620 research outputs found
KLUN+ peculiar velocity survey
The enhanced Kinematics of the Local Universe (KLUN+) galaxy sample is a
collection of galaxies suitable for Tully-Fisher (TF) or Faber-Jackson (FJ)
distance estimation. Here we extract a subsample of 6229 KLUN+ galaxies closer
than 80 Mpc/h, and calculate their distances and peculiar velocities with the
Iterative Normalized Distance method. Within this method we can derive an
analytical formula, independent from the density inhomogeneities, for
correcting the selection biases. The radial peculiar velocities can then be
derived from the redshifts and the corrected distances. The velocities are
smoothed, and the smoothed velocity field is used as a correction term at the
next derivation of normalized distances. This iterative procedure is repeated
until converging values are reached. Here we present the resulting map of the
radial peculiar velocity field at the < 80 Mpc/h environment. The infall
patterns towards the main galaxy clusters are clearly visible. The color
version of the map, other figures, and animations are provided on the project
web site
On the quiescence of the Hubble flow in the vicinity of the Local Group
Cepheid distances of local galaxies (<7 Mpc) are used to study the very
nearby velocity field, as pioneered by Sandage (Sandage 1986) who also pointed
out its remarkable properties: linearity and quietness. The new data show that
the velocity dispersion in the distance range as seen from the barycentre of
the Local Group 1-8 Mpc is as low as 38 km/sec. The local rate of expansion
coincides with the global Hubble constant. Down to 1.5 Mpc we cannot detect a
deviation from the linear Hubble flow. This puts an upper limit for the mass of
the Local Group, for a wide class of Friedman models, including those with the
cosmological constant.Comment: 4 pages, 3 figures. Accepted to Astron. Astrophys. Letter
Unexpectedly diverse forest dung beetle communities in degraded rain forest landscapes in Madagascar
Tropical forests, which harbor high levels of biodiversity, are being lost at an alarming speed. Madagascar, a biodiversity hotspot, has lost more than half of its original forest cover. Most of the remaining forests are small fragments of primary and secondary forest with differing degrees of human impact. These forests, as well as coffee and fruit plantations, may be important in supporting the forest-dependent biodiversity in Madagascar but this has been little studied. In Madagascar, dung beetles, which offer important ecosystem services, are largely restricted to forests. We examined the ability of fragmented and degraded forests to support dung beetle diversity, compared to the large areas of primary forest in eastern Madagascar. We found a general trend of a reduction of species with a loss of forest connectivity. In contrast, a higher level of forest disturbance was associated with higher species diversity. In several sites of low-quality forest as many or more species were found as in less disturbed and primary forests. The average size of dung beetles was smaller in the lower quality localities than in the primary forests. These findings suggest that many forest dung beetles in Madagascar are better adapted to forest disturbance than earlier expected, although they require some level of connectivity to surrounding forest. in Malagasy is available with online material.Peer reviewe
Scaling up the effects of inbreeding depression from individuals to metapopulations
Abstract Inbreeding is common in nature, and many laboratory studies have documented that inbreeding depression can reduce the fitness of individuals. Demonstrating the consequences of inbreeding depression on the growth and persistence of populations is more challenging because populations are often regulated by density- or frequency-dependent selection and influenced by demographic and environmental stochasticity. A few empirical studies have shown that inbreeding depression can increase extinction risk of local populations. The importance of inbreeding depression at the metapopulation level has been conjectured based on population-level studies but has not been evaluated. We quantified the impact of inbreeding depression affecting the fitness of individuals on metapopulation persistence in heterogeneous habitat networks of different sizes and habitat configuration in a context of natural butterfly metapopulations. We developed a spatial individual-based simulation model of metapopulations with explicit genetics. We used Approximate Bayesian Computation to fit the model to extensive demographic, genetic, and life-history data available for the well-studied Glanville fritillary butterfly (Melitaea cinxia) metapopulations in the Ă
land islands in SW Finland. We compared 18 semi-independent habitat networks differing in size and fragmentation. The results show that inbreeding is more frequent in small habitat networks, and consequently, inbreeding depression elevates extinction risks in small metapopulations. Metapopulation persistence and neutral genetic diversity maintained in the metapopulations increase with the total habitat amount in and mean patch size of habitat networks. Dispersal and mating behavior interact with landscape structure to determine how likely it is to encounter kin while looking for mates. Inbreeding depression can decrease the viability of small metapopulations even when they are strongly influenced by stochastic extinction-colonization dynamics and density-dependent selection. The findings from this study support that genetic factors, in addition to demographic factors, can contribute to extinctions of small local populations and also of metapopulations. This article is protected by copyright. All rights reserved.Peer reviewe
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How predation and landscape fragmentation affect vole population dynamics
Background: Microtine species in Fennoscandia display a distinct north-south gradient from regular cycles to stable
populations. The gradient has often been attributed to changes in the interactions between microtines and their predators.
