UBC Theses and Dissertations

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UBC Theses and Dissertations

The ecology of curvature in flowers and hummingbird bills Boehm, Mannfred Masahiro Asada


The diversity of shape and form is an intrinsic part of life on Earth. Evolution may often generate novel non-adaptive phenotypes through the process of drift or through pleiotropic effects. However, in some groups of organisms, morphological diversity is thought to increase individual fitness because different phenotypes mediate distinct behaviours, types of protection, or access to otherwise underused resources. The link between phenotypic diversity and niche partitioning offers an enticing explanation for global patterns of biodiversity. Flowering plants and hummingbirds are an intuitive and interesting system to test this theory because both clades occur in vastly greater numbers of species in the tropics than anywhere else. They are also potentially co-adapted to a mutual biotic landscape as much as the climatic and edaphic environment. In this thesis I examine the ecology of curvature in tubular flowers and hummingbird bills with the aim of understanding their role, if any, in niche partitioning, coexistence, and the potential for explaining diversity patterns across the Americas. In the first chapter I studied the natural history of a plant-hummingbird system exhibiting extreme curvature. I found evidence that trait-matching corresponded with a narrow niche breadth for both species. In the second chapter I reviewed the pollination ecology literature and found that the evidence supports curvature as a mediator of niche partitioning across many pollination systems. I also developed protocols and methods for more precisely measuring this trait. In the third chapter I compared the explanatory power of community phylogenetic structure and community-wide distributions of niche breadth in explaining bill diversity among hummingbird assemblages. I found that hummingbird bill shape (including curvature) generally does not play a significant role in niche partitioning, except in a minority of species with the most extreme bill shapes. Together, these three projects demonstrate the potential for flower-bill diversity in driving effective niche partitioning in special cases. The future of this field will hopefully see analyses testing niche partitioning as mediated by several traits. In plants and hummingbirds, much of the progress may come from focusing efforts on flowering phenology and foraging modes.

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