Bird community composition patterns in urban parks of Madrid: The role of age, size and isolation

This study intends to assess the influence of fragment age, size and isolat ion (from the regional species pool) on bird community composition patterns in urban parks in Madrid, and the role of local and regional factors on co mmunity structure. Park age was a good indicator of habitat complexity. Par k age and area accounted for 62% of the variability in species richness, bu t two measures of isolation from the regional species pool were not include d as significant: factors. Species composition in urban parks showed a high degree of nestedness, which was associated with park age and area, but not with two measures of isolation from the regional species pool. The degree of nestedness increased with park age; the distribution of species varying from nested in old and mature parks to random in young parks. The incidence (% of species occurrence in parks) in young parks was correlated with regi onal densities, whereas in mature and old parks the incidence was correlate d with local densities. In this urban landscape, species composition appear s to be regulated by local factors (particularly in mature and old parks), such that species accumulate in an orderly (not random) fashion in relation to park age and area. Regional influences seem to be more pronounced only in young parks, which are mainly colonized by species from the regional spe cies pool.