Niche Processes Research Articles

Space and spatially structured environmental variables account for variation in blackfly and mayfly communities in sub-tropical South African rivers

Using aquatic invertebrate assemblages for bioassessment of streams and rivers is a fast and cost-effective approach to studying the impact of environmental stressors in aquatic ecosystems. The use of aquatic invertebrates is premised on their predictable responses to environmental stressors. Assemblage structure is not, however, only influenced by environment, but also neutral processes and temporal variation. This study quantified the relative roles of the environment (niche processes), space (neutral processes) and temporal factors in structuring mayfly and blackfly assemblages at family and species levels. Asymmetric eigenvector maps in conjunction with canonical redundancy analysis and variation partitioning were used to explore the relative roles of these three factors in structuring macroinvertebrate assemblages. At a species level, flow and water temperature were more important in explaining assemblage structure than at the family level. At the family level, space was more important than temporal and environmental factors. Unexplained variation at species and family level was more than 50%. This suggests (i) caution in using family-level rapid assessments to infer the role of the environment in structuring aquatic macroinvertebrate assemblages, as neutral processes are also dominant; and (ii) that the importance of stochastic processes, such as dispersal, should not be underestimated in rapid assessments.

Species interactions drive continuous assembly of freshwater communities in stochastic environments

Understanding the factors driving the maintenance of long-term biodiversity in changing environments is essential for improving restoration and sustainability strategies in the face of global environmental change. Biodiversity is shaped by both niche and stochastic processes, however the strength of deterministic processes in unpredictable environmental regimes is highly debated. Since communities continuously change over time and space—species persist, disappear or (re)appear—understanding the drivers of species gains and losses from communities should inform us about whether niche or stochastic processes dominate community dynamics. Applying a nonparametric causal discovery approach to a 30-year time series containing annual abundances of benthic invertebrates across 66 locations in New Zealand rivers, we found a strong negative causal relationship between species gains and losses directly driven by predation indicating that niche processes dominate community dynamics. Despite the unpredictable nature of these system, environmental noise was only indirectly related to species gains and losses through altering life history trait distribution. Using a stochastic birth-death framework, we demonstrate that the negative relationship between species gains and losses can not emerge without strong niche processes. Our results showed that even in systems that are dominated by unpredictable environmental variability, species interactions drive continuous community assembly.

The spatial extent and the dispersal strategy of species shape the occupancy frequency distribution of stream insect assemblages.

Several theoretical models have been proposed as the underlying mechanisms behind occupancy frequency distribution (OFD) patterns. For instance, the metapopulation dynamic model predicts bimodal OFD pattern indicating the dominance of dispersal processes in structuring the assemblages, while the niche-based model predicts unimodal right-skewed OFD pattern, and thus assemblages are driven mostly by niche processes. However, it is well known that the observed OFD pattern reflects the interplay of several other factors (e.g. habitat heterogeneity, species specificity and sampling protocol parameters). It follows that the individual contribution of each factor to the OFD pattern is rather complicated to explore. Our main objective was to examine the role of the spatial extent of the sampling and the dispersal strategies of species in shaping OFD pattern. For this, we collected samples of stream insect assemblages inhabiting near-natural streams in the Pannon Ecoregion. We formed groups of species representing contrasting dispersal strategies (referred to as dispersal groups). Applying a computer program algorithm, we produced samples with different spatial extent. We found that with increasing spatial extent, the OFD pattern changed from bimodal to unimodal for active dispersers. Insect groups with different dispersal strategies differed in the strength of support for OFD patterns within all spatial extent. Furthermore, the strength of support for OFD patterns varied across dispersal groups differently as the spatial extent increased. Our results reflected underlying changes in mechanisms structuring assemblages along an increasing spatial extent. We also assumed that the stream insect dispersal strategy influences the relative role of dispersal and niche processes particularly as spatial extent increases from stream reaches to the extent of adjacent valleys. We could define spatial extents and dispersal strategies within which unique metacommunity processes could underlie the organisation of assemblages.

