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Julio L. Betancourt - One of the best experts on this subject based on the ideXlab platform.
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Creosote bush (Larrea tridentata) ploidy history along its diploid-tetraploid boundary in southeastern Arizona-southwestern New Mexico, USA
Journal of Arid Environments, 2019Co-Authors: Camille A. Holmgren, Kimberly L. Hunter, Julio L. BetancourtAbstract:Abstract Creosote bush (Larrea tridentata) is a dominant shrub in the warm deserts of North America and also a classic example of an autopolyploid complex. We determined ploidy levels for creosote leaves preserved in ancient packrat Middens from the Peloncillo Mountains, AZ to better understand the history of ploidy race distribution along its diploid-tetraploid boundary. We also measured modern creosote ploidy level at several sites spanning the AZ-NM border to augment sampling in this large geographic area. Modern plants were mostly diploids, with tetraploids only observed in our northernmost sites. Ancient creosote from the Peloncillo Middens (3170-145 cal yr BP) were all diploids. Modern creosote at the Peloncillo site is also diploid, but with significantly larger guard cells areas that may be a response to increasingly hot, dry conditions. The lack of tetraploids in the Midden fossils suggests the arrival of tetraploids at their eastern margin may have occurred only recently, mirroring the late arrivals of other Sonoran Desert plants (e.g., Simmondsia chinensis) along the AZ-NM border.
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vegetational and biogeographical dynamics in north-eastern Utah, USA
2016Co-Authors: Stephen T Jackson, Julio L. Betancourt, Mark E Lyford, Stephen T Gray, Kate Aasen Ryl, Correspondence Stephen T. JacksonAbstract:Aim A conspicuous climatic and biogeographical transition occurs at 40–45 N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) Middens to the south]. To overcome these limitations, we are extending the woodrat-Midden record northward into the lowlands of the central Rocky Mountains. Location Woodrat Middens were collected from crevices and rock shelters on south-facing slopes of Dutch John Mountain (2000–2200 m, 4057 ¢ N, 10925 ¢ W), situated on the eastern flanks of the Uinta Mountains in north-eastern Utah. The site is near the regional limits for Pinus ponderosa, P. edulis
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vegetation history along the eastern desert escarpment of the sierra san pedro martir baja california mexico
Quaternary Research, 2011Co-Authors: Camille A. Holmgren, Julio L. Betancourt, Kate Aasen RylanderAbstract:Abstract Plant macrofossils from 38 packrat Middens spanning the last ~ 33,000 cal yr BP record vegetation between ~ 650 and 900 m elevation along the eastern escarpment of the Sierra San Pedro Martir, northern Baja California. The Middens span most of the Holocene, with a gap between ~ 4600 and 1800 cal yr BP, but coverage in the Pleistocene is uneven with a larger hiatus between 23,100 and 14,400 cal yr BP. The Midden flora is relatively stable from the Pleistocene to Holocene. Exceptions include Pinus californiarum, Juniperus californica and other chaparral elements that were most abundant > 23,100 cal yr BP and declined after 14,400 cal yr BP. Despite being near the chaparral/woodland-desertscrub ecotone during glacial times, the Midden assemblages reflect none of the climatic reversals evident in the glacial or marine record, and this is corroborated by a nearby semi-continuous pollen stratigraphy from lake sediments. Regular appearance of C4 grasses and summer-flowering annuals since 13,600 cal yr BP indicates occurrence of summer rainfall equivalent to modern (JAS average of ~ 80–90 mm). This casts doubt on the claim, based on temperature proxies from marine sediments in the Guaymas Basin, that monsoonal development in the northern Gulf and Arizona was delayed until after 6200 cal yr BP.
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paleowetlands and regional climate change in the central atacama desert northern chile
Quaternary Research, 2008Co-Authors: Jay Quade, Julio L. Betancourt, Kate Aasen Rylander, Claudio Latorre, Jason A Rech, Barbra Quade, Timothy S FisherAbstract:Abstract Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?–9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent Middens from the study area, in both paleowetland and rodent Midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the “Central Andean Pluvial Event” — in two distinct intervals (15,900–13,800 and 12,700–9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Nina-like conditions).
