Marion Island is a sub-Antarctic volcanic island with a cold, wet climate. Much of the interior of the island is bare, with vegetation only found at lower altitudes. No soil classification has yet been undertaken for the Island, and literature on its soils and pedogenesis is sparse. As part of a broader research project on Geomorphology and Climate Change the morphological, physical, chemical, mineralogical and biological properties of soils from seven terrestrial habitats on Marion Island were analysed. It was determined that pedogenesis has taken place on Marion Island. A relationship was observed between soils and terrestrial habitats. Soils were classified according to the World Reference Base (WRB) soil classification system as Histosols, Histic Andosols, Andosols and Regosols. Generalised soil profiles were constructed for each of the seven terrestrial habitats. The spatial distributions of soil types for the Island were predicted with the use of a GIS model and are presented, together with the implications of climate change for pedogenesis and soil distribution on Marion Island. / Dissertation (MSc)--University of Pretoria, 2010. / Geography, Geoinformatics and Meteorology / MSc / Unrestricted

Thesis (PhD (Conservation Ecology and Entomology))--University of Stellenbosch, 2011. / AFRIKAANSE OPSOMMING: Min aandag is al gegee aan biogeomorfologiese interaksies in glasiale en periglasiale omgewings. Nietemin is hierdie interaksies, wat op die skeidingsvlak tussen ekologie en geomorfologie fokus, baie belangrik in hierdie omgewings, waar organismes in noue verband met die abiotiese omgewing saamleef. In hierdie tesis bestudeer ek die interaksies tussen die vaskulêre plantspesies met die hoogste voorkoms op sub-Antarktiese Marion Eiland, Azorella selago Hook. (Apiaceae), en die omringende geomorfologiese landskapsvorme, -prosesse en meettegnieke. Verder verskaf die tesis voorstelle om toekomstige geïntegreerde biogeomorfologiese navorsing te vergemaklik. Om die gevolge van A. selago-plante vir sedimentbeweging en -verspreiding te verstaan, het ek die verspreiding van sedimentgroottes om hierdie plante gemeet deur middel van 'n kombinasie van fotografiese analise-metodes. Deur as sedimentbewegingsobstruksies te dien, het plante 'n waarneembare effek op die omringende sedimentverdeling. Dit is veral belangrik om hierdie interaksies tussen A. selago en sy omgewing te verstaan in die lig van onlangse klimaatsverandering op die eiland, omdat sedimentgrootte belangrike grondeienskappe soos waterretensiekapasiteit en vriesgevoeligheid beïnvloed. Om die effek wat A. selago plante op die omringende mikroklimaat het beter te verstaan, is die kleinskaalse variabiliteit in grondtemperature om A. selago plante bestudeer. Grootskaalse grondligting as gevolg van fors is gemeet, ten spyte van relatief ligte forseienskappe. Dit dui daarop dat naaldys ook by temperature bo -2°C kan vorm. Wintergrondtemperature aan die oostekant van plante was effens laer en minder veranderlik as aan die westekant van plante, waarskynlik as gevolg van laer windsnelhede en/of sneeu wat ophoop aan die oostelike, lykant van plante. Die resultate benadruk dat A. selago plante 'n belangrike rol speel in die verandering van mikroklimate en dat dit belangrik is om die gevolge van sulke veranderings, soos die skep van mikrohabitatte vir grondorganismes, te verstaan. Daar word vermoed dat positiewe plantinteraksies negatiewe interaksies oorheers in omgewings met hoe abiotiese druk. Gevolglik wys ek dat daar 'n positiewe verband bestaan tussen A. selago plante en saailinge van beide A. selago self, asook van die meerjarige gras Agrostis magellanica Lam. (Poaceae). Ek stel voor dat beide plante en klippe sade, wat deur wind, reenval en/of afdraande sedimenttransportering as gevolg van vriesprosesse vervoer word, opvang. Verder dui verhoogde A. selago saailinggetalle om plante, maar nie om klippe nie, daarop dat plante een of ander biologiese voordeel aan A. selago saailinge bied. Dit is bekend dat die verspreidingspatrone van plantspesies as gevolg van abiotiese stresgradiente varieër. Met hierdie bevinding in gedagte, is moontlike faktore verantwoordelik vir A. selago saailinggetalle en -verspreidingspatrone, soos hoogte bo seespieël en substraatbedekking, bestudeer. Alhoewel dit wil voorkom asof daar 'n verband tussen saailinggetalle en hoogte bo seespieël is, is saailinggetalle en verpreidings meestal afhanklik van ongemeette perseel-spesifieke eienskappe. Plante kan die omringende geomorfologie beïnvloed, maar ook geomorfologiese meettegnieke. Om die potensiaal van kosmogeniese dateringsmetodes as geomorfologiese hulpmiddels in fellfield habitatte te verken, is die akkumulasietempo van die kosmogeniese isotoop ¹ºBe onder en langs 'n A. selago plant bepaal. Die resultate dui daarop dat ¹ºBe nie ten volle in die grondprofiel behoue bly nie en verskeie potensiële redes word bespreek. Verder dui die resultate daarop dat ¹ºBe konsentrasies in fellfield habitatte versigtig geïnterpreteer moet word, aangesien A. selago plante effektief ¹ºBe opvang in hulle grondryke kern. Om vordering in biogeomorfologie te vergemaklik, is dit belangrik om bewus te wees van die verskillende metodes wat geomorfoloë en ekoloë volg. Ekologiese benaderings is dikwels op strenger statistiese tegnieke gebaseer, terwyl geomorfoloë eerder fokus op 'n meer beskrywende benadering en teoretiese beredenering. Ek verduidelik hoekom die twee velde sulke uiteenlopende benaderings volg, benadruk moontlike struikelblokke en verskaf voorstelle om samewerking te vergemaklik. / ENGLISH ABSTRACT: There are few scientific publications that relate to biogeomorphological interactions in glacial and periglacial environments. Interactions that focus on the interface between ecology and geomorphology are very important in these environments, as a tight coupling often exists between organisms and their abiotic surroundings. In this thesis the interactions between the dominant vascular cushion plant species on sub-Antarctic Marion Island, Azorella selago Hook. (Apiaceae), and the surrounding geomorphological landforms, processes and measuring techniques were studied. In addition, the thesis provides suggestions to facilitate future integrated biogeomorphological research. To understand the consequences of A. selago cushions for substrate movement and sorting, the grain size distribution of sediment surrounding these cushions was quantified using a combination of image analysis approaches. Through obstructing frost-related sediment transport, A. selago cushions are shown to affect the grain size sorting of the surrounding sediment. Particle size affects soil properties such as water-holding capacity and frost susceptibility. It is therefore important to understand the interactions between A. selago cushions and sediment distributions, especially in the light of recent warming and drying on the island. Fine scale variability in soil temperature parameters was studied around cushions to improve understanding on how A. selago affects the surrounding soil microclimate. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms above the previously suggested required temperature of -2°C. Lower and less variable winter temperatures were found on eastern than on western cushion sides, probably as a result of lower wind speeds or leeside snow accumulation on eastern cushion sides. These research findings highlight the importance of A. selago cushions in modifying site microclimates. Such modifications could have important potential consequences, such as providing microhabitats for soil microorganisms and seedlings. Positive plant interactions have been suggested to dominate over negative interactions in environments with high abiotic stress. Positive associations were found between A. selago and both its own seedlings and those of the perennial grass, Agrostis magellanica Lam. (Poaceae) on Marion Island. It is suggested that both cushions and rocks trap seeds dispersed by wind, runoff and/or downslope sediment transport through frost creep. In addition, increased A. selago seedling numbers around cushions, but not around rocks, suggest that cushions provide a biological nurse effect to seedlings of their own kind. Plant species' distributions have been known to vary in response to abiotic stress gradients. In light of this, determinants of A. selago seedling distributions and abundance, such as altitude and substrate cover, were explored. Although there appears to be some altitudinal trend, seedling distributions and abundance patterns were largely attributed to unaccounted variation between sites. Plants can affect the surrounding geomorphology, but also geomorphological measuring techniques. To explore the potential of cosmogenic dating techniques as geomorphological tools in fellfield habitats, accumulation rates of the cosmogenic isotope ­¹ºBe were assessed underneath and adjacent to an A. selago cushion. The results show that ¹ºBe is not fully retained in the soil profile and various reasons are discussed. Furthermore, the results suggest that ¹ºBe concentrations should be interpreted cautiously in fellfield habitats, as A. selago cushions effectively intercept the isotope in their soil-rich core. To facilitate the integration of geomorphological and ecological principles, as was attempted in this thesis, it is important to understand the philosophies behind the different research approaches that ecologists and geomorphologists employ. Ecologists often employ a more statistics-based approach, whereas geomorphologists focus on a more descriptive approach and reasoning based on established theories. I attempt to explain why the two fields follow such different approaches, highlight some potential challenges and provide suggestions to facilitate progress in the interdisciplinary field of biogeomorphology.

