Abundance Distribution Function Research Articles

Differential response of mammals to agricultural fences — The effects of species vagility and body size

An increase in wolf populations during the 1990s in North-Eastern Israel compelled livestock growers to establish fenced calving enclosures to minimize cattle predation. We hypothesized that such fences form barriers to animals traversing the landscape, to which various wildlife species may respond differentially. In order to test this, an array of line transects were established near six enclosures at which scat pellets were monitored for 23 months. We identified 1496 pellets, belonging mainly to medium or large mammal species. To estimate pellet abundance and quantify mammal activity levels we used N-mixture models. We tested the performance of seven models assuming two abundance distribution functions: Poisson and zero-inflated Poisson (ZIP) distribution models which evaluated different combinations of explanatory variables: effects of time, enclosure and transect. Model selection was performed using the Akaike Information Criterion (AIC). Pellet counts and mean estimated abundance were greater in transects external to the enclosures, for all species combined, mountain gazelle (Gazella gazella) and wild boar (Sus scrofa). Additionally, two behavioral responses to the presence of protective fences were observed. Outside the enclosures a U-shaped response of decrease in abundance at a distance of 50m from the fence followed by an increase towards the distant transects at 200–700m from the fence. Inside the calving enclosures a decreasing abundance response was observed, which was negatively correlated with distance from the fence. This study identifies the spatial effects emerging from the presence of protective fences as habitat-fragmenting agents. It suggests that a protective fence imposes a habitat-independent behavioral filter at the landscape level which could be related to species vagility and body size. Inconsistent activity responses of the different species to the presence of fences are repeatedly observed, providing support for our initial hypothesis.

Composite stellar populations and element by element abundances in the Milky Way bulge and elliptical galaxies

This paper explores the integrated-light characteristics of the Milky Way (MW) bulge and to what extent they match those of elliptical galaxies in the local universe. We model composite stellar populations with realistic abundance distribution functions (ADFs), tracking the trends of individual elements as a function of overall heavy element abundance as actually observed in MW bulge stars. The resultant predictions for absorption feature strengths from the MW bulge mimic elliptical galaxies better than solar neighborhood stars do, but the MW bulge does not match elliptical galaxies, either. Comparing bulge versus elliptical galaxies, Fe, Ti, and Mg trend about the same for both but C, Na, and Ca seem irreconcilably different. Exploring the behavior of abundance compositeness leads to the concepts of "red lean" where a narrower ADF appears more metal rich than a wide one, and "red spread" where the spectral difference between wide and narrow ADFs increases as the ADF peak is moved to more metal-rich values. Tests on the systematics of recovering abundance, abundance pattern, and age from composite stellar populations using single stellar population models were performed. The chemical abundance pattern was recovered adequately, though a few minor systematic effects were uncovered. The prospects of measuring the width of the ADF of an old stellar population were investigated and seem bright using UV to IR photometry.

Robust computational analysis of rRNA hypervariable tag datasets.

Next-generation DNA sequencing is increasingly being utilized to probe microbial communities, such as gastrointestinal microbiomes, where it is important to be able to quantify measures of abundance and diversity. The fragmented nature of the 16S rRNA datasets obtained, coupled with their unprecedented size, has led to the recognition that the results of such analyses are potentially contaminated by a variety of artifacts, both experimental and computational. Here we quantify how multiple alignment and clustering errors contribute to overestimates of abundance and diversity, reflected by incorrect OTU assignment, corrupted phylogenies, inaccurate species diversity estimators, and rank abundance distribution functions. We show that straightforward procedural optimizations, combining preexisting tools, are effective in handling large () 16S rRNA datasets, and we describe metrics to measure the effectiveness and quality of the estimators obtained. We introduce two metrics to ascertain the quality of clustering of pyrosequenced rRNA data, and show that complete linkage clustering greatly outperforms other widely used methods.

Linking individual behaviour to community scale patterns in fungi

Abstract The fungi comprise a separate kingdom of life and epitomise the indeterminate growth form. Very little is known about the factors that influence the nature of fungal diversity and the link between individual behaviour and the structure and function of fungal communities is particularly poorly understood. Here, we present a theoretical framework that is capable of elucidating this link. An individual-based model for fungal community dynamics is introduced that has been developed from a physiologically based model for the fungal phenotype. The model is used to explore the role of individual interactions, the production of an external inhibitor field and the quality of the external environment on the structure and diversity of the resulting community. We show that traits relating to growth rate, autophagic behaviour and the production of inhibitors are key in influencing the success of a particular genotype in a community. The species richness increases with the amount of available resource. This is the first model of fungal community dynamics that introduces the concept of a biomass-based abundance distribution function that can be described by the log-normal form which typically corresponds to communities in equilibrium. The species abundance curve was stable to changes in the relative location of inocula, although the ranked abundance of the individuals was not. We present the first attempt to identify the traits that affect the form of that curve. Future studies should examine the role of environmental heterogeneity and spore dispersal.

