Explained Community Variation Research Articles

Effects of tidal cycles on the variability of microbial communities in a semiclosed bay

Shallow sediment-water plays an important role in transforming organic matter in estuaries. As a shallow bay often flanks a large estuary, the estuarine water enters the shallow bay during flood tides and exits during ebb tides. The inundation between flood and ebb tides in the shallow bay serves as an incubation of the bay water and sediment. However, little is known about the effects of tidal cycles on microbial diversity and biogeochemical processes. In Tangjiawan Bay, which is a small bay located on the west side of the Pearl River estuary, we examined changes in microbial diversity and environmental factors by collecting surface water samples between floods and ebbs. Using high-throughput sequencing targeting 16S and 18S rRNA genes, the results indicated that between floods and ebbs, the community composition of bacteria and eukaryotes differed significantly, the alpha diversity of bacteria and eukaryotes differed significantly, with floods harboring higher diversity. The analysis of RDA suggested that salinity and TOC were important in explaining community variation in both bacteria and eukaryotes. Moreover, the co-occurrence networks between bacteria and eukaryotes showed higher negative relationships in ebbs (83.87%) than in floods (64.29%), suggesting increased interactions between bacteria and eukaryotes during ebbs as the water was incubated in the bay. These findings demonstrated the dynamics of biogeochemical processes of nutrients and plankton communities in the shallow bay and tidal cycles are a dominant driving force in regulating variability in phytoplankton and bacterial community and the sediment-water interface exchange. The results indicate that we should not overlook at the importance of shallow water column fringing the shore lines.

Environmental filtering, spatial processes and biotic interactions jointly shape different traits communities of stream macroinvertebrates

The metacommunity concept has been widely used to explain the biodiversity patterns at various scales. It considers the influences of both local (e.g., environmental filtering and biotic interactions) and regional processes (e.g., dispersal limitation) in shaping community structures. Compared to environmental filtering and spatial processes, the influence of biotic interactions on biodiversity patterns in streams has received limited attention. We investigated the relative importance of three ecological processes, namely environmental filtering (including local environmental and geo-climatic factors), spatial processes and biotic interactions (represented by interactions of macroinvertebrates and diatom), in shaping different traits of macroinvertebrate communities in subtropical streams, Eastern China. We applied variance partitioning to uncover the pure and shared effects of different ecological processes in explaining community variation. The results showed that environmental filtering, spatial processes, and biotic interactions jointly determined taxonomic and trait compositions of stream macroinvertebrates. Spatial processes showed a stronger influence in shaping stream macroinvertebrate communities than environmental filtering. The contribution of biotic interactions to explain variables was, albeit significant, rather small, which was likely a result of insufficient representation (by diatom traits) of trophic interactions associated with macroinvertebrates. Moreover, the impact of three ecological processes on macroinvertebrate communities depends on different traits, especially in terms of environmental filtering and spatial processes. For example, spatial processes and environmental filtering have the strongest effect on strong dispersal ability groups; spatial processes have a greater effect on scrapers than other functional feeding groups. Overall, our results showed that the integration of metacommunity theory and functional traits provides a valuable framework for understanding the drivers of community structuring in streams, which will facilitate the development of effective bioassessment and management strategies.

Convergence in floodplain pond communities indicates different pathways to community assembly

Disturbance can strongly influence ecosystems, yet much remains unknown about the relative importance of key processes (selection, drift, and dispersal) in the recovery of ecological communities following disturbance. We combined field surveys with a field experiment to elucidate mechanisms governing the recovery of aquatic macroinvertebrates in habitats of an alluvial floodplain following flood disturbance. We monitored macroinvertebrates in 24 natural parafluvial habitats over 60 days after a major flood, as well as the colonization of 24 newly-built ponds by macroinvertebrates over 45 days in the same floodplain. We examined the sources of environmental variation and their relative effects on aquatic assemblages using a combination of null models and Mantel tests. We also used a joint species distribution model to investigate the importance of primary metacommunity structuring processes during recovery: selection, dispersal, and drift. Contrary to expectations, we found that beta diversity actually decreased among natural habitats over time after the flood or the creation of the ponds, instead of increasing. This result was despite environmental predictors showing contrasting patterns for explaining community variation over time in the natural habitats compared with the experimental ponds. Flood heterogeneity across the floodplain and spatial scale differences between the experimental ponds and the natural habitats seemingly constrained the balance between deterministic and stochastic processes driving the ecological convergence of assemblages over time. While environmental selection was the dominant structuring process in both groups, biotic interactions also had a prominent influence on community assembly. These findings have profound implications towards understanding metacommunity structuring in riverscapes that includes common linkages between disturbance heterogeneity, spatial scale properties, and community composition.

