scholarly journals Overkill, glacial history, and the extinction of North America’s Ice Age megafauna

2020 ◽  
Vol 117 (46) ◽  
pp. 28555-28563
Author(s):  
David J. Meltzer
Keyword(s):  
Climate Changes ◽  
Ice Age ◽  
Individual Species ◽  
Large Mammals ◽  
Glacial History ◽  
Large Mammal ◽  
Ecological Changes ◽  
Significant Difference ◽  
Human Predation ◽  
The One

The end of the Pleistocene in North America saw the extinction of 38 genera of mostly large mammals. As their disappearance seemingly coincided with the arrival of people in the Americas, their extinction is often attributed to human overkill, notwithstanding a dearth of archaeological evidence of human predation. Moreover, this period saw the extinction of other species, along with significant changes in many surviving taxa, suggesting a broader cause, notably, the ecological upheaval that occurred as Earth shifted from a glacial to an interglacial climate. But, overkill advocates ask, if extinctions were due to climate changes, why did these large mammals survive previous glacial−interglacial transitions, only to vanish at the one when human hunters were present? This question rests on two assumptions: that previous glacial−interglacial transitions were similar to the end of the Pleistocene, and that the large mammal genera survived unchanged over multiple such cycles. Neither is demonstrably correct. Resolving the cause of large mammal extinctions requires greater knowledge of individual species’ histories and their adaptive tolerances, a fuller understanding of how past climatic and ecological changes impacted those animals and their biotic communities, and what changes occurred at the Pleistocene−Holocene boundary that might have led to those genera going extinct at that time. Then we will be able to ascertain whether the sole ecologically significant difference between previous glacial−interglacial transitions and the very last one was a human presence.

scholarly journals Glacial history of Inglefield Land, north Greenland from combined in-situ <sup>10</sup>Be and <sup>14</sup>C exposure dating

2020 ◽  
Author(s):  
Anne Sofie Søndergaard ◽  
Nicolaj Krog Larsen ◽  
Olivia Steinemann ◽  
Jesper Olsen ◽  
Svend Funder ◽  
...  
Keyword(s):  
Climate Changes ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Age ◽  
Glacial History ◽  
Holocene Climate ◽  
Exposure Dating ◽  
History Of ◽  
North Greenland

Abstract. Exposing the sensitivity of the Greenland Ice Sheet (GrIS) to Holocene climate changes is a key prerequisite for understanding the future response of the ice sheet to global warming. In this study, we present new information on the Holocene glacial history of the GrIS in Inglefield Land, north Greenland. We use 10Be and in-situ 14C exposure dating to constrain the timing of deglaciation in the area and radiocarbon dating of reworked molluscs and wood fragments to constrain when the ice sheet retreated behind its present-day extent. The 10Be ages are scattered ranging from c. 92.7 to 6.8 ka whereas the in-situ 14C ages range from c. 14.2 to 6.7 ka. Almost half of the apparent 10Be ages predate the Last Glacial Maximum and up to 89 % are to some degree affected by nuclide inheritance. Based on the few reliable 10Be ages, the in-situ 14C ages and existing radiocarbon ages from Inglefield Land, we find that the deglaciation along the coast commenced c. 8.6–8.3 cal. ka BP in the western part and c. 7.9 ka in the central part, following the opening of Nares Strait and arrival of warm waters. The ice margin reached its present-day position c. 8.2 ka at the Humboldt Glacier and c. 6.7 ka in the central part of Inglefield Land. Radiocarbon ages of reworked molluscs and wood fragments show that the ice margin was behind its present-day extent from c. 5.8 to 0.5 cal. ka BP. After 0.5 cal. ka BP, the ice advanced towards its Little Ice Age position. Our results emphasize that the slowly eroding and possibly cold-based ice in north Greenland makes it difficult to constrain the deglaciation history based on 10Be ages alone unless it is paired with in-situ 14C ages. Further, combining our findings with those of recently published studies reveals distinct differences between deglaciation patterns of northwest and north Greenland. Deglaciation of the land areas in northwest Greenland occurred earlier than in north Greenland and periods of restricted ice extent were longer, spanning middle and late Holocene. Overall, this highlights past ice sheet sensitivity towards Holocene climate changes in an area where little information was available just a few years ago.

scholarly journals Glacial history of Inglefield Land, north Greenland from combined in situ <sup>10</sup>Be and <sup>14</sup>C exposure dating

