ALBERT

Description: Israde-Alcántara et al. (1) reported evidence for the Younger Dryas (YD) Impact Hypothesis (YDIH), which proposes that an extraterrestrial impact triggered the YD (2). Although most YDIH research has focused on the impact event itself, YDIH proponents, as in this article, have argued that the ecological consequences included “widespread biomass burning, and contributed to the extinction of Late Pleistocene megafauna and to major declines in human populations.” To fully test the YDIH, the authors must evaluate evidence and mechanisms for the ecological consequences of an impact. We believe there are flaws in both the interpretation of the paleoecological evidence reviewed...

Description: Communities have been shaped in numerous ways by past climatic change; this process continues today. At the end of the Pleistocene epoch about 11,700 years ago, North American communities were substantially altered by the interplay of two events. The climate shifted from the cold, arid Last Glacial Maximum to the warm, mesic Holocene interglacial, causing many mammal species to shift their geographic distributions substantially. Populations were further stressed as humans arrived on the continent. The resulting megafaunal extinction event, in which 70 of the roughly 220 largest mammals in North America (32%) became extinct, has received much attention. However, responses of small mammals to events at the end of the Pleistocene have been much less studied, despite the sensitivity of these animals to current and future environmental change. Here we examine community changes in small mammals in northern California during the last 'natural' global warming event at the Pleistocene-Holocene transition and show that even though no small mammals in the local community became extinct, species losses and gains, combined with changes in abundance, caused declines in both the evenness and richness of communities. Modern mammalian communities are thus depauperate not only as a result of megafaunal extinctions at the end of the Pleistocene but also because of diversity loss among small mammals. Our results suggest that across future landscapes there will be some unanticipated effects of global change on diversity: restructuring of small mammal communities, significant loss of richness, and perhaps the rising dominance of native 'weedy' species.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Blois, Jessica L -- McGuire, Jenny L -- Hadly, Elizabeth A -- England -- Nature. 2010 Jun 10;465(7299):771-4. doi: 10.1038/nature09077. Epub 2010 May 23.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biology, Stanford University, Stanford, California 94305, USA. blois@wisc.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20495547" target="_blank"〉PubMed〈/a〉

Description: Biotic interactions drive key ecological and evolutionary processes and mediate ecosystem responses to climate change. The direction, frequency, and intensity of biotic interactions can in turn be altered by climate change. Understanding the complex interplay between climate and biotic interactions is thus essential for fully anticipating how ecosystems will respond to the fast rates of current warming, which are unprecedented since the end of the last glacial period. We highlight episodes of climate change that have disrupted ecosystems and trophic interactions over time scales ranging from years to millennia by changing species' relative abundances and geographic ranges, causing extinctions, and creating transient and novel communities dominated by generalist species and interactions. These patterns emerge repeatedly across disparate temporal and spatial scales, suggesting the possibility of similar underlying processes. Based on these findings, we identify knowledge gaps and fruitful areas for research that will further our understanding of the effects of climate change on ecosystems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Blois, Jessica L -- Zarnetske, Phoebe L -- Fitzpatrick, Matthew C -- Finnegan, Seth -- New York, N.Y. -- Science. 2013 Aug 2;341(6145):499-504. doi: 10.1126/science.1237184.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Natural Sciences, University of California, Merced, Merced, CA 95343, USA. jblois@ucmerced.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23908227" target="_blank"〉PubMed〈/a〉

