Caloric Demands Research Articles

A Hypothalamic Circuit that Modulates Feeding and Parenting Behaviors.

Across mammalian species, new mothers undergo considerable behavioral changes to nurture their offspring and meet the caloric demands of milk production1-5. While many neural circuits underlying feeding and parenting behaviors are well characterized6-9, it is unclear how these different circuits interact and adapt during lactation. Here, we characterized the transcriptomic changes in the arcuate nucleus (ARC) and the medial preoptic area (MPOA) of the mouse hypothalamus in response to lactation and hunger. Furthermore, we showed that heightened appetite in lactating mice was accompanied by increased activity of hunger-promoting agouti-related peptide (AgRP) neurons in the ARC. To assess the strength of hunger versus maternal drives, we designed a conflict assay where female mice chose between a food source or a chamber containing pups and nesting material. Although food-deprived lactating mothers prioritized parenting over feeding, hunger reduced the duration and disrupted the sequences of parenting behaviors in both lactating and virgin females. We discovered that ARCAgRP neurons directly inhibit bombesin receptor subtype-3 (BRS3) neurons in the MPOA, a population that governs both parenting and satiety. Selective activation of this ARCAgRP to MPOABRS3 circuit shifted behaviors from parenting to food-seeking. Thus, hypothalamic networks are modulated by physiological states and work antagonistically during the prioritization of competing motivated behaviors.

Completely Plant-Based Diets That Meet Energy Requirements for Resistance Training Can Supply Enough Protein and Leucine to Maximize Hypertrophy and Strength in Male Bodybuilders: A Modeling Study.

Despite increasing awareness of plant-based diets for health and athletic performance, athletes are cautioned that careful dietary monitoring is necessary. Whether commonly consumed plant-based diets are nutritionally adequate for maximal muscular hypertrophy remains unknown. This modeling study assessed the nutrient composition of completely plant-based diets scaled to the caloric demands of maximal muscle mass and strength development in adult male bodybuilders. To model calorie requirements, anthropometric data from bodybuilders were input into the Tinsley resting metabolic rate prediction equation, and an appropriate physical activity factor and calorie surplus were applied. Dietary data from a large cohort following completely plant-based diets were then scaled to meet these needs. Modeled intakes for nutrients of interest were calculated as 1.8 g/kg/day of protein and 2.75 g/meal of leucine, which surpass mean requirements for maximal increases in muscle mass and strength and muscle protein synthesis, respectively. Daily levels for all micronutrients, except vitamin D, also exceeded requirements. Saturated fat levels were aligned with dietary guidelines, although sodium levels exceeded recommended limits. Consumption of larger portions of commonplace plant-based diets, scaled to meet the energy demands of maximal accrual of muscle mass and strength, satisfied protein and leucine requirements without the need for additional planning.

Model-based scenarios for achieving net negative emissions in the food system

Most climate mitigation scenarios point to a combination of GHG emission reductions and CO2removal for avoiding the most dangerous climate change impacts this century. The global food system is responsible for ~1/3 of GHG emissions and thus plays an important role in reaching emission targets. Consumers, technology innovation, industry, and agricultural practices offer various degrees of opportunity to reduce emissions and remove CO2. However, a question remains as to whether food system transformation can achieve net negative emissions (i.e., where GHG sinks exceed sources sector wide) and what the capacity of the different levers may be. We use a global food system model to explore the influence of consumer choice, climate-smart agro-industrial technologies, and food waste reductions for achieving net negative emissions for the year 2050. We analyze an array of scenarios under the conditions of full yield gap closures and caloric demands in a world with 10 billion people. Our results reveal a high-end capacity of 33 gigatonnes of net negative emissions per annum via complete food system transformation, which assumes full global deployment of behavioral-, management- and technology-based interventions. The most promising technologies for achieving net negative emissions include hydrogen-powered fertilizer production, livestock feeds, organic and inorganic soil amendments, agroforestry, and sustainable seafood harvesting practices. On the consumer side, adopting flexitarian diets cannot achieve full decarbonization of the food system but has the potential to increase the magnitude of net negative emissions when combined with technology scale-up. GHG reductions ascribed to a mixture of technology deployment and dietary shifts emerge for many different countries, with areas of high ruminant production and non-intensive agricultural systems showing the greatest per capita benefits. This analysis highlights potential for future food systems to achieve net negative emissions using multifaceted “cradle-to-grave” and “land-to-sea” emission reduction strategies that embrace emerging climate-smart agro-industrial technologies.

