Decay Of Community Similarity 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.

Dispersal and Distribution of Thermophilic Endospores in Deep-Sea Ecosystems

The distance-decay relationship is a central concept in biogeography and spatial biodiversity, describing how two distinct entities decrease in similarity as the distance between them increases. The decay of community similarity with geographical distance is driven by multiple factors, such as gene drift, environmental selection, and the accumulation of mutations over time. While the distance-decay relationship has been recognized for several decades, there are certain circumstances where the biogeographical patterns of certain species and communities cannot be predicted by this relationship. The example addressed in this project is the case of thermophilic endospore-forming bacteria found in permanently cold deep ocean sediments. Thermophilic endospores (thermospores) are routinely found on the deep ocean floor, a permanently cold environment that does not support their metabolic activity (Hubert et al. 2009). Thermospores are metabolically dormant states developed by some thermophilic bacteria having optimal growth temperatures between 40°C and 70°C. There is evidence that these heat-loving bacteria originate from the deep subsurface and are transported upward to the deep ocean via geological features of the oceanic crust including geofluid fluxes in high-temperature axial systems and natural hydrocarbon seeps (Gittins et al. 2022). Due to the ability of endospores to stay viable for thousands of years and resist a wide range of physicochemical stressors, they can disperse over long distances while remaining unaffected by changing factors such as selection, drift, or mutation (Gittins et al. 2022; Fig. 1). Consequently, these thermospores have the potential to challenge the distance-decay relationship and exhibit unique biogeographical patterns. This work quantifies endospores in sediment cores at and around hydrocarbon seeps using cores from deep-sea Scotian Slope sediments. Given the challenge of quantifying specific groups of endospores (e.g., thermophiles but not mesophiles), high-temperature germination assays that allow tracking of an exponential increase in signal as spores in marine sediment samples germinate and grow can be used. Distinct exponential increases can be attributed to different populations of germinated thermospores in the post-germination growth phase and are being monitored through measurements of sulfate reduction rates (using radiolabelled 35SO4), strain-specific quantitative PCR (qPCR), and fluorescence in-situ hybridization (FISH) (Rezende et al. 2017). These measurements revealed growth dynamics enabling an estimation of the initial cell numbers using exponential functions. These approaches are being applied to samples obtained via push coring using a remotely operated vehicle at different distances from deep sea hydrocarbon seeps, to test for the presence of abundance gradients of different thermospores. Current results already show a difference in thermospore abundance between sites at different distances from the seep. Quantitative tracking of the dispersal of thermospores by oceanic currents in the deep sea provides an excellent opportunity to investigate their distribution and potential to colonize more remote habitats, improving the understanding of microbial biodiversity and biogeography on our planet. By investigating thermospores and their interactions with the geophysical features of the deep sea and deep subsurface, this study aims to challenge the canonical idea that speciation occurs with distance and presents new perspectives on the theme of microbial biogeography. The evidence supporting the subsurface origin of thermophilic endospores, along with the proposed model for their dispersal and distribution, will contribute toward improving an integrated understanding of ecology and geology and their intersection in the microbial realm.

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.

Environmental filtering rather than dispersal limitation dominated plant community assembly in the Zoige Plateau.

Identifying the mechanisms that underlie the assembly of plant communities is critical to the conservation of terrestrial biodiversity. However, it is seldom measured or quantified how much deterministic versus stochastic processes contribute to community assembly in alpine meadows. Here, we measured the decay in community similarity with spatial and environmental distance in the Zoige Plateau. Furthermore, we used redundancy analysis (RDA) to divide the variations in the relative abundance of plant families into four components to assess the effects of environmental and spatial. Species assemblage similarity liner declined with geographical distance (p < .001, R 2 = .6388), and it decreased significantly with increasing distance of total phosphorus (TP), alkali‐hydrolyzable nitrogen (AN), available potassium (AK), nitrate nitrogen (NO3 +–N), and ammonia nitrogen (NH4 +–N). Environmental and spatial variables jointly explained a large proportion (55.2%) of the variation in the relative abundance of plant families. Environmental variables accounted for 13.1% of the total variation, whereas spatial variables accounted for 11.4%, perhaps due to the pronounced abiotic gradients in the alpine areas. Our study highlights the mechanism of plant community assembly in the alpine ecosystem, where environmental filtering plays a more important role than dispersal limitation. In addition, a reasonably controlled abundance of Compositae (the family with the highest niche breadth and large niche overlap value with Gramineae and Cyperaceae) was expected to maintain sustainable development in pastoral production. These results suggest that management measures should be developed with the goal of improving or maintaining suitable local environmental conditions.

