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1.
Flood control, drainage and irrigation (FCDI) schemes are widespread in Bangladesh. They are built to control water levels to improve agricultural production based on high yielding varieties (HYV) of rice that cannot tolerate rapid inundation or that require irrigation, and to provide protection from extreme flood events. The benefits to the agricultural sector can be significant. At some sites in Bangladesh, farmers report up to 80% more agricultural production inside the schemes than outside. However, fish production and species richness is typically lowered by these structures. Fish yields inside a typical flood control compartment can be 50% lower than outside, with up to 25 species of fish absent or less abundant. Lower rates of recruitment of migratory whitefish species, whose lateral migrations are obstructed by the embankments, were found to be largely responsible for these differences. With a risk of more extreme flooding during the monsoon season but hotter and more arid dry season conditions predicted as a consequence of climate change, more FCDI schemes may need to be constructed to provide flood protection and to meet increasing irrigation needs. Based on fisheries monitoring and mark-recapture studies undertaken at 3 sluice gates, nine recommendations for operating sluice gates to mitigate the impacts of FCDI schemes on fish production and biodiversity are described. These recommendations aim to improve the access of migratory whitefish to modified floodplains and to improve or sustain the production of resident (non-migratory) blackfish whilst minimising agricultural sector losses. Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries  相似文献   

2.
Summary 1. Evidence is reviewed which shows that a sexually dimorphic nucleus located in the dorsomedial portion of the male ferret's preoptic area/anterior hypothalamus (POA/AH), called the male nucleus of the POA/AH (Mn-POA/AH), develops during fetal life in response to the action of estradiol, which is formed directly in the nervous system from circulating testosterone over the final quarter of a 41-day gestation.2. Results are summarized which establish that neurons which make up the Mn-POA/AH are born prior to the critical period of estradiol's action in the male brain. Other data show that some radial glial processes, visualized immunocytochemically using antibodies against GFAP, emanate from proliferative zones at the base of the lateral ventricles in a dorsal-ventral orientation, whereas other glial processes emanate laterally from proliferative zones lining the third ventricle.3. We suggest that at least some neurons which constitute the dorsomedial POA/AH are born in proliferative zones surrounding the lateral ventricles, raising the question of whether estradiol acts in developing males to influence the migration of these neurons along radial glial guides into the Mn-POA/AH.4. Finally, evidence is summarized showing that excitotoxic lesions of the dorsomedial POA/AH enhance males' preference to approach and interact with another sexually active male, as opposed to an estrous female, when adult subjects are castrated and treated with estradiol benzoate. These data suggest that the sexually dimorphic Mn-POA/AH is an essential part of a CNS circuit which determines heterosexual partner preference in the male ferret.  相似文献   

3.
Land use cover and the current ecological condition of the natural resources of a 71,300 ha area were assessed quantitatively and qualitatively. The Systematic Reconnaissance Flight (SRF) was used to achieve the above within severe time constraints set by the terms of reference for the project. North–south grid lines, spaced 1 and 2 km apart, were flown using a helicopter. Changes in land use classes along flight transects were documented using a Global Positioning System. The co-ordinates were transformed within a Geographic Information System into land cover values. The SRF with sampling intensities ranging from 5.13 to 9.89% yielded a difference of only 0.2% between the estimated cover of sugar cane compared to the known area under sugar cane. The other land cover classes were considered adequately quantified. The qualitative assessment shows the natural resources to be under severe strain, in particular within the riparian zone. Recommendations as to future agricultural expansion are made. The SRF was highly cost-effective in achieving the stated objectives of the project.  相似文献   

4.
Chick JF 《Lab animal》2006,35(1):25-30
High rates of employee turnover are the source of a considerable loss of time and resources, but managers are not always aware of the reasons that motivate employees to stay in their positions. The author compares prominent theories of employee motivation and then puts them to the test by surveying 82 cagewashers, animal caretakers, animal technicians, and supervisors working in a laboratory animal facility to determine the job characteristics that motivate them.  相似文献   

