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Biodiversity in a Dynamic World: How Environmental Variability Influences Coexistence between Introduced and Native SpeciesLi, Yue January 2015 (has links)
Understanding broad patterns of biodiversity requires developing a unified and rigorously tested theory that explains how species coexist despite the risk of competitive exclusion. Species interactions are fundamentally shaped by environmental variability. Recent theoretical development has predicted a set of general mechanisms that promote species coexistence under variable environments. Nevertheless, this theoretical framework has received limited empirical tests. Biological invasions offer excellent opportunities to empirically test coexistence mechanisms in communities in which the stability of coexistence is likely affected by introduced species. I took this opportunity to directly test the theory of species coexistence in this dissertation work by investigating how environmental variability affected the invasion of introduced species and their coexistence with native species. My collaborators and I started the investigation of diversity maintenance by first examining the range expansion of introduced species. Studying range shifts can reveal drivers of diversity patterns, which are formed by overlapping ranges of different species. We used a novel spatial analysis to determine the scale-dependent expansion rate of an invasive winter annual species, Brassica tournefortii over North America as well as to infer the drivers of this scale dependency. We found that this species expanded rapidly on scales from 5 to 500 km historically but had ceased its current expansion on the 100-500 km scales due to climatic constraints. This finding left open the question why this species continued its spread on the 5-50 km scales and how it would impact native species within its invaded range. To address these questions, we examined relatively local scale interactions between B. tournefortii and its competitors. We compared key demographic rates of B. tournefortii with other invasive and native winter annuals over a Sonoran Desert landscape to check conditions necessary for their spatial and temporal niche differentiation. We found the presence of two essential requirements for their niche differentiation: species-specific germination responses that could differentiate species by their favored environments and buffered population growth in time and space that could prevent catastrophic population declines when species faced unfavorable conditions. These conditions could provide niche opportunities to promote both the establishment of B. tournefortii and the persistence of native species under its presence. Building upon this finding, we directly quantified one general mechanism of spatial niche differentiation between B. tournefortii and its native competitors. We measured the strength of this mechanism, the spatial storage effect, across a hierarchy of spatial scales (subhabitat -> habitat -> landscape). We found that this mechanism did not promote species coexistence on any of these scales over the study period. These species were not differentiated over their tested spatial niches because weak competition following dry growing conditions failed to intensify intraspecific competition relative to interspecific competition. The strength of this mechanism increased from occasionally producing negative effects on lower scales to consistently being non-negative on the highest scale. This scale-dependent pattern was in line with the expectation that coexistence potential would increase with scales as species interacted over a wider range of environmental heterogeneity. Our findings demonstrated empirically that environmental variability in time and space led to scale-dependent patterns of the coexistence potential between introduced and native species. This work showed that introduced and native species could be differentiated by their environmental responses given spatial and temporal environmental heterogeneity on higher scales. However, for those species to stably coexist on higher scales, competitive effects had to follow environmental responses to separate species by their own density-dependent feedback loops. This work is among the first few empirical tests of a body of theory that holds the promise to generalize the mechanisms of spatial and temporal niche differentiation. Its success and limitation can motivate more studies to adopt the guiding mathematical principles and to use similar yet more innovative approaches to address the grand question of biodiversity maintenance.
