Consequences of feeding for future feeding

The intake of food has physiological consequences via physical (e.g. distension) and chemical (e.g. glucose) stimulation of receptors in the viscera and, in the longer term, by changes in signals from adipose tissue (e.g. leptin), integrated by the CNS. These consequences are associated with the sensory properties of the food such that repeated exposure to a food generates a conditioned acceptance or rejection reflex with the physiological consequences of eating as the unconditioned stimulus (US) and the sensory characteristics of the food as the conditioned stimulus (CS). Such learnt preferences and aversions occur throughout the animal kingdom, from nematodes to human beings, with much of the research being carried out with insects, laboratory animals and farm animals. Preferences for and aversions to particular foods are manifested in non-random choices between two or more foods on offer but also influence the quantity eaten when only one food is available. These considerations have been developed into a theory of Minimal Total Discomfort which proposes that an animal experiments with the amount eaten per day, and its selection between different foods, until the total of the signals generated from excesses or deficiencies of food components is minimised. Changes in food composition and/or nutrient requirements can therefore be matched by appropriate changes in intake and selection.     

Representing infant feeding: content analysis of British media portrayals of bottle feeding and breast feeding

ObjectiveTo examine how breast feeding and bottle feeding are represented by the British media.DesignContent analysis.Subjects Television programmes and newspaper articles that made reference to infant feeding during March 1999.SettingUK mass media.ResultsOverall, 235 references to infant feeding were identified in the television sample and 38 in the newspaper sample. Bottle feeding was shown more often than breast feeding and was presented as less problematic. Bottle feeding was associated with “ordinary” families whereas breast feeding was associated with middle class or celebrity women. The health risks of formula milk and the health benefits of breast feeding were rarely mentioned.ConclusionsThe media rarely present positive information on breast feeding, even though this feeding practice is associated with the most health benefits. Health professionals and policy makers should be aware of patterns in media coverage and the cultural background within which women make decisions about infant feeding.     

Filtering and feeding rates of cyclopoid copepods feeding on phytoplankton

The algal biomass ingested by omnivorous cyclopoid copepods (Cyclops kolensis and C. vicinus) was measured by two methods in the hypertrophic Heiligensee in Berlin (West Germany). The clearance and ingestion rates inferred from measurements of natural populations of ¹⁴C labelled phytoplankton were compared with those obtained from chlorophyll a determinations using the presence/absence method (observed chlorophyll a content of natural lake phytoplankton with and without addition of cyclopoids). Both methods gave similar results. Nevertheless, the radio tracer method is preferred, mainly because the short feeding duration excludes high variations in both the food composition and food concentration that limit the presence/absence method.     

Sea-urchin feeding fronts

Sea-urchin feeding fronts are a striking example of spatial pattern formation in an ecological system. If it is assumed that urchins are asocial, and that they move randomly, then the formation of these dense fronts is an apparent paradox. The key lies in observations that urchins move further in areas where their algal food is less plentiful. This naturally leads to the accumulation of urchins in areas with abundant algae. If urchin movement is represented as a random walk, with a step size that depends on algal concentration, then their movement may be described by a Fokker–Planck diffusion equation. For certain combinations of algal growth and urchin grazing, traveling wave solutions are obtained. Two-dimensional simulations of urchin algal dynamics show that an initially uniformly distributed urchin population, grazing on an alga with a smoothly varying density, may form a propagating front separating two sharply delineated regions. On one side of the front algal density is uniformly low, and on the other side of the front algal density is uniformly high. Bounds on when stable fronts will form are obtained in terms of urchin density and grazing, and algal growth.     

Ascidian suspension feeding

Ascidians are a diverse group of benthic suspension feeders. This review presents and discusses the current literature on ascidian suspension feeding including the different structures involved in feeding as well as how feeding responds to variation in environmental parameters like water temperature and particle concentration. It is concluded that clearance rates in different species at identical conditions will not vary more than within the same species of different sizes, and that variation in clearance rate in ascidians in relation to temperature and particle concentration involves different regulatory mechanisms. Finally ascidian and mussel suspension feeding is compared. It is concluded that the two pumps are very alike with regard to pump performance and specific clearance rate, but whereas ascidian suspension feeding is characterised by high efficiency in terms of particle range and costs of pumping, mussel suspension feeding is more adapted to turbid conditions.     

Surface deposit feeding versus filter feeding in the amphipod Corophium volutator

The previously indicated ability of the amphipod Corophium volutator to switch between deposit feeding and filter feeding was confirmed and studied in more detail in controlled laboratory experiments in which filtration rate measurements were combined with simultaneous video recordings of surface-feeding activity of the amphipod exposed to different known concentrations of algal (Tetraselmis sp.) cells. When algal cells were added to the ambient water, this stimulated C. volutator, buried in natural sediment or transferred to glass tubes, to commence filter feeding, which was maintained as long as the algal concentration was kept above a certain threshold level. However, shortly after the algal concentration was grazed below the threshold level, filter feeding was abandoned and replaced by surface deposit feeding, as evident from a video observed increase in surface scraping frequency. The average frequency of surface scraping was 0.64±0.27 min^-1, with a residence time of 3.7±1.4 s on the sediment surface where the amphipod grabbed material within a semicircle. Such detailed knowledge of filter feeding versus deposit feeding in C. volutator is of importance for a better understanding of the ecological role of this key organism in many shallow-water ecosystems where the feeding conditions are frequently changing.     

Individual differences in feeding efficiencies and feeding preferences of captive great tits

The preferences of eight, adult, hand-reared great tits for feeding on four different types of feeding sites have been tested. There were significant differences between individuals in these preferences, and the preferences for the different objects were correlated with the birds' individual feeding efficiencies on the objects. This correlation was thought to be a result of the birds' experience and learning during training for the experiment. During the tests the birds tended to make runs of visits to the same object type. This effect was more marked for less-preferred objects, and when the birds had just made a successful visit.     

Functional relationships between plant feeding and prey feeding for a zoophytophagous bug

The consumption of plants by the zoophytophagous bug Macrolophus pygmaeus Rambur (Heteroptera : Miridae) in relation to the presence or absence of prey is monitored for 7 days. Tobacco plants enriched with ¹⁵N, a stable, nonradioactive isotope of nitrogen, are used for characterization. In the absence of prey, the relationship between time and ¹⁵N content (which equates to plant feeding) is linear, with a constant daily accumulation of ¹⁵N; however, if prey are available, the mathematical relationship becomes curvilinear. From day 1 to day 5, feeding on plants is independent of the consumption of prey. The rate of ¹⁵N accumulation decreases in the presence of prey after day 5, whereas the number of prey eaten remains unchanged.