We develop a novel class of measures to quantify sample completeness of a biological survey. The class of measures is parameterized by an order q ≥ 0 to control for sensitivity to species relative abundances. When q = 0, species abundances are disregarded and our measure reduces to the conventional measure of completeness, that is, the ratio of the observed species richness to the true richness (observed plus undetected). When q = 1, our measure reduces to the sample coverage (the proportion of the total number of individuals in the entire assemblage that belongs to detected species), a concept developed by Alan Turing in his cryptographic analysis. The sample completeness of a general order q ≥ 0 extends Turing's sample coverage and quantifies the proportion of the assemblage's individuals belonging to detected species, with each individual being proportionally weighted by the (q − 1)th power of its abundance. We propose the use of a continuous profile depicting our proposed measures with respect to q ≥ 0 to characterize the sample completeness of a survey. An analytic estimator of the diversity profile and its sampling uncertainty based on a bootstrap method are derived and tested by simulations. To compare diversity across multiple assemblages, we propose an integrated approach based on the framework of Hill numbers to assess (a) the sample completeness profile, (b) asymptotic diversity estimates to infer true diversities of entire assemblages, (c) non‐asymptotic standardization via rarefaction and extrapolation, and (d) an evenness profile. Our framework can be extended to incidence data. Empirical data sets from several research fields are used for illustration.

Understanding the structure of and spatial variability in the species composition of ecological communities is at the heart of biogeography. In particular, there has been recent controversy about possible latitudinal trends in compositional heterogeneity across localities (β‐diversity). A gradient in the size of the regional species pool alone can be expected to impose a parallel gradient on β‐diversity, but whether β‐diversity also varies independently of the size of the species pool remains unclear. A recently suggested methodological approach to correct latitudinal β‐diversity gradients for the species pool effect is based on randomization null models that remove the effects of gradients in α‐ and γ‐diversity on β‐diversity. However, the randomization process imposes constraints on the variability of α‐diversity, which in turn force γ‐ and β‐diversity to become interdependent, such that any change in one is mirrored in the other. We argue that simple null model approaches are inadequate to discern whether correlations between α‐, β‐ and γ‐diversity reflect processes of ecological interest or merely differences in the size of the species pool among localities. We demonstrate that this kind of Narcissus effect may also apply to other metrics of spatial or phylogenetic species distribution. We highlight that Narcissus effects may lead to artificially high rejection rates for the focal pattern (Type II errors) and caution that these errors have not received sufficient attention in the ecological literature.

Questions: Species-abundance distributions (SADs) have long been at the centre of ecological interest because they summarize various patterns of community assembly in condensed form. Here we link observed patterns of SAD shape and evenness to latitude and climatic conditions to infer global trends in abundance distributions. Location: Global.Methods: We compiled data on tree species abundances and climate covariates from 605 sites worldwide. We applied linear regression modelling and nonlinear least squares fitting of log-series and lognormal abundance distributions to species rank-order log-abundance plots to assess latitudinal and climatic gradients in abundance distributions and Pielou evenness. Results:We observed significant latitudinal trends in SAD shape and evenness, even after accounting for richness and spatial effects. Evenness tended to increase towards lower latitudes and was positively correlated with actual evapotranspiration and negatively with climatic variability. We observed an excess of log-series SADs at lower latitudes and an increase in lognormal distributions towards northern latitudes. Accordingly, the proportion of species less abundant than expected from a log-series distribution decreased towards the tropics. Conclusions:We speculate that the observed latitudinal trends are caused by respective gradients in the importance of dispersal for local tree community assembly. This interpretation implies the hypothesis that tropical communities tend to be more open and input-driven in comparison to temperate communities.

Aim A trait‐based biogeographical approach can be used to shed light on species‐sorting mechanisms that are driven by the interactions between species traits and abiotic conditions along large‐scale gradients. We tested the hypothesis that geographical patterns of woody plant assemblages are driven largely by environmental filtering, in relation to climate harshness and seasonality, acting on key functional traits. Location Japanese archipelago. Methods Using a large‐scale grid‐based dataset of 773 woody species and five functional traits measured in the field, spanning the Japanese archipelago, we analysed the influence of climate harshness (absolute minimum temperature and precipitation of driest month) and climate seasonality (temperature and precipitation seasonality, and the length of period suitable for photosynthesis) on three aspects of community trait structure: community mean trait values, functional richness and functional divergence. To confirm whether the influence of climate‐based species sorting on functional structure was stronger than the impact of dispersal limitation, we used null models that did or did not account for the difference in regional species pools as a result of vicariance. Results While climate harshness and historical dispersal limitation had a some influence on trait structure, temperature seasonality played a significant role. Greater seasonality was associated with functional similarity in wood density and leaf nitrogen concentration, but also contributed to increased diversity in leaf thickness, specific leaf area and maximum height. Main conclusions Our results demonstrate the importance of climate harshness and seasonality in shaping the geographical variation of functional trait structures in woody plant assemblages, while we found that species richness decreases with increasing climate harshness. Climate seasonality results in the convergence and divergence of co‐occurring traits across different vegetation zones. This suggests that seasonal environmental variability acts not only as a filter of species traits but also as a driver creating a greater difference in functional strategies among woody plant species.

A major research question concerning global pelagic biodiversity remains unanswered: when did the apparent tropical biodiversity depression (i.e., bimodality of latitudinal diversity gradient [LDG]) begin? The bimodal LDG may be a consequence of recent ocean warming or of deep-time evolutionary speciation and extinction processes. Using rich fossil datasets of planktonic foraminifers, we show here that a unimodal (or only weakly bimodal) diversity gradient, with a plateau in the tropics, occurred during the last ice age and has since then developed into a bimodal gradient through species distribution shifts driven by postglacial ocean warming. The bimodal LDG likely emerged before the Anthropocene and industrialization, and perhaps ∼15,000 y ago, indicating a strong environmental control of tropical diversity even before the start of anthropogenic warming. However, our model projections suggest that future anthropogenic warming further diminishes tropical pelagic diversity to a level not seen in millions of years.