Abundance Gradients Research Articles

Plant invasion alters trait composition and diversity across habitats.

Increased globalization has accelerated the movement of species around the world. Many of these nonnative species have the potential to profoundly alter ecosystems. The mechanisms underpinning this impact are often poorly understood, and traits are often overlooked when trying to understand and predict the impacts of species invasions on communities. We conducted an observational field experiment in Canada's first National Urban Park, where we collected trait data for seven different functional traits (height, stem width, specific leaf area, leaf percent nitrogen, and leaf percent carbon) across an abundance gradient of the invasive Vincetoxicum rossicum in open meadow and understory habitats. We assessed invasion impacts on communities, and associated mechanisms, by examining three complementary functional trait measures: community‐weighted mean, range of trait values, and species’ distances to the invader in trait space. We found that V. rossicum invasion significantly altered the functional structure of herbaceous plant communities. In both habitats V. rossicum changed the community‐weighted means, causing invaded communities to become increasingly similar in their functional structure. In addition, V. rossicum also reduced the trait ranges for a majority of traits indicating that species are being deterministically excluded in invaded communities. Further, we observed different trends in the meadow and understory habitats: In the understory, resident species that were more similar to V. rossicum in multivariate trait space were excluded more, however this was not the case in the meadow habitat. This suggests that V. rossicum alters communities uniquely in each habitat, in part by creating a filter in which only certain resident species are able to persist. This filtering process causes a nonrandom reduction in species' abundances, which in turn would be expected to alter how the invaded ecosystems function. Using trait‐based frameworks leads to better understanding and prediction of invasion impacts. This novel framework can also be used in restoration practices to understand how invasion impacts communities and to reassemble communities after invasive species management.

Spatial Gradients of Fungal Abundance and Ecology throughout a Damp Building

Dampness and fungal (mold) growth in buildings is a persistent environmental health problem. This study sought to determine the extent to which fungi grown on damp materials are distributed throughout a single family home. Samples were collected from fungi growing directly on building materials in the basement (direct mold), and, as a proxy for indoor and outdoor air, settled dust was collected from the top of door frames (basement, first, and second floor, exterior). Direct mold in the basement influenced both the fungal richness and ecology of air throughout the building. Fungal communities clustered by sample type (ANOSIM R=0.62, p-value=0.001) and floor (indoor samples: ANOSIM R=0.58, p-value=0.001) with the direct mold ecologies dominated by taxa (i.e. Sterigmatomyces, Stachybotrys, Aspergillus) associated with mold growth on building materials, and not present in outdoor samples. The relative abundances of these highly enriched direct mold taxa were also found to be inversely correlated to the dista...

Yule-Simpson’s paradox in Galactic Archaeology

Simpson's paradox, or Yule-Simpson effect, arises when a trend appears in different subsets of data but disappears or reverses when these subsets are combined. We describe here seven cases of this phenomenon for chemo-kinematical relations believed to constrain the Milky Way disk formation and evolution. We show that interpreting trends in relations, such as the radial and vertical chemical abundance gradients, the age-metallicity relation, and the metallicity-rotational velocity relation (MVR), can lead to conflicting conclusions about the Galaxy past if analyses marginalize over stellar age and/or birth radius. It is demonstrated that the MVR in RAVE giants is consistent with being always strongly negative, when narrow bins of [Mg/Fe] are considered. This is directly related to the negative radial metallicity gradients of stars grouped by common age (mono-age populations) due to the inside out disk formation. The effect of the asymmetric drift can then give rise to a positive MVR trend in high-[alpha/Fe] stars, with a slope dependent on a given survey's selection function and observational uncertainties. We also study the variation of lithium abundance, A(Li), with [Fe/H] of AMBRE:HARPS dwarfs. A strong reversal in the positive A(Li)-[Fe/H] trend of the total sample is found for mono-age populations, flattening for younger groups of stars. Dissecting by birth radius shows strengthening in the positive A(Li)-[Fe/H] trend, shifting to higher [Fe/H] with decreasing birth radius; these observational results suggest new constraints on chemical evolution models. This work highlights the necessity for precise age estimates for large stellar samples covering wide spatial regions.

