Extinction Time Research Articles

Late Quaternary megafaunal extinctions in India: How much do we know?

Understanding global patterns of late Quaternary megafaunal extinction is impeded by geographic variation in data quality and quantity. The magnitude, timing and drivers of megafaunal extinctions remain poorly understood for India, a region with a strong history of palaeontological research. We review available data for all putative extinct Indian megafaunal taxa with direct or indirect reported evidence of potential survival into the global “megafaunal extinction window” (from ∼50,000 years onwards). Assessment of late Quaternary megafaunal species richness is confused by multiple levels of taxonomic uncertainty, including the relationship of named Late Pleistocene taxa to extant taxa, and nomenclatural confusion over correct species names. There is sufficient evidence to recognise up to four genuine global megafaunal species-level extinctions in India during the Late Pleistocene: two proboscideans (Palaeoloxodon namadicus, Stegodon sp.), a hippopotamus (Hexaprotodon sp.), and possibly a horse (Equus namadicus). A fifth extinct megafaunal species, the Indian aurochs Bos [primigenius] namadicus, definitely persisted into the Holocene. Other Indian late Quaternary megafaunal species (Rhinoceros spp., Bubalus palaeindicus, Sus “palaeindicus”, Crocodylus palaeindicus) are likely to be synonyms of extant species. Reconstructing regional extinction dynamics is further impeded by chronological uncertainty; however, attempts to obtain new dates for vertebrate samples from six late Quaternary sites in five regions were unsuccessful. Accurate understanding of the dynamics of megafaunal extinctions in India will require robust taxonomic, chronological and palaeoecological data, and we encourage further investigation of the region’s rich late Quaternary record.

The effects of geographic range size and abundance on extinction during a time of “sluggish”’ evolution

AbstractGeographic range size and abundance are important determinants of extinction risk in fossil and extant taxa. However, the relationship between these variables and extinction risk has not been tested extensively during evolutionarily “quiescent” times of low extinction and speciation in the fossil record. Here we examine the influence of geographic range size and abundance on extinction risk during the late Paleozoic (Mississippian–Permian), a time of “sluggish” evolution when global rates of origination and extinction were roughly half those of other Paleozoic intervals. Analyses used spatiotemporal occurrences for 164 brachiopod species from the North American midcontinent. We found abundance to be a better predictor of extinction risk than measures of geographic range size. Moreover, species exhibited reductions in abundance before their extinction but did not display contractions in geographic range size. The weak relationship between geographic range size and extinction in this time and place may reflect the relative preponderance of larger-ranged taxa combined with the physiographic conditions of the region that allowed for easy habitat tracking that dampened both extinction and speciation. These conditions led to a prolonged period (19–25 Myr) during which standard macroevolutionary rules did not apply.

Experimental study of flame extinction with fuel diffusion combustion inside a wall-opening compartment under reduced ventilation conditions

The present study investigates experimentally the transient flame extinction behavior with fuel diffusion combustion inside a wall-opening compartments at reduced ventilation condition. The characteristic parameters to quantify the flame extinction mechanism include the Global Equivalence Ratio (GER) extinction time and critical gas temperature right before extinction. Their coupling effect on the dynamic process of flame extinction with fuel diffusion combustion inside compartments of various scales and opening sizes is quantified and formulated. It is found that: (1) flame extinction is easier to occur for smaller opening size or relatively larger compartment scale which could be well represented by two non-dimensional quantities i.e. the GER and non-dimensional heat loss; (2) the time to reach flame extinction is shorter as the fuel supply flow rate is higher while it is longer as the opening size is larger; (3) the gas temperature inside the compartment when flame extinction is reached first increases with fuel supply rate until a plateau is reached. A formula is established to describe the critical gas temperature right before extinction as a function of a newly defined non-dimensional integrated parameter including both fuel combustion heat release and heat loss factors in which the fuel supply rate opening ventilation compartment scale and transient extinction time scale are involved in general to reflect physically their interplay in controlling the flame extinction inside the compartment. The present study provides new observation quantification and formulation of the mechanism of flame extinction with fuel diffusion combustion inside a wall-opening compartment under reduced ventilation condition.

