Response of plant-pollinator interactions to landscape transformations in the Greater Cape Floristic Region (GCFR) biodiversity hotspot

Adedoja, Opeyemi Adebayo (2019-12)

Thesis (PhDAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Landscape transformation is one of the leading causes of global biodiversity decline. This decline is seen in terms of loss of species of ecological importance, and the collapse of important ecological interactions in terrestrial ecosystems. Ecological interactions are highly sensitive to environmental changes, as they are more vulnerable to disruptions than the species involved. Understanding the stability of these interactions in the face of growing environmental changes is key to identifying suitable conservation strategies for ameliorating species loss in transformed landscapes. This is of major conservation concern for the Greater Cape Floristic Region (GCFR), a globally important biodiversity hotspot and rich floral kingdom, which is home to many endemic species. I assessed here the response of plant-pollinator interaction networks to landscape transformation in the GCFR. I examined the influence of changing abiotic and biotic conditions across elevation zones, and I further investigated the influence of fire and invasive alien trees as drivers of environmental change on plant-pollinator interactions. I used a multi-taxon approach to highlight the effects of these drivers on these interactions. I sampled insects and flowering plants, as well as their interactions in areas impacted differentially by fire, invaded areas, and in areas with stratified elevation zones. My results showed a significant response of bees and beetles to environmental factors influencing species distribution across elevation gradients. Ecotones were an area of high conservation interest, as they were the most diverse in terms of species abundance and richness, although there was a mismatch between bees and flowering plant abundance peaks. Furthermore, species restricted to the highest elevation, peak zone are most at risk of local extinction, especially for the insect pollinators, as shown by interaction networks here having the lowest Shannon diversity index, generality, and interaction evenness. Fire influences plant-pollinator interactions and species dispersion patterns through its direct effect on flower abundance and nest provision. Bees were the only group associated with flower abundance. Results showed the importance of flower-rich fire refuges for the persistence of insect pollinators, especially the specialized species during fire events. Finally, increases in alien pine tree age and density were associated with a decline in plant-pollinator interactions, species abundance, and richness. However, dense, tall pine tree patches supported unique interactions involving large-sized pollinators. Overall, this study highlights the important response of plant-pollinator interaction networks to different drivers of environmental change. Habitat physical structure that sustains plant-pollinator interactions, especially those involving specialized species, holds important solutions for conservation action in this region. Controlled burning of overgrown areas should be encouraged for the proliferation of flowering plants. In addition, careful consideration should be given to trade-offs when instigating important conservation actions, such as restoration, especially when these actions can lead to local loss of some endemic species.

AFRIKAANSE OPSOMMING: Landskapstransformasie is een van die belangrikste oorsake van afname in globale biodiversiteit. Hierdie afname is as gevolg van die verlies van ekologiese belangrike spesies sowel as die ineenstorting van belangrike ekologiese interaksies in terrestriële ekosisteme. Hierdie ekologiese interaksies is hoogs sensitief vir omgewingsveranderinge, aangesien hulle meer vatbaar is vir veranderinge as die betrokke spesies. In die aangesien van toenemende omgewingsveranderinge, is dit belanrik om die stabiliteit van hierdie interaksies te verstaan, want hulle is kritiek tot die identifisering van geskikte bewarings-strategieë vir die voorkoming van spesieverlies in getransformeerde landskappe. Hierdie is ‘n groot bewarings-bekommernis vir die breër Kaapse Floristiese Streek (KFS), ‘n globale belangrike biodiversiteit-hotspot en ʼn weelderige blommeryk wat die tuiste van verskeie endemiese spesies is. Ek het hier die reaksie van plant-bestuiwer interaksie-netwerke op landskapstransformasie in die KFS geëvalueer. Ek het die invloed van veranderde abiotiese- en biotiese toestande op die hoogte bo seespieël-sones ondersoek, en het verder ondersoek ingestel na die invloed van brande en indringerplante as drywers van omgewingsveranderinge op plant-bestuiwer interaksies. Om die effek van dié drywers op hierdie interaksies te beklemtoon, het ek ‘n multitakson metode gebruik. Ek het monsters van insekte en blomplante geneem, asook hul interaksies ondersoek in gebiede wat deur verskillende tipes brande beïnvloed word, gebiede wat binnegedring is deur indringerplante, en in gebiede met verskillende hoogte bo seespieëlsones. My resultate het getoon dat bye en kewers model bestuiwer-takson is, vir die evaluering van omgewingsveranderinge, veral dié met betrekking tot ruimtelike of hoogte bo seespieël gradiënte. Die grens ekotone was areas van hoë bewaringsbelang, aangesien hulle die mees divers was in terme van die aantal individue en spesies-rykheid, alhoewel daar was ‘n wanverhouding tussen die hoeveelheid bye en blomplante. Verder, spesies wat beperk is tot die hoogste areas bo seespieël, die piek-sone, is die kwesbaarste vir plaaslike uitwissing, veral die insekbestuiwers, soos bewys deur die interaksie-netwerke met die laagste Shannon diversiteits-indeks, algemeenheid, en interaksie-gelykheid. Brande beïnvloed plant-bestuiwer interaksies en spesies-verspreidingspatrone deur sy direkte effek op blom-hoeveelheid en nes-bepaling. Bye was die enigste groep wat deur blomhoeveelheid gedryf word. Die resultate het ook die belangrikheid van blom-ryke brand-skuiltes vir die deursettingsvermoë van insekbestuiwers aangetoon, veral vir die espesialiseerde spesies gedurende brand gevalle. Ten slotte, ‘n styging in die ouderdom en digtheid van indringer dennebome het ‘n afname in plant-bestuiwer interaksies, aantal individue, en spesiesrykheid veroorsaak. Nietemin, digte, hoë denneboom plate het unieke interaksies ondersteun waarin groot bestuiwers betrokke is. Dus, in opsomming, hierdie studie beklemtoon die belangrike reaksie van plant-bestuiwer interaksie-netwerke tenoor die verskillende drywers van omgewingsveranderinge. Die fisiese strukture van habitatte wat plant-bestuiwer interaksies ondersteun, veral dié waarby gespesialiseerde spesies betrokke is, bevat belangrike oplossings vir bewaringsaksie in hierdie gebied. Beheerde verbranding van toegegroeide areas moet aangemoedig word vir die verspreiding van blomplante. Versigtige oorwegings ten opsigte van potensiële voor- en nadele moet ook geneem word wanneer belangrike bewaringsaksies van stapel gestuur word, soos byvoorbeeld restorasie, veral wanneer hierdie aksies na ‘n plaaslike verlies van sekere endemise spesies kan ly.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107006
This item appears in the following collections: