Late Pleistocene shrub expansion preceded megafauna turnover and extinctions in eastern Beringia

2021 ◽  
Vol 118 (52) ◽  
pp. e2107977118
Author(s):  
Alistair J. Monteath ◽  
Benjamin V. Gaglioti ◽  
Mary E. Edwards ◽  
Duane Froese
Keyword(s):  
Late Pleistocene ◽  
Keystone Species ◽  
Plant Macrofossils ◽  
Shrub Expansion ◽  
Top Down ◽  
Tundra Vegetation ◽  
Shrub Tundra ◽  
Postglacial Expansion ◽  
Sediment Layers ◽  
Mammal Communities

The collapse of the steppe-tundra biome (mammoth steppe) at the end of the Pleistocene is used as an important example of top-down ecosystem cascades, where human hunting of keystone species led to profound changes in vegetation across high latitudes in the Northern Hemisphere. Alternatively, it is argued that this biome transformation occurred through a bottom-up process, where climate-driven expansion of shrub tundra (Betula, Salix spp.) replaced the steppe-tundra vegetation that grazing megafauna taxa relied on. In eastern Beringia, these differing hypotheses remain largely untested, in part because the precise timing and spatial pattern of Late Pleistocene shrub expansion remains poorly resolved. This uncertainty is caused by chronological ambiguity in many lake sediment records, which typically rely on radiocarbon (14C) dates from bulk sediment or aquatic macrofossils—materials that are known to overestimate the age of sediment layers. Here, we reexamine Late Pleistocene pollen records for which 14C dating of terrestrial macrofossils is available and augment these data with 14C dates from arctic ground-squirrel middens and plant macrofossils. Comparing these paleovegetation data with a database of published 14C dates from megafauna remains, we find the postglacial expansion of shrub tundra preceded the regional extinctions of horse (Equus spp.) and mammoth (Mammuthus primigenius) and began during a period when the frequency of 14C dates indicates large grazers were abundant. These results are not consistent with a model of top-down ecosystem cascades and support the hypothesis that climate-driven habitat loss preceded and contributed to turnover in mammal communities.

scholarly journals Early and Middle Wisconsinan Environments of Eastern Beringia: Stratigraphic and Paleoecological Implications of the Old Crow Tephra

2007 ◽  
Vol 39 (3) ◽  
pp. 275-290 ◽  
Author(s):  
Charles E. Schweger ◽  
John V. Matthews
Keyword(s):  
Permafrost Degradation ◽  
Land Bridge ◽  
Radiocarbon Dates ◽  
Thermal Event ◽  
Climate Fluctuations ◽  
Climatic Oscillations ◽  
Tundra Vegetation ◽  
Stage 4 ◽  
Shrub Tundra ◽  
Late Wisconsinan

ABSTRACTThe widespread Beringian Old Crow tephra occurs in Imuruk Lake (Alaska) core V, above the Blake paleomagnetic event and below Radiocarbon dates, which provide an extrapolated tephra age between 87 000 - 105 000 BP. Exposure KY-11 (Alaska), where the tephra occurs in a dated lacustrine sequence, provides corroboration. Fossil pollen records show that O.C.T. was deposited across northern Beringia on birch-shrub tundra vegetation during an interval of colder climate. A series of climatic oscillations followed tephra deposition. A prolonged period of cold-arid climate ( = marine isotope Stage 4) preceded an interval of warmer than present climate starting ca. 60 000 BP (beginning Stage 3). During this interval, designated the Koy-Yukon thermal event, an exposed Bering land bridge promoted an interglacial type climate that led to significant biotic changes and permafrost degradation. O.C.T. occurs on drift of the Mirror Creek Glaciation which is equivalent to other presumed Early Wisconsinan glaciations in Alaska and Yukon. These glaciations could not have occurred later than marine Stage 5. Stage 4 was fully as cold as Stage 2 (Late Wisconsinan), yet seems not to have been a time of extensive glaciation. The Middle Wisconsinan, 30 000 to more than 80 000 BP, was a nonglacial interval with several climate fluctuations, one of which, the Koy-Yukon thermal event, was warmer than at present.

scholarly journals A late Quaternary record of eolian silt deposition in a maar lake, St. Michael Island, western Alaska

