 80% of land in Europe under intensive use. Here, we address the impact of arable and urban landscapes on taxon richness, Shannon–Wiener diversity, taxon rareness and taxonomic distinctness of eleven organism groups encompassing vertebrates, invertebrates and plants, occurring in five freshwater ecosystem types across Europe: rivers, floodplains, lakes, ponds and groundwater. In addition, nine geo-climatic descriptors (e.g. latitude, longitude, precipitation) were used to disentangle land use effects from those of natural drivers of biodiversity. Using a variance partitioning scheme based on boosted regression trees and generalised linear regression modelling, we sought: (i) to partition the unique, shared and unexplained variation in the metrics explained by both groups of descriptor variables, (ii) to quantify the contribution of each descriptor variable to biodiversity variation in the most parsimonious regression model and (iii) to identify interactions of land use and natural descriptors. The variation in biodiversity uniquely described by land use was consistently low across both ecosystem types and organism groups. In contrast, geo-climatic descriptors uniquely, and jointly with land use, explained significantly more variance in all 39 biodiversity metrics tested. Regression models revealed significant interactions between geo-climatic descriptors and land use for a third of the models, with interactions accounting for up to 17% of the model's deviance. However, no consistent patterns were observed related to the type of biodiversity metric and organism group considered. Subdividing data according to the strongest geo-climatic gradient in each dataset aimed to reduce the strength of natural descriptors relative to land use. Although data sub-setting can highlight land use effects on freshwater biodiversity, sub-setting our data often failed to produce stronger land use effects. There was no increase in spatial congruence in the subsets, suggesting that the observed land use effects were not dependent on the spatial extent of the subsets. Our results confirm significant joint effects of, and interactions between, land use and natural environmental descriptors on freshwater biodiversity, across ecosystem types and organism groups. This has implications for biodiversity monitoring. First, the combined analysis of anthropogenic and natural descriptors is a prerequisite for the analysis of human threats to biodiversity. Second, geo-climatically, but not necessarily geographically more homogeneous datasets can help unmask the role of anthropogenic descriptors. And third, whole community-based biodiversity metrics (including taxon richness) are not ideal indicators of anthropogenic effects on biodiversity at broad scales. [ABSTRACT FROM AUTHOR]