Geologically recent rearrangements in central Amazonian river network and their importance for the riverine barrier hypothesis

The riverine barrier hypothesis is a central concept in Amazonian biogeography. It states that large rivers limit species distributions and trigger vicariant speciation. Although the hypothesis has explanatory power, many recent biogeographical observations addressing it have produced conflicting results. We propose that the controversies arise because tributary arrangements in the Amazon river system have changed in geologically recent times, such that large tracts of forest that were on the same side of a river at one time got separated to different sides at another. Based on topographical data and sediment dating, we map about 20 major avulsion and river capture events that have rearranged the river network in central Amazonia during the late Pleistocene and Holocene. We identify areas where past riverine barrier effects might still linger in the absence of a major river, as well as areas where such effects may not yet have accumulated across an existing river. These results call for a reinterpretation of previous biogeographical studies and a reorientation of future works to take into account the idiosyncratic histories of individual rivers

Neogene History of the Amazonian Flora: A Perspective Based on Geological, Palynological, and Molecular Phylogenetic Data

The Amazon hosts one of the largest and richest rainforests in the world, but its origins remain debated. Growing evidence suggests that geodiversity and geological history played essential roles in shaping the Amazonian flora. Here we summarize the geo-climatic history of the Amazon and review paleopalynological records and time-calibrated phylogenies to evaluate the response of plants to environmental change. The Neogene fossil record suggests major sequential changes in plant composition and an overall decline in diversity. Phylogenies of eight Amazonian plant clades paint a mixed picture, with the diversification of most groups best explained by constant speciation rates through time, while others indicate clade-specific increases or decreases correlated with climatic cooling or increasing Andean elevation. Overall, the Amazon forest seems to represent a museum of diversity with a high potential for biological diversification through time. To fully understand how the Amazon got its modern biodiversity, further multidisciplinary studies conducted within a multimillion-year perspective are needed. ▪The history of the Amazon rainforest goes back to the beginning of the Cenozoic (66 Ma) and was driven by climate and geological forces. ▪In the early Neogene (23-13.8 Ma), a large wetland developed with episodic estuarine conditions and vegetation ranging from mangroves to terra firme forest. ▪In the late Neogene (13.8-2.6 Ma), the Amazon changed into a fluvial landscape with a less diverse and more open forest, although the details of this transition remain to be resolved. ▪These geo-climatic changes have left imprints on the modern Amazonian diversity that can be recovered with dated phylogenetic trees. ▪Amazonian plant groups show distinct responses to environmental changes, suggesting that Amazonia is both a refuge and a cradle of biodiversity

Geologically recent rearrangements in central Amazonian river network and their importance for the riverine barrier hypothesis

The riverine barrier hypothesis is a central concept in Amazonian biogeography. It states that large rivers limit species distributions and trigger vicariant speciation. Although the hypothesis has explanatory power, many recent biogeographical observations addressing it have produced conflicting results. We propose that the controversies arise because tributary arrangements in the Amazon river system have changed in geologically recent times, such that large tracts of forest that were on the same side of a river at one time got separated to different sides at another. Based on topographical data and sediment dating, we map about 20 major avulsion and river capture events that have rearranged the river network in central Amazonia during the late Pleistocene and Holocene. We identify areas where past riverine barrier effects might still linger in the absence of a major river, as well as areas where such effects may not yet have accumulated across an existing river. These results call for a reinterpretation of previous biogeographical studies and a reorientation of future works to take into account the idiosyncratic histories of individual rivers.</p

Freshwater fish diversity in the western Amazon basin shaped by Andean uplift since the Late Cretaceous

South America is home to the highest freshwater fish biodiversity on Earth, and the hotspot of species richness is located in the western Amazon basin. The location of this hotspot is enigmatic, as it is inconsistent with the pattern observed in river systems across the world of increasing species richness towards a river’s mouth. Here we investigate the role of river capture events caused by Andean mountain building and repeated episodes of flooding in western Amazonia in shaping the modern-day richness pattern of freshwater fishes in South America, and in Amazonia in particular. To this end, we combine a reconstruction of river networks since 80 Ma with a mechanistic model simulating dispersal, allopatric speciation and extinction over the dynamic landscape of rivers and lakes. We show that Andean mountain building and consequent numerous small river capture events in western Amazonia caused freshwater habitats to be highly dynamic, leading to high diversification rates and exceptional richness. The history of marine incursions and lakes, including the Miocene Pebas mega-wetland system in western Amazonia, played a secondary role

Neogene History of the Amazonian Flora: A Perspective Based on Geological, Palynological, and Molecular Phylogenetic Data

