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Ecosystem Consequences of Tree Monodominance for Nitrogen Cycling in Lowland Tropical Forest  [PDF]
E. N. Jack Brookshire, Steven A. Thomas
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0070491
Abstract: Understanding how plant functional traits shape nutrient limitation and cycling on land is a major challenge in ecology. This is especially true for lowland forest ecosystems of the tropics which can be taxonomically and functionally diverse and rich in bioavailable nitrogen (N). In many tropical regions, however, diverse forests occur side-by-side with monodominant forest (one species >60% of canopy); the long-term biogeochemical consequences of tree monodominance are unclear. Particularly uncertain is whether the monodominant plant-soil system modifies nutrient balance at the ecosystem level. Here, we use chemical and stable isotope techniques to examine N cycling in old-growth Mora excelsa and diverse watershed rainforests on the island of Trinidad. Across 26 small watershed forests and 4 years, we show that Mora monodominance reduces bioavailable nitrate in the plant-soil system to exceedingly low levels which, in turn, results in small hydrologic and gaseous N losses at the watershed-level relative to adjacent N-rich diverse forests. Bioavailable N in soils and streams remained low and remarkably stable through time in Mora forests; N levels in diverse forests, on the other hand, showed high sensitivity to seasonal and inter-annual rainfall variation. Total mineral N losses from diverse forests exceeded inputs from atmospheric deposition, consistent with N saturation, while losses from Mora forests did not, suggesting N limitation. Our measures suggest that this difference cannot be explained by environmental factors but instead by low internal production and efficient retention of bioavailable N in the Mora plant-soil system. These results demonstrate ecosystem-level consequences of a tree species on the N cycle opposite to cases where trees enhance ecosystem N supply via N2 fixation and suggest that, over time, Mora monodominance may generate progressive N draw-down in the plant-soil system.
Does Postponement Explain the Trend to Later Childbearing in France  [PDF]
Máire Ní Bhrolcháin,Laurent Toulemon
Vienna Yearbook of Population Research , 2005,
Abstract: Fertility rates in most developed societies have been declining at younger ages and rising at older ages. This phenomenon is widely referred to as reflecting the postponement of fertility. But is this an accurate description? The present paper considers whether recent changes in the age-pattern of childbearing in France can be described as postponement. The statistical features of time series of rates are distinguished from the underlying behavioural process generating them. Criteria for the presence of postponement are proposed. In the absence of detailed, longitudinal information on intentions, the occurrence or otherwise of postponement is assessed by indirect means. Some evidence is found consistent with fertility postponement in recent decades. However, it cannot be interpreted causally, and so cannot be used either to explain recent trends or to anticipate future trends. Much more detailed evidence is required to establish the existence of postponement in the behavioural sense than is generally assumed.
A review of phytoplankton dynamics in tropical African lakes
Mzime R. Ndebele-Murisa,Charles F. Musil,Lincoln Raitt
South African Journal of Science , 2010, DOI: 10.4102/sajs.v106i1/2.64
Abstract: This paper provides a synthesis of current knowledge on phytoplankton production, seasonality, and stratification in tropical African lakes and considers the effects of nutrient enrichment and the potential impacts of climate warming on phytoplankton production and composition. Tropical African lakes are especially sensitive to climate warming as they experience wide fluctuations in the thermocline over a narrow range of high water temperatures. Recent climate warming has reduced phytoplankton biomass and production in the lakes. A decline in the production of palatable chlorophytes and an increase in cyanobacteria has led to reduced zooplankton production and a consequent decline in fish stocks, all of which can be associated with the elevated water temperatures. This indicates that even moderate climate warming may destabilise phytoplankton dynamics in tropical African lakes, thereby reducing water quality and food resources for planktivorous fish, with consequent negative impacts on human livelihoods.