A warming Southern Ocean (SO), due to climate change and global warming, has many implications on the sub-Antarctic Islands in the SO. Due to the distance away from continental land these islands experience an oceanic climate, making them the perfect sentinels to climate change in this sector of the Southern Ocean. Studies have proposed that climate changes reported at the Prince Edward Islands (PEIs) correspond in time to a southward shift of the Antarctic Circumpolar Current (ACC) particularly the Subantarctic Front (SAF). While other studies have shown distinctive trends in ocean and atmospheric parameters such as sea surface temperature (SST), air temperature, sunshine, rainfall, air sea level pressure and wind speed and direction from the 1950s to the early 2000s, the aim of this study is to update those studies to a more recent time with updated time series. Among the changes recorded is an increase in SST and air temperature, which is a strong indication of the changing local and global climate. Using linear regression, this study showed that the rates of increase from 1949 to 2018 of the SST (0.022°C/year), minimum (0.0072°C/year) and maximum air temperatures (0.016°C/year) are smaller than estimated in previous studies. The increasing trend in SST and air temperature reported by previous papers has actually stopped since the 2000s, which reduces the formerly reported trend (0.028°C/year). Although the in-situ measured SST data had gaps, a good correlation with in-situ SST and large scale satellite derived Reynolds SST help to corroborate the covariation between SST, in-situ SST and air temperature giving weight to the hypothesis of a reversal of the positive temperature trends reported by others. The change in decadal variability a decrease in air pressure of 4 hPa since the late 1990s to late 2000s, which coincided with a decrease in minimum and maximum air temperatures of 1°C over the same period; decrease in westerly wind and an increase in the northerly component of the wind, which would explain the decrease of inshore sea surface temperature a while thereafter. This study further corroborates previous findings of a continued decrease in rainfall, while the sunshine has largely remained the same. The seasonal cycle of the air pressure is significantly associated with that of rainfall, showing that the bimodal high air pressure signature resulting from the Semi-annual Oscillation (SAO) is associated with a decrease in rainfall. The Southern Annual Mode (SAM) was significantly yet weakly correlated with the SST (0.24), rainfall (-0.25) and air pressure (0.16), indicating that it does have an impact at the PEIs but not as strong as previously speculated. The El Niño Southern Oscillation (ENSO) has very weak and insignificant relationships with the parameters examined except for a weak relationship with in-situ SST, sunshine and air pressure. These new insights, especially at the decadal timescale, could further our insight on how subAntarctic islands have responded to climatic changes.

Thesis (PhD)-- Stellenbosch University, 2012. / ENGLISH ABSTRACT: Climate change and biological invasions are major threats to biodiversity. In particular, these threats are predicted to influence terrestrial systems in the sub-Antarctic, where significant ecosystem responses to both have already been seen. In this thesis, the sub-Antarctic Prince Edward Island group is used as a model system in which to investigate key questions relating to climate change and invasive species impacts. The island group comprises two islands, Marion (MI) and Prince Edward (PEI), both of which are experiencing rapid warming, yet have different invasive assemblages and in consequence are experiencing different impacts. Variation in the patterns of invasive species richness and abundance and their underlying causes are matters of considerable ecological and conservation significance. While an increase in thermal energy availability typically results in an increase in species richness, the mechanisms underlying these patterns are poorly understood. In Chapter 2 of this thesis, these relationships are explored for springtails, an important component of the soil fauna on Marion Island. Energy explains a large amount of the spatial variation in indigenous and invasive springtail species richness. Disturbance thresholds and stressful temperatures are more important than increased population sizes in determining this variation in species richness. As both indigenous and invasive springtail species richness and abundance are strongly related to temperature, a warming climate could have far-reaching consequences for these organisms. In particular, invasive species are predicted to be at an advantage relative to indigenous species under warming conditions. One species where this seems especially likely, given its physiological responses to experimental warming and drying, is the large invasive tomocerid, Pogonognathellus flavescens. Determining whether this will be the case depends on understanding the factors underlying its range limits and abundance structure. Moreover, few studies have sought to distinguish the causal basis of abundance structure and range limits, particularly for invasive species. Thus, in Chapter 3, local microclimate variables and physiological tolerances of the invasive springtail, P. flavescens (a habitat generalist), are examined. The results suggest that the species should be widely distributed across a range of habitats on MI. However, the springtail is restricted to indigenous Poa cookii tussock grassland habitats in the southeast. The current range limits are set by dispersal limitation (i.e. contingent absences) whilst abundance structure is a function of variation in soil substrate quality. However, over time, the widening distribution of P. cookii, as a consequence of a major management intervention (the eradication of feral cats), may enable P. flavescens to colonise all suitable areas. In Chapter 4, the focus changes to what has been considered the third major response to climate change, along with range and phenological responses - changing animal body sizes. Body size is one of the most significant and obvious features of animals and is of considerable ecological and physiological importance. A prediction of the temperature-size rule (TSR) is that with warming, body size of the weevil species on both MI and PEI should decline. However, predation by mice of the weevils on MI should fundamentally affect the pattern of such change, causing it to differ from neighbouring PEI, indicating synergistic impacts between climate change and invasions. Analysis of a 24-year data set indicates a decline in the body size of all weevil species on PEI with increasing temperature. However, on MI, a negative relationship between mean annual temperature and body size is found only for Palirhoeus eatoni, a species not eaten by mice. A possible explanation for the positive relationships found for the other species could be due to higher metabolic demands imposed on mice in colder years than in warmer ones. Any increase in predation