Pollinator-mediated connectivity in fragmented urban green spaces—tracking pollen grain movements in the city center

Cities are expanding rapidly and emerging as complex ecosystems. This expansion of urbanized areas has resulted in the alteration and fragmentation of several natural habitats. Recent studies have shown that cities support a significant level of biodiversity. This unexpected role of cities holds promise for advancing knowledge of urban ecosystems and promoting their conservation. In particular, the connectivity of plant populations through pollen transfer is crucial for the long-term persistence of insect-pollinated plant species. In this study, we tracked pollen movement areas in four isolated patches of urban greenery in urbanized area using quantum dots. We studied Fritillaria imperialis (spring) and Hemerocallis sp. (mid-summer). Our research revealed frequent pollen transfer between small, isolated flowering patches, even when these locations were not connected by green corridors. Common elements found in urban ecosystems, such as streets, trails, and pavements, do not stop the dispersion of pollen grains. Moreover, the migration pathways of pollen grains vary for each species according to different factors. For F. imperialis, we identified the proportion of green areas in proximity to the study location as a key factor in shaping pollen transfer. For Hemerocallis, we discovered that the proportion of green areas, the distance between study sites, and the frequency of pollinator visits are influential factors. Our study demonstrates that small isolated plant populations exchange pollen due to pollinator movement, indicating that these small populations may serve as stepping stones for pollinators among larger populations.