Patterns Of Community Structure Research Articles

A bird's-eye view of phylosymbiosis: weak signatures of phylosymbiosis among all 15 species of cranes

In numerous animal clades, the evolutionary history of host species drives patterns of gut microbial community structure, resulting in more divergent microbiota with increasing phylogenetic distance between hosts. This phenomenon, termed phylosymbiosis, has been observed in diverse evolutionary lineages, but has been difficult to detect in birds. Previous tests of phylosymbiosis among birds have been conducted using wild individuals, and thus interspecific differences in diet and environment may have masked a phylogenetic signal. Therefore, we tested for phylosymbiosis among all 15 species of cranes (family Gruidae) housed in the same captive environment and maintained on identical diets. 16S rRNA sequencing revealed that crane species harbour distinct gut microbiota. Overall, we detected marginally significant patterns of phylosymbiosis, the strength of which was increased when including the estimates of absolute microbial abundance (rather than relative abundance) derived from microbial densities determined by flow cytometry. Using this approach, we detected the statistically significant signatures of phylosymbiosis only after removing male cranes from our analysis, suggesting that using mixed-sex animal cohorts may prevent the detection of phylosymbiosis. Though weak compared with mammals (and especially insects), these results provide evidence of phylosymbiosis in birds. We discuss the potential differences between birds and mammals, such as transmission routes and host filtering, that may underlie the differences in the strength of phylosymbiosis.

Belowground Competition Can Influence the Evolution of Root Traits.

Although root traits play a critical role in mediating plant-plant interactions and resource acquisition from the soil environment, research examining whether and how belowground competition can influence the evolution of root traits remains largely unexplored. Here we examine the possibility that root traits may evolve as a target of selection from interspecific competition using Ipomoea purpurea and I. hederacea, two closely related morning glory species that commonly co-occur in the United States, as a model system. We show that belowground competitive interactions between the two species can alter the pattern of selection on root traits in each species. Specifically, competition with I. purpurea changes the pattern of selection on root angle in I. hederacea, and competitive interactions with I. hederacea change the pattern of selection on root size in I. purpurea. However, we did not uncover evidence that intraspecific competition altered the pattern of selection on any root traits within I. hederacea. Overall, our results suggest that belowground competition between closely related species can influence the phenotypic evolution of root traits in natural populations. Our findings provide a microevolutionary perspective of how competitive belowground interactions may impact plant fitness, potentially leading to patterns of plant community structure.

Distribution and abundance of elasmobranchs and large teleost fishes in a subtropical seagrass ecosystem: community structure along environmental and spatial gradients

We used fishery-independent gillnet and longline surveys to document the elasmobranch and large teleost assemblages in the Florida Big Bend seagrass system and examine how ichthyofaunal assemblages were related to environmental factors across the region. A total of 159 paired gillnet sets were conducted in June through August from 2009 to 2012. The Big Bend, an expansive system nearly 300 km in length with seagrass from nearshore up to 20 km offshore, is inhabited by at least 13 species of elasmobranch and 56 species of larger teleost fishes during the summer. Five species dominate, including three species of sharks, two carcharhinids (Atlantic sharpnose sharks, Rhizoprionodon terraenovae Richardson, and blacktip sharks, Carcharhinus limbatus Mueller and Henle) and one sphyrnid (bonnethead sharks, Sphyrna tiburo Linnaeus), and two species of ariid catfishes (hardhead catfish, Ariopsis felis Linnaeus, and gafftopsail catfish, Bagre marinus Mitchill). We used a tiered community analysis approach which included hierarchical cluster analysis, indicator species analysis, and non-metric multidimensional scaling with environmental fitting using a Bray-Curtis dissimilarity matrix. Abiotic variables correlated with community structure included salinity, water clarity, and depth. Summer ichthyofaunal assemblages were spatially variable with a distinct southern zone where salinity and water clarity are consistently high relative to the rest of the system, and we hypothesize the observed patterns in community structure are related to a gradient of river influence in the Big Bend.