Description: Understanding how ecological communities are organized and how they change through time is critical to predicting the effects of climate change. Recent work documenting the co-occurrence structure of modern communities found that most significant species pairs co-occur less frequently than would be expected by chance. However, little is known about how co-occurrence structure changes through time. Here we evaluate changes in plant and animal community organization over geological time by quantifying the co-occurrence structure of 359,896 unique taxon pairs in 80 assemblages spanning the past 300 million years. Co-occurrences of most taxon pairs were statistically random, but a significant fraction were spatially aggregated or segregated. Aggregated pairs dominated from the Carboniferous period (307 million years ago) to the early Holocene epoch (11,700 years before present), when there was a pronounced shift to more segregated pairs, a trend that continues in modern assemblages. The shift began during the Holocene and coincided with increasing human population size and the spread of agriculture in North America. Before the shift, an average of 64% of significant pairs were aggregated; after the shift, the average dropped to 37%. The organization of modern and late Holocene plant and animal assemblages differs fundamentally from that of assemblages over the past 300 million years that predate the large-scale impacts of humans. Our results suggest that the rules governing the assembly of communities have recently been changed by human activity.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lyons, S Kathleen -- Amatangelo, Kathryn L -- Behrensmeyer, Anna K -- Bercovici, Antoine -- Blois, Jessica L -- Davis, Matt -- DiMichele, William A -- Du, Andrew -- Eronen, Jussi T -- Faith, J Tyler -- Graves, Gary R -- Jud, Nathan -- Labandeira, Conrad -- Looy, Cindy V -- McGill, Brian -- Miller, Joshua H -- Patterson, David -- Pineda-Munoz, Silvia -- Potts, Richard -- Riddle, Brett -- Terry, Rebecca -- Toth, Aniko -- Ulrich, Werner -- Villasenor, Amelia -- Wing, Scott -- Anderson, Heidi -- Anderson, John -- Waller, Donald -- Gotelli, Nicholas J -- England -- Nature. 2016 Jan 7;529(7584):80-3. doi: 10.1038/nature16447. Epub 2015 Dec 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA. ; Department of Environmental Science and Biology, The College at Brockport - SUNY, Brockport, New York 14420, USA. ; School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, California 95343, USA. ; Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA. ; Hominid Paleobiology Doctoral Program, Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, George Washington University, Washington DC 20052, USA. ; Department of Geosciences and Geography, University of Helsinki, PO Box 64, 00014 University of Helsinki, Finland. ; School of Social Science, The University of Queensland, Brisbane, Queensland 4072, Australia. ; Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA. ; Center for Macroecology, Evolution and Climate, University of Copenhagen, Copenhagen 2100, Denmark. ; Biological Sciences Graduate Program, University of Maryland, College Park, Maryland 20742, USA. ; Florida Museum of Natural History, University of Florida, Gainsville, Florida 32611, USA. ; Department of Entomology, University of Maryland College Park, College Park, Maryland 20742, USA. ; Key Lab of Insect Evolution and Environmental Changes, Capital Normal University, Beijing 100048, China. ; Department of Integrative Biology and Museum of Paleontology, University of California Berkeley, Berkeley, California 94720, USA. ; School Biology and Ecology &Sustainability Solutions Initiative, University of Maine, Orono, Maine 04469, USA. ; Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221, USA. ; Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia. ; Department of Anthropology, Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA. ; School of Life Sciences, University of Nevada-Las Vegas, Las Vegas, Nevada 89154, USA. ; Department of Integrative Biology, Oregon State University, Corvallis, Oregon 97331, USA. ; Chair of Ecology and Biogeography, Nicolaus Copernicus University, Lwowska 1, 87-100 Torun, Poland. ; Evolutionary Studies Institute, University of the Witwatersrand, Jorissen Street, Braamfontein, Johannesburg 2001, South Africa. ; Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA. ; Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26675730" target="_blank"〉PubMed〈/a〉

Description: Community ecology and paleoecology are both concerned with the composition and structure of biotic assemblages but are largely disconnected. Community ecology focuses on existing species assemblages and recently has begun to integrate history (phylogeny and continental or intercontinental dispersal) to constrain community processes. This division has left a “missing middle”:...

Description: Deciphering the evolution of global climate from the end of the Last Glacial Maximum approximately 19 ka to the early Holocene 11 ka presents an outstanding opportunity for understanding the transient response of Earth’s climate system to external and internal forcings. During this interval of global warming, the decay of ice sheets caused global mean sea level to rise by approximately 80 m; terrestrial and marine ecosystems experienced large disturbances and range shifts; perturbations to the carbon cycle resulted in a net release of the greenhouse gases CO2 and CH4 to the atmosphere; and changes in atmosphere and ocean circulation affected the global distribution and fluxes of water and heat. Here we summarize a major effort by the paleoclimate research community to characterize these changes through the development of well-dated, high-resolution records of the deep and intermediate ocean as well as surface climate. Our synthesis indicates that the superposition of two modes explains much of the variability in regional and global climate during the last deglaciation, with a strong association between the first mode and variations in greenhouse gases, and between the second mode and variations in the Atlantic meridional overturning circulation.

Description: The spatial coherence of turbulent flow structures throughout the flow field associated with a collision between a smaller upstream barchan laterally offset from a larger downstream barchan is investigated using inhomogeneous, two‐point correlation coefficients of fluctuating streamwise velocity, from which the distribution, size, and orientation of the large‐scale motions in the flow are analyzed. Measurements were made with fixed‐bed models in a refractive‐index‐matched flume environment allowing uninhibited optical access where the flow field is captured using particle‐image velocimetry in both streamwise‐wall‐normal and streamwise‐spanwise planes. The shear layer of a barchan produces flow structures of smaller length scale, yet still on the order of the barchan height, and stronger positive streamwise fluctuations near the bed as compared to the incoming boundary layer, and these effects prevail far downstream. Analysis of the orientations of the flow structures suggests secondary flow motions induced by the barchan horns, and interdune flow modification through collision stages indicates changing flow interaction regimes with decreasing interdune separation. The combination of enhanced positive streamwise fluctuations near the bed and significant spatial coherence indicates that for a field‐scale barchan of sufficient size, the coherence of flow structures produced in its wake is of comparable scale to the characteristic drag length associated with aeolian transport. As length scales nominally scale with barchan height, the morphodynamics of collisions between barchans of disparate size can be partially explained through this paradigm of flow structure coherence.

Description: “Space-for-time” substitution is widely used in biodiversity modeling to infer past or future trajectories of ecological systems from contemporary spatial patterns. However, the foundational assumption—that drivers of spatial gradients of species composition also drive temporal changes in diversity—rarely is tested. Here, we empirically test the space-for-time assumption by constructing orthogonal...