Near Absence (near + absence)

Distribution by Scientific Domains


Selected Abstracts


Process in the evolution of bird migration and pattern in avian ecogeography

JOURNAL OF AVIAN BIOLOGY, Issue 2 2000
Christopher P. Bell
Current ideas about the evolution of bird migration equate its origin with the first appearance of fully migratory populations, and attribute its evolution to a selective advantage generated by increased breeding success, gained through temporary emigration from resident populations to breed in under-exploited seasonal areas. I propose an alternative hypothesis in which migration first appears as a temporary directional shift away from the breeding site outside the reproductive period, in response to seasonal variation in the direction and/or severity of environmental gradients. Fully migratory populations then appear through either extinction of sedentary phenotypes, or colonisation of vacant seasonal areas by migrants. Where colonisation occurs, resident ancestral populations can be driven to extinction by competition from migrants which invade their range outside the breeding season, resulting in fully migratory species. An analogous process drives the evolution of migration between high latitudes and the tropics, since extension of breeding range into higher latitudes may drive low latitude populations to extinction, resulting in an overall shift of breeding range. This process can explain reverse latitudinal gradients in avian diversity in the temperate zone, since the breeding ranges of migratory species concentrate in latitudes where they enjoy the highest breeding success. Near absence of forest-dwelling species among Palaearctic-African migrants is attributable to the lack of forest in northern Africa for much of the Tertiary, which has precluded selection both for southward extension of migration by west Palaearctic forest species, and northward breeding colonisation by African forest species. [source]


Potentials and constraints of the farmer-to-farmer programme for environmental protection in Nicaragua

LAND DEGRADATION AND DEVELOPMENT, Issue 2 2003
S. Hawkesworth
Abstract The natural environment in Nicaragua has been damaged by rural development policies geared for the export of cash crops, by uneven land distribution and the near absence of concerns about the environmental effects of the prevailing model of development. The demands made by market forces for the export of primary materials have been reasons for land degradation in the big farms, and the need to survive a poverty stricken existence has forced the peasantry to damage the marginal and fragile land they worked. Successive governments did not address these underlying causes of environmental degradation, and even the opportunities afforded by the environment programme that resulted from the 1979 Sandinista revolution, did not result in significant environmental improvements. The paper briefly considers the constraints faced by the Sandinista administration and how the farmer-to-farmer programme (Campesino-a-Campesino) was brought about as a result of the impacts of the Sandinista era. The substantive part of the paper considers PCAC's significance as an agroecological programme and its advantages and limitations for improving peasants' livelihoods via dissemination of land-protective measures. The viability of the programme is assessed by field work carried out examining in detail the case of three communities, and the paper concludes that the gains made in environmental protection and conservation are in jeopardy without structural policy changes. The paper proposes that for the programme to improve its potential, adequate political will, power and organization are necessary to facilitate greater access to secure land tenure among the peasantry. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Geophysical survey of the proposed Tsenkher impact structure, Gobi Altai, Mongolia

METEORITICS & PLANETARY SCIENCE, Issue 3 2010
Jens ORMÖ
Extensive occurrences of brecciated rocks, mainly in the form of an ejecta blanket outside the elevated rim of the structure, support an explosive origin (e.g., cosmic impact, explosive volcanism). The host rocks in the area are mainly weakly magnetic, silica-rich sandstones, and siltstones. A near absence of surface exposures of volcanic rocks makes any major volcanic structures (e.g., caldera) unlikely. Likewise, the magnetic models exclude any large, subsurface, intrusive body. This is supported by an 8 mGal gravity low over the structure indicating a subsurface low density body. Instead, the best fit is achieved for a bowl-shaped structure with a slight central rise as expected for an impact crater of this size in mainly sedimentary target. The structure can be either root-less (i.e., impact crater) or rooted with a narrow feeder dyke with relatively higher magnetic susceptibility and density (i.e., volcanic maar crater). The geophysical signature, the solitary appearance, the predominantly sedimentary setting, and the comparably large size of the Tsenkher structure favor the impact crater alternative. However, until mineralogical/geochemical evidence for an impact is presented, the maar alternative remains plausible although exceptional as it would make the Tsenkher structure one of the largest in the world in an unusual setting for maar craters. [source]


1H- and 31P-MR spectroscopy of primary and recurrent human brain tumors in vitro: malignancy-characteristic profiles of water soluble and lipophilic spectral components

NMR IN BIOMEDICINE, Issue 5 2001
Fritz-Georg Lehnhardt
Abstract In vitro NMR spectrocopy was performed on specimen of human brain tumors. From all patients, tissue samples of primary tumors and their first recurrences were examined. 31P- and 1H-spectra were recorded from samples of meningioma, astrocytoma and glioblastoma. A double extraction procedure of the tissue samples permitted acquisition of information from the membrane fraction and from the cytosolic fraction. 31P-spectra were used to analyze the lipophilic fraction (phospholipids of the membrane) of the tissue extracts, while the 1H-spectra reflected information on the metabolic alterations of the hydrophilic, cytosolic fraction of the tissue. The tumor types showed distinctive spectral patterns in both the 31P- and the 1H-spectra. Based on the total detectable 31P signal, the level of phosphatidylcholine was about 34% lower in primary astrocytomas than in primary glioblastomas (p,=,0.0003), whereas the level of sphingomyelin was about 45% lower in primary gioblastomas than in primary astrocytomas (p,=,0.0061). A similar tendency of these phospholipids was observed when comparing primary and recurrent astrocytoma samples from the same individuals [+15% (p,=,0.0103) and ,23% (p,=,0.0314) change, respectively]. 1H-spectra of gliomas were characterized by an increase of the ratios of alanine, glycine and choline over creatine as a function of the degree of malignancy. In agreement with findings in the 31P-spectra, the 1H-spectra of recurrent astrocytomas showed metabolic profiles of increased malignancy in comparison to their primary occurrence. Since gliomas tend to increase in malignancy upon recurrence, this may reflect evolving tumor metabolism. 1H-spectra of meningiomas showed the highest ratio of alanine over creatine accompanied by a near absence of myo-inositol. Phospholipid profiles of meningiomas showed higher fractional contents of phosphatidylcholine along with lower phosphatidylserine compared to astrocytomas, while higher phosphatidylethanolamine and sphingomyelin fractional contents distinguished meningiomas from glioblastomas. The extraction method being used in this study combined with high-resolution 1H- and 31P-MRS provides a wide range of biochemical information, which enables differentiation not only between tumor types but also between primary and recurrent gliomas, reflecting an evolving tumor metabolism. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Behavioral adaptations to heat stress and water scarcity in white-faced capuchins (Cebus capucinus) in Santa Rosa National Park, Costa Rica

