scholarly journals Extinction in complex communities as driven by adaptive dynamics

2021 ◽  
Author(s):  
Vu Nguyen ◽  
Dervis Vural
Keyword(s):  
Time Scales ◽  
Computer Simulations ◽  
Analytical Solutions ◽  
Adaptive Dynamics ◽  
Mathematical Framework ◽  
Evolutionary Time ◽  
Community Interactions ◽  
Fitness Functions ◽  
Evolutionary Changes

In a complex community, species continuously adapt to each other. On rare occasions, the adaptation of a species can lead to the extinction of others, and even its own. ``Adaptive dynamics'' is the standard mathematical framework to describe evolutionary changes in community interactions, and in particular, predict adaptation driven extinction. Unfortunately, most authors implement the equations of adaptive dynamics through computer simulations, that require assuming a large number of questionable parameters and fitness functions. In this study we present analytical solutions to adaptive dynamics equations, thereby clarifying how outcomes depend on any computational input. We develop general formulas that predict equilibrium abundances over evolutionary time scales. Additionally, we predict which species will go extinct next, and when this will happen.

Computer Simulations of Dislocations

2006 ◽  
Author(s):  
Vasily Bulatov ◽  
Wei Cai
Keyword(s):  
Case Studies ◽  
Time Scales ◽  
Computer Simulations ◽  
Common Ground ◽  
Practical Knowledge ◽  
Simulation Methods ◽  
Computational Approaches ◽  
Learn By Doing ◽  
Data Files ◽  
Computational Materials

This book presents a broad collection of models and computational methods - from atomistic to continuum - applied to crystal dislocations. Its purpose is to help students and researchers in computational materials sciences to acquire practical knowledge of relevant simulation methods. Because their behavior spans multiple length and time scales, crystal dislocations present a common ground for an in-depth discussion of a variety of computational approaches, including their relative strengths, weaknesses and inter-connections. The details of the covered methods are presented in the form of "numerical recipes" and illustrated by case studies. A suite of simulation codes and data files is made available on the book's website to help the reader "to learn-by-doing" through solving the exercise problems offered in the book.

scholarly journals The Remarkable Evolution of the Post-Agb Star FG SGE

1998 ◽  
Vol 11 (1) ◽  
pp. 363-363
Author(s):  
Johanna Jurcsik ◽  
Benjamin Montesinos
Keyword(s):  
Time Scales ◽  
Effective Temperature ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolutionary Models ◽  
Single Star ◽  
Line Intensities ◽  
Evolutionary Changes ◽  
Evolutionary Studies

FG Sagittae is one of the most important key objects of post-AGB stellar evolutionary studies. As a consequence of a final helium shell flash, this unique variable has shown real evolutionary changes on human time scales during this century. The observational history was reviewed in comparison with predictions from evolutionary models. The central star of the old planetary nebula (Hel-5) evolved from left to right in the HR diagram, going in just hundred years from the hot region of exciting sources of planetary nebulae to the cool red supergiant domain just before our eyes becoming a newly-born post-AGB star. The effective temperature of the star was around 50,000 K at the beginning of this century, and the last estimates in the late 1980s give 5,000-6,500 K. Recent spectroscopic observations obtained by Ingemar Lundström show definite changes in the nebular line intensities. This fact undoubtedly rules out the possibility that, instead of FG Sge, a hidden hot object would be the true central star of the nebula. Consequently, the observed evolutionary changes are connected with the evolution of a single star.

