Mesozoic origin of coleoid cephalopods and their abrupt shifts of diversification patterns

2021 ◽  
pp. 107331
Author(s):  
David A. López-Córdova ◽  
Jorge Avaria-Llautureo ◽  
Patricio M. Ulloa ◽  
Heather E. Braid ◽  
Liam J. Revell ◽  
...  
Keyword(s):  
Abrupt Shifts

Econometrics for Modelling Climate Change

2021 ◽  
Author(s):  
Jennifer L. Castle ◽  
David F. Hendry
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Econometric Modeling ◽  
Complex Data ◽  
Explanatory Variables ◽  
Stochastic Trends ◽  
Trend Breaks ◽  
Abrupt Shifts ◽  
Climate Time Series ◽  
Do So

Shared features of economic and climate time series imply that tools for empirically modeling nonstationary economic outcomes are also appropriate for studying many aspects of observational climate-change data. Greenhouse gas emissions, such as carbon dioxide, nitrous oxide, and methane, are a major cause of climate change as they cumulate in the atmosphere and reradiate the sun’s energy. As these emissions are currently mainly due to economic activity, economic and climate time series have commonalities, including considerable inertia, stochastic trends, and distributional shifts, and hence the same econometric modeling approaches can be applied to analyze both phenomena. Moreover, both disciplines lack complete knowledge of their respective data-generating processes (DGPs), so model search retaining viable theory but allowing for shifting distributions is important. Reliable modeling of both climate and economic-related time series requires finding an unknown DGP (or close approximation thereto) to represent multivariate evolving processes subject to abrupt shifts. Consequently, to ensure that DGP is nested within a much larger set of candidate determinants, model formulations to search over should comprise all potentially relevant variables, their dynamics, indicators for perturbing outliers, shifts, trend breaks, and nonlinear functions, while retaining well-established theoretical insights. Econometric modeling of climate-change data requires a sufficiently general model selection approach to handle all these aspects. Machine learning with multipath block searches commencing from very general specifications, usually with more candidate explanatory variables than observations, to discover well-specified and undominated models of the nonstationary processes under analysis, offers a rigorous route to analyzing such complex data. To do so requires applying appropriate indicator saturation estimators (ISEs), a class that includes impulse indicators for outliers, step indicators for location shifts, multiplicative indicators for parameter changes, and trend indicators for trend breaks. All ISEs entail more candidate variables than observations, often by a large margin when implementing combinations, yet can detect the impacts of shifts and policy interventions to avoid nonconstant parameters in models, as well as improve forecasts. To characterize nonstationary observational data, one must handle all substantively relevant features jointly: A failure to do so leads to nonconstant and mis-specified models and hence incorrect theory evaluation and policy analyses.

scholarly journals Clockwise and counterclockwise hysteresis characterize state changes in the same aquatic ecosystem

2020 ◽  
Author(s):  
Amanda C. Northrop ◽  
Vanessa Avalone ◽  
Aaron M. Ellison ◽  
Bryan A. Ballif ◽  
Nicholas J. Gotelli
Keyword(s):  
Aquatic Ecosystem ◽  
Recovery Phase ◽  
Ecosystem Recovery ◽  
Pitcher Plant ◽  
Rapid Reduction ◽  
Long Time ◽  
High Enrichment ◽  
Change State ◽  
Abrupt Shifts ◽  
Clockwise Hysteresis

Incremental increases in a driver variable, such as nutrients or detritus, can trigger abrupt shifts in aquatic ecosys-tems. Once these ecosystems change state, a simple reduction in the driver variable may not return them to their original state. Because of the long time scales involved, we still have a poor understanding of the dynamics of ecosys-tem recovery after a state change. A model system for understanding ecosystem recovery is the aquatic microecosystem that inhabits the cup-shaped leaves of the pitcher plant Sarracenia purpurea. With enrichment of organic matter, this system flips within 1 to 3 days from an oxygen-rich state to an oxygen-poor (hypoxic) state. In a replicated green-house experiment, we enriched pitcher plant leaves at different rates with bovine serum albumin (BSA), a molecular substitute for detritus. Changes in dissolved oxygen ([O2]) and undigested BSA concentration were monitored during enrichment and recovery phases. At low enrichment rates, ecosystems showed a substantial lag in the recovery of [O2] (clockwise hysteresis). At intermediate enrichment rates, [O2] tracked the levels of undigested BSA with the same profile during the enrichment and recovery phases (no hysteresis). At high enrichment rates, we observed a novel response: changes in [O2] were proportionally larger during the recovery phase than during the enrichment phase (counter-clockwise hysteresis). These experiments demonstrate that detrital enrichment rate can modulate a diversity of hysteretic responses in a single aquatic ecosystem. With counter-clockwise hysteresis, rapid reduction of a driver variable following high enrichment rates may be a viable restoration strategy.

scholarly journals Abrupt shifts in phenology and vegetation productivity under climate extremes

