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A framework for estimating species-specific contributions to community indicators
Abstract
Community Weighted Means (CWM) are valuable tools describing community composition with respect to one given trait. They have been widely used as indicators in global change studies to measure biodiversity responses to environmental perturbations. However, how individual species contribute to such community indicators has hardly been investigated. One of the reasons lies in the absence of a methodological framework relating changes in community dynamics to species-specific population variations. Here, we present a comprehensive framework allowing a finer interpretation of changes in CWM, and we propose a way to compute species contributions to these indicators.
We present an analytical framework allowing the quantification of species-specific contributions to changes in the mean (CWM) and the variance (Community Weighted Variance, CWV) of trait distributions in species assemblages monitored through time and space. We apply this approach to a case study investigating the impact of climate change on common bird assemblages in the French Mediterranean area between 2001 and 2012.
This approach allows us to identify that a small proportion of the species drive the changes observed at the community level indicator, and allows the identification of those species. Moreover, we show that the species-specific contributions are not homogeneous between taxonomic groups and that migratory species tend to have a higher impact.
This novel decomposition and interpretation of Community Weighted Means and Variances (for which specific software package is provided along with this article) sheds new light on the drivers of community modifications in response to environmental changes across time and space. Moreover, it represents a relevant and simple way to assess particular aspects of species-specific responses to environmental changes and it is straightforward to use for widely used ecological data on any species group.
... We analysed the correlation between CWV and CWM of each trait category for each assemblage. Positive correlation between CWM and CWV indicates an increase in the relative abundance of taxa with unique traits (Gaüzère et al., 2019). Conversely, negative correlation between CWM and CWV indicate losses in taxa with unique traits. ...
... This indicates a low functional redundancy of these assemblages in both biomes. The low functional redundancy combined with the positive association between CWV and CWM suggests that fish, arthropod, and macrophyte assemblages are composed of taxa with unique traits (Gaüzère et al., 2019). These findings agrees with the low functional redundancy predicted for the Neotropics (Leitão et al., 2016;Rodrigues-Filho et al., 2018). ...
... Thus, focusing research on single land-uses types and individual traits of single assemblages hinders our ability to understand biodiversity responses to increasing human pressures in streams.We detected declines in CWV and CWM of traits related to recruitment and life-history, resource and habitat-use and body size of fish, arthropod and macrophyte assemblages with land-use intensification. Combined with the evidence that CWV and CWM were closely associated, this indicates that increasing land-use impacts cause local extirpations of species with unique trait combinations(Gaüzère et al., 2019). The decrease in multivariate FDis with increasing land-use cover illustrates a widespread multi-trait ...
Human land-use is changing Earth’s surface, causing a decline in biodiversity and altering ecosystem functioning. However, most of the empirical evidence of land-use impacts in the Neotropics comes from studies investigating isolated land-use types, and the pathways by which intensified land-uses affect ecosystem functioning are largely unknown. Using a database from 61 streams spanning two hyperdiverse Neotropical regions, we demonstrate that intensive human land-uses (agriculture, urbanization, pasture, and afforestation) strongly affect stream biodiversity and functioning. We showed negative associations of agriculture, pasture and urbanization with taxonomic richness, functional diversity, and diversity of trait categories (recruitment and life-history, resource and habitat-use, and body size) of fish, arthropod, and macrophyte. The impacts of intensive land-uses on standing biomass were negative and driven by direct and indirect effects mediated by declines in taxonomic and functional diversities. Our findings highlight that human land use can reshape stream biodiversity, with multiple negative consequences on ecosystem functioning.
... In contrast, vegetation shaped by intensive and re-peated human interference, such as cropland or ruderal communities, is hardly represented. We performed a natural log transformation of the functional trait data before calculating the CWM and CWV, which indicate intra-and interspecific trait variations regarding plant species composition [27]. The functional trait information was available for 21,854 species across all plots in order to quantify the CWM and CWV of the 18 functional traits evaluated in our study. ...
... In contrast, vegetation shaped by intensive and repeated human interference, such as cropland or ruderal communities, is hardly represented. We performed a natural log transformation of the functional trait data before calculating the CWM and CWV, which indicate intra-and interspecific trait variations regarding plant species composition [27]. The functional trait information was available for 21,854 species across all plots in order to quantify the CWM and CWV of the 18 functional traits evaluated in our study. ...
... In addition, different forest types have variations in species composition, which affects the CWM and CWV of the entire plant community. This study contributes to understanding how forest management can influence the FCPC using CWM and CWV, which are closely associated with ecosystem functions and services [6][7][8]27]. We found that plantation forests (rotation ≤ 15 years), planted forests (rotation > 15 years), and agroforestry positively affected the CWM and CWV to an even greater extent than intact for- Figure 3. Differences in the response ratio (RR) of CWM-PCs and CWV-PCs in plantation forests (i.e., planted forests and agroforestry) compared to natural forests (i.e., intact forests and managed forests with natural regeneration). ...
The functional composition of plant communities (FCPC) makes a significant contribution to ecosystem properties, functions, and services. Here, we used 18 plant functional traits from the sPlot database v2.1 and the global forest management type dataset to explore the links between forest management and the FCPC. We used the post hoc Tukey test to explore the differences in the community-weighted mean (CWM) and community-weighted variance (CWV) among different forest management types [i.e., intact forests, managed forests with natural regeneration, planted forests, plantation forests (with up to a 15-year rotation), and agroforestry]. We found that different forest management types can result in significant variability in plant communities’ functional composition. Plantation forests could result in significantly higher CWM and CWV compared to intact forests, and significant differences could occur between natural and managed forests with natural regeneration. Furthermore, the relationship between forest management practices and the FCPC depends on ecozone type changes. There were significant differences between natural and plantation forests for CWM and CWV in temperate forests. Our study provides an effective reference for applying plant functional traits to regulate and optimize the functions and services of forest ecosystems.
... We analysed the correlation between CWV and CWM of each trait category for each assemblage. Positive correlation between CWM and CWV indicates an increase in the relative abundance of taxa with unique traits (Gaüzère et al., 2019). Conversely, negative correlation between CWM and CWV indicate losses in taxa with unique traits. ...
... This indicates a low functional redundancy of these assemblages in both biomes. The low functional redundancy combined with the positive association between CWV and CWM suggests that fish, arthropod, and macrophyte assemblages are composed of taxa with unique traits (Gaüzère et al., 2019). These findings agrees with the low functional redundancy predicted for the Neotropics (Leitão et al., 2016;Rodrigues-Filho et al., 2018). ...
... Thus, focusing research on single land-uses types and individual traits of single assemblages hinders our ability to understand biodiversity responses to increasing human pressures in streams.We detected declines in CWV and CWM of traits related to recruitment and life-history, resource and habitat-use and body size of fish, arthropod and macrophyte assemblages with land-use intensification. Combined with the evidence that CWV and CWM were closely associated, this indicates that increasing land-use impacts cause local extirpations of species with unique trait combinations(Gaüzère et al., 2019). The decrease in multivariate FDis with increasing land-use cover illustrates a widespread multi-trait ...
Human land‐use change is a major threat to natural ecosystems worldwide. Nonetheless, the effects of human land‐uses on the structure of plant and animal assemblages and their functional characteristics need to be better understood. Furthermore, the pathways by which human land uses affect ecosystem functions, such as biomass production, still need to be clarified.
We compiled a unique dataset of fish, arthropod and macrophyte assemblages from 61 stream ecosystems in two Neotropical biomes: Amazonian rainforest and Uruguayan grasslands. We then tested how the cover of agriculture, pasture, urbanization and afforestation affected the taxonomic richness and functional diversity of those three species assemblages, and the consequences of these effects for animal biomass production. Single trait categories and functional diversity were evaluated, combining recruitment and life‐history, resource and habitat‐use, and body size.
The effects of intensive human land‐uses on taxonomic and functional diversities were as strong as other drivers known to affect biodiversity, such as local climate and environmental factors. In both biomes, the taxonomic richness and functional diversity of animal and macrophyte assemblages decreased with increasing cover of agriculture, pasture, and urbanization. Human land‐uses were associated with functional homogenization of both animal and macrophyte assemblages. Human land‐uses reduced animal biomass through direct and indirect pathways mediated by declines in taxonomic and functional diversities.
Our findings indicate that converting natural ecosystems to supply human demands results in species loss and trait homogenization across multiple biotic assemblages, ultimately reducing animal biomass production in streams.
... Similarly, Devictor et al. (2012) found increased numbers of "warm" dwelling species in breeding bird and butterfly communities in Western Europe. However, the losses of "cool/cold" dwelling species can have as much impact on a positive CTI trend as increases in "warm" dwelling species (Curley, 2020;Gaüzère et al., 2019Gaüzère et al., , 2020Tayleur et al., 2016). ...
... Recently, species trait-based approaches of CWMs (e.g. temperature affiliation, CTI) have been used in conjunction with concurrent changes in relative species' abundances to group species in a way that identifies ecological patterns or characteristics of species that are contributing to observed patterns of change (Curley, 2020;Gaüzère et al., 2019;Gaüzère et al., 2020). For example, positive CTI trends could be caused by increasing abundances of "warm" species-or decreasing abundances of "cool" species-in a community, which can occur concurrently and are not mutually exclusive processes. ...
... Elucidating the relationship between these indices can help identify which species might be more affected by changing climate patterns. To do this, we calculate species-specific contributions to the CTI and CPI models (Curley, 2020;Gaüzère et al., 2019;Gaüzère et al., 2020;Princé & Zuckerberg, 2015) in conjunction with relative abundance trends and range expansion/ contraction. ...
Aim
Species distributions are altered by climate change, resulting in changes in community composition. How communities are changing with climate is important for understanding the dynamics of changing diversity patterns. In this study, we employ two community weighted means (CWMs) of temperature (CTI) and precipitation (CPI) to evaluate patterns in climate‐driven community changes.
Location
Eastern North America between −100° and −60° longitude and 25°–50°N latitude.
Taxon
North American birds
Methods
We used North American Breeding Bird Survey (BBS) data from 1990 to 2018 to test the spatiotemporal trends of these indices at a sub‐continental (across all BBS routes) and at a regional scale (sub‐continental scale partitioned by 5° latitude bands). We employ a jackknife analysis to highlight individual species contributions to CTI and CPI trends and further identify group characteristics of species based on relative abundance trends and range expansion and contraction trends.
Results
Across all BBS routes, temperature marginally increased and precipitation significantly increased. At the sub‐continental scale, we found no correlation between CTI and temperature, but a positive correlation between CPI and precipitation. CTI and CPI both increased, driven by increased abundances of “warm” and “wet” dwelling species expanding in range. Regional scale CTI and CPI patterns deviated from sub‐continental patterns. CTI was driven by “warm” dwelling species increasing in abundance and expanding in range, whereas decreases in “dry” dwelling species contracting in range drove CPI trends at the highest latitudes.
Main conclusions
The concurrent use of CTI and CPI highlights that community dynamics are more complicated than using temperature metrics alone. Employing more than one community index demonstrates how simultaneous increases in two separate evaluative indices can have disproportionate effects on the number of species that contribute to a trend and highlight disparate mechanisms that contribute to these underlying differences.
... Community weighted variance is the plot-level variance in body size values weighted by species abundance and represents a measure of size diversity. Community weighted variance was calculated following Gaüzère et al. (2019), with higher values occurring when communities have greater size diversity. Last, skewness was calculated by allocating species into different size categories on the basis of its log-transformed body size (mm). ...
... Skew body size distributions can inform whether trait filtering is occurring along the landscape gradient (i.e., shifts in community body size distribution). Metrics were calculated using the FD (Laliberté et al. 2014) and S3cR (Gaüzère et al. 2019) packages in R. ...
... Species-specific contributions to community body size change across the landscape gradient.-To quantify the contribution of individual carabid species to community weighted mean (CWM), we followed the method proposed by Gaüzère et al. (2019). This method is based on a Jackknife procedure, where species are removed one by one from the data set and then the CWM is iteratively recalculated. ...
