- About
-
The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
Search results
Showing 101 to 110 of 110 (0.028 seconds)Spelling suggestions: "subject:"palaeoecology"" "subject:"palaeolecology""
| 101 |
Late Quaternary Vegetation History And Climate Change In The Gobi Desert, South Mongolia / Spätquartäre Vegetationsgeschichte und Klimaveränderungen in der Wüste Gobi, südliche MongoleiMurad, Waheed 28 June 2011 (has links)
No description available.
|
| 102 |
Late quaternary palaeoenvironments of the Mfabeni Peatland, Northern KwaZulu-Natal.Finch, Jemma M. January 2005 (has links)
To assist in developing a more precise understanding of past climatic changes in southern Africa, further pollen analytical research is required. In the past, pollen sites in the subregion have been restricted to swampy areas such as permanent springs and peat deposits. While such sites are often rare as a consequence of the aridity of the country, rich polliniferous deposits can be found in the peatlands surrounding coastal lakes in the Maputaland Coastal Plain. The Mfabeni peatland, situated on the eastern
shores of St. Lucia, contains relatively old sediments dating back to >45000 years bp at a depth of 7.80m. A multi-proxy approach, comprising radiocarbon, stable carbon isotope (513C) and palynological analysis, was applied in the investigation of Late Quaternary climatic conditions and vegetation changes along the Maputaland Coastal Plain. A single 10 m sediment core, dating back to >45000 years bp, was extracted
from the Mfabeni Peatland. A detailed fossil pollen analysis of Mfabeni sediments indicated the existence of extensive Podocarpus-abundant coastal forests before ca. 44500 years bp. The onset of wetter local conditions after this time is inferred from forest retreat and the development of swampy conditions, which prevailed until ca. 25000 Cal years BP. Conditions during the Last Glacial Maximum (LGM; 18000 years BP) are inferred to have been generally colder and drier, as evidenced by forest retreat and replacement of swampy reed/sedge communities by dry grassland. A significant depletion in 813C values at ca. 18200 Cal years BP indicates the dominance of C3 vegetation during the LGM, reflecting considerably colder conditions. This is in agreement with palaeoenvironmental indications from elsewhere in the Transvaalian Ecozone, although conditions at Mfabeni were more moderated in their manifestation, which can be attributed to the proximity of this site to the ocean. Cool, relatively moist conditions are inferred for the Holocene Altithermal (ca. 8000-6000 years BP), as evidenced by forest growth and expansion during this time. Warm, dry conditions are inferred for the Late Holocene, with the establishment of grassland/savanna type vegetation in the area after ca. 2000 Cal
years BP. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
|
| 103 |
Studies on late Quaternary environmental dynamics (vegetation, biodiversity, climate, soils, fire and human impact) on Mt KilimanjaroSchüler, Lisa 05 December 2012 (has links)
Zur Rekonstruktion der jungquartären Landschaftsentwicklung am Kilimanjaro werden Sedimente aus Paläoböden am Mt Kilimanjaro untersucht, um die lokale und regionale Ökosystem-, Klima-, Feuerdynamik in einem größeren Rahmen zu verstehen. Desweiteren soll die Reaktion der Ökosysteme auf Umweltveränderungen erforscht werden, um die Beziehungen verschiedener Ökosysteme und ihre Rolle hinsichtlich der Entwicklung von „Biodiversity Hot Spots“ in Ostafrika aufzudecken. Die Ergebnisse tragen zu einem besseren Verständnis der heutigen und zukünftigen Dynamik von Ökosystemen bei. Sie sind außerdem eine wichtige Grundlage im Naturschutz, da sie bedeutende Informationen für die Aufrechterhaltung und das Management der hohen Biodiversität in den ostafrikanischen Hochländern liefern.