Alpha and beta diversity patterns of polychaete assemblages across the nodule province of the eastern Clarion-Clipperton Fracture Zone (equatorial Pacific)

Abstract. In the abyssal equatorial Pacific Ocean, most of the seafloor of the Clarion-Clipperton Fracture Zone (CCFZ), a 6 million km2 polymetallic nodule province, has been preempted for future mining. In light of the large environmental footprint that mining would leave and given the diversity and the vulnerability of the abyssal fauna, the International Seabed Authority has implemented a regional management plan that includes the creation of nine Areas of Particular Environmental Interest (APEIs) located at the periphery of the CCFZ. The scientific principles for the design of the APEIs were based on the best – albeit very limited – knowledge of the area. The fauna and habitats in the APEIs are unknown, as are species' ranges and the extent of biodiversity across the CCFZ. As part of the Joint Programming Initiative Healthy and Productive Seas and Oceans (JPI Oceans) pilot action “Ecological aspects of deep-sea mining”, the SO239 cruise provided data to improve species inventories, determine species ranges, identify the drivers of beta diversity patterns and assess the representativeness of an APEI. Four exploration contract areas and an APEI (APEI no. 3) were sampled along a gradient of sea surface primary productivity that spanned a distance of 1440 km in the eastern CCFZ. Between three and eight quantitative box cores (0.25 m2; 0–10 cm) were sampled in each study area, resulting in a large collection of polychaetes that were morphologically and molecularly (cytochrome c oxidase subunit I and 16S genes) analyzed. A total of 275 polychaete morphospecies were identified. Only one morphospecies was shared among all five study areas and 49 % were singletons. The patterns in community structure and composition were mainly attributed to variations in organic carbon fluxes to the seafloor at the regional scale and nodule density at the local scale, thus supporting the main assumptions underlying the design of the APEIs. However, the APEI no. 3, which is located in an oligotrophic province and separated from the CCFZ by the Clarion Fracture Zone, showed the lowest densities, lowest diversity, and a very low and distant independent similarity in community composition compared to the contract areas, thus questioning the representativeness and the appropriateness of APEI no. 3 to meet its purpose of diversity preservation. Among the four exploration contracts, which belong to a mesotrophic province, the distance decay of similarity provided a species turnover of 0.04 species km−1, an average species range of 25 km and an extrapolated richness of up to 240 000 polychaete species in the CCFZ. By contrast, nonparametric estimators of diversity predict a regional richness of up to 498 species. Both estimates are biased by the high frequency of singletons in the dataset, which likely result from under-sampling and merely reflect our level of uncertainty. The assessment of potential risks and scales of biodiversity loss due to nodule mining thus requires an appropriate inventory of species richness in the CCFZ.

Piscine diversity, Community structure and Distribution patterns of the West Ramganga River: A mid-Himalayan tributary of River Ganga

The study documents the fish diversity, assemblage structure, distributional pattern and composition at different sampling sites along the stretches of the West Ramganga river of mid-Himalayas between 138 and 777 meters above sea level. Altogether 92 fish species representing 8 orders, 23 families and 64 genera were recorded. The most dominant family was Cyprinidae with 47 species (51%) followed by Bagridae with 7 fish species (8%). Labeo was the most dominant genera with 9 species, followed by Barilius (6), Garra and Mystus (4 species each). Species richness showed a trend of rapid decline along the altitude with highest records in the lowland sites, where ~93% of the total fish species recorded were between 138 and 320 masl. The Shannon Wiener Index (H’) was found to be maximum at R6 (3.254) followed by R7 (3.24) and R8 (3.074) sites, all constituting the lowland stretch of the river. Species composition showed a distinct assemblage of cold-water specific genera at higher elevation sites based on clustering As per IUCN status, one species each of endangered (Tor putitora) and vulnerable (Schizothorax richardsonii) category was reported from the river, while 6 species reported, fell into near threatened category (Tor tor, Labeo pangusia, Wallago attu, Ompok pabda, Hypophthalmichthys molitrix, Bagarius bagarius and Ailia colia). The high fish species richness in the river Ramganga provides an updated information for the policy makers to plan suitable conservation measures which is currently lacking in most of the threatened freshwater ecosystems especially in the Himalayan river basin.