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late quaternary vegetation and climate history of a perennial river canyon in the rio salado basin 22 s of northern chile
Quaternary Research, 2006Co-Authors: Julio L. Betancourt, Claudio Latorre, Mary T K ArroyoAbstract:Abstract Plant macrofossils from 33 rodent Middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the Rio Salado, northern Chile, yield a unique record of vegetation and climate over the past 22,000 cal yr BP. Presence of low-elevation Prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5°C and may have been near-modern at 16,270 cal yr BP. Displacements in the lower limits of Andean steppe and Puna taxa indicate that mean annual rainfall was twice modern at 17,520–16,270 cal yr BP. This pluvial event coincides with infilling of paleolake Tauca on the Bolivian Altiplano, increased ENSO activity inferred from a marine core near Lima, abrupt deglaciation in southern Chile, and Heinrich Event 1. Moderate to large increases in precipitation also occurred at 11,770–9550 (Central Atacama Pluvial Event), 7330–6720, 3490–2320 and at 800 cal yr BP. Desiccation occurred at 14,180, 8910–8640, and 4865 cal yr BP. Compared to other Midden sites in the region, early Holocene desiccation seems to have happened progressively earlier farther south. Emerging trends from the cumulative Midden record in the central Atacama agree at millennial timescales with improved paleolake chronologies for the Bolivian Altiplano, implying common forcing through changes in equatorial Pacific sea-surface temperature gradients.
Kate Aasen Rylander - One of the best experts on this subject based on the ideXlab platform.
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vegetation history along the eastern desert escarpment of the sierra san pedro martir baja california mexico
Quaternary Research, 2011Co-Authors: Camille A. Holmgren, Julio L. Betancourt, Kate Aasen RylanderAbstract:Abstract Plant macrofossils from 38 packrat Middens spanning the last ~ 33,000 cal yr BP record vegetation between ~ 650 and 900 m elevation along the eastern escarpment of the Sierra San Pedro Martir, northern Baja California. The Middens span most of the Holocene, with a gap between ~ 4600 and 1800 cal yr BP, but coverage in the Pleistocene is uneven with a larger hiatus between 23,100 and 14,400 cal yr BP. The Midden flora is relatively stable from the Pleistocene to Holocene. Exceptions include Pinus californiarum, Juniperus californica and other chaparral elements that were most abundant > 23,100 cal yr BP and declined after 14,400 cal yr BP. Despite being near the chaparral/woodland-desertscrub ecotone during glacial times, the Midden assemblages reflect none of the climatic reversals evident in the glacial or marine record, and this is corroborated by a nearby semi-continuous pollen stratigraphy from lake sediments. Regular appearance of C4 grasses and summer-flowering annuals since 13,600 cal yr BP indicates occurrence of summer rainfall equivalent to modern (JAS average of ~ 80–90 mm). This casts doubt on the claim, based on temperature proxies from marine sediments in the Guaymas Basin, that monsoonal development in the northern Gulf and Arizona was delayed until after 6200 cal yr BP.
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paleowetlands and regional climate change in the central atacama desert northern chile
Quaternary Research, 2008Co-Authors: Jay Quade, Julio L. Betancourt, Kate Aasen Rylander, Claudio Latorre, Jason A Rech, Barbra Quade, Timothy S FisherAbstract:Abstract Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?–9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent Middens from the study area, in both paleowetland and rodent Midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the “Central Andean Pluvial Event” — in two distinct intervals (15,900–13,800 and 12,700–9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Nina-like conditions).
