Short-distance pollen dispersal by bats in an urban setting: monitoring the movement of a vertebrate pollinator through fluorescent dyes

Pollen dispersal in tropical seed plants is established mainly by biotic vectors, both in intact and fragmented environments. In urban landscapes, the segregation of natural remnants by an artificial matrix can reduce pollinator foraging efficiency. It is unknown how nectarivorous bats, regarded as long-distance pollen dispersers, respond to such habitat structure combined with city-related factors. Here, we investigated the pollen dispersal pattern between spatially segregated individuals of the bat-pollinated Bignoniaceae Crescentia cujete within an urban environment. From 2015 to 2017, we assessed their spatiotemporal structure, breeding system and annual fruit set in order to relate these factors to the bat activity in the region. We employed fluorescent dyes as pollen analogues to infer the role of bats in pollen flow. Adding to the low density of individuals, we found a low daily flower emission and low flowering synchrony (S = 0,092), all of which are traits that favor outcrossing. Individuals were distributed in two distant groups (>600 m), with no occurrence of dye flow between them. In contrast, flow within the same individual was intense, which points toward bats’ territorial behavior. C. cujete is self-compatible, but not autogamous; therefore, despite few outcross events, bats could be ensuring the plant’s year-round fruit production mainly through self-pollination. Our findings show restricted bat foraging extent, which affects overall pollen dispersal distance and population connectivity. These results can be extrapolated to natural metapopulations inserted in an urban matrix and serve as a groundwork for studying directly the effect of city-related factors on pollinator behavior.