Pollination biology of Welwitschia mirabilis in the central Namib Desert, Namibia
| dc.contributor.advisor | Ellis, Allan George | en_ZA |
| dc.contributor.advisor | Marais, Eugene | en_ZA |
| dc.contributor.advisor | Maggs-Kolling, Gillian | en_ZA |
| dc.contributor.author | Ndilenga, Natanael Shuudifonya | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. | en_ZA |
| dc.date.accessioned | 2023-09-23T23:22:20Z | |
| dc.date.accessioned | 2024-01-08T13:16:06Z | |
| dc.date.available | 2023-09-23T23:22:20Z | |
| dc.date.available | 2024-01-08T13:16:06Z | |
| dc.date.issued | 2023-12 | |
| dc.description | Thesis (MSc)--Stellenbosch University, 2023. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Pollination is a vital ecological process that facilitates the reproduction of flowering plants. However, the characterization of pollination systems has often been limited to the observation of visiting insects and sporadic assessments of pollen loads. To have a more comprehensive understanding of pollination systems, it is important to consider multiple components of pollination effectiveness. Generalist plants are visited by many pollinators, while specialized pollination systems involve only a few species, and this is mostly because rewards are exclusively accessible to specific pollinators. Contrary to the common belief that animal pollination is predominantly associated with angiosperms, substantial evidence suggests that animal pollination is a characteristic of seed plants. This study focuses on Welwitschia mirabilis Hook. f., (Welwitschiaceae) an unusual dioecious lineage within seed plants found only in the Namib Desert of Namibia and Angola. The pollination system of Welwitschia has been the subject of significant controversy, but a single study determined flying insects as primary pollinators. However, that study was limited in terms of sampling and thus inconclusive as to whether these visitors are effective pollinators or not. My study built on these preliminary results and aimed to accurately characterize the pollination biology of Welwitschia, at three populations in the central Namib Desert. In Chapter 2, I conducted extensive pollinator observations to assess two things. First, I assessed the community of animal visitors associated with Welwitschia cones. I expected Welwitschia to have many visitors because it has a generalist phenotype where rewards (pollen and pollination droplets) are accessible to any visitor. I found that Welwitschia is visited by 24 insect morphospecies representing four orders, suggesting that Welwitschia is generalized in its pollination requirements. However, 86% of recorded visits were from only six insect species (four species of fly and two wasp species) that visited male and female cones at all three sites, and Mythicomyiidae flies accounted for 34% of all observed visits. This implies that most pollination in Welwitschia is likely attributed to a small group of fly and wasp insect species. Second, I investigated variation of visitors across male and female cones. Since male cones produce pollen in addition to sweet pollination droplets, providing two sources of potential food, while female plants only produce sweet pollination droplets that are consumed by insects, I expected that visitor species richness, composition and visitation rates should be higher on male cones, and that visitors to female cones should represent a subset of those visiting male cones. I found notable male-biased pollinator visitation where male cones received three times as many visits as female cones, with a significantly higher visitation rate. The visitor communities are also more species-rich on male cones, and the composition of visitors differs significantly between male and female cones. Lastly, I assessed visitor communities across different populations. As Welwitschia is generalist and populations occupy abiotically and biotically variable sites, I expected the community of available visitors to differ between sites. I found differences in pollinator communities and visitation rates across the three different study sites, suggesting the potential influence of both the abiotic environment and the local variation of co-flowering plant species at each site. In Chapter 3, I assessed the effectiveness of Welwitschia pollinators using two approaches. First, I quantified components of