High efficiency of the NH4H2PO4/Mg(OH)2 composite for guaranteeing safety of wood production

Currently, China's timber industry is in high demand with the development of real estate. However, there is a certain fire hazard in the production process of wood manufacturing. Once a fire occurs, the fire is violent and the spread is rapid. Therefore, to improve the safety of its production process, ammonium dihydrogen phosphate and magnesium hydroxide were selected to prepare a new composite superfine dry powder, which was denoted as the NH4H2PO4/Mg(OH)2 composite. Furthermore, to figure out dry powders' extinction effect on Class A fire, the wood-crib fire suppression effect of the NH4H2PO4/Mg(OH)2 composite was test, and then compared with that of ultrafine dry powder (UDP) and commercial ABC dry powder (C-ABC) in a 1 m³ chamber. Three parameters of the fire extinguishing process, namely flame extinction time, powder consumption and temperature drop were adopted to measure the fire suppression performance. The results demonstrated that UDP and C-ABC both had a larger flame extinction time and powder consumption than the NH4H2PO4/Mg(OH)2 composite. Besides, a fire (wood cribs) can be extinguished by the NH4H2PO4/Mg(OH)2 composite with the fastest temperature drop and a much-improved toxic gas suppression ability. In short, the NH4H2PO4/Mg(OH)2 composite can better guarantee the safety of the wood processing production process. Moreover, the reasons for performance advantages of the NH4H2PO4/Mg(OH)2 composite were discussed.

Kinetic Investigation on Tetrakis(4-Sulfonatophenyl)Porphyrin J-Aggregates Formation Catalyzed by Cationic Metallo-Porphyrins.

Under mild acidic conditions, various metal derivatives of tetrakis(4-N-methylpyridinium)porphyrin (gold(III), AuT4; cobalt(III), CoT4; manganese(III), MnT4 and zinc(II), ZnT4) catalytically promote the supramolecular assembling process of the diacid 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4) into J-aggregates. The aggregation kinetics have been treated according to a well-established model that involves the initial formation of a critical nucleus containing m porphyrin units, followed by autocatalytic growth, in which the rate evolves as a power of time. An analysis of the extinction time traces allows to obtain the rate constants for the auto-catalyzed pathway, kc, and the number of porphyrins involved in the initial seeding. The aggregation kinetics have been investigated at fixed H2TPPS4 concentration as a function of the added metal derivatives MT4. The derived rate constants, kc, obey a rate law that is first order in [MT4] and depend on the specific nature of the catalyst in the order AuT4 > CoT4 > MnT4 > ZnT4. Both resonance light scattering (RLS) intensity and extinction in the aggregated samples increase on increasing [MT4]. With the exception of AuT4, the final aggregated samples obtained at the highest catalyst concentration exhibit a negative Cotton effect in the J-band region, evidencing the occurrence of spontaneous symmetry breaking. The role of the nature of the metal derivative in terms of overall charge and presence of axial groups will be discussed.

Estimating the distribution of time to extinction of infectious diseases in mean-field approaches.

A key challenge for many infectious diseases is to predict the time to extinction under specific interventions. In general, this question requires the use of stochastic models which recognize the inherent individual-based, chance-driven nature of the dynamics; yet stochastic models are inherently computationally expensive, especially when parameter uncertainty also needs to be incorporated. Deterministic models are often used for prediction as they are more tractable; however, their inability to precisely reach zero infections makes forecasting extinction times problematic. Here, we study the extinction problem in deterministic models with the help of an effective ‘birth–death’ description of infection and recovery processes. We present a practical method to estimate the distribution, and therefore robust means and prediction intervals, of extinction times by calculating their different moments within the birth–death framework. We show that these predictions agree very well with the results of stochastic models by analysing the simplified susceptible–infected–susceptible (SIS) dynamics as well as studying an example of more complex and realistic dynamics accounting for the infection and control of African sleeping sickness (Trypanosoma brucei gambiense).