Milankovitch cycles and their effects on species in ecological and evolutionary time

Paleobiology ◽  
1990 ◽  
Vol 16 (1) ◽  
pp. 11-21 ◽  
Author(s):  
K. D. Bennett
Keyword(s):  
Time Scales ◽  
Climatic Changes ◽  
Milankovitch Cycles ◽  
Mass Extinctions ◽  
Geological Time ◽  
Evolutionary Time ◽  
Abiotic Environment ◽  
Earth History ◽  
Microevolutionary Change ◽  
Second Tier

The Quaternary ice ages were paced by astronomical cycles with periodicities of 20–100 k.y. (Milankovitch cycles). These cycles have been present throughout earth history. The Quaternary fossil record, marine and terrestrial, near to and remote from centers of glaciation, shows that communities of plants and animals are temporary, lasting only a few thousand years at the most. Response of populations to the climatic changes of Quaternary Milankovitch cycles can be taken as typical of the way populations have behaved throughout earth history. Milankovitch cycles thus force an instability of climate and other aspects of the biotic and abiotic environment on time scales much less than typical species durations (1–30 m.y.). Any microevolutionary change that accumulates on a time scale of thousands of years is likely to be lost as communities are reorganized following climatic changes. A four-tier hierarchy of time scales for evolutionary processes can be constructed as follows: ecological time (thousands of years), Milankovitch cycles (20–100 k.y.), geological time (millions of years), mass extinctions (approximately 26 m.y.). “Ecological time” and “geological time” are defined temporally as the intervals between events of the second and fourth tiers, respectively. Gould's (1985) “paradox of the first tier” can be resolved, at least in part, through the undoing of Darwinian natural selection at the first tier by Milankovitch cycles at the second tier.

scholarly journals The life cycle of Drosophila orphan genes

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Nicola Palmieri ◽  
Carolin Kosiol ◽  
Christian Schlötterer
Keyword(s):  
Life Cycle ◽  
Time Scales ◽  
High Rate ◽  
Sequence Evolution ◽  
Functional Requirements ◽  
Evolutionary Time ◽  
Orphan Genes ◽  
Functional Conservation ◽  
Close Relatives ◽  
Obscura Group

Orphans are genes restricted to a single phylogenetic lineage and emerge at high rates. While this predicts an accumulation of genes, the gene number has remained remarkably constant through evolution. This paradox has not yet been resolved. Because orphan genes have been mainly analyzed over long evolutionary time scales, orphan loss has remained unexplored. Here we study the patterns of orphan turnover among close relatives in the Drosophila obscura group. We show that orphans are not only emerging at a high rate, but that they are also rapidly lost. Interestingly, recently emerged orphans are more likely to be lost than older ones. Furthermore, highly expressed orphans with a strong male-bias are more likely to be retained. Since both lost and retained orphans show similar evolutionary signatures of functional conservation, we propose that orphan loss is not driven by high rates of sequence evolution, but reflects lineage-specific functional requirements.

scholarly journals Quantitative measure of hysteresis for memristors through explicit dynamics

2012 ◽  
Vol 468 (2144) ◽  
pp. 2210-2229 ◽  
Author(s):  
P. S. Georgiou ◽  
S. N. Yaliraki ◽  
E. M. Drakakis ◽  
M. Barahona
Keyword(s):  
Differential Equation ◽  
Analytical Solutions ◽  
Quantitative Measure ◽  
Explicit Solutions ◽  
Mathematical Framework ◽  
Input Output ◽  
Explicit Formulas ◽  
Hewlett Packard ◽  
Lumped Parameter ◽  
Proposed Model

We introduce a mathematical framework for the analysis of the input–output dynamics of externally driven memristors. We show that, under general assumptions, their dynamics comply with a Bernoulli differential equation and hence can be nonlinearly transformed into a formally solvable linear equation. The Bernoulli formalism, which applies to both charge- and flux-controlled memristors when either current or voltage driven, can, in some cases, lead to expressions of the output of the device as an explicit function of the input. We apply our framework to obtain analytical solutions of the i – v characteristics of the recently proposed model of the Hewlett–Packard memristor under three different drives without the need for numerical simulations. Our explicit solutions allow us to identify a dimensionless lumped parameter that combines device-specific parameters with properties of the input drive. This parameter governs the memristive behaviour of the device and, consequently, the amount of hysteresis in the i – v . We proceed further by defining formally a quantitative measure for the hysteresis of the device, for which we obtain explicit formulas in terms of the aforementioned parameter, and we discuss the applicability of the analysis for the design and analysis of memristor devices.

