Habitat fragmentation is a leading threat to biodiversity that can impact existing plant populations as well as future recruitment by affecting pollinator community structure and pollination rates. Previous research suggests that self-incompatible plant species should be most susceptible to the effects of fragmentation. To better understand the relationship between habitat fragmentation and pollinator-mediated reproductive success, I contrasted the pollinator communities and floral visitation rates of kanawao (Broussaisia arguta , Hydrangeaceae), a common dioecious species, in a naturally fragmented forest and a nearby continuous forest on the Island of Hawai'i over two flowering seasons. I also estimated plant reproductive success across the system through quantification of seed germination (2010) and pollen tube density (2011) of open-pollinated flowers, and estimated the strength of pollen limitation through supplemental hand-pollinations with excess pollen. In 2010, honeybees were the dominant pollinators in the forest and nearly absent from the fragments where moths were the principal pollinators; pollinator visitation rates were low and not different between fragments and continuous forest. In 2011, honeybees were absent in the forest, but moths were again the dominant pollinator in the fragments. Overall visitation rates were lower than in 2010 and the rate of visitation was higher in the fragments. Seed germination results in 2010 showed that plants in medium-sized fragments had lower reproductive success than plants in the small and large fragments, which had seed germination rates similar to those of continuous-forest plants. In contrast, pollen tube densities were intermediate to high for all maternal plants in the fragments in 2011. Pollen limitation was common across the study system, though with considerable variation among plants. In conclusion, fragmentation appears to have impacted kanawao by altering pollinator communities with considerable variation in the visitation rates between the years. The two measures of reproductive success—seed germination in 2010 and pollen tubes in 2011—conflict with one another, which may by the result of an observed drought effect in 2010 or low pollinator efficiency in the medium-sized fragments. Alternatively, pollen tubes may not be an adequate surrogate for reproductive success for kanawao. The spatial and temporal variation in pollinator communities observed in this study demonstrate the need for longer-term studies and the need to understand pollinator movements in fragmented landscapes.
|Commitee:||Giardina, Christian, Price, Jonathan|
|School:||University of Hawai'i at Hilo|
|Department:||Tropical Conservation Biology & Environmental Science|
|School Location:||United States -- Hawaii|
|Source:||MAI 50/06M, Masters Abstracts International|
|Subjects:||Plant biology, Ecology|
|Keywords:||Broussaisia arguta, Forest ecology, Habitat fragmentation, Hawaii, Pollination|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be