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A global meta-analysis of the relative extent of intraspecific trait variation in plant communities

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A global meta-analysis of the relative extent of intraspecific trait variation in plant communities

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... Ecologists are now being forced to reconsider this approach because of growing empirical evidence that a large fraction of the trait variation in nature occurs within, not just between species (Messier et al. 2010; Violle et al. 2012). Indeed, approximately 25% of the total trait variation within plant communities worldwide is found within species (Siefert et al. 2015). This is a striking pattern with unexplored but likely important consequences for species coexistence that deserve greater theoretical attention. ...
... Nevertheless, ecologists have recently argued that individual variation may provide a previously unrecognised route to species coexistence (Bolnick et al. 2003Bolnick et al. , 2011 Hubbell 2005; Fridley & Grime 2009; Clark 2010; Clark et al. 2010; Jung et al. 2010; Messier et al. 2010; Pfennig & Pfennig 2012; Violle et al. 2012). This conjecture is motivating a rapid change in focus in field assessments of diversity maintenance away from average differences between species to concentrate on differences between individuals within species (Jung et al. 2010; Messier et al. 2010; Violle et al. 2012; Siefert et al. 2015 ). However, in the absence of general quantitative theory, common expectations that individual variation promotes species coexistence may be premature. ...
... Much of our work has focused on individual variation in demographic rates and competitive parameters, while most field studies quantify intraspecific variation in species' functional traits, such as wood density or specific leaf area (Messier et al. 2010; Jung et al. 2014; Siefert et al. 2015). Nonlinear relationships between specific functional traits and the demographic rates that we consider will add yet another layer of nonlinear averaging, which can affect the distributions (means, variances and higher moments) of demographic rates in complex ways. ...
Conference Paper
Background/Question/Methods Recent theoretical and empirical studies suggest that variation among individuals promotes the maintenance of species diversity. Individual variation can create niche axes where none would exist otherwise, enhance the stabilizing effects of existing species-level niche differences, or equalize species-level fitness differences. However, while the idea that individual variation only promotes coexistence is appealing, these conclusions rarely account for the findings of population demographic theory. This theory demonstrates that variation among individuals combined with finite population size tends to reduce population growth and persistence of small populations. Therefore, because coexistence relies on the ability of species’ populations to increase when rare, we predict that variation among individuals may have negative consequences for the maintenance of diversity. We test this prediction by adding variation among individuals to a range of demographic variables in a commonly used theoretical competition model. We determine the consequences for coexistence of variation among individuals in populations of both residents and invaders across a range of community sizes. Results/Conclusions Our analysis suggests that, as a first approximation, variation among individuals can hinder stabilized coexistence or have no effect. Individual variation within populations of resident species has little consequence for coexistence if community size is sufficiently large. In contrast, variation among individuals of the invader tends to reduce the likelihood of coexistence, although this result depends on the demographic trait in which variation occurs. Variation in survival has no effect on coexistence times but variation in fecundity and interaction strengths tends to reduce coexistence times. Our results show that variation among individuals in demographic rates will often reduce the probability of coexistence such that any benefits of individual variation must overcome this effect. Therefore, a comprehensive understanding of the effects of individual variation on coexistence should take into account both the positive and negative consequences of that variation.
... The mechanisms of community assembly described above are often used to understand plant community responses to environmental gradients and are most commonly studied at the species level [4, 21]. However, intraspecific trait variability is known to play a fundamental role in plant community responses to environmental change and community assembly [19,[22][23][24][25][26][27][28][29][30][31]. Recent studies indicate that accounting for intraspecific trait variation could improve the detection of non-random patterns in community assembly [7, 19, 32]. ...
... Specifically, the total sum of squares of species trait variance for all plots (SS specific ) was decomposed into 'fixed' (SS fixed ), 'intraspecific' (SS intraspecific ) and 'covariation' (SS cov ) effects, thus SS specific = SS fixed + SS intraspecific + SS cov . For each plot and trait, 'specific' community mean trait values using species trait values as measured on each plot (which includes both inter-and intraspecific effects), and 'fixed' community mean trait values using species trait values averaged over all plots (which removes the intraspecific variability effect), 'intraspecific' plot means for each were calculated as the difference between 'specific' and 'fixed' plot mean trait values [22, 23, 31, 50] . Positive or negative covariation values indicate that the relationship between 'fixed' and 'intraspecific' effects reinforce or oppose each other, respectively. ...
... Unlike leaf physical traits, plant height is usually associated with climatic and topographic variables, while LNC and LPC are associated with photosynthetic rate and nutrient cycling [1, 46, 56]. High variability in plant height and leaf chemical trait responses to stress or environmental gradients has been reported in previous studies [19, 28, 29, 31, 37]. This indicates that plant height and chemical traits are more plastic than leaf physical traits in subalpine forests. ...
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Understanding how communities respond to environmental variation is a central goal in ecology. Plant communities respond to environmental gradients via intraspecific and/or interspecific variation in plant functional traits. However, the relative contribution of these two responses to environmental factors remains poorly tested. We measured six functional traits (height, leaf thickness, specific leaf area (SLA), leaf carbon concentration (LCC), leaf nitrogen concentration (LNC) and leaf phosphorus concentration (LPC)) for 55 tree species occurring at five elevations across a 1200 m elevational gradient of subalpine forests in Yulong Mountain, Southwest China. We examined the relative contribution of interspecific and intraspecific traits variability based on community weighted mean trait values and functional diversity, and tested how different components of trait variation respond to different environmental axes (climate and soil variables). Species turnover explained the largest amount of variation in leaf morphological traits (leaf thickness and SLA) across the elevational gradient. However, intraspecific variability explained a large amount of variation (49.3%–76.3%) in three other traits (height, LNC and LPC) despite high levels of species turnover. The detection of limiting similarity in community assembly was improved when accounting for both intraspecific and interspecific variability. Different components of trait variation respond to different environmental axes, especially soil water content and climatic variables. Our results indicate that intraspecific variation is critical for understanding community assembly and evaluating community response to environmental change.
... Ecologists are now being forced to reconsider this approach because of growing empirical evidence that a large fraction of the trait variation in nature occurs within, not just between species (Messier et al. 2010; Violle et al. 2012). Indeed, approximately 25% of the total trait variation within plant communities worldwide is found within species (Siefert et al. 2015). This is a striking pattern with unexplored but likely important consequences for species coexistence that deserve greater theoretical attention. ...
... Nevertheless, ecologists have recently argued that individual variation may provide a previously unrecognised route to species coexistence (Bolnick et al. 2003Bolnick et al. , 2011 Hubbell 2005; Fridley & Grime 2009; Clark 2010; Clark et al. 2010; Jung et al. 2010; Messier et al. 2010; Pfennig & Pfennig 2012; Violle et al. 2012). This conjecture is motivating a rapid change in focus in field assessments of diversity maintenance away from average differences between species to concentrate on differences between individuals within species (Jung et al. 2010; Messier et al. 2010; Violle et al. 2012; Siefert et al. 2015 ). However, in the absence of general quantitative theory, common expectations that individual variation promotes species coexistence may be premature. ...
... Much of our work has focused on individual variation in demographic rates and competitive parameters, while most field studies quantify intraspecific variation in species' functional traits, such as wood density or specific leaf area (Messier et al. 2010; Jung et al. 2014; Siefert et al. 2015). Nonlinear relationships between specific functional traits and the demographic rates that we consider will add yet another layer of nonlinear averaging, which can affect the distributions (means, variances and higher moments) of demographic rates in complex ways. ...
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Although the effects of variation between individuals within species are traditionally ignored in studies of species coexistence, the magnitude of intraspecific variation in nature is forcing ecologists to reconsider. Compelling intuitive arguments suggest that individual variation may provide a previously unrecognised route to diversity maintenance by blurring species-level competitive differences or substituting for species-level niche differences. These arguments, which are motivating a large body of empirical work, have rarely been evaluated with quantitative theory. Here we incorporate intraspecific variation into a common model of competition and identify three pathways by which this variation affects coexistence: (1) changes in competitive dynamics because of nonlinear averaging, (2) changes in species' mean interaction strengths because of variation in underlying traits (also via nonlinear averaging) and (3) effects on stochastic demography. As a consequence of the first two mechanisms, we find that intraspecific variation in competitive ability increases the dominance of superior competitors, and intraspecific niche variation reduces species-level niche differentiation, both of which make coexistence more difficult. In addition, individual variation can exacerbate the effects of demographic stochasticity, and this further destabilises coexistence. Our work provides a theoretical foundation for emerging empirical interests in the effects of intraspecific variation on species diversity.
... Demmig-Adams & Adams, 2006), and persistence against herbivores and physical hazards(Poorter, Niinemets, Poorter, Wright, & Villar, 2009) (PC2 driven by vegetation indices related to carotenoid content and LMA). Both trait spaces revealed considerable intraspecific trait variability, supporting the increased ecological awareness of considering it for predicting and understanding community assembly and ecosystem functioning(Aarssen et al., 2015). Nevertheless, they also indicated clear and consistent interspecific strategy differences. ...