coupled with a preference for larger sizes, which the mice clearly show, would lead to a decline in the mean size of the weevil species. Due to the relationship between body size and metabolic rate and the importance of the weevils in the islands’ food webs, changes to the body size of these organisms could have significant consequences for the island ecosystems’ functioning. The thermal environment experienced by organisms also has a direct effect on survival, growth and reproduction. The physiological response of organisms to rapidly changing climates is therefore a primary concern. Organisms may respond to variable environmental conditions through phenotypic plasticity as well as behaviour. Chapter 5 of this thesis shows that of the weevil species and populations investigated on MI, most display phenotypic plasticity, the form of which is in keeping with the ‘Hotter is Better’ hypothesis. This could be due to rare extreme temperature events and the advantage for the performance curves to incorporate high temperatures experienced in the environment. Mismatches between thermal optima and preferred temperatures displayed by all species could mean that these weevils are well equipped to cope with warming conditions on MI unless the prediction of an increase of rare extreme events such as extreme temperatures is realised. Rapidly changing climates and an increase in the introduction of non-indigenous species are issues of major conservation concern. This has increased the significance of studies on the impacts of these threats. However, this thesis shows that to understand such processes, it is essential that an integration of disciplines be undertaken. This thesis thus adopts a multidisciplinary approach and highlights key issues associated with both climate change and biological invasions. The patterns and predictions of species and community responses to these environmental changes are complex. Moreover, predicting such responses is likely to be problematic, especially as multiple factors will change concurrently and how these factors might change is unclear. This highlights the importance of long-term records for understanding organism responses to such changes. Furthermore, impacts on indigenous species are likely to be exacerbated by the predicted increase in the rate of introductions with climate change. This makes the case for preventing the dispersal of invasive species to new areas all the more important. / AFRIKAANSE OPSOMMING: Klimaatsverandering en indringer spesies is belangrike bedreigings vir biodiversiteit. In besonder word voorspel dat hierdie bedreigings terrestriële sisteme in die sub-Antarktiese sal beïnvloed, waar beduidende ekosisteem reaksie aan beide reeds gesien is. In hierdie tesis word die sub-Antarktiese Prince Edward eiland groep as a model sisteem gebruik om belangrike vrae met betrekking tot klimaatsverandering en die impak van indringer spesies te ondersoek. Die eiland groep bestaan uit twee eilande, Marion (ME) en Prince Edward (PEE), wat beide versnellende verwarming ervaar, maar tog verskillende indringer samestellings het en vervolgens verskillende impakte ervaar. Variasie in die patrone van indringerspesierykheid en vollopheid en hulle onderliggende oorsake is van aansienlike omgewings en bewarings betekenis. Terwyl 'n toename in die beskikbaarheid van energie tipies lei tot 'n toename in spesierykheid, word die onderliggend meganismes van hierdie patrone swak verstaan. In Hoofstuk 2 van hierdie tesis, word hierdie verhoudings vir springsterte ondersoek, 'n belangrike komponent van die grond fauna op ME. Energie verduidelik 'n groot hoeveelheid van die ruimtelike variasie in inheemse en indringende springstert spesierykheid. Versteuringsdrempels en stressvolle temperature is meer belangrik as die toename in bevolking groottes in die bepaling van hierdie variasie in spesierykheid. Aangesien beide inheemse en indringende springstert spesierykheid en vollopheid sterk verwant is aan temperatuur, kan 'n verwarmende klimaat verreikende gevolge vir hierdie organismes hê. In die besonder word voorspel dat indringerspesies bevoordeeld sal wees relatief tot inheemse spesies onder verwarmende toestande. Een spesie waar dit veral blyk om geneig te wees, gegewe sy fisiologiese reaksie tot eksperimentele verhitting en uitdroging, is die groot indringer tomocerid, Pogonognathellus flavescens. Om te bepaal of dit die geval sal wees, hang af van die begrip van die onderliggende faktore van sy voorkomsgrense en vollopheidstruktuur. Daarbenewens is daar min studies wat gepoog het om te onderskei tussen die veroorsakende basis van vollopheidstruktuur en voorkomsgrense, veral vir indringerspesies. Dus, in Hoofstuk 3, word plaaslike mikroklimaat veranderlikes en fisiologiese toleransies van die indringer springstert, P. flavescens ('n habitat generalis), ondersoek. Die resultate stel voor dat die spesie wyd verspreid moet wees oor 'n verskeidenheid van habitatte op ME. Maar, die springstert is beperk tot inheemse Poa cookii polle grasveldhabitatte in die suidooste. Die huidige voorkomsgrense word daar gestel deur verspreidingsbeperking (dws voorwaardelike afwesighede), terwyl vollopheidstruktuur 'n funksie is van die variasie in die grond substraat kwaliteit. Maar, die uitbreidende verspreiding van P. cookii as gevolg van 'n groot bestuursingryping (die uitwissing van wilde huiskatte), kan P. flavescens in staat stel om alle geskikte gebiede te koloniseer met verloop van tyd. In Hoofstuk 4 verander die fokus na wat as die derde groot reaksie op klimaatsverandering beskou word, saam met voorkoms en fenologiese reaksies - veranderende diere liggaamsgroottes. Liggaamsgrootte is een van die beduidendste en mees voor die hand liggende eienskappe van diere en is van aansienlike ekologiese en fisiologiese belang. 'n Voorspelling van die temperatuur-grootte-reël (TGR) is dat met verwarming, liggaamsgrootte van die snuitkewerspesies op beide ME en PEE sal afneem. Hoe ookal, predasie deur muise van die snuitkewers op ME moet fundamenteel die patroon van sodanige verandering op PEE beïnvloed, wat sinergistiese impakte tussen klimaatsverandering en indringings aandui. Die ontleding van 'n 24-jarige datastel dui aan op 'n afname in die liggaamsgrootte van alle snuitkewer spesies op PEI met ‘n toename in temperatuur. Maar, op ME is 'n negatiewe verhouding tussen die gemiddelde jaarlikse temperatuur en liggaamsgrootte net gevind vir Palirhoeus eatoni, 'n spesie wat nie deur die muise geëet word nie. 