Minimum Food Research Articles

Examination of a smallest CELSS (microcosm) through an individual-based model simulation

Research of the effect of space environment on an ecosystem consisting of plants and animals is essential when they are to be positively used in space. Although there have been experiments on various organisms under space environment in the past, they mainly studied the effect of space environment on an individual organism or a single species. Microcosm is drawing attention as an experimental material of an ecosystem consisting of multiple species. The object in this research is to understand the nature of this network system called ecosystem. Thus, a mixed microorganism culturing system consisting of three types of microorganisms which form a minimum food chain system as a closed ecosystem (chlorella as the producer, bacteria as the decomposer, and rotifer as the consumer) was taken for the subject, on which to research the universal characteristics of ecosystems. From the results of experiments under the terrestrial environment, formation of colonies, which is an ecological structure, has been observed at its mature stage. The organisms form an optimal substance circulation system. Therefore, formation of colonies in simulation models is important. Many attempts have been made to create ecosystem models. For example, the Lotka–Volterra model forms a simultaneous equation with the differential equation expressing predator and prey relationship and many numerical calculations have been conducted on various ecosystems based on expanded L–V models. Conventionally, these top-down methods have been used. However, since this method only describes the average concentration of organisms that are distributed uniformly throughout the system and cannot express the spatial structure of the system, it was difficult to express ecosystem structures like colonies and density distributions. In actual ecosystems, there is heterogeneity in the number of individuals and in substance density, and this is thought to have great significance in ecosystems. Consequently, an individual-based model was used that applies rules to predator–prey relationship, suppression, production, self suppression, etc., of each species. It enabled the emergence of the overall system only by its local rules, and it was possible to reproduce colony generation. In addition, the transition and the ratio of populations for each species match well with experimental results.

Feeding response of Nyctiphanes australis (Euphausiacea) to various nanoplankton sizes and taxa

Nanoplankton (2 to 20 µm) are a substantial fraction of the plankton in the sea, where they form a potential food source for zooplankton. Monocultures of 12 nanoplankton taxa of different cell size and 1 species of Thalassiosira (microplankton) were offered to Nyctiphanes australis to determine whether they would be consumed and, if so, determine rates of clearance and ingestion by the euphausiid. N. australis ingested very small cells (3.5 to 5.4 µm equivalent spherical diameter) at rates ≤ 5 × 10 5 cells h -1 . A total of 8 nanoplankton taxa were consumed at rates that provided N. aus- tralis with its minimum food requirement of 2% body carbon d -1 , and so could maintain it when microplankton abundance is low. Our results suggest that N. australis can detect and avoid unpalat- able food such as the chlorophytes Dunaliella and Nannochloris, but is susceptible to the toxic dinoflagellate Alexandrium minutum.

SMALL SCALE LABORATORY REARING OF A REDUVIID PREDATOR,RHYNOCORIS MARGINATUS FAB. (HEMIPTERA: REDUVIIDAE) ONCORCYRA CEPHALONICA STAINTON LARVAE BY LARVAL CARD METHOD

A reduviid predator, Rhynocoris marginatus Fab. was reared at four different densities (25, 50, 75 and 100) on Corcyra cephalonica Stainton larvae. Fifty predators per rearing container were the suitable density for small scale laboratory rearing of this predator because this density had shorter nymphal developmental, preoviposition and incubation periods, female biased sex ratios minimum food requirements and maximum fecundity and hatchability. A life table was constructed in relation to the predator density. The net reproductive rate was higher in the 50 predator group and it decreased with an increase in the predator density. R. marginatus population doubling time (14.9 days) was found to be higher in the 100 predator category and increased as the predator density decreased. Cost of production of this predator for field release was also lower when compared to insecticide or NPV application.