Host-associated microbiomes are predicted by immune system complexity and climate

BackgroundHost-associated microbiomes, the microorganisms occurring inside and on host surfaces, influence evolutionary, immunological, and ecological processes. Interactions between host and microbiome affect metabolism and contribute to host adaptation to changing environments. Meta-analyses of host-associated bacterial communities have the potential to elucidate global-scale patterns of microbial community structure and function. It is possible that host surface-associated (external) microbiomes respond more strongly to variations in environmental factors, whereas internal microbiomes are more tightly linked to host factors.ResultsHere, we use the dataset from the Earth Microbiome Project and accumulate data from 50 additional studies totaling 654 host species and over 15,000 samples to examine global-scale patterns of bacterial diversity and function. We analyze microbiomes from non-captive hosts sampled from natural habitats and find patterns with bioclimate and geophysical factors, as well as land use, host phylogeny, and trophic level/diet. Specifically, external microbiomes are best explained by variations in mean daily temperature range and precipitation seasonality. In contrast, internal microbiomes are best explained by host factors such as phylogeny/immune complexity and trophic level/diet, plus climate.ConclusionsInternal microbiomes are predominantly associated with top-down effects, while climatic factors are stronger determinants of microbiomes on host external surfaces. Host immunity may act on microbiome diversity through top-down regulation analogous to predators in non-microbial ecosystems. Noting gaps in geographic and host sampling, this combined dataset represents a global baseline available for interrogation by future microbial ecology studies.

The diversity of microbial community and function varied in response to different agricultural residues composting.

Microbial activities are the dynamic core in the soil nutrient cycle. To improve the knowledges about the responses of soil microbial community structure and potential function to long-term cover crops practice. The co-occurrence patterns of soil microbial community structure and functional genes were evaluated using 16SrRNA, ITS and metagenomic technique in 13years cover crops of orchard grass (OG, Dactylis glomerata L.) with high C/N and white clover (WC, Trifolium repens L.) with low C/N. Conventional tillage (CT) was control. The experiment was implemented in an apple orchard located on the Loess Plateau, China, from 2006 to 2018. We also measured soil physicochemical properties and enzyme activities related to carbon and nitrogen cycling. The conclusions showed that the dominant bacterial phyla were Actinobacteria 27.68% in OG treatment and Proteobacteria 25.89% in WC treatment. Organic matter inputs stimulated growth of the phyla of Actinobacteria, Firmicutes, Chloroflexi, Ascomycota and genera of Bacillus, Blastococcus, Streptomyces and Penicillium. Interestingly, the OG and WC treatments promoted the fungal and bacterial alpha-diversity compared to CT treatment, respectively. In addition, compared to CT treatment, OG treatment was beneficial to the increase of C-cycle enzyme activity, while WC treatment tended to increase the N-cycle enzyme activity. Notably, compared to CT treatment, they both enriched carbon fixation and cycle pathways genes, while WC treatment increased the nitrogen metabolism pathway genes. Moreover, OG treatment was more conducive to the enrichment of carbohydrate enzymes genes involved in the hydrolysis of cellulose and hemicellulose compared to WC treatment. Overall, different quality of plant residues stimulated the specific expressions of soil microbial community structure and function. Long-term planted white clover was effective strategy to improve soil quality.

Molecular sequencing and morphological identification reveal similar patterns in native bee communities across public and private grasslands of eastern North Dakota

