Rate Of Energy Acquisition Research Articles

Forum

Forum

Evolution of intrinsic growth and energy acquisition rates. I. Trade-offs with swimming performance in Menidia menidia.

Latitudinal populations of the Atlantic silverside, Menidia menidia, show substantial genetic variation in rates of energy acquistion and allocation. Reared in common environments, silversides from northern latitudes consume more food, grow faster and more efficiently, store more energy, and produce greater quantities of eggs than their southern conspecifics. The persistence of seemingly inferior southern genotypes in the face of ostensibly superior northern genotypes suggest that there are hidden evolutionary trade-offs associated with these elevated acquisition and allocation rates. We tested the hypothesis that rapid growth and high levels of food consumption trade-off against locomotory performance in M. menidia. We compared both aerobic (prolonged and endurance) and anaerobic (burst) swimming capacities between intrinsically fast-growing fish from the north (Nova Scotia, NS) and intrinsically slow-growing fish from the south (South Carolina, SC) and between growth-manipulated phenotypes within each population. We also compared swimming speeds and endurance between fasted and recently fed fish within populations. Maximum prolonged and burst swimming speeds of NS fish were significantly lower than those of SC fish, and swimming speeds of fast-growing phenotypes were lower than those of slow-growing phenotypes within populations. Fed fish had lower burst speeds and less endurance than fasted fish from the same population. Thus, high rates of growth and the consumption of large meals clearly diminish swimming performance, which likely increases vulnerability to predation and decreases survival and relative fitness. The submaximal growth rate of southern M. menidia appears to be adaptive, resulting from balancing selection on rates of somatic growth.

Adaptive Evolution of Seed Oils in Plants: Accounting for the Biogeographic Distribution of Saturated and Unsaturated Fatty Acids in Seed Oils.

Structural, energetic, biochemical, and ecological information suggests that germination temperature is an important selective agent causing seed oils of higher-latitude plants to have proportionately more unsaturated fatty acids than lower-latitude plants. Germination temperature is predicted to select relative proportions of saturated and unsaturated fatty acids in seed oils that optimize the total energy stores in a seed and the rate of energy production during germination. Saturated fatty acids store more energy per carbon than unsaturated fatty acids; however, unsaturated fatty acids have much lower melting points than saturated fatty acids. Thus, seeds with lower proportions of saturated fatty acids in their oils should be able to germinate earlier and grow more rapidly at low temperatures even though they store less total energy than seeds with a higher proportion of saturated fatty acids. Seeds that germinate earlier and grow more rapidly should have a competitive advantage. At higher germination temperatures, seeds with higher proportions of saturated fatty acids will be selectively favored because their oils will provide more energy, without a penalty in the rate of energy acquisition. Macroevolutionary biogeographical evidence from a broad spectrum of seed plants and the genus Helianthus support the theory, as do microevolutionary biogeography and seed germination performance within species of Helianthus.

Changes in reproductive strategy in the ruffe during a period of establishment in a new habitat

The pattern of maturation, body size and fecundity was examined in a population of ruffe (Gymnocephalus cernuus L.) three times during a period of rapid growth, and eventual stabilization, following its introduction to a new habitat. When the ruffe were less common, maturing ruffe were relatively large and immature ruffe relatively small, compared with when the ruffe were abundant. Intermediate ruffe population size showed a maturation pattern intermediate between these two extremes. It is suggested that this pattern of maturation is a response of the ruffe population to changing growth opportunity induced by changing intraspecific competition. This fluctuating maturation pattern is interpreted in terms of a threshold‐dependent maturation trigger, operating on the rate of accumulation of energy and a trade‐off between somatic growth and gonad development. When the ruffe population was large, high intraspecific competition resulted in low opportunity for growth; only fish with the highest rate of food acquisition were able to mature in a given year–the investment in gonadal tissue reducing somatic growth. When the ruffe population was low, the high rate of energy acquisition in the population resulted in the triggering of maturation, even at small size, only the very smallest fish remaining immature. High growth opportunity allowed maturing fish to develop gonad and maintain somatic growth. The pattern of size related fecundity also changed over the three periods. When growth opportunity was low, size related fecundity was greater than when opportunity for growth was high. This suggests that maturing females faced with poor growth conditions compensated by increasing egg number for a given body size either by decreasing egg size or by increasing total investment in ovarian tissue.