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A new model for aspects of the control of respiration in mammals has been developed. The model integrates a reduced representation of the brainstem respiratory neural controller together with peripheral gas exchange and transport mechanisms. The neural controller consists of two components. One component represents the inspiratory oscillator in the pre-Bötzinger complex (pre-BötC) incorporating biophysical mechanisms for rhythm generation. The other component represents the ventral respiratory group (VRG), which is driven by the pre-BötC for generation of inspiratory (pre)motor output. The neural model was coupled to simplified models of the lungs incorporating oxygen and carbon dioxide transport. The simplified representation of the brainstem neural circuitry has regulation of both frequency and amplitude of respiration and is done in response to partial pressures of oxygen and carbon dioxide in the blood using proportional (P) and proportional plus integral (PI) controllers. We have studied the coupled system under open and closed loop control. We show that two breathing regimes can exist in the model. In one regime an increase in the inspiratory frequency is accompanied by an increase in amplitude. In the second regime an increase in frequency is accompanied by a decrease in amplitude. The dynamic response of the model to changes in the concentration of inspired O2 or inspired CO2 was compared qualitatively with experimental data reported in the physiological literature. We show that the dynamic response with a PI-controller fits the experimental data better but suggests that when high levels of CO2 are inspired the respiratory system cannot reach steady state. Our model also predicts that there could be two possible mechanisms for apnea appearance when 100% O2 is inspired following a period of 5% inspired O2. This paper represents a novel attempt to link neural control and gas transport mechanisms, highlights important issues in amplitude and frequency control and sets the stage for more complete neurophysiological control models.  相似文献   

7.
Despite the prevalence of protected areas, evidence of their impacts on people is weak and remains hotly contested in conservation policy. A key question in this debate is whether socioeconomic impacts vary according to social subgroup. Given that social inequity can create conflict and impede poverty reduction, understanding how protected areas differentially affect people is critical to designing them to achieve social and biological goals. Understanding heterogeneous responses to protected areas can improve targeting of management activities and help elucidate the pathways through which impacts of protected areas occur. Here, we assessed whether the socioeconomic impacts of marine protected areas (MPAs)—designed to achieve goals for both conservation and poverty alleviation—differed according to age, gender or religion in associated villages in North Sulawesi, Indonesia. Using data from pre-, mid- and post-implementation of the MPAs for control and project villages, we found little empirical evidence that impacts on five key socioeconomic indicators related to poverty differed according to social subgroup. We found suggestive empirical evidence that the effect of the MPAs on environmental knowledge differed by age and religion; over the medium and long terms, younger people and Muslims showed greater improvements compared with older people and Christians, respectively.  相似文献   

8.
The adverse impacts of weeds on natural ecosystems, together with the inadequate outcomes from treating weeds as a symptom, have escalated interest in finding efficacious control methods. With the aim of protecting wetlands from invasive weeds, this contribution uses the woody shrub Mimosa pigra L. (mimosa) as a case history to examine the methodology of classical biological control and the reasons for the widely accepted 75% failure rate. Overall objectives are for all biocontrol agents to have the opportunity to fully express their potential and to insure that limited resources are spent wisely on attainable weed control. The three main conclusions were that (1) the premises on which biocontrol is based has restricted advancement of this method; (2) monitoring is the logical first step to improving the selection of agents and release sites; and (3) it may be more cost-effective to introduce fewer agents that have undergone agent/plant and host/home range pre- and post-release ecological studies. Weed control may remain elusive unless advantage is taken of every beneficial result. Innovative assistance to agents and the integration of different control methods may preserve a role for weed biological control and has the potential to be of great importance for future weed management. It is proposed that the climate in the Top End of the Northern Territory and the lack of competition on the floodplains has contributed to mimosa's invasiveness. Climate may also underly the difficulties faced by agents. Agents appear unable to impart effective control in the dry season because of low numbers which relates to mimosa's poor growth; nor in the wet season, when the impact from high numbers of agents is outstripped by mimosa's growth.  相似文献   

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The feeling of controlling events through one''s actions is fundamental to human experience, but its neural basis remains unclear. This ‘sense of agency’ (SoA) can be measured quantitatively as a temporal linkage between voluntary actions and their external effects. We investigated the brain areas underlying this aspect of action awareness by using theta-burst stimulation to locally and reversibly disrupt human brain function. Disruption of the pre-supplementary motor area (pre-SMA), a key structure for preparation and initiation of a voluntary action, was shown to reduce the temporal linkage between a voluntary key-press action and a subsequent electrocutaneous stimulus. In contrast, disruption of the sensorimotor cortex, which processes signals more directly related to action execution and sensory feedback, had no significant effect. Our results provide the first direct evidence of a pre-SMA contribution to SoA.  相似文献   

