Mechanisms responsible for the development of periphyton community structure during seasonal succession: the role of interspecies competition and plankton sedimentation

The development of periphyton community structure by exchange of organisms between substratum and water column (noninteractive mechanism) and by interspecific competition for surface (interactive mechanism) was studied during seasonal succession in Akulovsky water supply channel (the Upper Volga basin). The influence of exchange was assumed by similarity between the species composition of plankton and periphyton. At early stages of succession when the diatoms dominated in periphyton the community was formed mainly by phytoplankton sedimentation, while the competition for substratum didn't result in decrease of species diversity because the poor competitors were partly displaced by new colonists from the water column. Later when the green filamentous algae abundantly developed in periphyton, their numbers were probably controlled by factors not related to exchange of propagules. At the same time, the species structure of secondary periphyton cover developing on the thallus of filamentous algae depended mainly on the plankton sedimentation. At the last stages of seasonal succession when periphyton was represented by colonies of cyanobacteria and diatoms closely covering the substratum, the exchange of organisms between substratum and water column was not so important as interspecific competition for surface. As one could suppose, increase in biomass in this period resulted in the decrease of specificity as it was predicted by hypothesis of interactive community. In such a way, both mechanisms (interactive and noninteractive ones) took part in development of periphyton structure. Their relative influence changed in the course of seasonal succession.     

Spring grazing by sheep: effects on seasonal changes during early old field succession

This paper describes early secondary succession on an old field on limestone released from cultivation four years previously. Seasonal changes in plant composition after spring grazing by sheep are compared with those in ungrazed controls. Grazed and ungrazed paddocks were laid out in Latin squares. Plants were sampled before and several times after grazing in April, at several spatial scales.Major changes in plant abundance and sward characters such as height and density persisted throughout the growing season. Annual herbs increased after grazing, but annual grasses declined, as did short-lived perennial herbs. Effects on perennial herbs were weak; perennial grasses usually increased but this depended on the species. This pattern confirms that sheep grazing affects the direction, as well as the rate of succession.Some effects, such as increases in biennial herbs and in species richness, were only evident at large scales of sampling, suggesting that they arose from changes in rare and widely dispersed species. Other species were affected at different spatial scales, and no one sampling method detected the full range of effects.These results indicate the potential power of manipulating grazing early in secondary succession for directing the course of community change, for conservation or other purposes.Nomenclature follows Clapham et al. (1962)This study is funded by a grant from the Nuffield Foundation to V.K.B. We thank the Wytham Management Committee, Oxford University, for permission to use the site, and the staff of the University Farm, especially Richard Bampton and Cheryl Howes, for making the grazing possible. Alan Gange, Nicola marples, Fiona Matthews, Bridget Peace, Anne Storr and others helped at various times with field recording.     

Seasonal succession of lotic epiphyton: effects of macrophyte cover and grazing by chironomid larvae

The epiphyton is a community of periphyton on the aquatic plants. The seasonal dynamics of biomass, production and community structure of epiphytic algae on Potamogeton perfoliatus was studied at the Moscow River reach with low flow velocity from May to October 2000. The relative importance of physical-chemical environmental variables and herbivorous pressure in structuring the epiphyton community was accessed using multivariate redundancy analysis. Algal composition was mainly determined by the macrophyte cover, suggestion the overriding importance of the underwater light availability in seasonal development of epiphyton. There was a significant positive relationship between biomass of attached diatom Cocconeis placentula and abundance of chironomid larvae (r = 0.57; p < 0.01). This indicates that increase in herbivorous pressure caused the shift in epiphyton community structure. However, the intensity of herbivorous impact on epiphyton was ultimately determined by light availability in macrophyte stands. At low irradiance level and consequent slow growth of algae the upper layer of epiphyton was seriously destroyed by chironomids that resulted in dominance of C. placentula. As irradiance level and epiphyton productivity increased chironomids were unable to prevent biomass accumulation of the upper layer thus inhibiting the growth of C. placentula. The high concentrations of nutrients and relatively stable discharge determined the crucial role of light regime in the regulation of trophic interactions between epiphyton and chironomid larvae.     

