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Spatial patterns in the microarthropod community associated with Azorella selago (Apiaceae) on the sub-Antarctic Prince Edward IslandsHugo, Elizabeth Aletta 12 1900 (has links)
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.
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Patterns of variability in Azorella selago Hook. (Apiaceae) on sub-Antarctic Marion Island : climate change implicationsNyakatya, Mawethu Justice 12 1900 (has links)
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.
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The interaction between a keystone plant species and its dominant epiphyte on Marion Island : climate change implicationsBuwa, Ziphokazi Siyasanga 12 1900 (has links)
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.
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