Functional Trait Information Research Articles

Moss functional trait ecology: Trends, gaps, and biases in the current literature.

Functional traits are critical tools in plant ecology for capturing organism-environment interactions based on trade-offs and making links between organismal and ecosystem processes. While broad frameworks for functional traits have been developed for vascular plants, we lack the same for bryophytes, despite an escalation in the number of studies on bryophyte functional trait in the last 45 years and an increased recognition of the ecological roles bryophytes play across ecosystems. In this review, we compiled data from 282 published articles (10,005 records) that focused on functional traits measured in mosses and sought to examine trends in types of traits measured, capture taxonomic and geographic breadth of trait coverage, reveal biases in coverage in the current literature, and develop a bryophyte-function index (BFI) to describe the completeness of current trait coverage and identify global gaps to focus research efforts. The most commonly measured response traits (those related to growth/reproduction in individual organisms) and effect traits (those that directly affect community/ecosystem scale processes) fell into the categories of morphology (e.g., leaf area, shoot height) and nutrient storage/cycling, and our BFI revealed that these data were most commonly collected from temperate and boreal regions of Europe, North America, and East Asia. However, fewer than 10% of known moss species have available functional trait information. Our synthesis revealed a need for research on traits related to ontogeny, sex, and intraspecific plasticity and on co-measurement of traits related to water relations and bryophyte-mediated soil processes.

Frugivoria: A trait database for birds and mammals exhibiting frugivory across contiguous Neotropical moist forests

AbstractMotivationBiodiversity in many areas is rapidly declining because of global change. As such, there is an urgent need for new tools and strategies to help identify, monitor and conserve biodiversity hotspots. This is especially true for frugivores, species consuming fruit, because of their important role in seed dispersal and maintenance of forest structure and health. One way to identify these areas is by quantifying functional diversity, which measures the unique roles of species within a community and is valuable for conservation because of its relationship with ecosystem functioning. Unfortunately, the functional trait information required for these studies can be sparse for certain taxa and specific traits and difficult to harmonize across disparate data sources, especially in biodiversity hotspots. To help fill this need, we compiled Frugivoria, a trait database containing ecological, life‐history, morphological and geographical traits for mammals and birds exhibiting frugivory. Frugivoria encompasses species in contiguous moist montane forests and adjacent moist lowland forests of Central and South America—the latter specifically focusing on the Andean states. Compared with existing trait databases, Frugivoria harmonizes existing trait databases, adds new traits, extends traits originally only available for mammals to birds also and fills gaps in trait categories from other databases. Furthermore, we create a cross‐taxa subset of shared traits to aid in analysis of mammals and birds. In total, Frugivoria adds 8662 new trait values for mammals and 14,999 for birds and includes a total of 45,216 trait entries with only 11.37% being imputed. Frugivoria also contains an open workflow that harmonizes trait and taxonomic data from disparate sources and enables users to analyse traits in space. As such, this open‐access database, which aligns with FAIR data principles, fills a major knowledge gap, enabling more comprehensive trait‐based studies of species in this ecologically important region.Main Types of Variable ContainedEcological, life‐history, morphological and geographical traits.Spatial Location and GrainNeotropical countries (Mexico, Guatemala, Costa Rica, Panama, El Salvador, Belize, Nicaragua, Ecuador, Colombia, Peru, Bolivia, Argentina, Venezuela and Chile) with contiguous montane regions.Time Period and GrainIUCN spatial data: obtained February 2023, spanning range maps collated from 1998 to 2022. IUCN species data: obtained June 2019–September 2022. Newly included traits: span 1924 to 2023.Major Taxa and Level of MeasurementClasses Mammalia and Aves; 40,074 species‐level traits; 5142 imputed traits for 1733 species (mammals: 582; birds: 1147) and 16 sub‐species (mammals).Software Format.csv; R.

