ABSTRACT Mussununga, an oligotrophic sandy savanna ecosystem, comprises distinct physiognomies along fire, water and nutrient availability gradients. Grasslands and woodlands are constrained at the opposite poles of these gradients, with grasslands occurring in areas with poorer soils and higher levels of both water-stress and fire intensity. According to the stress-dominance hypothesis, one might expect the importance of competition for community assembly to increase from grasslands to woodlands. Assuming conservation of ecological niches within evolutionary lineages, this should increase phylogenetic overdispersion from grasslands towards woodlands. To test this, we calculated phylogenetic diversity and community structure using different null models as well as the phylogenetic signal of life form as a proxy of niche space. All indices indicate phylogenetic clustering for grasslands and phylogenetic overdispersion for woodlands. Considering that most life-forms showed a significant phylogenetic signal, findings indicate that competition and further density dependent factors may play a larger role in community assembly of physiognomies in less harsh positions along the gradient, while environmental filtering dominates the harsher positions. Our results indicate that the entire gradient should receive conservation priority in order to guarantee the effective conservation of this endangered ecosystem, including its species richness and ecological processes such as community assembly.

ABSTRACT The Cerrado is the largest savanna of South America and its physiognomy varies from savanna to woodlands. There are two main types of woodlands in the Cerrado: dystrophic woodlands, dominated by N-fixing leguminous trees (LEG), and mesotrophic woodlands dominated by non-leguminous drought-tolerant trees (DRY), which are calcicoles and sensitive to Al3+. The working hypothesis is that LEG and DRY are functional antagonists in terms of the acidification/alkalization processes involving different forms of inorganic nitrogen and pH, Ca2+ and Al3+ in soil. Tree species basal area and soil properties were used to investigate the antagonism between LEG and DRY using generalized linear models. The results suggest that LEG and DRY are antagonists. The LEG were positively associated with Al3+, NO3- and NH4+ content and negatively related to increasing Ca2+ content, whereas the DRY were negatively associated with Al3+, NO3- and NH4+ and positively associated with increasing Ca2+ content. The upper soil layer in plots dominated by LEG species became more acidic and the upper soil layer in plots dominated by DRY species became more alkaline. The results suggest that LEG and DRY are functional antagonists and their preferences for NH4+ or NO3- might influence the way the Cerrado woodland changes.

Antecedentes: la canasta básica de alimentos de Guatemala data de hace 30 años y no refleja la tendencia actual del consumo de alimentos de la población guatemalteca, además la familia promedio en esa época constaba de 5,4 miembros, mientras que para el año 2009-2010 es de 4,9. Objetivo: construir la nueva canasta básica de alimentos para Guatemala a nivel nacional, urbano y rural, sobre la base de los patrones de consumo de alimentos analizados a partir de la Encuesta nacional de ingresos y gastos familiares (ENIGFAM 2009-2010). Materiales y métodos: se siguió la metodología estándar; determinación de requerimientos energéticos y proteína; selección de alimentos más consumidos por la población y cantidades de consumo; conformación de la estructura de la canasta básica (alimentos, grupos, aporte energético y de macronutrientes, cantidad y medidas comunes consumidas); definición de la metodología para fijar precios. Resultados: se obtuvieron tres estructuras compuestas por 41 productos para la nacional, 44 para la urbana y 35 para la rural, de todos los grupos de alimentos. Las tres canastas tienen una metodología para fijar precios de acuerdo con la población a la que está dirigida. Conclusiones: las estructuras propuestas respetan los patrones de consumo observados en la población y cubren las cantidades recomendadas de energía y macronutrientes.

Background: the Guatemalan basic food basket (BFB) was designed 30 years ago. Its structure does not reflect the current trend on food consumption among the population. On the other hand, the average household size has decreased from 5.4 to 4.9; last evaluation 2009-2010. Aim: to design the new Guatemalan BFB, for urban and rural population, based on analysis of food consumption data from the ''National survey on family income and expenditure 2009-2010''. Materials and methods: a standardized methodology was followed. Initially, energy and protein requirements were seted. Then, the most-consumed foods and its consumption amounts were chosen. Later on, BFB basic structure was obtained (food and food groups, intake of energy and macronutrients, amount consumed and most used food measures). Finally, the methodology to set prices was defined. Results: three different structures were obtained, composed by 41 products (national BFB), 46 products (urban BFB), and 35 products (rural BFB); from all food groups. A methodology to set prices was developed for each BFB; according with the target population. Conclusions: the proposed structures comply with the observed population consumption patterns, and cover the recommended amounts of energy, protein, carbohydrates and fat.