Does natural selection explain the selforganization of the entire cosmos?  [PDF]
Jack Claycomb
Extreme Life, Biospeology & Astrobiology , 2012,
Abstract: Because only enduring systems ultimately persist, physicist D. B. Kelley’s theory of universalselection, or “preservation of the stable,” expounds enormously upon the genesis of every lastingphenomenon in history, making it arguably the most interdisciplinary discovery ever made in science. Inhis new book, The Origin of Everything, Kelley thus shows Darwin’s principle of natural selection, orsurvival of the fittest, to explain not only the origin of species as exposed in 1859, but the genesis ofevery steadfast assemblage ever to have endured. In other words, it isn’t just stable species that arenaturally selected to exist, as all of Nature’s many unwavering systems are ultimately selected. Kelleytherefore demonstrates that preservation of the stable is not an innate characteristic of being, but anextremely powerful process, or deterministic mechanism, which absolutely demands fitness from all suchensembles. It therein explains the tremendous amount of variation among Nature’s many assemblages,as well as their stability, or order. However extraordinary, it even unites Darwinism and Einsteinianrelativity, as it further clarifies the relative formation of every phenomenon ever to have been.Consequently, our Earth isn’t the only ecology governed by survival of the fittest, for our entire cosmosis an astronomical ecosystem determined in full via preservation of the stable itself. These findings arealso in perfect accord with the stringent demands of modern biology’s three-part algorithm, or the threefundamental mechanisms responsible for life’s stability and evolution. Remarkably, universal selectionhas even been confirmed at reputable laboratories through numerous experiments in physics, quantumphysics, chemistry and more. While Darwin thus revolutionized all of our various biological sciences byrevealing the immense logic behind every adaptation of every species, Kelley holds that universalselection revolutionizes science in its entirety. He claims that it illuminates “the natural origins andtherefore the natural order throughout our universe as a whole.”
Biodiversity Mapping in a Tropical West African Forest with Airborne Hyperspectral Data  [PDF]
Gaia Vaglio Laurin, Jonathan Cheung-Wai Chan, Qi Chen, Jeremy A. Lindsell, David A. Coomes, Leila Guerriero, Fabio Del Frate, Franco Miglietta, Riccardo Valentini
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0097910
Abstract: Tropical forests are major repositories of biodiversity, but are fast disappearing as land is converted to agriculture. Decision-makers need to know which of the remaining forests to prioritize for conservation, but the only spatial information on forest biodiversity has, until recently, come from a sparse network of ground-based plots. Here we explore whether airborne hyperspectral imagery can be used to predict the alpha diversity of upper canopy trees in a West African forest. The abundance of tree species were collected from 64 plots (each 1250 m2 in size) within a Sierra Leonean national park, and Shannon-Wiener biodiversity indices were calculated. An airborne spectrometer measured reflectances of 186 bands in the visible and near-infrared spectral range at 1 m2 resolution. The standard deviations of these reflectance values and their first-order derivatives were calculated for each plot from the c. 1250 pixels of hyperspectral information within them. Shannon-Wiener indices were then predicted from these plot-based reflectance statistics using a machine-learning algorithm (Random Forest). The regression model fitted the data well (pseudo-R2 = 84.9%), and we show that standard deviations of green-band reflectances and infra-red region derivatives had the strongest explanatory powers. Our work shows that airborne hyperspectral sensing can be very effective at mapping canopy tree diversity, because its high spatial resolution allows within-plot heterogeneity in reflectance to be characterized, making it an effective tool for monitoring forest biodiversity over large geographic scales.
Does Trade Policy Explain Total Factor Productivity Differences Across Countries?  [cached]
H.A. Abdurohman,A. Shakeel,Y. Muhammed
Current Research Journal of Economic Theory , 2012,
Abstract: This study examines whether variations in restrictiveness of trade policy on the flow of international trade explain Total Factor Productivity (TFP) differences across countries. The study employs Trade Restrictiveness Indices (TRIs) to measure trade policy. The TRIs are aggregated using data at the tariff line level, which enable the study to overcome the aggregation bias characterizing the commonly used trade policy measures such as average tariff and import-weighted average tariff. TRIs for Non-Tariff Barriers on imports (NTB), import tariffs and export restrictions are used to show the relative restrictiveness of various types of trade policy on TFP. In line with the political economy literature, the trade restrictiveness measure based on NTB is instrumented using past trade shares while identifying the former’s effect on TFP. Using IV regression, the study shows that trade restrictiveness based on NTB explains a significant variation in TFP across countries while trade restrictiveness based on import tariff or export restrictions does not have a significant effect on TFP. Hence, countries should reduce NTBs on their imports to allow a gain in TFP associated with trade. Besides, the findings suggest that countries should substitute the more restrictive and less transparent trade policy, i.e., NTBs with the less restrictive and more transparent trade policy, i.e., Tariffs.
