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It has been increasingly recognized that plant traits and their intraspecific variation play pivotal roles in determining how ecosystem structure and function respond to a changing environment. Yet, it remains unclear how and which plant traits regulate the assembly process and thus affect ecosystem structure and function under climate changes. Here, we selected six steppe sites with snow fences along a precipitation gradient in inner Mongolia. We measured traits including plant height and leaf carbon, nitrogen, and phosphorus concentrations. We incorporated intraspecific trait variation to quantify the strength of external filters (assembly processes outside the community at a larger spatial scale), the strength of internal filters (assembly processes within the local community), and functional redundancy (the number of species having a similar function to an ecosystem). We applied these assembly rules to explain the changes in biodiversity and productivity in response to changing precipitation. We found that increased rainfall reduced plant carbon (C), nitrogen (N), and phosphorous (P) concentrations, but did not affect plant height. High snowfall increased phosphorous concentration, but did not affect other traits. Latent variable models identified climate (rainfall) and soil nutrient conditions (soil total N and P content) were more important than external filtering processes in predicting species richness. However, external filtering processes were the most important predictor of productivity. More specifically, we found with the increase in steppe productivity, the strength of the external filtering on leaf N increased and on plant height decreased, leading to leaf N converging into a small range but broadening the range of plant height. The internal filters had no significant effects on species richness or productivity. Additionally, we found that low precipitation reduced functional redundancy. We emphasize that intraspecific trait‐variation drives plant productivity and richness responses to precipitation changes by regulating community assemblage. Our finding also underlines the importance to separate the contributions of different functional traits in regulating the responses of ecosystem structure and function to climate changes. [ABSTRACT FROM AUTHOR]

We assessed the potential influence of hydrological connectivity among subdrainages on the structural and functional organization of stream macroinvertebrate metacommunities in 2 adjacent, large Asian watersheds (~1.4 million km2). To examine the structural organization of metacommunities, we used multisite β-diversity partitioning and applied the Elements of Metacommunity Structure (EMS) framework to resolve aspects of taxon associations and metacommunity assembly. We also decomposed functional β diversity into nestedness and turnover to assess functional organization of metacommunities among watersheds of contrasting connectivity. To describe changes in functional composition, we used a multidimensional functional trait analysis to calculate the 3 primary components of functional diversity. The nestedness component of β diversity had a higher contribution in the watershed displaying isolated subdrainages, and apparent lack of hydrological connectivity had a significant effect on the ecological fitting of macroinvertebrate metacommunities, generating a discrete composition of communities. Partitioning of functional β diversity suggested no difference among watersheds in metacommunity functional organization and a high level of functional redundancy among communities of subdrainages independent of hydrological isolation. These results show that hydrological connectivity is potentially an important driver structuring stream macroinvertebrate metacommunities at a macroecological scale. Patterns of metacommunity structure were expressed better using taxonomic than functional-trait diversity. In spite of a perceived functional redundancy, a wider functional space was observed in the absence of hydrological connectivity, a result suggesting discrete but partially overlapping functional entities associated with hydrological isolation in these watersheds. [ABSTRACT FROM AUTHOR]

Abstract. The concept of functional redundancy is at the core of theory relating changes in ecosystem functioning to species loss. However, few empirical studies have investigated the strength and form of the relationship between species and functional diversity (i.e., the presence of functional redundancy in ecological communities) in this context. In particular, we know little about how local extinctions in real communities might impact functional diversity. Here, we examined the relationship between species and functional diversity in plant communities along a grazing gradient across Mongolian rangeland ecosystems. We applied a recently described measure of functional diversity that incorporates species' dissimilarities defined from plant functional traits and tested several hypothesized forms of the relationship between species and functional diversity using linear and nonlinear modeling techniques. We found a significant sigmoid logistic relationship between species richness and functional diversity in relatively benign environmental conditions. This indicates high functional redundancy at low levels of species richness followed by a rapid increase at intermediate levels, until functional diversity reaches an asymptote at high levels (i.e., two-phase functional redundancy). In contrast, we generally observed a positive linear relationship between these parameters in relatively harsh environmental conditions, indicating low functional redundancy. Observed functional redundancy probably resulted from two factors, intrinsic redundancy in species' functional traits and extrinsic redundancy caused by nonrandom compositional change that is nonrandom with respect to functional traits. Lack of either intrinsic or extrinsic redundancy may result in low functional redundancy. Two-phase functional redundancy suggests that functional traits are abruptly lost from a community below a certain level of species richness, and a community then shifts into a contrasting state that has a few limited functional groups characterized by disturbance-resistant traits, as a consequence of disturbances such as livestock grazing. This study represents a major step forward in predicting the consequences of livestock grazing on the functioning of Mongolian rangeland ecosystems. [ABSTRACT FROM AUTHOR]