Conventional functional classification schemes underestimate the relationship with ecosystem functioning

Studies linking the functional diversity of a biota to ecosystem functioning typically employ a priori classifications of species into hypothetically complementary groups. However, multiple alternate classifications exist in which the number of functional groups, the number of species per functional group, and the grouping of species differ from the a priori scheme. Without assessing the relative precision, or ability of an a priori scheme to accurately predict ecosystem functioning relative to its many alternatives, the validity and utility of analyses based on a single a priori classification scheme remains unclear. We examine the precision of a priori classifications used in 10 experimental grassland systems in Europe and the United States that have found evidence for a significant role of functional plant diversity in governing ecosystem function. The predictive precision of the a priori classifications employed in these studies was seldom significantly higher than the precision of random classifications. Post-hoc classification schemes that performed well in predicting ecosystem function resembled each other more with regard to species composition than average classifications, but there was still considerable variability in the manner in which these classification schemes grouped species. These results suggest that we need a more nuanced understanding of how the diversity of functional traits of species in an assemblage affects ecosystem functioning.     

Soil fungal communities reflect aspect-driven environmental structuring and vegetation types in a Pannonian forest landscape

In temperate regions, slope aspect is one of the most influential drivers of environmental conditions at landscape level. The effect of aspect on vegetation has been well studied, but virtually nothing is known about how fungal communities are shaped by aspect-driven environmental conditions. I carried out DNA metabarcoding of fungi from soil samples taken in a selected study area of Pannonian forests in northern Hungary to compare richness and community composition of taxonomic and functional groups of fungi between slopes of predominantly southerly vs. northerly aspect. The deep sequence data presented here (i.e. 980 766 quality-filtered sequences) indicate that both niche (environmental filtering) and neutral (stochastic) processes shape fungal community composition at landscape level. Fungal community composition correlated strongly with aspect, with many fungi showing preference for either south-facing or north-facing slopes. Several taxonomic and functional groups showed significant differences in richness between north- and south-facing slopes and strong compositional differences were observed in all functional groups. The effect of aspect on fungal communities likely is mediated through contrasting mesoclimatic conditions, that in turn influence edaphic processes as well as vegetation. The compositional differences observed in fungi are largely consistent with the coenologically described forest types, which indicates the usefulness of these habitat types as a framework to better understand environmental differences that influence fungal community composition at landscape level. Finally, the data presented here provide unprecedented insights into the diversity and landscape-level community dynamics of fungi in the Pannonian forests.     

Beauty before age: landscape factors influence bird functional diversity in naturally regenerating fragments,but regeneration age does not

Effective ecological restoration actions should be able to recover ecosystem processes that influence community development in the long term. However, there is scarce information on how landscape factors promote or accelerate fauna recovery. We used a landscape framework to evaluate how functional groups respond to natural regeneration in a highly fragmented region of Atlantic Forest. Using bird functional groups sampled in 15 regenerating forest fragments, we built and ranked models using a model selection approach to test the relative effect of landscape variables on each group. Our results showed that bird community recovery is not determined by the duration of the regeneration process (i.e. forest age), but by how the species responds to the landscape context. Functional diversity and the abundance of the functional groups were mainly related to composition metrics, whereas the functional metric affected only specific groups. Our findings highlight the importance of considering the landscape level to ensure both the colonization of fauna and the restoration of ecological functions.     

Extinction–immigration dynamics lag behind environmental filtering in shaping the composition of tropical dry forests within a changing landscape

