School of BioSciences - Theses
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ItemExploring adaptation in a key Australian genus Brachyscome through experimentation( 2017)This thesis focuses on species adaptation in a key Australian genus Brachyscome, using three central themes in ecological theory; plants perform better where they naturally occur (local adaptation), widespread species outperform narrow endemics (niche breadth—range size hypothesis), and warming responses and range size (related species show ecological similarity). This study incorporates a broad ecological and experimental approach to test these three hypotheses. This approach involves combining reciprocal field based designs with a common garden comparison, and a multispecies common garden with a warming treatment. Firstly, under a combined reciprocal and common garden approach, and using different populations (at the seedling stage) of broadly distributed B. decipiens I questioned whether there was a ‘home site advantage’ with the hypothesis of populations showing greater fitness at their sites of origin. I had undertaken prior survey work which indicated significant morphological variation between different populations. When tested in a reciprocal design this was not the case, and no local adaptation was detected, and further to this, no variation between populations was detected in the common garden comparison. Keeping the same reciprocal and common garden approach and increasing the study species so that I now had a related group, I explored the niche breadth— range size hypothesis at the seed and seedling stage of plant development. I predicted species that naturally occurred over a greater area were more likely to show a higher performance in terms of survival and growth than species with a restricted range in novel environments, and further restricted species would show higher performance at their site of origin due to their specialised habitat preferences. I found performance came at a cost to survival in three of the widespread species, and the opposite pattern in two of the narrow endemic species. A trade off may exist. The niche breadth—range size hypothesis was partially supported, given one species with the most restricted range showed a similar response to the widespread species. So, although we found a pattern, an exception to this also exists. Moving beyond the alpine environment, I used a common garden approach with a treatment to explore species responses to warming. I extended my study species to nineteen Brachyscome taxa under the following criteria; 1) only occur in an alpine zone, 2) occur in and beyond an alpine zone and 3) do not occur in an alpine zone. I predicted species would show a phylogenetic signature for warm temperature responses, and that alpine species would be particularly susceptible to the treatment. Findings suggest species which were endemic to alpine areas were less likely to benefit from warming than widespread species. I found evolutionary history did not have a detectable effect on warming responses. While there was a moderate phylogenetic signal for plant growth in the absence of warming, there was no signal for growth changes in response to warming, despite variability among species that ranged from positive to negative growth responses to warming. There was also no strong effect of ecological context, as species that showed a positive response to warming did not necessarily originate from hotter environments. In fact, several species originating from hot environments grew relatively poorly when exposed to higher soil temperature. We found a strong phylogenetic signal suggesting that closely related species tend to occur in areas with similar annual variability in precipitation. As Brachyscome is an iconic Australian genus of ~80 species of daisies with very few in cultivation, I included one widely cultivated species Brachyscome multifida (because it had already demonstrated horticultural potential) to explore the horticulture potential of species which responded positively to warming. Brachyscome stuartii, and B. rigidula, both compact plants with attractive foliage, showed horticultural potential under warmer soil conditions, as did B multifida, supporting its popularity as an ornamental cultivar. Brachyscome is an intriguing group of daisies that can be found across a myriad of habitats in the Australian landscape. Tapping into this complex group by taking representatives from across diverse clades to address the three ecological concepts, this thesis helps build our understanding of local adaptation and variation in alpine systems, and helps in the identification of correlates of species performance under warming within the context of the niche—breadth and range size hypotheses. It highlights how plants might be selected that respond positively to our changing climate.