Extinction time for the weaker of two competing SIS epidemics

We consider a simple Markov model for the spread of a disease caused by two virus strains in a closed homogeneously mixing population of size $N$. The spread of each strain in the absence of the other one is described by the stochastic SIS logistic epidemic process, and we assume that there is perfect cross-immunity between the two strains, that is, individuals infected by one are temporarily immune to re-infections and infections by the other. For the case where one strain is strictly stronger than the other, and the stronger strain on its own is supercritical, we derive precise asymptotic results for the distribution of the time when the weaker strain disappears from the population. We further extend our results to certain parameter values where the difference between the basic reproductive ratios of the two strains may tend to 0 as $N\to\infty$. In our proofs, we illustrate a new approach to a fluid limit approximation for a sequence of Markov chains in the vicinity of a stable fixed point of the limit differential equation, valid over long time intervals.

Identification of Single-Phase Reclosing Fault on AC Line Based on Virtual Instantaneous Power

Concerning the difficulty in distinguishing between permanent and transient faults on AC line in AC/DC hybrid system due to relatively low amplitudes of fault recovery voltage and fault arc voltage, a method to identify single-phase reclosing fault based on virtual instantaneous power is proposed. First, by analyzing AC-side networks in the case of permanent fault and transient fault, the calculation models of instantaneous power difference between two ends of AC line are built. And then, the instantaneous power difference is decomposed into two parts: virtual instantaneous power which is affected by the currents on two line ends and virtual instantaneous power which is affected by the current on one line end alone. On this basis, according to the feature of virtual instantaneous power affected by the currents on two line ends, i.e., it is 0 in the case of transient fault, but not 0 in the case of permanent fault, a fault nature identification criterion to distinguish between permanent and transient faults is constructed. Finally, simulation tests on RT-LAB platform verify that, the proposed method can correctly identify the fault nature and determine the fault arc extinction time in both permanent and transient fault cases, unaffected by the commutation failure and fault resistance.

Simulation of a single-phase arc grounding fault on a 220-kV cable transmission system

Cable tunnel fires are mainly caused by single-phase arc grounding faults. The massive energy generated by arc can threaten the safety of the densely laid cable tunnels. In this study, a digital arc fault model with a 220-kV cable transmission system was established on Power Systems Computer Aided Design(PSCAD). The arc model was improved because the parameters were acquired from the experimental results. The arc fault can be divided into two stages: a primary arc at the initiation of the fault and a secondary arc after the tripping of the circuit breakers. The primary arc contains few nonlinear components because of the large arc currents. The secondary arc voltages exhibit nonlinear characteristics because of arc elongation. The secondary arc power continues to increase, however, its amplitude is considerably smaller than the primary arc. The lifetime of the primary arc is dependent on the action of the relaying protection system. Further, some limits based on the energy balance theory were introduced to obtain the extinction time of the secondary arc. In addition, the total energy generated by the arc fault in the 220-kV cable transmission system will eventually become 4891 kJ. This digital arc fault model will significantly contribute to future research with respect to the mechanism of cable tunnel fires.

On the extinction of continuous-state branching processes in random environments

This paper establishes a model of continuous-state branching processes with time inhomogeneous competition in Levy random environments. Some results on extinction are presented, including the distribution of the extinction time, the limiting distribution conditioned on large extinction times and the asymptotic behavior near extinction. This paper also provides a new time-space transformation which can be used for further exploration in similar models. The results are applied to an epidemic model to describe the dynamics of infectious population and a virus model to describe the dynamics of viral load.

Evolutionary history and eco‐climatic diversification in southern African dung beetle Sisyphus