Changes in the seasonal rhythm of two forest communities during secondary succession

Changes in the seasonal rhythm of two plant phytocoenoses in a submountain beech forest during secondary succession were studied. Investigations were done on four monitoring plots with different stand density over the period of four successive years. The rhythm of the associations Dentario bulbiferae-Fagetum and Carici pilosae-Fagetum reflects the course of succession processes running six years after the human impact (cutting) in the ecosystem. Results of the phenological observations of the understorey species with the focus on the changes in flowering and colour spectrum allowed to make the comparisons between both associations in connection with different phyto-climatic conditions and in dependence on time. The most conspicuous changes in the seasonal rhythm and structure of the examined associations were found in conditions of the former clear-cut, currently in succession phase. A clear decrease (56%) in number of taxons with the dominance > 1% in one association towards the end of the 4-year study period was detected here. Simultaneously, a decrease in the number of flowering species was observed, while the relative rate of species being in the vegetative stage increased considerably (from 6 to 67%) over the growing season. The course of flowering of both of the associations missed discernible trends and peaks as well as colour spectra were partially changed during four monitored successive years on the formerly unstocked area.     

Interannual variability in the seasonal plankton succession of a shallow, warm-water lake

Common seasonal plankton succession patterns in temperate lakes are well understood, and were described in the popular PEG-model. Seasonal plankton succession in warm-water lakes, however, is not as well known. Recent theory suggests that some lake systems are characteristic of having alternate system-states, where one of the system-states is characterized by dominance of cyanobacteria, and transition between system-states can be abrupt and undeterminable. Lake Somerville, a shallow, well-mixed, warm-water reservoir located in eastern TX, U.S.A., experiences occasional periods of cyanobacteria dominance. To increase our understanding of seasonal plankton dynamics in warm-water systems, we analyzed 14-years of plankton data spanning a 22-year period. During this period, succession dynamics characteristic of those described by the PEG-model were observed, as well as succession dynamics expected during periods of cyanobacteria dominance, i.e., greater accumulated phytoplankton biovolume, low secondary productivity, and low light penetration. In addition to the PEG-model and cyanobacteria type system-states, other states of the system that were intermediate between these were observed. Therefore, we conclude the lake does not behave according to the alternate system-states model. The change from year to year in early-year cyanobacteria dominance was abrupt and non-monotonic during this period. In addition, the early year performance of cyanobacteria appeared to influence the plankton succession trajectory for the remainder of the season. While the magnitude of lake-flushing early in the year accounted for ～37% of variability in cyanobacteria prevalence, many of the traditional factors impacting cyanobacteria dominance appeared insignificant.     

甘南尕海湿地退化过程中植被生物量变化及其季节动态

为探讨尕海湿地退化过程中植被生物量变化规律,以尕海泥炭沼泽和沼泽化草甸为例,采用定位样地调查方法,研究了不同退化程度湿地植被生物量的时空分布格局。结果表明,1)随着湿地退化演替,两类湿地植被地上生物量逐渐减小,泥炭沼泽未退化(PⅠ)、退化阶段(PⅡ)地上生物量依次为334.19,290.72 g/m~2,沼泽化草甸未退化(SⅠ)、轻度退化(SⅡ)、中度退化(SⅢ)地上生物量依次为378.40,308.07,261.21 g/m~2;地上生物量季节动态规律均为单峰型,8月中下旬达到峰值;同一湿地类型各退化阶段地上生物量绝对增长率(AGR)和相对增长率(RGR)在同一年份变化趋势基本相同,但不同年份间存在差异,而同一湿地类型不同阶段AGR和RGR的大小存在差异。2)地下生物量也随退化程度加剧显著减小(P0.05),PⅠ,PⅡ地上生物量依次为23081.46,12607.72 g/m~2,SⅠ,SⅡ,SⅢ地下生物量依次为4583.16,3008.63,1290.73 g/m~2;地下生物量季节变化均表现出愈接近生长季始末值愈大;地下生物量由土壤表层向深层显著下降(P0.05),总体呈"T"形分布,0—10cm土层,泥炭沼泽、沼泽化草甸地下生物量都最大,分别占各自总地下生物量50%和70%以上。3)尕海2类高寒湿地5—9月平均根冠比均表现未退化高于退化,根冠比季节动态为越接近生长季始末值越大,生长旺盛季值越小。     

The effect of sedimentation and microbial nitrogen regeneration in a plankton community: a simulation investigation

A computer simulation model was developed to investigate nitrogenfluxes associated with microbial interactions in plankton communities.A short time scale was used, appropriate to the build-up anddecline of phytoplankton blooms in temperate shelf waters aftera mixing or upwelling event. The model depicts a continuum ofevents, many of which have been observed in coastal, upwellingand oceanic systems, including two phytoplankton peaks correspondingto ‘new production’ and ‘regenerated production’.It predicts that nitrogen loss through sedimentation of phytoplanktonand faeces may result in a smaller bloom with a delayed onsetand prolonged duration. Microbial regeneration of nitrogen wasfound to be important in sustaining the middle stages of a phytoplanktonbloom, whereas micro- and meso-zooplankton regeneration occurredtowards the end of the bloom.     

