Distance Decay Of Similarity In Communities Research Articles

Ectomycorrhizal fungi are influenced by ecoregion boundaries across Europe

AbstractAimEcoregions and the distance decay in community similarity are fundamental concepts in biogeography and conservation biology that are well supported across plants and animals, but not fungi. Here we test the relevance of these concepts for ectomycorrhizal (ECM) fungi in temperate and boreal regions.LocationEurope.Time Period2008–2015.Major Taxa StudiedEctomycorrhizal fungi.MethodsWe used a large dataset of ~24,000 ectomycorrhizas, assigned to 1350 operational taxonomic units, collected from 129 forest plots via a standardized protocol. We investigated the relevance of ecoregion delimitations for ECM fungi through complementary methodological approaches based on distance decay models, multivariate analyses and indicator species analyses. We then evaluated the effects of host tree and climate on the observed biogeographical distributions.ResultsEcoregions predict large‐scale ECM fungal biodiversity patterns. This is partly explained by climate differences between ecoregions but independent from host tree distribution. Basidiomycetes in the orders Russulales and Atheliales and producing epigeous fruiting bodies, with potentially short‐distance dispersal, show the best agreement with ecoregion boundaries. Host tree distribution and fungal abundance (as opposed to presence/absence only) are important to uncover biogeographical patterns in mycorrhizas.Main ConclusionsEcoregions are useful units to investigate eco‐evolutionary processes in mycorrhizal fungal communities and for conservation decision‐making that includes fungi.

Elevational microbial β diversity and community assembly processes in subarctic ponds

Abstract Knowledge about elevational β diversity patterns and processes is limited for microorganisms, especially in sensitive aquatic ecosystems at high latitudes. Our aim is to investigate elevational β diversity patterns and underlying assembly processes for three biofilm microbial groups in subarctic freshwater ponds. We sampled 89 ponds covering an elevational gradient from 10 to 1038 m above sea level in subarctic Finland and Norway. The microbial groups studied included benthic diatoms, cyanobacteria, and bacteria (i.e., bacteria other than cyanobacteria). We expected to find elevational distance decay in community similarity, driven primarily by variation in the local environment. We further tested whether the level of β diversity decreased towards higher elevations, and whether the relative influence of deterministic and stochastic processes on community assembly changed along the elevational gradient, with increasing effect of deterministic processes at higher elevations under more extreme environmental conditions. As statistical methods, we used generalised dissimilarity modelling, Mantel tests, and a null model with Raup–Crick dissimilarities. For all microbial groups, community dissimilarities increased with increasing environmental or elevational distances. The pure effects of environment were significant for all groups, and pH was the most important variable affecting community dissimilarities. Mean community dissimilarities generally decreased with elevation for all microbial groups. The communities were influenced by both deterministic and stochastic processes, the former of which was stronger towards higher elevations. The influence of deterministic processes was strongest for bacteria. Generally, the communities under deterministic control were more similar to each other than expected by chance. Elevational β diversity patterns of subarctic pond microorganisms primarily reflected environmental effects, showing decreasing β diversity towards high elevations owing to stronger environmental filtering. The relative effects of deterministic or stochastic assembly processes varied among microbial groups, highlighting the need for including multiple groups when studying biodiversity patterns and underlying ecological processes.

Analysing the distance decay of community similarity in river networks using Bayesian methods

The distance decay of community similarity (DDCS) is a pattern that is widely observed in terrestrial and aquatic environments. Niche-based theories argue that species are sorted in space according to their ability to adapt to new environmental conditions. The ecological neutral theory argues that community similarity decays due to ecological drift. The continuum hypothesis provides an intermediate perspective between niche-based theories and the neutral theory, arguing that niche and neutral factors are at the opposite ends of a continuum that ranges from competitive to stochastic exclusion. We assessed the association between niche-based and neutral factors and changes in community similarity measured by Sorensen’s index in riparian plant communities. We assessed the importance of neutral processes using network distances and flow connection and of niche-based processes using Strahler order differences and precipitation differences. We used a hierarchical Bayesian approach to determine which perspective is best supported by the results. We used dataset composed of 338 vegetation censuses from eleven river basins in continental Portugal. We observed that changes in Sorensen indices were associated with network distance, flow connection, Strahler order difference and precipitation difference but to different degrees. The results suggest that community similarity changes are associated with environmental and neutral factors, supporting the continuum hypothesis.

