Introducing spatial grazing impacts into the prediction of moorland vegetation dynamics     

S. C. F. Palmer  I. J. Gordon  A. J. Hester  R. J. Pakeman 《Landscape Ecology》2005,19(8):817-827

Grazing by large herbivores is a major determinant of vegetation dynamics in many semi-natural ecosystems, including the replacement of heather moorland by rough grassland in the British uplands. Herbivore foraging is influenced by vegetation patterns and, in turn, their grazing drives vegetation dynamics. Although vegetation impacts are local, spatially heterogeneous local impacts can have different consequences as would the same impacts distributed uniformly. We constructed a simulation model of the spatial effects of grazing by sheep on the vegetation dynamics of heather moorland, a vegetation community of international conservation importance in the UK. The model comprised three sub-models to predict (1) annual average heather utilisation, (2) spatial variation in heather utilisation (higher near the edge of grass patches) and (3) competition between heather and grass. Here we compare the predicted heather utilisation and vegetation dynamics of the spatial model, relative to those of a non-spatial model. The spatial model resulted in a reduced loss of heather cover for a given sheep stocking rate. The model demonstrates how spatial interactions between large herbivores and their forage drive vegetation dynamics, leading to changes in community structure and composition. Indeed, omitting spatial effects in grazing models may lead to inaccurate predictions. We have shown that ecosystem modelling, based around an iterative dialogue between developers and experienced researchers, has the potential to make a substantial contribution towards the conservation and management of vulnerable landscapes. Combining modelling with experimental studies will facilitate progress towards understanding long-term vegetation/herbivore dynamics.  相似文献   

Physiological and biochemical consequences of electroimobilisation in conscious sheep     

TR KUCHEL  LE MATHER†  WB RUNCIMAN†  RJ CARAPETIS† 《Australian veterinary journal》1990,67(2):33-38

An electroimmobilisation device has been developed to facilitate the automated shearing of sheep, but there is little information on its effects on the body. We have studied its effects on the cardiovascular system and on intermediary metabolism in sheep. Electroimmobilisation caused statistically significant increases in mean arterial pressure, heart rate, cardiac output, renal and hepatic and hindquarter glucose and lactate flux, organ and whole body oxygen flux, hindquarter blood flow and core temperature and decreases in arterial and posterior vena cava blood pH, renal and hepatic blood flow and PaCO2. Notably, no change occurred in PaO2. The metabolic changes demonstrated the capacity of sheep to respond to the increased muscular and cardiovascular work induced by electroimmobilisation. Pulmonary function was not compromised during electroimmobilisation as judged from blood gas changes, and the acid/base changes were rapidly reversed after electroimmobilisation. The recovery to control conditions for all perturbations generally took no longer than 30 min, consistent with a rapid and physiologically adequate reversal by the animal's homeostatic mechanisms.  相似文献   

The use of soil data in natural heritage planning and management     

W. Towers  A. J. Hester  A. Malcolm  D. Stone  H. Gray 《Soil Use and Management》2002,18(1):26-33

Abstract. Native woodland restoration is a conservation priority within the UK and there is an increasing awareness that a long-term strategy is required to guide this process. A GIS-based modelling approach has been developed, which links site conditions as expressed in an integrated soil and land cover dataset with the site requirements for different woodland types. There are three important aspects to the model – the parameter weightings, the added value of the integrated dataset, and the woodland categories which are described and predicted. The initial quantitative and qualitative validation has been encouraging although more is required and planned. The results indicate that for broad strategic planning purposes, predictions of woodland potential are not improved significantly when climatic factors are incorporated. The concept that soil acts as an integrator of other environmental variables is discussed alongside the practical application of the model by a range of users.  相似文献   

Dietary fats and the skin and coat of dogs     

Kirby NA  Hester SL  Bauer JE 《Journal of the American Veterinary Medical Association》2007,230(11):1641-1644