Bees play a key role in the functioning of human-modified and natural ecosystems by pollinating agricultural crops and wild plant communities. Global pollinator conservation efforts need large-scale and long-term monitoring to detect changes in species’ demographic patterns and shifts in bee community structure. The objective of this project was to test a molecular sequencing pipeline that would utilize a commonly used locus, produce accurate and precise identifications consistent with morphological identifications, and generate data that are both qualitative and quantitative. We applied this amplicon sequencing pipeline to native bee communities sampled across Conservation Reserve Program (CRP) lands and native grasslands in eastern North Dakota. We found the 28S LSU locus to be more capable of discriminating between species than the 18S SSU rRNA locus, and in some cases even resolved instances of cryptic species or morphologically ambiguous species complexes. Overall, we found the amplicon sequencing method to be a qualitatively accurate representation of the sampled bee community richness and species identity, especially when a well-curated database of known 28S LSU sequences is available. Both morphological identification and molecular sequencing revealed similar patterns in native bee community structure across CRP lands and native prairie. Additionally, a genetic algorithm approach to compute taxon-specific correction factors using a small subset of the most concordant samples demonstrated that a high level of quantitative accuracy could be possible if the specimens are fresh and processed soon after collection. Here we provide a first step to a molecular pipeline for identifying insect pollinator communities. This tool should prove useful for future national monitoring efforts as use of molecular tools becomes more affordable and as numbers of 28S LSU sequences for pollinator species increase in publicly-available databases.

Positive interaction facilitates landscape homogenization by shrub expansion in the forest–tundra ecotone

AbstractQuestionsChanges in vegetation structure, including shrub expansion, occur in forest–tundra ecotones in sub‐arctic regions. However, the community‐level processes driving vegetation change are poorly understood. We aimed to evaluate factors mediating the assembly processes for community initiators of vegetation change and determine the ecological processes driving vegetation changes.LocationKuujjuarapik/Whapmagoostui (55.31 N, 77.75 W), Quebec, Canada.MethodsVegetation was surveyed in eight 100‐m line transects with 16 quadrats (1 m × 1 m) per transect established in both forest and tundra habitats. To elucidate the assembly processes of the initiators of vegetation change and other community components of the forest–tundra ecotone, we evaluated β‐diversity among and within habitats and its causal factors (i.e. spatial and environmental factors). Interspecies interactions were estimated based on the patterns of co‐occurrence between all pairs of species.ResultsAlthough environmental and spatial factors significantly affected the community structure of the specific and shared species in the forest habitat, the variation in community structure within and among tundra habitats was not explained by environmental or spatial factors for any community components. Therefore, community assemblages of shared species in tundra habitat were independent from local conditions determined by environment and spatial location. However, we found a positive co‐occurrence pattern among the dominant shared shrubs to be a characteristic of the tundra habitat, and this relationship explained the patterns of community structure within tundra habitats.ConclusionsCommunity assemblages of initiators of vegetation change in tundra habitats are unrestricted by any external factors, such as dispersal limitation or environmental filtering. However, positive relationships in the abundance or occurrence of dominant shrubs may indicate a positive feedback loop between colonizing species and environmental modifications. This positive feedback loop may be a driving process in the expansion of shared species and vegetation change.

Population and Community Structure Pattern of Juniperous polycarpos K. Koch with Climate Change Effect in the Cold Desert Trans Himalayan Region, India

Juniperus polycarpos L. is one of the most threatened and livelihood plant species of the Himalayan region. The present study provides information about monitoring of its populations and proliferation rate in high altitude regions of Trans-Himalaya. The survey revealed comprehensive information on J. polycarpos such as distribution range, habitat characteristics, composition, structural pattern, population size, uses and diversity status. Its distribution and density were maximum in pure forest habitats as compared to mixed habitats recorded. Middle forest altitudinal zone (3100–3500 m for dominant J. polycarpos community and 2710–3100 m for mixed communities) showed suitability for its growth and high density. The occurrence of species above treeline altitudinal zone (4000 m) indicates effect by climate change. A total 281 species (158 genera, 48 families, 37.04% native, 2.06% endemic, 23.87% near-endemic, 74.44% economically important and 20.28% threatened species) were recorded within its populations. Frequent monitoring of populations under climate change scenarios is suggested.

Corrigendum to: Fish in the matrix: effects of landscape on community-structure patterns of the ichthyofauna of streams in Cerrado

This study aims to identify species richness and composition patterns of the ichthyofauna in different landscape matrices (forest, pasture and eucalypt crops) and to evaluate the variation of species composition in different matrices, identifying possible indicator species. We selected 21 streams; 7 were surrounded by native vegetation, 9 surrounded by pasture and 5 by eucalypt crops. We tested whether there was difference in the composition and species richness. In addition, we used the indicator value (IndVal) to verify if there were species faithful and specific to some land use and land cover. Streams located in forest presented the highest estimated species richness, followed by streams in pasturelands and eucalypt matrices. There was no difference between the composition of fishes in different matrices, but we observed a relationship between Phenacorhamdia somnians (Mees, 1974) and pasture matrix. The results indicated that the change in land use may benefit some generalist species such as Phenacorhamdia somnians.

