Phytoplankton community interactions and environmental sensitivity in coastal and offshore habitats

Assessing the relative importance of environmental conditions and community interactions is necessary for evaluating the sensitivity of biological communities to anthropogenic change. Phytoplankton communities have a central role in aquatic food webs and biogeochemical cycles, therefore, consequences of differing community sensitivities may have broad ecosystem effects. Using two long‐term time series (28 and 20 years) from the Baltic Sea, we evaluated coastal and offshore major phytoplankton taxonomic group biovolume patterns over annual and monthly time‐scales and assessed their response to environmental drivers and biotic interactions. Overall, coastal phytoplankton responded more strongly to environmental anomalies than offshore phytoplankton, although the specific environmental driver changed with time scale. A trend indicating a state shift in annual biovolume anomalies occurred at both sites and the shift's timing at the coastal site closely tracked other long‐term Baltic Sea ecosystem shifts. Cyanobacteria and the autotrophic ciliate Mesodinium rubrum were more strongly related than other groups to this trend with opposing relationships that were consistent across sites. On a monthly scale, biotic interactions within communities were rare and did not overlap between the coastal and offshore sites. Annual scales may be better able to assess general patterns across habitat types in the Baltic Sea, but monthly community dynamics may differ at relatively small spatial scales and consequently respond differently to future change.     

Hypertrophic phytoplankton and the Intermediate Disturbance Hypothesis

The provisions of Connell's Intermediate Disturbance Hypothesis (IDH) were investigated in relation to the behaviour of freshwater phytoplankton in a hypertrophic lagoon, paying special attention to the link between species-diversity and environmental disturbances. Phytoplankton diversity yielded different indices depending on the basic unit of calculations (cells, particles, phytoplankton units, biomass). Although their ranges were approximately equal, they did not covary so could not be considered mutually substitutable. For the purpose of IDH testing, biomass diversity was chosen.Equilibrium states were considered to obtain in those periods with a very high fraction of total phytoplankton biomass, shared by no more than three phytoplankton species. Disturbances were considered as counterparts of equilibrium states. Disturbance factors were mostly abiotic, environmental features of the lake operating on the phytoplankton community at different time scales (co-occurring and with 1- and 2-weeks' lags). These scales may relate to the time required to establish phytoplankton community structure.IDH could be suspected not to hold for the phytoplankton of this hypertrophic lake, which experienced seven near-equilibrium phases and six disturbance periods throughout the study. As a rule, equilibrium states lasted longer than disturbance periods. The expected relationships between both disturbance intensity or frequency were not shown. Furthermore, no relationship was demonstrated between diversity (and hence IDH) and the phytoplankton community change rate. Wind stress probably played a minor role in triggering disturbance events. Disturbances were shown partly to promote small-sized phytoplankton communities.Finally, a plea for studying hypertrophic phytoplankton in greater detail is stressed if its responses to disturbances are to be fully understood.     

Biodiversity–productivity relationship in ponds: Community and metacommunity patterns along time and environmental gradients

Primary production correlates with diversity in various ways. These patterns may result from the interaction of various mechanisms related to the environmental context and the spatial and temporal scale of analysis. However, empirical evidence on diversity‐productivity patterns typically considers single temporal and spatial scales, and does not include the effect of environmental variables. In a metacommunity of macrophytes in ephemeral ponds, we analysed the diversity‐productivity relationship patterns in the field, the importance of the environmental variables of pond size and heterogeneity on such relationship, and the variation of these patterns at local (community level) and landscape scales (metacommunity level) across 52 ponds on twelve occasions, over five years (2005–2009). Combining all sampling dates, there were 377 ponds and 1954 sample‐unit observations. Vegetation biomass was used as a proxy for productivity, and biodiversity was represented by species richness, evenness, and their interaction. Environmental variables comprised pond area, depth and internal heterogeneity. Productivity and species richness were not directly related at the metacommunity level, and were positively related at the community level. Taking environmental variables into account revealed positive species richness‐productivity relationships at the metacommunity level and positive quadratic relationships at the community level. Productivity showed both positive and negative linear and nonlinear relationships with the size and heterogeneity of ponds. We found a weak relationship between productivity and evenness. The identity of variables associated with productivity changed between spatial scales and through time. The pattern of relationships between productivity and diversity depends on spatial scale and environmental context, and changes idiosyncratically through time within the same ecosystem. Thus, the diversity‐productivity relationship is not only a property of the study system, but also a consequence of environmental variations and the temporal and spatial scale of analysis.     

