Onset Of Pleistocene Glaciation Research Articles

Unique functional diversity during early Cenozoic mammal radiation of North America.

Mammals influence nearly all aspects of energy flow and habitat structure in modern terrestrial ecosystems. However, anthropogenic effects have probably altered mammalian community structure, raising the question of how past perturbations have done so. We used functional diversity (FD) to describe how the structure of North American mammal palaeocommunities changed over the past 66 Ma, an interval spanning the radiation following the K/Pg and several subsequent environmental disruptions including the Palaeocene-Eocene Thermal Maximum (PETM), the expansion of grassland, and the onset of Pleistocene glaciation. For 264 fossil communities, we examined three aspects of ecological function: functional evenness, functional richness and functional divergence. We found that shifts in FD were associated with major ecological and environmental transitions. All three measures of FD increased immediately following the extinction of the non-avian dinosaurs, suggesting that high degrees of ecological disturbance can lead to synchronous responses both locally and continentally. Otherwise, the components of FD were decoupled and responded differently to environmental changes over the last ~56 Myr.

Reprint of: Disentangling drivers of plant endemism and diversification in the European Alps - a phylogenetic and spatially explicit approach

Plant endemism in the European Alps is clustered into particular geographic areas. Two contrasted and non exclusive hypotheses have been suggested to explain these hotspots of endemism: (i) those areas were glacial refugia, where endemism reflects survival-recolonisation dynamics since the onset of Pleistocene glaciations, (ii) those are high elevation mountain areas, where endemism was fostered by local speciation events due to geographic isolation and harsh environmental niches, or by low dispersal ability of inhabiting species.Here, we quantitatively compared these two hypotheses using data of species distribution in the European Alps (IntraBioDiv database), species phylogenetic relationships, and species ecological and biological characteristics. We developed a spatially and phylogenetically explicit modeling framework to analyze spatial patterns of endemism and the phylogenetic structure of species assemblages. Moreover, we analyzed interrelations between species trait syndromes and endemism.We found that high endemism occurrs in potential glacial refugia, but only those on calcareous bedrock, and also in areas with high elevation. Plant assemblages in calcareous refugia showed phylogenetic overdispersion − a signature of non-selective conservation forces, whereas those located in high mountain areas showed phylogenetic clustering − a signature of recent diversification and environmental filtering. Endemic species were either stress-tolerant, poorly dispersing species, or high elevation specialists with a wide distribution within the European Alps.While both calcareous refugia and high-elevation hotspots harbour a large portion of plant endemism in the European Alps, the species they host have substantially different characteristics. Our results suggest that hotspots of endemism in calcareous refugia are more important for nature conservation planning, as they host many range restricted endemic species and rather isolated evolutionary lineages.

Disentangling drivers of plant endemism and diversification in the European Alps – A phylogenetic and spatially explicit approach

Plant endemism in the European Alps is clustered into particular geographic areas. Two contrasted and non exclusive hypotheses have been suggested to explain these hotspots of endemism: (i) those areas were glacial refugia, where endemism reflects survival-recolonisation dynamics since the onset of Pleistocene glaciations, (ii) those are high elevation mountain areas, where endemism was fostered by local speciation events due to geographic isolation and harsh environmental niches, or by low dispersal ability of inhabiting species.Here, we quantitatively compared these two hypotheses using data of species distribution in the European Alps (IntraBioDiv database), species phylogenetic relationships, and species ecological and biological characteristics. We developed a spatially and phylogenetically explicit modelling framework to analyze spatial patterns of endemism and the phylogenetic structure of species assemblages. Moreover, we analyzed interrelations between species trait syndromes and endemism.We found that high endemism occurrs in potential glacial refugia, but only those on calcareous bedrock, and also in areas with high elevation. Plant assemblages in calcareous refugia showed phylogenetic overdispersion – a signature of non-selective conservation forces, whereas those located in high mountain areas showed phylogenetic clustering – a signature of recent diversification and environmental filtering. Endemic species were either stress-tolerant, poorly dispersing species, or high elevation specialists with a wide distribution within the European Alps.While both calcareous refugia and high-elevation hotspots harbour a large portion of plant endemism in the European Alps, the species they host have substantially different characteristics. Our results suggest that hotspots of endemism in calcareous refugia are more important for nature conservation planning, as they host many range restricted endemic species and rather isolated evolutionary lineages.