... This study was supported by the Belgian Science Policy Office in the framework of the STEREOIII program (project INPLANT (SR/01/321)).Accepted Article Accepted ArticleThis article is protected by copyright. All rights reserved.ReferencesAarssen, L. W., Siefert, A., Violle, C., Chalmandrier, L., Albert, C. H.,Taudiere, A., … Wardle, D. A. (2015). A global meta-analysis of the relative extent of intraspecific trait variation in plant communities. ...
Article
Collecting species‐level information on plant functional traits is highly relevant for understanding ecosystem functioning under global change. Measuring optical properties of plant species is a promising approach to retrieve such data, but standardized protocols are essential. Due to fine‐scale heterogeneity of many vegetation types, measuring the spectral response, as a proxy for functional traits, of individual plant species remains challenging using conventional approaches. Here we present a novel method for measuring the reflectance of individual species in situ. The procedure consists of measuring monospecific arrangements of plant individuals on a black, light absorbing table, preserving structural plant properties while avoiding admixture of other species, soil or non‐photosynthetically active vegetation. To evaluate the feasibility of the approach, a case study was conducted on forbs, where we collected and compared the reflectance of 16 herbaceous species at different phenological stages, both using common field spectroscopy and following our novel procedure. Our procedure accurately represented spectral and functional differences between species. Spectral shape, and to a lesser extent, amplitude differences between species were preserved (SAM: Mantel r = 0.69 and p = 0.001; Manhattan distance: Mantel r = 0.42 and p = 0.002). Moreover, the method was able to capture the pattern of functional traits present among the sampled species (Procrustes r = 0.8 and p = 0.001). The new method is promising for building databases of plant traits based on spectral libraries. It might, moreover, form a standardized procedure for field campaigns, especially in the context of mixed grasslands and forb systems where relatively small plants dominate the ecosystem. This article is protected by copyright. All rights reserved.
... Here, the contribution of dominant taxa did not change significantly between temperature treatments (9 vs. 15°C), but community mean size was still significantly smaller in the warm treatment compared to the cold treatment due to intraspecific decreases in phytoplankton cell size with increased temperature. For terrestrial plants, Siefert et al. (2015) explored the relative extent of intraspecific trait variation compared with interspecific trait variation in a global meta-analysis of plant communities and found that about 30% of the variation within and among communities was due to intraspecific variation. Furthermore, the result depended on the trait type, with the contribution of intraspecific variation increasing for whole-organism traits like size. ...
... In the literature on terrestrial biota, it has been indicated that the importance of intraspecific change decreases with increasing scale (Siefert et al., 2015). In this context, even if the magnitude of change is likely underestimated, our results support that it may be possible to investigate general patterns, that is, relative differences, in protist community mean size using interspecific size estimates at large spatial scales, for example, at the global scale (Chen et al., 2011) and/or at large temporal scales, for example, millennial or geological timescales (Finkel et al., 2005Finkel et al., , 2007). ...
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Mean body size decreases with increasing temperature in a variety of organisms. This size–temperature relationship has generally been tested through space but rarely through time. We analyzed the sedimentary archive of dinoflagellate cysts in a sediment record taken from the West Greenland shelf and show that mean cell size decreased at both intra- and interspecific scales in a period of relatively warm temperatures, compared with a period of relatively cold temperatures. We further show that intraspecific changes accounted for more than 70% of the change in community mean size, whereas shifts in species composition only accounted for about 30% of the observed change. Literature values on size ranges and midpoints for individual taxa were in several cases not representative for the measured sizes, although changes in community mean size, calculated from literature values, did capture the direction of change. While the results show that intraspecific variation is necessary to accurately estimate the magnitude of change in protist community mean size, it may be possible to investigate general patterns, that is relative size differences, using interspecific-level estimates.
... For example, globally established cross-species trait correlations may not hold across individual leaves or individual plants within community or populations ( Anderegg et al., 2018;Messier, McGill, Enquist, & Lechowicz, 2017). Intra-specific variation, which may be associated with plant size, within-canopy variation, or broader environmental gradients, may be comparable or even greater than among-species trait variation (Li, Pei, Kéry, Niklaus, & Schmid, 2017;Messier, McGill, & Lechowicz, 2010;Poorter, Castilho, Schietti, Oliveira, & Costa, 2018;Siefert et al., 2015), and traits can present contrasting sensitivities to these scale-dependent drivers (Messier et al., 2017;Rosas et al., 2019). ...
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Plants are enormously diverse in their traits and ecological adaptation, even within given ecosystems, such as tropical rainforests. Accounting for this diversity in vegetation models poses serious challenges. Global plant functional trait databases have highlighted general trait correlations across species that have considerably advanced this research program. However, it remains unclear whether trait correlations found globally hold within communities, and whether they extend to drought tolerance traits. For 134 individual plants spanning a range of sizes and life forms (tree, liana, understory species) within an Amazonian forest, we measured leaf drought tolerance (leaf water potential at turgor loss point, πtlp), together with 17 leaf traits related to various functions, including leaf economics traits and nutrient composition (leaf mass per area, LMA; and concentrations of C, N, P, K, Ca, and Mg per leaf mass and area), leaf area, water use efficiency (carbon isotope ratio), and time‐integrated stomatal conductance and carbon assimilation rate per leaf mass and area. We tested trait coordination and the ability to estimate πtlp from the other traits through model selection. Performance and transferability of the best predictive model were assessed through cross‐validation. πtlp was positively correlated with leaf area, and with N, P and K concentrations per leaf mass, but not with LMA or any other studied trait. Five axes were needed to account for > 80% of trait variation, but only three of them explained more variance than expected at random. The best model explained only 30% of the variation in πtlp, and out‐sample predictive performance was variable across life forms or canopy strata, suggesting a limited transferability of the model. Synthesis. We found a weak correlation among leaf drought tolerance and other leaf traits within a forest community. We conclude that higher trait dimensionality than assumed under the leaf economics spectrum may operate among leaves within plant communities, with important implications for species coexistence and responses to changing environmental conditions, and also for the representation of community diversity in vegetation models.
... In contrast to what we hypothesized, we found that in an experimental study different trait datasets may lead to different conclusions, based on the effects of treatments on the CWMs. In theoretical approaches, ITV has previously been shown to account for a significant proportion of total trait variation at species and community levels ( Siefert et al., 2015). For plants, this is especially true in three cases: at local geographical scales, for whole-organism traits, and in species-poor communities. ...
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1.Investigating the functional facet of biodiversity provides ecologists with a deeper understanding of community assembly and ecosystem processes, from local to biogeographical scales. A central assumption in functional ecology is that interspecific trait variability is higher than intraspecific variability. The ‘stable species hierarchy’ hypothesis states that for similar species found in different environmental conditions, their species trait ranking is conserved. In this study, we applied this trait hierarchy concept prevalent in plant ecology to the growing field of soil functional ecology, for which newly developed trait databases are being increasingly used. However, to date there have been few attempts to test for patterns of intraspecific trait variability in these databases. 2.We thus aimed to characterize how such patterns might influence (i) a species hierarchy based on trait values, and (ii) the conclusions of a trait‐based analysis at a community level. To examine this, we used Collembola body size data (extracted from the BETSI database) as model trait. The source consisted of four regional trait datasets (Poland, Scandinavia, Spain and UK) and one dataset for which species traits are defined at a continental (European) scale. 3.We found that, firstly, species were consistently ranked in all the trait datasets, although slight differences were observed between continental and northern European (i.e. Scandinavia and UK) trait datasets. In the two northern datasets, body size was higher (ca. 10%), indicating an intraspecific body size gradient from temperate to colder northern regions that we assumed could be explained by latitudinal patterns. 4.Secondly, using selected published species abundance matrices (from experimental studies), we calculated the community‐weighted mean body size using various trait datasets. The findings showed that the slight discrepancies observed between trait datasets can lead to different conclusions. 5.This work confirms that properly defining the extent of intraspecific trait variability in databases is of primary importance in order to ensure robust conclusions. This is particularly important for databases hosting large scale data, that might be influenced by biogeographical patterns as latitudinal gradients. We recommend using a local regional trait dataset when available or, if not, a continental trait dataset. As trait databases are now commonly used tools for performing trait‐based analyses, it is crucial to carefully select the data used to make inferences. This article is protected by copyright. All rights reserved.
... The weak contribution of ITV and the absence of CWM variation according to tested effects for other traits can reflect contrasted intraspecific responses among species resulting in weak or null change at communitylevel (Kichenin et al. 2013; Kumordzi et al. 2014). In addition, the sampling of non-randomly selected individuals for leaf traits measurement (as suggested by Cornelissen et al. 2003) can result in a underestimation of ITV (Siefert et al. 2015). We further note that other functional traits related to survival and reproduction can influence vegetation dynamics over time and in response to mowing (Klimešová et al. 2008). ...