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Evaluating the effects of invasive alien plants on water availability and usability of lake water in Gauteng ProvinceRwizi, Lameck 08 1900 (has links)
The invasion of ecosystems by alien species is a growing threat to the delivery of ecosystem
services. This study explored the spatial distribution of water hyacinth in the Benoni Lakes
and made analysis of its impact on water availability and usability in order to understand the
evolution and its propagation rates. The study used satellite imagery for lake level modelling
using Remote Sensing and Geographical Information Systems for calculations of area covered
by weeds in each lake from 2002 to 2012.The modelling approach illustrates the potential
usefulness in projecting invasive plants under climate change and enabled the quantification
of long term changes in aquatic weeds. The results showed that aquatic infestations in lakes
may be used as powerful predictors of correlations between plant abundance and climate
change. The study therefore informs decision makers to identify areas where invasion is likely
to occur and increase surveillance for early invaders. / Environmental Sciences / M. Sc. (Environmental Management)
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Electrical bioimpedance cerebral monitoring / fundamental steps towards clinical applicationSeoane Martínez, Fernando January 2007 (has links)
Neurologically related injuries cause a similar number of deaths ascancer, and brain damage is the second commonest cause of death in theworld and probably the leading cause of permanent disability. Thedevastating effects of most cases of brain damage could be avoided if itwere detected and medical treatment initiated in time. The passiveelectrical properties of biological tissue have been investigated for almost acentury and electrical bioimpedance studies in neurology have beenperformed for more than 50 years. Even considering the extensive effortsdedicated to investigating potential applications of electrical bioimpedancefor brain monitoring, especially in the last 20 years, and the specificallyacute need for such non-invasive and efficient diagnosis support tools,Electrical Bioimpedance technology has not made the expectedbreakthrough into clinical application yet. In order to reach this stage inthe age of evidence-based medicine, the first essential step is todemonstrate the biophysical basis of the method under study. The presentresearch work confirms that the cell swelling accompanying thehypoxic/ischemic injury mechanism modifies the electrical properties ofbrain tissue, and shows that by measuring the complex electricalbioimpedance it is possible to detect the changes resulting from braindamage. For the development of a successful monitoring method, after thevital biophysical validation it is critical to have available the properelectrical bioimpedance technology and to implement an efficient protocolof use. Electronic instrumentation is needed for broadband spectroscopymeasurements of complex electrical bioimpedance; the selection of theelectrode setup is crucial to obtain clinically relevant measurements, andthe proper biosignal analysis and processing is the core of the diagnosissupport system. This work has focused on all these aspects since they arefundamental for providing the solid medico-technological backgroundnecessary to enable the clinical usage of Electrical Bioimpedance forcerebral monitoring.
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Buffelgrass Expansion Rate and Dispersal Type on Recently Invaded Barry M. Goldwater Range of Southwestern ArizonaDamery-Weston, Jaron January 2016 (has links)
Land managers have struggled to develop successful control strategies to address buffelgrass invasion in the Sonoran Desert. Two important variables for control strategies are dispersal type and patch expansion rate (i.e. satellite or invasion front). We investigated these variables along a highway invaded within the last 10 years located south of Gila Bend, Arizona, USA. Dispersal type was calculated by documenting the location of each buffelgrass individual along a 16 km stretch of highway and using an average nearest neighbor analysis in ArcMap 10.2.2. Thirty-six patches were monitored for four years along a 56 km stretch of highway 85 by documenting the outlines of each patch. Dispersal type registered as satellite dispersal (i.e. clustered on the Nearest Neighbor test), z-score = -47.2, p < 0.01. Patch expansion exhibited a median doubling time of 0.81 years. The results of the dispersal type analysis represent an opportunity to enhance control strategies, by targeting buffelgrass satellites and theoretically reducing patch expansion exponentially. The patch expansion rates for buffelgrass were faster than found in past research, giving land managers a clearer understanding buffelgrass patch expansion behavior.
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Unravelling taxonomic uncertainties among balloon vine species within the genus Cardiospermum using a molecular approachGildenhuys, Enelge 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Alien invasive species are a global concern not only threating biodiversity, but also
negatively impacting regional economies. Consequently research aimed at understanding the
invasion process is crucial for management of invasive alien species to reduce these impacts.
