Diversity and similarity of butterfly communities in five different habitat types at Tam Dao National Park, Vietnam

Diversity and similarity of butterfly communities were assessed in five different habitat types (from natural closed forest to agricultural lands) in the mountains of Tam Dao National Park, Vietnam for 3 years from 2002 to 2004. The line transect count was used to record species richness and abundance of butterfly communities in the different habitat types. For each habitat, the number of species and individuals, and indices of species richness, evenness and diversity of butterfly communities were calculated. The results indicated that species richness and abundance of butterfly communities were low in the natural closed forest, higher in the disturbed forest, highest in the forest edge, lower in the shrub habitat and lowest in the agricultural lands. The indices of species richness, evenness and diversity of butterfly communities were low in agricultural lands and natural closed forest but highest in the forest edge and shrub habitats. The families Satyridae and Amathusiidae have the greatest species richness and abundance in the natural closed forest, with a reduction in their species richness and abundance from the natural closed forest to the agricultural lands. Species composition of butterfly communities was different among five different habitat types (40%), was similar in habitats outside the forest (68%) and was similar in habitats inside the forest (63%). Diversity and abundance of butterfly communities are not different between the natural closed forest and the agriculture lands, but species composition changed greatly between these habitat types. A positive correlation between the size of species geographical distribution range and increasing habitat disturbance was found. The most characteristic natural closed forest species have the smallest geographical distribution range.     

浙江舟山群岛山茶所在群落物种组成及多样性

以山茶Camellia japonica 所在的阔叶林和灌丛群落为研究对象,通过典型样地调查,对物种组成及多样性进行研究。结果表明,8 个植物群落共调查到维管束植物147 种,隶属于65 科118 属;地理成分多样,热带成分大于温带、亚热带成分,表现为亚热带向暖温带过渡的性质,同时反映出群落所在生境热量条件相对优越。山茶所在的阔叶林群落中,乔木层的丰富度和Shannon-Wiener 指数与演替趋势呈明显的负相关关系,处于岛屿较高海拔的灌丛和疏林,其灌木层和藤本层的丰富度和Shannon-Wiener 指数大于阔叶林;受相应群落乔木层的优势种红楠Machilus thunbergii、青冈Cyclobalanopsis glauca 或台湾蚊母树Distylium gracile 以及更新层的舟山新木姜子Neolitsea sericea 优势突出影响,乔木层与更新层的Pielou 指数波动幅度较大。     

天然和人工固沙灌木林蜘蛛和甲虫分布与环境因子的关系

干旱区人工植被恢复驱动的土地利用变化强烈影响了地表和土栖的节肢动物群落结构及多样性。然而,我们对地表节肢动物群落关键类群-蜘蛛和甲虫对固沙植被恢复的响应及与环境变化关系的认识还很有限。以天然固沙灌木林和2种人工固沙灌木林为研究对象,运用方差分析和多变量分析等方法定量研究了干旱区天然和人工固沙植被区地表蜘蛛和甲虫分布特征及影响要素。结果表明,天然灌木林与人工梭梭、柽柳林地表蜘蛛和甲虫群落组成明显不同,人工梭梭、柽柳林地表蜘蛛活动密度和甲虫多样性均显著高于天然灌木林,而地表甲虫密度和蜘蛛多样性变化与之相反。两种人工固沙灌木林之间蜘蛛和甲虫群落组成也存在一定差异,人工柽柳林地表蜘蛛活动密度、多样性和甲虫物种丰富度均显著高于人工梭梭林。进一步分析发现,蜘蛛群落中狼蛛科、平腹蛛科、皿蛛亚科和球蛛科与甲虫群落中拟步甲科、步甲科和象甲科等一些甲虫种属对3种生境的选择模式不同决定了蜘蛛和甲虫群落聚集结构。植被、土壤环境因子与蜘蛛和甲虫pRDA和pCCA结果表明,草本生物量、凋落物量、土壤含砂量、电导率和灌木盖度是影响蜘蛛分布的主要环境因子,它们解释了82.1%的蜘蛛群落变异;灌木盖度、草本生物量、土壤pH和砂含量是影响甲虫群落分布的主要环境因子,它们解释了60.6%的甲虫群落变异。总之,人工固沙灌木恢复影响了植被和土壤环境,它们相互作用改变了荒漠-绿洲过渡区蜘蛛和甲虫等地表节肢动物的分布格局。     

Flow permanence and macroinvertebrate community diversity within groundwater dominated headwater streams and springs