AbstractAimThe high diversity of species in southern Africa has been attributed to geological and palaeoclimatic factors. The timing of radiations in some groups is held to be linked to these geoclimatic trends. Using the Scarabaeinae dung beetle genus, Sisyphus, as a model system, we investigate how geological uplift and climatic changes in the late Cenozoic affected its diversification patterns in southern Africa.LocationSouthern Africa.TaxonThe dung beetle genus, Sisyphus Latreille, 1807 (Coleoptera: Scarabaeidae: Scarabaeinae).MethodsA dated molecular phylogeny of southern African Sisyphus was compared with a factor analysis of species distribution data that statistically defined groups of species according to current climatic distribution. We used these climatic clusters to estimate ancestral ranges using the “BioGeoBEARS” R package. A lineage through time plot was calculated using the R package ‘APE’. We used Bayesian diversification models (compound Poisson process on mass extinction times) to test hypotheses on how late Cenozoic uplift and climatic changes affected speciation and extinction of Sisyphus. Furthermore, we implemented ecological niche modelling in MaxEnt to predict the habitat suitability of species under present climatic conditions.ResultsFour species groups defined from factor analysis of current climatic distribution data are primarily restricted to the moist summer rainfall region in the northeast. Species diversification occurred from the mid‐Miocene until the Pleistocene, during which the central southern African plateau was uplifted in tandem with the advent of winter rainfall and arid climatic zones to the southwest. The ancestor of Sisyphus was centred in eastern low to mid‐altitude areas. Speciation rates were higher in the Miocene to Pliocene, followed by a dramatic drop during the transition to the Pleistocene.Main conclusionsThe taxonomic and eco‐climatic diversification of sisyphines is coincident with geological uplift and changes in climate in east‐central southern Africa. However, phylogenetic relationships of southern African Sisyphus species are not homogenously distributed with respect to geography and climate.

Adapt or Perish: Evolutionary Rescue in a Gradually Deteriorating Environment.

We investigate the evolutionary rescue of a microbial population in a gradually deteriorating environment, through a combination of analytical calculations and stochastic simulations. We consider a population destined for extinction in the absence of mutants, which can survive only if mutants sufficiently adapted to the new environment arise and fix. We show that mutants that appear later during the environment deterioration have a higher probability to fix. The rescue probability of the population increases with a sigmoidal shape when the product of the carrying capacity and of the mutation probability increases. Furthermore, we find that rescue becomes more likely for smaller population sizes and/or mutation probabilities if the environment degradation is slower, which illustrates the key impact of the rapidity of environment degradation on the fate of a population. We also show that our main conclusions are robust across various types of adaptive mutants, including specialist and generalist ones, as well as mutants modeling antimicrobial resistance evolution. We further express the average time of appearance of the mutants that do rescue the population and the average extinction time of those that do not. Our methods can be applied to other situations with continuously variable fitnesses and population sizes, and our analytical predictions are valid in the weak-to-moderate mutation regime.

Recognizing pulses of extinction from clusters of last occurrences

AbstractThe distribution of last occurrences of fossil taxa in a stratigraphic column are used to infer the pattern, timing and tempo of extinction from the fossil record. Clusters of last occurrences are commonly interpreted as an abrupt pulse of extinction. However, stratigraphic architecture alone can produce clusters of last occurrences that can be misinterpreted as an extinction pulse. These clusters will typically occur in strata that immediately underlie facies changes and sequence‐stratigraphic surfaces. It has been proposed that a basin‐wide analysis of the fossil record within a sequence‐stratigraphic framework can be used to distinguish between clusters of last occurrences caused solely by extinction pulses from those generated by sequence‐stratigraphic architecture. A basin‐wide approach makes it possible to observe lateral facies shifts in response to sea‐level change, mitigating the effects of stratigraphic architecture. Using computer simulations of plausible Late Ordovician mass‐extinction scenarios tuned to an inferred Late Ordovician sea‐level curve, we show that stratigraphically‐generated clusters of last occurrences are observed even in basin‐wide analyses of the simulated fossil records due to the basin‐wide loss of preferred facies for many taxa. Nonetheless, we demonstrate that by coarsening the stratigraphic resolution to the systems‐tract level and identifying facies preferences of simulated taxa, we can filter out taxa whose last occurrences coincide with the basin‐wide loss of their preferred facies. This enables consistent identification of the underlying extinction pattern for a wide variety of extinction scenarios. Applying this approach to empirical field data can help to constrain underlying extinction patterns from the fossil record.

