五台山南台山地草甸种群对旅游干扰的生态响应

以五台山南台为例,利用生态位的宽度指数,研究了草甸种群对旅游干扰的生态响应。结果表明:(1)紫羊茅、珠芽蓼和北方嵩草的生态位宽度较大,是群落的建群种。随着距离的增加,旅游干扰减小,不仅物种的数量越来越多,而且其生态优势也趋于增强,说明旅游干扰限制了种群对其周围资源的利用。其中,紫羊茅的相对优势在下降,而北方嵩草的相对优势却不断增强。(2)两种划分方法表明,北方嵩草、雪白委陵菜、零零香、歪头菜、小红菊和兰花棘豆是增长型的种类;扁蓄是衰退型的种类;地榆是波动型的种类。     

采伐干扰下次生林灌木层主要树种的生态位动态

为探讨采伐干扰下的灌木层主要树种的生态适应性,用Levins、Schoener和Pianka等生态位测度公式定量分析闽北天然次生林采伐后灌木层主要树种生态位动态。结果表明:样地中黄绒润楠和刺毛杜鹃的生态位最大,属优势树种;甜槠、石栎和映山红为衰退树种,在林分生产作业中需加以保护。采伐干扰促进了灌木层主要树种的生态位释放,各树种的生态位宽度在伐后10~15 a达到峰值,随后下降,伐后20 a接近于未采伐林的生态位;各树种弱度和中度择伐的生态位宽度值约占其生态位宽度总值的50%。生态位重叠值在伐后10 a最大,随后下降,到伐后20 a趋于稳定状态。因此灌木层主要树种生态位的最优期为伐后10~15 a,最佳采伐干扰强度为弱度和中度择伐。     

Fish functional diversity responses following flood pulses in the upper Paraná River floodplain

Flood pulses are the main force driving the dynamics of aquatic communities in floodplains. The responses of communities to environmental changes following flood pulses usually demand a time lag to appear and reach the climax. We assembled a data set of 16 years of fish samplings to assess the relationship between water level and four functional diversity measures, in the upper Paraná River floodplain. Specifically, we approached four aspects of each relationship between water level and functional diversity: nature (positive or negative), sensitivity (response intensity), responsiveness (response delay) and extent (response duration). The nature of the relationship between water level and functional diversity was positive in all cases. Functional richness (FRic) responded right after flood pulses, although with shorter extent. Abundance‐dependent functional measures (evenness—FEve; divergence—FDiv; and Rao's quadratic entropy—Rao's Q) presented delayed responses, reaching peaks more than 1.5 years after flood pulses. Significant effects of floods on fish functional diversity were observed for more than 3 years, although the highest functional diversity was observed with 1.8 years, on average. More importantly, flood pulses had no longer significant effects on functional diversity after 4 years. Regarding conservation strategies in regulated systems, flood events should occur every 2 or 3 years, with adequate timing (October‐November), intensity (up to 450 cm) and duration (at least 50 uninterrupted days). Intervals longer than 3 years or inadequate timing, intensity and duration could dramatically decrease functional diversity and compromise ecosystem services.     

Plant and Bird Community Dynamics in Mixed-Grass Prairie Grazed by Native and Domestic Herbivores

Native colonial and large ungulate herbivores infrequently coexist on contemporary landscapes but frequently would have in the past, and understanding these interactions is important for conservation in working landscapes—those lands managed for biological and economic objectives. Although many factors contribute to grassland bird declines, consistent and long-term removal of native herbivores from western grasslands promotes homogenous landscapes that are now uniformly grazed by cattle (Bos taurus). This shift in grassland disturbance patterns limits habitat availability for specialized grassland species. We investigated vegetation and bird community dynamics in pastures grazed by domestic cattle and a native colonial herbivore, the black-tailed prairie dog (Cynomys ludovicianus). The study occurred in the northern mixed-grass prairie of the United States on four experimental pastures stratified by the proportion of prairie dog occupancy to create an ecological gradient. Vegetation and bird surveys were conducted from 2012 to 2015 on and off prairie dog colonies. Vegetation and bird communities were not different along the experimental pasture gradient but did differ relative to location on versus off town. Prairie dogs induced changes in the plant community with midstatured grasses like side-oats grama (Bouteloua curtipendula) and green needlegrass (Nassella viridula) being associated with off-colony sites while on-colony sites were associated with disturbance-tolerant species such as fetid marigold (Dyssodia papposa). The bird community responded to changes in vegetation structure resulting from prairie dogs with grasshopper sparrows (Ammodramus savannarum) being more abundant off colonies in areas with greater vegetation structure, while bird species with more complex life histories, such as the upland sandpiper (Bartramia longicauda), were associated with both on ? and off ? prairie dog colonies. Our findings demonstrate the importance of maintaining spatial heterogeneity in working landscapes and show that native colonial herbivores can help achieve this in the presence of herbivory by domestic cattle.     