The response of aquatic macroinvertebrate communities to flow permanence within limestone springs and headwater streams was examined across the English Peak District. At the regional scale, macroinvertebrate communities of perennial and intermittent springs displayed significant differences in the number of taxa, macroinvertebrate community abundance, diversity indices (Shannon and Simpson indices) and the Berger–Parker dominance index at intermediate discharge. However, no significant difference was recorded between intermittent and perennial sites at high discharge or when all sampling occasions were pooled. At the catchment scale, the number of taxa, community abundance and Bray–Curtis similarity coefficients within the River Lathkill differed significantly between intermittent springs and other habitats. At both the regional and catchment scale the macroinvertebrate communities of intermittent springs were characterised by a small number of taxa displaying life cycle adaptations to intermittent aquatic habitats, particularly Trichoptera.     

Soil fungal composition changes with shrub encroachment in the northern Chihuahuan Desert

Woody species encroachment of grasslands globally causes many socioecological impacts, including loss of grazing pastures and decreased biodiversity. Soil microbial communities may partially regulate the pace of shrub encroachment, as plant-microbial interactions can strongly influence plant success. We measured fungal composition and activity under dominant plant species across a grassland to shrubland transition to determine if shrubs cultivate soil microbial communities as they invade. Specifically, soil microbial communities, abiotic soil properties, and extracellular enzyme activities were quantified for soils under four common Chihuahuan Desert plant species (three grasses, one shrub) in central New Mexico, U.S.A. Extracellular enzyme activity levels were fairly consistent under different plant species across the grassland to shrubland transition. Activity levels of two enzymes (alkaline phosphatase and beta-N-acetyl-glucosaminidase) were lower in the ecotone, presumably because soil organic matter content was also lower in ecotone soils. Community composition of soil fungi mirrored patterns in the plant community, with distinct plant and fungal communities in the shrubland and grassland, while grassland-shrubland ecotone soils hosted a mix of taxa from both habitats. We show that shrubs cultivate a distinct microbial community on the leading edge of the invasion, which may be necessary for shrub colonization, establishment, and persistence.     

Use of Multiplex Terminal Restriction Fragment Length Polymorphism for Rapid and Simultaneous Analysis of Different Components of the Soil Microbial Community▿

A multiplex terminal restriction fragment length polymorphism (M-TRFLP) fingerprinting method was developed and validated for simultaneous analysis of the diversity and community structure of two or more microbial taxa (up to four taxa). The reproducibility and robustness of the method were examined using soil samples collected from different habitats. DNA was PCR amplified separately from soil samples using individual taxon-specific primers for bacteria, archaea, and fungi. The same samples were also subjected to a multiplex PCR with the primers for all three taxa. The terminal restriction fragment length polymorphism profiles generated for the two sets of PCR products were almost identical not only in terms of the presence of peaks but also in terms of the relative peak intensity. The M-TRFLP method was then used to investigate rhizosphere bacterial, fungal, and rhizobial/agrobacterial communities associated with the dwarf shrub Calluna vulgaris growing in either open moorland, a mature pine forest, or a transition zone between these two habitats containing naturally regenerating pine trees. Rhizosphere microbial communities associated with Vaccinium myrtillus collected from the native pine forest were also investigated. In this study, individual PCR products from the three taxa were also pooled before restriction digestion and fragment size analysis. The terminal restriction fragment length polymorphism profiles obtained with PCR products amplified individually and with multiplexed and pooled PCR products were found to be consistent with each other in terms of the number, position, and relative intensity of peaks. The results presented here confirm that M-TRFLP analysis is a highly reproducible and robust molecular tool for simultaneous investigation of multiple taxa, which allows more complete and higher resolution of microbial communities to be obtained more rapidly and economically.     

Effects of a pulp and paper mill on the ecology of the La Trobe River,Victoria, Australia

Four riverine animal communities were measured to assess the impact of extensively treated wastewater from a pulp and paper mill on the lower La Trobe River in Victoria, Australia. Benthic macroinvertebrates in channel and bankside habitats were sampled using a new air-lift corer. Population density was expressed in relation to substrate volume. Other communities measured at five sites upstream and downstream of the mill's wastewater outfall were the zooplankton, and the animals associated with submerged littoral vegetation. Ten environmental variables were also measured during the two sampling periods.A total of 50 benthic macro-invertebrate taxa were dominated by Oligochaeta, Chironomidae and Bivalvia. Benthic communities upstream and downstream of the outfall were very similar. Benthic samples showed large unexplained variation between stations and seasons, despite the similarity of stations and the stratified sampling design, but within-sample variation was small. There was some evidence that benthic faunal patchiness was associated with patterns of stream-bed scouring and deposition in periods of high flow. Littoral samples collected 28 taxa, dominated by Decapoda and Hemiptera. The benthic and littoral communities were quite distinct, with only three species common to both.Only two of the biological and environmental variables responded to wastewater from the mill: total dissolved solids rose by 20–25% over upstream levels; and zooplankton density increased by 2–3 orders of magnitude. It was concluded that wastewater treatment had successfully avoided the major environmental problems often associated with pulp and paper mills.     

