Showing papers by "Marinez Ferreira de Siqueira published in 2007"

Threats to the cerrado remnants of the state of são paulo, brazil

Abstract: Patches of natural vegetation remaining in landscapes occupied by man are continuously under threat due to the edge effects and also to land use types around these remnants. The most frequent threats and land use types in the vicinity of 81 Cerrado (tropical savanna type) fragments in the State of Sao Paulo, Brazil, were analyzed in order to verify if the frequency of every type of disturbance to the natural ecosystem depends on the neighboring land use. The hypothesis of the study assumes that environmental threats are correlated with land use around protected areas. From the 81 areas, the most frequent human-induced land cover types around the Cerrado remnants were: pasture (recorded in 78% of the areas), sugarcane plantations (26%), roads (19%), annual crops and reforestation (14% each). The most frequent sources of threats were invasive grasses (35% of the areas partially or totally invaded) and cattle (observed in 32% of the areas), followed by deforestation (21%), and fire (21%). The chi-square analysis revealed that, with the exception of deforestation, which does not depend on land use, all other threats are influenced by the neighboring land use. The occurrence of invasive grasses and fires are strongly favored by the presence of roads and urban areas. Sugarcane, reforestation, and permanent crops were the less impacting land use types found in the study area, when only considering impact frequency. These land use types have fire and weed control, and also exclude cattle, indirectly protecting natural ecosystems.

Modelagem da distribuição geográfica de espécies lenhosas de cerrado no Estado de São Paulo

Abstract: Many different techniques are used today with different objectives to model species geographic distribution. Some of these techniques are based on environmental analysis where algorithms search for environmental conditions similar to those where the species are known to occur, resulting in potential areas where the environmental conditions would be favorable for the growth of these species. The present study is based on predictive modeling of species geographic distribution using genetic algorithm as a tool for plant conservation in modeling the "cerrado" biome of the State of Sao Paulo. The methodology used and the results obtained were considered satisfactory for the generation of geographic distribution models for plant species, based on abiotic data for the regions studied. The accuracy of the model in predicting the occurrence of species in the "cerrado" is greater if only points that occur within the "cerrado" and not in transition areas are used. In order to minimize problems due to the lack of convergence of the genetic algorithm GARP ("Genetic Algorithm for Rule Set Production"), 100 models were generated for each specie. The use of modeling tools can help understand the distribution patterns of a biome or ecosystem in a regional analysis.

Introducing Open Modeller - A fundamental niche modelling framework

Abstract: Introduction In 1957 Hutchinson (4) formalised the fundamental niche principle In essence, he proposed that if all the environmental conditions that allow a species to exist indefinately could be tabulated as a multidimensional hypercube, then the resulting hypercube could be considered to be the organismâ??s fundamental ecological niche Naturally, fully understanding all the ecological conditions for any given species is a monumental task, limited primarily by the lack of rich data that could drive such an analysis By extrapolation of the association between species occurrence localities and a set of GIS raster layers representing environmental conditions such as rainfall, temperature, solar radiation etc, a correlative approach can be taken towards describing an organismâ??s ecological niche (10) Using this technique, a raster layer can be produced with areas that most resemble the environmental conditions at the original known sites of occurrence for the organism Arguably, this approach first garnered widespread interest with the publication of â??A biogeographic analysis of Australian Elapid snakesâ?? (5), where the authors produced predicted distribution maps for Elapid snakes based on simple models of climatic preference As the world starts to engage more fully in the discussion of the potential impacts of global climate change, the abillity to predict the impact of these changes on the distribution of organisms has become more topical Fundamental niche modelling has been used to predict species loss in the face of future climate changes (12; 2) It has also been used to model invasive species, spread of disease vectors (6) and in phylogenetic modelling to produce distribution maps for hypothetical ancestors (13; 14)