Influence of morphometric and geographic factors on plant community composition of temporary freshwater rockpools in the Maltese Islands

ABSTRACT We investigated the influence of 6 morphometric and geographic factors on the structure and composition of plant communities in 56 temporary freshwater rockpools from 7 pool landscapes in the Maltese Islands. The factors considered were water depth, sediment depth, surface area, shading, distance from the coast, and elevation above sea level. Coverage data for 30 plant taxa in 3 functional forms (aquatic, amphibious, and terrestrial) were collected during one hydrological cycle. The relationships between pool morphometry, pool location, and community composition were tested using multivariate analyses. The contribution of spatial variables to variation in community composition across pools was examined using principal coordinate analysis of neighbour matrices (PCNM). The results suggested that pool morphometry varied both within and across landscapes, reflected in similar differences in community composition. Moreover, 47.6% of the explained community variation in the whole dataset was contributed exclusively by space predictors, suggesting that pool “location” is an important determinant of community composition. The morphometric property that exerted the highest influence on the dominance of a given plant functional form was the pool surface area, with greater surface areas promoting the presence of amphibious species relative to obligate hydrophytes. Conversely, the presence of specific species was mainly controlled by water depth and sediment depth. The most influential predictors of community composition varied across landscape, suggesting that pool location can be an important determinant of community structure and composition, and pool morphometry would favour certain functional forms and species over others.

Pollution tolerance, flight capacity and natural history explain metacommunity structure in high-altitude stream insects

Abstract: Aim To test how different taxonomic and functional groups of aquatic insects from high-altitude streams respond to environmental and spatial gradients at multiple scales in Southeast of Brazil. Methods Specimens were collected in 26 high-altitude streams distributed over a gradient of previously defined environmental quality. The taxonomic identification was made at the genus level and the functional classification was based on traits of flight capacity and pollution tolerance compiled from specific literature. We obtained local in situ data (limnological, sediments, and organic matter), as well as calculated land use at the riparian and drainage basin scale. A variation partitioning approach was used to explain species composition based on different response matrices deconstructed by both taxonomic groups and functional traits. The explanatory matrices encompassed environmental variables at three spatial scales and spatial variables extracted from Principal Components of Neighbor Matrices analysis. A linear model was applied to verify the possible correlation between spatial and environmental components. Results The contribution of the spatial and environmental components varied strongly between taxonomic and functional groups. For taxonomic groups, the pure environmental component was more important for Odonata and Trichoptera, while spatial variables were more important for Diptera (non-Chironomidae) and Chironomidae, Coleoptera, Ephemeroptera, Plecoptera and Megaloptera. The sensitive groups with good flight capacity showed a greater environmental signature while the tolerant groups with low flight capacity had a greater spatial signature. Moreover, the important variables for explaining community variation were from different spatial scale (local, riparian and watershed) depending either on the analyzed taxonomic or on functional groups. However, a general effect of forests was found in several groups. Conclusions It is necessary to consider the joint effect of evolutionary natural history of groups, as well as their functional traits in the structuring of metacommunities, since only taxonomic resolutions may not be sufficient to detect assembly processes at multiple spatial scales.

Scale-specific drivers of kelp forest communities.

Identifying spatial scales of variation in natural communities and the processes driving them is critical for obtaining a predictive understanding of biodiversity. In this study, we focused on diverse communities inhabiting productive kelp forests on shallow subtidal rocky reefs in southern California, USA. We combined long-term community surveys from 86 sites with detailed environmental data to determine what structures assemblages of fishes, invertebrates and algae at multiple spatial scales. We identified the spatial scales of variation in species composition using a hierarchical analysis based on eigenfunctions, and assessed how sea surface temperature (SST), water column chlorophyll, giant kelp biomass, wave exposure and potential propagule delivery strength contributed to community variation at each scale. Spatial effects occurring at multiple scales explained 60% of the variation in fish assemblages and 52% of the variation in the assemblages of invertebrates and algae. Most variation occurred over broad spatial scales (>200km) consistent with spatial heterogeneity in SST and potential propagule delivery strength, while the latter also explained community variation at medium scales (65-200km). Small scale (1-65km) community variation was substantial but not linked to any of the measured drivers. Conclusions were consistent for both reef fishes and benthic invertebrates and algae, despite sharp differences in their adult mobility. Our results demonstrate the scale dependence of environmental drivers on kelp forest communities, showing that most species were strongly sorted along oceanographic conditions over various spatial scales. Such spatial effects must be integrated into models assessing the response of marine ecosystems to climate change.

