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  • 21
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 73 (1987), S. 321-333 
    ISSN: 1432-1939
    Keywords: Orchids ; Pollination ; Bee population dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Abundance patterns during 6–7 years and orchid visitation were determined for 51 species of the 57 local euglossine bees. Male bees were counted at 3 chemical attractants presented in the same manner each month. Sites were separated by 75 km but included wet Atlantic forest at 500 m elevation, moist forest at 180 m near Barro Colorado Island, and cloud forest at 900 m near the Pacific ocean. 1. From 15 to 30 euglossine species of 4 genera were active in each month and site; monthly species number and general bee abundance were positively correlated. Many species had 3 annual abundance peaks (range 1–4) and were active throughout the year, but peak annual abundances rarely occurred during late wet or early dry seasons. In contrast, Eufriesea generally were present as adults only 1–2 months in a year. 2. Euglossine populations were exceptionally stable. Species at each site were more stable than any known insect population, and stability and abundance were positively associated. However, year-to-year population stability and the degree of seasonality were not correlated. Among the three sites, the more diverse (species rich) bee assemblages displayed lower stability; these were the wetter and upland sites. 3. The most abundant bees visited more orchid species. Eg. and El. each visited and average of 4 orchid species (range 0–13); Ex. and Ef. visited 0–3. Stable populations did not visit more or fewer orchid species than did unstable populations. 4. Less than 68% of species at each site visited orchid flowers; less than a few dozen of the 100–800 bees counted in a day carried orchid pollinaria. Over 20% of the euglossine species never were seen with pollinaria at any site and probably seldom visit orchids in central Panama. 5. Most bee species visited 1 or no fragrance orchids in a given habitat. Orchids tended to utilize common pollinators that seldom included more than 1 species, and they utilized stable or unstable, seasonal or aseasonal bees. However, the most stable and abundant bee, Eg. imperialis, rarely pollinated orchids; fewer than 10 of ca. 20000 bees carried pollinaria. 6. Orchids may interact primarily with discrete seasonal bee population peaks-probably the emerging adults. Although specialized orchid preferences are implicated for species that visit few or no local orchids but pollinate other species and carry pollinaria in other areas, euglossine bees do not need orchids to survive or reproduce.
    Type of Medium: Electronic Resource
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  • 22
    ISSN: 1432-1939
    Keywords: Disease ; Epiphyte ; Fitness ; Orchid ; Reproductive success
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of a rust infection (Sphenosphora saphena, Basidiomycetes) on several fitness components of the orchid Tolumnia (Oncidium) variegata were quantified in a subtropical moist forest of Puerto Rico. Infected and uninfected plants of two size categories were observed and manipulated by increasing natural levels of fruit production to determine the effects of infection on short and long-term sexual reproduction, subsequent vegetative and reproductive growth, and mortality. Under artificially high levels of fruit production, infection had no effect on short or long-term reproduction through male or female function except for a modest decline in seed viability in small plants. Under natural levels of fruit production, infection was only related to a reduction in the number of leaves per shoot. At artificially high levels of fruit production, infection reduced leaf length, leaf width, and the number of live shoots. Survival was not associated with rust occurrence. The rust appears to have minor ecological impact on this orchid population.
    Type of Medium: Electronic Resource
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  • 23
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 106 (1996), S. 192-198 
    ISSN: 1432-1939
    Keywords: Pollination limitation ; Selection potential ; Seed dispersal ; Microsite limitation ; Fruit production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Will increased fruit and seed production in a severely pollination-limited orchid stimulate population growth? We tested whether safe sites for germination and seedling establishment are limiting for the twig epiphyte, Tolumnia variegata, by manipulating fruit set and monitoring subsequent seedling establishment for two seasons (1991–1992, 1992–1993). In the Cambalache Forest Reserve of Puerto Rico, we established 36 plots along a transect. Each plot consisted of nine trees. A center tree was designated as the site for attaching Tolumnia and manipulating fruit set. The other eight potential host trees were 1–3 and 3–5 m from the center tree in each of the cardinal directions. A 1-m length of stem 1 m from the ground was monitored for recruits on each of the nine trees of 24 fruit-enhanced plots and 12 controls (23 and 13, respectively for the 1992–1993 season). Fruit enhancement plots were divided among two treatments: one-fruit and five-fruit additions for the 1st year and one to five and more than five fruits for the 2nd year. Availability of suitable host species was not limiting. T. variegata showed little specificity for host tree species, good host trees and shrubs were common, and there was no evidence that the orchid had a preference for small branches, despite possessing the entire suite of characteristics thought to respresent “obligate” twig epiphytes. Fruit enhancement increased seed rain and seedling establishment consistently in only the high-fruit treatment plots. Most recruitment occurred near fruiting plants. Over the 2-year period, mortality was 18% for adults and 85.5% for the 1991–1992 cohort of recruits. Net recruitment was positive for both the treatment (average = 1.74) and control plots (average = 0.67). Seedling establishment at our study site was not microsite-limited. If selection for increased pollinator attraction occurs, then an increase in seed output should result in population growth.
