Functional trait effects on ecosystem stability: assembling the jigsaw puzzle

The main mechanisms by which biodiversity affects the stability of ecosystem functions (dominant species, compensatory dynamics, and insurance effects) all act through the functional traits of organisms that form local communities. These mechanisms can be assessed using different components of trait value distributions within and between species [collectively referred as trait probability density (TPD)]. Variation in local populations can result in overall changes in community structure, which may or may not be propagated into changes in ecosystem functions. The extent of such propagation depends on: (i) the extent of TPD shifts, and (ii) the overlap between response and effect traits, and these effects will vary depending on the biotic mechanisms being assessed. Under global change, how biological diversity and ecosystem services are maintained in time is a fundamental question. Ecologists have long argued about multiple mechanisms by which local biodiversity might control the temporal stability of ecosystem properties. Accumulating theories and empirical evidence suggest that, together with different population and community parameters, these mechanisms largely operate through differences in functional traits among organisms. We review potential trait-stability mechanisms together with underlying tests and associated metrics. We identify various trait-based components, each accounting for different stability mechanisms, that contribute to buffering, or propagating, the effect of environmental fluctuations on ecosystem functioning. This comprehensive picture, obtained by combining different puzzle pieces of trait-stability effects, will guide future empirical and modeling investigations. Under global change, how biological diversity and ecosystem services are maintained in time is a fundamental question. Ecologists have long argued about multiple mechanisms by which local biodiversity might control the temporal stability of ecosystem properties. Accumulating theories and empirical evidence suggest that, together with different population and community parameters, these mechanisms largely operate through differences in functional traits among organisms. We review potential trait-stability mechanisms together with underlying tests and associated metrics. We identify various trait-based components, each accounting for different stability mechanisms, that contribute to buffering, or propagating, the effect of environmental fluctuations on ecosystem functioning. This comprehensive picture, obtained by combining different puzzle pieces of trait-stability effects, will guide future empirical and modeling investigations. deviation from a perfect synchrony in species’ fluctuations. prevailing negative covariance between species’ fluctuations (i.e., negative synchrony). link between an increase in species number and the decrease in the coefficient of variation (CV) of community abundance in the case of independent species fluctuations. the ability of a system to maintain given ecosystem functions, even despite species turnover. It is the opposite of propagation. the average of trait values weighted by the relative abundance of each species in a community. the changes in the relative abundance of some species that are offset, or compensated for, by changes in the relative abundance of other species. a stability component describing how invariable (i.e., as inverse of temporal variability) ecosystem properties are in a given period without particularly extreme events. the effect exerted by the dominance of species with particular traits, which governs how a community as a whole responds to environmental fluctuations and affects ecosystem functioning. It is linked to the mass–ratio hypothesis. It can be quantified by the community weighted mean (CWM). broadly defined as any measurable component of an ecosystem or its constituent components, including ecosystem functioning, population abundances, species composition, species diversity, etc. any characteristic of an organism that has repercussions for environmental conditions, community properties, ecosystem processes, or functions. the extent of trait differences among a set of organisms. It is commonly quantified with multiple indices reflecting, for example, average trait dissimilarity or the volume of trait space occupied by a set of species. a system’s ability to buffer the effect of perturbations on community or ecosystem processes by the replacement of species by others with similar effect traits. It depends on functional redundancy. interactions among species in a community in which they do not follow a linear hierarchy but a ‘rock-paper-scissors’ game without a single best competitor. functional trait differences between pairs of species in terms of given traits or multiple traits. Sometimes a phylogenetic distance (e.g., length of branches connecting two species in a phylogenetic tree) is used as well. a relatively sudden change in environmental conditions or in the disturbance regime beyond the range of the historical variability (e.g., exceptional fire, flood, or drought). the process by which species turnover is directly translated into changes in ecosystem function. the ability for a population, community, or ecosystem function to reorganize and return to its reference condition after it has been affected by a perturbation. the degree to which species perform similar functions. Communities with high redundancy are expected to be able to lose species without great changes in ecosystem functions due to replacement of dominant species by subordinate species with similar effect traits. the degree to which an ecosystem function can resist or recover rapidly from perturbations. the ability of an ecosystem to remain unchanged when being subjected to a perturbation. It is inversely proportional to vulnerability. the pattern that occurs when most of the species in a community respond in the same manner to variation in abiotic and biotic conditions, leading to concordant species fluctuations. distribution of trait values of an ecological unit, from the individual to ecosystem level, in a given functional space. Such trait distributions can be the basis of multiple indices and components. the rate or magnitude of change in species composition (e.g., replacement of species and changes in their abundances in space or time).