Community structure and concordance patterns among zooplankton life stages in subtropical temporary ponds

In this study, we assessed the community structure (species richness and composition) and examined concordance patterns between the active and dormant life stages of the zooplankton (Rotifera, Cladocera and Copepoda) in Southern Brazilian temporary ponds. We also examined pairwise concordance patterns in the species richness and composition between each taxonomic group. We recorded 77 species in the study area. Active communities had higher species richness and a higher number of exclusive species compared to the dormant community. Low concordance was observed in the species richness and composition of the active and dormant communities. Significant patterns were detected between similar life stages of zooplankton taxonomic groups. We found significant concordance between the species richness of dormant stages of Cladocera and Rotifera, and between the active stages of Cladocera and Copepoda. We also detected significant concordant patterns in the similarity for composition of the active stages of Cladocera and Copepoda, and of Rotifera and Copepoda. The lack of concordance between life stages indicates that the dormant communities are not adequate surrogates of the overall diversity of the zooplankton in Southern Brazilian temporary wetlands, at least under similar experimental incubation conditions. However, there is initial evidence that cladocerans and copepods can be employed as surrogates of other zooplankton groups, if the conclusions are strictly limited to active stages of the community.

Marine Vertebrate Biodiversity and Distribution Within the Central California Current Using Environmental DNA (eDNA) Metabarcoding and Ecosystem Surveys

Environmental DNA (eDNA) metabarcoding is a new approach for assessing marine biodiversity that may overcome challenges of traditional monitoring and complement both existing surveys and biodiversity assessments. There are limited eDNA studies that evaluate vertebrate biodiversity in the marine environment or compare patterns of biodiversity with traditional methods. This study uses eDNA metabarcoding of the mitochondrial 12S rRNA genes present in seawater samples to characterize vertebrate biodiversity and distribution within National Marine Sanctuaries located in the California Current upwelling ecosystem. The epipelagic community in the study region has been monitored using traditional (mid-water trawl and marine mammal) survey methods since 1983. During 2016 and 2017, we concurrently sampled the epipelagic community using traditional survey methods and water for eDNA analysis to assess agreement among the methods. We collected replicate eDNA samples from 25 stations at depths of 10, 40, and 80 m, resulting in 131 small volume (1 L) environmental water samples to examine eDNA sequences. Across the eDNA and traditional survey methods, 80 taxa were identified. Taxa identified by eDNA partially overlapped with taxa through trawl and marine mammal surveys, but more taxa were identified by eDNA. Diversity and distribution patterns of marine vertebrates inferred from eDNA sequences reflected known spatial distribution patterns in species occurrence and community structure (e.g., cross-shelf and alongshore patterns). During both years we identified fishery taxa Sebastes (rockfish), Merluccius (hake), Citharichthys (sanddab), and Engraulis (anchovy) across the majority of the stations using eDNA metabarcoding. The marine vertebrate assemblage identified by eDNA in 2016 was statistically different from the 2017 assemblage and more marine mammals were identified in 2017 than in 2016. Differences in assemblages identified by eDNA were coincident with different oceanographic conditions (e.g., upwelling and stratification). In 2016 weak upwelling and warmer than average conditions were measured, and vertebrate assemblages were not different among ecological regions (Point Reyes, Pescadero, and Monterey Bay). While in 2017, average upwelling conditions returned, vertebrate assemblages differed at each region. This study illustrates that eDNA provides a new baseline for vertebrate assessments that can both augment traditional biomonitoring surveys and aid our understanding of changes in biodiversity.