Understanding the mechanisms contributing to positive relationships between predator diversity and natural pest control is fundamental to inform more effective management practices to support sustainable crop production. Predator body size can provide important insights to better understand and predict such predator‐pest interactions. Yet, most studies exploring the link between predator body size and pest control have been conducted in species‐poor communities under controlled environmental conditions, limiting our ability to generalize this relationship across heterogeneous landscapes. Using the community of naturally occurring ground beetles in cabbage fields, we examined how landscape composition (percent cropland) influences the size structure (mean, variance, and skewness of body size distribution) of predator communities and the subsequent effects on pest control. We found that predator communities shifted their size distribution toward larger body sizes in agriculturally dominated landscapes. This pattern arose from increasing numerical dominance of a few large‐bodied species rather than an aggregated response across the community. Such landscape‐driven changes in community size structure led to concomitant impacts on pest control, as the mean body size of predators was positively related to predation rates. Notably, the magnitude of pest control depended not only on the size of the dominant predators but was also strongly determined by the relative proportion of small vs. large‐bodied species (i.e., skewness). Predation rates were higher in predator assemblages with even representation of small and large‐bodied species relative to communities dominated by either large or small‐bodied predators. Landscape composition may therefore modulate the relationship between predator body size and pest control by influencing the body size distribution of co‐occurring species. Our study highlights the need to consider agricultural practices that not only boost effective predators, but also sustain a predator assemblage with a diverse set of traits to maximize overall pest control.
... Figure 1 illustrates how the community adjustment to climate warming can be assessed with the intuitive community temperature index (hereafter, CTI), by measuring changes in community composition as a function of all species' thermal affinities (Devictor et al. 2008). In addition to the average community response measured with the CTI, the variance of the response provides a complementary indicator for conservation assessments, with which to investigate the species colonization-extinction processes relative to the species thermal affinities (Fig. 1, Gaüzère et al. 2019). Indeed, a community adjustment to climate warming may involve mainly extinction of colddwelling species (Fig. 1 scenario 2) or colonization by warm-dwelling species ( Fig. 1 scenario 3), which have different conservation implications. ...
... The CTI and CTI standard deviation (CTI sd ) were computed following Devictor et al. (2008) and Gaüzère et al. (2019) on species occurrence (presence/absence). The CTI is the average STI of the species present in the community per count event (Supporting Information). ...
... Indicators are essential tools to synthesize population dynamics and inform public policies (Tittensor et al. 2014). The CTI is an intuitive indicator with which to measure and communicate the impact of climate warming on communities (Devictor et al. 2012;Gaüzère et al. 2019). Here, we go one step further and used the CTI sd to identify the colonization-extinction patterns in response to climate warming (Supporting Information). ...
Climate warming is driving changes in species distributions and community composition. Many species have a so‐called climatic debt, that is, shifts in range lag behind shifts in temperature isoclines. Inside protected areas (PAs), community changes in response to climate warming can be facilitated by greater colonization rates by warm‐dwelling species, but also mitigated by lowering extirpation rates of cold‐dwelling species. An evaluation of the relative importance of colonization‐extirpation processes is important to inform conservation strategies that aim for both climate debt reduction and species conservation. We assessed the colonization‐extirpation dynamics involved in community changes in response to climate inside and outside PAs. To do so, we used 25 years of occurrence data of nonbreeding waterbirds in the western Palearctic (97 species, 7071 sites, 39 countries, 1993–2017). We used a community temperature index (CTI) framework based on species thermal affinities to investigate species turnover induced by temperature increase. We determined whether thermal community adjustment was associated with colonization by warm‐dwelling species or extirpation of cold‐dwelling species by modeling change in standard deviation of the CTI (CTISD). Using linear mixed‐effects models, we investigated whether communities in PAs had lower climatic debt and different patterns of community change than communities outside PAs. For CTI and CTISD combined, communities inside PAs had more species, higher colonization, lower extirpation, and lower climatic debt (16%) than communities outside PAs. Thus, our results suggest that PAs facilitate 2 independent processes that shape community dynamics and maintain biodiversity. The community adjustment was, however, not sufficiently fast to keep pace with the large temperature increases in the central and northeastern western Palearctic. Our results underline the potential of combining CTI and CTISD metrics to improve understanding of the colonization‐extirpation patterns driven by climate warming.
... The absence of linkage between community and species dynamics has also impaired a widespread use of community-aggregated indices in biodiversity conservation, which often focuses on the species and population scales (Davey et al., 2013). It is only recently that novel approaches have successfully provided a framework to link species and community-level dynamics (Princé and Zuckerberg, 2015;Tayleur et al., 2016;Gaget et al., 2018;Gaüzère et al., 2019). Bridging the gap between community and species level dynamics provides summarized information over large taxonomic inference, and allows a fine interpretation of changes through the quantification of species contribution to overall trends. ...
... Importantly, as we expected combined effects of land use and climate changes on bird community dynamics, we aimed at assessing whether independent, antagonistic, and/or additive effects between climate and land use changes were driving specific aspects of community dynamics (namely CTI and CGI). In order to provide a deeper und erstanding of community-scale dynamics, we calculated the relative species-specific contributions to changes in community indices (Gaüzère et al., 2019), and investigated how the link between species and community dynamics were related to their thermal and habitat preferences. ...
... To assess which species and/or trait values are declining or increasing with time, and how these trends drive the observed changes in community indices, we quantified the extent to which a species contributed to trends observed at the community level. To do so, we used the s3cR package implementing the methodological framework presented in (Gaüzère et al., 2019). The contribution of a species is defined as the difference between linear change in CTI/CGI estimated on the whole dataset and the linear change in slope value estimated on the whole dataset after excluding the focal species (Princé and Zuckerberg, 2015). ...
Rural landscapes of western Europe have considerably changed in the last decades under the combined pressure of climate and land use changes, leading to a dramatic decline of farmland biodiversity, including common farmland birds. The respective roles of climate and land use and cover changes in driving bird population trends are primarily assessed at national or continental levels. Yet, it is often challenging to integrate their intertwined effects at such large scales due to the lack of data on fine-scale land cover changes. Here, we used a long-term bird monitoring scheme, combined with a land cover survey, conducted during 30 years (1981-2011) across 780 sites in a 20,000 ha study area in southwestern France, dominated by low-intensity farming systems. We tested the direct effect of temporal changes in climate and land use on the dynamics of two community-level metrics: the bird Community Thermal Index (CTI) and bird Community Generalization Index (CGI). We used a novel method to assess the contribution of species-specific dynamics to CTI and CGI trends. We observed a significant increase in CTI and a significant decrease in CGI between 1981 and 2011, i.e., bird communities now have higher thermal preferences and are more specialized than 30 years ago. Bird CTI and CGI changes were both related to local climate-and land use-related drivers, especially mean temperature increase and hedgerow loss. Trends in CTI and CGI were primarily driven by the loss of cold-dwelling and generalist species, and secondly by a gain in hot-dwelling specialists. Our long-term study brings new empirical evidence that the effects of climate and land cover changes on bird communities are intrinsically intertwined, and need to be considered together to monitor and predict the future of farmland biodiversity. It also suggests that low-input, diversified agriculture combined with the maintenance of semi-natural habitat cover can contribute to the conservation of both specialist and generalist bird communities in agricultural landscapes experiencing rapid climate change.
... Community weighted variance is the plot-level variance in body size values weighted by species abundance and represents a measure of size diversity. Community weighted variance was calculated following Gaüzère et al. (2019), with higher values occurring when communities have greater size diversity. Last, skewness was calculated by allocating species into different size categories on the basis of its log-transformed body size (mm). ...
... Skew body size distributions can inform whether trait filtering is occurring along the landscape gradient (i.e., shifts in community body size distribution). Metrics were calculated using the FD (Laliberté et al. 2014) and S3cR (Gaüzère et al. 2019) packages in R. ...
... Species-specific contributions to community body size change across the landscape gradient.-To quantify the contribution of individual carabid species to community weighted mean (CWM), we followed the method proposed by Gaüzère et al. (2019). This method is based on a Jackknife procedure, where species are removed one by one from the data set and then the CWM is iteratively recalculated. ...
Biological control of pests by natural enemies is dependent not only on local conditions, but also on the surrounding landscape and the interplay between both spatial scales. The intermediate landscape complexity hypothesis states that on farm scale management such as the creation of habitat for natural enemies should be more successful to increase biocontrol services at landscapes of intermediate complexity. However, it is still unclear how augmentative biological control as a local practice is affected by the landscape context and the naturally occurring enemy communities. In this study, we provide empirical evidence of how the effect of augmentative biocontrol by the spined soldier bug, Podisus maculiventris (Hemiptera: Pentatomidae), is influenced by the surrounding landscape. We selected pairs of cabbage fields (one with augmentative biological control and the other unmanaged) along a landscape complexity gradient to determine the effects of augmentative releases on biocontrol levels and consequent plant damage and yield. We also used sentinel preys and surveillance video cameras to identifty the natural enemies that were attacking lepidopteran pest in the field and to determine their efficiency rates. Understanding interactions among natural enemies and landscape complexity will help us develop a sustainable management strategy based on augmentation of a generalist predator to control cabbage pests while maintaining high yields and profits.
... The trajectory of some species may also be driven by factors that do not affect other species within the index, resulting in different trends for those species compared to others and the aggregated index. There is currently a paucity of formal tools for investigating the structure and diversity among population trajectories in the group of species underlying biodiversity indicators (but see Gaüzère et al., 2019). Available approaches are to examine specieswise slope coefficients (Julliard et al., 2004), or simple sensitivity analyses where the effects of leaving species out in the computation of the index are examined (Leung et al., 2020). ...
... One species (the Ortolan bunting) does not belong to any clusters as its steep decline makes its time series singular and deviating strongly from the others. Although it is well known that population dynamics for farmland birds display variable pattern among species dynamics (Voříšek et al., 2010;Wretenberg et al., 2006), farmland birds have often been discussed or analysed as a group of species (Donald et al., 2001;Reif & Vermouzek, 2019; but see Gaüzère et al., 2019;Stjernman et al., 2013). Assessing the mechanisms explaining these differences among farmland birds will necessitate more studies, but our three tools provides new insights into how ...
In the light of declining biodiversity, monitoring its fate is essential for conservation strategies. Aggregation of temporal change of different species into multi-species indices such as geometric means makes it possible to identify species groups that are at risk as well as those that are doing well. However, aggregated indices mask the between-species variability in the temporal trajectories, which could be of high relevance for conservation actions.
We propose a toolbox, available as an r package, to investigate compositions of species dynamics in geometric mean multi-species indices. The toolbox is based on a dynamic factor analysis which uses species dynamics and their uncertainty to (1) identify common latent trends in those species dynamics, (2) display the variability of species dynamics and (3) extract clusters of species with similar dynamics within the species groups used for the indices.
We apply the toolbox to common breeding birds in Sweden and explore the variability in dynamics among species included in EU-official indices for farmland and woodland species, highlighting clusters of species with related dynamics previously hidden by averaging.
The toolbox is designed to be applicable to a wide range of ecological monitoring data. By enabling a deeper exploration of the structure behind existing indices, we may refine our understanding of biodiversity change to better inform subsequent conservation policies.
... To identify community assembly processes related to life history traits, we calculated the community-weighted variance (CWV) according to Gaüzère et al., (2019) ...
... The Community Weighted Mean (CWM), as defined in Gaüzère et al. (2019), is the average of the local distribution of a trait in a community (i.e. the expected value of the trait of an individual chosen randomly from the community). In our study, the CWM was calculated for each transect, using taxa densities and either sensitivity scores (for the first part of the statistical analysis) or each trait scores separately (for the second part).. ...
... To identify community assembly processes related to life history traits, we calculated the community-weighted variance (CWV) according to Gaüzère et al., (2019) ...
... The Community Weighted Mean (CWM), as defined in Gaüzère et al. (2019), is the average of the local distribution of a trait in a community (i.e. the expected value of the trait of an individual chosen randomly from the community). In our study, the CWM was calculated for each transect, using taxa densities and either sensitivity scores (for the first part of the statistical analysis) or each trait scores separately (for the second part).. ...
