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Actual Situation (actual + situation)

Distribution by Scientific Domains

Chemistry	33%

Selected Abstracts

Density dependence and population dynamics of black rhinos (Diceros bicornis michaeli) in Kenya's rhino sanctuaries

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2010
Benson Okita-Ouma
Abstract Density-dependent feedback mechanisms provide insights into the population dynamics and interactions of large herbivores with their ecosystem. Sex ratio also has particularly important implications for growth rates of many large mammal populations through its influence on reproductive potential. Therefore, the interrelationships between density-dependent factors, comprising density, sex ratio and underlying growth rates (r) were examined for the Eastern black rhino (Diceros bicornis michaeli) living in three rhino sanctuaries in Kenya using four population models. The exponential and logistic models gave similar results and the former were accepted because they better portrayed the actual situation on the ground. Sex ratios in all sanctuary populations were positively correlated with r but interpreted with realization of other factors also affecting r. We caution that the results of population models should be interpreted alongside ground-truthed observations. We recommend that future translocation strategies should take into account sex and age structures of the donor population, while future studies of density dependence should take into account both biotic and abiotic factors. Résumé Des mécanismes de feedback de densité-dépendance chez les grands herbivores donnent un aperçu de la dynamique des populations et de l'interaction avec l'écosystème. Les sex-ratios ont aussi d'importantes implications pour la dynamique des populations de nombreux grands mammifères, spécialement par leur influence sur le potentiel reproducteur. On a étudié ces relations croisées entre les facteurs densité-dépendants du rhino noir de l'Est Diceros bicornis michaeli, le sex-ratio et le taux de croissance (r) sous-jacent dans trois sanctuaires de rhinos du Kenya en utilisant quatre modèles de population. Les modèles exponentiel et logistique donnaient des résultats similaires, les résultats du premier étant acceptés parce qu'ils représentaient la situation actuelle sur le terrain. Les sex-ratios de toutes les populations étaient positivement liés àr mais interprétés en réalisant que d'autres facteurs affectent aussi r. Nous attirons l'attention sur le fait que les résultats de la modélisation des populations doivent être interprétés tout en les confirmant par des observations sur le terrain; nous recommandons des stratégies de translocations qui prélèvent des individus dans les diverses structures de sexe et d'âge de la population d'origine; et nous suggérons que de futures études de densité-dépendance tiennent compte de facteurs biotiques et abiotiques. [source]

Youth and violence: Phenomena and international data

NEW DIRECTIONS FOR YOUTH DEVELOPMENT, Issue 119 2008
Sandra Legge
The topic of youth, violence, and disintegration needs addressing because young women and men are the world's greatest capital. They have the energy, talent, and creativity for building a future. But this group also suffers grave vulnerabilities. The time of adolescence includes important and difficult periods of life (for example, becoming more independent from the family, finding an adequate position in society, and starting a family of one's own). All of these points are strongly correlated with social integration, employment, and a place in the labor market,important factors in this context. This article gives an overview of the international development and the actual situation of socially harmful behavior among youths,both fatal violence (homicide) and nonfatal violence (such as bullying, fighting, and carrying weapons). The author shows that different kinds of youth violence represent social problems in every society. The data show that youths are not only perpetrators but also the group with the highest risk of becoming victims of violence. Furthermore, the data from around the world show that their vulnerability is not limited to this sphere. It arises also from their social conditions, especially their high risk of being disintegrated from the labor market. The parallels in the data underline the significance of a functioning institutional structure without positing a deterministic relationship between the risk of economic disintegration and violent behavior. [source]

Upper susceptibility threshold limits with confidence intervals: a method to identify normal and abnormal population values for laboratory toxicological parameters, based on acetylcholinesterase activities in sea lice

PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 3 2006
Anders Fallang
Abstract The interpretation and importance of comparing field values of susceptibility to pesticides with a laboratory reference strain that might bear little resemblance to the actual situation in the field are problematic and a continuing subject of debate. In this paper a procedure for defining a ,normal sensitive' population from a field study of 383 individuals to provide a basis for analysing and interpreting in vitro results is described and examined. Instead of using only the 95th percentile, the upper and lower confidence limits for the 95th percentile were also compared to select the best estimation of the limit for the normal material. A field population constrained by the upper confidence limit for the 95th percentile provides appropriate descriptions of the normal material in this study. This approach should prove useful in studies of pesticide resistance in field populations. Copyright © 2006 Society of Chemical Industry [source]