Odonata responses to dispersal and niche processes differ across Amazonian endemism regions

Abstract Niche and dispersal‐based processes govern freshwater communities, such as aquatic insects, shaping their distribution and establishment in the environment. So, we aimed to address the relative influence of niche and dispersal‐based processes on Odonata diversity in Amazonian freshwater systems, and the influence of species dispersal functional traits on their longitudinal and latitudinal ranges. We used the Dispersal‐Niche Continuum Index (DNCI) to test (i) regions more distant would present a prevalence of dispersal‐based processes, and (ii) different patterns would come from the two Odonata suborders; and by applying generalised linear models, we tested (iii) dispersal‐related functional traits from the suborders would influence latitudinal and longitudinal midpoints of the species. We found that more distant regions had lower values of pairwise Dispersal–Niche Continuum, mainly for Zygoptera, corroborating our first hypothesis. Moreover, Zygoptera also presented the lowest absolute values of Dispersal–Niche Continuum and Anisoptera presented a joint influence of niche and dispersal‐based processes, agreeing with our second hypothesis. Only Zygoptera presented a significant association between dispersal functional traits and longitudinal midpoints, corroborating our third hypothesis. Our results indicated a prevalence of dispersal‐related processes for Zygoptera, which can be explained by massive geographical barriers, such as the rivers, and their narrow physiological and ecological tolerance. Moreover, dispersal‐related traits demonstrated significant influence on longitudinal midpoints of Zygoptera, a scenario that the presence of the rivers may explain. A better understanding of the prevalent predictors of the species and how their dispersal ability governs their distribution has conservational implications.

Rare and common species contribute disproportionately to alpine meadow community construction and functional variation.

It is widely accepted that rare species are the first species to become extinct after human-induced disturbances. However, the functional importance of rare species still needs to be better understood, especially in alpine meadow communities with harsher habitats, where the extinction rate of rare species may be higher. This study established a 1.85 × 105 m2 permanent research sample plot on the eastern Tibetan Plateau. We investigated data from 162 plots at 6 different sampling scales in alpine meadows to determine the contribution of rare and common species to alpine meadow communities' structural and functional variability. The results showed that (1) Asteraceae (Compositae) was the dominant family in the surveyed localities. The trends of species diversity indices were the same, and all of them increased with the increase of sampling scale, and the plant community showed apparent scale effects. (2) The community construction of rare species at small scales with high occupancy transitioned from neutral processes to ecological niche processes, while the community construction of common species at different sampling scales was all dominated by ecological niche processes. (3) The trait values of rare species at different sampling scales were different from those of common species, and their distribution in FEs (functional entities) was also different, indicating that they contributed differently to the ecological functions of the communities. Rare species with lower abundance in the surveyed communities had a higher proportion of FEs, indicating that rare species had a more significant proportion of contribution to FEs. The functional redundancy (FR) of rare species was lower than that of common species, and the functional vulnerability (FV) was higher than that of common species. Therefore, the loss of rare species is more likely to cause the loss of community ecological functions, affecting the function and resilience of alpine meadow ecosystems.

