An analysis of succession along an environmental gradient using data from a lawn

Differences in vegetation dynamics over a period of two years along an environmental gradient of shading on a lawn are examined. Communities (groups) recognized by numerical classification are correlated with degree of shading, season and differences between years by means of generalized linear model analysis. More of the variance is explained if environmental position is used instead of degree of shading as spatial distribution of a strongly competitive species (Trifolium repens) is confounded with shading. Transition probabilities are related to environmental position and season. Simulation with Markov matrices for each season and position demonstrate markedly different successions for different positions. These simulations have no predictive value however as accurate estimate of transition probabilities requires knowledge of the state of adjacent quadrats, i.e. individual observations of transition probabilities are not independent.Transition matrices are unlikely to be useful for predictive analysis of succession when spatial pattern is of significance in the community.We thank S. Kendall, S. Witts, A. Howard and C. Helman for their assistance with the data preparation and analysis, and R. Cunningham for advice on statistical analysis.     

Multi-species pattern analysis of Mediterranean pastures in three stages of ecological succession

Multi-species patterns were analyzed in three stages of ecological succession in oligotrophic pastures in Central Spain using a new method of analysis. The method is based on plotting the species coordinates of principal components analysis undertaken at different block sizes. It allows the detection of any heterogeneity present and reveals both microtopographical and macrotopographical trends in species patterns.Nomenclature follows Tutin et al., 1964–1980, Flora Europaea.     

Short-term succession dynamics of macrobenthos in a salinity-stressed estuary

It is postulated that early succession is influenced by environmental conditions directly after a disturbance event and the temporal scale of succeeding disturbances. For example, Rincon Bayou, Texas, U.S.A. is an estuary stressed by large fluctuations in salinity ranging from oligohaline to hypersaline conditions; leading to the question: are benthic succession dynamics interrupted or affected by the temporal scale of salinity fluctuations? To answer this question, succession dynamics were investigated by manipulation of 1) initial environmental conditions, and 2) time between severe disturbances. The influence of environmental conditions and time course of succession were investigated by comparing two experiments. A synoptic-deployment experiment where samples were deployed at the same environmental conditions and a synoptic-retrieval experiment where samples were collected from deployments under different environmental conditions. Both experiments were conducted at varying time courses of 2-, 4- and 8-week durations between severe disturbances. Severe disturbances were simulated with defaunated sediment. Ambient conditions were simultaneously sampled as a reference. Environmental conditions directly affected succession. In the ambient study, succession occurred in conjunction with changes in environmental conditions. In the synoptic-deployment and synoptic-retrieval studies, environmental conditions at the time of retrieval were more important in determining community structure than deployment duration or initial environmental conditions at time of deployment. Initial environmental conditions were not the primary mechanism in regulation of succession because succession is likely interrupted by frequent salinity disturbances. The salinity-stressed estuary of Rincon Bayou appears to be in a constant state of early and intermediate succession because of frequent salinity-related disturbances.     

恢复演替中草地斑块动态及尺度转换分析

研究了９ａ草地恢复油潜系列中斑块边界形状和斑块面积分布动态,并进行了凡度转换分析。獐茅斑块的边界分维数和斑块化指数最高,羊草斑块的较低,碱蓬斑块的斑块化指数略小于羊草斑块,边界分维数大于洋草斑块。共他类型斑块的两种指数基本上介于獐茅斑块之间,斑块化指数的年限变动滞后于斑块边界分维数,斑块边发维数在整个试验的尺度范围内符合同一自相似规律,斑块的面积分布格局在不同的尺度上有不同的自相似规律。     

Simulated dynamics of succession in a North American subtropical Prosopis savanna

