Dissertation (PhD)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: The spatial distribution of animals and plants at different scales is a central theme in ecology. Knowledge of biodiversity distribution is essential, especially with the current threat of climate change and invasion by alien species. Since the impact of climate change and alien species will be, and has already been pronounced in polar regions, information on the current spatial distributions of biota in these regions is critical to predict the consequences of climate change and alien species on the future survival, distribution and abundance of indigenous biota. This study was conducted on the sub- Antarctic Prince Edward Islands (consisting of Marion Island and Prince Edward Island), which have experienced rapid climate changes over the past 50 years. Additionally, a number of alien plant, vertebrate and invertebrate (also microarthropod) species have been introduced to these islands. Since microarthropods (mites and springtails) play an essential role in decomposition and mineralization of plant material on the islands, the loss of microarthropods from decomposer communities might have disastrous results for ecosystem processes. Therefore it is essential to know the current distributions of microarthropods in order to predict future distributions patterns in reaction to climate change and invasive species. In this study, the spatial distribution of mites and springtails inhabiting the cushion plant Azorella selago Hook, were examined at different scales of observation. Firstly, the microarthropod community was examined at a fine scale. The relationship between microarthropod species richness and abundance and plant size, isolation, within-plant variability, grass cover and microclimate variables were investigated. Thereafter, the spatial variability of microarthropod abundances was examined within stands of plants, with statistical methods using varying degrees of locational information to determine if microarthropod abundance is random, regular or aggregated at this scale. Further, the spatial variability of microarthropod communities in A. selago at different altitudes and on different sides of Marion Island, i.e. island-wide scale, was examined. The last scale of observation was the island-wide scale, in which microarthropod assemblages were compared between Marion Island and Prince Edward Island, as well as in different plant species. Microarthropods showed spatial heterogeneity within A. selago plants (higher abundances in eastern and southern sides of plants), island-wide (lower springtail abundance on the eastern side of the island and at high altitudes) and between islands (more alien species on Marion Island). In contrast, microarthropod abundance was not spatially heterogeneous within a stand of plants, i.e. mostly randomly distributed. The possible mechanisms responsible for these patterns differ between scales, and range from temperature and nutrient availability at the within plant and island wide scale to alien species between islands. Climate change is likely to alter these distribution patterns of microarthropods, either directly (unfavourable climate for indigenous species growth, development and dispersal) or indirectly (favouring alien microarthropod species; increase in grass cover on A. selago plants may alter community structure). The information presented here, is essential for predicting the possible impacts of climate change on microarthropods in fellfield ecosystems on sub-Antarctic islands. / AFRIKAANSE OPSOMMING: Die ruimtelike verspreiding van diere en plante op verskillende skale is ‘n sentrale tema in ekologie. Kennis van die verspreiding van biodiversiteit is belangrik, veral met die huidige bedreiging van klimaatsverandering en indringerspesies. Omdat die impak van klimaatsverandering en indringerspesies in die poolstreke alreeds duidelik is en nog meer so sal word, is inligting oor die huidige ruimtelike verspreiding van biota in hierdie streke noodsaaklik. Hierdie studie is op die sub-Antarktiese Prins Edward-eilande (bestaande uit Marion Eiland en Prins Edward Eiland) uitgevoer, waar die klimaat vinnig verander het oor die afeglope 50 jaar. Bykomend is ‘n aantal indringer plant, vertebraat en invertebraat (ook mikroartropood) spesies op die eilande ingebring. Omdat mikroartropoda (myte en springsterte) ‘n baie belangrike rol in ontbinding en mineralisering van plantmateriaal op hierdie eilande speel, sal die verlies van mikroartropoda uit die ontbindingsgemeenskap rampspoedige gevolge vir die prosesse in die ekosisteem hê. Kennis van die huidige verpreiding van mikroartropoda is dus noodsaaklik om die toekomstige verspreidingspatrone, asook oorlewing en volopheid van inheemse spesies in reaksie op klimaatsveranding en indringerspesies, te voorspel. In hierdie studie is die ruimtelike verspreiding van myte en springsterte wat in die kussingplant Azorella selago Hook voorkom, op verskillende ruimtelike skale ondersoek. Eerstens is die mikroartropood gemeenskap op ‘n