GLOBAL PATTERNS OF BIRD RICHNESS AND ABUNDANCE IN URBAN AREAS: A QUANTITATIVE REVISION OF URBANIZATION GRADIENTS AND THE SPECIES-URBAN GREEN AREA RELATIONSHIP

RUGGIERO, A.; LEVEAU, L.M.; MATTHEWS, T.; BELLOCQ, M.I.

Cartagena

Congreso; 28th International Congress for Conservation Biology; 2017

Because urbanization is expanding continuously over natural and seminatural areas, it is essential to analyze their impact on biodiversity. The hypothesis called the density- diversity paradox, propose that urbanization favor the presence of bird communities with highest densities than non-urban areas and the presence of fewer species; a pattern contrary to the more individuals hypothesis, in which higher densities are related to higher species richness. On the other hand, although green patch size is a primary factor to determine bird species richness in urban areas, the worldwide consistency in the species- urban green area relationship (SRAu) remains unexplored. The objectives of this study were: 1) to explore global patterns of bird richness and abundance along urbanization gradients in different biogeographic and socioeconomic contexts; and 2) to assess what is the best model explaining the SARu; and 3) to analyze the global heterogeneity of SARu parameters, such as the fit and slope of the power model. We made an intensive literature search, and performed meta-analysis to analyze global effects and the presence of significant heterogeneity in results. We found a significant positive relationship between urbanization and bird abundance, and a significant negative relationship between urbanization and bird richness, supporting the density-diversity paradox hypothesis. Study grain, latitude and the number of exotic species in each study affected significantly the relationship between bird richness and urbanization. Continent affected the relationship between bird abundance and urbanization. Regarding the SARu, the linear model was the best model explaining the SARu; however this model was affected by the number of patch in each study. The power function showed a consistent positive effect of area size on bird richness (slope = 0.20). However, there was an absence of significant relation between environmental and methodological variables with the slope and fit of the SARu. Overall, although our results showed that urbanization promotes bird communities with high bird abundance but low bird richness, these patterns are dependent on biological, methodological and socioeconomic characteristics. Considering urban green areas, management actions that promote large green urban environments will have positive effects on bird richness worldwide.