Selective grazing by cattle on spatially and seasonally heterogeneous rangeland in Sahel

The selective use by cattle of range resources in the Sahel was assessed in terms of quantity and nutritional quality of the herbage grazed and diet selected. Peak standing crop was 1951 kg ha⁻¹dry matter (DM) with 47·9 kg nitrogen (N) ha⁻¹and 7·4 kg phosphorus (P) ha⁻¹. Esophageally fistulated cattle diets were consistently (p<0·05) higher in N, P and organic matter digestibility (OMD) than the herbage grazed. Cattle consumed 48% of the mean annual herbage production. The results indicate grazing ruminants select a higher quality diet from Sahelian rangelands than can be predicted on the basis of pasture evaluation alone. Therefore, the foraging behaviour of the animals needs to be considered in the evaluation of Sahelian rangelands for animal production.     

围隔实验研究台湾海峡2005年夏季小型浮游动物对硅藻水华的摄食

为了研究小型浮游动物对近岸浮游植物藻华的摄食调控作用,于2005年7月,应用"稀释法"并结合高效液相色谱(HPLC)光合色素分析技术,研究了台湾海峡船基围隔实验条件下浮游植物生长率及小型浮游动物摄食率的日变动。结果表明:由于营养盐添加的影响,迅速形成了以尖刺伪菱形藻(Pseudo-nitzschia pungens)为优势种的藻华,生物量(叶绿素a)从实验初始7月6日的1.45μg/dm3迅速增加到7月8日的29.80μg/dm3,随后消退。镜检和光合色素分析的结果显示,实验期间一直以此硅藻占绝对优势。浮游植物的生长率在藻华峰值(7月8日)前保持了较高的生长速率(>1.0/d)且大于小型浮游动物的摄食率;小型浮游动物的摄食率也逐渐增加,7月7日时达到0.86/d,显示有57%以上的浮游植物现存量被摄食。7月8日后,水华迅速消退,摄食率除13日外,均大于浮游植物的生长率。小型浮游动物主要由急游虫(Strombidium spp.)、侠盗虫(Strobilidium spp.)等无壳纤毛虫、异养甲藻-螺旋环沟藻(Gyrodinium spirale)及砂壳纤毛虫等组成,其对浮游植物的生长迅速作出了反应,各类群的丰度在水华峰值后的7月9日均几达最大值,水华后期(11日)大型的无壳纤毛虫达最大值。小型浮游动物的这种组成及变动特点是其保持较高摄食率及一定程度上控制和促进藻华消退的原因之一。     

Depth-stratified phytoplankton dynamics in Cyclone Opal, a subtropical mesoscale eddy

As part of E-Flux III cruise studies in March 2005, we investigated phytoplankton community dynamics in a cyclonic cold-core eddy (Cyclone Opal) in the lee of the Hawaiian Islands. Experimental incubations were conducted under in situ temperature and light conditions on a drift array using a two-treatment dilution technique. Taxon-specific estimates of growth, grazing and production rates were obtained from analyses of incubation results based on phytoplankton pigments, flow cytometry and microscopy. Cyclone Opal was sampled at a biologically and physically mature state, with an 80–100 m doming of isopycnal surfaces in its central region and a deep biomass maximum of large diatoms. Depth-profile experimentation defined three main zones. The upper (mixed) zone (0–40 m), showed little compositional or biomass response to eddy nutrient enrichment, but growth, grazing and production rates were significantly enhanced in this layer relative to the ambient community outside of the eddy. Prochlorococcus spp. dominated the upper mixed layer, accounting for 50–60% of its estimated primary production both inside and outside of Opal. In contrast, the deep zone of 70–90 m showed little evidence of growth rate enhancement and was principally defined by a 100-fold increase of large (>20-μm) diatoms and a shift from Prochlorococcus to diatom dominance (80%) of production. The intermediate layer of 50–60 m marked the transition between the upper and lower extremes but also contained an elevated biomass of physiologically unhealthy diatoms with significantly depressed growth rates and proportionately greater grazing losses relative to diatoms above or below. Microzooplankton grazers consumed 58%, 65% and 55%, respectively, of the production of diatoms, Prochlorococcus and the total phytoplankton community in Cyclone Opal. The substantial grazing impact on diatoms suggests that efficient recycling was the major primary fate of diatom organic production, consistent with the low export fluxes and selective export of biogenic silica, as empty diatom frustules, in Cyclone Opal.     