Functional rarity and evolutionary uniqueness of threatened species across different scales and habitats in a Central European flora

Abstract With the potential extinction of threatened species, communities and species pools could become functionally and phylogenetically impoverished, especially if threatened species had distinct traits and evolutionary histories compared to least concern species. Alternatively, threatened species would have similar traits and evolutionary histories, and their extinction could imply the loss of functionally and phylogenetically ‘redundant’ species. We tested whether threatened plant species are functionally and phylogenetically rarer than least concern species. We considered two scales of plant assemblage (plots and species pools) from an intensively sampled temperate region (Czech Republic), using a sample of 23,072 vegetation plots classified into eight habitat groups. We analysed the traits and phylogeny of 1,730 species of angiosperms recorded in these plots. We found that the potential loss of threatened species could have minor functional and phylogenetic consequences for the communities in any habitat and at each assemblage scale. However, detailed analysis of individual traits revealed that some threatened species tend to have some unique trait value, such as being small and having lighter seeds. Phylogenetically unique species tended to be the most functionally rare, although this pattern was only weakly significant. This generally suggests similar conservation strategies for functionally rare and evolutionarily unique species. Policy implications. We show how novel tools related to functional rarity and phylogenetic uniqueness could be used to understand the role of threatened species in communities and different habitat types. This allows to understand which species and habitats could provide great functional and phylogenetic contributions to biodiversity to better guide management and conservation programmes. To fully achieve this potential, greater efforts in collecting functional trait information for threatened species remain urgent as well as considering both individual and combined trait information when estimating the functional originality of species.

Machine learning techniques to characterize functional traits of plankton from image data.

Plankton imaging systems supported by automated classification and analysis have improved ecologists' ability to observe aquatic ecosystems. Today, we are on the cusp of reliably tracking plankton populations with a suite of lab‐based and in situ tools, collecting imaging data at unprecedentedly fine spatial and temporal scales. But these data have potential well beyond examining the abundances of different taxa; the individual images themselves contain a wealth of information on functional traits. Here, we outline traits that could be measured from image data, suggest machine learning and computer vision approaches to extract functional trait information from the images, and discuss promising avenues for novel studies. The approaches we discuss are data agnostic and are broadly applicable to imagery of other aquatic or terrestrial organisms.

Evaluating different methods for retrieving intraspecific leaf trait variation from hyperspectral leaf reflectance

Leaf mass per area (LMA), leaf dry matter content (LDMC) and leaf water content/ equivalent water thickness (EWT) are commonly used functional plant traits in ecology. Whereas spectroscopy has recently proven to be a powerful tool to collect such functional trait information across large scales, it remains unclear whether these reflectance-based trait predictions are accurate enough to reliably model trait variation at the intraspecific level (i.e. across individuals of one species). We explored the potential of hyperspectral leaf reflectance-based methods to predict LMA, LDMC and EWT at the intraspecific level for two herbs (Hieracium umbellatum and Jacobaea vulgaris) and two shrubs (Rosa rugosa and Rubus caesius), based on 2400 leaf samples. More specifically we tested i) inversion of the PROSPECT-D radiative transfer model, ii) a generic PLSR approach using the multibiome LMA PLSR model and iii) a data-specific PLSR approach at the species level. For the latter approach we furthermore assessed both model transferability across species and the trade-off between sample size and model accuracy. Although the PROSPECT-D model inversion and the multibiome LMA PLSR model were relatively accurate for intraspecific LMA predictions of shrubs (R2 > 71 and 76%, respectively, however NRMSE = 33–47%), their performance was lower for herbs (R2 < 61%, NRMSE = 28–50%). PROSPECT-D was furthermore slightly less successful in retrieving EWT at the intraspecific level (R2 < 70%, NRMSE = 16–43%), and unsuccessful in retrieving LDMC through combining LMA and EWT inversion results (R2 < 10%, NRMSE = 9–192%). The highest correlation accuracy was obtained for all three traits with the species-specific PLSR models (R2 > 70%, NRMSE < 10%). If high predictive accuracy is needed, we thus suggest the use of species-specific PLSR models. The training of species-specific PLSR models comes at the cost of a needed sample size of 100–160 leaves however, depending on the trait. Although transferability of species-specific PLSR models seems limited overall, our results suggest potentially high transferability across herbaceous species.

