Advances, challenges and a developing synthesis of ecological community assembly theory

Phytoplankton assemblage structure, drivers, and thresholds with a focus on harmful algal bloom ecology in the Lake Okeechobee system, Florida, USA

Untangling the complexities of harmful algal bloom (HAB) dynamics is an ongoing effort that requires a fundamental understanding of spatiotemporal phytoplankton patterns and the environmental filters through which assemblages are structured. To this aim, monthly field surveys were conducted from 2019 to 2021 at 21 sites in Lake Okeechobee, Florida - a large, shallow, eutrophic, and heavily managed lake with coastal connectivity that experiences intense and recurrent HABs. Phytoplankton assemblages were strongly spatially structured forming 7 distinct lake zones with significant dissimilarity in composition and total abundance. While successional patterns were not apparent across seasons or wet/dry periods, total phytoplankton abundance was significantly greater towards the end of the wet season. Distance-based linear models using 16 abiotic variables were used to identify significant explanatory variables of spatial and temporal patterns. The spatial model explained 93 % of the variability suggesting deterministic processes largely control spatial patterns. The temporal model explained only 48 % of the temporal variability suggesting stochasticity in lake-wide shifts in assemblages over time. However, the strong spatial structuring of assemblages may preclude lake-wide succession patterns. Total algal abundance metrics were inversely related to nitrate, orthophosphate, and total alkalinity, the strongest explanatory variables of assemblage patterns, suggesting a lag between peak resources and peak abundance as phytoplankton cycle "boom-to-bust" phases. Consistent with this inverse relationship, Threshold Indicator Taxa Analysis returned almost exclusively negative responder indicator taxa for all three explanatory variable gradients. The assemblage-level threshold defined the gradient boundary between boom- and bust-associated indicator taxa. These data contribute novel information about HABs ecology pertinent to management strategies.

Co-Occurrence Patterns of Aquatic Macroinvertebrates in Laurentian Great Lakes Coastal Wetlands

In niche-based community assembly theory, it is presumed that communities in habitats with high natural disturbance regimes are less likely to be structured by competitive mechanisms. Laurentian Great Lakes (hereafter Great Lakes) coastal wetlands can experience drastic diel fluctuations in dissolved oxygen levels, severe wave action, ice scour, and near complete freezing during the winter such that conditions are inhospitable for most organisms. The high natural disturbance levels are thought to cause high interannual turnover for aquatic macroinvertebrate communities and support the hypothesis that these communities are less likely to experience less competitive interactions and negative co-occurrence structure. We hypothesize that non-random co-occurrence patterns will be rare in Great Lake coastal wetlands and non-competitive processes (e.g., through shared or differential microhabitat affinities, pollution tolerances, or biotic homogenization) will be more common than competitively driven negative co-occurrence patterns. Null model analysis was performed on 134 macroinvertebrate communities sampled from across the Great Lakes basin from 2000 to 2013. To disentangle the effects of alternative structuring mechanisms (i.e., shared/differential habitat affinities, shared/differential pollution tolerance, and biological homogenization/competitive exclusion), communities were parsed based on the year sampled, the vegetation type from which community samples were collected, and lastly species' functional feeding group assignment or taxonomic group. As expected, very few communities were non-randomly structured; however, all of those that were non-random exhibited showed more negative co-occurrences than by chance. Upon further investigation, these communities consisted of species that are known to overwinter in wetlands, and therefore, avoid having to recolonize after each spring thaw. With expected changes in habitat conditions due to climate change, we propose that null model analyses can be used as an early warning system for community change.

Spatial patterning and species coexistence: A case study using concentric circular vegetation patches in saline land

Spatial patterns in plant community structures within stressed ecosystems have drawn much attention in the field of ecology. However, the mechanisms underlying spatial formation and its impact on species coexistence and diversity remain controversial. In this study, we investigated concentric circular vegetation patches in coastal saline land, and analysed the spatial patterning of plant communities and associated soil physicochemical properties. Thereafter, we tested how the soil conditioned by plant communities from different locations within the vegetation patches influence the species growth and inter-specific competition. Our results show soil salinity enlarges in a centrifugal manner in horizontal direction in all patches. Soil salinity decreased and species diversity increased along with the increase of patch size. In addition, we found significant shifts in both the composition of plant communities and in soil physicochemical properties from outer to center. The results indicate that the pioneer species Suaeda salsa facilitated the subsequent species. However Suaeda salsa was inhibited and became inferior competitor in the soil conditioned by the subsequent species. We infer that the less-visible spatial patterns of soil physicochemical properties at small scales create ecological niches for specialized species, allowing them to coexist but not mix. We suggest that a trade-off between tolerance to salt stress and competitive ability under ameliorated conditions may underlie mechanisms of pattern formation in small scale. Our findings lend support to the idea that soil stress constraints community assembly and triggers spatial patterns, which, in turn, buffer the stress on plant communities and enhance species diversity.

The development of ecological systems along paths of least resistance

A long-standing question in biology is whether there are common principles that characterize the development of ecological systems (the appearance of a group of taxa), regardless of organismal diversity and environmental context.1,2,3,4,5,6,7,8,9,10,11 Classic ecological theory holds that these systems develop following a sequenced, orderly process that generally proceeds from fast-growing to slow-growing taxa and depends on life-history trade-offs.2,12,13 However, it is also possible that this developmental order is simply the path with the least environmental resistance for survival of the component species and hence favored by probability alone. Here, we use theory and data to show that the order from fast- to slow-growing taxa is the most likely developmental path for diverse systems when local taxon interactions self-organize in light of environmental resistance. First, we demonstrate theoretically that a sequenced development is more likely than a simultaneous one, at least until the number of iterations becomes so large as to be ecologically implausible. We then show that greater diversity of taxa and life histories improves the likelihood of a sequenced order from fast- to slow-growing taxa. Using data from bacterial and metazoan systems,14,15,16,17,18,19 we present empirical evidence that the developmental order of ecological systems moves along the paths of least environmental resistance. The capacity of simple principles to explain the trend in the developmental order of diverse ecological systems paves the way to an enhanced understanding of collective features of life.

Trait-based community assembly and functional strategies across three subtropical karst forests, Southwestern China

Background

Variations in community-level plant functional traits are widely used to elucidate vegetation adaptation strategies across different environmental gradients. Moreover, studying functional variation among different forest types aids in understanding the mechanisms by which environmental factors and functional strategies shift community structure.

Methods

Based on five plant functional traits, including four leaf and one wood trait, for 150 woody species, we analyzed shifts in the community-weighted mean trait values across three forest types in a karst forest landscape: deciduous, mixed, and evergreen forests. We also assessed the relative contributions of stochastic processes, environmental filtering, and niche differentiation to drive community structure using a trait-based null model approach.

Results

We found marked changes in functional strategy, from resource acquisition on dry, fertile soil plots in deciduous forests to resource conservation on moist, infertile soil conditions in evergreen forests. The trait-based null model showed strong evidence of environmental filtering and convergent patterns in traits across three forest types, as well as low niche differentiation in most functional traits. Some evidence of overdispersion of LDMC and LT occurred to partially support the recent theory of Scheffer and Van Nes that competition could result in a clumped pattern of species along a niche axis.

Discussion

Our findings suggest a change in environmental gradient from deciduous to evergreen forest, together with a shift from acquisitive to conservative traits. Environmental filtering, stochastic processes, niche differentiation, and overdispersion mechanisms together drive community assembly in karst forest landscapes. These findings will contribute to a deeper understanding of the changes in functional traits among karst plants and their adaptive strategies, with important implications for understanding other community assemblies in subtropical forest systems.

