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Questions: Community structure is the outcome of individual-level interactions. Recent work has shown that disaggregating trait information from the species to the individual level can elucidate ecological processes. We aim to integrate trait dispersion analyses across different aggregation levels including a broad range of traits that allow assessment of patterns of variation among co-occurring and non-co-occurring individuals. We ask the following questions: (1) what is the role of intra- and inter-specific dissimilarity within neighbourhoods vs. across neighbourhoods in promoting trait dispersion; (2) how is trait variation partitioned across all individuals in each study system; and (3) are the results consistent across traits and forests? Location: Puerto Rico and China. Methods: We measured allocation and organ-level (e.g. specific leaf area) traits on every individual in two seedling censuses in two tropical rain forests. Then, we partitioned trait variation within and across species, considering its impact on patterns of trait dispersion, and quantifying how these outcomes vary depending on whether allocation-related or organ-level traits are considered. Results: We found an increase in trait dispersion when individual-level traits are considered, reflecting conspecific differentiation for allocation of traits. Organ-level traits, however, do not necessarily promote strong phenotypic displacement within conspecifics. Consistent with this, we found that the majority of variation in allocation of traits was between conspecifics, while most of the variation in organ-level traits was found between species. Conclusions: Overall, trait displacement occurs within and across neighbourhoods, reflecting differentiation at inter- and intra-specific levels. Also, we identify two major phenotypic groups of variation, allocation and organ-level traits, that constitute two contrasting strategies for response to biotic and abiotic contexts: one highlights ecological differences among individuals, while the other highlights differences among species.

While the importance of floral odours for pollinator attraction relative to visual cues is increasingly appreciated, how they structure community‐level plant–pollinator interactions is poorly understood. Elucidating the functional roles of flowering plant species with respect to their floral volatile organic compounds (VOCs) and how those roles vary over the growing season is an initial step towards understanding the contribution of floral VOCs to plant–pollinator interaction structure. We sampled the floral VOCs, phenologies and bee visitors of naturally growing plants in a montane meadow in the Northern Rocky Mountains of USA in order to acquire a base understanding of how floral VOCs and other plant traits may structure plant–pollinator interactions across the growing season. We expected forb species with floral VOCs that were original (far from the community mean) and unique (far from the nearest neighbour) would have few pollinating partners (i.e. specialists), while forbs with non‐original or highly variable floral VOCs would form the generalist core of interactors, thereby contributing to network nestedness (specialists interacting with nested subsets of generalists). Network modularity (patterns of distinct, highly connected subnetworks) could be influenced by groups of pollinators that are attracted to or repelled by certain floral bouquets. Species blooming in early spring emitted similar floral VOC blends containing generalist attractants, whereas floral VOC complexity was highest in mid to late summer. Forb species varied in the originality, uniqueness, and intraspecific variation (i.e. dispersion) of their floral VOCs, indicating the potential for different functional roles in plant–pollinator networks. Specifically, the originality, uniqueness and dispersion of forb species’ floral VOCs increased across the growing season. Floral VOCs influenced forb interactions with pollinators. Floral VOCs contributed to the nested structure, but not modular structure, of community‐level plant–pollinator network structure. Forb species with more original floral VOCs were less connected, while forb species emitting more compounds and with higher intraspecific variation in floral VOCs were more connected to pollinators. These findings show that floral scent plays important roles in structuring bee–forb interactions and guiding seasonal patterns in complex communities. Understanding seasonal patterns in floral VOCs may have important implications for plant–pollinator interactions among communities differing in species composition, or as shifts occur in suites of co‐flowering species due to climate change. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

This article is a Commentary on Dong et al. (2020), 228: 82–94.