Conservation biogeography of the terrestrial mammals in Iran: diversity patterns, and vulnerability to climate change and extinction

Under the framework of a “conservation biogeography” approach, initially, I reviewed and updated the taxonomy and distribution of the rich but understudied mammalian diversity of Iran. This data then formed the basis for the biogeographical regionalization of this complex transitional area using hierarchical clustering and infomap network methods. I used linear models to explore the correlates of extinction risk for this threatened mammalian fauna. Functional grouping of target species was used to assess their vulnerability to the magnitude and velocity of climate change impacts. Both clustering and network methods successfully illuminated the intricate biogeographic patterns, while the network detected many more small bioregions, including two transition zones. The extinction risk analyses revealed that human activities, such as hunting and persecuting (direct impacts) played a major role in the decline of these taxa, as opposed to minor effect of indirect and instrinsic and extrinsic factors. The magnitude and velocity of climate change impacts varied significantly between functional groups, with the highest risk of exposure to extreme climates in large and threatened species occurring in lowlands. This study provides a foundation for future biogeographic, systematics and ecological studies of Iranian mammals while simultaneously adding to the limited available information on the bioregionalization at regional scales. And it highlights the importance of incorporating threats in extinction risk models and functional trait information in climate change impact assessments.

Canopy Leaf Traits, Basal Area, and Age Predict Functional Patterns of Regenerating Communities in Secondary Subtropical Forests

Secondary forests originate from natural regeneration after fallow (succession) or restoration. Species assembly in these communities, which can affect ecosystem functions and successional trajectories, is very unpredictable. Trait-based trajectories can shed light on the recovery of ecosystem functions and enable predictions of how the regenerating communities will change with forest age. Regeneration communities are affected by initial conditions and also by canopy structure and functional traits that alter dispersers' attractiveness and coexistence mechanisms. Here we evaluated how community functional traits change over time and tested if functional diversity and composition of the established canopy, as well as the structure of the canopy and forest age, influence the functional structure of regenerating tree communities when compared to their reference forests. For this, we calculated dissimilarity in trait composition (community-weighted means) and in functional diversity of regenerating communities of each succession/restoration stand, using the tree stratum of nearby mature forests as baseline values. Functional trait information comprises leaf, wood density, and reproductive traits from tree species. Our community data contain information from natural successional forests and restoration sites, in the South-Brazilian Atlantic Forest. Predictor variables of functional dissimilarities were forest age, canopy structural variables, canopy functional composition, and functional diversity. Results showed leaf traits (leaf dry matter content, leaf nitrogen content, leaf nitrogen-phosphorus ratio) and seed mass varying with forest age. Canopy functional composition based on leaf traits and total basal area significantly predicted multiple trait functional dissimilarity between the regeneration component of secondary forests and their reference community values. Dissimilarity increased when the canopy was composed of species with more acquisitive traits. Difference in functional diversity was only influenced by forest age. Mid-stage secondary forests showed lower functional diversity than early-stage forests. Our results indicated the importance of canopy traits on the natural regeneration of secondary subtropical forests. If functional similarity with reference forests is a desired objective in order to recover ecosystem functions through natural regeneration, leaf functional traits of canopy trees that establish or are planted in degraded areas must be considered in the successional processes.

A synthesis of life‐history traits, functional traits, and consequences of anthropogenic pressures on Madagascar’s threatened carnivorans, Eupleridae