Stable body sizes in soil nematodes across altitudes: The role of intrageneric variation in community assembly

Animal body size exhibits rapid responses to environmental variations and displays considerable variability across ecological scales, significantly influencing ecological community assembly. However, our understanding of the extent of body size variation and its responses to environmental differences within soil fauna remains limited, impeding a comprehensive grasp of soil fauna's functional ecology. Here, we aim to investigate the magnitude of intrageneric body size variation and its implications for soil nematode community assembly along an altitudinal gradient. We examined soil nematode body size responses along an altitudinal gradient spanning from 3136 to 4128 m in an alpine mountain region of the eastern Tibetan Plateau. We assessed the contributions of intra- and intergeneric variations in body size, both within and among communities, using individual body size values. The implications of these variations for community assembly processes were determined through phenotypic variance ratios employing permutation tests. Our analyses did not reveal statistically significant correlations between altitude and the community-weighted mean body mass, regardless of considering intrageneric trait variation (IGTV). Approximately 15% of the variation in body size among communities and a substantial 72% of the variation in body size within communities can be attributed to IGTV. Altitude did not significantly affect IGTV within or among communities. Furthermore, our results underscored the dominant role of internal filtering within the community in governing nematode community assembly, with external filtering outside the community playing a limited role within our altitudinal range. Our findings emphasize the dominant role of body size variation within communities rather than among communities, attributable to strong internal filtering processes. These findings advance our understanding of body size variation in soil nematodes across ecological scales and highlight the pivotal role of intrageneric variation in shaping the functional ecology of soil fauna.

Community assembly influences plant trait economic spectra and functional trade-offs at ecosystem scales

Plant functional traits hold the potential to greatly improve the understanding and prediction of climate impacts on ecosystems and carbon cycle feedback to climate change. Traits are commonly used to place species along a global conservative-acquisitive trade-off, yet how and if functional traits and conservative-acquisitive trade-offs scale up to mediate community and ecosystem fluxes is largely unknown. Here, we combine functional trait datasets and multibiome datasets of forest water and carbon fluxes at the species, community, and ecosystem-levels to quantify the scaling of the tradeoff between maximum flux and sensitivity to vapor pressure deficit. We find a strong conservative-acquisitive trade-off at the species scale, which weakens modestly at the community scale and largely disappears at the ecosystem scale. Functional traits, particularly plant water transport (hydraulic) traits, are strongly associated with the key dimensions of the conservative-acquisitive trade-off at community and ecosystem scales, highlighting that trait composition appears to influence community and ecosystem flux dynamics. Our findings provide a foundation for improving carbon cycle models by revealing i) that plant hydraulic traits are most strongly associated with community- and ecosystem scale flux dynamics and ii) community assembly dynamics likely need to be considered explicitly, as they give rise to ecosystem-level flux dynamics that differ substantially from trade-offs identified at the species-level.

Decoupled response of microbial taxa and functions to nutrients: The role of stoichiometry in plantations

The resource quantity and elemental stoichiometry play pivotal roles in shaping belowground biodiversity. However, a significant knowledge gap remains regarding the influence of different plant communities established through monoculture plantations on soil fungi and bacteria's taxonomic and functional dynamics. This study aimed to elucidate the mechanisms underlying the regulation and adaptation of microbial communities at the taxonomic and functional levels in response to communities formed over 34 years through monoculture plantations of coniferous species (Japanese larch, Armand pine, and Chinese pine), deciduous forest species (Katsura), and natural shrubland species (Asian hazel and Liaotung oak) in the temperate climate. The taxonomic and functional classifications of fungi and bacteria were examined for the mineral topsoil (0-10 cm) using MiSeq-sequencing and annotation tools of microorganisms (FAPROTAX and Funguild). Soil bacterial (6.52 ± 0.15) and fungal (4.46 ± 0.12) OTUs' diversity and richness (5.83*103±100 and 1.12*103±46.4, respectively) were higher in the Katsura plantation compared to Armand pine and Chinese pine. This difference was attributed to low soil DOC/OP (24) and DON/OP (11) ratios in the Katsura, indicating that phosphorus availability increased microbial community diversity. The Chinese pine plantation exhibited low functional diversity (3.34 ± 0.04) and richness (45.2 ± 0.41) in bacterial and fungal communities (diversity 3.16 ± 0.15 and richness 56.8 ± 3.13), which could be attributed to the high C/N ratio (25) of litter. These findings suggested that ecological stoichiometry, such as of enzyme, litter C/N, soil DOC/DOP, and DON/DOP ratios, was a sign of the decoupling of soil microorganisms at the genetic and functional levels to land restoration by plantations. It was found that the stoichiometric ratios of plant biomass served as indicators of microbial functions, whereas the stoichiometric ratios of available nutrients in soil regulated microbial genetic diversity. Therefore, nutrient stoichiometry could serve as a strong predictor of microbial diversity and composition during forest restoration.

Unlocking ensemble ecosystem modelling for large and complex networks

The potential effects of conservation actions on threatened species can be predicted using ensemble ecosystem models by forecasting populations with and without intervention. These model ensembles commonly assume stable coexistence of species in the absence of available data. However, existing ensemble-generation methods become computationally inefficient as the size of the ecosystem network increases, preventing larger networks from being studied. We present a novel sequential Monte Carlo sampling approach for ensemble generation that is orders of magnitude faster than existing approaches. We demonstrate that the methods produce equivalent parameter inferences, model predictions, and tightly constrained parameter combinations using a novel sensitivity analysis method. For one case study, we demonstrate a speed-up from 108 days to 6 hours, while maintaining equivalent ensembles. Additionally, we demonstrate how to identify the parameter combinations that strongly drive feasibility and stability, drawing ecological insight from the ensembles. Now, for the first time, larger and more realistic networks can be practically simulated and analysed.

Variations in root architecture traits and their association with organ mass fraction of common annual ephemeral species in the desert of northern Xinjiang

The variation of plant traits is closely related to the trade-offs between resource acquisition and conservation, as well as the accumulation of biomass. However, there has been a lack of comprehensive insights into the variation patterns, phylogenetic conservatism, and covariation with biomass allocation of root system architecture in desert areas. We examined the root systems of 47 annual ephemeral species and evaluated their biomass allocation and six key root system architecture traits. Our results indicated that the variation in root traits mainly originated from interspecific variation (48.78%-99.76%), but intraspecific variation should not be ignored as to why the contribution rate of root tissue density (RTD) reached 51.22%. The six root traits were mainly loaded on the first and second axes of the principal component analysis (PCA), these traits mainly vary along two dimensions. The highest interspecific variation is in RTD (51.63%) and the lowest in topological index (TI; 5.92%). The intraspecific variation value and range of specific root length (SRL), specific root area (SRA), and RTD were significantly higher than TI (p < .05), and they are not limited by phylogenetic relationships (0< K < 1, p > .05). The SRA is positively correlated with SRL (r = .72, p < .001) and negatively correlated with RTD (r = -.57, p < .05). The LMF is positively correlated with SRL, and SRA demonstrated the coordination between water consumption and acquisition. The positive correlation between RMF and MRD indicated the coordination of root carbon investment with exploring soil vertical space. The multi-dimensional variation of root traits, divergence of RTDs, and convergence of TI are important ecological strategies for annual short-lived plants to adapt to heterogeneous desert habitats. Meanwhile, these plants achieve optimal access to scarce resources through the high plasticity of resource acquisition (e.g., SRL and SRA) and conservation traits (e.g., RTD), as well as the trade-offs between them and organ mass fraction.

Environmental stress mediates groundwater microbial community assembly

Community assembly describes how different ecological processes shape microbial community composition and structure. How environmental factors impact community assembly remains elusive. Here we sampled microbial communities and >200 biogeochemical variables in groundwater at the Oak Ridge Field Research Center, a former nuclear waste disposal site, and developed a theoretical framework to conceptualize the relationships between community assembly processes and environmental stresses. We found that stochastic assembly processes were critical (>60% on average) in shaping community structure, but their relative importance decreased as stress increased. Dispersal limitation and 'drift' related to random birth and death had negative correlations with stresses, whereas the selection processes leading to dissimilar communities increased with stresses, primarily related to pH, cobalt and molybdenum. Assembly mechanisms also varied greatly among different phylogenetic groups. Our findings highlight the importance of microbial dispersal limitation and environmental heterogeneity in ecosystem restoration and management.

Niche types and community assembly

Studies of niche differentiation and biodiversity often focus on a few niche dimensions due to the methodological challenge of describing hyperdimensional niche space. However, this may limit our understanding of community assembly processes. We used the full spectrum of realized niche types to study arbuscular mycorrhizal fungal communities: distinguishing abiotic and biotic, and condition and resource, axes. Estimates of differentiation in relation to different niche types were only moderately correlated. However, coexisting taxon niches were consistently less differentiated than expected, based on a regional null model, indicating the importance of habitat filtering at that scale. Nonetheless, resource niches were relatively more differentiated than condition niches, which is consistent with the effect of a resource niche-based coexistence mechanism. Considering niche types, and in particular distinguishing resource and condition niches, provides a more complete understanding of community assembly, compared with studying individual niche axes or the full niche.

