The impact of birds on the Wadden Sea food web

The Wadden Sea at the western coasts of Germany, Denmark and the Netherlands is one of the globally most important foraging areas for breeding and migrating birds which act at the same time as indicators for the ecological condition of the ecosystem. However, little is known about how the intense predation pressure of birds influences the Wadden Sea food web. The aim of the interdisciplinary project STopP (From Sediment to Top Predator) is to determine the food web structure in different Wadden Sea habitat types in terms of the interaction between the basis of the food web and birds as top predators. Studied habitat types included the most important foraging areas of birds; mussel banks, cockle beds, sand flats, mud flats, seagrass meadows and beds of the immigrant razor clam Ensis directus a recently preferred prey item of several bird species. Data were analysed using the Ecological Network Analysis (ENA) that reflects trophic structures within the systems and reveals direct and indirect relations between the lower and the upper trophic levels. Preliminary results show that bird predation increases the complexity of the food web due to an increase in connections and a higher total system throughput. On the other hand the predation has also a destabilizing effect due to a high demand of system’s carbon stocks and increased exports out of the tidal system. In addition, analyses show considerable indirect dependencies of birds to lower trophic levels such as sediment POC and phytoplankton. Future scenarios modelled with ENA shall show how changes within the lower trophic levels would affect foraging birds due to anthropogenic or natural impacts. Further analysis will focus on the importance of special habitat types for different bird species and the influence of changes in the biomass of key species for the whole ecosystem food web

Abell 2384: the galaxy population of a cluster post-merger

We combine multi-object spectroscopy from the 2dF and EFOSC2 spectrographs with optical imaging of the inner 30'x30' of A2384 taken with the ESO Wide Field Imager. We carry out a kinematical analysis using the EMMIX algorithm and biweight statistics. We address the possible presence of cluster substructures with the Dressler-Shectman test. Cluster galaxies are investigated with respect to [OII] and H{\alpha} equivalent width. Galaxies covered by our optical imaging observations are additionally analysed in terms of colour, star formation rate and morphological descriptors such as Gini coefficient and M20 index. We study cluster galaxy properties as a function of clustercentric distance and investigate the distribution of various galaxy types in colour-magnitude and physical space. The Dressler-Shectman test reveals a substructure in the east of the 2dF field-of-view. We determine the mass ratio between the northern and southern subcluster to be 1.6:1. In accordance with other cluster studies, we find that a large fraction of the disk galaxies close to the cluster core show no detectable star formation. Probably these are systems which are quenched due to ram-pressure stripping. The sample of quenched disks populates the transition area between the blue cloud and the red sequence in colour-magnitude space. We also find a population of morphologically distorted galaxies in the central cluster region. The substructure in the east of A2384 might be a group of galaxies falling onto the main cluster. We speculate that our sample of quenched spirals represents an intermediate phase in the ram-pressure driven transformation of infalling field spirals into cluster S0s. This is motivated by their position in colour-magnitude space. The occurrence of morphologically distorted galaxies in the cluster core complies with the hypothesis of A2384 representing a post merger system.Comment: 14 pages, 18 figures, A&A accepte

Food web characteristics of six intertidal habitat types of the Wadden Sea

Ecological network analysis (ENA) is a helpful tool to study complex ecosystem processes. The diverse species interactions are described as flows of energy providing a simplified representation of the natural system based on attributes and features. In the Wadden Sea, a unique ecosystem along the coastline of Denmark, Germany and the Netherlands, physical forces form the vast intertidal areas to diverse habitat types that differ in their species composition and abundance. Those habitats are important foraging areas for top predators such as birds. In the present study the food web of six habitats characteristic for the Wadden Sea (cockle field, razor clam field, mud flat, mussel bank, sand flat and seagrass meadow) were analyzed in a modelling approach. The functional and structural properties of the food webs were compared to assess differences and similarities in the system functioning. Although all systems revealed a good balance between their degree of organization and their robustness against external perturbations, they differed in their detailed features. The cockle field and the mussel bank both exhibited a strong dependence of their efficiency on external imports. The razor clam field, dominated by the introduced species Ensis directus, appeared to be a rather small and stressed system with low energy transfer. The mud flat system was characterized by a high use of microphytobenthos and appeared to be not fully developed yet. Bird predation was most pronounced in the sand flat and the seagrass meadow and led to an increase in energy transfer, parallel pathways and pathways lengths in these habitats. Each system shows characteristic features and plays a different role in the Wadden Sea ecosystem by contributing significantly to the whole system functioning

