Metacommunity Structure Research Articles

Foundation Species Abundance Influences Food Web Topology on Glass Sponge Reefs

Foundation species support communities across a wide range of ecosystems. Non-trophic interactions are considered the primary way foundation species influence communities, with their trophic interactions having little impact on community structure. Here we assess the relative trophic importance of a foundation species and assess how its abundance can influence food web topology. Using empirical data and published trophic interactions we built food web models for 20 glass sponge reefs to examine how average live reef-building sponge abundance (proxied by percent cover) at the reef level is correlated with community structure and food web network topology. Then, using a generalized food web model and stable isotope data we examined the relative importance of sponges. Sponges were consumed by all species examined and contributed significantly to their diets. Additionally, sponges were the second most important node in our generalized reef food web. Several metrics of food web topology (connectance, clustering, and median degree) and community structure exhibited a threshold response to reef-building sponge cover, with the change point occurring between 8 and 13% live sponge cover. Below this threshold, as average sponge cover increases, the consumers observed on a reef rely on fewer sources and are consumed by fewer predators, resulting in food webs that are more clustered and less connected. Above the threshold, as average sponge cover increases, the reefs’ food webs are less clustered and more connected, with consumers utilizing more sources and having more predators. This corresponds with the finding that several generalist predators (e.g., rockfishes) are associated with high sponge cover reefs. Our results are not consistent with previous reports that increasing foundation species abundance decreases connectance in food webs. We propose that the influence of foundation species on food web topology may be dependent on palatability, and therefore relative trophic importance, of the foundation species. Finally, our findings have important implications for sponge reef conservation and management, as they suggest that reefs below the 10% sponge cover threshold support different communities than high live sponge cover reefs.

HELMINTH COMMUNITY STRUCTURE OF THREE SIGMODONTINE RODENTS IN THE ATLANTIC FOREST, SOUTHERN BRAZIL

Ecological studies of host-parasite interactions are common in rodents. However, despite the widespread occurrence of endoparasites in those animals, there is a lack of information about the community structure of these parasites. The aims of this study were to describe the species composition and the community structure of helminths of the rodents Oligoryzomys nigripes , Akodon montensis and Euryoryzomys russatus (Rodentia, Sigmodontinae), and to investigate the influence of host species, age and gender on the abundance and prevalence of helminths. The pattern of the metacommunity structure of the helminths of A. montensis was also analysed. Small mammals were captured in Serra do Tabuleiro State Park, Santo Amaro da Imperatriz, state of Santa Catarina, Brazil. Helminths were identified and counted. Each species had its abundance, intensity and prevalence estimated for each host. The influence of host species, age and gender on abundance and prevalence of helminths was tested using generalized linear models (GLM). The metacommunity was analysed by calculating the Elements of Metacommunity Structure (EEM) for infracommunities. In O. nigripes, the species Guerrerostrongylus zetta and Stilestrongylus lanfrediae (Nematoda, Heligmonellidae) were found. A. montensis harboured G. zetta , Trichofreitasia lenti (Nematoda, Heligmonellidae), Trichuris navonae (Nematoda, Trichuridae), Angiostrongylus sp. (Nematoda, Angiostrongylidae), Litomosoides chagasfilhoi (Nematoda, Onchocercidae) and Rodentolepis akodontis (Plathyhelmintes, Cestoda). In the E. russatus rodent, the species G. zetta, Stilestrongylus rolandoi (Nematoda, Heligmonellidae) and Raillietina guaricanae (Plathyhelmintes, Cestoda) were found. This study presented new records of the helminths S. rolandoi and R. guaricanae in E. russatus , and of L. chagasfilhoi in A. montensis . The helminth metacommunity structure of A. montensis presented a random pattern of species distribution, characterized by a non-coherent structure along the environmental gradient, indicating different environmental requirements due to the infection of this host by helminths with different life cycles.

Bacterial community assembly in Atlantic cod larvae (Gadus morhua): contributions of ecological processes and metacommunity structure.