Article
Questions: How do species composition, resource-use strategy and flowering phenology change and relate to each other in road slope plant communities along an ecological succession after construction work? How does recurrent mowing influence resource-use successional trajectory and flowering phenology in communities? Does intraspecific variation contribute to these community-level functional responses? Location: Road slopes in Mediterranean southern France. Methods: We designed a chronosequence of 25 road slopes, each including both unmown and yearly mown parts. We analysed the influence of age and mowing on community-level trait values (CWM) of Leaf Dry Matter Content (LDMC), Specific Leaf Area (SLA), Onset of Flowering Date (OFD), End of Flowering Date (EFD) and Flowering Duration (FDur). We tested for contribution of intraspecific variation of traits to these functional variations. We also tested for relationship between changes in taxonomic composition, environmental parameters and functional responses. Results: We found a slower successional variation of resource-use strategies in communities undergoing recurrent mowing, compared to unmown vegetation. Onset of flowering was earlier in mown communities. End of flowering and flowering duration did not directly depend on successional stage or mowing but related to resource-use strategies. Species turnover was an important driver of functional variation and the major components of plant taxonomic variation were primarily related to environmental and functional changes. Conclusions: On road slopes, successional changes in functional and taxonomic composition were influenced by mowing, which did not totally prevent vegetation changes. Disturbance by mowing impacted resource-use strategy and indirectly influenced flowering phenology by limiting plant investment into resource conservation in aerial parts. Community-level relationship between resource-use strategy and flowering phenology suggests a consistent trade-off between vegetative growth and flowering phenology among plant species within communities. Our findings help to understand how recurrent disturbances can influence successional trajectories in Mediterranean ecosystems.
... This approach would certainly gain predictive power by integrating intraspecific trait variability that can strongly impact plant community assembly (e.g. Le Pinguet et al. 2014 Siefert et al. 2015), and particularly by considering complex shapes of individual-level trait distributions (Laughlin et al. 2015). We show that interactions between climate and soil variables highlight the importance of environmental filtering and are fundamental in the understanding of trait diversity patterns. ...
Article
The environmental filtering hypothesis predicts that the abiotic environment selects species with similar trait values within communities. Testing this hypothesis along multiple - and interacting - gradients of climate and soil variables constitutes a great opportunity to better understand and predict the responses of plant communities to ongoing environmental changes. Based on two key plant traits, maximum plant height and specific leaf area (SLA), we assessed the filtering effects of climate (mean annual temperature and precipitation, precipitation seasonality), soil characteristics (soil pH, sand content and total phosphorus) and all potential interactions on the functional structure and diversity of 124 dryland communities spread over the globe. The functional structure and diversity of dryland communities were quantified using the mean, variance, skewness and kurtosis of plant trait distributions. The models accurately explained the observed variations in functional trait diversity across the 124 communities studied. All models included interactions among factors, i.e. climate-climate (9% of explanatory power), climate-soil (24% of explanatory power) and soil-soil interactions (5% of explanatory power). Precipitation seasonality was the main driver of maximum plant height, and interacted with mean annual temperature and precipitation. Soil pH mediated the filtering effects of climate and sand content on SLA. Our results also revealed that communities characterized by a low variance can also exhibit low kurtosis values, indicating that functionally contrasting species can co-occur even in communities with narrow ranges of trait values. Synthesis. We identified the particular set of conditions under which the environmental filtering hypothesis operates in drylands world-wide. Our findings also indicate that species with functionally contrasting strategies can still co-occur locally, even under prevailing environmental filtering. Interactions between sources of environmental stress should be therefore included in global trait-based studies, as this will help to further anticipate where the effects of environmental filtering will impact plant trait diversity under climate change.
... The objects can differ in the amount of charge or mass they have, but otherwise interact in the same way with each other. This is in contrast to biological systems, where individual organisms are described by a large number of traits, be it morphological, metabolic, or behavioral, which are not all identical even between individuals of the same species [1,2,3]. Any of these traits can affect the way an individual interacts with other organisms and the environment. ...
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Ecosystems are formed by networks of species and their interactions. Traditional models of such interactions assume a constant interaction strength between a given pair of species. However, there is often significant trait variation among individual organisms even within the same species, causing heterogeneity in their interaction strengths with other species. The consequences of such heterogeneous interactions for the ecosystem have not been studied systematically. As a theoretical exploration, we analyze a simple ecosystem with trophic interactions between two predators and a shared prey, which would exhibit competitive exclusion in models with homogeneous interactions. We consider several scenarios where individuals of the prey species differentiate into subpopulations with different interaction strengths. We show that in all these cases, whether the heterogeneity is inherent, reversible, or adaptive, the ecosystem can stabilize at a new equilibrium where all three species coexist. Moreover, the prey population that has heterogeneous interactions with its predators reaches a higher density than it would without heterogeneity, and can even reach a higher density in the presence of two predators than with just one. Our results suggest that heterogeneity may be a naturally selected feature of ecological interactions that have important consequences for the stability and diversity of ecosystems.
... leaf mass area and leaf dry matter content) showed no variation at a plot level when analyzed across six biological scales, highlighting the role of environmental filtering in determining plant community structure. Integrating inter-and intraspecific trait variation has provided important insights into the processes of community assembly (Jung et al., 2010; Lep s et al., 2011; Siefert, 2012; Siefert et al., 2015; Luo et al., 2016). 'Internal' and 'external' filters have been distinguished from 'traditional' ecological filter for community assembly. ...
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Characterizing trait variation across different ecological scales in plant communities has been viewed as a way to gain insights into the mechanisms driving species coexistence. However, little is known about how changes in intraspecific and interspecific traits across sites influence species richness and community assembly, especially in understory herbaceous communities. Here we partitioned the variance of four functional traits (maximum height, leaf thickness, leaf area and specific leaf area) across four nested biological scales: individual, species, plot, and elevation to quantify the scale-dependent distributions of understory herbaceous trait variance. We also integrated the comparison of the trait variance ratios to null models to investigate the effects of different ecological processes on community assembly and functional diversity along a 1200-m elevational gradient in Yulong Mountain. We found interspecific trait variation was the main trait variation component for leaf traits, although intraspecific trait variation ranged from 10-28% of total variation. In particular, maximum height exhibited high plasticity, and intraspecific variation accounted for 44% of the total variation. Despite the fact that species composition varied across elevation and species richness decreased dramatically along the elevational gradient, there was little variance at our largest (elevation) scale in leaf traits and functional diversity remained constant along the elevational gradient, indicating that traits responded to smaller scale influences. External filtering was only observed at high elevations. However, strong internal filtering was detected along the entire elevational gradient in understory herbaceous communities, possibly due to competition. Our results provide evidence that species coexistence in understory herbaceous communities might be structured by differential niche-assembled processes. This approach –– integrating different biological scales of trait variation –– may provide a better understanding of the mechanisms involved in the structure of communities.
... The theoretical and empirical studies have indicated that ecological system functionality and species interaction, which provides fundamental services for humanity, are affected by biodiversity (Hooper et al., 2005; May, 1973). Most studies addressing this topic focus on interspecific diversity (e.g., the number of species or functional groups); however, intraspecific variation can also be substantial and important in communities and ecosystems (Siefert et al., 2015). For example, increasing genetic and phenotypic variations within a species typically increases species diversity and abundance and primary productivity, promotes positive plant–soil interactions (reviewed in Crutsinger, 2016), and stabilizes ecosystem functions (Genung et al., 2010; Prieto et al., 2015). ...
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Intraspecific variation is a major component of biodiversity, yet it has received relatively little attention from governmental and non-governmental organizations, especially with regard to conservation plans and the management of wild species. This omission is ill-advised because phenotypic and genetic variation within and among populations can have dramatic effects on ecological and evolutionary processes, including responses to environmental change, the maintenance of species diversity, and ecological stability and resilience. At the same time, environmental changes associated with many human activities, such as land-use and climate change, have dramatic and often negative impacts on intraspecific variation. We argue for the need for local, regional, and global programs to monitor intraspecific genetic variation. We suggest that such monitoring should include two main strategies: (1) intensive monitoring of multiple types of genetic variation in selected species; and (2) broad-brush modeling for representative species for predicting changes in variation as a function of changes in population size, range extent, and connectivity. Overall, we call for collaborative efforts to initiate the urgently needed monitoring of intraspecific variation. This article is protected by copyright. All rights reserved.
... Evidence is increasing that intraspecific trait variability plays a significant role in demography and community assembly, and has (Bolnick et al. 2011; de Bello et al. 2011; Violle et al. 2012; Siefert et al. 2015). Within-species variability may originate from spatial variability in trait values within a species range, or may be due to genetic or environmental variation within a population at a single site. ...
