Petals to pollination: the functional ecology and evolution of floral traits

Flowers and floral traits are central to plant reproduction via pollination. In spite of this, floral traits have often been overlooked in macroecology, hampering our ability to assess large-scale variation in flowers and pollination across landscapes. Macroevolution, in contrast, often considers floral traits but typically from a systematic rather than an ecosystem function perspective. In this thesis I explore a range of functional floral traits, using the latest macroecological and macroevolutionary methods to develop new insights about the way flowers and pollination vary across landscapes and through evolutionary time.

In the first part of this thesis I consider flowering phenology at two different scales, with the macroecology of plant community flowering periods and the macroevolution of a more detailed measure, floral longevity. I find that community flowering periods are shaped by temperature and precipitation means and predictability across six of Australia’s biomes. Flowering is more concentrated and seasonal in cold, wet and predictable environments such as Australia’s alpine, and more dispersed and aseasonal in the dry, hot, unpredictable Australian deserts. I develop new methods to collect floral longevity field data and combine this with published data to assess how floral longevity has evolved with floral symmetry across the angiosperms. I discover a key cost of zygomorphy (bilateral symmetry) in flowers, as zygomorphic flowers open longer on average than actinomorphic flowers.

Floral traits rarely evolve in isolation, and I explore this further by considering flower size and flower colourfulness in Australia’s most diverse tree clade, the eucalypts. I show that eucalypt flower size and colourfulness have evolved in correlation, and larger, more colourful eucalypt flowers are more often found in southwest Australia. Unlike flowering period, the abiotic environment does not predict flower size and colourfulness well. Instead I find that pollination environment, and in particular the presence-absence of flower-visiting bats, better predict flower size and colourfulness in eucalypts.

Pollination is often the primary driver of floral traits, and the coordination of floral traits to suit particular pollinators creates ‘pollination syndromes’. In the final part of this thesis I use syndromes and pollination systems to conduct the first angiospermwide assessment of the macroevolution of pollination. I show that environmental shifts to more open habitats or higher latitudes may have accompanied shifts from animal to wind pollination, and angiosperms have been insect pollinated for approximately 86% of their history.

Overall, integrating floral traits into macroecology and taking an ecological approach to flower macroevolution can help us to better understand patterns of pollination and plant reproduction shaping the ecosystems around us. My thesis provides new evidence of the ways that the abiotic and biotic environment shape plants’ flowering strategies, which in turn will affect the many pollinators and other animals that depend on floral resources. I hope that the insights developed here will help deepen our understanding of flowers, pollinators and pollination, such that we can more effectively conserve this vital interaction.