ABSTRACTMany studies demonstrate the importance of the commensal microbiomes to animal health and development. However, the initial community assembly process is poorly understood. It is unclear to what extent the hosts select for their commensal microbiota, whether stochastic processes contribute, and how environmental conditions affect the community assembly. We investigated community assembly in Atlantic cod larvae exposed to distinct microbial metacommunities. We aimed to quantify ecological processes influencing community assembly in cod larvae and to elucidate the complex relationship between the bacteria of the environment and the fish. Selection within the fish was the major determinant for community assembly, but drift resulted in inter-individual variation. The environmental bacterial communities were highly dissimilar from those associated with the fish. Still, differences in the environmental bacterial communities strongly influenced the fish communities. The most striking difference was an excessive dominance of a single OTU (Arcobacter) for larvae reared in two of the three systems. These larvae were exposed to environments with higher fractions of opportunistic bacteria, and we hypothesise that detrimental host–microbe interactions might have made the fish susceptible to Arcobacter colonisation. Despite strong selection within the host, this points to a possibility to steer the metacommunity towards mutualistic host–microbe interactions and improved fish health and survival.

Spatial processes determine planktonic diatom metacommunity structure of headwater streams

Headwater streams are interesting ecological systems for studies of metacommunities given their high degrees of isolation, unidirectionality of water flow and hierarchical organization in the drainage network. In addition, for passively dispersing aquatic organisms (e.g. planktonic diatoms), connectivity between sites is unidirectional, which implies a higher isolation of headwaters, leading to a greater dispersal limitation between streams. The aim of this study was to evaluate the relative importance of local environmental (i.e., physicochemical variables) and spatial (i.e., distance between sites) components to the planktonic diatom community in 28 headwater streams of the Cerrado, central region of Brazil. Due the fact that each sampling point was located in a different headwater stream, we expected that spatial components (a proxy for diatom dispersal) were more important than local environmental conditions to the structure of the diatom metacommunity. We found 51 morphospecies of diatoms (Bacillariophyceae). The community composition of diatoms showed strong spatial variation, which was also indicated by high beta diversity (mainly contributed by the turnover component). The variation in diatom community composition, species richness, total density, and Local Contribution to Beta Diversity (LCBD) of headwaters streams was explained solely by spatial factors. Based on these results, we inferred that due to dispersal limitation, the diatom communities of these headwaters tend to show distinct species composition, with high species turnover among the local communities. We highlight the importance of headwater streams as reservoirs of biodiversity for a riverine diatom metacommunity.

Elements of lake macrophyte metacommunity structure: Global variation and community‐environment relationships

AbstractDocumenting the patterns of biological diversity on Earth has always been a central challenge in macroecology and biogeography. However, we are only beginning to generate an understanding of the global patterns and determinants of macrophyte diversity. Here, we studied large‐scale variation and community‐environment relationships of lake macrophytes along climatic and geographical gradients using regional data from six continents. We applied statistical routines typically used in the context of metacommunity studies to provide novel insights into macrophyte community compositional patterns within regions worldwide. We found that lake macrophyte metacommunities followed clumped species replacement structures, suggesting that two or more species groups were responding similarly to the environment within regions. Underlying such general convergence, our results also provided evidence that community‐environment relationships were largely context‐dependent, stressing that no single mechanism is enough to account for the complex nature of compositional variation. Surprisingly, we found no general relationships between functional or phylogenetic composition and main metacommunity types, suggesting that linking multi‐trait and evolutionary information to the elements of metacommunity structure is not straightforward. Our findings highlight that global conservation initiatives and biodiversity protection need to capture environmental variation at the metacommunity level, and acknowledge the highly context‐dependent patterns in the community‐environment relationships of lake macrophytes. Overall, we emphasize the need to embrace the potential complexity of ecological inferences in metacommunity organization across the globe.