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009
Fernando A. Campos
Abstract We examined thermoregulatory behaviors in a wild population of white-faced capuchins (Cebus capucinus) inhabiting a highly seasonal dry forest in Santa Rosa National Park (SRNP), Costa Rica. The dry season in SRNP lasts ,5 months and is characterized by high ambient temperatures regularly exceeding 37°C, low relative humidity, and the near absence of precipitation. This study demonstrates that capuchins rest more and travel shorter distances during the hottest and driest hours of the day, and suggests that they extend their tongues to lower body temperature via evaporative cooling. Seasonal weather patterns and group movement data reported here are based on 940 h of observations on three social groups of capuchins (wet season: 370 h, dry season: 570 h). In the dry season, the proportion of time spent resting increased at higher temperatures whereas the proportion of time spent traveling decreased. Distance traveled between location points taken at half-hour intervals decreased significantly as temperature increased, although the correlation was not strong. Capuchins exposed their tongues during hot, dry, windy conditions, and this behavior was much more frequent in the dry season. Temperature was significantly higher and humidity significantly lower for "tongue-out" events than expected for a random event in the dry season. Finally, as surface water became scarce, home-range areas of heavy use became increasingly centered on the remaining permanent water sources. These results suggest that heat stress and water scarcity are significant influences on the behavior of capuchins in hot, dry conditions. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc. [source]


Sterile pyuria in a population of wild white-handed gibbons (Hylobates lar)

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 10 2009
Barbara A. Beaman
Abstract Urinalysis is an emerging method for monitoring the health and energy balance of wild primates. Here, we report the first urinalysis of wild gibbons. We used multi-reagent test strips to monitor the health status of 52 individual white-handed gibbons (Hylobates lar) inhabiting Khao Yai National Park, Thailand. Most urinary reference values were within normal ranges; however, regardless of age- and sex-class or monthly fruit productivity, we found unexpectedly high rates of urinary leukocytes (50% and 90% of individuals in 2001,2003 and 2006, respectively). In contrast to previous studies of African apes, this finding is coupled with the near absence of urinary nitrites, demonstrating pervasive levels of sterile pyuria. This result is the first reported case of sterile pyuria in a population of wild primates. The etiology of human sterile pyuria is diverse, but in all cases it is diagnostic of systemic inflammation. We discuss the potential causes of sterile pyuria in the gibbons of Khao Yai. Am. J. Primatol. 71:880,883, 2009. © 2009 Wiley-Liss, Inc. [source]


Proinflammatory cytokine expression profile in degenerated and herniated human intervertebral disc tissues

ARTHRITIS & RHEUMATISM, Issue 7 2010
Mohammed F. Shamji
Objective Prior reports document macrophage and lymphocyte infiltration with proinflammatory cytokine expression in pathologic intervertebral disc (IVD) tissues. Nevertheless, the role of the Th17 lymphocyte lineage in mediating disc disease remains uninvestigated. We undertook this study to evaluate the immunophenotype of pathologic IVD specimens, including interleukin-17 (IL-17) expression, from surgically obtained IVD tissue and from nondegenerated autopsy control tissue. Methods Surgical IVD tissues were procured from patients with degenerative disc disease (n = 25) or herniated IVDs (n = 12); nondegenerated autopsy control tissue was also obtained (n = 8) from the anulus fibrosus and nucleus pulposus regions. Immunohistochemistry was performed for cell surface antigens (CD68 for macrophages, CD4 for lymphocytes) and various cytokines, with differences in cellularity and target immunoreactivity scores analyzed between surgical tissue groups and between autopsy control tissue regions. Results Immunoreactivity for IL-4, IL-6, IL-12, and interferon-, (IFN,) was modest in surgical IVD tissue, although expression was higher in herniated IVD samples and virtually nonexistent in control samples. The Th17 lymphocyte product IL-17 was present in >70% of surgical tissue fields, and among control samples was detected rarely in anulus fibrosus regions and modestly in nucleus pulposus regions. Macrophages were prevalent in surgical tissues, particularly herniated IVD samples, and lymphocytes were expectedly scarce. Control tissue revealed lesser infiltration by macrophages and a near absence of lymphocytes. Conclusion Greater IFN, positivity, macrophage presence, and cellularity in herniated IVDs suggests a pattern of Th1 lymphocyte activation in this pathology. Remarkable pathologic IVD tissue expression of IL-17 is a novel finding that contrasts markedly with low levels of IL-17 in autopsy control tissue. These findings suggest involvement of Th17 lymphocytes in the pathomechanism of disc degeneration. [source]