Cycles of Covers.

We initially consider an example of Flynn and Redmond, which gives an infinite family of curves to which Chabauty's Theorem is not applicable, and which even resist solution by one application of a certain bielliptic covering technique. In this article, we shall consider a general context, of which this family is a special case, and in this general situation we shall prove that repeated application of bielliptic covers always results in a sequence of genus 2 curves which cycle after a finite number of repetitions. We shall also give an example which is resistant to repeated applications of the technique

Optimierung von Saatgutbehandlungsmitteln mit Wirkung gegen Flugbrand an Gerste und Weizen (Ustilago nuda, U. tritici) unter Nutzung verbesserter Verfahren zum Nachweis der Erreger

Ziel des Projektes war die Entwicklung von Saatgutbehandlungsmitteln zur Flugbrandbekämpfung im Ökolandbau und von Techniken die geeignet sind, die Entwicklung solcher Saatgutbehandlungsmittel zu beschleunigen. In Inokulationsversuchen konnte im Feldversuch durch Ausstäuben von Sporen Saatgut mit 2-5% Flugbrandbefall erzeugt werden. Nach Einzelblüteninokulation lag der Befall oft über 60%. Anders als bei Weizen waren bei Gerste die Keimfähigkeit und das Tausendkorngewicht von solchem Saatgut deutlich reduziert. Von ca. 30 geprüften Pflanzenextrakten führten neun nach Inkorporation in PDA zu einer vollständigen Hemmung der Brandsporenkeimung. In Hemmtesten mit Mikroorganismen betrug der Anteil wirksamer Isolate bei den Trichoderma-Isolaten 43%, bei den Actinomyceten 30% und bei den übrigen Bakterien 11%. In mehrjährig durchgeführten Kleinparzellenversuchen mit flugbrandinfizierter Gerste und Weizen wurden mit einigen Behandlungsvarianten Bekämpfungserfolge erzielt. Die Effekte waren aber zu gering für die praktische Anwendung und nur bedingt reproduzierbar. Topfversuche im Gewächshaus mit hochinfizierten Saatgutchargen erbrachten ähnliche Ergebnisse. Die Wirksamkeit gegen Haferflugbrand wurde nur einmal überprüft. Wie im Falle von Gersten- und Weizenflugbrand war der Bekämpfungserfolg auch beim Haferflugbrand unbefriedigend. Eine Ausnahme bildete die Saatgutbehandlung mit Ethanol (70%). Mit ihr wurde bei Hafer eine Flugbrandwirksamkeit von ca. 80% erzielt. Nach Anfärbung mit dem Fluoreszenzfarbstoff Blankophor wurde beobachtet, dass der Pilz schon wenige Tage nach Beginn der Keimung in das Apikalmeristem und die Blattprimordien eindrang. Im 1-Knotenstadium waren die Ährenanlagen meist völlig besiedelt. Ein Protokoll für einen immunologischen (ELISA) und für einen molekularbiologischen (real-time PCR) Nachweis wurde entwickelt und zur Quantifizierung des Pilzes in Jungpflanzen angewendet. Die mit beiden Methoden erhaltenen Daten stimmten gut überein. In weiteren Versuchen konnte die Anwendbarkeit des mikroskopischen Nachweises und des ELISA für die Entwicklung von Saatgutbehandlungsmitteln und –verfahren exemplarisch gezeigt werden

A satellite-based snow cover climatology (1985–2011) for the European Alps derived from AVHRR data

Seasonal snow cover is of great environmental and socio-economic importance for the European Alps. Therefore a high priority has been assigned to quantifying its temporal and spatial variability. Complementary to land-based monitoring networks, optical satellite observations can be used to derive spatially comprehensive information on snow cover extent. For understanding long-term changes in alpine snow cover extent, the data acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensors mounted onboard the National Oceanic and Atmospheric Association (NOAA) and Meteorological Operational satellite (MetOp) platforms offer a unique source of information. <br><br> In this paper, we present the first space-borne 1 km snow extent climatology for the Alpine region derived from AVHRR data over the period 1985–2011. The objective of this study is twofold: first, to generate a new set of cloud-free satellite snow products using a specific cloud gap-filling technique and second, to examine the spatiotemporal distribution of snow cover in the European Alps over the last 27 yr from the satellite perspective. For this purpose, snow parameters such as snow onset day, snow cover duration (SCD), melt-out date and the snow cover area percentage (SCA) were employed to analyze spatiotemporal variability of snow cover over the course of three decades. On the regional scale, significant trends were found toward a shorter SCD at lower elevations in the south-east and south-west. However, our results do not show any significant trends in the monthly mean SCA over the last 27 yr. This is in agreement with other research findings and may indicate a deceleration of the decreasing snow trend in the Alpine region. Furthermore, such data may provide spatially and temporally homogeneous snow information for comprehensive use in related research fields (i.e., hydrologic and economic applications) or can serve as a reference for climate models