klein skaal ondersoek. Die verwantskap tussen mikroartropood spesies rykheid en volopheid en plantgrootte, isolasie, binne-plant variasie, gras bedekking en mikroklimaat faktore is ondersoek. Daarna is die ruimtelike variasie van mikroartropood volopheid binne in ‘n plantstand ondersoek deur gebruik te maak van metodes wat verskillende grade van ligging data gebruik. Dit is gedoen om uit te vind of mikroartropood volopheid lukraak, reëlmatig of versameld verspreid is. Verder is die ruimtelike verspreiding van mikroartropood gemeenskappe in A. selago op verskillende hoogtes bo seespieël en op verskillende kante van Marion Eiland ondersoek. Laastens is die mikroartropood gemeenskap op Marion Eiland en Prins Edward Eiland, asook die gemeenskap in verskillende plant spesies vergelyk. Mikroartropoda is ruimtelik heterogeen verspreid binne-in A. selago (meer individue in die oostelike en suidelike kante van plante), asook regoor Marion Eiland (minder springstert individue aan die ooste kant van die eiland asook minder op hoë hoogtes bo seespieël) en tussen eilande (meer indringerspesies op Marion Eiland). In teenstelling hiermee is mikroartropood volopheid ruimtelik homogeen oor ‘n plantstand, dus meestal lukraak verspreid. Die meganismes wat moontlik vir hierdie patrone verantwoordelik is wissel van temperatuur en voedselbeskikbaarheid op die binne-plant en oor die eiland skaal tot indringerspesies op die tussen-eiland skaal. Klimaatsverandering mag waarskynlik mikroartropood verspreidingspatrone direk (ongunstige klimaat vir inheemse spesies se groei, ontwikkeling en verspreiding), of indirek verander (indringer spesies word begunstig; toename in grasbedekking bo-op A. selago mag die gemeenskapstruktuur van mikroartropoda verander). Hierdie inligting is belangrik vir die voorspelling van die moontlike impak van klimaatsverandering op mikroartropoda in klipveld ekosisteme op sub-Antarktiese eilande.

Thesis (MSc)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Understanding the responses of species to climate change is a scientific problem that requires urgent attention, especially under current conditions of global climate change. The large and rapid rates of climate change reported for sub-Antarctic Marion Island makes the island highly suitable for studying the biotic consequences of climate change. Furthermore, the extreme environments on the island result in a close coupling of the biotic (e.g. population dynamics) and abiotic (e.g. climate) factors. Therefore, examining the response of the dominant and keystone plant species on the island, Azorella selago Hook. (Apiaceae), to climate-associated environmental change (e.g. temperature) may provide insight into how A. selago and the associated species communities will be affected by climate change. This study described the variability in microclimate temperatures associated with A. selago across altitudinal gradient and between the eastern and western sides of Marion Island. Microclimate temperatures were also compared to the island’s Meteorological data to determine variation between temperatures experienced by A. selago cushion-plants in the field and those recorded at the island’s Meteorological Station. Temperature variation inside and outside A. selago cushions was also examined. Azorella selago cushions were found to have a buffering effect on temperature, such that species occurring epiphytically on A. selago experience more moderate temperatures than the surrounding environment. However, A. selago were found to experience more extreme temperatures than temperatures recorded at the Meteorological Station. Therefore, A. selago may possibly experience greater environmental warming than recorded by the Meteorological Station. While temperatures decline with altitude, temperature conditions on the western side of the island were more temperate than the eastern side. This presents the first record of temperature conditions on the western side of the island. This study also quantified fine-scale (e.g. within-site) and broad-scale (e.g. island-wide) variability patterns of A. selago (morphology, phenology, and epiphyte load) across Marion Island. Altitudinal gradient and climatic exposure at different sides of the island were used to understand the likely effects of climate associated environmental change on this dominant component of the fellfield habitat. Site-specific processes were found to determine the spatial structure of A. selago characteristics at fine-scales. However, broad-scale observations established strong responses of A. selago characteristics to altitudinal gradients and different sides of the island. Azorella selago morphological features (e.g. plant size and leaf size) were found to be more responsive to differences between the eastern and western sides of the island than to altitudinal gradient. Azorella selago micro-morphological features (e.g. leaf trichomes and stomatal densities) were also found to be more responsive to climatic exposure at different sides of the island than to altitudinal