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Journal ArticleDOI

Changes in coexistence mechanisms along a long‐term soil chronosequence revealed by functional trait diversity

TL;DR: The results demonstrate that at high fertility dominant species differ in resource use strategy, but as soil fertility declines over the long-term, dominant species increasingly converge on a resource-retentive strategy, which suggests that differentiation in resourceUse strategy is required for co-existence at highertility but not in low fertility ecosystems.
Abstract: 1. Functional trait diversity can reveal mechanisms of species co-existence in plant communities. Few studies have tested whether functional diversity for foliar traits related to resource use strategy increases or decreases with declining soil phosphorus (P) in forest communities. 2. We quantified tree basal area and four foliar functional traits (i.e. nitrogen (N), phosphorus (P), thickness and tissue density) for all woody species along the c. 120 kyr Franz Josef soil chronosequence in cool temperate rainforest, where strong shifts occur in light and soil nutrient availability (i.e. total soil P declines from 805 to 100 mg g–1). We combined the abundance and trait data in functional diversity indices to quantify trait convergence and divergence, in an effort to determine whether mechanisms of co-existence change with soil fertility. 3. Relationships between species trait means and total soil N and P were examined using multiple regression, with and without weighting of species abundances. We used Rao’s quadratic entropy to quantify functional diversity at the plot scale, then compared this with random expectation, using a null model that randomizes abundances across species within plots. Taxonomic diversity was measured using Simpson’s Diversity. Relationships between functional and taxonomic diversity and total soil P were examined using jackknife linear regression. 4. Leaf N and P declined and leaf thickness and density increased monotonically with declining total soil P along the sequence; these relationships were unaffected by abundance-weighting of species in the analyses. Inclusion of total soil N did not improve predictions of trait means. All measures of diversity calculated from presence/absence data were unrelated to total soil N and P. There was no evidence for a relationship between Rao values using quantitative abundances and total soil P. However, there was a strongly positive relationship between Rao, expressed relative to random expectation, and total soil P, indicating trait convergence of dominant species as soil P declined. 5. Synthesis: Our results demonstrate that at high fertility dominant species differ in resource use strategy, but as soil fertility declines over the long-term, dominant species increasingly converge on a resource-retentive strategy. This suggests that differentiation in resource use strategy is required for co-existence at high fertility but not in low fertility ecosystems.
Citations
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Journal ArticleDOI
TL;DR: A single ‘fast–slow’ plant economics spectrum that integrates across leaves, stems and roots is a key feature of the plant universe and helps to explain individual ecological strategies, community assembly processes and the functioning of ecosystems.
Abstract: Summary 1. 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. 2. Evidence for economic trait spectra exists for stems and roots as well as leaves, and for traits related to water as well as carbon and nutrients. These apply generally within and across scales (within and across communities, climate zones, biomes and lineages). 3. There are linkages across organs and coupling among resources, resulting in an integrated whole-plant economics spectrum. Species capable of moving water rapidly have low tissue density, short tissue life span and high rates of resource acquisition and flux at organ and individual scales. The reverse is true for species with the slow strategy. Different traits may be important in different conditions, but as being fast in one respect generally requires being fast in others, being fast or slow is a general feature of species. 4. Economic traits influence performance and fitness consistent with trait-based theory about underlying adaptive mechanisms. Traits help explain differences in growth and survival across resource gradients and thus help explain the distribution of species and the assembly of communities across light, water and nutrient gradients. Traits scale up – fast traits are associated with faster rates of ecosystem processes such as decomposition or primary productivity, and slow traits with slow process rates. 5. Synthesis. Traits matter. A single ‘fast–slow’ plant economics spectrum that integrates across leaves, stems and roots is a key feature of the plant universe and helps to explain individual ecological strategies, community assembly processes and the functioning of ecosystems.

2,246 citations


Cites background from "Changes in coexistence mechanisms a..."

  • ...…and high tissue longevity, which excel at tolerating low resources and/or suppressing resource supply to neighbours, are successful under low nutrient supply (Tilman 1987; Tilman & Wedin 1991; Aerts & Chapin 2000; Craine et al. 2002; Craine 2009; Holdaway et al. 2011; Mason et al. 2012)....

