Changes In Assemblages Research Articles

Drivers of decadal-scale temporal change in epibenthic megafaunal assemblages on scallop fishing grounds in the Bay of Fundy

The Bay of Fundy presents a unique environment with extreme tidal range, strong currents, fresh-water river discharge, and diverse habitats that are also experiencing temperature increase at a faster rate than most of the world ocean. There is extensive commercial fishing, valuable beds of sea scallop (Placopecten magellanicus) being found in several areas, some of which have been fished for over a century. Previously, comparative analyses of data collected in 1967 and 1997 found that the epibenthic assemblage on the Digby scallop ground had become more homogenous over the 30 year interval, while species composition had changed significantly. Attached, fragile, epifaunal taxa declined, whereas scavengers and robust burrowing filter-feeders increased in frequency of occurrence, consistent with the physical impacts of fishing gears as a primary driver. The Digby ground along with the commercial scallop grounds around Grand Manan Island and on Lurcher Shoal were resampled in 2007–08 to determine whether the changes off Digby had continued and if they were also occurring in other parts of the Bay. Significant spatial differences among the three scallop grounds were observed. The leafy bryozoan, Flustra foliacea, which was expanding its local range through time, was the leading contributor to the spatial dissimilarity. Depth and mean tidal current speed were the most important environmental variables influencing species composition. Significantly more taxa were recorded per station in 1997 than in 2007–08, while assemblage compositions were significantly different between the two periods. Decadal-scale declines in the frequencies of occurrence of attached, epibenthic filter-feeders, including the polychaete Filograna implexa, were observed, continuing the trend previously reported and consistent with on-going impacts of bottom-contact fishing gears, despite decades of trawling and dredging. However, other and unknown drivers were also implicated in the observed changes.

Urbanization causes shifts in the functional traits and foraging activity, and alters food particle size preference and biomass removal of urban-dwelling ants

Urbanization may lead to changes in assemblage and result in shifts in trait distribution from natural habitats to highly urbanized habitats. The shift in functional traits can affect ecosystem functions in urban areas. This study explored the foraging period of ants over 72 h and determined the relationship between the behavioral, morphological, and physiological traits of local foragers ants and environmental conditions in urban and forest sites. In addition, this study examined the ants’ ecosystem functions and compared it with that of their forest counterparts. Our results revealed that the foraging period of ants (i.e., Cardiocondyla sp.1, Monomorium chinense, Paratrechina longicornis, Pheidole megacephala, and Solenopsis sp.1) in urban areas peaked between 0900 and 1500 and that of some ants (i.e., Carebara diversa, P. megacephala, Pheidole fervens, Plagiolepis longwang, and Nylanderia sp.1) in forest areas was constant over time. For urban ants, a weak correlation was observed between foraging period and body size traits (i.e., Weber’s length and head width). This finding indicates that the major factor underlying the change in the foraging period might not be related to body size. Rather, the change may be attributed to synchronization between food availability and human activity (waste disposal; i.e., between 0900 and 1800). The shift in the functional traits of ants affects ecosystem functions in urban areas. In urban areas, although only one predatory ant species (P. megacephala) was sampled, its activity density was high. Most of these individuals were active during the daytime, indicating that the predatory behavior of ants in the novel urban environment has decreased temporally and is limited to the daytime. Urban ants tended to choose smaller food particles, whereas forest ants preferred larger food particles and had a twofold higher food removal rate.

Changes in Coleopteran assemblages over a successional chronosequence in a Mexican tropical dry forest.

Coleopterans are the most diverse animal group on Earth and constitute good indicators of environmental change. However, little information is available about Coleopteran communities' responses to disturbance and land-use change. Tropical dry forests have undergone especially extensive anthropogenic impacts in the past decades. This has led to mosaic landscapes consisting of areas of primary forest surrounded by pastures, agricultural fields and secondary forests, which negatively impacts many taxonomic groups. However, such impacts have not been assessed for most arthropod groups. In this work, we compared the abundance, richness and diversity of Coleopteran morphospecies in four different successional stages in a tropical dry forest in western Mexico, to answer the question: How do Coleopteran assemblages associate with vegetation change over the course of forest succession? In addition, we assessed the family composition and trophic guilds for the four successional stages. We found 971 Coleopterans belonging to 107 morphospecies distributed in 28 families. Coleopteran abundance and richness were greatest for pastures than for latter successional stages, and the most abundant family was Chrysomelidae, with 29% of the individuals. Herbivores were the most abundant guild, accounting for 57% of the individuals, followed by predators (22%) and saprophages (21%) beetles. Given the high diversity and richness found throughout the successional chronosequence of the studied tropical dry forest, in order to have the maximum number of species associated with tropical dry forests, large tracts of forest should be preserved so that successional dynamics are able to occur naturally.