Identifying accurate natal ranges is the key first step for efficient alien plant management,
especially biological control. Such knowledge may assist in selecting host-specific biological
control agents and help prevent non-target impact on native species. A case in point is the
genus Cardiospermum of which species have been extensively moved around the globe with
two species now being possible widespread invaders (C. grandiflorum and C. halicacabum),
and a third species (C. corindum) having significant invasion potential. However, in some
regions the native statuses of these species are not clear, hampering management. In order
to minimize potential non-target impacts it is prudent to determine the relationships between
Cardiospermum taxa in unknown native ranges prior to the release of biological control
agents.
With this thesis I aim to review available literature on the genus Cardiospermum,
determine potential spread to suitable habitats globally for selected taxa, resolve unknown
native ranges in southern Africa, and investigate rapid speciation of an endemic Namib
Desert species of balloon vine.
Through exhaustive searches for available literature on the genus Cardiospermum I
report on the biology and ecology of selected species within the genus, with special focus on
the most widespread species. Specifically, using species distribution modelling I investigate
the potential spread of C. halicacabum, C. corindum and C. grandiflorum globally and assess
the accuracy with which this can be determined using known native ranges to predict current alien ranges. Results indicate that these species have significant potential to spread, though
highlighting that species distribution modelling over-fit predicted suitable ranges when using
native range data alone.
To resolve uncertain native ranges of selected species within the genus I reconstructed
a dated multi-gene phylogeny and chloroplast haplotype network to investigate relationships
within and among Cardiospermum species. I conclude that C. halicacabum is non-native in
southern Africa due to polyphyletic relationships among accessions, while C. corindum is
native due to natural long distance dispersal as indicated by a single monophyletic southern
African clade.
The close relationship observed between C. corindum and the African species, C.
pechuelii, lead to a population-level genetic investigation of these two taxa. For this, I
constructed a multi-gene phylogeny, chloroplast haplotype network and conducted population
genetic diversity analyses which all indicated that the African arid adapted taxa, C. pechuelii,
endemic to the Namib Desert of Namibia, evolved from C. corindum following long distance
dispersal from South America.
This study firstly provides insights into the ecology and biology of Cardiospermum,
warning against further introduction due to potential spread. Secondly I resolved the unknown
native statutes of Cardiospermum species in southern Africa and, lastly, illustrated the origin
of African C. pechuelii. My research findings have major implications for on-going biological
research against C. grandiflorum in South Africa and cautions strongly against the release of
already-identified biological control agents due to their potential non-target impacts. / AFRIKAANSE OPSOMMING: Indringerspesies is 'n wêreldwye probleem as gevolg van hul direkte bedreiging van
biodiversiteit asook hul negatiewe impakte op streeksekonomieë. Gevolglik is navorsing
aangaande die indringingsproses van uiterste belang om doeltreffende beheer van
indringerspesies te verseker. Die bepaling van die inheemse herkoms van
indringerpopulasies is die eerste belangrike stap tot doeltreffende beheer, veral biologiese
beheer. Hierdie informasie kan help met die identifisering van gasheer-spesifieke biologiese
agente en om potensiële nie-teiken impakte op inheemse plant spesies verhoed. ‘n Voorbeeld
is ballon rankplante in die genus Cardiospermum, waarvan verskeie spesies wêreldwyd
verspreid is, met die gevolg dat minstens twee spesies (C. halicacabum en C. grandiflorum)
nou moontlike wydverspreide indringers is en ‘n derde spesie (C. corindum) ook potensiaal
toon as ‘n indringerspesie. In sommige streke is die in- of uitheemse statusse van hierdie
spesies onbekend en belemmer gevolglik hul doeltreffende beheer.
Met hierdie tesis streef ek om die genus Cardiospermum te hersien en potensiële
verspreiding van geselekteerde spesies na geskikte habitatte te bepaal, om onbekende
inheemse streke binne Suider-Afrika op te los en laastens, om die herkoms van ‘n ware Afrika
spesie (C. pechuelii) te ondersoek.