MATERNAL CARE IN THE SUBANTARCTIC FUR SEALS ON AMSTERDAM ISLAND

This paper reports the first study of maternal input and care from birth to weaning in a fur seal with a long pup-rearing period: the subantarctic fur seal Arctocephalus tropicalis breeding on the temperate Amsterdam Island, Indian Ocean. The protracted weaning period provided the opportunity for examination of maternal care in relation to seasonal changes in the requirements of the mother–pup pair and environmental conditions. During the reproductive season 1995–1996, maternal care was investigated in terms of provisioning (maternal attendance) pattern while diving effort was investigated using time depth recorders in summer and winter. Maternal input was calculated in terms of the absolute rate of pup mass gain and, ultimately, pup growth rate and pup body mass at weaning. Lactating subantarctic fur seals perform one of the longest attendance cycles described in fur seals, spending on average 11–23 d at sea from summer to winter. The time mothers spend ashore suckling their pup is also long (∼4 d) but remains constant throughout the year. Throughout the year, maternal input should be described as follows: mothers spending a long time at sea store a large amount of body reserves that provide them a good body condition. Consequently, they spend a long time ashore to transfer their body reserves to their pups. However, mothers spending short attendance periods increase the mass transfer efficiency, probably by decreasing their metabolic overhead. In summer, maternal care was mostly controlled by pup traits: maternal absences appeared to be controlled by pup fasting ability, while maternal input was controlled by pup ingestion ability, i.e., pup body size and the time the pup was suckling. In fall, pups were no longer limited in milk ingestion, and maternal input was mostly controlled by maternal traits (e.g., body length and experience). In winter, maternal input decreased as the pup became older despite an increase in maternal diving effort. We propose that, in winter, maternal requirements increase, probably in response to increasing costs of gestation and because of a decrease in food resource availability. Pups whose mother performed short and regular foraging trips grew faster and were heavier at weaning than other pups. This is discussed in term of pup fasting endurance and maternal experience. Finally, we found a window of foraging trip durations that maximizes the net rate of energy acquisition of the pup, suggesting that in subantarctic fur seals there may not exist one optimal maternal attendance pattern, but a range of patterns promoting the same maternal fitness.

Intrapopulation variation in ecological energetics of the garter snake Thamnophis sirtalis, with analysis of the precision of doubly labeled water measurements.

The evolution of energetics must begin with variation within populations in ecologically realized rates of energy acquisition and expenditure. We measured aspects of field energy budgets (including metabolic rates, feeding rates, and growth rates) in a large sample of free-living garter snakes (Thamnophis sirtalis) from a single temperate/mesic population in northwestern California during their summer active season. We then analyzed interindividual variation for correlations among variables and patterns attributable to body size and sex. Field metabolic rates (measured with use of doubly labeled water) scaled in direct proportion to body mass. These rates of field energy expenditure were higher (both in absolute terms and in relation to resting metabolic rates) than those previously measured in snakes and iguanian lizards and were similar to those reported for highly active, widely foraging scincomorphan lizards. Feeding rates (as indexed by water influx rates) and growth rates were correspondingly high compared to those of other squamate reptiles. We found considerable residual variation in all measured variables not attributable to body size. Effects of sex were detected for water influx and growth rates (females > males), but not for field metabolic rate. Individual field metabolic rate was apparently consistent (repeatable) over time, water influx rate was not, and individual growth rates were strongly negatively correlated over two sequential time periods. We were unable to detect convincing correlations between any individual measures of field energetics and any commonly measured, standard laboratory measurements of oxygen consumption (standard metabolic rate at two body temperatures and maximal oxygen consumption for exercise) made on the same individuals. However, body-size-independent field rates of energy expenditure, energy intake, and growth were strongly and positively intercorrelated among individuals. We attribute these patterns to an overriding effect of costs associated with digestion and growth on field energetics, such that individual snakes that were effective foragers achieved high feeding rates and, hence, high growth rates, but also incurred high costs of growth and digestion that largely determined field metabolic rate.

In Vivo Measurement of Near Maximal Rates of Nutrient Absorption in a Mammal

The central limitation hypothesis postulates that energy budgets are limited by the capacity for energy assimilation. Contradictory evidence from in vitro studies of nutrient uptake capacity of intestinal tissues indicates a margin, however, that could allow a higher rate of energy acquisition than actually measured. As a more direct test, I measured nutrient uptake capacity in vivo. This is possible in animals such as the neotropical nectar-feeding bats (Glossophaginae: Phyllostomidae) that have both rapid gut transit times and high daily metabolic needs. Here, during the steady-state period of feeding, the rate of food intake is equal to the rate of food processing and food egestion. Therefore, the rate of food absorption can be determined directly from the rate of food ingestion. Maximal feeding rates were elicited by limiting the time period available for feeding during the 24-hr day through manipulation of the light/dark (LD) cycle. During 4-hr nights (LD 20:4), sugar intake averaged 488 J/g/hr and was 73% higher than during 12-hr nights (LD12:12). A 16.4-g bat would assimilate 96 kJ/day if feeding at this maximal rate during a regular 12-hr foraging period. This would be sufficient for maintaining a positive energy balance even during extreme physical activity under the natural conditions of its tropical environment. Nutrient assimilation capacity could thus not be identified as the single central factor setting the metabolic ceiling.