CHEMICAL SIGNATURE OF A MAJOR MERGER IN THE EARLY FORMATION OF THE SMALL MAGELLANIC CLOUD

The formation history of the Small Magellanic Cloud (SMC) is unraveled based on the results of our new chemical evolution models constructed for the SMC, highlighting the observed anomaly in the age–metallicity relation for star clusters in the SMC. We first propose that evidence of a major merger is imprinted in the age–metallicity relation as a dip in [Fe/H]. Our models predict that the major merger with a mass ratio of 1:1 to 1:4 occurred at ∼7.5 Gyr ago, with a good reproduction of the abundance distribution function of field stars in the SMC. Furthermore, our models predict a relatively large scatter in [Mg/Fe] for −1.4 ⩽ [Fe/H] ⩽ −1.1 as a reflection of a looping feature resulting from the temporally inverse progress of chemical enrichment, which can be tested against future observational results. Given that the observed velocity dispersion (∼30 km s−1) of the SMC is much smaller than that (∼160 km s−1) of the Galactic halo, our finding strongly implies that the predicted merger event happened in a small group environment that was far from the Galaxy and contained a number of small gas-rich dwarfs comparable to the SMC. This theoretical view is extensively discussed in the framework that considers a connection with the formation history of the Large Magellanic Cloud.

Fossil Imprints of Outflow from the Galactic Bulge in Elemental Abundances of Metal-rich Disk Stars

We explore the elemental abundance features of metal-rich disk stars, highlighting the comparisons made with those of the recently revealed Galactic bulge stars. A similarity between two of the comparisons leads to a new theoretical picture of the bulge-disk connection in the Galaxy, where a supermassive black hole resides at the center. We postulate that a metal-rich outflow, triggered by feedback from a black hole, was generated and quenched the star formation, which had lasted several billion years in the bulge. The expelled gas cooled down in the Galactic halo without escaping from the gravitational potential of the Galaxy. The gas gradually started to accrete to the disk around five billion years ago, corresponding to the time of sun's birth, and replaced a low-metallicity halo gas that had been accreting over nearly ten billion years. The metal-rich infalling gas, whose elemental abundance reflects that of metal-rich bulge stars, mixed with the interstellar gas already present in the disk. Stars formed from the mixture compose the metal-rich stellar disk. This scheme is incorporated into models for chemical evolution of the disk. The resultant elemental features are compatible with the observed abundance trends of metal-rich disk stars, including the upturning feature exhibited in some [X/Fe] ratios, whose interpretation was theoretically puzzling. Furthermore, the predicted abundance distribution function of disk stars covers all observational facts to be considered: (i) the deficiency of metal-poor stars, (ii) the location of peak, and (iii) the extended metal-rich tail up to [Fe/H] ~ +0.4.

Chemical Abundance Distributions of Galactic Halos and Their Satellite Systems in a ΛCDM Universe

We present a cosmologically motivated model for the hierarchical formation of the stellar halo that includes a semianalytic treatment of galactic chemical enrichment coupled to numerical simulations that track the orbital evolution and tidal disruption of satellites. A major motivating factor in this investigation is the observed systematic difference between the chemical abundances of stars in satellite galaxies and those in the Milky Way halo. Specifically, for the same [Fe/H] values, stars in neighboring satellite galaxies display significantly lower [α/Fe] ratios than stars in the halo. We find that the observed chemical abundance patterns are a natural outcome of the process of hierarchical assembly of the Galaxy. This result follows because the stellar halo in this context is built up from satellite galaxies accreted early on (more than 8-9 Gyr ago) and enriched in α-elements produced in Type II supernovae. In contrast, satellites that still survive today are typically accreted late (within the last 4-5 Gyr) with nearly solar [α/Fe] values as a result of contributions from both Type II and Type Ia supernovae. We use our model to investigate the abundance distribution functions (using both [Fe/H] and [α/Fe] ratios) for stars in the halo and in surviving satellites. Our results suggest that the shapes and peaks in the abundance distribution functions provide a direct probe of the accretion histories of galaxies.