High-Resolution Lacustrine Records of the Late Holocene Hydroclimate of the Sikhote-Alin Mountains, Russian Far East.

There is little information about moisture changes in different altitudinal belts in mountainous regions of the southern Russian Far East. We present ecological and taxonomic compositions of the diatom flora and identify the botanical composition of peat in small mountain lake/mire complexes located in the Central Sikhote-Alin Mountains, within large landslides on the paleovolcanic slopes. Frequent changes in diatom assemblages and peat-forming plants indicate unstable hydroclimatic conditions with varying degrees of wet and dry conditions up to the overgrowth of the lakes. Frequent change in sphagnum mosses with different trophic preferences was identified. The chronology is based on 11 radiocarbon dates. Accumulation rates reached 1.7-1.9 mm/year, and the temporal resolution for the reconstructions was up to 30-40 yr. The tendencies of lake evolution depended on different scale hydroclimatic changes over the last 4400 yr. The most detailed data for the last 2600 yr were obtained from the Nizhnee Lake sequence, which is more sensitive to climatic changes. The main reason for the change in the hydrological regime of the lakes was variations in precipitation during short-term climatic changes. The sediment record of moisture fluctuations is relatively well correlated with regional patterns reflecting summer monsoon intensity and cyclogenesis activity.

Pervasive impacts of climate change on the woodiness and ecological generalism of dry forest plant assemblages

Abstract Climate emergency is a significant threat to biodiversity in the 21st century, but species will not be equally affected. In summing up the responses of different species at the local scale, we can assess changes in the species quantity and composition of biotic assemblages. We used more than 420K curated occurrence records of 3060 plant species to model current and future patterns of plant species distribution in one of the world's largest tropical dry forests—the Caatinga. While allowing different model extrapolation scenarios, we estimated potential changes in the species richness and composition of dryland plant assemblages in response to projected climate change, and assessed how the ecological generalism and woodiness of plant assemblages can be impacted by the climate crisis. More than 99% of plant assemblages were projected to lose species by 2060, with biotic homogenisation—the decrease in spatial beta diversity—forecasted in 40% of the Caatinga. The replacement of narrow‐range woody species by wide‐range non‐woody ones should impact at least 90% of Caatinga plant assemblages. The exacerbated species loss in the dryland plant assemblages was connected to the heterogenisation and homogenisation of biotic assemblages. Still, the magnitude of climate change impacts on ecological generalism and woodiness patterns of dryland plant assemblages differ according to the direction of the biotic change process. Synthesis. The future increase in aridity will change the patterns of woodiness and ecological generalism of tropical dry forest plant assemblages by decreasing vegetation diversity and complexity. The projected biotic changes in dryland plant assemblages indicate the erosion of ecosystem services linked to biomass productivity and carbon storage. We highlight the importance of long‐term conservation planning for maintaining tropical dry forests.

The effect of seawater on the phase assemblage of hydrated cement paste: A study on PC, CAC and CSA

The present study investigates the effect of seawater on hydration of Portland cement (PC), calcium aluminate cement (CAC) and calcium sulfoaluminate cement (CSA). The cement samples were exposed to seawater at various curing ages and were characterized using thermogravimetric analysis and X-ray diffraction. The phase assemblages of the exposed samples are then compared with the unexposed samples to observe the changes that occur during the exposure to seawater. The exposure to seawater mainly affected the AFm phases in hydrated cements. The chloride uptake results in the formation of Friedel's salt. Monocarbonate, hemicarbonate and C2AH8 are the primary chloride binding phases in PC, CSA and CAC, respectively. Another observed effect of seawater exposure is the stabilization and formation of more ettringite in PC and CSA due to sulfate ions. The findings from these experiments are essential to better understand the phase assemblage changes that occur in structures exposed to marine environments.

