A test for interaction between brown trout (Salmo trutta) and inanga (Galaxias maculatus) in an artificial stream     

G. J. Glova 《Ecology of Freshwater Fish》2003,12(4):247-253

Abstract –  The interaction between brown trout ( Salmo trutta ; fork length (FL) range 255–390 mm) and inanga ( Galaxias maculatus ; FL range 55–115 mm) was tested during summer through autumn in an artificial stream consisting of a single run-riffle-pool sequence with a natural food supply. Each experimental trial lasted for 15 days, and consisted of two brown trout and 50 inanga collected fresh from a nearby stream, with each species given prior residence in four replicate tests, totalling eight trials in all. In addition, two control trials (each 10 days), with 50 inanga in each, were run. Brown trout almost exclusively occupied the pool, whereas inanga occupied all habitat types, although in different proportions, when tested with and without brown trout. The proportion of inanga in the pool was appreciably lower in the experimental trials with brown trout than in the control trials with no brown trout; prior residence had no significant effect on inanga habitat use. Mortality of inanga attributable to predation by brown trout ranged from 0 to 40% with a mean of 14.5 ± 4.7%. The results suggest that habitat use and survival of inanga populations in small streams can be adversely affected by brown trout.  相似文献   

Imperfect Competition and Common Resource Exploitation—An Analysis of Renewable Resource Management with Non—use Values     

XIAOLi 《东北农业大学学报(英文版)》2001,8(2):139-151

This article analyzes the importance of non-use values in the management of natural resources with a model of imperfect competition.By constucting a framework of duopolistic exploiters.the incorporation of non-use values based on self-interest and altruistic motives appears to be significant for determining the degree of inefficiency caused by the problem of common property at the non-cooperative Nash equilibrium.It is found that when the non-use value placed by the altruist exploiter is bounded by that placed by the pure selfinterest exploiter,the effect of market power is dominated by the effect of common exploitation.In this case,the exploiters‘ harvesting strategy will response in the same direction to the change of each other‘s harvesting at the non-cooperative Nash equilibrium.In contrast,when the non-use value placed by the altruist is substantially larger or smaller than that placed by the self-interest exploiter,one exploiter‘s increase in harvesting will lead to a decrease in harvesting of the other exploiter at the non-cooperative Nash equilibrium.  相似文献   

从土地覆盖变化看塔里木河中下游天然草地的退化     

徐海量  宋郁东  陈亚宁 《中国草地学报》2003,25(4):21-24

通过GIS技术和1990～2000年的TM影像图,分析了塔里木河中下游近10年的土地覆盖动态变化,结果显示:在塔里木河中下游地区,天然草地退化严重,高、中覆盖草地大幅减少,低覆盖草地的数量虽然增加但主要是流域河岸胡杨林群落退化后向荒漠灌丛草地演化的结果;而在自然环境更加恶劣的塔里木河下游地区,随着断流和地下水位的下降,天然草地正在向裸地和沙地演变。通过分析,提出了恢复塔里木河中下游天然草地的治理建议。  相似文献   

Estimating dispersibility of Acer,Fraxinus and Tilia in fragmented landscapes from patterns of seedling establishment     

W. Carter Johnson 《Landscape Ecology》1988,1(3):175-187

Relative dispersibility of Tilia americana L., Acer saccharum Marsh. and Fraxinus pennsylvanica Marsh, was inferred from the ratio among species-specific regression coefficients () computed from seedling density-distance plots. Density counts were made in spatially-uniform old fields adjacent to single seed sources or monotypic fencerows. Resultant seedling shadow curves approximate the negative exponential form expected for many seeds (log y=a–X). This basic curve shape fit species of differing dispersibility, dispersal under a range of wind directions and one-year-old or all-aged cohorts. The ratios of were 1:2.6:3.2 for Tilia, Acer and Fraxinus, respectively, in order of increasing dispersibility. Vegetation patches isolated from seed sources by several hundred meters or more should have extremely low input of seeds, especially Tilia and Acer.The finding that Fraxinus disperses farther than Acer was unexpected, since the samaras of the former have faster terminal velocities. The relationship can be explained by better performance of Fraxinus samaras in the stronger winds experienced by trees in open landscapes, poorer formation of the samara abscission layer, and release of samaras following leaf abscission and during the winter when winds are the strongest. Both the samara plan and dispersal phenology need to be considered in estimating relative dispersibility among species.  相似文献   

Some determinants of the spatio-temporal fire cycle in a mediterranean landscape (Corsica,France)     

Mouillot  Florent  Ratte  Jean-Pierre  Joffre  Richard  Moreno  Jose Manuel  Rambal  Serge 《Landscape Ecology》2003,18(7):665-674

Based on recent needs to accurately understand fire regimes and post-fire vegetation resilience at a supra-level for carbon cycle studies, this article focusses on the coupled history of fire and vegetation pattern for 40 years on a fire-prone area in central Corsica (France). This area has been submitted since the beginning of the 20^th century to land abandonment and the remaining land management has been largely controlled by frequent fires. Our objectives were to rebuild vegetation and fire maps in order to determine the factors which have driven the spatial and temporal distribution of fires on the area, what were the feed backs on the vegetation dynamics, and the long-term consequences of this inter-relationship. The results show a stable but high frequency of small fires, coupled with forest expansion over the study period. The results particularly illustrate the spatial distribution of fires according to topography and vegetation, leading to a strong contrast between areas never burnt and areas which have been burnt up to 7 times. Fires, when occuring, affect on average 9 to 12% of the S, SE and SW facing slopes (compared to only 2 to 5% for the N facing slopes), spread recurrently over ridge tops, affect all the vegetation types but reburn preferentially shrublands and grasslands. As these fire-proning parameters have also been shown to decrease the regeneration capacity of forests, this study highlights the needs in spatial studies (both in terms of fire spread and vegetation dynamic) to accurately apprehend vegetation dynamic and functionning in fire-prone areas.This revised version was published online in May 2005 with corrections to the Cover Date.  相似文献   