The Lifetime of Type Ia Supernova Progenitors Deduced from the Chemical Evolution in the Solar Neighborhood

view Abstract Citations (136) References (60) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Lifetime of Type Ia Supernova Progenitors Deduced from the Chemical Evolution in the Solar Neighborhood Yoshii, Yuzuru ; Tsujimoto, Takuji ; Nomoto, Ken'ichi Abstract Using the chemical evolution model which allows the material infall from outside the disk region, we have determined the lifetime tIa of Type Ia supernova progenitors and the timescale tin of the infall that simultaneously reproduce the major observational features in the solar neighborhood, such as the evolutionary change in [O/Fe] against [Fe/H] and the [Fe/H] abundance distribution function of long-lived stars. A full survey in the parameter space, including the linear and nonlinear relations between the star formation rate and the gas density, shows that a value of [Fe/H] at which the [0/Fe] break occurs is sensitive mostly to tIain. This decoupling enables a reliable determination of tIa from the [O/Fe] break almost independently of tinIa ∼1.5 Gyr from the observed [O/Fe] break at [Fe/H] ∼-1 and tin ∼5 Gyr from the observed paucity of long-lived stars below [Fe/H] ∼-1 in the solar neighborhood. We have furthermore examined what would happen if the lifetime of SN Ia progenitors has a range using some heuristic distribution functions of tIa. We conclude from extensive calculations that its range is strictly confined within tIa = 0.5-3 Gyr, otherwise it is ruled out by the data. In addition, comparing the 0 and Fe yields determined by the chemical evolution model with the supernova nucleosynthesis yields, we discuss the mass range of the IMF and the mass fraction of SN Ia progenitors which can be expressed in terms of the IMF slope index. Publication: The Astrophysical Journal Pub Date: May 1996 DOI: 10.1086/177147 Bibcode: 1996ApJ...462..266Y Keywords: GALAXY: ABUNDANCES; GALAXY: EVOLUTION; STARS: EVOLUTION; STARS: STATISTICS; STARS: SUPERNOVAE: GENERAL full text sources ADS |

Chemical evolution of primary elements in the Galactic disc: an analytical model

We model the evolution of abundances of oxygen, iron, α and r-process elements in the Galactic disc using the instantaneous and delayed production approximations which enable the problem to be handled analytically. In addition to using the new greatly improved data published by Edvardsson et al. and the oxygen abundance distribution function of G dwarfs in the solar neighbourhood as improved by Sommer-Larsen, we take into account new survey data on metal-deficient stars which show that the thick-disc population extends to arbitrarily low metallicities, meaning that a significant proportion of stars previously classified as belonging to the halo, on grounds of low metallicity, actually belong to the disc and should be modelled as such, without bringing in any prior phase associated with the halo. Comparison with theoretical yields from Type II and Type Ia supernovae shows good agreement, as has previously been found by Tsujimoto et al. using a different approach.

Inhomogeneous chemical evolution of the Galactic disk

We present analytical models for inhomogeneous chemical evolution (ICE) of systems in which the star formation history resembles a series of bursts, localized in space and/or time, with intermittent periods of remixing. The additional parameter of this model is the metallicity increment of bursting subsystems, but this parameter is constrained by the spread in the age-metallicity relation. We apply this model to the solar annulus in the Galactic disk and show that ICE models yield an improved fit to the observed shape of the stellar abundance distribution function (ADF). The G-dwarf problem can be alleviated with ICE models, but infall of metal poor gas and/or some preenrichment of the disk during the epoch of protogalactic evolution is still required to explain the paucity of low-metallicity dwarfs. ICE models also suggest an explanation of the reduced frequency of metal-rich G-dwarfs relative to the predictions of the simple model. It does not seem likely that chemical evolution of the solar annulus proceeded in a medium that was well-mixed at all times.

SPH Simulations of the Chemical and Dynamical Evolution of the Galactic Bulge

We simulate the chemical and dynamical evolution of the galactic bulge with the smoothed particle hydrodynamics (SPH) method. We calculate the early phase of galaxy formation in which the bulge is formed through a burst of star formation. The calculated abundance distribution function of stars in the bulge is consistent with the observations of bulge K giants, if the heavy element yields are three times larger than those expected from Salpeter's IMF.

Analysis of adsorbate-substrate configuration by admolecule-probe field emission microscopy

By means of field electron emission microscopy with Faraday collector and magnetic deflection the emission current fluctuations between two or more levels caused by single Cu-phthalocyanine admolecules have been recorded. Relative abundance distribution functions of the times of sojourn in distinct adsorption states are given. From measurements at various temperatures in case of stationary fluctuations Arrhenius plots of the mean time of sojourn were obtained. They yield the energy differences E i between trough and saddle positions of single admolecules as well as the preexponential factors A i and the entropy differences Δ S i, respectively, according to the Frenkel equation τ i = A i exp( E i /kT ) = ( h kT ) exp(− ΔS i k ) exp ( E i kT ) . The average values and standard deviations of all measurements are E i = 0.22 eV, σ E i = = 0.11 eV, and log A i = −6.0, σ log A i = 1.6. The use of Cu-phthalocyanine as a molecular probe to investigate and characterize the adsorbate-substrate configuration, is discussed.