Marine ecosystems face many pressures, the main ones being fishing and climate change. These pressures do not have the same consequences on the different facets of biodiversity, e.g. on taxa, traits and networks, and their study is necessary for the implementation of an ecosystem approach to fisheries. The Celtic Sea is a very important fishing area for European fisheries, with a specific richness greater than adjacent areas. Based on a time series from 2000 to 2016, I have studied the spatio-temporal dynamics of 101 species of the ecosystem. Over this period, taxonomic biodiversity was stable, and the importance of fishing as a structuring variable for communities decreased after 2009, and was lower than the environment (depth, chlorophyll a concentration and temperature). Following a local decrease in fishing pressure, the biomass of species with life history strategies characterised by a low renewal rate and present in the central Celtic Sea, increased. In particular, the increase in the biomass of six species of elasmobranchs has been linked to the creation of a seasonal fishing closure in the area. This vision of fishing sensitivity was enriched with data from the exploitation of underwater videos. This made it possible to highlight the presence of sensitive areas in the western Celtic Sea, along the continental slope. In addition, the study of interaction networks linking species, and in particular trophic networks, allowed considering the dynamics of the entire ecosystem based on its components. In the Celtic Sea, the sensitivity of species to fishing does not imply the sensitivity of the network to this pressure. On the other hand, the trophic network is not very robust to the loss of the 7% of the most exploited species and basal species.
... This approach consists in weighting the ecological trait for every species in a given haul (or 'community') by the relative abundance of said species in that given community. CWM and CWV for a given haul i are calculated following Gaüzère et al. (2019) as represented below. ...
Climate change is triggering shifts in species distribution eventually altering communities' biogeography. The composition of a community in terms of its species' ecological niche informs of a community's response to environmental conditions and impacts, which is central for a timely conservation. While the thermal niche has been widely explored, given it offers a direct link of warming effects on an assemblage, acknowledging the multivariate nature of a species niche can provide relevant insights of the reorganizations taking place at a community-level. We studied the mean and variance of 10 ecological traits at the community level in two regional ecosystems in the temperate East-Atlantic and the Mediterranean Sea, characterized by a distinct exposure to warming. Our findings revealed major temporal changes and spatial structuring in the traits and ranges explored over the last decades. Apart from confirming the expected general poleward, deep-ward shift, our results highlighted a widening of thermal and latitudinal ranges, possibly related to a 'flexibilitation' of the communities in a context of global change. In addition, temporal patterns reflected how communities have adjusted around regime shifts known in both areas. Regional differences arose concerning the variance of depth ranges and area of distribution, as well as to the global evolution of the communities, which we argue are consequence of their different geographical features and ecological history. The comparison of two large mul-titaxon assemblages has disclosed a broad-scale motion of response to warming in the bentho-demersal domain. We expect this study will contribute to the understanding of the multivariate nature of global-change effects on marine fauna, which ultimately informs adaptive management.
... In Ireland and Sweden species in clusters with increasing dynamics have on average a higher STI than species in clusters with decreasing dynamics. This might be expected as the species ability to cope with climate change and increasing temperatures could reinforce or mitigate the overall declining dynamics led by agricultural practices , and it has been shown that species associated with warm temperatures may fare better than those associated with lower temperature in some farmland systems (Gaüzère et al., 2019). Moreover, farmland specialists are declining more than generalists (Heldbjerg et al., 2018). ...
... From a mathematical viewpoint, they represent the expected values of a trait if we randomly select an individual from the community. As such, P k = (C jk , S jk , R jk ) represents a simple summary statistic of the pool of local strategies within a given community that can be used to summarize community-level functional responses to environmental drivers (Gaüzère et al., 2019). From the mean plot-level CSR strategies, we next calculated the community-level specialization of each plot σ k ...
... ingly common in the trait-based literatureGaüzère et al., 2019;Henn et al., 2018; Jónsdóttir et al., 2022; Ross et al., 2017), we currently lack a clear picture of the relative performance of these methods and how much common sampling strategies impact those performances. Here, we test the accuracy of different methods to estimate the four moments of trait distributions. ...
Estimating phenotypic distributions of populations and communities is central to many questions in ecology and evolution. These distributions can be characterized by their moments (mean, variance, skewness and kurtosis) or diversity metrics (e.g. functional richness). Typically, such moments and metrics are calculated using community‐weighted approaches (e.g. abundance‐weighted mean). We propose an alternative bootstrapping approach that allows flexibility in trait sampling and explicit incorporation of intraspecific variation, and show that this approach significantly improves estimation while allowing us to quantify uncertainty.
We assess the performance of different approaches for estimating the moments of trait distributions across various sampling scenarios, taxa and datasets by comparing estimates derived from simulated samples with the true values calculated from full datasets. Simulations differ in sampling intensity (individuals per species), sampling biases (abundance, size), trait data source (local vs. global) and estimation method (two types of community‐weighting, two types of bootstrapping).
We introduce the traitstrap R package, which contains a modular and extensible set of bootstrapping and weighted‐averaging functions that use community composition and trait data to estimate the moments of community trait distributions with their uncertainty. Importantly, the first function in the workflow, trait_fill , allows the user to specify hierarchical structures (e.g. plot within site, experiment vs. control, species within genus) to assign trait values to each taxon in each community sample.
Across all taxa, simulations and metrics, bootstrapping approaches were more accurate and less biased than community‐weighted approaches. With bootstrapping, a sample size of 9 or more measurements per species per trait generally included the true mean within the 95% CI. It reduced average percent errors by 26%–74% relative to community‐weighting. Random sampling across all species outperformed both size‐ and abundance‐biased sampling.
Our results suggest randomly sampling ~9 individuals per sampling unit and species, covering all species in the community and analysing the data using nonparametric bootstrapping generally enable reliable inference on trait distributions, including the central moments, of communities. By providing better estimates of community trait distributions, bootstrapping approaches can improve our ability to link traits to both the processes that generate them and their effects on ecosystems.
... From a mathematical viewpoint, they represent the expected values of a trait if we randomly select an individual from the community. As such, P k = (C jk , S jk , R jk ) represents a simple summary statistic of the pool of local strategies within a given community that can be used to summarize community-level functional responses to environmental drivers (Gaüzère et al., 2019). From the mean plot-level CSR strategies, we next calculated the community-level specialization of each plot σ k ...
Specialization refers to a species adaptation to a restricted range of environmental conditions. While generalist species are able to exploit a wide variety of resources in a broad range of habitats, specialist species tend to have narrower niche breadths. From an evolutionary perspective, specialization is the result of a functional syndrome in which a suite of traits covary to allow the effective exploitation of specific resources. Accordingly, the measurement of specialization should be based on a multi-trait approach. In plant ecology, a well-known classification of the adaptive strategies of plants is Grime's competitor, stress tolerator, ruderal (CSR) theory in which the three principal strategies represent relatively easily measurable trait combinations from the global spectrum of plant form and function arising under conditions of competition, abiotic restriction to growth or periodic disturbance, respectively. In this paper, we thus introduce a method to summarize the functional specialization of plant species and communities by applying inequality measures to Grime's CSR strategies. The general idea is that a plant species that can be exclusively assigned to one CSR strategy can be considered a specialist (as it adopts only one adaptive strategy to access resources), while species that share functional characteristics of multiple CSR strategies can be considered more generalist. The behavior of the proposed measures is shown with one case study on the functional changes of six Alpine vegetation types ordered along a gradient, from pioneer to more stable communities.
... While species distributions are much more complex than simple climate relationships, this index has been a useful approach for describing how population trends and demography of bird populations are responding to climate change (Gaüzère et al., 2020;Godet et al., 2011;Princé & Zuckerberg, 2015). The collective contributions of individual species responses can give an indication of how the ecological community is responding to change (Curley et al., 2022;Gaüzère et al., 2019). Species with low STI consistently show more negative population trends in response to high temperatures (Pearce-Higgins et al., 2015). ...
Aim:
To test whether the occupancy of shorebirds has changed in the eastern Canadian Arctic, and whether these changes could indicate that shorebird distributions are shifting in response to long-term climate change.
Location:
Foxe Basin and Rasmussen Lowlands, Nunavut, Canada.
Methods:
We used a unique set of observations, made 25 years apart, using general linear models to test if there was a relationship between changes in shorebird species' occupancy and their species temperature Index, a simple version of a species climate envelope.
Results:
Changes in occupancy and density varied widely across species, with some increasing and some decreasing. This is despite that overall population trends are known to be negative for all of these species based on surveys during migration. The changes in occupancy that we observed were positively related to the species temperature index, such that the warmer-breeding species appear to be moving into these regions, while colder-breeding species appear to be shifting out of the regions, likely northward.
Main conclusions:
Our results suggest that we should be concerned about declining breeding habitat availability for bird species whose current breeding ranges are centered on higher and colder latitudes.
... We calculated community-weighted means (CWMs) to describe the regulating effects of plant nutrient trait diversity on desert scrubs' sensitivity to climate variability (see Equations (2) and (3)). CWMs are essential for understanding community reorganization in response to environmental filtering [61] and are widely recommended and used in plant functional ecology research [62]. ...
Climate models predict the further intensification of global warming in the future. Drylands, as one of the most fragile ecosystems, are vulnerable to changes in temperature, precipitation, and drought extremes. However, it is still unclear how plant traits interact with soil properties to regulate drylands’ responses to seasonal and interannual climate change. The vegetation sensitivity index (VSI) of desert scrubs in the Qaidam Basin (NE Tibetan Plateau) was assessed by summarizing the relative contributions of temperature (SGST), precipitation (SGSP), and drought (temperature vegetation dryness index, STVDI) to the dynamics of the normalized difference vegetation index (NDVI) during plant growing months yearly from 2000 to 2015. Nutrient contents, including carbon, nitrogen, phosphorus, and potassium in topsoils and leaves of plants, were measured for seven types of desert scrub communities at 22 sites in the summer of 2016. Multiple linear and structural equation models were used to reveal how leaf and soil nutrient regimes affect desert scrubs’ sensitivity to climate variability. The results showed that total soil nitrogen (STN) and leaf carbon content (LC), respectively, explained 25.9% and 17.0% of the VSI variance across different scrub communities. Structural equation modeling (SEM) revealed that STN and total soil potassium (STK) mediated desert scrub’s VSI indirectly via SGST (with standardized path strength of −0.35 and +0.32, respectively) while LC indirectly via SGST and SGSP (with standardized path strength of −0.31 and −0.19, respectively). Neither soil nor leave nutrient contents alone could explain the VSI variance across different sites, except for the indirect influences of STN and STK via STVDI (−0.18 and 0.16, respectively). Overall, this study disentangled the relative importance of plant nutrient traits and soil nutrient availability in mediating the climatic sensitivity of desert scrubs in the Tibetan Plateau. Integrating soil nutrient availability with plant functional traits together is recommended to better understand the mechanisms behind dryland dynamics under global climate change.
... To identify community assembly processes related to life history traits over the 2000-2016 period, we calculated the communityweighted variance (CWV) according to Gaüzère et al. (2019) for the sensitivity score (and each of the six life history traits, see Fig. S2). Assembly rules were assessed using a standard effect size (SES) by comparing the CWV to a null model based on random community assembly (i.e. ...
Due to its selective removal, fishing pressure has long influenced the dynamics of species based on their life history traits. Sensitivity to fishing increases along a "fast-to-slow" gradient of life history strategies, and the "slow" species (large, long-lived, late-maturing, giving birth to few large offspring) require the most time to recover from fishing. In the North East Atlantic, after having reached extreme levels, fishing pressure has decreased since the 1980's due to management measures such as total allowable catch (TAC) or area closure. An effect on the distribution of species as well as a potential recovery could be expected. However, temporal patterns of life history strategies are rarely linked to management measures. In addition, a larger emphasis is often put on exploited or emblematic sensitive species but rarely on assembly processes at the ecosystem scale (both commercial and non-commercial species). Based on a 17-year time series of 101 taxa (fishes, elasmobranchs, bivalves, cephalopods and crustaceans), we observed a negative relationship between the biomass of taxa sensitive to fishing and bottom trawling pressure, as well as an increase in their total biomass in the Celtic Sea. Over the whole area, stochasticity appeared as the dominant assembly process. Deterministic assembly processes were at play in the centre of the area where significant overdispersion (caused by the presence of both slow and fast taxa) were observed. The absence of sensitive taxa from the rest of the Celtic Sea appeared to be caused mainly by a historical effect of environmental filtering when fishing was high. At the local scale, we related the decrease in fishing pressure to the increase in biomass of five of the most sensitive taxa. This local decrease in fishing pressure, resulting from the implementation of an area closure, highlights the positive effect of such management measures in less than two decades.