When Do Traits Tell More Than Species about a Metacommunity? A Synthesis across Ecosystems and Scales

AbstractLinking species traits with the variation in species assemblages across habitats has often proved useful for developing a more mechanistic understanding of species distributions in metacommunities. However, summarizing the rich tapestry of a species in all of its nuance with a few key ecological traits can also lead to an abstraction that provides less predictability than when using taxonomy alone. As a further complication, taxonomic and functional diversities can be inequitably compared, either by integrating taxonomic-level information into the calculation of how functional aspects of communities vary or by detecting spurious trait-environment relationships. To remedy this, we here synthesize analyses of 80 datasets on different taxa, ecosystems, and spatial scales that include information on abundance or presence/absence of species across sites with variable environmental conditions and the species' traits. By developing analyses that treat functional and taxonomic diversity equitably, we ask when functional diversity helps to explain metacommunity structure. We found that patterns of functional diversity explained metacommunity structure and response to environmental variation in only 25% of the datasets using a multitrait approach but up to 59% using a single-trait approach. Nevertheless, an average of only 19% (interquartile range = 0%-29%) of the traits showed a significant signal across environmental gradients. Species-level traits, as typically collected and analyzed through functional diversity patterns, often do not bring predictive advantages over what the taxonomic information already holds. While our assessment of a limited advantage of using traits to explain variation in species assemblages was largely true across ecosystems, traits played a more useful role in explaining variation when many traits were used and when trait constructs were more related to species' status, life history, and mobility. We propose future research directions to make trait-based approaches and data more helpful for inference in metacommunity ecology.

Understory vegetation diversity patterns of Platycladus orientalis and Pinus elliottii communities in Central and Southern China

As a vital component of arbor forests, understory vegetation serves as an essential buffer zone for storing carbon due to its strong capacity for community regeneration. This study aimed to identify the diversity pattern and construction mechanism of Platycladus orientalis and Pinus elliottii understory vegetation based on large-scale sample surveys. The Bayesian Information Criterion value of species abundance distribution (SAD) indicated that the Zipf and Zipf-Mandelbrot models were the best-fitting models. The SAD and gambin fitting results suggested that the Pi. elliottii community had a more balanced structure, with most species being relatively abundant. The multiple regression tree model detected four and six indicator species in P. orientalis and Pi. elliottii communities, respectively. The α-diversity index increased with a rise in altitude and showed a wavy curve with latitude. Linear regression between the β diversity and environmental and geographic distance indicated that the P. orientalis and Pi. elliottii understory communities tended to be dominated by different ecological processes. The partition of β diversity indicated that both communities were dominated by turnover processes, which were caused by environmental classification or spatial constraints. This study helped to understand the diversity maintenance in the P. orientalis and Pi. elliottii understory vegetation communities, and will benefit for diversity restoration and conservation of pure conifer forests.

Interspecific Host Variation and Biotic Interactions Drive Pathogen Community Assembly in Chinese Bumblebees

Bumblebees have been considered one of the most important pollinators on the planet. However, recent reports of bumblebee decline have raised concern about a significant threat to ecosystem stability. Infectious diseases caused by multiple pathogen infections have been increasingly recognized as an important mechanism behind this decline worldwide. Understanding the determining factors that influence the assembly and composition of pathogen communities among bumblebees can provide important implications for predicting infectious disease dynamics and making effective conservation policies. Here, we study the relative importance of biotic interactions versus interspecific host resistance in shaping the pathogen community composition of bumblebees in China. We first conducted a comprehensive survey of 13 pathogens from 22 bumblebee species across China. We then applied joint species distribution modeling to assess the determinants of pathogen community composition and examine the presence and strength of pathogen-pathogen associations. We found that host species explained most of the variations in pathogen occurrences and composition, suggesting that host specificity was the most important variable in predicting pathogen occurrences and community composition in bumblebees. Moreover, we detected both positive and negative associations among pathogens, indicating the role of competition and facilitation among pathogens in determining pathogen community assembly. Our research demonstrates the power of a pluralistic framework integrating field survey of bumblebee pathogens with community ecology frameworks to understand the underlying mechanisms of pathogen community assembly.

Hydrological niche regulation induced by different resistance strategies facilitates coexistence of P. longipes and L. communis under drought stress

Under global warming, the availability of water resources is one of the most important factors affecting trait evolution and plant species distribution across terrestrial ecosystems, and the relationships between drought resistance strategies and the hydrological niche characteristics of plants are worth studying. We continuously monitored physiological drought response parameters such as gs , Tr , proline, soluble sugar, gene expression and activities of SOD, POD, and CAT to assess drought resistance strategies of Platycarya longipes and Lindera communis; determined plant soil hydrological niche separation by stable H and O isotope analysis; and analysed the effects of interspecific water competition by comparing the differences in morphological and physiological parameters between solo and mixed planting. Under drought stress, L. communis exhibited a drought avoidance strategy, and P. longipes exhibited a drought tolerance strategy. L. communis utilized the water within the shallow soil layer, while P. longipes mainly utilized the water in the deeper soil layer; there were fewer parameters with significant differences between the solo planting and the mixed planting of L. communis compared to P. longipes. Overall, P. longipes benefited from coexistence with L. communis under drought stress, which may be because L. communis employs a drought avoidance strategy, reducing soil water consumption in the drought environment. These results suggested that differences in functional traits or resistance strategies among species benefit species' coexistence in a community under drought stress.

Forest habitats and plant communities strongly predicts Megachilidae bee biodiversity

Megachilidae is one of the United States' most diverse bee families, with 667 described species in 19 genera. Unlike other bee families, which are primarily ground nesters, most megachilid bees require biotic cavities for nesting (i.e., wood, pithy stems, etc.). For this group, the availability of woody-plant species may be as important as nectar/pollen resources in maintaining populations. We studied Megachilidae biodiversity in the continental United States. We confirmed that the highest species richness of Megachilidae was in the southwestern United States. We examined the relationship between species richness and climate, land cover, tree species richness, and flowering plant diversity. When examining environmental predictors across the conterminous United States, we found that forested habitats, but not tree diversity, strongly predicted Megachilidae richness. Additionally, Megachilidae richness was highest in areas with high temperature and low precipitation, however this was not linearly correlated and strongly positively correlated with flowering plant diversity. Our research suggests that the availability of nesting substrate (forested habitats), and not only flowering plants, is particularly important for these cavity-nesting species. Since trees and forested areas are particularly susceptible to climate change, including effects of drought, fire, and infestations, nesting substrates could become a potential limiting resource for Megachilidae populations.

The relative importance of abiotic and biotic environmental conditions for taxonomic, phylogenetic, and functional diversity of spiders across spatial scales

Both abiotic and biotic conditions may be important for biodiversity. However, their relative importance may vary among different diversity dimensions as well as across spatial scales. Spiders (Araneae) offer an ecologically relevant system for evaluating variation in the relative strength abiotic and biotic biodiversity regulation. We quantified the relative importance of abiotic and biotic conditions for three diversity dimensions of spider communities quantified across two spatial scales. Spiders were surveyed along elevation gradients in northern Sweden. We focused our analysis on geomorphological and climatic conditions as well as vegetation characteristics, and quantified the relative importance of these conditions for the taxonomic, phylogenetic, and functional diversity of spider communities sampled across one intermediate (500 m) and one local (25 m) scale. There were stronger relationships among diversity dimensions at the local than the intermediate scale. There were also variation in the relative influence of abiotic and biotic conditions among diversity dimensions, but this variation was not consistent across spatial scales. Across both spatial scales, vegetation was related to all diversity dimensions whereas climate was important for phylogenetic and functional diversity. Our study does not fully support stronger abiotic regulation at coarser scales, and conversely stronger abiotic regulation at more local scales. Instead, our results indicate that community assembly is shaped by interactions between abiotic constrains in species distributions and biotic conditions, and that such interactions may be both scale and context dependent.

