Abstract
Urbanization fragments, isolates or eliminates natural habitats, and changes the structure and composition of assemblages living in the remaining natural fragments. Knowing assembly rules is necessary to support and/or maintain biodiversity in urban habitats. We hypothesized that forest communities in rural sites are organized by environmental filtering, but this may be changed by urbanization, and in the suburban and urban forest fragments replaced by randomly organized assemblages, influenced by the colonization of species from the surrounding matrix. Evaluating simultaneously the functional and phylogenetic relationships of co-existing species, we showed that at the rural sites, co-existing ground beetle species were functionally and phylogenetically more similar than expected by chance, indicating that environmental filtering was the likely process structuring these communities. Contrary to this, in urban and suburban sites, the co-occurring species were functionally and phylogenetically not different from the null model, indicating randomly structured assemblages. According to our findings, changes in environmental and habitat characteristics accompanied by urbanization lead to assemblages of randomly colonized species from the surrounding matrix, threatening proper ecosystem functioning. To reassemble stochastically assembled species of urban and suburban fragments to structured, properly functioning communities, appropriate management strategies are needed which simultaneously consider recreational, economic and conservation criteria.
Highlights
Anthropogenic activities, like farming, forestry and urbanization are increasing worldwide, and cause significant changes to biodiversity[1]
We found that ground beetle communities organized previously by environmental filtering cannot remain intact by urbanization, and are replaced by randomly organised assemblages, influenced by colonization of species from the surrounding matrix in suburban and urban habitats
Standardized effect sizes were positively correlated with the position along the rural-suburban-urban gradient for all values of the phylogenetic-weighting parameter (a), showing that environmental filtering in the rural sites strongly selected for communities of functionally and phylogenetically similar species
Summary
Anthropogenic activities, like farming, forestry and urbanization are increasing worldwide, and cause significant changes to biodiversity[1]. Urbanization involves profound modification in deposition of pollutants[6], in environmental parameters (temperature[7], humidity8), in the amount of nutrients (carbon[9], nitrogen10), and in several biological processes (e.g. leaf -litter decomposition[10], gene flow[5]). These modifications cause changes in the structure and composition of biotic communities[11,12]. Earlier papers addressing the effects of changes in environmental and habitat parameters accompanied by urbanization on biotic communities have usually evaluated the abundance and/or taxonomic diversity (species richness and/or species diversity)[14]. Several recent urban studies tried to deepen such understanding using functional[21,22] or phylogenetic approaches[23,24]
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