pollination efficiency for different visitor species, including visitation rates, visitation patterns to male and female cones, contact with female cone droplets, and pollen loads. Based on the differences in pollinator foraging behaviours and potential to carry pollen, I hypothesized that there would be differences in the components of pollination effectiveness between visitor species and that visitor species could be ranked along a continuum from inefficient to efficient visitors. I also expected that for a visitor species to efficiently transfer pollen between male and female cones there should be significant temporal overlap in visitation to male and female cones. Second, I assessed the contribution of different pollinator groups to seed production using selective exclusion experiments. I expected Welwitschia to require pollinators for seed set, and that large-bodied insects would contribute most to seed set due to their ability to fly longer distances and carry larger pollen loads. I found substantial variation amongst pollinators in all components of pollinator effectiveness measured. I found that insect pollinators contribute significantly to seed set of Welwitschia, and that a core group of primary pollinators, comprising of both small and large-bodied flies and wasps, are important. However, surprisingly, the exclusion experiments show that seed set occurs in the absence of pollinators, suggesting facultative apomixis or alternatively a contribution of wind pollination. While the previous and only Welwitschia pollination study focused on observing visiting insects and assessing pollen loads, my study went a step further by quantifying pollinator effectiveness, thus providing a more accurate characterization of the pollination of this plant. Above all, this thesis represents a significant contribution to the field, as it is among the few studies that classify pollinators based on their quantified effectiveness in gymnosperms. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Bestuiwing is 'n noodsaaklike ekologiese proses wat die voortplanting van blomplantefassiliteer. Die karakterisering van bestuiwingstelsels is egter dikwels beperk tot die waarneming van besoekende insekte en sporadiese assesserings van stuifmeelladings. Om 'n meer omvattende begrip van bestuiwingstelsels te verkry, is dit belangrik om verskeie komponente van bestuiwingseffektiwiteit te oorweeg. Generalistiese plante word deur baie bestuiwers besoek, terwyl gespesialiseerde bestuiwingstelsels slegs 'n paar spesies behels, en dit is meestal omdat belonings uitsluitlik toeganklik is vir spesifieke bestuiwers. In teenstelling met die algemene opvatting dat dierebestuiwing hoofsaaklik met angiosperme geassosieer word, dui aansienlike bewyse daarop dat dierebestuiwing 'n kenmerk van saadplante is. Hierdie studie fokus op Welwitschia mirabilis Hook. f., (Welwitschiaceae) 'n ongewone tweehuisige ontwikkelingslyn binne saadplante wat slegs in die Namibwoestyn van Namibië en Angola voorkom. Die bestuiwingstelsel van Welwitschia was die onderwerp van aansienlike kontroversie, maar 'n enkele studie het vlieënde insekte as primêre bestuiwers geidentifiseer. Daardie studie was egter beperk in terme van steekproefneming en dus onbeslis of hierdie besoekers doeltreffende bestuiwers is of nie. My studie het voortgebou op hierdie voorlopige resultate en het ten doel gehad om die bestuiwingsbiologie van Welwitschia, by drie populasies in die sentrale Namibwoestyn, akkuraat te karakteriseer. In Hoofstuk 2 het ek uitgebreide bestuiwerwaarnemings gedoen om twee dinge te assesseer. Eerstens het ek die gemeenskap van dierebesoekers wat met Welwitschia-keëls geassosieer word, geassesseer. Ek het verwag dat Welwitschia baie besoekers sou hê omdat dit 'n algemene fenotipe het waar belonings vir enige besoeker toeganklik is. Ek het gevind dat Welwitschia deur 24 insekmorfospesies besoek word wat vier ordes verteenwoordig, wat daarop dui dat Welwitschia veralgemeen is in sy bestuiwingsbehoeftes. 