Growth pattern and changes in abundance of the endangered bat star Asterina stellifera          下载免费PDF全文

Pablo E. Meretta  Nahuel E. Farias  Maximiliano Cledón  Carlos Renato Rezende Ventura 《Marine Ecology》2016,37(6):1423-1433

The sea star Asterina stellifera has declined during the last decade and is currently abundant only in the southern limit of its former range. We surveyed this population over 5 years to model individual growth and explore the relationship of changes in local abundance with variation in environmental factors and the reproductive status of individuals. Our results show that A. stellifera is a species with slow growth and a relatively long lifespan. Contrary to expectations for temperate species, growth rates were fairly constant through the year and therefore models including seasonal oscillations were inappropriate. The abundance of this species increased significantly from early spring to early summer, likely due to augmented activity and small‐scale aggregation during the reproductive season that affected our estimates of abundance. No significant recruitment occurred during the 5 years studied. The lack of recruitment during long periods and the slow individual growth rates make A. stellifera particularly vulnerable to local extinction. This study was performed prior to the arrival in the study area of the invasive kelp Undaria pinnatifida and side‐gilled sea slug Pleurobranchaea maculata, species that threaten the community structure where A. stellifera lives. Therefore, the information reported here will be essential to assessing the impacts of these exotic species on this sea star population.  相似文献   

Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications     

Emre Aydınçakır 《Geodinamica Acta》2016,28(4):379-411

Mineral chemistry, major and trace elements, ⁴⁰Ar/³⁹Ar age and Sr–Nd–Pb isotopic data are presented for the Late Cretaceous Hamsilos volcanic rocks in the Central Pontides, Turkey. The Hamsilos volcanic rocks mainly consist of basalt, andesite and associated pyroclastics (volcanic breccia, vitric tuff and crystal tuff). They display shoshonitic and high-K calc-alkaline affinities. The shoshonitic rocks contain plagioclase, clinopyroxene, alkali feldspar, phlogopite, analcime, sanidine, olivine, apatite and titanomagnetite, whereas the high-K calc-alkaline rocks contain plagioclase, clinopyroxene, orthopyroxene, magnetite / titanomagnetite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic matrix. Mineral chemistry data reveal that the pressure condition of the clinopyroxene crystallisation for the shoshonitic rocks are between 1.4 and 6.3 kbar corresponds to 6–18-km depth and the high-K calc-alkaline rocks are between 5 and 12 km. ⁴⁰Ar/³⁹Ar age data changing between 72 ± .5 Ma and 79.0 ± .3 Ma (Campanian) were determined for the Late Cretaceous Hamsilos volcanic rocks, contemporaneous with the subduction of the Neo-Tethyan Ocean beneath the Pontides. The studied volcanic rocks were enriched in the large-ion lithophile and light rare earth element contents, with pronounced depletion in the contents of high-field-strength elements. Chondrite-normalised rare earth element patterns (La_N/Lu_N = 6–17) show low to medium enrichment, indicating similar sources of the rock suite. Initial ⁸⁷Sr/⁸⁶Sr values vary between .70615 and .70796, whereas initial ¹⁴³Nd/¹⁴⁴Nd values change between .51228 and .51249. Initial ²⁰⁶Pb/²⁰⁴Pb values vary between 18.001 and 18.349, ²⁰⁷Pb/²⁰⁴Pb values between 15.611 and 15.629 and ²⁰⁸Pb/²⁰⁴Pb values between 37.839 and 38.427. The main solidification processes involved in the evolution of the volcanic rocks consist of fractional crystallisation, with minor amounts of crustal contamination ± magma mixing. According to geochemical evidence, the shoshonitic melts in the Hamsilos volcanic rocks were possibly derived from the low degree of partial melting of a subcontinental lithospheric mantle (SCLM), while the high-K calc-alkaline melts were derived from relatively high degree of partial melting of SCLM that was enriched by fluids and/or sediments from a subduction of oceanic crust.  相似文献   

Improving landslide hazard and risk mapping in Guatemala using terrain aspect     

Yuri Gorokhovich  Elia Axinia Machado  Luis Iván Girón Melgar  Mahta Ghahremani 《Natural Hazards》2016,81(2):869-886