Dispersal constrains the biotic connectivity of mountain assemblages

AbstractAimClimate warming is shifting the bioclimatic optima of species towards mountaintops, but the ability of organisms to track these changes also depends on their dispersal skills. Here, we assessed the role of dispersal over niche‐driven processes in connecting assemblages along mountain slopes and between mountain massifs.LocationCantabrian Mountains, Spain.TaxonBirds (Animalia; Aves) and Lichens (Fungi; Ascomycota, Basidiomycota).MethodsWe examined the change with elevation of community‐level traits that are dispersal proxies (wing shape in birds and type of dispersing propagule in lichens) and ecological niche proxies (micro‐habitat, substrate, and foraging features). We then permutate species composition within sites and massifs to create models of species distribution constrained by dispersal and niche processes. These models were compared with observed species distribution to disclose the relative contribution of dispersal and niche‐based processes in the biotic interchange along mountain slopes (vertical connectivity) and between isolated summits (horizontal connectivity).ResultsBoth bird and lichen communities were formed by species with traits that enhance dispersal at high elevations. These groups also showed similarities in the elevational patterns of niche diversity, which dropped at high elevations. Dispersal was by far the dominant assembly mechanism in both taxa. Pairwise community comparisons among elevation belts showed weak vertical connectivity, with predominant dispersal limitations but also niche barriers between the extremes of the gradient. Among massifs, horizontal connectivity was higher among high mountain assemblages than those from lower elevations.Main ConclusionDispersal was found to be the dominant assembly mechanism in mountain systems, even in taxa with high dispersal potential. Highland assemblages had low functional diversity but their species had high mobility. This permits biotic interchange between isolated summits and, potentially, colonization of other summits as climate warms. Our framework combining traits and occurrence‐permutation models improve the understanding of community assembly mechanisms along elevation gradients and points to dispersal limitations, especially at low‐middle elevations.

From individual leaves to forest stands: importance of niche, distance decay, and stochasticity vary by ecosystem type and functional group for fungal community composition.

Community assembly is influenced by environmental niche processes as well as stochastic processes that can be spatially dependent (e.g. dispersal limitation) or independent (e.g. priority effects). Here, we sampled senesced tree leaves as unit habitats to investigate fungal community assembly at two spatial scales: (i) small neighborhoods of overlapping leaves from differing tree species and (ii) forest stands of differing ecosystem types. Among forest stands, ecosystem type explained the most variation in community composition. Among adjacent leaves within stands, variability in fungal composition was surprisingly high. Leaf type was more important in stands with high soil fertility and dominated by differing tree mycorrhizal types (sugar maple vs. basswood or red oak), whereas distance decay was more important in oak-dominated forest stands with low soil fertility. Abundance of functional groups was explained by environmental factors, but predictors of taxonomic composition within differing functional groups were highly variable. These results suggest that fungal community assembly processes are clearest for functional group abundances and large spatial scales. Understanding fungal community assembly at smaller spatial scales will benefit from further study focusing on differences in drivers for different ecosystems and functional groups, as well as the importance of spatially independent factors such as priority effects.

Drivers and mechanisms that contribute to microbial β‐diversity patterns and range sizes in mountains across a climatic variability gradient

Microbial communities are highly diverse, yet the mechanisms underlying microbial community assembly are not well understood. Janzen's mountain passes hypothesis proposed that climatic barriers and dispersal limitation shape communities to a greater extent in mountains with lower climatic variability and overlap, permitting higher levels of species coexistence. Here, we investigate changes in microbial community dissimilarities, distributional range sizes and ecological processes along elevational gradients in three montane ecosystems representing a climatic variability gradient. We found that climate, climatic variability and spatial distance play dominating roles in affecting microbial β‐diversity patterns and range sizes along elevational gradients. Janzen's mountain passes hypothesis can be applied to microbial community assembly: mountains with lower climatic variability and higher climatic difference between elevations exhibited higher β‐diversity, higher endemism, lower range sizes and steeper distance–decay trends. However, microbial communities experience clear climate‐driven limited range sizes and dispersal processes, and show typical endemic patterns, in all mountain ecosystems. Our results emphasize the importance of dispersal and climatic niche processes in shaping montane biodiversity. As a result, changes in climate may significantly impact soil biodiversity in montane ecosystems by altering the effects of dispersal limitation and climatic variability on bacterial and fungal community composition along elevational gradients.Keywords: community assembly, dispersal limitation, β‐diversity, montane biodiversity, microbial community

Major approaches to dental implants in the biological environment of bone regeneration: a systematic review

