Modelling the population dynamics of the sealworm Pseudoterranova decipiens

A host-parasite model is proposed to describe the dynamics of the P. decipiens complex life-cycle. Four developmental stages are considered: the adult worm in the final host's stomach, the larval stages in the invertebrate and fish hosts, and the free-living egg-larval stage. The dynamics of each stage are described by an ordinary differential equation.The sensitivity of the model to some parameter values forms the basis for a discussion of its potential use in the assessment of future management and control strategies. This is illustrated by examples of observed infections in cod (Gadus morhua) from Scottish waters in the light of the recent increase in the Grey seal (Halichoerus grypus) populations of the Orkney and Farne Islands.     

The European regional seas ecosystem model,a complex marine ecosystem model

This paper presents an overview of the concept, structure and implementation of the European Regional Seas Ecosystem Model (ERSEM). The model dynamically simulates the biogeochemical seasonal cycling of carbon, nitrogen, phosphorus and silicon in the pelagic and benthic food webs of the North Sea, and is forced by irradiance, temperature and transport processes.The model has a coarse spatial resolution into ten boxes, the ICES boxes, of which the five deepest have been resolved into surface (0 to 30 m) and deep (30 m to bottom) boxes.At the open boundaries, time series are prescribed for dissolved and particulate nutrients. River loads of nutrients for the rivers discharging into the North Sea are prescribed at monthly intervals. A general circulation model has been used to aggregate the exchange volumes across the box boundaries into daily in- and outflows. From these, the horizontal transports of dissolved and suspended constituents are calculated. Vertical transport is in the form of sinking and sedimentation for particulates and in the form of turbulent diffusion for dissolved constituents.The physical model contains all information specific to the area to be modelled, whereas the biological/chemical submodels have been constructed not to be site-specific.The biological variables are represented as functional groups expressed in units of organic carbon and the chemical variables as the internal pools in the biological variables and as the dissolved inorganic pools in water and sediment, expressed in units of N, P and Si.The model runs in a software environment (SESAME) developed for enabling the development of large and complex models in a modular way by a consortium of institutes, each focusing on different. aspects of the ecosystem, translating these into modules within the model. With the exception of fish populations, where size- and age-structure are explicity represented, all the other biological components have been modelled as unstructured populations aggregated into functional groups. This approach is shown to be appropriate for taxa having short generation times in relation to the annual cycle and for taxa which do not span more than one trophic level during their lifetime.     

On the population dynamics of dab,sole and flounder within bridgwater bay in the lower severn estuary,England

A ten year study of the population dynamics of the flatfish dab Limanda limanda, sole Solea solea and flounder Platichthys flesus was undertaken within Bridgwater bay in the Bristol Channel, England. Fish abundance was estimated from the rate of capture on power station intake filter screens at Hinkley Point Nuclear Power Station. The Bay was used as an 0-group nursery by all three species while flounder were alone in regularly using the area as adults. Using the coefficient of variation (CV) in annual catch as a measure of population stability these three flatfish were found to have some of the most stable populations within a fish community of 21 common species. When these species were classified according to their use of space as benthic, proximo-benthic or pelagic it was found that the benthic fish had the lowest CV values. It is argued that this stability is linked to their use of space. A notable feature was the differing seasonal occupancy of the Bay by the benthic fish which would act to reduce potential inter-specific competition. This suggests that spatial competition could only be intra-specific or against invertebrates. A search was made for biotic or physical factors correlated with year class abundance in the flatfish. The only significant correlation found was for sole, the abundance of which increased with increasing water temperature.     