Microbial Community Composition in Municipal Wastewater Treatment Bioreactors Follows a Distance Decay Pattern Primarily Controlled by Environmental Heterogeneity.

ABSTRACTUnderstanding spatiotemporal patterns in microbial community composition is a central goal of microbial ecology. The objective of this study was to better understand the biogeography of activated sludge microbial communities, which are important for the protection of surface water quality. Monthly samples were collected from 20 facilities (25 bioreactors) within 442 km of each other for 1 year. Microbial community composition was characterized by sequencing of PCR-amplified 16S rRNA gene fragments. Statistically significant distance decay of community similarity was observed in these bioreactors independent of clustering method (operational taxonomic units [OTUs] at 97% similarity, genus-level phylotypes) and community dissimilarity metric (Sørensen, Bray-Curtis, and weighted Unifrac). Universal colonizers (i.e., detected in all samples) and ubiquitous genus-level phylotypes (i.e., detected in every facility at least once) also exhibited a significant distance decay relationship. Variation partitioning analysis of community composition showed that environmental characteristics (temperature, influent characteristics, etc.) explained more of the variance in community composition than geographic distance did, suggesting that environmental heterogeneity is more important than dispersal limitation as a mechanism for determining microbial community composition. Distance decay relationships also became stronger with increasing distance between facilities. Seasonal variation in community composition was also observed from selected bioreactors, but there was no clear seasonal pattern in the distance decay relationships.IMPORTANCE Understanding the spatiotemporal patterns of biodiversity is a central goal of ecology. The distance decay of community similarity is one of the spatial scaling patterns observed in many forms of life, including plants, animals, and microbial communities. Municipal wastewater treatment relies on microorganisms to prevent the release of excessive quantities of nutrients and other pollutants, but relatively few studies have explored distance decay relationships in wastewater treatment bioreactors. Our results demonstrate a strong distance decay pattern in wastewater treatment bioreactors, regardless of the sequence clustering method or the community dissimilarity metric. Our results suggest that microbial communities in wastewater treatment bioreactors are not randomly assembled but rather exhibit a statistically significant spatial pattern.

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.

Relative importance of local habitat complexity and regional factors for assemblages of oribatid mites (Acari: Oribatida) in Sphagnum peat bogs.

We investigated communities of oribatid mites in five peat bogs in the north-west of the East European plain. We aimed to determine the extent to which geographic factors (latitude, separation distance), local environment (Sphagnum moss species, ground water level, biogeochemistry) and local habitat complexity (diversity of vascular plants and bryophytes in the surrounding plant community) influence diversity and community composition of Oribatida. There was a significant north-to-south increase in Oribatida abundance. In the variance partitioning, spatial factors explained 33.1% of variability in abundance across samples; none of the environmental factors were significant. Across all bogs, Oribatida species richness and community composition were similar in Sphagnum rubellum and Sphagnum magellanicum, but significantly different and less diverse in Sphagnum cuspidatum. Sphagnum microhabitat explained 52.2% of variability in Oribatida species richness, whereas spatial variables explained only 8.7%. There was no distance decay in community similarity between bogs with increased geographical distance. The environmental variables explained 34.9% of the variance in community structure, with vascular plants diversity, bryophytes diversity, and ground water level all contributing significantly; spatial variables explained 15.1% of the total variance. Overall, only 50% of the Oribatida community variance was explained by the spatial structure and environmental variables. We discuss relative importance of spatial and local environmental factors, and make general inferences about the formation of fauna in Sphagnum bogs.

Distance decay of similarity in fungivorous insect communities: assessing dispersal limitation using genetic data

AbstractWe evaluated how dispersal limitation affected spatial variation in the species composition of fungivorous insect communities inhabiting fruiting bodies of bracket fungi on scattered deadwoods. The insect communities showed significant distance decay of similarity pattern among deadwoods, which was not fully explained by differences in environmental conditions. To investigate whether insect dispersal limitation could explain the distance‐decay pattern, we analyzed mitochondrial haplotype data; limited dispersal is expected to generate an isolation‐by‐distance pattern of genetic structure in component species. However, genetic distance between deadwoods was not correlated with geographic distance in any species, and a simulation study suggested that the absence of genetic structure refutes the dispersal limitation hypothesis even when the resolution of genetic differences is not high, as in our study. Thus, dispersal limitation did not contribute to the observed community patterns within our study site, suggesting that unmeasured environmental factors may have played an important role. Our study demonstrates that genetic data can help determine whether dispersal limitation of component species is the primary cause of observed distance decay in community similarity.

