Effects of urbanization on plant-animal mutualistic interactions: how do network structure and diversity of interacting partners respond to urban areas?

Abstract

The expansion of urbanization worldwide increases the importance of the management of urban green areas to preserve ecosystem services derived from mutualistic plant-animal interactions. While interactions in urban areas are generally understudied, even less is known in tropical regions. Therefore, the objective of this thesis is to evaluate how mutualistic interactions between plants and animals, and distinct components of diversity (taxonomic, functional, and phylogenetic) of these groups respond to urban landscapes. Specifically, I aimed to (i) evaluate how the urbanization characteristics of different cities around the world affect the occurrence of frugivorous birds; (ii) review studies on the effects of urbanization on mutualistic plant-frugivorous animal interactions in tropical urban areas; and (iii) evaluate how the structure of frugivorous bird-plant interaction networks, and the diversity of interacting species varied among green areas under different landscape contexts in the city of Campo Grande-Brazil. Through the literature review we showed that: (i) most populous cities, recently founded, and at low latitudes harbor a greater richness of obligate and partial frugivores. Furthermore, we showed that (ii) exotic fruits are an important portion of the diet of frugivores, which present a great overlap in the use of resources in tropical urban areas. Finally, (iii) by testing the effects of urbanization empirically we show that landscapes covered by trees and shrubs isolated on impermeable surface matrices positively influence measures of diversity of species in the networks. These, in turn, influence the modularity (partition in the use of resources). Based on the results found across the three chapters, we suggest management actions in urban areas to improve the maintenance of interactions between plants and frugivorous birds. Specifically, we recommend (i) planting native plants to reduce the use, and consequently, the spread of exotic fruits through their consumption by these birds, (ii) considering plants’ fruiting phenology to ensure resources are available throughout the year, and (iii) creating habitat patches where wild fauna can take refuge in green areas. Furthermore, filling green areas with plants that have different functional characteristics (such as large and small fruits, tall and small plants) to contribute to a greater partition in the use of resources between species. Finally, the results suggest that green infrastructure is valuable for preserving frugivorous species, especially in tropical cities that retain high species diversity due to general biogeographical patterns, and in recently founded cities where afforestation of green areas is encouraged.