Abstract Madagascar’s native carnivorans are an endemic monophyletic group of eight extant species belonging to the family Eupleridae. The International Union for Conservation of Nature (IUCN) currently classifies seven of the species as threatened (Vulnerable or Endangered), as their populations are in decline due to intensifying anthropogenic pressures. However, little is known about these species’ ecology and population trends, precluding forecasts of extinction risk. Life‐history and functional traits govern species’ responses to environmental pressure and can be predictive of extinction risk. Incorporating relevant trait information can vastly improve risk assessments. Yet, information on the life‐history and functional traits of the Eupleridae has never been compiled into a single framework. Our aims were to: 1) synthesise the current state of knowledge of the life‐history and functional traits of euplerid species, 2) review empirical evidence of the effects of anthropogenic pressures on species, and 3) identify knowledge gaps and future research needs. We searched the published literature to compile life‐history and functional trait information and known effects of anthropogenic pressures for Eupleridae. Our review indicates that Madagascar’s carnivorans have high‐risk life‐history and functional traits that increase their vulnerability to anthropogenic pressures. Publications reported negative effects on euplerids from habitat degradation and fragmentation, logging, non‐native carnivorans, disease, and hunting and retaliatory killings. However, our synthesis revealed significant knowledge gaps, especially in species’ life‐history traits and in the spatial variability in most traits. For most species, we currently do not have the robust data needed to assess trait‐based risk dynamics. The culmination of reported traits, negative influence of ongoing anthropogenic pressures, and lack of robust metrics (e.g. population trends and trait variability) indicate that euplerids are at high risk, yet may reach the cusp of extinction without notice due to significant gaps in knowledge. Future research should prioritise filling gaps in knowledge of influential traits, evaluating anthropogenic pressures, and integrating trait information to improve risk assessments and extinction forecasts.

A phylogenetic and trait-based analysis of community assembly in a subtropical forest in central China.

Despite several decades of study in community ecology, the relative importance of the ecological processes that determine species co‐occurrence across spatial scales remains uncertain. Some of this uncertainty may be reduced by studying the scale dependency of community assembly in the light of environmental variation. Phylogenetic information and functional trait information are often used to provide potentially valuable insights into the drivers of community assembly. Here, we combined phylogenetic and trait‐based tests to gain insights into community processes at four spatial scales in a large stem‐mapped subtropical forest dynamics plot in central China. We found that all of the six leaf economic traits measured in this study had weak, but significant, phylogenetic signal. Nonrandom phylogenetic and trait‐based patterns associated with topographic variables indicate that deterministic processes tend to dominate community assembly in this plot. Specifically, we found that, on average, co‐occurring species were more phylogenetically and functionally similar than expected throughout the plot at most spatial scales and assemblages of less similar than expected species could only be found on finer spatial scales. In sum, our results suggest that the trait‐based effects on community assembly change with spatial scale in a predictable manner and the association of these patterns with topographic variables, indicates the importance of deterministic processes in community assembly relatively to random processes.

A framework for predicting competition between native and exotic hymenopteran parasitoids of lepidopteran larvae using taxonomic collections and species level traits

Functional traits quantify the distinctiveness of ecological communities and provide a theoretical basis for understanding inter-specific competition, competitive exclusion, and limiting similarity. Functional traits can also be used to evaluate the risk of exotic species and biological control agents. The generalist parasitoid Meteorus pulchricornis (Wesmael 1835) (Braconidae: Hymenoptera) was used as a case study to evaluate the potential for inter-specific competition with resident hymenopteran larval parasitoid species in New Zealand. Information on taxonomic and life history traits were collated from published and unpublished literature, while morphological traits were obtained by measuring specimens in the New Zealand Arthropod Collection. Functional trait information was gathered for 89 parasitoid species, and a hierarchical agglomeration approach was used to cluster species based on similarity. A principal component analysis identified several key traits, including host development (idiobiosis, koinobiosis), site of development (ectoparasitoid, endoparasitoid), progeny per host, the host stage attacked, and ovipositor morphology. Analysis show that M. pulchricornis has the potential to compete with a different range of species, including biocontrol agents, and endemic or native species. Functional trait information using the literature and taxonomic collections can be used to complement current risk assessment tools.

Plant Trait Dataset for Tree-Like Growth Forms Species of the Subtropical Atlantic Rain Forest in Brazil

Plant functional traits have been incorporated in studies of vegetation ecology to better understand the mechanisms of ecological processes. For this reason, a global effort has been made to collect functional traits data for as many species as possible. In light of this, we identified the most common species of an area of 15,335 km2 inserted in the subtropical Atlantic Rain Forest in Southern Brazil. Then, we compiled functional trait information mostly from field samples, but also from herbarium and literature. The dataset presents traits of leaf, branch, maximum potential height, seed mass, and dispersion syndrome of 117 species, including trees, tree ferns, and palms. We also share images of anatomical features of branches used to measure wood traits. Data tables present mean trait values at individual and species level. Images of wood and stomatal features may be useful to assess other anatomical traits that were not covered in the data tables for the anatomical determination of species and/or for educational purposes.