86% van aangetekende besoeke was egter van slegs ses insekspesies (vier spesies vlieë en twee wespspesies) wat manlike en vroulike keëls by alle lokaliteite besoek het, en Mythicomyiidae-vlieë het 34% van alle waargenome besoeke uitgemaak. Dit impliseer dat die meeste bestuiwing in Welwitschia waarskynlik aan 'n klein groepie vlieg- en perdeby-insekspesies toegeskryf word. Tweedens het ek variasie van besoekers tussen manlike en vroulike keëls ondersoek. Aangesien manlike keëls stuifmeel bykomend tot bestuiwingsdruppels produseer, wat twee bronne van potensiële voedsel verskaf, terwyl vroulike plante slegs bestuiwingsdruppels produseer, het ek verwag dat besoekersspesierykheid, -samestelling en besoeksyfers hoër op manlike keëls sou wees, en dat besoekers aan vroulike keëls ʼn onderafdeling van die besoekende manlike keëls sou verteenwoordig. Ek het gevind dat manlike keëls noemenswaardige bevooroordeelde bestuiwerbesoeke ondervind het, waar manlike keëls drie keer soveel besoeke as vroulike keëls ontvang het, met 'n beduidend hoër besoekersyfer. Die besoekersgemeenskappe aan manlike keëls is ook meer spesieryk, en die samestelling van besoekers verskil beduidend tussen manlike en vroulike keëls. Laastens het ek besoekersgemeenskappe oor verskillende populasies heen geassesseer. Aangesien Welwitschia algemene bestuiwing gebruik en die populasies verskil in terme van abioties en bioties veranderlikes, het ek verwag dat die gemeenskap van beskikbare besoekers tussen populasies sou verskil. Ek het verskille in bestuiwergemeenskappe en besoeksyfers oor die drie verskillende studie lokaliteite gevind, wat suggereer dat beide die abiotiese omgewing en die plaaslike variasie van ander blommende plantspesies hierdie besoeke beinvloed. In Hoofstuk 3 het ek die effektiwiteit van Welwitschia bestuiwers beoordeel deur twee benaderings te gebruik. Eerstens het ek komponente van bestuiwingsdoeltreffendheid vir verskillende besoekerspesies gekwantifiseer, insluitend besoeksyfers, besoekpatrone aan manlike en vroulike keëls, kontak met vroulike keëldruppels en stuifmeelladings. Gebaseer op die verskille in bestuiwers voedingsgedrag en potensiaal om stuifmeel te dra, het ek verwag dat daar verskille in die komponente van bestuiwingseffektiwiteit tussen besoekerspesies sou wees en dat besoekerspesies langs 'n kontinuum van ondoeltreffende na doeltreffende besoekers gerangskik sou kan word. Ek het ook verwag dat vir 'n besoekerspesie om stuifmeel doeltreffend tussen manlike en vroulike keëls oor te dra, daar beduidende tydsoorvleueling in besoeke aan manlike en vroulike keëls sou moes wees. Tweedens het ek die bydrae van verskillende bestuiwergroepe tot saadproduksie beoordeel deur gebruik te maak van selektiewe uitsluitingseksperimente. Ek het verwag dat Welwitschia bestuiwers sou benodig om sade te vorm, en dat insekte met groter lywe die meeste sou bydra tot saadvorming vanweë hul vermoë om oor langer afstande te vlieg en groter stuifmeelvragte te dra. Ek het aansienlike variasie tussen bestuiwers gevind in alle komponente van bestuiwer effektiwiteit wat gemeet is. Ek het gevind dat insekbestuiwers aansienlik bydra tot die vorming van Welwitschia saad , en dat 'n kerngroep primêre bestuiwers, bestaande uit beide klein en grootlyfvlieë en wespe, belangrik is. Verbasend genoeg het die uitsluitingseksperimente aangetoon dat saadvorming plaasvind in die afwesigheid van bestuiwers, wat fakultatiewe apomiksie suggereer, of dat windbestuiwing ʼn bydrae mag maak. Terwyl die vorige en enigste Welwitschia bestuiwingstudie gefokus het op die waarneming van besoekende insekte en die assessering van stuifmeelladings, het my studie 'n stap verder gegaan deur bestuiwerseffektiwiteit te kwantifiseer en sodoende 'n meer akkurate karakterisering van die bestuiwing van hierdie plant te verskaf. Bowenal verteenwoordig hierdie tesis 'n baanbrekerspoging in die veld, aangesien dit die eerste studie is om bestuiwers te klassifiseer op grond van hul gekwantifiseerde effektiwiteit in gimnosperme. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.identifier.uri | https://scholar.sun.ac.za/handle/10019.1/128848 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject.lcsh | Pollination -- Ecology | en_ZA |
| dc.subject.lcsh | Welwitschia mirabilis -- Namibia -- Namib Desert | en_ZA |
| dc.subject.lcsh | Pollination by insects -- Namib Desert (Namibia) | en_ZA |
| dc.subject.lcsh | Plant-pollinator relationships | en_ZA |
| dc.subject.lcsh | Pollinators -- Effect of insecticides on | en_ZA |
| dc.subject.name | UCTD | en_ZA |
| dc.title | Pollination biology of Welwitschia mirabilis in the central Namib Desert, Namibia | en_ZA |
| dc.type | Thesis | en_ZA |
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