Primary productivity and habitat diversity predict bird species richness and composition along urban-rural gradients of central Argentina

Abstract

Although the role of primary productivity and habitat diversity in determining patterns of species richness and composition have been explored in urban areas, they have been rarely analysed in the context of species-energy relationships (SERs). Therefore, two hypotheses related to SERs were tested in bird communities: the more individuals hypothesis (MIH) and the niche position hypothesis (NPH). The MIH states that sites with more energy availability have more individuals, with extinction probability decreased thereby increasing the species richness. The NPH predicts that the amount of rare resources increases at sites with greater energy availability and environmental heterogeneity, increasing species richness. Birds were counted along three urban-rural gradients in the Pampas region of Argentina during the breeding season. Productive energy was measured using the NDVI and environmental heterogeneity via the diversity of different substrates. Although there was a positive relationship between bird richness and abundance, there was no positive relationship between bird abundance and primary productivity. Bird richness showed a positive relationship with habitat diversity and primary productivity, supporting the NPH. The exclusion of exotic species resulted in a tight relationship between bird richness and abundance, and between bird abundance and primary productivity, supporting the MIH. Bird composition varied with changes in habitat diversity and primary productivity. Path analysis revealed that habitat diversity increased bird richness through an increase of bird abundance. The NPH was the most consistent to predict bird richness along urban-rural gradients. Therefore, it is necessary to create areas with greater amount and variety of vegetation to increase bird richness.