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.

Do shared traits create the same fates? Examining the link between morphological type and the biogeography of fungal and bacterial communities

Abstract Although it has been commonly observed that fungi and bacteria differ in their regional biogeographic patterns, it is not well understood what traits contribute to these different distributions. Here, we evaluate how morphological type (i.e. unicellular or filamentous growth form) influences the biogeography of soil fungal and bacterial communities across not only Euclidean (i.e. geographic) distances, but also across gradients of climate and edaphic factors and plant community composition. Specifically, we assessed the decay in community similarity over distance (distance-decay relationship) for microbes with unicellular and filamentous morphology in both fungi and bacteria across 40 ecologically diverse sampling sites in Minnesota, USA. Overall, we found that while distance-decay relationships were similar in fungal and bacterial communities over Euclidean distances, there were important differences among morphological groups of fungi and bacteria across gradients of environmental and plant community similarity. Specifically, the distance-decay relationship of unicellular fungi and unicellular bacteria were indistinguishable across environmental similarity. However, as plant community similarity decreased, only filamentous fungi and unicellular bacteria differed significantly in the strength of their distance-decay relationships. Like analyses of other study systems, we also found that pH explained much of the variance in community composition across microbial domains and morphological types and that plant community diversity was more closely correlated with fungal diversity than with bacterial diversity. Collectively, our results suggest that specific ecological traits such as morphological type along with microbial domain are key factors shaping the biogeography of microbial communities.

Evolutionary conservation of within-family biodiversity patterns

The tendency for species to retain their ancestral biological properties has been widely demonstrated, but the effect of phylogenetic constraints when progressing from species to ensemble-level properties requires further assessment. Here we test whether community-level patterns (environmental shifts in local species richness and turnover) are phylogenetically conserved, assessing whether their similarity across different families of lichens, insects, and birds is dictated by the relatedness of these families. We show a significant phylogenetic signal in the shape of the species richness-elevation curve and the decay of community similarity with elevation: closely related families share community patterns within the three major taxa. Phylogenetic influences are partly explained by similarities among families in conserved traits defining body plan and interactions, implying a scaling of phylogenetic effects from the organismal to the community level. Consequently, the phylogenetic signal in community-level patterns informs about how the historical legacy of a taxon and shared responses among related taxa to similar environments contribute to community assembly and diversity patterns.

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.