Social network analysis in humanitarian logistics research

PurposeThe purpose of this paper is to promote social network analysis (SNA) methodology within the humanitarian research community, surveying its current state of the art and demonstrating its utility in analyzing humanitarian operations.Design/methodology/approachA comprehensive survey of the related literature motivates a proposed agenda for interested researchers. Analysis of two humanitarian networks in Afghanistan demonstrates the use and utility of SNA, based on secondary data. In the second case study, the use of random graphs to detect network motifs is demonstrated using Monte Carlo simulation to create the benchmark null sets.FindingsSNA is an adaptable and highly useful methodology in humanitarian research, quantifying patterns of community structure and collaboration among humanitarian organizations. Network motifs suggesting distinct affinity between particular agencies within humanitarian clusters are observed.Research limitations/implicationsThe authors summarize common challenges of using SNA in humanitarian research and discuss ways to alleviate them.Practical implicationsPractitioners can use SNA as readily as researchers, to visualize existing networks, identify areas of concern and better communicate observations.Social implicationsBy making SNA more accessible to a humanitarian research audience, the authors hope its ability to capture complex, dynamic relationships will advance understanding of effective humanitarian relief systems.Originality/valueTo the best of knowledge, it is the first study to conduct a systematic analysis of the application of SNA in empirical humanitarian research and outline a concrete SNA-based research agenda. This is also a currently rare instance of a humanitarian study using random graphs to assess observed SNA measures.

Metrics and Models for Quantifying Ecological Resilience at Landscape Scales

An explicit link between the abiotic environment, the biotic components of ecosystems, and resilience to disturbance across multiple scales is needed to operationalize the concept of ecological resilience. To accomplish this, managers must be able to measure the ecological resilience of current conditions and project resilience under future scenarios of landscape change. The goal of this paper is to present metrics and describe a process for using geospatial data, landscape pattern analysis and landscape dynamic simulation modeling to evaluate ecosystem resilience at management scales. The dynamic equilibria of species abundances, community structure, and landscape patterns that are produced under a given combination of abiotic conditions, such as topography, soils, and climate, can form a foundation to define desired conditions and measure resistance and resilience. The degree of forcing required to push the system from this dynamic range is a measure of resistance, and the rate of return to the dynamic range after the perturbation is a measure of the resilience and recovery of the system. Several tools from the field of landscape ecology are useful in defining the dynamic range of an ecosystem under natural regulation and to measure the forcing required to drive departure and the rate of recovery. Simulation models provide means to quantify the expected range of species abundance, community structure, and landscape patterns under a variety of scenarios, including the natural disturbance regime, current disturbance regime, and possible future regimes under alternative management and climate scenarios. Landscape pattern analysis and multivariate trajectory analysis provide a means to quantify conditions and change vectors relative to this desired range. Together this combination of tools provides a means to define the conditions of a desired state for an ecosystem, to quantify the degree of resistance and resilience of the system to perturbation, and to measure and monitor the departure from the range of natural variability in the system dynamics.

Mapping the community structure of the rat cerebral cortex with weighted stochastic block modeling.

The anatomical architecture of the mammalian brain can be modeled as the connectivity between functionally distinct areas of cortex and sub-cortex, which we refer to as the connectome. The community structure of the connectome describes how the network can be parsed into meaningful groups of nodes. This process, called community detection, is commonly carried out to find internally densely connected communities-a modular topology. However, other community structure patterns are possible. Here we employ the weighted stochastic block model (WSBM), which can identify a wide range of topologies, to the rat cerebral cortex connectome, to probe the network for evidence of modular, core, periphery, and disassortative organization. Despite its algorithmic flexibility, the WSBM identifies substantial modular and assortative topology throughout the rat cerebral cortex connectome, significantly aligning to the modular approach in some parts of the network. Significant deviations from modular partitions include the identification of communities that are highly enriched in core (rich club) areas. A comparison of the WSBM and modular models demonstrates that the former, when applied as a generative model, more closely captures several nodal network attributes. An analysis of variation across an ensemble of partitions revealsthat certain parts of the network participate in multiple topological regimes. Overall, our findings demonstrate the potential benefits of adopting the WSBM, which can be applied to a single weighted and directed matrix such as the rat cerebral cortex connectome, to identify community structure witha broad definition that transcends the common modularapproach.