Altered microclimatic conditions and higher disturbance at forest edges create environmental stress and modify resource gradients from edge to interior, changing the selection pressures acting on individuals. Although community‐weighted trait‐mean (CWM) shifts along edge gradients have been widely documented at the species level, it is unclear how edge effects act at the individual level, and whether the direction of intraspecific trait shifts mirrors that of CWM shifts in response to edge effects. On 20 islands in the Thousand Island Lake, China, we established 484 plots (2 × 2 m) in a stratified random design across distances of 0–128 m from the forest edge. Within each plot, we sampled leaves (n = 34 768) from within and among all 2993 individuals of 68 species and measured five leaf traits (leaf area, LA; specific leaf area, SLA; leaf dry matter content, LDMC; thickness, LT; chlorophyll content, LCC). Using generalized linear mixed models, we found that different leaf traits exhibited contrasting shifts in inter‐ versus intraspecific trait variation in response to edge effects. For SLA, LT and LCC, negative covariance between inter‐ and intraspecific trait shifts resulted in dampening of community‐wide trends compared to CWM response to edge effects. In contrast, the community‐wide trend for LDMC was reinforced due to positive covariance between inter‐ and intraspecific trait shifts, while for LA the direction of covariance shifted from negative to positive on small versus large islands. Together, edge effects alter selection regimes in reassembling plant communities. Predicting the community‐wide consequences depends on the degree to which there is negative versus positive covariance between species sorting and within‐species adaptation. The widely‐used CWM approach can mask contrasting trait selection pressures acting on individuals within local populations. Individual‐level trait variation can improve understanding of community re‐assembly trajectories in response to global environmental change.

Light is considered a non-limiting factor for vascular epiphytes. Nevertheless, an epiphyte’s access to light may be limited by phorophyte shading and the spatio-temporal environmental patchiness characteristic of epiphytic habitats. We assessed the extent to which potential light interception in Rodriguezia granadensis, an epiphytic orchid, is determined by individual factors (plant size traits and leaf traits), or environmental heterogeneity (light patchiness) within the crown of the phorophyte, or both. We studied 104 adult plants growing on Psidium guajava trees in two habitats with contrasting canopy cover: a dry tropical forest edge, and isolated trees in a pasture. We recorded the number of leaves and the leaf area, the leaf position angles, and the potential exposure of the leaf surface to direct irradiance (silhouette area of the leaf blade), and the potential irradiance incident on each plant. We found the epiphytes experience a highly heterogeneous light environment in the crowns of P. guajava. Nonetheless, R. granadensis plants displayed a common light interception strategy typical of low-light environments, resembling terrestrial, forest understory plants. Potential exposure of the total leaf surface to direct irradiance correlated positively with plant size and within-plant variation in leaf orientation. In many-leaved individuals, withinplant variation in leaf angles produced complementary leaf positions that enhanced potential light interception. This light interception strategy suggests that, in contrast to current wisdom, enhancing light capture is important for vascular epiphytes in canopies with high spatio-temporal heterogeneity in light environments.

Global warming has caused widespread shifts in plant phenology among species in the temperate zone, but it is unclear how population‐level responses will scale to alter the structure of the flowering season at the community level. This knowledge gap exists largely because—while the climatic sensitivity of first flowering within populations has been studied extensively—little is known about the responsiveness of the duration of a population's flowering period. This limits our ability to anticipate how the entire flowering periods of co‐occurring species may continue to change under warming. Nonetheless, flowering sensitivity to temperature often varies predictably among species between and within communities, which may help forecast temperature‐related changes to a community's flowering season. However, no studies—empirical or theoretical—have assessed how patterns of variation in flowering sensitivity among species could scale to alter community‐level flowering changes under warming. Here, we provide a conceptual overview of how variation in the sensitivity of flowering onset and duration among species can mediate changes to a community's flowering season due to warming trends. Specifically, we focus on the effects of differences in (1) the mean sensitivity of flowering onset and duration among communities and (2) the sensitivity of flowering onsets and durations among species flowering sequentially through the season within a community. We evaluated the manner and degree in which these forms of between‐species variation in sensitivity might affect the structure of the flowering season—both independently and interactively—using simulations, which covered a wide but empirically informed range of parameter values and combinations representing distinct community‐level patterns. Our findings predict that communities across the temperate zone will exhibit varied and often contrasting flowering responses to warming across biomes, underscoring that accounting for the temperature sensitivity of both phenological onset and duration among species is essential for understanding community‐level flowering dynamics in a warming world.