Abstract. A transition matrix model was used to explore the dynamics, rate and potential extent of changes in landscape vegetation patterns on a southern Texas Prosopis savanna. Transitions between seven vegetation classes were determined for the periods 1941–1960 and 1960–1983 on aerial photographs of three sites. During these periods, the sites were heavily grazed by cattle and were fire-free. Vegetation states assessed in grids of 20 m x 20 m cells superimposed on photographs ranged from grass-dominated to woody plant-dominated. The 1941–1960 period (denoted DRY) was characterized by prolonged drought, whereas annual rainfall during the 1960–1983 period (denoted WET) was typically normal to above-normal. The 1941 landscape consisted of herbaceous zones (6% of cells), woodland (50% of cells) and savanna parkland (44% of cells with grass/woody plant mixtures). The woodland state was the most stable, with probabilities of no change being 0.970 and 0.873 in WET and DRY periods, respectively. The herbaceous state was least stable, with corresponding values of 0.074 and 0.353. Past and future landscape structure was modelled by randomly selecting DRY or WET transitions at 20 year time steps. The model was run under a series of rainfall scenarios where the probability of selecting the WET transition matrix (P[WET]) ranged from 0 (DRY always chosen) to 1 (WET always chosen). Historical records indicate P[WET] has approximated 0.3 to 0.4 in the region. The rate of succession to states of greater woody cover increased as P[WET] increased. Forward simulations based on P[WET] > 0.2 suggest the present landscape is unstable and will develop into a closed-canopy woodland within the next 180 years, assuming the processes operating between 1941 and 1983 continue (e.g. grazing by cattle and lack of fire). Reverse simulations concur with historical observations and projections derived from woody plant growth rates in other studies and suggest that 200 to 300 yr BP these landscapes contained a substantially greater proportion of cells dominated by grassland or grassland with scattered woody plants (43 to 74%) than was present in 1983 (19%). Based upon elapsed time between predicted past and future steady states, succession from open savanna to closed-canopy woodland may occur in ca. 400 to 500 yr for P(WET) ≥ 0.33. Arresting or reversing the projected trend may require changes in climate and/or changes in livestock grazing and land management practices. The approaches employed in this study illustrate how time series maps, aerial photographs and satellite imagery can be analyzed and used to interpret, project and reconstruct local and regional changes in ecosystem structure. Difficulties and limitations associated with the use of Markov chains to model succession are identified and discussed.     

Effects of nitrogen limitation on species replacement dynamics during early secondary succession on a semiarid sagebrush site

Summary A soil nitrogen (N) availability gradient was induced on a disturbed sagebrush site in northwestern Colorado by fertilizing with nitrogen (high available N), applying sucrose (low available N), and applying neither nitrogen nor sucrose (control). Species composition was studied for 3 years. At the end of the study, N concentration of aboveground tissue of 3 major species was determined. The rate of species replacement was most rapid on plots receiving the sucrose treatment and was slowest on plots receiving the N treatment. Early-seral dominats had greater tissue N concentrations when availability of the resource was high but lower tissue N concentrations when available soil N became limited. Midseral dominants displayed the opposite pattern. These results suggest that the supply of available soil N, and therefore the dynamics of N incorporation in perennial plant tissue, is a primary mechanism in controlling the rate of secondary succession within this semiarid ecosystem.     

Successional dynamics of a semiarid grassland: effects of soil texture and disturbance size

We evaluated effects of soil texture and disturbance size on the successional dynamics of a semiarid grassland dominated by the perennial bunchgrass, Bouteloua gracilis (H.B.K.) Lag. ex Griffiths. A spatially-explicit gap dynamics simulation model was used to evaluate recovery patterns. The model simulates establishment, growth, and mortality of individual plants on an array of small plots through time at an annual time step. Each simulated disturbance consisted of a grid of plots of the same soil texture interconnected by processes associated with dispersal of B. gracilis seeds. Soil texture was incorporated into the model as effects on seed germination, seedling establishment, and subsequent growth of B. gracilis. Five soil texture classes and five disturbance sizes were simulated.Soil texture was more important to recovery of B. gracilis than either size of a disturbance or location of plots within a disturbance. Constraints on recruitment of seedlings had a greater effect on recovery than constraints associated with plant growth. Fastest recovery occurred on soils with the largest silt content, the variable that affects seedling establishment. Disturbances with slowest recovery were on soils with low silt contents, and either high or low water-holding capacity, the variable that affects plant growth. Biomass and recovery decreased as disturbance size increased, and as distance from a disturbed plot to the edge of the disturbance increased. In most cases, important interactions between soil texture and disturbance size on recovery were not found.     

