Search results for "Population growth"
showing 10 items of 109 documents
RESISTANCE AND TOLERANCE IN A HOST PLANT–HOLOPARASITIC PLANT INTERACTION: GENETIC VARIATION AND COSTS
2002
Host organisms are believed to evolve defense mechanisms (i.e., resistance and/or tolerance) under selective pressures exerted by natural enemies. A prerequisite for the evolution of resistance and tolerance is the existence of genetic variation in these traits for natural selection to act. However, selection for resistance and/or tolerance may be constrained by negative genetic correlations with other traits that affect host fitness. We studied genetic variation in resistance and tolerance against parasitic infection and the potential fitness costs associated with these traits using a novel study system, namely the interaction between a flowering plant and a parasitic plant. In this system…
Loss of density-dependence and incomplete control by dominant breeders in a territorial species with density outbreaks
2011
Abstract Background A territory as a prerequisite for breeding limits the maximum number of breeders in a given area, and thus lowers the proportion of breeders if population size increases. However, some territorially breeding animals can have dramatic density fluctuations and little is known about the change from density-dependent processes to density-independence of breeding during a population increase or an outbreak. We suggest that territoriality, breeding suppression and its break-down can be understood with an incomplete-control model, developed for social breeders and social suppression. Results We studied density dependence in an arvicoline species, the bank vole, known as a terri…
Sexual advertisement and immune function in an arachnid species (Lycosidae)
2004
A simple version of the immunocompetence handicap hypothesizes that through condition-dependence, the size of the sexual trait may be positively related to immune function at the population level. In the present study, we investigated the relationship between sexual advertisement and immune function in a natural population of male wolf spiders, Hygrolycosa rubrofasciata (Araneae: Lycosidae). Males of H. rubrofasciata have a costly and condition-dependent acoustic signal, courtship drumming. In the mating season, males drum against dry leaves while wandering around the habitat searching for receptive females. Males increase their mating success by increasing their drumming rate and mobility.…
‘Adaptive cycles’ and climate fluctuations: a case study from Linear Pottery Culture in western Central Europe
2014
Abstract By applying cycle-based resilience theory the dynamics of the Early Neolithic west-central European Linear Pottery Culture (LBK) are investigated. These are interpreted as resulting from a combination of internal socio-economic processes as well as external environmental parameters. Resilience theory is helpful in understanding periods of increased vulnerability and inherent trends to social complexity. Cycles and threshold levels also help to understand why societies experience periods of increasing fragility and subsequent decline. Results are based on the correlation of a typology and dendrochronology-based archaeological chronology for western LBK and various palaeoclimatic pro…
Sex in an uncertain world: environmental stochasticity helps restore competitive balance between sexually and asexually reproducing populations
2014
Like many organisms, individuals of the freshwater ostracod species Eucypris virens exhibit either obligate sexual or asexual reproductive modes. Both types of individual routinely co-occur, including in the same temporary freshwater pond (their natural habitat in which they undergo seasonal diapause). Given the well-known two-fold cost of sex, this begs the question of how sexually reproducing individuals are able to coexist with their asexual counterparts in spite of such overwhelming costs. Environmental stochasticity in the form of 'false dawn' inundations (where the first hydration is ephemeral and causes loss of early hatching individuals) may provide an advantage to the sexual subpop…
Making progress against cancer in Europe in 2008.
2008
Europe is facing a cancer epidemic, with rapidly increasing incidence rates. Population growth and ageing will further increase the annual number of new patients with cancer. Cancer is a huge and growing contributor to the burden of disease and premature death within the European Union (EU). One in four of all deaths in the EU is attributable to cancer, and in the age range 45-64 years, the figure is almost one in two deaths. The 27 EU Member States differ greatly in cancer incidence, mortality and survival. Yet at least one-third of the cancer burden is preventable and a further third can be detected early and treated effectively, even on the basis of existing knowledge. "Cancer", however,…
Structural change in a Ricardian world economy: The role of extensive rent
2019
Abstract We study an implication of the Ricardian theory of differential extensive rent in a free trade regime. To this effect we develop a Ricardian two country two commodity open economy model. We assume that, unlike labour, land is heterogeneous both within and across countries and that the ratio of high to low quality land is different among the trading countries. By means of a numerical example we show that as the process of worldwide capital accumulation (and population growth) proceeds an industrial country may find it convenient to increase its domestic corn production and even reverse completely the pattern of its imports and exports.
New Arrivals, Old Places: Demographic Changes and New Planning Challenges in Palermo and Naples
2008
If we look at the demographic changes in the largest cities in Southern Italy, the most significant trend is a balance between population growth and decline, affecting in particular inner urban areas, which is due to the predominance of new ethnic inhabitants. After having described these demographic changes in Naples and Palermo, the paper will include some considerations on the ‘institutional’ landscape of planning and the related policies. How do planning policies and practices face this quick change in such peripheral contexts, which are new to the phenomenon? Can the plural composition of the local society be viewed as an opportunity, and not just as a threat? The paper will use some a…
Thresholds for impaired species recovery
2015
Studies on small and declining populations dominate research in conservation biology. This emphasis reflects two overarching frameworks: the small-population paradigm focuses on correlates of increased extinction probability; the declining-population paradigm directs attention to the causes and consequences of depletion. Neither, however, particularly informs research on the determinants, rate or uncertainty of population increase. By contrast, Allee effects (positive associations between population size and realized per capita population growth rate, r realized , a metric of average individual fitness) offer a theoretical and empirical basis for identifying numerical and temporal threshol…
Demographic change, tourism expenditure and life cycle behavior
2015
Abstract The paper explores how demographic changes in human populations may impact on tourism decision-making of households over their life cycle. By means of hurdle models, the study focuses respectively on the decision to travel domestically or abroad and investigates if statistically significant differences exist as to the impact of age and cohort on the decision to travel and tourism expenditure. Using a vast dataset on Italian Household Expenditures over the period 1997–2007 the empirical results show that demographic aspects do have a strong effect on the tourism behaviour of families and that cohort and age effects act differently on the decision of households to make a trip and on …