... The community-weighted mean (CWM) is the weighted average of the distribution of a trait in a community (i.e. the expected value of the trait of an individual chosen randomly in the community) (Diaz et al., 1998;Grime, 1998;Gaüzère et al., 2019). In our study, the CWM was calculated for each transect, using taxon densities and either sensitivity scores (for the first part of the statistical analysis) or the score of each trait separately (for the second part). ...
Coastal marine ecosystems are under many pressures, including bottom trawling, which is the most widespread human activity that directly affects seabed habitats. Therefore, it is of great importance to characterize the impacts of bottom trawling on bentho-demersal communities, which can be done through the study of indicators sensitive to trawling pressure. Using a functional indicator applied to 54 underwater video transects, we mapped the sensitivity to trawling of epibenthic invertebrates and fish communities in the Celtic Sea. We determined the relative influence of environmental and fishing variables on sensitivity and traits distribution. Our results suggest that community sensitivity to trawling is mainly driven by a spatial gradient of depth and primary productivity that separates the area into two main regions: a shallow, productive area, with low sensitivity and a higher abundance of swimming and crawling organisms, and a deeper, less productive area, with higher sensitivity due to a higher abundance of fixed, filter-feeding organisms. Fishing intensity also drives the sensitivity of communities confirming that they have already been shaped by a long history of mixed fisheries. The methodology used here provides a valuable monitoring tool and could be used to predict communities’ response to changes in fishing intensity and climate change.
... Additionally, while we examined trait groups according to categorical traits, applying such methods to community-weighted mean trait values rather than trait groups does not relive the issue, as major changes in trait dominance can be entirely driven by single species (de Bello et al., 2012Nickerson et al., 2018). While recent approaches have been developed to identify the contribution of different species to changes in a single community-weighted mean trait (e.g., temperature preference) (Gaüzère et al., 2019;Princé and Zuckerberg, 2015), this issue remains unresolved for multi-trait approaches. Here, for simplicity, we examined changes in multiple trait groups within the single trait 'diet,' ...
The ensemble of biological, geochemical, and physical processes that occur within ecosystems is driven by the interplay between biological communities and the abiotic environment. Explaining the spatial and temporal dynamics of biological communities in relation to environmental conditions is therefore essential for understanding ecosystem functioning, and ultimately for achieving sustainable development. In marine ecosystems, fish communities are key to ecosystem functioning, and fisheries provide livelihoods for over 10% of the world’s population. However, understanding the processes structuring fish communities remains difficult because community structure varies with both natural environmental fluctuations and, increasingly, human pressures. Effectively managing fisheries and marine ecosystems under global change therefore requires better characterizing fish community dynamics over time and space and disentangling the underlying drivers and mechanisms. While fish ecologists have traditionally relied on species-based approaches (i.e., taxonomic approaches) to study community structure, trait-based approaches (i.e., functional approaches) are increasingly used because they can provide better insight into community assembly and the mechanisms driving community responses. To meet this need for a better understanding of biodiversity dynamics, the present thesis took advantage of long-term scientific monitoring data to characterize the functional responses of fish communities to environmental gradients in the North Sea, Eastern English Channel, and Bay of Somme. All three ecosystems experienced temperature rises and oceanographic changes associated with a warming phase of the Atlantic Multidecadal Oscillation (AMO), which rapidly impacted fish community structure. Consistent biological responses were observed across the three ecosystems despite their different spatial scales, demonstrating that fish communities were affected by environmental change through bio-ecological traits associated with habitat preference and life history. In the North Sea and Eastern Channel, pelagic species were the most responsive and contributed largely to community dynamics, which is likely explained by their greater mobility, higher dispersal rates, and fewer habitat requirements. However, beyond habitat preference, species with r-selected life histories (e.g., low size and age at maturity, low parental investment, small offspring) had the fastest environmental responses whether or not they were pelagic, likely due to their rapid population turnover and generation time. Importantly, the way these species’ responses shaped community structure depended on environmental context. R-selected, pelagic species rapidly declined in the Bay of Somme and Eastern Channel, but rapidly increased in the North Sea. This likely reflects environmental suitability, indicating that after the phase change of the AMO, the Eastern Channel became a less favorable environment for these species, while the North Sea became more favorable. Thus, species with high mobility and fast life history cycles appear capable of rapidly tracking environmental conditions, shifting in abundance in response to environmental suitability. Additionally, as these ecosystems have warmed over the last 30 years, community responses were characterized by increases in mean thermal preference. Importantly, the amplitude of community changes was partially determined by communities’ initial structure and redundancy of bio-ecological traits, showing that community responses depended not only on environmental changes but also on biodiversity itself. Lastly, while fish community responses were consistently associated with climatic changes, historical fishing pressure on large-bodied, demersal species appeared to render fish communities more sensitive to environmental changes by increasing the relative of abundance of pelagic and r-selected species.
... Additionally, while we examined trait groups according to categorical traits, applying such methods to community-weighted mean trait values rather than trait groups does not relieve the issue, as major changes in trait dominance can be entirely driven by single species (de Bello et al. , 2012Nickerson et al. 2018). While recent approaches have been developed to identify the contribution of different species to changes in a single community-weighted mean trait (e.g., temperature preference) (Princé and Zuckerberg 2015;Gaüzère et al. 2019) , Fig. 3 Comparison of slope, PCA loadings, and the TR index for assessing the contributions of reef-fish trait groups to community responses following mass coral mortality due to coral bleaching this issue remains unresolved for multi-trait approaches. ...
Trait-based ecology strives to better understand how species, through their bio-ecological traits, respond to environmental changes, and influence ecosystem functioning. Identifying which traits are most responsive to environmental changes can provide insight for understanding community structuring and developing sustainable management practices. However, misinterpretations are possible, because standard statistical methods (e.g., principal component analysis and linear regression) for identifying and ranking the responses of different traits to environmental changes ignore interspecific differences. Here, using both artificial data and real-world examples from marine fish communities, we show how considering species-specific responses can lead to drastically different results than standard community-level methods. By demonstrating the potential impacts of interspecific differences on trait dynamics, we illuminate a major, yet rarely discussed issue, highlighting how analytical misinterpretations can confound our basic understanding of trait responses, which could have important consequences for biodiversity conservation.
Higher efficiency in large-scale and long-term biodiversity monitoring can be obtained through the use of Essential Biodiversity Variables, among which species population sizes provide key data for conservation programs. Relevant estimations and assessment of actual population sizes are critical for species conservation, especially in the current context of global biodiversity erosion. However, knowledge on population size varies greatly, depending on species conservation status and ranges. While the most threatened or restricted-range species generally benefit from exhaustive counts and surveys, monitoring common and widespread species population size tends to be neglected or is simply more challenging to achieve. In such a context, citizen science (CS) is a powerful tool for the long-term monitoring of common species through the engagement of various volunteers, permitting data acquisition on the long term and over large spatial scales. Despite this substantially increased sampling effort, detectability issues imply that even common species may remain unnoticed at suitable sites. The use of structured CS schemes, including repeated visits, enables to model the detection process, permitting reliable inferences of population size estimates. Here, we relied on a large French structured CS scheme (EPOC-ODF) comprising 27,156 complete checklists over 3,873 sites collected during the 2021–2023 breeding seasons to estimate the population size of 63 common bird species using hierarchical distance sampling (HDS). These population size estimates were compared to the previous expert-based French breeding bird atlas estimations, which did not account for detectability issues. We found that population size estimates from the former French breeding bird atlas were lower than those estimated using HDS for 65% of species. Such a prevalence of lower estimations is likely due to more conservative estimates inferred from semi-quantitative expert-based assessments used for the previous atlas. We also found that species with long-range songs such as the Common Cuckoo ( Cuculus canorus ), Eurasian Hoopoe ( Upupa epops ) or the Eurasian Blackbird ( Turdus merula ) had, in contrast, higher estimated population sizes in the previous atlas than in our HDS models. Our study highlights the need to rely on sound statistical methodology to ensure reliable ecological inferences with adequate uncertainty estimation and advocates for a higher reliance on structured CS in support of long-term biodiversity monitoring.
Large-scale and long-term biodiversity monitoring can be improved by the use of Essential Biodiversity Variables, among which species population sizes provide key data for conservation programs. Relevant estimations and assessment of actual population sizes are critical for species conservation, especially in the current context of global biodiversity erosion. However, knowledge on population size varies greatly, depending on species conservation status and ranges. While the most threatened or restricted-range species generally benefit from exhaustive counts and surveys, monitoring efficiently common and widespread species tends to be neglected or is simply more challenging to achieve. In such a context, citizen science (CS) is a powerful tool for the long-term monitoring of common species through the engagement of various volunteers, permitting data acquisition on the long term and over large spatial scales. Despite this substantially increased sampling effort, detectability issues imply that even common species may remain unnoticed at suitable sites. The use of structured CS schemes, including repeated visits, enables to model the detection process, permitting reliable inferences of population size estimates. Here, we relied on a large French structured CS scheme (EPOC-ODF) comprising 27 156 complete checklists over 3 873 sites collected during the 2021-2023 breeding seasons to estimate the population size of 63 common bird species using Hierarchical Distance Sampling (HDS). These population size estimates were compared to the previous expert-based French breeding bird atlas estimations, which did not account for detectability issues. Our results indicate strong under-estimations for 65% of species in the French atlas, likely due to more conservative estimates inferred from semi-quantitative expert-based assessments. We also found a few over-estimations for species with long-range songs such as Cuculus canorus, Upupa epops or Turdus merula. Our study highlights the need to rely on sound statistical methodology to ensure unbiased ecological inferences with adequate uncertainty estimation and advocates for a higher reliance on structured CS in support of biodiversity monitoring.
The variability in traits within species (intraspecific trait variability; ITV) has attracted an increased interest in functional ecology, as it can profoundly influence the detection of functional trait patterns, calculation of functional diversity (FD), and assessments of ecosystem functioning. This renewed focus stems from the recognition that species are not homogeneous entities but rather mosaics of individuals with varying traits. Researchers dealing with FD have increasingly recognized this issue, and consequently, multiple methods have emerged to explicitly incorporate ITV into FD calculations. Some methods treat individuals as the unit of analysis, while others characterize trait distributions around their means. Ecologists navigating this landscape of methods may face challenges in selecting the most appropriate approach to address their research questions. This synthesis provides an overview and guidelines on how and when to use the different methods available to quantify ITV in biological assemblages and integrate it into FD. As a case study, we computed correlations on simulated assemblages with varying degrees of trait variability. Our findings suggest that the choice of FD metric should be guided primarily by the ecological question being addressed and, to a lesser extent, by the number and types of traits. Simulations revealed strong correlations among FD metrics that account for ITV, particularly those indicating the size of the occupied functional trait space. As evidence accumulates and shows how ITV is key to shaping species' fitness and distribution as well as affecting ecosystem functioning, this synthesis will serve as a conceptual and practical tool inspiring and guiding researchers to integrate ITV in functional diversity analyses.
Aim
Animal communities around the world are responding to climate change by altering their taxonomic composition, mainly through an increase in the colonisation rate of warm‐dwelling species and the local extinction of cold‐dwelling ones. We assessed whether the taxonomic composition of bird assemblages in peninsular Spain has changed in accordance with the recent increase in temperature. We also evaluated the role of species thermal affinities and population dynamics on these changes.
Location
Peninsular Spain.
Taxon
Birds.