2020 ◽  
Vol 16 (5) ◽  
pp. 1999-2015
Author(s):  
Anne Sofie Søndergaard ◽  
Nicolaj Krog Larsen ◽  
Olivia Steinemann ◽  
Jesper Olsen ◽  
Svend Funder ◽  
...  
Keyword(s):  
Climate Changes ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Age ◽  
Glacial History ◽  
Holocene Climate ◽  
Exposure Dating ◽  
History Of ◽  
North Greenland

Abstract. Determining the sensitivity of the Greenland Ice Sheet (GrIS) to Holocene climate changes is a key prerequisite for understanding the future response of the ice sheet to global warming. In this study, we present new information on the Holocene glacial history of the GrIS in Inglefield Land, north Greenland. We use 10Be and in situ 14C exposure dating to constrain the timing of deglaciation in the area and radiocarbon dating of reworked molluscs and wood fragments to constrain when the ice sheet retreated behind its present-day extent. The 10Be ages are scattered ranging from ca. 92.7 to 6.8 ka, whereas the in situ 14C ages range from ca. 14.2 to 6.7 ka. Almost half of the apparent 10Be ages predate the Last Glacial Maximum and up to 89 % are to some degree affected by nuclide inheritance. Based on the few reliable 10Be ages, the in situ 14C ages and existing radiocarbon ages from Inglefield Land, we find that the deglaciation along the coast commenced at ca. 8.6–8.3 ka cal BP in the western part and ca. 7.9 ka in the central part, following the opening of Nares Strait and arrival of warm waters. The ice margin reached its present-day position at ca. 8.2 ka at the Humboldt Glacier and ca. 6.7 ka in the central part of Inglefield Land. Radiocarbon ages of reworked molluscs and wood fragments show that the ice margin was behind its present-day extent from ca. 5.8 to 0.5 ka cal BP. After 0.5 ka cal BP, the ice advanced towards its Little Ice Age position. Our results emphasize that the slowly eroding and possibly cold-based ice in north Greenland makes it difficult to constrain the deglaciation history based on 10Be ages alone unless they are paired with in situ 14C ages. Further, combining our findings with those of recently published studies reveals distinct differences between deglaciation patterns of northwest and north Greenland. Deglaciation of the land areas in northwest Greenland occurred earlier than in north Greenland, and periods of restricted ice extent were longer, spanning the Middle and Late Holocene. Overall, this highlights past ice sheet sensitivity to Holocene climate changes in an area where little information was available just a few years ago.

Compositional turnover and ecological changes related to the waxing and waning of glaciers during the late Paleozoic ice age in ice-proximal regions (Pennsylvanian, western Argentina)

Paleobiology ◽  
2016 ◽  
Vol 42 (2) ◽  
pp. 335-357 ◽  
Author(s):  
Diego Balseiro
Keyword(s):  
Regional Scale ◽  
Global Scale ◽  
Ice Age ◽  
Late Paleozoic ◽  
Taxonomic Structure ◽  
Diversity Gradient ◽  
Ecological Changes ◽  
Late Paleozoic Ice Age ◽  
The One ◽  
Diversity Structure

AbstractThe late Paleozoic ice age (LPIA) had a profound effect on the biota. Despite much research having been focused on paleotropical regions or global-scale analyses, regional ecological changes have seldom been studied in ice-proximal basins. Here, I study the compositional turnover and diversity structure across the main Carboniferous glacial event recorded in western Argentina and the subsequent nonglacial interval. Brachiopod and bivalve data from western Argentina suggest that the transition from glacial to nonglacial climates caused major compositional changes. Turnover, however, was not uniform across the bathymetric gradient, being higher in deep environments. Because extirpation was concentrated in brachiopods, but immigration was similar in both clades, the taxonomic structure of the region was significantly modified. Although regional hierarchical diversity structure and occupancy distributions remained stable, dissecting the analysis in brachiopods and bivalves underscores that both clades had different responses to climate change. Brachiopods, on the one hand, show stability in the diversity structure and a very slight decrease in occupancies of intermediate genera, while bivalves show an important rise in diversity, both at the environment and regional scale, and an increase in genera with intermediate occupancies. The bathymetric diversity gradient was also modified from hump shaped with maximum diversity in the deep subtidal to a linear gradient with maximum values toward the offshore. However, relative compositional differences within environments remained stable, with maximum values at intermediate depths both in glacial and nonglacial intervals. Moreover, local-scale coexistence between brachiopods and bivalves changed in the nonglacial interval, showing significant segregation, which indicates relevant modifications in community assembly dynamics. Results from western Argentina highlight the magnitude of regional-scale ecological changes during the LPIA in ice-proximal regions, suggesting that the waxing and waning of glaciers was able to cause regional taxonomic turnover and medium-scale ecological changes even during intervals of relative macroevolutionary quiescence.

