Three sigmoidal growth equations were tested for their usefulness in fitting mammalian growth curves. The von Bertalanffy, Gompertz, and logistic equations were fitted to growth data by nonlinear regression techniques. The residual sum of squares and deviations of predicted neonate, weaning, and adult masses from observed values were used as criteria to choose among the models. The von Bertalanffy equation provided the smallest residual sum of squares, while the Gompertz equation fitted equally well by this criterion. The logistic equation overestimated neonate mass and underestimated adult mass, the Gompertz overestimated neonate mass, and the von Bertalanffy overestimated weaning mass. The Gompertz model was chosen to fit a sample of 331 species; growth rate constants, K , for these species are presented. The relationship of K to adult mass was calculated and was found to have a slope similar to that of altricial birds. K -values were found to be comparable to those reported by Case (1978) and consistently higher than those of Millar (1977). Species having differing rates from those reported by Case or Millar were also identified; ground squirrels had faster growth rates and seals had slower growth rates when rate of growth was estimated by the Gompertz equation.

Fitting Sigmoidal Equations to Mammalian Growth Curves

An animal's nutritional status depends on (1) nutrient accessibility, (2) nutrient demand, and (3) physiological, metabolic, morphological, and behavioral compensations that avert or minimize discrepancies, if any, between the first two. The main thesis of this essay is that the diversity and potency of such compensatory mechanisms have often been underrated, and hence the frequency and intensity of nutritional stress in free-living animals have often been exaggerated. This theme is explored in conjunction with an inventory of the modes of compensation for actual or potential dietary deficiencies.

Periods of Nutritional Stress in the Annual Cycles of Endotherms: Fact or Fiction?

Heat production of fasting white-tailed deer (Odocoilus virginianus) was measured over all months of the year. The deer were maintained in outdoor enclosures, they voluntarily restricted their feed intake and activity in winter, and experienced weight changes typical of wild deer. FMR followed a cyclic pattern. Average FMR of adults in summer coat from May through August (52.2 kcal/kg/24 hrs) was 1.5 times as high as that of deer in winter coat from September through April (33.8 kcal/kg/ 24 hrs). Results confirm the previously reported finding of lower metabolism in winter, and are in gen- eral conformance with reported changes in weight of thyroid glands, and certain activities of deer in an area of similar latitude in New York State. Date of measurement apparently had a stronger influence on FMR than either body size or sex. Values obtained were variable, and high compared to the accepted interspecies mean of 70 kcal/kg W?'7/24 hrs. Cyclic changes in metabolism in deer subject to normal weather conditions may represent a response to season and/or weather, and, in combination with other physiological and behavioral changes, form part of a complex adaptation for survival of deer living near the northern extremity of their range. Additional studies for determining total energy requirements are suggested. Abstract: Heat production of fasting white-tailed deer (Odocoilus virginianus) was measured over all months of the year. The deer were maintained in outdoor enclosures, they voluntarily restricted their feed intake and activity in winter, and experienced weight changes typical of wild deer. FMR followed a cyclic pattern. Average FMR of adults in summer coat from May through August (52.2 kcal/kg/24 hrs) was 1.5 times as high as that of deer in winter coat from September through April (33.8 kcal/kg/ 24 hrs). Results confirm the previously reported finding of lower metabolism in winter, and are in gen- eral conformance with reported changes in weight of thyroid glands, and certain activities of deer in an area of similar latitude in New York State. Date of measurement apparently had a stronger influence on FMR than either body size or sex. Values obtained were variable, and high compared to the accepted interspecies mean of 70 kcal/kg W?'7/24 hrs. Cyclic changes in metabolism in deer subject to normal weather conditions may represent a response to season and/or weather, and, in combination with other physiological and behavioral changes, form part of a complex adaptation for survival of deer living near the northern extremity of their range. Additional studies for determining total energy requirements are suggested.

Fasting metabolism of white-tailed deer1

Highlight: Protein and energy requirements of deer and supplies of these nutrients in native forage are synthesized into a model to estimate carrying capacity of seasonal ranges of a migratory mule deer population in north central Colorado. The model indicates that summer forage will support many times the number of deer present, but winter forage will not sustain deer at any population level. Instead, duration and severity of winter determine the length of time deer can survive on these ranges. Habitat evaluation based on quantification of nutrient supplies and their availability offers a more logical alternative for evaluating deer winter ranges than traditional methods based on measurements of twig lengths of so-called "key" species.

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Evaluation of deer habitat on a nutritional basis.

Publisher Summary This chapter discusses the experiments done on male hamsters. It should be noted, however, that corresponding results have been obtained in females in nearly all cases, regardless of whether photoperiodic effects, the results after pineal manipulations or after application of melatonin are considered. Many mammalian species show a marked annual cycle of gonadal and other functions. In a number of cases it has been shown that the photoperiod, that is, the length of the daily light cycle and its changes, are involved in the regulation of this cycle. The pineal has been shown to participate in the transduction of photoperiodic effects of short photoperiods leading to regression and also of long photoperiods stimulating recrudescence. The latter effect is not only a suppression of antigonadotrophic effects from the pineal, but a positive stimulation. The exact role of melatonin in the photoperiodic mechanism and its site of action are still unclear. Strong effects of melatonin application have been found in photoperiodic mammals. Recent experiments suggest that not only the amount of melatonin, but its pattern of synthesis and release may be important in the conveyance of photoperiodic effects. No support for the assumption that the site of action of melatonin is the pineal itself has been found in experiments with pinealectomized animals.

L. C. McEwen

Papers

Nutrient requirements for growth and antler development in the white-tailed deer'

Responses of White-Tailed Bucks to Added Artificial Light

A technique for obtaining samples of mast