2015 ◽  
Vol 120 (10) ◽  
pp. 2036-2052 ◽  
Author(s):  
Xuanlong Ma ◽  
Alfredo Huete ◽  
Susan Moran ◽  
Guillermo Ponce-Campos ◽  
Derek Eamus
Keyword(s):  
Climate Extremes ◽  
Vegetation Productivity ◽  
Abrupt Shifts

scholarly journals Preoperative Noncoronary Cardiovascular Assessment and Management of Kidney Transplant Candidates

2019 ◽  
Vol 14 (11) ◽  
pp. 1670-1676 ◽  
Author(s):  
Jayson Rakesh Baman ◽  
Joseph Knapper ◽  
Zankhana Raval ◽  
Matthew E. Harinstein ◽  
John J. Friedewald ◽  
...  
Keyword(s):  
Kidney Transplant ◽  
Electrical Remodeling ◽  
Evidence Based ◽  
Phosphate Metabolism ◽  
Cardiovascular Assessment ◽  
Transplant Candidates ◽  
Abrupt Shifts ◽  
Evidence Based Model ◽  
Calcium Phosphate Metabolism ◽  
High Output

The pretransplant risk assessment for patients with ESKD who are undergoing evaluation for kidney transplant is complex and multifaceted. When considering cardiovascular disease in particular, many factors should be considered. Given the increasing incidence of kidney transplantation and the growing body of evidence addressing ESKD-specific cardiovascular risk profiles, there is an important need for a consolidated, evidence-based model that considers the unique cardiovascular challenges that these patients face. Cardiovascular physiology is altered in these patients by abrupt shifts in volume status, altered calcium-phosphate metabolism, high-output states (in the setting of arteriovenous fistulization), and adverse geometric and electrical remodeling, to name a few. Here, we present a contemporary review by addressing cardiomyopathy/heart failure, pulmonary hypertension, valvular dysfunction, and arrhythmia/sudden cardiac death within the ESKD population.

scholarly journals Rapid reorganization in ocean biogeochemistry off Peru towards the end of the Little Ice Age

2009 ◽  
Vol 6 (5) ◽  
pp. 835-848 ◽  
Author(s):  
D. Gutiérrez ◽  
A. Sifeddine ◽  
D. B. Field ◽  
L. Ortlieb ◽  
G. Vargas ◽  
...  
Keyword(s):  
Little Ice Age ◽  
Decadal Variability ◽  
Late Quaternary ◽  
Walker Circulation ◽  
Rapid Expansion ◽  
Ice Age ◽  
Ecosystem Structure ◽  
Ocean Biogeochemistry ◽  
Ocean Ecosystem ◽  
Abrupt Shifts

Abstract. Climate and ocean ecosystem variability has been well recognized during the twentieth century but it is unclear if modern ocean biogeochemistry is susceptible to the large, abrupt shifts that characterized the Late Quaternary. Time series from marine sediments off Peru show an abrupt centennial-scale biogeochemical regime shift in the early nineteenth century, of much greater magnitude and duration than present day multi-decadal variability. A rapid expansion of the subsurface nutrient-rich, oxygen-depleted waters resulted in the present-day higher biological productivity, including pelagic fish. The shift was likely driven by a northward migration of the Intertropical Convergence Zone and the South Pacific Subtropical High to their present day locations, coupled with a strengthening of Walker circulation, towards the end of the Little Ice Age. These findings reveal the potential for large reorganizations in tropical Pacific climate with immediate effects on ocean biogeochemical cycling and ecosystem structure.

Climate-Caused Abrupt Shifts in a European Macrotidal Estuary

2013 ◽  
Vol 36 (6) ◽  
pp. 1193-1205 ◽  
Author(s):  
Aurélie Chaalali ◽  
Grégory Beaugrand ◽  
Philippe Boët ◽  
Benoît Sautour
Keyword(s):  
Macrotidal Estuary ◽  
Abrupt Shifts

Drivers of cocoa encroachment into protected forests: the case of three forest reserves in Ghana

2020 ◽  
Vol 22 (4) ◽  
pp. 425-437
Author(s):  
L.K. Brobbey ◽  
F.K. Agyei ◽  
P. Osei-Tutu
Keyword(s):  
Rural Areas ◽  
Subsistence Farming ◽  
Forest Reserves ◽  
Pests And Diseases ◽  
Protected Forests ◽  
Cultivable Land ◽  
Proximate Causes ◽  
Abrupt Shifts ◽  
Community Workshops ◽  
Rural Appraisal

The study sought to unearth the immediate causes and underlying factors that fuel cocoa-driven deforestation in Ghana through four pathways: interviews, participatory rural appraisal techniques, facilitated community workshops and field observations in five forest-fringe and two admitted communities of Ghana's Ashanti and Western North Regions. The study found agricultural expansion and infrastructure extension to be the proximate causes of deforestation. These are driven by population growth, low cocoa productivity, inadequate cultivable land for cash and subsistence farming, abrupt shifts in government policies, droughts, wildfires, pests and diseases, land insecurity, limited alternative livelihoods in rural areas and lack of maintenance of admitted farm boundaries. The magnitude of the surge in cocoa encroachment in protected forests requires collaboration among diverse stakeholders and interlocutory action to stem the challenge while more holistic solutions are sought.

Sign in / Sign up

Export Citation Format

Share Document