Distance Decay Of Similarity Research Articles

Distinct fungal communities associated with different organs of the mangrove Sonneratia alba in the Malay Peninsula

Mangrove forests are key tropical marine ecosystems that are rich in fungi, but our understanding of fungal communities associated with mangrove trees and their various organs remains limited because much of the diversity lies within the microbiome. In this study, we investigated the fungal communities associated with the mangrove tree Sonneratia alba throughout Peninsular Malaysia and Singapore. At each sampling location, we collected leaves, fruits, pneumatophores and sediment samples and performed amplicon sequencing of the ribosomal internal transcribed spacer 1 to characterise the associated communities. Results show distinct fungal communities at each sampled location with further differentiation according to the plant part. We find a significant distance decay of similarity, particularly for sediment samples due to the greater variability of sediment environments relative to the more stable fungal habitats provided by living plant organs. We are able to assign taxonomy to the majority of sequences from leaves and fruits, but a much larger portion of the sequences recovered from pneumatophores and sediment samples could not be identified. This pattern underscores the limited mycological research performed in marine environments and demonstrates the need for a concerted research effort on multiple species to fully characterise the coastal microbiome and its role in the functioning of marine ecosystems.

Structure and Functional Diversity of Surface Bacterioplankton Communities in an Overwintering Habitat for Large Yellow Croaker, Pseudosciaena crocea, of the Southern East China Sea

Given the biogeochemical functions of marine microbes, the structure and functional diversity of bacterioplankton communities could be regarded as bioindicators that reflect environmental quality. The habitat of the large yellow croaker (Pseudosciaena crocea) is suffering from widespread degradation, but the study of croaker habitat is still insufficient. Here, we used 16S rRNA gene sequencing and functional prediction to investigate the surface bacterioplankton communities in an overwintering ground of P. crocea during the overwintering period (November 2018 to April 2019). Our results showed that the taxa and functions of the environmental bacterioplankton community exhibited obvious seasonality. Specifically, the bacterioplankton communities in autumn were characterized by animal parasites or symbionts, such as Acinetobacter baumannii and Moraxella, while organic substance-degrading bacteria, such as Rhodococcus, Stenotrophomonas and Alcanivorax, dominated in spring. Moreover, phylogenetic-based mean nearest taxon distance (MNTD) analyses indicated that dispersal limitation was the most important process governing the spatiotemporal assembly of the bacterioplankton communities. The distance decay of similarity also suggested the impact of dispersal limitation on the generation of biogeographical patterns. Furthermore, variation partitioning analysis and a partial Mantel test revealed that environmental filters, such as nutrients, temperature and salinity, had relatively weak deterministic effects on the bacterioplankton community assembly. Overall, these findings provide a basis for understanding the theory of surface microbial community assembly in the overwintering habitat of the large yellow croaker.

Forest management, canopy cover and geographical distance affect saproxylic beetle communities of small-diameter beech deadwood

Beetles (Coleoptera) are the most diverse and species-rich insect order in saproxylic communities, and play a key role in forest dynamics. To prioritize conservation measures, a clear understanding is needed of what habitat features are the most important for beetles that depend on deadwood. Here, we investigate (i) how the assemblages of saproxylic beetles emerging from small-diameter beech deadwood (Fagus sylvatica L.) are influenced by several environmental factors and type of forest management, and (ii) if geographical distance of the investigated sites influences the similarity of these saproxylic beetle assemblages. We visited 10 high beech forest stands along a latitudinal gradient from northern to southern Italy, and collected 200 logs of 50 cm length, 12 ± 2 cm diameter, and Hunter’s decay class 2, from deadwood lying on the forest floor. Logs were stored in ex-situ emergence traps, in common garden conditions, from April to September, and individuals emerging from the deadwood were collected weekly. A total of 2571 beetles were collected, including several species which were either threatened, firstly recorded or endemic. We found that, compared to even-aged stands, forests managed to increase structural heterogeneity (uneven-aged high forests, and former coppice stands converted to high forest), with closed canopy, were colonized by the richest and most abundant saproxylic beetle assemblages. Additionally, we observed distance decay of similarity between sites, indicating geographical structure in community composition. Our findings have important implications for biodiversity conservation in beech forests: (1) small-diameter deadwood hosts a rich biodiversity of Coleoptera and should therefore be left on the ground; (2) forest management practices should aim at preserving or restoring structural heterogeneity and closed canopies; (3) these conservation measures should be carried out along the entire area of occurrence of beech forests, due to turnover in species composition with geographical distance.