Tropical shrubs living in an extreme environment show convergent ecological strategies but divergent ecophysiological strategies

BACKGROUND AND AIMS

Trait-based frameworks assess plant survival strategies using different approaches. Some frameworks use functional traits to assign species to a priori defined ecological strategies. Others use functional traits as the central element of a species ecophysiological strategy. We compared these two approaches by asking: (1) what is the primary ecological strategy of three dominant co-occurring shrub species from inselbergs based on the CSR scheme, and (2) what main functional traits characterize the ecophysiological strategy of the species based on their use of carbon, water and light?

METHODS

We conducted our study on a Colombian inselberg. In this extreme environment with multiple stressors (high temperatures and low resource availability), we expected all species to be stress tolerant (S in the CSR scheme) and have similar ecophysiological strategies. We measured 22 anatomical, morphological and physiological leaf traits.

KEY RESULTS

The three species have convergent ecological strategies as measured by CSR (S, Acanthella sprucei; and S/CS, Mandevilla lancifolia and Tabebuia orinocensis) yet divergent resource-use strategies as measured by their functional traits. A. sprucei has the most conservative carbon use, risky water use and a shade-tolerant strategy. M. lancifolia has acquisitive carbon use, safe water use and a shade-tolerant strategy. T. orinocensis has intermediate carbon use, safe water use and a light-demanding strategy. Additionally, stomatal traits that are easy to measure are valuable to describe resource-use strategies because they are highly correlated with two physiological functions that are hard to measure: stomatal conductance and maximum photosynthesis per unit mass.

CONCLUSIONS

The two approaches provide complementary information on species strategies. Plant species can co-occur in extreme environments, such as inselbergs, because they exhibit convergent primary ecological strategies but divergent ecophysiological strategies, allowing them to use limiting resources differently.

A trait-based framework for seagrass ecology: Trends and prospects

In the last three decades, quantitative approaches that rely on organism traits instead of taxonomy have advanced different fields of ecological research through establishing the mechanistic links between environmental drivers, functional traits, and ecosystem functions. A research subfield where trait-based approaches have been frequently used but poorly synthesized is the ecology of seagrasses; marine angiosperms that colonized the ocean 100M YA and today make up productive yet threatened coastal ecosystems globally. Here, we compiled a comprehensive trait-based response-effect framework (TBF) which builds on previous concepts and ideas, including the use of traits for the study of community assembly processes, from dispersal and response to abiotic and biotic factors, to ecosystem function and service provision. We then apply this framework to the global seagrass literature, using a systematic review to identify the strengths, gaps, and opportunities of the field. Seagrass trait research has mostly focused on the effect of environmental drivers on traits, i.e., "environmental filtering" (72%), whereas links between traits and functions are less common (26.9%). Despite the richness of trait-based data available, concepts related to TBFs are rare in the seagrass literature (15% of studies), including the relative importance of neutral and niche assembly processes, or the influence of trait dominance or complementarity in ecosystem function provision. These knowledge gaps indicate ample potential for further research, highlighting the need to understand the links between the unique traits of seagrasses and the ecosystem services they provide.

Universal beta-diversity-functioning relationships are neither observed nor expected

Widespread evidence shows that local species richness (α-diversity) loss hampers the biomass production and stability of ecosystems. β-Diversity, namely the variation of species compositions among different ecological communities, represents another important biodiversity component, but studies on how it drives ecosystem functioning show mixed results. We argue that to better understand the importance of β-diversity we need to consider it across contexts. We focus on three scenarios that cause gradients in β-diversity: changes in (i) abiotic heterogeneity, (ii) habitat isolation, and (iii) species pool richness. We show that across these scenarios we should not expect universally positive relationships between β-diversity, production, and ecosystem stability. Nevertheless, predictable relationships between β-diversity and ecosystem functioning do exist in specific contexts, and can reconcile seemingly contrasting empirical relationships.

Odonata (Insecta) Communities in a Lowland Mixed Mosaic Forest in Central Kalimantan, Indonesia

Assessing a taxon’s response to change in environmental variables is fundamental knowledge to understanding trends in species diversity, abundance, and distribution patterns. This is particularly needed on Borneo, where knowledge on Odonata populations in different habitats is poor. To address this gap, we present the first study investigating the relationship between morphology and species distribution of Odonata communities in a heath (kerangas)-dominated mixed-mosaic-lowland forest in southern Borneo. We sampled 250-m line transects in three habitat types: mixed peatcswamp, kerangas, and low-pole peatcswamp, with weekly surveys from December 2019 to February 2020. A total of 309 individuals were detected from 25 species. Anisoptera and Zygoptera diversity was the highest in mixed peatcswamp and lowest in low pole, while abundance was the highest in low pole and lowest in kerangas; with kerangas notably harboring a very small sample size. Odonata community assemblages differed most between mixed peat swamp and low pole. Morphological data were compared between suborders and habitats. Anisoptera showed significantly larger thoraces, hindwings, and hindwing-to-body ratio than Zygoptera. Anisoptera in low pole were significantly smaller in body, thorax, and hindwing compared to both kerangas and mixed peat swamp. Anisoptera showed a strong association with pools and Zygoptera with flowing water. Heterogeneity, habitat characteristics, presence of specialists, body size, and the interaction between species’ morphological traits and habitat characteristics likely explained the trends observed.

Abundance and Dynamics of Small Mammals in New Zealand: Sequential Invasions into an Island Ecosystem Like No Other

New Zealand had no people or four-footed mammals of any size until it was colonised by Polynesian voyagers and Pacific rats in c. 1280 AD. Between 1769 and 1920 AD, Europeans brought three more species of commensal rats and mice, and three predatory mustelids, plus rabbits, house cats hedgehogs and Australian brushtail possums. All have in turn invaded the whole country and many offshore islands in huge abundance, at least initially. Three species are now reduced to remnant populations, but the other eight remain widely distributed. They comprise an artificial but interacting and fully functional bottom-up predator-prey system, responding at all levels to interspecific competition, habitat quality and periodic resource pulsing.

Biotic interactions shape trait assembly of marine communities across time and latitude

Assembly processes are highly dynamic with biotic filters operating more intensely at local scales, yet the strength of biotic interactions can vary across time and latitude. Predation, for example, can be stronger at lower latitudes, while competition can intensify at later stages of assembly due to resource limitation. Since biotic filters act upon functional traits of organisms, we explored trait-mediated community assembly in diverse marine assemblages from four regions along the Pacific coast of North and Central America. Using predator exclusion experiments and two assembly stages, we tested the hypotheses that non-random trait patterns would emerge during late assembly at all regions due to competition and at lower latitude regions regardless of assembly stage due to predation. As expected, trait divergence occurred in late assembly but only at higher latitude regions, while in tropical Panama, relaxed predation caused trait divergence during late assembly. Moreover, colonizing trait strategies were common during early assembly while competitive strategies were favoured during late assembly at higher latitude regions. Predation-resistant traits were only favoured in Panama during both assembly stages. Our large-scale manipulative study demonstrates that different biotic interactions across time and latitude can have important consequences for trait assembly.

Functional traits mediate individualistic species-environment distributions at broad spatial scales while fine-scale species associations remain unpredictable

PREMISE

Numerous processes influence plant distributions and co-occurrence patterns, including ecological sorting, limiting similarity, and stochastic effects. To discriminate among these processes and determine the spatial scales at which they operate, we investigated how functional traits and phylogenetic relatedness influence the distribution of temperate forest herbs.

METHODS

We surveyed understory plant communities across 257 forest stands in Wisconsin and Michigan (USA) and applied Bayesian phylogenetic linear mixed-effects models (PGLMMs) to quantify how functional traits and phylogenetic relatedness influence the environmental distribution of 139 herbaceous plant species along broad edaphic, climatic, and light gradients. These models also allowed us to test how functional and phylogenetic similarity affect species co-occurrence within microsites.

RESULTS

Leaf height, specific leaf area, and seed mass all influenced individualistic plant distributions along landscape-scale gradients in soil texture, soil fertility, light availability, and climate. In contrast, phylogenetic relationships did not consistently predict species-environment relationships. Neither functionally similar nor phylogenetically related herbs segregated among microsites within forest stands.