Radial abundance gradients in the outer Galactic disk as traced by main-sequence OB stars

Context. Elemental abundance gradients in galactic disks are important constraints for models of how spiral galaxies form and evolve. However, the abundance structure of the outer disk region of the Milky Way is poorly known, which hampers our understanding of the spiral galaxy that is closest to us and that can be studied in greatest detail. Young OB stars are good tracers of the present-day chemical abundance distribution of a stellar population and because of their high luminosities they can easily be observed at large distances, making them suitable to explore and map the abundance structure and gradients in the outer regions of the Galactic disk. Aims. Using a sample of 31 main-sequence OB stars located between galactocentric distances 8.4−15.6 kpc, we aim to probe the present-day radial abundance gradients of the Galactic disk. Methods. The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m telescope on Las Campanas. We used a non-NLTE analysis in a self-consistent semi-automatic routine based on TLUSTY and SYNSPEC to determine atmospheric parameters and chemical abundances. Results. Stellar parameters (effective temperature, surface gravity, projected rotational velocity, microturbulence, and macroturbulence) and silicon and oxygen abundances are presented for 28 stars located beyond 9 kpc from the Galactic center plus three stars in the solar neighborhood. The stars of our sample are mostly on the main-sequence, with effective temperatures between 20 800−31 300 K, and surface gravities between 3.23−4.45 dex. The radial oxygen and silicon abundance gradients are negative and have slopes of −0.07 dex kpc−1 and −0.09 dex kpc−1, respectively, in the region 8.4 ≤ RG ≤ 15.6 kpc. Conclusions. The obtained gradients are compatible with the present-day oxygen and silicon abundances measured in the solar neighborhood and are consistent with radial metallicity gradients predicted by chemodynamical models of Galaxy Evolution for a subsample of young stars located close to the Galactic plane.

Carbon isoscapes of rodent diets in the Great Plains USA deviate from regional gradients in C4 grass abundance due to a preference for C3 plant resources

Diet is an ecological attribute that species may adjust to cope with changing environments and may indicate how a population responds to changes in resource availability. In the Great Plains, plants utilizing the C4 photosynthetic pathway may increase in abundance in the future because of their high tolerance for warm and dry environments, which are projected to increase. How increased C4 abundance will influence grassland food webs remains unknown.Here, we evaluate how rodent diets vary relative to C4 plant biomass at the regional scale of the southern Great Plains in the U.S. We measured δ13C values of hair from 534 individuals of 14 rodent species. Resulting isoscapes of δ13C values were statistically compared to three proxies for local abundance of C4 grasses across the region.Overall, diets of most rodent species were dominated by C3-derived resources with a few species relying on C4 resources. Ordinary least squares linear regressions indicate that proxies for regional abundance of C4 grasses explain very little of the variance in δ13C values in hair for the entire rodent community, however the isoscape of rodent hair δ13C values does broadly correspond to that for δ13C values of soil organic matter. The difference between median δ13C values of granivores and folivores is significantly and highly correlated with SOM δ13C values.Results from this study can be used as a baseline for characterizing dietary shifts in response to environmental change both in the geological past and in the future, and they identify which dietary categories may be most sensitive to future changes in the regional abundance of C4 grasses.

Spectral observations of the systems with the disturbed spiral arms: Arp 42, Arp 82, and Arp 58

We study three Arp' systems of peculiar galaxies: Arp 42 (NGC 5829), Arp 82 (NGC 2535/36) and Arp 58 (UGC 4457), using the long-slit spectral observations carried out at the 6m telescope BTA of Special Astrophysical Observatory. Arp 82 and Arp 58 are the M51-type systems. In the third system - Arp 42, there are two extremely luminous kpc-sized clumps observed at the ends of the bifurcated spiral arm, however the source of perturbations remains unknown. From the emission line measurements we analyzed the distribution of gas line-of-sight (LOS) velocity, velocity dispersion and gas-phase metallicity along the slits estimated by different methods. A special attention is paid to the young regions of star formation at the peripheries of the galaxies and in tidal debris, their connection with gas kinematics and abundance. All three systems show the signs of velocity disturbances and the presence of regions of locally enhanced gas velocity dispersion, as well as the regions of diffuse ionized gas. A distribution of oxygen reveals shallow radial abundance gradients, typical for interacting systems. A faint spiral-like branches of tidal bridges which are observed in NGC 2535 and UGC 4457 may represent the remnants of pre-existing "old" mode of spiral waves.