Metacommunity structure analysis reveals nested patterns in deconstructed macroinvertebrates assemblages

Understanding processes driving patterns of species distribution and diversity is one of the main objectives of community ecology. The aim of our study was to evaluate the spatial variation in assemblage composition of stream‐dwelling macroinvertebrates and identify which factors (e.g. water quality, land cover) are the most important drivers. We applied the elements of the metacommunity structure approach on a dataset of 38 communities from the Futaleufú basin in northwestern Patagonia. To better understand assemblage variation, we deconstructed our macroinvertebrate dataset into different taxonomic and trait groups. We then identified the most influential factors driving community composition using random forests. We found that half of our datasets (i.e. macroinvertebrate groups) exhibited a nested structure with clumped species loss, while the other half showed a quasi‐nested pattern with either clumped or stochastic species loss. Overall, water quality was the most important driver of community variation, although climate, geography, and land cover were more or less relevant in particular cases. We found differences in the relative importance of the selected explanatory variables among datasets. This would suggest that different components of the macroinvertebrate community respond differently to environmental factors. Our findings could be of value for conservation planning, as they suggest that preserving the most species‐rich streams would, to some extent, guarantee the conservation of the entire species pool.

Chiropteran metacommunity structure in the Atlantic Forest of South America

AbstractAimSpatial patterns of local species composition are shaped by dispersal ability. Here we examine the effects of dispersal ability on metacommunity structure of bats throughout the Atlantic Forest of South America considering differences among communities, functional groups and species regarding environmental, spatial and connectivity‐related drivers of composition. We also examined phylogenetic and ecological correlates, such as incidence (i.e. frequency of occurrence across sites) and wing morphology, of the degree to which species respond to spatial and environmental drivers.LocationAtlantic Forest of Argentina, Brazil and Paraguay.TaxonPhyllostomid bats.MethodsData from the Atlantic Bats dataset were compiled for 39 species at 120 sites. Variation was partitioned into pure environmental, pure space, pure connectivity, joint and unaccounted variation fractions. Redundancy analyses or linear regression determined amount of variation in variation fractions that was accounted for by phylogeny or ecological characteristics of species.ResultsThe metacommunity of Atlantic Forest phyllostomid bats was significantly structured by environmental, space and connectivity characteristics. Animalivore, nectarivores and sanguinivore species composition was significantly related only to connectivity. Frugivores exhibited structure that was significantly related to all three kinds of characteristics (pure environmental, pure spatial and pure connectivity) and similar to that of the overall metacommunity. Species‐specific responses to environmental, spatial and connectivity drivers were variable but exhibited strong affinities related to phylogeny and functional group. As incidence of a species increased, variation in distribution and abundance was more related to environmental characteristics. There was no significant relationship between forearm length and magnitude of the connectivity variation partition.Main ConclusionsMetacommunity structure of bats in the Atlantic Forest is complex and includes variation across multiple scales of ecological organization. Structure is strongly associated with phylogenetic, functional and distributional characteristics of species, with these, in turn, related to responses to spatial and environmental gradients in the Atlantic Forest.

Environmental and Spatial Influences on Biogeography and Community Structure of Saltmarsh Benthic Diatoms

Benthic microalgae play important roles in energy flow and biogeochemistry of coastal ecosystems; however, factors influencing community composition remain largely unknown. Our purpose was to identify and compare spatial and environmental influences on benthic diatom biogeography at regional scales. In summer 2018, we sampled sediment at various spatial scales (0.0001–180 km) from five saltmarshes in South Carolina, USA, and characterized diatom assemblages using DNA metabarcoding. Twenty-three environmental variables from marsh sediments, adjacent creeks, and atmosphere were recorded. Multivariate analyses revealed that the saltmarsh communities were clearly distinct. Community dissimilarity was compared to both geographic distance and environmental differences to determine influences on community structure. Mantel tests and redundancy analysis revealed that spatial influences, in addition to several environmental factors (phosphate, grain size, sediment sorting, sediment moisture, and creek salinity), were significant. Variation partitioning revealed that 26% of community variation was explained by geographic distance alone, whereas 60% could be explained by combined spatial/environmental factors. In contrast, the independent explanatory power of individual environmental factors was negligible. Our findings suggest that spatially structured environmental variation mainly conditioned the saltmarsh diatom biogeography in this region. Dispersal limitation, as evinced by the large pure spatial effect and distance-decay pattern, was also important. Spatial effects were stronger relative to that previously observed in other microbial groups (marine bacteria and phytoplankton) and detected at finer spatial scales. Results support prior studies that suggest body size and dispersal mode are important drivers of metacommunity structure and therefore must be considered when studying aquatic microbial biogeography.

