Functional Beta Diversity Research Articles

Multiple aspects of tree beta diversity in coastal ecosystems in Brazil

AbstractAimPatterns of beta diversity reflect the formation dynamics of ecological communities. Here, we integrated geographic, phylogenetic, and phenotypic information of coastal woody vegetation to investigate (1) whether the observed dissimilarity between assemblages differs from that expected by chance, examining the roles of spatial and deterministic processes; (2) the relative contribution of beta‐diversity components (turnover and nestedness) for taxonomic, phylogenetic, and functional beta diversity; and (3) what environmental factors drive the differences in composition between assemblages for all these dimensions.LocationBrazil.TaxonAngiosperm trees.MethodsWe built dissimilarity matrices and partitioned the taxonomic, phylogenetic, and functional beta diversity from an incidence matrix, a phylogeny including the region's plants, and a matrix expressing functional distances. Using linear regressions, we tested the effects of different environmental predictors representative of the effects of water availability, thermal energy, habitat heterogeneity, edaphic constraints, climatic stability, and human influence on beta‐diversity patterns.ResultsTaxonomic, phylogenetic, and functional dissimilarities exhibited a typical pattern of greater dissimilarity with distance (i.e., as expected by chance). However, these patterns showed different contributions of beta‐diversity components, predominating turnover in taxonomic and phylogenetic dissimilarity, and nestedness in functional dissimilarity. Water availability had a slight effect on patterns of taxonomic and phylogenetic dissimilarities.Main conclusionsThe Brazilian coastal woody vegetation appears to have emerged through a dynamic of colonisation of evolutionarily distinct but functionally similar lineages that originated from adjacent phytogeographic domains, proportional to their diversity. This is consistent with a combination of both neutral and non‐neutral processes. Our findings underscore the complementary roles of different dimensions of beta diversity in explaining the dynamics of these vegetation communities.

Effects of plant taxonomic position on soil nematode communities in Antarctica.

Antarctica terrestrial ecosystems are facing the most threats from global climate change, which is altering plant composition greatly. These transformations may cause major reshuffling of soil community composition, including functional traits and diversity, and therefore affect ecosystem processes in Antarctica. We used high-throughput sequencing analysis to investigate soil nematodes under 3 dominant plant functional groups (lichens, mosses, and vascular plants) and bare ground in the Antarctic region. We calculated functional diversity of nematodes based on their diet, life histories, and body mass with kernel density n-dimensional hypervolumes. We also calculated taxonomic and functional beta diversity of the nematode communities based on Jaccard dissimilarity. The presence of plants had no significant effect on the taxonomic richness of nematodes but significantly increased nematode functional richness. The presence of plants also significantly decreased taxonomic beta diversity (homogenization). Only mosses and vascular plants decreased nematode functional beta diversity, which was mostly due to a decreased effect of the richness difference component. The presence of plants also increased the effect of deterministic processes potentially because environmental filtering created conditions favorable to nematodes at low trophic levels with short life histories and small body size. Increasing plant cover in the Antarctic due to climate change may lead to increased diversity of nematode species that can use the scarce resources and nematode taxonomic and functional homogenization. In a future under climate change, community restructuring in the region is possible.

Scale-dependent influences of environmental, historical, and spatial processes on taxonomic and functional beta diversity of Japanese bat assemblages.