Introduction: The presence of sufficient bone volume, both in width and height, is crucial for adequate implant placement and osseointegration, allowing stability of the peri-implant hard and soft tissues. Several bone augmentation techniques can be performed to preserve or reconstruct a resorbed alveolar ridge or pneumatized maxillary sinus. Bone remodeling of the ridge and buccal bone will still occur after tooth removal. Objective: It was to develop a systematic review to present the main approaches to dental implants in the biological environment of bone regeneration. Methods: The present study was followed by a systematic review model (PRISMA). The search strategy was performed in the PubMed, Cochrane Library, Web of Science Scopus, and Google Scholar databases. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: A total of 123 articles were found involving implantology and biomaterials. A total of 48 articles were fully evaluated and 34 were included in the systematic review. A total of 26 studies were excluded because they did not meet the GRADE criteria, and 22 studies were excluded because they had a high risk of bias. The symmetric funnel plot does not suggest a risk of bias between the small sample size studies. It was concluded that the search for a solution for large bone defects guided studies toward tissue regeneration therapy or bone regeneration. These studies can promote the use of fillers and epithelial barriers that assist in treatment as adjuvants to bone grafting techniques. Understanding host biological niche processes of signaling for neovascularization and bone regeneration and filling is necessary for subsequent dental success. Furthermore, implants placed in tobacco users, as well as in enlarged maxillary sinuses, simultaneously or in stages, and enlarged ridges lead to higher rates of implant failure.

Dam periodic storage drives the spatial pattern of vegetation towards banded evolution

Emerging and fragile ecosystems such as reservoir riparian zones are of increasing concern with the increasing number of damming projects worldwide. Current knowledge of riparian vegetation in reservoirs focuses on the individual and community level, with little understanding of spatial patterns and ecological processes at the landscape level. Here, we demonstrate the evolution process, evolution direction, and evolution mechanism of vegetation spatial patterns under persistent and periodic inundation disturbances in the reservoir riparian zone, through coupled analyses of landscape evolution and ecological processes, using continuous years of drone observation data in the riparian zones of two major reservoirs, Xiaowan and Nuozhadu of the Lancang River. We found that vegetation landscape evolution is driven by seed dispersal, environmental factors fluctuations, species tolerance differences, and competition for resource availability, showing a clear trend towards banded evolution. Ecological niche processes such as periodic wet-dry environmental filtering and interspecific competition dominated the formation of vegetation banding patches, and neutral processes of random seed dispersal dominated the areas where banding patches were formed. The water requirements of plants during the exposing period lead to a greater influence of environmental factors that are closely related to water, such as net rainfall, sunshine hours, groundwater storage, and soil moisture. Water redistribution between vegetated and bare ground patches is key to their formation and stability in the upper part of the riparian zone, where drought stress is severe, while in the lower part, vegetation is mainly affected by inundation stress during flooding periods. Therefore, riparian vegetation restoration is critical to maintain a certain area of bare ground patches for drought areas in the exposing period, in contrast to the emphasis on vegetation patch coverage. And it is possible to carry out spatial planning based on the development trend of the belt distribution, taking into account the flood and drought tolerance of the species as well as the fluctuating rhythms of the main factors, such as the rainfall, which is worth exploring further.

Niche processes shape zooplankton community structure in a sediment-laden river basin

Niche processes shape zooplankton community structure in a sediment-laden river basin

Three-dimensional species distribution modelling reveals the realized spatial niche for coral recruitment on contemporary Caribbean reefs.