Relationships between aboveground biomass and plant cover at two spatial scales and their determinants in northern Tibetan grasslands

The relationships between cover and AGB for the dominant and widely distributed alpine grasslands on the northern Tibetan Plateau is still not fully examined. The objectives of this study are to answer the following question: (1) How does aboveground biomass (AGB) of alpine grassland relate to plant cover at different spatial scales? (2) What are the major biotic and abiotic factors influencing on AGB–cover relationship? A community survey (species, cover, height, and abundance) was conducted within 1 m × 1 m plots in 70 sites along a precipitation gradient of 50–600 m. Ordinary linear regression was employed to examine AGB–cover relationships of both community and species levels at regional scale of entire grassland and landscape scale of alpine meadow, alpine steppe, and desert steppe. Hierarchical partitioning was employed to estimate independent contributions of biotic and abiotic factors to AGB and cover at both scales. Partial correlation analyses were used to discriminate the effects of biotic and abiotic factors on AGB–cover relationships at two spatial scales. AGB and community cover both exponentially increased along the precipitation gradient. At community level, AGB was positively and linearly correlated with cover for all grasslands except for alpine meadow. AGB was also linearly correlated with cover of species level at both regional and landscape scales. Contributions of biotic and abiotic factors to the relationship between AGB and cover significantly depended on spatial scales. Cover of cushions, forbs, legumes and sedges, species richness, MAP, and soil bulk density were important factors that influenced the AGB–cover relationship at either regional or landscape scale. This study indicated generally positive and linear relationships between AGB and cover are at both regional and landscape scales. Spatial scale may affect ranges of cover and modify the contribution of cover to AGB. AGB–cover relationships were influenced mainly by species composition of different functional groups. Therefore, in deriving AGB patterns at different spatial scales, community composition should be considered to obtain acceptable accuracy.     

Multi-scale segregations and edaphic determinants of marsh plant communities in a western Pacific estuary

Whether and how the roles of environmental factors in producing vegetation patterns in coastal marshes vary with spatial scale is not well understood. We investigated the relationship between plant communities and edaphic factors in the Yangtze estuary at three spatial scales. Plant communities and edaphic factors were quantified at high and low tidal levels in both freshwater and salt marshes. Canonical correspondence analyses were conducted to examine the relationship between plant communities and edaphic factors at the landscape scale (freshwater vs. salt marsh), the zonation scale (high vs. low tidal level) and the patch scale (dominant vs. other species). Soil salinity, moisture content, pH, bulk density, and organic carbon could well explain segregations of plants at the landscape and zonation scales. However, the same factors exhibited only very weak relationships to plant communities at the patch scale. These results suggest that plant communities in the Yangtze estuary are segregated at different spatial scales by different environmental factors. As spatial scale is often not explicitly addressed investigating community assembly rules, our study underscores the importance of scaling for an improved understanding of community organization in coastal wetlands.     

Patterns of species density and productivity at different spatial scales in herbaceous plant communities

A major challenge in evaluating patterns of species richness and productivity involves acquiring data to examine these relationships empirically across a range of ecologically significant spatial scales. In this paper, we use data from herb‐dominated plant communities at six Long‐Term Ecological Research (LTER) sites to examine how the relationship between plant species density and above‐ground net primary productivity (ANPP) differs when the spatial scale of analysis is changed. We quantified this relationship at different spatial scales in which we varied the focus and extent of analysis: (1) among fields within communities, (2) among fields within biomes or biogeographic regions, and (3) among communities within biomes or biogeographic regions. We used species density (D=number of species per m²) as our measure of diversity to have a comparable index across all sites and scales. Although we expected unimodal relationships at all spatial scales, we found that spatial scale influenced the form of the relationship. At the scale of fields within different grassland communities, we detected a significant relationship at only one site (Minnesota old‐fields), and it was negative linear. When we expanded the extent of analyses to biogeographic regions (grasslands or North America), we found significant unimodal relationships in both cases. However, when we combined data to examine patterns among community types within different biogeographic regions (grassland, alpine tundra, arctic tundra, or North America), we did not detect significant relationships between species density and ANPP for any region. The results of our analyses demonstrate that the spatial scale of analysis – how data are aggregated and patterns examined – can influence the form of the relationship between species density and productivity. It also demonstrates the need for data sets from a broad spectrum of sites sampled over a range of scales for examining challenging and controversial ecological hypotheses.     