Methods
We compared assemblages reported in the last Spanish breeding bird atlases (1998–2002 vs. 2014–2018) in 10 × 10 km squares. We described species' thermal niches by overlaying global species breeding distributions and world temperature metrics (based on mean, minimum, maximum and range), and then aggregated them to obtain a set of community thermal indices for each assemblage (CTIs and CTR for ranges). Long‐term average temperatures and local current temperatures were related to changes in CTIs using spatial GLMMs, which considered habitat change. We identified the species most responsible for variation in assemblages and regressed species' influence on thermal affinities and population dynamics.
Results
CTIs increased with temperature and warm‐dwelling species became more prevalent to the detriment of cold‐dwelling ones. However, we found a counteracting effect of temperature and habitat. Cold‐dwelling forest species were among the most influential species, mainly through colonisation, while warm‐dwelling farmland species contributed through local extinctions (both attenuated local increases in CTI). The mean thermal breadth of assemblages (CTR) decreased with temperatures.
Main conclusions
The taxonomic composition of bird assemblages shifted in line with the main expectations due to global change (thermophilisation), mainly due to local colonisation of warm‐dwelling species, although it did not show the pattern of thermal homogenisation suggested elsewhere. Our results add further evidence of the interplay between climate warming and land‐use change in the ongoing adjustment of animal communities.
Situé à la convergence entre trois empires biogéographiques, l’Iran est largement connu pour la grande diversité de sa flore et de sa faune. Par ailleurs, la relation entre la niche climatique et la biogéographie historique est une des clés permettant de comprendre les patrons actuels de distribution et d’endémisme. C’est aussi un élément central pour estimer la vulnérabilité des espèces au changement climatique actuel et sa prise en compte dans les stratégies de conservation est encore plus critique pour les reptiles de montagne dont les capacités de dispersion sont réduites. La thèse a eu pour objectif d’étudier l’influence de l’histoire évolutive et des changements climatiques sur la structure et la répartition de plusieurs espèces de serpents distribués dans deux points chauds de la biodiversité en Iran, le Caucase et l'Irano-Anatolie. L’analyse phylogéographique a été réalisée sur trois espèces (Gloydius halys caucasicus, Natrix tessellata and Hemorrhois ravergieri) sur la base de séquences mitochondriales et nucléaires. Une forte structuration génétique a été mise en évidence avec quatre lignées observées pour G. h. caucasicus, trois lignées pour N. tessellata et cinq lignées pour H. ravergieri. Les analyses de datation moléculaire et de biogéographie historique indiquent que les lignées iraniennes sont apparues entre 11 Mya et 0.63 Mya, ce qui indique une influence des oscillations paléo-climatiques du Quaternaire (derniers 2.8 Mya) mais aussi d’évènements plus anciens (aridification intense à 9-10 Mya ou crise messinienne à 5 Mya). La répartition de sept espèces de serpents des montagnes iraniennes a été modélisée en utilisant des modèles de distribution des espèces pour des conditions climatiques actuelles et futures (2070, moyenne de 2061 à 2080) afin d’identifier les zones favorables à chacune des espèces. Nos résultats prévoient un déplacement important, surtout altitudinal, des zones climatiquement adaptées aux espèces de serpents montagnards. Sur cette base, les résultats obtenus suggèrent que la répartition des espèces subira des changements à long terme qui devraient considérablement s’accélérer sous l’effet des pressions anthropiques. Sur la base de nos résultats concernant la diversité génétique, la future répartition et la définition d’unités évolutives significatives parmi les taxons étudiés, les enjeux en matière de conservation sont discutés en relation avec l’efficacité du réseau actuel d’aires protégées en Iran.
Motivation: The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.
Main types of variables included: The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.Spatial location and grain: BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2).
Time period and grain: BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year. Major taxa and level of measurement: BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.
Software format: .csv and .SQL.
Global changes are modifying the structure of species assemblages, but the generality of resulting diversity patterns and of their drivers is poorly understood. Any such changes can be detected and explained by comparing temporal trends in taxonomic and functional diversity over broad spatial extents. In this study, we addressed three complementary questions: How did bird taxonomic and functional diversity change over the past 40 years in the conterminous United States? Are these trends non-linear? Can temporal variations in functional diversity be explained by broad-scale changes in climate and vegetation productivity? We quantified changes in taxonomic and functional diversity for 807 bird assemblages over the past four decades (1970–2011) considering a suite of 16 ecological traits for 435 species. We found increases in local bird species richness and taxonomic equitability that plateaued in the early 2000’s while total abundance declined over the whole period. Functional richness, the total range of traits in an assemblage, increased due to the rising prevalence of species with atypical life-history strategies and under-represented habitat or trophic preferences. However, these species did not trigger major changes in the functional composition of bird assemblages. Inter-annual variations in climate and primary productivity explained the richness of bird life-history traits in local assemblages, suggesting that these traits are influenced by broad-scale environmental factors, while others respond more to more local drivers. Our results highlight that a comparative analysis of the multiple facets of functional diversity can raise novel insights on processes underlying temporal trends in biodiversity.
Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.
The local spatial congruence between climate changes and community changes has rarely been studied over large areas. We proposed one of the first comprehensive frameworks tracking local changes in community composition related to climate changes. First, we investigated whether and how 12 years of changes in the local composition of bird communities were related to local climate variations. Then, we tested the consequences of this climate-induced adjustment of communities on Grinnellian (habitat-related) and Eltonian (function-related) homogenization. A standardized protocol monitoring spatial and temporal trends of birds over France from 2001 to 2012 was used. For each plot and each year, we used the spring temperature, the spring precipitations and calculated three indices reflecting the thermal niche, the habitat specialization, and the functional originality of the species within a community. We then used a moving window approach to estimate the spatial distribution of the temporal trends in each of these indices and their congruency with local climatic variations. Temperature fluctuations and community dynamics were found to be highly variable in space but their variations were finely congruent. More interestingly, the community adjustment to temperature variations was non-monotonous. Instead, unexplained fluctuations in community composition were observed up to a certain threshold of climate change intensity, above which a change in community composition was observed. This shift corresponded to a significant decrease in the relative abundance of habitat specialists and functionally original species within communities, regardless of the direction of temperature change. The investigation of variations in climate and community responses appears to be a central step towards a better understanding of climate change effects on biodiversity. Our results suggest a fine scale and short-term adjustment of community composition to temperature changes. Moreover, significant temperature variations seem to be responsible for both the Grinnellian and Eltonian aspects of functional homogenization. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Species assemblages and natural communities are increasingly impacted by changes in the frequency and severity of extreme climatic events. Here we propose a brief overview of expected and demonstrated direct and indirect impacts of extreme events on animal communities. We show that differential impacts on basic biological parameters of individual species can lead to strong changes in community composition and structure with the potential to considerably modify the functional traits of the community. Sudden disequilibria have even been shown to induce irreversible shifts in marine ecosystems, while cascade effects on various taxonomic groups have been highlighted in Mediterranean forests. Indirect effects of extreme climatic events are ex-pected when event-induced habitat changes (e.g. soil stability, vegetation composition, water flows altered by droughts, floods or hurricanes) have differential consequences on species assembled within the communities. Moreover, in increasing the amplitude of trophic mismatches, extreme events are likely to turn many systems into ecological traps under climate change. Finally, we propose a focus on the potential impacts of an extreme heat wave on local assemblages as an empirical case study, analysing monitoring data on breeding birds collected in France. In this example, we show that despite specific populations were differently affected by local temperature anomalies, communities seem to be unaffected by a sudden heat wave. These results suggest that communities are tracking climate change at the highest possible rate [Current Zoology 57 (3): 406–413, 2011].
Much of the recent changes in North American climate have occurred during the winter months, and as result, overwintering birds represent important sentinels of anthropogenic climate change. While there is mounting evidence that bird populations are responding to a warming climate (e.g., poleward shifts) questions remain as to whether these species-specific responses are resulting in community-wide changes. Here, we test the hypothesis that a changing winter climate should favor the formation of winter bird communities dominated by warm-adapted species. To do this, we quantified changes in community composition using a functional index – the Community Temperature Index (CTI) – which measures the balance between low- and high-temperature dwelling species in a community. Using data from Project FeederWatch, an international citizen science program, we quantified spatiotemporal changes in winter bird communities (n = 38 bird species) across eastern North America and tested the influence of changes in winter minimum temperature over a 22-year period. We implemented a jackknife analysis to identify those species most influential in driving changes at the community level and the population dynamics (e.g., extinction or colonization) responsible for these community changes. Since 1990, we found that the winter bird community structure has changed with communities increasingly composed of warm-adapted species. This reshuffling of winter bird communities was strongest in southerly latitudes and driven primarily by local increases in abundance and regional patterns of colonization by southerly birds. CTI tracked patterns of changing winter temperature at different temporal scales ranging from 1 to 35 years. We conclude that a shifting winter climate has provided an opportunity for smaller, southerly distributed species to colonize new regions and promote the formation of unique winter bird assemblages throughout eastern North America.
Aim
The Hutchinsonian hypervolume is the conceptual foundation for many lines of ecological and evolutionary inquiry, including functional morphology, comparative biology, community ecology and niche theory. However, extant methods to sample from hypervolumes or measure their geometry perform poorly on high‐dimensional or holey datasets.
Innovation
We first highlight the conceptual and computational issues that have prevented a more direct approach to measuring hypervolumes. Next, we present a new multivariate kernel density estimation method that resolves many of these problems in an arbitrary number of dimensions.
Main conclusions
We show that our method (implemented as the ‘hypervolume’ R package) can match several extant methods for hypervolume geometry and species distribution modelling. Tools to quantify high‐dimensional ecological hypervolumes will enable a wide range of fundamental descriptive, inferential and comparative questions to be addressed.
The European protected-area network will cease to be efficient for biodiversity conservation, particularly in the Mediterranean region, if species are driven out of protected areas by climate warming. Yet, no empirical evidence of how climate change influences ecological communities in Mediterranean nature reserves really exists. Here, we examine long-term (1998-2011/2012) and short-term (2011-2012) changes in the butterfly fauna of Dadia National Park (Greece) by revisiting 21 and 18 transects in 2011 and 2012 respectively, that were initially surveyed in 1998. We evaluate the temperature trend for the study area for a 22-year-period (1990-2012) in which all three butterfly surveys are included. We also assess changes in community composition and species richness in butterfly communities using information on (a) species' elevational distributions in Greece and (b) Community Temperature Index (calculated from the average temperature of species' geographical ranges in Europe, weighted by species' abundance per transect and year). Despite the protected status of Dadia NP and the subsequent stability of land use regimes, we found a marked change in butterfly community composition over a 13 year period, concomitant with an increase of annual average temperature of 0.95°C. Our analysis gave no evidence of significant year-to-year (2011-2012) variability in butterfly community composition, suggesting that the community composition change we recorded is likely the consequence of long-term environmental change, such as climate warming. We observe an increased abundance of low-elevation species whereas species mainly occurring at higher elevations in the region declined. The Community Temperature Index was found to increase in all habitats except agricultural areas. If equivalent changes occur in other protected areas and taxonomic groups across Mediterranean Europe, new conservation options and approaches for increasing species' resilience may have to be devised.
As a consequence of climate warming, species usually shift their distribution towards higher latitudes or altitudes. Yet, it is unclear how different taxonomic groups may respond to climate warming over larger altitudinal ranges. Here, we used data from the national biodiversity monitoring program of Switzerland, collected over an altitudinal range of 2500 m. Within the short period of eight years (2003-2010), we found significant shifts in communities of vascular plants, butterflies and birds. At low altitudes, communities of all species groups changed towards warm-dwelling species, corresponding to an average uphill shift of 8 m, 38 m and 42 m in plant, butterfly and bird communities, respectively. However, rates of community changes decreased with altitude in plants and butterflies, while bird communities changed towards warm-dwelling species at all altitudes. We found no decrease in community variation with respect to temperature niches of species, suggesting that climate warming has not led to more homogenous communities. The different community changes depending on altitude could not be explained by different changes of air temperatures, since during the 16 years between 1995 and 2010, summer temperatures in Switzerland rose by about 0.07°C per year at all altitudes. We discuss that land-use changes or increased disturbances may have prevented alpine plant and butterfly communities from changing towards warm-dwelling species. However, the findings are also consistent with the hypothesis that unlike birds, many alpine plant species in a warming climate could find suitable habitats within just a few metres, due to the highly varied surface of alpine landscapes. Our results may thus support the idea that for plants and butterflies and on a short temporal scale, alpine landscapes are safer places than lowlands in a warming world.