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Journal ArticleDOI
TL;DR: It is argued that predicting future changes in biodiversity will require linking functional traits with recognised coexistence mechanisms involving spatial or temporal environmental heterogeneity, resource partitioning and natural enemies, and some mechanisms will be stronger and more widespread than others.
Abstract: Recent functional trait studies have shown that trait differences may favour certain species (environmental filtering) while simultaneously preventing competitive exclusion (niche partitioning). However, phenomenological trait-dispersion analyses do not identify the mechanisms that generate niche partitioning, preventing trait-based prediction of future changes in biodiversity. We argue that such predictions require linking functional traits with recognised coexistence mechanisms involving spatial or temporal environmental heterogeneity, resource partitioning and natural enemies. We first demonstrate the limitations of phenomenological approaches using simulations, and then (1) propose trait-based tests of coexistence, (2) generate hypotheses about which plant functional traits are likely to interact with particular mechanisms and (3) review the literature for evidence for these hypotheses. Theory and data suggest that all four classes of coexistence mechanisms could act on functional trait variation, but some mechanisms will be stronger and more widespread than others. The highest priority for future research is studies of interactions between environmental heterogeneity and trait variation that measure environmental variables at within-community scales and quantify species' responses to the environment in the absence of competition. Evidence that similar trait-based coexistence mechanisms operate in many ecosystems would simplify biodiversity forecasting and represent a rare victory for generality over contingency in community ecology.

414 citations


Cites background from "Changes in coexistence mechanisms a..."

  • ...Similarly, Mason et al. (2012) showed that increasing soil P in a New Zealand temperate forest favoured species with high leaf N and P. Spatial heterogeneity created by patchy disturbances can also interact with trait variation....

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Journal ArticleDOI
TL;DR: It is demonstrated that a reliable test for changes in assembly processes along stress gradients requires functional diversity indices measuring either functional richness or functional divergence, which provide good power to test for increasing niche complementarity with declining stress across a broad range of ecological contexts.
Abstract: Question Which functional diversity indices have the power to reveal changes in community assembly processes along abiotic stress gradients? Is their power affected by stochastic processes and variations in species richness along stress gradients? Methods We used a simple community assembly model to explore the power of functional diversity indices across a wide range of ecological contexts. The model assumes that with declining stress the influence of niche complementarity on species fitness increases while that of environmental filtering decreases. We separately incorporated two trait-independent stochastic processes – mass and priority effects – in simulating species occurrences and abundances along a hypothetical stress gradient. We ran simulations where species richness was constant along the gradient, or increased, decreased or varied randomly with declining stress. We compared observed values for two indices of functional richness – total functional dendrogram length (FD) and convex hull volume (FRic) – with a matrix-swap null model (yielding indices SESFD and SESFRic) to remove any trivial effects of species richness. We also compared two indices that measure both functional richness and functional divergence – Rao quadratic entropy (Rao) and functional dispersion (FDis) – with a null model that randomizes abundances across species but within communities. This converts them to pure measures of functional divergence (SESRao and SESFDis). Results When mass effects operated, only SESRao and SESFDis gave reasonable power, irrespective of how species richness varied along the stress gradient. FD, FRic, Rao and FDis had low power when species richness was constant, and variation in species richness greatly influenced their power. SESFRic and SESFD were unaffected by variation in species richness. When priority effects operated, FRic, SESFRic, Rao and FDis had good power and were unaffected by variation in species richness. Variation in species richness greatly affected FD and SESFD. SESRao and SESFDis had low power in the priority effects model but were unaffected by variation in species richness. Conclusions Our results demonstrate that a reliable test for changes in assembly processes along stress gradients requires functional diversity indices measuring either functional richness or functional divergence. We recommend using SESFRic as a measure of functional richness and either SESRao or SESFDis (which are very closely related mathematically) as a measure of functional divergence. Used together, these indices of functional richness and functional divergence provide good power to test for increasing niche complementarity with declining stress across a broad range of ecological contexts.

