Understanding what governs grassland biodiversity across different spatial scales is crucial for effective conservation and management. However, current evidence often focuses on single sampling grain sizes, leaving the mechanisms of biodiversity drivers and their scale-dependency unclear. Here, we investigated the impact of climate, soil properties, abiotic disturbance, and land use on plant diversity across fine spatial scales in various grassland types. We collected spatially explicit data on species presence, relative cover, and total community cover at two grain sizes (α- and γ-diversity) to assess the mechanisms driving scale-dependent diversity patterns (β-diversity). In our study, the most influential factors of plant diversity at both scales (grain sizes) were climate variables, followed by soil humus content, litter cover, and soil pH. The effects of soil and litter were primarily driven by the response of rare species, while climate and grazing effects were driven by locally common species. The strength of most of these effects varied between spatial scales and therefore affected β-diversity. We identified three key mechanisms through which these drivers affect the scale-dependency of biodiversity: total plant cover, species relative cover (commonness or rarity of species and species evenness in the community), and species intraspecific aggregation. Climate effects operated through changes in species relative cover and intraspecific aggregation. Soil humus influenced β-diversity by altering the total cover of the plant community and by increasing intraspecific aggregation, resulting in stronger effects of soil productivity on plant diversity at larger than smaller spatial scales. Microhabitat patchiness by litter altered distributions in the relative cover of species due to reduced asymmetric competition, and affected the total cover of the plant community. Our results underscore the importance of incorporating the scale-dependency of biodiversity drivers in conservation efforts, management strategies, and analyses of global change impacts, which would enhance our ability to predict potential biodiversity change.

Global change alters the stability of biological communities by affecting species richness and how species covary through time (i.e., synchrony). There are few large-scale empirical tests of stability-diversity-synchrony relationships and those mostly focus on the terrestrial realm. Moreover, the effect of synchrony is largely unknown when species only covary at either high or low extremes of abundance (i.e., tail-dependent synchrony), a common phenomenon in ecological communities. Here, we synthesized long-term community time-series data (20+ years of species’ abundances/biomass for 2,668 communities across 7 taxonomic groups) from both terrestrial and freshwater realms and explored how the relationships among richness, synchrony, and stability vary across realms. We also investigated the effect of tail-dependent synchrony on stability across 714 freshwater and 1,954 terrestrial communities. For terrestrial communities, we found a positive diversity-stability relationship and that the tail-dependent synchrony was a more important determinant of stability than the traditional measure of overall synchrony (i.e., based on the covariation of all species). For freshwater communities, only overall synchrony explained some variation in stability. Assessing tail-dependent synchrony can improve our ability to understand why stability varies across different ecosystems and thereby our inferences about the causes of human-mediated biodiversity loss.

Short title Macroevolution and ecology drive multiple facets of tree diversityMartha Paola Barajas Barbosa*1,2([email protected])Tiffany M. Knight1,3,4 Renske Onstein5,1 Jonathan Chase1,2 1 German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany2 Department of Computer Science, Martin Luther University Halle-Wittenberg, Germany3 Department for Community Ecology, Helmholtz Centre for Environmental Research–UFZ, Leipzig, Germany4 Institute of Biology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany5 Naturalis Biodiversity Center, Darwinweg 2, 2333CR Leiden, the Netherlands*Corresponding author

Patterns of biodiversity provide insights into the processes that shape biological communities around the world. Variation in species diversity along biogeographical or ecological gradients, such as latitude or precipitation, can be attributed to variation in different components of biodiversity: changes in the total abundance (i.e. more-individual effects) and changes in the regional species abundance distribution (SAD). Rarefaction curves can provide a tool to partition these sources of variation on diversity, but first must be converted to a common unit of measurement. Here, we partition species diversity gradients into components of the SAD and abundance using the effective number of species (ENS) transformation of the individual-based rarefaction curve. Because the ENS curve is unconstrained by sample size, it can act as a standardized unit of measurement when comparing effect sizes among different components of biodiversity change. We illustrate the utility of the approach using two datasets spanning latitudinal diversity gradients in trees and marine reef fish, and find contrasting results. Whereas the diversity gradient of fish was mostly associated with variation in abundance (86%), the tree diversity gradient was mostly associated with variation in the SAD (59%). These results suggest that local fish diversity may be limited by energy through the more-individuals effect, while species pool effects are the larger determinant of tree diversity. We suggest that the framework of the ENS-curve has the potential to quantify the underlying factors influencing most aspects of diversity change.

Global change drivers such as anthropogenic nutrient inputs simultaneously alter biodiversity, species composition, and ecosystem functions such as aboveground biomass. These changes are interconnected by complex feedbacks among extinction, colonization, and shifting relative abundance. Here, we use a novel temporal application of the Price equation to quantify the functional contributions of species that are lost, gained, and persist under ambient and experimental nutrient addition in 59 global grasslands. Under ambient conditions, compositional and biomass turnover was high, but species losses (i.e., local extinctions) were balanced by gains (i.e. colonization). There was biomass loss associated with species loss under fertilization. Few species were gained in fertilized conditions over time but those that were, and species that persisted, contributed to net biomass gains, outweighing biomass loss. These components of community change are key to understanding the relationship between change in composition, diversity and functioning.

Disturbances alter the diversity and composition of microbial communities, but whether microbiomes from different environments exhibit similar degrees of resistance or rates of recovery has not been evaluated. Here, we synthesized 86 time series of disturbed mammalian, aquatic, and soil microbiomes to examine how the recovery of microbial richness and community composition differed after disturbance. We found no general patterns in compositional variance (i.e., dispersion) in any microbiomes over time. Only mammalian microbiomes consistently exhibited decreases in richness following disturbance. Importantly, they tended to recover this richness, but not their composition, over time. In contrast, aquatic microbiomes tended to diverge from their pre-disturbance composition following disturbance. By synthesizing microbiome responses across environments, our study aids in the reconciliation of disparate microbial community assembly frameworks, and highlights the role of the environment in microbial community reassembly following disturbance.