Urbanization of seed dispersal networks

Rapid urban expansion is affecting the composition of wild communities and creating novel ecosystems worldwide. Seed dispersal is key for ecosystem persistence, particularly in fragmented landscapes. However, generalizations regarding the impacts of urbanization are still difficult due to the lack of studies encompassing the urban matrix. We examined the seed dispersal networks in natural forests and urban areas in Tenerife Island to explore the effects of urbanization on seed dispersal. For 1 year, we observed frugivory events and identified seeds in animal feces in natural forests and urban areas of the island. We also conducted transect surveys in each area to assess the abundance of fleshy fruits and frugivorous animals. We identified 150 interactions between 83 plant and 18 animal species in the forest and 89 interactions between 41 plant and 9 animal species in urban areas. The urban matrix supported half the species richness of fleshy-fruited plants and frugivorous animals relative to the forest. Urbanization simplified seed dispersal networks, reducing interaction diversity. Novel interactions dominated the urban seed dispersal network, where non-native plants were highly used by native frugivores, accounting for 61% of the interactions (vs. 15% in the forest). Eight frugivore species (42% of the frugivores) likely maintained the functional connectivity between these habitats, potentially facilitating the spread of non-native species from urban areas (where non-native species are more common) into the forests due to their generalist and flexible diets. Six frugivorous species (32%) completely avoided urban areas, which acted as barriers to dispersal, likely hindering the dispersal of many plants across urban landscapes. Our results underscore the importance of promoting the use of native plants as ornamentals, enhancing habitat connectivity between forests and urban areas, and preventing the introduction of non-native fleshy-fruited plants. Ultimately, these findings highlight the need for sustainable urban planning and active stakeholder engagement to protect the seed dispersal service.