Fuel effects on aqueous film formation and foam degradation and their impact on fire suppression by foams containing fluorosurfactants

SummarySpreading coefficient, foam degradation, fuel transport through a foam layer, foam spread, and fire extinction time were collected by varying fuels for a given fluorosurfactant formulation. Varying fuel structure systematically enabled variation of foam‐fuel interactions, and spreading coefficients, which affected aqueous film formation. A wide range of spreading coefficients were studied using two foam formulations. Surfactant formulations with near‐zero or negative spreading coefficients (−1.2, −0.12 mN/m) suppressed the fires within the same time or faster than those with positive spreading coefficients (1.77, 3.28 mN/m). Both foams extinguished an iso‐octane and methylcyclohexane pool fire despite negative spreading coefficients on iso‐octane and positive spreading coefficients on methylcyclohexane. The fire extinction times collected relate more closely to foam degradation than to film formation. Foam degradation results showed a roughly 20% variation in lifetime between the two foams and the three fuels, consistent with fire extinction times. To understand the relationship between foam degradation and solution properties, a single lamella experiment was designed that monitors lamella thickness and lifetime. This experiment, relating solution to foam properties, will aid in the development of environmentally friendly surfactant replacements in firefighting foams.

The effect of graph connectivity on metastability in a stochastic system of spiking neurons

We consider a continuous-time stochastic model of spiking neurons originally introduced by Ferrari et al. in Ferrari et al. (2018). In this model, we have a finite or countable number of neurons which are vertices in some graph G where the edges indicate the synaptic connection between them. We focus on metastability, understood as the property for the time of extinction of the network to be asymptotically memory-less, and we prove that this model exhibits two different behaviors depending on the nature of the specific underlying graph of interaction G that is chosen. In this model the spiking activity of any given neuron is represented by a point process, whose rate fluctuates between 1 and 0 over time depending on whether the membrane potential is positive or null. The membrane potential of each neuron evolves in time by integrating all the spikes of its adjacent neurons up to the last spike of the said neuron, so that when a neuron spikes, its membrane potential is reset to 0 while the membrane potential of each of its adjacent neurons is increased by one unit. Moreover, each neuron is exposed to a leakage effect, modeled as an abrupt loss of membrane potential which occurs at random times driven by a Poisson process of some fixed rate γ. It was previously proven that when the graph G is the infinite one-dimensional lattice, this model presents a phase transition with respect to the parameter γ. It was also proven that, when γ is small enough, the renormalized time of extinction (the first time at which all neurons have a null membrane potential) of a finite version of the system converges in law toward an exponential random variable when the number of neurons goes to infinity. The present article is divided into two parts. First we prove that, in the finite one-dimensional lattice, this last result does not hold anymore if γ is large enough, and in fact we prove that for γ>1 the renormalized time of extinction is asymptotically deterministic. Then we prove that conversely, if G is the complete graph, the result of metastability holds for any positive γ.

Remembrance Day for Lost Species: Remembering and mourning extinction in the Anthropocene

This article examines what is lost and remembered at a time of mass extinction; identifying the Anthropocene – the geological epoch in which the incremental and disruptive impact of the human species has become the main planetary force – as an epoch of mourning. The paper explores the memory and future memory of extinction through the example of Remembrance Day for Lost Species, an international initiative encouraging people all over the world to gather annually on 30thNovember in funeral ceremonies to mourn extinct species. The article particularly draws on Ursula Heise’s concept of ‘eco-cosmopolitanism’ (2008, 2016) and Michael Rothberg’s ‘multidirectional memory’ (2009) as well as fieldwork notes and interviews conducted during Lost Species Day 2018 in Brighton, UK. The analysis considers the conditions of future memory at a time of ecological loss by examining the extinction memorial and funerary practices formulated and performed during the Remembrance Day’s events.

Extinction and dawn of the modern world in the Carnian (Late Triassic).

The Carnian Pluvial Episode (Late Triassic) was a time of global environmental changes and possibly substantial coeval volcanism. The extent of the biological turnover in marine and terrestrial ecosystems is not well understood. Here, we present a meta-analysis of fossil data that suggests a substantial reduction in generic and species richness and the disappearance of 33% of marine genera. This crisis triggered major radiations. In the sea, the rise of the first scleractinian reefs and rock-forming calcareous nannofossils points to substantial changes in ocean chemistry. On land, there were major diversifications and originations of conifers, insects, dinosaurs, crocodiles, lizards, turtles, and mammals. Although there is uncertainty on the precise age of some of the recorded biological changes, these observations indicate that the Carnian Pluvial Episode was linked to a major extinction event and might have been the trigger of the spectacular radiation of many key groups that dominate modern ecosystems.