Die Durchführung von paläoökologischen Untersuchungen ist unerlässlich, da die Prozesse der Vergangenheit eine wichtige Rolle bei der Entwicklung der Ökosysteme und Biodiversität spielen. Die vorliegende Arbeit erforscht die spätquartäre Vegetation-, Klima- und Feuerdynamik am Kilimanjaro, um das Verständnis der dortigen Ökosystem zu vertiefen. Sowohl Pollen als auch weitere Klima-Proxies von zwei Sedimentkernen werden analysiert, um die Vegetationsdynamik vom frühen Spätglazial bis heute zu rekonstruieren und die jeweiligen Einflußfaktoren aufzudecken. Die Ergebnisse vom Maundi Krater, welcher auf 2780 m Höhe am südostlichen Hang des Kilimanjaros gelegen ist, stellen eines der längsten, terrestrischen Klimaarchive im tropischen Ostafrika dar, und ermöglichen den Einblick in fast 100 000 Jahre Vegetations- und Klimageschichte. Das WeruWeru Paläobodenprofil aus dem montanen Waldgürtel am Kilimanjaro ermöglicht die detaillierte Rekonstruktion der Reaktionsdynamik der Vegetation auf Veränderungen in der Umwelt. Die Ergebnisse beider Untersuchungen zeigen, dass Klimaveränderungen zu einer Verschiebung der montanen Vegetationsgürtel entlang des Höhengradienten des Mt Kilimanjaro geführt haben. Das Pollenarchiv des WeruWeru Profils dokumentiert starke Veränderungen in den höchsten Vegetationgürteln, dem Erikagürtel und dem oberen montanen Wald. Trotz markanter Klimaveränderungen scheint Mt Kilimanjaro aber auch als eiszeitliches Refugium für Waldarten gedient zu haben. Feuerereignissen spielten hinsichtlich der Ausbildung des Erikagürtels eine entscheidende Rolle. Hinweise auf verstärkte menschliche Aktivitäten können an keinem der beiden Untersuchungsstandorte festgestellt werden.
Die Pollenregen-Studie entlang des Höhengradienten am Kilimanjaro zeigt, dass es sehr entscheidend ist, die quantitative Beziehung zwischen Pollen-Niederschlag und moderner Vegetation zu untersuchen, um die Rekonstruktionen der Vergangenheit zu kalibrieren. Die Ergebnisse ermöglichen eine weitaus präzisere Interpretation der Vegetations- und Klimarekonstruktionen im tropischen Ostafrika.
|
| 104 |
Vegetation history and human-environment interactions through the late Holocene in Konar Sandal, Kerman, SE IranGurjazkaite, Karolina January 2017 (has links)
The Jiroft valley, in southeastern Iran, was an important agricultural centre since the Early Bronze Age (3rd millennium BCE). The valley is characterized by harsh environmental settings: hot climate with poor rainfall. However, more optimal conditions may have prevailed earlier that supported ancient settlements. A 250-cm sediment core was retrieved from a peat-land at Konar Sandal, a major archaeological find attributed to Jiroft culture. The palynological data from this core was combined with geochemical and sedimentological proxies aimed at establishing the human-environment interactions in the area. The study focus was directed at vegetation history and landscape evolution, hydroclimatic changes and past human activities, that started just after the projected collapse of the Jiroft (4 ka) and extended all the way from the late Bronze Age to the Mongol invasion (0.6 ka). The results indicate that the valley was dominated by Saharo-Sindian open pseudo-savannah vegetation for the last 4000 years. However, due to anthropogenic clearance and intensified agro-pastoral activities, and also climatic factors, the land cover shifted from open xeric scrubland forests to more open, degraded landscapes. The principal human practice in these early settlements was cereal cultivation. But it is likely that during the more arid periods, communities retreated and abandoned agriculture, facilitating successional processes. Such droughts occurred in 4-3.8 ka and 3.4-2.8 ka and were supported by palynological data, C/N and Fe2O3 content. Peat formation was characteristic to the wetland during these arid periods. These droughts corresponded to drought phases detected in other studies, and were attributed to changes in Siberian Anticyclones. Dynamics of Artemisia and desert shrubs indicate milder climate around 3.8-3.4 ka and 2.8-0.6 ka. In the latter episode, during the rule of Persian Empire (ca. 550 BCE-650 CE) and Islamic epoch, the highest vegetation degradation state and most intensive human activities were observed. Some inconspicuous human practices, such as date cultivation, may have occurred on site as an adaptation to extreme environmental conditions. / High-resolution paleolimnological records from Lake Jazmurian: Climate-culture evolution at Jiroft in southeast Iran during the Holocene
|
| 105 |
Palaeoenvironmental changes in the northern boreal zone of Finland: local versus regional driversShala, Shyhrete January 2014 (has links)