Changes in trophic state and aquatic communities in high Arctic ponds in response to increasing goose populations

Abstract The high Arctic, including the Svalbard archipelago in the North Atlantic, has been exposed to direct and indirect drivers of climatic change such as rising temperatures and associated changes in hydrology and nutrient fluxes. In addition, the number of migrating birds, particularly geese, increased remarkably in the Svalbard archipelago during the second half of the last century. The higher number of breeding birds potentially affects water quality and the biota in ponds and lakes. We aimed to investigate the potential influence of increasing goose abundance on trophic state, taxon richness, and species composition of freshwater communities in the high Arctic. We hypothesised that higher goose abundance affects the trophic state of shallow lakes and ponds and their taxon richness and species composition. We conducted a survey of selected ponds at Svalbard along a goose abundance gradient. We used the number of area‐specific goose droppings (range of 0–94 droppings m2) as a proxy of goose presence and measured proxies for productivity as well as taxon richness and composition of phytoplankton and invertebrate communities. Presence and abundance of geese were associated with higher productivity of ponds. Invertebrate and phytoplankton taxon richness correlated (positively) with goose abundance. Both phytoplankton and invertebrate taxon richness increased with increasing nitrogen (N) concentrations. Goose abundance significantly affected phytoplankton species composition, while concentrations of total‐N and total phosphorus (P) did not. Species composition of aquatic invertebrates was most strongly affected by goose abundance, but the effect of total‐N concentration was also significant. Increased goose abundance was associated with bird driven nutrient enrichment, increased phytoplankton and invertebrate taxon richness and changes of these biological communities. Thus, in addition to climate change, the higher abundances of large migratory water fowl in many polar areas may pose a major additional stress to arctic lakes and ponds. In fact, climate change and bird impact may interact, accelerating ongoing environmental change of arctic freshwater ecosystems.

Human altered disturbance patterns and forest succession: impacts of competition and ungulate herbivory.

Human activities are altering patterns of ungulate herbivory and wildfire regimes globally with large potential impacts on plant community succession and ecosystem resilience. Aspen (Populus tremuloides) is a keystone species which co-exists with conifer species across temperate forests in North America. Aspen sucker regeneration which is the foundation of aspen-conifer forests succession is often a targeted food source by multiple ungulate species. Using a region-wide exclosure network across a broad gradient of aspen-conifer overstory abundance, we empirically tested the effects of ungulate herbivory and conifer competition (that increases with fire suppression), on the regeneration and recruitment of aspen forests over a 4-year period. The study results indicate that ungulate herbivory and increasing abundance of overstory conifers dramatically reduced aspen regeneration and recruitment success. The average height of aspen suckers exposed to ungulate herbivory was 72% shorter than aspen suckers in fenced plots and resulted in 24% less recruitment. There was a 9% decrease in aspen recruitmentand 12% decrease in averageaspen height with every 20% increase in overstory conifer density. Aspen suckers were most vulnerable to herbivory at 70cm height, with the probability of herbivory decreasing under 50cm or above 90cm. Steep slope angles and higher winter precipitation increased aspen regeneration and recruitment success. Reduction in aspen recruitment in response to ungulate herbivory and competition by conifers may result in loss of biodiversity, altered forest function and loss of key ecosystem services because of the important role that aspen plays in facilitating forest succession and biodiversity.

The Last 5 Gyr of Galactic Chemical Evolution Based on H ii Region Abundances Derived from a Temperature Independent Method

Abstract Most of the chemical evolution models are not very reliable for the last 5 Gyr of galactic evolution; this is mainly because abundance gradients found in the literature show a big dispersion for young objects; a big culprit of this is the dispersion found in H ii region gradients. Part of this dispersion arises from two different methods used to determine O/H in H ii regions: the direct method (DM), based on forbidden lines; and the temperature independent method (TIM), based on permitted lines; the differences between these two methods are about 0.25 dex. We present two chemical evolution models of our galaxy to fit the O/H gradients of H ii regions, one obtained from the DM and the other obtained from the TIM. We find that the model based on the TIM produces an excellent fit to the observational stellar constraints (B-stars, Cepheids, and the Sun), while the model based on the DM fails to reproduce them. Moreover the TIM model reproduces the flattening observed in the 3–6 kpc galactocentric range; this flattening is attained with an inside-out star formation quenching in the inner disk starting ∼9 Gyr ago.