This study investigated the relative influences of environmental, spatial, and historical factors, including the island-specific history of land connectivity, on bat assemblages in the Japanese Archipelago. We collected bat distribution data from 1408 studies and assigned them to Japan's First Standard Grid (approximately 6400 km2). Japanese bat assemblages were analyzed at two scales: the entire Japanese Archipelago comprised 16 islands and exclusively the four main islands. At first, we calculated taxonomic and functional total beta diversity (β total) by Jaccard pairwise dissimilarity and then divided this into turnover (β repl) and richness-difference (β rich) components. We conducted hierarchical clustering of taxonomic beta diversity to examine the influence of the two representative sea straits, Tsugaru and Tokara, which are considered biogeographical borders. Variation partitioning was conducted to evaluate the relative effects of the three factors on the beta diversity. Clustering revealed that the Tokara Strait bordered the two major clades; however, the Tsugaru Strait did not act as a biogeographical border for bats. In the variation partitioning, shared fraction between spatial and historical factors significantly explained taxonomic and functional β total and taxonomic β repl at the entire archipelago scale, but not at the four main islands scale extending only Tsugaru Strait but not Tokara Strait. Pure environmental factors significantly explained functional β total at both scales and taxonomic β total only at the four main islands scale. These results suggest that spatial and historical factors are more pronounced in biogeographical borders, primarily structuring assemblage composition at the entire archipelago scale, especially in taxonomic dimension. However, current environmental factors primarily shape the assemblage composition of Japanese bats at the main island scale. The difference in results between the two scales highlights that the primary processes governing assemblages of both dimensions depend on the quality of the dispersal barriers between terrestrial and aquatic barriers for bats.

Relationships between functional alpha and beta diversities of flea parasites and their small mammalian hosts.

We studied the relationships between functional alpha and beta diversities of fleas and their small mammalian hosts in 4 biogeographic realms (the Afrotropics, the Nearctic, the Neotropics and the Palearctic), considering 3 components of alpha diversity (functional richness, divergence and regularity). We asked whether (a) flea alpha and beta diversities are driven by host alpha and beta diversities; (b) the variation in the off-host environment affects variation in flea alpha and beta diversities; and (c) the pattern of the relationship between flea and host alpha or beta diversities differs between geographic realms. We analysed alpha diversity using modified phylogenetic generalized least squares and beta diversity using modified phylogenetic generalized dissimilarity modelling. In all realms, flea functional richness and regularity increased with an increase in host functional richness and regularity, respectively, whereas flea functional divergence correlated positively with host functional divergence in the Nearctic only. Environmental effects on the components of flea alpha diversity were found only in the Holarctic realms. Host functional beta diversity was invariantly the best predictor of flea functional beta diversity in all realms, whereas the effects of environmental variables on flea functional beta diversity were much weaker and differed between realms. We conclude that flea functional diversity is mostly driven by host functional diversity, whereas the environmental effects on flea functional diversity vary (a) geographically and (b) between components of functional alpha diversity.

Host population crashes disrupt the diversity of associated marine microbiomes.

Host-associated microbial communities are shaped by myriad factors ranging from host conditions, environmental conditions and other microbes. Disentangling the ecological impact of each of these factors can be particularly difficult as many variables are correlated. Here, we leveraged earthquake-induced changes in host population structure to assess the influence of population crashes on marine microbial ecosystems. A large (7.8 magnitude) earthquake in New Zealand in 2016 led to widespread coastal uplift of up to ~6 m, sufficient to locally extirpate some intertidal southern bull kelp populations. These uplifted populations are slowly recovering, but remain at much lower densities than at nearby, less-uplifted sites. By comparing the microbial communities of the hosts from disturbed and relatively undisturbed populations using 16S rRNA gene amplicon sequencing, we observed that disturbed host populations supported higher functional, taxonomic and phylogenetic microbial beta diversity than non-disturbed host populations. Our findings shed light on microbiome ecological assembly processes, particularly highlighting that large-scale disturbances that affect host populations can dramatically influence microbiome structure. We suggest that disturbance-induced changes in host density limit the dispersal opportunities of microbes, with host community connectivity declining with the density of host populations.