Multiple proxies derived from the Lake Loitsana sediment sequence (NE Finland) are employed to determine the timing of deglaciation, characterise an early Holocene proglacial lake stage and reconstruct Holocene lake development. Local-scale processes causing shifts in biological assemblages are identified and the most likely Holocene mean July air temperature (Tjul) development is assessed. The study area was deglaciated shortly prior to 10 700 cal. a BP. The sediment record reflects four local events; the presence of a glacial lake, glacial lake drainage and formation of Lake Loitsana, changes in fluvial input due to progressive wetland expansion, and gradual lake infilling. The results suggest that local events have driven changes in biological assemblages through various processes, and that biotic proxies reflect changes in environmental parameters in a highly individual manner. Furthermore, biological assemblages can themselves act as important drivers, influencing the composition of other assemblages. It is suggested that future studies should consider macrophyte abundance and food-web interactions as equally important factors when assessing changes in biological assemblages. Quantitative Tjul reconstructions based on biotic proxies display contrasting trends. While Tjul reconstructions based on pollen found in the Loitsana sequence display relatively low early Holocene values, plant macrofossil and chironomid data reflect warm summer conditions also during the early Holocene, i.e. at the peak of summer insolation. The early Holocene Tjul recorded by terrestrial pollen are affected by local factors possibly combined with a delayed response of the terrestrial ecosystem compared to the aquatic one. This study emphasises the importance of using multiple proxies in palaeoenvironmental studies and shows that local factors have a potential to drive changes in biological assemblages that can affect transfer-function based temperature reconstructions. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Epub ahead of print. Paper 2: Accepted. Paper 3: Manuscript.</p>
|
| 106 |
Palaeoekologie interakcí rostlin a členovců ze spodního miocénu mostecké pánve v severních Čechách / Palaeocology of plant-arthropod associations from the Lower Miocene of the Most Basin in northern Bohemia (Czech Republic)Knor, Stanislav January 2010 (has links)
Terrestrial plants and insects account for the majority of the Earth's biodiversity today, and almost half of all insect species are herbivores. Thus, insects and plants share ancient associations date back for more than 400 million years. However, investigation of their interactions stands largely at the beginning in Western Europe. Nearly 4300 plant remains showing various kinds of feeding damages are available for the present study. These trace fossils are classified as so-called functional feeding-groups supply an outstanding example of the complexity, the structure and the changes of terrestrial ecosystems, are not well known during this interval. In Europe, the Neogene is characterized by palaeogeographic re- organization due to the collision of the African with the Eurasian plates. The Neogene plant record in Europe is rich and diverse offering a profound large-scale understanding of the floristic and vegetational development. A database of fossil traces from the Most Basin was compiled and analyzed by various statistical methods in terms of the diversity and intensity of palaeo-herbivory. The primary objective is to present results on the development of insect herbivory through the section of the Bílina Mine in North Bohemia, with the aim of understanding principal factors that caused the...
|
| 107 |
Crustacea (Decapoda, Cirripedia) z české křídové pánve / Crustacea (Decapoda, Cirripedia) from the Bohemian Cretaceous BasinKočová Veselská, Martina January 2018 (has links)
This thesis deals with systematic revision, evolutionary trends, palaeoecology and migration patterns of crustaceans (Cirripedia and Decapoda) from the Upper Cretaceous of the Bohemian Cretaceous Basin. Thesis is presented as a compilation of 9 papers that were published in scientific peer-reviewed journals and includes not only old museum material, but also numerous crustacean specimens which have been recovered in the last decade. Besides, short remarks on fossil crustaceans currently under study or in the process of being published (Paraclythia, Oncopareia, Acrothoracica) are also included in this thesis. In view of the fact that the fossil crustaceans from the BCB were most recently recorded in the turn of the 19th and the 20th centuries (and partially revised in the first half of the 20th century) and since the systematics and taxonomy have changed significantly, all papers presented here focus primarily on systematic revision and modern description. The essential part of the thesis thus deals with taphonomy and its bearing on the identification of fossil material. Thanks to a modern description, new species of Ctenocheles fritschi (axiidean shrimp), Archaeochionelasmus nekvasilovae (acorn barnacle), Myolepas reussi and Capitulum sklenari (pedunculate barnacles) were erected. C. fritschi is...
