Seed dispersal in urban green space - Does the rook Corvus frugilegus L. contribute to urban flora homogenization?

The role of human-independent dispersal vectors in the structuring of urban flora is hardly known. Our goal was to evaluate the role and scale of endozoochorous seed dispersal mediated by the rook into habitats located in 11 cities of eastern Poland. This bird is a frequent user of anthropogenic food sources: agricultural fields (outside the cities) and garbage cans and refuse dumps (inside the cities). We wanted to: (i) assess the seed pool dispersed by the rook during wintering, when the bird forms huge winter roosts in the centre of cities, and (ii) evaluate if the rook-mediated dispersal may cause homogenization of vegetation at the sites where seeds were deposited. We found 2257 seeds belonging to 60 taxa in 1008 regurgitation pellets; the proportion of archaeophytes in pellets was significantly higher than in vegetation under roosts and it was negatively correlated with city size. On the basis of the Jaccard index we can conclude that the dispersed seed pool is more homogenous than stabilized vegetation in sites where pellets were deposited, but because of the high participation of weeds and ruderal species in pellets, the bird can facilitate the transfer of these groups of species into the cities. Plant and animal dispersers interactions should be further studied and taken into consideration during the planning and management of urban green space, which is claimed to be the most important habitat type for conservation of biodiversity within modern cities. It is especially important in the case of abundant animals forming huge concentrations in the urban landscape because of their high potential impact on vegetation composition at the local scale. (C) 2013 Elsevier GmbH. All rights reserved.