Does isolation influence the relative role of environmental and dispersal‐related processes in stream networks? An empirical test of the network position hypothesis using multiple taxa

Abstract Quantifying the relative importance of how local (environmental or niche‐based) and regional (dispersal‐related or spatial) processes regulate the assembly of communities has become one of the main research avenues of community ecology. It has been shown that the degree of isolation of local habitats in the landscape may substantially influence the relative role of environmental filtering and dispersal‐related processes in metacommunities. Dendritic stream networks are unique habitats in the landscape, where more isolated upstream sites have been predicted to be primarily structured by environmental variables, while more central mainstem rivers by both environmental and spatial variables (hereafter the network position hypothesis, NPH). However, the NPH has almost exclusively been tested for stream macroinvertebrates, and therefore its predictions warrant confirmation from multiple taxa. We examined the validity of the NPH for benthic diatoms, macrophytes, macroinvertebrates and fish in the Pannon Ecoregion, Hungary. Following the NPH we predicted a clear dominance of environmental over spatial variables in headwaters, and a larger effect of spatial variables in rivers compared to headwaters. We tested these predictions using variance partitioning analyses separately for the different taxa in headwater and in riverine habitats. We found large differences in the explained community variance when the impact of environmental (physical and chemical) and spatial (overland and watercourse distance) variables for various taxa was studied. In general, total explained variance was lower for the more passively dispersing plant taxa than for animal taxa with more active dispersal in both streams and rivers. However, similar to other studies, the total explained variance was low for both headwater streams and rivers. Community structure of diatoms could be best explained by both environmental and spatial variables in streams, whereas their community structure could not be explained by either variable group in rivers. The significance of environmental and spatial variables depended on the distance measure (overland versus watercourse) in the case of macrophytes. Community structure of macroinvertebrates could be explained by environmental variables in streams and by both environmental and spatial variables in rivers. Moreover, variation was explained by different predictors when macroinvertebrate taxa were divided into flying and non‐flying groups, suggesting the importance of dispersal mode in explaining community variation. Finally, community structure of fishes could be explained by both environmental and spatial variables in streams and only by environmental variables in rivers. In conclusion, we found no clear evidence of the NPH in our multi‐taxa comparison. For example, while patterns in macroinvertebrate communities seem to support the NPH, those in fish communities run counter with the predictions of the NPH. This study thus shows that different taxa may behave differently to isolation effects in stream networks. We discuss alternatives in the interpretation of dispersal (or spatial) effects which may partly explain differences in the observed patterns from the NPH, and emphasise the need for further studies in unravelling the importance of isolation in stream metacommunity structuring.

Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change.

Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we expect a reduction in both environmental filtering and dispersal limitation, inducing a taxonomic homogenization of the aquatic fauna in glacierized catchments as well as the extinction of specialized species in headwater groundwater and glacier-fed streams, and consequently an irreversible reduction in regional diversity.

Are the landscape‐level drivers of water column and surface sediment diatoms different?

Summary Threats to biodiversity are fostering new collaboration between aquatic ecologists and palaeolimnologists, who have traditionally asked ecological questions on different time scales. While the differences between surface sediment and water column or snapshot sampling are well understood, less so are the consequences of comparing the predominant drivers of aquatic assemblages resulting from these two types of sampling. Using diatom data from the 2007 USEPA National Lakes Assessment (NLA) program (468 lakes), we compared the main environmental and spatial drivers of diatom community composition between samples derived from the water column and surface sediments. We hypothesised that, in explaining community variation across the conterminous United States, the effect of environment would be stronger in diatom assemblages preserved in surface sediments because of the inclusion of benthic members and temporal integration. We used a combination of ordination overlays and variation partitioning to examine differences in community drivers between palaeolimnological (surface sediment) and water column sampling. We found that these two types of sampling were significantly correlated with respect to the drivers of community composition in addition to having congruent patterns of ordination. Congruency between sampling methods further increased when the water column data were temporally integrated and may be explained by variation in seasonally dynamic taxa. To our knowledge, this is the first study that has tested for differences in environmental structuring patterns between palaeolimnological and water column samples using such a highly replicated and landscape‐level approach. On the basis of our results, we encourage ecologists to consider the joint analysis of these two types of data sets where data are available.

