Urbanization filters woodpecker assemblages: Habitat specialization limits population abundance of dead wood dependent organisms in the urban landscape

Abstract

Although urban landscapes are regarded as unsuitable for dead wood dependent organisms, some species, including woodpeckers, commonly occur in cities. As the availability of trees and dead wood resources is a primary dimension of the habitat-niche for most woodpeckers, we hypothesized that increasing habitat specialization (decreasing habitat-niche-volume) would limit species abundance within an urban landscape. We surveyed the woodpecker assemblage in the urban landscape, and for seven species we quantified the habitat-niche relying on four dimensions (the availability of trees, snags, fallen logs and dead tree branches). Then, we analysed the habitat preferences and habitat-niche partitioning of the woodpecker assemblage. For each species, we calculated the habitat-niche-volume and tested whether this trait correlated with species abundance in the urban landscape. Woodpeckers selected habitats with a high availability of either trees or dead wood (especially dead tree branches). The habitat-niches partially overlapped, but varied between species in terms of the availability of trees, dead tree branches, snags or fallen logs. The habitat-niche-volume varied among species and was positively associated with species abundance in the urban landscape. The regional abundance of species, body size and relative brain size did not affect the abundance of urban woodpecker populations. Our study highlights that urbanization filters woodpecker assemblages by limiting habitat-specialists and promoting habitat-generalists. We suggest that the alteration of woodpecker assemblages in the urban landscape may have a cascading effect on entire assemblages of dead wood dependent organisms, including cavity-nesters, saproxylic insects and wood-decomposing fungi. Urban development, which limits dead wood resources, is therefore a serious threat to biodiversity, whereas sustainable management of urban green spaces, e.g. the preservation of dead wood, may mitigate biodiversity loss.