gradient. However, differences in A. selago epiphyte density (e.g. Agrostis magellanica) and phenology resembled microclimate temperatures in that they were more responsive to altitudinal gradient than to side of the island differences. From these results it can therefore be predicted that the A. selago of Marion Island is likely to be morphologically fairly resilient to moderate climatic shifts, although at lower altitudes and on the eastern side of the island, it may be outcompeted by the epiphytic grass, Agrostis magellanica. The results also suggest that the warming climate of Marion Island may result in an early occurrence of phenological processes particularly at lower altitudes and the eastern side. Azorella selago at lower altitudes and on the eastern side of Marion Island are therefore expected to largely show more symptoms of climate change (e.g. warming) on this species. Azorella selago is also predicted to move up altitudinal gradients in response to warming. / AFRIKAANSE OPSOMMING: ’n Begrip van hoe spesies reageer op klimaatsverandering is ’n wetenskaplike vraag wat onmiddellike aandag benodig, veral onder huidige globale klimaatsverandering. Die groot en snelle tempo waarteen klimaatsverandering waargeneem word op sub-Antarktiese Marion Eiland, maak die eiland hoogs geskik om die biotiese gevolge van klimaatsverandering te bestudeer. Verder veroorsaak die uiterste omgewing van die eiland tot ’n nabye koppeling tussen die biotiese (bv. populasie dinamika) en abiotiese (bv. klimaat) faktore. Dus, deur die reaksies van ’n dominante- en sleutel-spesie op die eiland, Azorella selago Hook. (Apiaceae), op klimaat-geassosieerde omgewings verandering (bv. temperatuur) te bestudeer, mag insig verskaf hoe A. selago en geassosieerde spesie gemeenskappe geaffekteer sal word deur klimaatsverandering. Hierdie studie beskryf die wispelturigheid in mikroklimaat temperature geassosieer met A. selago oor ’n hoogte gradiënt asook tussen die oostelike en westelik dele van Marion Eiland. Mikroklimaat temperature was ook vergelyk met die eiland se Meteorologiese data met die doel om die mate van variasie tussen temperature verduur deur A. selago kussing-plante in die natuurlike omgewing met die van die eiland se Meteorologiese stasie te vergelyk. Temperatuur variasie binne en buite A. selago kussing-plante is ook vasgestel. Dit was gevind dat Azorella selago kussing-plante die temperatuur buffer, met die gevolg dat spesies wat epifities op A. selago voorkom, meer gematigde temperature ondervind as die onmiddellike omgewing om die plant. Daar is egter gevind dat A. selago meer uiterste temperature ondervind as temperature gemeet by die Meteorologiese stasie. Dus mag A. selago groter omgewings verwarming ervaar as wat temperature gemeet by die Meteorologiese stasie dui. Terwyl temperatuur afneem met ’n toename in hoogte, was temperatuur aan die westekant van die eiland mere gematig as die oostekant. Dit verskaf die eerste rekord van temperatuur toestande aan die westekant van die eiland. Hierdie studie bepaal ook die fyn-skaal (e.g. binne-terrein) en groot-skaal (e.g. oor die eiland) variasie patrone van A. selago (morfologie, fenologie, en epifiet lading) oor Marion Eiland. Die hoogte gradiënt en klimaat blootstelling aan verskillende kante van die eiland is gebruik om die waarskynlike effekte van klimaats-geassosieerde omgewings verandering op die dominante deel van die felfield habitat te verstaan. Daar is gevind dat terrein spesifieke prosesse die ruimtelike struktuur van A. selago se klein-skaal eienskappe bepaal. Groot-skaalse waarnemings dui egter ’n sterk antwoord van A. selago eienskappe op die hoogte gradiënt en aan verskillende kante van die eiland. Azorella selago morfologiese eienskappe (e.g. plant- en blaar grootte) is gevind om meer te reageer op verskille tussen oostelike en westelike kante van die eiland as op die hoogte gradiënt. Azorella selago mikromorfologiese eienskappe (e.g. blaar trigome en stomata digtheid) is ook gevind om meer te reageer op omgewings blootstelling tussen verskillende kante van die eiland as op die hoogte gradiënt. Verskille in A. selago epifiet digtheid (e.g. Agrostis magellanica) en fenologie het egter mikroklimaat temperature gevolg, in dat beide meer gereageer het op die hoogte gradiënt as eiland-kant verskille. Hierdie resultate voorspel dus dat dit waarskynlik is dat A. selago van Marion Eiland morfologies redelik terugspringend sal wees ten opsigte van matige klimaatsverandering, al mag dit uitgekompeteer word deur die epifitiese gras, Agrostis magellanica by lae hoogtes en aan die oostekant van die eiland. Hierdie resultate dui ook dat verwarming van Marion Eiland se klimaat ’n vervroeging van fenologiese prosesse mag hê, veral by lae hoogtes en aan die oostekant van die eiland. Dus word dit verwag dat Azorella selago by lae hoogtes en aan die oostekant van Marion Eiland om meer simptome van klimaatsverandering (e.g. verwarming) te dui. Dit word ook voorspel dat Azorella selago opwaarts teen die hoogte gradiënt sal beweeg in reaksie tot verwarming.

Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Climate has shown some remarkable changes over the past century, especially at the polar and sub-polar regions. Southern Ocean Islands provide good models for studies related to climate change effects, since effects may be evident in the short term and may also be clearer. Marion Island is an example of such a system with a harsh abiotic environment, and low species richness often vulnerable to change. Climate change is predicted, and also reported, to have biological consequences on plant communities, affecting the phenology, morphology, and the interaction between individuals and species. This study examines the association between the keystone plant species, Azorella selago Hook. (Apiaceace), and its dominant epiphyte Agrostis magellanica Lam. (Poaceae). Two complimentary approaches were used, one observational and the other experimental. The main objective for the observational study was to quantify bioticallyrelevant microclimate temperature, as well as the morphology, epiphyte load and phenology of A. selago at three different altitude sites on Marion Island. This provided information on baseline variation for understanding specific variability in plant response to the experimental part of this study, against which future patterns arising from biological monitoring can be compared. Studying plants at different altitudes provides a possible analogue for temperature-related climate change consequences for the ecology of A. selago, and its interaction with A. magellanica. The microclimate temperature associated with A. selago differed between the three sites examined. This difference was related to local topographic conditions and altitude differences. Cushion size differed distinctively between the three altitude sites, with this difference related to environmental heterogeneity such as differences in age and substrate structure. Azorella selago annual growth rate was estimated through stem length and the number of leaves on both exposed and shaded stems. Within-site variability, as well as epiphyte cover were found to be the contributing factors on A. selago annual growth rate. This highlights the importance of site-specificity when estimating growth rate within and between different altitude sites. Leaf characteristics differed between the sites, with this attributed to local habitat conditions, such as topography, as well as epiphyte cover. As expected, the difference in leaf size between exposed and shaded leaves demonstrated a larger specific leaf area on leaves shaded by A. magellanica. Agrostis magellanica abundance and density were altitudinally related, with A. selago demonstrating facilitation effects on A. magellanica. The trend shown in this study suggests that in spite of general facilitative effect of A. selago on A. magellanica towards higher altitudes, the abiotic environmental threshold for A. magellanica occurs at lower altitudes than it does for A. selago. Phenological differences were also apparent between the three sites. The objectives of the experimental part of this study were to quantify the effect of the dominant epiphyte, A. magellanica on biotically-relevant microclimatic temperatures, as well as on the phenology and physical condition of A. selago. Different treatments were applied to cushions at the three altitude sites to examine the shading effect of epiphytic A. magellanica on cushion plants, as well as the effect of treatment-related disturbance. Azorella selago microclimate temperature showed no significant difference between treatments, suggesting that on average epiphytic A. magellanica cover has no effect on cushion microclimate temperature. The percentage of flower budding and flowering of A. selago was negatively related to epiphyte cover. Cushion vitality was also responsive to epiphyte cover, with higher vitality scores on low grass covered cushions than on high grass cushions. This shows that A. magellanica competes with A. selago, while A. selago facilitates A. magellanica. Heavy epiphyte numbers impose negative effects on A. selago vegetative and reproductive performance, as well as cushion vitality. Therefore, the results of this research show that the vegetative and reproductive performance of A. selago and cushion vitality are likely to be negatively affected under ongoing climate change on Marion Island if this brings about heavier epiphyte loads on this keystone cushion plant species. / AFRIKAANSE OPSOMMING: In die afgelope eeu het die klimaat in die Antarktiese en sub-Antarktiese gebiede merkwaardige