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a 40 000 year woodrat Midden record of vegetational and biogeographical dynamics in north eastern utah usa
Journal of Biogeography, 2005Co-Authors: Stephen T Jackson, Julio L. Betancourt, Mark E Lyford, Stephen T Gray, Kate Aasen RylanderAbstract:Aim A conspicuous climatic and biogeographical transition occurs at 40–45� N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) Middens to the south]. To overcome these limitations, we are extending the woodrat-Midden record northward into the lowlands of the central
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a 16 000 14c yr b p packrat Midden series from the usa mexico borderlands
Quaternary Research, 2003Co-Authors: Camille A. Holmgren, Kate Aasen Rylander, Cristina M Penalba, Julio L. BetancourtAbstract:A new packrat Midden chronology from Playas Valley, southwestern New Mexico, is the first installment of an ongoing effort to reconstruct paleovegetation and paleoclimate in the U.S.A.–Mexico Borderlands. Playas Valley and neighboring basins supported pluvial lakes during full and/or late glacial times. Plant macrofossil and pollen assemblages from nine Middens in the Playas Valley allow comparisons of two time intervals: 16,000–10,000 and 4000–0 14C yr B.P. Vegetation along pluvial lake margins consisted of open pinyon–juniper communities dominated by Pinus edulis, Juniperus scopulorum, Juniperus cf. coahuilensis, and a rich understory of C4 annuals and grasses. This summer-flowering understory is also characteristic of modern desert grassland in the Borderlands and indicates at least moderate summer precipitation. P. edulis and J. scopulorum disappeared or were rare in the Midden record by 10,670 14C yr B.P. The late Holocene is marked by the arrival of Chihuahuan desert scrub elements and few departures as the vegetation gradually became modern in character. Larrea tridentata appears as late as 2190 14C yr B.P. based on macrofossils, but may have been present as early as 4095 14C yr B.P. based on pollen. Fouquieria splendens, one of the dominant desert species present at the site today, makes its first appearance only in the last millennium. The Midden pollen assemblages are difficult to interpret; they lack modern analogs in surface pollen assemblages from stock tanks at different elevations in the Borderlands.
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a vegetation history from the arid prepuna of northern chile 22 23 s over the last 13 500 years
Palaeogeography Palaeoclimatology Palaeoecology, 2003Co-Authors: Claudio Latorre, Julio L. Betancourt, Kate Aasen Rylander, Jay Quade, O MattheiAbstract:The Quaternary paleoclimate of the central Andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region. The exact timing,duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another,and there have been few opportunities to compare climatic records from the same proxy along environmental gradients. Vegetation histories from fossil rodent Middens provide one such opportunity on the Pacific slope of the Andes. We previously reported a vegetation history from the upper margin (2400^3000 m) of the absolute desert in the central Atacama Desert of northern Chile. That record identified a distinct wet phase that peaked between 11.8 and 10.5 ka,when steppe grasses and other upland elements expanded as much as 1000 m downslope,and a secondary wet period during the middle to late Holocene (7.1^3.5 ka). The latter wet phase remains controversial and is not as readily apparent in our lowelevation Midden record. We thus sought to replicate both phases in a Midden record from the mid-elevations (3100^ 3300 m) of the arid prepuna,where slight precipitation increases would be amplified. Midden records from these elevations identify conditions wetter than today at 13.5^9.6,7.6^6.3,4.4^3.2 and possibly 1.8^1.2 ka. Dry phases occurred at 9.4^8.4 ka and possibly at ca. 5.1 ka. Present floras and modern hyperarid conditions were established after 3.2 ka. The records from the two elevational bands generally match with some important differences. These differences could reflect both the discontinuous aspect of the Midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert. : 2003 Elsevier Science B.V. All rights reserved.
Claudio Latorre - One of the best experts on this subject based on the ideXlab platform.
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calibrating the pollen signal in modern rodent Middens from northern chile to improve the interpretation of the late quaternary Midden record
Quaternary Research, 2015Co-Authors: Maria Eugenia De Porras, Antonio Maldonado, Andres Zamoraallendes, Claudio LatorreAbstract:The use of rodent Middens from northern Chile as paleoecological archives has at times been questioned due to concerns about their biogenic origin and the degree to which their record represents vegetation composition rather than rodent habits. To address such concerns, we carried out a modern calibration study to assess the representation of vegetation by pollen records from rodent Middens. We compared vegetation censuses with soil-surface and Midden (matrix and feces) pollen samples from sites between 21° and 28°S. The results show that (1) the pollen signal from the Midden matrix provides a more realistic reflection of local vegetation than soil-surface samples due to the pollen-deposition processes that occur in Middens; and (2) in contrast to feces pollen assemblages, which feature some biases, rodent dietary habits do not seem to influence Midden matrix pollen assemblages, probably because Midden agents are dietary generalists. Our finding that modern pollen data from rodent Middens reflect vegetation patterns confirms the reliability of Midden pollen records as paleoecological archives in northern Chile.