'n Moontlike verduideliking vir hierdie positiewe verhoudings wat gevind is vir die ander spesies kan wees as gevolg van hoër metaboliese eise op die muise in kouer jare as in warmer jare. Enige toename in predasie, tesame met 'n voorkeur vir groter mates, wat die muise duidelik wys, sou lei tot 'n afname in die gemiddelde grootte van die snuitkewer spesies. As gevolg van die verhouding tussen liggaamsgrootte en metaboliese tempo, sowel as die belangrikheid van die snuitkewers in die eilande se voedselwebbe, kan veranderinge in die liggaamsgrootte van hierdie organismes beduidende gevolge op die eiland ekosisteme se funksionering hê. Die termiese omgewing wat deur organismes ervaar word het ook 'n direkte invloed op oorlewing, groei en voortplanting. Die fisiologiese reaksie van organismes op vinnig veranderende klimate is dus 'n primêre bron van kommer. Organismes kan reageer op veranderlike omgewingstoestande deur fenotipiese plastisiteit sowel as gedrag. Hoofstuk 5 van hierdie tesis toon dat van die snuitkewerspesies en bevolkings wat ondersoek is op ME, die meeste fenotipiese plastisiteit vertoon, die vorm wat in ooreenstemming is met die ‘Warmer is Beter’ hipotese. Dit kan wees as gevolg van seldsame uiterste temperatuur gebeure en die voordeel vir die prestasie kurwes om hoë temperature wat ervaar word in die omgewing in te sluit. Mismatches tussen termiese optima en voorkeur temperature vertoon deur alle spesies kan beteken dat hierdie snuitkewers goed toegerus is om die verhitting op ME te hanteer, tensy die voorspelling van 'n toename van seldsame uiterste gebeure soos uiterste temperature gerealiseer word. Vinnig veranderende klimate en 'n toename in die bekendstelling van nie-inheemse spesies is kwessies van groot bewarings kommer. Dit het die betekenis van studies oor die impak van hierdie bedreigings verhoog. Hierdie tesis toon egter dat om sulke prosesse te verstaan, dit noodsaaklik is dat 'n integrasie van die dissiplines onderneem word. Hierdie tesis aanvaar dus 'n multi-dissiplinêre benadering en beklemtoon die belangrike kwessies wat verband hou met beide klimaatverandering en biologiese indringing. Die patrone en voorspellings van spesies en die gemeenskapsreaksies op hierdie omgewingsveranderinge is kompleks. Verder, die voorspelling van sodanige reaksies sal waarskynlik problematies wees, veral omdat verskeie faktore gelyktydig sal verander en hoe hierdie faktore kan verander is onduidelik. Dit beklemtoon die belangrikheid van lang termyn rekords vir die begrip van organisme reaksies op sulke veranderinge. Verder, die impak van inheemse spesies is geneig om te vererger deur die voorspelde toename in die tempo van bekendstellings met klimaatsverandering. Dit maak die taak vir die bestuur van die voorkoming dat indringerspesies nuwe gebiede bereik al hoe meer belangrik.

Thesis (MSc)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: Macroecological relationships have rarely been studied at wide spatial scales and across geographic ranges of species in the field in the sub-Antarctic. In this thesis I examined the occupancy, distribution and abundance, and the relationships thereof, of indigenous plants and alien species at broad (island-wide) and fine scales across sub-Antarctic Marion Island. The impacts of alien species and their interactions with indigenous plants were also investigated. I examined the nature of the abundance structure of a cushion-forming, vascular plant, Azorella selago, at the island-wide scale. Moreover, the hypothesis that species reach their highest abundances at the centre of their geographic range and decline in abundance towards the range edges was tested. Azorella selago cushions were counted in 8 m x 8 m quadrats, placed regularly at 1 minute latitude and longitude intervals across Marion Island. Using spatially non-explicit and explicit methods, this study showed that the abundance structure of A. selago had a more complex pattern of high abundance patches and low abundance gaps in its island-wide distribution. Subsequently, the hypothesis of an abundant centre distribution was not supported for A. selago across Marion Island. Rather, there were sharp discontinuities at both the coastal and altitudinal (667 m a.s.l.) limits for the species, between which little pattern in altitudinal abundance structure existed. Mice (Mus musculus) have recently been found to cause extensive structural damage to A. selago. The structural influence of mice on vegetation structure at the landscape scale has largely been overlooked on many sub-Antarctic islands. I mapped the distribution of evidence of mouse damage within the cushions of A. selago across the island using systematic (at 1 minute latitude and longitude intervals) and opportunistic sampling. Approximately 40 % of the systematically sampled sites had evidence of mouse damage to A. selago. Furthermore, a third of cushions in opportunistically sampled sites was damaged. Mouse damage was high in sites of low A. selago abundance, emphasizing that impacts of mice may be greater in low cushion abundance areas. This damage sometimes led to the disintegration of entire cushions. Given that A. selago acts as a nurse plant and supports high abundances of indigenous invertebrates, the impacts of mice on this keystone species may have significant ecological implications. Studies on interactions between alien and indigenous plants are limited within the sub-Antarctic. I examined the fine-scale distributions and co-occurrences of alien plants, Agrostis stolonifera and Sagina procumbens, and the indigenous Acaena magellanica (in 2 m x 2 m plots, subdivided into 0.25 m x 0.25 m quadrats) along rivers on Marion Island. Environmental variables were important for the occurrence of these species. In particular, 42.95 % and 24.82 % of the deviance in the occurrence of A. stolonifera and S. procumbens, respectively, was explained by environmental variables, compared to 17.35 % for A. magellanica. Furthermore, the co-occurrence of A. magellanica with A. stolonifera was significantly influenced by environmental variables. Significant positive spatial associations between A. magellanica and A. stolonifera were found, while the interactions of either species with S. procumbens were either spatially dissociated or random. Therefore, this study highlighted that alien species are responding to different environmental variables and conditions on Marion Island. Sagina procumbens seems to be less sensitive to the island’s environmental conditions and may thus be affecting biodiversity at broader ranges. This thesis provides unparalleled data on the distributions and interactions of indigenous plants and alien species for Marion Island. Alien species are undoubtedly posing significant threats to indigenous plants on the island and this thesis presents insight into interactions of species, specifically plants, an approach underrepresented in the sub-Antarctic to date. / AFRIKAANSE OPSOMMING: Makro-ekologiese verhoudings is selde bestudeer op wye ruimtelike skale en oor geografiese gebiede van spesies in die veld in die sub-Antarktiek. In hierdie tesis het ek die digtheid, bewoning, verspreiding en die verhoudings daarvan, van inheemse plante en uitheemse spesies ondersoek op breë (eiland-wyd) en smal skale oor sub-Antarktiese Marion Eiland. Die impakte van uitheemse spesies en hul interaksies met inheems plante is ook ondersoek. Ek het die aard van die digtheidstruktuur ondersoek van 'n kussing-vormende, vaatplant, Azorella selago, op die eiland-wydte skaal. Bowenal is die hipotese dat spesies hul hoogste digtheid bereik in die sentrum van hul geografies gebied en afneem in digtheid na die grense van die gebied getoets. Azorella selago kussings is getel in 