Competition among the pioneers in a seasonal soft-bottom benthic succession: field experiments and analysis of the Gilpin-Ayala competition model

Summary Controlled experiments, designed to assess the effects of pioneers on succession on an intertidal sandflat, provided evidence for interspecific competition between juvenile Hobsonia florida (Polychaeta, Ampharetidae) and oligochaetes. The field data were fitted to both the linear Volterra and non-linear Gilpin-Ayala competition equations. With its greater number of parameters, the Gilpin-Ayala model must provide a better fit to observed population abundances. The Gilpin-Ayala model is flawed as an explanation of the population trajectories of the H. florida and oligochaetes, because its non-linearity parameter affects only intraspecific competion. With either model our field data demonstrate a solution to Hutchinson's paradox. With competition coefficients near unity and similar carrying capacities, the predicted population trajectories are heavily dependent on initial conditions. The predicted times to competitive exclusion are long and can easily exceed the typical period of environmental constancy. Our study offers evidence for Neill's competitive bottleneck: competition acts primarily on the developmental stages of one of a pair of competing species. The permanent meiofauna may act as a competitive bottleneck for the population growth of benthic macrofauna. The mechanism of this competitive interaction probably involves exploitative interspecific competition for benthic diatoms.     

Vegetation succession on the dunes near Oostvoorne,The Netherlands; a comparison of the vegetation in 1959 and 1980

The vegetation of a 150 ha coastal dune area in the SW Netherlands was carefully analyzed and mapped at a scale of 1:2500 in 1959 and 1980. About 600 relevés were treated numerically. 127 vegetation types were distinguished, the overlap in community composition between the two years was very small. An intermediate level between this community level and the level of the structural-physiognomic formation was adopted. 56 so-called subformations, in which floristic and structural characters are combined, have been recognized and the overlap was then considerably larger, at least in number of types. Ordination results suggest that in each subset: grasslands, dune slacks, woodlands + scrubs, the first axis reflects floristic differentiation along with progression. The ordination of the entire material shows moisture as the main factor underlying the first axis, zonation as the second and nutrient status as the third factor. Change in vegetation was detected through a network overlay with 2 300 points for each of which the transition between 1959 and 1980 was scored. The pattern of change between 1959 and 1980 is apparently multiple pathway in type. This would be one of the few examples of such a pattern to be established on the medium term level of change, which is considered as succession sensu strictu. On an areal basis the change in vegetation is extremely large; even on the subformation level only 15% of the area was found to be unchanged, and on the community level only 4%. The overall trend is progression with a strong increase in the area of tall scrubs and woodlands. Retrogression also occurs, partly as a result of disturbances such as fire, partly due to local death of a dominant woody species. This latter phenomenon is interpreted against the background of the starting point of the succession; a sudden release of the inner dune area from overgrazing by cattle and a subsequent rapid dune development (outer dunes) on the beach in front of the inner dunes. Both species and community diversity increased, which is related to both differentiation under progression and to retrogression.     

Zooplankton succession on seasonal floodplains: surfing on a wave of food

Floodplains represent ecotones with frequent high productivity mediated by regular shifts between aquatic and terrestrial ecosystems. We examined interaction along this intercept on a seasonal floodplain of the Okavango Delta, Botswana. We focused on the zooplankton communities in order to gain knowledge on the energetic and stoichiometric interplay of the two systems involved. A conspicuous horizontal migration and pulsed biomass increase was found for the dominant zooplankton species (Moina micrura, Daphnia laevis, Mesocyclops leuckarti), culminating in truly extreme numbers before a final collapse. There was a distinct succession in the peak abundance of these species, apparently subsidized by hatchlings from the seed bank of resting eggs as the flood proceeded over the savannah. The high productivity of the system seems to be driven by a strong coupling of the terrestrial and aquatic phase of the floodplains via a mobilization of terrestrially derived nutrients, through nutrients from grazing ungulates during dry periods. Carbon of terrestrial origin, however, appeared to be of minor importance for the planktonic part of the food web. Handling editor: S. Dodson     