The statistical need to include phylogeny in trait‐based analyses of community composition

SummaryA growing number of studies incorporate functional trait information to analyse patterns and processes of community assembly. These studies of trait–environment relationships generally ignore phylogenetic relationships among species. When functional traits and the residual variation in species distributions among communities have phylogenetic signal, however, analyses ignoring phylogenetic relationships can decrease estimation accuracy and power, inflate type I error rates and lead to potentially false conclusions.Using simulations, we compared estimation accuracy, statistical power and type I error rates of linear mixed models (LMM) and phylogenetic linear mixed models (PLMM) designed to test for trait–environment interactions in the distribution of species abundances among sites. We considered the consequences of both phylogenetic signal in traits and phylogenetic signal in the residual variation in species distributions generated by an unmeasured (latent) trait with phylogenetic signal.When there was phylogenetic signal in the residual variation in species among sites, PLMM provided better estimates (closer to the true value) and greater statistical power for testing whether the trait–environment interaction regression coefficient differed from zero. LMM had unacceptably high type I error rates when there was phylogenetic signal in both traits and the residual variation in species distributions. When there was no phylogenetic signal in the residual variation in species distributions, LMM and PLMM had similar performances.Linear mixed models that ignore phylogenetic relationships can lead to poor statistical tests of trait–environment relationships when there is phylogenetic signal in the residual variation in species distributions among sites, such as caused by unmeasured traits. Therefore, phylogenies and PLMMs should be used when studying how functional traits affect species abundances among communities in response to environmental gradients.

Leaf spectral clusters as potential optical leaf functional types within California ecosystems

Our ability to measure and map plant function at multiple ecological scales is critical for understanding current and future changes in Earth's ecosystems and the global carbon budget. Conventional plant functional types (cPFTs) based on a few productivity-related traits have been previously used to simplify and represent major differences in global plant functions, but more recent research has directly focused on the use of functional trait information. Still, sampling limitations have constrained efforts to truly understand the variance and covariance of functional traits globally. Reflectance spectra offer a fast, repeatable, simultaneous measurement of a wide variety of leaf functional traits and could be used to optically define leaf functional types. To evaluate this concept, we measured leaf reflectance from a wide range of species in a diverse set of ecosystems across central and northern California, including observations from multiple individuals, sites, and seasons. Using principal components analysis, we analyzed spectral variation in relation to categorical attributes such as species and cPFTs, as well as to a set of functional trait metrics calculated from the spectra. We found the first three principal components (PCs) to be weakly related to categorical attributes and more strongly related to spectrally-derived functional metrics. Each PC was more strongly associated with different portions of the spectrum and contained different functional information. We applied a hybrid clustering algorithm to the PC coordinates of the observations to define potential optical leaf functional types. Twelve spectral clusters were identified, and these did not correspond directly to either single cPFTs or species. However, each cluster had a unique functional metric profile. Clusters represented both inter- and intra-species and cPFT functional differences driven by taxonomy, trait evolution and environmental responses, demonstrating their value as optical leaf functional types and the value of the clustering approach used here for defining optical types from leaf spectra. Our findings support the notion that cPFTs do not adequately capture differences in leaf function. They demonstrate that spectral measurements can be used to improve both the definition of PFTs as well as our knowledge regarding the covariance of functional traits within these classes.

Strong paleoclimatic legacies in current plant functional diversity patterns across Europe.

