Increasing Population Density (increasing + population_density)

Distribution by Scientific Domains

Selected Abstracts

Characteristics of river floods and flooding: a global overview, 1985,2003,,

Klaas-Jan Douben
inondation; victims; dommages; stratégies de protection contre les inundations Abstract Since ancient times people have settled in flood-prone areas due to favourable geographic conditions which facilitate economic growth, such as accessibility (transportation) and food production (fertile land). This fact forces societies all over the world to protect valuable assets against flooding. Nevertheless flooding is still the most damaging of all natural disasters. One-third of the annual natural disasters and economic losses and more than half of all victims are flood related. Flood mitigation policies and measures have been implemented, enabling societies to increase their resilience to flood hazards. With increasing population densities, often associated with improved living standards and consequently higher values of property and infrastructure, flood defence receives more importance and the consequences of flooding become less acceptable. Trends in flood frequencies and flooding damage seem to be increasing, primarily due to a growing vulnerability arising from societal changes such as interference by occupation, developments, investments and land-use changes in flood-prone areas. The Asian continent was particularly affected by floods and flooding between 1985 and 2003. It recorded nearly half of all flooding events; together with Europe and North America it was confronted with the majority of flooding damage and it incurred nearly three-quarters of all casualties. Copyright © 2006 John Wiley & Sons, Ltd. Depuis toujours les populations se sont installées dans les zones à risque d'inondation du fait de conditions géographiques favorables à la croissance économique, telles que l'accessibilité (transport) et la production de nourriture (terre fertile). Ceci oblige les sociétés partout dans le monde à protéger les biens contre les inondations. Mais celles-ci sont toujours les plus préjudiciables de tous les désastres naturels. Chaque année, un tiers des désastres naturels et des dommages économiques ainsi que plus de la moitié des victimes sont liés aux inondations. Des politiques et des actions de protection contre les inondations ont été mises en oeuvre, permettant aux sociétés d'augmenter leur résistivité aux risques d'inondation. Avec l'augmentation des densités de population, souvent liée à la progression des niveaux de vie et donc à la valeur plus élevée des habitations et des infrastructures, la protection contre les inondations devient plus importante et leurs conséquences moins acceptables. La fréquence des inondations et de leurs dommages semble en augmentation, principalement en raison d'une vulnérabilité croissante résultant de changements sociaux tels que les interférences des activités, aménagements, investissements et occupation de l'espace dans les zones à risque. Le continent asiatique a été particulièrement affecté entre 1985 et 2003. Il a enregistré presque la moitié de tous les événements d'inondation, a dû faire face à la majorité des dommages avec l'Europe et l'Amérique du Nord et a compté presque trois quarts de toutes les victimes. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Density-dependent growth of young-of-the-year Atlantic salmon (Salmo salar) revisited

I. Imre
Imre I, Grant JWA, Cunjak RA. Density-dependent growth of young-of-the-year Atlantic salmon (Salmo salar) revisited. Ecology of Freshwater Fish 2010: 19: 1,6. © 2009 John Wiley & Sons A/S Abstract,,, The length of individual young-of-the-year (YOY) Atlantic salmon (Salmo salar) in Catamaran Brook decreases with increasing population density following a negative power curve. Because most of this decrease in growth rate occurs at low densities (<1 fish·m,2), (Imre et al. 2005; Journal of Animal Ecology, 74: 508,516) suggested that exploitation competition for drifting prey rather than space limitation might be responsible for this pattern. Recently, (Ward et al. 2007; Journal of Animal Ecology, 76: 135,138) showed that the negative power curve of growth rate versus density can be caused by other mechanisms and suggested that Imre et al.'s evidence for density-dependent growth would have been stronger if we had analysed final size versus initial density rather than final density. We examined (i) whether the negative power curve of size versus density was also apparent in an analysis of final size versus initial density and tested two predictions that emerge from Ward et al.'s model, (ii) the variance in body size increases with population density, and (iii) the maximum fish size at a site is density-independent. The final size of YOY salmon decreased with increasing initial density following a negative power curve. Our data did not provide strong support for the above predictions emerging from Ward et al.'s model. Our analyses of different years, sites and seasons were consistent with the hypothesis of density-dependent growth of YOY salmon. [source]

