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Occasional periods of drought are typical of most tropical forests, but climate change is increasing drought frequency and intensity in many areas across the globe, threatening the structure and function of these ecosystems. The effects of intermittent drought on tropical tree communities remain poorly understood and the potential impacts of intensified drought under future climatic conditions are even less well known. The response of forests to altered precipitation will be determined by the tolerances of different species to reduced water availability and the interactions among plants that alleviate or exacerbate the effects of drought. Here, we report the response of experimental monocultures and mixtures of tropical trees to simulated drought, which reveals a fundamental shift in the nature of interactions among species. Weaker competition for water in diverse communities allowed seedlings to maintain growth under drought while more intense competition among conspecifics inhibited growth under the same conditions. These results show that reduced competition for water among species in mixtures mediates community resistance to drought. The delayed onset of competition for water among species in more diverse neighbourhoods during drought has potential implications for the coexistence of species in tropical forests and the resilience of these systems to climate change. Reduced competition for water among species in mixed tropical plant communities mediates community resistance to drought: weaker competition permits growth maintenance in drought, whereas stronger competition inhibits it.

Widespread forest die-back due to the increasing frequency and intensity of drought in many parts of the planet is focusing attention on the mechanisms of tree drought resistance. This study provides direct experimental evidence that greater non-structural carbohydrate concentrations before drought help maintain hydraulic function and thereby prolong drought tolerance in seedlings of ten tropical tree species.

The importance of biodiversity for the integrated functioning of ecosystems remains unclear because most evidence comes from analyses of biodiversity's effect on individual functions. Here we show that the effects of biodiversity on ecosystem function become more important as more functions are considered. We present the first systematic investigation of biodiversity's effect on ecosystem multifunctionality across multiple taxa, trophic levels and habitats using a comprehensive database of 94 manipulations of species richness. We show that species-rich communities maintained multiple functions at higher levels than depauperate ones. These effects were stronger for herbivore biodiversity than for plant biodiversity, and were remarkably consistent across aquatic and terrestrial habitats. Despite observed tradeoffs, the overall effect of biodiversity on multifunctionality grew stronger as more functions were considered. These results indicate that prior research has underestimated the importance of biodiversity for ecosystem functioning by focusing on individual functions and taxonomic groups., The influence of biodiversity on multiple ecosystem processes is not well understood. Analysing 94 biodiversity-ecosystem functioning experiments, Lefcheck et al. find that increased species richness maintains more ecological functions, across multiple taxa, trophic levels and habitats.

The impact of biodiversity loss on the functioning of ecosystems and their ability to provide ecological services has become a central issue in ecology. Several experiments have provided evidence that reduced species diversity may impair ecosystem processes such as plant biomass production. The interpretation of these experiments, however, has been controversial because two types of mechanism may operate in combination. In the 'selection effect', dominance by species with particular traits affects ecosystem processes. In the 'complementarity effect', resource partitioning or positive interactions lead to increased total resource use. Here we present a new approach to separate the two effects on the basis of an additive partitioning analogous to the Price equation in evolutionary genetics. Applying this method to data from the pan-European BIODEPTH experiment reveals that the selection effect is zero on average and varies from negative to positive in different localities, depending on whether species with lower- or higher-than-average biomass dominate communities. In contrast, the complementarity effect is positive overall, supporting the hypothesis that plant diversity influences primary production in European grasslands through niche differentiation or facilitation.

Plant growth is an essential ecological process, integrating across scales from physiology to community dynamics. Predicting the growth of plants is essential to understand a wide range of ecological issues, including competition, plant-herbivore interactions and ecosystem functioning.A challenge in modeling plant growth is that growth rates almost universally decrease with increasing size, for a variety of reasons. Traditional analyses of growth are hampered by the need to remain within the structures of linear models, which handle this slowing poorly. We demonstrate the implementation of a variety of non-linear models that are more appropriate for modeling plant growth than are the traditional, linear, models.Ecological inference is frequently based on growth rates, rather than model parameters. Traditional calculations of absolute and relative growth rates assume that they are invariant with respect to time or biomass, which is almost never valid. We advocate and demonstrate the calculation of function-derived growth rates, which highlight the time- and biomass-varying nature of growth. We further show how uncertainty in estimated parameter values can be propagated to express uncertainty in absolute and relative growth rates.The use of non-linear models and function-derived growth rates can facilitate testing novel hypotheses in population and community ecology. Even so, we acknowledge that fitting non-linear models can be tricky. To foster the spread of these methods, we make many recommendations for ecologists to follow when their hypotheses lead them into the subject of plant growth.

A consequence of Darwin's 'principle of divergence' is that loss of species can harm the functioning of ecosystems. A study of algal communities in artificial streams suggests that he was right. See Letter p.86 Studies in recent years have suggested that the conservation of biodiversity improves the ability of an ecosystem to retain nutrients and remain productive. These papers have proved controversial, in part because of a lack of direct evidence for a mechanism to explain the phenomenon. Now, in experiments involving manipulation of the number of algal species in model stream systems, Bradley Cardinale provides one such mechanism. Uptake of nitrogen nutrients increased linearly with species richness in response to changes in flow habitats and disturbance regimes. But when niche structure was experimentally removed, the relationship disappeared. This suggests that habitats with more species take greater advantage of the niche opportunities in an environment than do less-species-rich habitats, allowing the more diverse systems to capture a greater fraction of biologically active resources such as nitrogen.

Nature, 412, 72–76 (2001). In Figures 2 and 3, some regression lines were very faint or missing. The corrected panels are reproduced below. All panels in both figures should also have shown the null hypothesis as a horizontal dashed line through zero.