Ecological relationships between phytoplankton communities and different spatial scales in European reservoirs: implications at catchment level monitoring programmes

Phytoplankton communities are structured by factors acting over temporal and spatial scales. Identifying which factors are driving spatial patterns in aquatic communities is the central aim of ecology. In this study, data sets of phytoplankton communities and environmental data of two Portuguese reservoirs types (lowland “riverine reservoirs” and higher altitude “artificial lake reservoirs”) were used to determine the importance of environmental variables at different spatial (geographical, regional and local) and time scales (seasons, years) on the community structure. In all the data sets, the multivariate ordination technique Canonical Correspondence Analysis (CCA) showed that regional and local scales explained the majority (9–18% and 13–19%, respectively) of the taxa variance. However, for “riverine reservoirs”, time variables were more important, explaining 27% of the variability in phytoplankton assemblages. Variance partitioning was used to assess the individual importance of the three spatial scales and time for the community structure of the two reservoir types. The majority of among-site variability (5.9–21.4%) was accounted for by time variables, with local, regional, and geographical scale variables accounting for 3.3–5.6%, 3.7–4.5% and 2.6–2.9%, respectively. The effects of different spatial scales on phytoplankton communities were clearly interrelated; thus, implying that phytoplankton assemblages are capable of detecting stress from catchment to site scales. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Padisak     

Interaction between wind-induced seiches and convective cooling governs algal distribution in a canyon-shaped reservoir

1. Wind is considered the dominant factor controlling phytoplankton distribution in lentic environments. In canyon‐shaped reservoirs, wind tends to blow along the main axis generating internal seiches and advective water movements that jointly with biological features of algae can produce a heterogeneous phytoplankton distribution. Turbulence generated by wind stress and convection will also affect the vertical distribution of algae, depending on their sinking properties. 2. We investigated the vertical and horizontal distribution of phytoplankton during the stratification period in Sau Reservoir (NE Spain). Sites along the main reservoir axis were sampled every 4 h for 3 days, and profiles of chlorophyll‐a and temperature were made using a fluorescent FluoroProbe, which can discriminate among the main algal groups. Convective and wind shear velocity scales, and energy dissipation were calculated from meteorological data, and simulation experiments were performed to describe non‐measured processes, like vertical advection and sinking velocity of phytoplankton. 3. Wind direction changed from day to night, producing a diel thermocline oscillation and an internal seiche. Energy dissipation was moderate during the night, and mainly attributed to convective cooling. During the day the energy dissipation was entirely attributed to wind shear, but values indicated low turbulence intensity. 4. The epilimnetic algal community was mainly composed of diatoms and chlorophytes. Chlorophytes showed a homogeneous distribution on the horizontal and vertical planes. Diatom horizontal pattern was also homogeneous, because the horizontal advective velocities generated by wind forcing were not high enough to develop phytoplankton gradients along the reservoir. 5. Diatom vertical distribution was heterogeneous in space and time. Different processes dominated in different regions of the reservoir, due to the interaction between seiching and the daily cycle of convective‐mediated turbulence. As the meteorological forcing followed a clear daily pattern, we found very different diatom sedimentation dynamics between day and night. Remarkably, these dynamics were asynchronous in the extremes of the seiche, implying that under the same meteorological forcing a diatom population can show contrasting sedimentation dynamics at small spatial scales (approximately 10³ m). This finding should be taken into account when interpreting paleolimnological records from different locations in a lake. 6. Vertical distribution of non‐motile algae is a complex process including turbulence, vertical and horizontal advection, variations in the depth of the mixing layer and the intrinsic sinking properties of the organisms. Thus, simplistic interpretations considering only one of these factors should be regarded with caution. The results of this work also suggest that diatoms can persist in stratified water because of a synergistic effect between seiching and convective turbulence.     

