Species interactions in fig-wasp-ant community on Ficus benguetensis Merrill
Date Issued
2016
Date
2016
Author(s)
Lin, Shang-Yang
Abstract
The interaction between figs (Ficus spp.) and their pollinating fig wasp (Hymenoptera: Agaonidae) is one of the classic examples of obligate mutualism. However, the rewards that provided by the mutualistic partners to one another also attract amounts of species, ranging from the nonpollinating fig wasp to ants. This dissertation focuses on one dioecious Ficus species, F. benguetensis, explores the following issues: interactions between fig trees and fig wasps via fig phenology, as well as the impact of nonpollinating fig wasps and ants that might influence the stability of mutualism, and also the unknown mechanisms underlying defense against those exploiters. To understanding the fig phenology of F. benguetensis, which their pollinating wasps, Ceratosolen wui, rely on, I conducted a two-year survey on 17 trees (11 male and 6 female trees) of dieocious F. benguetensis in Xindian District, New Taipei City, Taiwan. I found F. benguetensis showed clear sexual difference between sexes, not only in the phenological patterns but also the positions that figs produce within one tree. Male continues fruiting mainly on the trunk, while female only produces figs in the suitable season and mainly on the twig. This difference could be the results of evolutionary response that provides a selective advantage by maintaining the pollinator population understory on male tree and facilitating the uptake by seed dispersers in canopy on female tree. Next, in order to quantify the impact of the nonpollinating fig wasps on the pollinators, I conducted bagging experiments in Fu-Yang Eco-Park. I manipulated the number of nonpollinators (0-5 individuals), Philotrypesis sp., to each fig and traced their developmental outcomes: complete growing to wasp-releasing phase, total numbers of emerged wasp, and the proportion of pollinating wasps. From 51 figs succeeded from bagging experiments, I found high density of Philotrypesis sp. did significantly increase the fig abortion rates and decrease the number of pollinators emerged. Then, from mathematic modeling, I found selective abortion of fig in early stage can serve as an alternative defensive mechanism by depressing the population of nonpollinating fig wasp and elevates the fitness of fig tree and their pollinating wasp. On the community of Ficus-wasps, ants were common attendants on fig trees. I have observed and collected 6253 ant individuals belonging to 13 species during two years survey in Xindian sampling area. The co-existed sympatric species were generally predicted to experience high levels of niche overlap and competition. I examined the spatial, temporal variation of ant communities, and also the inter-specific interactions and the effect of the food resource provided by fig tree. I found the ant abundance was positively associated with the temperature and the fig abundance. Correlations between fig abundance in different stages and ant abundance of each species could be reflecting their feeding habits. No species segregation pattern (i.e., interspecific competition) was detected in spatial analysis. It could be due to the absence of dominance and other factors related to resource, including resource accessibility, temporal variation and nature of the resources. I suggest that the coexistance of 13 ant species on F. benguetensis (no evidence of competition) was shaped by resource partitioning. Finally, to determine the role of ants played on the interaction between fig tree and the associated wasps, I conduct ant-exclusion experiments at Fu-Yang Eco Park. Comparing with control groups, I found that the proportion of pollinator during emerging phase was significantly drop, as well as the proportion of figs that successfully grows to wasp-releasing phase and the total numbers of emerged wasp. I also examine the preference of ant to fig at different stages and quantify the sugars (carbohydrates) deposited on the surface of figs to explore the chemical cues that induced this indirect defense. This dissertation explores previously unstudied aspects of the interactions between Ficus and associated hymenopteran insects, and provides important directions for future study of this ecologically important issue.
Subjects
Ficus benguetensis
Phenology
Ants
Interactions
Defense
Type
thesis
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