Estimating food consumption of marine predators: Antarctic fur seals and macaroni penguins

Summary Estimating food consumption is central to defining the ecological role of marine predators. This study developed an algorithm for synthesizing information about physiology, metabolism, growth, diet, life history and the activity budgets of marine predators to estimate population energy requirements and food consumption. Two species of marine predators (Antarctic fur seal Arctocephalus gazella and macaroni penguin Eudyptes chrsolophus) that feed on krill in the Southern Ocean were used as examples to test the algorithm. A sensitivity analysis showed that estimates of prey consumed were most sensitive to uncertainty in some demographic variables, particularly the annual survival rate and total offspring production. Uncertainty in the measurement of metabolic rate led to a positive bias in the mean amount of food consumed. Uncertainty in most other variables had little influence on the estimated food consumed. Assuming a diet mainly of krill Euphausia superba, annual food consumption by Antarctic fur seals and macaroni penguins at the island of South Georgia was 3·84 [coefficient of variation (CV) = 0·11] and 8·08 (CV = 0·23) million tonnes, respectively. This was equivalent to a total annual carbon consumption of 0·35 (CV = 0·11) and 0·72 (CV = 0·23) G tonnes year−1. Carbon expired as CO2 was 0·26 (CV = 0·06) and 0·65 (CV = 0·19) G tonnes year−1 for fur seals and macaroni penguins, respectively. The per capita food consumption varied depending upon sex and age but, overall, this was 1·7 (CV = 0·22) tonnes year−1 for Antarctic fur seals and 0·45 (CV = 0·22) tonnes year−1 for macaroni penguins. The algorithm showed that the seasonal demand for food peaked in both species in the second half of the breeding season and, for macaroni penguins, there was a second peak immediately after moult. Minimum food demand occurred in both species during the first half of the breeding season. As both Antarctic fur seals and macaroni penguins compete for krill with a commercial fishery, these results provide an insight into the seasons and stages of the life cycle in which competition is likely to be greatest.

Living Standards and Economic Vulnerability in Turkey between 1987 and 1994

Until recently, poverty was a relatively unexplored field of studies in Turkey. This is one of the first attempts outside Turkey to use household survey data from two nationally representative surveys conducted in 1987 and 1994 to get a picture of poverty and its main driving forces. The 1994 data remain until today the latest household level data available for Turkey. The paper finds that Turkey does not face a problem of absolute poverty by the standards of a developing country (in 1994 only 2.5 percent of population lived at less than 1 dollar a day at 1985 purchasing power parity). However, applying a standard that is adequate to Turkey’s level of development we find that 7 percent of the population were not able to afford a minimum food basket in 1994 and 36 percent were below the threshold that included alongside minimum food requirements also essential non-food spending. There was a rather small reduction in the poverty risk in Turkey between 1987 and 1994, despite an impressive economic growth, - largely due to negative effects of the macroeconomic crisis of 1996. Poverty in Turkey affects mostly specific groups of the population. Employment and earnings opportunities are key determinants of poverty risks. The profile of poverty by labor market characteristics has remained stable in the 1987-94 period. Macroeconomic and demographic factors (falling fertility and migration from the poorest rural areas to cities) were the main driving forces behind changes in the number of poor.

Nutrition and Aging in Africa: Transitional Changes

Although the proportion of elderly blacks is much smaller than that of white populations in Africa, it is increasing. Since the vast majority of blacks in Africa are in poor economic circumstances, questions arise as to how well they manage, particularly regarding their eating habits and nutritional state. On the one hand, the limited information available indicates major shortfalls compared to international dietary allowances of nutrients. Yet, outwardly, elderly Africans appear to cope better than would be expected. Unfortunately, no cross-sectional nor prospective studies have been undertaken on representative groups of African elderly. In view of the increasing poverty of the populations of most African countries, it would be of value to learn from nutritional and clinical studies what are minimum food intakes that are still consistent with everyday good health.

Effect of food concentration on the growth and production rate of Artemia franciscana feeding on algae (T. iso)