Comparative Biology of Tetranychus urticae Koch (Acari: Tetranychidae) on Three Solanaceous Plants and the Predator Amblyseius hutu (Prichard & Baker) Acari: Phytoseiidae) as a Potential Biological Control Agent for Tetranychus urticae

The two-spotted spider mite Tetranychus urticae Koch is an emerging pest of solanaceous crops worldwide. Herbivore life history parameters are useful tools for evaluating resistance or susceptibility of host plants to pests. Under laboratory conditions (27±1.0°C, 70.0±5% RH), developmental times and reproductive parameters of T. urticae were evaluated on leaves of three plants (eggplant Solanium melongena, tomato Lycopersicon esculentum, and pepperCapsicum annum). Total developmental time (egg- adult), longevity, life span and fecundity show significant differences by effect of the three plants. Eggplant was most favorite plant for T. urticae , it recorded shorter life cycle ( 9.66 & 8.52 days for female and male), longest longevity ( 9.90 & 6.50 days for female and male), longest life span (19.56 & 15.02 days for female and male) and richened fecundity (75.72 eggs /female). While pepper was the lowest favorable plant for T. urticae because the pepper leaves when offered as a food for T. urticae longest life cycle (11.99 days for female), shortest longevity and life span (5.12 & 17.11 days for female respectively) and reduced fecundity (19.66 eggs /female). Also Predatory mite Amblyseius hutu (Prichard & Baker) was reared on adult stages of two-spotted spider mite, T. urticae at 27±1.0 °C, 70.0±5 % RH and 16:8 L: D to evaluate the developmental period, fecundity rate and predatory potential of A. hutu after feeding different prey densities of T. urticae. There were three treatment with ratio two, four and six predator for Each experiment with 60 eggs and ten newly emerged T. urticae females. A. hutu female when fed on adult stages of T. urticae completed the developmental period in 4.90 days, while longevity and life span lasted 9.80 and 14.20 days respectively and fecundity reached 9.80 per female. Total of T. urticae females and eggs consumed throughout the whole experiment by 2, 4 and 6 individuals predator of A. hutu under laboratory conditions were 0.34, 0.75 and 3.00 prey females and, 6.00, 9.00 and 12.27 prey eggs for treatments 3, 4 and 6 individuals predator respectively. The time taken by the different treatment of A. hutu to drive the total spider mite populations to zero was significantly different among the treatments, while the treatment three (6 individuals predator) had the shortest extinction time for spider mite (6 days).Whenoverall daily changes in spider mite populations studied was found that, the total spider mite population started to increase rapidly until the eighth day, and then it decreased gradually to the end of the experiment.

Noise-induced stabilization of saddle-node ghosts

It is known that saddle-node (s-n) bifurcations leave a saddle remnant (or ghost) in the region of the phase space where the annihilation of the fixed points occurred. The corresponding time delay, td, found right after the bifurcation is known to follow the scaling law , where ϵ and ϵc are the control parameter and its critical value, respectively. While the properties of such delays are well understood for deterministic systems, much less is known about how intrinsic noise influences this phenomenon. As a first step towards analysing this issue, in this article we explore a model with autocatalysis and a two-species hypercycle to analyse the impact of noise on delayed transitions in one- and two-dimensional dynamical systems suffering a s-n bifurcation. The first model is investigated with Gillespie simulations and the diffusion approximation, focusing on the behaviour and properties close to the bifurcation. A Fokker–Planck equation is derived, together with the stochastic potential. We show that the slowing down of the dynamics remains robust to noise. In fact, we prove both analytically and numerically that increasing noise lengthens the delays after bifurcation threshold. Furthermore, the inverse square-root scaling law is not robust to fluctuations. By contrast, scaling properties are identified in the mean extinction times as criticality is approached from above the bifurcation. This noise-induced stabilisation of the delays is also found in the two-dimensional system.

Asymptotic Behavior Analysis for a Three-Species Food Chain Stochastic Model with Regime Switching

This paper discusses the asymptotic behavior of a class of three-species stochastic model with regime switching. Using the Lyapunov function, we first obtain sufficient conditions for extinction and average time persistence. Then, we prove sufficient conditions for the existence of stationary distributions of populations, and they are ergodic. Numerical simulations are carried out to support our theoretical results.