scholarly journals Evolution and Diversity of Inherited Spiroplasma Symbionts in Myrmica Ants

2017 ◽  
Vol 84 (4) ◽  
Author(s):  
Matthew J. Ballinger ◽  
Logan D. Moore ◽  
Steve J. Perlman
Keyword(s):  
Time Scales ◽  
Genome Sequencing ◽  
Host Species ◽  
Species Interactions ◽  
Bacterial Symbiont ◽  
Evolutionary Time ◽  
Content Type ◽  
Myrmica Ants ◽  
Microbial Symbionts ◽  
Nutrient Provisioning

ABSTRACT Microbial partners play important roles in the biology and ecology of animals. In insects, maternally transmitted symbionts are especially common and can have host effects ranging from reproductive manipulation to nutrient provisioning and defense against natural enemies. In this study, we report a genus-wide association of Myrmica ants with the inherited bacterial symbiont Spiroplasma . We screen Myrmica ants collected from the wild, including the invasive European fire ant, Myrmica rubra , and find an extraordinarily high prevalence of this symbiont—8 of 9 species, 42 of 43 colonies, and 250 of 276 individual workers harbored Spiroplasma —only one host species was uninfected. In our screens, each host species carried a distinct Spiroplasma strain, and none were infected with more than one strain. All symbionts belong to the citri clade, allied most closely with pathogenic strains of Spiroplasma infecting corn crops and honeybees, and there is strong evidence of host-symbiont persistence across evolutionary time scales. Genome sequencing of two Spiroplasma symbionts revealed candidate genes that may play a part in the symbiosis, a nutrient transporter absent from other Spiroplasma strains, and a ribosome-inactivating protein previously implicated in parasite defense. These results together suggest long-term, likely mutualistic, relationships atypical of Spiroplasma -insect associations with potential significance for broad ecological interactions with Myrmica . IMPORTANCE Animal-associated microbial symbionts can dramatically affect the biology of their hosts. The identification and characterization of these intimate partnerships remain an essential component of describing and predicting species interactions, especially for invasive host species. Ants perform crucial ecological functions as ecosystem engineers, scavengers, and predators, and ants in the genus Myrmica can be aggressive resource competitors and reach high densities in their native and invaded habitats. In this study, a novel symbiosis is identified between Myrmica ants and the facultative bacterial symbiont Spiroplasma . Broad host distribution, high frequencies of infection, and host-symbiont codivergence over evolutionary time scales, an uncommon feature of Spiroplasma associations, suggest an important likely mutualistic interaction. Genome sequencing identified highly divergent gene candidates that may contribute to Spiroplasma 's role as a possible defensive or nutritional partner in Myrmica .

Genetics and plant breeding, 1910—80

1981 ◽  
Vol 292 (1062) ◽  
pp. 401-405 ◽  
Keyword(s):  
Plant Breeding ◽  
Time Scales ◽  
Natural Law ◽  
Primary Source ◽  
Genetic System ◽  
Chromosome Study ◽  
Evolutionary Time ◽  
Classical Models

The early successes of genetics and plant breeding and the still earlier successes of microscopy and chromosome study led to disputes, which were aggravated by lack of understanding between languages, professions and techniques. But their primary source lay in each pioneer’s insistence on a uniformity of his own natural law. Bateson’s exclusion of nucleus and cytoplasm was followed (in 1926) by Morgan’s exclusion merely of the cytoplasm. An anti-genetic and anti-evolutionary revival was favoured by these disputes and has left its traces with us today. The idea of a uniformity in heredity or the genetic system is once again an obstacle to understanding. For, in the practice of plant breeding, we are faced by a conflict between evidence on experimental and evolutionary time-scales. Louis de Vilmorin, Darwin and Mendel thought of this problem under the title of the ‘causes of variability’. We can now recognize that the experimental or classical models of mutation and recombination of genes and chromosomes is no longer universally sufficient either for organisms or for their chromosomes. Variability in higher organisms seems to have a variety of pre-nuclear as well as nuclear foundations.

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