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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21696 |
| Date | 12 1900 |
| Creators | Nyakatya, Mawethu Justice |
| Contributors | McGeoch, M.A., 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 | Unknown |
| Type | Thesis |
| Format | vi, 115 leaves : ill., maps |
| Rights | Stellenbosch University |
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