The stability of ecological communities is critical for the stable provisioning of ecosystem services, such as food and forage production, carbon sequestration, and soil fertility. Greater biodiversity is expected to enhance stability across years by decreasing synchrony among species, but the drivers of stability in nature remain poorly resolved. Our analysis of time series from 79 datasets across the world showed that stability was associated more strongly with the degree of synchrony among dominant species than with species richness. The relatively weak influence of species richness is consistent with theory predicting that the effect of richness on stability weakens when synchrony is higher than expected under random fluctuations, which was the case in most communities. Land management, nutrient addition, and climate change treatments had relatively weak and varying effects on stability, modifying how species richness, synchrony, and stability interact. Our results demonstrate the prevalence of biotic drivers on ecosystem stability, with the potential for environmental drivers to alter the intricate relationship among richness, synchrony, and stability.

Aim To assess the spatial congruence between hotspots based on taxonomic, phylogenetic and functional diversity, after accounting for the correlation between diversity metrics, and the spatial scale and sampling completeness of data.Location The Ordesa and Monte Perdido National Park (Central Pyrenees, Spain), a species-rich area subjected to intensive botanical sampling. Methods We selected hotspots using different diversity metrics and two different data sources (~49,000 occurrence records of 1379 vascular plants in 1 9 1 km grid cells and 1218 inventories of plant communities containing a total of 859 taxa) and compared their spatial congruence. The effect of sampling completeness of data was explicitly assessed. Phylogenetic diversity and functional diversity (measured with richness-dependent and richness-independent metrics) were based on a molecular phylogeny, and a functional dendrogram, respectively. The effectiveness of different types of hotspots in representing other diversity components was tested with permutation tests. ResultsWe found that spurious correlations between diversity metrics explained the congruence between taxonomic, phylogenetic and functional hotspots. When richness-independent metrics were used, diversity hotspots were no longer congruent regardless of the source of data. Hotspots were biased towards intensively sampled grid cells, and the amount of diversity they captured was exaggerated due to the coarse spatial scale of species-occurrence data. The efficiency of hotspots in terms of integrating different diversity components was lower at community scale and not significantly higher than expected at random, regardless of the sampling completeness.Main conclusions Our results stress that the arbitrary use of diversity metrics and the scale of analyses along with the sampling bias in data can distort the true location of hotspots, and exaggerate their spatial congruence. After accounting for such methodological issues, we found a clear mismatch between diversity components that questions the utility of hotspots as a conservation tool of multiple diversity components.

How reliable are results on spatial distribution of biodiversity based on databases? Many studies have evidenced the uncertainty related to this kind of analysis due to sampling effort bias and the need for its quantification. Despite that a number of methods are available for that, little is known about their statistical limitations and discrimination capability, which could seriously constrain their use. We assess for the first time the discrimination capacity of two widely used methods and a proposed new one (FIDEGAM), all based on species accumulation curves, under different scenarios of sampling exhaustiveness using Receiver Operating Characteristic (ROC) analyses. Additionally, we examine to what extent the output of each method represents the sampling completeness in a simulated scenario where the true species richness is known. Finally, we apply FIDEGAM to a real situation and explore the spatial patterns of plant diversity in a National Park. FIDEGAM showed an excellent discrimination capability to distinguish between well and poorly sampled areas regardless of sampling exhaustiveness, whereas the other methods failed. Accordingly, FIDEGAM values were strongly correlated with the true percentage of species detected in a simulated scenario, whereas sampling completeness estimated with other methods showed no relationship due to null discrimination capability. Quantifying sampling effort is necessary to account for the uncertainty in biodiversity analyses, however, not all proposed methods are equally reliable. Our comparative analysis demonstrated that FIDEGAM was the most accurate discriminator method in all scenarios of sampling exhaustiveness, and therefore, it can be efficiently applied to most databases in order to enhance the reliability of biodiversity analyses.

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