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Reduced Feeding (reduced + feeding)
Selected AbstractsThe impact of predation risk from small mustelids on prey populationsMAMMAL REVIEW, Issue 3-4 2000Kai Norrdahl ABSTRACT Small mustelids are ,snake-like' mammals adapted to hunt small rodents, which are their principal prey, in tunnels leaving practically no refuge for the prey. Prey rodents have adaptive behaviours to situations where the predation risk from mustelids is high, including reduced activity and escape by climbing. Small mustelids may affect prey population dynamics directly through killing (increased mortality) and/or indirectly through behavioural changes in prey as a response to the presence of mustelids (predation risk). The Predator-Induced Breeding Suppression hypothesis (PIBS) states that a trade-off between survival and reproduction should lead to delayed breeding under temporarily high predation risk, so that the mere presence of predators may reduce reproductive output. Current results suggest that small mustelids mainly affect prey population growth rate directly through killing. In many cyclic rodent populations, small mustelid predation is a major mortality factor, and experimental evidence supports the hypothesis that these predators drive prolonged summer declines in prey. In contrast, the evidence for PIBS is controversial. Experimental evidence shows that the indirect effects of small mustelids on prey populations are negligible during the best breeding season. However, in other seasons, the presence of predators may indirectly affect prey populations, although this has not been studied experimentally. Prey rodents may decrease mobility as a response to high predation risk by small mustelids, and this reduction in mobility decreases feeding. Reduced feeding affects the energy reserves of voles, and may delay maturation or lower the size of the first litter. [source] Behavioural changes in Schistocerca gregaria following infection with a fungal pathogen: implications for susceptibility to predationECOLOGICAL ENTOMOLOGY, Issue 3 2001Steven Arthurs Summary 1. Field observations have indicated that infection of locusts and grasshoppers by the fungal entomopathogen Metarhizium anisopliae var. acridum may result in a substantial increase in the host's susceptibility to predation, before death is caused directly by the disease. 2. Laboratory experiments were conducted to examine how the behaviour of the desert locust Schistocerca gregaria Forskål changes following infection by M. anisopliae var. acridum to explore some potential mechanisms underlying this phenomenon. 3. In the first experiment, which involved monitoring general locust activity in small cages throughout the disease incubation period, infected locusts were observed to increase locomotion and bodily movement from 3 days after infection until death (average survival time of 11 days). There was some evidence of reduced feeding and mating behaviour following infection. 4. In a second experiment, locusts were exposed individually to a simulated predator attack and the initiation and strength of any escape responses were measured. Infected locusts were observed to have a reduced escape capability (both the propensity to escape and the strength of the response). In contrast to the relatively early changes in general activity observed in the first experiment, this was only apparent at the late stages of infection shortly before death. 5. Both an increase in movement and general apparency early in the infection process, and reduced escape capability late on, suggest mechanisms whereby the susceptibility of locusts and grasshoppers to predation might be enhanced following infection with M. anisopliae var. acridum. [source] Restricted fish feeding reduces cod otolith opacityJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2008H. Høie Summary The purpose of this work was to examine the effect of reduced feeding and constant temperature on cod otolith opacity. Three groups of juvenile cod were given restricted food rations at different times for 4 months, resulting in depressed somatic growth. Otolith opacity was measured on pictures of the otolith sections. The otolith carbonate deposited during the experimental period was generally opaque compared to the more translucent otolith material deposited prior to and after the experimental period, when the fish were kept in a pond and in sea-cages at higher temperatures. Large variations in otolith opacity were found between individual fish both within groups and between groups. In two of the three groups significantly more translucent otolith material was deposited in response to reduced feeding. Our results show that variations in feeding and hence fish growth resulted in variation in otolith opacity, but the effect was minor compared to that of variations in ambient temperature. The combined influence of these effects, which both act on fish metabolism, are most likely controlling the seasonal opacity changes observed in wild fish. Our results help explain the variations seen in fish at constant temperatures. [source] Mechanism of a plastic phenotypic response: predator-induced shell thickening in the intertidal gastropod Littorina obtusataJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2007J. I. BROOKES Abstract Phenotypic plasticity has been the object of considerable interest over the past several decades, but in few cases are mechanisms underlying plastic responses well understood. For example, it is unclear whether predator-induced changes in gastropod shell morphology represent an active physiological response or a by-product of reduced feeding. We address this question by manipulating feeding and growth of intertidal snails, Littorina obtusata, using two approaches: (i) exposure to predation cues from green crabs Carcinus maenas and (ii) reduced food availability, and quantifying growth in shell length, shell mass, and body mass, as well as production of faecal material and shell micro-structural characteristics (mineralogy and organic fraction) after 96 days. We demonstrate that L. obtusata actively increases calcification rate in response to predation threat, and that this response entails energetic and developmental costs. That this induced response is not strictly tied to the animal's behaviour should enhance its evolutionary potential. [source] Feeding and survival of Culicoides sonorensis on cattle treated with permethrin or pirimiphos-methylMEDICAL AND VETERINARY ENTOMOLOGY, Issue 3 2000B. A. Mullens Summary The persistence of permethrin (5% a.i.) and pirimiphos-methyl (27% a.i.), applied to the dorsum of calves in the field against Culicoides sonorensis Wirth and Jones (Diptera: Ceratopogonidae), was estimated using a hair-blood-feeding bioassay in the laboratory. Hair clippings were taken before treatment and 3, 7, 14, 21, 28, 42 and 56 days after treatment from the dorsum, side and belly of treated and control calves. Laboratory-reared insects were allowed to feed through thin hair layers and a parafilm membrane on sheep blood warmed using a water-jacketed feeder. Some intoxication after exposure to hair was noted up to 28 days after treatment with permethrin and up to 14 days after treatment with pirimiphos-methyl. Hair from the dorsum caused more intoxication for a longer period than hair from other body regions. Permethrin and pirimiphos-methyl applied to the back did not significantly reduce overall engorgement (body regions pooled) after treatment. Permethrin residues on hair remained far higher on the back than other body regions and were related to insect intoxication and reduction in engorgement in the laboratory. Residues on belly hair never exceeded 12 p.p.m. and did not result in significantly reduced feeding at any time. Engorged insects that exhibited sublethal intoxication from feeding through permethrin-treated hair did recover and matured numbers of eggs comparable to controls. Field trials using treated and control calves and enclosure nets showed that dorsal applications of 5% permethrin were not effective in reducing engorgement, despite some intoxication. Vacuum samples from a calf showed that C. sonorensis fed primarily on the belly. A 0.2% permethrin application on the belly (250 ml) did result in >,80% reduction of C. sonorensis in the enclosure nets at 3 and 7 days after treatment, but activity had subsided by 10 days after treatment. The utility of insecticidal treatments for suppression of this vector is discussed. [source] | ||||||||||