Na deeglike ondersoek van beskikbare literatuur doen ek verslag omtrent die biologie
en ekologie van spesies binne Cardiospermum, met spesiale fokus op die mees
wydverspreidste spesies. Deur gebruik te maak van spesies verspreidings modelle bestudeer
ek die potensiaal van verdere verspreiding wêreldwyd vir C. halicacabum, C. corindum en C.
grandiflorum en rapporteer ook omtrent die akkuraatheid van hierdie tegniek. Resultate toon dat alle spesies aansienlike potensiaal toon om verder te versprei, maar beklemtoon ook dat
hierdie metode inheemse streek data “oor-aanpas”.
Om enige onsekerhede aangaande inheemse streke op te los, het ek ‘n gedateerde
multi-geen filogenie en ‘n chloroplas haplotipe netwerk opgetrek om die verhoudings binne en
tussen geselekteerde Cardiospermum spesies te bepaal. Ek kom tot gevolgtrekking dat C.
halicacabum nie inheems in Suider-Afrika is nie, as gevolg van polifiletiese verhoudings, en
dat C. corindum inheems is en moontlik ook ‘n voorbeeld van natuurlike langafstand
verspreiding, soos aangedui deur ‘n enkele monofiletiese groep.
Die naverwante filogetiese verhouding tussen C. corindum en C. pechuelii het daartoe
gelei dat ek die herkoms van C. pechuelii in Afrika ondersoek het. ‘n Multi-geen filogenie,
chloroplas haplotipe netwerk en populasie genetiese diversiteit analises het aangedui dat C.
pechuelii endemies is tot die Namib Woestyn van Namibië, en die produk is van lang afstand
verspreiding van C. corindum vanaf Suid-Amerika.
Hierdie studie gee eerstens insig tot die ekologie en biologie van Cardiospermum en
waarsku teen verdere verspreiding. Tweedens dui my studie ook die opgeloste inheemse
streke in Suider-Afrika aan van sekere Cardiospermum spesies, en laastens, illustreer ek die
herkoms van C. pehuelii. My navorsing het baie belangrike gevolge vir die huidige biologiese
beheer program teen C. grandiflorum in Suid-Afrika en waarsku teen die vrystelling van reeds
geïndentifiseerde biologiese beheer agente weens potensiële nie-teiken impakte op
inheemse spesies.
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The invasion ecology of Acacia elata (A. Cunn. Ex Benth.) with implications for the management of ornamental wattlesDonaldson, Jason Ernest 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This thesis explores how human dictated methods of introduction and species-specific traits interact to define spatial patterns in invasive plant populations using Acacia elata as a model species. I initially asked whether the relatively small invasive extent (when compared to congeners introduced for forestry or dune stabilization) of a species used widely for ornamental purposes (A. elata) is due to low rates of reproduction in South Africa. Results indicate that A. elata has similar traits to other invasive Australia Acacia species: annual seed input into the leaf litter was high (up to 5000 seeds m-2); large seedbanks develop (>20 000 seeds m-2) in established stands; seed germinability is very high (>90%); seeds accumulate mostly in the top soil layers but can infiltrate to depths of 40cm; and seed germination appears to be stimulated by fire. I argue that the current limited distribution of invasive A. elata populations is not attributable to species-specific reproductive traits. Following on from this I addressed the relative importance of species traits, the recipient environment, and introduction dynamics using species distribution models and spread models defined using a range of parameters representative of invasive Australian acacia species. Results indicate that in the early stages of simulated invasions, the number of trees introduced was the most important parameter influencing abundance and extent, while the placement of introduction foci in urban areas associated with ornamental introductions limited the extent and abundance of invasive populations. I suggest that conditions relating to human-mediated introduction events initially mask the influence of intrinsic species traits and help to explain the failure and success of species associated with specific human-shaped pathways. Third, I used scale-area curves