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  • Molnár, Valéria, et al. (författare)
  • Zum Kontrastbegriff aus kontrastiver Perspektive
  • 2002
  • Ingår i: Text im Kontext 4. Beiträge zur 4. Arbeitstagung schwedischer Germanisten (Schriften des Germanistischen Instituts Universität Stockholm, 99-3493602-7 ; 29). - Stockholms universitet : Germanistisches Institut. - 91-89192-09-5 ; s. 141-154
  • Konferensbidrag (refereegranskat)
  • Molnár, Valéria, et al. (författare)
  • Zur Pragmatik und Grammatik des TOPIK-Begriffes
  • 1993
  • Ingår i: Wortstellung und Informationsstruktur (Linguistische Arbeiten, 0344-6727 ; 306). - Max Niemeyer Verlag. - 3-484-30306-9 ; s. 155-202
  • Bokkapitel (övrigt vetenskapligt)
  • Molnar, Z, et al. (författare)
  • Influence of fadA(G203R) and Delta flba mutations on morphology and physiology of submerged Aspergillus nidulans cultures
  • 2004
  • Ingår i: Applied Biochemistry and Biotechnology. - Humana Press. - 1559-0291. ; 118:1-3, s. 349-360
  • Tidskriftsartikel (refereegranskat)abstract
    • Morphologic and physiologic changes taking place in carbon-limited submerged cultures of Aspergillus nidulans DeltaflbA and fadA(G203R) strains were studied. Loss-of-function mutation of the flbA gene resulted in an altered germination with unusually thick germination tubes, "fluffy" pellet morphology, as well as a reduced fragmentation rate of hyphae during autolysis. In the fadA(G203R) mutant strain, conidiophores formed in the stationary phase of growth, and the size of pellets shrank considerably. There were no significant differences in the generation of reactive oxygen species (ROS) and in the specific catalase and superoxide dismutase activities by the tested mutants and the appropriate parental strains. Therefore, the participation of ROS or antioxidative enzymes in FadA/FlbA signaling pathways seems to be unlikely in submerged cultures. On the other hand, earlier increases in the extracellular-protease and ammonia production were recorded with the DeltaflbA strain, whereas the protease and ammonia production of the fadA(G203R) mutant lagged behind those of the wild-type strains. Similar changes in the time courses of the induction of gamma-glutamyltranspeptidase and the degradation of glutathione were observed. These results suggest that FadA/FlbA signaling may be involved in the mobilization of protein and peptide reserves as energy sources during carbon starvation.
  • Molokwu, Mary (författare)
  • Costs of foraging in a dry tropical environment
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This study evaluates the costs associated with foraging for birds in a savannah woodland area in central Nigeria. Specifically, it looks at the following questions: 1) how does seasonal variability in food and water availability affect the value of resources to birds in dry environments? 2) Does proximity to water affect foraging decisions? What implication will this have in the management of savannah birds? 3) Are tropical birds mostly affected by metabolic or predation costs? 4) What factors affect diet selection in birds and how? 5) How are birds adapted to hot dry environments? I carried out experiments in the field and in an aviary and provided artificial food patches, consisting of feeding trays with seeds mixed in sand or pebbles (in the aviary study). I used the giving-up density (GUD; amount of food left in a depletable patch after a foraging bout) of birds as a behavioral indicator and compared GUDs between different microhabitats, varying in levels of predation risk or thermal hazard, across different seasons and between years. In one study, I also placed out water pots to observe the effects of water on foraging, in another I looked at the diet selection strategy of birds offered two seed types differing in energetic content and in another looked at the effect of temperature on birds. Results showed that temporal (seasonal) variations in GUDs appear to be driven by food availability and water while small-scale spatial variation in GUDs seems to be driven by predation risk. Although birds seem to be willing to trade-off food for thermoregulation, they may resort to more costly means of thermoregulation e.g. hyperthermia (elevation of body temperature), when energy demand increases. Also proximity to drinking water will affect the extent to which granivorous birds exploit their environment and the diet selection strategy employed by these birds may be largely dependent on seed quality. My studies have revealed that the behavior observed among animals is shaped by the circumstances they are faced with in their environment. Therefore foraging behavior can be used to evaluate the magnitude and significance of the effects of the different costs associated with a foraging area and may serve as a useful tool in conservation.