Despite dramatic local changes, the metacommunity structure of a semiarid scrub remains unaffected after 23 years

Background: Understanding changes in local community composition along environmental gradients is essential for studying the long-term metacommunity dynamics. The metacommunity structure depends on the distribution of species along environmental gradients in terms of their coherence (continuity in their distribution range), species turnover and grouping of their range limits. A Clementsian structure would be defined by coherent ranges, significant turnover and sharp limits between local communities. All other things equal, a Gleasonian structure is distinguished by the absence of clear boundaries between local communities.
 Questions: The structure of a scrubland/semiarid/xeric metacommunity changes 23 years after its first characterization? Do environment and spatial variables determine the metacommunity structure?
 Species studied: 104 perennial-plant species.
 Study site and dates: Zapotitlán semi-arid valley, Puebla, in 1980 and 2003.
 Methods: Metacommunity structure and its relationship to environmental (edaphic) and spatial (altitude, slope and geographical location) variables were analyzed using data from the two historic surveys.
 Results: In 1980 a Clementsian structure was determined, which remained unchanged after 23 years. The importance of environmental filters decreased from 1980 to 2003.
 Conclusions: The prediction that, due to stochastic dispersion of propagules, the metacommunity would tend toward a Gleasonian structure was not fulfilled. There was no evidence for homogenization, although local tetechera communities (with dominance of the giant columnar cactus Cephalocereus tetetzo) had been invaded and transformed into shrubland communities. Local communities and the metacommunity should be monitored continuously to understand of the long-term structuration of these systems.

Changes in the roles of spatial and environmental processes in the structuring of rodent metacommunities

We studied the role of spatial (regional) and environmental (local) processes in the structuring of rodent metacommunities in three contiguous ecoregions that share the same species pool. The two northern ecoregions are mainly affected by anthropogenic processes (agriculture and urbanization) while the southern one is mainly affected by natural processes (flood and drought pulses). Local communities were described based on the analysis of 77 samples of barn owl pellets. To identify which processes (patch dynamics, species sorting, mass effect or neutral theory) structure each metacommunity we evaluated the percentage of variance explained by space (spatial arrangement of communities) and environment (topography, climate and land cover) in three Variation Partitioning Redundancy Analyses. The percentage of variance in rodent metacommunities composition explained by space and environment was between 38 and 61%, and was significant in all three analyses. The pure space fraction was significant for two of the three ecoregions, while the pure environmental fraction was significant for all three ecoregions. The processes that structure rodent metacommunities change across the region. In all three ecoregions the species sorting played a key role, while, mass effect was a structuring factor for northern metacommunities. These results can be explained by species-specific dispersal characteristics and environmental filtering.

The relative influence of the environment, land use, and space on the functional and taxonomic structures of phytoplankton and zooplankton metacommunities in tropical reservoirs

Disentangling the effects of space and the environment on species distribution is one of the current goals of ecology and biogeography. In this study, we aimed to determine the relative influence of local, spatial (directional and non-directional), and land-use predictors on the taxonomic and functional trait compositions of phytoplankton and zooplankton assemblages. We collected data from 25 sampling points within shallow artificial water reservoirs in the central-western region of Brazil. This study was conducted in an area with a small spatial extent (<50 km between sampling sites) and in a reservoir of a typical hierarchical branching river network. The explanatory variables included 8 environmental features, 2 land-use predictors, and 2 spatial proxies (non-directional and directional spatial eigenvectors). We used a partial redundancy analysis to evaluate the relative influence of each predictor. Only spatial predictors, mainly directional, were important in explaining the phytoplankton and zooplankton metacommunity structure (functional and taxonomic). According to the metacommunity perspective, our results indicated that the phytoplankton and zooplankton metacommunities could be classified as species sorting with high dispersal, that is, a mass-effect perspective. We expected to see mass-effect processes in our study area, in which highly-dispersive species occur in a small-scale, highly-connected area where upstream reservoirs act as sources for dispersing species downstream. Moreover, some functional traits and morphofunctional attributes of phytoplankton (presence of flagella and small size) and zooplankton (suspensivore, carnivore, and littoral habitats) were associated with an increase in dispersal. Finally, this study contributes to the understanding of how environment, space, and land-use components structure plankton metacommunities.

