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Results for “Population Growth Estimation”

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At least 109 records · Page 6Linked to original sources
PubMed2002

Extinction risk to herring gull populations from DDT exposure.

The impact of toxic chemicals on wild animals and plants can be quantified in terms of the enhanced risk of population extinction. To illustrate the method, we estimated it for herring gull (Larus argentatus) populations in Long Island (NY, USA) exposed to DDT (p,p'-dichlorodiphenyltrichloroethane) and its metabolites (abbreviated as DDTs) with a strong biomagnification effect. The method is based on a formula of the mean time to population extinction derived for a stochastic differential equation (the canonical model). The intrinsic rate of natural population growth was estimated from the doubling time of an exponentially growing population and the intensity of the environmental fluctuation from the magnitude of population size fluctuation. The effect of exposure to DDTs in reducing the population growth rate was evaluated based on an age-structured population model by assuming that age-specific fertilities (including chick survivorship) are density dependent and sensitive to DDTs exposure but age-specific survivorships are not. The results are expressed in terms of the risk equivalent-the decrease in the carrying capacity K that causes the same enhancement of extinction risk as chemical exposure at a given level. The high concentration reported in Long Island in the 1960s corresponds to the equivalent loss of carrying capacity by 42.5% when K is 100 (the number of breeding females), and coefficient of variation (CV) = 0.2 (sigma2 = 0.0298) [corrected]. Risk equivalent allows us to compare different risk factors and is useful in mitigation banking.

Animals↗
PubMed1986

Population redistribution towards core areas of less developed countries, 1950-1980.

"This paper presents estimates of the rate of population redistribution to the core areas of 44 developing countries over the period 1950-80. Particular attention is given to the period 1970-80, a time during which the core areas of developed countries experienced substantial declines in their rates of net inmigration. The principal finding is that the core areas of most developing countries are still experiencing high and, in a number of cases, increasing rates of net inmigration." The author contends that "this finding confirms the developmental model of spatial concentration and dispersal and should lay to rest other explanations of deconcentration, including arguments that focus on diseconomies of absolute size in the core area or on fluctuations in the aggregate economy." The difference between the population growth rates of entire nations and of core areas is used as a measure of interregional migration. Data for the 44 countries and information on the data sources are included in appendixes.

Demography↗
PubMed1995

An analysis of the growth of the retinal cell population in embryonic chicks yielding proliferative ratios, numbers of proliferative and non-proliferative cells and cell-cycle times for successive generations of cell cycles.

Growth curves of the retinal cell population of embryonic chicks were fitted by a branching-process model of cell population growth, thereby estimating the proliferative ratios and mean cell-cycle times of the generations of cell cycles that underlie retinal growth. The proliferative ratio determines the proportion of cells that divides in the next generation, so the numbers of proliferative and non-proliferative cells in each generation of cell cycles were obtained. The mean cell-cycle times determine the times over which the generations are extant. Assuming growth starts from one cell in generation 0, the proliferative cells reach 3.6 x 10(6) and the non-proliferative cells reach 1.1 x 10(6) by generation 23. The next four generations increase the proliferative cell numbers to 13.9 x 10(6) and produce 20.1 x 10(6) non-proliferative cells. In the next five generations in the end phase of growth, non-proliferative cells are produced in large numbers at an average of 13.9 x 10(6) cells per generation as the retinal lineages are completed. The retinal cell population reaches a maximum estimated here at 98.2 x 10(6) cells. The mean cell-cycle time estimates range between 6.8 and 10.1 h in generations before the end phase of growth and between 10.6 and 17.2 h in generations in the end phase. The retinal cell population growth is limited by the depletion of the proliferative cell population that the production of non-proliferative cells entails. The proliferative ratios and the cell-cycle-time distribution parameters are the likely determinants of retinal growth rates. The results are discussed in relation to other results of spatial and temporal patterns of the cessation of cell cycling in the embryonic chick retina.

Animals↗
PubMed1985

[Simulation of possible developments in urbanization in the German Democratic Republic by the use of a multi-regional population model].

An attempt is made to forecast likely trends in urbanization in the German Democratic Republic over the next 50 years using the multi-regional approach developed at the International Institute for Applied Systems Analysis in Laxenburg, Austria. "Three scenarios describe possible variants in the changes of fertility, mortality and interregional migration as demographic factors. The term 'region' is applied to 4 sizes of communities each grouped as rural communities, small towns, small medium-size towns, and large medium-size towns/large towns. The results of the simulation indicate for all three scenarios an absolute and relative decline in population of the rural communities and a continuation of the process of concentration among the population." (summary in ENG, RUS)

Demography↗