The influence of birds on the structure and functioning of coastal food webs

The Wadden Sea is one of the most important stop-over sites for migrating and breeding birds. About 10-12 million birds per year use the area for foraging and consume about 25 to 45% of the standing stock of macrozoobenthos. But little is known about the influence of birds on the entire ecosystem. We conducted Ecological Network Analysis (ENA) in an important breeding and resting site in the north-eastern German Wadden Sea to determine the influence of birds on the food web. The model was based on the yearly average of empirical data taken in the study site. In its current condition, the system appears to be in a well-balanced status, with a relative Ascendency of 32.3% and a robustness of 36.5%. The diversity of flows was high showed by a Flow Diversity of 5.1 and numerous parallel pathways represented by an Effective Link-Density of 3.3. A large variety of different bird species uses the area for foraging. As top predators, these bird species are included directly or indirectly in most of the pathways. Birds induce a huge negative impact on their prey items with a less pronounced positive feedback reaction to the competitors and food resources of those organisms. There is also a strong negative impact among the bird compartments probably due to competition between the bird species on the intertidal flats. Changes in the biomass of the birds revealed alterations in the food web structure. With a decline in the avian biomass the system showed a decrease in connectivity and diversity of flows but an increase in recycling. Birds therefore appear to be an important factor for the food web structure. Changes in the bird population could affect the complexity and functioning of the entire ecosystem. Thus, it is recommended to include birds in coastal food web studies which has rarely been done before. The use of such holistic approaches would facilitate undertaking management measures

Ram pressure and dusty red galaxies - key factors in the evolution of the multiple cluster system Abell 901/902

We present spectroscopic observations of 182 disk galaxies (96 in the cluster and 86 in the field environment) in the region of the Abell 901/902 multiple cluster system, which is located at a redshift of $z\sim 0.165$. The presence of substructures and non-Gaussian redshift distributions indicate that the cluster system is dynamically young and not in a virialized state. We find evidence for two important galaxy populations. \textit{Morphologically distorted galaxies} are probably subject to increased tidal interactions. They show pronounced rotation curve asymmetries at intermediate cluster-centric radii and low rest-frame peculiar velocities. \textit{Morphologically undistorted galaxies} show the strongest rotation curve asymmetries at high rest-frame velocities and low cluster-centric radii. Supposedly, this group is strongly affected by ram-pressure stripping due to interaction with the intra-cluster medium. Among the morphologically undistorted galaxies, dusty red galaxies have particularly strong rotation curve asymmetries, suggesting ram pressure is an important factor in these galaxies. Furthermore, dusty red galaxies on average have a bulge-to-total ratio higher by a factor of two than cluster blue cloud and field galaxies. The fraction of kinematically distorted galaxies is 75% higher in the cluster than in the field environment. This difference mainly stems from morphological undistorted galaxies, indicating a cluster-specific interaction process that only affects the gas kinematics but not the stellar morphology. Also the ratio between gas and stellar scale length is reduced for cluster galaxies compared to the field sample. Both findings could be best explained by ram-pressure effects.Comment: Electronic version published in Astronomy and Astrophysics Volume 549, Page 0; 19 pages, 21 figure