Comparison of Equations Estimating Resting Metabolic Rate in Older Adults with Type 2 Diabetes.

Measuring resting metabolic rate (RMR) is time-consuming and expensive, and thus various equations for estimating RMR have been developed. This study’s objective was to compare five equations in elderly people with type 2 diabetes (T2DM). RMR was measured in 90 older adults (≥65 years) with T2DM (mean body mass index (BMI) of 31.5 kg/m2), using indirect calorimetry. Results were compared to four frequently used equations (those of Cunningham, Harris and Benedict, and Gougeon developed for young adults with T2DM, and that of Lührmann, which was developed for the elderly), in addition to a new equation developed recently at the Academic College at Wingate (Nachmani) for overweight individuals. Estimation accuracy was defined as the percentage of subjects with calculated RMR within ±10% of measured RMR. Measured RMR was significantly underestimated by all equations. The equations of Nachmani and Lührmann had the best estimation accuracy: 71.4% in males and 50.9% in females. Skeletal muscle mass, fat mass, hemoglobin A1c (HbA1c), and the use of insulin explained 70.6% of the variability in measured RMR. RMR in elderly participants with T2DM was higher than that calculated using existing equations. The most accurate equations for this specific population were those developed for obesity or the elderly. Unbalanced T2DM may increase caloric demands in the elderly. It is recommended to adjust the RMR equations used for the target population.

Radioactive Games? Radiation Hazard Assessment of the Tokyo Olympic Summer Games.

We conducted a comprehensive radiation hazard assessment of the Tokyo Olympic Games (Tokyo 2020, postponed to 2021). Our combined experimental and literature study focused on both external and internal exposure to ionizing radiation for athletes and visitors of the Games. The effective dose for a visit of 2 weeks ranges from 57 to 310 μSv (including flight dose). The main contributors to the dose are cosmic radiation during the flights (approximately 10-81%), inhalation of natural radon (approximately 9-47%), and external exposure (approximately 8-42%). In this complex exposure, anthropogenic radionuclides from the Fukushima nuclear accident (2011) always play a minor role and have not caused a significant increase of the radiological risk compared to pre-Fukushima Japan. Significantly elevated air dose rates were not measured at any of the Tokyo Olympic venues. The average air dose rates at the Tokyo 2020 sites were below the average air dose rates at the sites of previous Olympic Games. The level of radiological safety of foods and water is very high in Japan, even for athletes with increased water and caloric demands, respectively.

817 A Proactive Feeding Regimen on Meeting Caloric Goals with Continuous Enteral Nutrition Support: A Quality Improvement Project

