Rate Of Body Mass Gain Research Articles

Daily accumulation of body reserves under increased predation risk in captive Greenfinches Carduelis chloris

The effect of increased perceived risk of predation on the trajectory describing the daily gain in body mass of captive Greenfinches Carduelis chloris was tested. Theoretically, increased risk of predation is expected to shift the gain in body mass towards the latter part of the day and reduce body mass. The perceived risk of predation was increased with a stuffed flying hawk three times per day. Following each presentation of the predator, foraging stopped and the birds lost mass. When feeding resumed, the birds compensated for the mass loss by increasing the rate of body mass gain, in line with theoretical predictions. In the presence of the predator, the daily accumulation of body reserves was lower compared with risk‐free situations. However, on the days following presentation of the hawk, when the birds were presumably aware of an increased risk of predation, Greenfinches did not exhibit the predicted change in reserve accumulation, but rather maintained their usual pattern of body mass gain.

Effects of Diet on Rate of Body Mass Gain by Wintering Canvasbacks

Because habitat degradation has led to the lobs of submerged vegetation in Chesapeake Bay, wintering canvasbacks (Aythya valisineria) have shifted from a plant diet of American wildcelery (Vallisneria americana) to an animal diet of Baltic clams (Macoma bathica). We conducted experiments with pen-reared canvasbacks (n = 32, 1990; n = 32, 1991) to assess the effect of this diet change on mass recovery rate following a simulated period of food deprivation. During the recovery phase, canvasbacks were fed ad libitum either (1) Baltic clams (1991 only), (2) tubers of wildcelery, (3) corn, or (4) commercial control diet. Initial body mass of ducks did not differ between years (P = 0.754) or among pens (P > 0.264) or diets within years (1990, P = 0.520; 1991, P = 0.684). Body mass decline during food deprivation (x = 26.0 g/day ± 0.6 SE) did not differ among diets (1990, P = 0.239; 1991, P = 0.062) or between sexes in 1990 (P = 0.197), but was greater (P = 0.039) for males (x = 28 g/day ± 0.8 SE) than females (x = 25 g/day ± 0.9) in 1991. Mass recovery rate differed between diets (clams excluded) in 1990 (P = 0.003) and 1991 (clams included) (P = 0.011); mean = 42 g.bird −1 .day −1 ± 3.8 (SE) control diet, mean = 32 g.bird −1 .day −1 ± 2.8 wildcelery tubers, mean = 24 g.bird −1 .day −1 ± 4.9 whole corn, and mean = 23 g.bird −1 .day −1 ± 1.0 Baltic clams. Canvasbacks consumed an average of 2,169 g.bird −1 day −1 of Baltic clams, 1,158 g.bird −1 day −1 of wildcelery tubers, 152 g.bird −1 .day −1 whole corn, and 208 g.bird −1 .day −1 (dry mass) control diet during recovery. Managers should restore and maintain aquatic plant foods that enhance winter survival of canvasbacks and other waterfowl in response to declining habitat quality

Energetics, osmoregulation, and food consumption by free-living desert lizards, Ctenophorus (= Amphibolurus) nuchalis

Abstract The ecophysiology of the agamid lizard Ctenophorus nuchalis was studied near Shark Bay, Western Australia, during three seasons, over four years, in order to evaluate seasonal and year-to-year variation in energy and material balance, and to compare this agamid with similar-sized iguanid lizards. We measured water influx and efflux rates and field metabolic rates with doubly-labelled water, sodium fluxes with radiosodium, and osmotic status (plasma osmotic and ionic concentrations) in free-ranging adults of both sexes, as well as juveniles. Feeding rates were calculated from diet composition information in conjunction with rates of water and sodium intake, and body condition indices were also determined. There were marked seasonal and year-to-year differences in body condition, and in rates of body mass gain or loss, and these correlated with drought periods. Rates of resource use were highest in spring, and declined through summer and autumn, and rates were lowest during 1983, a year having unusually low winter rainfall. Hatchlings, which emerged in autumn, were able to find and capture food resources, even though adults were eating little during that season. The annual pattern of energy, water and salt balance in this agamid lizard is quite similar to that of an equivalent-sized iguanid lizard.

Effect of Gender on the Response to a High Fat Diet in Aging Fischer 344 Rats

The purpose of this study was to describe the effects of high fat (HF) and low fat (LF) diets in male and female Fischer 344 (F344) rats ages 5, 23 and 27 mo. Rats were fed the diet for 3 mo, and then resting metabolic rate, body composition and adipose tissue cellularity were evaluated. Although body mass was greater in rats fed the HF diet, this difference was due to a rapid increase in mass within the first 2 wk. There was no difference in the rate of body mass gain after this period. Resting mass-independent metabolic rate did not significantly differ due to age, diet or gender. In general, percentage fat mass was greater in rats fed the HF diet and in female than in male rats in both diet groups. However, lean body mass (%) was not altered due to diet or age. Cell number of the retroperitoneal depot increased with age and diet between 5 and 23 mo of age in both male and female rats. There was no effect of age, diet or gender on retroperitoneal cell size or gonadal cell number and size. These data suggest that age, gender and diet do not significantly alter the ability of F344 rats to regulate body composition or fat cell proliferation.