CONCLUSIONS

Trait-mediated ecological sorting appears to drive temperate-forest community assembly, generating individualistic plant distributions along regional environmental gradients. This finding links classic studies in plant ecology and prior research in plant physiological ecology to current trait-based approaches in community ecology. However, our results fail to support the common assumption that limiting similarity governs local plant co-occurrences. Strong ecological sorting among forest stands coupled with stochastic fine-scale interactions among species appear to weaken deterministic, niche-based assembly processes at local scales.

Functional traits mediate individualistic species-environment distributions at broad spatial scales while fine-scale species associations remain unpredictable

PREMISE

Numerous processes influence plant distributions and co-occurrence patterns, including ecological sorting, limiting similarity, and stochastic effects. To discriminate among these processes and determine the spatial scales at which they operate, we investigated how functional traits and phylogenetic relatedness influence the distribution of temperate forest herbs.

METHODS

We surveyed understory plant communities across 257 forest stands in Wisconsin and Michigan (USA) and applied Bayesian phylogenetic linear mixed-effects models (PGLMMs) to quantify how functional traits and phylogenetic relatedness influence the environmental distribution of 139 herbaceous plant species along broad edaphic, climatic, and light gradients. These models also allowed us to test how functional and phylogenetic similarity affect species co-occurrence within microsites.

RESULTS

Leaf height, specific leaf area, and seed mass all influenced individualistic plant distributions along landscape-scale gradients in soil texture, soil fertility, light availability, and climate. In contrast, phylogenetic relationships did not consistently predict species-environment relationships. Neither functionally similar nor phylogenetically related herbs segregated among microsites within forest stands.

CONCLUSIONS

Trait-mediated ecological sorting appears to drive temperate-forest community assembly, generating individualistic plant distributions along regional environmental gradients. This finding links classic studies in plant ecology and prior research in plant physiological ecology to current trait-based approaches in community ecology. However, our results fail to support the common assumption that limiting similarity governs local plant co-occurrences. Strong ecological sorting among forest stands coupled with stochastic fine-scale interactions among species appear to weaken deterministic, niche-based assembly processes at local scales.

Soil nematode community assembly in a primary tropical lowland rainforest

More than half of the world's tropical lowland rainforests have been lost due to conversion to agricultural land (such as rubber plantations). Thus, ecological restoration in degraded tropical lowland rainforests is crucial. The first step to restoration is restoring soil functioning (i.e., soil fertility, carbon, and nitrogen cycling) to levels similar to those in the primary tropical lowland rainforest. This requires understanding soil nematode community assembly in primary tropical lowland rainforest, which has never been explored in this habitat. In this study, we measured species compositions of plant and soil nematode communities and soil characteristics (pH, total and available nitrogen, phosphorus, and soil water content) in a primary tropical lowland rainforest, which is located on Hainan Island, China. We performed two tests (the null-model test and distance-based Moran's eigenvector maps (MEM) and redundancy analysis-based variance partitioning) to quantify the relative contribution of the deterministic (abiotic filtering and biotic interactions) and stochastic processes (random processes and dispersal limitation) to the soil nematode community. We found that a deterministic process (habitat filtering) determined nematode community assembly in our tropical lowland rainforest. Moreover, soil properties, but not plant diversity, were the key determinants of nematode community assembly. We have, for the first time, managed to identify factors that contribute to the nematode community assembly in the tropical lowland rainforest. This quantified community assembly mechanism can guide future soil functioning recovery of the tropical lowland rainforest.

Functional traits and phylogeny explain snake distribution in the world's largest dry forest ecoregion, the Gran Chaco

Macroecological studies describe large-scale diversity patterns through analyses of species distribution patterns and allows us to elucidate how species differing in ecology, physical requirements, and life histories are distributed in a multidimensional space. These patterns of distributions can be explained by vegetation, and climatic factors, and are determined by historical and current factors. The continuous accumulation of information on the distribution patterns of species is essential to understand the history and evolution of the biota. In this study, we aimed to identify functional and evolutionary drivers that explain the geographic patterns of vertical stratification. We compiled morphological, ecological, and distribution data of 140 species of Chacoan snakes and constructed null models to map their geographic pattern. We used a range of environmental variables to assess which drivers are influencing these biogeographic patterns. Lastly, we used evolutionary data to build the first map of the phylogenetic regions of Chacoan snakes. We found a latitudinal pattern, with a marked verticality in the snake assemblies in the Chaco. Verticality and long-tailed species richness increased in areas with high stratified habitats and stable temperature. Fossoriality is driven mainly by soil conditions, especially soils with fewer sand particles and less stratified habitat. Phylogenetic regions in the Chaco showed a marked latitudinal pattern, like that observed in the geographic pattern of verticality. The distribution pattern of Chacoan snakes also reflects their evolutionary history, with a marked phylogenetic regionalization.

Biological control needs evolutionary perspectives of ecological interactions

While ecological interactions have been identified as determinant for biological control efficiency, the role of evolution remains largely underestimated in biological control programs. With the restrictions on the use of both pesticides and exotic biological control agents (BCAs), the evolutionary optimization of local BCAs becomes central for improving the efficiency and the resilience of biological control. In particular, we need to better account for the natural processes of evolution to fully understand the interactions of pests and BCAs, including in biocontrol strategies integrating human manipulations of evolution (i.e., artificial selection and genetic engineering). In agroecosystems, the evolution of BCAs traits and performance depends on heritable phenotypic variation, trait genetic architecture, selection strength, stochastic processes, and other selective forces. Humans can manipulate these natural processes to increase the likelihood of evolutionary trait improvement, by artificially increasing heritable phenotypic variation, strengthening selection, controlling stochastic processes, or overpassing evolution through genetic engineering. We highlight these facets by reviewing recent studies addressing the importance of natural processes of evolution and human manipulations of these processes in biological control. We then discuss the interactions between the natural processes of evolution occurring in agroecosystems and affecting the artificially improved BCAs after their release. We emphasize that biological control cannot be summarized by interactions between species pairs because pests and biological control agents are entangled in diverse communities and are exposed to a multitude of deterministic and stochastic selective forces that can change rapidly in direction and intensity. We conclude that the combination of different evolutionary approaches can help optimize BCAs to remain efficient under changing environmental conditions and, ultimately, favor agroecosystem sustainability.

Distinct and Temporally Stable Assembly Mechanisms Shape Bacterial and Fungal Communities in Vineyard Soils

Microbial communities in agricultural soils are fundamental for plant growth and in vineyard ecosystems contribute to defining regional wine quality. Managing soil microbes towards beneficial outcomes requires knowledge of how community assembly processes vary across taxonomic groups, spatial scales, and through time. However, our understanding of microbial assembly remains limited. To quantify the contributions of stochastic and deterministic processes to bacterial and fungal assembly across spatial scales and through time, we used 16 s rRNA gene and ITS sequencing in the soil of an emblematic wine-growing region of Italy.Combining null- and neutral-modelling, we found that assembly processes were consistent through time, but bacteria and fungi were governed by different processes. At the within-vineyard scale, deterministic selection and homogenising dispersal dominated bacterial assembly, while neither selection nor dispersal had clear influence over fungal assembly. At the among-vineyard scale, the influence of dispersal limitation increased for both taxonomic groups, but its contribution was much larger for fungal communities. These null-model-based inferences were supported by neutral modelling, which estimated a dispersal rate almost two orders-of-magnitude lower for fungi than bacteria.This indicates that while stochastic processes are important for fungal assembly, bacteria were more influenced by deterministic selection imposed by the biotic and/or abiotic environment. Managing microbes in vineyard soils could thus benefit from strategies that account for dispersal limitation of fungi and the importance of environmental conditions for bacteria. Our results are consistent with theoretical expectations whereby larger individual size and smaller populations can lead to higher levels of stochasticity.

Signals of Potential Species Associations Offer Clues about Community Organisation of Stream Fish across Seasons

Simple Summary

Species interactions are one of the main factors affecting community assembly, yet the role of such interactions remains mostly unknown. Here, we investigated roles of potential species associations in fish community assembly in the Qiupu River, China. Our results suggested that potential species associations might have been underestimated in stream fish community assembly. The contribution of potential species associations to fish community assembly can be reflected by interaction network structures. Omnivorous species play an important role in maintaining network structure as they may have more associations with other species. This study highlights the importance of capturing species associations in river ecosystems across different geographical and environmental settings.