Effects of spatial distance, physical barriers, and habitat on a stream fish metacommunity

Metacommunity structure depends on environmental and spatial factors. Stream fishes are constrained to disperse within dendritic networks and waterfalls and other barriers add resistance to species dispersal. We evaluated the importance of environmental and spatial effects on fish metacommunity composition, adopting different models of spatial distance: overland, watercourse, resistance (physical barriers), cost distance (watercourse resistance), and asymmetrical dispersal (considering flow direction). Fishes were sampled in 31 riffle sites of a small subtropical basin of southern Brazil (~ 250 km2 effective study area). Using redundancy analysis (RDA) and variance partitioning, we found the best model was the one including flow direction weighted by watercourse distance plus environmental variables (overall adj-R2 = 0.42). However, the explanation of fish composition was greatly improved by weighting spatial distance by stream channel sinuosity or height of barriers. Reach slope and width were the two significant environmental variables. Our study supports that dispersal, in addition to environmental factors, affects stream fish metacommunity even in a watershed of small spatial extent. Detecting spatial effects in a small watershed depends on considering realistic watershed features that affect fish dispersal in drainage networks such as waterfalls and other physical barriers, and distance along the watercourse and flow direction.

Spatial factors control the structure of fish metacommunity in a Mediterranean intermittent river

While in recent years intermittent rivers and ephemeral streams (IRES) are receiving increasing attention from ecologists, fish metacommunity dynamics have drawn less attention than other taxa. In this study, we explored fish metacommunity dynamics at a Mediterranean intermittent river (Evrotas River, Southern Greece) to unravel which factors (i.e. environmental and/or spatial) best explain fish metacommunity structure. To this end, we investigated fish compositional structure in perennial and intermittent sites distributed longitudinally along the river during the low flow period of a wet year (2009), following two extremely dry years (2007-2008). To disentangle the effects of spatial control versus local environmental variables in shaping fish metacommunities, asymmetric eigenvector map (AEM) analysis designed to model directional spatial processes, and variation partitioning were applied. Our results point out that fish metacommunity structure was largely explained by spatial (53%) rather than local environmental (3%) factors, whereas only a small fraction (16%) was explained by the spatial structure of the environmental variables. Irrespectively of their hydrological regime, neighboring sites harbored similar fish communities, with a strong longitudinal gradient in local community structure, suggesting a homogenizing effect of dispersal. Local environmental factors were not associated with shifts in community structure. These results differ markedly from those drawn from most perennial aquatic ecosystems, where environmental factors are prevailing. Overall, this study emphasizes the need to account for regional processes in IRES and adopt a metacommunity perspective for guiding conservation and restoration efforts, by promoting the connectivity within the river network and the protection of perennial refugia.

Stream fish metacommunity organisation across a Neotropical ecoregion: The role of environment, anthropogenic impact and dispersal-based processes.

Understanding how assemblages are structured in space and the factors promoting their distributions is one of the main goals in Ecology, however, studies regarding the distribution of organisms at larger scales remain biased towards terrestrial groups. We attempt to understand if the structure of stream fish metacommunities across a Neotropical ecoregion (Upper Paraná—drainage area of 820,000 km2) are affected by environmental variables, describing natural environmental gradient, anthropogenic impacts and spatial predictors. For this, we obtained 586 sampling points of fish assemblages in the ecoregion and data on environmental and spatial predictors that potentially affect fish assemblages. We calculated the local beta diversity (Local Contribution to Beta Diversity, LCBD) and alpha diversity from the species list, to be used as response variables in the partial regression models, while the anthropogenic impacts, environmental gradient and spatial factors were used as predictors. We found a high total beta diversity for the ecoregion (0.41) where the greatest values for each site sampled were located at the edges of the ecoregion, while richer communities were found more centrally. All sets of predictors explained the LCBD and alpha diversity, but the most important was dispersal variables, followed by the natural environmental gradient and anthropogenic impact. However, we found an increase in the models’ prediction power through the shared effect. Results suggest that environmental filters (i.e. environmental variables such as climate, hydrology and anthropogenic impact) and dispersal limitation together shape fish assemblages of the Upper Paraná ecoregion, showing the importance of using multiple sets of predictors to understand the processes structuring biodiversity distribution.