The impact of rapid habitat loss and fragmentation on biodiversity is a major issue. However, we still lack an integrative understanding of how these changes influence biodiversity dynamics over time. In this study, we investigate the effects of these changes in terms of both niche-based and neutral dynamics. We hypothesize that habitat loss has delayed effects on neutral immigration–extinction dynamics, while edge effects and environmental heterogeneity in habitat patches have rapid effects on niche-based dynamics. We analyzed taxonomic and functional composition of 100 tree communities in a tropical dry forest landscape of New-Caledonia subject to habitat loss and fragmentation. We designed an original, process-based simulation framework, and performed Approximate Bayesian Computation to infer the influence of niche-based and neutral processes. Then, we performed partial regressions to evaluate the relationships between inferred parameter values of communities and landscape metrics (distance to edge, patch area, and habitat amount around communities), derived from either recent or past (65 yr ago) aerial photographs, while controlling for the effect of soil and topography. We found that landscape structure influences both environmental filtering and immigration. Immigration rate was positively related to past habitat amount surrounding communities. In contrast, environmental filtering was mostly affected by present landscape structure and mainly influenced by edge vicinity and topography. Our results highlight that landscape changes have contrasting spatio-temporal influences on niche-based and neutral assembly dynamics. First, landscape-level habitat loss and community isolation reduce immigration and increase demographic stochasticity, resulting in slow decline of local species diversity and extinction debt. Second, recent edge creation affects environmental filtering, incurring rapid changes in community composition by favoring species with edge-adapted strategies. Our study brings new insights about temporal impacts of landscape changes on biodiversity dynamics. We stress that landscape history critically influences these dynamics and should be taken into account in conservation policies.     

Plant functional classifications: from general groups to specific groups based on response to disturbance

Predicting the effects of anthropogenic changes in climate, atmospheric composition and land use on vegetation patterns has been a central concern of recent ecological research. This aim has revived the search for classification schemes that can be to group plant species according to their response to specified environmental factors. One way forward is to adopt a hierarchical classification, where different sets of traits are examined depending on growth form. Also, at the level of interpretation, the environmental context and purpose of functional classifications need to be specified explicitly, so that global generalizations can be made by comparing across environments functional classifications derived from similar methodologies.     

Predicting local biological characteristics in streams: a comparison of landscape classifications

1. Landscape classifications group tracts of land based on similar physico‐chemical attributes that may affect the biological characteristics of streams at local scales. We tested the ability of five landscape models to account for variation in algal and macroinvertebrate biomass, brook trout (Salvelinus fontinalis) growth and macroinvertebrate community composition from 132 riffles in 15 catchments in the Big Horn Mountains, Wyoming. 2. A model created by the U.S. Forest Service (FS) combined catchment and ecoregion approaches to classify the landscape. Our model used digital elevations to create a landscape classification for streams (DEM). The last three models were based on: (1) standard ecoregions (Ecoregion), (2) the type of underlying bedrock (Geology) and (3) the geographical distance between sites (Site Proximity model). 3. Overall, the Ecoregion and Geology models performed better than the two catchment models (FS and DEM) in predicting local biological characteristics. The Geology model was best at predicting differences in algal and macroinvertebrate biomass, the Site Proximity and Ecoregion models were best at predicting patterns of similarity in macroinvertebrate community composition, and the Site Proximity, Ecoregion, Geology, and FS models, in order from best to worst, accounted for significant variation in brook trout growth. The Site Proximity model performed well because of the effects of spatial autocorrelation. The DEM was consistently one of the worst models at predicting local biological characteristics because it failed to include important attributes (e.g. dominant geology). Calcareous geology was positively associated with greater macroinvertebrate biomass and faster brook trout growth, but it was inversely related to algal biomass. 4. None of the models accounted for a large amount of variation in local biological characteristics. Single‐scale, landscape classifications may never accurately predict variation in local biological characteristics because: (1) landscapes show a high degree of spatial heterogeneity, (2) local effects are stronger than landscape attributes and (3) there are too many intervening levels between landscape and local scales in the nested hierarchy of streams. However, landscape classifications did account for significant variation in biological characteristics. Thus, they would be a valuable management tool as part of a multi‐scale, hierarchical technique for classifying stream ecosystems.     