to determine how these human-dictated introduction conditions influenced the spatial structure of populations. The fractal dimension (Dij) of A. elata populations indicates plot scale (2.5-25m) spread with high densities that are increasing. Artefacts of introduction history were observed at the regional scale (2.5-25km) - populations are contiguous around introduction foci such as towns and roads. Moreover, fragmentation of A. elata populations at local to landscape scales (0.25-2.5km) is due to a combination of the haphazard regional placement and limited secondary dispersal vectors, both of which can be linked to their introduction history. In summary, this study used a combination of field-based data, modelling techniques and broad-scale sampling methods to assess how intrinsic species traits and introduction conditions mediate invasive spread. I conclude that introduction history can have a long-lasting (100+ years) influence on the spatial structure and distribution of invasive plants, which can mask the influence of individual species traits. / AFRIKAANSE OPSOMMING: Alhoewel menigte plant spesies deur mense ingevoer word, word slegs 'n klein hoeveelheid van plante indringers. Die beperkte aantal spesies wat in nuwe habitatte vestig en versprei, kan grotendeels toegeskryf word aan die omgewing en mensgemaakte hindernisse ten opsigte van oorlewing, voortplanting en verspreiding. In hierdie tesis gebruik ek Acacia elata as ʼn model spesie om te ondersoek hoe die invoeringsproses sowel as spesie spesifieke eienskappe die ruimtelike struktuur van indringende populasies bepaal. Aanvanklik was my vraag of die relatiewe klein indringingsarea van ʼn spesie wat ingevoer is vir ornamentele doeleindes (Acacia elata), teenoor die groot indringingsareas van Australiese Acacia-spesies wat ingevoer is vir bosbou of duin stabilisering, die gevolg is van lae voortplantings tempo in Suid-Afrika. Resultate dui daarop dat A. elata soortgelyke eienskappe as ander indringende Australië akasia spesies het: jaarlikse saad produksie is hoog (tot 5000 sade m - 2); groot ontwikkelde saadbanke (> 20 000 sade m - 2); hoë saad ontkieming (> 90 %); saad versamel in die boonste grondlae, alhoewel dit kan infiltreer tot 'n diepte van 40 cm; laastens, ontkieming word deur vuur gestimuleer. Hierdie resultate stel voor dat die huidige beperkte verspreiding van indringende A. elata populasies nie die gevolg is van spesie spesifieke voortplantings eienskappe nie. Gevolglik het ek 11 indringende Australiese akasia-spesies ondersoek om die relatiewe belangrikheid van spesie eienskappe, die area waar hul geplant is, asook invoerings aspekte te ondersoek. Resultate wys dat die aantal bome wat ingevoer is, die belangrikste eienskap was ten opsigte van digtheid en verspreiding van ʼn indringende spesie, terwyl invoering naby fokuspunte in stedelike gebiede weer spesie digtheid en verspreiding beperk. Hierdie resultate toon dat spesies eienskappe aanvanklik nie ʼn groot invloed het op hul sukses nie, maar dat hul sukses eerder afhang van waar hul geplant word. Derdens, gebruik ek skaal - area kurwes om te bepaal hoe die invoering van A. elata die ruimtelike struktuur van populasies beïnvloed het. Die fraktale dimensie (Dij) van A. elata bevolkings dui op verspreiding by die plaaslike vlak (2,5 - 25m), wat voorstel dat verspreiding nie op hierdie skaal beperk is nie. Eienskappe van die rede/metode van invoering was wel waargeneem op die groter skaal (2.5 - 25km) waar populasies digter was naby dorpe en paaie. Die intermediêre skaal (0,25 - 2.5km) dui daarop dat A. elata populasies huidiglik beperk word deur 'n kombinasie van lukrake plasing en beperkte sekondêre verspreiding, albei wat gekoppel kan word aan hul invoer geskiedenis. Hierdie studie maak dus gebruik van 'n kombinasie van veld gebaseerde data, modellerings tegnieke en breë skaal steekproefmetodes om te evalueer hoe algemene spesies eienskappe en invoer toestande verspreiding bepaal. Sodoende verskaf ek ʼn raamwerk om die invloed van invoer toestande op die ruimtelike struktuur en verspreiding van ornamentele plant indringers te verstaan.