The three-dimensional structure of habitats is a critical component of species' niches driving coexistence in species-rich ecosystems. However, its influence on structuring and partitioning recruitment niches has not been widely addressed. We developed a new method to combine species distribution modelling and structure from motion, and characterized three-dimensional recruitment niches of two ecosystem engineers on Caribbean coral reefs, scleractinian corals and gorgonians. Fine-scale roughness was the most important predictor of suitable habitat for both taxa, and their niches largely overlapped, primarily due to scleractinians' broader niche breadth. Crevices and holes at mm scales on calcareous rock with low coral cover were more suitable for octocorals than for scleractinian recruits, suggesting that the decline in scleractinian corals is facilitating the recruitment of octocorals on contemporary Caribbean reefs. However, the relative abundances of the taxa were independent of the amount of suitable habitat on the reef, emphasizing that niche processes alone do not predict recruitment rates.

Spatial scale affects the importance of deterministic and stochastic factors in the structuring of tadpole assemblages in Brazilian Cerrado

Many factors influence the structure of natural assemblages. Species interaction and environmental factors may generate deterministic patterns, whereas dispersal and ecological drift may generate stochastic patterns. We used pond systems to understand how deterministic and stochastic factors interact and influence tadpole assemblages at different spatial scales. We used variation partitioning and a co-occurrence analysis to evaluate how local environment heterogeneity, species interaction, and spatial variables affected species composition at local and regional scales in Brazilian savanna. Both deterministic and stochastic processes were important to explain tadpole distribution at regional scale, but with a greater contribution of stochastic factors. At local scales, environmental and niche traits were more important to explain tadpole distribution into the habitats. We demonstrate that in Brazilian Cerrado, species composition can be explained by the "MacArthur paradox", in which niche processes are important at local scales, whereas dispersal constraints and population processes lead to stochastic patterns in species distribution at large spatial scales.

Fatores associados à diversidade beta de macrófitas na Baía de Caxiuanã, localizada na Amazônia Oriental

Abstract Aim In this study, we investigated the beta diversity of macrophytes (total, turnover, and nestedness) in Caxiuanã Bay, localized in the Eastern Amazon. We also investigated the environmental factors determining the beta diversity and its components. Methods Macrophytes and physical-chemical variables (pH, water temperature, electrical conductivity, dissolved oxygen, and water turbidity) were sampled in 45 sites in 2017. Beta diversity was calculated based on Jaccard dissimilarity (using a presence/absence matrix) and partitioned in turnover and nestedness. We performed a Generalized Dissimilarity Modeling to analyze the influence of local (physical-chemical) and spatial factors (geographic distance) on total beta diversity and its components. Results A total of 16 macrophyte species were identified belonging to five morphological groups (free-floating, emergent, submerged, epiphytes, and rooted with floating leaves). The total beta diversity of macrophytes was 0.29, the turnover component had the highest contribution to total beta compared to nestedness. The beta total was influenced by geographic distance and conductivity, turnover by geographic distance and turbidity, and nestedness was explained by conductivity and pH. Conclusions In our study, physical-chemical factors influenced the structure of the macrophyte community, indicating that niche processes (deterministic) were acting and changing species composition. However, the spatial component and the low explanatory power of the models, especially for turnover, can also indicate the influence of stochastic processes such as ecological drift and/or limitations in dispersal. Our study provides new insights into the diversity patterns of macrophytes in Amazonian ecosystems, particularly in blackwater rivers. Our data also contribute to a better understanding of the processes that structure the species composition of macrophytes in these environments.

Matrix-associated microbial communities in a nitrogen-removing on-site wastewater treatment system are largely structured by niche processes.

