The role of intraguild predation in the population dynamics of small pelagic fish

In this paper, we argue that understanding marine ecosystem functioning requires a thorough appreciation of the role of intraguild predation to system dynamics. The theoretical predictions of intraguild predation models might explain some of the community features observed in marine ecosystems such as low diversity in upwelling and productive systems and species alternation in response to moderate external forcing. Finally, we argue that an ecosystem approach to fisheries requires that the size–structure of fish populations should be taken into account and that it is extremely important to account for the predators of early stages (eggs and larvae) to gain a thorough understanding of the key interactions between species.     

Modeling the refuge effect of submerged macrophytes in ecological dynamics of shallow lakes: A new model of fish functional response

Submerged macrophytes often provide refuge for zooplankton from fish predation in temperate and subtropical shallow lakes. However, since the relationship between submerged macrophyte abundance and its refuge effect has not been well established, the refuge effect is difficult to be simulated. In this paper, we constructed mathematical models to describe the refuge effect of submerged macrophytes on fish foraging activities and ecological dynamics of shallow lakes based on the previous studies. We clarified the underlying behavioral mechanisms of the observed functional responses through analyses of the fish foraging behavior, extracted the affected variables related to the refuge effect, formulized the relationship between the affected variables and submerged vegetation density, and determined parameter values with a compensative procedure. Calibration and validation results indicated that the new functional response model was successful to simulate the refuge effect on interfering with fish foraging behavior. Moreover, the model was cooperated into a minimal ecological model for shallow lakes. Modeling results showed that the model was able to simulate the refuge effect in ecological dynamics, and made the ecological model produce significantly different results from those with the existing functional response models.     

Sensitivity of stand dynamics to grazing in mixed Pinus sylvestris and Quercus pubescens forests: A modelling study

Only recently, studies of forest succession have started to include the effects of browsing by wild or domestic ungulates. We aim to contribute to this topic by analysing the influence of goat grazing on the long-term coexistence of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) in the low-elevation forests of an inner-Alpine dry valley. The forest gap model ForClim was first adapted to these site conditions by examining the site-dependent sensitivity of the model with regard to the species-specific parameterisation of the drought tolerance as well as the light demand of establishing and adult trees. In a second step, the behaviour of the model was investigated with respect to different grazing intensities and species-specific browsing susceptibilities. The last step was the application of a grazing scenario based on forest history, with 150 years of heavy browsing (by goats) at the beginning of the simulated forest succession, followed by less intensive grazing pressure.     

Trophic role of small cyclopoid copepod nauplii in the microbial food web: a case study in the coastal upwelling system off central Chile

Copepod grazing impact on planktonic communities has commonly been underestimated due to the lack of information on naupliar feeding behaviour and ingestion rates. That is particularly true for small cyclopoid copepods, whose nauplii are mainly in the microzooplankton size range (<200 μm). The trophic role of Oithona spp. nauplii was investigated off Concepción (central Chile, ~36°S) during the highly productive upwelling season, when maximum abundances of these nauplii were expected. Diet composition, ingestion rates, and food-type preferences were assessed through grazing experiments with different size fractions of natural planktonic assemblages (<3, <20, <100, and <125 μm) and cultures of the nanoflagellate Isochrysis galbana. When the Oithona spp. nauplii were offered a wide range of size fractions as food (pico- to microplankton), they mostly ingested small (2–5 μm) nanoflagellates (5–63 × 10³ cells nauplius⁻¹ day⁻¹). No ingestion on microplankton was detected, and picoplankton was mainly ingested when it was the only food available. Daily carbon (C) uptake by the nauplii ranged between 28 and 775 ng C nauplius⁻¹, representing an overall mean of 378% of their body C. Our relatively high ingestion rate estimates can be explained by methodological constraints in previous studies on naupliar feeding, including those dealing with “over-crowding” and “edge” effects. Overall, the grazing impact of the Oithona spp. nauplii on the prey C standing stocks amounts up to 21% (average = 13%) for picoplankton and 54% (average = 28%) for nanoplankton. These estimates imply that the nauplii of the most dominant cyclopoid copepods exert a significant control on the abundances of nanoplankton assemblages and, thereby, represent an important trophic link between the classical and microbial food webs in this coastal upwelling system.     

An individual-based model to study the reproduction of egg bearing copepods: Application to Eurytemora affinis (Copepoda Calanoida) from the Seine estuary,France

Limited empirical studies have elucidated the daily egg production and associated reproductive processes of egg bearing copepod. Herein, we present an individual-based model which constitutes a realistic representation of the reproduction in egg bearing copepods. The model has been parameterized using an extensive set of experimental data obtained from the literature and from the laboratory and field experiments on the estuarine copepod Eurytemora affinis. The proposed model takes into account the adult female longevity, the clutch size and interclutch duration, which is a function of egg maturation time and latency time required by the female after egg hatching to produce a new clutch. The embryonic development time and hatching success are also taken into account. The effect of temperature on the means and variances of above-mentioned reproductive parameters has been also incorporated. A multi agent system based generic platform “Mobidyc” has been used to generate and calibrate the model. The model demonstrates the reproductive parameters of females of E. affinis which is validated through individual based experiments. Temperature specific simulations provide a dynamical explanation of temperature effect on the cumulative egg production. The daily survival principally affects the number of clutches produced per female during its life span. The results obtained in the present study by combining temperature and survival effects reveal the relatively greater importance of the first factor on the daily egg production of egg-carrying copepods. The present model is generic and hence easily applicable to other animals with comparable reproductive strategy.     