2003 ◽  
Vol 60 (1) ◽  
pp. 110-122 ◽  
Author(s):  
Daniel R. Muhs ◽  
Thomas A. Ager ◽  
Josh Been ◽  
J. Platt Bradbury ◽  
Walter E. Dean
Keyword(s):  
Lake Sediments ◽  
Late Quaternary ◽  
Geochemical Data ◽  
Unexpected Finding ◽  
The Holocene ◽  
Tundra Vegetation ◽  
Shrub Tundra ◽  
Loess Deposition ◽  
Maar Lake ◽  
Glacial Time

AbstractRecent stratigraphic studies in central Alaska have yielded the unexpected finding that there is little evidence for full-glacial (late Wisconsin) loess deposition. Because the loess record of western Alaska is poorly exposed and not well known, we analyzed a core from Zagoskin Lake, a maar lake on St. Michael Island, to determine if a full-glacial eolian record could be found in that region. Particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian. Silt deposition took place from at least the latter part of the mid-Wisconsin interstadial period through the Holocene, based on radiocarbon dating. Based on the locations of likely loess sources, eolian silt in western Alaska was probably deflated by northeasterly winds from glaciofluvial sediments. If last-glacial winds that deposited loess were indeed from the northeast, this reconstruction is in conflict with a model-derived reconstruction of paleowinds in Alaska. Mass accumulation rates in Zagoskin Lake were higher during the Pleistocene than during the Holocene. In addition, more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape. The thinner loess record on land may be due to the sparse, herb tundra vegetation that dominated the landscape in full-glacial time. Herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height. The lack of abundant, full-glacial, eolian silt deposition in the loess stratigraphic record of central Alaska may be due, therefore, to a mimimal ability of the landscape to trap loess, rather than a lack of available eolian sediment.

scholarly journals Sediment record from the Kamyshovoe Lake: history of vegetation during late Pleistocene – early Holocene (Kaliningrad District, Russia)

Baltica ◽  
2015 ◽  
Vol 28 (2) ◽  
pp. 121-134 ◽  
Author(s):  
Olga Druzhinina ◽  
Dmitry Subetto ◽  
Miglė Stančikaitė ◽  
Giedrė Vaikutienė ◽  
Jury Kublitsky ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Early Holocene ◽  
Sediment Record ◽  
Environmental Regime ◽  
Maximum Value ◽  
History Of Vegetation ◽  
Shrub Tundra ◽  
History Of ◽  
Pollen Records

Newly obtained pollen and diatom data from the Kamyshovoe Lake (germ. Dobauen, Vishtynets Highland, Baltic Uplands) controlled by radiocarbon dating allowed to reconstruct the history of local vegetation during late Pleistocene – early Holocene. Pollen records show the formation of birch-predominating forest at ca. 13.4 ka cal. BP and the flourishing of pine towards the second half of the chronozone since about 13.2 ka cal. BP. The transition to the Younger Dryas around 12.7 ka cal. BP led to the development of sparse shrub tundra with Juniperus and communities of steppe herbs. Amelioration of the environmental regime enabled birch and pine woods to spread during the second part of GS-1 event and the Preboreal. The late Preboreal time is marked by the appearance of Populus and an increase in the role of grasses in the vegetation cover, which can be correlated to similar open vegetation phases deduced from other pollen records in Europe (11.3–11.1 ka cal. BP). During the Boreal (since ca. 10.0 ka cal. BP) Corylus had its maximum value, Alnus, Tilia and Quercus appeared and spread while the birch-pine forests retreated.

scholarly journals Top-down identification of keystone species in the microbiome

2021 ◽  
Author(s):  
Guy Amit ◽  
Amir Bashan
Keyword(s):  
Native Species ◽  
Keystone Species ◽  
Metagenomic Data ◽  
Ecological Communities ◽  
Top Down ◽  
Cross Sectional ◽  
Pairwise Interactions ◽  
Total Influence ◽  
The Stability ◽  
Longitudinal Sampling

Keystone species in ecological communities are native species that play an especially important role in the stability of their ecosystem and can also be potentially used as its main drivers. However, we still lack an effective framework for identifying these species from the available metagenomic data without the notoriously difficult step of reconstructing the detailed network of inter-specific interactions. Here we propose a top-down identification framework, which detects keystones by their total influence on the rest of the species. Our method does not assume pairwise interactions or any specific underlying dynamics and is appropriate to both perturbation experiments and metagenomic cross-sectional surveys. When applied to real metagenomic data of the human gastrointestinal microbiome, we detect a set of candidate keystones and find that they are often part of a keystone module -- multiple candidate keystones species with correlated occurrence. The keystones analysis of single-time-point cross-sectional data is also later verified by evaluation of two-time-points longitudinal sampling. Our framework represents a necessary advancement towards the reliable identification of these key players of complex, real-world microbial communities.