Advancing fish diversity monitor in degraded marine ecosystem with environmental DNA approach: Unveiling hidden riches

Comprehending fish diversity through multiple dimensions is a crucial aspect in advancing our understanding of fish populations and promoting sustainable fisheries as well as diversity conservation. Traditional research on fish diversity has been limited to non-genetic methods. The advent of environmental DNA (eDNA) technology enables simultaneous examination of both non-genetic and genetic aspects of fish diversity. In this study, we evaluated the ability of eDNA to capture multidimensional fish diversity in the northern South China Sea, with emphasis on phylogenetic diversity. The effect of environmental change and geographical location on multidimensional fish diversity across different seasons was also investigated. The analysis of species accumulation curves revealed that the observed species richness approached an asymptote, achieving 94.7% and 89.5% of the predicted values during the summer and winter, respectively. Alpha diversity of taxonomic (species, 225 vs. species, 102), functional (FRic, 0.51 vs. FRic, 0.19), and phylogenetic (PD, 26.27 vs. PD, 15.81) dimensions were found to be higher in summer compared to winter, with environmental factors significantly influencing these diversities across seasons. Regarding the three dimensions of beta diversity, replacement made a greater relative contribution to total taxonomic, functional, and phylogenetic beta diversity than richness difference. These effects were primarily influenced by water environment factors (e.g., NO2−, SiO32−, surface temperature) during the summer and geographical factors (e.g., longitude and latitude) during the winter. This study provides evidence supporting the feasibility of utilizing eDNA techniques to uncover fish diversity in multiple dimensions, with a specific emphasis on its intrinsic genetic characteristics, which hold substantial value for the protection of diversity and the scientific administration of fishery resources.

Drivers of desert plant beta diversity on the Qinghai-Tibet plateau.

The desert ecosystem of the Qinghai-Tibet Plateau (QTP) is an important component of China's desert ecosystem. Studying the mechanisms shaping the taxonomic, phylogenetic, and functional beta diversity of plant communities in the QTP desert will help us to promote scientific conservation and management of the region's biodiversity. This study investigated the effects of environmental (including altitude, climate factors, and soil factors) and geographic distances on three facets of beta diversity as well as their turnover and nestedness components based on field survey data. The results showed that turnover components dominate the three facets of beta diversity. However, the turnover contributions to phylogenetic and functional beta diversity were lower than for taxonomic beta diversity. Environmental distance had a greater influence than geographic distance, with the former uniquely explaining 15.2%-22.8% of beta diversity and the latter explaining only 1.7%-2.4%. Additionally, the explanatory power of different factors for beta diversity differed between herbs and shrubs, with environmental distance being more important for the latter. Distance-based redundancy analysis suggested that soil total potassium content had a substantial impact on the beta diversity of three dimensions, with mean temperature of the coldest month and soil total phosphorus content having a substantial impact on taxonomic and functional beta diversity as well. Our results support that environmental sorting plays a predominant role in shaping plant community composition across QTP desert ecosystems. To maintain the plant diversity of this region, it is crucial to prioritize the conservation of its diverse environmental conditions and actively mitigate its degradation by anthropogenic pressures.

Environmental filtering and landscape composition drive multifaceted diversity of bird assemblages in vineyards

Abstract Agricultural landscapes are productive areas with high biodiversity potential, but their conversion to monocultures and intensification of practices are recognised drivers of bird biodiversity loss worldwide. This challenges the compatibility of agricultural land use with bird conservation, as landscape composition affects both the diversity of bird species and traits and the assembly of bird communities. We address the underlying mechanisms of avian community assembly in vineyards at the plot and landscape levels in relation to landscape composition in one of the major wine producing regions of France. We jointly analyse how the taxonomic, functional, and phylogenetic facets of bird alpha and beta diversity respond to a gradient of landscape heterogeneity and test for a non‐random assembly rule. We found that birds tended to avoid vineyard monocultures. There was consistent support for the co‐occurrence of both closely related species and similar functional traits within vineyard plots (namely, phylogenetic and functional clustering, respectively). Landscape composition, both within plots and on a large scale (1000 m), was critical in explaining the occurrence of species and traits within plots. Landscape composition determined a nested pattern of functional and phylogenetic beta diversity from vineyard monoculture to more complex landscapes with increasing seminatural land cover. Synthesis and applications. Landscape composition in seminatural vegetation features significantly influenced both the alpha and beta bird diversity in vineyard‐dominated agricultural landscapes. Interspersed shrubs and woodland can help increase bird abundance and species richness in vineyards, while large‐scale land cover diversity might help promote functional and phylogenetic bird diversity.