三亚湾夏秋两季微型浮游动物摄食研究

根据2005年8月和11月的调查资料,利用现场稀释法,以叶绿素a为检测对象,分别对三亚湾海区夏秋两季微型浮游动物的摄食情况进行研究。结果表明,夏秋两季浮游植物瞬时生长率(k)分别为0.9~1.32/d和1.81~3.30/d,而微型浮游动物的摄食率(g)则为0.85~1.79/d和1.29~2.57/d。对浮游植物现存量和初级生产力的摄食压力分别是,夏季为57.26%~83.30%和78.13%~140.38%,秋季为72.47%~92.35%和86.65%~97.90%。秋季微型浮游动物以微型浮游植物为其主要食物来源,其摄食率和对初级生产力的摄食压力最高,平均分别为1.09/d和107.98%;微型浮游植物的瞬时生长率也是最高的,平均为0.94/d,为浮游植物群体的主要组成部分。在三亚湾夏秋两季可把微型浮游动物作为控制浮游植物生长的重要影响因子之一,同时与秋季相比,夏季微型浮游动物在物质循环和能量流动方面起到更显著的作用。     

Alpine Ecosystems of Northwest Yunnan, China： an Initial Assessment for Conservation

Implementing conservation actions on-the-ground is not a straightforward process,especially when faced with high scientific uncertainty due to limited available information. This is especially acute in regions of the world that harbor many unique species that have not been well studied,such as the alpine zone of the Hengduan Mountains of Northwest Yunnan (NWY),a global biodiversity hotspot and site of The Nature Conservancy’s Yunnan Great Rivers Project. We conducted a quantitative,but rapid regional-level assessment of the alpine flora across NWY to provide a broad-based understanding of local and regional patterns of the alpine flora,the first large-scale analysis of alpine biodiversity patterns in this region. Multivariate analyses were used to classify the major plant community types and link community patterns to habitat variables. Our analysis indicated that most species had small distributions and/or small population sizes. Strong patterns emerged with higher diversity in the more northern mountains,but beta diversity was high,averaging only 10% among sites. The ordinations indicated that elevation and geographic location were the dominant environ-mental gradients underlying the differences in the species composition among communities. The high beta diversity across the alpine of these mountains implies that conservation strategies ultimately will require the protection of large numbers of species over a large geographical area. However,prioritiza-tion should be given to areas where potential payoffs are greatest. Sites with high species richness also have a greater number of endemic species,and,by focusing efforts on these sites,conservation investments would be maximized by protecting the greatest number of unique species.     

外来种福寿螺(Pomacea canaliculata)对3种沉水植物的牧食偏好及水体理化因子的响应

外来种福寿螺(Pomacea canaliculata)相较我国本土螺类其牧食量更大且繁殖速度更快,对栖息地水生植物的现存量和实施水生植被恢复的生态治理工程的成功性可能构成威胁,目前对福寿螺影响浅水湖泊沉水植物的重建缺乏足够的研究.本文通过设置不同沉水植物种类组合系统,研究福寿螺对3种常用于浅水富营养化湖泊治理的沉水植物密刺苦草(Vallisneria denseserrulata)、轮叶黑藻(Hydrilla verticillata)、穗花狐尾藻(Myriophyllum spicatum)的牧食偏好以及不同植物配置系统理化因子的响应变化,结果表明福寿螺对沉水植物植株附着偏好为密刺苦草轮叶黑藻穗花狐尾藻,而牧食破坏强度为轮叶黑藻穗花狐尾藻密刺苦草,轮叶黑藻最容易受到福寿螺牧食影响而快速消亡,穗花狐尾藻叶片也会被全部牧食仅剩下茎,而苦草存活受到的影响较小.福寿螺会导致轮叶黑藻+密刺苦草组合系统中总氮、氨氮、总磷、正磷酸盐浓度显著升高,而密刺苦草+穗花狐尾藻组合中总磷、正磷酸盐浓度显著升高,但是在轮叶黑藻+穗花狐尾藻组合中仅总氮浓度显著升高.研究表明福寿螺能够影响沉水植物间的竞争关系,但是3种沉水植物均不能阻止福寿螺的牧食;福寿螺牧食会显著降低沉水植物生物量,最终会影响草型清水态系统的稳定性.     