328 citations


Cites background from "Changes in coexistence mechanisms a..."

  • ...Functional richness should increase when niche complementarity enhances probabilities of species occurrence (Mason et al. 2012)....

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  • ...…that functional diversity should decline with stress assumes facilitation effectswill beminor comparedwith the influence of environmental filtering in stressed communities and is based on field evidence from plant communities occurring along a soil phosphorus gradient (Mason et al. 2012)....

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  • ...There is recent field evidence for this in plant communities (Mason et al. 2012)....

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  • ...There is a good precedent for this based on field studies showing that single traits may simultaneously influence species’ occurrences along stress gradients as well as influencing competitive interactions between species at the local community level (Cornwell & Ackerly 2009; Mason et al. 2012)....

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  • ...Functional divergence should increase when niche complementarity enhances species’ relative abundances (Mason et al. 2012)....

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Journal ArticleDOI
TL;DR: This study highlights how the combination of abundance data with traits capturing different functional niches is critical to the detection of complex functional responses of plant communities to environmental gradients, and demonstrates that patterns of trait divergence and filtering are strongly contingent on both trait and environment.
Abstract: Summary 1. Understanding how environmental factors drive plant community assembly remains a major challenge in community ecology. The strength of different assembly processes along environmental gradients, such as environmental filtering and functional niche differentiation, can be quantified by analysing trait distributions in communities. While environmental filtering affects species occurrence among communities, functional divergence or convergence is strongly related to species abundances within communities, which few studies have taken into account. We examine the trait-mediated effect of these two processes along a stress-resource gradient. 2. We measured species abundances and the distributions of eight traits related to vegetative and regenerative phases in plant communities along a gradient of soil depth and resource availability in Mediterranean rangelands. We quantified environmental filtering, defined as a local restriction of trait range, and trait divergence, based on abundance-weighted trait variance, using a two-step approach with specifically designed null models. 3. Communities presented a clear functional response to the soil gradient, as evidenced by strong trends in community-weighted trait means. We detected environmental filtering of different traits at both ends of the gradient, suggesting that, contrary to widespread expectations, trait filtering may not necessarily be the result of abiotic filtering under harsh conditions but could likely also result from biotic interactions in productive habitats. 4. We found marked shifts in trait abundance distributions within communities along the gradient. Vegetative traits (e.g. leaf dry matter content) diverged on shallow soils, reflecting the coexistence of distinct water- and nutrient-use strategies in these constrained habitats and converged with increasing soil resource availability. By contrast, regenerative traits (e.g. seed mass) tended to diverge towards deeper soils, while plant reproductive heights diverged all along the gradient. 5. Synthesis: Our study highlights how the combination of abundance data with traits capturing different functional niches is critical to the detection of complex functional responses of plant communities to environmental gradients. We demonstrate that patterns of trait divergence and filtering are strongly contingent on both trait and environment such that there can be no expectation of a simple trend of increasing or decreasing functional divergence along a gradient of resource availability.

321 citations


Cites result from "Changes in coexistence mechanisms a..."

  • ...Schamp, Chau & Aarssen 2008) and often contradictory results (e.g. Weiher, Clarke & Keddy 1998; Pakeman, Lennon & Brooker 2011; Mason et al. 2012)....

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  • ...Despite the allure of these ideas, previous efforts for detecting trait assembly patterns have yielded sometimes inconclusive (e.g. Schamp, Chau & Aarssen 2008) and often contradictory results (e.g. Weiher, Clarke & Keddy 1998; Pakeman, Lennon & Brooker 2011; Mason et al. 2012)....

