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South Africa's endemic Knysna seahorse, Hippocampus capensis Boulenger 1900, is a rare example of a marine fish listed as Endangered by the IUCN because of its limited range and habitat vulnerability. It is restricted to four estuaries on the southern coast of South Africa. This study reports on its biology in the Knysna and Swartvlei estuaries, both of which are experiencing heavy coastal development. We found that H. capensis was distributed heterogeneously throughout the Knysna Estuary, with a mean density of 0.0089 m-2 and an estimated total population of 89 000 seahorses (95% confidence interval: 30 000 to 148 000). H. capensis was found most frequently in low density vegetation stands ( 20% cover) and grasping Zostera capensis. Seahorse density was not otherwise correlated with habitat type or depth. The size of the area in which any particular seahorse was resighted did not differ between males and females. Adult sex ratios were skewed in most transects, with more males than females, but were even on a 10 m by 10 m focal study grid. Only three juveniles were sighted during the study. Both sexes were reproductively active but no greeting or courtship behaviours were observed. Males on the focal study grid were longer than females, and had shorter heads and longer tails, but were similar in colouration and skin filamentation. The level of threat to H. capensis and our limited knowledge of its biology mean that further scientific study is urgently needed to assist in developing sound management practices.
Dringliche Rechte am Wohnungseigentum und Rechtsgeschäfte der Wohnungseigentümer untereinander
(2003)
Naturschutzplanung
(2003)
State, administration and governance in Germany: competing traditions and dominant narratives
(2003)
Methodik der Dramatherapie
(2003)
Toeplitz operators, and ellipticity of boundary value problems with global projection conditions
(2003)
Compact white-light source with an average output power of 2.4 W and 900 nm spectral bandwidth
(2003)
Eigennamen referieren - Referieren mit Eigennamen : zur Kontextinvarianz der namentlichen Bezugnahme
(2003)
Verbales Arbeitgedächtnis und die Verarbeitung lexikalisch ambiger Wörter in Wort- und Satzkontexten
(2003)
Verwaltungslexikon
(2003)
Rechtsgrundlagen und Grenzen zulässiger Maßnahmen bei der Durchsuchung von Wohn- und Geschäftsräumen
(2003)
Konflikte in Sportvereinen
(2003)
Zwischen Gemeinschaftsorientierung und Selbstverwirklichung : Motive zu freiwilligem Engagement
(2003)
Helming, K. (Hrsg.), Sustainable Development of Multifunctional Landscapes; Berlin, Springer, 2003
(2003)
Protostellar jets most probably originate in turbulent accretion disks surrounding young stellar objects. We investigate the evolution of a disk wind into a collimated jet under the influence of magnetic diffusivity, assuming that the turbulent pattern in the disk will also enter the disk corona and the jet. Using the ZEUS-3D code in the axisymmetry option we solve the time-dependent resistive MHD equations for a model setup of a central star surrounded by an accretion disk. The disk is taken as a time-independent boundary condition for the mass flow rate and the magnetic flux distribution. We derive analytical estimates for the magnitude of magnetic diffusion in a protostellar jet connecting our results to earlier work in the limit of ideal MHD. We find that the diffusive jets propagate slower into the ambient medium, most probably due to the lower mass flow rate in the axial direction. Close to the star we find that a quasi stationary state evolves after several hundred (weak diffusion) or thousand (strong diffusion) disk rotations. Magnetic diffusivity affects the protostellar jet structure as follows. The jet poloidal magnetic field becomes de- collimated. The jet velocity increases with increasing diffusivity, while the degree of collimation for the hydrodynamic flow remains more or less the same. We suggest that the mass flux is a proper tracer for the degree of jet collimation and find indications of a critical value for the magnetic diffusivity above which the jet collimation is only weak. We finally develop a self-consistent picture in which all these effects can be explained in the framework of the Lorentz force.
The classical (Levins) metapopulation scenario envisions a species persisting in a network of habitat patches through a balance between frequent local (within-patch) extinctions and recolonizations. Although this is the dominant paradigm for species in fragmented habitats, empirical support is limited and it has been argued that very restrictive conditions on migration rates are required: high enough for recolonization to balance extinctions, but low enough that local populations do not fluctuate in synchrony. Through simulation and analysis of a stochastic spatial model, we argue that the likelihood of persistence via the classical scenario is strongly affected by some basic properties of within- patch successional dynamics whose importance has not been emphasized in metapopulation theory: the distribution of successional stage durations, and whether patches are "refractory" versus immediately available for recolonization after an extinction has occurred. These properties are tied to the biological causes of extinction (e.g., demographic accident versus regular successional changes) and patch recovery (e.g., recolonization by a host species versus regeneration of an exhausted resource base). Our results indicate that metapopulation theory needs to incorporate the patch-dynamics perspective of a landscape in a dynamic mosaic of successional states, with particular attention to links between colonization-extinction processes and local succession.
Ecological and evolutionary dynamics can occur on similar timescales. However, theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions. Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey (rotifer-algal) cycles in laboratory microcosms. Our experiments tested explicit predictions from a model for our system that allows prey evolution. We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption, and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population. Single-clone algal cultures (lacking genetic variability) produced short cycle periods and typical quarter-period phase lags between prey and predator densities, whereas multi-clonal (genetically variable) algal cultures produced long cycles with prey and predator densities nearly out of phase, exactly as predicted. These results confirm that prey evolution can substantially alter predator-prey dynamics, and therefore that attempts to understand population oscillations in nature cannot neglect potential effects from ongoing rapid evolution.