  相似文献   

Runner formation on strawberry plants in autumn and winter     

L. Smeets  Hester G. Kronenberg 《Euphytica》1955,4(1):53-57

Summary In order to test strawberry selections for viruses, for which runners are necessary, the second writer tried, in connection with experiments carried out by Borthwick and Parker (1), to produce runners in the autumn and winter of 1952–53 by interrupting the dark period, however, without any result. Experiments carried out in 1953–54 have shown that too low a temperature was the cause of this failure, for runner formation in autumn and winter is dependent not only on day length but also on temperature.In the course of our 1953–54 experiments we found that in 1937 Darrow (2) had already made mention of the interrelation of temperature and day length in runner formation. However, it is not likely that sufficient runner formation would have taken place, had we applied his findings.  相似文献   

Strawberry breeding for red core resistance in the Netherlands     

Hester G. Kronenberg  C. P. J. Van de Lindeloof  L. M. Wassenaar 《Euphytica》1971,20(2):228-234

Summary The appearance, a few years ago, of red core disease (Phytophthora fragariae Hickman) in strawberry crops in the Netherlands, has made it desirable to grow resistant varieties and to include red core resistance in our breeding programme.An account is given of the results of some field trials in 1968–1970 on a very wet, sandy soil, infected with P. fragariae, involving varieties, selections and seedling progenies.In both years distinct differences in resistance and susceptibility occurred between varieties and selections. The seedling progenies gave significant differences in percentages of surviving, healthy plants.Samenvatting Het optreden van rood wortelrot (Phytophthora fragariae Hickman) enkele jaren geleden in de aardbeiteelt in Nederland, heeft het gewenst gemaakt resistente rassen te telen en resistentie in ons veredelingsprogramma op te nemen.In dit artikel worden de resultaten vermeld van enkele veldproeven met rassen, selecties en zaailingpopulaties in de jaren 1968–69 en 1969–70 op een zeer natte, met P. fragariae besmette zandgrond.In beide jaren traden duidelijke verschillen in vatbaarheid op tussen de rassen en selecties. De zaailingpopulaties vertoonden eveneens duidelijke verschillen in de percentages overlevende, gezonde planten.  相似文献   

Testing strawberries for resistance to verticillium wilt     

Hester G. Kronenberg  A. C. Van Der Giessen 《Euphytica》1968,17(2):141-152

Summary The resistance to Verticillium wilt was investigated by inoculating the roots of runner plants and young seedlings of strawberry (Fragaria x ananassa Duch). In the glasshouse tests a satisfactory method was to raise the plants in jiffy pots and to remove the bottom of the pots prior to inoculation. This has the advantage that only slight root damage and no growth stagnation are caused.Both in the glasshouse and field tests inoculation resulted in a distinct infection reflected in reduced plant vigour and lesions on the petioles followed by wilting. In this way reliable differences between varieties could be demonstrated.The varieties grown in the glasshouse did not always exhibit the same degree of susceptibility as observed in practice. For example, Talisman and Redgauntlet were susceptible, while Gorella seemed to be more resistant because clear disease symptoms were not visible; the reduced plant vigour, however, indicated definite susceptibility. Generally the degree of infection and the reduction in growth were found to be significantly correlated.The two field trials carried out with plants the roots of which were infected by immersion in a suspension before planting, produced results which agreed better with practical findings than the glasshouse tests. In these trials Siletz appeared to be the most resistant variety, some American varieties and selections were nearly resistant, Vola and Juspa being not very susceptible.  相似文献   

Production of fumonisin B and C analogues by several fusarium species     

Sewram V  Mshicileli N  Shephard GS  Vismer HF  Rheeder JP  Lee YW  Leslie JF  Marasas WF 《Journal of agricultural and food chemistry》2005,53(12):4861-4866