Feeding and respiration by giant barrel sponges across a gradient of food abundance in the Red Sea

AbstractWhile sponges are well‐known to be suspension feeders, consumption of dissolved organic carbon (DOC) has recently been highlighted as a mechanism whereby sponges may avoid food limitation. Further, the sponge‐loop hypothesis proposes that sponges consume DOC and then release shed cellular detritus back to the reef benthos. We examined the carbon flux mediated by the giant barrel sponge, Xestospongia testudinaria, on reefs in the Red Sea across an inshore–offshore gradient that had previously been proposed to affect sponge nutrition in other parts of the tropics. Seawater samples were collected from the incurrent and excurrent flow of 35 sponges. Concentrations of total organic carbon and its components, DOC, live particulate organic carbon (LPOC), and detritus, were all significantly higher in incurrent seawater on inshore than offshore reefs. The diet of X. testudinaria was comprised primarily of DOC and detritus, with mean values across all reef sites of 61.5% DOC, 34.6% detritus, and 3.9% LPOC. Across the inshore–offshore gradient, there was evidence (1) of a threshold concentration of DOC (≈ 79 μmol C Lseawater−1) below which sponges ceased to be net consumers of DOC, and (2) that sponges on offshore reefs were food limited, with a mean carbon deficit relative to sponges on inshore reef sites. Sponges on offshore reef sites exhibited higher pumping rates, perhaps indicating optimal foraging for POC. As previously demonstrated for Xestospongia muta, and contrary to the sponge‐loop hypothesis, there was no evidence that X. testudinaria returned DOC to the benthos in the form of detritus.

Strength of forest edge effects on litter‐dwelling macro‐arthropods across Europe is influenced by forest age and edge properties

AbstractAimForests are highly fragmented across Western Europe, making forest edges important features in many agricultural landscapes. Forest edges are subject to strong abiotic gradients altering the forest environment and resulting in strong biotic gradients. This has the potential to change the forest's capacity to provide multiple ecosystem services such as nutrient cycling, carbon sequestration and natural pest control. Soil organisms play a key role in this perspective; however, these taxa are rarely considered in forest edge research.LocationA latitudinal gradient of 2,000 km across Western Europe.MethodsWe sampled six dominant taxa of litter‐dwelling macro‐arthropods (carabid beetles, spiders, harvestmen, centipedes, millipedes and woodlice) in forest edges and interiors of 192 forest fragments in 12 agricultural landscapes. We related their abundance and community composition to distance from the edge and the interaction with forest age, edge orientation and edge contrast (contrast between land use types at either side of the edge).ResultsThree out of six macro‐arthropod taxa have higher activity‐density in forest edges compared to forest interiors. The abundance patterns along forest edge‐to‐interior gradients interacted with forest age. Forest age and edge orientation also influenced within‐fragment compositional variation along the forest edge‐to‐interior gradient. Edge contrast influenced abundance gradients of generalist predators. In general, older forest fragments, south‐oriented edges and edges along structurally more continuous land use (lower contrast between forest and adjacent land use) resulted in stronger edge‐to‐interior gradients while recent forests, north‐oriented edges and sharp land use edges induced similarity between forest edge and interior along the forest edge‐to‐interior gradients in terms of species activity‐density and composition.Main conclusionsEdge effects on litter‐dwelling macro‐arthropods are anticipated to feedback on important ecosystem services such as nutrient cycling, carbon sequestration and natural pest control from small forest fragments.