Classifying behavior from short‐interval biologging data: An example with GPS tracking of birds

1. Recent advances in digital data collection have spurred accumulation of immense quantities of data that have potential to lead to remarkable ecological insight, but that also present analytic challenges. In the case of biologging data from birds, common analytical approaches to classifying movement behaviors are largely inappropriate for these massive data sets.
2. We apply a framework for using K‐means clustering to classify bird behavior using points from short time interval GPS tracks. K‐means clustering is a well‐known and computationally efficient statistical tool that has been used in animal movement studies primarily for clustering segments of consecutive points. To illustrate the utility of our approach, we apply K‐means clustering to six focal variables derived from GPS data collected at 1–11 s intervals from free‐flying bald eagles (Haliaeetus leucocephalus) throughout the state of Iowa, USA. We illustrate how these data can be used to identify behaviors and life‐stage‐ and age‐related variation in behavior.
3. After filtering for data quality, the K‐means algorithm identified four clusters in >2 million GPS telemetry data points. These four clusters corresponded to three movement states: ascending, flapping, and gliding flight; and one non‐moving state: perching. Mapping these states illustrated how they corresponded tightly to expectations derived from natural history observations; for example, long periods of ascending flight were often followed by long gliding descents, birds alternated between flapping and gliding flight.
4. The K‐means clustering approach we applied is both an efficient and effective mechanism to classify and interpret short‐interval biologging data to understand movement behaviors. Furthermore, because it can apply to an abundance of very short, irregular, and high‐dimensional movement data, it provides insight into small‐scale variation in behavior that would not be possible with many other analytical approaches.

     

植物-土壤反馈与草地群落演替:菌根真菌和土壤病原菌的调控作用

由植物引起的根际土壤生物或非生物环境的改变能够反馈影响群落中不同植物的生长,直接改变共存植物的相对竞争关系,推动群落结构的动态变化。作为土壤生物群落的重要组成部分,土壤微生物在植物-土壤反馈关系中起到重要的调控作用,对解释植物群落的演替进程和方向有着重要的意义。在草地植物群落演替的早期阶段和外来物种入侵的过程中,宿主植物对丛枝菌根真菌（AMF）的依赖性较低,受本地病原菌的影响较小,一般不存在负反馈。在演替后期,植物对AMF更具依赖性,而积累的病原菌则产生较强的负反馈效应,从而促进群落物种共存和植物多样性,提高草地生产力和稳定性。研究微生物-植物反馈机制不仅有助于完善草地退化与恢复理论,还对退化草地恢复治理的实践有着指导意义。未来关于根际微生物-植物反馈在草地群落演替中的作用应该加强以下几方面的研究：（1）在实验方法上,开展专性微生物-植物反馈研究;（2）在测定指标上,进一步量化不同微生物在反馈关系中的功能差异;（3）在研究对象上,加强土壤微生物在植物群落水平的反馈研究;（4）在应用上,明晰植物-土壤反馈在退化草地恢复过程中的作用,指导草地管理实践。     

Recovery and succession in a multi-species tropical seagrass meadow following experimental disturbance: the role of sexual and asexual reproduction

