Doctor of Philosophy
Biology, Environmental Studies
Date of Defense
Godfrey R. Bourne, PhD
Urban development, the pinnacle of human land use, has drastic effects on native ecosystems and the species they contain. For the first time in recorded history there are more people living in cities than in the rural areas surrounding them. Furthermore, the global rate of urbanization continues increasing; raising serious concerns for earth's tropical regions as they harbor a disproportionate amount of the earth's species, and where the impacts of urban development on natural communities are poorly known. Therefore, for my dissertation research I investigated the impacts of urban development on avian community structure and organization at both local and regional scales in Costa Rica. To address this concern I followed a nested design and established survey sites following a complete development gradient that ran from the mature, interior forests of a large national park or reserve and into the urban core of a nearby city. Between both extremes I identified seven other key development steps and established 16 ha sites at each one. At each survey site I conducted annual surveys of the avifauna and characterized the local environmental conditions using remote sensing techniques. I identified three such development gradients within the drier habitats of Costa Rica's Pacific Northwest ecoregion, and three other development gradients in the wetter, Atlantic lowland ecoregion. In total, my 54 survey sites divided evenly across the two ecoregions, and spread across three replicate gradients in each, generated a dataset with over 27,000 observations representing over 36,000 individual birds and 328 species. With this dataset I could generalize the impact urban development had on the structure and organization of local avian assemblages, and determine the key factors driving such patterns by running different analyses at different levels.
Norris, Jeff L., "Urban development in Costa Rica: the direct and indirect impacts on local and regional avian assemblages" (2012). Dissertations. 344.