Trait variation and integration across scales: is the leaf economic spectrum present at local scales?

Trait‐based approaches have taken an increasingly dominant role in community ecology. Although trait‐based strategy dimensions such as the leaf economic spectrum (LES) have been identified primarily at global‐scales, trait variation at the community scale is often interpreted in this context. Here we argue from several lines of evidence that a research priority should be to determine whether global‐scale trait relationships hold at more local scales. We review recent literature assessing trait variation at smaller scales, and then present a case study exploring the relationship between the correlation strength of leaf traits and their similarity in variation structure across ecological scales. We find that the correlation strength between pairs of leaf traits does not predict whether the traits respond similarly to different drivers of variation. Instead, correlation strength only sets an upper bound to the dissimilarity in trait variation structure. With moderate correlation strengths, LES traits largely retain the ability to respond independently to different drivers of phenotypic variation at different scales. Recent literature and our results suggest that LES relationships may not hold at local scales. Clarifying under what conditions and at which scales the LES is consistently expressed is necessary for us to make the most of the emerging trait toolbox.     

Disturbance, diversity and phytoplankton production in a reservoir affected by inter-basin water transfers

The effect of water transfers between two reservoirs on the phytoplankton community of the receiving reservoir was investigated over a 9-year period. Canonical correspondence analysis was used to demonstrate the significance of water transfers as an anthropogenic disturbance to the phytoplankton community and its diversity. A mass balance associated with a Granger causality test was applied to discriminate between the cell transport effect from the upstream reservoir and internal processes within the receiving reservoir, and to quantify the net phytoplankton growth in the receiving reservoir. Low and high disturbance regimes were identified and diversity was maximised during low disturbance conditions. The decrease of diversity during high disturbance conditions was explained by decreasing retention time, increasing silica loads and by the transport of specific phytoplankton genera, i.e. diatoms, from the upstream reservoir. Disturbance regimes significantly affected the relationship between phytoplankton production and diversity. Low disturbance regimes were described by phytoplankton dynamics likely influenced by complementarity effects, while high disturbance regimes were characterised by a phytoplankton community dominated by highly productive species and increased productivity, thus indicating an advantage of selection behaviour over complementarity effects. The phytoplankton diversity, expressed as evenness, was identified as a key variable explaining the relationship disturbance-diversity-phytoplankton production.     

Weedbeds and big bugs: the importance of scale in detecting the influence of nutrients and predation on macroinvertebrates in plant‐dominated shallow lakes

1. The scale of investigations influences the interpretation of results. Here, we investigate the influence of fish and nutrients on biotic communities in shallow lakes, using studies at two different scales: (i) within‐lake experimental manipulation and (ii) comparative, among‐lake relationships. 2. At both scales, fish predation had an overriding influence on macroinvertebrates; fish reduced macroinvertebrate biomass and altered community composition. Prey selection appeared to be size based. Fish influenced zooplankton abundance and light penetration through the water column also, but there was no indication that fish caused increased resuspension of sediment. 3. There were effects of nutrients at both scales, but these effects differed with the scale of the investigation. Nutrients increased phytoplankton and periphyton at the within‐lake scale, and were associated with increased periphyton at the among‐lake scale. No significant effect of nutrients on macroinvertebrates was observed at the within‐lake scale. However, at the among‐lake scale, nutrients positively influenced the biomass and density of macroinvertebrates, and ameliorated the effect of fish on macroinvertebrates. 4. Increased prey availability at higher nutrient concentrations would be expected to cause changes in the fish community. However, at the among‐lake scale, differences were not apparent in fish biomass among lakes with different nutrient conditions, suggesting that stochastic events influence the fish community in these small and relatively isolated shallow lakes. 5. The intensity of predation by fish significantly influences macroinvertebrate community structure of shallow lakes, but nutrients also play a role. The scale of investigation influences the ability to detect the influence of nutrients on the different components of shallow lake communities, particularly for longer lived organisms such as macroinvertebrates, where the response takes longer to manifest.     

