| Summary: | Thesis (PhD)--Stellenbosch University, 2012. === ENGLISH ABSTRACT: This study tested the proposal that fleshy-fruited alien shrubs competed more effectively for avian
dispersal services than indigenous shrubs. Several different quantitative measures of increasing
complexity were applied to test bird foraging preferences for fruits of two established alien shrubs
(Lantana camara, Solanum mauritianum), two emergent alien shrubs (Myoporum tenuifolium,
Pittisporum undulatum) and two indigenous shrubs (Chrysanthemoides monilifera, Olea europaea
subsp. africana). Overall the simplest quantitative measure, namely that of bird visitation frequency
identified foraging preferences of individual bird species for fruits of alien and indigenous shrubs.
Moreover, even the more complex measures of numbers of foraging birds, foraging times and
products of these in the computed consumption intensity and seed dispersal efficiency were
positively correlated to visitation frequency. There was a distinct preference of several, especially
heavily fugivorous, bird species for fruits of established alien than indigenous shrubs and several
moderately fugivorous bird species preferred fruits of emergent than established alien shrubs.
Intricate photographic and experimental approaches were applied to obtain precise
numerical data on seed removal rates by birds from the alien and indigenous shrubs. Deficiencies
associated with the experimental approach included its inability to discriminate between
asynchronous fruit production and fruit ripening, individual foraging bird species, and fruit
consumption by other fruit foraging vertebrates. The advantages of the photographic approach
were in its provision of a detailed permanent record of individual foraging bird species, their total
numbers and precise foraging times and the proportions of whole fruits consumed, as well as other
behavioural foraging traits. Tested also was the proposal that frugivorous birds remove larger
amounts of fruits from plants with high fruit production and nutritional contents and that the
germination of the bird-ingested seeds is enhanced. In compliance with this proposal, canopy fruit
mass and monosaccharide content were all positively correlated with the total numbers of seeds
removed by birds and viable seeds excreted by birds. Only defecated seeds of the indigenous C.
monilifera and alien L. camara displayed enhanced germination following their ingestion by birds
Seed dispersal distances of alien and indigenous shrubs by birds were estimated from
published records of bird body masses, gut retention times of consumed seed and flight speeds.
Estimated seed dispersal distances ranged between 0.41 and 0.81 km for the subset of heavily and
moderately frugivorous bird species examined. However, their foraging distances derived from birdring
recapture records were much greater, these peaking between 2.5 and 50 km in some heavily
frugivorous bird species.
It is concluded 1. that bird visitation frequency be applied as the most efficient and practical
quantitative measure for gauging bird foraging preferences in future surveys which should involve
large complements of indigenous, emergent and established alien species, 2. that flight speeds and gut passage times of ingested alien and indigenous seeds need to be measured in local bird
species so long distance seed dispersal potentials can be more precisely determined and 3. that
control measures should be focused on eradicating especially emergent alien species with fleshy
fruits from urban environments to prevent their transport by birds into adjacent natural areas. === AFRIKAANSE OPSOMMING: Hierdie studie het die voorstel getoets dat uitheemse vlesige-vrug struike meer effektief kompeteer
vir voël verspreidingsdienste as inheemse vlesige-vrug struike. Verskeie kwantitatiewe maatstawwe
van toenemende kompleksiteit was toegepas om die voedingsvoorkeure van voëls vir vrugte van
twee gevestigde uitheemse struike (Lantana camara, Solanum mauritianum), twee ontluikende
uitheemse struike (Myoporum tenuifolium, Pittisporum undulatum) en twee inheemse struike
(Chrysanthemoides monilifera, Olea europaea subsp. africana) te toets. Algeheel het die
eenvoudigste kwantitatiewe maatstaf, naamlik voël besoek frekwensie, voedingsvoorkeure van
individuele voël spesies vir vrugte van uitheemse en inheemse struike geïdentifiseer. Addisioneel
het die meer komplekse maatstawwe soos voël getalle, voedings tye, asook produkte hiervan in die
berekende verbruiks intensiteit en saadverspreiding effektiwiteit almal positiewe korrelasies met
besoek frekwensie. Predominant vrugtevretende voël spesies het ‘n duidelike voorkeur getoon vir
vrugte van gevestigde uitheemse eerder as inheemse struike. Verskeie meer gematigde
vrugtevretende voël spesies het egter vrugte van ontluikende eerder as gevestigde uitheemse
struike verkies.
Ingewikkelde fotografiese en eksperimentele benaderings was gebruik om presiese
numeriese data van saad verwyderingstempo’s deur voëls vanaf die bestudeerde struike te bekom.
Tekortkominge geassosieerd met dié eksperimentele benadering sluit in die onvermoë om te
onderskei tussen asinkrone vrug produksie en vrug rypwording, individuele kos soekende voël
spesies, asook vrug verbruik deur ander vrugvretende werweldiere. Die voordele van die
fotografiese benadering was die verskaffing van ‘n gedetailleerde permanente rekord van
individuele kos soekende voël spesies, hul totale getalle, presiese voedingstye, proporsie heel
vrugte verbruik, asook ander voedingsgedrag eienskappe. Ook getoets was die voorstel dat
vrugtevretende voëls groter hoeveelhede vrugte verwyder van plante met hoë vrugproduksie en
hoë nutriënt inhoud, en dat ontkieming van voëlingeneemde sade verhoogd is. In nakoming met
die voorstel, was blaredak vrugte massa en monosakkaried inhoud albei positief gekorreleer met
totale aantal sade verwyder deur voëls en lewensvatbare sade uitgeskei deur voëls. Slegs sade
van die inheemse C. monilifera en die uitheemse L. camara het verhoogde ontkieming gewys na
inname deur voëls.
Saadverspreiding afstande van uitheemse asook inheemse struike deur voëls was bepaal
vanaf gepubliseerde rekords van liggaams massa, saad behoud tye in die maag na inname, en
vliegspoed. Beraamde saadverspreiding afstande het gestrek tussen 0.41 en 0.81 km vir dié
subgroep van predominant en gematigde vrugtevretende voël spesies bestudeer. Nogtans was
voedings afstande, afgelei van geringde voël hervangs rekords, veel groter, en het gepiek tussen
2.5 en 50 km vir sommige predominant vrugtevretende spesies. Gevolglik weet ons nou dat 1) voël besoek frekwensie toegepas kan word as die mees
effektiewe en praktiese kwantitatiewe maatstaf vir die bepaling van voël voedings voorkeure in
toekomstige opnames waar komplementêre groepe inheemse, ontluikende en gevestigde
uitheemse spesies bestudeer word; 2) vliegspoed en maag passeer tye van ingeneemde
uitheemse en inheemse sade gemeet moet word in plaaslike voël spesies sodat langafstand
saadverspreiding potensiaal meer presies bepaal kan word; en 3) beheer maatstawwe moet fokus
op die verwydering van spesifiek ontluikende uitheemse vlesige-vrug spesies vanuit stedelike
omgewings, om sodoende saad vervoer deur voëls na naasliggende natuurlike areas the verhoed.
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