  相似文献   

Spatial distribution and comparison of aridity indices in Extremadura,southwestern Spain     

Francisco J. Moral  Francisco J. Rebollo  Luis L. Paniagua  Abelardo García-Martín  Fulgencio Honorio 《Theoretical and Applied Climatology》2016,123(3-4):801-826

  相似文献   

A conceptual model for glacial cycles and the middle Pleistocene transition     

István Daruka  Peter D. Ditlevsen 《Climate Dynamics》2016,46(1-2):29-40

  相似文献   

The role of ENSO and PDO in variability of winter precipitation over North America from twenty first century CMIP5 projections     

Ramón Fuentes-Franco  Filippo Giorgi  Erika Coppola  Fred Kucharski 《Climate Dynamics》2016,46(9-10):3259-3277

  相似文献   

Modeling the Stakeholder Profile in Territorial Management: The Segarra-Garrigues Irrigation System,Spain     

Sandra Ricart  Anna Ribas  David Pavón 《The Professional geographer》2016,68(3):496-510

Interest in obtaining a more accurate snapshot of irrigation management from a geographical perspective is increasingly relevant. This proposal is based on existing qualitative approaches in combination with an alternative method (the territorial irrigation management model) to identify and present key stakeholders attitudes and perceptions in the Segarra-Garrigues irrigation system in Spain. Advantages are (1) the focus on interrelations and context, (2) the applicability and extrapolation of the irrigation system, and (3) the irrigator-driven rather than researcher-driven perspective. Results revealed that there are conceptual and practical heterogeneities between the preferences of stakeholders' groups regarding water resources management, environmental protection, and agricultural challenges.  相似文献   

Impact Of The PROCEEDINGS ON THE ANNUAL MEETING OF THE ASSOCIATION OF AMERICAN GEOGRAPHERS: A COMPARISON OF SCIENTIFIC INFORMATION EXCHANGE AT THE 1967 AND 1969 ANNUAL MEETINGS*     

Carnot E. Nelson  Kazuo Tomica 《The Professional geographer》1970,22(4):221-226

  相似文献   

The Voyager 1/Saturn encounter and the cosmogonic shadow effect     

Hannes Alfvén 《Astrophysics and Space Science》1981,79(2):491-505

If an electrically conducting medium (e.g. a dusty plasma) rotates around a gravitating central body, which possesses an axisymmetric dipole field, the medium is supported to two-thirds by the centrifugal force and to one-third by electromagnetic forces under the condition that the magnetic field is strong enough to controll the motion. If the electromagnetic forces disappear — e.g. by a de-ionisation of the dusty plasma — the medium will fall down to two-thirds of its original central distance. The result of this process will be a cosmogonic shadow effect which is described in some detail.The Voyager 1/Saturn results demonstrate that the macro-structure of the Saturnian ring system can be explained as a result of this effect working at the formation of the system. The agreement between the theoretical results and the observations is better than a few percent.A similar analysis of the asteroidal belt shows that its macro-structure can also be explained by the cosmogonic shadow effect. The agreement between theory and observations is perhaps even better than in the Saturnian ring system.The observational results demonstrate that during their formation both the Saturnian ring and the asteroidal belt passed a plasma state dominated by electromagnetic effects.  相似文献   

Time distribution of flare events on UV Cet stars     

V. Pazzani  M. Rodonò 《Astrophysics and Space Science》1981,77(2):347-355

A statistical analysis of the flare data on three UV Cet stars obtained at Catania Observatory in the indicated periods-UV Cet (1968–1976), EQ Peg (1969–1975) and YZ CMi (1968–1976)-is presented. The distributions of the four variables (i) , the time elapsed from the start of a continuous observation interval to the occurrence of the first flare; (ii) , the time interval between consecutive flares; (iii)k, the number of flares occurring in time intervals of given duration; (iv) , the ratio between the number of flares observed in each continuous observing interval to that expected for a Poisson process, indicate that the flares of the three stars considered are not randomly distributed in time.  相似文献