Künstliche Inokulation von Gerstenpflanzen mit dem Flugbranderreger (Ustilago nuda) und Infektionsverlauf auf dem Fruchtknoten

ZusammenfassungZiel der Arbeit war die Prüfung künstlicher Inokulationsverfahren von Gerstenpflanzen mit dem Flugbranderreger (Ustilago nuda) und das Erlangen von Erkenntnissen zum genauen Infektionsverlauf auf dem Fruchtknoten. Diese Versuche sollten die Basis sein, um zukünftig hoch befallenes Saatgut in ausreichender Menge herstellen zu können, was für Folgeexperimente von großer Wichtigkeit wäre. Hierzu wurden drei Inokulationsmethoden – Inokulation mit der Spritze, Vakuuminfiltration und Besprühen mit Sporensuspension – hinsichtlich der erhaltenen Befallsraten und ihrem Einfluss auf die Keimfähigkeit miteinander verglichen. Weiterhin wurde untersucht, ob die Position des inokulierten Blütchens an der Ähre einen Einfluss auf den späteren Befall des daraus hervorgehenden Korns hat. Zu diesem Zweck wurden die Ähren zunächst per Spritze inokuliert und anschließend beim Ernten in jeweils drei Teile zerlegt und gesondert über einen Embryotest ausgewertet. Als aussichtsreichste Inokulationsmethode kristallisierte sich die Inokulation mit der Spritze heraus. Ein Einfluss der Ährenregion auf den späteren Befall konnte nicht nachgewiesen werden. Des Weiteren wurden mikroskopische Untersuchungen durchgeführt, die zu einem besseren Verständnis des Infektionsverlaufes auf dem Fruchtknoten führen sollten. Hierfür wurde ein lactophenolbasierendes Autoklavieranfärbeverfahren verwendet. Es konnte gezeigt werden, dass eine Infektion des Fruchtknotens nicht zwingend über die Narbe stattfinden muss, und dass der Pilz bei einer erfolgreichen Infektion die obersten Zellschichten der Fruchtknotenwand intrazellulär mit einer Infektionshyphe penetriert.Stichwörter: Brandkrankheiten, Flugbrandbefall, BlüteninokulationAbstract The aim of this study was the examination of artificial inoculation techniques of barley with the pathogen (Ustilago nuda) and to obtain detailed new findings on the mode of infection on the ovary. These tests were designed to be the base to produce a sufficient amount of highly infected seeds, which would be of great importance for further experiments. Three inoculation techniques - by injection, vacuum infiltration or spraying with spore suspension - were compared with respect to the resulting infection rates and their influence on the germination rate. Moreover, it was evaluated, if the position of the inoculated floret on the ear has any influence on subsequent infection of the developing grain. Therefore the ears were inoculated by injection and, after harvesting, divided in three parts and separately evaluated with an embryo test. The most promising inoculation technique turned out to be inoculation by injection. An influence of the ear area on subsequent infection was not detected. In addition, microscopic analyses were carried out, which should provide a better understanding of the mode of infection on the ovary. A lactophenolbased autoclave staining technique was applied. The analysis showed that an infection of the ovary does not necessarily originate from the stigma, and that in case of an effective infection the fungus penetrates the uppermost cell layers of the ovary intracellularly with an infection hypha.Keywords: smuts, loose smut, flower inoculatio

Revealing four decades of snow cover dynamics in the Hindu Kush Himalaya

Knowledge about the distribution and dynamics of seasonal snow cover (SSC) is of high importance for climate studies, hydrology or hazards assessment. SSC varies considerably across the Hindu Kush Himalaya both in space and time. Previous studies focused on regional investigations or the influence of snow melt on the local hydrological system. Here, we present a systematic assessment of metrics to evaluate SSC dynamics for the entire HKH at regional and basin scale based on AVHRR GAC data at a 0.05° spatial and daily temporal resolution. Our findings are based on a unique four-decade satellite-based time series of snow cover information. We reveal strong variability of SSC at all time scales. We find significantly decreasing SSC trends in individual summer and winter months and a declining tendency from mid-spring to mid-fall, indicating a shift in seasonality. Thanks to this uniquely spatio-temporally resolved long-term data basis, we can particularly highlight the unique temporally variable character of seasonal snow cover and its cross-disciplinary importance for mountain ecosystems and downstream regions