The effects of local, buffer zone and geographical variables on lake plankton metacommunities

Lake plankton metacommunities are affected by their surrounding multidimensional landscape. Hence, understanding mechanisms shaping lake plankton communities requires considering not only local or geographical drivers, but also drivers at buffer zone level, indicating fluxes of nutrients and organic compounds. We investigated the effects of local, buffer zone (characterised via remote sensing) and geographical level variables on the phyto- and zooplankton community composition in 100 lakes distributed over five watersheds in Finland. We examined the community variation at two spatial scales using redundancy analysis with variation partitioning. Among watersheds, phyto- and zooplankton showed a small spatial imprint in their metacommunity structure, suggesting weak dispersal limitation. Environmental drivers explained negligible shares of the community variation, indicating weak species sorting. However, within single watersheds, larger fractions of the variation in communities were explained by the effects of multi-scale variables, suggesting that communities may be structured by species sorting and mass effects. Groups of variables exerted a relatively equal influence on the community composition. Including buffer zone variables into models increased the explained community variation by one-third. Due to the unique effects of the buffer zone on plankton composition, remotely sensed buffer zone variables may serve as useful proxies in analyses of lake plankton metacommunities.

Community Structure of Aquatic Insects in the Karstic Jadro River in Croatia

This study focused on the aquatic insect community in the longitudinal gradient and temporal scales of the Jadro River. The river was sampled for a period of ten years (2000–2010), four times per year through the various seasons, along the river course. Sampling stations were selected in the upper, middle, and downstream parts of the river. A total of 21,852 specimens of aquatic insects belonging to six orders were obtained. The species determination confirmed 27 different species in the river. The data were analyzed by the multivariate methodologies of correspondence analysis and cluster analysis (unweighted pair group method with arithmetic mean) using the similarity index of Morosita for all ten years. Canonical correspondence analysis was applied to the data to check which of the mesured physicochemical variables significantly explained community variation. According to those data, significant variables for the upper station were water temperature and dissolved oxygen, and chlorides was the significant variable for the lower stations.

Community structure of aquatic insects in the karstic Jadro River in Croatia.

This study focused on the aquatic insect community in the longitudinal gradient and temporal scales of the Jadro River. The river was sampled for a period of ten years (2000– 2010), four times per year through the various seasons, along the river course. Sampling stations were selected in the upper, middle, and downstream parts of the river. A total of 21,852 specimens of aquatic insects belonging to six orders were obtained. The species determination confirmed 27 different species in the river. The data were analyzed by the multivariate methodologies of correspondence analysis and cluster analysis (unweighted pair group method with arithmetic mean) using the similarity index of Morosita for all ten years. Canonical correspondence analysis was applied to the data to check which of the mesured physicochemical variables significantly explained community variation. According to those data, significant variables for the upper station were water temperature and dissolved oxygen, and chlorides was the significant variable for the lower stations.

Relationships between Host Phylogeny, Host Type and Bacterial Community Diversity in Cold-Water Coral Reef Sponges

Cold-water coral reefs are known to locally enhance the diversity of deep-sea fauna as well as of microbes. Sponges are among the most diverse faunal groups in these ecosystems, and many of them host large abundances of microbes in their tissues. In this study, twelve sponge species from three cold-water coral reefs off Norway were investigated for the relationship between sponge phylogenetic classification (species and family level), as well as sponge type (high versus low microbial abundance), and the diversity of sponge-associated bacterial communities, taking also geographic location and water depth into account. Community analysis by Automated Ribosomal Intergenic Spacer Analysis (ARISA) showed that as many as 345 (79%) of the 437 different bacterial operational taxonomic units (OTUs) detected in the dataset were shared between sponges and sediments, while only 70 (16%) appeared purely sponge-associated. Furthermore, changes in bacterial community structure were significantly related to sponge species (63% of explained community variation), sponge family (52%) or sponge type (30%), whereas mesoscale geographic distances and water depth showed comparatively small effects (<5% each). In addition, a highly significant, positive relationship between bacterial community dissimilarity and sponge phylogenetic distance was observed within the ancient family of the Geodiidae. Overall, the high diversity of sponges in cold-water coral reefs, combined with the observed sponge-related variation in bacterial community structure, support the idea that sponges represent heterogeneous, yet structured microbial habitats that contribute significantly to enhancing bacterial diversity in deep-sea ecosystems.