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Journal ArticleDOI
TL;DR: The strength and direction of inter- and intraspecific plant community trait responses along a 900 m elevation gradient spanning alpine and subalpine plant communities in southern New Zealand are quantified to reveal highly complex plastic responses of plants to environmental changes, and highlight the need for greater consideration of the role that intrapecific variation plays in community-level processes.
Abstract: Summary 1. Despite widespread focus on interspecific variation in trait-based ecology, there is growing evidence that intraspecific trait variability can play a fundamental role in plant community responses to environmental change and community assembly. 2. Here, we quantify the strength and direction of inter- and intraspecific plant community trait responses along a 900 m elevation gradient spanning alpine and subalpine plant communities in southern New Zealand. We measured five commonly used leaf traits (i.e. dry matter content, N and P concentrations, leaf area and specific leaf area) on all 31 dominant and subordinate species recorded along the gradient, and examined their species-specific and community-level responses to elevation using both abundance-weighted and nonweighted averages of trait values. 3. By decomposing the variance of community-level measures of these traits across the gradient, we showed that the contribution of interspecific variation to the response of plant assemblages to elevation was stronger than that of intraspecific variation, for all traits except specific leaf area. Further, the relative contributions of interspecific effects were greater when abundance-weighted rather than nonweighted measures were used. We also observed contrasting intraspecific trait responses to the gradient among species (particularly for leaf N and P concentrations), and found both positive and negative covariation between inter- and intraspecific effects on community-level trait values. 4. The weak community-average trait responses to elevation, as found for specific leaf area (SLA) and leaf N and P concentrations, resulted from strong but opposing responses among vs. within species, which are not typically accounted for in species-based measures of plant community responses. For instance, increasing elevation (and associated factors such as a decrease in soil nutrient availability) favoured the dominance of species with relatively high leaf nutrient concentrations while simultaneously triggering an intraspecific decrease in the leaf nutrient concentrations of these species. 5. The context dependency of positive and negative covariation between inter- and intraspecific trait variability, and the species-specific nature of intraspecific shifts in functional trait values, reveal highly complex plastic responses of plants to environmental changes, and highlights the need for greater consideration of the role that intraspecific variation plays in community-level processes.

279 citations


Additional excerpts

  • ...Nonweighted average trait values for each trait in each plot were calculated as the mean of all collected species, including all dominant and subordinate species but excluding rare species (Mason et al. 2012)....

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References
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Book
19 Jun 2013
TL;DR: The second edition of this book is unique in that it focuses on methods for making formal statistical inference from all the models in an a priori set (Multi-Model Inference).
Abstract: Introduction * Information and Likelihood Theory: A Basis for Model Selection and Inference * Basic Use of the Information-Theoretic Approach * Formal Inference From More Than One Model: Multi-Model Inference (MMI) * Monte Carlo Insights and Extended Examples * Statistical Theory and Numerical Results * Summary

36,993 citations


"Changes in coexistence mechanisms a..." refers background or methods in this paper

  • ...In all analyses, evidence for nonlinear (logarithmic, quadratic and power) relationships was assessed using Akaike Information Criterion (AIC) weights (Burnham & Anderson 2002)....

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  • ...The linear model was rejected if one of the nonlinear models received a weight of > 0.9 (which would indicate a >90% chance that the nonlinear model was the most parsimonious, Burnham & Anderson 2002)....

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Journal ArticleDOI
22 Apr 2004-Nature
TL;DR: Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.
Abstract: Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.

6,360 citations


"Changes in coexistence mechanisms a..." refers background or methods in this paper

  • ...We chose to analyse patterns for four traits (Leaf N, Leaf P, thickness and density) as they are closely aligned to the global leaf economics spectrum (Wright et al. 2004) and thus are reliable indicators of plant resource-use strategy....

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  • ...Changes in functional diversity for key traits linked to plant resource-use strategy (Grime 1974; Wright et al. 2004) along ecological gradients can reveal shifts in species coexistence*Correspondence author....

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  • ...We explore shifts in resource-use strategy by examining changes in species means for foliar traits (leaf N and P, leaf thickness and density) used to contrast fast and leaky resource acquirers with slow and tight resource retainers (Cornelissen et al. 2003; Diaz et al. 2004; Wright et al. 2004)....

