Competition for food between Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) over different substrate types

Abstract –  Food consumption by Eurasian perch ( Perca fluviatilis L.) and ruffe ( Gymnocephalus cernuus [L.]) was studied in single and mixed-species treatments in the laboratory, where alternative food resources, chironomids and zooplankton, were offered simultaneously. The effects of structural complexity, which was represented by substrate grain size, and of feeding level on food consumption were analysed. Across all experiments, the outcome of competition between perch and ruffe depended on food abundance and on the structural complexity of the environment. Perch and ruffe both changed their food consumption in the presence of a heterospecific competitor. With high food supply, perch consumed more benthic food than ruffe. With low food supply, the consumption of perch decreased strongly, while that of ruffe remained high on fine sediment. Under all conditions tested, the mechanism of competition appeared to be of interference rather than of exploitative nature. It is suggested that with decreasing lake productivity caused by re-oligotrophication, habitat shifts of both species will occur, which will alleviate interspecific competition. Ruffe will forage over fine sediment and perch over coarse sediment, whereby both species will achieve the highest foraging efficiency under conditions of low food supply.     

Weed competition in cauliflower (Brassica oleracea L. var. botrytis) in the Jordan Valley

A field experiment was carried out in 1996/1997 and repeated in 1997/1998 at the Jordan University Research Station located in the central Jordan Valley to determine the effect of weed competition on growth and yield of cauliflower Brassica oleracea var. botrytis cv. “White Cloud”. The treatments consisted of either allowing weeds to infest the crop or maintaining plots weed-free for increasing durations after transplanting. Results showed that longer periods of weed/cauliflower competition greatly reduced crop growth and head yield. Average reductions in shoot dry weight and head yield were 81% and 89%, respectively. Maintaining a weed-free crop for any period after transplanting increased cauliflower growth and head yield compared with the weed-infested control. Weed competition for 14 days after transplanting reduced cauliflower average head yield by 41%. To determine the critical period of weed competition and the influence of weed infestation on cauliflower head yield the Gompertz and logistic equations were fitted to data representing increasing duration of weed-free and weed-infested periods, respectively. Based upon an arbitrary 5% level of head yield loss, the critical period of weed competition occurred at 0–38 days after cauliflower transplanting which corresponded with the rapid increase in weed biomass. Results indicated that early weed removal is necessary to prevent yield loss.     

Life-history variation in relation to nest site abundance in males of the freshwater goby Tridentiger brevispinis

Abstract –  Age at maturity in males of the freshwater goby Tridentiger brevispinis , a species with exclusive paternal care, was investigated in two populations in Lake Biwa, Japan, that differed markedly in nest site abundance. At Ohmi-maiko, where nest sites were scarce, most males matured at age 3, and mean body size of males guarding eggs in nests was larger than that of males sampled randomly (including both guarding and nonguarding males) in the population. Conversely, at Minamihama, where nest sites were abundant, many males matured at age 1, and there was no difference in body size between guarding males and males collected randomly. The slope of regression lines between body size of the guarding male and the number of eggs in his nest was greater in Ohmi-maiko than in Minamihama. These results suggest that the shortage of nest sites enhances reproductive success in larger males, probably through male–male competition for nest sites and female mate choice for larger males. I conclude that in nest spawners, the availability of nest sites should strongly affect life-history traits of males through sexual selection.     

Comparison of uptake of different N forms by soil microorganisms and two wet-grassland plants: A pot study

Two common plant species of temperate wet grasslands, Carex acuta and Glyceria maxima, were tested for their preferences in the uptake of different nitrogen (N) sources (amino acid, ammonium, nitrate) and their ability to compete for these sources with soil microorganisms. The experiment was a one-day incubation study with plants growing in soil obtained from the field, which was supplied with a solution containing the three N sources, one at a time labeled with ¹⁵N. The bulk of the N demand of both species was covered by nitrate-N, which was the dominant N form in the soil at the time of the experiment. Ammonium-N was taken up less strongly, and organic N formed only a negligible part of their nutrition. The assimilated inorganic N was preferentially transported to apical meristem of the youngest leaf, while organic N remained mostly in the roots. The fast-growing Glyceria took up more N and was a better competitor vis-à-vis soil microbes for rarer N forms than Carex. However, both plants were poor competitors for N vis-à-vis soil microbes, irrespective of the N form. Microbes took up nitrate ca. five times faster and organic N more than a hundred times faster than plants. Correspondingly, the calculated turnover time of microbial N was 17 days, compared to 40 days for N in plant roots. A significant amount of added ¹⁵N was found at non-exchangeable sites in the soil, which points to the importance of microbial N transformation and abiotic N fixation for N retention in soil. In summary, the preferential assimilation of inorganic N by the wetland plants studied here and their poor ability to compete for N with soil microbes over the short term agree with the results of studies carried out with other species from temperate grasslands.     