Improving habitat models by incorporating pelagic measurements from coastal ocean observatories

As in all temperate coastal seas, habitats in the Mid-Atlantic Bight are spatially and temporally dynamic. Understanding how species respond to the dynamics of their environment is important for developing effective management strategies. In this study, we used canonical corre- spondence analysis (CCA) to determine habitat variables most important in explaining variation in fish and invertebrate communities sampled with bottom trawls. We also quantified the relative explanatory power of seabed habitat features, pelagic features measured in situ and pelagic fea- tures measured remotely, all of which can be used to explain species variability. Pelagic habitat features, most notably surface and bottom temperature and stratification, explained 76% of the community variation observed, compared with 40.9% explained by seabed features, mainly depth. Remotely sensed pelagic characteristics explained 46.9% of the variation that was accounted for and were redundant for features measured in situ; this suggests that remotely sensed features are representative of features measured in situ including certain subsurface fea- tures. Cross-shelf and seasonal variation in environmental variables were the major predictors of species distributions and accounted for 71.3% of the total explained community variation. We described the seasonal dynamics of important habitat gradients and the responses of species with different habitat requirements and geographic range distributions to those gradients. We argue that consideration of dynamic pelagic features in addition to slowly changing features is impor- tant. Dynamic approaches are necessary for effective management and ocean observing systems can be used to develop dynamic space-based management strategies.

Explaining Community Variation in Pesticide Use and Health Outcomes in Andean Ecuador

Explaining Community Variation in Pesticide Use and Health Outcomes in Andean Ecuador

ANT BIODIVERSITY IN SEMIARID LANDSCAPE MOSAICS: THE CONSEQUENCES OF GRAZING VS. NATURAL HETEROGENEITY

The conservation of biodiversity in landscape mosaics requires an under- standing of the impacts of human land use within mosaic elements and an evaluation of the biological uniqueness of different elements. We address these issues by examining patterns of ant diversity in three semiarid rangeland landscapes used predominantly for grazing. These landscapes lie along a regional gradient from shortgrass steppe through a transitional zone to desert grassland, along which climate and ant species composition vary. Within each landscape, we compared the effects of grazing and natural variation in soils and vegetation on ant diversity and community composition. Grazing had little effect on ant richness, diversity, or composition at the transitional zone or the desert grassland site, but ungrazed areas at the shortgrass steppe site had a higher overall richness and favored the abundance of some species. Some samples of saltbush (Atriplex canescens) shrubland were similar to ungrazed samples in richness and species composition. In both the tran- sitional zone and the desert grassland, creosotebush (Larrea tridentata)-dominated habitats harbored comparatively species-rich and distinct ant communities. In addition, mesquite (Prosopis glandulosa) coppice dunes at the desert grassland site favored the abundance of several species that were rare across the site. Canonical correspondence analysis revealed that variation in soil strength and texture best explained community variation at the short- grass steppe site, whereas soil texture and associated differences in shrub density best explained differences in composition at the transitional and desert grassland sites. The characterization of habitats based upon vegetation classification did not adequately reflect environmental variation that was important to ants in shortgrass steppe, but reflected im- portant soil textural variation in the transitional and desert grassland sites. These results suggest that ant conservation in these semiarid rangelands should emphasize patterns of variation in soil properties. The results add to a growing consensus that a variety of variables determined by the responses of several focal taxa may be needed to characterize biodiversity patterns.

Ant Biodiversity in Semiarid Landscape Mosaics: The Consequences of Grazing vs. Natural Heterogeneity

The conservation of biodiversity in landscape mosaics requires an understanding of the impacts of human land use within mosaic elements and an evaluation of the biological uniqueness of different elements. We address these issues by examining patterns of ant diversity in three semiarid rangeland landscapes used predominantly for grazing. These landscapes lie along a regional gradient from shortgrass steppe through a transitional zone to desert grassland, along which climate and ant species composition vary. Within each landscape, we compared the effects of grazing and natural variation in soils and vegetation on ant diversity and community composition. Grazing had little effect on ant richness, diversity, or composition at the transitional zone or the desert grassland site, but ungrazed areas at the shortgrass steppe site had a higher overall richness and favored the abundance of some species. Some samples of saltbush (Atriplex canescens) shrubland were similar to ungrazed samples in richness and species composition. In both the transitional zone and the desert grassland, creosotebush (Larrea tridentata)-dominated habitats harbored comparatively species-rich and distinct ant communities. In addition, mesquite (Prosopis glandulosa) coppice dunes at the desert grassland site favored the abundance of several species that were rare across the site. Canonical correspondence analysis revealed that variation in soil strength and texture best explained community variation at the shortgrass steppe site, whereas soil texture and associated differences in shrub density best explained differences in composition at the transitional and desert grassland sites. The characterization of habitats based upon vegetation classification did not adequately reflect environmental variation that was important to ants in shortgrass steppe, but reflected important soil textural variation in the transitional and desert grassland sites. These results suggest that ant conservation in these semiarid rangelands should emphasize patterns of variation in soil properties. The results add to a growing consensus that a variety of variables determined by the responses of several focal taxa may be needed to characterize biodiversity patterns.