Six strains of Fusarium verticillioides, two of F. oxysporum, one strain of F. proliferatum, and a strain of an unidentified species were cultured on maize patties and rice and evaluated for their ability to simultaneously produce fumonisin B (FB) and C (FC) series analogues. Fumonisins were quantified by LC-MS-MS using positive ion electrospray ionization. FC1 provided characteristic fragment ions at m/z 690, 672, 654, 532, 514, and 338 corresponding to sequential loss of H2O and tricarboxylic acid moieties from the alkyl backbone, while FC3 and FC4 provided equivalent product ions 16 and 32 amu lower than the corresponding FC1 fragments, respectively. All isolates cultured on maize produced FC4. All isolates except for that of F. proliferatum also produced FC1, and three of the six strains of F. verticillioides produced FC3. All isolates except those of F. oxysporum produced detectable amounts of FB1, FB2, and FB3. Isolates that produced fumonisin B analogues produced at least 10 fold more of the B series analogues than they did of the C series analogues. The results confirm that at least some strains of F. oxysporum produce FC, but not FB, fumonisin analogues and also suggest that the genetics and physiological regulation of fumonisin production may be more complicated than previously envisaged since some strains of F. verticillioides and F. proliferatum as well as the strain of the unidentified species can simultaneously produce both FB and FC analogues.  相似文献   

The nutritional status of asymptomatic HIV-infected Africans: directions for dietary intervention?     

Vorster HH  Kruger A  Margetts BM  Venter CS  Kruger HS  Veldman FJ  Macintyre UE 《Public health nutrition》2004,7(8):1055-1064

OBJECTIVE: To compare the relationships between food (nutrient) intakes and biochemical markers of nutritional status of asymptomatic HIV-infected with HIV-uninfected subjects, to gain more information on the appropriate diet for HIV-infected persons at an early stage of infection. DESIGN: Cross-sectional population-based survey. SETTING: North West Province, South Africa. SUBJECTS: Two hundred and sixteen asymptomatic HIV-infected and 1550 HIV-uninfected men and women volunteers aged 15 years and older, recruited as 'apparently healthy' subjects from 37 randomly selected sites. OUTCOME MEASURES: Food and nutrient intakes, measured with a validated food-frequency questionnaire, and nutritional status indicated by anthropometric and biochemical variables, measured by a standardised methodology. RESULTS: The prevalence of HIV infection in the study population was 11.9%. The anthropometric indices and nutrient intakes of HIV-infected and uninfected subjects did not differ significantly, indicating that these 216 HIV-infected subjects were at an early stage of infection. Of the biochemical nutritional status variables, high-density lipoprotein cholesterol and total cholesterol, haemoglobin, albumin and triglycerides were significantly lower in infected subjects. They also had higher globulin and liver enzyme levels than uninfected subjects. In infected subjects, serum albumin correlated significantly with serum lipids, serum vitamin A, serum vitamin E, serum iron, total iron-binding capacity and haemoglobin. The significant positive correlations of the liver enzymes with serum lipids, albumin, vitamin A and iron, observed in HIV-uninfected subjects, disappeared in the infected subjects. Polyunsaturated fat intake showed significant positive correlations with the increased liver enzymes in infected subjects. A principal components analysis indicated that, in infected subjects, increased liver enzymes correlated with higher consumption of maize meal and lower consumption of meat and vegetables. CONCLUSIONS AND RECOMMENDATIONS: This survey indicated that asymptomatic HIV-infected subjects who followed a diet rich in animal foods had smaller decreases in serum albumin, haemoglobin and lipid variables, and smaller increases in liver enzymes, than those who consumed a diet based on staple foods. This suggests that animal foods are associated with improved nutritional status in HIV-infected persons. These results should be confirmed with intervention studies before dietary recommendations for asymptomatic HIV-infected individuals can be made.  相似文献   

Cultivation Is Necessary     

Hester JB  Isaacs RL 《Science (New York, N.Y.)》1948,108(2814):635

  相似文献