8 m x 8 m kwadrante, wat eweredig geplaas is op 1 minuut breedte- en lengtegraad intervalle oor Marion Eiland. Deur gebruik te maak van ruimtelik nie-eksplisiete en eksplisiete metodes, het hierdie studie getoon dat die digtheidstruktuur van A. selago ‘n meer komplekse patroon van hoë digtheidslaslappe en lae digtheidsgapings in sy eiland-wyd verspreiding het. Vervolgens is die hipotese van 'n digte sentrum verspreiding nie gesteun vir A. selago oor Marion Eiland nie. Daar was eerder skerp diskontinuïteite by beide die kus- en hoërliggende (667 m bo seespieël) grense vir die spesie, waartussen daar ’n oneweredige patroon in digtheidstruktuur bestaan het. Onlangs is bevind dat muise (Mus musculus) uitgebreide struktuele skade aan A. selago veroorsaak. Die struktuele invloed van muise op plantegroei struktuur op landskapskaal is grootliks oor die hoof gesien op baie sub-Antarktiese eilande. Ek het die verspreiding van die bewyse van muisskade binne die kussings van A. selago oor die eiland gekarteer deur gebruik te maak van sistematiese (tot 1 minuut breedte- en lengtegraad intervalle) en opportunistiese opnames. Ongeveer 40 % van die sistematiese opname kwadrante het bewyse van muis skade aan A. selago vertoon. Verder, ‘n derde van die kussings in die opportunistiese opname kwadrante was beskadig. Muisskade was hoog in plotte met lae A. selago volopheid, wat beklemtoon dat impakte van muise groter mag wees in lae kussing digtheid gebiede. Hierdie skade het partykeer gelei tot die verbrokkeling van hele kussings. Gegewe dat A. selago as 'n verpleegsterplant optree en ’n hoë digtheid van inheemse invertebrata ondersteun, mag die impakte van muise op hierdie hoeksteen spesie beduidende ekologiese implikasies tot gevolg hê. Studies oor interaksies tussen uitheemse- en inheemse plante is beperk in die sub-Antarktiese gebied. Ek het die smal-skaal verspreidings ondersoek en medevoorkoms van uitheemse plante, Agrostis stolonifera en Sagina procumbens, en die inheems Acaena magellanica (in 2 m x 2 m kwadrante, subverdeel in 0. 25 m x 0. 25 m kwadrante) langs riviere op Marion Eiland. Omgewingsveranderlikes was belangrik vir die voorkoms van hierdie spesies. In besonder, 42.95 % en 24.82 % van die afwykings in die voorkoms van A. stolonifera en S. procumbens, onderskeidelik, is verduidelik deur omgewingsveranderlikes, vergeleke met 17.35 % vir A. magellanica. Verder, die medevoorkoms van A. magellanica saam met A. stolonifera is beduidend beinvloed deur omgewingsveranderlikes. Beduidende positiewe ruimtelike assosiasies tussen A. magellanica en A. stolonifera is gevind, terwyl die interaksies van beide spesies met S. procumbens was of ruimtelik nie-geassosieerd of lukraak. Daarom het hierdie studie uitgelig dat uitheemse spesies reageer op verskillende omgewingsveranderlikes op Marion Eiland. Sagina procumbens blyk minder sensitief te wees tot die eiland se omgewingsomstandighede en mag dus moontlik biodiversiteit op breër vlakke beïnvloed. Hierdie tesis voorsien onge-ewenaarde data oor die verspreiding en interaksies van inheems plante en uitheemse spesies vir Marion Eiland. Uitheemse spesies hou ongetwyfeld ’n beduidende bedreiging in vir inheems plante op die eiland, en hierdie tesis bied insig in die interaksies van spesies, spesifiek plante – ’n benadering wat swak verteenwoordig was in die sub-Antarktiese gebied tot op hede.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Species’ seasonal behaviour is of paramount importance in understanding community functioning and dynamics. Recently, plant phenology has further gained significance as a reliable indicator of climate change impacts. Despite the importance of understanding plant dynamics, there are relatively few plant phenological records for the sub-Antarctic region, and where records exist they are often not extensive. Sub-Antarctic Marion Island, typical of Southern Ocean Islands, offers a useful setting for addressing these knowledge gaps. This study documented the vegetative and reproductive phenologies (or aggregate phenological patterns) of twelve indigenous and three alien vascular plant species on the island. The phenological differences among the species and distinct seasonal groupings (e.g. early, intermediate and late species) were examined. I also investigated the phenological differences among the indigenous and alien plant species. Furthermore, the onset of selected reproductive phenophases from the current records was compared with historical records for determining the extent of climate change-related alterations in phenology. Phenological data were collected fortnightly on five, 5 m x 5 m permanent plots per species (except for a few species) for a full growing season. Thus the sample size is n = 5 for all plant species except for Crassula moschata (n = 4), Juncus effusus (n=4) and Rumex acetosella (n=1). Sites of the same species were separated by at least 500 m except for the alien plant, Juncus effusus, where all four known populations were selected despite two of these populations being < 500 m apart. This study indicated that Marion Island plants grow throughout the year with no major peaks except in Azorella selago and Acaena magellanica which showed winter dormancy. However, reproduction in most plant species predominately occurred in spring and summer months. Pringlea antiscorbutica and Poa cookii were the first two species to set flower buds in September while most species dispersed their seeds in summer except for Agrostis magellanica and Crassula moschata which dispersed in early autumn. Distinct from most temperate systems, the reproductive seasonality displayed by Marion Island plant species is explained more by daylength than by temperature, perhaps due to the region’s typical thermal aseasonality. Interestingly, many cooccurring species and/or clades across the Falkland, Kerguelen, Macquarie and South Georgia Islands also showed similar flowering onset date to the Marion Island plants, further confirming their daylength sensitivity. However, other external factors seem to come into play at later events of reproduction. Consequently, fruit maturation time of similar species across the sub-Antarctic islands varied substantially despite the plants having flowered in the same month. Although plant species showed similar reproductive seasonality, there were significant differences among species phenologies i.e. phenophase timing, duration and peak occurrence dates. However, using 95% confidence intervals of Generalized Linear Models weighted means, and/or one-way ANOVA (Tukey post hoc test), three homogenous sets of species (early, late, or intermediate onsets) were identified based on flower bud, flowering and seed dispersal phenophase onset dates. The homogenous species groupings observed for flower buds also remained unchanged during flowering onset except for Cotula plumosa and Callitriche antarctica which switched groups. As for the seed dispersal timing, the pattern was not consistent with that of the flower bud and flowering onset homogenous groupings, except for Acaena magellanica and Agrostis magellanica which remained in