Relations between abundance characteristics and rotation velocity for star-forming MaNGA galaxies

We derive rotation curves, surface brightness profiles, and oxygen abundance distributions for 147 late-type galaxies using the publicly available spectroscopy obtained by the MaNGA survey. Changes of the central oxygen abundance (O/H)0, the abundance at the optical radius (O/H)R25, and the abundance gradient with rotation velocity Vrot were examined for galaxies with rotation velocities from 90 km s−1 to 350 km s−1. We find that each relation shows a break at Vrot∗ ∼ 200 km s−1. The central (O/H)0 abundance increases with rising Vrot and the slope of the (O/H)0–Vrot relation is steeper for galaxies with Vrot ≲ Vrot∗. The mean scatter of the central abundances around this relation is 0.053 dex. The relation between the abundance at the optical radius of a galaxy and its rotation velocity is similar; the mean scatter in abundances around this relation is 0.081 dex. The radial abundance gradient expressed in dex/kpc flattens with the increase of the rotation velocity. The slope of the relation is very low for galaxies with Vrot ≳ Vrot∗. The abundance gradient expressed in dex/R25 is roughly constant for galaxies with Vrot ≲ Vrot∗, flattens towards Vrot∗, and then again is roughly constant for galaxies with Vrot ≳ Vrot∗. The change of the gradient expressed in terms of dex/hd (where hd is the disc scale length), in terms of dex/Re, d (where Re, d is the disc effective radius), and in terms of dex/Re, g (where Re, g is the galaxy effective radius) with rotation velocity is similar to that for gradient in dex/R25. The relations between abundance characteristics and other basic parameters (stellar mass, luminosity, and radius) are also considered.

Characterizing the radial oxygen abundance distribution in disk galaxies

Context. The relation between the radial oxygen abundance distribution (gradient) and other parameters of a galaxy such as mass, Hubble type, and a bar strength, remains unclear although a large amount of observational data have been obtained in the past years. Aims. We examine the possible dependence of the radial oxygen abundance distribution on non-axisymmetrical structures (bar/spirals) and other macroscopic parameters such as the mass, the optical radius R25, the color g − r, and the surface brightness of the galaxy. A sample of disk galaxies from the third data release of the Calar Alto Legacy Integral Field Area Survey (CALIFA DR3) is considered. Methods. We adopted the Fourier amplitude A2 of the surface brightness as a quantitative characteristic of the strength of non-axisymmetric structures in a galactic disk, in addition to the commonly used morphologic division for A, AB, and B types based on the Hubble classification. To distinguish changes in local oxygen abundance caused by the non-axisymmetrical structures, the multiparametric mass–metallicity relation was constructed as a function of parameters such as the bar/spiral pattern strength, the disk size, color index g − r in the Sloan Digital Sky Survey (SDSS) bands, and central surface brightness of the disk. The gas-phase oxygen abundance gradient is determined by using the R calibration. Results. We find that there is no significant impact of the non-axisymmetric structures such as a bar and/or spiral patterns on the local oxygen abundance and radial oxygen abundance gradient of disk galaxies. Galaxies with higher mass, however, exhibit flatter oxygen abundance gradients in units of dex/kpc, but this effect is significantly less prominent for the oxygen abundance gradients in units of dex/R25 and almost disappears when the inner parts are avoided (R > 0.25R25). We show that the oxygen abundance in the central part of the galaxy depends neither on the optical radius R25 nor on the color g − r or the surface brightness of the galaxy. Instead, outside the central part of the galaxy, the oxygen abundance increases with g − r value and central surface brightness of the disk.

A Closer Look at Some Gas-phase Depletions in the ISM: Trends for O, Ge, and Kr versus , f(H2), and Starlight Intensity*

Abstract In a survey of archived ultraviolet spectra of 100 stars recorded by the echelle spectrograph of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we measure the strengths of the weak absorption features of O i, Ge ii, and Kr i in the interstellar medium. Our objective is to undertake an investigation that goes beyond earlier abundance studies to see how these elements are influenced independently by three different environmental properties: (1) values of a generalized atomic depletion factor F * due to condensations onto dust grains (revealed here by the abundances of Mg and Mn relative to H), (2) the fraction of H atoms in the form of H2 f(H2), and (3) the ambient intensity I of ultraviolet starlight relative to an average value in our part of the Galaxy I 0. As expected, the gas-phase abundances of all three elements exhibit negative partial correlations with F *. The abundances of free O atoms show significant positive partial correlations with and , while Ge and Kr exhibit negative partial correlations with at marginal levels of significance. After correcting for these trends, the abundances of O relative to H show no significant variations with location, except for the already-known radial gradient of light-element abundances in the Milky Way. A comparison of Ge and O abundances revealed no significant regional enhancements or deficiencies of neutron-capture elements relative to α-process ones.