Hydroperiod length, not pond age, determines zooplankton taxonomic and functional diversity in temporary ponds

Mediterranean Temporary ponds (MTPs) are suffering severe alterations in their hydrological and salinity regime through global change, and restoration or conservation of these habitats is a priority. However, there is little information that can be used as a scientific basis for restoration.We studied the taxonomic and functional diversity of zooplankton communities in a set of 96 ponds in Doñana, Spain during four consecutive hydroperiods after their creation. We examined the differences across hydroperiods in alpha and beta diversity (and its turnover and nestedness components) of the rotifer, cladoceran and copepod community, as well as the influence of local environmental variables including the proximity to natural wetlands.There was no general increase in diversity indices after the first two hydroperiods. We found that shorter hydroperiods significantly reduced taxonomic diversity, but increased the contribution to functional beta diversity through turnover. Shorter hydroperiods also reduced community complexity, with long-term effects. Conductivity was the most important predictor of zooplankton alpha and beta diversity, but the direction of its effects changed between hydroperiods. The distance from a natural source of colonists, and pond depth, were key during the early stage of community assembly and after a hydrological perturbation.Our results suggest that new restoration projects for MTPs should focus on increasing local environmental heterogeneity and on reducing vulnerability to salinization.The use of functional approaches in monitoring studies can improve our understanding of mechanisms and processes affecting zooplankton community assembly under dynamic hydrological regimes. This in turn can help us predict the consequences of management and restoration policies for biodiversity conservation in MTPs.

Deterministic processes drive turnover-dominated beta diversity of breeding birds along the central Himalayan elevation gradient

Beta diversity, the variation of community composition among sites, bridges alpha and gamma diversity and can reveal the mechanisms of community assembly through applying distance-decay models and/or partitioning beta diversity into turnover and nestedness components from functional and phylogenetic perspectives. Mountains as the most natural experiment system provide good opportunities for exploring beta diversity patterns and the underlying ecological processes. Here, we simultaneously consider distance-decay models and multiple dimensions of beta diversity to examine spatial variations of bird communities, and to evaluate the relative importance of niche-based and neutral community assembly mechanisms along a 3600-m elevational gradient in the central Himalayas, China. Our results showed that species turnover dominates taxonomic, functional, and phylogenetic beta diversity. We observed strongest evidence of spatial distance decays in taxonomic similarities of birds, followed by its phylogenetic and functional analogues. Turnover component was highest in taxonomic beta diversity, while nestedness component was highest in functional beta diversity. Further, all correlations of assemblage similarity with climatic distance were higher than that with spatial distances. Standardized values of overall taxonomic, functional, and phylogenetic beta diversity and their turnover components increase with increasing elevational distance, while the standardized values of taxonomic and phylogenetic nestedness decreased with increasing elevational distance. Our results highlighted the niche-based deterministic processes in shaping elevational bird diversity patterns that were determined by the relative roles of decreasing trend of environmental filtering and increasing trend of limiting similarity along elevation distances.

Scales matter: regional environment factors affect α diversity but local factors affect β diversity of macroinvertebrates in Thousand Islands Lake catchment area

A more profound comprehension of various facets of biodiversity is essential for advancing sustainable governance of biodiversity and its associated ecosystem services. In this study, we delved into the composition of beta diversity within macroinvertebrates communities in the Thousand Islands Lake catchment area. Subsequently, we investigated the factors influencing the diverse facets of macroinvertebrates alpha and beta diversity, and ultimately employed structural equation modeling to analyze the pathways through which both regional environmental factors, like climate and land use, and local environmental variables collectively impact distinct facets of alpha and beta diversity within the ecosystem. Our results showed that (i) taxonomic and phylogenetic beta diversities were primarily determined by turnover, while functional beta diversity is predominantly determined by nestedness; (ii) alpha and beta diversity are primarily influenced by spatial variables, with local environment and climate ranking the second, and land use explaining the lowest proportion according to the results of variance partitioning; (iii) alpha diversity is mainly affected by regional variables, especially climatic factors (precipitation) while beta diversity is more affected by local variables, especially hydrological factors (depth) revealed by the structural equation modeling. These results offer compelling evidence that biodiversity composition, ecological drivers, and the specific pathways of influence vary across different scales. Future studies of macroinvertebrates could focus on different facets of alpha and beta diversity as well as consider the effects of environment variables at different scales, which would provide new insights into potential patterns of community associations.

