Culling prey promotes predator recovery--alternative states in a whole-lake experiment     

Persson L  Amundsen PA  De Roos AM  Klemetsen A  Knudsen R  Primicerio R 《Science (New York, N.Y.)》2007,316(5832):1743-1746

Many top-predator fish stocks in both freshwater and marine systems have collapsed as a result of overharvesting. Consequently, some of these communities have shifted into seemingly irreversible new states. We showed, for predators feeding on prey that exhibit food-dependent growth, that culling of fish prey may promote predator recovery. We removed old stunted individuals of a prey-fish species in a large, low-productive lake, which caused an increase in the availability of small-sized prey and allowed the predator to recover. The shift in community state has been sustained for more than 15 years after the cull ended and represents an experimental demonstration of an alternative stable state in a large-scale field system. Because most animals exhibit food-dependent growth, shifts into alternative stable states resulting from overcompensating prey growth may be common in nature and may require counterintuitive management strategies.  相似文献   

NEW ORLEANS MEETING,DECEMBER 28, 1931-JANUARY 2, 1932     

Roos CF 《Science (New York, N.Y.)》1931,74(1925):516-519

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四川盆南紫色土颗粒及化学组成的研究   总被引：3，自引：0，他引：3  

魏朝富  谢德体  车福才 《西南大学学报(自然科学版)》1989,(5)

四川盆南紫色土颗粒深受母质的影响,红棕紫泥和灰棕紫泥具有适宜的颗粒组成。紫色土粘粒矿物以伊利石为主,其中的一部份是在土壤形成过程中形成的。红紫泥具有明显的富铁铝化过程。  相似文献   

Causal protein-signaling networks derived from multiparameter single-cell data     

Sachs K  Perez O  Pe'er D  Lauffenburger DA  Nolan GP 《Science (New York, N.Y.)》2005,308(5721):523-529

Machine learning was applied for the automated derivation of causal influences in cellular signaling networks. This derivation relied on the simultaneous measurement of multiple phosphorylated protein and phospholipid components in thousands of individual primary human immune system cells. Perturbing these cells with molecular interventions drove the ordering of connections between pathway components, wherein Bayesian network computational methods automatically elucidated most of the traditionally reported signaling relationships and predicted novel interpathway network causalities, which we verified experimentally. Reconstruction of network models from physiologically relevant primary single cells might be applied to understanding native-state tissue signaling biology, complex drug actions, and dysfunctional signaling in diseased cells.  相似文献   

Bright Spots, Structure, and Magmatism in Southern Tibet from INDEPTH Seismic Reflection Profiling   总被引：8，自引：0，他引：8  

LD Brown  W Zhao  KD Nelson  M Hauck  D Alsdorf  A Ross  M Cogan  M Clark  X Liu  J Che 《Science (New York, N.Y.)》1996,274(5293):1688-1690

INDEPTH seismic reflection profiling shows that the decollement beneath which Indian lithosphere underthrusts the Himalaya extends at least 225 kilometers north of the Himalayan deformation front to a depth of approximately 50 kilometers. Prominent reflections appear at depths of 15 to 18 kilometers near where the decollement reflector apparently terminates. These reflections extend north of the Zangbo suture to the Damxung graben of the Tibet Plateau. Some of these reflections have locally anomalous amplitudes (bright spots) and coincident negative polarities implying that they are produced by fluids in the crust. The presence of geothermal activity and high heat flow in the regions of these reflections and the tectonic setting suggest that the bright spots mark granitic magmas derived by partial melting of the tectonically thickened crust.  相似文献   

Trans-endocytosis of CD80 and CD86: a molecular basis for the cell-extrinsic function of CTLA-4   总被引：1，自引：0，他引：1  

Qureshi OS  Zheng Y  Nakamura K  Attridge K  Manzotti C  Schmidt EM  Baker J  Jeffery LE  Kaur S  Briggs Z  Hou TZ  Futter CE  Anderson G  Walker LS  Sansom DM 《Science (New York, N.Y.)》2011,332(6029):600-603

Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an essential negative regulator of T cell immune responses whose mechanism of action is the subject of debate. CTLA-4 shares two ligands (CD80 and CD86) with a stimulatory receptor, CD28. Here, we show that CTLA-4 can capture its ligands from opposing cells by a process of trans-endocytosis. After removal, these costimulatory ligands are degraded inside CTLA-4-expressing cells, resulting in impaired costimulation via CD28. Acquisition of CD86 from antigen-presenting cells is stimulated by T cell receptor engagement and observed in vitro and in vivo. These data reveal a mechanism of immune regulation in which CTLA-4 acts as an effector molecule to inhibit CD28 costimulation by the cell-extrinsic depletion of ligands, accounting for many of the known features of the CD28-CTLA-4 system.  相似文献   

Analysis of methanogenic archaeal communities of rumen fluid and rumen particles from Korean black goats     

