Estudo do efeito da fragmentação do habitat sobre padrões de biodiversidade

Abstract

Despite the complexity of factors that influence the growth and dispersion of individuals in species, some general patterns are observed in the study of ecosystems. One of these patterns is the relationship between the number of species and the size of the area occupied by these species (species-area relationship). This relationship is one of the oldest rules of ecology and has been used to estimate population distributions, species diversity of animals and plants.In this work, the main objective was to determine how the habitat fragmentation affects the behavior of the species-area relationship, based on the colonization of an area or region without any existence of life. The model was built to describe the occupation of a determined area by species. Bidimensional lattices, containing sites, represent these areas. For each site is attributed a capacity, which is characterized by the amount of resources available to people who will colonize the area. Each species has been assigned a f itness, which is defined as the sum of the capacities of sites colonized by the same species. In the process of colonization, mutations can occur causing an increase of the diversity of species. The proposed modelwas extended to simulate fragmented habitats as well. In this situation were considered lattices containing a proportion of sites not available for colonization. For the analysis of the pattern of that relationship, it was considered sampled areas in two contexts: different evolutionary histories and continents. It was observed that the sampling procedure changes the shape of the species-area curve. The analysis of the behavior of the system in the context of different evolutionary histories, shows that increasing the proportion of sites that can not be occupied p, there was an increase in the value of the exponent z for the different scale regions in power laws for large a value, indicating faster growth of diversity in relation to the case where the lattice is not fragmented. Considering the context of continents, it was noted that there are three scaling regions described by power laws for some values of a. However, as the proportion p of sites that can not be colonized was increased, there was a reduction in the number of laws for large a value. It was found that the value of exponent z is higher in large areas. Analyzing the distribution of the species size, it appears that the fragmentation increases the frequency of species with smaller populations.