Hossie, Thomas

Measuring biodiversity has become increasingly complex as biologists and ecologists have gradually learned more about how biotic systems are structured and interact. Given the wide range of tools, techniques and approaches now in use to quantify biological diversity, it is useful to consider different "dimensions of diversity" to classify these measurements and provide context for their interpretation. Even within the genetic dimension of diversity alone, recent improvements in theory, technology, and statistics has generated several approaches which can provide distinct insights into natural systems. In this thesis, I use multiple "axes of diversity" to subdivide the dimension of genetic diversity to better understand a complex ecological system - the unisexual Ambystoma complex on Pelee Island, Ontario. By focusing on the genomotype axis, I found that the composition of local unisexual Ambystoma assemblages generally reflects the current relative abundance of the local sexual host populations. This suggests that sexual hosts can be thought of as a keystone species for the complex not only because they are required for unisexual Ambystoma to reproduce, but also because their relative abundance governs the composition of entire unisexual Ambystoma assemblages. Comparatively, when assessing the lineage axis of genetic diversity, unisexual Ambystoma assemblage diversity patterns primarily reflected historic landscape structure, and spatial patterns of increased lineage richness were linked to areas where both potential hosts were locally available (currently or historically). Thus, while both of the investigated axes of diversity are forms of genetic diversity, each revealed distinct factors that have shaped contemporary diversity patterns across the landscape operating at different spatial and temporal scales. Critically, our understanding of complex ecological systems is likely to be broadened by including additional axes of diversity (e.g., allelic, loci, or chromosomal structure axes), and such investigations are not limited to clonal hybrid systems. Overall, this work illustrates the importance of combining insights from distinct conceptual and analytical toolkits to generate a comprehensive understanding of the factors which have shaped the patterns of diversity we observe today.

Author Keywords: Biological diversity, Dimensions of diversity, Ecological genetics, Metacommunity ecology, Unisexual Ambystoma

Habitat loss and fragmentation have significantly contributed to amphibian population declines, globally. Evaluating the state of remaining habitat patches can prove to be beneficial in identifying areas to prioritize in conservation efforts. Pelee Island, Ontario is home to a complex of salamanders including small-mouthed salamanders (Ambystoma texanum), blue-spotted salamanders (A. laterale) and unisexual Ambystoma (small-mouthed salamander dependent population). These populations have declined from intense landscape changes since the late 1800s, particularly from the historical drainage of wetlands. In this thesis, I evaluated the suitability and connectivity of habitat patches occupied by these salamanders to assess the size of, and dispersal capabilities between, remaining habitat patches. I found that there was a low amount of suitable terrestrial habitat available for this complex of salamanders, and existing habitat patches were small and isolated. Forested areas and non-breeding wetlands were considered to be suitable habitat when adjacent to existing breeding locations, suggesting that these habitats should be a focus for conservation efforts. Notably, intervention may be necessary to maintain this amphibian complex as many assemblages are isolated from one another and potential corridors currently consist of primarily unsuitable habitat. Given that much of the salamander complex is reliant on one species for reproduction, the long-term viability of this population of Ambystoma salamanders may rely on the enhancement of suitable habitat near current breeding sites by conservation organizations and local stakeholders. Ultimately, the approach used in this thesis emphasizes the value of evaluating habitat within a fragmented landscape to focus conservation efforts on imperilled species.

Author Keywords: amphibians, connectivity, habitat suitability, landscape fragmentation, landscape resistance, unisexual