The effect of changes in pollinator community composition following Hurricanes Frances and Jeanne (2004) on the pollination dynamics of white mangrove (Laguncularia racemosa)

Background/Question/Methods

Hurricanes can directly and indirectly affect the reproductive ecology of coastal plant species such as white mangrove (Combretaceae: Laguncularia racemosa), a major component of Neotropical mangrove forests.  Hurricanes could indirectly affect the reproductive success of white mangrove, an insect-pollinated, self-compatible plant species, by altering the insect pollinator community composition and species abundances.  Depending on the population, 15-20 different insect pollinator species are known to visit white mangrove in these populations. The insect species have different foraging behaviors, which can affect the plant mating system by altering the frequency of geitonogamous pollination. White mangrove is also capable of self-pollination, so changes in pollinator floral visitation rates can also alter the frequency of autogamous pollination. In this study, I compared the insect pollinator community composition, floral visitation rates and foraging bout lengths of floral visitors to white mangrove in three populations in east-central Florida (USA), before and after Hurricanes Frances and Jeanne (2004). The two hurricanes made landfall in Florida three weeks apart; both landfalls were within 60 miles of the three populations. Pollinator observations performed during July 2001-2003 were compared with observational data collected during July 2005 and July 2009.

Results/Conclusions

While the mean floral visitation rates to white mangrove differed significantly between populations in all years, the mean visitation rates decreased significantly in all populations between 2003 and 2005, suggesting that pollination services were disrupted by the hurricanes. Further, mean visitation rates increased in all populations between 2005 and 2009, and significantly increased in two of the three populations, which suggests that pollination services to white mangrove are recovering. However, visitation rates in two of the three populations in 2009 were still lower than visitation rates in 2003, prior to the hurricanes.  Insect pollinator species richness declined continuously between 2003 and 2009 in all populations. Species that were not lost declined in abundance between 2003 and 2005, but by 2009, several species had increased abundance relative to 2005. In 2009, Apis mellifera had increased abundance relative to 2003, prior to the hurricanes; Apis mellifera was a dominant species in all populations before the hurricanes (23-51% of visitors), but by 2009 represented 44-87% of visitors to white mangrove. Differences in floral visitation rates and the patterns of insect foraging behaviors since the hurricanes may have resulted in an increase in selfing in this self-compatible, self-pollinating plant species.