192 research outputs found
Uncovering the Role of Propagule Pressure in Determining Establishment Success Using a Synthetic Biology Approach
The spread of invasive species poses a major ecological and economical threat. Consequently there are ongoing efforts to develop a generalizable mechanism to predict establishment success of non-native species. One proposed mechanism to predict establishment success is propagule pressure, which is defined as the number of individuals introduced at a given time. Although some studies have demonstrated a positive correlation between propagule pressure and establishment success, others have not, and the effect of propagule pressure on establishment success remains unclear. To address this challenge, a strain of bacteria engineered with an Allee effect, a growth dynamic that is often associated with establishing species, was used. The timing between successive introduction events that resulted in establishment success was measured. It was observed that if the time between two introduction events was sufficiently long, growth did not occur. By manipulating the growth rate of the bacteria, it was shown that that the minimal time between the two introduction events that resulted in growth was constrained as growth rate decreased. Moreover, it was concluded that asymmetry in the density of bacteria introduced in the introduction events increased the maximum time between introduction events that resulted in growth. These results help to remedy conflicting data in the literature by identifying conditions where propagule pressure has, and does not have, a positive impact on establishment success. These findings can have major implications in understanding and predicting the unique population dynamics of invasive species
Demonstrating Diversity in Star Formation Histories with the CSI Survey
We present coarse but robust star formation histories (SFHs) derived from
spectro-photometric data of the Carnegie-Spitzer-IMACS Survey, for 22,494
galaxies at 0.3<z<0.9 with stellar masses of 10^9 Msun to 10^12 Msun. Our study
moves beyond "average" SFHs and distribution functions of specific star
formation rates (sSFRs) to individually measured SFHs for tens of thousands of
galaxies. By comparing star formation rates (SFRs) with timescales of 10^10,
10^9, and 10^8 years, we find a wide diversity of SFHs: 'old galaxies' that
formed most or all of their stars early; galaxies that formed stars with
declining or constant SFRs over a Hubble time, and genuinely 'young galaxies'
that formed most of their stars since z=1. This sequence is one of decreasing
stellar mass, but, remarkably, each type is found over a mass range of a factor
of 10. Conversely, galaxies at any given mass follow a wide range of SFHs,
leading us to conclude that: (1) halo mass does not uniquely determine SFHs;
(2) there is no 'typical' evolutionary track; and (3) "abundance matching" has
limitations as a tool for inferring physics. Our observations imply that SFHs
are set at an early epoch, and that--for most galaxies--the decline and
cessation of star formation occurs over a Hubble-time, without distinct
"quenching" events. SFH diversity is inconsistent with models where galaxy
mass, at any given epoch, grows simply along relations between SFR and stellar
mass, but is consistent with a 2-parameter lognormal form, lending credence to
this model from a new and independent perspective.Comment: 17 pages, 10 figures; accepted by ApJ; version 2 - no substantive
changes; clarifications and correction
The Coma - Leo I Distance Ratio and the Hubble Constant
The diameter - velocity dispersion relation in B, V, and K for three
early-type galaxies in the Leo I (M96) group is derived from published
photometry and kinematic data. The relations in all three colors have slopes
which agree well with those for the Coma cluster. The RMS scatter of the Leo I
galaxies in each color is extremely small, consistent with the group's
compactness. These relations yield estimates of the Coma-Leo I distance ratio
of 9.01 +/- 0.51, 8.77 +/- 0.43, and 8.82 +/- 0.31, respectively, with a
weighted mean of 8.84 +/- 0.23. The general agreement among the three colors
indicates that the early-type galaxies in Leo I and Coma have similar stellar
populations.