Numerous studies indicate that environmental changes during the late Quaternary have elicited long‐term disequilibria between species diversity and environment. Despite its importance for ecosystem functioning, the importance of historical environmental conditions as determinants of FD (functional diversity) remains largely unstudied. We quantified the geographic distributions of plant FD (richness and dispersion) across Europe using distribution and functional trait information for 2702 plant species. We then compared the importance of historical and contemporary factors to determine the relevance of past conditions as predictors of current plant FD in Europe. For this, we compared the strength of the relationships between FD with temperature and precipitation stability since the LGM (Last Glacial Maximum), accessibility to LGM refugia, and contemporary environmental conditions (climate, productivity, soil, topography, and land use). Functional richness and dispersion exhibited geographic patterns with strong associations to the environmental history of the region. The effect size of accessibility to LGM refugia and climate stability since the LGM was comparable to that of the contemporary predictors. Both functional richness and dispersion increased with temperature stability since the LGM and accessibility to LGM refugia. Functional richness' geographic pattern was primarily associated with accessibility to LGM refugia growing degree‐days, land use heterogeneity, diversity of soil types, and absolute minimum winter temperature. Functional dispersion's geographic pattern was primarily associated with accessibility to LGM refugia growing degree‐days and absolute minimum winter temperature. The high explained variance and model support of historical predictors are consistent with the idea that long‐term variability in environmental conditions supplements contemporary factors in shaping FD patterns at continental scales. Given the importance of FD for ecosystem functioning, future climate change may elicit not just short‐term shifts in ecosystem functioning, but also long‐term functional disequilibria.

Geographic patterns in functional diversity deficits are linked to glacial‐interglacial climate stability and accessibility

AbstractAimLate Quaternary climate change can be an important determinant of large‐scale species richness patterns, but it is currently unknown if its effects also extend to functional diversity (FD) and thus potentially ecosystem functioning. This study assessed whether deficits in contemporary FD, relative to expectations based on contemporary environmental regions and species richness, were associated with glacial‐interglacial climate stability and accessibility from glacial refugia.LocationEuropeMethodsAtlas data on distributions of plant species and functional trait information were used to estimate functional richness (FRich) and dispersion (FDisp) for ∼50 × 50 km grid cells across Europe. Maximum expected FD was calculated using both quantile regression and a null‐model approach, with species richness and contemporary environmental regions as constraints. Then, the proportion of the potential FD present in a grid cell – the realized‐to‐potential FD ratio (R/P) – was estimated. Spatial autoregressive modeling with information‐theoretic multi‐model selection were used to estimate the explanatory importance and predictive ability of glacial‐interglacial climate instability and accessibility to recolonization from glacial refugia for R/P ratios.ResultsMinimum and median R/P ratios were 58% and 74% for FRich and 82% and 93% for FDisp, showing that realized FD is often lower than expectations from species richness and contemporary environmental regions. FD deficits were significantly associated with glacial‐interglacial Quaternary climate change (FRich‐R2: 0.52; FDisp‐R2: 0.41), even after accounting for contemporary climate. FRich and FDisp R/P ratios were the highest in areas with low climatic instability and close to the major glacial temperate refuge regions.Main ConclusionsRealized macro‐scale FD patterns appear to be in moderate disequilibrium with contemporary richness and environmental regions. Importantly, small R/P ratios are significantly associated with both historical and contemporary climate. These findings suggest that future climate change may elicit long‐term functional disequilibria and thus also have long‐term consequences for ecosystem functioning.

Landscape-scale changes in forest structure and functional traits along an Andes-to-Amazon elevation gradient

Abstract. Elevation gradients provide opportunities to explore environmental controls on forest structure and functioning. We used airborne imaging spectroscopy and lidar (light detection and ranging) to quantify changes in three-dimensional forest structure and canopy functional traits in twenty 25 ha landscapes distributed along a 3300 m elevation gradient from lowland Amazonia to treeline in the Peruvian Andes. Elevation was positively correlated with lidar-estimated canopy gap density and understory vegetation cover, and negatively related to canopy height and the vertical partitioning of vegetation in canopies. Increases in canopy gap density were tightly linked to increases in understory plant cover, and larger gaps (20–200 m2) produced 25–30 times the response in understory cover than did smaller gaps (&lt; 5 m2). Vegetation NDVI and photosynthetic fractional cover decreased, while exposed non-photosynthetic vegetation and bare soil increased, with elevation. Scaling of gap size to gap frequency (λ) was, however, nearly constant along the elevation gradient. When combined with other canopy structural and functional trait information, this suggests near-constant canopy turnover rates from the lowlands to treeline, which occurs independent of decreasing biomass or productivity with increasing elevation. Our results provide the first landscape-scale quantification of forest structure and canopy functional traits with changing elevation, thereby improving our understanding of disturbance, demography and ecosystem processes in the Andes-to-Amazon corridor.