Fungal endophyte communities are mainly driven by host plant identity and geographic location. However, little is known about interactions between endophytes and characteristics of the host plant such as leaf functional traits, which vary both among and within host species. Previous studies focused on a limited number of host plant species and did not control for varying conditions in the host's neighborhood, which affect leaf functional traits and, in turn, might affect fungal endophyte communities. Using a tree diversity experiment in which all trees grow under standardized conditions, we were able to assess the contributions of host tree identity, host neighborhood species richness, and host community composition as well as the variation of leaf traits caused by these factors on taxonomic richness and community composition of foliar fungal endophytes. We used next‐generation amplicon sequencing to analyze the fungal endophyte community and visible–near infrared spectrometry data to predict the mean values and the intra‐individual variation of leaf traits in individual trees. We found both mean trait values and intra‐individual trait variation to have significant effects on endophyte richness. Mean trait values of leaf dry matter content, leaf carbon, leaf nitrogen, and leaf carbon‐to‐nitrogen ratio exhibited negative effects on endophyte richness, whereas specific leaf area and leaf phosphorus content increased endophyte richness. Additionally, intra‐individual leaf‐trait variation generally had positive effects on richness. Overall endophyte community composition was influenced by mean leaf dry matter content and specific leaf area. Ascomycota were influenced by the specific leaf area, whereas Basidiomycota responded to leaf dry matter content. We demonstrate that functional leaf traits affect foliar endophyte communities, with positive diversity effects of host leaf nutrients that are essential, and likely limiting, for fungal endophytes. Although our study emphasizes the role of leaf traits in shaping fungal communities, we also acknowledge that these dynamic interactions could lead to traits being influenced by microbes through microbe–plant interactions. Our study demonstrates that functional leaf traits play a crucial role in shaping fungal endophyte richness and community composition, even beyond the effects of tree species identity. Traits associated with the leaf economics spectrum exhibited both positive and negative relationships with endophyte richness depending on specific trait and taxa combinations, whereas intra‐individual variation in leaf traits had a generally positive relationship with endophyte richness by creating heterogeneous microhabitats within the tree crown. Additionally, fungal community composition responded primarily to specific leaf area and leaf dry matter content, with Ascomycota and Basidiomycota exhibiting distinct trait associations, highlighting the complexity of endophyte–plant interactions.

High alpine regions are threatened but understudied ecosystems that harbor diverse endemic species, making them an important biome for testing the role of environmental factors in driving functional trait‐mediated community assembly processes. We tested the hypothesis that plant community assembly along a climatic and elevation gradient is influenced by shifts in habitat suitability, which drive plant functional, phylogenetic, and spectral diversity. In a high mountain system (2400–3500 m) Región Metropolitana in the central Chilean Andes (33°S, 70°W). We surveyed vegetation and spectroscopic reflectance (400–2400 nm) to quantify taxonomic, phylogenetic, functional, and spectral diversity at five sites from 2400 to 3500 m elevation. We characterized soil attributes and processes by measuring water content, carbon and nitrogen, and net nitrogen mineralization rates. At high elevation, colder temperatures reduced available soil nitrogen, while at warmer, lower elevations, soil moisture was lower. Metrics of taxonomic, functional, and spectral alpha diversity peaked at mid‐elevations, while phylogenetic species richness was highest at low elevation. Leaf nitrogen increased with elevation at the community level and within individual species, consistent with global patterns of increasing leaf nitrogen with colder temperatures. The increase in leaf nitrogen, coupled with shifts in taxonomic and functional diversity associated with turnover in lineages, indicate that the ability to acquire and retain nitrogen in colder temperatures may be important in plant community assembly in this range. Such environmental filters have important implications for forecasting shifts in alpine plant communities under a warming climate. We tested the hypothesis that plant–soil feedbacks along a climatic and elevation gradient influence plant community assembly through shifts in habitat suitability, which drive plant functional, phylogenetic, and spectral diversity in a high mountain system (2400–3500 m) of Región Metropolitana in the Chilean Andes (33°S, 70°W). We found that leaf nitrogen increased with increasing elevation, and taxonomic and functional diversity associated with turnover in lineages peaked at mid‐elevations, indicating that the ability to acquire and retain nitrogen in colder temperatures may be important in plant community assembly in this range. Such environmental filters have important implications for forecasting shifts in alpine plant communities under a warming climate.

