نتایج جستجو برای: population fluctuations
تعداد نتایج: 762077 فیلتر نتایج به سال:
We study the population profile in a simple discrete time model of population dynamics. Our model, which is closely related to certain “bit–string” models of evolution, incorporates competition for resources via a population dependent death probability, as well as a variable reproduction probability for each individual as a function of age. We first solve for the steady–state of the model in me...
Density dependence plays an important role in population regulation and is known to generate temporal fluctuations in population density. However, the ways in which density dependence affects spatial population processes, such as species invasions, are less understood. Although classical ecological theory suggests that invasions should advance at a constant speed, empirical work is illuminating...
Two contrasting approaches to the analysis of population dynamics are currently popular: demographic approaches where the associations between demographic rates and statistics summarizing the population dynamics are identified; and time series approaches where the associations between population dynamics, population density, and environmental covariates are investigated. In this paper, we devel...
A major question in ecology is how age-specific variation in demographic parameters influences population dynamics. Based on long-term studies of growing populations of birds and mammals, we analyze population dynamics by using fluctuations in the total reproductive value of the population. This enables us to account for random fluctuations in age distribution. The influence of demographic and ...
Organismal response to environmental variability is an important aspect of ecological processes. We propose new mechanisms whereby environmental variability can cause cyclic population outbreaks due to the nonlinearity of the organismal response. We consider stage-structured populations that respond to variable environments with variable diapause or dormancy, and in which cyclic changes of the ...
Latitudinal gradients in population dynamics can arise through regional variation in the deterministic components of the population dynamics and the stochastic factors. Here, we demonstrate an increase with latitude in the contribution of a large-scale climate pattern, the North Atlantic Oscillation (NAO), to the fluctuations in size of populations of two European hole-nesting passerine species...
Ecological theory suggests that several demographic factors influence metapopulation extinction risk, including synchrony in population size between subpopulations, metapopulation size and the magnitude of fluctuations in population size. Theoretically, each of these is influenced by the rate of migration between subpopulations. Here we report on an experiment where we manipulated migration rat...
We have derived the relationship between polarization and intensity fluctuations due to point sources. In the case of a Poisson distribution of a population with uniform evolution properties and constant polarization degree, polarization fluctuations are simply equal to intensity fluctuations times the average polarization degree. Conservative estimates of the polarization degree of the classes...
Introduction: The relationship between population health and income inequality has attracted much attention during the last two decades. But the question on which there is no consensus is that whether fluctuations in economic inequality would lead to changes in population health indices. Methods: In response to this question, life expectancy and mortality rate as health indicators and Gini coef...
The mz"crobz"al assessment of skz"n-washed water samples taken from 39 poultry carcasses and the wash water from a poultry processz"ng unz"t revealed cumulatz"ve z"ncreases z"n the number of mz"croflora at each stage ofprocessz"ng. A comparzson of the bacterz"al population densz"tz"es on the skz'n at the' start and at the end ofprocessz"ng showed that the levels of E. coli and coliforms z"ncrea...
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