Blended divergences: local food and medicinal plant uses among Arbëreshë, Occitans,and autochthonous Calabrians living in Calabria,Southern Italy

Abstract

A study focusing on traditional uses of wild plants for gastronomic and medicinal purposes was carried out among three linguistic communities in Calabria, southern Italy. Ninety interviews with local elderly informants were conducted among Occitans and Arbëreshë, two linguistic minorities, and the dominant culture of autochthonous Calabrians. We recorded 85 taxa belonging to 39 botanical families and 66 different detailed use-reports including 35 culinary and 31 medicinal uses. Our overall data show the permanence of traditional ecological knowledge related to wild and semi-domesticated food and medicinal plants; however, high similarity indices among the three communities demonstrate that traditional ecological knowledge is following the pathway of homogenization and standardization toward the dominant culture, facilitated by a context of linguistic erosion, limited intergenerational transmission, and a centuries-old diffusion with Calabrian culture. Moreover, our study calls for further field surveys in isolated areas of Calabria to analyze how traditional ecological practices can be key tools in the development of local small-scale economies through the promotion of artisanal food entrepreneurship of wild food plant transformation.     

河西走廊天然固沙植被区地表甲虫多样性及其对沙漠化的指示作用

干旱、半干旱区沙漠化强烈影响动植物分布及多样性,地表甲虫是荒漠中主要的动物类群,它们对沙漠化引起的植被和土壤环境变化响应十分敏感。鉴于此,以河西走廊中部张掖绿洲外围的天然固沙植被区作为研究区,依据沙漠化发育程度选择流动沙丘（ASD）、丘间低地（IL）、半固定（SFSD）和固定沙丘（FSD）4种生境,调查了地表甲虫群落组成及影响甲虫分布的植被和土壤环境。研究发现,4种生境地表甲虫群落组成明显不同并存在季节变异,5月ASD与IL、SFSD和FSD生境地表甲虫群落的相异性大于8月。5月和8月SFSD生境地表甲虫活动密度均显著高于其他生境,8月FSD生境地表甲虫多样性指数显著高于其他生境。不同大小甲虫对沙漠化的响应模式不同,大中型甲虫对沙漠化的响应较小型甲虫敏感,这在5月表现尤为明显。地表甲虫与环境因子的RDA分析结果表明,12个植被和土壤环境因子解释了49.8%的地表甲虫群落变异,其中植被环境解释了甲虫群落变异的16.3%,土壤环境解释了甲虫群落变异的4.2%,植被和土壤环境相互作用解释了甲虫群落变异的29.3%。pRDA分析结果表明,草本物种丰富度、灌木盖度、土壤有机碳含量和粗砂含量是影响地表甲虫分布的主要环境因子,它们解释了43.7%的地表甲虫群落变异。Pearson相关分析表明,草本物种丰富度与地表甲虫活动密度呈显著正相关,而与地表甲虫均匀度呈显著负相关;灌木盖度与地表甲虫多样性呈显著正相关;地表甲虫物种丰富度与灌木盖度和草本物种丰富度均呈显著正相关。此外,研究还发现戈壁琵甲、克氏扁漠甲、中华砚甲和甘肃齿足象可以用于指示FSD生境,东鳖甲属昆虫可以用于指数SFSD生境,谢氏宽漠王可以用于指示IL及ASD生境。     

Use of multiplex terminal restriction fragment length polymorphism for rapid and simultaneous analysis of different components of the soil microbial community