Similar composition of functional roles in Andean seed-dispersal networks, despite high species and interaction turnover.

The species composition of local communities varies in space, and its similarity generally decreases with increasing geographic distance between communities, a phenomenon known as distance decay of similarity. It is, however, not known how changes in local species composition affect ecological processes, that is, whether they lead to differences in the local composition of species' functional roles. We studied eight seed-dispersal networks along the South American Andes and compared them with regard to their species composition and their composition of functional roles. We tested (1) if changes in bird species composition lead to changes in the composition of bird functional roles, and (2) if the similarity in species composition and functional-role composition decreased with increasing geographic distance between the networks. We also used cluster analysis to (3) identify bird species with similar roles across all networks based on the similarity in the plants they consume, (i) considering only the species identity of the plants and (ii) considering the functional traits of the plants. Despite strong changes in species composition, the networks along the Andes showed similar composition of functional roles. (1) Changes in species composition generally did not lead to changes in the composition of functional roles. (2) Similarity in species composition, but not functional-role composition, decreased with increasing geographic distance between the networks. (3) The cluster analysis considering the functional traits of plants identified bird species with similar functional roles across all networks. The similarity in functional roles despite the high species turnover suggests that the ecological process ofseed dispersalis organized similarly along the Andes, with similar functional roles fulfilled locally by different sets of species. The high species turnover, relative to functional turnover, also indicates that a large number of bird species are needed to maintain the seed-dispersal process along the Andes.

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.

High diatom species turnover in a Baltic Sea rock pool metacommunity

Different metacommunity perspectives have been developed to describe the relationship between environmental and spatial factors and their relative roles for local communities. However, only little is known about temporal variation in metacommunities and their underlying drivers. We examined temporal variation in the relative roles of environmental and spatial factors for diatom community composition among brackish-watered rock pools on the Baltic Sea coast over a 3-month period. We used a combination of direct ordination, variation partition, and Mantel tests to investigate the metacommunity patterns. The studied communities housed a mixture of freshwater, brackish, and marine species, with a decreasing share of salinity tolerant species along both temporal and spatial gradients. The community composition was explained by both environmental and spatial variables (especially conductivity and distance from the sea) in each month; the joint effect of these factors was consistently larger than the pure effects of either variable group. Community similarity was related to both environmental and spatial distance between the pools even when the other variable group was controlled for. The relative influence of environmental factors increased with time, accounting for the largest share of the variation in species composition and distance decay of similarity in July. Metacommunity organization in the studied rock pools was probably largely explained by a combination of species sorting and mass effect given the small spatial study scale. The found strong distance decay of community similarity indicates spatially highly heterogeneous diatom communities mainly driven by temporally varying conductivity gradient at the marine-freshwater transition zone.

Seagrass-associated fungal communities show distance decay of similarity that has implications for seagrass management and restoration.

Marine fungal biodiversity remains vastly understudied, and even less is known of their biogeography and the processes responsible for driving these distributions in marine environments. We investigated the fungal communities associated with the seagrass Enhalus acoroides collected from Singapore and Peninsular Malaysia to test the hypothesis that fungal communities are homogeneous throughout the study area. Seagrass samples were separated into different structures (leaves, roots, and rhizomes), and a sediment sample was collected next to each plant. Amplicon sequencing of the fungal internal transcribed spacer 1 and subsequent analysis revealed significant differences in fungal communities collected from different locations and different structures. We show a significant pattern of distance decay, with samples collected close to each other having more similar fungal communities in comparison with those that are more distant, indicating dispersal limitations and/or differences in habitat type are contributing to the observed biogeographic patterns. These results add to our understanding of the seagrass ecosystem in an understudied region of the world that is also the global epicenter of seagrass diversity. This work has implications for seagrass management and conservation initiatives, and we recommend that fungal community composition be a consideration for any seagrass transplant or restoration programme.