The Coma-Leo I distance ratio coupled with estimates of the absolute distance
to the Leo I group allows the Hubble constant to be determined, free of the
uncertainties which arise when working with the Virgo cluster. Several high
quality distance estimates are available from a variety of techniques: Cepheids
in M96 (Tanvir et al. 1995) and M95 (Graham et al. 1997), surface brightness
fluctuations (Tonry et al. 1997), planetary nebulae luminosity functions
(Ciardullo et al. 1993), and the luminosity of the red giant branch tip (Sakai,
Freedman, & Madore 1996). Adopting a cosmic recession velocity of the Coma
cluster in the microwave background frame of 7200 +/- 300 km/s, these distance
estimates lead to values of the Hubble constant ranging from 70 to 81 km/s/Mpc,
with an unweighted mean of 75 +/- 6 km/s/Mpc.Comment: To appear in New Astronomy; 15 pages including 3 figures and 2 table
«Consonancia cultural»: una teoría y un método para el estudio de la cultura y la salud
Both as a theoretical concept and a method for the study of culture, ‘cultural consonance’ is wellestablished in the cognitive anthropological literature of the United States. It is also well represented in Latin American literature, but generally not in European anthropology. To date, cultural consonance has mainly been used in research into the relationship between culture and health, but it is perfectly applicable to other cultural domains. The theoretical source of this concept is the theory of cultural consensus and it seeks to resolve, in an operational manner, some of the classic dilemmas of the concept of culture. This paper seeks to demonstrate its theoretical and methodological utility and to present its current state of development in medical anthropological investigations into the relationship between culture and health. In short, we seek to highlight and disseminate the potential of ‘cultural consonance’ for the study of culture, both within the area of medical anthropology and beyond.La consonancia cultural, como concepto teórico y método para el estudio de la cultura, tiene ya una sólida trayectoria en la literatura antropológica norteamericana de orientación cognitiva, con apreciables ejemplos también en la antropología latinoamericana, aunque muchos menos en la europea. Por ahora, la consonancia cultural ha sido empleada mayoritariamente en la investigación sobre las relaciones entre cultura y salud, pero podría ser perfectamente aplicable a otros dominios culturales. Tiene su fuente teórica primordial en la teoría del consenso cultural y trata como ésta de resolver, operativamente, algunos de los dilemas clásicos del concepto de cultura. Este artículo pretende mostrar su utilidad teórica y metodológica, y dar cuenta del estado en que se encuentra su desarrollo científico, a través de diversas investigaciones en el campo de la antropología médica. En otras palabras, queremos poner de relieve y difundir las potencialidades de la consonancia cultural para el estudio de la cultura, tanto en ése como en otros campos de la investigación antropológica
Evolution in the Disks and Bulges of Group Galaxies since z=0.4
We present quantitative morphology measurements of a sample of optically
selected group galaxies at 0.3 < z < 0.55 using the Hubble Space Telescope
(HST) Advanced Camera for Surveys (ACS) and the GIM2D surface
brightness--fitting software package. The group sample is derived from the
Canadian Network for Observational Cosmology Field Redshift survey (CNOC2) and
follow-up Magellan spectroscopy. We compare these measurements to a similarly
selected group sample from the Millennium Galaxy Catalogue (MGC) at 0.05 < z <
0.12. We find that, at both epochs, the group and field fractional bulge
luminosity (B/T) distributions differ significantly, with the dominant
difference being a deficit of disk--dominated (B/T < 0.2) galaxies in the group
samples. At fixed luminosity, z=0.4 groups have ~ 5.5 +/- 2 % fewer
disk--dominated galaxies than the field, while by z=0.1 this difference has
increased to ~ 19 +/- 6 %. Despite the morphological evolution we see no
evidence that the group environment is actively perturbing or otherwise
affecting the entire existing disk population. At both redshifts, the disks of
group galaxies have similar scaling relations and show similar median
asymmetries as the disks of field galaxies. We do find evidence that the
fraction of highly asymmetric, bulge--dominated galaxies is 6 +/- 3 % higher in
groups than in the field, suggesting there may be enhanced merging in group
environments. We replicate our group samples at z=0.4 and z=0 using the
semi-analytic galaxy catalogues of Bower et al (2006). This model accurately
reproduces the B/T distributions of the group and field at z=0.1. However, the
model does not reproduce our finding that the deficit of disks in groups has
increased significantly since z=0.4.Comment: Accepted for publication in MNRAS. 20 pages, 17 figure
Matching the Evolution of the Stellar Mass Function Using Log-Normal Star Formation Histories
We show that a model consisting of individual, log-normal star formation histories for a volume-limited sample of z ≈ 0 galaxies reproduces the evolution of the total and quiescent stellar mass functions at z ≲ 2.5 and stellar masses {{M}*}≥slant {{10}10} {{M}☉ }. This model has previously been shown to reproduce the star formation rate/stellar mass relation (SFR-{{M}*}) over the same interval, is fully consistent with the observed evolution of the cosmic SFR density at z≤slant 8, and entails no explicit “quenching” prescription. We interpret these results/features in the context of other models demonstrating a similar ability to reproduce the evolution of (1) the cosmic SFR density, (2) the total/quiescent stellar mass functions, and (3) the SFR-{{M}*} relation, proposing that the key difference between modeling approaches is the extent to which they stress/address diversity in the (star-forming) galaxy population. Finally, we suggest that observations revealing the timescale associated with dispersion in SFR({{M}*}) will help establish which models are the most relevant to galaxy evolution
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