|
| 108 |
Conditions de l'accumulation du carbone dans une tourbière du Québec méridional : l'influence des facteurs autogènes et des contrôles allogènesMuller, Serge D. 09 1900 (has links)
Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / Thèse de doctorat effectuée en cotutelle au Département de Géographie Université de Montréal et à l'Institut Méditerranéen d'Écologie et de Paléoécologie Université de Droit, d'Économie et de Sciences d'Aix-Marseille 111 / La tourbière de Mirabel (basses terres du St-Laurent, Québec méridional) a été étudiée dans
le but de préciser l'influence exercée par les différents paramètres autogènes et allogènes
sur l'accumulation postglaciaire du carbone. (l) Les dynamiques végétales régionales
révèlent un contrôle climatique général, modulé localement par le contexte
paléogéographique, la physiographie et les processus écologiques. (2) L'histoire
postglaciaire du climat régional fut reconstituée par la méthode des analogues modernes,
contrainte par les fluctuations du niveau du lac Hertel (Mont St-Hilaire). Les résultats
obtenus témoignent d'un important réchauffement entre 13 000 et 11 000 cal. BP, d'un
optimum thermique autour de 8000 cal. BP, et de deux périodes sèches (10 000-6500 et
5000-3000 cal. BP). (3) Les dynamiques postglaciaires internes de la tourbière furent
indépendamment reconstituées en trois dimensions par l'analyse pluridisciplinaire de sept
profils. Ces derniers montrent des successions végétales similaires, conformes au modèle de
terrestrialisation, mais asynchrones. Ils témoignent en outre de conditions de surface très
humides avant 6700 cal. BP, suivies de nombreuses fluctuations asynchrones sur
l'ensemble du site. L'accumulation du carbone présente en revanche des tendances
similaires dans tous les profils, caractérisées par de fortes accumulations avant 6200 cal. BP
(moyennes de 7.1 à 19.1 gC.m .an'1) et de faibles accumulations depuis (moyennes de 2.7 à
6.3 gC.m'2.an ). (4) Les différentes conditions postglaciaires du développement de la
tourbière sont confrontées. L'accumulation du carbone paraît avoir été essentiellement
contrôlée par les interrelations entre la physiographie (alimentation minérotrophe initiale) et
les processus autogènes, qui ont progressivement isolé la végétation tourbigène de la nappe
phréatique. Notamment, ni le climat, ni les feux ne semblent avoir joué de rôle significatif. / Mirabel bog (St. Lawrence lowlands, southern Quebec) was studied with the aim to specify
the influences exerted by the different autogenic and allogenic parameters on postglacial
carbon accumulation. (1) Regional vegetation dynamics reveal a general climatic control,
locally modified by the palaeogeographical context, physiography and ecological processes.
(2) The postglacial history of the regional climate was reconstructed by the modem
analogues method, constrained by the water level fluctuations of Lac Hertel (Mont St-
Hilaire). Obtained results provide evidence for an important climate improvement between
13 000 and 11 000 cal. BP, a thermal optimum around 8000 cal. BP and two dry periods
(10000-6500 and 5000-3000 cal. BP). (3) Postglacial internal dynamics were
independently reconstmcted in three dimensions by the multidisciplinary analysis of seven
profiles. They show similar plant successions, conforming to the terrestrialisation model but
were asynchronous. They moreover attest the occurrence of very humid conditions prior to
6700 cal. BP, followed by numerous asynchronous fluctuations throughout the site. By
contrast, carbon accumulation presents similar trends in all proiïles, characterised by high
accumulation rates prior to 6200 cal. BP (averages from 7.1 to 19.1 gC.m .year ) and low
rates since this date (averages from 2.7 to 6.3 gC.m'2.year-l). (4) The different postglacial
conditions of peatland development arc coirfronted. Carbon accumulation appears to have
been essentially controlled by the interplay between physiography (initial minerotrophic
supply) and autogenic processes, which progressively isolated the peat-forming vegetation
from groundwater. Notably, neither climate nor fire seem to have played a significant role.
