Diversidade taxonômica e funcional em assembleias de aves em uma área urbana no hotspot do Cerrado

Abstract

High rates of urbanization and rapid habitat loss in urban centers pose major challenges for biodiversity conservation, making cities complex ecosystems for sustaining diverse biological communities. Increased population density is often associated with reduced biodiversity, as it intensifies the negative effects of urbanization on ecosystems. Together, these processes create significant challenges for the persistence of certain bird species in urban environments. The new conditions imposed by urban areas reduce the availability of green spaces, which can negatively affect the occurrence of less tolerant species, the so-called urban avoiders, while favoring those more adapted to disturbance. Thus, cities that preserve fragments of native vegetation and structures capable of harboring local bird species can sustain greater urban diversity, playing a key role in the conservation and maintenance of these communities. To understand how the urbanization process impacts biodiversity in a tropical city located in the Cerrado biome, one of the world’s main biodiversity hotspots, this thesis used birds as a model group. I investigated different levels of urbanization in the city of Campo Grande (MS), and the potential effect of tree cover on the structure of bird assemblages. In Chapter 1, I examined how tree cover, building density, and population density influence bird abundance and species richness in urban areas. In addition, I evaluated whether these patterns vary among different ecological guilds (habitat, trophic niche, and primary lifestyle) and which component of beta diversity (turnover or nestedness) explains variation in community composition. The results showed that tree cover was the most important variable, having a positive effect on the richness and abundance of forest species while negatively affecting species associated with human-modified environments, granivores, and terrestrial species. Beta diversity between sites was mostly explained by the turnover component (97%), indicating species replacement along the urban gradient. Variation in community composition was significantly associated with tree cover, with areas of greater vegetation cover hosting more similar communities, in contrast to highly urbanized areas, which exhibited greater heterogeneity and a predominance of generalist species. In Chapter 2, I evaluated how environmental variables (tree cover, building density, and population density) at three spatial scales (75 m, 200 m, and 500 m) influence the functional diversity of bird communities across 30 urban locations. Four complementary functional diversity metrics (richness, evenness, divergence, and functional dispersion) were calculated from morphological traits (beak, tail, wing length, and body mass). The results showed that functional evenness (FEve) was negatively related to tree cover at all scales and positively related to the proportion of urban area at the 75 m and 200 m scales, indicating a more homogeneous distribution of functions in more urbanized environments. The other functional diversity metrics (FRic, FDis, and FDiv) showed no significant relationships with environmental variables. Moreover, the community-weighted means (CWMs) of morphological traits indicated a positive effect of urbanization on wing length, suggesting that species with greater flight capacity tend to be favored in more urbanized areas. In Chapter 3, I assessed the potential of urban road verges (median strips between avenues) to maintain and conserve bird communities across different levels of urbanization (low 90%). The alpha, beta, and gamma diversity of bird assemblages sampled in 30 urban road verges distributed among these classes were compared. The results showed that sites with low urbanization had higher average species richness (alpha diversity) and higher total species numbers (gamma diversity) than those with intermediate and high urbanization. Total beta diversity was also higher in the low and intermediate urbanization classes, reflecting greater heterogeneity among communities. In contrast, highly urbanized areas exhibited more homogeneous communities, with lower species turnover and greater nestedness. Turnover was the main component of the driving variation in beta diversity, especially in less urbanized areas. These results indicate that urban road verges with greater vegetation cover and lower urbanization intensity play an important role in maintaining local and regional diversity, functioning as complementary habitats and potential ecological corridors for birds in highly modified urban landscapes. Our findings highlight the importance of managers and decision-makers prioritizing the maintenance and expansion of native vegetation along the urban gradient. Heterogeneous environments within anthropogenic areas favor more diverse bird communities, with greater resource availability and, consequently, enhanced ecosystem service provision. Strengthening programs for the restoration and proper management of native vegetation, therefore, represents an essential strategy for conserving urban biodiversity and promoting more sustainable and resilient cities.