International audienceThe Amazon hosts one of the largest and richest rainforests in the world, but its origins remain debated. Growing evidence suggests that geodiversity and geological history played essential roles in shaping the Amazonian flora. Here we summarize the geo-climatic history of the Amazon and review paleopalynological records and time-calibrated phylogenies to evaluate the response of plants to environmental change. The Neogene fossil record suggests major sequential changes in plant composition and an overall decline in diversity. Phylogenies of eight Amazonian plant clades paint a mixed picture, with the diversification of most groups best explained by constant speciation rates through time, while others indicate clade-specific increases or decreases correlated with climatic cooling or increasing Andean elevation. Overall, the Amazon forest seems to represent a museum of diversity with a high potential for biological diversification through time. To fully understand how the Amazon got its modern biodiversity, further multidisciplinary studies conducted within a multimillion-year perspective are needed. ▪ The history of the Amazon rainforest goes back to the beginning of the Cenozoic (66 Ma) and was driven by climate and geological forces. ▪ In the early Neogene (23–13.8 Ma), a large wetland developed with episodic estuarine conditions and vegetation ranging from mangroves to terra firme forest. ▪ In the late Neogene (13.8–2.6 Ma), the Amazon changed into a fluvial landscape with a less diverse and more open forest, although the details of this transition remain to be resolved. ▪ These geo-climatic changes have left imprints on the modern Amazonian diversity that can be recovered with dated phylogenetic trees. ▪ Amazonian plant groups show distinct responses to environmental changes, suggesting that Amazonia is both a refuge and a cradle of biodiversity

The Miocene wetland of western Amazonia and its role in Neotropical biogeography

In the Miocene (23-5 Ma), a large wetland known as the Pebas System characterized western Amazonia. During the Middle Miocene Climatic Optimum (c. 17-15 Ma), this system reached its maximum extent and was episodically connected to the Caribbean Sea, while receiving sediment input from the Andes in the west, and the craton (continental core) in the east. Towards the late Miocene (c. 10 Ma) the wetland transitioned into a fluvial-dominated system. In biogeographic models, the Pebas System is often considered in two contexts: one describing the system as a cradle of speciation for aquatic or semi-aquatic taxa such as reptiles, molluscs and ostracods, and the other describing the system as a barrier for dispersal and gene flow for amphibians and terrestrial taxa such as plants, insects and mammals. Here we highlight a third scenario in which the Pebas System is a permeable biogeographical system. This model is inspired by the geological record of the mid-Miocene wetland, which indicates that sediment deposition was cyclic and controlled by orbital forcing and sea-level change, with environmental conditions repeatedly altered. This dynamic landscape favoured biotic exchange at the interface of (1) aquatic and terrestrial, (2) brackish and freshwater and (3) eutrophic to oligotrophic conditions. In addition, the intermittent connections between western Amazonia and the Caribbean Sea, the Andes and eastern Amazonia favoured two-way migrations. Therefore, biotic exchange and adaptation was probably the norm, not the exception, in the Pebas System. The myriad of environmental conditions contributed to the Miocene Amazonian wetland system being one of the most species-rich systems in geological history.ISSN:0024-4074ISSN:1095-833

Geologically recent rearrangements in central Amazonian river network and their importance for the riverine barrier hypothesis

The riverine barrier hypothesis is a central concept in Amazonian biogeography. It states that large rivers limit species distributions and trigger vicariant speciation. Although the hypothesis has explanatory power, many recent biogeographical observations addressing it have produced conflicting results. We propose that the controversies arise because tributary arrangements in the Amazon river system have changed in geologically recent times, such that large tracts of forest that were on the same side of a river at one time got separated to different sides at another. Based on topographical data and sediment dating, we map about 20 major avulsion and river capture events that have rearranged the river network in central Amazonia during the late Pleistocene and Holocene. We identify areas where past riverine barrier effects might still linger in the absence of a major river, as well as areas where such effects may not yet have accumulated across an existing river. These results call for a reinterpretation of previous biogeographical studies and a reorientation of future works to take into account the idiosyncratic histories of individual rivers

Prisma Flow Diagram;ArcGIS Pro Project File from Geodiversity in the Amazon drainage basin

This diagram explains Identification and screening of studies via databases and registers;The ArcGIS Pro Project File consists of all the map data shown in this review [link is embedded in the main text

Celebrating Alexander von Humboldt’s 250 th anniversary: Exploring bio- and geodiversity in the Andes (IBS Quito 2019)

Alexander von Humboldt conducted his best-known work on the slopes of the Ecuadorian Andes. He did this by applying his own characteristic brand of multidisciplinary scientific approach. This consisted of thorough data collection while synthesizing and visualizing the data in innovative formats. Also important for his scientific success in South America was his collaborative network that helped him to identify specimens and formulate his transformative scientific thoughts. It is no surprise that Humboldt was captivated by Ecuador, as it is one of the most biodiverse places in the world, and this astounding diversity was formed in an intricate, dynamic geological and climatological setting. As of yet, this biodiversity is far from being fully documented and the processes that generated it are still poorly understood. The IBS meeting in Quito 1 and the Second Latin American Congress of Biogeography will form the perfect platform to both commemorate Humboldt while addressing current and unresolved matters concerning the biodiversity of Ecuador and South America at large