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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21743 |
| Date | 12 1900 |
| Creators | Hugo, Elizabeth Aletta |
| Contributors | McGeoch, M.A., Chown, S.L., Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | viii, 162 leaves : ill., maps |
| Rights | Stellenbosch University |
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