Invertebrate drift densities in the Njoro and Kamweti Rivers in the Kenyan highlands that differ in the level of anthropogenic disturbances

Invertebrate drift is one of several fundamental ecological processes in streams. However, little is known about the dynamics of invertebrate drift in Kenyan streams. In this study, we assessed invertebrate drift in two rivers, i.e. Njoro and Kamweti, that differ in the level of anthropogenic disturbances, between February and March, 2016. The aim was to evaluate the effect of river sampling duration (5, 10, 15, 20 and 25 min) and sampling period (day or night) on invertebrate drift densities. The 5-minute sampling period resulted in significantly higher mean drift densities than the other time intervals in both rivers. The highest mean drift density (2.0 ± 0.9 individuals m^?3) was recorded at the Njoro River during the day, whereas the lowest drift density (0.3 ± 0.2 individuals m^?3) was recorded at the Kamweti River during the day. A strong nocturnal drift pattern was noted at the less disturbed river (Kamweti). The present results suggest that anthropogenic perturbations influence invertebrate drift densities, and sampling duration and sampling period are important factors to consider when sampling invertebrate drift.     

Soil solution chemistry at different positions on slope in a conifer plantation forest

It is known that soil property varies along the slope. It suggests that soil solution chemistry also differs topographically. To determine the variation in soil solution chemistry within one watershed, soil solution chemistry at the different positions of the slope was investigated. Soil N transformation changed along the slope. NH₄ ⁺ ratio to inorganic N (NH₄ ⁺ + NO₃ ⁻) increased upslope. The tendency was verified by laboratory incubation. After incubation most of the mineralized N was nitrified at the lower part of the slope, while little nitrification occurred at the upper part of the slope. At the ridge and the backslope inorganic N form in soil solution was concomitant with inorganic N form by incubation. At the ridge NH₄ ⁺ was predominant form in soil solution, at that time major anion was sea salt originated Cl⁻. From this, soil solution chemistry seems to be regulated by the external nutrient source at the ridge. In the second year of lysimeter installation NO₃ ⁻ concentration increased in both sites and the ratio of NH₄ ⁺ to inorganic N decreased. It was considered due to the effect of lysimeter installation. The lag time and the magnitude of NO₃ ⁻ increase were different between the ridge and the backslope. It would be related with soil N transformation in pre-disturbance. The influence of disturbance were shown in other solute concentrations of soil solution.     

从自然干扰看人类干扰的合理性

人类活动对自然生态系统来说又称人类干扰．总结了人类干扰的特点：①干扰方式的相似性与作用时间的同步性;②干扰历时的长期性与作用程度的深刻性;③干扰范围的广泛性与作用方式的多样性;④干扰活动的小尺度与作用后果的大尺度．在此基础上,应用景观生态学的理论分析了自然干扰与人类干扰在作用机制和尺度等方面的差异,指出自然干扰的运行机制对于人类活动具有重要的指导和借鉴意义．     

Responses of Australian sea lions,Neophoca cinerea,to anthropogenic activities in the Perth metropolitan area,Western Australia

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基于离散元法的板结草地破土切根刀优化设计与试验

不同结构形式的破土切根刀作业性能差异较大,为更好的打破草地土壤板结结构,对破土切根刀进行了结构设计与参数优化。应用离散元法构建土壤模型,并通过直剪试验对该模型进行参数标定;以破土切根刀的刃口角、滑切角及切齿角为试验因素,以耕作阻力、土壤扰动失效面积及比阻为目标参数,进行单因素试验和三因素五水平二次正交旋转中心组合设计试验,得到最优结构参数组合并加工优化破土切根刀进行草地试验。参数优化试验结果显示,当刃口角为37.8°、滑切角为33.6°、切齿角为51.8°时,破土切根刀作业效果最佳;草地试验表明,与三角形破土切根刀相比,优化破土切根刀在不同坚实度草地土壤的减阻率分别为11.8%和12.8%,作业后地表平整度更小且未出现明显翻垡,更符合草地作业农艺要求。研究结果可为破土切根刀的标准化设计提供理论依据。