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paleowetlands and regional climate change in the central atacama desert northern chile
Quaternary Research, 2008Co-Authors: Jay Quade, Julio L. Betancourt, Kate Aasen Rylander, Claudio Latorre, Jason A Rech, Barbra Quade, Timothy S FisherAbstract:Abstract Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?–9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent Middens from the study area, in both paleowetland and rodent Midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the “Central Andean Pluvial Event” — in two distinct intervals (15,900–13,800 and 12,700–9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Nina-like conditions).
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late quaternary vegetation and climate history of a perennial river canyon in the rio salado basin 22 s of northern chile
Quaternary Research, 2006Co-Authors: Julio L. Betancourt, Claudio Latorre, Mary T K ArroyoAbstract:Abstract Plant macrofossils from 33 rodent Middens sampled at three sites between 2910 and 3150 m elevation in the main canyon of the Rio Salado, northern Chile, yield a unique record of vegetation and climate over the past 22,000 cal yr BP. Presence of low-elevation Prepuna taxa throughout the record suggests that mean annual temperature never cooled by more than 5°C and may have been near-modern at 16,270 cal yr BP. Displacements in the lower limits of Andean steppe and Puna taxa indicate that mean annual rainfall was twice modern at 17,520–16,270 cal yr BP. This pluvial event coincides with infilling of paleolake Tauca on the Bolivian Altiplano, increased ENSO activity inferred from a marine core near Lima, abrupt deglaciation in southern Chile, and Heinrich Event 1. Moderate to large increases in precipitation also occurred at 11,770–9550 (Central Atacama Pluvial Event), 7330–6720, 3490–2320 and at 800 cal yr BP. Desiccation occurred at 14,180, 8910–8640, and 4865 cal yr BP. Compared to other Midden sites in the region, early Holocene desiccation seems to have happened progressively earlier farther south. Emerging trends from the cumulative Midden record in the central Atacama agree at millennial timescales with improved paleolake chronologies for the Bolivian Altiplano, implying common forcing through changes in equatorial Pacific sea-surface temperature gradients.
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a vegetation history from the arid prepuna of northern chile 22 23 s over the last 13 500 years
Palaeogeography Palaeoclimatology Palaeoecology, 2003Co-Authors: Claudio Latorre, Julio L. Betancourt, Kate Aasen Rylander, Jay Quade, O MattheiAbstract:The Quaternary paleoclimate of the central Andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region. The exact timing,duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another,and there have been few opportunities to compare climatic records from the same proxy along environmental gradients. Vegetation histories from fossil rodent Middens provide one such opportunity on the Pacific slope of the Andes. We previously reported a vegetation history from the upper margin (2400^3000 m) of the absolute desert in the central Atacama Desert of northern Chile. That record identified a distinct wet phase that peaked between 11.8 and 10.5 ka,when steppe grasses and other upland elements expanded as much as 1000 m downslope,and a secondary wet period during the middle to late Holocene (7.1^3.5 ka). The latter wet phase remains controversial and is not as readily apparent in our lowelevation Midden record. We thus sought to replicate both phases in a Midden record from the mid-elevations (3100^ 3300 m) of the arid prepuna,where slight precipitation increases would be amplified. Midden records from these elevations identify conditions wetter than today at 13.5^9.6,7.6^6.3,4.4^3.2 and possibly 1.8^1.2 ka. Dry phases occurred at 9.4^8.4 ka and possibly at ca. 5.1 ka. Present floras and modern hyperarid conditions were established after 3.2 ka. The records from the two elevational bands generally match with some important differences. These differences could reflect both the discontinuous aspect of the Midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert. : 2003 Elsevier Science B.V. All rights reserved.