Late Quaternary History of Tundra Vegetation in Northwestern Alaska

1994 ◽  
Vol 41 (3) ◽  
pp. 306-315 ◽  
Author(s):  
Patricia M. Anderson ◽  
Patrick J. Bartlein ◽  
Linda B. Brubaker
Keyword(s):  
Vegetation Type ◽  
Late Quaternary ◽  
Vegetation Types ◽  
The Past ◽  
Modern Pollen ◽  
Qualitative Approaches ◽  
Tundra Vegetation ◽  
Shrub Tundra ◽  
History Of ◽  
Quaternary History

AbstractPollen analysis of a new core from Joe Lake indicates that the late Quaternary vegetation of northwestern Alaska was characterized by four tundra and two forest-tundra types. These vegetation types were differentiated by combining quantitative comparisons of fossil and modern pollen assemblages with traditional, qualitative approaches for inferring past vegetation, such as the use of indicator species. Although imprecisely dated, the core probably spans at least the past 40,000 yr. A graminoid-Salix tundra dominated during the later and early portions of the glacial record. The middle glacial interval and the transition from glacial to interglacial conditions are characterized by a graminoid-Betula-Salix tundra. A Populus forest-Betula shrub tundra existed during the middle potion of this transition, being replaced in the early Holocene by a Betula-Alnus shrub tundra. The modern Picea forest-shrub tundra was established by the middle Holocene. These results suggest that the composition of modem tundra communities in northwestern Alaska developed relatively recently and that throughout much of the late Quaternary, tundra communities were unlike the predominant types found today in northern North America. Although descriptions of vegetation variations within the tundra will always be restricted by the innate taxonomic limitations of their herb-dominated pollen spectra, the application of multiple interpretive approaches improves the ability to reconstruct the historical development of this vegetation type.

Plio-Pleistocene decline of African megaherbivores: No evidence for ancient hominin impacts

Science ◽  
2018 ◽  
Vol 362 (6417) ◽  
pp. 938-941 ◽  
Author(s):  
J. Tyler Faith ◽  
John Rowan ◽  
Andrew Du ◽  
Paul L. Koch
Keyword(s):  
Evolutionary History ◽  
Homo Sapiens ◽  
Top Down ◽  
Large Mammal ◽  
Meat Eating ◽  
The Past ◽  
History Of ◽  
Mammal Communities ◽  
Herbivore Communities

It has long been proposed that pre-modern hominin impacts drove extinctions and shaped the evolutionary history of Africa’s exceptionally diverse large mammal communities, but this hypothesis has yet to be rigorously tested. We analyzed eastern African herbivore communities spanning the past 7 million years—encompassing the entirety of hominin evolutionary history—to test the hypothesis that top-down impacts of tool-bearing, meat-eating hominins contributed to the demise of megaherbivores prior to the emergence ofHomo sapiens. We document a steady, long-term decline of megaherbivores beginning ~4.6 million years ago, long before the appearance of hominin species capable of exerting top-down control of large mammal communities and predating evidence for hominin interactions with megaherbivore prey. Expansion of C4grasslands can account for the loss of megaherbivore diversity.

California Condor Associated with Spruce-Jack Pine Woodland in the Late Pleistocene of New York

1987 ◽  
Vol 28 (3) ◽  
pp. 415-426 ◽  
Author(s):  
David W. Steadman ◽  
Norton G. Miller
Keyword(s):  
New York ◽  
Late Pleistocene ◽  
Plant Macrofossils ◽  
Jack Pine ◽  
Western North America ◽  
Large Mammals ◽  
California Condor ◽  
In Captivity ◽  
Gymnogyps Californianus ◽  
Warm Temperate

AbstractA humerus, coracoid, and pedal phalanx of the California Condor, Gymnogyps californianus, were recovered from the Hiscock Site in western New York, in an inorganic stratum containing wood that is 11,000 radiocarbon years old. Associated vertebrates include mastodont, wapiti, and caribou. Pollen and plant macrofossils from the sediments indicate a spruce-jack pine woodland and a local, herb-dominated wetland community. Historic records (all from western North America) and previous late Pleistocene fossils of the California Condor are associated mainly with warm-temperate climates and floras. The New York fossils show that this bird was able to live in a colder climate and in a boreal, coniferous setting at a time when appropriate food (large mammal carrion) was available. The California Condor, which survives only in captivity, has suffered a greater reduction in geographical range than previously suspected. Much of this reduction in range probably occurred ca. 11,000 yr B.P. when the extinction many North American large mammals resulted in severely reduced availability of food for the California Condor and other large scavenging birds.