Effect of landscape context on fish metacommunity structuring in stream networks

Summary The metacommunity framework has shed light upon the significance of local and regional processes in shaping ecological communities. However, our knowledge is limited how landscape context (i.e. type and positioning of habitats) influences the structuring of metacommunities. We examined the role of environmental selection (niche‐based species sorting), dispersal and drift (i.e. stochastic changes in species abundance) mechanisms on the structuring of fish metacommunities in riverscapes. We used a hierarchical design and examined metacommunity structuring (i) in individual running water habitat types, namely highland streams, lowland streams, highland rivers and lowland rivers; (ii) in landscape types, where patterns in highland and in lowland types were examined separately and (iii) at the level of the whole riverscape, where samples from all running water types were pooled. Elements of metacommunity structure (EMS) analysis, community–environmental relationships in redundancy analysis, and decay of community similarity with distance (distance decay) complemented with partial Mantel tests were used to reveal the mechanisms behind the observed patterns. Both the EMS framework and community–environment relationships revealed the prevalent role of selection (niche‐based species sorting mechanisms) on fish metacommunity structuring, although stochastic variability also influenced the results. Metacommunity structures reflecting niche‐based mechanisms (Clementsian or quasi‐Clementsian) were observed at higher hierarchical levels (i.e. at the riverscape and the landscape type levels), while quasi‐Clementsian or random patterns were found within single running water types. Distance decay relationships indicated that dispersal limitation did not clearly affect metacommunity structuring in any combination of running water types. Partial Mantel tests showed that some part of the variation in distance decay could be explained by the correlation between environmental variables and fish assemblage structure in some habitat types, which further suggests the importance of niche‐based mechanisms in metacommunity structuring. Our study shows that different metacommunity structures can arise in a hierarchy of habitat types in riverscapes, and niche‐based species sorting mechanisms are more influential in their structuring than dispersal ones. Landscape classifications are useful for a better understanding of the structuring of metacommunities in both the freshwater and terrestrial realms.

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.

Mapping species distributions: living with uncertainty

news and update ISSN 1948‐6596 commentary Mapping species distributions: living with uncertainty decreases with time because of range changes associated with factors such as climate and land‐ use change, habitat degradation, biological inva‐ sions, etc. Moreover, changes in taxonomic status resulting from reclassifications (Hey et al. 2003) may mean that even if the assemblage remains unchanged, the quality of the information de‐ grades. Thus, the utility and accuracy of informa‐ tion about species occurrences to describe current distributions depends upon when the database is consulted. This process of information decay also applies to data based on expert assessments, such as range maps, which are ultimately based on knowledge coming from surveys and observa‐ tions. Finally, the decay in community similarity with increasing geographic distances is a well known pattern in biogeography (Nekola & White 1999). The main drivers of this pattern are envi‐ ronmental gradients (e.g. climate, soil chemistry, etc.), spatial configuration of habitats and popula‐ tion aggregation (Morlon et al. 2008). Species dis‐ tribution maps are typically based on the spatial extrapolation of survey data through expert as‐ sessment or species distribution modeling (Rocchini et al. 2011). It follows that their accu‐ racy for unsurveyed regions will decrease with distance from the original samples, and (in the absence of comprehensive coverage of the study area) our knowledge about the actual distribution of the species may be poor. The proposed Map of Life project aspires to create a type of omniscient GIS for all the Earth’s living species – such as the one imagined by Colwell & Coddington (1994). This is a wonderful target, with the potential to dramatically improve the spatial and temporal resolution of biodiversity data. Nevertheless, the biodiversity data that un‐ derpin any such enterprise have intrinsic and un‐ avoidable limitations that result in loss of knowl‐ edge over both time and space. This is well known A recent paper by Jetz et al. (2012) presents the ‘Map of Life’, a web‐based tool that aims to pro‐ vide a representation of the distribution of every species on Earth 1 . This database, if it is fully real‐ ized, would provide an invaluable resource for the advancement of biogeographical research, in addi‐ tion to its potential utility for conservation plan‐ ning. As most biogeographers, we would give al‐ most unconditional support to any initiatives that may improve the quantity, quality and availability of species distribution data – such as the Map of Life, GBIF 2 , Encyclopedia of Life 3 , etc. (see review in Riddle et al. 2010). We are certain that they will provide a deeper and wider knowledge about life on Earth through the uprising field of biodiversity informatics (see Soberon & Peterson 2004). Even so, it is important to bear in mind that there are intrinsic limitations to the quality, longevity and coverage of biodiversity data. There are at least three factors that com‐ promise the quality of our knowledge of species distributions at any given spatial scale: survey completeness, and the decay of information with time and space. First, as any field ecologist knows, many taxa are difficult to detect because of their phenotype (cryptic coloration and behavior, high mobility, phenology, etc.) and the characteristics of the habitat. Thus, most biological surveys on which species distribution maps are based are un‐ avoidably incomplete, even when a range of sam‐ pling methodologies is utilized (Colwell & Cod‐ dington 1994). In other words, it is normally im‐ possible to record the entire assemblage for a de‐ fined area at a given moment of time. Moreover, the completeness of a sample will typically de‐ crease with increasing extent of the survey area (see Chiarucci et al. 2011). Second, knowledge about species distribu‐ tions and the composition of local assemblages is in a constant state of information decay. The reli‐ ability of the information provided by any survey 1 http://www.mappinglife.org/ 2 http://www.gbif.org/ 3 http://eol.org/ frontiers of biogeography 5.1, 2013 — © 2013 the authors; journal compilation © 2013 The International Biogeography Society