基于技能竞赛培养高职学生创新能力的探索

高职学生技能竞赛有着日常教学无法起到的特殊教育功能,对培养学生创新能力,精细化人才培养过程,提高教学水平,具有独特的、不可替代的作用。搭建基于技能竞赛平台的大学生创新能力培养新模式,旨在建立长效的工作机制,形成技能竞赛系列化、规范化和品牌化,并使技能竞赛成为创新能力培养的有效途径。     

Different longitudinal distribution patterns of native white-spotted charr and non-native brown trout in Monbetsu stream, Hokkaido, northern Japan

Abstract  This study focused on longitudinal distribution patterns of native white-spotted charr and non-native brown trout in a mountainous stream in Hokkaido, Japan. Brown trout ratio, which is the proportion of brown trout in the catch of salmonids, was decreasing from downstream to upstream. Brown trout ratio correlated negatively with water temperature. Thus, our results suggested that temperature may influence the possible competition between native white-spotted charr and non-native brown trout.     

竞争种群最优开发与管理的生态经济模型

建立了具有竞争关系的2资源种群开发与管理的生态经济模型,给出了开发多种资源种群时应遵循的基本原则,详细地说明了该模型所隐含的生态经济意义.认为要使相互竞争的多个种群能够共存,就必须以适当的力度开发资源种群,且这种开发力度要取决于种群的生态学特征.     

论广告创新的动力

创新是广告的核心和灵魂。广告的创新动力源自设计主体的内在需要和市场竞争、科技进步、产权制度等外在环境的激励。理性分析设计创新的动力,有助于我们进一步挖掘广告的创新潜能,改善环境的激励机制,激发广告创新的活力。     

我国罗非鱼产业现状分析及提高罗非鱼出口竞争力的措施

综述了我国罗非鱼生产、质量安全及出口贸易情况,分析了我国罗非鱼在出口贸易中可能遇到的技术性贸易壁垒问题,提出了提高我国罗非鱼出口贸易竞争力的相关措施,以期为我国罗非鱼产业的持续稳定健康发展提供参考意见。     

AM真菌对加拿大一枝黄花与菌根植物和非菌根植物种间作用的影响

为明确丛枝菌根(arbuscular mycorrhizal,AM)真菌对加拿大一枝黄花Solidago canadensis与本地菌根植物和非菌根植物种间竞争格局的调控作用,采用温室盆栽试验,通过接种摩西球囊霉Glomus mosseae(GM)、根内球囊霉G. intraradices(GI)及其混合菌种(GM+GI)3种处理,分析AM真菌对加拿大一枝黄花与本地菌根植物玉米Zea mays和非菌根植物油菜Brassica campestris种间作用的影响。结果表明:与对照相比,接种AM真菌均显著提高了加拿大一枝黄花和玉米的菌根侵染率,菌根侵染率为13.720%～50.015%,且前者的菌根侵染率明显高于后者。单独种植时,与对照相比,接种AM真菌尤其是接种混合菌种显著提高了加拿大一枝黄花的株高、叶片数和总干重。在加拿大一枝黄花与玉米混合种植时,与单独种植相比,加拿大一枝黄花的株高、叶片数、根长和总干重均较低;同时,与对照相比,接种AM真菌显著提高了玉米的相对竞争强度而对加拿大一枝黄花的相对竞争强度没有显著影响。在加拿大一枝黄花和油菜混合种植时,与对照相比,接种AM真菌则显著提高了加拿大一枝黄花的株高、叶片数、净光合速率和总干重;同时,接种AM真菌促进了入侵种的竞争优势而抑制了非菌根植物油菜的生长。说明加拿大一枝黄花与本地种的竞争格局受到与之混生物种的菌根依赖性强度以及AM真菌的种类差异影响。