On-site wastewater treatment systems (OWTSs) can be designed to promote microbial communities with naturally occurring metabolic functions desirable to wastewater treatment. Among such OWTSs are nitrogen-removing biofilters (NRBs), comprising a sand layer overlying a sand-lignocellulose (sand-lc) layer and intended to promote sequential nitrification and denitrification. The design of NRBs is based on the hypothesis that niche processes like environmental selection strongly structure the microbial communities, which predicts that immigrating wastewater communities and matrix-associated communities will be distinct and that the matrix communities in the two layers will be distinct. We characterized NRB microbial communities by 16S ribosomal RNA amplicon sequencing. Selection of the matrix-associated communities was indicated by clear differences from the immigrating community. For matrix-associated communities, alpha and beta diversity differed between the matrix layers, as did the relative abundances of many functional groups and genera. Functional groups with strict metabolisms were nearly exclusively detected in either the sand (ammonia and nitrite oxidizers) or sand-lc layer (methanogens), consistent with the niche hypothesis. Contrary to expectations, denitrifiers as a functional group were not present at greater relative abundance in the sand-lc than sand matrix because of a portfolio effect: some denitrifying genera were more abundant in the sand layer, whereas others were more abundant in the sand-lc layer. This study reveals niche processes acting at different levels of community organization for different biogeochemical functions, a crucial consideration in designing effective and reliable OWTSs to mitigate nitrogen pollution.

Stronger niche than dispersal effects on α‐ and β‐diversity of stream algae, insects, and fish across latitudes in the United States

AbstractAimNiche and dispersal processes influence biodiversity, but their relative importance along latitude is unclear. We predicted that: (a) niche processes would dominate at high latitudes due to increased climatic stress, consistent with the physiological tolerance hypothesis and the Dobzhansky–MacArthur hypothesis and (b) dispersal limitation would prevail at low latitudes due to narrower niches and smaller range sizes, as postulated by the dispersal–ecological specialization trade‐off hypothesis, the latitude–niche breadth hypothesis, and Rapoport's rule.LocationCentral United States.Time period1993–2019.Major taxa studiedStream algae, insects, and fish.MethodsWe examined the relative effects of environment (climate and physicochemistry) versus space on stream biodiversity in seven latitudinal zones, spanning 19 latitudinal degrees. In each zone, species richness (α‐diversity) was analysed with multiple regression and variance partitioning. Compositional dissimilarity (β‐diversity) within zones was assessed with distance‐based redundancy analysis (dbRDA) and variance partitioning.ResultsFor α‐diversity, latitudinal variability of niche and dispersal processes conformed to our predictions in all three groups, except for dispersal processes in insects. However, the drivers of β‐diversity did not follow our predictions. The latitude–niche breadth hypothesis and Rapoport's rule were weakly supported only in fish.Main conclusionsThe importance of niche and dispersal processes varied predictably along the latitudinal gradient only for α‐diversity. However, the niche effects were driven mostly by physicochemistry, and the dispersal effects were not always linked with ecological specialization and range size. This suggests that climate‐based biodiversity theories do not have particular relevance for the streams in our study. Niche processes had a greater impact than dispersal processes across species groups and diversity metrics, emphasizing the primary role of the environment.

Assessing the niche development of carbon capture and storage through strategic niche management approach: The case of China

Carbon capture and storage (CCS) is an important strategic technology choice for the future reduction of greenhouse gas emissions, which plays a crucial role as part of an economically sustainable route. Although some studies have discussed CCS demonstration projects and early developments, CCS has not been investigated as an innovative niche for sustainable transition. In an attempt to fill this gap, this study studies CCS as an innovative niche and assess the niche development of CCS in China by using a strategic niche management (SNM) framework. The evolution of three interlinked niche processes (expectations, social networks and learning process) is analysed with a comprehensive analytical approach that includes policy, social network and bibliometric analysis. Results show that a CCS niche has formed in China, but it is at a relatively low level of niche development in terms of the three internal processes. The expectations for CCS evolved linearly and are constantly being reinforced. The actor network supporting CCS niche development is sparse, and network cohesion is gradually decreasing. CCS learning continues to deepen but remains insufficient; it focuses on technical aspects and provides little attention to policy and social issues. The results indicate that expectations have been well-established at various levels in China, but the network and the learning process still need to be improved. Our findings help to identify problems in the development of technology and provide useful references for technology planning and the further development of CCS.