Abstract

Environmental filtering, spatial factors and species interactions are fundamental ecological mechanisms for community organisation, yet the role of such interactions across different environmental and spatial settings remains mostly unknown. In this study, we investigated fish community organisation scenarios and seasonal species-to-species associations potentially reflecting biotic associations along the Qiupu River (China). Based on a latent variable approach and a tree-based method, we compared the relative contribution of the abiotic environment, spatial covariates and potential species associations for variation in the community structure, and assessed whether different assembly scenarios were modulated by concomitant changes in the interaction network structure of fish communities across seasons. We found that potential species associations might have been underestimated in community-based assessments of stream fish. Omnivore species, since they have more associations with other species, were found to be key components sustaining fish interaction networks across different stream orders. Hence, we suggest that species interactions, such as predation and competition, likely played a key role in community structure. For instance, indices accounting for network structure, such as connectance and nestedness, were strongly correlated with the unexplained residuals from our latent variable approach, thereby re-emphasising that biotic signals, potentially reflecting species interactions, may be of primary importance in determining stream fish communities across seasons. Overall, our findings indicate that interaction network structures are a powerful tool to reflect the contribution of potential species associations to community assembly. From an applied perspective, this study should encourage freshwater ecologists to empirically capture and manage biotic constraints in stream ecosystems across different geographical and environmental settings, especially in the context of the ever-increasing impacts of human-induced local extinction debts and species invasions.

Community assembly, functional traits, and phylogeny in Himalayan river birds

Heterogeneity in riverine habitats acts as a template for species evolution that influences river communities at different spatio-temporal scales. Although birds are conspicuous elements of these communities, the roles of phylogeny, functional traits, and habitat character in their niche use or species' assembly have seldom been investigated. We explored these themes by surveying multiple headwaters over 3000 m of elevation in the Himalayan Mountains of India where the specialist birds of montane rivers reach their greatest diversity on Earth. After ordinating community composition, species traits, and habitat character, we investigated whether river bird traits varied with elevation in ways that were constrained or independent of phylogeny, hypothesizing that trait patterns reflect environmental filtering. Community composition and trait representation varied strongly with increasing elevation and river naturalness as species that foraged in the river/riparian ecotone gave way to small insectivores with direct trophic dependence on the river or its immediate channel. These trends were influenced strongly by phylogeny as communities became more clustered by functional traits at a higher elevation. Phylogenetic signals varied among traits, however, and were reflected in body mass, bill size, and tarsus length more than in body size, tail length, and breeding strategy. These variations imply that community assembly in high-altitude river birds reflects a blend of phylogenetic constraint and habitat filtering coupled with some proximate niche-based moulding of trait character. We suggest that the regional co-existence of river birds in the Himalaya is facilitated by this same array of factors that together reflect the highly heterogeneous template of river habitats provided by these mountain headwaters.

Effects of Habitat and Competition on Niche Partitioning and Community Structure in Neotropical Ants

Competition for limited resources can yield two contrasting outcomes in community structure, namely, either (i) dominance of most competitive species (with functional convergence of the traits conferring this ability), or (ii) niche partitioning of species using distinct resources. In addition, varying resource availability in different environmental contexts is expected to yield varying community dynamics and composition between the contexts (habitat filtering). We addressed resource-based ant community structure in a tropical ecosystem. We expected ant species to display varying trophic preferences and foraging behaviors, allowing habitat selection and niche differentiation in ant assemblages. Furthermore, we expected habitat filtering to occur between open and forested areas in the landscape mosaic, and competition to further influence local species co-occurrence. We assessed resource use in nine ant assemblages distributed in two habitats (i.e., forests and croplands), devising two separate experiments using bait-traps to characterize ant species’ trophic preference (e.g., eating prey, seeds, sugars) and their ability to obtain a same resource in heterogeneous forms (e.g., on vegetation, litter, with variable amounts…). The majority of baits offered were rapidly exploited in the two habitats suggesting important resource limitations. Forest and cropland ant communities differed, however, in the proportions of resources exploited, suggesting different competitive pressures toward specific resources between habitats. Within each habitat, ants preferentially exploited the same resources, suggesting habitat filtering, but locally, interspecific resource partitioning resulted in a reduction of resource overlap compared to habitat scale. Our study provides evidence of the effects of habitat filtering and competition for resource in tropical ant community structure. Our findings also suggest that niche filtering and niche partitioning are co-variant forces determining the identity of the species present in local assemblages.

From diversity to complexity: Microbial networks in soils

Network analysis has been used for many years in ecological research to analyze organismal associations, for example in food webs, plant-plant or plant-animal interactions. Although network analysis is widely applied in microbial ecology, only recently has it entered the realms of soil microbial ecology, shown by a rapid rise in studies applying co-occurrence analysis to soil microbial communities. While this application offers great potential for deeper insights into the ecological structure of soil microbial ecosystems, it also brings new challenges related to the specific characteristics of soil datasets and the type of ecological questions that can be addressed. In this Perspectives Paper we assess the challenges of applying network analysis to soil microbial ecology due to the small-scale heterogeneity of the soil environment and the nature of soil microbial datasets. We review the different approaches of network construction that are commonly applied to soil microbial datasets and discuss their features and limitations. Using a test dataset of microbial communities from two depths of a forest soil, we demonstrate how different experimental designs and network constructing algorithms affect the structure of the resulting networks, and how this in turn may influence ecological conclusions. We will also reveal how assumptions of the construction method, methods of preparing the dataset, and definitions of thresholds affect the network structure. Finally, we discuss the particular questions in soil microbial ecology that can be approached by analyzing and interpreting specific network properties. Targeting these network properties in a meaningful way will allow applying this technique not in merely descriptive, but in hypothesis-driven research. Analysing microbial networks in soils opens a window to a better understanding of the complexity of microbial communities. However, this approach is unfortunately often used to draw conclusions which are far beyond the scientific evidence it can provide, which has damaged its reputation for soil microbial analysis. In this Perspectives Paper, we would like to sharpen the view for the real potential of microbial co-occurrence analysis in soils, and at the same time raise awareness regarding its limitations and the many ways how it can be misused or misinterpreted.

Plant diversity and soil properties regulate the microbial community of monsoon evergreen broad-leaved forest under different intensities of woodland use

A key aspect of global forest management, woodland use intensity (WUI) greatly affects the composition and diversity of soil microbial communities, thereby affecting multiple ecosystem functions and services. However, the effects of WUI on soil microbial community composition and enzymatic activities remains unclear. The effects of anthropomorphic alterations to a natural monsoon evergreen broad-leaved forest in terms of the composition and diversity of soil fungal and bacterial communities, was investigated at a site in Yunnan Province, Southwest China. Soil microbial communities were assessed under four levels of disturbance with increasing levels of WUI: (i) none, undisturbed forest (control), (ii) light, naturally-regenerated Pinus kesiya Royle ex Gordon forest, (iii) intermediate, shrub and grassland communities formed through grazing, and (iv) severe, continuously managed coffee (Coffea arabica L.) plantations. With increasing WUI, the diversity of soil fungal and bacterial communities increased, while similarities in community composition decreased for fungi but increased for bacteria. Among fungal functional guilds, ectomycorrhizal fungi decreased significantly with increasing WUI, whereas saprotrophic fungi (undefined, wood, and soil saprotrophs) increased significantly. The species richness of woody plants remarkably affected fungal functional guilds. Ectomycorrhizal fungi interacted in a synergistic manner with the fungal network structure. Significantly affecting microorganismal network structure, WUI increases led to more homogeneous networks with less integration within modules within the microbial community. The WUI strongly altered hub identity and module composition in the microbial community. According to structural equation models, WUI had direct positive effects on soil fungal community composition via its effects on plant species richness. The diversity of bacterial and fungal communities and composition of bacterial communities were jointly regulated by the indirect effects of plant species richness and soil nutrients (including enzyme activity). Deterministic processes largely determined the composition of soil fungal and bacterial communities. This study highlights the importance of maintaining the diversity of soil fungal and bacterial communities despite changes in woodland use to sustain ecosystem functions. These results can be used to develop management practices in subtropical forests and help sustain plant and soil microbial diversity at levels sufficient to maintain long-term ecosystem function and services.