Tully-Fisher analysis of the multiple cluster system Abell 901/902

We derive rotation curves from optical emission lines of 182 disk galaxies (96 in the cluster and 86 in the field) in the region of Abell 901/902 located at $z\sim 0.165$. We focus on the analysis of B-band and stellar-mass Tully-Fisher relations. We examine possible environmental dependencies and differences between normal spirals and "dusty red" galaxies, i.e. disk galaxies that have red colors due to relatively low star formation rates. We find no significant differences between the best-fit TF slope of cluster and field galaxies. At fixed slope, the field population with high-quality rotation curves (57 objects) is brighter by \Delta M_{B}=-0\fm42\pm0\fm15 than the cluster population (55 objects). We show that this slight difference is at least in part an environmental effect. The scatter of the cluster TFR increases for galaxies closer to the core region, also indicating an environmental effect. Interestingly, dusty red galaxies become fainter towards the core at given rotation velocity (i.e. total mass). This indicates that the star formation in these galaxies is in the process of being quenched. The luminosities of normal spiral galaxies are slightly higher at fixed rotation velocity for smaller cluster-centric radii. Probably these galaxies are gas-rich (compared to the dusty red population) and the onset of ram-pressure stripping increases their star-formation rates. The results from the TF analysis are consistent with and complement our previous findings. Dusty red galaxies might be an intermediate stage in the transformation of infalling field spiral galaxies into cluster S0s, and this might explain the well-known increase of the S0 fraction in galaxy clusters with cosmic time.Comment: Accepted for publication in Astronomy and Astrophysics; 16 pages, 14 figure

Projektbericht (Mediumfassung)

Der Mediumbericht fasst die einzelnen Teile des Berichts in der Langfassung zusammen. Zunächst wird anhand von statistischen Zahlen und Fakten nachgewiesen, dass das männliche Ernährermodell noch immer sehr prägend für die Existenzsicherung von Frauen und Männern in Deutschland ist. Dies wird darauf zurückgeführt, dass im bundesdeutschen Recht diverse Schnittstellen des ehelichen Unterhaltsrechts mit dem Arbeits-, Sozial- und Steuerrecht existieren, die das Ernährermodell voraussetzen, faktisch auch auf Unverheiratete ausdehnen und gleichzeitig perpetuieren. Da aber auch der Gleichberechtigungsgrundsatz für Frauen und Männer gilt und ein Staatsziel sogar die "tatsächliche Durchsetzung der Gleichberechtigung" fordert, sind normative Wertungswidersprüche entstanden, die nach einer Reform der Schnittstellen und der Gesamtkonzeption der Berücksichtigung von Unterhalt und finanzieller Paarsolidarität in verschiedenen Regelungsbereichen verlangen. Anschließend an die Darstellung und Kritik der Schnittstellenregelungen wird am Beispiel der Anrechnung von Partnereinkommen und -vermögen gemäß SGB II ("Hartz IV") die subjektive Seite der sozialrechtlichen Einstandspflicht beleuchtet, indem Ergebnisse einer Befragung von Betroffenen referiert werden. Ein abschließendes Kapitel resümiert den Reformbedarf und skizziert die nötigen politischen Entwicklungen und Maßnahmen zur Überwindung der noch immer starken Stellung des männlichen Ernährermodells in Deutschland.200

Do birds influence the structure and functioning of coastal food webs?

The Wadden Sea is one of the most important stop-over sites for 10 to 12 Million migrating birds per year. But little is known about the influence of birds on the entire ecosystem. We conducted Ecological Network Analysis (ENA) in an important resting site in the Wadden Sea to determine the influence of birds on the food web. A large variety of different bird species uses the area for foraging and is included directly or indirectly in most of the pathways. Birds induce a negative impact on their prey items with a positive feedback reaction to the preys’ competitors and food sources. There is also a strong negative impact among the bird compartments probably due to competition between the birds. Changes in the biomass of the birds revealed alterations in the food web structure. With a decline in the avian biomass the system showed a decrease in connectivity and diversity of flows but an increase in recycling. Changes in the bird population could affect the complexity and functioning of the entire ecosystem. Thus, the use of such holistic approaches would facilitate undertaking management measures