Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: My master’s research combines aspects of pollination biology and invasion biology to
explore the invasive predictors and impacts of a globally invasive group of plants –
Australian acacias. Specifically, I investigate the role of reproductive biology in their
invasion success (Chapter 2), the impacts of a specific species, Acacia saligna, on native
plant-pollinator communities in South Africa (Chapter 3), and if the impact of A. saligna on
native plant species can be predicted, based on floral trait similarity (Chapter 4).
Australian acacias possess many floral traits implicated in plant invasion success,
including extensive, dense floral displays, prolific seed production, long-lived seed banks,
and propensity for vegetative reproduction. In Chapter 2 of my thesis, co-authors and I
investigate if such reproductive traits influence whether or not a species becomes invasive
once it is introduced by qualitatively and quantitatively analyzing literature and data
collected from published and unpublished data. We found that invasive species reach
reproductive maturity earlier and are more commonly able to resprout. Our findings have
important implications for management of existing Acacia invasions as well as the
assessment and prevention of further introductions of Acacia species leading to invasion.
Impacts of invasive plant species on native plant visitation and consequent reproduction
are often negative and have important implications for future ecosystem health. Acacia
saligna is a problematic woody invasive shrub in many Mediterranean regions, and in
South Africa, it invades fynbos vegetation, which boasts one of the highest plant diversities
per area in the world as well as many specialized pollination mutualisms. It blooms during
the flowering peak of most native species and forms dense, showy floral displays, thus the
possibility of pollinator-mediated interactions with co-flowering native species is high. In
Chapter 3, I assess the impact of flowering A. saligna on insect visitation to co-flowering
native species by conducting flower observations at both an invaded and uninvaded
(control) site. One of the native species most-visited by native honeybees, Roepera fulva,
had high flower visitor overlap with A. saligna and suffered significantly lower visitation
from all insects and from bees when A. saligna was present than at the control site. The
native honeybee appears to be the most important visitor to A. saligna as it was the most
frequent and mobile. Due to its foraging efficiency and dominance in pollinator
communities, Apis mellifera subsp. capensis could be an important mediator of the negative effect of A. saligna on co-flowering natives, especially those frequently visited by
honeybees.
The use of floral traits as predictors of a species’ effect on co-flowering plants via
pollination is commonly used in pollination biology. In the fourth chapter of my thesis, I
apply the predictive principle of floral traits on flower visitation to see if floral traits can
predict the impact of an invasive plant species on co-flowering native species, and if so,
which floral traits are the most important. Following the same flower observation protocol
as Chapter 3, I assess two measures of invasion impact on native flowers – change in
visitation rate to native plant species between invaded and uninvaded sites and flower
visitor overlap between A. saligna and native species – and test for a correlation with floral
trait similarity of native species to and A. saligna. Similarity of categorical traits and all
traits combined (categorical and continuous) were significantly positively correlated with
flower visitor overlap, indicating that native species with categorical traits similar to A.
saligna were more likely to share flower visitors with A. saligna. Floral symmetry and
shape similarity were the most important categorical traits in driving flower visitor overlap.
Findings suggest an important link between categorical floral traits and ability to predict
invasive plant impact on native flower-insect interactions; however, more comprehensive
studies are required for conclusive results. / AFRIKAANSE OPSOMMING: My Meestersgraad se navorsing kombineer aspekte van bestuiwingsbiologie en
indringerbiologie om ondersoek in te stel na die indringing-voorspelbaarheid en die impak
van Australiese Akasias, 'n wêreldwye indringende groep van plante. Ek het spesifiek
gekyk na die rol van voortplantingsbiologie in hul indringing sukses (Hoofstuk 2), die impak
van 'n spesifieke spesie, Acacia saligna, op die inheemse plant-bestuiwer gemeenskappe
in Suid-Afrika (Hoofstuk 3), en of die impak van Acacia saligna op inheemse plantspesies
voorspel kan word, gebaseer is op die ooreenkomste in blomeienskappe (Hoofstuk 4).
Australiese Akasias het baie voortplantingseienskappe wat geassisioeer word met
plantindringing sukses, insluitend ‘n uitgebreide, digte blommedrag, uitermatige hoë
saadproduksie, langlewende saadbank, en die geneigdheid vir vegetatiewe voortplanting.