Shifting Limitations to Restoration across Dryland Ecosystems in Hawaiʻi

Hawaiian dryland ecosystems are important for global biodiversity conservation and contain numerous species threatened with extinction. Over the past century, wildfire frequency and size have increased dramatically because of invasion by fire-promoting non-native invasive species, greatly threatening these ecosystems. Native species restoration is a tool that can disrupt the cycle of increased fire and invasion in lowland dry forest communities, but restoration prescriptions have not been studied systematically in other dryland plant communities. We examined the restoration of three Hawaiian dryland plant communities (a high-productivity Diospyros sandwicensis and Metrosideros polymorpha lowland dry forest (HP), a moderate-productivity Myoporum sandwicense and Sophora chrysophylla dry forest/woodland (MP), and a low-productivity Dodonaea viscosa shrubland (LP)), using a community-assembly framework to understand the abiotic and biotic constraints to species establishment and growth in each community. Because active restoration methods are often needed, at both high and low levels of productivity, we also examined restoration treatments and outcomes across the three sites, which spanned a gradient of rainfall and substrate age. At each site, we used the same factorial field experiment with three factors: habitat quality (high or low), weed control (yes or no), and species addition (none, seeding, or outplanting). Outplants (cohort 1) and seeds were added in the winter of 2009–2010, and outplants were added again in March 2011 (cohort 2). Dispersal limitation was apparent at the LP and HP sites, but was not observed in the MP site, which had, overall, greater native diversity and abundance. Outplant survival was greater in high-quality habitats at the HP site, likely due to reduced abiotic stress. Invasive species were found in greater abundance in certain types of microsites at the LP and MP sites, suggesting that shade or topography can be used to plan restoration and weed-control activities. Overall, active restoration methods improved restoration outcomes at the high- and low-productivity sites, and less so at the moderately productive site. Weed removal and outplanting were effective restoration prescriptions at the LP and HP sites, and habitat quality could also be used to increase survival at the HP site. Active restoration could be a lower priority for moderately invaded, moderate-productivity communities, which have the capability to maintain a native ecosystem state.

Plant community impact on productivity: Trait diversity or key(stone) species effects?

Outside controlled experimental plots, the impact of community attributes on primary productivity has rarely been compared to that of individual species. Here, we identified plant species of high importance for productivity (key species) in >29,000 diverse grassland communities in the European Alps, and compared their effects with those of community-level measures of functional composition (weighted means, variances, skewness and kurtosis). After accounting for the environment, the five most important key species jointly explained more deviance of productivity than any measure of functional composition alone. Key species were generally tall with high specific leaf areas. By dividing the observations according to distinct habitats, the explanatory power of key species and functional composition increased and key-species plant types and functional composition-productivity relationships varied systematically, presumably because of changing interactions and trade-offs between traits. Our results advocate for a careful consideration of species' individual effects on ecosystem functioning in complement to community-level measures.

Distinct Co-occurrence Relationships and Assembly Processes of Active Methane-Oxidizing Bacterial Communities Between Paddy and Natural Wetlands of Northeast China

Studies of methane-oxidizing bacteria are updating our views of their composition and function in paddy and natural wetlands. However, few studies have characterized differences in the methane-oxidizing bacterial communities between paddy and natural wetlands. Here, we conducted a ¹³C stable isotope-probing experiment and high-throughput sequencing to determine the structure profiling, co-occurrence relationships, and assembly processes of methanotrophic communities in four wetlands of Northeast China. There was a clear difference in community structure between paddy and natural wetlands. LEfSe analyses revealed that Methylobacter, FWs, and Methylosinus were enriched in natural wetlands, while Methylosarcina were prevailing in paddy, all identified as indicative methanotrophs. We observed distinct co-occurrence relationships between paddy and natural wetlands: more robust and complex connections in natural wetlands than paddy wetlands. Furthermore, the relative importance of stochastic processes was greater than that of deterministic processes, as stochastic processes explained >50% of the variation in communities. These results demonstrated that the co-occurrence relationships and assembly processes of active methanotrophic communities in paddy and natural wetlands were distinct. Overall, the results of this study enhance our understanding of the communities of methane-oxidizing bacteria in paddy and natural wetlands of Northeast China.

Modulation of microbial community dynamics by spatial partitioning

Microbial communities inhabit spatial architectures that divide a global environment into isolated or semi-isolated local environments, which leads to the partitioning of a microbial community into a collection of local communities. Despite its ubiquity and great interest in related processes, how and to what extent spatial partitioning affects the structures and dynamics of microbial communities is poorly understood. Using modeling and quantitative experiments with simple and complex microbial communities, we demonstrate that spatial partitioning modulates the community dynamics by altering the local interaction types and global interaction strength. Partitioning promotes the persistence of populations with negative interactions but suppresses those with positive interactions. For a community consisting of populations with both positive and negative interactions, an intermediate level of partitioning maximizes the overall diversity of the community. Our results reveal a general mechanism underlying the maintenance of microbial diversity and have implications for natural and engineered communities.

Phylogenetic signal of sub-arctic beetle communities

Postglacial dispersal and colonization processes have shaped community patterns in sub-Arctic regions such as Churchill, Manitoba, and Canada. This study investigates evolutionary community structure within the beetle (Coleoptera) families of Churchill and tests whether biological traits have played a role in governing colonization patterns from refugial and southerly geographic regions. This study quantifies sub-Arctic beetle phylogenetic community structure for each family using the net relatedness index (NRI) and nearest taxon index (NTI), calculated using publicly available data from the Barcode of Life Data Systems (BOLD); compares patterns across families with different traits (habitat, diet) using standard statistical analysis (ANOVA) as well as phylogenetic generalized least squares (PGLS) using a family-level beetle phylogeny obtained from the literature; and compares community structure in Churchill with a region in southern Canada (Guelph, Ontario). These analyses were also repeated at a genus level. The dominant pattern detected in our study was that aquatic families were much better represented in Churchill compared to terrestrial families, when compared against richness sampled from across Canada and Alaska. Individually, most families showed significant phylogenetic clustering in Churchill, likely due to the strong environmental filtering present in Arctic environments. There was no significant difference in phylogenetic structure between Churchill and Guelph but with a trend toward stronger clustering in the North. Fungivores were significantly more overdispersed than other feeding modes, predators were significantly more clustered, and aquatic families showed significantly stronger clustering compared to terrestrial. This study contributes to our understanding of the traits and processes structuring insect biodiversity and macroecological trends in the sub-Arctic.

Opposing community assembly patterns for dominant and nondominant plant species in herbaceous ecosystems globally

Biotic and abiotic factors interact with dominant plants-the locally most frequent or with the largest coverage-and nondominant plants differently, partially because dominant plants modify the environment where nondominant plants grow. For instance, if dominant plants compete strongly, they will deplete most resources, forcing nondominant plants into a narrower niche space. Conversely, if dominant plants are constrained by the environment, they might not exhaust available resources but instead may ameliorate environmental stressors that usually limit nondominants. Hence, the nature of interactions among nondominant species could be modified by dominant species. Furthermore, these differences could translate into a disparity in the phylogenetic relatedness among dominants compared to the relatedness among nondominants. By estimating phylogenetic dispersion in 78 grasslands across five continents, we found that dominant species were clustered (e.g., co-dominant grasses), suggesting dominant species are likely organized by environmental filtering, and that nondominant species were either randomly assembled or overdispersed. Traits showed similar trends for those sites (<50%) with sufficient trait data. Furthermore, several lineages scattered in the phylogeny had more nondominant species than expected at random, suggesting that traits common in nondominants are phylogenetically conserved and have evolved multiple times. We also explored environmental drivers of the dominant/nondominant disparity. We found different assembly patterns for dominants and nondominants, consistent with asymmetries in assembly mechanisms. Among the different postulated mechanisms, our results suggest two complementary hypotheses seldom explored: (1) Nondominant species include lineages adapted to thrive in the environment generated by dominant species. (2) Even when dominant species reduce resources to nondominant ones, dominant species could have a stronger positive effect on some nondominants by ameliorating environmental stressors affecting them, than by depleting resources and increasing the environmental stress to those nondominants. These results show that the dominant/nondominant asymmetry has ecological and evolutionary consequences fundamental to understand plant communities.