How to predict biodiversity in space? An evaluation of modelling approaches in marine ecosystems

AbstractAimBiodiversity prediction becomes increasingly important in the face of global diversity loss, whereas substantial challenges still exist in both conceptual and technical aspects. There exist many predictive models, and an integrative evaluation can help understand their performance in handling the multifacets of biodiversity. This study aims to evaluate the performance of these modelling approaches to predict both α‐ and β‐diversity in diverse ecological contexts.LocationNorth Yellow Sea, China.MethodsThe biodiversity models follow three strategies, “assemble first, predict later”, “predict first, assemble later” and “assemble and predict together”. Hill diversity profile, Fisher's log‐series parameter and the distance decay of similarity are used to measure α‐ and β‐diversity. The evaluation study is conducted based on seasonal bottom trawl surveys from October 2016 to August 2017 in North Yellow Sea, China, allocated to coastal and offshore areas. We evaluate the predictive power of the models using cross‐validation.ResultsFollowing the “assemble first, predict later” approach, macroecological model (MEM) provided the most accurate prediction overall, whereas stacked species distribution model (SSDM) and joint species distribution model (JSDM), following the second and third modelling approaches, tended to overestimate α‐diversity and underestimate β‐diversity. The performances of SSDM and JSDM could be improved by moderately down‐weighting rare species. The relative performances of the three modelling approaches were consistent among seasons and spatial regions.Main conclusionsThe superior performances of MEM in a range of temporal and spatial contexts favour the “assemble first, predict later” approach and imply a tight community assembly in the studied area. The overall predictive powers of varying models suggest that the spatial pattern of marine biodiversity could be fairly well predicted with commonly accessible hydrologic data in a mesoscales. The approach of multi‐model evaluations is applicable to a variety of ecosystems for biodiversity prediction.

Variations in Total Species Richness and the Unevenness of Species Abundance Distribution between Two Distant Conus Communities (Neogastropoda): A Case Study in Mannar Gulf (India)

The genus Conus forms a conspicuous and rather homogeneous group within marine Gastropods. This makes it all the more interesting to focus on the sub-communities formed by Conus species and to analyze the potential specificities in the internal organization of species in these communities, in particular species richness, species abundance distribution and the effect of geographical distance between communities on differences in their respective species composition. Accordingly, two Conus communities along the coast in Mannar Gulf (India), separated by 80 km, are considered. Reliable analysis requires, first, to treat exhaustive data from complete samplings or, else – as here – to implement an appropriate extrapolation procedure to complete numerically the partial samplings. After numerical completion, substantial differences were highlighted between the two communities, not only in terms of true (total) species richness but, even more, as regards the profile and the average unevenness of the distributions of species abundance. Also, significant dissimilarity in species composition was found between the two communities, that may be tentatively attributed to either deterministic distance decay in similarity of species composition or, alternatively, to the persistence in the stochastic process of species recruitment from the regional stock of Conus planktonic larvae. This preliminary study yet requests to be complemented by other similar case studies, before drawing any safer interpretative conclusions.

Understanding dispersal limitation through the assessment of diversity patterns across phylogenetic scales below the species level

AbstractAimWe show how macroecological patterns at different phylogenetic scales below the species level may aid the identification of the predominant process controlling biological assemblages (niche versus dispersal). We compare two taxa with different ecological and dispersal requirements (terrestrial molluscs and leaf beetles) in the same geographical setting.LocationIberian Peninsula.Time period2010–2015.Major taxaTerrestrial molluscs and leaf beetles.MethodsThecox1‐5′ fragment was sequenced for 1,592 mollusc specimens in 20 localities. Leaf beetle assemblages had been sequenced previously in 15 of these localities. Species richness, distance decay of similarity, endemism and range size were measured at two levels: molecular variants (i.e., haplotypes) and putative species (i.e., operational taxonomic units). Using a multi‐hierarchical macroecology approach, distance‐decay patterns were measured at multiple intermediate genealogical levels (nested clades) to assess whether the geometry of the ranges of lineages followed a fractal pattern.ResultsRichness and distance‐decay patterns at both molecular variant and species levels were different in leaf beetles and terrestrial molluscs, although both taxa showed a fractal pattern in the distance decay of similarity across genealogical levels. The self‐similarity of the distance‐decay pattern across phylogenetic scales suggests a predominance of neutral, but limited, dispersal driving macroecological patterns in both taxa. Endemism was similar in both taxa at the level of molecular variants but higher at the species level in terrestrial molluscs, and range size was smaller at both levels in terrestrial molluscs. Taken altogether, our results suggest that dispersal limitation is stronger in terrestrial molluscs.Main conclusionThe assessment of how diversity patterns change at different phylogenetic scales below the species level allowed us to identify unifying characteristics in otherwise seemingly heterogeneous biological systems. Congruence was observed in diversity patterns of leaf beetles and terrestrial molluscs, suggesting that dispersal is a relevant process in both taxa but acts at a different strength.