Direct and indirect effects of grazing on the phytoplankton seasonal succession in an oligotrophic lake

We examined the simultaneous dynamics of phytoplankton and zooplanktonin an oligotrophic lake, as well as the algal response to experimentalmanipulations of herbivore population structure and density.The seasonal succession of phytoplankton is characterized bya shift in dominance from eukaryotic species to prokaryoticcyanobacteria, as in a eutrophic lake. This unusual patternfor an oligotrophic lake is related to the release of zooplanktonphosphorus, rather than to the amount of total phosphorus. Thehighest estimated values of this released phosphorus occur duringthe co-dominance of small-sized species and of one calanoidpopulation, both under natural and experimental conditions.Our experimental results clearly reveal that a blue-green speciesreplaces non-blue-green ones when environmental conditions renderlow or intermediate values for released phosphorus, irrespectiveof the grazing pressure. The absence of predators or high levelsof released phosphorus stimulate non-blue-green growth. Theseresults agree with the successional pattern observed for thealgal assemblage under natural conditions. Nutrient recyclingplays an essential role in the maintenance of the metabolismof the pelagic system, and therefore the prevalence of a topdownregulation mechanism as proposed for such low-nutrient environmentsshould be reconsidered.     

群落结构和叶面积指数在具茨山植被次生演替中的变化

采取3S(GIS,RS和GPS)技术和野外作业相结合的方法,研究了河南省具茨山人为干扰后植被次生演替过程。在此基础上,从宏观和微观尺度对不同演替阶段典型群落的结构变化和植被叶面积指数(LAI)动态进行分析。结果表明:乔木阶段的植被LAI均值为4.1～5.5;灌木阶段为3.0～3.7;草本阶段为1.0～1.5。部分灌木林在生长季的LAI和盖度高于乔木林。随着演替进行,群落结构也发生很大变化,乔木种类和数量逐步上升。植被系统的复杂度和稳定性不断增强,其发挥的生态功能和生态服务价值随之提高。     

Changes in the community structure of ammonia-oxidizing bacteria during secondary succession of calcareous grasslands

The community structure of β-subclass Proteobacteria ammonia-oxidizing bacteria was determined in semi-natural chalk grassland soils at different stages of secondary succession. Both culture-mediated (most probable number; MPN) and direct nucleic acid-based approaches targeting genes encoding 16S rRNA and the AmoA subunit of ammonia monooxygenase were used. Similar shifts were detected in the composition of the ammonia oxidizer communities by both culture-dependent and independent approaches. A predominance of Nitrosospira sequence cluster 3 in early successional fields was replaced by Nitrosospira sequence cluster 4 in late successional fields. The rate of this shift differed between the two areas examined. This shift occurred in a background of relative stability in the dominant bacterial populations in the soil, as determined by domain-level polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE). Molecular analysis of enrichment cultures obtained using different ammonia concentrations revealed biases towards Nitrosospira sequence cluster 3 or Nitrosospira sequence cluster 4 under high- or low-ammonia conditions respectively. High-ammonia MPNs suggested a decease in ammonia oxidizer numbers with succession, but low-ammonia MPNs and competitive PCR targeting amoA failed to support such a trend. Ammonia turnover rate, not specific changes in plant diversity and species composition, is implicated as the major determinant of ammonia oxidizer community structure in successional chalk grassland soils.     

Soil conditions and phylogenetic relatedness influence total community trait space during early plant succession

Aims The total space of traits covered by the members of plant communities is an important parameter of ecosystem functioning and complexity. We trace the variability of trait space during early plant succession and ask how trait space co-varies with phylogenetic community structure and soil conditions. Particularly, we are interested in the small-scale variability in trait space and the influence of biotic and abiotic filters.Methods We use data on species richness and soil conditions from the first 7 years of initial succession of an artificial catchment in north-eastern Germany. Total functional attribute diversity serves as a proxy to total trait space.Important findings Total trait space steadily increased during succession. We observed high small-scale variability in total trait space that was positively correlated with species richness and phylogenetic segregation and negatively correlated with total plant cover. Trait space increased with soil carbonate content, while pH and the fraction of sandy material behaved indifferently. Our results indicate that during early succession, habitat filtering processes gain importance leading to a lesser increase in trait space than expected from the increase in species richness alone.     