热带森林植物功能群及其动态研究进展

热带森林极高的物种多样性和结构复杂性给生态学研究带来了很多挑战。植物功能群是对特定环境响应相似或对主要的生态过程具有相似作用的物种组合。应用植物功能群的方法是有效减少热带森林群落复杂性,并揭示其格局和过程的良好途径。在介绍植物功能群概念和划分途径的基础上,分析了热带森林植物功能群的时空动态规律。一般来讲,划分植物功能群通常有3种途径,并可通过5个步骤来完成。热带森林植物功能群的空间分布常受景观格局的制约,而环境异质性往往是影响不同植物功能群组配比例变化的直接原因。不同类型的植物功能群随演替过程发生显著的替代,而干扰体系和全球气候变化对功能群的动态过程具有重要的驱动作用。以功能群为基础的动态模型在模拟热带林群落动态和预测植被潜在分布等方面具有广阔的发展前景。探索有效的植物功能分类方法、构建完善的植物功能性状数据库、开发更为精确的功能群动态模型以及加强基于景观水平的植物功能群动态机制的认识等是未来热带森林植物功能群及其动态研究的重要方向。     

Can functional classification of tropical trees predict population dynamics after disturbance?

Question: How far can we simplify the fioristic complexity of a tropical rainforest into functional groups in order to predict tree population dynamics after logging‐induced disturbance? Location: Paracou experimental site, French Guiana. Methods: We used data from over 15 years in control and disturbed plots from a silvicultural trial started in 1984. We selected 53 common tree species assigned to five functional groups based on potential size and light requirement. For each species, we quantified: the fate, i.e. variation in population size, and dynamic processes, i.e. mortality, recruitment and growth, driving this fate. We investigated the links between dynamic processes, fate and functional groups. Results: Disturbance stimulated growth and recruitment for most species, but had a heterogeneous impact on mortality. Species fate in disturbed plots depended on recruitment and was more favourable than in control plots. The functional classification was more predictive for most separate dynamic processes than for species fate: after disturbance, significant differences were found between all functional groups for growth. Pioneer+heliophilous species showed significantly higher recruitment rates. Mortality of shade‐tolerant species slightly increased and of mid‐tolerant and heliophilous species decreased. Conclusions: A combination of three species classifications separately built from the growth, recruitment and mortality processes is more informative than a global classification combining the processes. Identifying the pioneer+heliophilous species on the basis of their growth rate is crucial to predict species fate after disturbance. We showed that potential growth rate could be used as a reliable indicator to identify this group.     

Functional spatial scale of community composition change in response to windthrow disturbance in a deciduous temperate forest

Community dynamics in local habitats are affected by landscape characteristics such as the area and connectivity of surrounding habitats at a functional spatial scale where the community responds to landscape structure. However, the functional spatial scale at which community composition is affected by landscape structure has never been explored. We assessed the functional spatial scales of composition change in birds and in three types of arthropod communities (canopy, forest-floor and flying ones) with regard to landscape heterogeneity resulting from a large typhoon in a temperate forest of Japan. We examined the effects of tree-fall disturbance on the communities at various spatial scales, with special attention to compositional evenness. The spatial scale of the best-fitting model, which was selected from models fitted to the disturbance area at stepwise spatial scales, was interpreted as the community-specific functional spatial scale. The composition of all communities studied was all significantly dependent on gap area. The functional spatial scale was highest in birds (370 m in radius), intermediate in flying arthropods (90 m) and lowest in canopy and forest-floor arthropods (10 m). This result may reflect typical dispersal ability and the spatial range of resource use in the community. Compositional changes in each community were consistent with theory regarding traits and responses of component taxa, although the enhancement of evenness was observed only in the arthropod communities. These results imply that management and reserve selection based on functional spatial scales can be effective in the conservation of biodiversity and ecosystem services at the community level.     

A trait-based approach for modelling microbial litter decomposition

Trait-based models are an emerging tool in ecology with the potential to link community dynamics, environmental responses and ecosystem processes. These models represent complex communities by defining taxa with trait combinations derived from prior distributions that may be constrained by trade-offs. Herein I develop a model that links microbial community composition with physiological and enzymatic traits to predict litter decomposition rates. This approach allows for trade-offs among traits that represent alternative microbial strategies for resource acquisition. The model predicts that optimal strategies depend on the level of enzyme production in the whole community, which determines resource availability and decomposition rates. There is also evidence for facilitation and competition among microbial taxa that co-occur on decomposing litter. These interactions vary with community investment in extracellular enzyme production and the magnitude of trade-offs affecting enzyme biochemical traits. The model accounted for 69% of the variation in decomposition rates of 15 Hawaiian litter types and up to 26% of the variation in enzyme activities. By explicitly representing diversity, trait-based models can predict ecosystem processes based on functional trait distributions in a community. The model developed herein illustrates that traits influencing microbial enzyme production are some of the key controls on litter decomposition rates.     