Temporal and spatial patterns of macrozoobenthos community structure in the yellow river estuary: under the pressure of water and sediment regulation and natural environmental variables seasonal variation

The community structure of aquatic organisms is quite different in different rivers. The corresponding community structure will be formed in various ecological processes of different spatial scales. The existence of species is the result of the comprehensive influence of local environmental characteristics and geographical factors. Therefore, we can effectively predict the functions of various biological indicators according to environmental changes. Firstly, this paper analyses the methods of detecting the community structure of Macrobenthos in the Yellow River estuary. Then, the temporal and spatial patterns of water and sediment regulation and seasonal variation are analyzed.

An overview of meiofaunal and nematode distribution patterns in lake ecosystems differing in their trophic state

In the benthos of lakes, habitat size and structure as well as oxygen or resource availability can affect species distribution at local scales. By contrast, there is little knowledge about the mechanisms that determine the structure of benthic communities at larger scales. Here, we compiled data from the literature (23 studies monitoring 129 sites from 75 lakes located in central and northern Europe) to search for broad patterns in abundance, biomass, and community structure linked to lake trophic state (oligo-, meso-, or eutrophic), habitat features (hard vs. soft substrates), and water depth (littoral vs. profundal). The benthic meiofauna appeared much more abundant in the periphyton, and biomass was lower in oligotrophic lakes. Focusing on free-living nematodes, community structure differed markedly in hard vs soft substrates. Further, nematodes were especially dominant in profundal zones, where their diversity was significantly influenced by lake trophic state. In profundal zones of eutrophic lakes, nematode assemblages were less diverse and dominated by larger, mostly omnivorous or predacious taxa.

Biotic interactions are the dominant drivers of phylogenetic and functional structure in bird communities along a tropical elevational gradient

AbstractUnderstanding how biotic and abiotic interactions influence community assembly and composition is a fundamental goal in community ecology. Addressing this issue is particularly tractable along elevational gradients in tropical mountains that feature substantial abiotic gradients and rates of species turnover. We examined elevational patterns of avian community structure on 2 mountains in Malaysian Borneo to assess changes in the relative strength of biotic interactions and abiotic constraints. In particular, we used metrics based on (1) phylogenetic relatedness and (2) functional traits associated with both resource acquisition and tolerance of abiotic challenges to identify patterns and causes of elevational differences in community structure. High elevation communities were composed of more phylogenetically and functionally similar species than would be expected by chance. Resource acquisition traits, in particular, were clustered at high elevations, suggesting low resource and habitat diversity were important drivers of those communities. Traits typically associated with tolerance of cold temperatures and low atmospheric pressure showed no elevational patterns. All traits were neutral or overdispersed at low elevations suggesting an absence of strong abiotic filters or an increased influence of interspecific competition. However, relative bill size, which is important for thermoregulation, was larger in low elevation communities, suggesting abiotic factors were also influential there. Regardless of metric, clustered and neutral communities were more frequent than overdispersed communities overall, implying that interspecific competition among close relatives may not be a pervasive driver of elevational distribution and community structure of tropical birds. Overall, our analyses reveal that a diverse set of predominantly biotic factors underlie elevational variation in community structure on tropical mountains.

Linking spatial patterns of terrestrial herbivore community structure to trophic interactions.

Large herbivores influence ecosystem functioning via their effects on vegetation at different spatial scales. It is often overlooked that the spatial distribution of large herbivores results from their responses to interacting top-down and bottom-up ecological gradients that create landscape-scale variation in the structure of the entire community. We studied the complexity of these cascading interactions using high-resolution camera trapping and remote sensing data in the best-preserved European lowland forest, Białowieża Forest, Poland. We showed that the variation in spatial distribution of an entire community of large herbivores is explained by species-specific responses to both environmental bottom-up and biotic top-down factors in combination with human-induced (cascading) effects. We decomposed the spatial variation in herbivore community structure and identified functionally distinct landscape-scale herbivory regimes ('herbiscapes'), which are predicted to occur in a variety of ecosystems and could be an important mechanism creating spatial variation in herbivory maintaining vegetation heterogeneity.