Modelling the dynamics of the North Sea's Mesozooplankton

A simple biomass-only zooplankton submodel is presented, describing the dynamics of copepods and carnivorous zooplankton in the North Sea. This submodel together with the other process-oriented submodels (viz. phytoplankton dynamics, the microbial food web, benthic processes, fish dynamics and large-scale advective transport) forms a spatially resolved simulation model of the North Sea ecosystem, the European Regional Seas Ecosystem Model (ERSEM). A large set of field measurements of zooplankton abundance has been assembled against which to compare the ERSEM's performance. These data are not only internally consistent, but have also gathered at the large spatial scales appropriate to the ERSEM. In addition to the spatially resolved, monthly estimates of zooplankton abundance, several instantaneous, in situ estimates of the carbon fluxes between different components of the planktonic web in the northern North Sea are presented. Simulated dynamics are in good agreement with the data only during the mid-summer to mid-winter period. During the latter part of the winter and throughout the spring period zooplankton abundance is underpredicted and the simulated zooplankton growth rate is overpredicted during spring. The excessive decline of mesozooplankton biomass during winter may be caused by failing to capture many of the behavioural/physiological changes which zooplankton manifest during winter. It is suggested that the excessive spring growth is a consequence of a. a failure to properly distinguish between somatic and population growth, b. an inadequate representation of the small scale processes which influence feeding success, and c. an excessive spring phytoplankton bloom. The large phytoplankton bloom is, in part at least, a consequence of the excessively low simulated standing crop of omnivorous zooplankton in spring.     

氮肥施用量对稻飞虱与稻叶蝉及其捕食性天敌种群的影响*

为评价氮肥对田间稻飞虱和稻叶蝉及其捕食性天敌种群密度和种群动态的影响,在田间设立0、90、150和210 kg ha-1四个氮肥水平,研究田间白背飞虱、褐飞虱、灰飞虱、黑尾叶蝉、电光叶蝉和二点叶蝉以及捕食性天敌拟水狼蛛、驼背额角蛛、食虫沟瘤蛛和黑肩绿盲蝽的平均密度和种群密度的时间动态。结果表明,210 kg ha-1氮肥水平下,稻田白背飞虱、灰飞虱及稻飞虱(三种飞虱之和)的平均密度均显著高于0、90和150 kg ha-1稻田。0、90、150和210 kg ha-1氮肥稻田间,黑尾叶蝉、电光叶蝉、二点叶蝉和稻叶蝉(三种叶蝉之和)以及拟水狼蛛、驼背额角蛛、食虫沟瘤蛛和黑肩绿盲蝽的平均密度均无显著差异。不同氮肥施用量田间稻飞虱与稻叶蝉及捕食性天敌种群密度的时间动态走势基本一致。表明高水平的氮肥施用会显著促进田间稻飞虱种群密度增多,但对稻叶蝉及捕食性天敌种群密度均无显著影响。     

Population redistribution within metropolitan regions in the 1980s: core,satellite, and exurban growth

"This paper evaluates the hypothesis that the growth experiences of core parts of metropolitan areas [in the United States] tend to predict the growth of satellite, exurban, and even more distant non-metropolitan areas. Particular attention is paid to evidence of spillover of growth into adjacent smaller metropolises and smaller cities, and to the hypothesis that spillover is especially marked in areas of rapid growth, growth restrictions, and housing price inflation. The hypotheses are supported by 1980-1990 patterns of change, as is the continuing attractiveness of exurban and non-metropolitan environmental amenities."     

QTL mapping for chromium-induced growth and zinc, and chromium distribution in seedlings of a rice DH population

Chromium contamination in soil has become a severe threat to crop production and food safety. The experiment was conducted using a rice DH population to detect the QTLs associated with Cr tolerance. Seventeen putative QTLs associated with growth traits included three additive loci and fourteen epistatic loci. These loci were distributed on 11 rice chromosomes, and their contribution to the phenotypic variation ranged from 2.44 to 10.08%. Two QTLs located at the similar genetic region on chromosome ten were associated with shoot Cr concentration and translocation from roots to shoots, respectively; and they accounted for 11.65 and 11.22% of the phenotypic variation. In addition, six QTLs related to Zn concentration and translocation was found on chromosomes 1, 2, 4, 5, 7 and 12. Meanwhile epistatic effect existed in the two additive QTLs of qRZC1 and qRZC7. Most of QTLs controlling Zn concentration had small genotypic variance and qSRZ4 related to Zn translocation showed growth condition-dependent expression.     

