Differences In Abundance Patterns Research Articles

Spectroscopic survey of γ Doradus stars – I. Comprehensive atmospheric parameters and abundance analysis of γ Doradus stars

We present a spectroscopic survey of known and candidate $\gamma$\,Doradus stars. The high-resolution, high signal-to-noise spectra of 52 objects were collected by five different spectrographs. The spectral classification, atmospheric parameters (\teff, $\log g$, $\xi$), $v\sin i$ and chemical composition of the stars were derived. The stellar spectral and luminosity classes were found between G0-A7 and IV-V, respectively. The initial values for \teff\ and \logg\ were determined from the photometric indices and spectral energy distribution. Those parameters were improved by the analysis of hydrogen lines. The final values of \teff, \logg\ and $\xi$ were derived from the iron lines analysis. The \teff\ values were found between 6000\,K and 7900\,K, while \logg\,values range from 3.8 to 4.5\,dex. Chemical abundances and $v\sin i$ values were derived by the spectrum synthesis method. The $v\sin i$ values were found between 5 and 240\,km\,s$^{-1}$. The chemical abundance pattern of $\gamma$\,Doradus stars were compared with the pattern of non-pulsating stars. It turned out that there is no significant difference in abundance patterns between these two groups. Additionally, the relations between the atmospheric parameters and the pulsation quantities were checked. A strong correlation between the $v\sin i$ and the pulsation periods of $\gamma$\,Doradus variables was obtained. The accurate positions of the analysed stars in the H-R diagram have been shown. Most of our objects are located inside or close to the blue edge of the theoretical instability strip of $\gamma$\,Doradus.

Seasonal fluctuations and dietary analysis of fouling caprellids (Crustacea: Amphipoda) from marinas of southern Spain

In marinas, native caprellids usually share their habitat with exotic species, and can eventually be replaced by them. The invasive Caprella scaura is spreading quickly and has successfully settled in many marinas of southern Spain, potentially threatening the native taxa. We selected two marinas (El Rompido, Huelva and La Línea, Cádiz) in which C. scaura has not yet been found, in order to explore the seasonal dynamic patterns of the resident species before the arrival of the non-native species. Sampling was carried out bimonthly from July 2010 to July 2011. Two caprellid species were recorded, Caprella dilatata and C. equilibra. In El Rompido, both caprellids were found on two substrates (the bryozoan Bugula neritina and the hydroid Ectopleura crocea), whereas in La Línea, B. neritina hosted only C. equilibra, and C. dilatata was absent. Caprella dilatata showed maximum densities in July, with a second peak of abundance in November, and was absent during the winter (January–March). Caprella equilibra showed differences in abundance patterns, body length and fecundity between the two marinas, probably due to differences in environmental measures between the marinas. The dominant component of the diet of the two species was detritus, followed by copepods, which were more abundant in specimens collected from E. crocea, suggesting the possibility of cleptocommensalist behaviour.

Reduced Diversity and High Sponge Abundance on a Sedimented Indo-Pacific Reef System: Implications for Future Changes in Environmental Quality

Although coral reef health across the globe is declining as a result of anthropogenic impacts, relatively little is known of how environmental variability influences reef organisms other than corals and fish. Sponges are an important component of coral reef fauna that perform many important functional roles and changes in their abundance and diversity as a result of environmental change has the potential to affect overall reef ecosystem functioning. In this study, we examined patterns of sponge biodiversity and abundance across a range of environments to assess the potential key drivers of differences in benthic community structure. We found that sponge assemblages were significantly different across the study sites, but were dominated by one species Lamellodysidea herbacea (42% of all sponges patches recorded) and that the differential rate of sediment deposition was the most important variable driving differences in abundance patterns. Lamellodysidea herbacea abundance was positively associated with sedimentation rates, while total sponge abundance excluding Lamellodysidea herbacea was negatively associated with rates of sedimentation. Overall variation in sponge assemblage composition was correlated with a number of variables although each variable explained only a small amount of the overall variation. Although sponge abundance remained similar across environments, diversity was negatively affected by sedimentation, with the most sedimented sites being dominated by a single sponge species. Our study shows how some sponge species are able to tolerate high levels of sediment and that any transition of coral reefs to more sedimented states may result in a shift to a low diversity sponge dominated system, which is likely to have subsequent effects on ecosystem functioning.