Although the spatial structure of the environment is known to influence predator-prey dynamics of a wide range of species,
it has scarcely been considered in relation to the Fennoscandian gradient. Furthermore, the length of microtine breeding
season also displays a north-south gradient. However, little consideration has been given to its role in shaping or generating
population cycles. Because these factors covary along the gradient it is difficult to distinguish their effects experimentally in
the field. The distinction is here attempted using realistic agent-based modelling.
Methodology/Principal Findings: By using a spatially explicit computer simulation model based on behavioural and
ecological data from the field vole (Microtus agrestis), we generated a number of repeated time series of vole densities
whose mean population size and amplitude were measured. Subsequently, these time series were subjected to statistical
autoregressive modelling, to investigate the effects on vole population dynamics of making predators more specialised, of
altering the breeding season, and increasing the level of habitat fragmentation. We found that fragmentation as well as the
presence of specialist predators are necessary for the occurrence of population cycles. Habitat fragmentation and predator
assembly jointly determined cycle length and amplitude. Length of vole breeding season had little impact on the
oscillations.
Significance: There is good agreement between our results and the experimental work from Fennoscandia, but our results
allow distinction of causation that is hard to unravel in field experiments. We hope our results will help understand the
reasons for cycle gradients observed in other areas. Our results clearly demonstrate the importance of landscape
fragmentation for population cycling and we recommend that the degree of fragmentation be more fully considered in
future analyses of vole dynamics
Host--parasite models on graphs
The behavior of two interacting populations, ``hosts''and ``parasites'', is
investigated on Cayley trees and scale-free networks. In the former case
analytical and numerical arguments elucidate a phase diagram, whose most
interesting feature is the absence of a tri-critical point as a function of the
two independent spreading parameters. For scale-free graphs, the parasite
population can be described effectively by
Susceptible-Infected-Susceptible-type dynamics in a host background. This is
shown both by considering the appropriate dynamical equations and by numerical
simulations on Barab\'asi-Albert networks with the major implication that in
the termodynamic limit the critical parasite spreading parameter vanishes.Comment: 10 pages, 6 figures, submitted to PRE; analytics redone, new
calculations added, references added, appendix remove
Kinematics of the Local Universe XIII. 21-cm line measurements of 452 galaxies with the Nan\c{c}ay radiotelescope, JHK Tully-Fisher relation and preliminary maps of the peculiar velocity field
This paper presents 452 new 21-cm neutral hydrogen line measurements carried
out with the FORT receiver of the meridian transit Nan\c{c}ay radiotelescope
(NRT) in the period April 2003 -- March 2005. This observational programme is
part of a larger project aiming at collecting an exhaustive and
magnitude-complete HI extragalactic catalogue for Tully-Fisher applications
(the so-called KLUN project, for Kinematics of the Local Universe studies, end
in 2008). The whole on-line HI archive of the NRT contains today reduced
HI-profiles for ~4500 spiral galaxies of declination delta > -40°
(http://klun.obs-nancay.fr). As an example of application, we use direct
Tully-Fisher relation in three (JHK) bands in deriving distances to a large
catalog of 3126 spiral galaxies distributed through the whole sky and sampling
well the radial velocity range between 0 and 8000 km/s. Thanks to an iterative
method accounting for selection bias and smoothing effects, we show as a
preliminary output a detailed and original map of the velocity field in the
Local Universe
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