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- Alva, Omar, et al.
(författare)
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The loss of biodiversity in Madagascar is contemporaneous with major demographic events
- 2022
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Ingår i: Current Biology. - : Elsevier. - 0960-9822 .- 1879-0445. ; 32:23, s. 4997-
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Tidskriftsartikel (refereegranskat)abstract
- Only 400 km off the coast of East Africa, the island of Madagascar is one of the last large land masses to have been colonized by humans. While many questions surround the human occupation of Madagascar, recent studies raise the question of human impact on endemic biodiversity and landscape transformation. Previous genetic and linguistic analyses have shown that the Malagasy population has emerged from an admixture that happened during the last millennium, between Bantu-speaking African populations and Austronesian-speaking Asian populations. By studying the sharing of chromosome segments between individuals (IBD determination), local ancestry information, and simulated genetic data, we inferred that the Malagasy ancestral Asian population was isolated for more than 1,000 years with an effective size of just a few hundred individuals. This isolation ended around 1,000 years before present (BP) by admixture with a small African population. Around the admixture time, there was a rapid demographic expansion due to intrinsic population growth of the newly admixed population, which coincides with extensive changes in Madagascar's landscape and the extinction of all endemic large- bodied vertebrates. Therefore, our approach can provide new insights into past human demography and associated impacts on ecosystems.
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| 4. |
- Katrantsiotis, Christos, et al.
(författare)
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Late Quaternary hydroclimate variability in Madagascar and its connection to atmospheric circulation patterns
- 2024
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 649
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Tidskriftsartikel (refereegranskat)abstract
- Large uncertainties still exist about the long-term mechanisms influencing the hydroclimate variability of southeast Africa where proxy data and model simulations indicate rainfall dipoles between subtropical and tropical areas. The topography of Madagascar, located off the southeastern coast of Africa, modulates these dipoles while its climate is influenced by the position of the Intertropical Convergence Zone (ITCZ) and the Subtropical High as well as the sea surface temperature (SST) of SW Indian Ocean. The island can thus be considered a key location for the understanding of the tropical SE African climatic variability and the interplay between atmospheric patterns. However, the scarcity of continuous records from Madagascar has made the evolution of regional late Quaternary climate and its driving mechanisms difficult to assess. Here, we present a 26-kyr record of the deuterium/hydrogen isotope ratio (δD) of biomarkers (n-alkanes) from the central eastern part of the island at Antananarivo at around 1250 m a.s.l. Preliminary summary pollen data are also presented as a comparison. The δD profiles of aquatic plant and terrestrial plant-derived n-alkanes generally exhibit similar trends implying that they all record changes in the isotope composition of source water, namely meteoric water that recharges soil and lake waters. In this tropical region, the δD variability of precipitation is mainly influenced by the amount effect reflecting the intensity of precipitation associated with the monsoon. We observe: (i) stable and wet conditions during the Last Glacial Maximum, (ii) drier conditions from 18.5 to 15 ka (ka before present) during the Heinrich Stadial 1 (iii) high humidity after 15 ka culminating at the Younger Dryas (YD), (iv) drier conditions from 11.7 ka to 8.2 ka, (v) a return to humid climate until 2.8 ka, and (vi) an arid phase followed by increased wetness after 0.9 ka, although the record is likely influenced by human-induced vegetation changes the last 1.2 ka. This climate signal is similar to other records from the Mozambique Channel but opposite to records from the East African mainland and the subtropical southern Africa, especially between 20 and 25°S. Although there is a good correspondence of our record with insolation- driven migrations of ITCZ during the LGM and the early Holocene, the dipoles are largely consistent with the modern rainfall anomaly and are best explained by the interlinked effects of the SST changes and the variability of the Mozambique Channel Trough.
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| 5. |
- Radimilahy, Chantal
(författare)
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Mahilaka : An archaeological investigation of an early town in northwestern Madagascar
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In 1988, at the beginning of the 'Urban Origins in Eastern Africa' research project, it was thought that no towns existed in Madagascar prior to the 17th century. This thesis shows that Madagascar did in fact support an urban population with a wide range of local and regional contacts from the end of the first millennium AD. Mahilaka is similar in date and structural morphology to sites such as Kilwa and Manda in Eastern Africa.Previous historical, anthropological and archaeological research in Madagascar is reviewed. The environ-mental context of Mahilaka is presented with an emphasis on resource availability for foraging, herding, hunting and fishing and mineral exploitation. Can the favourable environment available today be extrapolated into the past? Was the productivity of the Mahilaka area sufficient to sustain an urban population?Northwestern Madagascar has been settled for at least 1000 years. Mahilaka was previously investigatedarchaeologically by Vérin to a limited degree in the 1970s. It is now known as a result of the work carried out for this thesis to be the most important and largest town in the region. It contains a wide range of locally produced and imported items.More than 600 drillcores, 50 mm in diameter, and additional augering defined the extent of the site. Thethickness, extension and contents of archaeological deposits were ascertained. Phosphate analyses wereundertaken and combined with soil colour and texture to establish the archaeological sequence of the site. Four main phases were identified, the initial occupation (Ia), a consolidation period (I b), followed by the maximum area of occupation (IIa) and the final settlement phase (IIb). Additional information about surface substructures including the perimeter wall was obtained through electroresistivity survey. Together these results have deter; mined the choice for excavation of c. 150 m3 of the site.Finds including pottery, glass, beads, bones and metal finds have been analysed and show the spatial organisation of the site. Local production of glass beads and stone bowls is proposed. Finally Mahilaka is placed in its inter-regional context of the trading networks of the western Indian Ocean.
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