Authors: Török, Edina; Riho, Marja;Batáry, Péter;

Human population growth leads to globalization and an increase in urban areas. It is not clear how urbanization affects different insect pollinator groups. For instance, urban areas can be an ecological trap for pollinators because of habitat degradation (e.g. increase in concrete surface areas) and pollution. However, recent literature shows different various, even contradictory results, as urban environments can provide additional food resources, fewer predators, and further nesting places in buildings. We performed a meta-analysis to increase our understanding of urbanization effect on wild pollinators. We extracted 131 effect sizes from 58 studies for abundance and 114 effect sizes from 51 studies for species richness. We used pollinator taxonomical groups, urban-suburban-rural gradients, global urban heat island data, and river (as a natural element) presence as moderators. Pollinator abundance and species richness significantly decreased with increasing urbanization, a clear sign of biotic homogenization. Temperature difference (heat-island effect) between urban and suburban areas of more than 2°C significantly amplified the negative effect of urbanization on pollinators diversity. Cities with rivers have a lower urbanization effect. For pollinator conservation in urban areas, there is a need to restore and maintain natural and green areas in cities, which can alleviate the heat island effect.