Abstract Individual dry weight and carbon content, ingestion rate, growth rate and production rate were determined for different developmental stages of Artemia franciscana feeding on six different concentrations of Isochrysis galbana (Tahiti). The cultures were grown at nearly constant food concentrations, ranging from 0.2 to 20 mg C l−1 for 12 days at a temperature of 26–28°C and 34 ppt salinity. The individual body dry weight increased exponentially with age to a point of inflection before the growth rate gradually decreased when the animals reached the pre-adult stage. The growth of A. franciscana was strongly influenced by the food concentration. Minimum food concentration required for maximum growth was 10 mg C l−1. At this food concentration the individual dry weigh increased from 2.3 μg ind−1 (newly hatched nauplii) to 195±7.03 μg ind−1 (mean±SE) when the animals had reached pre-adult stage (11 days growth). In the same period A. franciscana grown at lower food concentrations, 7, 5 and 3 mg C l−1, reached 134±3.41, 88±3.53 and 29±3.09 μg (mean±SE), respectively. At the lowest food concentration tested (0.2 mg C l−1) the individual dry weight was reduced by 14–18% after 5 days of cultivation, indicating that the animals were starving. The carbon and nitrogen content (% of dry weight) of newly hatched nauplii was 45.5 and 10.1%, respectively. During the growth period the carbon content varied between 40.1 and 45.5%, and the nitrogen content between 9.1 and 10.5%. The specific growth rate (μ, day−1) and the ingestion rate (ng C ind−1 day−1) were strongly affected by the size of the animals and the food concentration. Both rates increased with increasing food concentration and reached a maximum level at an algal concentration of 10 mg C l−1. The specific growth rate and the ingestion rate were not influenced by an increase of the food concentration above 10 mg C l−1. At these food concentrations the specific growth rate showed a maximum value when the animals were in the range 6–51 μg ind−1 (μmax=0.9–1.15 day−1). The weight specific ingestion rate (IW, h−1) also increased with increasing food concentration. A. franciscana in the range of 7–20 μg ind−1, grown at food concentrations ≥10 mg C l−1, ingested on carbon basis approximately 20–28% of the individual carbon content per hour (IW=0.20–0.28 h−1). At the lower food concentrations (3 and 5 mg C l−1) the ingestion rate was reduced and the weight specific ingestion rate varied between 0.05 and 0.1 h−1. The production rate (Pr, μg C ind−1 day−1) showed a distinct maximum for animals grown at the two highest food concentrations. When individual dry weight exceeded 6 μg ind−1 (post-metanauplius II) animal size affected both the production rate and the relative production rate (%, day−1). Thereafter the food concentration had a more pronounced effect on the production rate of the animals. The conversion of ingested food into biomass (yield, day−1) was dependent on food concentration and animal size. Animals fed at the lowest food concentrations (3, 5 and 7 mg C l−1) attained a yield of 0.50–0.65 at post-metanauplius stage III, and remained at this level until post-metanauplius stage VII (dry weight; 10–50 μg ind−1). Animals at the same size but fed at the highest food concentrations (10 and 20 mg C l−1), showed a yield close to 0.15–0.20 at post-metanauplius stage III increasing to 0.50 at post-metanauplius stage VI–VII. In the older stages the yield decreased from a mean of 0.46 to 0.05–0.10 when the animals attained pre-adult stage.

The daily feeding rhythm to demand feeders and the effects of timed meal-feeding on the growth of juvenile Florida pompano, Trachinotus carolinus

The circadian feeding rhythm of juvenile Florida pompano, Trachinotus carolinus, to demand feeders, was electronically recorded. The fish were maintained under artificial light–dark conditions (LD 15:9) and given continuous access to food via demand bars. A distinct circadian feeding rhythm was displayed. Food demands occurred almost exclusively (99.0%) during the light phase. Feeding activity was highest early in the light period and progressively lessened as the day progressed. The fish made significantly more food demands during the 2-h period of maximum demand (0600–0800 h, 21.5±5.2% SEM of the total daily food demands) than during the period of minimum demand (1800–2000 h, 6.8±2.1%) ( P<0.01, ANOVA). The maximum and minimum food demand periods were then used to test the effects of meal feeding time on food consumption and growth performance in juvenile T. carolinus. The fish were fed by hand, at either 0600–0800 h or 1800–2000 h, for 5 weeks. During the 2-h feeding period, the fish were fed 4% of their body weight (bw) in four equal allotments, 1% bw/30 min. At the end of the study, the fish fed in the morning, the preferred feeding time, had significantly lower bw, shorter body length and lower food conversion efficiency than the fish fed in the evening ( P<0.05, One-way ANOVA). Results of this study indicate that feeding schedules that take advantage of circadian rhythms may be used to enhance growth performance of T. carolinus, and that the preferred feeding time may not necessarily be the best time for feeding.

An African perspective on nutrition and ageing

Although the proportion of elderly in African populations is much smaller than that in white populations, it is increasing. Since the huge majority of Africans are in poor economic circumstances, questions arise as to how well they manage, particularly regarding their eating habits and nutritional state. On the one hand the limited information available indicates major shortfalls from international dietary recommended allowances of nutrients. Yet, outwardly, elderly Africans appear to manage better than would be expected. Unfortunately, no cross-sectional nor prospective studies in this area have been undertaken on representative groups of African elderly. In view of the increasing poverty of the populations of most African countries, it would be of value to learn from nutritional and clinical studies, of minimum food intakes which are still consistent with everyday good health.