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molecular analysis of a 11 700 year old rodent Midden from the atacama desert chile
Molecular Ecology, 2002Co-Authors: Melanie Kuch, Julio L. Betancourt, Claudio Latorre, Nadin Rohland, Scott J Steppan, Hendrik N PoinarAbstract:DNA was extracted from an 11 700-year-old rodent Midden from the Atacama Desert, Chile and the chloroplast and animal mitochondrial DNA (mtDNA) gene sequences were analysed to investigate the floral environment surrounding the Midden, and the identity of the Midden agent. The plant sequences, together with the macroscopic identifications, suggest the presence of 13 plant families and three orders that no longer exist today at the Midden locality, and thus point to a much more diverse and humid climate 11 700 years ago. The mtDNA sequences suggest the presence of at least four different vertebrates, which have been putatively identified as a camelid (vicuna), two rodents (Phyllotis and Abrocoma), and a cardinal bird (Passeriformes). To identify the Midden agent, DNA was extracted from pooled faecal pellets, three small overlapping fragments of the mitochondrial cytochrome b gene were amplified and multiple clones were sequenced. These results were analysed along with complete cytochrome b sequences for several modern Phyllotis species to place the Midden sequence phylogenetically. The results identified the Midden agent as belonging to an ancestral P. limatus. Today, P. limatus is not found at the Midden locality but it can be found 100 km to the north, indicating at least a small range shift. The more extensive sampling of modern Phyllotis reinforces the suggestion that P. limatus is recently derived from a peripheral isolate.
Brian M Chase - One of the best experts on this subject based on the ideXlab platform.
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stable isotope analyses of rock hyrax faecal pellets hyraceum and associated vegetation in southern africa implications for dietary ecology and palaeoenvironmental reconstructions
Journal of Arid Environments, 2016Co-Authors: Andrew S Carr, Brian M Chase, Arnoud Boom, Javier MedinasanchezAbstract:Rock hyrax Middens are important palaeoenvironmental archives in southern Africa. Carbon and nitrogen isotope measurements on Middens (hyraceum) are key components of climate reconstructions, but their interpretations require refinement. Although δ15N in hyraceum often correlates with independent proxies for palaeo-aridity, the impacts of dietary and physiological controls on hyraceum δ15N remain to be resolved. We analyse δ13C and δ15N in plant foliage, hyrax faecal pellets and hyraceum from 21 sites across southern Africa. Faeces are generally depleted in 13C (δ13C typically < −20‰), suggesting significant browsing. Grazing is rarely dominant and probably occurs only when palatable grass is available. Variability in faecal and foliar δ15N is large, but foliar δ15N is positively correlated with faecal δ15N. The diet-faeces δ15N offset is uncorrelated with climate (aridity), but is correlated with %N in faeces. Faecal δ15N is positively correlated with modern hyraceum δ15N, and the relationships with aridity index for foliar and faecal (body tissue) δ15N are comparable. These observations implicate diet as a significant control on hyraceum δ15N and we observe no strong evidence for metabolic controls on hyraceum δ15N. More data are required to refine these relationships, but these observations are consistent with current palaeoenvironmental interpretations of Midden δ15N and δ13C.
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rock hyrax Middens a palaeoenvironmental archive for southern african drylands
Quaternary Science Reviews, 2012Co-Authors: Brian M Chase, Louis Scott, Paula J Reimer, Graciela Gilromera, Andrew S Carr, Loic Truc, Michael E. Meadows, Arnoud Boom, Verushka ValsecchiAbstract:Abstract Like many of the world's subtropical regions, southern Africa is highly sensitive to changes in the earth's climate system, but a dearth of reliable palaeoenvironmental records means that relatively little is known about how regional environments have been affected over centennial to multi-millennial timescales. To a large extent this sensitivity is a function of the position of these regions at the interface between temperate and tropical circulation systems. The resulting seasonality and irregularity of rainfall have limited the development of suitable archives, such as lakes and wetlands, for the preservation of palaeoenvironmental proxies. This paper reviews and evaluates the value of rock hyrax Middens as novel palaeoenvironmental archives in southern Africa. Considered are (1) the contemporary taxonomy, distribution and ecology of hyraxes, (2) the mechanisms of hyrax Midden development, their physical and chemical structure, rates of accumulation and age; and (3) the palaeoenvironmental proxies preserved within hyrax Middens, including fossil pollen, stable isotopes and biomarkers. The interpretive constraints and opportunities offered by these various Midden characteristics are assessed with a view to demonstrating the potential of these deposits, widespread as they are through arid and semi-arid southern Africa, in providing a more detailed and chronologically resolved view of late Quaternary palaeoenvironments across the subcontinent.