A multiplex terminal restriction fragment length polymorphism (M-TRFLP) fingerprinting method was developed and validated for simultaneous analysis of the diversity and community structure of two or more microbial taxa (up to four taxa). The reproducibility and robustness of the method were examined using soil samples collected from different habitats. DNA was PCR amplified separately from soil samples using individual taxon-specific primers for bacteria, archaea, and fungi. The same samples were also subjected to a multiplex PCR with the primers for all three taxa. The terminal restriction fragment length polymorphism profiles generated for the two sets of PCR products were almost identical not only in terms of the presence of peaks but also in terms of the relative peak intensity. The M-TRFLP method was then used to investigate rhizosphere bacterial, fungal, and rhizobial/agrobacterial communities associated with the dwarf shrub Calluna vulgaris growing in either open moorland, a mature pine forest, or a transition zone between these two habitats containing naturally regenerating pine trees. Rhizosphere microbial communities associated with Vaccinium myrtillus collected from the native pine forest were also investigated. In this study, individual PCR products from the three taxa were also pooled before restriction digestion and fragment size analysis. The terminal restriction fragment length polymorphism profiles obtained with PCR products amplified individually and with multiplexed and pooled PCR products were found to be consistent with each other in terms of the number, position, and relative intensity of peaks. The results presented here confirm that M-TRFLP analysis is a highly reproducible and robust molecular tool for simultaneous investigation of multiple taxa, which allows more complete and higher resolution of microbial communities to be obtained more rapidly and economically.     

Competition matters: Determining the drivers of land snail community assembly among limestone karst areas in northern Vietnam

The insular limestone karsts of northern Vietnam harbor a very rich biodiversity. Many taxa are strongly associated with these environments, and individual species communities can differ considerably among karst areas. The exact processes that have shaped the biotic composition of these habitats, however, remain largely unknown. In this study, the role of two major processes for the assembly of snail communities on limestone karsts was investigated, interspecific competition and filtering of taxa due to geographical factors. Communities of operculate land snails of the genus Cyclophorus were studied using the dry and fluid‐preserved specimen collections of the Natural History Museum, London. Phylogenetic distances (based on a Bayesian analysis using DNA sequence data) and shell characters (based on 200 semilandmarks) were used as proxies for ecological similarity and were analyzed to reveal patterns of overdispersion (indicating competition) or clustering (indicating filtering) in observed communities compared to random communities. Among the seven studied karst areas, a total of 15 Cyclophorus lineages were found. Unique communities were present in each area. The analyses revealed phylogenetic overdispersion in six and morphological overdispersion in four of seven karst areas. The pattern of frequent phylogenetic overdispersion indicated that competition among lineages is the major process shaping the Cyclophorus communities studied. The Coastal Area, which was phylogenetically overdispersed, showed a clear morphological clustering, which could have been caused by similar ecological adaptations among taxa in this environment. Only the community in the Cuc Phuong Area showed a pattern of phylogenetic clustering, which was partly caused by an absence of a certain, phylogenetically very distinct group in this region. Filtering due to geographical factors could have been involved here. This study shows how museum collections can be used to examine community assembly and contributes to the understanding of the processes that have shaped karst communities in Vietnam.     

Spatial structure of epiphytic yeast communities on fruits of <Emphasis Type="Italic">Sorbus aucuparia</Emphasis> L.

The subject of this research is epiphytic yeast communities formed on the surface of Sorbus aucuparia. The object is to make quantitative assessment of the yeast communities’ differentiation of the same but distant substratum. Results of the nested ANOVA demonstrated that with increase in distances, there are increases in the variation of total number and relative abundance of the dominant yeast communities. The average similarity between groups of single fruits (Sørensen’s f Similarity Coefficient) regularly decreased with distance. The results demonstrate that the number and structure of separate yeast groups depend not only on ecological factors but also on proximity to other communities. Such aggregation in the distribution of the microorganisms’ species caused by migration and colonial resettlement should be taken into account when analyzing their diversity in natural habitats.     

Environmental and historical imprints on beta diversity: insights from variation in rates of species turnover along gradients

A common approach for analysing geographical variation in biodiversity involves using linear models to determine the rate at which species similarity declines with geographical or environmental distance and comparing this rate among regions, taxa or communities. Implicit in this approach are weakly justified assumptions that the rate of species turnover remains constant along gradients and that this rate can therefore serve as a means to compare ecological systems. We use generalized dissimilarity modelling, a novel method that accommodates variation in rates of species turnover along gradients and between different gradients, to compare environmental and spatial controls on the floras of two regions with contrasting evolutionary and climatic histories: southwest Australia and northern Europe. We find stronger signals of climate history in the northern European flora and demonstrate that variation in rates of species turnover is persistent across regions, taxa and different gradients. Such variation may represent an important but often overlooked component of biodiversity that complicates comparisons of distance–decay relationships and underscores the importance of using methods that accommodate the curvilinear relationships expected when modelling beta diversity. Determining how rates of species turnover vary along and between gradients is relevant to understanding the sensitivity of ecological systems to environmental change.     