scholarly journals Tundra shrub expansion may amplify permafrost thaw by advancing snowmelt timing

2019 ◽  
Vol 5 (4) ◽  
pp. 202-217 ◽  
Author(s):  
Evan J. Wilcox ◽  
Dawn Keim ◽  
Tyler de Jong ◽  
Branden Walker ◽  
Oliver Sonnentag ◽  
...  
Keyword(s):  
Active Layer ◽  
Snow Depth ◽  
Structural Equation ◽  
The Arctic ◽  
Equation Modeling ◽  
Active Layer Thickness ◽  
Snow Surface ◽  
Shrub Expansion ◽  
Shrub Tundra ◽  
Temporal Influence

The overall spatial and temporal influence of shrub expansion on permafrost is largely unknown due to uncertainty in estimating the magnitude of many counteracting processes. For example, shrubs shade the ground during the snow-free season, which can reduce active layer thickness. At the same time, shrubs advance the timing of snowmelt when they protrude through the snow surface, thereby exposing the active layer to thawing earlier in spring. Here, we compare 3056 in situ frost table depth measurements split between mineral earth hummocks and organic inter-hummock zones across four dominant shrub–tundra vegetation types. Snow-free date, snow depth, hummock development, topography, and vegetation cover were compared to frost table depth measurements using a structural equation modeling approach that quantifies the direct and combined interacting influence of these variables. Areas of birch shrubs became snow free earlier regardless of snow depth or hillslope aspect because they protruded through the snow surface, leading to deeper hummock frost table depths. Projected increases in shrub height and extent combined with projected decreases in snowfall would lead to increased shrub protrusion across the Arctic, potentially deepening the active layer in areas where shrub protrusion advances the snow-free date.

Palynology of six sections of Late Quaternary sediments from the Old Crow River, Yukon Territory

1973 ◽  
Vol 51 (3) ◽  
pp. 553-564 ◽  
Author(s):  
Sigrid Lichti-Federovich
Keyword(s):  
Late Quaternary ◽  
Yukon Territory ◽  
Quaternary Sediments ◽  
Pollen Assemblage ◽  
Alluvial Deposits ◽  
Pollen Stratigraphy ◽  
Tundra Vegetation ◽  
Pollen Diagrams ◽  
Shrub Tundra ◽  
Basin Fill

The Old Crow Plain, northern Yukon Territory, Canada, is a large flat lowland consisting of basin-fill sediments of Late Quaternary age. The modern Arctic treeline passes across the northern tip of the lowland, and much of the vegetation consists of tundra and shrub tundra, with scattered groves of spruce mainly on alluvial deposits. Steep scarps have been exposed by the downcutting of the Old Crow River in these basin-fill sediments, and good exposures of Late Quaternary sediments are available for investigation. Samples from six of these exposures were analyzed for pollen. Although many parts of the sections were barren, it has been possible to derive pollen diagrams with discrete pollen zones for the six sections, and four pollen assemblage types have been identified. Their occurrence in the stratigraphie sequence suggests the following pattern of pollen stratigraphy: the lowermost sedimentary units, probably deposited early in the interstadial following an Early Wisconsin glaciation, are of pollen assemblage types III (Glumiflorae–herb) or IV (Betula–herb), both indicative of tundra vegetation; the middle levels of the sediment show, consistently, pollen spectra of type II (Picea–Betula–Glumiflorae–herb), indicating forest groves with tundra, quite similar to the modern vegetation. The sediment underlying the Upper Glaciolacustrine Unit (correlative, according to Hughes (1969), with the Classical Wisconsin Stadial) yields pollen assemblage type III (Glumiflorae–herb), which is interpreted as indicating a rich and varied tundra. These vegetation reconstructions are consonant with a tentative palaeoclimatic interpretation in terms of a tripartite interstadial climate showing severe tundra climate – milder forest or forest–tundra climate – severe tundra climate. Two of the sections have incomplete pollen stratigraphy for the uppermost postglacial silts and peats. They suggest that vegetation similar to the present day became established in the Old Crow Plain in mid-postglacial time.

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