Formation of the Isthmus of Panama

The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed manymillions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways,withformationof theIsthmus of Panama sensustricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.Facultad de Ciencias Naturales y Muse

Geologic-climatic history and zoogeographic significance of the urabá region in northwestern colombia

The existence of a continuous landbridge connecting Central and South America during the uppermost Cretaceous and/or the lowermost Tertiary  cannot be proven on the basis of presently available field evidence. Scattered outcrops of Upper Cretaceous and Paleocene to Lower Eocene shales indicate the continuation of sedimentation in northwestern Colombia during these time intervals. The volcanic "basement complex" consistsmostly of basaltic igneous rocks which intrude Middle Eocene shales and limestones. The pre-Upper Eocene orogeny and the strong pre-Upper Miocene orogeny led to the temporary uplift of the "Cuchillo bridge" which connected the Western Andes of Colombia with the Serranía del Darién of eastern Panamá. Both these orogenies were followed by periods of subsidence when parts of the previously uplifted areas foundered and were covered by the Oligo-Miocene and Upper Miocene-Pliocene seas, respectively. The main uplift of the northern Andes and of the mountains of southern Central America took place during the uppermost Pliocene and lowermost Pleistocene; vertical movements continued throughout the Pleistocene to the present day. The final connection of Central and South America was established during the Upper Pliocene. The exchange of the Middle and South American faunas during the generally warm Tertiary period was mainly influenced by the emergenceand subsidence of low islands and partial land bridges in southern Central America and northwestern Colombia. On the other hand, faunal migrations in these regions during the Quaternary were mainly determined by the following events: (1) The closing of the last water gap separating Central and South America in the Urabá region during the late Pliocene.  (2) The strong uplift of the South and Central American mountains which caused the expansión of dense tropical forests along the foot hills on the windward side and the increased aridity of the lowlands on the leeward side. The mountains themselves formed new zoogeographic barriers which had not existed before, (3) The alternation of cold-wet and warm-dryclimatic phases throughout the Quaternary. These climatic changes influenced the distribution of forest and non-forest vegetation and also determined the changing altitudinal position of the temperature life zones and their continuity or discontinuity along the slopes of the mountain ranges.  The Urabá region was a transit area for the faunas of the more open and drier vegetation during dry climatic periods of the past and is an important meeting place of various Central and South American forest faunas today.The existence of a continuous landbridge connecting Central and South America during the uppermost Cretaceous and/or the lowermost Tertiary  cannot be proven on the basis of presently available field evidence. Scattered outcrops of Upper Cretaceous and Paleocene to Lower Eocene shales indicate the continuation of sedimentation in northwestern Colombia during these time intervals. The volcanic "basement complex" consistsmostly of basaltic igneous rocks which intrude Middle Eocene shales and limestones. The pre-Upper Eocene orogeny and the strong pre-Upper Miocene orogeny led to the temporary uplift of the "Cuchillo bridge" which connected the Western Andes of Colombia with the Serranía del Darién of eastern Panamá. Both these orogenies were followed by periods of subsidence when parts of the previously uplifted areas foundered and were covered by the Oligo-Miocene and Upper Miocene-Pliocene seas, respectively. The main uplift of the northern Andes and of the mountains of southern Central America took place during the uppermost Pliocene and lowermost Pleistocene; vertical movements continued throughout the Pleistocene to the present day. The final connection of Central and South America was established during the Upper Pliocene. The exchange of the Middle and South American faunas during the generally warm Tertiary period was mainly influenced by the emergenceand subsidence of low islands and partial land bridges in southern Central America and northwestern Colombia. On the other hand, faunal migrations in these regions during the Quaternary were mainly determined by the following events: (1) The closing of the last water gap separating Central and South America in the Urabá region during the late Pliocene.  (2) The strong uplift of the South and Central American mountains which caused the expansión of dense tropical forests along the foot hills on the windward side and the increased aridity of the lowlands on the leeward side. The mountains themselves formed new zoogeographic barriers which had not existed before, (3) The alternation of cold-wet and warm-dryclimatic phases throughout the Quaternary. These climatic changes influenced the distribution of forest and non-forest vegetation and also determined the changing altitudinal position of the temperature life zones and their continuity or discontinuity along the slopes of the mountain ranges.  The Urabá region was a transit area for the faunas of the more open and drier vegetation during dry climatic periods of the past and is an important meeting place of various Central and South American forest faunas today

The Late Miocene Gomphothere Amahuacatherium peruvium (Proboscidea: Gomphotheriidae) from Amazonian Peru: Implications for the great american faunal interchange - [Boletín D 23]