Elements of metacommunity structure of diatoms and macroinvertebrates within stream networks differing in environmental heterogeneity

AbstractAimIdealized metacommunity structures (i.e. checkerboard, random, quasi‐structures, nested, Clementsian, Gleasonian and evenly spaced) have recently gained increasing attention, but their relationships with environmental heterogeneity and how they vary with organism groups remain poorly understood. Here, we tested two main hypotheses: (a) gradient‐driven patterns (Clementsian and Gleasonian) occur frequently in heterogeneous environments and (b) small organisms (here, diatoms) are more likely to exhibit gradient‐driven patterns than large organisms (here, macroinvertebrates).LocationStreams in three regions in China.TaxonDiatoms and macroinvertebrates.MethodsThe stream diatom and macroinvertebrate data, as well as the environmental data collected from the same set of sites were used to examine the idealized metacommunity structures via the elements of the metacommunity structure (EMS; coherence, turnover and boundary clumping) analysis in three regions. We extended the traditional EMS approach by ordering sites along known environmental gradients.ResultsWe found that Clementsian structure with high degrees of coherence and turnover, and significantly positive clumping was typically observed in the high‐heterogeneity regions, whereas randomness was prevalent in the low‐heterogeneity region. Macroinvertebrates exhibited clearer Clementsian structures compared with diatoms, while diatoms showed more randomness compared with macroinvertebrates, indicating a stronger role of environmental filtering for macroinvertebrates than diatoms. In most cases, the results of the more novel EMS approach differed from the results of the traditional EMS technique.Main conclusionsOur results suggested that the occurrence of different metacommunity structures may be related with the degree of regional environmental heterogeneity. However, diatom metacommunities were more random than those of macroinvertebrate, and such an unexpected result may result from different dispersal abilities between the two organism groups. In addition, we found that the novel EMS approach increased power in discerning metacommunity structure in comparison to the traditional EMS technique.

Biofilms Provide New Insight into Pesticide Occurrence in Streams and Links to Aquatic Ecological Communities.

Streambed sediment is commonly analyzed to assess occurrence of hydrophobic pesticides and risks to aquatic communities. However, stream biofilms also have the potential to accumulate pesticides and may be consumed by aquatic organisms. To better characterize risks to aquatic life, the U.S. Geological Survey Regional Stream Quality Assessment measured 93 current-use and 3 legacy pesticides in bed sediment and biofilm from 54 small streams in California across a range of land-use settings. On average, 4 times as many current-use pesticides were detected in biofilm at a site (median of 2) as in sediment (median of 0.5). Of 31 current-use pesticides detected, 20 were detected more frequently in biofilm than in sediment and 10 with equal frequency. Pyrethroids as a class were the most potentially toxic to benthic invertebrates, and of the 9 pyrethroids detected, 7 occurred more frequently in biofilm than sediment. We constructed general additive models to investigate relations between pesticides and 6 metrics of benthic community structure. Pesticides in biofilm improved fit in 4 of the 6 models, and pesticides in sediment improved fit in 2. The results indicate that the sampling of stream biofilms can complement bed-sediment sampling by identification of more current-use pesticides present and better estimation of ecological risks.

Phytoplankton Community Composition Determined From Co-variability Among Phytoplankton Pigments From the NAAMES Field Campaign

Analysis of phytoplankton chemotaxonomic markers from high performance liquid chromatography (HPLC) pigment determination is a common approach for evaluating phytoplankton community structure from ocean samples. Here, HPLC phytoplankton pigment concentrations from samples collected underway and from CTD bottle sampling on the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) are used to assess phytoplankton community composition over a range of seasons and environmental conditions. Several data-driven statistical techniques, including hierarchical clustering, Empirical Orthogonal Function, and network-based community detection analyses, are applied to examine the associations between groups of pigments and infer phytoplankton communities found in the surface ocean during the four NAAMES campaigns. From these analyses, five distinguishable phytoplankton community types emerge based on the associations of phytoplankton pigments: diatom, dinoflagellate, haptophyte, green algae, and cyanobacteria. We use this dataset, along with phytoplankton community structure metrics from flow cytometric analyses, to characterize the distributions of phytoplankton biomarker pigments over the four cruises. The physical and chemical drivers influencing the distribution and co-variability of these five dominant groups of phytoplankton are considered. Finally, the composition of the phytoplankton community across the onset, accumulation, and decline of the annual phytoplankton bloom in a changing North Atlantic Ocean is compared to historical paradigms surrounding seasonal succession.