Multi-annual spatial and numeric dynamics of the white-headed duck Oxyura leucocephala in southern Europe: seasonality, density dependence and climatic variability

Summary 1A statistical model is developed for the globally threatened white-headed duck during its regional expansion throughout Spain from 1980 to 2000; the model estimates the relative intrinsic, climatic and stochastic effects on population fluctuations and spatial expansion on several time-scales. Facing the current lack of knowledge on the nature and consequences of regulation for waterfowl populations, this type of study seems timely. 2A measure of population density accounting for the spatial patchiness of the population was constructed for breeding and wintering counts. No relationship was found between spatial and numeric dynamics, which suggests different mechanisms for both dynamical patterns. 3Although a lagged non-linear climatic effect during the period of chick rearing enhanced numeric brood recruitment through a cohort effect, in the short term brood production appeared to decrease with increasing population density, despite a long-term exponential numeric growth. 4Both wintering population density and rainfall during post-nuptial moult exerted a positive effect on subsequent spatial expansion during breeding, which suggest a major role for social interactions during wintering and wetlands availability on spatial dynamics. 5Altogether, the results suggest that seasonality, density-dependence and climatic forcing are all major processes in the spatio-temporal dynamics of the white-headed duck. Ignoring the relative biotic and abiotic effects and their temporal scale of interaction on population dynamics might thus yield misleading conclusions on the factors affecting the short- and long-term abundance of waterfowl populations. [source]

Habitat heterogeneity affects population growth in goshawk Accipiter gentilis

Oliver Krüger
Summary 1The concept of site-dependent population regulation combines the ideas of Ideal Free Distribution-type of habitat settlement and density dependence in a vital rate mediated by habitat heterogeneity. The latter is also known as habitat heterogeneity hypothesis. Site-dependent population regulation hypothesis predicts that increasing population density should lead to inhabitation of increasingly poor territories and decreasing per capita population growth rate. An alternative mechanism for population regulation in a territorial breeding system is interference competition. However, this would be expected to cause a more even decrease in individual success with increasing density than site-dependent regulation. 2We tested these ideas using long-term (1975,99) population data from a goshawk Accipiter gentilis population in Eastern Westphalia, Germany. 3Goshawk territory occupancy patterns and reproduction parameters support predictions of site-dependent population regulation: territories that were occupied more often and earlier had a higher mean brood size. Fecundity did not decrease with increasing density in best territories. 4Using time-series modelling, we also showed that the most parsimonious model explaining per capita population growth rate included annual mean habitat quality, weather during the chick rearing and autumn period and density as variables. This model explained 63% of the variation in per capita growth rate. The need for including habitat quality in the time-series model provides further support for the idea of site-dependent population regulation in goshawk. [source]

Seasonal dynamics, dispersion, sequential sampling plans and treatment thresholds for the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), in a mature lemon block in coastal New South Wales, Australia

Zhong Min Liu
Abstract, Studies of citrus leafminer in a coastal orchard in NSW, Australia indicated that an increase in abundance to about one mine per flush was followed during the midseason flush by a rapid increase in population that was related to an increase in the percentage of leaves infested within flushes and the number of mines per leaf. The fits of frequency distributions and Iwao's patchiness regression indicated that populations were highly contagious initially, and as the exponent k of the negative binomial distribution increased with increasing population density, the distribution approached random. Concurrently, the coefficient of variation of mines per flush (which was strongly related to the proportion of un-infested flushes) decreased to about unity as the proportion of un-infested flushes reached zero and fell further as the number of mines per flush increased. Both numerative and binomial sequential sampling plans were developed using a decision threshold based on 1.2 mines per flush. The binomial sampling plan was based on a closely fitting model of the functional relationship between mean density and proportion of infested flushes. Functional relationships using the parameters determined from Iwao's patchiness regression and Taylor's power law were equally satisfactory, and one based on the negative binomial model also fitted well, but the Poisson model did not. The three best fitting models indicated that a decision threshold of 1.2 mines per flush was equivalent to 50% of flushes infested. From a practical point of view, the transition from 25% infestation of flushes through 50% is so rapid that it may be prudent to take action when the 25% level is reached; otherwise, the 50% may be passed before the crop is checked again. For valuable nursery stock should infestation be detected in spring, it may be advisable to apply prophylactic treatment as the midseason flush starts. [source]