Effect of the alien octocoral Carijoa riisei on benthic fauna assemblages on natural and artificial substrates

AbstractCarijoa riisei is an invasive octocoral whose dispersal in the tropics has increased considerably in recent years. This study evaluated the changes in the benthic fauna assemblages associated with C. riisei growing on rocks from a sea port and on the metal of a submerged shipwreck in the bays of Manzanillo, Colima, in the Mexican Central Pacific. Quarterly samples were collected between April 2021 and January 2022, with the presence or absence of C. riisei. The effect of C. riisei on the benthic fauna according to the type of substrate was evaluated with PERMANOVA models. The presence of C. riisei was found to affect taxonomic diversity. In the absence of the octocoral, 209 species were recorded, whereas in its presence, 190 were found. The decline of taxa occurred at the level of families, genera, and species. The interaction of the presence/absence of C. riisei and substrate generated significant changes in the Shannon (1D) and Simpson (2D) diversity indexes. However, the presence of C. riisei coincided with higher abundances of Ophiothela mirabilis, Ericthonius brasiliensis, and Pseudobranchiomma schizogenica. In conclusion, the snowflake coral favors the dominance of some species and reduces the biological diversity of several taxa, mainly mollusks, polychaetes, sipunculids, and anthozoans, generating significant changes in the structure of benthic communities. This study highlights the need to evaluate species composition in areas where the octocoral grows, to determine whether its presence has an ecological impact and whether control measures are required.

On the varied impact of the Storegga tsunami in northwest Scotland

ABSTRACTIn this paper we evaluate new data and those from previous studies in northwest Scotland and perform a modelling study to test the hypothesis that the Storegga tsunami (submarine slope failure off the continental shelf of Central Norway dated to 8120–8175 bp) impacted this region. The model used is a 2D non‐linear, non‐conservative, Shallow Water Equation solver incorporating inundation and realistic glacial isostatic adjustment‐corrected palaeobathymetry, with horizontal resolution down to 30 m at sites of interest. The 15 coastal study sites analysed range from south of the Isle of Skye to Assynt. We predict run‐up between 2.7 and 9.4 m above contemporaneous mean tide level across the region, with the highest on the west coast of the Outer Hebrides, the east coast of Skye and at the head of long sea lochs east of Skye. We re‐evaluate evidence from previously studied open coastal marshes, isolation basins and barrier locations for the tsunami and suggest that in many locations the Storegga tsunami is the most likely cause of erosion, deposition and changes in microfossil assemblages in the early Holocene. The predictions of wave height and inundation produced by the tsunami modelling fit well with the range of available field evidence in the region. We predict significant wave heights at least as far south as Mull on the west coast.

Drivers of the changing abundance of European birds at two spatial scales.

Detecting biodiversity change and identifying its causes is challenging because biodiversity is multifaceted and temporal data often contain bias. Here, we model temporal change in species' abundance and biomass by using extensive data describing the population sizes and trends of native breeding birds in the United Kingdom (UK) and the European Union (EU). In addition, we explore how species' population trends vary with species' traits. We demonstrate significant change in the bird assemblages of the UK and EU, with substantial reductions in overall bird abundance and losses concentrated in a relatively small number of abundant and smaller sized species. By contrast, rarer and larger birds had generally fared better. Simultaneously, overall avian biomass had increased very slightly in the UK and was stable in the EU, indicating a change in community structure. Abundance trends across species were positively correlated with species' body mass and with trends in climate suitability, and varied with species' abundance, migration strategy and niche associations linked to diet. Our work highlights how changes in biodiversity cannot be captured easily by a single number; care is required when measuring and interpreting biodiversity change given that different metrics can provide very different insights. This article is part of the theme issue 'Detecting and attributing the causes of biodiversity change: needs, gaps and solutions'.

Taxonomical and functional diversity dynamics of conspicuous echinoderms in the northeastern tropical Pacific over a decade

Understanding what determines spatio-temporal changes in echinoderm assemblages from an integrative perspective that considers biodiversity, species evenness, and species’ niches could permit superior community-scale characterizations of habitat resilience to disturbance. Such an approach was taken herein by tracking a Central Mexican Pacific echinoderm assemblage between 2012 and 2021, and higher richness, diversity, evenness, and functional entity counts were associated with more heterogeneous benthic assemblages. Echinoderm taxonomic composition was influenced by ENSO events, with higher functional diversity found during La Niña events. Conservation strategies should focus on species with unique functional traits to maintain the balance of coral community functionality.