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Trait-based approaches are increasingly being used to test mechanisms underlying species assemblages and biotic interactions across a wide range of organisms including terrestrial arthropods and to investigate consequences for ecosystem processes. Such an approach relies on the standardized measurement of functional traits that can be applied across taxa and regions. Currently, however, unified methods of trait measurements are lacking for terrestrial arthropods and related macroinvertebrates (terrestrial invertebrates hereafter). Here, we present a comprehensive review and detailed protocol for a set of 29 traits known to be sensitive to global stressors and to affect ecosystem processes and services. We give recommendations how to measure these traits under standardized conditions across various terrestrial invertebrate taxonomic groups. We provide considerations and approaches that apply to almost all traits described, such as the selection of species and individuals needed for the measurements, the importance of intraspecific trait variability, how many populations or communities to sample and over which spatial scales. The approaches outlined here provide a means to improve the reliability and predictive power of functional traits to explain community assembly, species diversity patterns, and ecosystem processes and services within and across taxa and trophic levels, allowing comparison of studies and running meta-analyses across regions and ecosystems. This handbook is a crucial first step towards standardizing trait methodology across the most studied terrestrial invertebrate groups, and the protocols are aimed to balance general applicability and requirements for special cases or particular taxa. Therefore, we envision this handbook as a common platform to which researches can further provide methodological input for additional special cases. This article is protected by copyright. All rights reserved.
... Recent literature has emphasised the role of intraspecific trait variation in community ecology (Violle et al. 2012). However, as the vast majority of trait variation fell among rather than within many of the most common species in our study (81 and 88% of the variation in SLA and WSG, respectively, Kraft et al. 2008; Osazuwa-Peters et al. 2014; Siefert et al. 2015), we used species mean traits, recognising that it may be valuable (but a substantial effort) to quantify individual-level trait variation for all species in the plot in the future. A phylogenetic tree from Kraft & Ackerly (2010) was used for phylogenetic analyses. ...
Article
As distinct community assembly processes can produce similar community patterns, assessing the ecological mechanisms promoting coexistence in hyperdiverse rainforests remains a considerable challenge. We use spatially explicit neighbourhood models of tree growth to quantify how functional trait and phylogenetic similarities predict variation in growth and crowding effects for the 315 most abundant tree species in a 25-ha lowland rainforest plot in Ecuador. We find that functional trait differences reflect variation in (1) species maximum potential growth, (2) the intensity of interspecific interactions for some species, and (3) species sensitivity to neighbours. We find that neighbours influenced tree growth in 28% of the 315 focal tree species. Neighbourhood effects are not detected in the remaining 72%, which may reflect the low statistical power to model rare taxa and/or species insensitivity to neighbours. Our results highlight the spectrum of ways in which functional trait differences can shape community dynamics in highly diverse rainforests.
... Previous studies of grazing effects have focused on the importance of species turnover in changing community structure and ecosystem function (Grime 2001; D ıaz et al. 2004; Hooper et al. 2005). Only recently have the possible effects of ITV been considered, mostly from the point of view of community assembly (Post et al. 2008; Jung et al. 2010; Bolnick et al. 2011; Siefert et al. 2015). The influence of ITV on shifts in ecosystem function following disturbance remains largely unstudied, especially in the case of biomass production and soil fertility (Mason et al. 2011; Mouillot et al. 2013). ...
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1.The functional structure of plant communities can be altered by grazing through two main mechanisms: species turnover (i.e. changes in species occurrence and relative abundance), and by intraspecific trait variability (ITV), which is driven by phenotypic responses of individual plants and shifts in the relative abundance of genotypic variants within species. Studies of grassland ecosystem function under grazing often focus on community changes induced by species turnover, which ignores the effects of ITV on biomass productivity, soil carbon, or nutrient availability. By quantifying the relative contribution of both effects on shifts in community-wide traits, we highlight the role of ITV in community functional response to grazing and its implications for ecosystem function in Tibetan alpine meadows.
... We measured trophic cascades as the effect of predator exclusion on plant growth and survival as well as the effects of predators on aphids. Based on published differences between the two species, and the expectation that variation within species is likely to be less than variation among species (e.g., Siefert et al. 2015), we predicted that cascades would be stronger on the faster-growing, putatively more nutritious and less-defended A. incarnata than on A. syriaca. We focused on various processes that can generate variation in cascade strength between the two species in order to generate hypotheses about the particular traits and mechanisms important in this system. ...
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The leaf economics spectrum (LES) describes large cross-species variation in suites of leaf functional traits ranging from resource-acquisitive to resource-conservative strategies. Such strategies have been integral in explaining plant adaptation to diverse environments, and have been linked to numerous ecosystem processes. The LES has previously been found to be significantly modulated by climate, soil fertility, biogeography, growth form, and life history. One largely unexplored aspect of LES variation, whole-plant ontogeny, is investigated here using multiple populations of three very different species of sunflower: Helianthus annuus, Helianthus mollis, and Helianthus radula. Plants were grown under environmentally controlled conditions and assessed for LES and related traits at four key developmental stages, using recently matured leaves to standardize for leaf age. Nearly every trait exhibited a significant ontogenetic shift in one or more species, with trait patterns differing among populations and species. Photosynthetic rate, leaf nitrogen concentration, and leaf mass per area exhibited surprisingly large changes, spanning over two-thirds of the original cross-species LES variation and shifting from resource-acquisitive to resource-conservative strategies as the plants matured. Other traits being investigated in relation to the LES, such as leaf water content, pH, and vein density, also showed large changes. The finding that ontogenetic variation in LES strategy can be substantial leads to a recommendation of standardization by developmental stage when assessing 'species values' of labile traits for comparative approaches. Additionally, the substantial ontogenetic trait shifts seen within single individuals provide an opportunity to uncover the contribution of gene regulatory changes to variation in LES traits.
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This chapter considers the nature, role, and evolutionary implications of phenotypic plasticity as an adaptive property in plants. Plasticity is here defined as variation in phenotypic expression of a genotype that occurs in response to particular environmental conditions and which enhances the capacity of the individual to survive and reproduce under those conditions. A distinction is made [following Dobzhansky (1969) and Harper (1982)] between adaptive, defined as conferring a benefit on the organism with regard to its present relationship with its environment, and adapted, which describes a character that is thought to be the product of natural selection over previous generations—i.e., which was adaptive in the past and was therefore fixed by natural selection. “Adapted” refers to the causal origin of the character in evolutionary history; “adaptive” says nothing about the origin of the trait, but merely describes its present value in a given environment.
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Are patterns of intra- and inter-specific functional trait variation consistent with greater abiotic filtering on community assembly at high latitudes and elevations, and greater biotic filtering at low latitudes and elevations? Area de Conservación Guanacaste, Costa Rica; Santa Catalina Mountains, Arizona; Siskiyou Mountains, Oregon. We measured woody plant species abundance and a key functional trait associated with competition for resources and environmental tolerance (specific leaf area, SLA) along elevational gradients in low-latitude tropical (Costa Rica), mid-latitude desert (Arizona) and high latitude mediterranean (southern Oregon) biomes. We explored patterns of abiotic and biotic filtering by comparing observed patterns of community-weighted means and variances along elevational and latitudinal gradients to those expected under random assembly. In addition, we related trait variability to niches and explored how total trait space and breadth vary across broad spatial gradients by quantifying the ratio of intra- to inter-specific variation. Both the community-wide mean and variance of SLA decreased with increasing latitude, consistent with greater abiotic filtering at higher latitudes. Further, low-elevation communities had higher trait variation than expected by chance, consistent with greater biotic filtering at low elevations. Finally, in the tropics and across latitude the ratio of intra- to inter-specific variation was negatively correlated to species richness, which further suggests that biotic interactions influence plant assembly at low latitudes. Intra- and inter-specific patterns of SLA variation appeared broadly consistent with the idea that the relative strength of biotic and abiotic drivers on community assembly changes along elevational and latitudinal gradients; evidence for biotic drivers appeared more prominent at low latitudes and elevations and evidence for abiotic drivers appeared more prominent at high latitudes and elevations.
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Drought reduces plant productivity, induces widespread plant mortality and limits the geographic distribution of plant species(1-7). As climates warm and precipitation patterns shift in the future(8,9), understanding the distribution of the diversity of plant drought tolerance is central to predicting future ecosystem function and resilience to climate change(10-12). These questions are especially pressing for the world's 11,000 grass species(13), which dominate a large fraction of the terrestrial biosphere(14), yet are poorly characterized with respect to responses to drought. Here, we show that physiological drought tolerance, which varied tenfold among 426 grass species, is well distributed both climatically and phylogenetically, suggesting most native grasslands are likely to contain a high diversity of drought tolerance. Consequently, local species may help maintain ecosystem functioning in response to changing drought regimes without requiring long-distance migrations of grass species. Furthermore, physiologically drought-tolerant species had higher rates of water and carbon dioxide exchange than intolerant species, indicating that severe droughts may generate legacies for ecosystem functioning. In all, our findings suggest that diverse grasslands throughout the globe have the potential to be resilient to drought in the face of climate change through the local expansion of drought-tolerant species.