Altitudinal dispersal process drives community assembly of montane small mammals

Montane small mammals are subjected to strong forces of dispersal limitation and habitat filtering that mainly operate on their community structures along the altitudinal direction. However, so far little is known about the relative contributions of dispersal and niche processes to their community assembly. By applying the newly proposed PER‐SIMPER/DNCI (dispersal–niche continuum index) framework to small mammal occurrence data collected from 21 extensive altitudinal gradients, we quantitatively assessed the relative importance of dispersal and niche processes on mammalian community assembly in a large mountainous region of southwestern China. We compared the pairwise DNCI values among assemblages from low, middle and high altitudinal zones and overall DNCI values between glires and insectivores that differ in dispersal abilities to test three explicit (altitudinal connectivity, environmental difference and dispersal ability) hypotheses. The overall DNCI values for all small mammal species combined (−12.7 ± 0.4, 90 species), glires (−12.8 ± 0.5, 56 species) and insectivores (−13.5 ± 1.4, 34 species) values were all negative, while insectivores showed a lower value than glires. For both all species combined and glires, we found a lower pairwise DNCI value between the low and high altitudinal zones than that between the other two pairs of altitudinal zones. Our study indicated that an altitudinal dispersal process dominates the taxonomic composition of small mammal assemblages in this region. Importantly, the results reinforced the idea that community structures of less vagile taxa are more subject to dispersal limitation; and yet another idea that assemblages from further altitudinal areas are more differentiated by dispersal process was only supported in glires and all species combined. Community biologists should, therefore, pay attention to recent climate‐induced upward range shifts by montane species, which may dramatically alter their community structures in different altitudinal zones through dynamics of immigration and mountaintop extinction.

Stochasticity of individual competition and local matchup inequality for saplings in a niche-structured forest.

Ecologists have recently accepted the notion that species coexistence involves both niche and neutral processes, but few studies have explained how both of these opposite views can explain coexistence in the same community. Here we focus on competition among sessile organisms and explored first the extent to which species-based niche reflects local "matchups" between nearby individuals, using 726 saplings of 10 temperate tree species, and second the members engaging in the matchups, which have rarely been quantified despite the importance in mixed-species forests. Growth responses to light showed considerable species-level differences, suggesting commonly seen regeneration niches. Outcomes of the individual matchups were basically predictable from the species mean response, but also with substantial contribution of within-species variation. We found strong imbalance in matchup frequencies, such that some individuals meet more individuals of differing species but others meet fewer, as well as many isolated, competition-free ones. The niche and neutral processes appear to reflect, respectively, between- and within-species differences, and our findings suggest that even when niche segregation is discernible, the role of stochasticity for the frequency of local competition, as well as its outcomes, cannot be discounted in species coexistence.

Improved detection of mass effect species assembly for applied metacommunity thinking

Abstract Dispersal mass effects pose major challenges and opportunities for applied metacommunity ecology. A recent paper in Journal of Applied Ecology (https://doi.org/10.1111/1365‐2664.13701) presented a mass effect (ME) detection framework and grouped the species prone to ME in an extensive stream diatom survey. We tested the putative ME diatom group and two other reported species groups for signatures of (a) dispersal‐based to joint niche–dispersal assembly using the dispersal–niche continuum index and (b) metacommunity homogenization based on total compositional variance and individual species contributions to beta diversity. Signatures of ME were found in all three diatom groups, raising uncertainty about which species were distributed by ME. Due to the ambiguity and data demands we propose an alternate framework that enables more precise and robust ME detection with simpler data requirements. Demonstrating this approach on the same dataset, we assembled a new candidate ME group and systematically removed niche processes, dispersal limitation, stochasticity and generalist tendency as alternative explanations. Synthesis and applications. Mass effects have strong implications for biomonitoring and spatial prioritization within dispersal networks, yet standardized methodology explicitly aligned to ME has been lacking. Ecologists now have options to enable ME research and application in more projects, datasets and study systems. Ultimately these new frameworks will help to integrate metacommunity thinking with more spatially informed resource protection and management.