Anthropogenic stressor impacts on hypolimnetic dissolved oxygen in Lake Erie: A chironomid-based paleolimnological assessment

The central basin of Lake Erie is annually subject to hypolimnetic hypoxia, which affects biochemical processes and aquatic biota. Since European settlement, water quality in Lake Erie has degraded due to land-use changes within its catchment, cultural eutrophication, climate change, and the effects of invasive species. As limnological monitoring data for Lake Erie are largely unavailable prior to the 1970s, paleolimnological methods were used to infer long-term trends in hypolimnetic dissolved oxygen. Changes in lake water quality affect benthic community composition, and those communities can be used as indicators of long-term environmental changes, particularly those that affect hypolimnetic oxygen concentrations. Chironomid subfossil remains preserved in dated sediment cores indicated that the hypolimnion of the central basin was exhibiting low oxygen conditions prior to major Euro-American settlement impacts, and it has been mesotrophic to eutrophic since ∼1850. The disappearance of oxic-type taxa and a transition towards anoxic-tolerant chironomid communities by the 1950s suggest that the severity and duration of hypolimnetic anoxia has increased in recent decades. Variance partitioning analysis (VPA) indicated that both land use and climate variables were significant drivers of these changes in chironomid assemblages in the central basin.

Increasing stability of a native freshwater fish assemblage following flow rehabilitation.

Stream restorations are increasingly critical for managing and recovering freshwater biodiversity in human-dominated landscapes. However, few studies have quantified how rehabilitative actions promulgate through aquatic communities over decades. Here, a long-term dataset is analyzed for fish assemblage change, incorporating data pre- and post-restoration periods, and testing the extent to which native assemblage stability has increased over time. In the late 1950s, a large capacity dam was installed on Putah Creek (Solano County, CA, USA), which altered the natural flow regime, channel structure, geomorphic processes, and overall ecological function. Notably, downstream flows were reduced (especially during summer months) resulting in an aquatic assemblage dominated by warm-water nonnative species, while endemic native species subsisted at low levels as subordinates. A court-mediated Accord was ratified in 2000, providing a more natural flow regime, specifically for native and anadromous fishes in the stream. The richness of nonnative species decreased at every site following the Accord, while the richness of native species increased or stayed constant. At the three most upstream sites, native species richness increased over time and ultimately exceeded nonnative richness. Native assemblage recovery was strongest upriver, closer to flow releases and habitat restoration activities, and decreased longitudinally downstream. Rank-abundance curves through time revealed that, while species evenness was low throughout the study, dominance shifted from nonnative to native species in the upstream sites coincident with rehabilitation efforts. Mean rank shifts decreased following flow rehabilitation; thus the assemblage became increasingly stable over time following flow rehabilitation. Putah Creek's rehabilitation may represent a model for others interested in improving endemic freshwater communities in degraded ecosystems.

Winners and losers over a ½ century of change in crayfish assemblages of Wyoming, USA

Next article No AccessWinners and losers over a half century of change in crayfish assemblages of Wyoming, U.S.A.Braxton Moran Newkirk, Eric R. Larson, Andrew D. Walker, and Annika W. WaltersBraxton Moran Newkirk Search for more articles by this author , Eric R. Larson Search for more articles by this author , Andrew D. Walker Search for more articles by this author , and Annika W. Walters Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Freshwater Science Just Accepted Published on behalf of the Society for Freshwater Science Article DOIhttps://doi.org/10.1086/725318 HistoryAccepted March 29, 2023 © 2023 Society for Freshwater Science. All Rights reserved.PDF download Crossref reports no articles citing this article.

Elevated compositional change in plant assemblages linked to invasion.

Alien species are widely linked to biodiversity change, but the extent to which they are associated with the reshaping of ecological communities is not well understood. One possible mechanism is that assemblages where alien species are found exhibit elevated temporal turnover. To test this, we identified assemblages of vascular plants in the BioTIME database for those assemblages in which alien species are either present or absent and used the Jaccard measure to compute compositional dissimilarity between consecutive censuses. We found that, although alien species are typically rare in invaded assemblages, their presence is associated with an increase in the average rate of compositional change. These differences in compositional change between invaded and uninvaded assemblages are not linked to differences in species richness but rather to species replacement (turnover). Rapid compositional restructuring of assemblages is a major contributor to biodiversity change, and as such, our results suggest a role for alien species in bringing this about.