Field experimental evidence that stochastic processes predominate in the initial assembly of bacterial communities.

To assess the relative importance of environmental selection, dispersal and stochastic processes in structuring ecological communities, we conducted a bacterial community assembly experiment using microcosms filled with sterile liquid medium under field conditions in the Inner Mongolian grasslands. Multiple replicate microcosms containing different carbon substrates were placed at nine locations across three spatial scales (10, 300 and 10 000 m distance between locations) in such a way that the environment of microcosms varies independently of the geographical distance. The operational taxonomic units within the experimental communities were assessed via the terminal restriction fragment length polymorphism techniques on the 10th and 17th days after the onset of the experiment. We found no evidence of distance decay in community similarity, and communities within a given location were more similar to each other regardless of environment than communities at other locations within the same spatial scale. Variance partitioning indicated that location explained more compositional variation in microbial communities than environment, particularly on the 17th day, despite that environment and location in combination could only explain less than half of the total variation. These results suggest that bacterial dispersal is not limited by distance in this experiment, and community assembly in microcosms is not environmentally determined but governed by stochastic processes.

Are cities different? Patterns of species richness and beta diversity of urban bird communities and regional species assemblages in Europe

AbstractAimTo compare macroecological patterns between bird communities of European cities and regional species assemblages in the surrounding landscape, and to reveal geographical trends in the urbanization of native avifauna.LocationForty‐one towns and cities in continental Europe.MethodsWe compiled data on the species richness and community composition of urban avifauna from 41 European city breeding bird atlases, and of species assemblages comprising nine grid cells (each about 50 km × 50 km) from the EBCC Atlas of European Breeding Birds (hereafter regional assemblages). Species–area relationships (SARs), latitudinal trends in diversity and the distance decay of community similarity were compared using regression models (generalized linear models). Observed urban communities were compared with randomly assembled ones to reveal systematic effects of the urban environment on native bird communities across Europe. We employed variance partitioning to quantify the relative effect of environmental parameters and the spatial position of cities on species richness.ResultsThe species–area relationships did not differ significantly between cities and regional assemblages. Species richness of both types of communities increased towards higher latitudes, although the relationship was unimodal for regional assemblages, in contrast to cities. The increase in beta diversity with distance was on average less pronounced in cities than in regional assemblages, and was lower between individual cities than between communities of the same size randomly drawn from regional species assemblages. Moreover, average beta diversity was lower in northern cities, which are characterized by a relatively higher proportion of species from regional species pools.Main conclusionsThe species–area relationship and latitudinal trends are largely congruent between cities and the regional assemblages. However, city avifaunas tend to be relatively more uniform across space, revealing biotic homogenization. Urban communities in northern cities are more uniform as a higher proportion of bird species breeds in cities.

Spatial predictors of fish species composition in European lowland lakes

Composition of animal communities can be shaped by both local and regional processes. Among others, dispersal of organisms links local and regional patterns and determines the similarity of communities at increasing spatial distances. Unique and shared spatial and environmental contributions to fish community composition were calculated for watercourse distances between 49 hydrologically connected lakes in the German lowland area. Variation partitioning indicated a dominant unique effect of spatial predictors on fish community composition, whereas the effects of lake morphometry and productivity were weaker. The spatial effect was attributable to an uneven occurrence of small, littoral fish species found even at the small spatial extension covered here (maximum spatial distance ˜550 km). Distance decay of community similarity was moderate, but significant, if all 31 fish species were considered, but the slope of the decay function became steeper if only 11 small‐sized, primarily littoral species were included. These results suggest that fish in European lowland lakes can be considered a metacommunity with limited dispersal along watercourse connections in particular for small‐sized species. The analysis supports that for an appropriate evaluation of spatial effects on fish community similarity, reliable estimates of local richness are required which include in particular also rare, small‐sized species occurring primarily in littoral areas. Furthermore, watercourse distance is a more reliable approximation than Euclidean distance to the real spatial dimension of fish dispersal.

