Pollen dispersal plays a key role in gene flow in plants, yet few studies have examined pollen dispersal in urban landscapes. Studies in rural systems suggest that pollen dispersal generally decreases as distance from the pollen source increases, with the exact pattern varying with species, pollen dispersal mechanism, and habitat. This distance effect has also been observed in the few studies conducted in urban habitats, but none of these studies have investigated pollen dispersal patterns in roof habitats. Therefore, we investigated pollen dispersal patterns in a wind-pollinated species (Amaranthus tuberculatus) and an insect-pollinated species (Solanum lycopersicum) in two ground sites and two roof sites in the New York metropolitan area. To determine pollen dispersal distance, we performed parentage assignment by genotyping parent plants and seeds. We used seed and fruit production as proxies for effective pollen dispersal in A. tuberculatus and S. lycopersicum, respectively. We hypothesized that 1) A. tuberculatus and S. lycopersicum pollen dispersal would decrease with increasing distance from the pollen source and 2) the effect of distance on A. tuberculatus and S. lycopersicum pollen dispersal would differ among sites.
Results/Conclusions
Results suggest that A. tuberculatus pollen dispersal decreases with increasing distance from the pollen source at both ground sites and both roof sites. We also found S. lycopersicum fruit production decreased with distance to the pollen source at both ground sites and both roof sites. The effect of distance on A. tuberculatus seed production did not clearly vary among sites. However, the effect of distance on S. lycopersicum fruit production varied among sites, with one site exhibiting both a larger response to the effect of distance and more fruit production at a given distance compared with the other three sites. Our study focused on the effect of distance on pollen dispersal, but we will also investigate the effect of plant size (i.e. biomass, height) on dispersal in future analyses. Although urban habitats are typically small, fragmented spaces with unique climatic challenges, our results agree with studies on pollen dispersal in non-urban areas (i.e. pollen dispersal decreases with increasing distance from the pollen source). This suggests that distance from the pollen source may be an important factor in effective pollen dispersal in a wide variety of habitats.