Invasive species and habitat destruction are considered to be the leading causes of biodiversity decline, signaling declining ecosystem health on a global scale. Ants (Formicidae) include some on the most widespread and impactful invasive species capable of establishing in high numbers in new habitats. The tropical grasslands of Indonesia are home to several invasive species of ants. Invasive ants are transported in shipped goods, causing many species to be of global concern. My dissertation explores ant communities in the grasslands of southeastern Indonesia. Communities are described for the first time with a special focus on the Tropical Fire Ant, Solenopsis geminata, which consumes grass seeds and can have negative ecological impacts in invaded areas. The first chapter describes grassland ant communities in both disturbed and undisturbed grasslands. The second chapter narrows in focus to describe the utilization of grass seeds as a food resource for S. geminata and the potential for spread of this invasive ant given an unlimited food supply. The third, and final, chapter describes competition between ant species at food resources. Solenopsis geminata competes with several native and introduced ant species. These interactions are analyzed and I report on the ability of invasive ants to dominate invaded habitats.
Chapter 1 includes a large-scale diversity survey across eight islands in and around Komodo National Park, Nusa Tenggara Timur, Indonesia. Invasive ants are able to disrupt native habitats and the communities of ants found in them. Land use plays a role in invasion as human-mediated disturbances facilitate the introduction of non-native species. Biogeography, land use, climate, and habitat structure help to shape local communities. We surveyed eight islands using pitfall trap transects. Transects were placed in undisturbed and disturbed grasslands. Data on ant species counts and identification was used to test four hypotheses related to species distribution and abundance. 1. Introduced species will have broader distributions than native species across space, habitat, and seasons. 2. Habitat structure (grass and trees) influences ground-dwelling ant species abundance, diversity, and composition. 3. Grassland disturbance is associated with an increase in introduced species richness and abundance. 4. Development (human-made landscape elements) and distance from a port (measures of connectivity) have a greater influence on diversity than island size. We found that introduced species are generally more numerous than native species, but that some introduced species present in the region were fairly restricted both spatially and numerically. Season and vegetation structure were related and influenced by land use. Differences are linked to differences in ant community compositions. In addition to differences related to habitat structure, species richness and diversity was influenced by the distance between the site and the port of Labuan Bajo.
The second chapter of my dissertation focuses on fire ant diets. The Tropical Fire Ant consumes large quantities of grass seeds. We described the diet of S. geminata in populations that inhabit grasslands and villages with comparisons to other ant species. Omnivorous ants are able to utilize a wide range of food resources, and this can enable invasion and even dominance in novel landscapes. Dietary specialization has evolved numerous times and can confer competitive advantages, optimal nutrition, and reduced cognitive needs in foraging. The Tropical Fire Ant, Solenopsis geminata, is a globally distributed invasive species. Solenopsis geminata, has evolved a major worker caste for seed milling and granivory while the species is largely a dietary generalist. Here we used stable isotope analyses and behavioral assays to describe dietary shifts in S. geminata during range expansion from villages into disturbed grassland. These methods were used to question the benefits and draw-backs of dietary specialization in range expansion across habitat types with seemingly unlimited seed resources. We analyzed δ13C and δ15N in four ant species in adjacent village, disturbed grassland, and undisturbed grassland habitats on one island in Nusa Tenggara Timur, Indonesia. Isotope analysis was coupled with behavioral assays that delineated preferences for some grasses over others. Seed-size was manipulated to assess the influence of a worker’s ability to move a seed relative to its attractiveness. Solenopsis geminata, shifts from a diet of animal-based foods and C3 plants in villages to a largely C4 grass seed-based diet in grasslands. Co-occurring ant species are within the same trophic level but show lower utilization of C4 plants in savannas. Solenopsis geminata, collects seeds from exotic grasses common in disturbed Indonesian grasslands at higher rates than larger seeds of native grasses. When the larger native seeds are cut to smaller sizes, they are collected at a higher rate. Foraging assays show that large seed size in native grasses may pose a barrier to seed consumption and expansion into undisturbed grasslands with otherwise similar structure and environmental conditions. (Abstract shortened by ProQuest.)
|Advisor:||Tsutsui, Neil D.|
|Commitee:||Fisher, Brian, Gillespie, Rosemary, Simms, Ellen|
|School:||University of California, Berkeley|
|Department:||Environmental Science, Policy, and Management|
|School Location:||United States -- California|
|Source:||DAI-B 80/08(E), Dissertation Abstracts International|
|Keywords:||Food resources, Grassland disturbance, Habitat structure, Human-made landscape elements, Komodo National Park, Measures of connectivity|
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