Unravelling the relationship between a seasonal environment and the dynamics of forage growth in grazed swards

It is well reported in the scientific literature that pastures can have similar net forage accumulation when managed with contrasting structures. However, we hypothesized that the dynamics of forage accumulation in grazed swards is linked to seasonal-environmental conditions. Marandu palisadegrass (Brachiaria brizantha [Hochst. ex A. Rich.] was used as the forage species model. The experimental treatments were four grazing heights (10, 20, 30 and 40 cm) allocated to experimental units according to a randomized complete block design with four replicates and evaluated throughout four contrasting environmental seasons (summer, autumn, winter–early spring and late spring). Under rainy and warm periods, greater net forage accumulation was observed in pastures maintained taller; on the contrary, during the mild and dry periods, net forage accumulation rate reduced as grazing height increased. Such patterns of responses were related to compensations between tiller population density and tissues flows during summer and late spring and the reduced capacity of taller canopies to compensate lower population with greater growth rates during autumn and winter–early spring. Grazed swards changed their patterns of forage growth as they transitioned from favourable to more abiotic stressful conditions, suggesting that seasonal adjustments in grazing intensities are necessary in order to maximize forage production.     

Food intake and growth of Sarsia tubulosa (SARS, 1835), with quantitative estimates of predation on copepod populations

In laboratory tests food intake by the hydromedusa Sarsia tubulosa, which feeds on copepods, was quantified. Estimates of maximum predation are presented for 10 size classes of Sarsia. Growth rates, too, were determined in the laboratory, at 12°C under ad libitum food conditions. Mean gross food conversion for all size classes averaged 12%.From the results of a frequent sampling programme, carried out in the Texelstroom (a tidal inlet of the Dutch Wadden Sea) in 1983, growth rates of Sarsia in the field equalled maximum growth under experimental conditions, which suggests that Sarsia in situ can feed at an optimum level. Two estimates of predation pressure in the field matched very closely and lead to the conclusion that the impact of Sarsia predation on copepod standing stocks in the Dutch coastal area, including the Wadden Sea, is generally negligible.     

西花蓟马在月季上的空间分布和种群动态研究

摘要：通过田间调查,和应用聚集度指标检验和线形回归方程检验,研究探讨了西花蓟马的空间分布型和种群动态。结果表明,该害虫在月季上呈聚集分布, 其分布的基本成分是个体群,个体间相互吸引,这种聚集主要是由环境条件和西花蓟马本身聚集习性引起。运用Iwao的m*-m直线回归方程建立了理论抽样数模型,田间理论抽样数可用N=1/D2[6.7692/m+0.4799]进行估计。田间抽样调查以棋盘式为最佳。6月8日到7月4日之间西花蓟马在月季上种群动态为单峰型,6月19日为种群密度最高时期。     

绿萍在稻鸭共作系统中的消长动态及增产效应

本文系统分析了稻鸭萍共作系统的生态结构,绿萍在系统中的生长动态和增产效应。结果表明,通过鸭子和绿萍在稻田生态位的添加,使原来的稻田食物链结构趋向复杂化,增加了稻田生态系统的稳定性,有效促进了水稻产量性状的表达和稻米品质的改善。稻鸭萍处理由于鸭子的作用,利于绿萍的分萍、倒萍,促其生长,绿萍生长后期倒萍速度明显低于稻萍处理。随着鸭子的不断成长,对萍的采食量也不断增加,整个共作期间每只鸭可食鲜萍量40.8kg。总之,稻鸭萍共作系统是一项种养相结合,节本增效的生态工程技术。     

Life history and reproductive biology of Corophium volutator (crustacea: amphipoda) and the influence of shorebird predation on population structure in chignecto bay,bay of fundy,Canada

Intertidal populations of Corophium volutator were sampled over a 17-month period at 5 locations in Chignecto Bay, Bay of Fundy, Canada. This is a macrotidal environment with extensive mudflats. Two generations were produced annually. The lengths of gravid females and brood sized were larger than those previously reported in most European studies. Production was highest during May-September. During late summer (July-September) the larger animals were selectively removed from the population by predatory shorebirds (Charadriiformes) thus modifying the population structure from a bimodal to a unimodal distribution composed of numerous but small animals. Although shorebird predation was extensive, the associated reductions in Corophium densities were temporary-Densities increased following the birds' departure from the study sites in early fall. Frequency distribution histograms of size classes remained unimodal and growth was low, until the next breeding season. Annual net production over 2 one-year periods was 6250 and 3277 mg·m⁻² (dry weight).     