The seasonal dynamics of the succession rate in a near-shore macrophytic community

This paper discusses a method for computing an index that reflects the rate of changes in the community species structure. This index is illustrated based on the example of the macrophyte community of Vityaz Bay in the Sea of Japan. The mean annual succession rate of this community was estimated as 0.030 day^?1.     

Changes in plankton and fish larvae communities across hydrographic fronts off West Greenland

The variability in plankton community structure was studiedin Disko Bay and across important fishing banks off the westcoast of Greenland. The primary goal of the study was to investigatepossible linkages between hydrographical processes and planktonstructures, hypothesizing that hydrographic fronts would bepresent in the area, and that these to a large extent determineplankton distribution, composition and productivity. We sampledalong four cross-shelf transects, one covering Disko Bay andDisko Bank, while the other three covered Store Hellefiske Bank,Lille Hellefiske Bank and Sukkertop Bank. The hydrography wasexamined by CTD profiling, the phytoplankton by fluorescenceprofiling and water bottle sampling, while mesozooplankton andichthyoplankton were sampled by vertical or oblique net hauls,respectively. We observed distinct along-shelf flowing currentsin the area (e.g. the West Greenland Current, the Polar Currentand the Irminger Current), and the physical characteristicsindicated frontogenesis at the shelf slope, in regions of 80–100m water depth. Phytoplankton and ichthyoplankton showed a cross-shelfstructuring with apparent linkages to frontal characteristics,while a more diverse pattern was observed for the mesozooplanktonwhich were dominated by Calanus finmarchicus, Calanus glacialisand Calanus hyperboreus. The relationship between hydrographiccharacteristics and plankton distribution differed among species,and apparently specific plankton communities were establishedin different areas of the shelf. For example the larvae of Boreogadussaida, Ammodytes sp., Reinhardtius hippoglossoides and Stichaeuspunctatus differed markedly in distributional characteristics.In addition to the cross-shelf structuring, marked differencesin species composition and total plankton abundance were observedin the along-shelf (north–south) direction. The latitudinaldifferences in the unicellular plankton communities are interpretedlargely within a seasonal successional framework (i.e. an earlydominance of diatoms followed by increasing importance of smallerunicellular plankton), while the ichthyo- and zooplankton communitiesalso differed by the respective dominance of species with polarversus temperate origin. Our findings suggest that the flowof major currents and the establishment of hydrographical frontsare of primary importance to the plankton communities in theWest Greenland shelf area, influencing the early life of fishand the recruitment to the important fisheries resources.     

Impacts of two biomanipulation fishes stocked in a large pen on the plankton abundance and water quality during a period of phytoplankton seasonal succession

Silver and bighead carp were stocked in a large pen to control the nuisance cyanobacterial blooms in Meiliang Bay of Lake Taihu. Plankton abundance and water quality were investigated about once a week from 9 May to 7 July in 2005. Biomass of both total crustacean zooplankton and cladocerans was significantly suppressed by the predation of pen-cultured fishes. There was a significant negative correlation between the N:P weight ratio and phytoplankton biomass. The size-selective predation by the two carps had no effect on the biomass of green alga Ulothrix sp. It may be attributed to the low fish stocking density (less than 40 g m⁻³) before June. When Microcystis dominated in the water of fish pen, the pen-cultured carps effectively suppressed the biomass of Microcystis, as indicated by the significant decline of chlorophyll a in the >38 μm fractions of the fish pen. Based on the results of our experiment and previous other studies, we conclude that silver and bighead carp are two efficient biomanipulation tools to control cyanobacterial (Microcystis) blooms in the tropical/subtropical eutrophic waters. Moreover, we should maintain an enough stocking density for an effective control of phytoplankton biomass.     

Changes in the plankton community following introduction of filter-feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter-feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined.
2. During a summer experiment, a bloom of Anabaena flos-aquae developed (≈ 8000 cells mL⁻¹) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700–14 400 organisms L⁻¹) after the bloom in this fish-free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass.
3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (≈ 24 °C) inhibited active feeding of this warm-water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans.
4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.     