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Many facets of plant form and function are reflected in general cross-taxa scaling relationships. Metabolic scaling theory (MST) and the leaf economics spectrum (LES) have each proposed unifying frameworks and organisational principles to understand the origin of botanical diversity. Here, we test the evolutionary assumptions of MST and the LES using a cross of two genetic variants of Arabidopsis thaliana. We show that there is enough genetic variation to generate a large fraction of variation in the LES and MST scaling functions. The progeny sharing the parental, naturally occurring, allelic combinations at two pleiotropic genes exhibited the theorised optimum ¾ allometric scaling of growth rate and intermediate leaf economics. Our findings: (1) imply that a few pleiotropic genes underlie many plant functional traits and life histories; (2) unify MST and LES within a common genetic framework and (3) suggest that observed intermediate size and longevity in natural populations originate from stabilising selection to optimise physiological trade-offs.
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Ecological communities and their response to environmental gradients are increasingly being described by various measures of trait composition. Aggregated trait averages (i.e. averages of trait values of constituent species, weighted by species proportions) are popular indices reflecting the functional characteristics of locally dominant species. Because the variation of these indices along environmental gradients can be caused by both species turnover and intraspecific trait variability, it is necessary to disentangle the role of both components to community variability. For quantitative traits, trait averages can be calculated from ‘fixed’ trait values (i.e. a single mean trait value for individual species used for all habitats where the species is found) or trait values for individual species specific to each plot, or habitat, where the species is found. Changes in fixed averages across environments reflect species turnover, while changes in specific traits reflect both species turnover and within-species variability in traits. Here we suggest a practical method (accompanied by a set of R functions) that, by combining ‘fixed’ and ‘specific averages’, disentangles the effect of species turnover, intraspecific trait variability, and their covariation. These effects can be further decomposed into parts ascribed to individual explanatory variables (i.e. treatments or environmental gradients considered). The method is illustrated with a case study from a factorial mowing and fertilization experiment in a meadow in South Bohemia. Results show that the variability decomposition differs markedly among traits studied (height, Specific Leaf Area, Leaf N, P, C concentrations, leaf and stem dry matter content), both according to the relative importance of species turnover and intraspecific variability, and also according to their response to experimental factors. Both the effect of intraspecific trait variability and species turnover must be taken into account when assessing the functional role of community trait structure. Neglecting intraspecific trait variability across habitats often results in underestimating the response of communities to environmental changes.
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1. Trait-based approaches applied to community ecology have led to a considerable advance in understanding the effect of environmental filters on species assembly. Although plant traits are known to vary both between and within species, little is known about the role of intraspecific trait variability in the non-random assembly mechanisms controlling the coexistence of species, including habitat filtering and niche differentiation. 2. We investigate the role of intraspecific variability in three key functional traits – specific leaf area (SLA), leaf dry matter content (LDMC) and height – in structuring grassland communities distributed along a flooding gradient. We quantified the contribution of intraspecific variability relative to interspecific differences in the trait–gradient relationship, and we used a null model approach to detect patterns of habitat filtering and niche differentiation, with and without intraspecific variability. 3. Community mean SLA and height varied significantly along the flooding gradient and intraspecific variability accounted for 44% and 32%, respectively, of these trait–gradient relationships. LDMC did not vary along the gradient, with and without accounting for intraspecific variability. Our null model approach revealed significant patterns of habitat filtering and niche differentiation for SLA and height, but not for LDMC. More strikingly, considering intraspecific trait variability greatly increased the detection of habitat filtering and was necessary to detect niche differentiation processes. 4. Synthesis. Our study provides evidence for a strong role of intraspecific trait variability in community assembly. Our findings suggest that intraspecific trait variability promotes species coexistence, by enabling species to pass through both abiotic and biotic filters. We argue that community ecology would benefit from more attention to intraspecific variability.
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Today's scientists are facing the enormous challenge of predicting how cli-mate change will affect species distributions and species assemblages. To do so, ecologists are widely using phenomenological models of species dis-tributions that mainly rely on the concept of species niche and generally ignore species' demography, species' adaptive potential, and biotic interac-tions. This review examines the potential role of the emerging synthetic disci-pline of evolutionary community ecology in improving our understanding of how climate change will alter future distribution of biodiversity. We review theoretical and empirical advances about the role of niche evolution, inter-specific interactions, and their interplay in altering species geographic ranges and community assembly. We discuss potential ways to integrate complex feedbacks between ecology and evolution in ecological forecasting. We also point at a number of caveats in our understanding of the eco-evolutionary consequences of climate change and highlight several challenges for future research.
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1. The sun¿shade acclimation and plasticity of 16 functional leaf traits of 38 tropical tree species were studied in relation to their light demand, maximum adult stature and ontogenetic changes in crown exposure. 2. Species differed significantly in all leaf traits, which explained a large part of the observed variation (average R2 = 0·72). Light had a significant effect on 12 traits and species showed a similar proportional response to light, indicating that the species ranking in trait performance is largely maintained in different light environments. 3. Specific leaf area, leaf nutrient content and chlorophyll : nitrogen ratio showed the largest plasticity to irradiance. These traits are important for maximizing growth in different light conditions because they are closely linked to the photosynthetic capacity and carbon balance of the plant. 4. Plasticity is generally thought to be greatest for pioneer species that occupy early successional habitats with a large variation in irradiance. This hypothesis was rejected because short-lived pioneers showed the lowest plasticity to irradiance. 5. An alternative hypothesis states that plasticity is largest for tall species that experience large ontogenetic changes in irradiance during their life cycle. Yet plasticity was barely related to adult stature or ontogenetic changes in crown exposure. Short-lived pioneers that experience consistently high light levels did have low plasticity, but shade-tolerant species that experience consistently low light levels had high plasticity. 6. Tropical rainforest species show a large variation in plasticity. Plasticity is a compromise between many factors and constraints, and all of these may explain the observed patterns to some extent.
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1. Patterns of species co-existence and species diversity in plant communities remain an important research area despite over a century of intensive scrutiny. To provide mechanistic insight into the rules governing plant species co-existence and diversity, plant community ecologists are increasingly quantifying functional trait values for the species found in a wide range of communities. 2. Despite the promise of a quantitative functional trait approach to plant community ecology, we suggest that, along with examining trait variation across species, an assessment of trait variation within species should also be a key component of a trait-based approach to community ecology. Variability within and between individuals and populations is likely widespread due to plastic responses to highly localized abiotic and biotic interactions. 3. In this study, we quantify leaf trait variation within and across ten co-existing tree species in a dry tropical forest in Costa Rica to ask: (i) whether the majority of trait variation is located between species, within species, within individuals or within the leaves themselves; (ii) whether trait values collected using standardized methods correlate with those collected using unstandardized methods; and (iii) to what extent can we differentiate plant species on the basis of their traits? 4. We find that the majority of variation in traits was often explained by between species differences; however, between leaflet trait variation was very high for compound-leaved species. We also show that many species are difficult to reliably differentiate on the basis of functional traits even when sampling many individuals. 5. We suggest an ideal sample size of at least 10, and ideally 20, individuals be used when calculating mean trait values for individual species for entire communities, though even at large sample sizes, it remains unclear if community level trait values will allow comparisons on a larger geographic scale or if species traits are generally similar across scales. It will thus be critical to account for intraspecific variation by comparing species mean trait values across space in multiple microclimatic environments within local communities and along environmental gradients. Further, quantifying trait variability due to plasticity and inheritance will provide a better understanding of the underlying patterns and drivers of trait variation as well as the application of functional traits in outlining mechanisms of species co-existence.
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1. Functional traits are increasingly used to investigate community structure, ecosystem functioning or to classify species into functional groups. These functional traits are expected to be variable between and within species. Intraspecific functional variability is supposed to influence and modulate species responses to environmental changes and their effects on their environment. However, this hypothesis remains poorly tested and species are mostly described by mean trait values without any consideration of variability in individual trait values.
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The links between plant diversity and ecosystem functioning remain highly controversial. There is a growing consensus, however, that functional diversity, or the value and range of species traits, rather than species numbers per se, strongly determines ecosystem functioning. Despite its importance, and the fact that species diversity is often an inadequate surrogate, functional diversity has been studied in relatively few cases. Approaches based on species richness on the one hand, and on functional traits and types on the other, have been extremely productive in recent years, but attempts to connect their findings have been rare. Crossfertilization between these two approaches is a promising way of gaining mechanistic insight into the links between plant diversity and ecosystem processes and contributing to practical management for the conservation of diversity and ecosystem services.
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Tools for performing model selection and model averaging. Automated model selection through subsetting the maximum model, with optional constraints for model inclusion. Model parameter and prediction averaging based on model weights derived from information criteria (AICc and alike) or custom model weighting schemes. [Please do not request the full text - it is an R package. The up-to-date manual is available from CRAN].