陕西延安北洛河流域蝗虫群落多样性研究

为了寻求有害蝗虫的防治对策,深入研究蝗虫生物多样性,用多样性指数、相似性分析等方法比较分析了延安北洛河流域不同生境中蝗虫群落组成。结果表明:草地中占有的属种数量均最高,灌草丛和农田中蝗虫的科属种都相对较低。不同生境蝗虫多样性指数的排列顺序为草地>河滩>灌草丛>农田,草地的多样性指数最高,农田的多样性指数最低。丰富度指数的变化趋势与多样性指数一致,而优势度指数却恰好与二者的顺序相反。在相似性分析中,草地和河滩相似性系数最大,说明草地和河滩这两种生境蝗虫种类组成的相似性较大,具有更多的共同种,从而可以推知草地和河滩的生境条件有一定的相似性,而农田和草地是两种完全不同的生境。     

The potential for mycobiont sharing between shrubs and seedlings to facilitate tree establishment after wildfire at Alaska arctic treeline

Root‐associated fungi, particularly ectomycorrhizal fungi (EMF), are critical symbionts of all boreal tree species. Although climatically driven increases in wildfire frequency and extent have been hypothesized to increase vegetation transitions from tundra to boreal forest, fire reduces mycorrhizal inoculum. Therefore, changes in mycobiont inoculum may potentially limit tree‐seedling establishment beyond current treeline. We investigated whether ectomycorrhizal shrubs that resprout after fire support similar fungal taxa to those that associate with tree seedlings that establish naturally after fire. We then assessed whether mycobiont identity correlates with the biomass or nutrient status of these tree seedlings. The majority of fungal taxa observed on shrub and seedling root systems were EMF, with some dark septate endophytes and ericoid mycorrhizal taxa. Seedlings and adjacent shrubs associated with similar arrays of fungal taxa, and there were strong correlations between the structure of seedling and shrub fungal communities. These results show that resprouting postfire shrubs support fungal taxa compatible with tree seedlings that establish after wildfire. Shrub taxon, distance to the nearest shrub and fire severity influenced the similarity between seedling and shrub fungal communities. Fungal composition was correlated with both foliar C:N ratio and seedling biomass and was one of the strongest explanatory variables predicting seedling biomass. While correlative, these results suggest that mycobionts are important to nutrient acquisition and biomass accrual of naturally establishing tree seedlings at treeline and that mycobiont taxa shared by resprouting postfire vegetation may be a significant source of inoculum for tree‐seedling establishment beyond current treeline.     

Threatened Corals Provide Underexplored Microbial Habitats

Contemporary in-depth sequencing of environmental samples has provided novel insights into microbial community structures, revealing that their diversity had been previously underestimated. Communities in marine environments are commonly composed of a few dominant taxa and a high number of taxonomically diverse, low-abundance organisms. However, studying the roles and genomic information of these “rare” organisms remains challenging, because little is known about their ecological niches and the environmental conditions to which they respond. Given the current threat to coral reef ecosystems, we investigated the potential of corals to provide highly specialized habitats for bacterial taxa including those that are rarely detected or absent in surrounding reef waters. The analysis of more than 350,000 small subunit ribosomal RNA (16S rRNA) sequence tags and almost 2,000 nearly full-length 16S rRNA gene sequences revealed that rare seawater biosphere members are highly abundant or even dominant in diverse Caribbean corals. Closely related corals (in the same genus/family) harbored similar bacterial communities. At higher taxonomic levels, however, the similarities of these communities did not correlate with the phylogenetic relationships among corals, opening novel questions about the evolutionary stability of coral-microbial associations. Large proportions of OTUs (28.7–49.1%) were unique to the coral species of origin. Analysis of the most dominant ribotypes suggests that many uncovered bacterial taxa exist in coral habitats and await future exploration. Our results indicate that coral species, and by extension other animal hosts, act as specialized habitats of otherwise rare microbes in marine ecosystems. Here, deep sequencing provided insights into coral microbiota at an unparalleled resolution and revealed that corals harbor many bacterial taxa previously not known. Given that two of the coral species investigated are listed as threatened under the U.S. Endangered Species Act, our results add an important microbial diversity-based perspective to the significance of conserving coral reefs.     

