Hurricane Causes Resource and Pollination Limitation of Fruit Set in a Bird-Pollinated Shrub

Abstract

Hurricanes can strip leaves from plants and provide other stresses that can reduce resource availability for subsequent reproduction. In addition, hurricanes commonly reduce populations of bird pollinators. I measured both resource and pollination limitation of fruit set for Bahama Swamp-bush (Pavonia bahamensis) on San Salvador Island in the Bahamas before and after two seasons of hurricanes. Before the hurricanes in the winter flowering season in 1994–1995, fruit set of P. bahamensis was 100% for most shrubs. After a mild hurricane, in 1995–1996, fruit set was 48%. After the severe Hurricane Lili (Category 2) in 1996–1997, mean fruit set was only 11%. In both years after the hurricanes, lower fruit set reflected resource limitation. In 1996–1997 after Hurricane Lili, fruit set was severely reduced an additional 74% by pollination limitation. Pollination limitation was caused by declines of the two bird pollinators, Bananaquits and Bahama Woodstars. In 1994–1995, both species were frequent visitors to flowers, but in 1996–1997 these birds were rarely seen on the island. A concurrent mist-netting study indicated that Bananaquit populations were decimated after Hurricane Lili in 1996. Nectar removal was virtually absent, and pollen deposition on stigmas was low. In 1994–1995, 98% of the stigmas had received pollen by the end of floral life. In contrast, in 1996–1997, 51% of the flowers had received no pollen, supporting the conclusion that pollination limitation of fruit set was strong. There was no compensatory pollination by other pollinators, either other bird species or insects. These results indicate that severe hurricanes can affect fruit set directly through resource limitation and indirectly through reducing bird pollinators and causing pollination limitation of fruit set. Reduced fruit set after a hurricane could be especially disadvantageous because hurricanes can create sites for plant recruitment. Although resource limitation of fruit set may affect many plant species, bird-pollinated species may be faced with a double jeopardy of resource limitation of fruit set and pollination limitation of fruit set. Whether this disadvantage affects the recruitment of bird-pollinated plants after hurricanes or their adaptations for recruiting after hurricanes remains to be examined.