Influence of host migration between woodland and pasture on the population dynamics of the tick Ixodes ricinus: A modelling approach

Ticks act as vectors of pathogens that can be harmful to animals and/or humans. Epidemiological models can be useful tools to investigate the potential effects of control strategies on diseases such as tick-borne diseases. The modelling of tick population dynamics is a prerequisite to simulating tick-borne diseases and the corresponding spread of the pathogen. We have developed a dynamic model to simulate changes in tick density at different stages (egg, larva, nymph and adult) under the influence of temperature. We have focused on the tick Ixodes ricinus, which is widespread in Europe. The main processes governing the biological cycles of ticks were taken into account: egg laying, hatching, development, host (small, mainly rodents, or large, like deer and cattle, mammals) questing, feeding and mortality. This model was first applied to a homogeneous habitat, where simulations showed the ability of the model to reproduce the general patterns of tick population dynamics. We considered thereafter a multi-habitat model, where three different habitats (woodland, ecotone and meadow) were connected through host migration. Based on this second application, it appears that migration from woodland, via the ecotone, is necessary to sustain the presence of ticks in the meadow. Woodland can therefore be considered as a source of ticks for the meadow, which in turn can be regarded as a sink. The influence of woodland on surrounding tick densities increases in line with the area of this habitat before reaching a plateau. A sensitivity analysis to parameter values was carried out and demonstrated that demographic parameters (sex ratio, development, mortality during feeding and questing, host finding) played a crucial role in the determination of questing nymph densities. This type of modelling approach provides insight into the influence of spatial heterogeneity on tick population dynamics.     

The lateral-line organs of the larvae of the deep-sea fish Cataetyx memorabilis (Ophidiidae): A scanning-electron and light-microscope study

A prominent lateral-line system found in 10 mm long larvae of the deep-sea fish Cataetyx memorabilis Meyer-Rochow (1970) is not present in the adults. Size and height of larval lateral-line papillae measured in stereo pairs of electron micrographs are compared with light microscopy of sectioned material. Lateral-line papillae are separated from each other by 3 to 7 myomeres (0.5 to 1 mm). A papilla is 50 m wide and approximately 15 m high. The 7 or 8 sensory hairs, which are about 30 to 40 m long, are not embedded in a jellylike transparent substance. Behavioural and taxonomical consequences of the findings are discussed.     

An overview of the impacts of changes in common property resources management in the context of globalisation: A case study of India

Socio-economic development of mankind and well-being depend on the environment and the way in which development influences the environment. Thus, environment and development are interdependent. In fact, economic development is closely linked with the development of resources. These resources can be classified into three categories: public goods, semi-public goods (also known as common property resources) and private goods. In poor countries common property resources make a valuable contribution to the sustainable livelihoods of rural populations. The impact of globalisation on the commons shows various patterns of ownership, control, use and misuse. The commons were subjected to degradation as well as conservation in the process of centralized management in India. After the reform period, the administration of natural resources was given significant attention by specialized departments such as the Forest Department and the Revenue Department. All the land, apart from private land, was regarded as state property and controlled by the state. This paper highlights the need to examine the common property resources sector in the context of wider economic policy reform processes in the Indian economy.     

金沙江干热河谷退化生态系统植被恢复生态功能评价——以元谋小流域典型模式为例

针对干热河谷具有光热资源丰富、气候干旱燥热、水热矛盾突出、植被覆盖率低、水土流失严重、生态环境强烈退化、植被恢复困难等特点,文章总结千热河谷植被恢复的技术体系,研究分析了植被恢复对生态系统的水保功能、环境功能、生物多样性等生态功能的影响,结果表明:植被恢复后,生态系统的土壤侵蚀程度明显下降,其中轻度退化土地减少了22.03%;中度退化土地减少了21.15%;强度退化土地减少了34.15%;植被恢复后,小流域的气候环境有较大的改善,气温下降、湿度提高,改变了该区域"干"、"热"的恶劣环境;对系统多样性的研究主要针对强度以上退化系统的人工生态林模式和自然禁封治理模式进行分析多样性与生态系统功能的关系,结合前期研究结果认为,自然禁封治理模式使系统具有生物多样性,有助于系统生态功能完善稳定,而银合欢(Leucaena leucocephal)人工林恢复模式,虽然物种多样性减少,但系统具备优化的生态功能.因此,就干热河谷强度、极强度退化生态系统而言,银合欢冲沟治理模式和自然禁封治理模式是较优化的模式.