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An assessment of the impacts of invasive Australian wattle species on grazing provision and livestock production in South AfricaYapi, Thozamile Steve 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: I investigated the impacts of the invasive wattle species (Acacia mearnsii, A. dealbata, A. decurrens), on the ecological function and productivity of rangelands in South Africa and their ability to sustain livestock production. More specifically, this study set out to: (1) assess grazing areas at a national scale; (2) identify evidence of progressive impacts of these species on livestock production across a selection of magisterial districts; (3) determine the effects of A. mearnsii density on growth form dominance of indigenous plant species, and highlight how this translates into impacts in forage quality and quantity; (4) determine the effects of A. mearnsii invasion on soil resources and conditions (key determinates of ecological function) required to support grazing production; and finally (5) determine to effects that clearing operations have had on the provision of grazing resources.
My results indicate that the level of overlap between wattle invasion and areas with a high grazing potential, at the national scale, is relatively low (2.9%). However, at a magisterial district scale, areas with a high grazing potential have a moderate (approximately 35.1% high grazing potential area under wattle invasion for highest invaded district) level of invasion. Scattered and moderate levels of invasion currently dominate or characterise these species invasion patterns. Both light and dense A. mearnsii invasions reduce grazing capacity. Dense invasion had the most severe effect reducing grazing capacity from 2 ha, required to support one large stock unit, to 8 ha. The clearing of this species was found to improve grazing capacity within 5 years. The reduction in grazing capacity following invasion was largely due to reduced basal cover and herbaceous biomass. The clearing of invaded sites was found to increase both basal cover and herbaceous biomass to pre-invasion levels. Acacia mearnsii invasion was found to affect certain soil properties. Under an A. mearnsii canopy, plant litter, carbon content of the soil and nitrogen concentrations were all found to be elevated. Overall, this study demonstrates that Acacia invasions have a significant effect on grazing resources at a local or site scale, and that for the eastern region of South Africa, these effects are ultimately scaled up to a district level. This is likely to have important financial and human well-being repercussions. However clearing and restoration programs are clearly able to reverse or mitigate these effects. This study therefore lends support to or complements other ecosystem service provision arguments for clearing alien invasive species. / AFRIKAANSE OPSOMMING: Die impak van die indringer- wattelbome spesies ( A. mearnsii , A. dealbata , A. decurrens) , op die ekologiese funksie en produktiwiteit van weivelde in Suid-Afrika en hul vermoë om vee produksie te onderhou was ondersoek. Meer spesifiek, is hierdie studie uiteengesit om: (1) ondersoek in te stel na die mate van oorvleueling tussen indringing deur wattelbome spesies en belangrike weidingsgebiede op 'n nasionale skaal; (2) bewyse te verskaf van die progressiewe impak van hierdie spesies op vee-produksie oor 'n seleksie van politieke distrikte, (3) die gevolge van A. mearnsii digtheid op groei vorm en oorheersing van inheemse plante te wys, en hoe dit voer kwaliteit en kwantiteit affekteer; (4) die gevolge van A. mearnsii indringing op grond hulpbronne sowel as die kondisie (sleutel bepalende faktore van ekologiese funksie) wat benodig word om weiding produksie te ondersteun vas te stel, en uiteindelik (5) om die gevolge van skoonmaak bedrywighede op die voorsiening van weiding hulpbronne te bepaaal.