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Journal ArticleDOI
01 Mar 1973-Ecology
TL;DR: Three commonly used measures of diversity, Simpson's index, Shannon's entropy, and the total number of species, are related to Renyi's definition of a generalized entropy, according to which there is a continuum of possible diversity measures.
Abstract: Three commonly used measures of diversity, Simpson's index, Shannon's entropy, and the total number of species, are related to Renyi's definition of a generalized entropy. A unified concept of diversity is presented, according to which there is a continuum of possible diversity measures. In a sense which becomes apparent, these measures provide estimates of the effective number of species present, and differ only in their tendency to include or to ignore the relatively rarer species. The notion of the diversity of a community as opposed to that of a sample is examined, and is related to the asymptotic form of the species—abundance curve. A new and plausible definition of evenness is derived.

4,957 citations

Journal ArticleDOI
TL;DR: It is shown that when an individual dies, it may or may not be replaced by an individual of the same species, which is all‐important to the argument presented.
Abstract: SUMMARY 1According to ‘Gause's hypothesis’ a corollary of the process of evolution by natural selection is that in a community at equilibrium every species must occupy a different niche. Many botanists have found this idea improbable because they have ignored the processes of regeneration in plant communities. 2Most plant communities are longer-lived than their constituent individual plants. When an individual dies, it may or may not be replaced by an individual of the same species. It is this replacement stage which is all-important to the argument presented. 3Several mechanisms not involving regeneration also contribute to the maintenance of species-richness: (a). differences in life-form coupled with the inability of larger plants to exhaust or cut off all resources, also the development of dependence-relationships, (b) differences in phenology coupled with tolerance of suppression, (c) fluctuations in the environment coupled with relatively small differences in competitive ability between many species, (d) the ability of certain species-pairs to form stable mixtures because of a balance of intraspecific competition against interspecific competition, (e) the production of substances more toxic to the producer-species than to the other species, (f) differences in the primary limiting mineral nutrients or pore-sizes in the soil for neighbouring plants of different soecies, and (g) differences in the competitive abilities of species dependent on their physiological age coupled with the uneven-age structure of many populations. 4The mechanisms listed above do not go far to explain the indefinite persistence in mixture of the many species in the most species-rich communities known. 5In contrast there seem to be almost limitless possibilities for differences between species in their requirements for regeneration, i.e. the replacement of the individual plants of one generation by those of the next. This idea is illustrated for tree species and it is emphasized that foresters were the first by a wide margin to appreciate its importance. 6The processes involved in the successful invasion of a gap by a given plant species and some characters of the gap that may be important are summarized in Table 2. 7The definition of a plant's niche requires recognition of four components: (a) the habitat niche, (b) the life-form niche, (c) the phenological niche, and (d) the regeneration niche. 8A brief account is given of the patterns of regeneration in different kinds of plant community to provide a background for studies of differentiation in the regeneration niche. 9All stages in the regeneration-cycle are potentially important and examples of differentiation between species are given for each of the following stages: (a) Production of viable seed (including the sub-stages of flowering, pollination and seed-set), (b) dispersal, in space and time, (c) germination, (d) establishment, and (e) further development of the immature plant. 10In the concluding discussion emphasis is placed on the following themes: (a) the kinds of work needed in future to prove or disprove that differentiation in the regeneration niche is the major explanation of the maintenance of species-richness in plant communities, (b) the relation of the present thesis to published ideas on the origin of phenological spread, (c) the relevance of the present thesis to the discussion on the presence of continua in vegetation, (d) the co-incidence of the present thesis and the emerging ideas of evolutionists about differentiation of angiosperm taxa, and (e) the importance of regeneration-studies for conservation.

4,057 citations

Journal ArticleDOI
TL;DR: The total number of species is proportional to the total range of the environment divided by the niche breadth of the species, which is reduced by unequal abundance of resources but increased by adding to the dimensionality of the niche.
Abstract: 1. There is a limit to the similarity (and hence to the number) of competing species which can coexist. The total number of species is proportional to the total range of the environment divided by the niche breadth of the species. The number is reduced by unequal abundance of resources but increased by adding to the dimensionality of the niche. Niche breadth is increased with increased environmental uncertainty and with decreased productivity. 2. There is a different evolutionary limit, L, to the similarity of two coexisting species such that a) If two species are more similar than L, a third intermediate species will converge toward the nearer of the pair. b) If two species are more different than L, a third intermediate species will diverge from either toward a phenotype intermediate between the two.

3,946 citations

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