Urban development in Costa Rica| The direct and indirect impacts on local and regional avian assemblages
Author(s)Norris, Jeff L.
Full recordShow full item record
Abstract<p> 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. </p><p> 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. </p><p> My first level of analyses was directed at the impact urban development has on avian diversity patterns, and discovered that urban development drives a monotonic loss of avian species at the local, 16 ha scale in both of the distinct ecoregions. Although somewhat predictable, such results suggested that alternative patterns such as peaks of species richness at intermediate levels of urban development are unlikely for the species rich Neotropics. Additionally, beta diversity in both ecoregions also decreased with an overall increase of urban development. Although local environmental conditions such as level of urban development or percentage of forest cover greatly influenced diversity patterns, they were dependent upon the ecoregion in which they were nested. For example, local alpha diversity was higher in the more species rich Atlantic ecoregion, and beta diversity did not decline as sharply in the Pacific Northwest. Furthermore, on a landscape scale the same level of urban development had a disproportionate effect on avian species richness near a large park or reserve than it did closer to the urban core. In the end, the results of this first level of analysis led to me to suggest particular management policies for avian species conservation along urbanization gradients for similar ecoregions of the Neotropics. </p><p> In my second level of analyses I took a closer look at the species composition and abundance of the 54 avian assemblages and how they were affected by increasing levels of urban development. I found that urban development did acts as an environmental filter and drove convergence of assemblage structure and organization. The biotic homogenization of urban avifaunas was strongly correlated with factors such as the level of urban development and percentage of forest cover, but again within an ecoregional context. Within each ecoregion urban development acted as a deterministic filter since similarly developed sites from different cities or gradients were more often associated together from the results of multivariate analyses. The results of these multivariate analyses provided additional support for the management policies suggested in the first chapter. Not only did the results support the establishment of distinct management areas based on thresholds of urban development, they did so at an ecoregional scale given the similarity of results across the nested gradients. </p><p> Finally, I wanted to investigate the phenomenon that urban development also may have negative effects on native species conservation indirectly through social interactions in what is referred to as the "<i>extinction of experience </i>". In the first two chapters I clearly demonstrated a direct relationship between urban development, its impact on avian species, and the consequences for avian conservation in an urbanizing world. However less well known, but potentially more devastating, is the impact a lack of knowledge or awareness about nature could have on species conservation efforts. If we accept popular conservation paradigms that "we only save what we love and love what we know", then a lack of knowledge could be devastating to conservation efforts. Therefore, I established a survey-based outreach program to determine if 1) there is a lack of knowledge or a difference in perceptions across generations, and 2) outline the relationship of this knowledge with urban development in Costa Rica, a tropical, species-rich country well-known for its environmental awareness. In a survey of 310 upper-elementary students, their parents (n = 219) and grandparents (n = 83), the older generations outperformed the students on questions relating to knowledge of native and exotic species of birds. However, more alarming were the results that students did better identifying exotic birds like penguins and ostriches from other continents than they did the national bird and other common backyard species. Furthermore, most students do not agree with their older relatives that the state of the environment is declining over the next 50 years, and a proportion of urban students actually believe the environment will improve. </p><p> Although my results from this last chapter may not be as straightforward as those investigated in the first two chapters, they were nonetheless informative about the conditions in which conservationists, urban planners, and to a large degree educators will need to operate in the coming decades. Using my comprehensive results from the direct impact urban development has on avian assemblages, I believe they can and should be used to establish the management practices put forward that would benefit species conservation well-into the areas where we live and work throughout the Neotropics. However, to what degree such plans will be accepted by the general populace will be much harder to determine. </p>