the early and late groups, respectively. Conversely, in the case of the timing of other phenophases (pollen release, fruit set and fruit ripening), entire phenophase durations, and peak occurrence dates, species overlapped greatly, resulting in an unbroken progression or continuum of phenology among species. Similarly, the three alien plant species investigated here (Cerastium fontanum, Juncus effusus and Rumex acetosella) showed no consistent phenological differences from the rest of the species. However, a widespread alien plant species on Marion Island, C. fontanum, reproduced for most of the year, although its reproduction peak was in summer months as was the case for the rest of the species. This study also indicated that indigenous plant species have altered their reproductive phenologies since 1965. Although the response was species-specific, the majority of plant species significantly delayed the onset of reproductive activities in 2007 by comparison with 1965. However, it is not clear if the observed species response was caused by the now drier and warmer Marion Island climate or by discrepancies in reporting in the earlier studies and/or sampling differences between the recent and historical records. Therefore, these results should be taken with caution. In conclusion, this research provided a detailed phenological dynamics record for vascular plant species on the island. Over time these records may be used as a basis for monitoring and modelling the impact of climate on plant phenology on the island. / AFRIKAANSE OPSOMMING: Spesies se seisoenale gedrag is van die allergrootste belang in die begrip van gemeenskapsfunksionering en dinamika. Meer onlangs het plant fenologie verdere betekenis verwerf as ‘n betroubare indikator vir die impakte van klimaatsverandering. Ondanks die belangrikheid om plant dinamika te verstaan, is daar relatief min plant fenologiese rekords vir die sub-Antarktiese streek en waar rekords wel bestaan is dit dikwels nie omvangryk nie. Sub- Antarktiese Marion Eiland, tipies van Suidelike Oseaan Eilande, bied ‘n nuttige ligging om hierdie kennis gapings aan te spreek. Hierdie studie het die vegetatiewe en voorplantingsfenologieë (of gesamentlike fenologiese patrone) van elf inheemse en drie uitheemse vaatplantspesies op die eiland gedokumenteer. Die fenologiese verskille tussen die spesies en duidelike seisoenale groeperings (bv. vroeë, intermediêre en laat spesies) is ondersoek. Ek het ook die betekenisvolle fenologiese verskille tussen die inheemse en uitheemse plantspesies ondersoek. Voorts, die aanvang van gekose voortplanting feno-fases van huidige rekords is vergelyk met historiese rekords om die mate van klimaatsverandering verbandhoudende veranderings in die fenologie te bepaal. Fenologiese data is twee weekliks ingesamel op vyf, 5 m x 5 m permanente plotte per spesie (behalwe vir ‘n paar spesies) vir ‘n volle groei seisoen. Dus, die insamelings grootte is n = 5 vir al die plantspesies behalwe vir C. moschata (n = 4), Juncus effusus (n=4) en Rumex acetosella (n=1). Persele vir dieselfde spesies is geskei deur ten minste 500 m, behalwe vir die uitheemse plant, Juncus effusus, waar al vier populasies wat bekend is gekies is, ten spyte daarvan dat twee van hierdie populasies < 500 m uitmekaar is. Hierdie studie het aangedui dat Marion Eiland plante regdeur die jaar groei, met geen belangrike spitstye nie, behalwe in Azorella selago en Acaena magellanica wat ‘n winter rusperiode wys. Hoe ookal, voortplanting in meeste van die plantspesies het hoofsaaklik voorgekom tussen die lente en somermaande. Pringlea antiscorbutica en Poa cookii was die eerste twee spesies om blomknoppe uit te stoot in September, terwyl die meeste spesies hulle sade versprei het gedurende die somer, behalwe vir Agrostis magellanica en Crassula moschata wat versprei het in vroeg herfs. Duidelik van meeste gematigde sisteme, word die voortplanting seisoenaliteit, getoon deur die Marion Eiland plantspesies, verduidelik meer deur daglengte as deur temperatuur, moontlik weens die streek se tipiese termiese a-seisoenaliteit. Interessant, baie spesies en/of afstameling-groeperings wat saam aangtref word dwarsoor die Falkland, Kerguelen, Macquarie en Suid Georgia Eilande wys ook soortgelyke bloei aanvangsdatums as die Marion Eiland plante, nog meer bevestigend van hulle dag-lengte sensitieweteit. Hoe ookal, ander eksterne faktore blyk betrokke te raak by latere gebeure van voortplanting. Gevolglik het vrug rypwordingstyd van dieselfde spesies oor die sub-Antarktiek noemenswaardig verskil, ten spyte daarvan dat die plante in dieselfde maand geblom het. Alhoewel plantspesies dieselfde voortplanting seisoenaliteit gewys het, was daar ‘n noemenswaardige veskil tussen spesie fenologieë, m. a. w. feno-fase tydsberekenning, tydsduur en spits voorkomsdatums. Hoe ookal, deur gebruik te maak van 95% betroubaarheid intervalle van Algemene Lineêre Modelle gewigte gemiddelde en/of een rigting ANOVA (Turkey post hoc toets), is drie homogene stelle van spesies (vroeë, laat en intermediêre aanvang) geïdentifiseer gebasseer op blomknop, bloei en saad verspreiding feno-fase aanvangsdatums. Die homogene spesie groeperings waargeneem op blomknoppe het ook onveranderd gebly gedurende bloei aanvang behalwe vir Cotula plumosa en Crassula antarctica wat groepe geruil het. Vir die saadverspreiding tydsberekenning was die patroon nie konstant met die van die blomknop en bloei aanvang homogene groepe nie, behalwe vir Acaena magellanica en Agrostis magellanica wat in die vroeë en laat groepe respektiewelik gebly het. Omgekeerd, in die geval van tydsberekenning van ander feno-fases (stuifmeel vrysetelling, vrugwerp, vrugrypwording), volledige feno-fase tydsduur en spits voorkomsdatums het spesies grootliks oorvleuel, wat ‘n ongebroke vordering of deurlopendheid van fenologie tussen die spesies tot gevolg het. Ooreenkomstig het die drie uitheemse spesies wat hier ondersoek is (Cerastium fontanum, Juncus effusus en Rumex acetosella) geen bestendige fenologiese verskille van die res van die spesies gewys nie. Hoe ookal, ‘n wydverspreide uitheemse spesie op Marion Eiland, Cerastium fontanum, het deur die meeste van die jaar voortgeplant, hoewel met ‘n voorplanting spits in die somer maande soos die res van die spesies. Hierdie studie dui ook aan dat inheemse plantspesies hulle voortplanting fenologieë verander het sedert 1965. Alhoewel die reaksie spesiespesifiek was, het die meerderheid van die plantspesies hulle voortplanting aanvang aansienlik vertraag gedurende 2007 in vergelyking met 1965. Hoe ookal, dis nie duidelik of die waargeneemde spesie reaksie was as gevolg van die nou droër en warmer Marion Eiland klimaat of deur teenstrydighede in verslagewing gedurende die vroëre studies en/of insameling verskille tussen die onlangse en historiese rekords. Daarom moet hierdie resultate met versigtigheid hanteer word. In samevatting, hierdie navorsing voorsien ‘n gedetaileerde fenologiese dinamieka rekord vir vaatplantspesies op die eiland. Oor tyd kan hierdie rekords gebruik word as basis vir monitering en modellering van die impak van klimaat.