Min‐Jung GU  Md. Jahangir ALAM  Seon‐Ho KIM  Che‐Ok JEON  Moon‐Baek CHANG  Young‐Kyoon OH  Sang‐Cheol LEE  Sang‐Suk LEE 《Animal Science Journal》2011,82(5):663-672

Molecular diversity of methanogens in the rumen of Korean black goats was investigated with 16S rRNA gene clone libraries using methanogen‐specific primers. The libraries were composed of rumen fluid‐associated methanogens (FAM) and rumen particle‐associated methanogens (PAM) from rumen‐fistulated Korean black goats. Among the 141 clones of the FAM library, the sequences were mostly related to two phyla, the Methanobacteriaceae family (77.3%) and the Thermoplasmatales family (22.7%); and among the 68 clones of the PAM library, sequences were also mainly clustered in the two phyla, the Thermoplasmatales family (63.24%) and the Methanobacteriaceae family (35.29%). Most of the sequenced clones in the two libraries were closely related to uncultured methanogenic archaeon. Quantitative real‐time PCR revealed that PAM (8.97 log 10) had significantly higher (P < 0.01) density of methanogens by the methanogenic 16S rRNA gene copies than FAM (7.57 log 10). The two clone libraries also showed difference in Shannon index (FAM library 1.70 and PAM library 1.59) and Chao 1 estimator (FAM library 18 and PAM library 17 operational taxonomic units). Apparent differences found in the microbial community from the two 16S rRNA gene libraries could be a result of such factors as the chemical and physical nature of the target material surface, types or component of diets, the interaction between the methanogens and other microbes, and age of the experimental goats.  相似文献   

紫花苜蓿茎秆在常压热风干燥中的传质模拟研究     

车刚  李成华  汪春  万霖 《农业工程学报》2007,23(5):27-31

根据斐克定律和质量守恒原理，建立了可以预测干燥过程中苜蓿茎秆内部水分分布的常压热风干燥的传质数学模型。通过对扩散模型边界条件的处理，结合紫花苜蓿茎秆内部水分扩散的干燥试验结果，采用数值模拟方法确定了干燥苜蓿茎秆的传质系数。结果表明，干燥苜蓿样本的含水率与模拟分析含水率的决定系数为R²=0.927，模拟分析具有较高的准确度。在此基础上进行的苜蓿茎秆内部水分分布的模拟计算保证了与苜蓿非稳态干燥过程的一致性。  相似文献   

不同有机材料覆盖对土壤保水效果的影响   总被引：2，自引：0，他引：2  

车飞伟  李素艳  孙向阳  曲炳鹏  贠炳辉  王心语  熊凯毅 《水土保持通报》2020,40(2):182-187

[目的]研究不同有机材料覆盖对土壤水分蒸发量、土壤含水量的影响,并筛选出保水效果最佳的材料。[方法]以木片、树皮及经过堆腐的园林废弃物为研究对象,进行模拟蒸发及桶装控制试验。[结果]不同粒径的园林废弃物覆盖均能降低土壤水分日蒸发量,日蒸发量从大到小依次为CK,3～5 cm粒径(M_3)、0～1 cm粒径(M_1)、1～3 cm粒径(M_2)。在连续蒸发14 d后,M_2,M_1,M_3和CK的土壤水分累积蒸发量分别为193.0,269.5,304.0和1 037.0 g,与CK相比,分别减少了81.4%,74.0%,70.7%;不同有机材料覆盖均能提高土壤含水量。除了雨季之外,不同土层土壤含水量从高到低依次表现为:木片覆盖(M_4)树皮覆盖(M_5)1～3 cm粒径园林废弃物覆盖(M_2)CK。土壤含水量的年变化整体呈现出双峰趋势,一年中4—5月含水量较低,6—8月含水量较高,不同土层土壤含水量的年变化趋势基本一致。M_4,M_5,M_2和CK的0—40 cm土层土壤年平均含水量分别为32.9%,30.3%,27.4%,26.8%。[结论]木片为保水效果最好的有机材料,其次是树皮和园林废弃物。  相似文献   

福州第三中学水土保持综合实践活动总结     

车云 《亚热带水土保持》2005,17(2):68-70

本主要通过对福建省水土流失现状的调查及学习水土保持治理措施，针对目前水土保持工作中把主要的财力、物力和人力放在对水土流失的监测和治理上，但宣传工作力度不够这一问题，特别创作了福建省水土保持科普网站“水土流失生命流失”(www．fzsz．net／地理组／水土流失、生命流失，或www．fzsz．net／comp／luse)，确定了以研究性学习为主，网络协作学习为辅的主题思想，制定了由初步学习→野外考察→社会实践→归纳整理→总结探究→网络创新这六大部分组成的主体框架结构。目的是：展示最新水土保持案例和学生学习成果，为广大中小学生和社会各界人士提供水土保持研究性学习的网络平台。  相似文献