Environmental forcing on the interactions of plankton communities across a continental shelf in the Eastern Atlantic upwelling system

To investigate whether phytoplankton is the main factor determining mesozooplankton distribution in a continental shelf affected by upwelling, oceanographic surveys were conducted off NW Portugal in 2002 and 2003. During four different seasons, we investigated how the mesoscale relationship between these two communities was forced by environmental conditions across the shelf. The horizontal and vertical distribution of phytoplankton was shaped by wind stress over the water. Diatoms dominated mixed and upwelled waters, whereas dinoflagellates prevailed with thermal stratification. Mesozooplankton was less influenced by wind forcing and concentrated mostly at mid-shelf, on the outer margin of main phytoplankton patches. We found that this pattern, under strong thermal stratification conditions, can be associated with localized grazing “hot spots”. Copepods were dominant, contributing to the mesozooplankton community variability between cruises whereas phytoplankton presented a clearer seasonal pattern. Nevertheless, the distribution and abundance of mesozooplankton were directly correlated with all phytoplankton groups at the inner-mid-shelf, while no correlation was observed offshore the outer-shelf. The relative composition of mesozooplankton did not vary between depth strata, whereas a cross-shelf separation occurred between nearshore and widespread clusters of species. This reflected a dependence on phytoplankton and reflected the high variability of oceanographic conditions of the study area.     

The Intermediate Disturbance Hypothesis and its applicability to planktonic communities: Comments on the views of Padisak and Wilson

The relevance of Connell's Intermediate Disturbance Hypothesis (IDH) to explanations of diversity and co-existence among plant species generally and in the phytoplankton in particular has been debated recently. Compared to terrestrial vegetation, planktonic communities experience distorted time and space scales, Generation times are in the order of days, not years to decades, Advective fluid transport raises the critical patch size to the order of kilometers, Within these scales, species survival and growth, community assembly and successional development in the phytoplankton conform to all the standards (compositional, strategic, thermodynamic) of conventional community organisation. These processes are known to move toward competitively excluded outcomes, Equally, they are liable to be interrupted by externally imposed disturbances, which reset the succession or alter its potential outcome, These findings are not only illustrative of intermediate disturbance but are instructive in the nature of diversity- disturbance relationships generally, IDH has considerable potential to explaining persistent species co-existence.     

Spatial and temporal variability among marine Bacteroidetes populations in the NW Mediterranean Sea

The abundance and structure of Bacteroidetes populations at diverse temporal and spatial scales were investigated in the Northwestern Mediterranean Sea. At a temporal scale, their relative abundance exhibited a marked seasonality, since it was higher in spring and decreased in winter. Similarly, Bacteroidetes community structure encompassed three main groups (winter, spring and summer-fall), which mimicked global bacterioplankton seasonality. At the spatial scale, relative abundances were similar in all surface samples along an inshore–offshore transect, but they decreased with depth. Analysis of the community structure identified four markedly different groups mostly related to different depths. Interestingly, seasonal changes in abundance and community structure were not synchronized. Furthermore, richness was higher when Bacteroidetes were less abundant. The variability of Bacteroidetes contributions to community structure in the temporal and spatial scales was correlated with different environmental factors: day length was the most important factor at the temporal scale, and salinity at the spatial scale. The community composition in terms of phylotypes changed significantly over time and along the depth gradients, but season or depth-specific phylogenetic clusters were not identified. Delineation of coherent Bacteroidetes sub-clusters should help to uncover higher resolution patterns within Bacteroidetes, and explore associations with environmental and biological variables.     

Quantifying the ecological stability of a phytoplankton community: The Lake Kinneret case study