<p>Marion Island is situated in the South Indian Ocean and belongs to the sub-Antarctic island group, Prince Edward Islands. The islands in the sub-Antarctic have over the past few decades been exposed to a warmer and drier climate trend. The aim of this thesis is to achieve better understanding of the small-scale spatial and temporal variability between Azorella selago andthe surrounding microclimate. Due to the consequences of climate change, the interactions between Azorella selago, landforms and soil processes are important for the future of the terrestrial ecosystems in the sub-Antarctic. The theory part in this thesis describes different processes and features that are essential to understand the context of this thesis. The energy balance and the insolation is shown to be an important aspect when looking at the spatialvariability of the microclimate. The summary of the results in the thesis is based on temperature and moisture measurements within two grids. One on the east and one on the west side of the island</p><p>The most important result from the measurements is that different weather conditions create different situations for the microclimate. The weather condition ‘sunny no wind’ created a high spatial variability in temperature on the ground, which was completely absent during overcast days. Temperature variability is highly dependent on cloud cover according to these results. Moisture changes also seem to be less weather dependent than temperaturechanges.</p><p>The data provide a first confirmation that an increase in sunshine hours gives increased spatial variability in temperature (not moisture) and soil frost. An increase in spatial variability of the microclimate within small areas could give rise to an expansion in the patchiness of soil frost processes in the landscape. The representivity of single point measurements of ground surface temperature should be questioned.</p><p>Patterns of areas with low moisture content within the grid correlate with points where measurements were taken on Azorella selago. The Azorella cushion could, according to the results of this thesis, be associated with dry areas within the grid. Azorella selago is thereby suggested to increase the spatial variability of moisture and also contribute to a locally drier microclimate. Moisture variability varies more between the east and west side of the island, than that it is weather dependent.</p><p>Shaded areas show a pattern of lower temperature than for the other variables under sunny conditions. If more shaded areas are created by for example landforms like Azorella selago or solifluction deposits, the temperatures would probably be lower and also create a wider spatial variability.</p><p>This study provides first data on the important interactions between Azorella selago and how it affects through spatial variability in micro-climate, ground frost potential and resulting soil disturbance by frost creep and solifluction.</p>

Marion Island is situated in the South Indian Ocean and belongs to the sub-Antarctic island group, Prince Edward Islands. The islands in the sub-Antarctic have over the past few decades been exposed to a warmer and drier climate trend. The aim of this thesis is to achieve better understanding of the small-scale spatial and temporal variability between Azorella selago andthe surrounding microclimate. Due to the consequences of climate change, the interactions between Azorella selago, landforms and soil processes are important for the future of the terrestrial ecosystems in the sub-Antarctic. The theory part in this thesis describes different processes and features that are essential to understand the context of this thesis. The energy balance and the insolation is shown to be an important aspect when looking at the spatialvariability of the microclimate. The summary of the results in the thesis is based on temperature and moisture measurements within two grids. One on the east and one on the west side of the island The most important result from the measurements is that different weather conditions create different situations for the microclimate. The weather condition ‘sunny no wind’ created a high spatial variability in temperature on the ground, which was completely absent during overcast days. Temperature variability is highly dependent on cloud cover according to these results. Moisture changes also seem to be less weather dependent than temperaturechanges. The data provide a first confirmation that an increase in sunshine hours gives increased spatial variability in temperature (not moisture) and soil frost. An increase in spatial variability of the microclimate within small areas could give rise to an expansion in the patchiness of soil frost processes in the landscape. The representivity of single point measurements of ground surface temperature should be questioned. Patterns of areas with low moisture content within the grid correlate with points where measurements were taken on Azorella selago. The Azorella cushion could, according to the results of this thesis, be associated with dry areas within the grid. Azorella selago is thereby suggested to increase the spatial variability of moisture and also contribute to a locally drier microclimate. Moisture variability varies more between the east and west side of the island, than that it is weather dependent. Shaded areas show a pattern of lower temperature than for the other variables under sunny conditions. If more shaded areas are created by for example landforms like Azorella selago or solifluction deposits, the temperatures would probably be lower and also create a wider spatial variability. This study provides first data on the important interactions between Azorella selago and how it affects through spatial variability in micro-climate, ground frost potential and resulting soil disturbance by frost creep and solifluction.

All previous taxonomic studies on the Ectemnorhinus group of weevils have been based primarily on morphological data. While these studies are invaluable, some questions can only be addressed adequately through molecular studies. This is especially true when studying the genetic relationships and phylogeograpic patterns of taxa endemic to the South Indian Ocean Province (SIP) biotas that have long been controversial. The Ectemnorhinus group of genera is a monophyletic unit of weevils endemic to the region. The present study focused mainly on the Ectemnorhinus group of weevils found on the Prince Edward Islands archipelago (PEIA). The mitochondrial cytochrome oxidase I gene was targeted when investigating relationships among members of this weevil group. On the PEIA, it is important to note that Marion Island (MI) and Prince Edward Island (PEI) differ in terms of alien invasive species, such as the introduced house mouse Mus musculus and in conservation management strategies. Since emergence, a series of volcanic and glaciation events have occurred on Marion Island, whilst Prince Edward Island has remained largely unaffected by glaciation. Phylogenetic analyses revealed the presence of two genetically and morphometrically distinct species of Ectemnorhinus weevils on PEI, whilst evidence for a single species, comprising diverse genetically discrete populations was found on MI. Based on these results, the species unique to PEI has been designated E. kuscheli n. sp., whilst the present study confirmed the synonymy between E. similis and E. marioni, the two species originally described from MI. Ectemnorhinus kucheli appears to be restricted to PEI, whereas E. similis occurs on both MI and PEI. When investigating the population dynamics of the Ectemnorhinus weevils on the PEIA, the data indicated that PEI was the first of the two islands of the PEIA to be colonized by Ectemnorhinus weevils, at an estimated time of coalescence of approximately 0.3116 million years ago (MYA). The PEI population then acted as the source population for the colonization of MI by Ectemnorhinus weevils some time before the last glaciation, approximately 10 000 to 35 000 years ago. The separation by distance of the PEI Ectemnorhinus weevils from those on MI then gave rise to two species by allopatric speciation on MI. During the last glaciations, MI was extensively glaciated with only the southwestern corner of the island being free of ice. This extensive glaciation of MI would have resulted in the eradication of all E. similis on MI except for those occurring on the ice-free southwestern corner of the island. At the end of the last glacial maximum, when the ice started to melt, the coastal areas of MI emerged first from beneath the ice and were available for re-colonization by weevils. The movement of weevils that were isolated in the south-western corner of MI, along the coastal areas of the island, was assisted by strong, frequent