404 research outputs found
Pattern formation and spatial correlation induced by the noise in two competing species
We analyze the spatio-temporal patterns of two competing species in the
presence of two white noise sources: an additive noise acting on the
interaction parameter and a multiplicative noise which affects directly the
dynamics of the species densities. We use a coupled map lattice (CML) with
uniform initial conditions. We find a nonmonotonic behavior both of the pattern
formation and the density correlation as a function of the multiplicative noise
intensity.Comment: 10 pages, 7 figures. accepted for publication in Acta Phys. Pol.
Asymptotic regime in N random interacting species
The asymptotic regime of a complex ecosystem with \emph{N}random interacting
species and in the presence of an external multiplicative noise is analyzed. We
find the role of the external noise on the long time probability distribution
of the i-th density species, the extinction of species and the local field
acting on the i-th population. We analyze in detail the transient dynamics of
this field and the cavity field, which is the field acting on the
species when this is absent. We find that the presence or the absence of some
population give different asymptotic distributions of these fields.Comment: 11 pages, 6 figures. To be published in Eur. Phys. J.
Noise in ecosystems: a short review
Noise, through its interaction with the nonlinearity of the living systems,
can give rise to counter-intuitive phenomena such as stochastic resonance,
noise-delayed extinction, temporal oscillations, and spatial patterns. In this
paper we briefly review the noise-induced effects in three different
ecosystems: (i) two competing species; (ii) three interacting species, one
predator and two preys, and (iii) N-interacting species. The transient dynamics
of these ecosystems are analyzed through generalized Lotka-Volterra equations
in the presence of multiplicative noise, which models the interaction between
the species and the environment. The interaction parameter between the species
is random in cases (i) and (iii), and a periodical function, which accounts for
the environmental temperature, in case (ii). We find noise-induced phenomena
such as quasi-deterministic oscillations, stochastic resonance, noise-delayed
extinction, and noise-induced pattern formation with nonmonotonic behaviors of
patterns areas and of the density correlation as a function of the
multiplicative noise intensity. The asymptotic behavior of the time average of
the \emph{} population when the ecosystem is composed of a great number
of interacting species is obtained and the effect of the noise on the
asymptotic probability distributions of the populations is discussed.Comment: 27 pages, 16 figures. Accepted for publication in Mathematical
Biosciences and Engineerin
Transient behavior of a population dynamical model
The transient behavior of an ecosystem with N random interacting species in
the presence of a multiplicative noise is analyzed. The multiplicative noise
mimics the interaction with the environment. We investigate different
asymptotic dynamical regimes and the role of the external noise on the
probability distribution of the local field.Comment: 5 pages, 2 figures, accepted for publication in Progress of
Theoretical Physic
Nonmonotonic Pattern Formation in Three Species Lotka-Volterra System with Colored Noise
A coupled map lattice of generalized Lotka-Volterra equations in the presence
of colored multiplicative noise is used to analyze the spatiotemporal evolution
of three interacting species: one predator and two preys symmetrically
competing each other. The correlation of the species concentration over the
grid as a function of time and of the noise intensity is investigated. The
presence of noise induces pattern formation, whose dimensions show a
nonmonotonic behavior as a function of the noise intensity. The colored noise
induces a greater dimension of the patterns with respect to the white noise
case and a shift of the maximum of its area towards higher values of the noise
intensity.Comment: 6 pages, 3 figure
Translocation time of periodically forced polymer chains
We show the presence of both a minimum and clear oscillations in the
frequency dependence of the translocation time of a polymer described as a
unidimensional Rouse chain driven by a spatially localized oscillating linear
potential. The observed oscillations of the mean translocation time arise from
the synchronization between the very mean translocation time and the period of
the external force. We have checked the robustness of the frequency value for
the minimum translocation time by changing the damping parameter, finding a
very simple relationship between this frequency and the correspondent
translocation time. The translocation time as a function of the polymer length
has been also evaluated, finding a precise scaling. Furthermore, the role
played by the thermal fluctuations described as a Gaussian uncorrelated noise
has been also investigated, and the analogies with the resonant activation
phenomenon are commented.Comment: 7 pages, 11 figures. Physical Review E (in press
Active translocation of a semiflexible polymer assisted by an ATP-based molecular motor
In this work we study the assisted translocation of a polymer across a
membrane nanopore, inside which a molecular motor exerts a force fuelled by the
hydrolysis of ATP molecules. In our model the motor switches to its active
state for a fixed amount of time, while it waits for an ATP molecule binding
and triggering the impulse, during an exponentially distributed time lapse. The
polymer is modelled as a beads-springs chain with both excluded volume and
bending contributions, and moves in a stochastic three dimensional environment
modelled with a Langevin dynamics at fixed temperature. The resulting dynamics
shows a Michaelis-Menten translocation velocity that depends on the chain
flexibility. The scaling behavior of the mean translocation time with the
polymer length for different bending values is also investigated.Comment: 10 pages, 10 figure
Role of the Colored Noise in Spatio-Temporal Behavior of Two Competing Species
We study the spatial distributions of two randomly interacting species, in
the presence of an external multiplicative colored noise. The dynamics of the
ecosystem is described by a coupled map lattice model. We find a nonmonotonic
behavior in the formation of large scale spatial correlations as a function of
the multiplicative colored noise intensity. This behavior is shifted towards
higher values of the noise intensity for increasing correlation time of the
noise.Comment: 6 pages, 3 figure
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