Linking local community structure to the dispersal of aquatic invertebrate species in a rock pool metacommunity

Dispersal allows species to immigrate and emigrate to and from habitat patches and is an important factor in determining community structure. The influence of species dispersal in a metacommunity is poorly understood, particularly its effect at the local community level. We aimed to address this deficiency by evaluating the potential influence of dispersal on local community structure in a rock pool metacommunity. Short term dispersal was quantified over an 11 day period by intercepting propagules dispersing via overflowing pool water and via wind. The composition of dispersing organisms was compared to natural local communities in the rock pools surveyed annually on 11 occasions. On average, the composition and abundance of dispersing species was approximately 54.1 ± 9.3% (mean ± SD) similar to the established pool community. Some species were more abundant among dispersers than they were in the pool community. This may be attributed to several factors including a variation in tolerance to environmental conditions, dispersal capacity, and local scale species interactions (predation and competition). In general, we found considerable similarity between short term dispersal and long term local community structure across a metacommunity. Differences in abundance patterns between the resident rock pool community and the dispersal assemblage emphasize that dispersal, a regional process, must interact with local factors in structuring communities.

CHEMICAL COMPOSITION OF THE COMPONENTS OF ECLIPSING BINARY STAR ZZ BOOTIS

We investigated ZZ Boo using a high-resolution (R = 80,000) spectrum obtained at the BOES echelle spectrograph attached to a 1.8?m telescope at the Bohuynsan observatory in Korea. The atmospheric parameters of the components were found using the published photometrical observations and the abundance analysis of iron lines: the flux ratio of the components FA /FB = 1.12 ? 0.15, the effective temperatures of the components T eff = 6860 ? 20?K and 6930 ? 20?K, the surface gravities log g = 3.72 ? 0.10 and 3.84 ? 0.10, the metallicities [Fe/H] = ?0.10 ? 0.08 and ?0.03 ? 0.10, and the projected rotation velocities vsin i = 11.9 ? 0.4?km?s?1 and 19.3 ? 0.8?km?s?1 for the primary and secondary components, respectively. The pointed errors are the formal errors of the methods used; the systematic errors of the temperatures, gravities, metallicities, and projected rotational velocities can be as high as 250-300?K, 0.3?dex, 0.15?dex, and 4?km?s?1, respectively. The abundances of 24 and 22 chemical elements were determined in the atmospheres of the components. The abundance pattern of the primary component shows the solar or slightly undersolar abundances of all elements. CNO abundances are close to solar values. The abundance pattern of this component resembles those of ? Boo type stars. The abundances of light elements, except oxygen, in the atmosphere of the secondary component are practically solar. The abundances of barium and two detected lanthanides are close to the solar values; the overabundance of oxygen is 0.9?dex. The abundances of two components are evidently different. The comparison of relative abundances with the condensation temperatures and second ionization potentials of the elements confirms the difference in abundance patterns and allows discussion of the different accretion scenarios for two components of this binary system.

THE PECULIAR SOLAR COMPOSITION AND ITS POSSIBLE RELATION TO PLANET FORMATION

We have conducted a differential elemental abundance analysis of unprecedented accuracy (∼0.01 dex) of the Sun relative to 11 solar twins from the Hipparcos catalog and 10 solar analogs from planet searches. We find that the Sun shows a characteristic signature with a ≈20% depletion of refractory elements relative to the volatile elements in comparison with the solar twins. The abundance differences correlate strongly with the condensation temperatures of the elements. This peculiarity also holds in comparisons with solar analogs known to have close-in giant planets while the majority of solar analogs found not to have such giant planets in radial velocity monitoring show the solar abundance pattern. We discuss various explanations for this peculiarity, including the possibility that the differences in abundance patterns are related to the formation of planetary systems like our own, in particular to the existence of terrestrial planets.