Changes in distance decay relationships after river regulation: similarity among fish assemblages in a large Amazonian river

AbstractThe construction of large dams has changed natural hydrology of many rivers in South America. Considering that little is known about the reorganisation of nonmigratory fish assemblages following an impoundment, we investigated changes caused by the construction of Lajeado Dam on the spatial distribution of nonmigratory fish along the Tocantins River, a large Amazonian river. In particular, we investigated changes in distance decay of community similarity (initial similarity and halving distance) in periods that preceded and followed the construction of the dam. For this study, we analysed data collected over a four‐year period, including seven sites distributed along the Tocantins River (~270 km). Initial similarity showed high values and little variation over the years. Halving distance, on the other hand, changed considerably after impoundment, showing progressive smaller values. In the first 2 years after impoundment, halving distance decreased by more than half of the initial value, indicating changes in distance decay relationships. An ordination analysis nonmetric multidimensional scaling (NMDS) indicated substantial changes in assemblage structure between pre‐ and postimpoundment periods, especially in sites close to the dam. In addition, after river regulation, we recorded shifts in species abundance across sites, while numerical dominance increased and local richness decreased in sites near the dam. Our results indicate that the dam changed diversity gradients along the river corridor, increasing the distance decay of assemblage similarity. All these findings evidence that nonmigratory fish assemblages are particularly vulnerable to river regulation.

Functional beta-diversity patterns reveal deterministic community assembly processes in eastern North American trees

Aim Determining the relative influence of niche-based and neutral processes in driving the spatial turnover of community composition is a central challenge in community ecology. Spatial patterns of functional turnover, or functional beta diversity, may capture important signals of niche-based assembly processes, but these patterns have not been quantified for communities across broad geographic and environmental gradients. Here, we analyse continental-scale patterns of species and functional beta diversity in relation to space and the environment to assess the relative importance of niche-based and neutral community assembly mechanisms. Location Eastern North America. Methods We use a continental-scale forest plot dataset and functional trait data to quantify spatial patterns of species and functional beta diversity. We use redundancy analysis-based variance partitioning to evaluate the influence of space, soil and climate on beta-diversity metrics. We use a null model approach to test for non-random functional beta diversity given the observed patterns of species turnover across spatial scales. Results Species and functional beta diversity increased with increasing geographic distance (i.e. distance decay of community similarity). Results of variance partitioning analysis show that species and functional beta diversity were spatially structured and significantly related to environmental, particularly climatic, variation. Results of null model analysis show that functional beta diversity was lower than expected based on species turnover at fine scales (< 600 km) and higher than expected at broad scales (> 1800 km). Main conclusions The observed patterns of functional beta diversity support a niche-based model of community assembly, driven by the deterministic filtering of species across environmental gradients based on their functional traits.

Distance Decay of Similarity in Neotropical Diatom Communities

BackgroundThe regression of similarity against distance unites several ecological phenomena, and thus provides a highly useful approach for illustrating the spatial turnover across sites. Our aim was to test whether the rates of decay in community similarity differ between diatom growth forms suggested to show different dispersal ability. We hypothesized that the diatom group with lower dispersal ability (i.e. periphyton) would show higher distance decay rates than a group with higher dispersal ability (i.e. plankton).Methods/Principal findingsPeriphyton and phytoplankton samples were gathered at sites distributed over an area of approximately 800 km length in the Negro River, Amazon basin, Brazil, South America (3°08′00″S; 59°54′30″W). Distance decay relationships were then estimated using distance-based regressions, and the coefficients of these regressions were compared among the groups with different dispersal abilities to assess our predictions. We found evidence that different tributaries and reaches of the Negro River harbor different diatom communities. As expected, the rates of distance decay in community similarity were higher for periphyton than for phytoplankton indicating the lower dispersal ability of periphytic taxa.Conclusions/SignificanceOur study demonstrates that the comparison of distance decay relationships among taxa with similar ecological requirements, but with different growth form and thus dispersal ability provides a sound approach to evaluate the effects of dispersal ability on beta diversity patterns. Our results are also in line with the growing body of evidence indicating that microorganisms exhibit biogeographic patterns. Finally, we underscore that clumbing all microbial taxa into one group may be a flawed approach to test whether microbes exhibit biogeographic patterns.

