389 research outputs found
The role of neighbours selection on cohesion and order of swarms
We introduce a multi-agent model for exploring how selection of neighbours
determines some aspects of order and cohesion in swarms. The model algorithm
states that every agents' motion seeks for an optimal distance from the nearest
topological neighbour encompassed in a limited attention field. Despite the
great simplicity of the implementation, varying the amplitude of the attention
landscape, swarms pass from cohesive and regular structures towards fragmented
and irregular configurations. Interestingly, this movement rule is an ideal
candidate for implementing the selfish herd hypothesis which explains
aggregation of alarmed group of social animals.Comment: 15 pages, 9 figures, Plos One, May 201
Speciational view of macroevolution: are micro and macroevolution decoupled?
We introduce a simple computational model that, with a microscopic dynamics
driven by natural selection and mutation alone, allows the description of true
speciation events. A statistical analysis of the so generated evolutionary tree
captures realistic features showing power laws for frequency distributions in
time and size. Albeit these successful predictions, the difficulty in obtaining
punctuated dynamics with mass extinctions suggests the necessity of decoupling
micro and macro-evolutionary mechanisms in agreement with some ideas of Gould's
and Eldredge's theory of punctuated equilibrium.Comment: Europhys. Lett. 75:342--34
Growth-rate distributions of gut microbiota time series: neutral models and temporal dependence
Logarithmic growth-rates are fundamental observables for describing
ecological systems and the characterization of their distributions with
analytical techniques can greatly improve their comprehension. Here a neutral
model based on a stochastic differential equation with demographic noise, which
presents a closed form for these distributions, is used to describe the
population dynamics of microbiota. Results show that this model can
successfully reproduce the log-growth rate distribution of the considered
abundance time-series. More significantly, it predicts its temporal dependence,
by reproducing its kurtosis evolution when the time lag is increased.
Furthermore, its typical shape for large is assessed, verifying that the
distribution variance does not diverge with . The simulated processes
generated by the calibrated stochastic equation and the analysis of each
time-series, taken one by one, provided additional support for our approach.
Alternatively, we tried to describe our dataset by using a logistic model with
an environmental stochastic term. Analytical and numerical results show that
this model is not suited for describing the leptokurtic log-growth rates
distribution found in our data. These results effectively support a neutral
model with demographic stochasticity for describing the growth-rate dynamics
and the stationary abundance distribution of the considered microbiota. This
suggests that there are no significant parametric demographic differences among
the species, which can be statistically characterized by the same vital rates.Comment: 14 pages, 6 figure
Conventions spreading in open-ended systems
We introduce a simple open-ended model that describes the emergence of a
shared vocabulary. The ordering transition toward consensus is generated only
by an agreement mechanism. This interaction defines a finite and small number
of states, despite each individual having the ability to invent an unlimited
number of new words. The existence of a phase transition is studied by
analyzing the convergence times, the cognitive efforts of the agents and the
scaling behavior in memory and timeComment: 11 pages, 5 figure
Analysis of a spatial Lotka-Volterra model with a finite range predator-prey interaction
We perform an analysis of a recent spatial version of the classical
Lotka-Volterra model, where a finite scale controls individuals' interaction.
We study the behavior of the predator-prey dynamics in physical spaces higher
than one, showing how spatial patterns can emerge for some values of the
interaction range and of the diffusion parameter.Comment: 7 pages, 7 figure
Scaling properties of the Penna model
We investigate the scaling properties of the Penna model, which has become a
popular tool for the study of population dynamics and evolutionary problems in
recent years. We find that the model generates a normalised age distribution
for which a simple scaling rule is proposed, that is able to reproduce
qualitative features for all genome sizes.Comment: 4 pages, 4 figure
Comment on "Universal and accessible entropy estimation using a compression algorithm"
In a recent Letter [1] a framework for estimating entropy was introduced and
applied to one-dimensional and two-dimensional systems. In this Comment we show
that the method is not well suited for estimating entropy in bidimensional
systems presenting long-range correlations.Comment: 2 pages, 1 figur
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