    Type of Medium: Electronic Resource
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  • 24
    ISSN: 1432-0827
    Keywords: Key words: Densitometry — Bone mineral content — Hydroxyapatite — MRI.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. A solid state magnetic resonance imaging technique is used to measure true three-dimensional mineral density of synthetic hydroxyapatite phantoms and specimens of bone ex vivo. The phosphorus-31 free induction decay at 2.0 T magnetic field strength is sampled following application of a short, hard radiofrequency excitation pulse in the presence of a fixed amplitude magnetic field gradient. Multiple gradient directions covering the unit sphere are used in an efficient spherical polar to Cartesian interpolation and Fourier transform projection reconstruction scheme to image the three-dimensional distribution of phosphorus within the specimen. Using 3–6 Gauss/cm magnetic field gradients, a spatial resolution of 0.2 cm over a field of view of 10 cm is achieved in an imaging time of 20–35 minutes. Comparison of solid state magnetic resonance imaging with dual energy X-ray absorptiometry (DXA), gravimetric analysis, and chemical analysis of calcium and phosphorus demonstrates good quantitative accuracy. Direct measurement of bone mineral by solid state magnetic resonance opens up the possibility of imaging variations in mineral composition as well as density. Advantages of the solid state magnetic resonance technique include avoidance of ionizing radiation; direct measurement of a constituent of the mineral without reliance on assumptions about, or models of, tissue composition; the absence of shielding, beam hardening, or multiple scattering artifacts; and its three-dimensional character. Disadvantages include longer measurement times and lower spatial resolution than DXA and computed tomography, and the inability to scan large areas of the body in a single measurement, although spatial resolution is sufficient to resolve cortical from trabecular bone for the purpose of measuring bone mineral density.
    Type of Medium: Electronic Resource
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  • 25
    ISSN: 1279-8517
    Keywords: Aortic bifurcation ; Vena cava confluence ; Computed tomography ; Ageing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The object of this retrospective study was to determine the sites of abdominal aortic bifurcation and inferior vena cava confluence in relation to age and sex. The study group comprised 180 subjects (90 males and 90 females) divided into 9 groups by age (in decades). The positions of the aortic bifurcation and the inferior vena cava confluence were evaluated by CT, and linear regression models were fitted to the data. The positions of the aortic bifurcation and venous confluence showed a highly significant downward shift with increasing age (p=0.0001). The shift was more pronounced in women. The mean site of the aortic bifurcation for the whole group was at lower L4 (range, upper L3 to upper S1); in males, it was at upper L4 (range, upper L3 to upper L5), and in females at lower L4 (range, upper L3 to upper S1). The mean site of the venous confluence for the whole group was at disc L4-L5 (range, lower L3 to upper S1); in males, it was at disc L4-L5 (range, upper L4 to disc L5-S1), and in females at disc L4-L5 (range, lower L3 to upper S1). Thus, the aorta and the inferior vena cava can extend as low as the level of S1. These data are of relevance in laparoscopic procedures, especially in laparoscopic lumbar discectomy.