|
| 109 |
Ancient environmental DNA as a means of understanding ecological restructuring during the Pleistocene-Holocene transition in Yukon, CanadaMurchie, Tyler James January 2021 (has links)
Humans evolved in a world of giant creatures. Current evidence suggests that most ice age megafauna went extinct around the transition to our current Holocene epoch. The ecological reverberations associated with the loss of over 65% of Earth’s largest terrestrial animals transformed ecosystems and human lifeways forever thereafter. However, there is still substantial debate as to the cause of this mass extinction. Evidence variously supports climate change and anthropogenic factors as primary drivers in the restructuring of the terrestrial biosphere. Much of the ongoing debate is driven by the insufficient resolution accessible via macro-remains. To help fill in the gaps in our understandings of the Pleistocene-Holocene transition, I utilized the growing power of sedimentary ancient DNA (sedaDNA) to reconstruct shifting signals of plants and animals in central Yukon. To date, sedaDNA has typically been analyzed by amplifying small, taxonomically informative regions. However, this approach is not ideally suited to the degraded characteristics of sedaDNA and ignores most of the potential data. Means of isolating sedaDNA have also suffered from the use of overly aggressive purification techniques resulting in substantial loss. To address these limitations, I first experimentally developed a novel means of releasing and isolating sedaDNA. Secondly, I developed a novel environmental bait-set designed to simultaneously capture DNA informative of macro-scale ecosystems. When combined, we identify a substantial improvement in the quantity and breadth of biomolecules recovered. These optimizations facilitated the unexpected discovery of horse and mammoth surviving thousands of years after their supposed extirpation. I followed up these results by extracting DNA from multiple permafrost cores where we confirm the late survival signal and identify a far more complex and high-resolution dataset beyond those identifiable by complementary methods. I was also able to reconstruct mitochondrial genomes from multiple megafauna simultaneously solely from sediment, demonstrating the information potential of sedaDNA. / Dissertation / Doctor of Philosophy (PhD) / A new addition to the rapidly growing field of palaeogenetics is environmental DNA (eDNA) with its immense wealth of biomolecules preserved over millennia outside of biological tissues. Organisms are constantly shedding cells, and while most of this DNA is metabolized or otherwise degraded, some small fraction is preserved through sedimentary mineral-binding. I experimentally developed new ancient eDNA methods for recovery, isolation, and analysis to maximize our access to these biomolecules and demonstrate that this novel approach outperforms alternative protocols. Thereafter, I used these methods to extract DNA from ice age permafrost samples dating between 30,000–6,000 years before present. These data demonstrate the power of ancient eDNA for reconstructing ecosystem change through time, as well as identifying evidence for the Holocene survival of caballine horse and woolly mammoth in continental North America. This late persistence of Pleistocene fauna has implications for understanding the human ecological and climatological factors involved in the Late Pleistocene mass extinction event. This effort is paralleled with megafaunal mitogenomic assembly and phylogenetics solely from sediment. This thesis demonstrates that environmental DNA can significantly augment macro-scale buried records in palaeoecology.
|
| 110 |
Postglazialer Anstieg des Meeresspiegels, Paläoklima und Hydrographie, aufgezeichnet in Sedimenten der Bermuda inshore waters / Postglacial rise of sea level, palaeoclimate and hydrography, recorded in sediments of the Bermuda inshore watersVollbrecht, Rüdiger Dr. 13 January 1997 (has links)
No description available.
|
Page generated in 0.1831 seconds