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Reproductive Co-Existence Among Five Sympatric Single-Stemmed Aloes in the Gamtoos River Valley, Eastern Cape

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Reproductive Co-Existence Among Five Sympatric Single-Stemmed Aloes in the Gamtoos River Valley, Eastern Cape Reproductive co-existence among five sympatric single-stemmed aloes in the Gamtoos River Valley, Eastern Cape by Christo Botes 200303686 Thesis submitted towards the requirement for the degree of Masters in Science in the Department of Botany at the Nelson Mandela Metropolitan University, Port Elizabeth 2007 Supervised by Prof. Richard M. Cowling (NMMU) Co-Supervised by Prof. Steven D. Johnson (UKZN) i Foreword What started off as a study of the phenological shifts of plants has metamorphosed into an understanding of the co-existence of species within one of our most charismatic and economically important group of plants, the aloes. The collaborative input of my two supervisors contributed to the success of this project. The expert guidance of Richard, sourcing years of experience from his field work in the region, and the input of Steve on the pollination techniques, pushed me sometimes to the near ends of my abilities to do that what was needed regardless of the pain factor involved when working in spinescent vegetation, because hey “it will be worth it”, and it was. Thanks to the Kouga Municipality and the farming community of the Gamtoos River Valley for allowing unrestricted access to their land and for taking me to their secret spots at the back of their kloofs where the aloes are abundant. I am informed that there is still enquiry about the “aloe guy” from the many farmers who took a keen interest in the project, and thanks especially to the Youngs for their observational inputs and all the fruit. To my hosts for the flowering seasons, Grant and Tandi Meredith: thanks for the “foods from around the world” evenings and the long exchanges of travels over a good but not quality (it is Hankey after all) bottle of red. The 12km driveway through seven drifts each day en route to Craggy Burn after a hard day in the field was exceptional and will be sorely missed. I thank the Hankey Speurdiens for checking up on me in the remote localities and gladly shared my telescope with them for their efforts to root out crime in the township. My time in the valley has afforded me the privilege of being considered a local, and the last three years have seen me grow through some truly amazing experiences and I still can remember each one, from the enlightened conversation with Miriam, Mabel and Mavis (three local ladies funding their part-time university education as seasonal workers at the Patensie Co-op) with the white supremacists sneering from the bar, through to the vicious attack by one pissed-off swarm of Honeybees at the end, and it was all good. I found a place where time passes with a leisurely pace set by the eternal summer climate, where nature is still refreshingly wild and the culture, well is rural hence not their fault but sufficiently diverse, and will definitely be back for good someday… Prof. Sue Nicolson, the external examiner, is thanked for her comments that improved the thesis. The NRF is greatly acknowledged for the grant holder linked bursary that was proved. _____________________ Christo Botes Botanist, Naturalist, Sailor 2007 ii Abstract In this study I documented the convergence of five congeneric bird-pollinated plants (Aloe pluridens, A. lineata var. muirii, A. speciosa, A. africana, and A. ferox) into three functional groups based on size, shape, and the arrangements of flowers on the inflorescence, but also nectar rewards, pollen deposition sites on the bird-pollinators, and the degree to which bees play a role in their pollination. Individuals of similar functional groups were divergent in their peak flowering times and limited their degree of flowering overlap further by spatial aggregation and niche separation, within the Thicket of the Gamtoos River Valley. The nectar properties were especially useful in structuring the bird pollinator community, which resulted in greater ethological isolation and hence, greater reproductive assurance in the mixed co-flowering plant communities. Choice array experiments revealed that it was the fine scale aggregation of flowering individuals that ensured that bird-pollinators feed selectively, since when equal choice was available, interspecific visitation increased significantly compared to natural scenarios. Bird behaviour and the ecological intermediateness of one to the species explained its prominence in hybrid combinations. The spatial occurrence of hybrid individuals can be traced back to the energetics of foraging and its influence on bird floral constancy. The pollination ecology of similar South African Aloe species were extrapolated from these and recent findings by various authors, but emphasises the need for a robust natural phylogeny of the Aloaceae in order to draw comprehensive conclusions on the evolutionary radiation of this highly charismatic group. Keywords: Aloe, Aloaceae, pollination, convergence, bird, bee, ethological isolation, co- flowering, hybridization iii Table of content Foreword .........................................................................................................................................i Abstract...........................................................................................................................................ii Table of content .............................................................................................................................iii List of Figures................................................................................................................................iv List of Tables................................................................................................................................... v List of Plates ..................................................................................................................................vi GENERAL INTRODUCTION TO THE ALOES...............................................................................1 CHAPTER 1 – REPRODUCTIVE CO-EXISTENCE AMONG FIVE SYMPATRIC ALOE SPECIES IN THE GAMTOOS RIVER VALLEY, EASTERN CAPE.............................................4 ABSTRACT............................................................................................................................................4 INTRODUCTION.....................................................................................................................................4 METHODS .............................................................................................................................................6 Breeding systems.............................................................................................................................6 Flowering phenology ......................................................................................................................7 Floral ontogeny...............................................................................................................................7 Nectar .............................................................................................................................................7 Bird pollinators, feeding positions and pollen deposition sites ......................................................8 Bees as potential pollinators...........................................................................................................8 Statistical analyses..........................................................................................................................8 RESULTS...............................................................................................................................................9 Breeding systems.............................................................................................................................9 Flowering phenology ......................................................................................................................9 Floral ontogeny.............................................................................................................................10 Nectar ...........................................................................................................................................13 Bird pollinators, feeding positions and pollen deposition sites ....................................................14 Bees as potential pollinators.........................................................................................................17 DISCUSSION........................................................................................................................................20 CHAPTER 2 – EXTRAPOLATING POLLINATION SYNDROMES FOR SOUTH AFRICAN ALOE SPECIES....................................................................................................................................24 ABSTRACT..........................................................................................................................................24 INTRODUCTION...................................................................................................................................24 METHODS ...........................................................................................................................................25 RESULTS.............................................................................................................................................25 DISCUSSION........................................................................................................................................29
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