Recolonisation and succession in a multi-species tropical seagrass meadow was examined by creating gaps (50×50 cm) in the meadow and manipulating the supply of sexual and asexual propagules. Measurements of leaf shoot density and estimates of above-ground biomass were conducted monthly to measure recovery of gaps between September 1995 and November 1997. Measurements of the seeds stored in the sediment (seed bank) and horizontal rhizome growth of colonising species were also conducted to determine their role in the recovery process.Asexual colonisation through horizontal rhizome growth from the surrounding meadow was the main mechanism for colonisation of gaps created in the meadow. The seed bank played no role in recolonisation of cleared plots. Total shoot density and above-ground biomass (all species pooled) of cleared plots recovered asexually to the level of the undisturbed controls in 10 and 7 months, respectively. There was some sexual recruitment into cleared plots where asexual colonisation was prevented but seagrass abundance (shoot density and biomass) did not reach the level of unmanipulated controls. Seagrass species did not appear to form seed banks despite some species being capable of producing long-lived seeds.The species composition of cleared plots remained different to the undisturbed controls throughout the 26-month experiment. Syringodium isoetifolium was a rapid asexual coloniser of disturbed plots and remained at higher abundances than in the control treatments for the duration of the study. S. isoetifolium had the fastest horizontal rhizome growth of species asexually colonising cleared plots (6.9 mm day⁻¹). Halophila ovalis was the most successful sexual coloniser but was displaced by asexually colonising species. H. ovalis was the only species observed to produce fruits during the study.Small disturbances in the meadow led to long-term (>2 years) changes in community composition. This study demonstrated that succession in tropical seagrass communities was not a deterministic process. Variations in recovery observed for different tropical seagrass communities highlighted the importance of understanding life history characteristics of species within individual communities to effectively predict their response to disturbance. A reproductive strategy involving clonal growth and production of long-lived, locally dispersed seeds is suggested which may provide an evolutionary advantage to plants growing in tropical environments subject to temporally unpredictable major disturbances such as cyclones.     

Realistic population dynamics in epidemiological models: the impact of population decline on the dynamics of childhood infectious diseases. Measles in Italy as an example

Most contributions in the field of mathematical modelling of childhood infectious diseases transmission dynamics have focused on stationary or exponentially growing populations. In this paper an epidemiological model with realistic demography is used to investigate the impact of the non-equilibrium conditions typical of the transition to sustained below replacement fertility (BRF) recently observed in a number of western countries, upon the transmission dynamics of measles. The results depend on the manner we model the relation between the (changing) age distribution of the population and contacts. Under some circumstances the transitional ageing phase typical of BRF populations might complexly interact with epidemiological variables leading to (i) a substantial reduction in the amount of vaccination effort required for eliminating the disease; (ii) a significant magnification of the perverse impact of vaccination in terms of the burden of severe age related morbidity.     

Anthropometry and numerical taxonomy in clinical genetics: An example of applied biological anthropology

Biological anthropologists can contribute a unique perspective as well as technical expertise to the diagnosis and classification of genetic disorders. Anthropometry has been used with increasing frequency to characterize syndromes and to establish ranges of variation within syndromes. The specific anthropometric-radiologic technique of metacarpophalangeal pattern profile analysis has proven useful in discriminating individuals with the Prader-Labhart-Willi (PLW) syndrome from unaffected persons. Analysis of these data also indicate a negative correlation between age and Z-score transformations of individual hand bone lengths. These findings sound a cautionary note to clinical investigators who would use the Z-score transformation to standardize for age and sex. Problems encountered in the classification of genetic syndromes afford many parallels with those faced by anthropologists in the classification of living and fossil populations. The reliance on “key” traits and the necessity of focusing on pedigree analysis results in a deemphasis of the total range of variation and typological thinking. Application of numerical taxonomic techniques to the classification of the heterogeneous connective tissue disease osteogenesis imperfecta (OI) illustrates the heuristic value of this technique and points out the need to consider phenotypic overlap when defining typologies. Clinical genetics affords just one example of an area in medicine where the unique training and generalist perspective of the biological anthropologist is in demand. The decline in the availability of positions in the traditional academic habitat for biological anthropologists makes it imperative that graduate students be aware of alternatives and that they obtain training in the practical skills which such alternatives will demand.     