Host patch traits have scale‐dependent effects on diversity in a stickleback parasite metacommunity

Many metacommunities are distributed across habitat patches that are themselves aggregated into groups. Perhaps the clearest example of this nested metacommunity structure comes from multi‐species parasite assemblages, which occupy individual hosts that are aggregated into host populations. At both spatial scales, we expect parasite community diversity in a given patch (either individual host or population) to depend on patch characteristics that affect colonization rates and species sorting. But, are these patch effects consistent across spatial scales? Or, do different processes govern the distribution of parasite community diversity among individual hosts, versus among host patches? To answer these questions, we document the distribution of parasite richness among host individuals and among populations in a metapopulation of threespine stickleback Gasterosteus aculeatus. We find some host traits (host size, gape width) are associated with increased parasite richness at both spatial scales. Other patch characteristics affect parasite richness only among individuals (sex), or among populations (lake size, lake area, elevation and population mean heterozygosity). These results demonstrate that some rules governing parasite richness in this metacommunity are shared across scales, while others are scale‐specific.

Consistent metacommunity structure despite inconsistent drivers of assembly at the continental scale.

A fundamental goal of community ecology is to understand the drivers of community assembly and diversity. Local factors acting on community assembly are typically related to environmental conditions while regional factors are typically related to dispersal. Previous research has not consistently demonstrated the importance of local or regional factors, but this is likely because these factors act in concert and not in isolation. Studies that simultaneously integrate local and regional factors into analyses of community assembly can be a useful avenue to further our understanding of this core concept in community ecology. Here, we aimed to identify metacommunity structure and diversity and the local and regional drivers of community assembly at the continental scale. We evaluated metacommunity structure and drivers of assembly of macroinvertebrate communities in 941 rivers and streams nested within nine ecoregions distributed across the conterminous United States. Pattern-based metacommunity analyses and boosted regression tree techniques were used to (a) assign metacommunity structures and (b) identify the environmental, landscape and network drivers of assembly. We also evaluated how biodiversity scaled across hierarchical levels and varied among ecoregions. Metacommunity structures were consistent for the conterminous United States and each of the nine ecoregion subsets, with each ecoregional metacommunity displaying a Clementsian structure. Environmental variables were the predominant drivers of assembly, suggesting the importance of species sorting and environmental filtering on community structure; however, the identity of the most influential environmental variables differed among ecoregions and suggested hierarchical filtering on assembly. Partitioned diversity was found to be lower at the local and ecoregional levels, but turnover in diversity among ecoregions was higher than expected. Our results demonstrate contingencies in community assembly, notwithstanding consistency in metacommunity structure and support the importance of environmental control over community assembly and biodiversity. Moreover, biodiversity at the continental scale is likely maintained through this inherent variation in the drivers of assembly and concomitant changes in community composition among ecoregions. We suggest that further work should evaluate the assembly of other facets of community structure and the underlying mechanisms of the contingency in assembly drivers.

Environmental and spatial influences on stream zooplankton communities of the Brazilian Cerrado

The integration of species dispersal dynamics with environmental predictors has become indispensable to understanding the pattern of communities’ organization. Thus, we evaluated the relative importance of environmental and spatial variables on the structure of zooplankton metacommunities in 20 Brazilian Cerrado streams. In multivariate models, we used the Partial Redundancy Analysis and found that space is mostly responsible for determining the structuring of the zooplankton community. However, the environmental predictors did not present a significant explanation. Our results indicate that space might act as a co-variable that explains and filters spatial variation when tested between species distributions and environmental factors. We understand that metacommunity studies with stream zooplankton demand more attention because space explained only a minor part of the variation of the zooplankton community. Therefore, advances in the research for environmental variables that can predict zooplankton in the Cerrado streams are important to understand the effects of anthropogenic change on aquatic communities.