Intraspecific variability (IV) has been proposed as a new track to explain species coexistence. Previous studies generally assumed that IV results from intrinsic differences between conspecifics that widen species’ fundamental niches and blur differences among species, thus impeding stable coexistence, but also slowing down the rate of competitive exclusion. Based on a body of evidence, we here argue that IV does not necessarily imply differences among conspecifics, nor species niches overlap: conspecifics differ in their measured attributes mainly due to differences in the micro-environment they thrive in. Consequently, they respond more similarly to environmental variation than heterospecifics, thereby concentrating competition within species – a necessary condition for species coexistence. We call for new studies exploring observed IV as an outcome of species-specific responses to high-dimensional environmental variations that can lead to inversions of species hierarchy in space and time promoting stable coexistence.

Context Intraspecific variability (IV) has been proposed to explain species coexistence in diverse communities. Assuming, sometimes implicitly, that conspecific individuals can perform differently in the same environment and that IV blurs species differences, previous studies have found contrasting results regarding the effect of IV on species coexistence. Objective We aim at showing that the larg IV observed in data does not mean that conspecific individuals are necessarily different in their response to the environment and that the role of high-dimensional environmental variation in determining IV has been largely underestimated in forest plant communities. Methods and Results We first used a simulation experiment where an individual attribute is derived from a high-dimensional model, representing “perfect knowledge” of individual response to the environment, to illustrate how a large observed IV can result from “imperfect knowledge” of the environment. Second, using growth data from clonal Eucalyptus plantations in Brazil, we estimated a major contribution of the environment in determining individual growth. Third, using tree growth data from long-term tropical forest inventories in French Guiana, Panama and India, we showed that tree growth in tropical forests is structured spatially and that despite a large observed IV at the population level, conspecific individuals perform more similarly locally than compared with heterospecific individuals. Synthesis As the number of environmental dimensions that are typically quantified is generally much lower than the actual number of environmental dimensions influencing individual attributes, a great part of observed IV might be misinterpreted as random variation across individuals when in fact it is environmentally-driven. This mis-representation has important consequences for inference about community dynamics. We emphasize that observed IV does not necessarily impact species coexistence per se but can reveal species response to high-dimensional environment, which is consistent with niche theory and the observation of the many differences between species in nature.

Global change drivers such as anthropogenic nutrient inputs simultaneously alter biodiversity, species composition, and ecosystem functions such as aboveground biomass. These changes are interconnected by complex feedbacks among extinction, colonization, and shifting relative abundance. Here, we use a novel temporal application of the Price equation to quantify the functional contributions of species that are lost, gained, and persist under ambient and experimental nutrient addition in 59 global grasslands. Under ambient conditions, compositional and biomass turnover was high, but species losses (i.e., local extinctions) were balanced by gains (i.e. colonization). There was biomass loss associated with species loss under fertilization. Few species were gained in fertilized conditions over time but those that were, and species that persisted, contributed to net biomass gains, outweighing biomass loss. These components of community change are key to understanding the relationship between change in composition, diversity and functioning.

Cheating in microbial communities is often regarded as a precursor to a “tragedy of the commons”, ultimately leading to over-exploitation by a few species, and destabilisation of the community. However, this view does not explain the ubiquity of cheaters in nature. Indeed, existing evidence suggests that cheaters are not only evolutionarily and ecologically inevitable, but also play important roles in communities, like promoting cooperative behaviour. We developed a chemostat model with two microbial species and a single, complex nutrient substrate. One of the organisms, an enzyme producer, degrades the substrate, releasing an essential and limiting resource that it can use both to grow and produce more enzymes, but at a cost. The second organism, a cheater, does not produce the enzyme but benefits from the diffused resource produced by the other species, allowing it to benefit from the public good, without contributing to it. We investigated evolutionarily stable states of coexistence between the two organisms and described how enzyme production rates and resource diffusion influence organism abundances. We found that, in the long-term evolutionary scale, monocultures of the producer drive themselves extinct because selection always favours mutant invaders that invest less in enzyme production. However, the presence of a cheater buffers this runaway selection process, preventing extinction of the producer and allowing coexistence. Resource diffusion rate controls cheater growth, preventing it from outcompeting the producer. These results show that competition from cheaters can force producers to maintain adequate enzyme production to sustain both itself and the cheater. This is known in evolutionary game theory as a “snowdrift game” – a metaphor describing a snow shoveler and a cheater following in their clean tracks. We move further to show that cheating can stabilise communities and possibly be a precursor to cooperation, rather than extinction.