Methods for tracking sagebrush‐steppe community trajectories and quantifying resilience in relation to disturbance and restoration

Understanding how plant community dynamics are impacted by altered disturbance regimes is a pressing challenge for restoration ecology. Most assessments of community dynamics involve computationally intensive statistical techniques, while management often defers to derived, qualitative “state‐and‐transition” models. Here, we demonstrate an intermediate approach to track and predict community resilience, diversifying the tools available to assess ecosystem change. First, we develop indices of sagebrush‐steppe community structure in permanent monitoring plots based on plant functional types and our conceptual understanding of the ecosystem. The indices define a bivariate space within which the trajectories of permanent monitoring plots can be tracked. Second, we quantify two metrics of community resilience: resistance (overall change during the time period) and stability (average amount of movement per monitoring period). Plots dominated by obligate seeder shrubs displayed low resilience relative to those dominated by grasses and forbs or resprouting shrubs. Resilience was strongly related to initial plant functional type composition and elevation. Our results suggest restoration objectives should consider how plant traits control ecosystem responses to disturbance. We suggest that the approach developed here can help assess longer‐term resilience, evaluate restoration success, and identify communities at risk of state transitions.     

A comparison of five classifications of species into functional groups in tropical forests of French Guiana

Classifying species into functional groups is a way to understand the functioning of species-rich ecosystems, or to model the dynamics of such ecosystems. Many statistical techniques have been defined to classify species into groups, and a question is whether different techniques bring consistent classifications. In a tropical rain forest in French Guiana, five species classifications have been defined by different authors for the purpose of forest growth modelling but using different data sets and different statistical techniques. The correspondence between the five classifications was measured using four indices that are generalizations of existing indices to compare two classifications. A multiple correspondence analysis was used to identify associations between groups of different classifications. In a second step, two-table multivariate analyses were used to characterize the relationships between species classifications and eight species traits (consisting of seven populational traits and one functional trait). We evidenced a consensus on the potential size of trees: species were similarly clustered by the five classifications along this trait that is correlated to turnover rate. More surprisingly, no consensus was found for growth rate, nor wood density, traits that are correlated with light requirement.     

Functional traits,spatial patterns and species associations: what is their combined role in the assembly of wetland plant communities?

Studies of community assembly focus on finding rules that predict which species can become member of a plant community. Within a community, species can be categorized in two ways: functional groups classify species according to their functional traits, whereas generalized guilds group species based on their (co-)occurrence, spatial distribution and abundance patterns. This study searches for community assembly rules by testing for coherence among functional groups and generalized guilds, as well as for correlations between the individual functional traits and assembly features, in two wetland plant communities in South Africa. The classifications of functional groups and generalized guilds were not consistent. However, rhizome internode length was related to fine-scale spatial pattern, suggesting that in systems dominated by clonal species (including wetlands, where recruitment sites are strongly limited) community assembly may be strongly linked to colonization ability. Functional groups do not predict guilds in wetland plant communities, precluding their use as the basis for assembly rules. However, an explicit consideration of clonal strategies and their effect on species’ spatial patterns appears to be important for understanding community assembly in systems dominated by clonal plants.     

The ecological causes of functional distinctiveness in communities

Recent work has shown that evaluating functional trait distinctiveness, the average trait distance of a species to other species in a community offers promising insights into biodiversity dynamics and ecosystem functioning. However, the ecological mechanisms underlying the emergence and persistence of functionally distinct species are poorly understood. Here, we address the issue by considering a heterogeneous fitness landscape whereby functional dimensions encompass peaks representing trait combinations yielding positive population growth rates in a community. We identify four ecological cases contributing to the emergence and persistence of functionally distinct species. First, environmental heterogeneity or alternative phenotypic designs can drive positive population growth of functionally distinct species. Second, sink populations with negative population growth can deviate from local fitness peaks and be functionally distinct. Third, species found at the margin of the fitness landscape can persist but be functionally distinct. Fourth, biotic interactions (positive or negative) can dynamically alter the fitness landscape. We offer examples of these four cases and guidelines to distinguish between them. In addition to these deterministic processes, we explore how stochastic dispersal limitation can yield functional distinctiveness. Our framework offers a novel perspective on the relationship between fitness landscape heterogeneity and the functional composition of ecological assemblages.     

