Seed dispersal mutualisms, including seed dispersal by ants, are critical to the assembly of communities and the function of ecosystems. However, the consequences of human-caused global change factors, such as habitat fragmentation and climate change, for the future of these mutualisms are not fully understood. My dissertation consists of five chapters that investigated the effects of habitat fragmentation and climate change on ants and their seed dispersal mutualisms. Chapter 1 is an introduction that provides background information on habitat fragmentation and anthropogenic climate change and their impacts on biodiversity. In Chapter 1, I also introduce my study system of ant-mediated seed dispersal mutualisms, myrmecochory. My next two chapters (Chapters 2 and 3) explored the effects of reconnecting fragmented habitat patches with corridors in restored longleaf pine savanna systems in South Carolina. We used a landscape scale experiment to investigate how reducing isolation affects the assembly of ant communities over time (Chapter 2) and seed dispersal of the myrmecochorous forb, Piriqueta cistoides (Chapter 3). For Chapter 2, we found evidence that both habitat connectivity and edge effects underly the effects of corridors on ant communities over time. We found that connected patches accumulated ant species faster than isolated patches over time suggesting that corridors function by facilitating colonization. We also found evidence that edge effects play a role with greater ant functional group diversity in patches with higher edge than patches with lower edge amounts. For Chapter 3, we also found evidence of corridor and edge effects with ants dispersing seeds of P. cistoides longer distances in patches connected via corridors than isolated patches, but only in the center of patches. In Chapter 4, we investigated the effects of predicted climate change scenarios for seed dispersal mutualisms in eastern deciduous forests. For this chapter, we conducted a mesocosm experiment in which we crossed temperature with altered precipitation magnitude and frequency. Our mesocosms contained a common spring ephemeral wildflower, Sanguinaria canadensis, and whole colonies of their mutualist seed disperser, Aphaenogaster rudis. This design allowed us to collect high-resolution data on how ants interacted with seeds under different climate change scenarios that incorporated warming temperatures and altered precipitation. We found that warming effects depended on the precipitation treatment with negative effects of warming on the collection of seeds by ants under historical precipitation regimes and positive effects of warming under simulated precipitation conditions altered under predicted climate change. Finally, Chapter 5 describes my general conclusions from this body of work. Taken together, the research making up my dissertation provides valuable insights into how changing environmental conditions under habitat fragmentation and climate change may alter ant seed dispersal mutualisms. Importantly, we often found that the impacts of global change were context dependent and that our experiments were important tools in disentangling that context dependency. Further, this work demonstrates the value of understanding the basic ecology of the interactions among organisms. Understanding the natural history of organisms across changing environmental conditions will benefit the ways in which we conserve and restore ecosystems in a fragmented and warmer world. / Doctor of Philosophy / Most plants and animals engage in mutualisms, which are interactions between species in which both benefit from interacting with each other. The focus of this dissertation are the impacts of human-caused environmental change on the mutualism between ants and plants in which ants move a plant's seeds. The dispersal of ant-dispersed plants is considered a mutualism because the ants receive a food reward in the form of a fat- and protein-rich appendage that grows on the seed while the seeds of the plant get moved to a better location for germination. The mutualisms between ants and the plants they disperse are critical to how plants are distributed in many ecosystems, yet the consequences of human-caused environmental change, such as habitat loss and climate change, for these mutualisms are not fully understood. My dissertation consists of five chapters that investigated the effects of habitat fragmentation (the breaking apart of larger habitats into smaller, more isolated patches as a result of habitat loss) and climate change on ants and their seed dispersal mutualisms. My first chapter introduces background on the consequences of habitat fragmentation and climate change on organisms, ant seed dispersal mutualisms, and the potential effects of altered environmental conditions on seed dispersal by ants. My second two chapters (Chapters 2 and 3) explored the effects of reconnecting isolated habitat patches with habitat corridors (strips of habitat restored between the isolated habitat patches). In restored longleaf pine savanna systems in South Carolina, we used a long-term, landscape scale experiment to study how increasing connectivity and changing the shape of habitats via corridors affects ant community diversity over time (Chapter 2) and seed dispersal of the ant-dispersed plant, pitted stripeseed (Piriqueta cistoides) (Chapter 3). For Chapter 2, we found both habitat connectivity and patch shape effects underly the effects of corridors on ant community over time. We found that connected patches accumulated ant species faster than isolated patch types which suggests that corridors may function by facilitating colonization into the patches they connect. We also found evidence that patch shape plays a role in supporting greater ant functional group diversity in patches with greater perimeter (more edge habitat) than patches with less perimeter (less edge habitat). We found that ants in patches with more edge habitat represented a greater number of functional groups, which are categories that describe the roles ants play in ecosystems. For Chapter 3, we also found evidence of corridor and patch shape effects with ants dispersing seeds of pitted stripeseed longer distances in patches connected via corridors than isolated patches, but only in the center of patches. In Chapter 4, we investigated the effects of predicted climate change scenarios on seed dispersal mutualisms in eastern deciduous forests. For this chapter, we conducted an experiment in which we crossed temperature with altered precipitation in mesocosms, which are small, simulated ecosystems that allowed us to investigate the effects of warming and altered precipitation in a controlled setting. Our mesocosms contained a common spring ephemeral wildflower, bloodroot (Sanguinaria canadensis), and whole colonies of their mutualist seed disperser, winnow ants (Aphaenogaster rudis). We found that the effects of warming temperatures depended on the precipitation treatment. Warming had a negative effect on the number of seeds collected by ants under historical precipitation regimes, but a positive effect under simulated precipitation conditions under predicted climate change (higher in magnitude and lower in frequency). Finally, Chapter 5 describes my general conclusions from this body of work. Taken together, the research making up my dissertation provides valuable insights into how changing environmental conditions under habitat fragmentation and climate change may alter ant seed dispersal mutualisms. Importantly, we often found that the impacts of global change were context dependent. Our experiments were important tools in disentangling that context dependency. Further, this work demonstrates the value of understanding the basic ecology of the interactions among organisms. Understanding the natural history of organisms, especially their responses to changing environmental conditions, will ultimately benefit the ways in which we conserve and restore ecosystems in a fragmented and warmer world.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119033 |
| Date | 20 May 2024 |
| Creators | Burt, Melissa Ann |
| Contributors | Biological Sciences, Whitehead, Susan, Mims, Meryl C., Reid, John Leighton, Brown, Bryan Lyle |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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