11.
This study evaluated parasitological and molecular techniques for the diagnosis and assessment of cure of schistosomiasis mansoni. A population-based study was performed in 201 inhabitants from a low transmission locality named Pedra Preta, municipality of Montes Claros, state of Minas Gerais, Brazil. Four stool samples were analysed using two techniques, the Kato-Katz® (KK) technique (18 slides) and the TF-Test®, to establish the infection rate. The positivity rate of 18 KK slides of four stool samples was 28.9% (58/201) and the combined parasitological techniques (KK+TF-Test®) produced a 35.8% positivity rate (72/201). Furthermore, a polymerase chain reaction (PCR)-ELISA assay produced a positivity rate of 23.4% (47/201) using the first sample. All 72 patients with positive parasitological exams were treated with a single dose of Praziquantel® and these patients were followed-up 30, 90 and 180 days after treatment to establish the cure rate. Cure rates obtained by the analysis of 12 KK slides were 100%, 100% and 98.4% at 30, 90 and 180 days after treatment, respectively. PCR-ELISA revealed cure rates of 98.5%, 95.5% and 96.5%, respectively. The diagnostic and assessment of cure for schistosomiasis may require an increased number of KK slides or a test with higher sensitivity, such as PCR-ELISA, in situations of very low parasite load, such as after therapeutic interventions.  相似文献   

12.
Metabolic control analysis predicts that effects on tumor growth are likely to be obtained with lower concentrations of drug, if an enzyme with a high control coefficient on tumor growth is being inhibited. Here we measure glucose-6-phosphate dehydrogenase (G6PDH) control coefficient on in vivo tumor growth using mice bearing Ehrlich ascites tumor cells. We used dehydroepiandrosterone-sulphate (DHEA-S), an uncompetitive inhibitor of this enzyme and the in situ cytochemical method to measure the enzyme activity changes that accompany changes on tumor cell growth. This method ensures that the enzyme activity determined is the one existing in the in situ conditions and enables computing a control coefficient in in situ conditions. From the data obtained on tumor cell number and the in situ enzyme activities in absence and presence of DHEA-S, a control coefficient of 0.41 for G6PDH on tumor cell growth was computed. This value is approximately the half of the transketolase control coefficient value of 0.9 previously reported. Moreover, the use of in situ methods to assess enzyme activities, applied for first time for the calculation of control coefficients in this study, opens new avenues to the use of uncompetitive inhibitors for the measurement of in situ control coefficients.  相似文献   

13.
The late Holocene stratigraphic evolution of a back-barrier tidal basin in the East Frisian Wadden Sea, southern North Sea, was investigated on the basis of a conceptual model relating the rate of sea-level rise to the rate of sediment supply. For this purpose, more than 20 vibra-cores and box-cores were evaluated, complemented by 14C ages of in situ peats and historical charts. In spite of interspersed short regressive events, the late Holocene stratigraphy generally reveals upward-coarsening grain-size trends indicative of transgressive deposition in the course of sea-level rise rather than erosion and redeposition by migrating channels. A particular feature is the general absence of down-core bioturbation traces, which stands out in sharp contrast to the intensely burrowed modern surface layer. Thus, in the Wadden Sea, high sediment turnover in the course of rapid transgression evidently obliterates most bioturbation traces and other tidal signals such as minor regressive deposits, thereby emphasising the importance of preservation potential.  相似文献   

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We studied vegetation dynamics at peatlands, differing in their climate, land use management history and vegetation community in Ireland and Finland over a two-year period. Our aim was to develop a species-specific method to be used to (1) describe the seasonal dynamics of green (photosynthetic) area (GA) of the vegetation and (2) incorporate these changes into CO2 exchange models. The extent of temporal and spatial variation between and within communities indicated the need for a two-step calculation approach for each community. Firstly, at biweekly to monthly intervals, GA of all species within a range of vascular plant communities was estimated by non-destructive field measurements. Gaussian or log-normal models were fitted to describe the seasonal dynamics of each species. Secondly, an estimate of community vascular green area (VGA) was obtained by summing the modelled daily GA of all species within the community. The highest values of VGA (2.1–6.0 m2 m−2) occurred within the reed communities at the rewetted cutaway peatland in Ireland and the lowest at the ombrotrophic lawn communities in Finland (0.5–1.0 m2 m−2). The relationship between light saturated gross photosynthesis (P G) and VGA was either linear or hyperbolic depending on the degree of self-shading that occurred within each community. The addition of the VGA term into P G models improved the explaining power of the model by 57.6, 24.5 and 23% within the Typha latifolia, Phalaris arundinacea and Eriophorum angustifolium/Carex rostrata communities, respectively. VGA proved useful in recording the seasonal development of a wide range of peatland vascular plant communities over geographically and climatically different regions.  相似文献   