The European functional tree of bird life in the face of global change.

Despite the recognized joint impact of climate and land cover change on facets of biodiversity and their associated functions, risk assessments have primarily evaluated impacts on species ranges and richness. Here we quantify the sensitivity of the functional structure of European avian assemblages to changes in both regional climate and land cover. We combine species range forecasts with functional-trait information. We show that species sensitivity to environmental change is randomly distributed across the functional tree of the European avifauna and that functionally unique species are not disproportionately threatened by 2080. However, projected species range changes will modify the mean species richness and functional diversity of bird diets and feeding behaviours. This will unequally affect the spatial structure of functional diversity, leading to homogenization across Europe. Therefore, global changes may alter the functional structure of species assemblages in the future in ways that need to be accounted for in conservation planning.

Phylogenetic and trait-based assembly of arbuscular mycorrhizal fungal communities.

Both competition and environmental filtering are expected to influence the community structure of microbes, but there are few tests of the relative importance of these processes because trait data on these organisms is often difficult to obtain. Using phylogenetic and functional trait information, we tested whether arbuscular mycorrhizal (AM) fungal community composition in an old field was influenced by competitive exclusion and/or environmental filtering. Communities at the site were dominated by species from the most speciose family of AM fungi, the Glomeraceae, though species from two other lineages, the Acaulosporaceae and Gigasporaceae were also found. Despite the dominance of species from a single family, AM fungal species most frequently co-existed when they were distantly related and when they differed in the ability to colonize root space on host plants. The ability of AM fungal species to colonize soil did not influence co-existence. These results suggest that competition between closely related and functionally similar species for space on plant roots influences community assembly. Nevertheless, in a substantial minority of cases communities were phylogenetically clustered, indicating that closely related species could also co-occur, as would be expected if i) the environment restricted community membership to single functional type or ii) competition among functionally similar species was weak. Our results therefore also suggest that competition for niche space between closely related fungi is not the sole influence of mycorrhizal community structure in field situations, but may be of greater relative importance than other ecological mechanisms.

The Assembly of Ecological Communities Inferred from Taxonomic and Functional Composition

Among-site variation in metacommunities (beta diversity) is typically correlated with the distance separating the sites (spatial lag). This distance decay in similarity pattern has been linked to both niche-based and dispersal-based community assembly hypotheses. Here we show that beta diversity patterns in community composition, when supplemented with functional-trait information, can be used to diagnose assembly processes. First, using simulated data, we show how the relationship between distance decay patterns in taxonomic and functional measures of community composition can be used to predict the influence of a given trait on community assembly. We then use the patterns generated by the simulation as a template to show that the sorting of benthic macroinvertebrate metacommunities in headwater streams is likely influenced by different sets of functional traits at regional and local scales. We suggest that functional-trait databases and spatially referenced taxonomic surveys can be used to predict the spatial scales at which different aspects of interspecific functional variation are involved in niche-based community assembly while accounting for the influence of dispersal-based community assembly processes.

Functional‐diversity indices can be driven by methodological choices and species richness

Functional diversity is an important concept in community ecology because it captures information on functional traits absent in measures of species diversity. One popular method of measuring functional diversity is the dendrogram-based method, FD. To calculate FD, a variety of methodological choices are required, and it has been debated about whether biological conclusions are sensitive to such choices. We studied the probability that conclusions regarding FD were sensitive, and that patterns in sensitivity were related to alpha and beta components of species richness. We developed a randomization procedure that iteratively calculated FD by assigning species into two assemblages and calculating the probability that the community with higher FD varied across methods. We found evidence of sensitivity in all five communities we examined, ranging from a probability of sensitivity of 0 (no sensitivity) to 0.976 (almost completely sensitive). Variations in these probabilities were driven by differences in alpha diversity between assemblages and not by beta diversity. Importantly, FD was most sensitive when it was most useful (i.e., when differences in alpha diversity were low). We demonstrate that trends in functional-diversity analyses can be largely driven by methodological choices or species richness, rather than functional trait information alone.