Food supply capacity study at global scale

The world population is expected to grow to 10 billion people in 2040, requiring food production at least to triple, as a combined result of population growth and dietary changes. In this study scenarios for food security are developed for 15 major regions of the world. Food production is calculated on a 1°x1° grid basis, using inputs from a digital data base containing soil, climatic, agronomic and demographic data. This allows us to study impacts of different production scenarios and their environmental side effects. Soil area data are derived from the digitized FAO soil map, considered to be representative for soil units on a 1°x1° grid; weather variables of 978 stations are allocated to the grid cells. Food production estimations are made with a simple crop growth module, a soil water balance and a soil nitrogen balance. Calculations are done on a grid basis, each grid cell being characterized by its suitability for arable farming or grassland, soil and climatic conditions and the availability of irrigation water. Results of Yield Oriented Agriculture (YOA) and Environment Oriented Agriculture (EOA) production scenarios on food self-sufficiency are presented. If we assume that there is no limit to transport of food across the globe, YOA allows the entire globe an affluent diet, while EOA allows only a moderate diet. For this scenario, regional self sufficiency indices vary widely: most regions can produce food required for an affluent diet, but not East, South and West Asia that account for 48% of the expected global population in 2040. Also Southeast Asia (9% of expected global population in 2040) and West and North Africa (10%) come close to the lower limit for food self-sufficiency. With EOA, only the former USSR, North and South America, Central and Southern Africa and Oceania can offer their future populations an affluent diet. Southern Asia will experience food shortages even under minimum food demand, and less affluent diets do not provide a solution. In this paper, attention is given to the methodology regarding soils, and to the uncertainty regarding soil and water in input data. Particularly soil suitability for agriculture for each of the grid cells has a large effect on model calculations, as it is a rather rough approximation. Knowledge of soils across the world shows important weaknesses with respect to the extent of coverage, extrapolation of point observations to grid cells, definition of soil characteristics compatible with crop models, and handling of preferential flow in soil profiles. We emphasize the need for digitized, reliable and readily available natural resource information in the fields of soil surveys, climatology, irrigation water availability, land use and land cover. The ultimate goal of the approach is not to predict the future of global agriculture, but to allow decision makers to compare various scenarios for food self-sufficiency, and to raise awareness regarding issues related to food security. In spite of the above-mentioned shortcomings in basic data, it is demonstrated that it is possible to develop the required scenarios now, instead of having to wait on more reliable soil information.

Modeling oyster populations. V. Declining phytoplankton stocks and the population dynamics of American oyster ( Crassostrea virginica) populations

Phytoplankton standing stocks have shown a steady decline in Galveston Bay, Texas over the last 20 years. Phytoplankton provides the primary food resource for oyster populations in Galveston Bay. We used a time-dependent population dynamics model of oyster populations to examine the impact of a decline in phytoplankton stocks on oyster populations. Simulations were run with two different types of mortality: winter mortality, assuming that the oyster fishery is the primary source of mortality; and summer mortality, assuming that predators and disease are the primary source of mortality. All simulations showed the same qualitative trends. Market-size adults disappear from the population in about 4 years, with an approximate 15% decline in food supply. Submarket-size adults maintained an increasing or steady population density for 10–14 years, after which the populations crashed to near extinction in 2–4 years. The proximate cause was a cessation in reproductive activity when food supply ceased to be sufficient to generate a fall spawn, an approximate 60% drop in food from current levels in Galveston Bay. The temporal sequence of mortality affected the outcome very little. The simulations suggest that populations decline rapidly in response to declining food supplies because a minimum food level is required to support a market-size population and a minimal reproductive activity. The simulations suggest that a reduction in market-size individuals is the primary early-warning signal of decreased food supply within the affected population and that this warning signal might easily be mistaken for overfishing. Proper management requires the monitoring of food supply and the use of a mathematical model to assess the importance of observed declines in population abundance. Unfortunately, once the fishery is affected, little time may remain before the termination of spawning and population extinction.