verandering getoon. Die Suidelike See Eilande dien as goeie modelle vir studies verwant aan die gevolge van klimaatsverandering, aangesien die kort termyn effekte in die gebiede duideliker mag wees in die toekoms. Marion Eiland is ‘n voorbeeld van so ‘n sisteem, met ‘n ruwe abiotiese omgewing en lae spesies rykheid, wat vatbaar is vir verandering. Daar word voorspel, en is reeds bevind dat klimaatsverandering biologiese gevolge op plant gemeenskappe het, in terme van morfologie, fenologie en die interaksie tussen individue en spesies. Hierdie studie ondersoek die assosiasie tussen die hoeksteen plant spesie, Azorella selago (Apiaceace), en sy dominante epifietiese gras, Agrostis magellanica Lam. (Poaceae). Die studie is op twee komplimentêre maniere benader, naamlik deur waarneming en eksperiment. Die hoof doel van die studie was om die biotiese belang van mikroklimaat temperatuur te kwantifiseer, en die hoeveelheid epifiete, die morfologie en die fenologie van A. selago te bepaal by drie verskillende hoogtes op Marion Eiland. Laasgenoemde het inligting verskaf oor die variasie in die reaksie van plante tot die eksperimentele aspek van die studie, waarteen patrone vanaf toekomstige biologiese beheer vergelyk kon word. Deur plante te bestudeer by verskillende hoogtes bo seespieël word ‘n moontlike analoog vir die gevolge van temperatuur-verwante klimaatverandering in terme van die ekologie van A. selago, en laasgenoemde se interaksie met A. magellanica verskaf. Die mikroklimaat temperatuur geassosieer met A. selago verskil tussen dié drie liggings. Die versil was verwant aan die plaaslike topografiese toestande en die verskillende hoogtes bo seespieël. Die grootte van die kussingplante het duidelik versil tussen die drie liggings, met die verskille verwant aan die omgewing se heterogeneïteit, byvoorbeeld die verskille in ouderdom en substraat struktuur. Azorella selago se jaarlikse groeitempo was bepaal deur die stingel lengte en die aantal blare, op beide die wat oorskadu is deur die gras, en die was nie oorskadu is nie. Daar is gevind dat die faktore wat bygedra het tot die jaarlikse groeitempo van A. selago, varieër binne die verskillende liggings, en bedekking deur epifiete. Dit beklemtoon die belang van spesifisiteit van ligging wanneer groeitempo in en tussen die liggings van verskillende hoogtes bepaal word. Die blaar eienskappe het verskil tussen verskillende liggings, as gevolg van plaaslike habitat toestande, soos topografie en bedekking deur epifiete. Soos verwag, het die blare wat oorskadu was deur A. magellanica ‘n groter spesifieke blaar area getoon as blare wat blootgestel was. Die hoeveelheid en digtheid van Agrosits magellanica was verwant aan hoogte bo seespieël, met A. selago wat fasiliterende effekte toon op A. magellanica. Die tendens waargeneem in hierdie studie is dat ten spyte van die algemene fasiliterende effek van A. selago op A. magellanica, die abiotiese omgewingsdrempel op ‘n laer hoogte is vir A. magellanica as vir A. selago. Fenologiese verskille was ook duidelik tussen die drie liggings. Die doel van die eksperimentele deel van die studie was om die effek van die dominante epifiet, A. magellanica, te bepaal op bioties relevante mikroklimaat temperature, asook op die fenologie en fiesiese toestand van A. selago. Verskeie behandelings is aangewend op die kussingplante by die drie liggings om die effek van skaduwee van die epifietiese A. magellanica op die plante te bepaal, asook die effek van versteurings versoorsaak deur die behandelings. Azorella selago se mikroklimaat temperatuur het geen betekenisvolle verskille tussen behandelings getoon nie, wat voorstel dat epifitiese A. magellanica oor die algemeen geen effek op die kussingplante se mikroklimaat temperatuur het nie. Daar was ‘n negatiewe verwantskap tussen die hoeveelheid epifiete op A. selago en die persentasie blomme en blomknoppe op die kussingplante. Die plante se vitaliteit was ook afhanklik van epifiet bedekking, met ‘n hoër vitaliteit telling vir kussingplante bedek met lae gras as die bedek met hoë gras. Dit toon dat A. magellanica met A. selago wedywer, terwyl A. selago vir A. magellanica fasiliteer. Hoë epifiet getalle het negatiewe effekte op A. selago se vegetatiewe en reproproduktiewe nakoming, asook die kussingplante se vitaliteit. Die resultate van hierdie studie toon dus dat die vegetatiewe en reproduktiewe nakoming van A. selago en kussingplant vitaliteit heel moontlik negatief geaffekteer sal word indien klimaatsverandering op Marion Eiland hoër epifiet getalle op die sleutel kussingplant spesie tot gevolg sal hê.