Summary: One of the primary goals in community ecology is to determine the relative importance of processes and mechanisms that control biodiversity. Here, we examined habitat‐driven species assemblages and species distribution patterns as well as their temporal variations for three life stages of two censuses of a 25‐ha mixed dipterocarp forest at Sinharaja (Sri Lanka). Our general objective was to find out whether the species assemblages and associated habitat types changed with life stage, spatial scale and species attributes. We also analyse whether the habitat types were related to certain indicator species. Habitat types were determined with multivariate regression tree analyses driven by topographic variables. We found species assemblages associated with five distinct habitat types that appeared consistently for all life stages of the two censuses. These habitats were related to ridge‐valley gradients and a pronounced contrast in south‐west versus north‐east aspect. Habitat‐driven structuring was weak at the recruit stage but strong in the juvenile and adult stages. The species assemblage variance explained by topographic variables for different life stages ranged between 10% for recruits and 23% for juveniles. The species assemblages determined for different spatial scales (10, 20, 50 m) showed similar habitat partitioning, but the variance explained by the topographic variables increased in all life stages with spatial scale. This could be due to the homogenizing effect of topographic variables at the larger scales and unaccounted environmental variation at the smaller scales. The number of indicator species identified in the two censuses was higher in the juvenile stage than in the adult stage, and nearly all indicator species in the adult stage were also indicator species in the juvenile stage. Synthesis. Our study showed that approximately 75% of the variance in local species composition is unexplained. This may be due to spatially structured processes such as dispersal limitation, unaccounted biotic and abiotic environmental variables, and stochastic effects, but only 25% were due to topographic habitat association. Although the pronounced ridge‐valley gradient and contrast of south‐west versus north‐east aspect created consistent habitats, our results suggest that local species assemblages at Sinharaja forest are jointly shaped by neutral and niche processes.

Aim: Climate change alters the water cycle, potentially affecting the distribution of species. Using an ensemble of species distribution models (SDMs), we predicted changes in distribution of the Asian elephant in South Asia due to increasing climatic variability under warming climate and human pressures.Location: India and Nepal.Methods: We compiled a comprehensive geodatabase of 115 predictor variables, which included climatic, topographic, human pressures and land use, at a resolution of 1 km², and an extensive database on current distribution of elephants. For variable selection, we first developed 14 candidate models based on different hypotheses on elephant habitat selection. For each candidate model, a series of 240 individual models were evaluated using several metrics. Using three climatic and one land use change datasets for two greenhouse gas scenarios, ensemble SDMs were used to predict future projections.Results: Nine predictor variables were selected for ensemble SDMs. Elephant distribution is driven predominantly by changes in climatic water balance (>60%), followed by changes in temperature and human‐induced disturbance. The results suggest that around 41.8% of the 256,518 km² of habitat available at present will be lost by the end of this century due to combined effects of climate change and human pressure. Projected habitat loss will be higher in human‐dominated sites at lower elevations due to intensifying droughts, leading elephants to seek refuge at higher elevations along valleys with greater water availability in the Himalayan Mountains.Main conclusions: Changes in climatic water balance could play a crucial role in driving species distributions in regions with monsoonal climates. In response, species would shift their range upwards along gradients of water availability and seasonal droughts. Conservation and management of elephant populations under global change should include design of movement corridors to enable dispersal of the elephant and other associated species to more conducive environments.

Summary: 1.Recent studies have documented shifts in habitat associations of single tropical tree species from one life stage to the next. However, the community‐level consequences of such shifts have not been investigated, and it is not clear whether they would amplify, neutralize or completely alter habitat structuring during the transitions to the adult community.2.We compared habitat‐driven species assemblages at three life stages (i.e. recruitment, juvenile and reproductive stages) and six censuses for tree and shrub species in a fully censused 50‐ha plot of Panamanian lowland forest. Habitat types were determined using multivariate regression trees that group areas with similar species composition (i.e. species assemblages) according to their topographical characteristics.3.Three topographical variables (a topographical wetness index, slope and elevation) were major determinants of species assemblages. When analysing individuals of all life stages together, we found a distinct and temporally consistent structuring of the plot into four dominant habitat types (low and high plateaus, slope and swamp) which was consistent with previous classifications. Basically, the same habitat structuring emerged for the juvenile communities of individual censuses. However, recruits showed a weak and temporally inconsistent habitat structuring.4.A notable homogenization in species assemblages occurred during the transition from juvenile to reproductive, through both a reduction in the number of species assemblages (in 3 censuses, one large reproductive assemblage covered 93% of the plot, and in others, an additional slope habitat emerged) and a reduction in the classification error. Overall, habitat structuring became noisier and weaker over the 25 years of the study.5.Synthesis.Our results suggest that mortality processes during the transition from recruits to juveniles must enhance the signal of habitat structuring. However, during the transition to the reproductive stage, species may have lost the advantage of being in the habitat with which they had become associated, or the quality of habitat changed during their life span because of larger climatic changes. The homogeneous assemblages of the reproductive stage could be interpreted as support for neutral theories, but further research is required to unravel the mechanisms behind these intriguing observations.