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Question: Understanding functional change in vegetation and how it might impact on vegetation change and ecosystem function entails measuring plant traits and attributes in situ. However, it is not realistically possible to sample every species for every trait, hence we need to address the consequences of not sampling all species. Location: Nine arable and grassland sites from the machair of the Western Isles, UK and twenty grassland and woodland sites from Nynäs Nature Reserve, southern Sweden. Methods: The effects of progressively reducing the proportion of species used to estimate the weighted mean of a range of continuous and qualitative traits were assessed. Results: Relative abundance and species traits were related, and hence there is a cost in accuracy in reducing the number of species sampled in estimating the weighted mean for the vegetation. This cost was higher for qualitative traits than quantitative ones. Conclusion: The analysis suggested that for the quantitative traits a minimum of those species that make up at least 80% of the vegetation should be sampled if traits do not vary greatly between species. If this variability is high and the trait is likely to be correlated to abundance then greater effort in sampling species for traits is required. Qualitative information on the rarer species should still be entered into the analysis if it can be accessed in any way, even if quantitative information for that species is unavailable.
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Several recent studies demonstrate that yield of individual plants, and their allocation of biomass between roots and shoots, can be profoundly affected by the pattern of supply of soil-based resources. Patchy provision of soil-based resources can affect the location of root biomass, as roots often proliferate in nutrient-rich patches. Root system size is important in determining whether plants access nutrient-rich patches, and the proportion of root systems located within such patches. This proportion will alter as growth proceeds. Species with small root systems have a limited ability to place roots in nutrient-rich patches even when they are very close. Of four species with different root system sizes, the growth of the species with the smallest root system was significantly limited by being located in nutrient-poor substrate even when nutrient-rich substrate was only 3.5 cm away, whereas three species with larger root systems were not disadvantaged. Both in the laboratory and in the field, root density is higher in nutrient-rich patches, and such patches can contain roots of many plants. Recent work showing that plants can respond to non-self roots sharing the same, nutrient supply suggests that competition will be more severe in nutritionally patchy substrates than in homogeneous environments with the same overall nutrient supply. Taken together, these facts lead to the prediction that inter- and intraspecific plant interactions will be influenced by patterns of nutrient supply. We present evidence supporting this prediction, and indicating that population and community structure are also affected by patterns of nutrient supply. Significant differences in population yield, plant size distribution, and mortality have been recorded between populations growing under patchy and uniform conditions. Plant communities grown from, identical seed inocula, with the same overall nutrient supply, provided in different spatial and temporal patterns, differed by up to 44% in total biomass, up to 70% in root biomass, and differed in species composition. These significant effects of heterogeneous resource supply on plants merit further detailed study. We present a framework of predictions of the impacts of different types of spatial heterogeneity in nutrient supply on the performance of single plants, and on plant interactions, plant populations, and plant communities.
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The leaf economics spectrum (LES) provides a useful framework for examining species strategies as shaped by their evolutionary history. However, that spectrum, as originally described, involved only two key resources (carbon and nutrients) and one of three economically important plant organs. Herein, I evaluate whether the economics spectrum idea can be broadly extended to water – the third key resource –stems, roots and entire plants and to individual, community and ecosystem scales. My overarching hypothesis is that strong selection along trait trade-off axes, in tandem with biophysical constraints, results in convergence for any taxon on a uniformly fast, medium or slow strategy (i.e. rates of resource acquisition and processing) for all organs and all resources.
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Functional trait-based approaches have seen rapid development in community ecology and biogeography in recent years, as they promise to offer a better mechanistic and predictive understanding of community structure. However, several key challenges remain. First, while many studies have explored connections between functional traits and abiotic gradients, far fewer have directly tested the common assumption that functional trait differences influence interspecific interactions. Second, empirical studies often ignore intraspecific trait variation within communities, even though intraspecific variation has been known to have substantial impacts on community dynamics. Here we present an experiment designed to assess the role of functional trait differences in predicting the outcome of interspecific species interactions among a suite of California vernal pool annual plants. Eight species were grown in pairwise combinations in two levels of inundation in a greenhouse and functional traits were measured on all individuals. Nested models predicting focal plant performance were fit to the data. For seven of the eight species in the experiment, the best model included a functional trait difference term that was consistent with a competitive hierarchy, indicating that focal species tended to do better when they had larger leaf size, lower specific leaf area, and greater investment in lateral canopy spread than their neighbors. Models that included individually measured trait values generally performed better than models using species trait averages. We tested if the same trait measurements predicted tolerance of inundation (a feature of vernal pool habitats), and species depth distributions from extensive field surveys, though we did not find strong relationships. Our results suggest that functional traits can be used to make inferences about the outcome of interspecific interactions, and that greater predictive power can come from considering intraspecific variation in functional traits, particularly in low diversity communities.
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Spatial patterns of functional traits have received little attention in community ecology but have the potential to provide insights into the processes that structure communities. In this study, I used semivariograms to describe spatial patterns of functional traits and evaluate processes (niche differentiation, environmental filtering, and dispersal limitation) driving functional divergence in old-field plant communities. I collected spatially explicit data on key plant functional traits (vegetative height, specific leaf area [SLA], and leaf dry matter content [LDMC]) and environmental variables (soil depth and soil moisture) across a range of spatial scales (<1-1500 m) in old fields in central New York. All traits displayed nonrandom spatial patterns consistent with the environmental filtering hypothesis, but patterns differed among traits. Height had strong spatial dependence at scales congruent with spatial heterogeneity of soil depth, indicating that soil depth acted as a spatial template for divergence in height. SLA and LDMC had much weaker spatial dependence, with >90% of total divergence occurring within 1-m² plots, demonstrating that high levels of functional divergence may occur at very fine spatial scales. Spatial patterns of intraspecific functional divergence differed among four common species (Solidago canadensis, Bromus inermis, Poa pratensis and Galium mollugo), indicating that species differed in their trait responses to environmental variation. This study provides novel descriptions of spatial patterns of functional traits in plant communities and demonstrates how these patterns can help understand the processes driving functional divergence across spatial scales.
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Biodiversity is comprised of genetic and phenotypic variation among individual organisms, which might belong to the same species or to different species. Spatial patterns of biodiversity are of central interest in ecology and evolution for several reasons: to identify general patterns in nature (e.g., species-area relationships, latitudinal gradients), to inform conservation priorities (e.g., identifying hot-spots, prioritizing management efforts), and to draw inferences about processes, historical or otherwise (e.g., adaptation, the center of origin of particular clades). There are long traditions in ecology and evolutionary biology of examining spatial patterns of biodiversity among species (i.e., in multi-species communities) and within species, respectively, and there has been a recent surge of interest in studying these two types of pattern simultaneously. The idea is that examining both levels of diversity can materially advance the above-stated goals, and perhaps lead to entirely novel lines of inquiry. Here we review two broad categories of approach to merging studies of inter- and intraspecific variation: (i) the study of phenotypic trait variation along environmental gradients, and (ii) the study of relationships between patterns of molecular-genetic variation within species and patterns of distribution and diversity across species. For the latter, we report a new meta-analysis in which we find that correlations between species diversity and genetic diversity are generally positive and significantly stronger in studies with discrete sampling units (e.g., islands, lakes, forest fragments) than in studies with non-discrete sampling units (e.g., equal-area study plots). For each topic, we summarize the current state of knowledge and key future directions.This article is protected by copyright. All rights reserved.
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One central assumption of trait screening approaches in comparative plant ecology, i.e. simultaneous measurement of traits on a large number of species or populations, is that the species level captures a major part of trait variation. The current development of large databases has led to a new screening approach that relies on the extraction of trait values from databases, rather than on measurement of traits in the field. We tested this assumption with the following questions: (1) is the magnitude of intra-specific variability of co-occurring species lower than inter-specific variability for a given trait, in comparisons at different spatial scales; (2) is species hierarchy based on trait values conserved across different spatial scales and data sets (stable species hierarchy hypothesis); and (3) when we compare different traits, what is the more stable trait that is conserved across different spatial scales and data sets?
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1.Considering both within- and between-species functional diversities in plant communities has been recently suggested as a way to understand potential assembly mechanisms that control species co-existence. In particular, relating variations in species richness to within- and between-species functional diversities can provide a useful framework for evaluating the importance of alternative community assembly theories. In addition little is known about whether the relationship between species richness and functional diversity components arises from direct or indirect effects of the abiotic environment. 2.We tested the relationship between functional diversity and species richness by disentangling functional diversity components into within-species, between-species and total functional diversities and by considering potential direct and indirect effects of the abiotic conditions. Multi- and single-trait approaches were applied using three key plant functional traits (height, SLA, LMDC). Traits were measured on species coexisting across sixteen species-rich limestone grasslands. Direct and indirect effects of the abiotic conditions were evaluated using multiple soil properties including heterogeneity in soil depths. 3.The within-species functional diversity ranged between 13.5% and 33.6% of the total functional diversity. Within-species diversity was the main functional component linked to variations in species richness, despite the within-species functional diversity being lower than between-species functional diversity. Environmental soil properties had a direct effect on species richness but did not affect functional diversity components. 4.Synthesis: Our results provide evidence that increasing the trait overlap between species, due to an increase in within-species diversity, may relate to greater species coexistence. Disentangling multiple functional diversity components indicated that there may be equalizing mechanisms that act as potential drivers of species coexistence. In addition it suggests the possibility that this approach may provide a better understanding of the processes involved in the structure of plant communities. This article is protected by copyright. All rights reserved.
