Urbanization is increasing on a global scale, much to the detriment of native plant and animal communities. Nowhere is this pattern more evident than in the species-rich developing countries of the Neotropics. Ecologists urgently need to incorporate an urban framework into traditional ecology and conservation paradigms to stave off future deterioration. Therefore, my dissertation research focused on documenting the changes in the structure and organization of local and regional avian assemblages along urbanization gradients in Costa Rica. To address this issue I established 6 urban development gradients evenly divided among two distinct ecoregions; the wet Altlantic lowlands, and the lowlands of the drier Pacific Northwest. Each urban development gradient ran from a city core to the interior mature forest of a nearby national park or reserve, and contained nine, 16 ha quadrats that varied in their level of urban development. I conducted variable circle point counts from four sub-sampling points in each quadrat using both aural and visual cues from June 2008 through December 2009. During this period I completed 14 surveys in all the quadrats and gradients in each ecoregion. These avian surveys were evenly divided among the two migrant periods when either North American migrant species are either present or absent.
Results/Conclusions
I observed 17,696 individual birds representing 271 species from the wet Altantic ecoregion, and 17,283 individual birds from 157 species in the drier Pacific Northwest ecoregion. NMS ordinations show a good spread of survey quadrats based on their levels of urban development along axis 1, with axis 2 showing a distinct split between the gradients and quadrats of the two ecoregions (i.e. 2-dimension solution final stress=13.87, p=0.0196, cumulative variance= 0.687). In both ecoregions, both estimated and rarified species richness decrease as levels of urban development increase from national parks towards the city core. Combined with highly significant results from MRPP tests (T= -11.40, A=0.728, p< 0.001), the above results indicate there are three distinct management areas based on differences in avian species richness, abundance, and composition along a Neotropical urbanization gradient. The results also demonstrate development thresholds for each area, above which, increases in development will have negligible effects on the avifauna until the next threshold is reached. These results provide an important beginning framework for ecologists, municipal leaders, and land developers charged with the duty of decreasing the anthropogenic footprint as the global landscape becomes more urban.