Testing the Species–Genetic Diversity Correlation in the Aegean Archipelago: Toward a Haplotype-Based Macroecology?

A positive correlation between species diversity and genetic diversity has been proposed, consistent with neutral predictions in macroecology. We assessed the species--genetic diversity correlation in tenebrionid beetle communities of the Aegean archipelago on 15 islands of different sizes, distances to mainland, and ages of isolation. Alpha and beta diversity of species and haplotypes were assessed using sequences of > 1,000 individuals (mitochondrial cytochrome oxidase 1 and nuclear muscular protein 20). We show that (i) there is a strong species-area and haplotype-area relationship; (ii) species richness in island communities is correlated with intraspecific genetic diversity in the constituent species except when island size or distance to mainland is factored out in partial correlations; (iii) community similarity declines exponentially at an increasing rate when calculated on the basis of species, nuclear, and mtDNA haplotypes; and (iv) distance decay of community similarity is slower in dispersive sand-dwelling lineages compared with less dispersive lineages that are not sand obligate. Taken together, these correlated patterns at the species and haplotype level are consistent with individual-based stochastic dispersal proposed by neutral theories of biodiversity. The results also demonstrate the utility of haplotype data for exploring macroecological patterns in poorly known biota and predicting large-scale biodiversity patterns based on genetic inventories of local samples.

Distance decay of similarity in freshwater communities: do macro‐ and microorganisms follow the same rules?

ABSTRACTAim An intensively debated issue in macroecology is whether unicellular organisms show biogeographic patterns different from those of macroorganisms. One aspect of this debate addresses beta diversity, that is, do microbial organisms exhibit distance‐decay patterns similar to those of macroorganisms? And if so, is the decay of community similarity caused by spatially limited dispersal or by niche‐related factors? We studied the community similarity of stream diatoms, macroinvertebrates and bryophytes across the same set of sites in relation to environmental and geographic distance.Location A geographical gradient of c. 1100 km in Finland.Methods We first identified the subset of environmental variables that produced the highest correlation with community similarities for each taxonomic group. Based on these variables, we used partial Mantel tests to separate the independent influences of environmental and geographical distance for distance decay of community similarity, separately for diatoms, bryophytes and macroinvertebrates. Finally, macroinvertebrates were divided into three groups based on their different dispersal categories and a partial Mantel test was used to assess whether each of these groups were differently affected by environmental versus geographic distance, i.e. is dispersal a key factor in tests of niche versus neutral models.Results The level of environmental control was by far the strongest for diatoms; however, all groups were controlled more by environmental factors than by limited dispersal. Macroinvertebrate species with low dispersal ability were significantly related to geographic distance, while more effective dispersers showed no relationship to geography but were instead strongly related to environmental distance.Main conclusions Our results suggest that patterns between macro‐ and microorganisms are not fundamentally different, but the level of environmental control varies according to dispersal ability. The relative importance of niche versus dispersal processes is not simply a function of organism size but other traits (e.g. life‐history type, dispersal capacity) may obscure this relationship.

Making more out of sparse data: hierarchical modeling of species communities

Community ecologists and conservation biologists often work with data that are too sparse for achieving reliable inference with species-specific approaches. Here we explore the idea of combining species-specific models into a single hierarchical model. The community component of the model seeks for shared patterns in how the species respond to environmental covariates. We illustrate the modeling framework in the context of logistic regression and presence-absence data, but a similar hierarchical structure could also be used in many other types of applications. We first use simulated data to illustrate that the community component can improve parameterization of species-specific models especially for rare species, for which the data would be too sparse to be informative alone. We then apply the community model to real data on 500 diatom species to show that it has much greater predictive power than a collection of independent species-specific models. We use the modeling approach to show that roughly one-third of distance decay in community similarity can be explained by two variables characterizing water quality, rare species typically preferring nutrient-poor waters with high pH, and common species showing a more general pattern of resource use.