A Hint of Three-section Halo As Seen from the APOGEE DR14

Abstract Based on the [M/H] versus [Mg/Fe] diagram and distances from APOGEE data release 14, we compare the spatial distributions, the l − V los diagram, and the abundance gradients between high-[Mg/Fe] and low-[Mg/Fe] sequences. The two sequences are clearly shown at in the metallicity range of −1.6 < [M/H] < −0.7, where the halo at consists of low-[Mg/Fe] stars only. In the intermediate-metallicity range of −1.1 < [M/H] < −0.7, a [Mg/Fe] gradient is detected for stars at and it flattens out at . The l − V los diagram is adopted to separate halo stars from the disk by defining the transition metallicity, which is of [M/H] ∼ −1.1 ± 0.05 dex for the high-[Mg/Fe] sequence and of [M/H] ∼ −0.7 ± 0.05 dex for the low-[Mg/Fe] sequence. The R and distributions for the high-[Mg/Fe] sequence, the thick disk at −1.1 < [M/H] < −0.7 and the in situ halo at −1.6 < [M/H] < −1.1, have a cutoff at R ∼ 15 kpc and , beyond which low-[Mg/Fe] halo stars are the main contributions. In the metallicity range of −1.6 < [M/H] < −0.7, there is a negative metallicity gradient for the high-[Mg/Fe] halo at , while only a marginal or no slope in the [M/H] versus diagram for the low-[Mg/Fe] halo at , beyond which both the high-[Mg/Fe] halo and low-[Mg/Fe] halo flatten out toward . These results indicate a complicated formation history of the Galaxy and we may see a hint of a three-section halo, i.e., the inner in situ halo within , the intermediately outer dual-mode halo at , and the extremely outer accreted halo with .

Fishing pressure impacts the abundance gradient of European lobsters across the borders of a newly established marine protected area.

Marine protected areas (MPAs) are considered viable fisheries management tools due to their potential benefits of adult spillover and recruitment subsidy to nearby fisheries. However, before–after control–impact studies that explore the biological and fishery effects of MPAs to surrounding fisheries are scarce. We present results from a fine-scale spatial gradient study conducted before and after the implementation of a 5 km2 lobster MPA in southern Norway. A significant nonlinear response in lobster abundance, estimated as catch-per-unit-effort (CPUE) from experimental fishing, was detected within 2 years of protection. After 4 years, CPUE values inside the MPA had increased by a magnitude of 2.6 compared to before-protection values. CPUE showed a significant nonlinear decline from the centre of the MPA, with a depression immediately outside the border and a plateau in fished areas. Overall fishing pressure almost doubled over the course of the study. The highest increase in fishing pressure (by a magnitude of 3) was recorded within 1 km of the MPA border, providing a plausible cause for the depression in CPUE. Taken together, these results demonstrate the need to regulate fishing pressure in surrounding areas when MPAs are implemented as fishery management tools.

Effective temperature of ionizing stars in extragalactic H iiregions – II. Nebular parameter relationships based on CALIFA data

We calculate the effective temperature ($T_{\rm eff}$) of ionizing star(s), oxygen abundance of the gas phase $(\rm O/H)$, and the ionization parameter $U$ for a sample of H\,{\sc ii} regions located in the disks of 59 spiral galaxies in the 0.005 < z < 0.03 redshift range. We use spectroscopic data taken from the CALIFA data release 3 (DR3) and theoretical (for $T_{\rm eff}$ and $U$) and empirical (for O/H) calibrations based on strong emission-lines. We consider spatial distribution and radial gradients of those parameters in each galactic disk for the objects in our sample. Most of the galaxies in our sample ($\sim70$ \%) shows positive $T_{\rm eff}$ radial gradients even though some them exhibit negative or flat ones. The median value of the $T_{\rm eff}$ radial gradient is 0.762 kK/$R_{25}$. We find that radial gradients of both $\log U$ and $T_{\rm eff}$ depend on the oxygen abundance gradient, in the sense that the gradient of $\log U$ increases as $\log(\rm O/H)$ gradient increases while there is an anti-correlation between the gradient of $T_{\rm eff}$ and the oxygen abundance gradient. Moreover, galaxies with flat oxygen abundance gradients tend to have flat $\log U$ and $T_{\rm eff}$ gradients as well. Although our results are in agreement with the idea of the existence of positive $T_{\rm eff}$ gradients along the disk of the majority of spiral galaxies, this seems not to be an universal property for these objects.