Specialization is a concept based on a broad theoretical framework developed by evolutionary biologists and ecologists. In the past 10 years, numerous studies have reported that - in many contexts - generalist species are "replacing" specialist species. We review recent research on the concept of the ecological niche and species specialization, and conclude that (1) the observed worldwide decline in specialist species is predicted by niche theory, (2) specialist declines cause "functional homogenization" of biodiversity, and (3) such homogenization may be used to measure the impact of disturbance on communities. Homogenization at the community level could alter ecosystem functioning and productivity, as well as result in the deterioration of ecosystem goods and services. We propose community-level specialization as an indicator of the impact of global changes (habitat and climate disturbances) on biodiversity.
Marine fishes and invertebrates respond to ocean warming through distribution shifts, generally to higher latitudes and deeper waters. Consequently, fisheries should be affected by 'tropicalization' of catch (increasing dominance of warm-water species). However, a signature of such climate-change effects on global fisheries catch has so far not been detected. Here we report such an index, the mean temperature of the catch (MTC), that is calculated from the average inferred temperature preference of exploited species weighted by their annual catch. Our results show that, after accounting for the effects of fishing and large-scale oceanographic variability, global MTC increased at a rate of 0.19 degrees Celsius per decade between 1970 and 2006, and non-tropical MTC increased at a rate of 0.23 degrees Celsius per decade. In tropical areas, MTC increased initially because of the reduction in the proportion of subtropical species catches, but subsequently stabilized as scope for further tropicalization of communities became limited. Changes in MTC in 52 large marine ecosystems, covering the majority of the world's coastal and shelf areas, are significantly and positively related to regional changes in sea surface temperature. This study shows that ocean warming has already affected global fisheries in the past four decades, highlighting the immediate need to develop adaptation plans to minimize the effect of such warming on the economy and food security of coastal communities, particularly in tropical regions.
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.
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.
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.
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.
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.
Are patterns of intra- and inter-specific functional trait variation consistent with greater abiotic filtering on community assembly at high latitudes and elevations, and greater biotic filtering at low latitudes and elevations?
Area de Conservación Guanacaste, Costa Rica; Santa Catalina Mountains, Arizona; Siskiyou Mountains, Oregon.
We measured woody plant species abundance and a key functional trait associated with competition for resources and environmental tolerance (specific leaf area, SLA) along elevational gradients in low-latitude tropical (Costa Rica), mid-latitude desert (Arizona) and high latitude mediterranean (southern Oregon) biomes. We explored patterns of abiotic and biotic filtering by comparing observed patterns of community-weighted means and variances along elevational and latitudinal gradients to those expected under random assembly. In addition, we related trait variability to niches and explored how total trait space and breadth vary across broad spatial gradients by quantifying the ratio of intra- to inter-specific variation.
Both the community-wide mean and variance of SLA decreased with increasing latitude, consistent with greater abiotic filtering at higher latitudes. Further, low-elevation communities had higher trait variation than expected by chance, consistent with greater biotic filtering at low elevations. Finally, in the tropics and across latitude the ratio of intra- to inter-specific variation was negatively correlated to species richness, which further suggests that biotic interactions influence plant assembly at low latitudes.
Intra- and inter-specific patterns of SLA variation appeared broadly consistent with the idea that the relative strength of biotic and abiotic drivers on community assembly changes along elevational and latitudinal gradients; evidence for biotic drivers appeared more prominent at low latitudes and elevations and evidence for abiotic drivers appeared more prominent at high latitudes and elevations.
Understanding the processes shaping biological communities under multiple disturbances is a core challenge in ecology and conservation science. Traditionally, ecologists have explored linkages between the severity and type of disturbance and the taxonomic structure of communities. Recent advances in the application of species traits, to assess the functional structure of communities, have provided an alternative approach that responds rapidly and consistently across taxa and ecosystems to multiple disturbances. Importantly, trait-based metrics may provide advanced warning of disturbance to ecosystems because they do not need species loss to be reactive. Here, we synthesize empirical evidence and present a theoretical framework, based on species positions in a functional space, as a tool to reveal the complex nature of change in disturbed ecosystems.
Climate changes have profound effects on the distribution of numerous plant and animal species. However, whether and how different taxonomic groups are able to track climate changes at large spatial scales is still unclear. Here, we measure and compare the climatic debt accumulated by bird and butterfly communities at a European scale over two decades (1990-2008). We quantified the yearly change in community composition in response to climate change for 9,490 bird and 2,130 butterfly communities distributed across Europe. We show that changes in community composition are rapid but different between birds and butterflies and equivalent to a 37 and 114ĝ€‰km northward shift in bird and butterfly communities, respectively. We further found that, during the same period, the northward shift in temperature in Europe was even faster, so that the climatic debts of birds and butterflies correspond to a 212 and 135ĝ€‰km lag behind climate. Our results indicate both that birds and butterflies do not keep up with temperature increase and the accumulation of different climatic debts for these groups at national and continental scales.
The contemporary literature accepts that disturbance strongly influences pat-terns of species diversity, and that the relationship is peaked, with a maximum at inter-mediate levels of disturbance. We tested this hypothesis using a compilation of published species diversity–disturbance relationships that were gleaned from a literature search of papers published from 1985 through 1996 and from references therein. We identified 116 species richness–, 53 diversity–, and 28 evenness–disturbance relationships in the literature, which we grouped according to shape of relationship (nonsignificant, peaked, negative monotonic, positive monotonic, or U-shaped). We tested the relationships between the strength and shapes of these relationships and attributes of the community, disturbance, and sampling and study design. Nonsignificant relationships were the most common, com-prising 35% of richness, 28% of diversity, and 50% of evenness studies. Peaked responses were reported in only 16% of richness, 19% of diversity, and 11% of evenness cases. Explained variation in the three measures of diversity was variable among studies but averaged 50%. It was higher when few samples and few disturbance levels were examined and when organisms within the samples were not exhaustively censused, suggesting that procedural artifact contributes to these relationships. Explained variation was also higher in studies in which disturbance was measured as a gradient of time passed since the last disturbance (mean r 2 61%), vs. studies of spatial variation in richness (mean r 2 42%). Peaked richness relationships had the greatest odds of being observed when sampled area and actual evapotranspiration were small, when disturbances were natural rather than an-thropogenic in origin, and when few disturbance levels were examined. Thus, on average, diversity–disturbance relationships do not have consistently high r 2 and are not as consis-tently peaked as the contemporary consensus would suggest.
Functional diversity (FD) is a key facet of biodiversity used to address central questions in ecology. Despite recent methodological advances, FD remains a complex concept and no consensus has been reached either on how to quantify it, or on how it influences ecological processes. Here we define FD as the distribution of trait values within a community. When and how to account for intraspecific trait variability (ITV) when measuring FD remains one of the main current debates. It remains however unclear to what extent accounting for population-level ITV would modify FD quantification and associated conclusions. In this paper, we address two critical questions: (1) How sensitive are different components of FD to the inclusion of population-level ITV? (2) Does the omission of ITV obscure the understanding of ecological patterns? Using a mixture of empirical data and simulation experiments, we conducted a sensitivity analysis of four commonly used FD indices (community weighted mean traits, functional richness, Rao's quadratic entropy, Petchey and Gaston's FD index) and their relationships with environmental gradients and species richness, by varying both the extent (plasticity or not) and the structure (contingency to environmental gradient due to local adaptation) of population-level ITV. Our results suggest that ITV may strongly alter the quantification of FD and the detection of ecological patterns. Our analysis highlights that 1) species trait values distributions within communities are crucial to the sensitivity to ITV, 2) ITV structure plays a major role in this sensitivity and 3) different indices are not evenly sensitive to ITV, the single-trait FD from Petchey and Gaston being the most sensitive among the four metrics tested. We conclude that the effects of intraspecific variability in trait values should be more systematically tested before drawing central conclusions on FD, and suggest the use of simulation studies for such sensitivity analyses.
Summary • Climate change impacts have been observed on individual species and species subsets; however, it remains to be seen whether there are systematic, coherent assemblage-wide responses to climate change that could be used as a representative indicator of changing biological state. • European shelf seas are warming faster than the adjacent land masses and faster than the global average. We explore the year-by-year distributional response of North Sea bottom-dwelling (demersal) fishes to temperature change over the 25 years from 1980 to 2004. The centres of latitudinal and depth distributions of 28 fishes were estimated from species-abundance–location data collected on an annual fish monitoring survey. • Individual species responses were aggregated into 19 assemblages reflecting physiology (thermal preference and range), ecology (body size and abundance-occupancy patterns), biogeography (northern, southern and presence of range boundaries), and susceptibility to human impact (fishery target, bycatch and non-target species). • North Sea winter bottom temperature has increased by 1·6 °C over 25 years, with a 1 °C increase in 1988–1989 alone. During this period, the whole demersal fish assemblage deepened by ~3·6 m decade−1 and the deepening was coherent for most assemblages. • The latitudinal response to warming was heterogeneous, and reflects (i) a northward shift in the mean latitude of abundant, widespread thermal specialists, and (ii) the southward shift of relatively small, abundant southerly species with limited occupancy and a northern range boundary in the North Sea. • Synthesis and applications. The deepening of North Sea bottom-dwelling fishes in response to climate change is the marine analogue of the upward movement of terrestrial species to higher altitudes. The assemblage-level depth responses, and both latitudinal responses, covary with temperature and environmental variability in a manner diagnostic of a climate change impact. The deepening of the demersal fish assemblage in response to temperature could be used as a biotic indicator of the effects of climate change in the North Sea and other semi-enclosed seas.
Human land use and climate change are regarded as the main driving forces of present-day and future species extinction. They may potentially lead to a profound reorganisation of the composition and structure of natural communities throughout the world. However, studies that explicitly investigate both forms of impact--land use and climate change--are uncommon. Here, we quantify community change of Dutch breeding bird communities over the past 25 years using time lag analysis. We evaluate the chronological sequence of the community temperature index (CTI) which reflects community response to temperature increase (increasing CTI indicates an increase in relative abundance of more southerly species), and the temporal trend of the community specialisation index (CSI) which reflects community response to land use change (declining CSI indicates an increase of generalist species). We show that the breeding bird fauna underwent distinct directional change accompanied by significant changes both in CTI and CSI which suggests a causal connection between climate and land use change and bird community change. The assemblages of particular breeding habitats neither changed at the same speed and nor were they equally affected by climate versus land use changes. In the rapidly changing farmland community, CTI and CSI both declined slightly. In contrast, CTI increased in the more slowly changing forest and heath communities, while CSI remained stable. Coastal assemblages experienced both an increase in CTI and a decline in CSI. Wetland birds experienced the fastest community change of all breeding habitat assemblages but neither CTI nor CSI showed a significant trend. Overall, our results suggest that the interaction between climate and land use changes differs between habitats, and that comparing trends in CSI and CTI may be useful in tracking the impact of each determinant.
A common bioassay problem in applied ecology is to estimate values of an environmental variable from species incidence or abundance data. An example is the problem of reconstructing past changes in acidity (pH) in lakes from diatom assemblages found in successive strata of the bottom sediment. The method of weighted averaging is based on indicator values, the indicator value of a species being, intuitively, the value of the environmental variable most preferred by that species. Indicator values of all species present in a site are averaged to give an estimate of the value of the environmental variable at the site. The average is weighted by species abundances, if known, with absent species having zero weight. Using field data, several authors have compiled lists of indicator values of species for various environmental variables for use in weighted averaging, e.g. pH indicator values of diatom species. In this paper the properties of the method of weighted averaging are studied, starting from the idea that indicator values are parameters of response curves that describe the expected abundance of each species in relation to the environmental variable. In practice the response curves must be estimated by regression methods, but here they are assumed to be known in advance. Conditions are derived under which the weighted average is a consistent and efficient estimator for the value of an environmental variable at a site. Because weighted averaging is central to the ordination technique known as reciprocal averaging or correspondence analysis, the conditions also define models that are implicitly invoked when reciprocal averaging is used in ecological ordination studies.