Effects of global change on bird and beetle populations in boreal forest landscape: An assemblage dissimilarity analysis

AbstractAimDespite an increasing number of studies highlighting the impacts of climate change on boreal species, the main factors that will drive changes in species assemblages remain ambiguous. We study how species community composition would change following anthropogenic and natural disturbances. We determine the main drivers of assemblage dissimilarity for bird and beetle communities.LocationCôte‐Nord, Québec, Canada.MethodsWe quantify two climate‐induced pathways based on direct and indirect effects on species occurrence under different forest harvest management scenarios. The direct climate effects illustrate the impact of climate variables while the indirect effects are reflected through habitat‐based climate change. We develop empirical models to predict the distribution of 127 and 108 species under climate‐habitat and habitat‐only models, respectively, over the next century. We analyse the regional and the latitudinal species assemblage dissimilarity by decomposing it into balanced variation in species occupancy and occurrence and occupancy and occurrence gradient.ResultsBoth pathways increased dissimilarity in species assemblage. At the regional scale, both effects have an impact on decreasing the number of winning species. Yet, responses are much larger in magnitude under mixed climate effects. Regional assemblage dissimilarity reached 0.77 and 0.69 under mixed effects versus 0.09 and 0.10 under indirect effects for beetles and birds, respectively, between RCP8.5 and baseline climate scenarios when considering forest harvesting. Latitudinally, assemblage dissimilarity increased following the climate conditions pattern.Main conclusionsThe two pathways are complementary and alter biodiversity, mainly caused by species turnover. Yet, responses are much larger in magnitude under mixed climate effects. Therefore, inclusion of climatic variables considers aspects other than just those related to forest landscapes, such as life cycles of animal species. Moreover, we expect differences in occupancy between the two studied taxa. This could indicate the potential range of change in boreal species concerning novel environmental conditions.

Climate-induced changes in fluvial ichnofossil assemblages of the Pennsylvanian–Permian Appalachian Basin

Climate-induced changes in fluvial ichnofossil assemblages of the Pennsylvanian–Permian Appalachian Basin

The photic-aphotic divide is a strong ecological and evolutionary force determining the distribution of ciliates (Alveolata, Ciliophora) in the ocean.

The bulk of knowledge on marine ciliates is from shallow and/or sunlit waters. We studied ciliate diversity and distribution across epi- and mesopelagic oceanic waters, using DNA metabarcoding and phylogeny-based metrics. We analyzed sequences of the 18S rRNA gene (V4 region) from 369 samples collected at 12 depths (0-1,000 m) at the Bermuda Atlantic Time-series Study site of the Sargasso Sea (North Atlantic) monthly for 3 years. The comprehensive depth and temporal resolutions analyzed led to three main findings. First, there was a gradual but significant decrease in alpha-diversity (based on Faith's phylogenetic diversity index) from surface to 1,000-m waters. Second, multivariate analyses of beta-diversity (based on UniFrac distances) indicate that ciliate assemblages change significantly from photic to aphotic waters, with a switch from Oligotrichea to Oligohymenophorea prevalence. Third, phylogenetic placement of sequence variants and clade-level correlations (EPA-ng and GAPPA algorithms) show Oligotrichea, Litostomatea, Prostomatea, and Phyllopharyngea as anti-correlated with depth, while Oligohymenophorea (especially Apostomatia) have a direct relationship with depth. Two enigmatic environmental clades include either prevalent variants widely distributed in aphotic layers (the Oligohymenophorea OLIGO5) or subclades differentially distributed in photic versus aphotic waters (the Discotrichidae NASSO1). These results settle contradictory relationships between ciliate alpha-diversity and depth reported before, suggest functional changes in ciliate assemblages from photic to aphotic waters (with prevalence of algivory and mixotrophy versus omnivory and parasitism, respectively), and indicate that contemporary taxon distributions in the vertical profile have been strongly influenced by evolutionary processes. Integration of DNA sequences with organismal data (microscopy, functional experiments) and development of databases that link these sources of information remain as major tasks to better understand ciliate diversity, ecological roles, and evolution in the ocean.