Disturbed habitats locally reduce the signal of deep evolutionary history in functional traits of plants

The functioning of present ecosystems reflects deep evolutionary history of locally cooccurring species if their functional traits show high phylogenetic signal (PS). However, we do not understand what drives local PS. We hypothesize that local PS is high in undisturbed and stressful habitats, either due to ongoing local assembly of species that maintained ancestral traits, or to past evolutionary maintenance of ancestral traits within habitat species-pools, or to both. We quantified PS and diversity of 10 traits within 6704 local plant communities across 38 Dutch habitat types differing in disturbance or stress. Mean local PS varied 50-fold among habitat types, often independently of phylogenetic or trait diversity. Mean local PS decreased with disturbance but showed no consistent relationship to stress. Mean local PS exceeded species-pool PS, reflecting nonrandom subsampling from the pool. Disturbance or stress related more strongly to mean local than to species-pool PS. Disturbed habitats harbour species with evolutionary divergent trait values, probably driven by ongoing, local assembly of species: environmental fluctuations might maintain different trait values within lineages through an evolutionary storage effect. If functional traits do not reflect phylogeny, ecosystem functioning might not be contingent on the presence of particular lineages, and lineages might establish evolutionarily novel interactions.

Distinct Assembly Processes and Determinants of Soil Microbial Communities between Farmland and Grassland in Arid and Semiarid Areas

It is critical to identify the assembly processes and determinants of soil microbial communities to better predict soil microbial responses to environmental change in arid and semiarid areas. Here, soils from 16 grassland-only, 9 paired grassland and farmland, and 16 farmland-only sites were collected across the central Inner Mongolia Plateau, covering a steep environmental gradient. Through analyzing the paired samples, we discovered that land uses had strong effects on soil microbial communities but weak effects on their assembly processes. For all samples, although no environmental variables were significantly correlated with the net relatedness index (NRI), both the nearest taxon index (NTI) and the β-nearest taxon index (βNTI) were most related to mean annual precipitation (MAP). With the increase of MAP, soil microbial taxa at the tips of the phylogenetic tree were more clustered, and the contribution of determinism increased. Determinism (48.6%), especially variable selection (46.3%), and stochasticity (51.4%) were almost equal in farmland, while stochasticity (75.0%) was dominant in grassland. Additionally, Mantel tests and redundancy analyses (RDA) revealed that the main determinants of soil microbial community structure were MAP in grassland but mean annual temperature (MAT) in farmland. MAP and MAT were also good predictors of the community composition (the top 200 dominant operational taxonomic units) in grassland and farmland, respectively. Collectively, in arid and semiarid areas, soil microbial communities were more sensitive to environmental change in farmland than in grassland, and unlike the major impact of MAP on grassland microbial communities, MAT was the primary driver of farmland microbial communities. IMPORTANCE As one of the most diverse organisms, soil microbes play indispensable roles in many ecological processes in arid and semiarid areas with limited macrofaunal and plant diversity, yet the mechanisms underpinning soil microbial community are not fully understood. In this study, soil microbial communities were investigated along a 500-km transect covering a steep environmental gradient across farmland and grassland in the areas. The results showed that precipitation was the main factor mediating the assembly processes. Determinism was more influential in farmland, and variable selection of farmland was twice that of grassland. Temperature mainly drove farmland microbial communities, while precipitation mainly affected grassland microbial communities. These findings provide new information about the assembly processes and determinants of soil microbial communities in arid and semiarid areas, consequently improving the predictability of the community dynamics, which have implications for sustaining soil microbial diversity and ecosystem functioning, particularly under global climate change conditions.

Integrating terrestrial laser scanning with functional-structural plant models to investigate ecological and evolutionary processes of forest communities

BACKGROUND

Woody plants (trees and shrubs) play an important role in terrestrial ecosystems, but their size and longevity make them difficult subjects for traditional experiments. In the last 20 years functional-structural plant models (FSPMs) have evolved: they consider the interplay between plant modular structure, the immediate environment and internal functioning. However, computational constraints and data deficiency have long been limiting factors in a broader application of FSPMs, particularly at the scale of forest communities. Recently, terrestrial laser scanning (TLS), has emerged as an invaluable tool for capturing the 3-D structure of forest communities, thus opening up exciting opportunities to explore and predict forest dynamics with FSPMs.

SCOPE

The potential synergies between TLS-derived data and FSPMs have yet to be fully explored. Here, we summarize recent developments in FSPM and TLS research, with a specific focus on woody plants. We then evaluate the emerging opportunities for applying FSPMs in an ecological and evolutionary context, in light of TLS-derived data, with particular consideration of the challenges posed by scaling up from individual trees to whole forests. Finally, we propose guidelines for incorporating TLS data into the FSPM workflow to encourage overlap of practice amongst researchers.

CONCLUSIONS

We conclude that TLS is a feasible tool to help shift FSPMs from an individual-level modelling technique to a community-level one. The ability to scan multiple trees, of multiple species, in a short amount of time, is paramount to gathering the detailed structural information required for parameterizing FSPMs for forest communities. Conventional techniques, such as repeated manual forest surveys, have their limitations in explaining the driving mechanisms behind observed patterns in 3-D forest structure and dynamics. Therefore, other techniques are valuable to explore how forests might respond to environmental change. A robust synthesis between TLS and FSPMs provides the opportunity to virtually explore the spatial and temporal dynamics of forest communities.

Seasonal dynamics of Diptera in individual biotopes in the center of the European part of Russia

In a changing climate, phenological observations are gaining new importance. They can tell what changes are taking place in certain environmental conditions. The studies were conducted in 2019 within the territory of the Republic of Mordovia (the center of the European part of Russia). Beer traps (beer as a bait) were used to collect Diptera. The material was collected in the period from April to October in different forest biotopes (pine forest, lime forest, aspen forest, birch forest and oak forest) and the air temperature was recorded at the same time. In total, more than 14.000 specimens of Diptera were recorded. Overall, 29 families were recorded. The largest number of families was observed for birch (23 families) and pine (24 families) forests, the smallest number – in aspen forest (16 families). The families Muscidae, Drosophilidae, Calliphoridae had the largest number of captured individuals (44.5%, 35.2%, 7.6% of the total number of individuals respectively). The highest number of individuals was captured in oak forest. The dynamics of abundance in all biotopes were similar and were characterized by the same number of declines and rises. The first small significant peak in the number of Diptera occurred in the first half of summer. A slight increase in the number of specimenі occurred in mid-June. In the second half of September, there was a gradual increase in the number and the maximum peak was recorded in mid-October, then there was a decline. The autumn increase in the number of Diptera in all five biotopes exceeded the summer peak by several times. This dynamic was typical for most families. However, species from the family Lonchaeidae had the peak in July. For our better understanding of the changes in the seasonal dynamics of the number of Diptera, long-term observations in different climatic zones are needed.

Seasonal dynamics of Diptera in individual biotopes in the center of the European part of Russia

In a changing climate, phenological observations are gaining new importance. They can tell what changes are taking place in certain environmental conditions. The studies were conducted in 2019 within the territory of the Republic of Mordovia (the center of the European part of Russia). Beer traps (beer as a bait) were used to collect Diptera. The material was collected in the period from April to October in different forest biotopes (pine forest, lime forest, aspen forest, birch forest and oak forest) and the air temperature was recorded at the same time. In total, more than 14.000 specimens of Diptera were recorded. Overall, 29 families were recorded. The largest number of families was observed for birch (23 families) and pine (24 families) forests, the smallest number – in aspen forest (16 families). The families Muscidae, Drosophilidae, Calliphoridae had the largest number of captured individuals (44.5%, 35.2%, 7.6% of the total number of individuals respectively). The highest number of individuals was captured in oak forest. The dynamics of abundance in all biotopes were similar and were characterized by the same number of declines and rises. The first small significant peak in the number of Diptera occurred in the first half of summer. A slight increase in the number of specimenі occurred in mid-June. In the second half of September, there was a gradual increase in the number and the maximum peak was recorded in mid-October, then there was a decline. The autumn increase in the number of Diptera in all five biotopes exceeded the summer peak by several times. This dynamic was typical for most families. However, species from the family Lonchaeidae had the peak in July. For our better understanding of the changes in the seasonal dynamics of the number of Diptera, long-term observations in different climatic zones are needed.