4,564 research outputs found
Spatial patterns in mesic savannas: the local facilitation limit and the role of demographic stochasticity
We propose a model equation for the dynamics of tree density in mesic
savannas. It considers long-range competition among trees and the effect of
fire acting as a local facilitation mechanism. Despite short-range facilitation
is taken to the local-range limit, the standard full spectrum of spatial
structures obtained in general vegetation models is recovered. Long-range
competition is thus the key ingredient for the development of patterns. The
long time coexistence between trees and grass, and how fires affect the
survival of trees as well as the maintenance of the patterns is studied. The
influence of demographic noise is analyzed. The stochastic system, under the
parameter constraints typical of mesic savannas, shows irregular patterns
characteristics of realistic situations. The coexistence of trees and grass
still remains at reasonable noise intensities.Comment: 12 pages, 7 figure
Online games: a novel approach to explore how partial information influences human random searches
Many natural processes rely on optimizing the success ratio of a search
process. We use an experimental setup consisting of a simple online game in
which players have to find a target hidden on a board, to investigate the how
the rounds are influenced by the detection of cues. We focus on the search
duration and the statistics of the trajectories traced on the board. The
experimental data are explained by a family of random-walk-based models and
probabilistic analytical approximations. If no initial information is given to
the players, the search is optimized for cues that cover an intermediate
spatial scale. In addition, initial information about the extension of the cues
results, in general, in faster searches. Finally, strategies used by informed
players turn into non-stationary processes in which the length of each
displacement evolves to show a well-defined characteristic scale that is not
found in non-informed searches.Comment: 17 pages, 10 figure
Vegetation pattern formation in semiarid systems without facilitative mechanisms
Regular vegetation patterns in semiarid ecosystems are believed to arise from
the interplay between long-range competition and facilitation processes acting
at smaller distances. We show that, under rather general conditions, long-range
competition alone may be enough to shape these patterns. To this end we propose
a simple, general model for the dynamics of vegetation, which includes only
long-range competition between plants. Competition is introduced through a
nonlocal term, where the kernel function quantifies the intensity of the
interaction. We recover the full spectrum of spatial structures typical of
vegetation models that also account for facilitation in addition to
competition.Comment: 21 pages, 3 figure
Minimal mechanisms for vegetation patterns in semiarid regions
The minimal ecological requirements for formation of regular vegetation
patterns in semiarid systems have been recently questioned. Against the general
belief that a combination of facilitative and competitive interactions is
necessary, recent theoretical studies suggest that, under broad conditions,
nonlocal competition among plants alone may induce patterns. In this paper, we
review results along this line, presenting a series of models that yield
spatial patterns when finite-range competition is the only driving force. A
preliminary derivation of this type of model from a more detailed one that
considers water-biomass dynamics is also presented. Keywords: Vegetation
patterns, nonlocal interactionsComment: 8 pages, 4 figure
Temporal disorder in up-down symmetric systems
The effect of temporal disorder on systems with up-down Z2 symmetry is
studied. In particular, we analyze two well-known families of phase
transitions: the Ising and the generalized voter universality classes, and
scrutinize the consequences of placing them under fluctuating global
conditions. We observe that variability of the control parameter induces in
both classes "Temporal Griffiths Phases" (TGP). These recently-uncovered phases
are analogous to standard Griffiths Phases appearing in systems with quenched
spatial disorder, but where the roles of space and time are exchanged. TGPs are
characterized by broad regions in parameter space in which (i) mean
first-passage times scale algebraically with system size, and (ii) the system
response (e.g. susceptibility) diverges. Our results confirm that TGPs are
quite robust and ubiquitous in the presence of temporal disorder. Possible
applications of our results to examples in ecology are discussed
Violencia de género en la familia: perspectiva jurídico penal
Se analizan desde una perspectiva garantista la Constitución Federal y los tratados internacionales que obligan al Estado a tutelar penalmente el derecho humano de la mujer a una vida libre de violencia en el hogar. Se concluye que para cumplir con este deber es ineludible la creación legislativa de tipo penal que sancione la violencia familiar asociada a la violencia de género. Esta acción legislativa sería parte de una nueva política criminológica dedicada específicamente a la prevención, sanción y erradicación de la violencia de género en el hogar
Demographic effects of aggregation in the presence of a component Allee effect
Intraspecific interactions are key drivers of population dynamics because
they establish relations between individual fitness and population density. The
component Allee effect is defined as a positive correlation between any fitness
component of a focal organism and population density, and it can lead to
positive density dependence in the population per capita growth rate. The
spatial structure is key to determining whether and to which extent a component
Allee effect will manifest at the demographic level because it determines how
individuals interact with one another. However, existing spatial models to
study the Allee effect impose a fixed spatial structure, which limits our
understanding of how a component Allee effect and the spatial dynamics jointly
determine the existence of demographic Allee effects. To fill this gap, we
introduce a spatially-explicit theoretical framework where spatial structure
and population dynamics are emergent properties of the individual-level
demographic rates. Depending on the intensity of the individual processes the
population exhibits a variety of spatial patterns that determine the
demographic-level by-products of an existing individual-level component Allee
effect. We find that aggregation increases population abundance and allows
populations to survive in harsher environments and at lower global population
densities when compared with uniformly distributed organisms. Moreover,
aggregation can prevent the component Allee effect from manifesting at the
population level or restrict it to the level of each independent group. These
results provide a mechanistic understanding of how component Allee effects
operate for different spatial population structures and show at the population
level. Our results contribute to better understanding population dynamics in
the presence of Allee effects and can potentially inform population management
strategies
Species exclusion and coexistence in a noisy voter model with a competition-colonization tradeoff
We introduce an asymmetric noisy voter model to study the joint effect of
immigration and a competition-dispersal tradeoff in the dynamics of two species
competing for space in regular lattices. Individuals of one species can invade
a nearest-neighbor site in the lattice, while individuals of the other species
are able to invade sites at any distance but are less competitive locally,
i.e., they establish with a probability . The model also accounts for
immigration, modeled as an external noise that may spontaneously replace an
individual at a lattice site by another individual of the other species. This
combination of mechanisms gives rise to a rich variety of outcomes for species
competition, including exclusion of either species, mono-stable coexistence of
both species at different population proportions, and bi-stable coexistence
with proportions of populations that depend on the initial condition.
Remarkably, in the bi-stable phase, the system undergoes a discontinuous
transition as the intensity of immigration overcomes a threshold, leading to a
half loop dynamics associated to a cusp catastrophe, which causes the
irreversible loss of the species with the shortest dispersal range.Comment: 13 pages, 9 figures, 3 appendice
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