Bridging the Gap between Ornithology and Fisheries Science: Use of Seabird Data in Stock Assessment Models

Seabirds and marine fish share habitats and food webs, but there is too little contact between the disciplines that study them. Fish stock assessment models, designed for use on teleost fishes with high fecundity, high recruitment variability, and continued growth throughout life, may be strengthened by inclusion of seabird data. In some circumstances seabird-based indices of prey abundance could assist in calibration of sequential population analysis of fish stocks. Seabird energy acquisition rates, equivalent to fisheries catch per unit effort, are the most promising avian indicators of stock size. Seabird data may be useful in predicting recruitment of commercial fisheries and in improving estimates of natural fish mortality. The impact of seabird predation on fish stocks depends on the age of targeted fish and their subsequent growth and mortality. Yield-per-recruit analyses, derived from fisheries science, suggest that under plausible conditions the impact of seabird predation on fish stocks may be amplified by avian preference for small prey. Increased collaboration between seabird biology and fisheries science will benefit conservation of both birds and fish.

Body size, prey handling efficiency and choice of diet in three coniferous forest tits (Paridae)

The main purpose of this study was to link morphological differences between great tit (Parus major), willow tit (P. montanus) and coal tit (P. ater) and their rate of energy acquisition and choice of diet in order to explore the potential for competitive relations between them more directly. Handling times were measured in the laboratory by presenting mealworms of different sizes to the birds. Great tits were more efficient in handling large prey than were the smaller-bodied willow- and coal tits; for small prey sizes the coal tit was the least efficient species. Using the ratio of prey mass to the handling time value, a utility function for each species was constructed. These results suggests a potential for a segregation of the species on the food axis. However, results from the prey choice experiment show that despite considerable differences in functional morphology between the three species they do not differ significantly in the range of prey size exploited. My results suggest that the alleged importance of prey size partitioning is not likely to play the major role for the coexistence of these coniferous forests tits.

Variation in Time and Energy Budgets of Breeding Wheatears

Abstract We examined the sources of variation in time allocation of males and females of the wheatear (Oenanthe oenanthe) on the island of Öland, South Sweden, throughout the breeding season. We quantified rates of prey capture attempts and specified foraging methods used. From respirometric measurements of basal metabolic rate and temperature-dependent metabolism on captive wheatears, and after having made certain assumptions abour the costs of different activities, we estimated the energy budgets of both sexes during the different reproductive phases. Males and females differed in their time allocation and foraging rates during prelaying, laying, and incubation, but not while feeding grown nestlings. During prelaying and laying, females foraged at higher rates than males; they also perched less often, gleaned more on the ground, and flew less. Although incubation was the least costly phase for females because of their low activity, high foraging rates yet indicated that this phase may represent an energetic bottleneck as a result of restrictions on foraging time. After incubation, females switched from foraging mostly on the ground during early breeding phases to hunting from elevated perches during later breeding phases. The shift in foraging behavior corresponds to the drastic changes in time allocation. Relatively high daily energy expenditures (DEE) by brooding females coupled with low foraging rates may explain the observed posthatching body mass losses. In both sexes, high required energy acquisition rates when feeding large nestlings indicate that parent wheatears then may encounter another energetic bottleneck. Postfledging was the least costly phase because, compared with the period of feeding nestlings, there were reduced thermostatic costs and a marked drop in flight time. Males and females had similar DEEs during prelaying, laying and nestling feeding, but females had lower needs during incubation. The elective components of energy budgets during nestling feeding, as well as the estimated sum of the elective components throughout the season, were 12% higher for males than for females. The elective components of the energy budgets varied more than the obligatory components (basal + thermoregulation), especially in females, and were more important in determining the variation of DEE throughout the breeding season. A validation study with doubly labeled water indicated that the energy budget model used was accurate enough for comparisons between sexes or breeding phases, but not for measuring individual variation.

