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Demographic Impact (demographic + impact)

Distribution by Scientific Domains

Humanities and Social Sciences	80%

Selected Abstracts

The United Nations on the Demographic Impact of the AIDS Epidemic

POPULATION AND DEVELOPMENT REVIEW, Issue 3 2000
Article first published online: 27 JAN 200
A report prepared by the Joint United Nations Programme on HIV/AIDS (UNAIDS) and released in Geneva on 27 June 2000 (just prior to the XIIIth International AIDS Conference held in Durban, South Africa) updates estimates of the demographic impact of the epidemic. It characterizes AIDS in the new millennium as presenting "a grim picture with glimmers of hope",the latter based on the expectation that national responses aimed at preventing and fighting the disease are in some places becoming more effective. According to the report, which emphasizes the considerable statistical weaknesses of its global estimates, the number of people living with HIV/AIDS in 1999 was 34.3 million (of which 33.0 million were adults and 1.3 million were children under age 15; slightly less than half of the adults affected, 15.7 million, were women). Deaths attributed to AIDS in 1999 amounted to 2.8 million, bringing the total since the beginning of the epidemic to 18.8 million. These figures represent moderate upward revisions of earlier UN estimates shown in the Documents section of PDR 25, no. 4. The revised estimate of the number of persons newly infected with HIV in 1999 is, in contrast, slightly lower: 5.4 million, of which 4.7 million were adults and 2.3 million were women. An excerpt from the 135-page Report on the Global HIV/AIDS Epidemic, focusing on countries in the worst-affected area, sub-Saharan Africa, is reproduced below. (Figures shown have been renumbered.) [source]

Californian mixed-conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico

JOURNAL OF BIOGEOGRAPHY, Issue 1 2000
R. A. Minnich
Abstract Aim,This study appraises historical fire regimes for Californian mixed-conifer forests of the Sierra San Pedro Mártir (SSPM). The SSPM represents the last remaining mixed-conifer forest along the Pacific coast still subject to uncontrolled, periodic ground fire. Location,The SSPM is a north,south trending fault bound range, centred on 31°N latitude, 100 km SE of Ensenada, Baja California. Methods,We surveyed forests for composition, population structure, and historical dynamics both spatially and temporally over the past 65 years using repeat aerial photographs and ground sampling. Fire perimeter history was reconstructed based on time-series aerial photographs dating from 1942 to 1991 and interpretable back to 1925. A total of 256 1-ha sites randomly selected from aerial photographs were examined along a chronosequence for density and cover of canopy trees, density of snags and downed logs, and cover of non-conifer trees and shrubs. Twenty-four stands were sampled on-the-ground by a point-centred quarter method which yielded data on tree density, basal area, frequency, importance value, and shrub and herb cover. Results,Forests experience moderately intense understory fires that range in size to 6400 ha, as well as numerous smaller, low intensity burns with low cumulative spatial extent. SSPM forests average 25,45% cover and 65,145 trees per ha. Sapling densities were two to three times that of overstory trees. Size-age distributions of trees , 4 cm dbh indicate multi-age stands with steady-state dynamics. Stands are similar to Californian mixed conifer forests prior to the imposition of fire suppression policy. Livestock grazing does not appear to be suppressing conifer regeneration. Main conclusions,Our spatially-based reconstruction shows the open forest structure in SSPM to be a product of infrequent, intense surface fires with fire rotation periods of 52 years, rather than frequent, low intensity fires at intervals of 4,20 years proposed from California fire-scar dendrochronology (FSD) studies. Ground fires in SSPM were intense enough to kill pole-size trees and a significant number of overstory trees. We attribute long fire intervals to the gradual build-up of subcontinuous shrub cover, conifer recruitment and litter accumulation. Differences from photo interpretation and FSD estimates are due to assumptions made with respect to site-based (point) sampling of fire, and nonfractal fire intensities along fire size frequency distributions. Fire return intervals determined by FSD give undue importance to local burns which collectively use up little fuel, cover little area, and have little demographic impact on forests. [source]

The United Nations on the Demographic Impact of the AIDS Epidemic

When does parameter drift decrease the uncertainty in extinction risk estimates?

ECOLOGY LETTERS, Issue 12 2003
Stephen P. Ellner
Abstract Halley (2003) proposed that parameter drift decreases the uncertainty in long-range extinction risk estimates, because drift mitigates the extreme sensitivity of estimated risk to estimated mean growth rate. However, parameter drift has a second, opposing effect: it increases the uncertainty in parameter estimates from a given data set. When both effects are taken into account, parameter drift can increase, sometimes substantially, the uncertainty in risk estimates. The net effect depends sensitively on the type of drift and on which model parameters must be estimated from observational data on the population at risk. In general, unless many parameters are estimated from independent data, parameter drift increases the uncertainty in extinction risk. These findings suggest that more mechanistic PVA models, using long-term data on key environmental variables and experiments to quantify their demographic impacts, offer the best prospects for escaping the high data requirements when extinction risk is estimated from observational data. [source]

ORIGINAL ARTICLE: Big dams and salmon evolution: changes in thermal regimes and their potential evolutionary consequences

EVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 2 2008
Michael J. Angilletta Jr
Abstract Dams designed for hydropower and other purposes alter the environments of many economically important fishes, including Chinook salmon (Oncorhynchus tshawytscha). We estimated that dams on the Rogue River, the Willamette River, the Cowlitz River, and Fall Creek decreased water temperatures during summer and increased water temperatures during fall and winter. These thermal changes undoubtedly impact the behavior, physiology, and life histories of Chinook salmon. For example, relatively high temperatures during the fall and winter should speed growth and development, leading to early emergence of fry. Evolutionary theory provides tools to predict selective pressures and genetic responses caused by this environmental warming. Here, we illustrate this point by conducting a sensitivity analysis of the fitness consequences of thermal changes caused by dams, mediated by the thermal sensitivity of embryonic development. Based on our model, we predict Chinook salmon likely suffered a decrease in mean fitness after the construction of a dam in the Rogue River. Nevertheless, these demographic impacts might have resulted in strong selection for compensatory strategies, such as delayed spawning by adults or slowed development by embryos. Because the thermal effects of dams vary throughout the year, we predict dams impacted late spawners more than early spawners. Similar analyses could shed light on the evolutionary consequences of other environmental perturbations and their interactions. [source]