The widely used term “stability” has multiple meanings and is rarely quantified in limnological studies. The main objective of this study was to develop an approach for quantifying the stability of a phytoplankton community using Lake Kinneret as a case study. It is a first attempt of calculating an index of stability for each of the five main taxonomic groups of the Kinneret phytoplankton (Bacillariophyta, Chlorophyta, Cryptophyta, Cyanophyta and Dinophyta), and for the entire community. A simple statistical approach to calculate the stability index was devised, using phytoplankton wet-weight biomass as the parameter being manipulated. The period 1970–1979 was selected as a reference period. The following stability indices were established and applied (each at three time scales): (1) a stability index for each of five main taxonomic groups; (2) a combined index of the stability, aggregating the stabilities of the individual taxonomic groups and (3) a stability index of entire community based on total phytoplankton biomass. The dynamics of these indices during 1969–2011 were examined. Destabilization of the community structure was triggered by an increase in the variability of Bacillariophyta biomass shortly after the reference period, in 1981–1983. Only 10 years later, the community destabilization become associated with progressively increasing biomass of Cyanobacteria. Dinophyta were the last to destabilize in the mid 1990s. Despite notable changes in the community structure, the total phytoplankton biomass remained relatively stable. Therefore, in 1969–2011 the stability index based on total phytoplankton biomass was higher than the combined index based on the stabilities of the individual taxonomic groups. Only weak relationships were found between the stability index values and potential driving forces (lake water level fluctuations and nutrient loads). While this approach was applied to Lake Kinneret, the concept presented is not lake specific and could be applied to other lakes.     

Regional species pools control community saturation in lake phytoplankton

Recent research has highlighted that positive biodiversity–ecosystem functioning relationships hold for all groups of organisms, including microbes. Yet, we still lack understanding regarding the drivers of microbial diversity, in particular, whether diversity of microbial communities is a matter of local factors, or whether metacommunities are of similar importance to what is known from higher organisms. Here, we explore the driving forces behind spatial variability in lake phytoplankton diversity in Fennoscandia. While phytoplankton biovolume is best predicted by local phosphorus concentrations, phytoplankton diversity (measured as genus richness, G) only showed weak correlations with local concentrations of total phosphorus. By estimating spatial averages of total phosphorus concentrations on various scales from an independent, spatially representative lake survey, we found that close to 70 per cent of the variability in local phytoplankton diversity can be explained by regionally averaged phosphorus concentrations on a scale between 100 and 400 km. Thus, the data strongly indicate the existence of metacommunities on this scale. Furthermore, we show a strong dependency between lake productivity and spatial community turnover. Thus, regional productivity affects beta-diversity by controlling spatial community turnover, resulting in scale-dependent productivity-diversity relationships. As an illustration of the interaction between local and regional processes in shaping microbial diversity, our results offer both empirical support and a plausible mechanism for the existence of common scaling rules in both the macrobial and the microbial worlds. We argue that awareness of regional species pools in phytoplankton and other unicellular organisms may critically improve our understanding of ecosystems and their susceptibility to anthropogenic stressors.     

巢湖双桥河底泥疏浚过程中浮游植物功能群分类研究

浮游植物功能群分类分析可以精确地反映水体环境变化对水生生物群落的影响。为探究巢湖双桥河底泥疏浚工程对浮游植物群落及水生生态系统的影响,对2017年6月—2018年3月双桥河底泥疏浚期间的水体理化因子、浮游植物群落结构和功能群划分开展了研究。研究发现,底泥疏浚工程能够大量削减双桥河水体中的氮、磷营养盐,但疏浚后的双桥河仍处于中-富营养状态;双桥河浮游植物群落依据其生态功能可划分为M、H1、H2、MP、S1、L_O、X2、X1、J、F、N、G、X3、C、D、Y、W1、L_M、E、T、S_N、K、P等23个功能群,绝对优势功能群为以微囊藻为主的M功能群和以硅藻为主的MP、P功能群。底泥疏浚工程对双桥河浮游植物种类的影响不大,但藻类密度和生物量在疏浚后有显著地下降,浮游植物多样性指数也有提升。将浮游植物功能群生物量与环境因子进行冗余分析(RDA)和Pearson分析发现,水环境因子变化对双桥河浮游植物功能群产生了较大影响,双桥河浮游藻类优势功能群由底泥疏浚前的M、MP、P、W1、Y类转变为底泥疏浚后的C、F、J、M、MP、P、Y类。其中,底泥疏浚工程造成的氮营养盐削减可以对双桥河浮游植物功能群产生较大影响。研究认为双桥河底泥疏浚工程在改善河流浮游植物生态功能,减轻水体污染程度上有积极的作用。     