放牧管理模式对高寒草甸鼢鼠鼠丘群落演替的影响

高寒草甸放牧利用下高原鼢鼠(Eospalax baileyi)等危害的发生是草地管理的关键难题,分析放牧管理模式对鼢鼠鼠丘植被群落演替的影响能为草地管理提供重要依据。研究选择划区轮牧(RG)、生长季休牧(GSG)、连续放牧(CG)和禁牧(PG)4种放牧管理模式,以及各模式下不同年限鼠丘(一年(ZM1)、两年(ZM2)、三年(ZM3)和多年鼠丘(ZMM))与对照(CM)草地。分析不同放牧管理模式对鼠丘植被群落特征和生物量等的影响,结果发现:PG和GSG下所有年限鼠丘的植被高度、地上生物量均高于RG和CG;RG和GSG下ZM1和ZM2物种Shannon-wiener指数均高于对照样地物种Shannon-wiener指数。主成分分析表明:RG下地上生物量和物种丰富度指数是影响鼠丘植被群落演替的重要因子,PG下地上生物量、盖度、Shannon-wiener指数和均匀度指数是鼠丘植被群落演替的重要因子,CG下物种丰富度和重要值是影响鼠丘植被群落演替的重要指标,GSG下Shannon-wiener指数、盖度和高度是影响鼠丘植被群落演替的重要指标。可见,不同放牧制度对鼠丘植被群落演替的影响不同,禁牧...     

Nutrient availability and grazing influence the strength of priority effects during freshwater bacterial community coalescence

When bacterial communities mix, immigration history can fundamentally affect the community composition as a result of priority effects. Priority effects arise when an early immigrant exhausts resources and/or alters habitat conditions, thereby influencing the establishment success of the late arriver. The strength of priority effects is context-dependent and expected to be stronger if environmental conditions favour the growth of the first arriver. In this study, we conducted a two-factorial experiment testing the importance of nutrient availability and grazing on the strength of priority effects in complex aquatic bacterial communities. We did so by mixing two dissimilar communities, simultaneously, and with a 38 h time-delay. Priority effects were measured as the invasion resistance of the first community to the invading second community. We found stronger priority effects in treatments with high nutrient availability and absence of grazing, but in general, the arrival timing was less important than the selection by nutrients and grazing. At the population level, the results were complex, but priority effects may have been driven by bacteria belonging to for example, the genera Rhodoferax and Herbaspirillum. Our study highlights the importance of arrival timing in complex bacterial communities, especially if environmental conditions favour rapid community growth.     

The effects of grazing on local colonisation and extinction during early succession

Estimates of colonisation of plant species were made at three spatial scales in an old-field on limestone subject to five experimental sheep grazing regimes. Local extinctions within grazing treatments were estimated in 1-m² permanent quadrats. These data were used to assess the effects of grazing treatment and spatial scale on the process of species change over a period of six years. Colonisation of the lOha field was virtually a random draw of plant species from adj acent vegetation, irrespective of plant life-history traits including dispersal strategy. The effects of grazing on colonisation increased at smaller spatial scales. Colonisation rates changed little during the study on the 10 ha scale, but declined steeply with time at smaller scales. Colonisation rates of short-lived species declined more than those of perennials, and short-lived species were subject to erratic episodes of extinction which did not affect perennials. Short periods of grazing enhanced colonisation rates of all species, but extinction rates were the same as in ungrazed controls. Grazing for longer periods further enhanced colonisation rates, but also increased extinction rates. This produced diversity patterns consistent with a ‘hump-backed model’, except that no grazing treatment was heavy enough to decrease diversity. Ungrazed controls had low species diversity, but areas grazed for longer periods were no more diverse after six years than those grazed for short periods.     

Temporal patterns in rates of community change during succession

While ecological dogma holds that rates of community change decrease over the course of succession, this idea has yet to be tested systematically across a wide variety of successional sequences. Here, I review and define several measures of community change rates for species presence-absence data and test for temporal patterns therein using data acquired from 16 studies comprising 62 successional sequences. Community types include plant secondary and primary succession as well as succession of arthropods on defaunated mangrove islands and carcasses. Rates of species gain generally decline through time, whereas rates of species loss display no systematic temporal trends. As a result, percent community turnover generally declines while species richness increases--both in a decelerating manner. Although communities with relatively minor abiotic and dispersal limitations (e.g., plant secondary successional communities) exhibit rapidly declining rates of change, limitations arising from harsh abiotic conditions or spatial isolation of the community appear to substantially alter temporal patterns in rates of successional change.