Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?

dc.contributor.advisorHoffmann, Timmen_ZA
dc.contributor.authorDuncan, John Aen_ZA
dc.date.accessioned2017-10-30T14:01:35Z
dc.date.available2017-10-30T14:01:35Z
dc.date.issued2004en_ZA
dc.date.updated2017-03-10T10:27:51Z
dc.description.abstractAloe pillansii populations in the biodiversity hotspot of the Succulent Karoo in Southern Africa are thought to be under threat of extinction. This study investigated the population at the type locality; Cornell's Kop in the Richtersveld, South Africa. It has been suggested that theft, animal damage and more recently climate change have caused a decline in the population by over 50% in the last decade, however very little is known about this rare species. Repeat photography and surveys were used to analyse life history patterns and dynamics of the population and thus establish what the potential threats to this keystone species actually are. Repeat photography indicates that there have been high rates of adult mortality over the last fifty years (1.8% of the population dies annually), which results in an average predicted lifespan of 39 years for the remaining adult population on Cornell's Kop. However, a recent survey reported that over 40% of the population recorded were seedlings, which weren't found in a 1995 survey, which is indicative of a recent recruitment pulse on Cornell's Kop and that conditions on the hill are still habitable for A. pillansii. Growth analyses suggest that A. pillansii has an average annual growth rate of 20 mm.yr⁻¹, which in tum means that 8 m individuals may be up to 453 years old. This long-lived strategy would require A. pillansii to only recruit infrequently, during periods of high rainfall, in order to sustain a viable population, which is consistent with findings on other large desert succulents. Seedling ages were estimated from their heights and it was found that 50% of the seedlings appear to have germinated five to ten years ago; this is consistent with rainfall records from the area which indicate that rainfall was consistently above the annual average for this same period. The findings indicate that although the adult A. pillansii population is declining, the presence of 30 seedlings suggest that the population is entering a recruitment phase after just coming out of a lengthy senescent phase. Although A. pillansii 's extensive lifespan makes it a potentially useful indicator species of climate change, the evidence presented in this study does not suggest that climate change has affected the dynamics of this population.en_ZA
dc.identifier.apacitationDuncan, J. A. (2004). <i>Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?</i>. (Thesis). University of Cape Town ,Faculty of Science ,Plant Conservation Unit (PCU). Retrieved from http://hdl.handle.net/11427/25928en_ZA
dc.identifier.chicagocitationDuncan, John A. <i>"Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?."</i> Thesis., University of Cape Town ,Faculty of Science ,Plant Conservation Unit (PCU), 2004. http://hdl.handle.net/11427/25928en_ZA
dc.identifier.citationDuncan, J. 2004. Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Duncan, John A AB - Aloe pillansii populations in the biodiversity hotspot of the Succulent Karoo in Southern Africa are thought to be under threat of extinction. This study investigated the population at the type locality; Cornell's Kop in the Richtersveld, South Africa. It has been suggested that theft, animal damage and more recently climate change have caused a decline in the population by over 50% in the last decade, however very little is known about this rare species. Repeat photography and surveys were used to analyse life history patterns and dynamics of the population and thus establish what the potential threats to this keystone species actually are. Repeat photography indicates that there have been high rates of adult mortality over the last fifty years (1.8% of the population dies annually), which results in an average predicted lifespan of 39 years for the remaining adult population on Cornell's Kop. However, a recent survey reported that over 40% of the population recorded were seedlings, which weren't found in a 1995 survey, which is indicative of a recent recruitment pulse on Cornell's Kop and that conditions on the hill are still habitable for A. pillansii. Growth analyses suggest that A. pillansii has an average annual growth rate of 20 mm.yr⁻¹, which in tum means that 8 m individuals may be up to 453 years old. This long-lived strategy would require A. pillansii to only recruit infrequently, during periods of high rainfall, in order to sustain a viable population, which is consistent with findings on other large desert succulents. Seedling ages were estimated from their heights and it was found that 50% of the seedlings appear to have germinated five to ten years ago; this is consistent with rainfall records from the area which indicate that rainfall was consistently above the annual average for this same period. The findings indicate that although the adult A. pillansii population is declining, the presence of 30 seedlings suggest that the population is entering a recruitment phase after just coming out of a lengthy senescent phase. Although A. pillansii 's extensive lifespan makes it a potentially useful indicator species of climate change, the evidence presented in this study does not suggest that climate change has affected the dynamics of this population. DA - 2004 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2004 T1 - Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change? TI - Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change? UR - http://hdl.handle.net/11427/25928 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/25928
dc.identifier.vancouvercitationDuncan JA. Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?. [Thesis]. University of Cape Town ,Faculty of Science ,Plant Conservation Unit (PCU), 2004 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/25928en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentPlant Conservation Unit (PCU)en_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherSystematics and Biodiversity Sciencesen_ZA
dc.subject.otherPlant Conservationen_ZA
dc.subject.otherBotanyen_ZA
dc.subject.otherClimate Changeen_ZA
dc.subject.otherrepeat photographyen_ZA
dc.titleAloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?en_ZA
dc.typeBachelor Thesis
dc.type.qualificationlevelHonours
dc.type.qualificationnameBSc (Hons)en_ZA
uct.type.filetype
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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