Hydrological connectivity structures concordant plant and animal assemblages according to niche rather than dispersal processes

Summary1. Understanding the processes that structure community assembly across landscapes is fundamental to ecology and for predicting and managing the consequences of anthropogenically induced changes to ecosystems.2. We assessed the community similarity of fish, macroinvertebrate and vegetation communities against geographic distances ranging from 4 to 480 km (i.e. distance–decay relationships) to determine the balance between local environmental factors and regional dispersal processes, and thus whether species‐sorting (niche processes) or dispersal limitation (neutral processes) was more important in structuring these assemblages in Australia’s wet‐dry tropics. We investigated whether the balance between niche and dispersal processes depended on the degree of hydrological connectivity, predicting that dispersal processes would be more important at connected sites, and also whether there was spatial concordance among these three assemblage types.3. There was significant but weak spatial concordance among the study communities, suggesting limited potential for surrogacy among them. Distance–decay in community similarity was not observed for any study assemblage at perennial sites, suggesting dispersal was not limiting and assemblages were structured more strongly by local niche processes at these connected sites. At intermittent sites, weak distance–decay relationships for each assemblage type were confounded by significant relationships with environmental dissimilarity, suggesting that dispersal limitation contributed, albeit weakly, to niche processes in structuring our three study assemblages at disconnected sites.4. Two environmental factors, flow regime and channel width, explained significant proportions of variation in all three assemblages, potentially contributing to the observed spatial concordance between them and representing local environmental gradients along which these communities re‐assemble after the wet season, according to niche rather than dispersal processes.

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.

Predicting the similarity of parasite communities in freshwater fishes using the phylogeny, ecology and proximity of hosts

Parasite communities tend to be dissimilar in hosts that are geographically, phylogenetically, ecologically and developmentally distant from one another. The decay of community similarity is a powerful and increasingly common method of studying parasite beta diversity, but most studies have examined only a single type of distance. Here, we evaluate distances based on the phylogeny, ecology, spatial proximity and size of hosts, as predictors of the similarity of parasite communities in individual hosts, host populations and host species. We surveyed parasites in six species of fish collected simultaneously from six localities in the St. Lawrence River, Canada, and species in a common group of larval parasites were discriminated using DNA sequences from barcode region of cytochrome c oxidase I. Distances based on the habitat use patterns of host species were good predictors of short‐term, ecological similarity of parasite communities, such as that operating at the scale of the individual host. The genetic distance between host species was associated with almost all types of similarity at all scales, particularly qualitative and phylogenetic similarity of parasite communities at the level of populations and meta‐populations of hosts. The trophic level, diet, spatial proximity and size of hosts were poor predictors of parasite community similarity. The increased taxonomic resolution provided by molecular data increased the explanatory power of regression models, and different factors were implicated when parasite species were distinguished with DNA barcodes than when larval parasites were lumped into morphospecies, as is commonly practiced.