The ,digital natives' debate: A critical review of the evidence

BRITISH JOURNAL OF EDUCATIONAL TECHNOLOGY, Issue 5 2008
Sue Bennett
The idea that a new generation of students is entering the education system has excited recent attention among educators and education commentators. Termed ,digital natives' or the ,Net generation', these young people are said to have been immersed in technology all their lives, imbuing them with sophisticated technical skills and learning preferences for which traditional education is unprepared. Grand claims are being made about the nature of this generational change and about the urgent necessity for educational reform in response. A sense of impending crisis pervades this debate. However, the actual situation is far from clear. In this paper, the authors draw on the fields of education and sociology to analyse the digital natives debate. The paper presents and questions the main claims made about digital natives and analyses the nature of the debate itself. We argue that rather than being empirically and theoretically informed, the debate can be likened to an academic form of a ,moral panic'. We propose that a more measured and disinterested approach is now required to investigate ,digital natives' and their implications for education. [source]

Lipid and Fatty Acid Composition of Diatoms Revisited: Rapid Wound-Activated Change of Food Quality Parameters Influences Herbivorous Copepod Reproductive Success

CHEMBIOCHEM, Issue 10 2007
Thomas Wichard Dr.
Abstract Lipid and fatty acid composition are considered to be key parameters that determine the nutritive quality of phytoplankton diets for zooplanktonic herbivores. The fitness, reproduction and physiology of the grazers are influenced by these factors. The trophic transfer of lipids and fatty acids from algal cells has been typically studied by using simple extraction and quantification approaches, which, as we argue here, do not reflect the actual situation in the plankton. We show that cell disruption, as it occurs during a predator's grazing on diatoms can drastically change the lipid and fatty acid content of the food. In some algae, a rapid depletion of polyunsaturated fatty acids (PUFAs) is observed within the first minutes after cell disruption. This fatty acid depletion is directly linked to the production of PUFA-derived polyunsaturated aldehydes (PUA); these are molecules that are thought to be involved in the chemical defence of the algae. PUA-releasing diatoms are even capable of transforming lipids from other sources if these are available in the vicinity of the wounded cells. Fluorescent staining reveals that the enzymes involved in lipid transformation are active in the foregut of copepods, and therefore link the depletion processes directly to food uptake. Incubation experiments with the calanoid copepod Temora longicornis showed that PUFA depletion in PUA-producing diatoms is correlated to reduced hatching success, and can be compensated for by externally added single fatty acids. [source]

Estimation and forecasting in first-order vector autoregressions with near to unit roots and conditional heteroscedasticity

JOURNAL OF FORECASTING, Issue 7 2009
Theologos Pantelidis
Abstract This paper investigates the effects of imposing invalid cointegration restrictions or ignoring valid ones on the estimation, testing and forecasting properties of the bivariate, first-order, vector autoregressive (VAR(1)) model. We first consider nearly cointegrated VARs, that is, stable systems whose largest root, lmax, lies in the neighborhood of unity, while the other root, lmin, is safely smaller than unity. In this context, we define the ,forecast cost of type I' to be the deterioration in the forecasting accuracy of the VAR model due to the imposition of invalid cointegration restrictions. However, there are cases where misspecification arises for the opposite reasons, namely from ignoring cointegration when the true process is, in fact, cointegrated. Such cases can arise when lmax equals unity and lmin is less than but near to unity. The effects of this type of misspecification on forecasting will be referred to as ,forecast cost of type II'. By means of Monte Carlo simulations, we measure both types of forecast cost in actual situations, where the researcher is led (or misled) by the usual unit root tests in choosing the unit root structure of the system. We consider VAR(1) processes driven by i.i.d. Gaussian or GARCH innovations. To distinguish between the effects of nonlinear dependence and those of leptokurtosis, we also consider processes driven by i.i.d. t(2) innovations. The simulation results reveal that the forecast cost of imposing invalid cointegration restrictions is substantial, especially for small samples. On the other hand, the forecast cost of ignoring valid cointegration restrictions is small but not negligible. In all the cases considered, both types of forecast cost increase with the intensity of GARCH effects. Copyright © 2009 John Wiley & Sons, Ltd. [source]