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a 19 5 kyr vegetation history from the central cederberg mountains south africa palynological evidence from rock hyrax Middens
Palaeogeography Palaeoclimatology Palaeoecology, 2011Co-Authors: Lynne J Quick, Brian M Chase, Louis Scott, Michael E. Meadows, Paula J ReimerAbstract:Abstract In arid and semi-arid areas such as southern Africa, rock hyrax ( Procavia capensis ) Middens represent an exceptionally valuable source of late Quaternary palaeoenvironmental information. Pollen and stable isotope data derived from two rock hyrax Middens extracted from De Rif in the Cederberg Mountains of the southwestern Cape, casts new light on climatic changes that occurred across the Last Glacial–Interglacial Transition (LGIT) and the Holocene (19.5–0.7 cal kBP) and how the region's vegetation responded to these changes. Significant changes in vegetation community composition would be expected in response to environmental changes characteristic of the contrast between ‘glacial’ and ‘interglacial’ climates. However, the pollen assemblages in general indicate that mountain fynbos remained dominant throughout the record and that most of the pollen taxa exhibited only muted frequency variations. This finding could be considered to be inconsistent with indications of marked climatic variations recorded in the stable isotope records for the same Midden. An analysis of the geological setting and the bioclimatic affinities of the taxa suggest that the explanation for this inconsistency may lie in the dominating influence of sandstone substrates and the relative resilience of mountain fynbos vegetation to climate change.
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the potential of plant biomarker evidence derived from rock hyrax Middens as an indicator of palaeoenvironmental change
Palaeogeography Palaeoclimatology Palaeoecology, 2010Co-Authors: Andrew S Carr, Arnoud Boom, Brian M ChaseAbstract:Abstract Hyrax Middens are unique environmental archives with the potential to provide unprecedented high-resolution palaeoenvironmental records, particularly in the arid regions of southern Africa. This study provides the first detailed characterisation of the organic matter composition of hyraceum and aims to identify biomarker evidence capable of providing new or supplementary palaeoenvironmental data from these novel archives. Pyrolysis gas chromatography mass spectrometry reveals hyraceum to be dominated by nitrogen-containing aromatic compounds, notably benzamide. This is almost certainly derived directly from the hyrax urine and is probably the main source of nitrogen as measured in bulk δ 15 N measurements. Solvent-extractable lipids comprise homologous suites of long-chain n -alkanes (C 24 –C 34 ) and n -alkanols (C 16 –C 26 ), characteristic of higher plant leaf waxes, along with an abundance of animal-derived sterols, higher plant sterols and terpenoids; as well as the ubiquitous benzamide. n -alkane distributions and compound specific δ 13 C clearly differentiate samples from the C 3 vegetation dominated Cape Floristic Region, and the more arid, C 4 grass-rich savannas of central Namibia (Klein Spitzkoppe). Distinct changes in n -alkane distribution and δ 13 C are observed within the Spitzkoppe Midden; most notably the mid to late Holocene period (c. 6000–2000 cal yr BP), which records a progressive reduction in grass-derived organic matter inputs. Based on the animal's feeding behaviour and contemporary site ecology, a phase of increasing aridity is inferred, which is consistent with other proxy data from this site (e.g. bulk δ 15 N). The excellent preservation of plant and animal biomarkers suggests that there is significant potential for Midden-derived biomarkers to provide long-term palaeoenvironmental proxies.
Stephen T Jackson - One of the best experts on this subject based on the ideXlab platform.