Incision history of Glenwood Canyon, Colorado, USA, from the uranium-series analyses of water-table speleothems

Uranium-series analyses of water-table-type speleothems from Glenwood Cavern and “cavelets” near the town of Glenwood Springs, Colorado, USA, yield incision rates of the Colorado River in Glenwood Canyon for the last ~1.4 My. The incision rates, calculated from dating cave mammillary and cave folia calcite situated 65 and 90 m above the Colorado River, are 174 ± 30 m/My for the last 0.46 My and 144 ± 30 m/My for the last 0.62 My, respectively. These are consistent with incision rates determined from nearby volcanic deposits. In contrast, δ234U model ages (1.39 ± 0.25 My; 1.36 ± 0.25 My; and 1.72 ± 0.25 My) from three different samples of mammillary-like subaqueous crust collected from Glenwood Cavern, 375 m above the Colorado River, yield incision rates of 271 +58/-41 m/My, 277 +61/-42 m/ My, and 218 +36/-27 m/My. These data suggest a relatively fast incision rate between roughly 3 and 1 Ma. The onset of Pleistocene glaciation may have influenced this rate by increasing precipitation on the Colorado Plateau starting at 2.5 Ma. Slowing of incision just before 0.6 Ma could be related to the change in frequency of glacial cycles from 40 to 100 kyr in the middle Pleistocene. This interpretation would suggest that the cutting power of the Colorado River prior to 3 Ma was smaller. An alternative interpretation involving tectonic activity would invoke an episode of fast uplift in the Glenwood Canyon region from 3 to 1 Ma.

New species of Anillinus Casey (Carabidae: Trechinae: Bembidiini) from the Southern Appalachians and phylogeography of the A. loweae species group

The Anillinus loweae–species group comprises five species occurring in the southern Appalachian Mountains and adjacent upland terrains in southeastern United States. Three new species are described herein. Two are members of the loweae-group, Anillinus merritti sp. nov. from Great Smoky Mountains National Park (GSMNP) (southeastern Tennessee and western North Carolina) and A. juliae sp. nov., from McMinn County, Tennessee. The third, A gimmeli sp. nov. from GSMNP, is closely allied to them morphologically. Loweae-group species may be distinguished from those of other species groups by the presence of paramedian areas without microsculpture on the head. They occur in forest litter habitats and the group’s distribution extends from Mississippi and Alabama in the south to the French Broad River of North Carolina and Tennessee in the north. Species within the group are distinguished mainly using characters of the male genitalia and to a lesser extent, differences in shapes of female spermathecae, body size, and relative proportions of body parts. A phylogeny of loweae-group species based on analyses of COI gene sequences, in combination with geographic distributions and correlations to likely physiographic isolating mechanisms, allow a hypothetical reconstruction of the biogeographic history of the group. The following major factors affected speciation within the loweae-group: (1) division of former ancestral ranges, due to changes in major drainage systems beginning prior to the onset of Pleistocene glaciation; (2) Pliocene-Pleistocene climate cooling and subsequent dispersal constrained by physical barriers; (3) Early Pleistocene glacial cycles influencing altitudinal stratification among species.