Island Biogeography of Cryoconite Hole Bacteria in Antarctica's Taylor Valley and Around the World

Cryoconite holes are holes in a glacier’s surface caused by sediment melting into the glacier. These holes are self-contained ecosystems that include abundant bacterial life within their sediment and liquid water, and have recently gained the attention of microbial ecologists looking to use cryoconite holes as “natural microcosms” to study microbial community assembly. Here, we explore the idea that cryoconite holes can be viewed as “islands”, in the same sense that an island in the ocean is an area of habitat surrounded by a barrier to entry. In the case of a classic oceanic island, the ocean is a barrier between islands, but in the case of cryoconite holes, the ocean is comprised of impermeable solid ice. We test two hypotheses, born out of island biogeographic theory, that can be readily applied to cryoconite hole bacteria. First, we ask to what extent the size of a cryoconite hole is related to the amount of bacterial diversity found within it. Second, we ask to what extent cryoconite holes exhibit distance decay of similarity, meaning that geographically close holes are expected to harbor similar bacterial communities, and distant holes are expected to harbor more different bacterial communities. To test the island size hypothesis, we measured the sizes of cryoconite holes on three glaciers in Antarctica’s Taylor Valley and used DNA sequencing to measure diversity of bacterial communities within them. We found that for two of these glaciers, there is a strong relationship between hole size and bacterial phylogenetic diversity, supporting the idea that cryoconite holes on those glaciers are “islands.” The high biomass dispersing to the third glacier we measured could explain the lack of size-diversity relationship, remaining consistent with island biogeography. To test the distance decay of similarity hypothesis, we used DNA sequence data from several previous studies of cryoconite hole bacteria from across the world. Combined with our Taylor Valley data, those data showed that cryoconite holes have strong spatial structuring at scales of one to several hundred kilometers, also supporting the idea that these dirty holes on glaciers are really islands in the cryosphere.

Biogeography of parasite abundance: latitudinal gradient and distance decay of similarity in the abundance of fleas and mites, parasitic on small mammals in the Palearctic, at three spatial scales

We tested whether biogeographic patterns characteristic for biological communities can also apply to populations and investigated geographic patterns of variation in abundance of ectoparasites (fleas and mites) collected from bodies of their small mammalian hosts (rodents and shrews) in the Palearctic at continental, regional and local scales. We asked whether (i) there is a relationship between latitude and abundance and (ii) similarity in abundance follows a distance decay pattern or it is better explained by variation in extrinsic biotic and abiotic factors. We analysed the effect of latitude on mean intraspecific abundance using general linear models including proportional abundance of its principal host as an additional predictor variable. Then, we examined the relative effect of geographic distance, biotic and abiotic dissimilarities among regions, subregions or localities on the intraspecific dissimilarity in abundance among regions, subregions or localities using Generalized Dissimilarity Modelling. We found no relationship between latitude and intraspecific flea or mite abundance. In both taxa, environmental dissimilarity explained the largest part of the deviance of spatial variation in abundance, whereas the effect of the dissimilarity in the principal host abundance was of secondary importance and the effect of geographic distance was minor. These patterns were generally consistent across the three spatial scales, although environmental variation and dissimilarity in principal host abundance were equally important at the local scale in fleas but not in mites. We conclude that biogeographic patterns related to latitude and geographic distance do not apply to spatial variation of ectoparasite abundance. Instead, the geographic distribution of abundance in arthropod ectoparasites depends on their responses, mainly to the off-host environment and to a lesser extent the abundance of their principal hosts.

Variation among European beetle taxa in patterns of distance decay of similarity suggests a major role of dispersal processes

The decay of assemblage similarity with spatial distance can be explained by alternative mechanisms: dispersal limitation and species sorting. To understand their relative contributions, we compare the decay in faunal similarity with spatial distance and, independently, with climatic distance, of 21 beetle taxa with varying dispersal abilities and ecological niches, in southern and northern Europe. Similarity in beetle faunas was associated to spatial but not to climatic distances, pointing to the preponderance of dispersal processes rather than niche constraints. In most taxa, southern faunas were more dissimilar than northern ones: smaller initial similarity and steeper distance decay rate. Distance decay patterns in the north were relatively flat and very similar across taxa, suggesting that only good dispersers would have reached those latitudes after the glacial retreat. The difference in distance decay patterns between north and south is correlated with the taxon's slope of the distance decay pattern in the south and with its latitudinal richness difference. That is, in taxa with distance decay patterns similarly flat in the south and the north, the latitudinal richness gradient is weak. This correlation points again to differences in dispersal ability as a major determinant of biogeographic patterns in European beetles. Both dispersal and niche‐related characteristics explained north‐south slope differences, but dispersal attributes turned out to be more relevant when initial similarity and distance decay strength were considered together. Our results show that, to understand diversity patterns in Europe, closely related biological groups cannot be assumed to be surrogates and regions with different historical biogeography should be analysed separately. Paradoxically, the study of beetle faunas of southern Europe will shed light on the processes controlling the recolonization of northern latitudes.