Genetic mapping within the wheat D genome reveals QTL for germination, seed vigour and longevity, and early seedling growth

Quantitative trait loci (QTL) controlling germination, seed vigour and longevity, and early seedling growth were identified using a set of common wheat lines carrying known D genome introgression segments. Seed germination (capacity, timing, rate and synchronicity) was characterized by a standard germination test, based either on the 1 mm root protrusion (germination sensu stricto) or the development of normal seedlings. To quantify seed vigour, the same traits were measured from batches of seed exposed for 72 h at 43°C and high (ca. 100%) humidity. Seed longevity was evaluated from the relative trait values. Seedling growth was assessed both under non-stressed and under osmotic stress conditions. Twenty QTL were mapped to chromosomes 1D, 2D, 4D, 5D, and 7D. Most of the QTL for germination sensu stricto clustered on chromosome 1DS in the region Xgwm1291–Xgwm337. A region on chromosome 7DS associated with Xgwm1002 harboured loci controlling the development of normal seedlings. Seed vigour-related QTL were present in a region of chromosome 5DL linked to Xgwm960. QTL for seed longevity were coincident with those for germination or seed vigour on chromosomes 1D or 5D. QTL for seedling growth were identified on chromosomes 4D and 5D. A candidate homologues search suggested the putative functions of the genes within the respective regions. These results offer perspectives for the selection of favourable alleles to improve certain vigour traits in wheat, although the negative effects of the same chromosome regions on other traits may limit their practical use.     

Effects of harvest management on growth dynamics, forage and seed yield in berseem clover

Berseem clover (Trifolium alexandrinum L.) is an annual forage crop widely grown in Mediterranean environments. However, there is little information available on the patterns of accumulation and partitioning of assimilate in berseem and how this varies with harvest management, plant ontogeny or is influenced by genotype. Field experiments were conducted in Foggia (Italy) during three growing seasons (1991–92, 1992–93 and 1993–94), with the aim of evaluating the effects of different harvest managements on growth dynamics, forage yield and seed yield of one population of Egyptian (cv. ‘Giza 10’) as well as Italian (cv. ‘Sacromonte’) origin. Cutting treatments were applied at three different plant ages: sixth internode elongation (A), early flowering (B), and uncut control (C). The growth and development of the shoot and root systems were followed by destructive harvests made at about 5-day intervals during 9 weeks in spring in all treatments. Seasonal growth pattern, determined as dry matter accumulation, forage yield and seed production were greatly influenced by harvest management. The maximum value (20.5 g per plant on average) of dry weight was reached at about 250 days after sowing for treatment C. Defoliation induced a decrease of crown and root dry matter, however, as shown by the allometric relationships, the growth of roots and shoots was closely correlated and in most cases, shoot growth was higher than root growth and stem relative growth rate (RGR) was higher than leaf RGR. Berseem clover is a defoliation-tolerant species because after cutting, regrowth was accompanied by higher values of leaf-stem ratio (LSR), RGR and stem elongation rate (SER) than in control plants. The highest value for total forage yield (1.6 Kg m⁻²) and seed yield (60.5 g m⁻²) were obtained in treatment B and A, respectively. Plants cut at the sixth internode elongation showed a good seed yield and a small decrease (15%) in total forage yield as regards treatment B. Therefore, treatment A appeared the most favourable for obtaining double utilization (forage and seed yield) in a berseem crop. Berseem plants were greatly influenced by harvest treatments applied, but the response did not vary according to the genetic characteristics of the two cultivars examined.     

Rural-to-rural migrants: the neglected component of rural population growth

An examination of the importance of rural-to-rural migration in the United States is presented. Data are from a 1977 telephone survey of migrants and residents in 75 high net in-migration counties in the North Central region. Rural-origin and urban-origin migrants are compared with rural residents and with each other. Characteristics examined include age, education, and income.     