The Overkill Hypothesis as a Plausible Explanation for the Extinctions of Late Wisconsin Megafauna

1983 ◽  
Vol 20 (1) ◽  
pp. 110-112 ◽  
Author(s):  
W. Geoffrey Spaulding
Keyword(s):  
Western Hemisphere ◽  
Ice Age ◽  
Differential Impact ◽  
Large Mammal ◽  
Noble Savage ◽  
Last Ice Age ◽  
Human Predation ◽  
Ecological Catastrophe

AbstractThe pulse of large mammal extinctions at the close of the last ice age was a pronounced ecological catastrophe in the Western Hemisphere. Available paleoenvironmental, paleontological, and archeological data are largely concordant with the “overkill” hypothesis proposing that human predation was the cause of these extinctions. Climatic explanations fail to postulate specific mechanisms accounting for the event's timing, differential impact, geographic extent, and stratigraphic singularity. Lack of provisional acceptance of the overkill hypothesis, when no viable alternatives exist, may be in part because this unconventional hypothesis violates a strong sociocultural bias, the image of prehistoric man as the “noble savage”.

scholarly journals Large Mammal Diversity and Endemism at Geremba Mountain Fragment, Southern Ethiopia

2020 ◽  
Vol 2020 ◽  
pp. 1-11 ◽  
Author(s):  
Zerubabel Worku ◽  
Zerihun Girma
Keyword(s):  
Diversity Index ◽  
Abundant Species ◽  
Southern Ethiopia ◽  
Bamboo Forest ◽  
Large Mammals ◽  
Habitat Types ◽  
Mammal Species ◽  
Papio Anubis ◽  
Large Mammal ◽  
Significant Difference

Outside protected areas in Ethiopia, there is a lack of information concerning mammalian diversity and ecology. Consequently, the findings of the research on large mammals at Geremba Mountain constitute one of the steps towards a continuing effort to document the diversity and distribution of Ethiopian mammals. The survey was conducted to investigate the species composition, relative abundance, and population structure of large mammals at Geremba Mountain fragment from August 2017 to February 2018, covering both dry and wet seasons. Direct (sighting) and indirect (scat) survey techniques were employed using systematically established transect lines and sampling plots, respectively. Transects and plots were established across three dominant habitat types (modified dry ever green Afromontane forest, alpine bamboo forest, and Erica scrubland). A total of 10 large mammal species were recorded including two endemic mammals, namely, Chlorocebus djamdjamensis and Tragelaphus scriptus meneliki. There was a statistically significant difference in the abundance of species among habitat types at Geremba Mountain. The highest diversity index was recorded in the alpine bamboo forest habitat (D = 7.142, H′ = 2.052), and the Erica scrubland had the lowest. Papio anubis was the most abundant species while Felis serval was the least abundant species. The populations of most of the species were characterized by more adult and more female individuals. However, promising young individuals of the endemic mammals (C. djamdjamensis and T. s. meneliki) and Papio anubis were recorded. The mountain fragment is an isolated island that is totally disconnected with other fragments in the region, so attempts should be made to connect the fragment with other fragments using wildlife corridors.

F.VIII R:Ag in Hepatitis

1979 ◽  
Author(s):  
R. Kotitschke ◽  
J. Scharrer
Keyword(s):  
Chronic Hepatitis ◽  
Blood Donors ◽  
Blood Donation ◽  
Normal Population ◽  
Rabbit Antiserum ◽  
Two Dimensional ◽  
Plastic Plate ◽  
Significant Difference ◽  
Acute Hepatitis B ◽  
The One