Despite being recognized as a promoter of diversity and a condition for local coexistence decades ago, the importance of intraspecific variance has been neglected over time in community ecology. Recently, there has been a new emphasis on intraspecific variability. Indeed, recent developments in trait-based community ecology have underlined the need to integrate variation at both the intraspecific as well as interspecific level. We introduce new T-statistics ('T' for trait), based on the comparison of intraspecific and interspecific variances of functional traits across organizational levels, to operationally incorporate intraspecific variability into community ecology theory. We show that a focus on the distribution of traits at local and regional scales combined with original analytical tools can provide unique insights into the primary forces structuring communities.
Predicting species' responses to the combined effects of habitat and climate changes has become a major challenge in ecology and conservation biology. However, the effects of climatic and habitat gradients on species distributions have generally been considered separately. Here, we explore the relationships between the habitat and thermal dimensions of the ecological niche in European common birds. Using data from the French Breeding Bird Survey, a large-scale bird monitoring program, we correlated the habitat and thermal positions and breadths of 74 bird species, controlling for life history traits and phylogeny. We found that cold climate species tend to have niche positions in closed habitats, as expected by the conjunction of the biogeographic history of birds' habitats, and their current continent-scale gradients. We also report a positive correlation between thermal and habitat niche breadths, a pattern consistent with macroecological predictions concerning the processes shaping species' distributions. Our results suggest that the relationships between the climatic and habitat components of the niche have to be taken into account to understand and predict changes in species' distributions.
Metacommunity theory has advanced understanding of how spatial dynamics and local interactions shape community structure and biodiversity. Here, we review empirical approaches to metacommunities, both observational and experimental, pertaining to how well they relate to and test theoretical metacommunity paradigms and how well they capture the realities of natural ecosystems. First, we show that the species-sorting and mass-effects paradigms are the most commonly tested and supported paradigms. Second, the dynamics observed can often be ascribed to two or more of the four non-exclusive paradigms. Third, empirical approaches relate only weakly to the concise assumptions and predictions made by the paradigms. Consequently, we suggest major avenues of improvement for empirical metacommunity approaches, including the integration across theoretical approaches and the incorporation of evolutionary and meta-ecosystem dynamics. We hope for metacommunity ecology to thereby bridge existing gaps between empirical and theoretical work, thus becoming a more powerful framework to understand dynamics across ecosystems.
Different components of global change can have interacting effects on biodiversity and this may influence our ability to detect the specific consequences of climate change through biodiversity indicators. Here, we analyze whether climate change indicators can be affected by land use dynamics that are not directly determined by climate change. To this aim, we analyzed three community-level indicators of climate change impacts that are based on the optimal thermal environment and average latitude of the distribution of bird species present at local communities. We used multiple regression models to relate the variation in climate change indicators to: i) environmental temperature; and ii) three landscape gradients reflecting important current land use change processes (land abandonment, fire impacts and urbanization), all of them having forest areas at their positive extremes. We found that, with few exceptions, landscape gradients determined the figures of climate change indicators as strongly as temperature. Bird communities in forest habitats had colder-dwelling bird species with more northern distributions than farmland, burnt or urban areas. Our results show that land use changes can reverse, hide or exacerbate our perception of climate change impacts when measured through community-level climate change indicators. We stress the need of an explicit incorporation of the interactions between climate change and land use dynamics to understand what are current climate change indicators indicating and be able to isolate real climate change impacts.
Effects of climate change on species occupying distinct areas during their life cycle are still unclear. Moreover, although effects of climate change have widely been studied at the species level, less is known about community responses. Here, we test whether and how the composition of wader (Charadrii) assemblages, breeding in high latitude and wintering from Europe to Africa, is affected by climate change over 33 years. We calculated the temporal trend in the community temperature index (CTI), which measures the balance between cold and hot dwellers present in species assemblages. We found a steep increase in the CTI, which reflects a profound change in assemblage composition in response to recent climate change. This study provides, to our knowledge, the first evidence of a strong community response of migratory species to climate change in their wintering areas.
Natural populations consist of phenotypically diverse individuals that exhibit variation in their demographic parameters and intra- and inter-specific interactions. Recent experimental work indicates that such variation can have significant ecological effects. However, ecological models typically disregard this variation and focus instead on trait means and total population density. Under what situations is this simplification appropriate? Why might intraspecific variation alter ecological dynamics? In this review we synthesize recent theory and identify six general mechanisms by which trait variation changes the outcome of ecological interactions. These mechanisms include several direct effects of trait variation per se and indirect effects arising from the role of genetic variation in trait evolution.
Aims
Climate change is known to drive both the reshuffling of whole assemblages and range shifts of individual species. Less is known about how local colonizations and extinctions of individual species contribute to changes at the community level. Our aim was to estimate the contribution of individual species to a change in community composition attributed to climate change and to relate these species‐specific contributions to species’ commonness, climatic niche characteristics and life history traits most likely to influence species sensitivity to climate change.
Location
Sweden.
Methods
Focussing on birds, we analysed changes from 1998 to 2012 in the Community Temperature Index ( CTI ), a measure of the average climatic niche of a community. Using a jackknife approach we assessed the contribution of individual species to the temporal trend in CTI in four different regions across Sweden, controlling for habitat distribution. We further tested whether species contribution was related to population trends and rarity to identify species most vulnerable to climate change.
Results
Community Temperature Index had increased over time with the greatest gains occurring in the north of the country, reflecting the larger temperature increases in this area. Changes in the regional CTI were driven both by warm‐dwelling species colonizing new sites and by extirpations of cold‐dwelling species. Furthermore, the community changes were influenced by both rare and common species. At the same time, the distribution changes of a large number of species were seemingly unaffected by climate change.
Main conclusions
Both range expansion and contractions contributed to the relative increase of warm‐dwelling species in Swedish bird communities. We successfully identified the climatic impacts on some of Sweden's rarest species, including cold‐dwelling species in the mountainous north. Our approach may be an efficient tool to use when characterizing the impacts of climate change on species and communities.
A measure of diversity can be based on Simpson's index λ, which is the abundance-weighted mean of species proportions. Likewise, an index of evenness, E(MS)=(Σ p(i)/2)2/Σ p(i)/3, can be based on the abundance-weighted coefficient of variation of species proportions p(i). E(MS) measures the shape of the species-abundance relation, and is 0.75 + 0.25λ2 for the geometric series distribution. This simple relation allows the geometric series to be used as a benchmark; communities that have relatively long 'tails' of rare species have correspondingly low evenness, whereas communities with short 'tails' have high evenness. Except for species richness, there is no necessity to reject the view that diversity and evenness are measurable parameters of a community rather than statistics of a sample.
Humans are transforming the biosphere in unprecedented ways, raising the important question of how these impacts are changing biodiversity. Here we argue that our understanding of biodiversity trends in the Anthropocene, and our ability to protect the natural world, is impeded by a failure to consider different types of biodiversity measured at different spatial scales. We propose that ecologists should recognize and assess 15 distinct categories of biodiversity trend. We summarize what is known about each of these 15 categories, identify major gaps in our current knowledge, and recommend the next steps required for better understanding of trends in biodiversity.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Biodiversity is undergoing unprecedented global decline. Efforts to slow this rate have focused foremost on rarer species, which are at most risk of extinction. Less interest has been paid to more common species, despite their greater importance in terms of ecosystem function and service provision. How rates of decline are partitioned between common and less abundant species remains unclear. Using a 30-year data set of 144 bird species, we examined Europe-wide trends in avian abundance and biomass. Overall, avian abundance and biomass are both declining with most of this decline being attributed to more common species, while less abundant species showed an overall increase in both abundance and biomass. If overall avian declines are mainly due to reductions in a small number of common species, conservation efforts targeted at rarer species must be better matched with efforts to increase overall bird numbers, if ecological impacts of birds are to be maintained.
Intraspecific trait variability (ITV) plays a central part in various ecological processes, though using mean trait values may be sufficient in some instances. Ecologists need thus to find under which circumstances. Carlucci et al. (2014, this issue) bring new evidence on the importance of ITV for community assembly across a strong gradient. Sampling design may affect ITV quantification across gradients.
Theory predicts a positive relationship between biodiversity and stability in ecosystem properties, while diversity is expected to have a negative impact on stability at the species level. We used virtual experiments based on a dynamic simulation model to test for the diversity–stability relationship and its underlying mechanisms in Central European forests. First our results show that variability in productivity between stands differing in species composition decreases as species richness and functional diversity increase. Second we show temporal stability increases with increasing diversity due to compensatory dynamics across species, supporting the biodiversity insurance hypothesis. We demonstrate that this pattern is mainly driven by the asynchrony of species responses to small disturbances rather than to environmental fluctuations, and is only weakly affected by the net biodiversity effect on productivity. Furthermore, our results suggest that compensatory dynamics between species may enhance ecosystem stability through an optimisation of canopy occupancy by coexisting species.
Although climate change is acknowledged to affect population dynamics and species distribution, details of how community composition is affected are still lacking. We investigate whether ongoing changes in bird community composition can be explained by contemporary changes in summer temperatures, using four independent long-term bird census schemes from Sweden (up to 57 yr); two at the national scale and two at local scales. The change in bird community composition was represented by a community temperature index (CTI) that reflects the balance in abundance between low- and high-temperature dwelling species. In all schemes, CTI tracked patterns of temperature increase, stability or decrease remarkably well, with a lag period of 1–3 yr. This response was similar at both the national and local scale. However, the communities did not respond fast enough to cope with temperature increase, suggesting that community composition lags behind changes in temperature. The change in CTI was caused mainly by changes in species’ relative abundances, and less so by changes in species composition. We conclude that ongoing changes in bird community structure are driven to a large extent by contemporary changes in climate and that CTI can be used as a simple indicator for how bird communities respond.
Biomass production in grasslands, a key component of food provision for domestic herbivores, is known to depend on climate, resource availability, and on the functional characteristics of communities. However, the combined effects of these different factors remain largely unknown. The aim of the present study was to unravel the causes of variations in the standing biomass of plant communities using a long‐term experiment conducted in a Mediterranean rangeland of Southern France. Two management regimes, sheep grazing and grazing associated with mineral fertilization, were applied to different areas of the study site over the past 25 years. Abiotic (temperature, available water, nutrients) and biotic (components of the functional structure communities) factors were considered to explain interannual and spatial variations in standing biomass in these rangelands.
Standing biomass was highly predictable, with the best model explaining ∼80% of variations in the amount of biomass produced, but the variation explained by abiotic and biotic factors was dependent on the season and on the management regime. Abiotic factors were found to have comparable effects in both management regimes: The amount of biomass produced in the spring was limited by cold temperatures, while it was limited by water availability and high temperatures in the summer. In the fertilized community, the progressive change in the functional structure of the communities had significant effects on the amount of biomass produced: the dominance of few productive species which were functionally close led to higher peak standing biomass in spring.
The spatial distributions of species, and the resulting composition of local communities, are shaped by a complex interplay between species' climatic and habitat preferences. We investigated this interaction by analyzing how the climatic niches of bird species within given communities (measured as a community thermal index, CTI) are related to vegetation structure. Using 3129 bird communities from the French Breeding Bird Survey and an information theoretic multimodel inference framework, we assessed patterns of CTI variation along landscape scale gradients of forest cover and configuration. We then tested whether the CTI varies along local scale gradients of forest structure and composition using a detailed data set of 659 communities from six forests located in northwestern France. At landscape scale, CTI values decreased with increasing forest cover, indicating that bird communities were increasingly dominated by cold-dwelling species. This tendency was strongest at low latitudes and in landscapes dominated by unfragmented forest. At local scale, CTI values were higher in mature deciduous stands than in conifer or early stage deciduous stands, and they decreased consistently with distance from the edge of forest. These trends underpin the assertion that species' habitat use along forest gradients is linked with their climatic niche, although it remains unclear to what extent it is a direct consequence of microclimatic variation among habitats, or a reflection of macroscale correlations between species' thermal preferences and their habitat choice. Moreover, our results highlight the need to address issues of scale in determining how habitat and climate interact to drive the spatial distribution of species. This will be a crucial step towards accurate predictions of changes in the composition and dynamics of bird communities under global warming.