Variation between freshwater and terrestrial fungal communities on decaying bamboo culms

Fungal communities on decaying culms of a bamboo host (Phyllostachys bambusoides) from freshwater and adjacent terrestrial habitats were identified. Collections were made at Xiao Bai Long Mountain, Yiliang, Yunnan, China in the winter and summer. In each collection, 100 similar-sized bamboo culms were collected, comprising 50 submerged samples from a stream and 50 terrestrial samples from adjacent riparian vegetation. A total of 82 fungal taxa were recorded from the samples, including 30 ascomycetes and 52 anamorphic fungi. The frequency of occurrence of these fungi were recorded and the Shannon–Weiner indices (H′) were applied to evaluate fungal diversity. The results showed that variation of the fungal diversity between the summer and winter collections was insignificant (0.2<p<0.5). Fungal diversity on submerged bamboo however, was significantly higher than that on terrestrial bamboo (p<0.001). Further findings were that: (1) some commonly recorded freshwater and terrestrial taxa were found in both habitats, but overall there were only 15 overlapping species between the two habitats; (2) the dominant species in each habitat were considerably different, and (3) only a few fungi were dominant, while most species were rare, being recorded only once or twice. Factors responsible for the distribution patterns and variations in composition of the fungal communities are discussed.     

Molecular analysis of autosomal dominant hereditary ataxias in the Indian population: high frequency of SCA2 and evidence for a common founder mutation

Expansion of CTG/CAG trinucleotide repeats has been shown to cause a number of autosomal dominant cerebellar ataxias (ADCA) such as SCA1, SCA2, SCA3/ MJD, SCA6, SCA7, SCA8 and DRPLA. There is a wide variation in the clinical phenotype and prevalence of these ataxias in different populations. An analysis of ataxias in 42 Indian families indicates that SCA2 is the most frequent amongst all the ADCAs we have studied. In the SCA2 families, together with an intergenerational increase in repeat size, a horizontal increase with the birth order of the offspring was also observed, indicating an important role for parental age in repeat instability. This was strengthened by the detection of a pair of dizygotic twins with expanded alleles showing the same repeat number. Haplotype analysis indicates the presence of a common founder chromosome for the expanded allele in the Indian population. Polymorphism of CAG repeats in 135 normal individuals at the SCA loci studied showed similarity to the Caucasian population but was significantly different from the Japanese population.     

环境和扩散对草地群落构建的影响

植物群落构建机制是生态学研究的热点之一.长久以来这个难题并没有得到很好的解释,且争议较多.生态位理论或中性理论,或是二者的共同作用,这样的结论在不同的研究中都有印证.以黄土高原子午岭地区的草地群落为例,对3种不同的草地群落(5a的弃耕地、阴坡和阳坡的草地)进行了野外群落学调查,采用Mantel test和主轴邻距法(PCNM)分析方法,研究了空间地理距离和环境资源差异对于草本植物群落分布的影响,结果表明:地理距离和环境差异共同解释了群落组成相似性的79.3％,剔除环境因子的影响,地理距离解释了群落组成相似性的33.8％;而剔除地理距离的影响,环境因子解释了群落组成相似性的14.2％.无论是生态位理论还是中性理论,其在黄土高原草本群落构建过程中都有作用,但中性理论扮演了更为重要的角色.     

Community assembly of a euryhaline fish microbiome during salinity acclimation

Microbiomes play a critical role in promoting a range of host functions. Microbiome function, in turn, is dependent on its community composition. Yet, how microbiome taxa are assembled from their regional species pool remains unclear. Many possible drivers have been hypothesized, including deterministic processes of competition, stochastic processes of colonization and migration, and physiological ‘host‐effect’ habitat filters. The contribution of each to assembly in nascent or perturbed microbiomes is important for understanding host–microbe interactions and host health. In this study, we characterized the bacterial communities in a euryhaline fish and the surrounding tank water during salinity acclimation. To assess the relative influence of stochastic versus deterministic processes in fish microbiome assembly, we manipulated the bacterial species pool around each fish by changing the salinity of aquarium water. Our results show a complete and repeatable turnover of dominant bacterial taxa in the microbiomes from individuals of the same species after acclimation to the same salinity. We show that changes in fish microbiomes are not correlated with corresponding changes to abundant taxa in tank water communities and that the dominant taxa in fish microbiomes are rare in the aquatic surroundings, and vice versa. Our results suggest that bacterial taxa best able to compete within the unique host environment at a given salinity appropriate the most niche space, independent of their relative abundance in tank water communities. In this experiment, deterministic processes appear to drive fish microbiome assembly, with little evidence for stochastic colonization.