Urbanization as a causal agent of changes in mutualistic networks between bees and plants

Abstract

Urbanization is a major driver of species declines, which consequently also depletes the ecological interactions in which they participate. Plant-pollinator networks are the basis of ecosystem productivity, so the breakdown of these relationships has far-reaching ecological implications across multiple levels. Given the considerable potential of network studies to enhance our understanding of community ecology, here we aim to understand how urbanization affects plant-bee interactions and the topological structure of its network. Our study focused on a database of plant-bee interactions across ten sites within an urban gradient in southern Brazil. Data was collected by sampling bees in flowers with an entomological net over a period of ten months between 2017 and 2018. We examined two landscape variables associated with urbanization, vegetation cover and landscape diversity, to assess their influence on some species metrics (specialization – d'; among and within module connectivity – c and z) and network metrics (specialization – H₂'; modularity – ΔQ; nestedness – NODF). We found no relationship between the urbanization variables and the species metrics. On the other hand, sites with lower landscape diversity presented more specialized, modular and nestedness networks. In these sites, bees shared fewer resources, showed more compartmentalized networks, and had fewer interactions among specialized species. This study highlights the importance of considering landscape diversity and its role in shaping ecological networks, particularly in urbanized environments.