The North American Breeding Bird Survey (BBS) is an annual transect point-count survey of >500 species and >3,500 survey routes (transects). Observers drive and record birds seen and heard within a radius of 400 m of 50 survey points (“stops”) evenly spaced along a 39.4-km survey route. Thus, the land area along both sides of a route composes a linear or curvilinear landscape. Although BBS data have been used in many studies and conservation plans, there have been few attempts to determine how well the landscapes along BBS routes represent landscapes at larger spatial extents, particularly with regard to land-cover composition. Using data from the 2001 National Land Cover Database, we conducted a study of representativeness of 3,230 routes by comparing the differences in percent cover of 15 land-cover types in BBS landscapes (buffer width of 0.4 km surrounding a route) to larger local landscapes (10 km buffer width) and regions. At the local level, BBS landscapes were representative for most of the cover types except open water, which was underrepresented, and lightly developed open space, which was overrepresented. At the regional level, the collective composition of BBS landscapes was very similar to the composition within entire Bird Conservation Regions. Overall, these results should encourage the continued use of BBS data in ornithological and ecological research and in conservation planning.
Volunteer-based standardized monitoring of birds has been widely implemented in Europe and North America. In France, a breeding bird survey is running since 1989 and offers keen birdwatchers to count spring birds annually during 5 min exactly on 10 fix points within a randomly selected square. The first goal of such breeding bird surveys is to measure temporal trends in order to detect possible species declines. Combining annual indices of species sharing ecological affinities or a protected/red list status further provides biodiversity indicators for policy makers. Because the sampling effort is similar among sites, and because the initial selection of monitored sites is random, the temporal trends can be considered representative of national trends, and spatial comparisons of the obtained metrics are possible. Species abundance, community richness but also community specialization and average trophic level can be estimated for each site and each year and further related to the wide range of habitat and landscape characteristics and to agricultural or forestry practices. The large number of sites allows overcoming the opposition between adaptive and passive monitoring, making such schemes fitted to adaptive monitoring. This provides opportunities to determine which type of management or practices favour biodiversity. The comparison of population fate or community dynamics across a wide range of climates and temperatures, e.g. from southern to northern Europe, revealed how European birds are already affected by climate change. Bird communities are shifting northwards, but at a slower rate than temperatures, while bird populations have larger growth rates away from their hot thermal limit. Finally, such large-scale long-term monitoring data on a complete taxonomic group (Aves) is original and offers the opportunity to compare different measures of biological diversity, such as taxonomic, phylogenetic and functional diversity. Such a citizen science scheme is an efficient scientific tool (numerous papers published in international peer-reviewed journals) which is furthermore highly cost-effective, with a reduced permanent staff in a state insitution coordonating the network and analysing the data, while a similar survey conducted by state staff only would cost more than one million euros annually. The future development of bio-economic dynamic models for providing scenarios of sustainable farming and logging to maintain biodiversity will further highlight the necessity of such volunteer monitoring for policy makers and decision planning. Scientific and logistic partnerships could be proposed to help developing such a monitoring scheme in China.
Although climate is known to play an important role in structuring biological communities, high‐resolution analyses of recent climatic impacts on multiple components of diversity are still sparse. Additionally, there is a lack of knowledge about which species drive community response to environmental change.
We used a long‐term breeding bird data set that encompasses a large latitudinal and altitudinal range to model the effect of temperature on spatial and temporal patterns in alpha and beta diversity. We also established a novel framework for identifying species‐specific contributions to these macroecological patterns, hence combining two different approaches for identifying climatic impacts.
Alpha diversity increased over time, whilst beta diversity declined; both diversity metrics showed a significant relationship with recent temperature anomalies. By partitioning beta diversity, we showed that the decline was predominately driven by changes in species turnover rather than nestedness suggesting a process of replacement by more common species.
Using jackknife analyses we identified how individual species influenced the modelled relationships of diversity with temperature and time. Influential species tended to be habitat generalists with moderate to large distributions.
We demonstrate that different facets of avian diversity can respond rapidly to temperature anomalies and as a result have undergone significant changes in the last decade. In general, it appears that warming temperatures are driving compositional homogenization of temperate bird communities via range expansion of common generalist species.
Recent studies from mountainous areas of small spatial extent (<2,500 km2) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2,500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT), and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1,000-m2 units (community-inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1-km2 units; (2) the relationship between CiT range and topographically- and geographically-derived predictors at 1-km resolution; and (3) whether spatial turnover in CiT is greater than spatial turnover in GiT within 100-km2 units. Ellenberg temperature indicator values in combination with plant assemblages explained 46-72% of variation in LmT and 92-96% of variation in GiT during the growing season (June, July, August). Growing-season CiT range within 1-km2 units peaked at 60-65°N and increased with terrain roughness, averaging 1.97°C (SD = 0.84°C) and 2.68°C (SD = 1.26°C) within the flattest and roughest units, respectively. Complex interactions between topography-related variables and latitude explained 35% of variation in growing-season CiT range when accounting for sampling effort and residual spatial autocorrelation. Spatial turnover in growing-season CiT within 100-km2 units was, on average, 1.8 times greater (0.32°C km-1) than spatial turnover in growing-season GiT (0.18°C km-1). We conclude that thermal variability within 1-km2 units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains.
Questions: How can one explicitly quantify, and separately measure, stress and disturbance gradients? How do these gradients affect functional composition in early successional plant communities and to what extent? Can we accurately predict trait composition from knowledge of these gradients?
Location: Southern Quebec, Canada.
Methods: Using eight environmental variables measured in 48 early successional plant communities, we estimated stress and disturbance gradients through structural equation modelling. We then measured 10 functional traits on the most abundant species of these 48 communities and calculated their community-level mean and variance weighted by the relative abundance of each species. Finally, we related these community-weighted means and variances to the estimated stress and disturbance gradients using general linear models or generalized additive models.
Results: We obtained a well-fitting measurement model of the stress and disturbance gradients existing in our sites. Of the 10 studied traits, only average plant reproductive height was strongly correlated with the stress (r2=0.464) and disturbance (r2=0.543) gradients. Leaf traits were not significantly related to either the stress or disturbance gradients.
Conclusions: The well-fitting measurement model of the stress and disturbance gradients, combined with the generally weak trait–environment linkages, suggests that community assembly in these early successional plant communities is driven primarily by stochastic processes linked to the history of arrival of propagules and not to trait-based environmental filtering.
Aim Worldwide, functional homogenization is now considered to be one of the most prominent forms of biotic impoverishment induced by current global changes. Yet this process has hardly been quantified on a large scale through simple indices, and the connection between landscape disturbance and functional homogenization has hardly been established. Here we test whether changes in land use and landscape fragmentation are associated with functional homogenization of bird communities at a national scale.
Location France.
Methods We estimated functional homogenization of a community as the average specialization of the species present in that community. We studied the spatial variation of this community specialization index (CSI) using 1028 replicates from the French Breeding Bird Survey along spatial gradients of landscape fragmentation and recent landscape disturbance, measured independently, and accounting for spatial autocorrelation.
Results The CSI was very sensitive to both measures of environmental degradation: on average, 23% of the difference in the CSI values between two sample sites was attributed to the difference in fragmentation and the disturbance between sites. This negative correlation between CSI and sources of landscape degradation was consistent over various habitats and biogeographical zones.
Main conclusions We demonstrate that the functional homogenization of bird communities is strongly positively correlated to landscape disturbance and fragmentation. We suggest that the CSI is particularly effective for measuring functional homogenization on both local and global scales for any sort of organism and with abundance or presence–absence data.
In its simplest definition, a trait is a surrogate of organismal performance, and this meaning of the term has been used by evolutionists for a long time. Over the last three decades, developments in community and ecosystem ecology have forced the concept of trait beyond these original boundaries, and trait-based approaches are now widely used in studies ranging from the level of organisms to that of ecosystems. Despite some attempts to fix the terminology, especially in plant ecology, there is currently a high degree of confusion in the use, not only of the term “trait” itself, but also in the underlying concepts it refers to. We therefore give an unambiguous definition of plant trait, with a particular emphasis on functional trait. A hierarchical perspective is proposed, extending the “performance paradigm” to plant ecology. “Functional traits” are defined as morpho-physio-phenological traits which impact fitness indirectly via their effects on growth, reproduction and survival, the three components of individual performance. We finally present an integrative framework explaining how changes in trait values due to environmental variations are translated into organismal performance, and how these changes may influence processes at higher organizational levels. We argue that this can be achieved by developing “integration functions” which can be grouped into functional response (community level) and effect (ecosystem level) algorithms.
Few studies have examined how life history traits and the climate envelope influence the ability of species to respond to climate change and habitat degradation. In this study, we test whether 18 species-specific variables, related to the climate envelope, ecological envelope and life history, could predict recent population trends (over 17 years) of 71 common breeding bird species in France. Habitat specialists were declining at a much higher rate than generalists, a sign that habitat quality is decreasing globally. The lower the thermal maximum (temperature at the hot edge of the climate envelope), the more negative are the population trends and the less tolerant these species are climate warming, regardless of the thermal range over which these species occur. The life history trait ‘the number of broods per year’ was positively related to recent trends, suggesting that single-brooded species might be more sensitive to advances in food peak due to climate change, as it increases the risk of mistiming their single-breeding event. Annual fecundity explained long-term declines, as it is a good proxy for most other demographic rates, with shorter-lived species being more sensitive to global change: individuals of species with higher fecundity might have too short a life to learn to adapt to directional changes in their environment. Finally, there was evidence that natal dispersal was a predictor of recent trends, with species with high natal dispersal experiencing smaller population declines than species with low natal dispersal. This is expected if the higher the natal dispersal, the larger the ability to shift spatially when facing changes in local habitat or climate, in order to track optimal conditions and adapt to global change. Identifying decline-promoting factors allow us to infer mechanisms responsible for observed declines in wild bird populations facing global change, and by doing so allow for a more pre-emptive approach to conservation planning.
Climate change, habitat degradation, and direct exploitation are thought to threaten biodiversity. But what makes some species more sensitive to global change than others? Approaches to this question have relied on comparing the fate of contrasting groups of species. However, if some ecological parameter affects the fate of species faced with global change, species response should vary smoothly along the parameter gradient. Thus, grouping species into few, often two, discrete classes weakens the approach. Using data from the common breeding bird survey in France – a large set of species with much variability with respect to the variables considered – we show that a quantitative measure of habitat specialization and of latitudinal distribution both predict recent 13 year trends of population abundance among 77 terrestrial species: the more northerly distributed and the more specialized a species is, the sharper its decline. On the other hand, neither hunting status, migrating strategy nor body mass predicted population growth rate variation among common bird species. Overall, these results are qualitatively very similar to the equivalent relationships found among the British butterfly populations. This constitutes additional evidence that biodiversity in Western Europe is under the double negative influence of climate change and land use change.
Evidence is accumulating of shifts in species' distributions during recent climate warming. However, most of this information comes predominantly from studies of a relatively small selection of taxa (i.e., plants, birds and butterflies), which may not be representative of biodiversity as a whole. Using data from less well-studied groups, we show that a wide variety of vertebrate and invertebrate species have moved northwards and uphill in Britain over approximately 25 years, mirroring, and in some cases exceeding, the responses of better-known groups.
Two decades of intensive research have provided compelling evidence for a link between biodiversity and ecosystem functioning (B-EF). Whereas early B-EF research concentrated on species richness and single processes, recent studies have investigated different measures of both biodiversity and ecosystem functioning, such as functional diversity and joint metrics of multiple processes. There is also a shift from viewing assemblages in terms of their contribution to particular processes toward placing them within a wider food web context. We review how the responses and predictors in B-EF experiments are quantified and how biodiversity effects are shaped by multitrophic interactions. Further, we discuss how B-EF metrics and food web relations could be addressed simultaneously. We conclude that addressing traits, multiple processes and food web interactions is needed to capture the mechanisms that underlie B-EF relations in natural assemblages.