Habitat‐dependent occupancy and movement in a migrant songbird highlights the importance of mangroves and forested lagoons in Panama and Colombia

Climate change is predicted to impact tropical mangrove forests due to decreased rainfall, sea‐level rise, and increased seasonality of flooding. Such changes are likely to influence habitat quality for migratory songbirds occupying mangrove wetlands during the tropical dry season. Overwintering habitat quality is known to be associated with fitness in migratory songbirds, yet studies have focused primarily on territorial species. Little is known about the ecology of nonterritorial species that may display more complex movement patterns within and among habitats of differing quality. In this study, we assess within‐season survival and movement at two spatio‐temporal scales of a nonterritorial overwintering bird, the prothonotary warbler (Protonotaria citrea), that depends on mangroves and tropical lowland forests. Specifically, we (a) estimated within‐patch survival and persistence over a six‐week period using radio‐tagged birds in central Panama and (b) modeled abundance and occupancy dynamics at survey points throughout eastern Panama and northern Colombia as the dry season progressed. We found that site persistence was highest in mangroves; however, the probability of survival did not differ among habitats. The probability of warbler occupancy increased with canopy cover, and wet habitats were least likely to experience local extinction as the dry season progressed. We also found that warbler abundance is highest in forests with the tallest canopies. This study is one of the first to demonstrate habitat‐dependent occupancy and movement in a nonterritorial overwintering migrant songbird, and our findings highlight the need to conserve intact, mature mangrove, and lowland forests

Early Evidence of Natal-Habitat Preference: Juvenile Loons Feed on Natal-Like Lakes After Fledging

Many species show natal habitat preference induction (NHPI), a behavior in which young adults select habitats similar to those in which they were raised. However, we know little about how NHPI develops in natural systems. Here, we tested for NHPI in juvenile common loons (Gavia immer) that foraged on lakes in the vicinity of their natal lake after fledging. Juveniles visited lakes similar in pH to their natal lakes, and this significant effect persisted after controlling for spatial autocorrelation. On the other hand, juveniles showed no preference for foraging lakes of similar size to their natal one. When lakes were assigned to discrete classes based on size, depth, visibility, and trophic complexity, both juveniles from large lakes and small lakes preferred to visit large, trophically diverse lakes, which contained abundant food. Our results contrast with earlier findings, which show strict preference for lakes similar in size to the natal lake among young adults seeking to settle on a breeding lake. We suggest that NHPI is relaxed for juveniles, presumably because they select lakes that optimize short‐term survival and growth. By characterizing NHPI during a poorly studied life stage, this study illustrates that NHPI can take different forms at different life stages

The dynamic trophic niche of an island bird of prey

Optimal foraging theory predicts an inverse relationship between the availability of preferred prey and niche width in animals. Moreover, when individuals within a population have identical prey preferences and preferred prey is scarce, a nested pattern of trophic niche is expected if opportunistic and selective individuals can be identified. Here, we examined intraspecific variation in the trophic niche of a resident population of striated caracara (Phalcoboenus australis) on Isla de los Estados (Staten Island), Argentina, using pellet and stable isotope analyses. While this raptor specializes on seabird prey, we assessed this population\u27s potential to forage on terrestrial prey, especially invasive herbivores as carrion, when seabirds are less accessible. We found that the isotopic niche of this species varies with season, age, breeding status, and, to a lesser extent, year. Our results were in general consistent with classic predictions of the optimal foraging theory, but we also explore other possible explanations for the observed pattern. Isotopic niche was broader for groups identified a priori as opportunistic (i.e., nonbreeding adults during the breeding season and the whole population during the nonbreeding season) than it was for individuals identified a priori as selective. Results suggested that terrestrial input was relatively low, and invasive mammals accounted for no more than 5% of the input. The seasonal pulse of rockhopper penguins likely interacts with caracara\u27s reproductive status by constraining the spatial scale on which individuals forage. Niche expansion in spatially flexible individuals did not reflect an increase in terrestrial prey input; rather, it may be driven by a greater variation in the types of marine prey items consumed