Comparative Ecology and Life History of the Racer (Coluber constrictor) in Michigan

The racer, Coluber constrictorfoxii, was studied over a six-year period in southeastern Michigan. The minimum age at maturity was 11 months in males and two years in females. Both sexes grew rapidly, exceeded 600 mm SVL at the end of the first full season of growth, and individuals of both sexes attained SVL >1300 mm. There was no sexual size dimorphism. Autumn body mass was correlated strongly with SVL (r = 0.994). There was a single clutch per year averaging 15.0 eggs, and clutch size was positively correlated with female SVL (r = 0.937). All hatchlings and some yearlings overwintered at dispersed locations, while some yearlings and all large adults overwintered at communal dens. Adults dispersed up to at least 2.2 km from major hibernacula. During the warm season, mean distance between recaptures was 424 m for large adults, 188 m for yearlings, and 62 m for small juveniles. These traits indicate high rates of energy acquisition and use. In contrast, adult survivorship appears to have been low, at an estimated 0.54 per annum. Adult and subadult survivorship appear to be uncertain because of winter frost penetration, consistent with a bet-hedging hypothesis explaining life-history differences among this population and those previously studied in Kansas and Utah. Published data on variation of body size throughout the geographic range of the racer were examined to test this hypothesis; small body sizes found in subspecies inhabiting relatively stable climatic regions were not consistent with the hypothesis. Instead, racer size and diet, and the presence of snake species with similar habits and diets, were correlated across the geographic range of the racer.

Stopover of Neotropical Landbird Migrants on East Ship Island Following Trans-Gulf Migration

The ecophysiology of Neotropical landbird migrants was studied in relation to energetic condition following trans-Gulf migration in 1987, 1988, and 1989. Most birds captured on East Ship Island, a barrier island off the Mississippi coast, had exhausted fat reserves crossing the Gulf of Mexico and were near fat-free mass. Few birds were recaptured after the day of their first capture, suggesting that migrants departed the day of their arrival or that night. Lean migrants occurred more frequently in samples of recaptured migrants, although length of stay was not a clear function of arrival mass nor did change in mass simply increase with stopover length. Most species were characterized by loss of body mass or by rates of change that essentially maintained arrival mass during stopover. Rates of change in mass were positively correlated with energy demand for several species. Fat-depleted birds appeared to compensate for their condition, presumably by increasing their rate of energy acquisition. Estimates of prey abundance did not differ between years, which might explain why stopover length and rate of gain did not vary between years. We conclude that many migrants left ESI because they found few opportunities to satisfy energy demand, while others stayed because of constraints unrelated to their energy balance or because the benefits of rejecting the habitat were outweighed by the cost of finding a more suitable site.

The constraints of digestive rate: An alternative model of diet selection

A general model is developed to predict diet selection when digestive capacity is limited and when food items differ in digestibility and digestive turnover time. Under these conditions, in order to maximize the rate of energy acquisition, animals should maximize digestive rate, by selecting food with high digestibility and rapid passage through the digestive tract. They should spend as much time as they have available to search for this food. These and other predictions differ from those of the widely used Contingency Model, which maximizes the rate of ingestion of energy. Many experiments in the literature have not discriminated between predictions of these two models. Moreover, clarification of the conditions under which these two general models apply leads to a new perspective on the diversity of foraging behavior in animals.

Physiological energetics of Japanese scallop Patinopecten yessoensis larvae

Growth and ingestion rates were determined for Japanese scallop Patinopecten yessoensis larvae reared at temperatures between 10 and 18 °C and fed concentrations of Isochrysis aff. galbana (clone T-ISO) cells between 5 and 30 cells · μl −1 to gain insight into energy balance. Veliger larvae were held in experimental chambers at densities of 0.5–100 · ml −1 to assess the influence of crowding on growth, respiratory and feeding rates. Long-term growth studies lasting 28 days indicated that growth was most rapid at highest food concentrations of 30 cells · μl −1 despite indications from short-term feeding studies that ingestion was at a maximum and independent of concentration between 15 and 30 cells · μl −1. Growth and ingestion are both reduced as the density of larvae increases. Feeding rates (6 h) remained fairly constant between densities of 1–5 larvae · ml −1 if food availability was increased proportionately. However, growth experiments lasting 28 days revealed extremely low survivorship if larvae are reared at densities of >1 2 · ml −1. Respiratory rates were higher than previously reported for bivalve larvae and reaching values of 13 nl · h −1 or 13–29 ml O 2 · g −1 [AFDW] · h −1. Oxygen consumption was reduced ≈ 35% at larval densities between 5 and 25 · ml −1 which are typical densities used when measuring metabolic rates of veliger larvae. Assimilation efficiencies between ≈ 55 and 80% were comparable to published values for mussel and oyster larvae but higher respiratory demand and comparatively slow growth rates for this species were reflected in lower growth efficiencies than those previously reported for bivalve larvae. Japanese scallop larvae apparently require a minimum food concentration of 7–15 cells · μl −1 (depending on size) to gain sufficient energy to support respiration and growth. Despite morphological similarities between species of bivalve larvae they may differ in their rates of energy acquisition and utilization.

