PARENT SESSION
Poster Session #51: Rare, Threatened, and Endangered Species.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Pollination biology of two Maui endemics: potential impacts of alien insects on plant reproduction.

FORSYTH, STACEY¹, ¹

ABSTRACT- Alien species can potentially disrupt interspecific interactions in ecological communities. I investigated the pollination biology of two Maui endemics in the Hawaiian Silversword Alliance, the threatened Haleakala silversword (Argyroxiphium sandwicense ssp. macrocephalum) and Dubautia menziesii, and examined the impact of alien ants and bees on plant reproduction. I measured self-incompatibility, the relative effectiveness of different insect visitors as pollinators, and the degree of pollen limitation in each plant species. I assessed alien Argentine ant (Linepithema humile) impacts on plant reproduction by comparing seed set in ant-infested and non-infested areas. A. sandwicense and D. menziesii are both strongly self-incompatible, and are dependent on insect-mediated pollen transfer. In both species, pollination is effected by diurnal visitors, primarily native yellow-faced bees (Hylaeus sp.). Honeybees are common visitors, but are not effective pollinators. A. sandwicense was pollen-limited in non-infested areas in both 1998 and 1999, while the more widespread D. menziesii was not pollen-limited in either year. In 1997, A. sandwicense was pollen-limited in ant-infested areas, but not in non-ant-infested areas. Reduced seed set in ant-infested areas may be due to reduced numbers of Hylaeus in these areas. Results suggest that alien insects may decrease seed set in native plants through competition with, or predation on, native pollinators

KEY WORDS: silversword, Argentine ant, alien species impacts, pollination