University of Alcalá

About: University of Alcalá is a education organization based out in Alcalá de Henares, Spain. It is known for research contribution in the topics: Population & Context (language use). The organization has 10795 authors who have published 20718 publications receiving 410089 citations. The organization is also known as: University of Alcala & University of Alcala de Henares.

Global spatial patterns and temporal trends of burned area between 1981 and 2000 using NOAA‐NASA Pathfinder

Abstract: An analysis of the spatial and temporal patterns of global burned area with the Daily Tile US National Oceanic and Atmospheric Administration-Advanced Very High-Resolution Radiometer Pathfinder 8 km Land dataset between 1981 and 2000 is presented. Nine distinct temporal and spatial fire patterns were identified at the global scale using principal components and cluster analysis. Three major fire seasons were identified from June to December and from February to June for different areas of the northern hemisphere and from October to March for the southern hemisphere. The area burned primarily followed the annual cycle and secondarily, an important 6-month cycle. Temporal cycles were unimportant in some equatorial and tropical areas in the northern hemisphere. The total annual burned area has not increased in the last 20 years but a significant increase was found in the mid-latitude and subtropical areas of the northern hemisphere which was offset by a slight decrease in burned area in tropical southeast Asia and Central America. Additionally, burned area has significantly increased during the summer in the mid-latitudes of the northern hemisphere and in the boreal region, and the fire season starts earlier in the mid-latitudes. Total burned area was explained by the extent of savanna (wooded grassland) cover. Latitude was not determinative as divergent fire patterns were encountered and did not have an impact on extent of burned area at our spatial level of analysis.

Surrogate markers of visceral adiposity in young adults: waist circumference and body mass index are more accurate than waist hip ratio, model of adipose distribution and visceral adiposity index.

Abstract: Surrogate indexes of visceral adiposity, a major risk factor for metabolic and cardiovascular disorders, are routinely used in clinical practice because objective measurements of visceral adiposity are expensive, may involve exposure to radiation, and their availability is limited. We compared several surrogate indexes of visceral adiposity with ultrasound assessment of subcutaneous and visceral adipose tissue depots in 99 young Caucasian adults, including 20 women without androgen excess, 53 women with polycystic ovary syndrome, and 26 men. Obesity was present in 7, 21, and 7 subjects, respectively. We obtained body mass index (BMI), waist circumference (WC), waist-hip ratio (WHR), model of adipose distribution (MOAD), visceral adiposity index (VAI), and ultrasound measurements of subcutaneous and visceral adipose tissue depots and hepatic steatosis. WC and BMI showed the strongest correlations with ultrasound measurements of visceral adiposity. Only WHR correlated with sex hormones. Linear stepwise regression models including VAI were only slightly stronger than models including BMI or WC in explaining the variability in the insulin sensitivity index (yet BMI and WC had higher individual standardized coefficients of regression), and these models were superior to those including WHR and MOAD. WC showed 0.94 (95% confidence interval 0.88–0.99) and BMI showed 0.91 (0.85–0.98) probability of identifying the presence of hepatic steatosis according to receiver operating characteristic curve analysis. In conclusion, WC and BMI not only the simplest to obtain, but are also the most accurate surrogate markers of visceral adiposity in young adults, and are good indicators of insulin resistance and powerful predictors of the presence of hepatic steatosis.

Diversity, function and stability in parasitoid communities

Abstract: The parasitoid assemblages associated with grass-feeding chalcid wasps in Great Britain were used to examine the relationships between diversity (species richness), community function (total parasitism rate) and stability (variability in parasitism rate over time). Species-rich communities did not generate higher parasitism rates than species-poor communities, nor was temporal variation of parasitism rates related to parasitoid community richness. The mechanisms underlying hypotheses linking species richness and community function and stability are discussed in the light of these results. Because all parasitoid species represent a single functional group, a lack of complementarity in the ways they use their resources may explain why diversity is not linked to function or community stability. A second likely reason is that these parasitoid communities are under bottom-up control, thus exerting little or no influence on total system function and variability. This is likely to be common in parasitoid communities.

Mechanisms maintaining biodiversity in Mediterranean pine-oak forests: insights from a spatial simulation model

Abstract: Recurrent anthropogenic and natural perturbations, resource limitations and heterogeneous environments contribute to the maintenance of a remarkable biodiversity in Mediterranean plant communities. Yet, the essential mechanisms of community assembly in these systems remain largely unexplored. In the current paper we investigate the coexistence of Aleppo pine (Pinus halepensis Mill.) and Holm oak (Quercus ilex L.), two of the most widely distributed species in the Iberian Peninsula, in relation to gradients in water availability and disturbance. A spatial model of landscape forest dynamics was implemented, calibrated with experimental data, with stands arranged on a heterogeneous lattice and coupled by dispersal. It was found that pine population persistence in the landscape can be explained independently by a competition-colonization tradeoff (in mesic homogeneous environments) and by a tradeoff between shade and drought tolerance (in heterogeneous low disturbed environments). Both mechanisms reinforce mutually to maintain a shifting mosaic of both taxa along disturbance and aridity gradients. This view is consistent with palynological, historical and forest inventory records. In turn, equilibrium theories of vegetation dynamics (phytosociological), that neglect the role of heterogeneity and disturbances may be inadequate for Mediterranean forests, and have been shown to result in mismanagement practices. We claim that biologically informed models of forest dynamics are desperately needed as diagnosis tools for sustainable forest management.