The distance decay of similarity in tropical rainforests. A spatial point processes analytical formulation

In this paper we are concerned with the analytical description of the change in floristic composition (species turnover) with the distance between two plots of a tropical rainforest due to the clustering of the individuals of the different species. We describe the plant arrangement by a superposition of spatial point processes and in this framework we introduce an analytical function which represents the average spatial density of the Sørensen similarity between two infinitesimal plots at distance r. We see that the decay in similarity with the distance is essentially described by the pair correlation function of the superposed process and that it is governed by the most abundant species. We test our analytical model with empirical data obtained for the Barro Colorado Island and Pasoh rainforests. To this end we adopt the statistical estimator for the pair correlation function in Shimatani (2001) and we design a novel one for the Sørensen similarity. Furthermore, we test our analytical formula by modeling the forest study area with Neyman–Scott point processes. We conclude comparing the advantages of our approach with other ones existing in literature.

Seasonal and annual variation in fungal communities associated with epigeic springtails (Collembola spp.) in boreal forests

Soil fauna mediate nutrient cycling through engineering physical properties and altering microbial communities in soil. Collembola is one of the most abundant groups of soil fauna, which regulates microbial communities by consumption and dispersal. The spatial structure of associations between Collembola and soil microbes have been described in several studies, but temporal variation of these associations remains unclear. Using high-throughput sequencing, we studied the fungal communities on Collembola (Entomobrya nivalis, Orchesella flavescens, Pogonognathellus longicornis) body surface, gut and their immediate habitat (topsoil samples) in four seasons across three years. The soil samples were characterized by fairly uniform relative abundance of saprotrophic and mycorrhizal fungi, whereas collembolans were associated mostly with saprotrophs. The structure of fungal communities from all substrate types exhibited comparable patterns of temporal distance decay of similarity. Unlike in soil, fungal richness and composition in Collembola body and gut samples exhibited seasonal and annual variation, with a significant interaction term, indicating low predictability. These results reflect spatial and temporal plasticity of the fungal communities associated with epigeic Collembola, indicating the high adaptability of collembolans to available conditions. We found that the Collembola associations with fungi (including diet) did not vary among the studied epigeic Collembola species. The detected high diversity of fungi associated with Collembola suggests that dispersal by arthropod vectors may represent a powerful alternative to aerial dispersal of fungal propagules.

Which Latitudinal Gradients for Genetic Diversity?

A recent global analysis of GenBank DNA sequences from amphibians and mammals indicated consistent poleward decrease of intraspecific genetic diversity in both classes. We highlight that this result was biased by not accounting for distance decay of similarity and reanalyse the datasets, revealing distinct latitudinal gradients in mammals and amphibians.

Intra- and interspecific similarity in species composition of helminth communities in two closely-related rodents from South Africa

To reveal factors responsible for spatial variation in parasite community composition we studied patterns of similarity in helminth species composition in two closely-related rodents (Rhabdomys pumilio and Rhabdomys dilectus) that differ in their social and spatial behaviour and live under different environmental conditions across 20 localities in South Africa. We asked whether the two hosts harbour similar assemblages, whether these are more dissimilar between than within hosts and if host social structure, behaviour or environment affects similarity patterns in helminth infracommunities within and among localities. We also investigated whether similarity in species composition of helminth component communities decreases with an increase of geographic distance between host populations. We found that the pattern of space use by the hosts rather than their social behaviour promotes differences in helminth species composition between host species as well as among host populations from different localities. The rate of distance decay of similarity in species composition of helminth component communities differed between the two hosts due to difference in the degree of environmental variation across their geographic ranges. We conclude that patterns of spatial variation in helminth species composition are driven mainly by host spatial behaviour and, to a lesser extent, by environment-associated factors.