Se presentan en detalle los caracteres osteológicos del proboscideo Amahuacatherium peruvium (Proboscidea: Gomphotheriidae). Este proboscideo fue recuperado de los depósitos del Mioceno (Chasicoan) expuestos a lo largo del río Madre de Dios en las tierras bajas al sudeste del Perú. Este proboscideo fue un gomphothere tetrabelodonte y brevirostrino con mandíbulas inferiores que conservan los incisivos y molares con un patrón de esmalte ligeramente complicado. El Amahuacatherium peruvium proviene de la parte baja de la discordancia que se formó durante un período de gran erosión en toda la cuenca del Amazonas al comienzo del Mioceno tardío, cuando el nivel del mar comenzó a descender globalmente hace doce millones de años. Este taxón representa la ocurrencia más temprana de proboscideos, o de cualquier mamífero norteamericano en América del Sur, también representa la ocurrencia más temprana en América del Norte y en América del Sur de cualquier participante en el gran intercambio faunal americano. Algunos proboscideos norteamericanos pueden derivarse de linajes que se originaron en América del Sur durante el Mioceno tardío o Plioceno. Se propone que los proboscideos de América del Norte dispersados en América del Sur siguieron una ruta a través de Panamá vía las serranías de San Blas que conectó al arco de Baudo y el terreno alóctono de Chocó y finalizó en las colinas Istmina de Colombia. El informe presenta bibliografía

Evolutionary Assembly of the Neotropical Montane Avifauna

Three fundamental processes are thought to underlie biodiversity patterns: speciation, dispersal, and extinction. Biodiversity patterns in species-rich tropical mountains vary along horizontal (barriers), and vertical (elevation) dimensions. In this dissertation, I set out to explore the interplay between historical and ecological mechanisms hypothesized to shape diversification of Neotropical cloud forest birds. In the second chapter, I conducted comparative analyses using species-specific ecological traits, and 3,175 mtDNA sequences collected across the range of 45 co-distributed birds. First, I found that niche breadth, dispersal ability, and clade age influence lineage diversity (population differentiation). In particular, species that are old, poor dispersers, and specialized to narrow elevational zones, accumulate greater lineage diversity with time. These results are consistent with predictions of the time-for-speciation effect, Janzen’s climatic zonation model, and niche conservatism. Second, I found weak support for simultaneous divergence between multiple population-pairs separated by the same barriers, suggesting temporal idiosyncrasies in differentiation. In the third chapter, I explored geographic patterns of evolutionary assembly using the same dataset. Overall, birds that presently co-occur in the same mountain range represent avian groups that originated in disjunct geographic areas (e.g., Southern Andes, Northern Andes, or Central American mountains), and subsequently occupied the entire Neotropical montane region. In the fourth chapter, I conducted a more in-depth investigation of the role niche breadth and elevational distribution on multi-species divergence. Using 2,475 mtDNA sequences, I estimated genetic divergence between population pairs (287 comparisons) divided by three major Andean barriers: the North Peruvian Low, the Táchira Depression, and the Motilones Pass. I found that genetic divergences were not randomly distributed with respect to minimum elevation (i.e., elevational distribution) and elevational amplitude (i.e., niche breadth). Elevation specialists (i.e., birds with narrow amplitudes) and the upper limits of elevational distributions (i.e., high minimum elevations) exhibited deeper genetic divergences. These results support the hypothesis of greater genetic divergence with increasing elevational distribution and decreasing niche breadth. In summary, my dissertation suggests that the present-day assemblages of Neotropical montane birds resulted from localized speciation in isolation and subsequent colonization. The effect of physical barriers is modulated by niche specialization along elevational gradients, dispersal ability, and time

The temporal and spatial variability of nursery habitats for fishes in macrotidal mangrove systems of Colombia and Brazil

This thesis highlight (1) the stability in time and across regions of tidal- and diel-related patterns of intertidal mangrove fish distribution in neotropical macrotidal areas, (2) the major effect that specific environmental conditions (e.g. rainfall regime) and seascape settings can produce in local fish community structure, (3) the varying importance that distinctive tropical intertidal habitats can have for coastal fishes, and (4) the importance that historical biogeography (of freshwater and marine fishes) can have in explaining the current patterns of distribution of mangrove fish faunas in estuarine areas of the Neotropics. Taking these four aspects into consideration will benefit our global understanding of the role of mangroves as important habitats for fishes and will aid in the development of sound comparative studies between mangrove areas of the world. Ultimately, the search for generality in patterns and processes explaining the organization of mangrove fish communities will increase our ability to better manage mangrove-associated fisherie

The temporal and spatial variability of nursery habitats for fishes in macrotidal mangrove systems of Colombia and Brazil

This thesis highlight (1) the stability in time and across regions of tidal- and diel-related patterns of intertidal mangrove fish distribution in neotropical macrotidal areas, (2) the major effect that specific environmental conditions (e.g. rainfall regime) and seascape settings can produce in local fish community structure, (3) the varying importance that distinctive tropical intertidal habitats can have for coastal fishes, and (4) the importance that historical biogeography (of freshwater and marine fishes) can have in explaining the current patterns of distribution of mangrove fish faunas in estuarine areas of the Neotropics. Taking these four aspects into consideration will benefit our global understanding of the role of mangroves as important habitats for fishes and will aid in the development of sound comparative studies between mangrove areas of the world. Ultimately, the search for generality in patterns and processes explaining the organization of mangrove fish communities will increase our ability to better manage mangrove-associated fisherie

11th International Coral Reef Symposium Abstracts

https://nsuworks.nova.edu/occ_icrs/1001/thumbnail.jp

Notas y reseñas

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