Abstract Introduction Severe burn injuries are characterized by elevated metabolic demands. Numerous studies have documented iatrogenic underfeeding of critical care patients, which can lead to malnutrition, impaired wound healing, weakened immune response, and increased risk of infections. Enteral nutrition (EN) support is often utilized to help meet the increased caloric demands of burn patients. However, discrepancies between prescribed and delivered EN can occur due to frequent interruptions, delays initiating EN, gradual advancement of EN rate, and/or physician directed changes. The objective of this quality improvement project is to assess whether a proactive calculation of EN regimens can improve the provision of calories compared to a traditional calculation method. Methods A retrospective review of patients in a pediatric acute burn unit that received continuous EN for greater than three days was performed. The pre-protocol group consisted of patients from January 1st, 2017 to November 30th, 2017 who had continuous EN rates calculated by the dietitian based on 24 hours per day. This group was compared to patients from September 1st, 2018 to July 31st, 2019 who had EN rates calculated by the dietitian based on 23 hours per day (post-protocol group). Periods in which parenteral nutrition was administered or the EN regimen was prescribed in a non-continuous fashion were excluded. The primary outcome measure was the percentage of admissions in which patients met at least 85% of calorie estimations. This project was undertaken as a Quality Improvement initiative and, as such, was not formally supervised by an Institutional Review Board. Results A total of 132 patients (73 pre- and 59 post-protocol) from 134 separate inpatient admissions (73 pre- and 61 post-protocol) were identified. The average total body surface area burn was 40.9% (SD 18.8) vs. 49.4% (SD 19.8) and average age was 8.6 years (SD 5.9) vs. 7.9 years (SD 5.4) in the pre- and post-protocol groups, respectively. Continuous EN ran for an average of 20 hours a day (SD 2.2, median = 21) vs. 21 hours a day (SD 2.7, median = 22) in the pre- and post-protocol groups, respectively. The average number of days on continuous EN was comparable in both groups. The post-protocol group had 75% of admissions meet at least 85% of calorie estimations compared to the pre-protocol group with 52% of admissions having met the goal. Conclusions Due to the heightened metabolic demands of burn patients and the barriers to meeting caloric goals, it is important to minimize calorie deficits with EN support. Although a seemingly small change, calculating continuous EN rates based on 23 hours per day can yield improved caloric provisions compared to rates based on 24 hours per day. Applicability of Research to Practice A proactive approach to calculating continuous EN support should be considered to help decrease caloric deficits.

Investigation and Determination of Mineral Nutrient of Composition of Cassava, at Selected Woreda’s of Jimma Zone, Ethiopia

Cassava (Manihot esculenta Crantz) is one of the oldest root and tuber crops, used by humans to produce food, feed and beverages. It can be produced adequately in drought conditions making it the ideal food security crop in marginal environments. Although cassava can tolerate drought stress, it can be genetically improved to enhance productivity in such harsh environments. Currently, cassava is produced in more than 100 countries and fulfills the daily caloric demands of millions of people living in tropical America, Africa, and Asia. In this study the nutritional composition, toxic heavy metal and cyanide content of cassava root grown in Jimma Zone, Ethiopia were investigated. Cassava samples were collected from five selected Woredas (Districts) of the Zone, where the plant usually grows. The concentration of the mineral elements; calcium, magnesium iron and copper analyzed ranged from 153-436 mg/kg, 65-207 mg/kg, 54.23-127.03 mg/kg, and 0.09-0.36 mg/kg respectively. In addition to the above parameters, the recovery of the mineral and toxic heavy metals determined was between 81-120%. Wet sample digestion method was used for mineral and toxic heavy metal determination purpose. The results of mineral composition of analyzed cassava root samples were rich in mineral contents. The composition of cassava depends on the specific tissue (root or leaf) and on several factors, such as geographic location, variety, age of the plant, and environmental conditions.

Safety and efficacy of uninterrupted perioperative enteral feeding in pediatric burn patients

IntroductionBurn injuries are a significant cause of morbidity. Early enteral nutrition has been shown to improve outcomes, however enteral nutrition is often held for procedures receiving general anesthesia. Limited data is available on uninterrupted perioperative nutrition in pediatric burn patients. MethodsA single, American Burn Association verified burn center database was queried for patients ≤18 years of age with ≥15% total body surface area (TBSA) burn injuries who underwent surgeries with general anesthesia. Demographic and clinical details were analyzed comparing patients who were fed continuously and those with interrupted feeds. ResultsThirty-one patients met inclusion criteria. Eighteen had continuous feeds and thirteen had interrupted feeds. We found perioperative enteral feeds safe as there were no aspiration events in these patients. Patients with interrupted feeds lost an average of 119.1kcal/kg and 1.4days of estimated energy needs. This was a 125% fall below metabolic needs. This loss was more pronounced with multiple operations and for patients <30kg. Patients with continuous feeds gained an average of 144.4kcal/kg and 1.7days of estimated energy needs. These patients surpassed metabolic needs by 173%. Again, this had the biggest impact in patients with multiple operations and those <30kg. ConclusionsThe metabolic demands of burn patients are above most critically ill patients. To meet these demands, we implemented uninterrupted perioperative feeding. There were no aspiration events. Continuous feeds were an effective means to achieve caloric demands and moderate catabolic injury. We demonstrated safety and efficacy of uninterrupted perioperative feeding of pediatric burn patients.

