Date of Graduation

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Sagers, Cynthia L.

Committee Member

Etges, William J.

Second Committee Member

Huxel, Gary R.

Third Committee Member

Coley, Phyllis D.

Keywords

Biological sciences; Community structures; Neotropics; Plant-ant interactions; Stable isotopes

Abstract

Positive associations among species have contributed to the maintenance of biodiversity. These interactions are typically studied in pairwise fashion where two interacting organisms are the focus. This dissertation uses network theory to analyze positive plant-ant associations in three Neotropical forests. Obligate plant-ant mutualisms were used, where plants host the ants in domatia and provide food bodies while the ants protect the plants and can feed them. A network approach was used to depict all obligate plant-ant interactions within a community. The main questions asked at the community level were: 1) Do network structure and levels of specialization change geographically and, 2) What is the level of resilience of these associations if plants become extinct? I found that network structure and levels of specialization in three forests do not vary and that these associations are not resilient to host plant loss. In a second project I explored if traits of plants that host ants change between lowland and pre-montane tropical forests and if the differences impact plant-ant associations. Stable isotope analyses of plants and ants, in addition to plant measurements such as specific leaf area, trichome number, nitrogen per area and leaf thickness, were used. Plant traits differed by locale and by plant species. Location, but not ant species, affected herbivory. Finally, I explored the influence of ant metamorphosis, fat body and diet on stable isotope measurements. Stable isotope analysis is commonly used in ecological studies to determine trophic structure. However, the physiology of organisms analyzed can influence the results obtained. Fire ant colonies were used to explore if metamorphosis, fat body extraction and diet type impact isotopic signatures. Laboratory reared fire ant colonies were maintained with cricket and a sucrose diet. The addition of tuna to the diet was tested on additional colonies. Ant fats were dissolved using hexane-isopropanol or 95% ethanol. Metamorphosis had a significant effect only on δ15N and the availability of tuna produced further shifts in isotope ratios for all developmental stages. Treatment with organic solvents had no effect on δ13C, but resulted in enriched d15N values.

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