Natural history is replete with observations on feeding, yet only recently have investigators begun to treat feeding as a device whose performance­ as measured in net energy yield/feeding time or some other units assumed commensurate with fitness-may be maximized by natural selection (44, 1 13, 135, 156, 181) . The primary task of a theory of feeding strategies is to specify for a given animal that complex of behavior and morphology best suited to gather food energy in a particular environment. The task is one, therefore, of optimization, and like all optimization problems, it may be tri­ sected: 1. Choosing a currency: What is to be maximized or minimized? 2. Choosing the appropriate cost-benefit functions: What is the mathematical form of the set of expressions with the currency as the dependent variable? 3. Solving for the optimum: What computational technique best finds ex­ trema of the cost-benefit function? In this review, most of the following section is devoted to possible answers to the first problem. Then four key aspects of feeding strategies will be considered: (a) the optimal diet, (b) the optimal foraging space, (c) the optimal foraging period, and (d) the optimal foraging-group size. For each, possible cost-benefit formulations will be discussed and compared, and predictions derived from these will be matched with data from the literature on feeding. Because the third problem is an aspect of applied mathematics, it will be mostly ignored. Throughout, emphasis will be placed on strategic aspects of feeding rather than on what Holling (75) has called "tactics."

Theory of Feeding Strategies

The nitrogen content of a plant is only one of the many plant characteristics that are vitally important to herbivores. However, because of its central role in all metabolic processes as well as in cellular structure and genetic coding, nitrogen is a critical element in the growth of all organisms. Supplementary N often elicits enhanced health, growth, reproduction, and survival in many organisms. This suggests that N is a limiting factor. Since N makes up a large portion of the earth's atmosphere (about 78%), the problem is not an absolute but a relative shortage-that is, a scarcity of usable or metaboliza­ ble N during critical growth periods (159, 328). Plants encounter shortages of inorganic nitrogen (nitrate and/or ammonium ions); animals experience shortages of organic nitrogen (specific proteins and/or amino acids). This article reviews and examines the evidence (a) that N is scarce and perhaps a limiting nutrient for many herbivores, and (b) that in response to this selection pressure, many herbivores have evolved specific behavioral, morphological, physiological, and other adaptations to cope with and uti­ lize the ambient N levels of their normal haunts. McNeill & Southwood (201) and White (328) have also reviewed these general questions. There­ fore, this review explores additional evidence and further develops the fundamental arguments. The review is organized into three major divisions. The first focuses on important sources of variation in plant N (seasonal and ontogenetic trends, different tissues and species, etc) because such variation may be the basis

Herbivory in relation to plant nitrogen content

We tested the hypothesis that tannins defend plants against large herbivores by decreasing protein availability. Digestion trials were conducted with mule deer (Odo- coileus hemionus) and results from previous trials with white-tailed deer (O. virginianus), moose (Alces alces), caribou/reindeer (Rangifer tarandus), and elk (Cervus elaphus) were summarized to evaluate dietary factors affecting protein availability. The digestibility of plant protein in feeds with minimal tannins, such as grasses and agriculturally produced legumes and grains, was a highly predictable function of the total protein content and the amount of nondigestible, fiber-bound protein. Digestible protein in plants containing sig? nificant tannins was lower than predicted from regressions for low-tannin feeds. The re? duction in digestible protein was proportional to the protein-precipitating capacity of the plant tannins. Deciduous browse stems collected in winter had very low levels of protein- precipitating tannins and only a slightly lower protein availability than predicted. Tannins are not important in the defense of most deciduous tree and shrub stems consumed by these herbivores. Tannins in flowers and forb, tree, and shrub leaves markedly reduced protein availability. Tannins must be considered in understanding the defensive strategies of leaves and flowers. Voluntary intake of the high-phenolic forages was significantly re? duced below ingestion rates for grasses, legumes, and pelleted diets. It is hypothesized that soluble phenolics that do not inhibit digestion but are absorbed and reduce intake through their toxicity are more important in defending some plant parts against ruminants than are digestion-reducing tannins.

https://www.jstor.org/stable/pdf/1938809.pdf

Role of Tannins in Defending Plants Against Ruminants: Reduction in Protein Availability

Basal metabolic rates in mammals: taxonomic differences in the allometry of BMR and body mass.

The scaling of the basal rate of metabolism in mammals is reexamined. Both the power and level of the scaling function are sensitive to various factors that interact with body mass and rate of metabolism, including the precision of temperature regulation, food habits, and activity level. This sensitivity implies that the rate of metabolism is a highly plastic character in the course of evolution. Consequently, the singular effect of mass on the rate of metabolism is most effectively analyzed in ecologically and physiologically uniform sets of species, rather than in taxonomically defined groups, which often are ecologically and physiologically diverse. Otherwise, all fitted curves for mammals integrate a variety of competing factors, thereby reflecting the species used and denying unique analytic significance to the power in scaling relations. Kleiber's eutherian curve may represent a relatively uniform set of data because all the species included were domesticated and because selection for high rates of ...

