Rural–urban gradient and land use in a millenary metropolis: how urbanization affects avian functional groups and the role of old villas in bird assemblage patterning

Abstract

Abstract. Urbanization generally leads to a complex environmental gradient, ranging from almost undisturbed natural areas to highly modified urban landscapes. Here we analyse the effects of a rural-urban gradient on breeding bird communities and functional species groups in remnant natural and semi-natural areas of Rome. A total of 69 breeding bird species were found in the study area. Species richness decreased with increasing urbanization at two spatial scales: the point count station and the landscape scales. Evenness showed a negative trend from periphery to city centre, whereas for dominant species the opposite was true. Functional species groups responded to the urbanization gradient with functional group-specific patterns. Those groups linked to open habitats (nesting and habitat functional groups) decreased in abundance along the rural-urban gradient, whereas those associated with forests exhibited a mixed trend. Generalist species' occurrence increased with urbanization. As for predators and granivorous species, we found a negative relationship with urbanization whereas for omnivorous species the opposite trend was true. The distribution of old villas (largesized remnant green areas) in the inner city areas influenced species composition along the studied gradient, usually showing higher species richness than surrounding fragments. Agricultural areas hosted richer and better balanced bird assemblages in respect to those found in urban and forested areas. Our findings proved that an urban gradient plays a major role in structuring bird communities, although the extent and distribution of land use categories was another factor that influenced avian assemblages. The presence of historical villas also influenced bird assemblages, making it possible to preserve high bird diversity even in inner city-areas.

Environmental filtering of avian communities along a rural‐to‐urban gradient in Greater Washington, D.C., USA

“…For example, despite our expectations that omnivores and ground‐foraging species are positively associated with urbanization, the estimated total abundances of these guilds declined with increasing impervious surface (Vignoli et al. ). While we expected granivores to be positively affiliated with urban environments, the null model that excluded impervious surface received equivalent model support to the model which showed an increase in the estimated abundance with increasing impervious surface for this guild.…”

“…, Vignoli et al. ). Moreover, the associations between life history guilds and habitat characteristics may vary widely among biogeographic regions (Hansen and Urban ); thus, guild‐specific measures of environmental filtering in response to urbanization have often produced conflicting results (Evans et al.…”

“…); (2) functional diversity, as expressed by the diversity of life history guilds, declines along the rural‐to‐urban gradient, controlling for species richness (Schütz and Schulze ); and (3) species with life history traits associated with specialist dietary habits and foraging behaviors (e.g., insectivores and foliage‐gleaners, Beissinger and Osborne ), nesting habits (e.g., cavity‐ and ground‐nesting species; Blewett and Marzluff , Vignoli et al. ), and long‐distance migration are more sensitive to urbanization than other species within the regional species pool (e.g., Kark et al. , Fig.…”

Perda de diversidade taxonômica e funcional de aves em área urbana no sul do Brasil

“…Considerando apenas o substrato de nidificação, a diversidade funcional se mostrou a mais afetada pela intensidade de urbanização, mesmo resultado obtido por Vignoli et al (2013). Uma vez que diminuem as possibilidades de locais para nidificação (Lim & Sodhi, 2004), espécies que fazem ninhos em vegetação, em locais baixos e no solo foram mais abundantes em locais menos urbanizados e positivamente relacionados ao número de árvores, à proporção de áreas abertas e à presença de ambientes aquáticos.…”

“…A onivoria foi o atributo relacionado à dieta predominante em áreas mais urbanizadas, resultado comum encontrado em outros estudos (tais como Lancaster & Rees, 1979;Clergeau et al, 1998;Jokimäki & Suhonen, 1998;Kark et al, 2007;Croci et al, 2008;Conole & Kirkpatrick, 2011;Vignoli et al, 2013). As espécies onívoras apresentam maior vantagem nas cidades, onde existe uma maior variedade de itens, já que os humanos produzem estes recursos, inclusive o lixo (Clergeau et al, 1998).…”