棉花调亏灌溉的生理基础研究   总被引：8，自引：2，他引：8  

史文娟  康绍忠  宋孝玉 《干旱地区农业研究》2004,22(3):91-95

以盆栽棉花为材料,通过苗期和现蕾期不同程度的亏水处理(低、中、高三个水平),对调亏灌溉节水效应及生理机制进行了研究。结果表明:适时适度的水分亏缺可使植株旺盛的营养生长得以有效控制,株型和根冠比都更为理想。调亏期间,蒸腾速率和气孔导度都明显下降,而光合速率下降不明显,复水后光合速率和气孔导度明显恢复且接近或高于对照;此外,水分亏缺不仅影响棉桃的数量,而且影响单果重。表明适度的亏水处理可使水分利用效率明显提高,而经济产量接近或高于对照,同时节水20%以上。  相似文献   

赤峰市松山区土地利用动态变化及其原因分析   总被引：8，自引：6，他引：8  

贾宝全王成  马玉峰 《干旱区研究》2004,21(3):235-239

以TM遥感资料为信息源 ,利用 3S技术手段 ,对内蒙古自治区赤峰市松山区 1987,1993,2 0 0 0年的土地利用变化进行了分析。结果表明 ,在不同年度内 ,其主要的土地利用类型为耕地、草地和林地。土地利用类型的总量变化也以这 3种土地利用类型和建设用地变化最大。而从年变化速率看 ,1987- 2 0 0 0年 ,以建设用地的增加和未利用土地类型的减少最为快速。从土地利用类型转化的方向看 ,以耕地、草地和林地相互之间的转化最为频繁。从土地利用类型的空间稳定性看 ,耕地的稳定性最高 ,其次为草地 ;而最不稳定的土地利用类型为未利用土地。利用相关分析所作的土地利用变化动因显示 ,该地区土地利用变化的驱动因素主要是社会与经济因素 ,其中以总人口、农业总产值、粮食作物产量总计、农牧民人均纯收入、化肥使用面积和化肥实物量等因子的作用最大 ,而自然因素对该地区土地利用变化的影响极小。  相似文献   

我国北部农牧交错区城郊土地利用时空变化—以包头市为例     

任志远  武永峰 《干旱区资源与环境》2004,(Z2)

以包头市城郊区为例 ,在地理信息系统支持下 ,以乡镇 (苏木 )为研究单元 ,研究本地区土地利用时空动态变化过程 ,并分析其变化驱动因素。从微观角度分析了北方农牧交错区城郊区土地利用变化特征。农牧交错区是人类活动影响强烈之地带 ,土地利用变化与土地持续研究利用 ,对生态安全和地区持续发展具有十分重要的意义。  相似文献   

The value of vegetation cover for ecosystem services in the suburban context     

《Urban Forestry & Urban Greening》2016

Latin-American cities can be characterized by dynamic processes of urbanization that encroach upon the natural and semi-natural surrounding landscapes. Our study presents the effects of landscape development, transformed from semi-natural conditions into a mostly disperse suburban settlement. We explore the impact that this transformation has had on this context by three ecosystem services that regulate rainwater runoff, enhance microclimate conditions and help to improve air quality by monitoring vegetation cover. We have designed a spatio-temporal hierarchical analysis which employs remote sensing techniques to capture the structural changes of this landscape over long, medium and short term scales on two spatial levels. This methodological approach was tested in the Metropolitan Area of Santiago (MAS) as case study area. Despite of the increase in impervious surfaces due to urban processes, there has also been an increase in vegetation cover, which has led to an improvement in the provision of the above-mentioned ecosystem services. Hence, if diverse urbanization processes continue and they are coupled with an increase in vegetation cover, the provision of ecosystem services could also expand. This phenomenon can be observed in some areas, where public and private green spaces are created and maintained. Our data analyses give evidence that certain types of suburban areas which increase the share of vegetation cover can provide daily ecological benefits for urban neighborhoods, and beyond, for adjacent areas. Moreover, suburban development can successfully provide ecological benefits to citizens. Such processes can only be ecologically sustainable if the composition of vegetation is well-adapted to the regional climatic conditions.  相似文献   

Response of confection sunflower (Helianthus annuus L.) grown in a semi‐arid environment to planting date and early termination of irrigation          下载免费PDF全文

V. R. Joshi  J. J. Heitholt  A. Garcia y Garcia 《Journal of Agronomy and Crop Science》2017,203(4):301-308

Adjustments on planting date and on the time to terminate irrigation may reduce agricultural water use. However, such management practices in regions with extreme weather conditions have the potential to negatively affect yield. A 3‐year (2012–2014) study was conducted on a clay‐loam soil in a cool, semi‐arid environment to (i) determine the response of confection sunflower to planting date and irrigation termination timing and (ii) identify the relative importance of yield components in irrigated confection sunflower across planting dates. Early May planting had considerable negative effects on all studied variables, except on the percentage of large seeds. The highest yield of total and large seeds was obtained from the late May plantings, averaging 3,777 and 3,379 kg/ha, respectively. None of the irrigation strategies affected the measured variables. However, the interaction between planting date and termination of irrigation significantly affected the 1,000‐seed weight. Our study revealed the last week of May as suitable planting period for confection sunflower in the semi‐arid north‐western region of Wyoming, USA, and that irrigation on heavy soils may be terminated as early as at R5.5 stage without a significant yield reduction. The path‐coefficient analysis indicated head diameter and the number of seeds per head as important traits that significantly influence the yield of confection sunflower across planting dates.  相似文献