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TÍTULO

A NECTAR OASIS FOR URBAN BATS: POLLINATION BIOLOGY AND POLLEN FLOW OF THE ORNAMENTAL CRESCENTIA CUJETE (BIGNONIACEAE)

Resumo

The urban environment presents a series of constraints to the fauna dwelling within it, such as reduced or unpredictable resource availability. Nectar bats are a potentially impacted group in terms of quality and quantity of feeding sites due to the low abundance of bat-pollinated species used in the planned ornamental flora. Crescentia cujete, however, is a model bat-pollinated Bignoniaceae that is often used as an ornamental species in Brazilian urban areas. We aimed to assess which species of urban bats benefit from the presence of C. cujete in the campus of the Federal University of Pernambuco, Recife, northeastern Brazil, how bats interact with the species, and what is their role as its pollinators and pollen dispersers. We examined the behavior and identity of floral visitors to C. cujete flowers, while assessing its phenology and resource dynamics. Additionally, we employed fluorescent dyes as pollen analogs to infer the special patterns of pollen dispersal by bats in the region. Crescentia cujete showed a year-round flowering pattern, with no significant seasonality (Z = 1.901; p = 0.149). Its large flowers open at twilight (ca. 06:00 pm) and secrete copious amounts of diluted nectar, with an average of 415.3 μl per flower per night at a 17.3% sugar concentration. The Flowers of C. cujete were visited exclusively by the Pallas long-tongued bat Glossophaga soricina (Phyllostomidae: Glossophaginae), a common city-dweller throughout Latin America. Visiting frequency was intense, with 5- to 15-minute intervals between visiting bouts, in which bats accessed all flowers from the observed individual, and with peaks shortly after anthesis (6:00 pm to 7:30 pm). During the first three hours of anthesis, individual flowers would frequently reach up to 80 bat visits. Despite frequent visitation, pollen flow surveys showed that dispersal occurred at an average range of 75 m and not beyond 144 m, while consistently decreasing in function of the distance between individuals (r2=0.133; p = 0.001). From 213 flow events, only 18.3% occurred between individuals. The intensity of pollen flow between flowers of the same individual was much more frequent and intense than that between individuals (Mann-Whitney Z = 5.523, p < 0.0001). Our results suggest overexploitation of floral resources from C. cujete by urban bats. Moreover, its continuous flowering and copious nectar offering may become a reliable resource in an environment generally lacking bat-pollinated plants, which, when present, frequently show phenological seasonality. This can be important information during urban planning, aiming specifically to the conservation of this pollinator guild and the ecosystem services linked to it. However, the competition for resources seems to have resulted in an uncommonly strong territorial behavior of bats, which limited dispersal distances. This may have an impact on plant reproduction and can be of conservational concern, especially if extrapolated to plant species within natural remnants segregated by urban matrices, which is an increasingly common scenario in tropical ecosystems.

Palavras-chave

Fluorescent dyes, Glossophaga soricina, phenology, pollen dispersal, urban ecosystems.

Financiamento

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), grant numbers: U.M.D. - 138381/2016; S.A.L. - 106160/

2017-6; I.C.M. -  311021/2014-0 and 459485/2014-8.