4,240 research outputs found
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
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
Neuroanthropology: Evolution and Emotional Embodiment
The Decade of the Mind is a proposal for a research initiative focused on four areas of neuroscience, including mental health, high-level cognitive function, education, and computational applications. Organizing efforts to date have primarily included cognitive scientists, computer scientists, and engineers, as well as physicians. At the same time anthropologists have started to explore the implications of neuroscience for understanding culture. Here we suggest that evolutionary neuroscience can be used to bridge knowledge obtained by social scientists with that obtained in the neurosciences for a more complete appreciation of the mind. We consider such a perspective as neuroanthropology. We use embodiment, an anthropological concept that has been substantiated by recent findings in neuroscience, to illustrate an integrative biocultural approach within neuroanthropology and suggest future possible directions for research
Uncertainties in Atmospheric Muon-Neutrino Fluxes Arising from Cosmic-Ray Primaries
We present an updated calculation of the uncertainties on the atmospheric
muon-neutrino flux arising from cosmic-ray primaries. For the first time, we
include recent measurements of the cosmic-ray primaries collected since 2005.
We apply a statistical technique that allows the determination of correlations
between the parameters of the GSHL primary-flux parametrisation and the
incorporation of these correlations into the uncertainty on the muon-neutrino
flux. We obtain an uncertainty related to the primary cosmic rays of around
, depending on energy, which is about a factor of two smaller
than the previously determined uncertainty. The hadron production uncertainty
is added in quadrature to obtain the total uncertainty on the neutrino flux,
which is reduced by . To take into account an unexpected hardening
of the spectrum of primaries above energies of observed in
recent measurements, we propose an alternative parametrisation and discuss its
impact on the neutrino flux uncertainties
A not-so-grim tale: how childhood family structure influences reproductive and risk-taking outcomes in a historical U.S. Population.
Childhood family structure has been shown to play an important role in shaping a child's life course development, especially in industrialised societies. One hypothesis which could explain such findings is that parental investment is likely to be diluted in families without both natural parents. Most empirical studies have examined the influence of only one type of family disruption or composition (e.g. father absence) making it difficult to simultaneously compare the effects of different kinds of family structure on children's future outcomes. Here we use a large, rich data source (n=16,207) collected by Alfred Kinsey and colleagues in the United States from 1938 to 1963, to examine the effects of particular childhood family compositions and compare between them. The dataset further allows us to look at the effects of family structure on an array of traits relating to sexual maturity, reproduction, and risk-taking. Our results show that, for both sexes, living with a single mother or mother and stepfather during childhood was often associated with faster progression to life history events and greater propensity for risk-taking behaviours. However, living with a single father or father and stepmother was typically not significantly different to having both natural parents for these outcomes. Our results withstand adjustment for socioeconomic status, age, ethnicity, age at puberty (where applicable), and sibling configuration. While these results support the hypothesis that early family environment influences subsequent reproductive strategy, the different responses to the presence or absence of different parental figures in the household rearing environment suggests that particular family constructions exert independent influences on childhood outcomes. Our results suggest that father-absent households (i.e. single mothers or mothers and stepfathers) are most highly associated with subsequent fast life history progressions, compared with mother-absent households, and those with two natural parents
Childhood family disruption and adult height: is there a mediating role of puberty?
BACKGROUND AND OBJECTIVES: Childhood family background is known to be associated with child growth and development, including the onset of puberty, but less is known about the influence of childhood family disruption on outcomes in later life. Given the associations between early family disruption and childhood development, we predicted that there may be long-term health-relevant consequences of childhood disruption. METHODOLOGY: Using data from a large US interview sample (n = 16 207), we test if death or divorce of parents, at different childhood periods, was associated with adult stature, and whether age at puberty mediated this relationship, for men and women. RESULTS MEN: : parental death and divorce during early childhood was associated with shorter adult height, and later puberty. Later puberty was associated with shorter adult height. Path analyses demonstrated that the relationship between parental divorce and height was completely mediated by age at puberty; although parental death was only partially mediated by age at puberty. WOMEN: the father's death during early childhood was associated with earlier puberty, which was in turn associated with shorter adult stature. The relationship between paternal death and height is entirely mediated by age at puberty; no evidence of a direct relationship between childhood family disruption and adult height. CONCLUSIONS: Early childhood familial disruption is associated with shorter height for men, and is partially mediated by later puberty. For women, the relationship between father's death, and height was completely mediated by earlier puberty. These findings indicate that disruption during childhood can have long-reaching health repercussions, particularly for boys
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