south-western winds. Subsequent, post-glacial volcanism during the Holocene was then responsible for the fragmentation of the new migrants, resulting in small population pockets surrounded by fresh, uninhabitable lava and subsequent divergence of each populations. When the Holocene black lava became re-colonizeable, the weevils from the different isolated populations migrated to the remainder of the island. Currently, members of the different genetically-identified populations occur in sympatry and in some cases even on the same plant, but no noticeable geneflow was detected between them. It is thus suggested that the time of isolation, before the post-glacial black lava during Holocene became hospitable, was sufficiently long and the populations sufficiently small that a number of genetically-discrete populations arose. Consequently, the present study recognises two genetically discrete populations of E. kucheli on PEI and seven discrete E. similis populations on MI that are morphologically indistinct. When examining the relationships among 13 species from five different islands within the South Indian Ocean Province (SIP) that are representative of 22 populations within the genera Palirhoeus, Bothrometopus and Ectemnorhinus, there was little support for separating the genus Palirhoeus from Bothrometopus, and no support for the morphologically-delineated species groups currently recognized within Bothrometopus. The present study shows that colonization of the Prince Edward Islands is likely to have occurred repeatedly from other islands within the SIP and that Bothrometopus parvulus on the PEIA comprises two species that are not sister taxa. The second novel con-generic species was therefore designated Bothrometopus huntleyi n. sp. and examination of the genetically identified specimens resulted in the indentification of distinguishing morphological characteristics. The analyses indicated that B. huntleyi arose approximately 0.5 million years ago from a high-altitude population that is still present on MI. The first major intra- and inter-island dispersal event occurred ~0.338 MYA, coinciding with the glaciation-free second volcanic stage on MI. Apart from this early inter-island colonisation, only one other between-island dispersal event, corresponding with the glaciation-free seventh volcanic stage, was detected. Genetically discrete weevil complexes on each of the islands of the PEIA together with the low levels of inter-island gene flow reaffirm the need to control alien invasive mice, which are restricted to MI, and which prey on these weevil species. / Thesis (PhD)--University of Pretoria, 2012. / Zoology and Entomology / unrestricted

La croissance des activités anthropiques au cours du dernier siècle a contribué à la dispersion et à l’établissement d’espèces végétales non-natives à travers le monde. Ces espèces sont des moteurs importants de changements environnementaux puisqu’elles ont la capacité de modifier les communautés végétales natives notamment à travers la compétition. Puisque les humains sont un des principaux moteurs d'introduction, d'établissement et de propagation d'espèces non-natives et que toute mesure de gestion, pour être efficace, dépend d’une acceptabilité sociale, il est nécessaire de comprendre les perceptions et les choix relatifs à leur utilisation et à leur gestion. La présente recherche a servi à : i) comprendre les perceptions des différentes parties prenantes envers les différentes espèces végétales non-natives de l’île Navarino, une zone tampon de la Réserve de la Biosphère du Cap Horn (RBCH) dans la région subantarctique chilienne ainsi qu’à ii) identifier les dynamiques de niches et les zones à haut potentiel d’établissement (i.e. points chauds) de quatre de ces espèces, qui serviront ensemble d’outils à la gestion de la RBCH. Pour répondre au premier objectif, sept groupes de parties prenantes ont été identifiés (i.e. résident-e-s, résident-e-s aîné-e-s, conservationnistes, membres de la marine, touristes, membres de la communauté autochtone yaghan, employé-e-s des services publics), à l’intérieur desquels 21 entrevues semi-dirigées ont été conduites. Pour répondre au deuxième objectif, les données de présence globales et régionales de quatre espèces végétales herbacées non-natives particulièrement abondantes i.e. Bellis perennis, Cerastium fontanum, Taraxacum officinale et Trifolium repens ainsi que les données climatiques associées ont servi à développer des modèles de distribution des espèces utilisant la méthode d’entropie maximale (MaxENT). En ce qui concerne le premier objectif, les résultats ont révélé des lacunes dans la compréhension du concept d’espèces non-natives parmi les différentes parties prenantes dans le contexte local. D’autre part, les analyses ont révélé de nombreuses valeurs positives associées aux espèces de plantes non-natives à Navarino, notamment la valeur esthétique. Aussi, cette recherche a montré que la plupart des parties prenantes étaient indifférentes à la gestion des espèces de plantes herbacées non-natives. En ce qui concerne le deuxième objectif, les résultats ont révélé un changement de niche habituellement utilisée par les espèces liée au climat moins favorable de Navarino ainsi qu’une forte plasticité pour les quatre espèces mentionnées ci-haut. Néanmoins, les quatre populations auraient atteint l’équilibre à Navarino. Finalement, la combinaison des modèles globaux et régionaux montre que les zones de points chauds se situent plus particulièrement sur la côte sud de l’île et s’étendent au Nord dépendamment des espèces. Basés sur les résultats obtenus, nous suggérons donc (i) de sensibiliser davantage les parties prenantes aux plantes non-natives, (ii) d'intégrer leurs valeurs dans les décisions de gestion futures et (iii) de surveiller les distributions des espèces végétales non-natives à Navarino à des fins de prévention en considérant l’emplacement stratégique de l'île de Navarino comme un tremplin potentiel pour la dispersion des espèces non-natives vers l'Antarctique. / The growth of human activities over the last century has contributed to the dispersal and establishment of non-native plant species around the world. These species are important drivers of environmental change since they have the capacity to modify native plant communities, especially through competition. Since human are the main drivers of introduction, establishment and spread of non-native species and since management strategies need to take into account public attitudes to be successful, it is necessary to understand the perceptions and choices regarding their use and management. The present study aimed to: i) understand the perceptions of different stakeholders towards the different non-native plant species of Navarino Island, a buffer zone of the Cape Horn Biosphere Reserve (CHBR) in the Chilean sub-Antarctic region and ii) identify niche dynamics and high potential establishment areas (i.e. hotspots) of four of these species, which together will serve as multidisciplinary tools for the CHBR management. To address the first objective, seven stakeholder groups were identified (i.e residents, elder residents, conservationists, marine members, tourists, Yaghan community members, public service employees), within which 21 semi-directed interviews were conducted. To address the second objective, global and regional occurrences of four of the most abundant species, i.e. Bellis perennis, Cerastium fontanum, Taraxacum officinale and Trifolium repens and associated climatic data were used to develop species distribution models using the maximum entropy method (MaxENT). Regarding the first objective, results of this study revealed shortcomings in the non-native concept understanding among stakeholders in a local context. On the other hand, the analyzes revealed many positive values associated with non-native plant species in Navarino, notably the aesthetic value. Nevertheless, this study showed that most stakeholders were indifferent to the management of non-native herbaceous plant species. Regarding the second objective, results revealed a niche shift usually used by species due to the less favorable climate of Navarino Island as well as high plasticity for the four plant species mentioned above. However, plant populations might have reached the equilibrium. Finally, the combination of global and regional models shows that hotspots areas are located more particularly on the south coast of the island and extend to the north depending on the species. Based on the results obtained in this study, we therefore suggest (i) increasing awareness of non-native plant among stakeholders, (ii) integrating their values into future decisions, and (iii) preventing dispersal of non-native plant species through Antarctica by monitoring species distribution on Navarino.