    Type of Medium: Electronic Resource
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  • 26
    ISSN: 1279-8517
    Keywords: Aortic bifurcation ; Vena cava confluence ; Computed tomography ; Ageing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé Le but de cette étude rétrospective était de déterminer la topographie de la bifurcation de l'aorte abdominale et de la confluence cave caudale en fonction de l'âge et du sexe. Le groupe étudié comprenait 180 sujets (90 de sexe masculin et 90 de sexe féminin) divisés en 9 groupes d'âge (9 décennies). Les positions de la bifurcation aortique et de la confluence veineuse cave caudale ont été évaluées par tomodensitométrie, et des modèles de régression linéaire ont été appliqués aux données recueillies. Un déplacement caudal des positions de la bifurcation aortique et de la confluence cave caudale était hautement corrélé à l'âge (p=0.0001). Le déplacement était plus prononcé chez les femmes. La position moyenne de la bifurcation aortique pour le groupe entier était la partie caudale de L4 (extrémités : partie supérieure de L3, partie supérieure de S1) ; chez les sujets de sexe masculin, elle se situait à la partie supérieure de L4 (extrémités : partie supérieure de L3, partie supérieure de L5), et dans le sexe féminin à la partie caudale de L4 (extrémités : partie supérieure de L3, partie supérieure de S1). La situation moyenne de la confluence cave caudale pour le groupe entier était au niveau du disque L4–L5 (extrémités : partie caudale de L3, partie craniale de S1) ; dans le sexe masculin elle se situait en regard du disque L4–L5 (extrémités : partie craniale de L4, disque L5–S1) et dans le sexe féminin au niveau du disque L4–L5 (extrémités : partie caudale de L3, partie craniale de S1). Ainsi, l'aorte et la veine cave caudale peuvent s'étendre aussi bas qu'au niveau de S1. Ces données trouvent leur application dans les procédures laparoscopiques, en particulier dans la discectomie lombaire.
    Notes: Summary The object of this retrospective study was to determine the sites of abdominal aortic bifurcation and inferior vena cava confluence in relation to age and sex. The study group comprised 180 subjects (90 males and 90 females) divided into 9 groups by age (in decades). The positions of the aortic bifurcation and the inferior vena cava confluence were evaluated by CT, and linear regression models were fitted to the data. The positions of the aortic bifurcation and venous confluence showed a highly significant downward shift with increasing age (p=0.0001). The shift was more pronounced in women. The mean site of the aortic bifurcation for the whole group was at lower L4 (range, upper L3 to upper S1); in males, it was at upper L4 (range, upper L3 to upper L5), and in females at lower L4 (range, upper L3 to upper S1). The mean site of the venous confluence for the whole group was at disc L4–L5 (range, lower L3 to upper S1); in males, it was at disc L4–L5 (range, upper L4 to disc L5–S1), and in females at disc L4–L5 (range, lower L3 to upper S1). Thus, the aorta and the inferior vena cava can extend as low as the level of S1. These data are of relevance in laparoscopic procedures, especially in laparoscopic lumbar discectomy.
    Type of Medium: Electronic Resource
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  • 27
    ISSN: 1279-8517
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 28
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 182 (1981), S. 2297-2304 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of four solvent-extracted lignins were subjected to solid-state 13C NMR analysis using the cross polarization-magic angle (CP/MAS) technique. Comparisons are made between the solid-sample spectra and high-field spectra obtained on solutions of these lignins. Specific signals in both the solid-state and solution spectra can be assigned to structural features present in the lignins. Most of the spectral information present in the solution-state spectra are seen by CP/MAS, a technique that shows great promise for the study of lignin in solid samples.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 29
    Electronic Resource
    Electronic Resource
    Springer
    Plant systematics and evolution 222 (2000), S. 167-185 
    ISSN: 1615-6110
    Keywords: Anemophily ; hydrophily ; wind pollination ; water pollination ; biomechanics ; fluid dynamics ; ephydrophily ; hyphydrophily ; dicliny ; dichogamy ; autogamy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The transport and capture of pollen in ~20% of all angiosperm families occurs in air and water. In other words, pollination is abiotic and occurs via the fluid media, not an animal vector. Whereas some early concepts considered abiotic pollination to be largely a stochastic phenomenon, there is sufficient evidence to indicate that wind pollination (i.e. anemophily) and water pollination (i.e. hydrophily) have deterministic features and are sophisticated fluid dynamic solutions to the problem of pollen release, dispersal, and capture. An abiotic pollination syndrome is defined in which there is spatial or temporal separation of carpellate and staminate flowers, which are drab, a reduction in perianth parts, stigmas and anthers are exposed to the fluid, and typically unclumped pollen may be produced in large amounts. Separate pollination syndromes are defined for anemophilous (i.e. wind-pollinated), ephydrophilous (i.e. surface-pollinated), and hydrophilous (i.e. submarine-pollinated) plants. Distinctions are based on habitat and physical conditions for pollination, pollen size, shape, and ultrastructure, morphology and ultrastructure of stigmas, and outcrossing rates. For example, anemophilous pollen are spherical and small, ephydrophilous pollen are spherical or reniform and large, while hydrophilous pollen are filiform (i.e. filamentous) or functionally filiform. The pollination mechanisms and mechanics associated with these syndromes reveals a strong evolutionary relationship between plant morphology and fluid dynamics.
    Type of Medium: Electronic Resource
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