Intraspecific trait variation (ITV), based on available genetic diversity, is one of the major means plant populations can respond to environmental variability. The study of functional trait variation and diversity has become popular in ecological research, for example, as a proxy for plant performance influencing fitness. Up to now, it is unclear which aspects of intraspecific functional trait variation (iFDCV) can be attributed to the environment or genetics under natural conditions. Here, we examined 260 individuals from 13 locations of the rare (semi‐)dry calcareous grassland species Trifolium montanum L. in terms of iFDCV, within‐habitat heterogeneity, and genetic diversity. The iFDCV was assessed by measuring functional traits (releasing height, biomass, leaf area, specific leaf area, leaf dry matter content, Fv/Fm, performance index, stomatal pore surface, and stomatal pore area index). Abiotic within‐habitat heterogeneity was derived from altitude, slope exposure, slope, leaf area index, soil depth, and further soil factors. Based on microsatellites, we calculated expected heterozygosity (He) because it best‐explained, among other indices, iFDCV. We performed multiple linear regression models quantifying relationships among iFDCV, abiotic within‐habitat heterogeneity and genetic diversity, and also between separate functional traits and abiotic within‐habitat heterogeneity or genetic diversity. We found that abiotic within‐habitat heterogeneity influenced iFDCV twice as strong compared to genetic diversity. Both aspects together explained 77% of variation in iFDCV (Radj2 = .77, F2, 10 = 21.66, p < .001). The majority of functional traits (releasing height, biomass, specific leaf area, leaf dry matter content, Fv/Fm, and performance index) were related to abiotic habitat conditions indicating responses to environmental heterogeneity. In contrast, only morphology‐related functional traits (releasing height, biomass, and leaf area) were related to genetics. Our results suggest that both within‐habitat heterogeneity and genetic diversity affect iFDCV and are thus crucial to consider when aiming to understand or predict changes of plant species performance under changing environmental conditions. Up to now, it is unclear which aspect of intraspecific functional trait variation (ITV) can be attributed to the environment or to genetics under natural and present environmental conditions. Here, we used data from an extensive field study (260 individuals from 13 locations) on the (semi-)dry calcareous grassland species Trifolium montanum (mountain clover). We demonstrated that abiotic within-habitat heterogeneity had twice as much impact as genetic diversity on ITV explaining together 77% of variation.

Trait variation among heterospecific and conspecific organisms may substantially affect community and food web dynamics. While the relevance of competition and feeding traits have been widely studied for different consumer species, studies on intraspecific differences are more scarce, partly owing to difficulties in distinguishing different clones of the same species. Here, we investigate how intraspecific trait variation affects the competition between the freshwater ciliates Euplotes octocarinatus and Coleps hirtus in a nitrogen‐limited chemostat system. The ciliates competed for the microalgae Cryptomonas sp. (Cry) and Navicula pelliculosa (Nav), and the bacteria present in the cultures over a period of 33 days. We used monoclonal Euplotes and three different Coleps clones (Col 1, Col 2, and Col 3) in the experiment that could be distinguished by a newly developed rDNA‐based molecular assay based on the internal transcribed spacer (ITS) regions. While Euplotes feeds on Cry and on bacteria, the Coleps clones cannot survive on bacteria alone but feed on both Cry and Nav with clone‐specific rates. Experimental treatments comprised two‐species mixtures of Euplotes and one or all of the three different Coleps clones, respectively. We found intraspecific variation in the traits “selectivity” and “maximum ingestion rate” for the different algae to significantly affect the competitive outcome between the two ciliate species. As Nav quickly escaped top‐down control and likely reached a state of low food quality, ciliate competition was strongly determined by the preference of different Coleps clones for Cry as opposed to feeding on Nav. In addition, the ability of Euplotes to use bacteria as an alternative food source strengthened its persistence once Cry was depleted. Hence, trait variation at both trophic levels codetermined the population dynamics and the outcome of species competition. Intraspecific variation in the traits “selectivity” and “maximum ingestion rate” for their prey significantly affected the competition between two freshwater ciliate species. Exclusion of either one of the ciliates or long‐term persistence depended on which of the competitors benefited more from feeding on a less abundant algal resource of high food quality, on severe nutrient limitation that affected the food quality of the dominant algal resource, and on the ability of one competitor to use bacteria as an alternative food source. Hence, trait variation at both trophic levels codetermined the population dynamics and the outcome of species competition.