Crops that feed the world: Production and improvement of cassava for food, feed, and industrial uses

Cassava (Manihot esculenta Crantz) is one of the oldest root and tuber crops, used by humans to produce food, feed and beverages. Currently, cassava is produced in more than 100 countries and fulfils the daily caloric demands of millions of people living in tropical America, Africa, and Asia. Its importance as a food security crop is high in Western, Central and Eastern Africa due to its ability to produce reasonable yields (~10 t/ha) in poor soils and with minimal inputs. Traditionally a famine reserve and a subsistence crop, the status of cassava is now evolving fast as a cash crop and as raw material in the production of starch (and starch based products), energy (bio-ethanol) and livestock feed in the major producing countries. Cassava leaves, which are rich in protein and beta-carotenoids, are also used as a vegetable and forage (fresh or dehydrated meal) in various parts of the world. In recent years, some of the problems in the production of cassava have been increasing infection with cassava mosaic disease (CMD), cassava brown streak disease (CBSD) and cassava bacterial blight (CBB). Inherent post-harvest physiological disorder (PPD) and cyanogenic glycosides (CG) are some of the most prominent challenges for scientists, producers and consumers in the post-production systems. Collaborative research in participatory plant breeding is ongoing at leading international research institutes such as IITA and CIAT to improve crop resistance to virus diseases, reduce PPD and CG, and improve the overall nutritional characteristics. Further research should also focus on post-production systems by developing enhanced storage and transportation techniques, mechanisation (peeling, size reduction, drying and dewatering) and improved packaging. Moreover, a robust national policy, market development, and dissemination and extension program are required to realise the full potential of innovations and technologies in cassava production and processing.

Facultative Scavenging and Carrion Guild Participation byLynx rufusin the Presence of Young

Abstract The bobcat (Lynx rufus) is typically described as an obligatory predator that infrequently scavenges and displays a strong preference for fresh prey. Scavenging behavior of the species has rarely been directly observed or documented and instead has been generally inferred from stomach content analysis. We observed a female bobcat and cub scavenging domestic pig (Sus scrofa) carcasses for a total of seven consecutive days during a carrion utilization study in central Oklahoma. These observations suggest that bobcats will readily exploit fresh carrion when under the caloric demands of rearing young. Bobcats possibly play an overlooked role in the guild of carrion recyclers in suburban and semirural ecosystems subjected to human encroachment.

Ecosystem services from rainwater harvesting in India

Availability of a safe and reliable water supply is an issue in developing nations, including India. Rainwater harvesting (RWH) is a site-specific source control used to satisfy human, agricultural, and safety demands for water. This study analyzed the effects of capturing rainwater for a 12.5 year period (Jan 1999–Jun 2011) to provide three ecosystem services: water supplementation for indoor use, water supplementation for food production and groundwater recharge (GWR). A hydrologic analysis was completed using satellite rainfall data and a water balance approach. Two demand scenarios, indoor and outdoor, were considered, with water in excess of demand and storage directed to recharge groundwater. An economic analysis quantified RWH system net present value. The results indicated significant ecosystem services benefits were possible from RWH in India. RWH for the purpose of providing irrigation to a small garden and allowing overflow to a drywell for GWR was concluded to be an approach to maximize benefits. This scenario provided the greatest net present value (21,764–38,851 INR), fastest payback period (0.30–0.98 years), and recharge to groundwater of more than 40% of onsite rainfall. The benefit of the outdoor vegetable irrigation was determined and the results showed that the caloric demands of the typical Indian household (2.75 kg of tomatoes and 1.05 kg of lettuce) could be met with a 20 m2 garden, and excess food could be sold to offset the capital cost of the system and later for economic gain.