Gradients in abundance and diversity of ground dwelling arthropods as a function of distance to tree rows in temperate arable agroforestry systems

Ground dwelling arthropods present in agricultural systems regulate multiple ecosystem services (ES), such as nutrient and carbon cycling and biological pest control. The presence of semi-natural landscape features, such as the tree component of agroforestry systems (AFS), can contribute to functional agrobiodiversity and optimize the delivery of such ES in agricultural landscapes. In temperate AFS, however, potential patterns in abundance and diversity have scarcely been investigated for detritivorous soil dwelling arthropods and only to a limited extent for predatory arthropods. Therefore, we have assessed the abundance and diversity of woodlice (Isopoda), millipedes (Diplopoda), rove beetles (Coleoptera: Staphylinidae) and carabids (Coleoptera: Carabidae) as a function of the distance to the tree row in a set of temperate arable AFS. Abundance and diversity of woodlice and millipedes were significantly higher in the tree rows than in the arable zone. In the case of mature trees, a higher abundance of detritivores was also observed in the arable zone close to the trees. Tree presence did not consistently lead to higher abundance of predatory arthropods, but a limited increase in carabid diversity was observed in the arable zone close to the tree rows. These results indicate that in temperate AFS, the trees and the associated understory vegetation strip contribute to the preservation of arthropod biodiversity and the enhancement of associated ES in the tree rows and in the arable field zone.

Radial Velocity and Chemical Composition of Evolved Stars in the Open Clusters NGC 6940 and Tombaugh 5

Abstract We present and discuss medium resolution (R ∼ 13000), high signal-to-noise ( ), spectroscopic observations in the field of the open clusters NGC 6940 and Tombaugh 5. Spectra were recorded for seven candidate red giant stars in both clusters. For the latter, we present the very first chemical abundance analysis. We derive radial velocities for all the stars in NGC 6940, confirming membership to the cluster for all of them, while on the same ground, we exclude two stars in To 5. We perform a chemical abundance analysis of different atomic species, in particular Fe i, Si i, Ca i, Ti i, and Ni i. The mean metallicity of NGC 6940 is [Fe/H] = +0.09 ± 0.06 dex, in good agreement with previous works, while for To 5 is [Fe/H] = +0.06 ± 0.11 dex. Therefore, both clusters exhibit a chemical composition close to the solar value and do not deviate from the [Fe/H] Galactic radial abundance gradient. With these new values, we estimate the fundamental cluster parameters, after having derived clusters’ distances from the Gaia DR2 database. By adopting these distances, we derive updated estimated for the clusters ages: 1.0 ± 0.1 Gyr of NGC 6940 and 0.25 ± 0.05 Gyr for Tombaugh 5.

Search for gas accretion imprints in voids – I. Sample selection and results for NGC 428

We present the first results of a project aimed at searching for gas accretion events and interactions between late-type galaxies in the void environment. The project is based on long-slit spectroscopic and scanning Fabry-Perot interferometer observations performed with the SCORPIO and SCORPIO-2 multimode instruments at the Russian 6-m telescope, as well as archival multiwavelength photometric data. In the first paper of the series we describe the project and present a sample of 18 void galaxies with oxygen abundances that fall below the reference `metallicity-luminosity' relation, or with possible signs of recent external accretion in their optical morphology. To demonstrate our approach, we considered the brightest sample galaxy NGC 428, a late-type barred spiral with several morphological peculiarities. We analysed the radial metallicity distribution, the ionized gas line-of-sight velocity and velocity dispersion maps together with WISE and SDSS images. Despite its very perturbed morphology, the velocity field of ionized gas in NGC 428 is well described by pure circular rotation in a thin flat disc with streaming motions in the central bar. We also found some local non-circular gas motions clearly related to stellar feedback processes. At the same time, we revealed a circumnuclear inclined disc in NGC 428 and a region with significant residual velocities that could be considered as a result of a recent (<0.5 Gyr) accretion event. The observed oxygen abundance gradient does not contradict this conclusion.