Article
1 Climate change is expected to increase the magnitude and the frequency of extreme climatic events such as droughts. Better understanding how plant communities will respond to these droughts is a major challenge. We expect the response to be a shift in functional trait values resulting from both species turnover and intraspecific trait variability, but little research has addressed the relative contribution of both components. 2 We analysed the short-term functional response of subalpine grassland communities to a simulated drought by focusing on four leaf traits (LDMC: leaf dry matter content, SLA: specific leaf area, LNC: leaf nitrogen concentration and LCC: leaf carbon concentration). After evaluating species turnover and intraspecific variability separately, we determined their relative contribution in the community functional response to drought, reflected by changes in community-weighted mean traits. 3 We found significant species turnover and intraspecific variability, as well as significant changes in community-weighted mean for most of the traits. The relative contribution of intraspecific variability to the changes in community mean traits was more important (42–99%) than the relative contribution of species turnover (1–58%). Intraspecific variability either amplified (for LDMC, SLA and LCC) or dampened (for LNC) the community functional response mediated by species turnover. We demonstrated that the small contribution of species turnover to the changes in community mean LDMC and LCC was explained by a lack of covariation between species turnover and interspecific trait differences. 4 Synthesis. These results highlight the need for a better consideration of intraspecific variability to understand and predict the effect of climate change on plant communities. While both species turnover and intraspecific variability can be expected following an extreme drought, we report new evidence that intraspecific variability can be a more important driver of the short-term functional response of plant communities.
Article
We measured specific leaf area (SLA) and six of its determinants (the thickness of lamina, mesophyll, epidermis, mid-vein and mid-vein support tissues and leaf water content) in a collection of 22 herbaceous species grown in factorial combinations of high μ1100 (mol m-2 s-1) and low (200) irradiance crossed with high (1:1) and low (1:6 dilution) concentrations of a modified Hoagland hydroponic solution. SLA increased with both decreasing irradiance and with increasing nutrient availability but there was a strong interaction between the two. Lamina and mesophyll thickness both increased with increasing irradiance and nutrient availability without any interaction. The experimental treatments had complicated effects on mid-vein thickness and its support tissues. Leaf water content (a measure of leaf tissue density) decreased with increasing irradiance levels and with decreasing nutrient supply, but with an interaction between the two treatments. Changes in nutrient supply had no effect on SLA at high irradiance because leaf thickness and leaf tissue density changed in a compensatory way. A path analysis revealed that each of the components affected SLA when the others were statistically controlled but the strengths of the effects of mesophyll thickness, mid-vein thickness and water content differed between treatment groups. The effect of epidermal thickness on SLA was constant across environments and it showed no significant covariation with the other determinants. There was significant covariation between mesophyll thickness, mid-vein thickness and water content and this covariation was constant across the treatment groups.
Article
Summary 1 Although outbreeding populations of many grassland plants exhibit substantial genetic and phenotypic variation at fine spatial scales (< 100 m 2 ), the implications of local genetic diversity for community structure are poorly understood. Genetic diversity could contribute to local species diversity by mediating the effects of competition between species and by enhancing species persistence in the face of environmental variation. 2 We assayed the performance of three genotypes each of a dominant tussock grass ( Koeleria macrantha (Ledeb.) J.A. Schultes) and dominant sedge ( Carex caryophyllea Lat.) derived from a single 10 × 10 m quadrat within a limestone grassland in Derbyshire, UK. Genotypes were grown in monoculture and grass-sedge mixtures of different genetic composition in two environments of contrasting fertility. Species mixtures also included one genotype of the subordinate forb Campanula rotundifolia L. 3 When grown without neighbours, intraspecific genotypes responded similarly to environmental treatments. One genotype of the sedge performed worse in both environments than the other two sedge genotypes. 4 When grown in species mixtures, genotype performance was significantly influenced by the genetic identity of the neighbouring species for both the sedge and the grass. At high fertility, differential genotype performance was not sufficient to alter the expectation of competitive exclusion of the sedge by the grass. However, at low fertility, the competitive dominant depended on the genetic identity of both the grass and the sedge. In addition, each genotype of the grass performed best next to a different genotype of the sedge, and the identity of the best genotype pairings switched with environment. 5 Performance of a single genotype of the subordinate Campanula was not predictable by fertility alone, but by how fertility interacted with different neighbouring genotypes of both the grass and the sedge. 6 Results support the hypothesis that the genetic identity of interspecific neighbours influences plant performance in multispecies assemblages and mediates species' responses to environmental variation. Such interactions could be a key factor in the contribution of local intraspecific genetic diversity to species diversity.
Article
Summary • Given the speed and extent of changes in vegetation as a result of human activity, there is a need to investigate ways in which individual species’ impacts on ecosystem processes can be generalized and scaled-up to the community level. • We focus on linking community functional parameters (mean of the traits of the plants in the community, weighted using four different methods) with litter chemistry and decomposition, in a chronosequence of currently managed and abandoned semi-natural grasslands in southern Sweden. • Changes in plant community composition with age since abandonment were reflected in community functional parameters: as expected, aggregated specific leaf area (SLA) declined, and aggregated leaf dry matter content (LDMC) and leaf carbon : nitrogen ratio (C : N) increased with plot age. • Several litter chemistry indices were closely linked with plant traits at the community level; in particular, community aggregated LDMC was correlated with the lignin and fibre content of the community litter. • Aggregated LDMC stood out as the trait most closely linked to community litter decomposition. This relationship was consistent across all three incubation periods (by which time up to c. 70% mass loss had occurred) and as strong as that between the best single chemical index of litter quality (lignin : N ratio) and litter mass loss. • Mass loss of whole community litter, incubated in its plot of origin, was related to mass loss of the same litter incubated under standard conditions, but not to decomposition of a standard substrate, indicating dominant substrate quality control over decomposition. • This study demonstrates the potential of the traits of living plants as a tool to link changes in species composition with ecosystem processes at the community level. Functional Ecology (2007) doi: 10.1111/j.1365-2435.2007.01324.x
Article
In its simplest definition, a trait is a surrogate of organismal performance, and this meaning of the term has been used by evolutionists for a long time. Over the last three decades, developments in community and ecosystem ecology have forced the concept of trait beyond these original boundaries, and trait-based approaches are now widely used in studies ranging from the level of organisms to that of ecosystems. Despite some attempts to fix the terminology, especially in plant ecology, there is currently a high degree of confusion in the use, not only of the term “trait” itself, but also in the underlying concepts it refers to. We therefore give an unambiguous definition of plant trait, with a particular emphasis on functional trait. A hierarchical perspective is proposed, extending the “performance paradigm” to plant ecology. “Functional traits” are defined as morpho-physio-phenological traits which impact fitness indirectly via their effects on growth, reproduction and survival, the three components of individual performance. We finally present an integrative framework explaining how changes in trait values due to environmental variations are translated into organismal performance, and how these changes may influence processes at higher organizational levels. We argue that this can be achieved by developing “integration functions” which can be grouped into functional response (community level) and effect (ecosystem level) algorithms.
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1. Intraspecific trait variability is a crucial, often neglected, component of functional diversity (FD) in ecological communities. In particular, uncertainty remains as to the importance of intraspecific variability in the quantification of FD. 2. To explore this uncertainty, we propose two methods addressing two critical and complementary, but largely unexplored, questions: (i) what is the extent of within- vs. between-species FD in different communities? and (ii) to what extent is the response of FD to environment because of compositional turnover vs. intraspecific trait variability across habitats? The methods proposed to address these questions are built on a variance partitioning approach and have the advantage of including species relative abundance, therefore taking into account species dominance and rarity. For each of the questions, we illustrate one dedicated case study in semi-natural grasslands with associated sampling strategies. 3. The decomposition of total community variance into within- vs. between-species effects can be implemented in a manner similar to the decomposition of quadratic entropy on pairwise individual dissimilarity. The approach can be applied with single and multiple traits, although it proves more informative for single traits. It can prove particularly useful when assessing the role of different sources of trait variability in the assembly of communities. 4. The assessment of the relative contribution of intraspecific trait variability and species turnover to the response of FD to environment is based on a variance partitioning comparing FD indices computed (i) either using individuals measured in a specific habitat alone (FDhabitat) or (ii) all individuals measured across different habitats (FDfixed). This approach provides a more complete understanding of the response of FD to environment. 5. We further propose a guide to apply these two methods and to choose the most suitable method for intraspecific trait measurements. Assessing the role of intraspecific trait variability should allow a more comprehensive understanding of the processes that link species and ecosystems.
