The role of the urban landscape on species with contrasting dispersal ability: Insights from greening plans for Barcelona

With the expansion of urban areas, promoting urban biodiversity is now a priority. Many municipalities are implementing greening strategies to improve and increase green space within city boundaries. The effectiveness of these strategies, while rarely assessed, likely depends on the landscape and on relevant species intrinsic traits such as dispersal ability. Using a spatially explicit individual-based model, we evaluated the effect of the urban landscape on the projected distribution of three butterfly species with contrasting dispersal abilities, and assessed the effectiveness of the Barcelona greening strategy as a case study. Species distribution (in terms of patch occupancy) and effectiveness (in terms of population size and number of occupied gardens) were analysed using generalised linear models. The percentage of (semi)natural source area around each urban green space (garden hereafter) was the most important variable for the distribution of all three types of species, followed by the percentage of neighbouring gardens and by the garden carrying capacity, although the effect of neighbouring gardens was negative in the early phase of colonisation. The planned Barcelona greening strategy increased the number of gardens occupied by high and medium, but not by low dispersive species. Increasing the carrying capacity of the gardens improved colonisation for all three species types. While the best strategies can be context dependent, our results indicated that increasing garden area might be more effective in the long term but it can be overridden by garden capacity in the short term, especially if there are constraints to increasing garden area.