Tropical Atlantic Hurricanes, Easterly Waves, and West African Mesoscale Convective Systems  [PDF]
Yves K. Kouadio,Luiz A. T. Machado,Jacques Servain
Advances in Meteorology , 2010, DOI: 10.1155/2010/284503
Abstract: The relationship between tropical Atlantic hurricanes (Hs), atmospheric easterly waves (AEWs), and West African mesoscale convective systems (MCSs) is investigated. It points out atmospheric conditions over West Africa before hurricane formation. The analysis was performed for two periods, June–November in 2004 and 2005, during which 12 hurricanes (seven in 2004, five in 2005) were selected. Using the AEW signature in the 700?hPa vorticity, a backward trajectory was performed to the African coast, starting from the date and position of each hurricane, when and where it was catalogued as a tropical depression. At this step, using the Meteosat-7 satellite dataset, we selected all the MCSs around this time and region, and tracked them from their initiation until their dissipation. This procedure allowed us to relate each of the selected Hs with AEWs and a succession of MCSs that occurred a few times over West Africa before initiation of the hurricane. Finally, a dipole in sea surface temperature (SST) was observed with a positive SST anomaly within the region of H generation and a negative SST anomaly within the Gulf of Guinea. This SST anomaly dipole could contribute to enhance the continental convergence associated with the monsoon that impacts on the West African MCSs formation. 1. Introduction The tropical North Atlantic is a World Ocean basin where cyclonic activity is intense. It presents a substantial interannual and interdecadal variability [1], depending directly on atmospheric and oceanic conditions. The Atlantic hurricane (H) activity occurs between July and November, and major Hs form in the Main Development Region (MDR), defined as the tropical North Atlantic south of 21°N and the Caribbean Sea. This cyclonic activity mainly originates from the African atmospheric easterly waves (AEWs) that propagate from West Africa towards the tropical North Atlantic basin and the Caribbean Sea [2, 3]. These waves, which have a 3-to-4-day period [4], are responsible for about 60% of tropical storms and minor Hs, and 85% of Hs of strong intensity [5–7]. Several studies [5, 8, 9] have even suggested that some tropical cyclones occurring in the eastern Pacific develop in association with AEWs that were initially generated in Africa and then propagated across the tropical Atlantic and Central America. Upstream in their propagation across the ocean, these AEWs are themselves generally accompanied by mesoscale convective systems (MCSs), which cross the center Sahel region between 8°N–18°N and 10°W–17°E and dissipate in the tropical Atlantic Ocean towards 20°W
GPS and GIS Methods in an African Rain Forest: Applications to Tropical Ecology and Conservation  [cached]
Nathaniel J. Dominy,Brean Duncan
Ecology and Society , 2002,
Abstract: Since the completion of the Navstar Global Positioning System (GPS) in 1995, the integration of GPS and Geographical Information Systems (GIS) technology has expanded to a great number of ecological and conservation applications. In tropical rain forest ecology, however, the technology has remained relatively neglected, despite its great potential. Notwithstanding cost, this is principally due to (1) the difficulty of quality satellite reception beneath a dense forest canopy, and (2) a degree of spatial error unacceptable to fine-scale vegetation mapping. Here, we report on the technical use of GPS/GIS in the rain forest of Kibale National Park, Uganda, and the methodology necessary to acquire high-accuracy spatial measurements. We conclude that the stringent operating parameters necessary for high accuracy were rarely obtained while standing beneath the rain forest canopy. Raising the GPS antenna to heights of 25–30 m resolved this problem, allowing swift data collection on the spatial dispersion of individual rain forest trees. We discuss the impact of the 1996 Presidential Decision Directive that suspended U.S. military-induced GPS error on 1 May 2000, and comment on the potential applications of GPS/GIS technology to the ecological study and conservation of tropical rain forests.