Fulfilling caloric demands according to indirect calorimetry may be beneficial for post cardiac arrest patients under therapeutic hypothermia

IntroductionWe sought to investigate the energy requirements for patients under therapeutic hypothermia, and the relationship of energy fulfillment to patient outcome. Patients and methodsAdult patients admitted to our ICU after successful resuscitation from cardiac arrest for post resuscitation therapeutic hypothermia from April, 2012 to March, 2014 were enrolled. Body temperature was managed using the surface cooling device (Arctic Sun®, IMI). Calorimeter module on the ventilator (Engström carestation®, GE) was used for indirect calorimetry. Energy expenditure (EE) and respiratory quotient (RQ) were recorded continuously, as the average of the recent 2h. Measurements were started at the hypothermic phase and continued until the rewarming was completed. Cumulative energy deficit was calculated as the sum of difference between EE and daily energy provision for the 4 days during hypothermia therapy. ResultsSeven patients were eligible for analysis. Median EE for the hypothermic phase (day 1) was 1557.0kcald−1. EE was elevated according with the rise in body temperature, reaching 2375kcald−1 at normothermic phase. There was significant association between cumulative energy deficit and the length of ICU stay, among patients with good neurologic recovery (cerebral performance category (CPC): 1–3). ConclusionThe EE for patients under therapeutic hypothermia was higher than expected. Meeting the energy demand may improve patient outcome, as observed in the length of ICU stay for the present study. A larger, prospective study is awaited to validate the results of our study.

Nutritional Armor for the Injured Warfighter: Omega-3 Fatty Acids in Surgery, Trauma, and Intensive Care

Nutrients have traditionally been viewed as a means to provide basic energy for cellular homeostasis and amino acids for protein synthesis in all humans. Young, healthy men and women in the military today are presumed to be well nourished and mentally and physically fit to perform their duties in austere environments. Exposure to high-intensity projectiles, blast injuries, and other wounds of war, however, is an everyday occurrence during deployment that potentially challenges all homeostatic mechanisms. After sustaining such devastating injuries, critically ill, surgical, and trauma patients are in a constant dynamic state between the systemic inflammatory response syndrome (and compensatory anti-inflammatory response syndrome. Compelling evidence supports both immune and metabolic response modulation by specific nutrients, including omega-3 fatty acids, primarily eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). The concept of providing nutrients as therapeutic rather than supportive agents to meet the basic cellular caloric and metabolic demands requires a major paradigm shift. Although the exact route and dose of these metabolically active lipids has yet to be determined, data from large clinical studies of cellular ex-vivo experiments in patients support the liberal use of eicosapentaenoic acid and docosahexaenoic acid in the setting of trauma, surgery, and intensive care.

Feeding 10 billion people under climate change: How large is the production gap of current agricultural systems?

The human population is projected to reach more than 10 billion in the year 2100. Together with changing consumption pattern, population growth will lead to increasing food demand. The question arises whether or not the Earth is capable of fulfilling this demand. In this study, we approach this question by estimating the carrying capacity of current agricultural systems (KC), which does not measure the maximum number of people the Earth is likely to feed in the future, but rather allows for an indirect assessment of the increases in agricultural productivity required to meet demands. We project agricultural food production under progressing climate change using the state-of-the-art dynamic global vegetation model LPJmL, and input data of 3 climate models. For 1990 to 2100 the worldwide annual caloric yield of the most important 11 crop types is simulated. Model runs with and without elevated atmospheric CO2 concentrations are performed in order to investigate CO2 fertilization effects. Country-specific per-capita caloric demands fixed at current levels and changing demands based on future GDP projections are considered to assess the role of future dietary shifts. Our results indicate that current population projections may considerably exceed the maximum number of people that can be fed globally if climate change is not accompanied by significant changes in land use, agricultural efficiencies and/or consumption pathways. We estimate the gap between projected population size and KC to reach 2 to 6.8 billion people by 2100. We also present possible caloric self-supply changes between 2000 and 2100 for all countries included in this study. The results show that predominantly developing countries in tropical and subtropical regions will experience vast decreases of self-supply. Therefore, this study is important for planning future large-scale agricultural management, as well as the critical assessment of population projections, which should take food-mediated climate change feedbacks into account.