My resultate dui daarop dat die vlak van oorvleueling tussen die wattelbome indringing en gebiede met 'n hoë weiding potensiaal, by die nasionale skaal, relatief laag is (2’9 %). Maar op 'n landdrosdistrik skaal, het gebiede met 'n hoë weiding potensiaal 'n matige (ongeveer 35.1 % weiding potensiaal area onder wattelbome indringing vir die hoogste binnegevalde distrik ) vlak van indringing. Verspreide en matige vlakke van indringing oorheers tans of kenmerk hierdie spesies se indringings patrone. Beide lig en digte A. mearnsii besettings verminder dravermoë. Digte inval het die mees ernstige uitwerking en verminder dravermoë van 2 ha, wat nodig is om een grootvee-eenheid te ondersteun na 8 ha. Bevindinge wys dat die verwydering van hierdie spesies weiding kapasiteit kan verbeter binne 'n tydperk van 5 jaar. Die afname in dravermoë na indringing is grootliks te wyte aan die afname in basale bedekking en kruidagtige biomassa. Na die skoonmaak van indringer persele is bevind dat beide basale bedekking en biomassa weer verhoog tot voor- indringings vlakke. Acacia mearnsii indringing beïnvloed sekere grondeienskappe. Onder A. mearnsii blaredak, is alle blaarafval, koolstof-inhoud van die grond en stikstof konsentrasies verhef. In die algeheel, toon hierdie studie dat die Acacia indringings 'n beduidende uitwerking op weidings hulpbronne by 'n plaaslike of perseel skaal het, en vir die oostelike streek van Suid-Afrika, is hierdie effekte ook uiteindelik vertaalbaar tot 'n distrik vlak. Dit sal waarskynlik belangrike finansiële en menslike welsyn gevolge hê, maar die skoonmaak en herstel programme is duidelik daartoe instaat om die gevolge te keer of te verminder. Hierdie studie leen dus ondersteuning aan of komplimenteer ander ekostelsel dienslewering argumente (soos dié van die Werk vir Water program) vir die verwydering van indringerspesies.
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Effects of a highly invasive plant (Lantana camara) on an agricultural flower visitation networkNel, Lyndre 04 1900 (has links)
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.
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Exotic plant invasion of upland plant communities in Hong Kong, ChinaLeung, Pui-chi., 梁佩芝. January 2005 (has links)
published_or_final_version / abstract / Ecology and Biodiversity / Master / Master of Philosophy
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Spectral diagnosis of skin cancerRajaram, Narasimhan 17 September 2010 (has links)
The number of skin cancer cases reported in the United States is increasing every year and nearly equals the total cancer cases detected from every other part of the body. Current detection strategies of skin cancers include a visual examination followed by a tissue biopsy. This procedure is subjective, invasive and time-consuming. Therefore, considering the number of cancer cases reported and the number biopsies performed, there is a critical need for a non-invasive diagnostic aid to help clinicians reduce the significantly large numbers of unnecessary biopsies.
This dissertation presents a quantitative method based on optical spectroscopy for performing a non-invasive ‘optical biopsy’ of melanoma and non-melanoma skin cancers. We have developed the hardware, software and optical algorithms necessary to implement such a device. First, we present a novel lookup table-based model for determining the optical properties of tissue that is valid for fiber-based probe geometries with close source-detector separations and in highly absorbing tissue. These optical properties are quantitative parameters that can be correlated with the physiology of tissue. Second, we present experimental validation of the effects of microvasculature pigment packaging on diffuse reflectance spectra. We have conducted experiments using microfluidic devices over a physiologically relevant range of optical properties and blood vessel sizes. Third, we present the development of a probe-based portable and clinically compatible instrument capable of in vivo spectral measurements. The instrument combines two modalities – diffuse reflectance and intrinsic fluorescence spectroscopy – to provide complementary information regarding tissue morphology, function and biochemical composition.
Finally, we present the results of a pilot clinical study using our portable instrument to determine the accuracy of spectral diagnosis of non-melanoma skin cancers. Our results show that the mean optical properties and fluorophore contributions of normal skin and non-melanoma skin cancers are significantly different from each other and can potentially be used as biomarkers for non-invasive diagnosis of skin cancer. / text
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