17.
AIMS: Produce an evidence-based ranking of the major contributing factors and sources of Campylobacter occurrence in broilers produced in England, Scotland and Wales - Great Britain (GB). METHOD AND RESULTS: Relevant data were extracted from 159 research papers and findings were grouped into 14 sources of on-farm contamination and 37 contributing factors. A relevancy score was developed to take into account various measures from each study of applicability to GB broilers and strength of findings. Results indicate that major sources of Campylobacter include a depopulation event, another house on-farm, on-farm staff, and other animals on farm. The depopulation schedule (staggered slaughter) and multiple houses on-farm were identified as contributing factors associated with increasing the risk, and those decreasing the risk were use of a hygiene barrier, parent company and certain seasons of rearing. CONCLUSIONS: Although the review was more resource intensive compared to narrative studies, the system allows an increased level of transparency and the ability to investigate patterns and trends. SIGNIFICANCE AND IMPACT OF THE STUDY: This paper provides the first evidence-based ranking of the major sources and contributing factors for Campylobacter presence in broilers in GB using a systematic review.  相似文献   

18.
Abstract A possible stimulatory effect of overwintering on gyne development in Iridomyrmex humilis (Mayr) was investigated. Although gyne-potent larvae are present in the nest throughout the year, small queenless colony fragments composed of freshly overwintered ants (collected in late winter or early spring) produced 3–8 times more gynes than comparable fragments made up of non-freshly overwintered ants (collected at other times of the year). Apparently, this stimulatory effect of overwintering acts on both the developmental potential of larvae and the tendency of workers to rear sexually competent larvae as gynes; queenless colony fragments in which either the brood or workers were freshly overwintered produced more gynes than fragments composed of non-freshly overwintered workers or brood but fewer than fragments containing both brood and workers freshly overwintered. This increased sexualization potential of larvae due to overwintering is enough to overcome weak pheromonal inhibition of queens associated with low queen number; a single queen in a large freshly overwintered colony fragment is insufficient to inhibit gyne development, whereas ten queens are totally inhibitory. In non-freshly overwintered colony fragments one queen is completely inhibitory. Variability in egg developmental potential according to queen age does not appear to play a major role in the seasonal production of gynes, because at least some eggs of very young queens (less than 3 weeks old) are capable of gyne development. In the field this stimulatory effect of overwintering is superimposed on a seasonal fluctuation in the combined strength of pheromonal queen control. In southern France, gynes are produced only in spring where they arise primarily from overwintered larvae just after a sharp drop in queen number, and presumably the total level of inhibitory queen pheromone, due to the massive execution of queens by workers.  相似文献   

19.
Most studies of tiller development have not related the physiological and morphological features of each culm to its subsequent fertility. This introduces problems when trying to account for the effects of tillering on yield in crop models. The objective of this study was to detect the most likely early determinants of tiller fertility in sorghum by identifying hierarchies for emergence, fertility and grain number of tillers over a wide range of assimilate availabilities. Emergence, phenology, leaf area development and dry weight partitioning were quantified weekly for individual tillers and main culms of tillering and uniculm plants grown at one of four densities, from two to 16 plants m(-2). For a given plant in any given density, the same tiller hierarchy applied for emergence of tillers, fertility of the emerged tillers and their subsequent grain number. These results were observed over a range of tiller fertility rates (from 7 to 91%), fertile tiller number per plant at maturity (from 0.2 to 4.7), and tiller contribution to grain yield (from 5 to 78 %). Tiller emergence was most probably related to assimilate supply and light quality. Development, fertility and contribution to yield of a specific tiller were highly dependent on growing conditions at the time of tiller emergence, particularly via early leaf area development of the tiller, which affected its subsequent leaf area accumulation. Assimilate availability in the main culm at the time of tiller emergence was the most likely early determinant of subsequent tiller fertility in this study.  相似文献   

20.
1 A factorial fertilizer experiment was conducted in a 15-year-old coastal barrier salt marsh with a low soil nitrogen content, and in an older 100-year-old marsh with a higher nitrogen content. Plots were fertilized at high and low marsh elevations in both marshes. Nitrogen and phosphorus were applied at low and high concentrations both separately and in combination in each of 3 successive years.
2 Nitrogen limited above-ground plant growth in both young and old salt marshes in all years. Phosphorus limitation of plant growth was apparent in the first year in the young marsh and in the last year in both marshes. In young marshes with low soil organic matter, phosphorus limitation may occur. In addition, phosphorus limitation occurs at both successional stages when a marsh is saturated with nitrogen.
3 Plant species that are typical of nitrogen-rich habitats and late successional stages significantly increased in biomass after fertilization. Limonium vulgare , a low stature species of early and intermediate successional stages, decreased in biomass, whereas the taller Elymus pycnanthus and Artemisia maritima increased. After 3 years of fertilization, plant species composition in a young marsh was similar to the species composition in an unfertilized older marsh. Fertilization of a 100-year-old marsh, however, still resulted in a change in plant species composition, suggesting that succession was still occurring and that, overall, plants in marshes of different age are similar in their response to fertilization.  相似文献   

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