The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher's alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼ 40,000 and ∼ 53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼ 19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼ 4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

The PREDICTS project—Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)—has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.

Understanding the determinants of range location and size is fundamental to our understanding of spatial patterns in species richness. Here, we aimed to test the role of ‘climatic stability’ in determining latitudinal trends in range size and as a consequence on species richness of tropical woody plants. Using primary data from 156 (0.06 ha) plots comprising 20,400 occurrences of more than 400 species of tropical woody plants, we built a biome-wide species database that covers the entire latitudinal extent of the wet-evergreen forests of the Western Ghats (8 o to 20 o N), India. We consolidated this database using secondary data from other published species inventories. We then calculated the range sizes and climatic niche width of woody plants to test the predictions of the climatic stability hypothesis and examined the relationship between range position and climatic tolerance of species. Our results show a significant latitudinal gradient in species richness and turnover where local and regional species richness increase monotonically from higher latitudes to lower latitudes of the Western Ghats. We found strong support for Rapoport’s Rule with an increase in range size from lower to higher latitudes; our results are consistent with the predictions of the climatic stability hypothesis, where species at higher latitudes exhibited greater tolerance to temperature and rainfall seasonality. Contrary to earlier work, our findings suggest that Rapoport’s Rule and the climatic stability hypothesis can operate over regional scales, and even at lower latitudes. We suggest that latitude associated climatic seasonality through its influence on species ranges, can influence latitudinal patterns in species turnover as well as species richness.

Aim How seasonal drought influences tree species distributions might shape future vegetation composition with impending changes to rainfall patterns. Theory suggests that across a seasonal drought gradient, dry‐tolerant species might have wider distributions than species sensitive to seasonal drought, which will be restricted to less seasonal conditions. As wet‐associated species drop out with increasing seasonality, the community will contain mainly dry‐tolerant species. Time period Present. Location Western Ghats Biodiversity Hotspot in peninsular India. Major taxa studied Woody angiosperms. Methods Across a 1,200 km seasonal drought gradient, we modelled occurrences of 183 species using Gaussian logistic regression in a hierarchical Bayesian framework. We used the first‐order model coefficients to attribute the association of species to seasonality (dry/wet) and second‐order coefficients to assess modal responses. For 92 species, we checked for an interaction between dry/wet association and two traits: wood density and specific leaf area (SLA). Finally, we assessed the consequences of the seasonality associations of species for regional community assembly. Results Of 183 species, 38% were significantly wet associated, 27% dry associated and 34% indifferent to seasonality. Nearly 80% of species had estimated modes of occurrence within the seasonality range considered here. Species with lower SLA and lower wood density were more likely to occur in more seasonal sites where dry‐associated species formed the majority of co‐occurring species. The proportion of wet‐associated species increased only after intermediate levels of seasonality. The community proportion of extreme wet‐associated species decreased prominently from less to more seasonal sites. Main conclusions Dry‐associated species persisted in less seasonal sites, but not vice versa. A shift toward more seasonal rainfall might favour dry‐associated species and shrink the ranges of wet‐associated species. Future work should assess how the intensity and duration of drought and interactions with other drivers of global change regulate the relative performance of species at more and less seasonal sites.