Unveiling the local determinants of population growth in the European Union

This paper studies the population growth dynamics in European NUTS3 regions over the period of 2000–2015 and offers generalizable evidence on the main drivers of population change at this sub‐level of analysis, which is so far rather unexplored. Results obtained by means of a spatial Durbin model highlight the roles of economic and demographic regional conditions in shaping population dynamics and the minor role of geography and environmental conditions. The fact that geographical polarization of population is occurring, which might result in an increase in regional imbalances, calls for policy actions in mitigating this phenomenon.     

The importance of population growth, seed dispersal and habitat suitability in determining plant invasiveness

Summary This paper examines the roles of plant demography, seed dispersal ecology and habitat suitability in influencing invasiveness of horticulturally important species. Section one investigates the relative invasiveness of two woody species, Crataegus monogyna and Prunus mahaleb, and concentrates on differences in demographic and dispersal traits. The second section delineates the invasion of two Asparagus spp. and concentrates on differences in seed dispersal ecology. Section three reports the use of a geographical information system analysis to determine whether habitat suitability, seed dispersal or land management is more important in determining threat of invasion by adventive Olea europaea. C. monogyma, P. mahaleb are closely related with similar habits and overlapping home ranges in Europe. Crataegus monogyna is very invasive in northern New South Wales, having spread rapidly and conspicuously throughout the region and elsewhere in southern Australia at rates of 80–120 m yr⁻¹. Prunus mahaleb is far less invasive, being restricted to a small population, which is expanding at 20 m yr⁻¹. Demographic analysis showed that potential growth rates of P. mahaleb (1.713–1.490) are greater than those for C. monogyna (1.138–1.103). Assessment of the seed dispersal ecology of both species revealed that C. monogyna had seeds dispersed by one bird and three mammals over many kilometers. P. mahaleb had seeds dispersed by six birds and four mammals over distances generally < 100 m. The role of humans in introducing both species and the characteristics of seed dispersal are more influential than demography in determining invasiveness. The more invasive Asparagus asparagoides has smaller fruit with a bicoloured display up to 1.5 m above ground. Less invasive A. declinatus has larger, translucent white fruit displayed at heights < 0.5 m above ground. The role of humans has also been important in shaping the course of invasion. Sensitivity analysis confirms that land management practices, which affect Olea europaea seedling establishment and survival, are most important at a landscape scale in determining invasiveness. The main factors determining the difference in invasiveness relate directly to the changing nature of human management of each species and the ecological interactions between the plants and the invaded environment. This research has implications for the prediction and management of biological invasions; emphasizing the importance of seed dispersal and human activities in determining the course of invasions: both of which cannot be readily predicted.     

Sustainable urbanization in Southeast Asia and beyond: Challenges of population growth,land use change,and environmental health

As economic growth centres, the Southeast Asian cities feature high population pressure, unsustainable land use, environmental degradation, and large ecological footprints. It is difficult to manage environmental health and basic services for urban dwellers, and ensure optimum flow of ecosystem services in the context of rapid, unplanned, and haphazard urbanization. These challenges are particularly multifaceted in the developing countries of Southeast Asian region. This study, based on secondary sources, adopted multidisciplinary lenses, such as geographical information systems, socio‐economic perspective, and sustainability science to examine the population situation, land use change pattern, and drivers of environmental degradation in the Southeast Asian cities as well as the Dhaka megacity, and brought forth a fresh perspective to look into contemporary urban ecosystems, population dynamics, environmental health, and sustainability. It also focused on identifying the commonalities among the cities under study to create a common understanding towards promoting collaborative urban development. This study shows that the urbanization process in the Southeast Asia region is taking place mostly in an unplanned and haphazard manner. With little concern for nature, life‐supporting ecological systems, and the environment, urban spatial growth continues unabated. The data surveyed and discussed in this paper shows that the current style of urbanization in Southeast Asia can best be called unsustainable. The findings also suggest that the general wellbeing and welfare of the current and future generations in Southeast Asian cities as well as in Dhaka is at risk. The paper recommends concerted efforts towards making the urbanization process sustainable, including better urban planning, policymaking, and international and regional cooperation.