Tasks and Content of Landscape Management Planning and Landscape Implementation Planning - Requirements in terms of feasibility of re-checks Zusammenfassung Vor dem Hintergrund in Nachkontrollen vielfach festgestellter Abweichungen des Landschaftspflegerischen Ausführungsplans (LAP) von den Aussagen des Landschaftspflegerischen Begleitplans (LBP) werden Aufgabenverteilung und "Abschichtung" zwischen beiden Planwerken kritisch beleuchtet. Im Landschaftspflegerischen Ausführungsplan nachträglich vorgenommene Anpassungen von z.B. Zielen und räumlicher Lage von Ausgleichs- und Ersatzmaßnahmen können u.U. auch Auswirkungen auf die im LBP zu erstellende Bilanz der Beeinträchtigungen und Kompensationswirkungen und damit auf die Genehmigungsvoraussetzungen haben. Verschiedene Fallbeispiele belegen, dass immer dann, wenn Ausgleichs- und Ersatzmaßnahmen im Landschaftspflegerischen Begleitplan nicht hinreichend konkretisiert werden, der Bezug zu den Beeinträchtigungen schnell verloren geht. Durchgeführte Maßnahmen entsprechen dann zwar i.d.R. noch den Zielen von Naturschutz und Landschaftspflege im betroffenen Naturraum, aber häufig nicht mehr den rechtlichen Anforderungen der Eingriffsregelung. Nachkontrollen sind nur noch im Hinblick auf die korrekte Durchführung, nicht mehr jedoch auf die Funktionserfüllung der Maßnahmen möglich. Als Konsequenz aus den Ergebnissen wird der Vorschlag einer klaren Aufgabenteilung von Landschaftspflegerischem Begleit- und Ausführungsplan entwickelt. Er beinhaltet neben einer hinreichenden Zieldefinition für die Kompensation im Landschaftspflegerischen Begleitplan eine durchgängige Beibehaltung der Maßnahmenbezeichnungen in beiden Planwerken sowie eine gesonderte Darlegung im Landschaftspflegerischen Ausführungsplan vorgenommener Änderungen.
The non-LTE radiative transfer problem requires the consistent solution of two sets of equations: the radiative transfer equations, which couple the spatial points, and the equations of the statistical equilibrium, which couple the frequencies. The "Accelerated Lambda Iteration" (ALI) method allows for an iterative scheme, in which both sets of equations are solved in turn. For moving atmospheres the radiative transfer is preferably formulated in the co-moving frame-of-reference, which leads to a partial differential equation. "Classical" numerical solution methods are based on differencing schemes. For better numerical stability, we prefer "short characteristics" integration methods. Iron line blanketing is accounted for by means of the "superlevel" concept. In contrast to static atmospheres, the frequencies can not be re-ordered in the moving case because of the frequency coupling from Doppler shifts. One of our future aims is the coupling of elaborated radiative transfer calculations with the hydrodynamical equations in order to understand the driving of strong stellar winds, especially from Wolf-Rayet stars.
Im Zuge der Modernisierung des Schuldrechts hat der Gesetzgeber auch das Recht der Leistungsstörungen grundlegend reformiert. Die kodifikatorische Umsetzung der rechtspolitischen Intentionen erscheint gerade bei $ 280 Abs. 1 BGB, der zentralen Vorschrift im Schadensersatzrecht, besonders ungereimt und dogmatisch fragwürdig. Wie beispielsweise sollte eine allein durch den Gläubiger (!) zu verantwortende Unmöglichkeit der Leistung als Pflichtverletzung des Schuldners aufgefaßt werden können? Der Autor weist darauf hin, daß materiellrechtliche Kategorien von der Ebene des Beweislastrechts zu unterscheiden sind und sieht gerade in deren Vermischung eine mögliche Ursache für die Schwierigkeiten, die die Anwendung des $ 280 Abs. 1 BGB bereitet.
We present a detailed study of the effects of gravitational microlensing on compact and distant gamma-ray blazars. These objects have gamma-ray-emitting regions that are small enough to be affected by microlensing effects produced by stars lying in intermediate galaxies. We compute the gravitational magnification taking into account effects of the lensing and show that, whereas the innermost gamma-ray spheres can be significantly magnified, there is little magnification either for very high gamma-ray energies or for lower (radio) frequencies (because these wavelengths are emitted from larger regions). We analyse the temporal evolution of the gamma-ray magnification for sources moving in a caustic pattern field, where the combined effects of thousands of stars are taken into account using a numerical technique. We propose that some of the unidentified gamma-ray sources (particularly some of those lying at high galactic latitude with gamma-ray statistical properties that are very similar to detected gamma-ray blazars) are indeed the result of gravitational lensing magnification of background undetected active galactic nuclei (AGN). This is partly supported from a statistical point of view: we show herein as well, using the latest information from the third EGRET catalogue, that high-latitude gamma-ray sources have similar averaged properties to already detected gamma-ray AGN. Some differences between both samples, regarding the mean flux level, could also be understood within the lensing model. With an adequate selection of lensing parameters, it is possible to explain a variety of gamma-ray light curves with different time-scales, including non-variable sources. The absence of strong radio counterparts could be naturally explained by differential magnification in the extended source formalism.