Influence of Food Quantity and Lead Exposure on Maturation in Daphnia magna; Evidence for a Trade-Off Mechanism

1. The start of reproduction is an important life-history trait in both ecology and ecotoxicology. Effects of food availability and toxic stress on maturation in female Daphnia magna are presented. 2. Five instars to maturation were observed under conditions of moderate to high food levels. Age and size at subsequent stages of the maturation process, i.e. ovary provisioning and egg deposition, depended on the rate of body growth. 3. At low food, a trade-off between reproduction and growth occurred. Within the same environment, some females reproduced at early age and small size, whereas others gave priority to growth over reproduction. In the latter resorption of yolk from the ovaries was observed. 4. Except for the production of malformed young, effects of lead on maturation resembled increased food stress. With abundant food, toxic effects were different to effects at low food. The results of standardized laboratory tests may therefore underestimate toxic effects at reduced food availability. 5. The phenomena observed in our studies can only partly be explained by a food-independent size threshold for maturation, which initiates resource allocation to reproduction; a minimum food uptake is required to enable the production of eggs

Simultaneous Determination of Thermal Conductivity and Diffusivity of Foods using a Point Heat Source Probe: A Theoretical Analysis

A computerized mathematical model was developed to examine theoretically the applicability of a continuous point heat source method for simultaneous determination of thermal conductivity (κ) and thermal diffusivity (α) of foods by developing proper data reduction methods. A probe of composite structure as well as an overall finite contact conductance coefficient between the probe and the food was assumed. Glycerol and agar gel were used as reference materials to obtain a mean effective distance 'r' from the point heat source to the temperature sensor location that is needed in the determination. Estimated κ for 15 different foods was in good agreement with values obtained from the literature (2.5% maximum deviation), whereas the agreement for α was reasonably good only for foods with large α values. A small overall thermal contact conductance coefficient introduced an error of 46% in κ and 35% in α determination. The minimum food size for accurate determination of thermal transport properties was 22 mm height × 8 mm radius, but was further reduced to 17 mm × 5 mm when the heater dimensions were decreased by a factor of four.

In vitro characteristics of white cell‐reduced single‐unit platelet concentrates stored in syringes

Platelet concentrates (PCs) for premature infants may be subjected to filtration, centrifugation, and various storage conditions before transfusion. As there are few data on the cumulative effect of these procedures on PCs, platelet properties (including biochemical and functional in vitro assays) were evaluated after the processing of single units of PCs through a 1-unit-capacity high-efficiency white cell (WBC)-reduction filter followed by syringe storage at either 22 or 37 degrees C for 6 hours. Two- and 5-day-old PCs, volume-reduced PCs, and prestorage WBC-reduced PCs were evaluated. WBC filtration consistently resulted in a 3 to 4 log10 reduction in WBCs, with less than 15-percent platelet loss. No adverse effects of platelet function or evidence of increased platelet activation as determined by the percentage of P-selectin positivity were noted. A decrease in pH associated with increased lactate production and consumption of glucose was observed following syringe storage under all conditions tested. Such changes were most pronounced, however, with volume-reduced PCs stored at 37 degrees C (pH 6.31 +/- 0.15, lactate 23.0 +/- 3.06 mmol/L). All pH levels at the end of storage were above the minimum Food and Drug Administration requirement (pH 6.0). The in vitro data suggest that single units of PCs can undergo WBC filtration followed by syringe storage for up to 6 hours and still maintain acceptable storage characteristics. The practice of maintaining volume-reduced PCs in syringes for 6 hours at 37 degrees C in isolettes during transfusion should, however, be avoided.

Evaluation of the effect of extrusion cooking of jackbean ( Canavalia ensiformis L.) seed on short-term feed intake in chicks