Phylogeography and evolution of the triplefin Tripterygion delaisi (Pisces, Blennioidei)

The genus Tripterygion (Risso 1826) is restricted to the eastern Atlantic and the Mediterranean, and comprises only three species. T. melanuros and T. tripteronotus are essentially endemic to the Mediterranean, while Tripterygion delaisi occurs in the Atlantic and in the Mediterranean. Two subspecies of T. delaisi have been described (T. d. xanthosoma in the Mediterranean and T. d. delaisi in the Atlantic). Several scenarios have been proposed for the evolution of T. delaisi subspecies, but so far its subspeciation process is not clear. In this study we present a population survey of T. delaisi including specimens from the two recognized subspecies. We combined a phylogeographic approach with estimates of the direction of migration (between the Atlantic and the Mediterranean) and of the coalescence time of the two subspecies, using polymorphic mitochondrial and nuclear genes. The results of this study clearly support the existence of two Tripterygion delaisi clades, one in the eastern Atlantic islands and another in the Atlantic coasts of Europe and in the Mediterranean. Historical migration between the islands and Western Europe plus Mediterranean was restricted, and showed a westbound trend, with a higher number of migrants going from the Western Europe plus Mediterranean into the islands. We estimated the time of coalescence of both groups of T. delaisi to be more recent than the onset of Pleistocene glaciations (1.7 Mya). Our results are consistent with previous hypothesis that consider successive dispersal events of a Tripterygion ancestor from the western African coast colonizing the Atlantic islands and the Mediterranean, promoting the evolutionary divergence between these areas.

On the origin of Darwin's finches.

Darwin's finches comprise a group of 15 species endemic to the Galápagos (14 species) and Cocos (1 species) Islands in the Pacific Ocean. The group is monophyletic and originated from an ancestral species that reached the Galápagos Archipelago from Central or South America. Descendants of this ancestor on the Archipelago then colonized Cocos Island. In the present study, we used sequences of two mitochondrial (mt) DNA segments (922 bp of the cytochrome b gene and 1,082 bp of the control region), as well as two nuclear markers (830 bp of numt2, consisting of 140 bp of mtDNA control region and 690 bp of flanking nuclear DNA; and 740 bp of numt3, consisting of 420 bp of mt cytochrome b sequence flanked by 320 bp of nuclear DNA) to identify the species group most closely related to the Darwin's finches. To this end, we analyzed the sequences of 28 species representing the main groups (tribes) of the family Fringillidae, as well as 2 outgroup species and 13 species of Darwin's finches. In addition, we used mtDNA cytochrome b sequences of some 180 additional Fringillidae species from the database for phylogeny reconstruction by maximum-parsimony, maximum-likelihood, minimum-evolution, and neighbor-joining methods. The study identifies the grassquit genus Tiaris, and specifically the species Tiaris obscura, as the nearest living relative of Darwin's finches among the species surveyed. Darwin's finches diverged from the Tiaris group shortly after the various extant species of Tiaris diverged from one another. The initial adaptive radiation of the Tiaris group apparently occurred on the Caribbean islands and then spread to Central and South America, from where the ancestors of Darwin's finches departed for the Galápagos Islands approximately 2.3 MYA, at the time of the dramatic climatic changes associated with the closure of the Panamanian isthmus and the onset of Pleistocene glaciation.

The onset of Pleistocene glaciation in the Barents Sea: implications for glacial isostatic adjustment

SUMMARY In this paper the effect of a delayed onset of glaciation in the Barents Sea on glacial isostatic adjustment is investigated. The model calculations solve the sea-level equation governing the total mass redistributions associated with the last glaciation cycle on a spherically symmetric, linear, Maxwell viscoelastic earth for two different scenarios for the growth phase of the Barents Sea ice sheet. In the first ice model a linear growing history is used for the Barents Sea ice sheet, which closely relates its development to the build-up of other major Late Pleistocene ice sheets. In the second ice model the accumulation of the Barents Sea ice sheet is restricted to the last 6 ka prior to the last glacial maximum. The calculations predict relative sea levels, present-day radial velocities, and gravity anomalies for the area formerly covered by the Weichselian ice sheet. The results show that observed relative sea levels in the Barents Sea are appropriate for distinguishing between the different glaciation histories. In particular, present-day observables such as the free-air gravity anomaly over the Barents Sea, and the present-day radial velocities are sensitive to changes in the glaciation history on this scale. A palaeobathymetry derived from relative sea-level predictions before the last glacial maximum based on the second ice model essentially agrees with a palaeobathymetry derived by Lambeck (1995). The additional emerged areas provide centres for the build-up of an ice sheet and thus support the theory of Hald, Danielsen & Lorentzen (1990) and Mangerud et al. (1992) that the Barents Sea was an essentially marine environment shortly before the last glacial maximum.