Effects of grassland management on plant nitrogen use efficiency (NUE): Evidence from a long-term experiment

Grassland management intensification can greatly influence nitrogen (N) dynamics between aboveground and belowground compartments mainly because of the large amount of available N forms, which are repeatedly added to soils. A better understanding of how chronic fertilisation might affect N use efficiency (NUE) in plants can contribute to reducing N losses from soils and improve the sustainability of managed grasslands. Here we address how NUE might be affected by (1) the addition of key nutrients (e.g. N, P, K, Mg) in different combinations, (2) grazing by rabbits, and (3) liming (i.e. CaCO₃ applications) in a 22-year-old permanent grassland experiment established in Berkshire, UK, in 1991. We first calculate seven different NUE indexes, which are known to respond either to changes in soil N availability (i.e. endogenous N inputs from soil N mineralization processes) or to exogenous N inputs (i.e. synthetic N fertiliser). We found that plant NUE calculated as plant biomass produced per unit of N acquired significantly decreased under the chronic addition of multiple nutrients (NPKMg) and was even lower under N-only applications. Most NUE indexes significantly decreased under grazing but greatly increased under liming applications. We found evidence that NUE indexes, which accounted for endogenous N sources decreased at increased rates of soil N mineralization. Finally, we found no significant relationships between any of the NUE indexes and estimates of soil N losses (Mg N ha⁻¹) or N retention in soils (i.e. units of soil N retained per unit of N added) calculated from changes in net soil N budget over 22 years. Our study carried out on relatively acidic sandy soils suggests how liming applications in combination with low levels of multi-nutrient additions (NPKMg) can significantly improve plant biomass production per unit of N added thus contributing to enhance the sustainability of managed grassland ecosystems.     

InterPro as a new tool for complete genome analysis: An example of comparative analysis

InterPro, an integrated documentation resource for protein families, protein domains, and functional sites, was developed to amalgamate the individual efforts of the PROSITE, PRINTS, Pfam, and ProDom databases. InterPro can be used for the computational functional classification of newly determined amino acid sequences that lack biochemical characterization and for comparative genome analysis. InterPro contains over 3500 entries for more than 1 000 000 hits in SWISS-PROT and TrEMBL. The database is accessible for text-and sequence-based searches at http://www.ebi.ac.uk/interpro/. InterPro was used for the complete analysis of the proteome of the pathogenic microorganism Mycobacterium tuberculosis and the comparison with the predicted protein-coding sequences of the complete genomes of Bacillus subtilis and Escherichia coli. It was found that 64.8% of proteins in the proteome of M. tuberculosis matched InterPro entries and can be classified by their functions. The comparison with B. subtilis and E. coli provided information on the most common protein families and domains and on the most highly represented protein families in each organism. Thus, InterPro is a useful tool for general comparison of complete proteomes and their compositions.     

Assignment and evaluation of ground beetle (Coleoptera: Carabidae) assemblages to sites on different scales in a grassland landscape

Carabid beetles and environmental parameters were investigated in 52 grassland sites with three replicate pitfall traps in each site and in the valley of the River Eider in Schleswig–Holstein (northern Germany) with 61 pitfall traps. Environmental parameters included water content of soil, sand content, organic matter content and pH. Ground beetle assemblages were derived by detrended correspondence analyses (DCA) and characterised by the specific environmental conditions as means for each assemblage. On the regional scale including all investigated sites of Schleswig–Holstein, five assemblages were differentiated. On the local scale including the investigated sites in the valley of the River Eider, three assemblages were found corresponding well with those found on the regional scale. Environmental conditions at the sites of the five assemblages were correlated with land use data, soil types, and water level stages provided by three maps of a geographic information system (GIS). The GIS maps were combined to develop smaller areas with land use, soil type and water level stage information. The characteristic environmental conditions were assigned to each area to derive the spatial distribution of the five ground beetle assemblages. Spatial prediction was correct for 65% of investigated sites. The potential area of each assemblage was estimated for the valley. The different grassland areas were evaluated as potential habitats for ground beetle species comparing total species richness with the regional species richness of each assemblage. The comparison shows that species richness in the evaluated assemblages is relatively low compared to the regional potential.