Prevalence and causes of blindness in a tropical African population
Caroline O Adeoti
West African Journal of Medicine , 2004,
Abstract: A population based survey of Egbedore Local Government area (LGA), a tropical African population in Osun State, Nigeria was conducted to determine the prevalence and causes of blindness in the community, Osun State, one of the new states created on 27th August, 1991 is situated in the southwest region of Nigeria. It has a population of about 2, 654, 244 using the population growth rate of 3.0 percent per year. Egbedore LGA has a population of 49,555 being the projected estimate of the local census done in 1991. Study design: The study was in accordance with World Health Organisation recommendations. 3204 rural dwellers were examined. The survey team was divided into: 1. Registration team 2. Retrieval team 3. Visual acuity team 4.Ocular examination team. The survey candidates, once registered were asked to go to a nearby school or health center where visual acuity and ocular examination teams completed the assignment. The retrieval team consisted of an ophthalmic nurse and a local escort who persuaded and brought to examination site registered individuals who failed to appear voluntarily. Ocular examination team performed the eye examination. Analysis of data was done using personal computer AT model and systat package for analysis. Result:- It is found that 1.18% of the population was blind by WHO standard. Cataract alone accounted for 47.4% of the blind, uncorrected aphakia 18.4%, glaucoma 15.8%, phthisis bulbi 5.3%, uveitis, optic atrophy, macular degeneration, retinitis pigmentosa and refractive error all accounted for 2.6% each. Conclusion:- More than half of the burden of blindness is potentially curable. About a third is preventable through health education, early diagnosis and prompt treatment. A cataract outreach programme with provision of low cost aphakic glasses will go a long way in reducing blindness in this community and Osun State in general. Key Words: Prevalence, Causes, Blindness, Osun state. Résumé Introduction:- Une étude basée sur la population du government Local du milieu d'Egbedore (LGA), une population africaine tropicale dans l'Etat d'Osun, au Nigeria a été effectuée afin de décider la fréquence et les causes de la cécité dans la communuaté. L'état d'Osun, un des nouveaux états crée le 27 a ut 1991 est situé dans la région du sud ouest du Nigeria compte environ 2,654,244 habitants tout en utilisant le taux de croissance de 3, 0 pourcent par an. Egbedore LGA compte 49,555 habitants d'après le recensement de la population locale fait en 1991. Plan d'étude:- L'étude était comforme aux recommendations de l'Organisation Mondiale de la Sante. 3204 habitants rural ont été étudiés. Le groupe d'étude s'était reparti ainsi: (1) Groupe d'inscription (2) Groupe de récupération (3) Groupe d'acuité visuelle (4) Groupe d'examen oculaire. Aussi t t qu'on inscrit les sujets, ils vont directement a une école où au centre de soins, tout près, où les groupes d'acuité visuelle et examen oculaire achevent le travail. Le groupe de récupération
Tropical Atlantic Hurricanes, Easterly Waves, and West African Mesoscale Convective Systems  [PDF]
Yves K. Kouadio,Luiz A. T. Machado,Jacques Servain
Advances in Meteorology , 2010, DOI: 10.1155/2010/284503
Abstract: The relationship between tropical Atlantic hurricanes (Hs), atmospheric easterly waves (AEWs), and West African mesoscale convective systems (MCSs) is investigated. It points out atmospheric conditions over West Africa before hurricane formation. The analysis was performed for two periods, June–November in 2004 and 2005, during which 12 hurricanes (seven in 2004, five in 2005) were selected. Using the AEW signature in the 700 hPa vorticity, a backward trajectory was performed to the African coast, starting from the date and position of each hurricane, when and where it was catalogued as a tropical depression. At this step, using the Meteosat-7 satellite dataset, we selected all the MCSs around this time and region, and tracked them from their initiation until their dissipation. This procedure allowed us to relate each of the selected Hs with AEWs and a succession of MCSs that occurred a few times over West Africa before initiation of the hurricane. Finally, a dipole in sea surface temperature (SST) was observed with a positive SST anomaly within the region of H generation and a negative SST anomaly within the Gulf of Guinea. This SST anomaly dipole could contribute to enhance the continental convergence associated with the monsoon that impacts on the West African MCSs formation.
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