Two hundred years of a diverse Daphnia community in Lake Naivasha (Kenya): effects of natural and human‐induced environmental changes

Summary1. We used fossil diapausing eggs extracted from 210Pb‐dated sediment cores to reconstruct historical changes in the Daphnia community of Lake Naivasha, a climate‐sensitive lake in Kenya which over the past 200 years has experienced a series of well‐documented natural and anthropogenic environmental changes.2. Contiguous sampling and analysis of four cores yielded ephippial capsules of eight Daphnia species. Only two of these had been recorded previously in live collections from Lake Naivasha, and one species is new to science. The four more common species (Daphnia barbata, D. laevis, D. magna, and D. pulex) show striking differences in abundance patterns and population dynamics through time. Four other species (D. lumholtzi, D. curvirostris, D. longispina s.l., and Daphnia sp. nov. type Limuru.) appear to have been present only occasionally. Nevertheless, between 1895 and 1915 seven species of Daphnia inhabited Lake Naivasha simultaneously.3. Despite considerable natural environmental change associated with climate‐driven lake‐level fluctuations, the Daphnia community of Lake Naivasha has been severely affected by human activities over the past century, especially the introduction of exotic fishes and water‐quality changes because of agricultural soil erosion. The recent reappearance of large‐bodied Daphnia species (D. magna, D. barbata, D. lumholtzi, Daphnia sp. nov. type Limuru) after 20–110 years of absence can be explained by their release from fish predation, following a dramatic increase in turbidity caused by excess clastic sediment input from eroded catchment soils. The small‐bodied species D. laevis has fared less well recently, presumably because the benefit of lowered predation pressure is counteracted by more pronounced negative effects of increased turbidity on this species and loss of submerged macrophyte beds which formerly served as predation refuge.4. Our results suggest that, despite considerable environmental instability and the absence of specialised zooplanktivores, top‐down control of fish on large zooplankton is important in Lake Naivasha. Predation pressure from fish has led to clear‐cut shifts in local Daphnia species composition, but failed to drive the larger taxa to extinction.

Abundances in globular cluster red giants. IV - M22 and Omega Centauri

A detailed abundance analysis has been performed for three members of M22 and five of ..omega.. Cen. The three giants in M22 are chemically identical with (Fe/H) = -1.78 dex except for a range of Na and, less certainly, Ba larger than the observational and modeling errors. The ..omega.. Cengiants show a range of abundance for all elements, with the light elements and the rare earths (plus Ba) enhanced by a larger factor than the Fe peak nuclei in the more metal-rich ..omega.. Cen stars. The two most metal-rich ..omega.. Cen stars have vastly different Na/Mg and Al/Mg ratios and Sc abundances. Explosive nucleosynthesis fails to predict the Na/Mg observed ratios at large Al/Mg values. The deduced neutron excesses are etaroughly-equal10/sup -2/ and 5 x 10/sup -4/; the former is the largest known for any star. These high values of eta require massive (M> or =12 M/sub sun/) supernova progenitors and may also produce via the s-process the strong enhancement of Ba and the rare earths seen in the metal-rich ..omega.. Cen giants. It is suggested that such massive supernovae were much rarer in the less dense halo field, leading to the observed differences in abundance patterns of globular clustermore » giants versus halo field dwarfs.« less

Seasonal Features of Zooplankton Assemblages in the Nearshore Area of Southeastern Lake Michigan

Zooplankton in a nearshore area in southeastern Lake Michigan displayed strong seasonal and depth-related trends in abundance (#/m 3) during the period 1971 to 1977. Depth-related assemblages defined by principal component analysis varied with season. From mid-spring to mid-autumn, zooplankton assemblages were strongly related to water depth. In general, zooplankton were least abundant in the inner region (5–10 m) where small organisms such as nauplii, Asplanchna spp., and Bosmina longirostris and epibenthic organisms such as Eurytemora affinis dominated. Zooplankton were most abundant between 20 and 30 m, with a peak July 1972–1977 mean density of 87,000/m 3. Larger zooplankton, including Cyclops spp., Diaptomus spp., Daphnia spp., and Eubosmina coregoni dominated the outer region (20–50 m). During autumn, the inner region was dominated by cladocerans while the outer region was dominated by copepods. After thermal stratification disappeared in late autumn and before the thermal bar moved beyond the survey area in early spring, zooplankton tended to occur in higher densities in the shallow depths of the survey area. Also, in contrast to the mid-spring to mid-autumn period, zooplankton occurred in similar compositions over the survey grid. Factors implicated in producing seasonal differences in abundance patterns include temperature regimes, phytoplankton standing stocks, and predation by fish and invertebrates.