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vegetational and biogeographical dynamics in north-eastern Utah, USA
2016Co-Authors: Stephen T Jackson, Julio L. Betancourt, Mark E Lyford, Stephen T Gray, Kate Aasen Ryl, Correspondence Stephen T. JacksonAbstract:Aim A conspicuous climatic and biogeographical transition occurs at 40–45 N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) Middens to the south]. To overcome these limitations, we are extending the woodrat-Midden record northward into the lowlands of the central Rocky Mountains. Location Woodrat Middens were collected from crevices and rock shelters on south-facing slopes of Dutch John Mountain (2000–2200 m, 4057 ¢ N, 10925 ¢ W), situated on the eastern flanks of the Uinta Mountains in north-eastern Utah. The site is near the regional limits for Pinus ponderosa, P. edulis
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reliability of macrofossils in woodrat neotoma Middens for detecting low density tree populations
Paleobiology, 2011Co-Authors: Mark R Lesser, Stephen T JacksonAbstract:Abstract Macrofossils from woodrat (Neotoma) Middens serve as an important proxy for reconstructing past vegetation in arid and semiarid regions of North America. The presence/absence of plant macrofossils in Middens can provide valuable information on temporal and spatial patterns of plant migration and range boundaries. The primary aim of this study was to determine how local plant abundance, distance of plant populations from Midden sites, and species population density on the landscape affect the probability of occurrence of macrofossils in Middens. The study was designed with the primary intent of determining the reliability of Middens in detecting scattered populations of Pinus ponderosa. We analyzed macrofossil assemblages from 42 modern woodrat Middens from West Carrizo Canyon in southeastern Colorado, near the current eastern range margin of Pinus ponderosa. We compared Midden contents with composition of the surrounding vegetation, measuring distance from the Midden to the nearest individual of ...
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a 40 000 year woodrat Midden record of vegetational and biogeographical dynamics in north eastern utah usa
Journal of Biogeography, 2005Co-Authors: Stephen T Jackson, Julio L. Betancourt, Mark E Lyford, Stephen T Gray, Kate Aasen RylanderAbstract:Aim A conspicuous climatic and biogeographical transition occurs at 40–45� N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) Middens to the south]. To overcome these limitations, we are extending the woodrat-Midden record northward into the lowlands of the central
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validating the use of woodrat neotoma Middens for documenting natural invasions
Journal of Biogeography, 2004Co-Authors: Mark E Lyford, Stephen T Jackson, Stephen T Gray, Robert G EddyAbstract:Aim Plant macrofossils in fossil woodrat (Neotoma) Middens are the primary source of information on late Quaternary biogeographical history of plants in arid and semi-arid regions of North America. Macrofossil records from Middens are playing particularly important roles in documenting spatial and temporal patterns of plant migrations and invasions since the last glacial maximum 21,000 years ago. However, relatively few actualistic studies comparing contents of modern Middens with surrounding flora and vegetation have been carried out. The primary aim of this study is to assess the reliability of Midden assemblages in detecting the presence of tree, shrub and several other plant species growing on the surrounding landscape. The secondary aims are to determine whether probability of occurrence of species in Middens is related to abundance in vegetation, and whether representation of individual species in Middens is contingent on presence/absence or abundance of other species. Location Our five study sites were bedrock escarpments or canyons in the central Rocky Mountains (north-eastern Utah, central Wyoming and south-central Montana). All sites were in conifer woodland or forest/woodland variously dominated by Juniperus osteosperma, J. scopulorum, Pinus edulis, P. flexilis and Pseudotsuga menziesii. Neotoma cinerea is the only woodrat species in the region. Methods Macrofossil assemblages from 59 modern Middens (all showing clear signs of recent or ongoing woodrat activity) were compared with floristic composition of vegetation within 50 m of the Middens, and with percent cover of vegetation within 30 m of the Middens. Results Coniferous trees and shrubs were well-represented in Middens, occurring consistently even when abundance in the local vegetation was very low. Juniperus osteosperma and J. scopulorum were particularly well-represented, occurring in Middens regardless of local abundance. Other conifers (P. edulis, P. flexilis, P. ponderosa, Pseudotsuga menziesii) were occasionally absent from Middens when abundance in vegetation was low (< 20% canopy cover). Occurrence of dicot shrubs and graminoids was less consistent. Main conclusions Middens constructed by N. cinerea are highly reliable sensors of presence/absence of J. osteosperma and J. scopulorum, and hence can be used to infer invasions and past biogeographical distributions of these species. The Middens are also reliable in registering populations of other conifers, although presence in Middens may be contingent on local abundance. Additional comparative studies are needed to develop a sound empirical basis for using Middens of N. cinerea and other species to infer past presence/absence of plant species on the landscape, and to explore the vegetation-sensing properties of Midden assemblages.