J. M. de Miguel

Pulmonary aspergillosis in patients with chronic obstructive pulmonary disease: incidence, risk factors, and outcome

We describe a large series of patients with chronic obstructive pulmonary disease (COPD) and probable invasive pulmonary aspergillosis (IPA), and the risk factors and incidence of the disease in patients with isolation of Aspergillus from lower respiratory tract samples. From 2000 to 2007, we retrospectively studied all patients admitted with COPD and isolation of Aspergillus (239; 16.3/1000 admissions). Multivariate logistic regression and survival curves were used. Fifty-three patients had probable IPA (3.6 cases of IPA per 1000 COPD admissions). IPA affects at least 22.1% of patients with COPD and isolation of Aspergillus in culture. In 33 of the 53 patients with probable IPA, serum galactomannan was determined; in 14 (42.4%) of these, the result was positive. Five variables were independent predictors of IPA with statistical significance: admission to the intensive-care unit, chronic heart failure, antibiotic treatment received in the 3 months prior to admission, the accumulated dosage of corticosteroids equivalent to >700 mg prednisone received in the 3 months prior to admission, and the similar accumulated dosage of corticosteroids received from admission to the first clinical isolation of Aspergillus. Multivariate analysis gave an area under the curve of 0.925 (95% CI 0.888-0.962; p <0.001). The overall mean survival of the cohort was 64.1% (28.3% for IPA patients and 75.2% for non-IPA patients). The median number of days of survival was 48 (95% CI 33.07-62.92). However, we found statistically significant differences between patients with IPA (29 days; 95% CI 20.59-37.40) and patients without IPA (86 days; 95% CI 61.13-110.86) (log rank, p <0.001).

Shrub encroachment in Argentinean savannas

Abstract In the Wet Chaco region of Argentina, increasing shrub encroachment in savannas over the last few decades has led to important changes in the structure and functioning of the landscape. Some sectors of this territory are characterized by the appearance of circular clusters of woody patches, dispersed throughout the grassland matrix. The increasing size of these patches leads to a gradual change from grassland to dense shrubland. We studied these circular woody patches in the eastern region of the Argentine province of Formosa and characterized the variation in terms of floristic composition, diversity and predominant seed dispersal mode in different size patches. We observed an increase in species richness, diversity and compositional heterogeneity among patches with increasing patch size. Seed dispersal by animals, especially birds, is an important factor in the expansion of these woody vegetation patches within the grassland matrix. Nomenclature: Zuloaga et al. (1994, 1996a, b). Some native names were included using quotation marks.

Production and spatial structure of Mediterranean pastures in different stages of ecological succession

The aim of this paper is to describe the changes of Mediterranean pasture phytomass and their dependence on succession, slope geomorphology and herbivore consumption. Four neighbouring slopes of similar aspect and steepness, located in a pasture area of Central Spain, were chosen for sampling. The slopes had not been cultivated for 1, 3, 8 and 40 years respectively. On each slope both the upper, erosion zone and the lower, accumulation zone were sampled during the months of plant growth (April to July), phytomass being recorded in plots where herbivore consumption was avoided with protection cages and in unprotected plots. Results from the protected plots show that the upper and lower parts of slopes undergo a different development during succession. The highest values of phytomass reached, tended to decrease during succession in the upper zones, the same being true for production. However in the lower zones both parameters tended to increase in time. The ratio P/B, widely known in ecology to decrease with time, did not seem to behave as a usual index of succession in the studied ecosystem. In the upper zone this ratio tended to decrease but in the lower zone it increased with succession after the first years. Phytomass consumption by herbivores was progressively concentrated during succession in the slope sectors of greater production, mainly in the lower zone, which increased its productivity as the slope-talweg system became functional. The evolution of the ecological structure of a slope should be interpreted not only as a result of the tolerance of species to phsysico-chemical factors. It may also reveal the existence of an important interaction between the pasture and the grazing behaviour of exploiting animals. Multivariate analysis of phytomass records revealed a trend of temporal variation which should be identified with the progress of succession.

Successional changes in the morphology and ecological responses of a grazed pasture ecosystem in Central Spain

Morphological characteristics related to spatial occupation, reproduction and adaptations to grazing were used to characterize the most frequent species in a therophytic pastureland of Central Spain. Periodic ploughing is a traditional practice in these pastures and allows observation of successional change. In the present study, four neighbouring slopes of differing time since last ploughing were chosen. Species biomass was measured at different times during the annual growing season for two different slope positions. Grazing pressure is an important environmental factor affecting ecosystem organization, the most palatable plants tending to show increasing biomass with succession. In the most mature stages, there is a predominance of species characterized by horizontal occupation of space and sprouting after mowing or grazing. During succession segregation of the different morphological characteristics occurs in slope sectors related to geomorphological dynamics. Similarly, phenological development tends to be later in pastures in the lowest slope zones, due probably to their greater summer soil moisture content.

Ecological structures recognized by means of entropy analysis: Assessment of differences between entropy values

A procedure is outlined for the assessment of differences between entropy values obtained from a data set. The problem posed is that of identifying the data matrix representing least uncertainty in the disposition of its elements from two or more given matrices. Monte Carlo simulations were used, through which the maximum and minimum entropy values that could be obtained from each data set were estimated. Such values could be obtained by randomly interchanging the elements of each matrix and may serve as references in estimating the degree of order or randomness that an original matrix possesses.

Plant species richness and spatial organization at different small scales in western Mediterranean landscapes

The relationship between plant species richness and the space organization of the community at different small scales was studied. The study was based on 51 sites distributed along a belt from Central Spain to Portugal. Each site was analyzed with a transect cutting across the boundary between two neighboring patches of shrubland and grassland. Local spatial organization of vegetation was analyzed at different levels of detail and each transect was divided into successively smaller portions. The first division coincides with a physiognomic perception of the site in two patches (shrubland and grassland). The average spatial niche width of the species was used to calculate the spatial organization of the vegetation of each division in each site. The correlation between species richness and spatial organization depended on the block size under consideration. A physiognomic criterion, sectorizing the sites into patches of shrubland and grassland, determines noteworthy floristic changes but does not enable us to express satisfactorily the variability in plant richness. In order to account for this variation, other factors must be taken into account which act at a more detailed small-scale and which determine the internal variability of these patches. In the case studied, the species richness of the sites increases along with an increase in the percentage of species whose occupation of the space is relatively restricted within the site. Many of these species are, however, frequent within the whole of the territory studied. The results highlight the importance of the level of local scale at which the factors influencing occupation of the space, and consequentially, plant richness, preferentially act. This circumstance ought to be taken into consideration in strategies for the conservation of biological diversity, and based on the delimitation of protected spaces with criteria frequently linked to the physiognomy of the vegetation.

An objective method for partitioning dendrograms based on entropy parameters

A simple method for determining the optimum number of groups in a dendrogram is presented. This method uses the mean niche width of variables (A). This parameter is calculated for each partitioning level in the dendrogram and provides information about the degree of segregation of the variables in the obtained groups. The partitioning level at which parameter A has the minimal value provides the most contrasted groups according to their variables composition.The proposed method is independent from the number and size of plots or groups utilised in the calculation. These features allow comparisons among different classification methods (including subjective classification methods) applied to the same data.