In hoofstuk 2 van my tesis, ondersoek ek en my medeskrywers of sulke
voortplantingseienskappe beïnvloed of 'n spesie ‘n indringer raak, deur 'n ontleding van die
literatuur en data wat versamel is uit gepubliseerde en ongepubliseerde data. Ons het
gevind dat indringerspesies geslagsrypheid vroeër bereik en meer algemeen in staat is om
weer uit te loop. Ons bevindinge het belangrike implikasies vir die bestuur van die
bestaande Akasiastande sowel as die evaluering en die voorkoming van verdere vestiging
van Akasia spesies wat lei tot indringers.
Impakte van uitheemse plantspesies op inheemse plant-besoeke deur bestuiwers, en
gevolglike voortplanting is dikwels negatief en het belangrike implikasies vir die
toekomstige ekosisteem gesondheid. Acacia saligna is 'n problematiese houtagtige
indringende struik in baie Mediterreense streke, en in Suid-Afrika. Dit dring in die Fynbos
in, wat spog met een van die wêreld se hoogste plant diversiteit per oppervlak, sowel as
baie gespesialiseerde bestuiwing-mutualismes. Dit blom gedurende die bloeiseisoen van
die meeste inheemse spesies en vorm digte, pronkerige blomuitstallings, dus is die
moontlikheid hoog vir bestuiwer-gemedieerde interaksies met inheemse spesies wat saam
blom. In Hoofstuk 3, het ek die impak van Acacia saligna, op insek besoeke aan saamblommende
inheemse spesies bepaal, deur waarnemings op beide ingedringde en
natuurlike studie gebiede. Een van die inheemse spesies, Roepera fulva, wat die meeste
besoek is deur inheemse heuningbye, het 'n hoë blom besoeker oorvleueling met Acacia
saligna en het aansienlik minder besoeke van alle insekte en van bye gekry toe Acacia saligna teenwoordig was as by die natuurlike studie gebied. Die inheemse heuningby, Apis
mellifera subsp. capensis, blyk die mees belangrikste besoeker aan Acacia saligna te
wees aangesien dit die mees gereeldste en beweeglikste was. As gevolg van sy
oorheersing in bestuiwer gemeenskappe, is die by 'n belangrike faktor van die negatiewe
uitwerking van Acacia saligna op die inheemse plante wat dieselfde tyd blom, veral dié wat
gereeld besoek word deur heuningbye.
Die gebruik van blomeienskappe as voorspellers van 'n spesie se effek op
saamblommende plante deur middel van bestuiwing, word algemeen gebruik in
bestuiwingsbiologie. In die vierde hoofstuk van my tesis, het ek die voorspellende beginsel
van die blomeienskappe op blombesoeking toegepas, om te sien of blomeienskappe die
impak van 'n uitheemse plantspesie kan voorspel op saamblommende inheemse spesies,
en indien wel, watter blomeienskappe die belangrikste is. Deur dieselfde blom waarneming
protokol as in Hoofstuk 3 te gebruik, het ek twee maatstawwe van indringings impakte op
inheemse blomme vergelyk - verandering in besoek gereeldheid aan inheemse plante
tussen ingedringde en natuurlike studie gebiede en blom besoeker oorvleueling tussen die
Acacia saligna en inheemse spesies – en die toets vir 'n korrelasie van blomeienskap
ooreenkomste in inheemse spesies en Acacia saligna. Soortgelykheid van kategoriese
eienskappe en al die eienskappe gekombineer (kategoriese en deurlopende) is beduidend
positief gekorreleerd met blombesoeker oorvleueling, wat aandui dat inheemse spesies
met kategoriese eienskappe soortgelyk aan Acacia saligna meer geneig was om blom
besoekers te deel met Acacia saligna. Blom simmetrie en vorm ooreenkoms was die
belangrikste kategoriese eienskappe wat ly tot blombesoeker oorvleueling. Bevindinge dui
op 'n belangrike skakel tussen die die kategoriese blomeienskappe en die vermoë om
indringerplant impakte op inheemse blom-insek interaksies te voorspel, alhoewel, meer
omvattende studies nog nodig is. / DST-NRF Centre of Excellence for Invasion Biology and the Department of Botany and Zoology at
Stellenbosch University for research funding
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20399 |
| Date | 03 1900 |
| Creators | Gibson, Michelle Rene |
| Contributors | Richardson, David M., Pauw, Anton, Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xi, 226 p. : ill. |
| Rights | Stellenbosch University |
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