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Understanding patterns of species diversity is crucial for ecological research and conservation, and this understanding may be improved by studying patterns in the two components of species diversity, species richness and evenness of abundance of species. Variation in species richness and evenness has previously been linked to variation in total abundance of communities as well as productivity gradients. Exploring both components of species diversity is essential because these components could be unrelated or driven by different mechanisms.The aim of this study was to investigate the relationship between species richness and evenness in European bird communities along an extensive latitudinal gradient. We examined their relationships with latitude and Net Primary Productivity, which determines energy and matter availability for heterotrophs, as well as their responses to territory densities (i.e. the number of territories per area) and community biomass (i.e. the bird biomass per area).We applied a multivariate Poisson log‐normal distribution to unique long‐term, high‐quality time‐series data, allowing us to estimate species richness of the community as well as the variance of this distribution, which acts as an inverse measure of evenness.Evenness in the distribution of abundance of species in the community was independent of species richness. Species richness increased with increasing community biomass, as well as with increasing density. Since both measures of abundance were explained by NPP, species richness was partially explained by energy‐diversity theory (i.e. the more energy, the more species sustained by the ecosystem). However, species richness did not increase linearly with NPP but rather showed a unimodal relationship. Evenness was not explained either by productivity nor by any of the aspects of community abundance.This study highlights the importance of considering both richness and evenness to gain a better understanding of variation in species diversity. We encourage the study of both components of species diversity in future studies, as well as use of simulation studies to verify observed patterns between richness and evenness. [ABSTRACT FROM AUTHOR]

Long time series of primary production are rarely available, restricting our mechanistic understanding of vegetation and ecosystem dynamics under climate change. Dendrochronological tools are increasingly used instead, particularly in the Arctic—the world's most rapidly warming biome. Yet, high‐latitude plant species are subject to strong energy allocation trade‐offs, and whether annual allocations to secondary growth (e.g. "tree‐rings") actually reflect primary production above‐ground remains unknown. Taking advantage of a unique ground‐based monitoring time series of annual vascular plant biomass in high Arctic Svalbard (78°N), we evaluated how well retrospective ring growth of the widespread dwarf shrub Salix polaris represents above‐ground biomass production of vascular plants.Using a balanced design in permanent plots for plant biomass monitoring, we collected 30 S. polaris shrubs across five sites in each of two habitats. We established annual ring growth time series using linear mixed‐effects models and related them to weather records and 13 years of above‐ground biomass production in six habitats.Annual ring growth was positively correlated with above‐ground biomass production of both S. polaris (r = 0.56) and the vascular plant community as a whole (r = 0.70). As for above‐ground biomass, summer temperature was the main driver of ring growth, with this ecological signal becoming particularly clear when accounting for plant, site and habitat heterogeneity. The results suggest that ring growth measurements performed on this abundant shrub can be used to track fluctuations in past vascular plant production of high arctic tundra.Synthesis. Dendrochronological tools are increasingly used on arctic shrubs to enhance our understanding of vegetation dynamics in the world's most rapidly warming biome. Fundamental to such applications is the assumption that annual differences in ring growth reflect between‐year variation in above‐ground biomass production. We showed that ring growth indeed was a robust proxy for the annual above‐ground productivity of both the focal shrub and the vascular plant community as a whole. Despite the challenges of constructing ring growth chronologies from irregularly growing arctic shrubs, our findings confirm that shrub dendrochronology can open new opportunities for community‐dynamic studies, including in remote places where annual field sampling is difficult to achieve. Dendrochronological tools are increasingly used on arctic shrubs to enhance our understanding of vegetation dynamics in the world's most rapidly warming biome. Fundamental to such applications is the assumption that annual ring growth reflects between‐year variation in above‐ground biomass production. We found that ring growth indeed was a robust proxy for the annual above‐ground productivity of both the focal shrub and the vascular plant community as a whole. Despite the challenges of constructing ring growth chronologies from irregularly growing arctic shrubs, our findings show that shrub dendrochronology can open new opportunities for community‐dynamic studies under climate change, including in remote places where annual field sampling is difficult to achieve. [ABSTRACT FROM AUTHOR]