F.VIII R:Ag was determined by quantitative immunelectrophoresis (I.E.) with a prefabricated system. The prefabricated system consists of a monospecific f.VIII rabbit antiserum in agarose on a plastic plate for the one and two dimensional immunelectrophoresis. The lognormal distribution of the f.VIII R:Ag concentration in the normal population was confirmed (for n=70 the f.VIII R:Ag in % of normal is = 95.4 ± 31.9). Among the normal population there was no significant difference between blood donors (one blood donation in 8 weeks; for n=43 the f.VIII R:Ag in % of normal is = 95.9 ± 34.0) and non blood donors (n=27;f.VIII R:Ag = 94.6 ± 28.4 %). The f.VIII R:Ag concentration in acute hepatitis B ranged from normal to raised values (for n=10, a factor of 1.8 times of normal was found) and was normal again after health recovery (n=10, the factor was 1.0). in chronic hepatitis the f.VIII R:Ag concentration was raised in the majority of the cases (for n=10, the factor was 3.8). Out of 22 carrier sera 20 showed reduced, 2 elevated levels of the f.VIII R:Ag concentration. in 5 sera no f.VIII R:Ag could be demonstrated. The f.VIII R:Ag concentration was normal for n=10, reduced for n=20 and elevated for n=6 in non A-non B hepatitis (n=36). Contrary to results found in the literature no difference in the electrophoretic mobility of the f.VIII R:Ag was found between hepatitis patients sera and normal sera.

IMMUNOLOGICAL REACTIVITY OF INSULIN IN HUMAN SERUM

1966 ◽  
Vol 53 (4) ◽  
pp. 673-680 ◽  
Author(s):  
Torsten Deckert ◽  
Kai R. Jorgensen
Keyword(s):  
Normal Subjects ◽  
The Other ◽  
Human Pancreas ◽  
Porcine Pancreas ◽  
Crystalline Insulin ◽  
Endogenous Insulin ◽  
Significant Difference ◽  
Human Sera ◽  
Normal Human ◽  
The One

ABSTRACT The purpose of this study was to investigate whether a difference could be demonstrated between crystalline insulin extracted from normal human pancreas, and crystalline insulin extracted from bovine and porcine pancreas. Using Hales & Randle's (1963) immunoassay no immunological differences could be demonstrated between human and pig insulin. On the other hand, a significant difference was found, between pig and ox insulin. An attempt was also made to determine whether an immunological difference could be demonstrated between crystalline pig insulin and crystalline human insulin from non diabetic subjects on the one hand and endogenous, circulating insulin from normal subjects, obese subjects and diabetic subjects on the other. No such difference was found. From these experiments it is concluded that endogenous insulin in normal, obese and diabetic human sera is immunologically identical with human, crystalline insulin from non diabetic subjects and crystalline pig insulin.

A Relativistic Newtonian Mechanics Predicts with Precision the Results of Recent Neutrino-Velocity Experiments

2014 ◽  
Vol 6 (1) ◽  
pp. 1032-1035 ◽  
Author(s):  
Ramzi Suleiman
Keyword(s):  
Null Hypothesis ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Newtonian Mechanics ◽  
Speed Of Light ◽  
Symmetry Principle ◽  
Proposed Model ◽  
Significant Difference ◽  
The One ◽  
Complete Collapse

The research on quasi-luminal neutrinos has sparked several experimental studies for testing the "speed of light limit" hypothesis. Until today, the overall evidence favors the "null" hypothesis, stating that there is no significant difference between the observed velocities of light and neutrinos. Despite numerous theoretical models proposed to explain the neutrinos behavior, no attempt has been undertaken to predict the experimentally produced results. This paper presents a simple novel extension of Newton's mechanics to the domain of relativistic velocities. For a typical neutrino-velocity experiment, the proposed model is utilized to derive a general expression for . Comparison of the model's prediction with results of six neutrino-velocity experiments, conducted by five collaborations, reveals that the model predicts all the reported results with striking accuracy. Because in the proposed model, the direction of the neutrino flight matters, the model's impressive success in accounting for all the tested data, indicates a complete collapse of the Lorentz symmetry principle in situation involving quasi-luminal particles, moving in two opposite directions. This conclusion is support by previous findings, showing that an identical Sagnac effect to the one documented for radial motion, occurs also in linear motion.