温带落叶阔叶林地表鞘翅目成虫小尺度空间格局动态分析

土壤动物空间格局是格局—过程以及生物多样性维持机制研究的重要基础,目前小尺度空间土壤动物空间格局动态特征仍不清楚。基于地统计空间分析方法,以鞘翅目成虫为研究对象,研究帽儿山温带落叶阔叶林小尺度空间(5m)地表鞘翅目成虫群落及类群的空间格局动态特征。结果表明:4次调查共捕获鞘翅目成虫11科、29类、1021只个体,调查月份鞘翅目成虫群落具有较强的时空变异性;Moran'sⅠ系数表明鞘翅目成虫群落和类群具有复杂的正的空间自相关性,其空间异质性可用球状、指数、高斯和线性模型进行拟合。这种空间异质性具有一定的时间变化特征,且这种空间分异是由随机性因素单一调控或结构性因素和随机性因素共同调控的结果;类群之间在多种尺度上表现为复杂的以负相关居多的空间关联性,这种空间关联性的形成主要是结构性因素或随机性因素单一调控的结果。本实验表明地表鞘翅目成虫群落在小尺度空间具有明显的空间异质性特征,这种空间异质性时间变异性较明显。     

Scaling effects of grazing in a semi-arid grassland

Abstract. Previous studies have demonstrated relationships between spatial scale and spatial pattern and developed general hypotheses of scaling effects. Few studies, however, have examined the interactive relationship between scale and pattern-driving processes such as grazing. The goal of this study is to evaluate scale-dependent patterns across three spatial scales for three grazing intensities over 45 yr and to identify some mechanisms that may be associated with scale related differences. Correlation analysis and analysis of the coefficients of variation indicate that the relationships between units are dependent upon spatial scale and treatment. Across all grazing treatments, the relationship between units of the same scale becomes stronger as the spatial scale is increased. However, the rate of increase in the correlation coefficient is different for each treatment. The coefficient of variation responded inversely across scales with the greatest variation between small-scale units and little difference between the intermediate- and large scales. In addition to different relationships between units at each scale, differences in heterogeneity within treatments over time is illustrated by the relationship between small-scale units within each treatment and their associated larger scale units. The strongest relationship occurred in the heavily grazed treatments where correlation coefficients of small-scale units with intermediate- and large-scale units were ca. 0.60, indicating similar dynamics across scales. For the moderately grazed and ungrazed treatments this relationship varied from 0.40 to 0.47. Results from this study suggest that grazing alters scaling effects. Variability between small-scale units was greatest in the ungrazed treatment which had greater heterogeneity and less predictability than grazed treatments because of the influence of grazing on plant morphology, demography and composition. At the intermediate scale, relationships between units were fairly similar with the least variation occurring in the moderately grazed treatment. Alternatively, variation between large-scale units was greatest in the moderately grazed treatment because of the relationship between rest cycles, weather patterns, and patch grazing. Therefore, grazing can have a positive, a negative, or no influence on heterogeneity between units depending upon the scale of observation. Evaluation of long-term dynamics across these treatments at the same small spatial scale results in different variances within each treatment which may violate assumptions of some statistical and experimental designs. Therefore, evaluations of temporal dynamics should consider scale relative to the relationship between plant size, density and longevity (relative scale).     

太湖浮游细菌与春末浮游藻类群落结构演替的相关分析

为研究浮游细菌与浮游藻类群落演替的相关性,2005年4月至6月在太湖5个观测点采集浮游细菌及浮游藻类样本。分别采用聚合酶链式反应-变性梯度凝胶电泳（PCR—DGGE）和显微观察的方法分析浮游细菌及浮游藻类群落组成。结果表明,春末夏初,浮游细菌与藻类均呈现较高的多样性,浮游细菌DGGE图谱具有43种不同条带,浮游藻类的常见种有29种。浮游细菌群落聚类分析显示,丝藻（Ulothrix sp．）和微囊藻（Microcystis spp．）占优势时,浮游细菌群落基因组成存在明显差异。以藻类种群Shannon—Wiener多样性指数（Hp）,浮游藻类总细胞数（N）以及Microcystis spp．（M）百分含量为变量,典型对应分析（CCA）结果显示浮游细菌与浮游藻类群落结构变化的相关系数为30．9％,表明春末夏初太湖浮游细菌与浮游藻类群落演替具有较高的相关性。