Methods for studying the energetics of freely diving animals

Advances in instrumentation and labeled water methodologies are providing new insights into at-sea behavior and energetics of freely diving animals. Used concurrently, these approaches can add significantly to our understanding of the physiological ecology of diving animals. In this paper I review existing information on at-sea behavior and free-ranging metabolism of diving mammals and birds, and discuss the methods available to assess at-sea diving food consumption, energy expenditure, and behavior. Finally, using the limited available data for northern fur seals, I present approaches for the analysis of concurrently collected data on at-sea metabolism and diving behavior. These include estimation of prey capture success per dive, rate of energy acquisition per dive, time–energy budget analysis, and diving metabolic rate derived from regression analysis. I hope that this discussion will stimulate interest in a potentially powerful method of understanding the physiology and ecology of freely diving animals in nature.

Differential Loss of Fat and Protein by Mule Deer during Winter

Body composition of hand-reared mule deer (Odocoileus hemionus) was studied by use of tritiated water (HTO) over a 120-day period. Energy intake was controlled at different levels for three treatment groups. All treatment groups received submaintenance rations to ensure catabolism of energy reserves. Changes in total body water indicated catabolism of both fat and protein reserves. High-intake animals lost less fat (38%) than either medium(46%) or low(67%) intake deer. High and medium groups lost similar amounts of protein (16% and 18%, respectively), whereas low-intake animals lost 31% of their body protein. Significant loss of protein occurred in all groups within the first 40 days. Fat reserves were depleted at similar rates among treatments. Rates of protein loss between high-and medium-intake groups were similar, but the low-intake group differed significantly. Analysis of the amount of energy contributed to the energy pool by catabolism of fat or protein suggested three phases of protein catabolism, similar to those observed in starvation studies with other mammals. Consequences of fat and protein catabolism in wintering mule deer are discussed. J. WILDL. MANAGE. 49(1):80-85 During winter, wild North American ruminants may face a shortage of forage (Moen 1976, Wallmo et al. 1977). Even if an adequate quantity of forage is available, its quality may be so low that it cannot be effectively utilized (Short et al. 1966, Dietz 1967); because low quality forages are not readily digestible, they may not support large rumen microflora populations. As a result, wintering animals may extract energy so slowly that they enter negative energy balance despite presence of adequate quantities of available forage. Additionally, the rate at which ungulates are able to extract protein from such forages may be insufficient to meet their metabolic requirements. Thus, even when the quantity of winter forage is not limiting, forage quality may still impede the rate of energy acquisition by wild ungulates. During periods of prolonged negative energy balance, an animal draws upon fat and protein to meet its energy requirements. Differential use of these two reserves may affect the animal's survival probability or production of viable offspring. Catabolism of fat for maintenance appears to be a normal, nondetrimental part of the animal's annual cycle. Both synthesis and catabolism of fat proceed at high levels of energetic efficiency (van Es 1977). Protein synthesis and catabolism for energy use is less efficient than that of adipose tissue (Thorbek 1977); therefore, it is not energetically advantageous to rely heavily upon protein reserves to meet an energy deficit. Cahill (1970) suggested that mammals could not withstand a loss of onethird of total protein stores. Little is known about differential use of these two energy reserves in wild ruminants. de Calesta et al. (1975) suggested that protein and fat catabolism occurred simultaneously in starving mule deer. Panaretto (1964) showed both fat and protein catabolism had occurred in two groups of undernourished domestic sheep. Conditions that trigger substantial protein catabolism are not known, nor is it understood how the magnitude or duration of nutritional deprivation affects priorities associated with use of adipose and lean body tissue. Accordingly, we investigated in vivo catabolism of protein and fat reserves of mule deer during winter. Financial support was provided by Fed. Aid Proj. W-126-R, Colo., and Natl. Sci. Found. grant #DEB 7917293. We wish to thank P. H. Neil, D. L. Baker, E. S. Williams, P. A. Smith, and K. N. Callahan for their assistance in all phases of this investigation. MATERIALS AND METHODS

Primate Carnivory and Its Significance to Human Diets

Most primates are omnivorous. Omnivores increase the proportion of dietary animal matter when this increases the rate of energy acquisition. Humans, being omnivores, share this dietary predisposition, increasing animal-matter consumption beyond levels available to humans when dietary predispositions were limited by resource availability. These relations probably are the evolutionary and economic bases for the tendency of contemporary humans with access to luxury diets to consume health-hazardous quantities of meat.