A cheia não causou homogeneização taxonômica e funcional da comunidade de Chironomidae (Diptera) em uma planície de inundação neotropical

Abstract: Aim We investigated the hypothesis that flood decreases the taxonomic and functional beta diversity of Chironomidae (Diptera) larvae among floodplain lakes, causing biotic homogenization. Methods We collected benthic samples using a modified Petersen grab in 18 lakes in a flood period (March 2011) and a drought period (September 2011) in the Upper Paraná River floodplain. We compared the taxonomic and functional beta diversity of Chironomidae among lakes in flood and drought periods using a multivariate dispersion analysis (PERMDISP). Results We found similar taxonomic and functional beta diversity of the Chironomidae between hydrological periods. Conclusions We did not find evidence of biotic homogenization due to flood pulse. Our findings suggest other mechanisms besides increasing connectivity and environmental similarity due to flood pulse that may structure the benthic community, such as variation in the identity of flood-tolerant morphospecies across lakes.

Comparative metatranscriptomics reveals effect of host plant on microbiota gene expression of Anastrepha obliqua (Diptera: Tephritidae) larvae.

The microbiota associated with phytophagous insects perform several functions that help insects exploit plant resources. Thus, microorganisms contribute to the dispersal of phytophagous species to new host plants, thereby promoting diversification. In this study, metatranscriptomic analysis was used to compare the gene expression of the microbiome of Anastrepha obliqua Macquart larvae feeding on 3 of its host plants: Spondias purpurea L (red mombin), Mangifera indica L (mango), and Averrhoa carambola L (starfruit). To identify differential gene expression in relation to the host plant, transcript abundance was compared. The results of the taxonomic and functional beta-diversity analysis showed that there were significant differences in the structures and activities of the microbial communities depending on the infested plant. Among the microorganisms, bacteria and fungi were active components of the microbiota. Differential expression analyses showed that the different active genes in each of the plants analyzed were mainly grouped into categories related to carbohydrate and amino acid metabolism, with some of these genes coding for cytochrome o ubiquinol oxidase, cytochrome c, and the enzyme isocitrate dehydrogenase. The microbiota of A. carambola larvae differed more at the level of community structure and gene function, possibly due to the different nutritional composition of the A. carambola and the presence of a set of secondary metabolites specific to the family Oxalidaceae. In conclusion, the transcriptional activity of the microbiota of A. obliqua larvae is influenced by diet, which is important because it could influence the performance of the insect on each of its different host plants.

Multiple stressors determine the process of the benthic diatom community assembly and network stability in urban water bodies in Harbin

Human activities have triggered biodiversity loss, often resulting in biotic homogenization, which poses a threat to human well-being. Nevertheless, the overall influence of diverse environmental stressors on intra- and inter-community diversity remains insufficiently elucidated. This study aimed to quantify and reveal the impact of environmental stressors on the alpha and beta diversities of benthic diatom communities in the Harbin urban river network during the summer and autumn of 2022 and spring of 2023. The marked seasonal variations observed in alpha and beta diversity indices highlighted the distinct community compositions. Nonetheless, varying types of urban water pollutants were the primary drivers of biotic homogenization in terms of both taxonomic and functional diversities and played a prominent role in steering diversity shifts. These pollutants indirectly led to biotic homogenization by altering water quality parameters and affecting the ecological dynamics of benthic diatom communities. Furthermore, diverse responses to stressors were identified in taxonomic and functional diversities, providing additional insights for understanding ecological shifts in communities. Taxonomic beta diversity was related to environmental filtering, whereas functional beta diversity resulted from stressor–spatial dimension interactions. Our study emphasises that relying solely on traditional water quality monitoring may not fully reveal the current state of river ecosystem protection, and the need to study the continuous changes in biodiversity across seasons in urban waterbodies from the perspective of various stressors is highlighted.