  • Molokwu, Mary, et al. (författare)
  • Diet selection in birds: trade-off between energetic content and digestibility of seeds
  • 2011
  • Ingår i: Behavioral Ecology. - Oxford University Press. - 1045-2249. ; 22:3, s. 639-647
  • Tidskriftsartikel (refereegranskat)abstract
    • Partial preferences may occur due to differences in profitability and encounter probability between food types within a patch. In the expanding specialist diet strategy, a forager goes from being partially selective on the preferred, most profitable food, to being opportunistic, after the preferred food has been depleted to a certain critical level. We studied the diet selection strategies of birds foraging on 2 seed types-crushed peanut Arachis hypogaea and husked millet Pennisetum gambiense, in a woodland savannah near Jos, Nigeria. Peanut contains more fat and energy, whereas millet is richer in carbohydrates. We tested 2 hypotheses: 1) energy content will determine seed preference for seeds with relatively similar handling times and 2) diet selection will vary seasonally in response to nutritional demands. We carried out 2 experiments, one with both seed types occurring in a single patch and another with both occurring in 2 separate patches during different seasons. The diet selection strategy of the birds was similar to the expanding specialist. Initially, peanuts seemed to be the preferred food, probably due to their high profitability, but overall millet was preferred. However, the expansion point was not determined by the amount of peanut seeds left, as predicted, but rather by the amount eaten. We propose that a trade-off is created by the fact that peanut has higher energy density but at the same time contains secondary compounds. Selectivity for millet decreased slightly in the wet season when more peanuts were taken possibly due to increasing nutritional demands during breeding. Key words: diet model, diet selection, dry tropics, energy, expanding specialist, foraging behavior, granivorous birds, savannah, seasonality, secondary compounds, seed preference, water. [Behav Ecol 22: 639-647 (2011)]
  • Molokwu, Mary, et al. (författare)
  • Effects of season, water and predation risk on patch use by birds on the African savannah
  • 2010
  • Ingår i: Oecologia. - Springer. - 1432-1939. ; 164:3, s. 637-645
  • Tidskriftsartikel (refereegranskat)abstract
    • Birds from semi-arid regions may suffer dehydration during hot, dry seasons with low food availability. During this period, both energetic costs and water requirements for thermoregulation increase, limiting the scope of activity. For granivorous birds feeding on dry seeds, this is a major challenge and availability of water may affect the value of food. Water availability could (1) increase the value of a food patch when the surrounding environment is poor, due to an increase in the marginal value of energy, and (2) increase the value of the entire environment to the forager when environmental quality increases, due to an increase in the marginal value of time. We aimed to test this by measuring giving-up densities (GUDs, remaining food densities after foraging) of granivorous birds in the presence or absence of filled water pots, at different seasons differing in background food and water availability. We predicted that GUDs will increase with water provision during the dry season with moderate food, but in the early wet season with low food and water availability, GUDs will decrease with water provision. Later in the wet season, our experimental addition of water should have no effect. During seasons with low water availability but differing in food availability, results confirmed our predictions. However, when water became more abundant as the wet season progressed, birds still foraged more intensely during days with added water. In all seasons, birds fed more intensely in cover than in exposed areas, suggesting that predation risk rather than heat influenced microhabitat selection.
  • Molokwu, Mary Ngozi, et al. (författare)
  • Feeding behaviour of birds foraging on predictable resources in habitats of different quality
  • 2007
  • Ingår i: Ostrich. - BirdLife South Africa. - 0030-6525. ; 78:2, s. 295-298
  • Tidskriftsartikel (refereegranskat)abstract
    • Using the density of food left in a patch after foraging - i.e. the giving-up density (GUD) - as a behavioural indicator, short-term foraging studies on birds in the dry and wet fringing forests and savanna habitats of the Amurum Forest Reserve, Laminga, Nigeria, were used to evaluate whether widespread food abundance will affect their behaviour in these apparently-different habitats. The effect of the dry season on feeding activity and the effects of temperature within, and between, days were also investigated. Results showed that GUDs were highest in dry fringing forests, intermediate in wet fringing forests, and lowest in savanna. This difference may have been as a result of a difference in food abundance between habitats. The availability of water in the wet fringing forests may have affected the feeding behaviour of the birds in the wet gully habitat compared with those of the dry gully. The behaviour of birds in response to time of day was affected by temperature, as there was no difference between GUDs in open and covered habitats in the mornings at lower temperatures, but lower GUDs were recorded in cover (at higher temperatures) in the afternoon when birds may - due to thermoregulatory costs - retreat to cover more often. However, temperature had no effect on GUDs over season. A reduction in GUDs towards the end of the dry season, as food resources deplete, gives further credence to the observation that food abundance affects behaviour.
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