Browsing by Subject "SOUTH-AMERICA"

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  • Schmidt, Alexander; Kaulfuss, Uwe; Bannister, Jennifer; Baronov, Victor; Beimforde, Christina; Bleile, Natalie; Borkent, Art; Busch, Ariane; Conran, John; Engel, Michael; Harvey, Mark; Kennedy, Elisabeth; Kerr, Peter; Kettunen, Elina Johanna; Kiecksee, Anna; Lengeling, Franziska; Lindqvist, Jon; Maraun, Mark; Mildenhall, Dallas; Perrichot, Vincent; Rikkinen, Jouko; Sadowski, Eva-Maria; Seyfullah, Leyla; Stebner, Frauke; Szwedo, Jacek; Ulbrich, Philipp; Lee, Daphne (2018)
    Terrestrial ecosystems of the long-isolated former Gondwanan landmass of New Zealand are hotspots of modern global biodiversity, based on the level of endemism and distinctiveness of the biota. However, little is known of the evolutionary history of the rarely preserved but diverse, distinctive, fragile, mainly soft-bodied organisms such as arthropods and fungi that comprise 95% of biodiversity in forest ecosystems. Our discovery of fossils preserved in Oligocene/Miocene amber of araucarian origin reveals a diverse invertebrate and fungal biota and complex ecological networks. These fossils comprise 10 orders and approximately 20 families of terrestrial arthropods and include representatives of Pseudoscorpiones, Acari, Araneae, Collembola, Hemiptera, Psocoptera, Hymenoptera, Coleoptera, Lepidoptera and Diptera, together with nematodes, mold fungi and araucarian wood. Ecologically the fossils encompass predators such as spiders with web remains, soil and bark mites, detritivores, parasites, fungivores and decomposers, fungi that grew on solidified resin flows, as well as predatory fungi. This study reports the first major amber deposit with an abundance of biological inclusions from the Southern Hemisphere and the only Cenozoic one of verified araucarian origin. These fossils expand the global record and evolutionary history of many arthropod and fungal groups, providing insights into mid-Cenozoic araucarian forest ecosystems and resolving controversial issues around the antecedents of the modem New Zealand terrestrial biota. (C) 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
  • Schütt, Jorina Marlena; Whipp, David Michael (2020)
    Strain partitioning onto margin-parallel thrust and strike-slip faults is a common process at obliquely convergent plate margins, leading to the formation and migration of crustal slivers. The degree of strain partitioning and rate of sliver migration can be linked to several factors including the angle of convergence obliquity, the dip angle of subduction, frictional coupling between the plates and the strength of the upper plate, among others. Although these factors are known to be important, their relative influence on strain partitioning is unclear, particularly at natural margins where the factors often vary along strike. Here we use a 3-D mechanical finite-element model to investigate the relationship between continental crustal strength, the convergence obliquity angle, the subduction angle, and strain partitioning in the Northern Volcanic Zone (NVZ) of the Andes (5 degrees N-3 degrees S). In the NVZ the subduction dip and obliquity angles both vary along strike, weaknesses in the continental crust may be present in suture zones or regions of arc volcanism, and strain partitioning is only observed in some regions. Thus, it is an ideal location to gain insight in which of the factors have the largest influence on deformation and sliver formation in the upper plate. Our numerical experiments confirm that a moderately high obliquity angle is needed for partitioning and that a continental crustal weakness is also required for movement of a coherent continental sliver at rates similar to geodetic observations from the NVZ. In contrast, the subduction dip angle is only of secondary importance in controlling strain partitioning behavior. Key Points Factors influencing formation of continental slivers investigated using 3-D numerical models of finite-width oblique subduction systems Model results indicate that convergence obliquity and the presence of weak zones in the upper plate are key to formation of well-defined slivers Model predictions are in good agreement with geodetic observations of sliver motion in the Northern Volcanic Zone of the Andes
  • Mei, L.; Xue, Y.; de Leeuw, G.; Guang, J.; Wang, Y.; Li, Y.; Xu, H.; Yang, L.; Hou, T.; He, X.; Wu, C.; Dong, J.; Chen, Z. (2011)
  • Morales-Garcia, Nuria Melisa; Saila, Laura K.; Janis, Christine M. (2020)
    Savanna-like ecosystems were present at high latitudes in North America during much of the Neogene. Present-day African savannas, like the Serengeti, have been proposed to be modern analogs of these paleosavannas, particularly those from the middle Miocene of the Great Plains region of the United States. Both these extant and extinct savannas contain a preponderance of artiodactyl (even-toed ungulate) species; however, the taxonomic composition of each fauna is different. While present-day African savannas are dominated by ruminants (primarily bovids), the Neogene savannas of North America were dominated by a diversity of both camelid and non-bovid ruminant families. This study provides a quantitative test of the similarity of the artiodactyl faunas of the North American Neogene paleosavannas to those of the modern-day African savannas. A correspondence analysis of ecomorphological features revealed considerable overlap between modern and fossil faunas. The morphospace occupation of the extinct North American ruminants falls within that of the African bovids. Some of the extinct camelids also fall within this same morphospace, but many do not, perhaps indicating an environmental difference such as greater aridity in Neogene North America. The diversity and disparity of artiodactyl faunas through the Neogene of North America changed along with changing temperatures and precipitation regimes. The taxonomic and ecomorphological diversity of the Serengeti ruminant fauna is statistically comparable to those North American paleofaunas occurring during or immediately after the Middle Miocene Climatic Optimum (MMCO), but the later, more depauperate faunas are no longer comparable. This study quantitatively analyzes artiodactyl communities as they changed with the cooling and drying trend seen during the Neogene.
  • Janssen, Thomas A. J.; Hölttä, Teemu; Fleischer, Katrin; Naudts, Kim; Dolman, Han (2020)
    Functional relationships between wood density and measures of xylem hydraulic safety and efficiency are ambiguous, especially in wet tropical forests. In this meta-analysis, we move beyond wood density per se and identify relationships between xylem allocated to fibers, parenchyma, and vessels and measures of hydraulic safety and efficiency. We analyzed published data of xylem traits, hydraulic properties and measures of drought resistance from neotropical tree species retrieved from 346 sources. We found that xylem volume allocation to fiber walls increases embolism resistance, but at the expense of specific conductivity and sapwood capacitance. Xylem volume investment in fiber lumen increases capacitance, while investment in axial parenchyma is associated with higher specific conductivity. Dominant tree taxa from wet forests prioritize xylem allocation to axial parenchyma at the expense of fiber walls, resulting in a low embolism resistance for a given wood density and a high vulnerability to drought-induced mortality. We conclude that strong trade-offs between xylem allocation to fiber walls, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees. Moreover, the benefits of xylem allocation to axial parenchyma in wet tropical trees might not outweigh the consequential low embolism resistance under more frequent and severe droughts in a changing climate.