The Zoogeography of the Fishes of the Youghiogheny River System, Pennsylvania, Maryland and West Virginia

A total of 266 fish collections were made at 172 stations in the Youghiogheny River drainage, the largest tributary to the Monongahela River. Collections were made using seines, electrofishing gear, gill nets and trap nets. A comprehensive literature review yielded 99 species of fishes reported from the Youghiogheny River system. Six species collected during this survey (Amia calva, Carassius auratus, Ericymba buccata, Notropis rubellus, Ictalurus catus and Fundulus diaphanus) established new distributional records for the system, increasing the total to 105 species. Of this total, 78 species were verified either by our collections (57 species), museum records (10) or stocking records (11), whereas 27 could not be verified. Of the 27 unverified species, 21 are expected to occur and six are considered misidentifications or erroneous records. An additional 24 species are expected to have occurred historically in the Youghiogheny or have the potential to do so based on their distribution in the Monongahela or Allegheny rivers. Of the 78 species of fishes confirmed to have occurred in the Youghiogheny River, 57 were collected during this survey, 11 were unsuccessful introductions and nine have probably been extirpated. One species, Esox masquinongy, is considered extant, but was not collected during this study. The ichthyofauna of the Youghiogheny River system was largely derived from Teays River by dispersal up the newly formed Ohio River after the onset of Pleistocene glaciation. Two species, Clinostomus elongatus and Catostomus catostomus, dispersed into the Youghiogheny from the N during the Pleistocene. Rhinichthys atratulus atratulus dispersed into the Youghiogheny from Potomac River via stream capture. Several species, (Jampostoma a. anomalum, Ericymba buccata, Nocomis micropogon, Notropis spilopterus and Etheostoma b. blennioides, may have used Youghiogheny-Potomac stream captures as a dispersal route eastward into the Atlantic slope.

K-Ar Mineral Age of Ash Bed in Pico Formation, Ventura Basin, California: ABSTRACT

A widespread volcanic ash layer, 1-4 inches thick, in the Pliocene Pico Formation (Wheelerian microfaunal stage) has been dated radiometrically. Twenty-five-pound samples of ash were taken from each of two localities. Each sample yielded about 4 grams of sanidine and 1 gram of biotite. These minerals are unaltered and show euhedral grain boundaries; some sanidine crystals have rims of glass. The glass matrix, comprising 95 per cent of the sample, is isotropic and apparently unaltered. Radiometric ages follow. Table All ages were run at Shell Development Company except the biotite from Ventura River, which was run by John Obradovitch, United States Geological Survey, Denver, Colorado. The mineral ages are consistent within the range 8.4-9.7 m.y. The glass ages are discordant, apparently because of argon leakage; the glass is therefore useless in radiometric dating despite its unaltered appearance. The upper part of the Pico is divided into two molluscan zones, a lower warm-water zone, and an upper zone containing a molluscan assemblage resembling that living today in Pacific Northwest waters. The temperature shift from warm to cold previously was correlated with the onset of Pleistocene glaciation and, because beds containing the cold-water mollusks are folded, the age of folding (Coast Range orogeny) traditionally has been considered to be intra-Pleistocene. R. F. Meade has shown that the base of the cold-water molluscan zone is just below the ash bed near South Mountain; it is possible that the molluscan shift is not caused by glaciation but by a pre-Pleistocene change in oceanic current patterns accompanying a general late Tertiary cooling. The new radiometric age and the invalidation by Durham, Jahns, and Savage (1954) of mammalian evidence for a Pleistocene age of folding suggest that both the molluscan temperature shift and Coast Range orogeny occurred in Pliocene time. End_of_Article - Last_Page 486------------