Diet and childhood asthma in a society in transition: a study in urban and rural Saudi Arabia.
(73/4953)
BACKGROUND: The causes of the worldwide increases in asthma and allergic diseases in childhood, which seem to relate to increasing prosperity, are unknown. We have previously hypothesised that a reduction in the antioxidant component of the diet is an important factor. An investigation was undertaken of dietary and other risk factors for asthma in Saudi Arabia where major lifestyle differences and prevalences of allergic disease are found in different communities. METHODS: From a cross sectional study of 1444 children with a mean age of 12 (SD 1) years in Jeddah and a group of rural Saudi villages, we selected 114 cases with a history of asthma and wheeze in the last 12 months and 202 controls who had never complained of wheeze or asthma, as recorded on the ISAAC questionnaire. Risk factors for asthma and allergies (family history, social class, infections, immunisations, family size, and diet) were ascertained by questionnaire. Atopy was assessed by skin prick testing. RESULTS: In univariate analyses, family history, atopy, and eating at fast food outlets were significant risk factors for wheezy illness, as were the lowest intakes of milk and vegetables and of fibre, vitamin E, calcium, magnesium, sodium, and potassium. These differences were present also in the urban children considered separately. Sex, family size, social class, infections, and parental smoking showed no relationship to risk. In multiple logistic regression analysis, urban residence, positive skin tests, family history of allergic disease, and the lowest intakes of vitamin E, magnesium and sodium related significantly and independently to risk. The lowest tertile of intake of vitamin E was associated with a threefold (95% CI 1.38 to 6.50) increase in risk when adjusted for the other factors. Intake of milk and vegetables both showed inverse linear relationships to being a case. CONCLUSIONS: This study suggests that dietary factors during childhood are an important influence in determining the expression of wheezy illness, after allowing for urban/rural residence, sex, family history, and atopy. The findings are consistent with previous studies in adults and with the hypothesis that change in diet has been a determinant of the worldwide increases in asthma and allergies. (+info)
Predictions of biodiversity response to genetically modified herbicide-tolerant crops.
(74/4953)
We simulated the effects of the introduction of genetically modified herbicide-tolerant (GMHT) crops on weed populations and the consequences for seed-eating birds. We predict that weed populations might be reduced to low levels or practically eradicated, depending on the exact form of management. Consequent effects on the local use of fields by birds might be severe, because such reductions represent a major loss of food resources. The regional impacts of GMHT crops are shown to depend on whether the adoption of GMHT crops by farmers covaries with current weed levels. (+info)
Extinction dynamics and the regional persistence of a tree frog metapopulation.
(75/4953)
The concept of a metapopulation acknowledges local extinctions as a natural part of the dynamics of a patchily distributed population. However, if extinctions are not balanced by recolonizations or if there is a high degree of spatial synchrony of local extinctions, this poses a threat to and will reduce the metapopulation persistence time. Here we show that, in a metapopulation network of 378 pond patches used by the tree frog (Hyla arborea), even though extinctions are frequent (mean extinction probability p(e) = 0.24) they pose no threat to the metapopulation as they are balanced by recolonizations (p(c) = 0.33). In any one year there was a pattern of large populations tending to persist while small populations became extinct. The total number of individuals belonging to populations that went extinct was small (< 5%) compared with those populations that persisted. A spatial autocorrelation analysis indicated no clustering of local extinctions. The tree frog metapopulation studied consisted of a set of larger, persistent populations mixed with smaller populations characterized by high turnover dynamics. (+info)
Adaptation to marginal habitats: contrasting influence of the dispersal rate on the fate of alleles with small and large effects.