放牧对内蒙古羊草群落土壤呼吸的影响

采用静态暗箱法,比较测定了放牧对内蒙古锡林河流域羊草群落土壤呼吸的影响以及水热等相关环境因子与土壤呼吸的关系。结果表明:放牧没有改变羊草群落土壤呼吸的季节性变化特征,但降低了土壤呼吸速率的年幅度;生长季放牧样地土壤呼吸速率显著低于封育样地,非生长季两样地土壤呼吸强度均处于较低水平,而且出现负通量的现象,放牧使羊草群落土壤呼吸年总量下降了约33.95％;从全年来看,无论是围栏还是放牧样地,封育样地和放牧样地土壤呼吸与温度因子均显著正相关(p<0.01,n=15),其中与10cm处地温相关性最好,但放牧降低了土壤呼吸对温度变化的敏感性;生长季水分影响作用高于温度,围栏封育样地0~10cm土壤含水量的变化可以解释土壤呼吸变异的87.4％,放牧样地10~20cm和20~30cm土壤含水量的变化共同可以解释土壤呼吸变异的74.9％。     

气候变化及人为干扰对西藏地区草地退化的影响研究

随着草地保护政策的实施,气候及人为干扰对西藏地区草地退化的影响作用发生变化,明确草地退化的影响因素,评价草地保护政策对草地退化恢复的效用,是合理保护西藏地区草地生态平衡的基础.本文以西藏地区为研究区,基于1995-2015年GIMMS-NDVI及统计数据估测草地退化情况,并通过残差分析及回归分析评估了气候变化、人为干扰...     

青藏高原放牧强度空间化方法与应用

人类活动强度空间化是分析人类活动区域差异及其变化过程的基础,也是准确辨识土地变化驱动因素、合理调控人类活动的科学依据。当前人类活动强度研究多以数理方法对代用指标进行空间化,缺乏对人类活动机理过程的反映,也制约了人类活动强度空间异质性的展现。本文以青藏高原放牧活动为研究对象,在综合放牧喜好和草地管理策略的基础上,从放牧行为机理的角度,提出了区分放牧区与非放牧区的方法;以放牧密度衡量草地整体放牧压力,以放牧概率刻画放牧活动的空间差异,构建了区域放牧强度空间化模型。并以高原典型牧业县—泽库县为例,基于乡镇级牧业数据和自然地理基础信息进行了实证研究。结果表明：空间化结果较好反映了泽库县放牧强度的空间特征;直接指标的选取和客观的赋值方法提高了放牧强度空间化结果的准确性;比现有研究结果更能体现出县域内放牧强度的空间差异,且放牧强度变化过程与同期NDVI值变化具有较好的耦合性。本文为人类活动空间化方法研究提供了有益参考。     

Mnemiopsis leidyi (Ctenophora) in Narragansett Bay, 1975–1979: Abundance,size composition and estimation of grazing

Surveys of the distribution, abundance and size of the ctenophore Mnemiopsis leidyi were carried out in Narragansett Bay, R.I. over a 5-year period, 1975–1979. Yearly variations were observed in time of initiation of the ctenophore increase and maximum abundance. Biomass maxima ranged from 0·2 to 3 g dry weight m^?3 at Station 2 in lower Narragansett Bay while maximum abundance varied from 20 to 100 animals m^?3. Ctenophores less than 1 cm in length generally composed up to 50% of the biomass and 95% of the numerical abundance during the peak of the M. leidyi pulse. During the 1978 maxima and the declining stages of the pulse each year, 100% of the population was composed of small animals. M. leidyi populations increased earlier, reached greater maximum abundances, and were more highly dominated by small animals in the upper bay than toward the mouth of the bay. The averageclearance rate of M. leidyi larvae feeding on A. tonsa at 22°C was 0·36 l mg^?1 dry weight day^?1, with apparent selection for nauplii relative to copepodites. Predation and excretion rates applied to ctenophore biomass estimated for Narragansett Bay indicated that M. leidyi excretion is minor but predation removed a bay-wide mean of 20% of the zooplankton standing stock daily during August of 1975 and 1976. Variation in M. leidyi predation at Station 2 was inversely related to mean zooplankton biomass during August and September, which increased 4-fold during the 5-year period.