The importance of niches in defining phytoplankton functional beta diversity during a spring bloom

The importance of niches in defining phytoplankton functional beta diversity during a spring bloom

Homogenization of Functional Diversity of Rotifer Communities in Relation to Eutrophication in an Urban River of North China.

Rapid urbanization has triggered nutrient loading, which will inevitably lead to the eutrophication of water bodies and further affect the structure of aquatic populations. At present, eutrophication is a significant challenge for urban aquatic ecosystems. However, we still know little about the correlation between eutrophication in urban rivers and the composition of aquatic functional groups. The effects of urban river eutrophication on rotifer communities were investigated using an annual field survey of the Jinan section of the Xiaoqing River, a typical urban river in northern China. Using functional diversity (FD) and beta diversity, the spatiotemporal variation of the aquatic biological functional groups regime along stretches subject to different eutrophication was investigated. The functional evenness (FEve) and functional divergence (FDiv) decreased significantly with the increment of the trophic level index. Functional diversity exhibits an extremely low level across functional groups, with the richness difference (RichDiff) being an important component. The results indicate that eutrophication led to the homogenization of rotifer communities. This can be attributed to the functional homogenization of the rotifer community in the Jinan section of the Xiaoqing River. The observed homogenization may be due to widely distributed species complementing the ecological niche space. Our findings provide valuable information on the conservation of the urban river under the threat of eutrophication caused by high-intensity human activities.

Interdecadal changes in ichthyofauna in a tropical bay with high anthropogenic influences: functional stability despite turnover predominance.

Functional characteristics of species are of great importance for understanding their roles in ecosystems and can be used to detect long-term chances in the environment. We evaluated temporal changes (1983-1985 and 2017-2019) in taxonomic and functional indices of the fish fauna in shallow areas of a tropical bay heavily impacted by anthropogenic activities in recent decades. The hypothesis that functional indices change over time as a result of environmental degradation was tested. Our results showed a significant decrease in species richness and abundance over time, and in functional richness, while others functional diversity indices (divergency, evenness, and originality) remained stable. Thirteen functional groups were detected, some of which contained only one species, raising concerns about the loss of ecosystem functions due to ongoing changes. We also observed an increase in beta diversity over time, which may be the result of a decrease in local richness without leading to regional extinctions. Turnover was the most important process in structuring the fish fauna at the evaluated time scale. The relative stability of the functional structure and the higher levels of turnover seem to be related to the dominance of functional groups, within which species replace each other according to their responses to environmental filters that select for specific functional traits. Incorporating functional diversity indices and beta diversity variations in the fish community helped to enhance the existing information about this coastal system by offering improved estimates of biological diversity through diverse approaches. The predominance of turnover identified in the preset study suggests a dynamic and fluctuating species composition within the habitat. In this sense, habitat preservation should prioritize the protection of diverse habitats to accommodate a broad spectrum of species.

Differential patterns of taxonomic and functional diversity for two groups of canopy arthropods across spatial scales