(76/4953)
The focus of this paper is the relationship between the dispersal rate and the conditions for invasion of a rare allele that improves performance in a marginal sink habitat at the expense of reducing fitness in the main source habitat. Classic multiple-niche population-genetic models predict that the conditions for the invasion of such an allele always become more favourable as the dispersal rate decreases. Precisely the opposite prediction was reached in demographic fitness-sensitivity studies. This study reconciles those contradictory predictions and identifies the assumptions responsible for the discrepancy. I show that whether a lower dispersal rate makes the conditions for the invasion of the allele more or less stringent depends on the magnitude of the effects of the allele. If the effect is large relative to the degree of maladaptedness of the original genotype to the marginal habitat, the conditions become less stringent with decreasing dispersal rate. The opposite is the case for mutations with very small effects. For a broad range of mutations with intermediate effects the conditions are most stringent under an intermediate dispersal rate. (+info)
Population consequences of reproductive decisions.
(77/4953)
Behaviour can be a key component of animal population ecology yet the population consequences of behavioural decisions are poorly understood. We conducted a behavioural and demographic study of the bitterling Rhodeus sericeus, a freshwater fish that spawns in live unionid mussels. We used a population model incorporating game theory decisions and measurements of demographic parameters in order to provide predictions of population size among 13 populations of this fish. Our model predicted that the observed behavioural spawning decisions, while maximizing individual fitness, cause a significant 6% reduction in population size compared with randomly distributed spawnings. We discuss our findings in the context of the population consequences of adaptive behaviour. (+info)
Use of ELISAs in field studies of rabbit haemorrhagic disease (RHD) in Australia.
(78/4953)
ELISA techniques developed for the veterinary diagnosis of Rabbit Haemorrhagic Disease (RHD) in domestic rabbits were used for studying the epidemiology of RHD in Australian wild rabbits. The combination of ELISA techniques that distinguished IgA, IgG and IgM antibody responses and a longitudinal data set, mainly based on capture-mark-recapture of rabbits, provided a reliable basis for interpreting serology and set the criteria used to classify rabbits' immunological status. Importantly, young with maternal antibodies, immune rabbits and rabbits apparently re-exposed to RHD were readily separated. Three outbreaks of RHD occurred in 1996-7. The timing of RHD outbreaks was mainly driven by recruitment of young rabbits that generally contracted RHD after they lost their maternally derived immunity. Young that lost maternal antibodies in summer were not immediately infected, apparently because transmission of RHDV slows at that time, but contracted RHD in the autumn when conditions were again suitable for disease spread. (+info)
Visibility of the environmental noise modulating population dynamics.
(79/4953)
Characterizing population fluctuations and their causes is a major theme in population ecology. The debate is on the relative merits of density-dependent and density-independent effects. One paradigm (revived by the research on global warming and its relation to long-term population data) states that fluctuations in population densities can often be accounted for by external noise. Several empirical models have been suggested to support this view. We followed this by assuming a given population skeleton dynamics (Ricker dynamics and second-order autoregressive dynamics) topped off with noise composed of low- and high-frequency components. Our aim was to determine to what extent the modulated population dynamics correlate with the noise signal. High correlations (with time-lag -1) were observed with both model categories in the region of stable dynamics, but not in the region of periodic or complex dynamics. This finding is not very sensitive to low-frequency noise. High correlations throughout the entire range of dynamics are only achievable when the impact of the noise is very high. Fitted parameter values of skeleton dynamics modulated with noise are prone to err substantially. This casts doubt as to what degree the underlying dynamics are any more recognizable after being modulated by the external noise. (+info)
Priorities in care and services for elderly people: a path without guidelines?
(80/4953)
The growing gap between demands and resources is putting immense pressure on all government spending in Sweden. The gap is especially apparent in care and services for elderly people in light of the rapid aging of the population. The article considers the decisions and priorities concerning resource allocation in the welfare sector in general and in elderly care in particular. The aim is to describe the political and administrative setting and to provide a conceptual structure that outlines the nature of the problem. Various levels of decision making are identified and discussed in the context of political accountability. Current transitions in elderly care are described with respect to service provision, marketisation, coverage rates, and eligibility standards. Basic principles of distribution are highlighted in order to clarify some central concepts of efficiency and justice, and a number of strategies for actual prioritising are identified. The article concludes with an endorsement of more conscious decisions in resource allocation. Existing knowledge and information concerning the effects of various strategies must be utilised, and the values and assumptions used for setting priorities must be made explicit. (+info)