Bird Diversity in Urban Ecosystems: The Role of the Biome and Land Use Along Urbanization Gradients

Abstract

Urbanization is an expanding process worldwide, causing major threats to biodiversity through both species extinction and biotic homogenization. Most studies focusing on urban ecosystems have been conducted in temperate forests of the Northern hemisphere; the ecological and socioeconomic contexts, however, may influence biodiversity responses to urbanization. We ask whether the biomes (here, the humid subtropical forest and the semiarid shrubland) where human settlements and land uses are developed determine bird diversity along urbanization gradients in the southern Neotropics. We propose theoretical responses based on expected variations in vegetation cover along urbanization gradients and fit our data to different models of bird richness from highly developed to non-urban areas and also examine changes in species composition. Species richness was positively correlated to vegetation cover in both human settlements. Results supported some of our predictions. In the city located in the arid biome, the highly developed area supported higher bird richness than the natural habitat, unlike the city from the humid biome; yet, the native bird assemblage was better preserved in the urban area established in the humid biome. Richness in moderately developed areas was either higher than or similar to that in rural or natural areas in the settlement from the arid biome, but lower than or similar to richness in the humid biome. In all the studied urban–rural gradients, bird richness reached a plateau in moderately developed areas, in contrast to urban-natural habitat gradients, where richness either increased (in the humid biome) or declined (in the arid biome). Our study helps to understand how the mechanisms changing biodiversity in urbanized areas may act in different biomes and land uses, and therefore contributes to the search of global explanations of diversity patterns.