The difference in enteral nutrition (EN) versus total parenteral nutrition (TPN) in acute pancreatitis by etiology and disease severity

Background: Supplemental nutrition improves long-term outcomes/mortality in acute pancreatitis, with Enteral Nutrition (EN) superior to Total Parenteral Nutrition (TPN). Differences in EN/TPN based upon etiology or disease severity have never been established. Methods: We performed a randomized retrospective case control on subjects admitted to Cooper University Hospital from 06/2007 to 01/2010 with acute pancreatitis who received supplemental nutrition (n = 161). These subjects were examined for caloric and protein demands. Subjects were matched for demographics, weight, albumin, prealbumin eliminating confounders. Demands among disease etiology/severity subgroups and statistical significance were determined. The incidence of EN v.TPN was determined. Results: Significant differences were found in total caloric demands, namely gallstone (n = 50) and alcohol (n = 36) (p = 0.04). Differences in protein demand were not established between these two groups (p = 0.24). Differences in caloric demand were found in bed-side index for severity in acute pancreatitis (BISAP) of 1, 2 and 3 versus 5. Protein demands were different between BISAP of 0 versus all others. 24% of the sample received EN. Conclu: sion: There are significant differences in total caloric demands for subjects with acute pancreatitis by disease severity and in gallstone versus alcohol-induced pancreatitis. These differences are not variations in the sample populations. Finally, EN is under-utilized despite knowledge of its value.

Energy Balance Assessment of Students on a National Outdoor Leadership School Course

Proper energy balance and nutrition are paramount to the success and enjoyment of all participants on backcountry expeditions (Howley Ryan, 2008). Planning a diet that meets both the nutrient and caloric demands while also overcoming the packing, preservation, and cooking obstacles unique to the backcountry can be challenging. Current recommendations for such diets include estimates for the proper amounts of carbohydrates, protein, fats, and micronutrients (FAO/WHO/UNU 1985, Howley Ryan 2008). However, there are few direct measurements of the energetic needs of backcountry enthusiasts and athletes while in the wilderness (Rejc et al. 2010).

Caloric stress alters fat characteristics and Hsp70 expression in milk somatic cells of lactating beef cows

Selection for higher production rate in cattle inhabiting challenging habitats may be considered disadvantageous because of possible deleterious effects on immunity and reproduction and, consequently, on calf crop percentage. In Israel, free-grazing high productive beef cows experience reduction in nutritional quality of forage during up to 8 months of the year. As milk production by dams dictates calf performance, dam's nutritional needs and rebreeding rates, the aim of the present study was to test how lactating beef cows deal with combined caloric and protein stress both at the productive and self protective levels. For this purpose, we studied the effect of long-term caloric stress on milk characteristics and gene expression of stress and milk components producing proteins. Lactating dams responded to caloric stress by decreased body weight, milk, and milk protein production. To compensate for total energy loses in milk, they produced milk of higher fat concentration and shifted the proportions of its fatty acids towards long and unsaturated ones. This was reflected by increased mRNA transcription of the fatty acid binding protein. Prolonged low-energy diet promoted cell-specific heat shock protein (Hsp) response; whereas significant increase of Hsp90 but unchanged levels of Hsp70 proteins were observed in white blood cells, the expression of Hsp70 in milk somatic cells was markedly attenuated, in parallel with a marked increase of alpha(s1)-casein expression. At the mammary gland level, these results may indicate a decrease in turnover of proteins and a shift to an exclusive expression of milk components producing factors. Similar responses to caloric stress were revealed also in ketotic dairy cows. Ketosis promoted a shift towards long and unsaturated fatty acids and an increased expression of alpha(s1)-casein in milk somatic cells. These findings may reflect an evolutionary-preserved mechanism in lactating cows for coping with caloric restriction. Overall, our results provide an index to test suitability of beef cattle breeds to inadequate caloric demands.