AbstractArthropod diversity is often linked to variation in resource use, dispersal ability, habitat connectivity, and climate factors that differ across spatial scales. The aim of this research was to examine how species richness, functional diversity, and community composition of two taxa differing in functional roles and dispersal ability are structured across spatial scales and to identify the importance of vegetation, climate, and landscape in explaining these patterns at different scales. Organisms were collected from tree canopies using insecticidal fogging in the summer of 2000 from 96 trees in 24 stands of 6 deciduous forest sites in 2 ecoregions of the eastern United States. Taxonomic and functional beta diversity of ants (Hymenoptera: Formicidae) and spiders (Araneae) were partitioned across four hierarchical spatial scales (individual tree, forest stand, site, and ecoregion). The contributions of climatic, landscape, and vegetation variables were determined using model selection. Ant and spider species richness, functional diversity, and community composition differed between taxa and across spatial scales. Alpha diversity (within trees) was lower than expected for both taxa and types of diversity, with host tree species supporting different species of ants and spiders. While the beta components of species diversity among trees and forest stands were greater than expected for both taxa, spiders also showed significant levels of beta diversity among sites. Functional beta diversity was less scale‐dependent than taxonomic beta diversity. Stand‐level patterns of beta diversity were significantly predicted by variation in climate and landscape connectivity. The effects of climate and landscape fragmentation on the diversity and community structure of both taxa indicate that anthropogenic climate change and land use change will alter canopy arthropod communities. Results also suggest that patterns of diversity among fragmentation metrics are influenced by differences in dispersal ability.

A global synthesis and meta‐analysis of the environmental heterogeneity effects on the freshwater biodiversity

The spatial environmental heterogeneity (EH) has been invoked as an important factor to explain biodiversity. It is expected that higher spatial EH provides a wider range of resources and conditions for species with different requirements, leading to an increase of biodiversity. However, differences among geographical locations, ecosystem types, taxonomic groups, their occurrence zone, and methodological approaches may reveal idiosyncrasy between studies. Thus, we aimed to synthesize the global knowledge about the relationship between spatial EH and freshwater biodiversity (i.e. taxonomic and functional diversity, and their respective α and β components). Through a systematic review, we integrated results from 98 studies, published in 33 different countries, about the role of spatial EH – biodiversity relationship in freshwater ecosystems. Through meta‐analysis, we demonstrated that spatial EH has a positive effect over taxonomic and functional alpha diversity. Besides, we confirmed that the positive effect of spatial EH over taxonomic alpha diversity is consistent across geographical locations, ecosystem types, taxonomic groups, occurrence zones and between experiments with different methodological designs. Nonetheless, there was not enough evidence to robustly estimate the overall effect of spatial EH over taxonomic and functional beta diversity. Further, we discuss the mechanisms addressed to explain spatial EH‐biodiversity relationship, and implications for the management, conservation and restoration plans for freshwater ecosystems.

Functional diversity and redundancy of rotifer communities affected synergistically by top-down and bottom-up effects in tropical urban reservoirs

Rotifers are one of the most important functional groups in lentic freshwaters, and mainly structured by predation or competition from crustaceans and food availability from phytoplankton. Their functional traits involving in defense and food utilization provides insights into the functional diversity and assembly of their communities. Tropical urban reservoirs are commonly subjected to intense fish culture and strong eutrophication, and rotifers become the dominant component of the zooplankton communities and play an important role in ecosystem functioning. Knowledge about the functional diversity and functional redundancy of rotifers is therefore of relevance for effective ecosystem management. In tropical reservoirs, we hypothesized that functional diversity and redundancy of rotifer communities are synergistically affected by top-down and bottom-up effects, and that they strongly change seasonally with environmental conditions at local scale as well as with connectivity between reservoirs at regional scale. To test these hypotheses, we investigated the seasonal dynamics of taxonomic and functional diversities in twenty-five tropical urban reservoirs. Traits of rotifers mainly associated with body size, feeding behavior, and defensive strategies were used to explore the drivers of functional diversity and functional redundancy. We found that, at the local scale, both taxonomic alpha and functional alpha diversities of rotifers increased from the wet to the dry season, whereas the functional alpha redundancy showed no significant change. Crustacean abundance (top-down effect) and phytoplankton biomass (bottom-up effect) were the dominant variables explaining the variation of taxonomic and functional alpha diversities. At the regional scale, both the taxonomic and the functional beta diversities of rotifer communities decreased from the wet to the dry season. However, functional beta redundancy increased, accompanied by a reduction in environmental distance, i.e., biological and physicochemical distance. Thus, weakened environmental heterogeneity and strengthened homogenization of biological selection resulted in a more similar functional trait composition than a more similar taxonomic composition between reservoirs.