Long-term changes in unionid community in Kentucky Lake: Implications for understanding the effects of impoundment on river systems

Freshwater mussels are both critically important in their ecosystems and rapidly declining around the world. Damming is a key reason for this decline in many locations because it affects the flow and turbidity of river systems, leading to numerous detrimental effects on benthic communities. Although the ecological effects of impoundment have been well studied on timescales ranging from years to decades, the ecological effects of impoundment on longer (50–100 years) timescales are less well understood, with a key question being: how long after the building of dams and impoundments do we expect community structure to continue changing? In this study, we explore historical changes in the freshwater mussel assemblages in Kentucky Lake (dammed in 1944) using decades-long collections housed at Murray State University in combination with other historical records. After digitizing these collections and applying a robust rarefaction protocol to account for uneven sampling, we quantify changes in unionid assemblage structure alongside coeval water quality data collected through the Kentucky Lake Long-Term Monitoring Program. We find that subsampled richness exhibited declines after dam construction with losses among opportunistic taxa, channelization-tolerant taxa, and impoundment-intolerant taxa. We also find increases in the proportions of equilibrium taxa throughout the dataset. Overall, the assemblage composition reached an equilibrium by the year 2000 (50 years after impoundment). In concert, river water quality data show a decline in turbidity and increase in light penetration in the period 1988–2020. Although the geohistorical records treated in this study are patchy in time, we argue that they are nonetheless valuable and illustrate that freshwater ecosystems may serve as potential sites of restoration decades after anthropogenic disturbance. In turn, this emphasizes the importance of geohistorical collections to studying long-term changes in community structure and developing strategies for conservation and environmental remediation.

Observed and projected functional reorganization of riverine fish assemblages from global change.

Climate and land-use/land-cover change ("global change") are restructuring biodiversity, globally. Broadly, environmental conditions are expected to become warmer, potentially drier (particularly in arid regions), and more anthropogenically developed in the future, with spatiotemporally complex effects on ecological communities. We used functional traits to inform Chesapeake Bay Watershed fish responses to future climate and land-use scenarios (2030, 2060, and 2090). We modeled the future habitat suitability of focal species representative of key trait axes (substrate, flow, temperature, reproduction, and trophic) and used functional and phylogenetic metrics to assess variable assemblage responses across physiographic regions and habitat sizes (headwaters through large rivers). Our focal species analysis projected future habitat suitability gains for carnivorous species with preferences for warm water, pool habitats, and fine or vegetated substrates. At the assemblage level, models projected decreasing habitat suitability for cold-water, rheophilic, and lithophilic individuals but increasing suitability for carnivores in the future across all regions. Projected responses of functional and phylogenetic diversity and redundancy differed among regions. Lowland regions were projected to become less functionally and phylogenetically diverse and more redundant while upland regions (and smaller habitat sizes) were projected to become more diverse and less redundant. Next, we assessed how these model-projected assemblage changes 2005-2030 related to observed time-series trends (1999-2016). Halfway through the initial projecting period (2005-2030), we found observed trends broadly followed modeled patterns of increasing proportions of carnivorous and lithophilic individuals in lowland regions but showed opposing patterns for functional and phylogenetic metrics. Leveraging observed and predicted analyses simultaneously helps elucidate the instances and causes of discrepancies between model predictions and ongoing observed changes. Collectively, results highlight the complexity of global change impacts across broad landscapes that likely relate to differences in assemblages' intrinsic sensitivities and external exposure to stressors.

Dynamic variation of bacterial community assemblage and functional profiles during rice straw degradation.

Bacteria is one of the most important drivers of straw degradation. However, the changes in bacterial community assemblage and straw-decomposing profiles during straw decomposition are not well understood. Based on cultivation-dependent and independent technologies, this study revealed that the "common species" greatly contributed to the dynamic variation of bacterial community during straw decomposition. Twenty-three functional strains involved in straw decomposition were isolated, but only seven were detected in the high-throughput sequencing data. The straw decomposers, including the isolated strains and the agents determined by functional prediction, constituted only 0.024% (on average) of the total bacterial community. The ecological network showed that most of the identified decomposers were self-existent without associations with other species. These results showed that during straw composition, community assembly might be greatly determined by the majority, but straw decomposition functions might be largely determined by the minority and emphasized the importance of the rare species in community-specific functions.