Habitat fragmentation, variable edge effects, and the landscape-divergence hypothesis

Edge effects are major drivers of change in many fragmented landscapes, but are often highly variable in space and time. Here we assess variability in edge effects altering Amazon forest dynamics, plant community composition, invading species, and carbon storage, in the world's largest and longest-running experimental study of habitat fragmentation. Despite detailed knowledge of local landscape conditions, spatial variability in edge effects was only partially foreseeable: relatively predictable effects were caused by the differing proximity of plots to forest edge and varying matrix vegetation, but windstorms generated much random variability. Temporal variability in edge phenomena was also only partially predictable: forest dynamics varied somewhat with fragment age, but also fluctuated markedly over time, evidently because of sporadic droughts and windstorms. Given the acute sensitivity of habitat fragments to local landscape and weather dynamics, we predict that fragments within the same landscape will tend to converge in species composition, whereas those in different landscapes will diverge in composition. This 'landscape-divergence hypothesis', if generally valid, will have key implications for biodiversity-conservation strategies and for understanding the dynamics of fragmented ecosystems.     

Homogeneity analysis: Assessing the utility of classifications and maps of natural resources

Abstract A quantitative measure of homogeneity, based on the average within-group association between samples, is proposed as a multivariate measure of the information content of classifications and maps. Homogeneity analyses are used to investigate questions of scale and the choice of attributes in the context of vegetation mapping. Previous studies in classification and mapping of soil types suggested that an optimum map scale or number of classification groups can be defined using homogeneity. This does not seem to be the case with vegetation data although homogeneity analysis can be used to define the coarsest acceptable scale and to quantity the benefits of mapping at finer scales. Homogeneity analysis is used here to compare the information content of classifications derived from various attributes with one based on the whole flora. For the data set examined, a classification derived from canopy species composition is as informative as one based on full rloristic composition for the scales at which we would normally map, whereas an environmental classification is less so. Further applications of homogeneity analysis are suggested.     

植物功能多样性与功能群研究进展

综述了植物功能多样性与功能群研究的最新进展。介绍了植物功能群的定义及植物功能群的划分方法。在功能多样性与生态系统资源动态关系方面．抽样效应和生态位互补效应用来解释植物多样性在生态系统资源动态中的作用。功能多样性与生态系统的稳定性间的关系可以用生态冗余或生态保险概念来解释,这两个概念是一个问题的两个侧面,是多样性与生态系统功能争论的焦点。     

Multi‐scale habitat modification by coexisting ecosystem engineers drives spatial separation of macrobenthic functional groups

By changing habitat conditions, ecosystem engineers increase niche diversity and have profound effects on the distribution and abundances of other organisms. Although many ecosystems contain several engineering species, it is still unclear how the coexistence of multiple engineers affects the physical habitat and the structure of the community on a landscape scale. Here, we investigated through a large‐scale field manipulation how three coexisting engineers on intertidal flats (cockles Cerastoderma edule; lugworms Arenicola marina; blue mussels Mytilus edulis) influence the functional composition of the local macrobenthic community and what the consequences are at the landscape level. By using biological trait analysis (BTA), we show that on the local scale biogenic changes in sediment accumulation and organic matter content translated into specific shifts in the distribution of functional traits within the community. At a landscape scale, the co‐occurrence of multiple ecosystem engineers resulted in the spatial separation of different functional groups, i.e. different functional groups dominated unique complementary habitats. Our results emphasize the role of co‐occurring multiple engineers in shaping natural communities, thus contributing to a better knowledge of community assembly rules. This understanding can profitably be used to improve ecosystem‐based management and conservation actions.