Determinants of cyanobacterial species composition in the splash zone of two Croatian islands

ABSTRACT Cyanobacterial communities of the splash zone of two Croatian islands, Veruda and Ugljan, were surveyed. At each island, we studied eight localities with different aspects. From all 336 samples, a total of 42 cyanobacterial species, one green alga, and one red alga were found. In both islands Hyella spp. and Gloeocapsopsis crepidinum dominated and Entophysalis deusta, Solentia spp., Kyrtuthrix dalmatica and Mastigocoleus testarum were found frequently. Multivariate statistical analysis of species composition shows that the vertical gradient is the strongest determinant of species composition and that there are statistically significant but not very pronounced differences in species composition between the two islands. Species composition among individual sites within islands differed slightly, and between localities decreased rather slowly with the distance of individual samples (i.e. the similarity distance decay was very slow), showing that even close samples can have quite different species composition. The species accumulation curves do not reach their asymptote, indicating that many samples are needed to reasonably cover the species richness of a site. This study highlights the importance of in-depth species counts and high density sampling along vertical gradients for satisfactory cyanobacterial community assessments in marine coastal splash zones.

Local and Regional Diversity Reveals Dispersal Limitation and Drift as Drivers for Groundwater Bacterial Communities from a Fractured Granite Formation.

Microorganisms found in terrestrial subsurface environments make up a large proportion of the Earth’s biomass. Biogeochemical cycles catalyzed by subsurface microbes have the potential to influence the speciation and transport of radionuclides managed in geological repositories. To gain insight on factors that constrain microbial processes within a formation with restricted groundwater flow we performed a meta-community analysis on groundwater collected from multiple discrete fractures underlying the Chalk River Laboratories site (located in Ontario, Canada). Bacterial taxa were numerically dominant in the groundwater. Although these were mainly uncultured, the closest cultivated representatives were from the phenotypically diverse Betaproteobacteria, Deltaproteobacteria, Bacteroidetes, Actinobacteria, Nitrospirae, and Firmicutes. Hundreds of taxa were identified but only a few were found in abundance (>1%) across all assemblages. The remainder of the taxa were low abundance. Within an ecological framework of selection, dispersal and drift, the local and regional diversity revealed fewer taxa within each assemblage relative to the meta-community, but the taxa that were present were more related than predicted by chance. The combination of dispersion at one phylogenetic depth and clustering at another phylogenetic depth suggest both niche (dispersion) and filtering (clustering) as drivers of local assembly. Distance decay of similarity reveals apparent biogeography of 1.5 km. Beta diversity revealed greater influence of selection at shallow sampling locations while the influences of dispersal limitation and randomness were greater at deeper sampling locations. Although selection has shaped each assemblage, the spatial scale of groundwater sampling favored detection of neutral processes over selective processes. Dispersal limitation between assemblages combined with local selection means the meta-community is subject to drift, and therefore, likely reflects the differential historical events that have influenced the current bacterial composition. Categorizing the study site into smaller regions of interest of more closely spaced fractures, or of potentially hydraulically connected fractures, might improve the resolution of an analysis to reveal environmental influences that have shaped these bacterial communities.

Dissecting global turnover in vascular plants

AbstractAimTo provide a global assessment of turnover in vascular plants across geographical settings and taxonomic and functional groups. We tested whether turnover and its spatial and environmental drivers are affected by the geographical setting and whether taxonomic and functional groups exhibit specific turnover patterns that are associated with their ecological characteristics.LocationGlobal.MethodsWe collated a global dataset of vascular plant checklists comprising 258 island and 346 mainland units. We created subsets based on the geographical setting of study units (mainland, islands, different island types) as well as taxonomic and functional properties of species (angiosperms, gymnosperms, pteridophytes, trees, shrubs, herbs). For the entire dataset, and each subset, the distance decay of similarity was assessed using generalized linear models. To disentangle the relative importance of spatial and environmental drivers of turnover, we employed generalized dissimilarity models. Finally, the model results were used to predict compositional similarity of vascular plants across a global grid.ResultsThe distance decay of similarity was stronger for mainland units than for islands. Among taxonomic and functional groups, the rate of decay was lowest for pteridophytes and highest for shrubs. Partitioning of turnover into distance‐ and environment‐related effects revealed fundamental differences between mainland and island systems, with geographical distance being more important on the mainland than on islands. This trend was consistent across taxonomic and functional groups.Main conclusionsOur results reveal an important role of geographical context in shaping beta‐diversity patterns. We argue that geographical settings are characterized by specific configurations of ecological filters that have a strong impact on the magnitude and structure of turnover. Moreover, taxonomic and functional groups are differentially successful in passing these filters, resulting in group‐ and setting‐specific turnover patterns. Exploring these interdependences for different taxa and geographical settings at different scales will help to improve our understanding of beta diversity.