24 research outputs found
Plio-Pleistocene climatic change had a major impact on the assembly and disassembly processes of Iberian rodent communities
Comprehension of changes in community composition through multiple spatio-temporal scales is a prime challenge in ecology and palaeobiology. However, assembly, structuring and disassembly of biotic metacommunities in deep-time is insufficiently known. To address this, we used the extensively sampled Iberian Plio-Pleistocene fossil record of rodent faunas as our model system to explore how global climatic events may alter metacommunity structure. Through factor analysis, we found five sets of genera, called faunal components, which co-vary in proportional diversity over time. These faunal components had different spatio-temporal distributions throughout the Plio-Pleistocene, resulting in non-random changes in species assemblages, particularly in response to the development of the Pleistocene glaciations. Three successive metacommunities with distinctive taxonomic structures were identified as a consequence of the differential responses of their members to global climatic change: (1) Ruscinian subtropical faunas (5.3–3.4 Ma) dominated by a faunal component that can be considered as a Miocene legacy; (2) transition faunas during the Villafranchian–Biharian (3.4–0.8 Ma) with a mixture of different faunal components; and (3) final dominance of the temperate Toringian faunas (0.8–0.01 Ma) that would lead to the modern Iberian assemblage. The influence of the cooling global temperature drove the reorganisation of these rodent metacommunities. Selective extinction processes due to this large-scale environmental disturbance progressively eliminated the subtropical specialist species from the early Pliocene metacommunity. This disassembly process was accompanied by the organisation of a diversified metacommunity with an increased importance of biome generalist species, and finally followed by the assembly during the middle–late Pleistocene of a new set of species specialised in the novel environments developed as a consequence of the glaciations
Room-Temperature C–H Arylation: Merger of Pd-Catalyzed C–H Functionalization and Visible-Light Photocatalysis
Visible Light Photocatalytic Synthesis of Benzothiophenes
The photocatalytic reaction of o-methylthio-arenediazonium salts with alkynes yields substituted benzothiophenes regioselectively through a radical annulation process. Green light irradiation of eosin Y initiates the photoredox catalysis. The scope of the reaction was investigated by using various substituted diazonium salts and different alkynes
RESEARCH ARTICLE Body-size structure of Central Iberian mammal fauna reveals semidesertic conditions during the middle Miocene Global Cooling Event
We developed new quantitative palaeoclimatic inference models based on the body-size
structure of mammal faunas from the Old World tropics and applied them to the Somosaguas
fossil site (middle Miocene, central Iberian Peninsula). Twenty-six mammal species
have been described at this site, including proboscideans, ungulates, carnivores, insectivores,
lagomorphs and rodents. Our analyses were based on multivariate and bivariate
regression models correlating climatic data and body-size structure of 63 modern mammal
assemblages from Sub-Saharan Africa and the Indian subcontinent. The results showed an
average temperature of the coldest month higher than 26ĂŠC for the Somosaguas fossil site,
a mean annual thermal amplitude around 10ĂŠC, a drought length of 10 months, and an
annual total precipitation greater than 200 mm per year, which are climate conditions typical
of an ecotonal zone between the savanna and desert biomes. These results are congruent
with the aridity peaks described over the middle Aragonian of Spain and particularly in the
local biozone E, which includes Somosaguas. The aridity increase detected in this biozone
is associated with the Middle Miocene Global Cooling Event. The environment of Somosaguas
around 14 Ma was similar to the current environment in the Sahel region of North
Africa, the Horn of Africa, the boundary area between the Kalahari and the Namib in Southern
Africa, south-central Arabia, or eastern Pakistan and northwestern India. The distribution
of modern vegetation in these regions follows a complex mosaic of plant communities,
dominated by scattered xerophilous shrublands, semidesert grasslands, and vegetation
linked to seasonal watercourses and ponds.Peer reviewe
Functionalization of C(sp2)–H Bonds of Arenes and Heteroarenes Assisted by Photoredox Catalysts for the C–C Bond Formation
International audienceThe formation of C–C bonds from arenes and heteroarenes through transition metal-catalyzed C–H bond functionalizations is one of the major achievements of these last decades. It is now possible to perform such transformations under mild reaction conditions with the help of visible light photocatalysis leading to eco-friendly and safer process to build organic molecules or materials. This chapter will focus on photoredox catalysis which involves a C(sp2)–H bond functionalization step for the formation of C(sp2)–C bonds [i.e., direct arylations and (perfluoro)alkylations] and will show how this hot topic contributes to the development of green chemistry