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Species diversity and genetic diversity remain the nearly exclusive domains of community ecology and population genetics, respectively, despite repeated recognition in the literature over the past 30 years of close parallels between these two levels of diversity. Species diversity within communities and genetic diversity within populations are hypothesized to co-vary in space or time because of locality characteristics that influence the two levels of diversity via parallel processes, or because of direct effects of one level of diversity on the other via several different mechanisms. Here, we draw on a wide range of studies in ecology and evolution to examine the theoretical underpinnings of these hypotheses, review relevant empirical literature, and outline an agenda for future research. The plausibility of species diversity–genetic diversity relationships is supported by a variety of theoretical and empirical studies, and several recent studies provide direct, though preliminary support. Focusing on potential connections between species diversity and genetic diversity complements other approaches to synthesis at the ecology–evolution interface, and should contribute to conceptual unification of biodiversity research at the levels of genes and species.
Article
Niche differentiation and ecological filtering are primary ecological processes that shape community assembly, but their relative importance remains poorly understood. Analyses of the distributions of functional traits can provide insight into the community structure generated by these processes. We predicted the trait distributions expected under the ecological processes of niche differentiation and environmental filtering, then tested these predictions with a dataset of 4672 trees located in nine 1-ha plots of tropical rain forest in French Guiana. Five traits related to leaf function (foliar N concentration, chlorophyll content, toughness, tissue density and specific leaf area), and three traits related to stem function (trunk sapwood density, branch sapwood density, and trunk bark thickness), as well as laminar surface area, were measured on every individual tree. There was far more evidence for environmental filtering than for niche differentiation in these forests. Furthermore, we contrasted results from species-mean and individual-level trait values. Analyses that took within-species trait variation into account were far more sensitive indicators of niche differentiation and ecological filtering. Species-mean analyses, by contrast, may underestimate the effects of ecological processes on community assembly. Environmental filtering appeared somewhat more intense on leaf traits than on stem traits, whereas niche differentiation affected neither strongly. By accounting for within-species trait variation, we were able to more properly consider the ecological interactions among individual trees and between individual trees and their environment. In so doing, our results suggest that the ecological processes of niche differentiation and environmental filtering may be more pervasive than previously believed.
Article
A leaf-height-seed (LHS) plant ecology strategy scheme is proposed. The axes would be specific leaf area SLA (light-capturing area deployed per dry mass allocated), height of the plant's canopy at maturity, and seed mass. All axes would be log-scaled. The strategy of a species would be described by its position in the volume formed by the three axes.The advantages of the LHS scheme can be understood by comparing it to Grime's CSR scheme, which has Competitors, Stress-tolerators and Ruderals at the corners of a triangle. The CSR triangle is widely cited as expressing important strategic variation between species. The C–S axis reflects variation in responsiveness to opportunities for rapid growth; in the LHS scheme, SLA reflects the same type of variation. The R axis reflects coping with disturbance; in the LHS scheme, height and seed mass reflect separate aspects of coping with disturbance.A plant ecology strategy scheme that permitted any species worldwide to be readily positioned within the scheme could bring substantial benefits for improved meta-analysis of experimental results, for placing detailed ecophysiology in context, and for coping with questions posed by global change. In the CSR triangle the axes are defined by reference to concepts, there is no simple protocol for positioning species beyond the reference datasets within the scheme, and consequently benefits of worldwide comparison have not materialized. LHS does permit any vascular land plant species to be positioned within the scheme, without time-consuming measurement of metabolic rates or of field performance relative to other species. The merits of the LHS scheme reside (it is argued) in this potential for worldwide comparison, more than in superior explanatory power within any particular vegetation region.The LHS scheme avoids also two other difficulties with the CSR scheme: (a) It does not prejudge that there are no viable strategies under high stress and high disturbance (the missing quadrant in the CSR triangle compared to a two-axis rectangle); (b) It separates out two distinct aspects of the response to disturbance, height at maturity expressing the amount of growth attempted between disturbances, and seed mass (inverse of seed output per unit reproductive effort) expressing the capacity to colonize growth opportunities at a distance.The advantage of LHS axes defined through a single readily-measured variable needs to be weighed against the disadvantage that single plant traits may not capture as much strategy variation as CSR's multi-trait axes. It is argued that the benefits of potential worldwide comparison do actually outweigh any decrease in the proportion of meaningful variation between species that is captured. Further, the LHS scheme opens the path to quantifying what proportion of variation in any other ecologically-relevant trait is correlated with the LHS axes. This quantification could help us to move forward from unprofitable debates of the past 30 years, where CSR opponents have emphasized patterns that were not accommodated within the scheme, while CSR proponents have emphasized patterns that the scheme did account for.
Article
Linking intraspecific variation in plant traits to ecosystem carbon uptake may allow us to better predict how shift in populations shape ecosystem function. We investigated whether plant populations of a dominant old-field plant species (Solidago altissima) differed in carbon dynamics and if variation in plant traits among genotypes and between populations predicted carbon dynamics. We estab-lished a common garden experiment with 35 genotypes from three populations of S. altissima from either Tennessee (southern populations) or Connecticut (north-ern populations) to ask whether: (1) southern and northern Solidago populations will differ in aboveground productivity, leaf area, flowering time and duration, and whole ecosystem carbon uptake, (2) intraspecific trait variation (growth and repro-duction) will be related to intraspecific variation in gross ecosystem CO 2 exchange (GEE) and net ecosystem CO 2 exchange (NEE) within and between northern and southern populations. GEE and NEE were 4.8× and 2× greater in southern rela-tive to northern populations. Moreover, southern populations produced 13× more aboveground biomass and 1.4× more inflorescence mass than did northern popu-lations. Flowering dynamics (first-and last-day flowering and flowering duration) varied significantly among genotypes in both the southern and northern popula-tions, but plant performance and ecosystem function did not. Both productivity and inflorescence mass predicted NEE and GEE between S. altissima southern and northern populations. Taken together, our data demonstrate that variation between S. altissima populations in performance and flowering traits are strong predictors of ecosystem function in a dominant old-field species and suggest that populations of the same species might differ substantially in their response to environmental perturbations.
Article
Environmental filtering and niche differentiation are processes proposed to drive community assembly, generating nonrandom patterns in community trait distributions. Despite the substantial intraspecific trait variation present in plant communities, most previous studies of trait-based community assembly have used species mean trait values and therefore not accounted for intraspecific variation. Using a null model approach, I tested for environmental filtering and niche differentiation acting on three key functional traits-vegetative height, specific leaf area (SLA), and leaf dry matter content (LDMC)-in old-field plant communities. I also examined how accounting for intraspecific variation at the among-plot and individual levels affected the detection of nonrandom assembly patterns. Tests using fixed species mean trait values provided evidence of environmental filtering acting on height and SLA and niche differentiation acting on SLA. Including plot-level intraspecific variation increased the strength of these patterns, indicating an important role of intraspecific variation in community assembly. Tests using individual trait data indicated strong environmental filtering acting on all traits, but provided no evidence of niche differentiation, although these signals may have been obscured by the effects of dispersal limitation and spatial aggregation of conspecific individuals. There was also strong evidence of nonrandom assembly of individuals within single species, with the strength of environmental filtering varying among species. This study demonstrates that, while analyses using fixed species mean trait values can provide insights into community assembly processes, accounting for intraspecific variation provides a more complete view of communities and the processes driving their assembly.
Article
Herbivore damage is generally detrimental to plant fitness, and the evolu- tionary response of plant populations to damage can involve either increased resistance or increased tolerance. While characters that contribute to resistance, such as secondary chem- icals and trichomes, are relatively well understood, characters that contribute to a plant's ability to tolerate damage have received much less attention. Using Helianthus annuus (wild sunflower) and simulated damage of Haplorhynchites aeneus (head-clipping weevil) as a model system, we examined morphological characters and developmental processes that contribute to compensatory ability. We performed a factorial experiment that included three levels of damage (none, the first two, or the first four inflorescences were clipped with scissors) and eight sires each mated to four dams. We found that plants compensated fully for simulated head-clipper damage and that there was no variation among plant families in compensatory ability: seed production and mean seed mass did not vary among treat- ments, and sire X treatment interactions were not significant. Plants used four mechanisms to compensate for damage: (1) Clipped plants produced significantly more inflorescences than unclipped plants. Plants produced these additional inflorescences on higher order branches at the end of the flowering season. (2) Clipped plants filled significantly more seeds in their remaining heads than did unclipped plants. (3) Clipped plants, because they effectively flowered later than unclipped plants, were less susceptible to damage by seed- feeding herbivores other than Haplorhynchites. (4) In later heads, seed size was greater on clipped plants, which allowed mean seed size to be maintained in clipped plants. Although there was genetic variation among the families used in this experiment for most of the characters associated with compensation for damage (seed number, mean seed size, mean flowering date, length of the flowering period, and branching morphology), in analyses of these characters, no sire X treatment interactions were significant indicating that all of the families relied on similar mechanisms to compensate for damage.