Changes in serum leptin, insulin, androstenedione and luteinizing hormone during ovarian cycle in the bat,Taphozous longimanus

Detailed reproductive pattern and associated endocrine characteristics have been documented in only a few species of order Chiroptera. The aim of the present study was to examine the changes in body weight, serum insulin, leptin, androstenedione and luteinizing hormone (LH) concentrations during annual ovarian cycle in the sheath-tailed bat, Taphozous longimanus. Bats were sampled over three years. Leptin, a satiety hormone produced primarily by adipose tissue, provides information to feeding center of the brain about nutritional status, fat mass, appetite and energy expenditure. The circulating concentration of leptin begins to increase from October and attains a peak in December. The peak serum leptin concentration coincides with body weight in November before winter dormancy in December. The serum leptin levels dissociate from body weight during December. The other peaks of serum leptin levels coincide with late stages of the two successive pregnancies. The serum insulin concentration begins to increase from September and attains a peak during December. The insulin concentration remains low from January to August. The circulating androstenedione concentration begins to increase in October, reaching a peak in December. This increase in androstenedione concentration correlated with the period of heavy accumulation of abdominal fat and increase in body weight. There was a sharp decline in androstenedione concentration and body weight in January. The serum LH shows peaks, in November, coinciding with the peaked body weight, the other peaks in January and May, coinciding with ovulation for the two successive pregnancies. The high leptin and insulin levels might be responsible for the maintenance of reproductive response and gonadal function during adverse environmental condition in the winter, while high androstenedione, and associated body weight along with LH might be responsible for maintaining basal gonadal function. We conclude that high leptin, androstenedione and insulin serve, as signal for the reproductive functions in that sufficient body fat are available to meet the caloric demands and maintain normal function during adverse winter conditions.

Consuming Fuel and Fuelling Consumption: Modelling Human Caloric Demands and Fuelwood Use

This paper describes a conceptual framework that was developed to integrate livestock, human, cultivation and forest constraints to model community fuelwood consumption over a 25-year planning horizon. This framework was constructed as an energy balance based on human caloric requirements in order to examine the effects of household-level decisions for nutrition, fuelwood and land use. A scenario from a virtual community in Uganda is presented to illustrate the utility of this model to allow rapid policy and scenario evaluation. User-defined inputs combined with published research data are used in simulating resource responses and energy consumption rates. This model is a potential tool to monitor fuelwood consumption and to understand the implications of various land-use practices.

KILLER APPETITES: ASSESSING THE ROLE OF PREDATORS IN ECOLOGICAL COMMUNITIES

Large body size, carnivory, and endothermic costs lead to exceptionally high caloric demands in many mammalian predators. The potential impact on prey resources may be marked but is difficult to demonstrate because of the mobility, sparseness, and cryptic nature of these animals. In this study, we developed a method based on comparative bioenergetics and demographic modeling to evaluate predator effects and then used this approach to assess the potential impact of killer whales on sea otter and Steller sea lion populations in the Aleutian Islands. Daily caloric requirements of killer whales determined from allometric regressions for field metabolic rate show that an adult killer whale requires 51–59 kcal·kg−1·d−1 (2.5–2.9 W/kg). Caloric values of prey items determined by bomb calorimetry ranged from 41 630 kcal for an adult female sea otter to sequentially higher values for male otters, sea lion pups, and adult Steller sea lions. Integrating these results with demographic changes in marine mammal populations show that fewer than 40 killer whales could have caused the recent Steller sea lion decline in the Aleutian archipelago; a pod of five individuals could account for the decline in sea otters and the continued suppression of sea lions. The collapse of the historical prey base of killer whales due to human whaling may have contributed to a sequential dietary switch from high to low caloric value prey, thereby initiating these declines. This study demonstrates that a combined physiological–demographic approach increases our ability to critically evaluate the potential impact of a predator on community structure and enables us to define underlying mechanisms that drive or constrain top-down forcing in dynamic ecosystems.