Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Invasive alien plants threaten natural and agricultural pollination systems as they integrate into and disrupt flower visitation networks. Mango (Mangifera indica) production on commercial mango farms in Hoedspruit, South Africa, is an important part of the local economy. Mangoes require pollination for fruiting success, and depend on the native insect community, facilitated by managed bee colonies (Apis mellifera), to pollinate flowers. Managed honeybees and wild insect flower visitors to mango have previously been observed visiting other flowering plants in surrounding natural vegetation, including the alien invasive plant Lantana camara. Lantana camara and mango share similar floral characteristics and co-occur in close proximity, so they may share pollinators/flower visitors. Here, I determined L. camara’s influence on mango flower visitation networks, specifically whether it facilitates visitation, through greater abundance and diversity of insect flower visitors (facilitation), or competes for flower visitors (competition), and whether it supports mango flower visitors when mango trees are not in flower. This study was conducted on the margins of three mango farms and bordering natural vegetation. Firstly, L. camara’s effect on mango flower visitation was investigated by comparing flower visitation to mango in plots with and without L. camara nearby. The presence of L. camara was associated with greater mango flower visitation, with increases in both flower visitor species abundance and richness. Secondly, the composition of flower visitor communities of mango orchard boundaries and bordering natural vegetation were evaluated. Although some flower visitors were shared between mango and naturally occurring plants, flower visitor community assemblages were significantly different between natural vegetation and mango orchard boundaries. In natural vegetation, flies, butterflies, wasps, wild bees and ants played a primary role in the visitation networks, whereas honeybees, wild bees and flies were the main visitors in mango orchards. The presence of L. camara significantly influenced community structure in both natural vegetation and orchards. Natural vegetation with L. camara had a more diverse flower visitor community than natural vegetation without L. camara. Lantana camara seems to facilitate mango flower visitation during mango flowering, attracting a larger visitor abundance and species richness where it occurs in bordering natural vegetation and nearby mango orchard boundaries. However, L. camara was seen to be visited by few species known to visit mango outside of mango flowering, suggesting that L. camara may benefit more from facilitation than mango. Given its extreme invasive nature and threat to local plants which sustain native pollinators, L. camara should be removed from mango orchards and bordering natural vegetation. Furthermore, farm managers are encouraged to plant and maintain indigenous flowering plants, especially plants with a facilitative value to mango, in land surrounding mango orchards to sustain native wild pollinators beneficial to mango pollination. / AFRIKAANSE OPSOMMING: Indringerplante bedreig natuurlike- en landboubestuiwingsisteme deur blombesoekingsnetwerke binne te dring en te ontwrig. Mango (Mangifera indica) produksie op kommersiële plase in Hoedspruit, Suid-Afrika, speel 'n belangrike rol in die plaaslike ekonomie. Suksesvolle mangovrugproduksie is afhanklik van bestuiwing deur inheemse insekte, gefasiliteer deur bestuurde heuningbykolonies (Apis mellifera). Dit is vantevore waargeneem dat hierdie heuningbye en inheemse insekblombesoekers ook ander blomme besoek in die omliggende natuurlike plantegroei, veral Lantana camara wat in hierdie areas ook voorkom. Lantana camara en mango deel soortgelyke blomeienskappe en groei baie na aan mekaar op die buitenste rande van mango boorde. In hierdie studie bepaal ek L. camara se invloed op mangoblominsekbesoekers, en kyk spesifiek of dit mangoblombesoeking fasiliteer, deur om die aantal blombesoekers en blombesoekerspesies te verhoog (fasilitering), of mee kompeteer vir blombesoekers (kompetisie), en of dit mangoblombesoekers onderhou wanneer mango bome nie blom nie. Hierdie studie is uitgevoer op die grensgebied tussen die mangoboorde en natuurlike plantegroei van drie mangoplase. Eerstens is L. camara se effek op mango ondersoek deur mangoblombesoeking te vergelyk tussen plotte met en sonder L. camara. Daar is gevind dat L. camara mangoblombesoeking fasiliteer deur om die aantal blombesoekers en besoekerspesies te verhoog. Tweedens is die gemeenskapsamestelling van blombesoekers in mangoboordrande en aangrensende plantegroei geëvalueer. Alhoewel sommige blombesoekers by mango én ander plante gevind word, is hul gemeenskapsamestelling aansienlik verskillend tussen die mangoboordrande en aangrensende plantegroei. Vlieë, skoenlappers, wespe, bye en miere speel 'n primêre rol in die blombesoekingsnetwerke van natuurlike plantegroei, waar hierdie rol in mangoboord-besoekingsnetwerke vervul word deur heuningbye, wilde bye en vlieë. Die teenwoordigheid van L. camara het die gemeenskapstruktuur in beide gebiede beduidend beïnvloed. Die aangrensende natuurlike plantegroei, waar L. camara voorkom, het ‘n meer diverse blombesoekersgemeenskap as dié sonder L. camara. Mangoboorde wat grens aan plantegroei, wat L. camara insluit, het soortgelyk 'n groter blombesoekerspesierykheid en aantal blombesoekers gehad. Dit blyk dat, waar hierdie plant voorkom, Lantana camara mangoblombesoeking fasiliteer tydens mangoblomtyd sowel as om 'n groter aantal blombesoekersinsekte met ‘n groter spesierykheid te lok in beide die mangoboorde en aangrensende natuurlike plantegroei. Daar is egter geen bewyse gevind wat voorstel dat L. camara mangoblombesoekers ondersteun buite mangoblomtyd nie, wat aandui dat L. camara voordeel trek uit die fasiliterende verband met mango. Gegewe L. camara se uiterse indringende geaardheid en bedreiging aan die plaaslike inheemse plantgemeenskap wat inheemse bestuiwers onderhou, word L. camara se verwydering vanuit die aangrensende plantegroei aanbeveel. Dit word aanbeveel om L. camara se fasiliterende rol te vervang deur inheemse blomplante in dié areas aan te plant en natuurlike blomplantegroei te bewaar en te onderhou.

Background: Pollen transfer via animals is necessary for reproduction by ~80 % of flowering plants, and most of these plants live in multispecies communities where they can share pollinators. While diffuse plant-pollinator interactions are increasingly recognized as the rule rather than the exception, their fitness consequences cannot be deduced from flower visitation alone, so other proxies, functionally closer to seed production and amenable for use in a broad variety of diverse communities, are necessary. Scope: We conceptually summarize how the study of pollen on stigmas of spent flowers can reflect key drivers and functional aspects of the plant-pollinator interaction (e.g. competition, facilitation or commensalism). We critically evaluate how variable visitation rates and other factors (pollinator pool and floral avoidance) can give rise to different relationships between heterospecific pollen and (1) conspecific pollen on the stigma and (2) conspecific tubes/grain in the style, revealing the complexity of potential interpretations. We advise on best practices for using these proxies, noting the assumptions and caveats involved in their use, and explicate what additional data are required to verify interpretation of given patterns. Conclusions: We conclude that characterizing pollen on stigmas of spent flowers provides an attainable indirect measure of pollination interactions, but given the complex processes of pollen transfer that generate patterns of conspecific-heterospecific pollen on stigmas these cannot alone determine whether competition or facilitation are the underlying drivers. Thus, functional tests are also needed to validate these hypotheses.