Patterns of beta diversity in Europe: the role of climate, land cover and distance across scales

AbstractAim We test the prediction that beta diversity (species turnover) and the decay of community similarity with distance depend on spatial resolution (grain). We also study whether patterns of beta diversity are related to variability in climate, land cover or geographic distance and how the independent effects of these variables depend on the spatial grain of the data.Location Europe, Great Britain, Finland and Catalonia.Methods We used data on European birds, plants, butterflies, amphibians and reptiles, and data on British plants, Catalonian birds and Finnish butterflies. We fitted two or three nested grids of varying resolutions to each of these datasets. For each grid we calculated differences in climate, differences in land‐cover composition (CORINE) and beta diversity (βsim, βJaccard) between all pairs of grid cells. In a separate analysis we looked specifically at pairs of adjacent grid cells (the first distance class). We then used variation partitioning to identify the magnitude of independent statistical associations (i.e. independent effects in the statistical sense) of climate, land cover and geographic distance with spatial patterns of beta diversity.Results Beta diversity between grid cells at any given distance decreased with increasing grain. Geographic distance was always the most important predictor of beta diversity for all pairwise comparisons at the extent of Europe. Climate and land cover had weaker but distinct and grain‐dependent effects. Climate was more important at relatively coarse grains, whereas land‐cover effects were stronger at finer grains. In the country‐wide analyses, climate and land cover were more important than geographic distance. Climatic and land‐cover models performed poorly and showed no systematic grain dependence for beta diversity between adjacent grid cells.Main conclusions We found that relationships between geographic distance and beta diversity, as well as the environmental correlates of beta diversity, are systematically grain dependent. The strong independent effect of distance indicates that, contrary to the current belief, a substantial fraction of species are missing from areas with a suitable environment. Moreover, the effects of geographic distance (at continental extents) and land cover (at fine grains) indicate that any species distribution modelling should take both environment and dispersal limitation into account.

Spatial patterns and local diversity in soil oribatid mites (Acari: Oribatida) in three pine plantation forests

The study investigates diversity patterns in communities of soil oribatid mites (Acari: Oribatida) in three pine plantation forests in New Zealand. The distribution patterns at the metacommunity level were analyzed as the decay in community similarity as a function of intersample distance. The local diversity was analysed at the soil core level.Oribatida communities were characterized by high local diversity coupled with high degree of dominance in local distribution of abundances, and by spatially structured metacommunities, with high species turnover and significant distance decay in species presence/absence at all sampled distances. In all three sites community assemblages were spatially autocorrelated. In two sites the spatial dependence was present at all sampled distances. In the third site spatial autocorrelation in community structure existed at separation distances below approx. 40 m.The observed patterns appear to be consistent with ecological drift and stochastic model of community assembly under assumption of low dispersal, although there is some indication that spatial heterogeneity in habitat quality contributes to the species distribution. The results suggest that Oribatida communities separated by distances as large as 60 m may not be spatially independent. Soil cores collected within such vicinity should not be used as independent examples of community response to environmental factors, and should not be treated as independent replicates in statistical analysis.

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.

Fish trophic level and the similarity of non-specific larval parasite assemblages

Whereas the effect of parasites on food webs is increasingly recognised and has been extensively measured and modelled, the effect of food webs on the structure of parasite assemblages has not been quantified in a similar way. Here, we apply the concept of decay in community similarity with increasing distance, previously used for parasites in geographical, phylogenetic and ontogenetic contexts, to differences in the trophic level (TL) based on diet composition of fishes. It is proposed as an accurate quantitative method to measure rates of assemblage change as a function of host feeding habits and is applied, to our knowledge for the first time, across host species in marine waters. We focused on a suite of 15 species of trophically-transmitted and non-specific larval helminths across 16 fish species (1783 specimens, six orders, 14 families) with different sizes and TLs, gathered from the same ecosystem. Not all host species harboured the same number and types of parasites, reflecting the differences in their ecological characteristics. Using differences in TL and body length as measurements of size and trophic distances, we found that similarity at both infracommunity and component community levels showed a very clear decay pattern, based on parasite abundance and relative abundance, with increasing distance in TL, but was not related to changes in fish size, with TL thus emerging as the main explanatory factor for similarity of parasite assemblages. Furthermore, the relationships between host TL and assemblage similarity allowed identification of fishes for which the TL was under- or over-estimated and prediction of the TL of host species based on parasite data alone.