Complications inherent in scaling the basal rate of metabolism in mammals

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

Nutrition of White-Tailed Deer. I. Energy Requirements of Fawns

Six adult white-tailed deer (Odocoileus virginianus) were equipped with heart rate telemeters and placed in a temperature-controlled, indirect respiration calorimeter to measure heart rate and metabolic rate simultaneously. Over a 4-year period, from 1970 to 1973, 20 trials were conducted covering 9 calendar months. In each trial 5 to 12 different ambient temperatures were maintained, each for 12 consecutive hours (period), giving a wide range in the traits being measured; in all, 165 such periods were studied. An equation is presented for predicting metabolic rate from mean heart rate; it accounts for 78 percent of the variation in metabolic rate. Further application of this tool to improve our understanding of the relationship of deer to their environment is discussed. J. WILDL. MANAGE. 40(4):626-629 Work at our laboratory (Silver et al. 1969, Thompson et al. 1973) has revealed remarkable seasonal variability in maintenance net energy requirements (fasting metabolic rate) of fawns and adult deer. Numerous investigators (including Silver and Colovos 1957, Wood et al. 1962, Thompson et al. 1973) have noted cessation of growth (measured as maintenance or loss of body weight) during winter, although Thompson et al. found that body protein deposition continued in fawns despite negative energy balance, apparently caused by self-imposed restriction of feed intake. Therefore, a knowledge of the energy needed by deer for body maintenance, for use as a base line in estimating energy needed for various productive functions, could be helpful in their proper management. Even during winter, when deer often subsist on submaintenance diets, a knowledge of maintenance energy needs can serve as a reference for evaluating degree of undernutrition. To be able eventually to predict metabolic rate in deer not confined to a respiration calorimeter, Skutt et al. (1973) developed small, implantable transmitters to monitor heart rate and other physiological data, remotely, from unrestrained deer. The objective of this experiment was to develop an equation for predicting metabolic rate from mean heart rate. MATERIALS AND METHODS Six adult white-tailed deer, 3 does and 3 bucks, were used in 20 trials covering 9 different calendar months over a 4-year period (1970-73). Deer were reared in captivity (outdoor pens) and conditioned to the laboratory environment and to routine crating and transport. In each trial a series of 5 to 12 different ambient temperatures was maintained, each temperature for 12 consecutive hours (period), in a temperaturecontrolled, indirect respiration calorimeter; such periods also were consecutive within trials. Trials were summarized by seasons of the year, summer beginning 21 June. Because of the complexity of integrating animal availability, surgical and calorimetric procedures, and food intake with seasons, the schedule of experimentation led to imbalances in subclasses. Distribution of pe1 Published with the approval of the Director of the New Hampshire Agricultural Experiment Station as Scientific Contribution 696. Research partially supported by a contribution of P-R Proj. W-51-R, New Hampshire. 626 J. Wildl. Manage. 40(4):1976 This content downloaded from 207.46.13.127 on Wed, 28 Jun 2017 17:57:56 UTC All use subject to http://about.jstor.org/terms PREDICTING METABOLIC RATE IN DEER * Holter et al. 627 Table 1. Distribution of 10-hour periods (n = 165) among classes of main effects. Main effect No. 10-hour class periods

Predicting Metabolic Rate from Telemetered Heart Rate in White-Tailed Deer

Eight hand-reared white-tailed deer (Odocoileus virginianus) fawns were randomly paired and pairs were randomly assigned to 1 of 4 isocaloric diets containing 11, 15, 20, and 25 percent crude protein (dry matter basis) to study their protein requirement. Thirty-two complete digestibility, nitro- gen balance, and energy balance trials were carried out. Partition of dietary energy was not signifi- cantly affected by protein level in the diet, except that proportion of energy lost in urine, presumably ketones, increased significantly (P < 0.05) with increasing dietary crude protein. Apparent digestibility of protein increased significantly up to 20 percent ration crude protein, but most of this difference was attributable to decreasing proportion of metabolic nitrogen (0.37 g/100 g diet dry matter) in feces; proportion of ingested nitrogen lost in urine increased with increasing nitrogen intake. The fawn's re- quirement for maximum growth (body retention of dietary protein), estimated by regression analysis, was 19 g digestible crude protein per kilogram of metabolic body weight (W075) daily. J. WILDL. MANAGE. 39(3):582-589 White-tailed deer, an aesthetically and economically valuable resource, are increas- ingly threatened by the effects of urban- ization in many areas. Their survival in optimum quantity and quality will depend largely on intensive management based on biologically sound principles. Deer man- agers will need information on the nutri- tional requirements of different age classes of deer throughout the year, and on the value of natural foods in meeting these re- quirements. Fawns probably are the age class most vulnerable to undernutrition during the winter. Certainly the food consumed dur- ing the preceding fall contributes greatly to winter survival. Thompson et al. (1973: 307) reported that the metabolizable energy required for maintenance of fawns is higher (38 percent, our calculation) during pe- riods of weight gain than in winter. They also found that the component of growth described by deposition of body protein may continue despite body weight loss and negative energy balance during the winter. Although energy generally is the most crit- ical factor in deer nutrition, the work of Murphy and Coates (1966) suggested that low protein content of foods may account for low productivity and suboptimum phys- ical development as in most other species.

Protein requirement of white-tailed deer fawns'

Six adult white-tailed deer (Odocoileus virginianus borealis) were exposed to 165 periods of 12 consecutive hours of controlled constant ambient temperature in an indirect respiration calorimeter. ...

Helenette Silver

Papers

Fasting metabolism of white-tailed deer1

Nutrition of White-Tailed Deer. I. Energy Requirements of Fawns

Predicting Metabolic Rate from Telemetered Heart Rate in White-Tailed Deer

Protein requirement of white-tailed deer fawns'

Ambient temperature effects on physiological traits of white-tailed deer.