Climate-induced treeline mortality during the termination of the Little Ice Age in the Greater Yellowstone Ecoregion, USA

The Holocene ◽  
2021 ◽  
pp. 095968362110116
Author(s):  
Maegen L Rochner ◽  
Karen J Heeter ◽  
Grant L Harley ◽  
Matthew F Bekker ◽  
Sally P Horn
Keyword(s):  
Climate Change ◽  
Tree Ring ◽  
Little Ice Age ◽  
Climate Changes ◽  
Frost Damage ◽  
Ice Age ◽  
Spatial And Temporal Variability ◽  
Whitebark Pine ◽  
Engelmann Spruce ◽  
Greater Yellowstone

Paleoclimate reconstructions for the western US show spatial variability in the timing, duration, and magnitude of climate changes within the Medieval Climate Anomaly (MCA, ca. 900–1350 CE) and Little Ice Age (LIA, ca. 1350–1850 CE), indicating that additional data are needed to more completely characterize late-Holocene climate change in the region. Here, we use dendrochronology to investigate how climate changes during the MCA and LIA affected a treeline, whitebark pine ( Pinus albicaulis Engelm.) ecosystem in the Greater Yellowstone Ecoregion (GYE). We present two new millennial-length tree-ring chronologies and multiple lines of tree-ring evidence from living and remnant whitebark pine and Engelmann spruce ( Picea engelmannii Parry ex. Engelm.) trees, including patterns of establishment and mortality; changes in tree growth; frost rings; and blue-intensity-based, reconstructed summer temperatures, to highlight the terminus of the LIA as one of the coldest periods of the last millennium for the GYE. Patterns of tree establishment and mortality indicate conditions favorable to recruitment during the latter half of the MCA and climate-induced mortality of trees during the middle-to-late LIA. These patterns correspond with decreased growth, frost damage, and reconstructed cooler temperature anomalies for the 1800–1850 CE period. Results provide important insight into how past climate change affected important GYE ecosystems and highlight the value of using multiple lines of proxy evidence, along with climate reconstructions of high spatial resolution, to better describe spatial and temporal variability in MCA and LIA climate and the ecological influence of climate change.

scholarly journals One Room Schoolhouse: A Novel Intervention for Inspired Academic Half-Day Learning in Distributed Campus Settings

2021 ◽  
Vol 8 ◽  
pp. 238212052110294
Author(s):  
Sheila Harms ◽  
Anita Acai ◽  
Bryce JM Bogie ◽  
Meghan M McConnell ◽  
Ben McCutchen ◽  
...  
Keyword(s):  
Clinical Experiences ◽  
Pedagogical Strategies ◽  
Main Campus ◽  
Self Confidence ◽  
Significant Difference ◽  
Regional Campus ◽  
Educational Engagement ◽  
Learner Agency ◽  
Multi Method Approach ◽  
The One

Introduction: Some studies on academic half days (AHDs) suggest that learning in this context is associated with a lack of educational engagement. This challenge may be amplified in distributed campus settings, where geographical disadvantages demand reliance on videoconferencing or considerable time spent travelling to in-person learning events. Concerns about the educational effectiveness of AHDs by learners within our distributed campus setting led to the development and evaluation of the One Room Schoolhouse (ORS), a unique, evidence-informed, community-based curriculum that partially replaced the AHD sessions delivered at the main campus. It was hypothesized that creating an AHD experience that was clinically reflective of the community in which residents practiced and where residents were given the autonomy to implement novel pedagogical elements would result in better test scores and improved learner satisfaction among ORS learners. Methods: The ORS was implemented at McMaster University’s Waterloo Regional Campus in 2017. Residents across training cohorts (N = 9) engaged in co-learning based on scenarios co-developed from clinical experiences within the region. The learning approach relied on multiple, evidence-informed pedagogical strategies. A multi-method approach was used to evaluate the ORS curriculum. Between-subject analyses of variance were used to compare scores on practice exams (COPE and PRITE), in-training assessment reports (ITARs), and objective structured clinical exams (OSCEs) between learners who took part in the ORS and learners at the main campus. A semi-structured focus group probing residents’ experiences with the ORS was analyzed using interpretive description. Results: ORS learners significantly outperformed learners at the main campus on the November OSCE ( p = .02), but not on the COPE, PRITE, ITARs, or September OSCE ( p’s < .05). Qualitative themes suggested advantages of the ORS in inspiring learning, engaging learners, and improving self-confidence in knowledge acquisition. These findings are aligned with the broader literature on learner agency, social development, and communities of practice. Conclusion: While the quantitative data only showed a significant difference between the 2 curricula on 1 measure (ie, the November OSCE), the qualitative findings offered an opportunity for educators to reimagine what medical education might consist of beyond the confines of a “traditional” AHD. Creating opportunities to enhance personal agency when acquiring knowledge, inspiring engagement about patient-related problems, and incorporating interdisciplinary learning through community engagement were critical pedagogical elements that were attributed to the success of the ORS.

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