Experiments were conducted to investigate the relationship between various extrusion cooking conditions, the chemical composition of jackbean samples and the short-term control of food intake in chicks. All data were analysed using a principal component analysis computerized program. Ground jackbean was extruded on a pilot-scale twin-screw extruder. Water addition at the feed inlet, filling rate of the screws, barrel temperature in the last section of the extruder and reverse-screw element position were tested as operating variables. Three sets of experiments (A, B and C) and a total of 20 trials were performed. Process variables were specific mechanical energy, product temperature measured at the die and resulting pressure exerted on the shafts. Also, colour values were determined on all jackbean samples. Experimental diets containing 300 g kg −1 extruded jackbean were fed to 7-day-old chicks to measure the short-term variations in food intake. Inactivation of the lectin (concanavalin A) was monitored using a haemagglutination assay. In addition, starch solubility, and reactive lysine and canavanine contents were determined on samples from Experiment A. Pilot-scale extrusion cooking of Canavalia appears to be feasible: water addition decreased energy consumption ( r = −0.76), filling rate and position of the reverse-screw element are correlated to product temperature ( r = +0.61 and −0.66, respectively). Food intake inhibition index, used as an expression of toxicity for chicks, was reduced in proportion to a decrease in the amount of water added and to the filling rate ( r = +0.8 and +0.6, respectively). The minimum food intake inhibition index was 70% in Experiment A, 61% in Experiment B and 35% in Experiment C according to our experimental conditions. The lower the food intake inhibition index, the more delayed the inhibition effect on food intake. Lightness and specific mechanical energy appeared to be accurate indicators of the detoxification level ( r = +0.85 and +0.72). No significant relationship was apparent between toxicity and haemagglutination activity of the meal. Additional research is needed to understand the high correlation found among canavanine, reactive lysine content and the reduced feed intake shown by the chicks.

The Effects of Temperature on Food Passage Time through the Digestive Tract in Notophthalmus viridescens

Movement of food through digestive tracts of red-spotted newts from southern Ohio was studied to better understand seasonal changes in energy processing. To determine minimum food passage time through the gastrointestinal tract, blood-worms marked with carbon black were consecutively in- tubated five times to one group of newts at 25 C and twice to a second group at 5 C. Minimum food passage time at 25 C averaged 33 h, with no significant differences among the five feedings. The newts tested at 5 C required an average of 220 h for the passage of food, with significant differences between the two feedings: 157 h for the first and 284 h for the second. Other newts, intubated with worms labeled with iron powder, were X-rayed at periodic intervals to investigate passage of food through the digestive tract. Full stomachs were completely evacuated in 2 d at 25 C, with a half evacuation time of 20 h, but only after 15 d or more at 5 C, with a half evacuation time of 55 h. Maximal amounts of food in the intestines were attained by 20 h at 25 C, but were achieved only after 3 d at 5 C. Evacuation of labeled food from the intestines was completed in about 40 h at 25 C, whereas most of the food was still in the intestines after 15 d at 5 C. It appears that newts are able to process food in all seasons; however, passage time is greatly influenced by temperature.

Survival enhancement through food sharing: A means for parental control of natal dispersal

The value of food sharing among relatives is analyzed for a situation where fitness equals survival. In seasonal environments the minimum food abundance may set a limit to group living. Delayed dispersal is predicted to be linked to relaxed winter competition and high parental survival. Enhanced survival for the offspring when parents share food could be a sufficient reason to delay dispersal, while early dispersal in advance of food shortage periods may be induced by a competitive relationship. At low resource abundance dominant parents do best by being competitive and retaining all resources. For food abundance higher than the expected requirements food sharing with independent offspring is possible, although it has a non-zero cost. Food sharing parents still retain most of resources to themselves, but the resource share given to subordinate offspring gradually gets larger when food abundance increases. Except for at very low food abundance, where subordinates may adopt a “suicidal” behaviour and cede their resources to the dominant, there is a conflict over how to share the resources.

Population Dynamics of Poikilotherm and Homeotherm Vertebrates: Effects of Food Shortage

We have investigated how the population dynamics of two types of vertebrates is influenced by food shortage. One type consists of animals which show indeterminate growth rate (cut the coat to the cloth) e.g. fish. The other type includes animals which show a determinate type of growth rate (require a minimum daily food supply to survive), e.g. mammals and birds. To this end we have developed a model which assumes that animals biomass is regulated by food biomass alone (i.e. no predation), while food biomass follows self-regulating dynamics. The model predicts stable biomass for the first type of animals and unstable, cyclic biomass for the other. The results help to explain why fish in a pond often develop a stable population of numerous, small individuals, while e.g. hares or moose on an island, shielded from predation, develop a fluctuating population

Cannibalistic feeding behavior of the brackish-water copepod Sinocalanus tenellus

Cannibalistic feeding behavior of the brackish-water copepod Sinocalanus tenellus was examined in the laboratory using CI-II, CHI-IV and CVI female as predators and NI-II, NIII-IV, NV-VI and CI-II as prey. In each prey-predator combination, the mgestioo rate increased with increasing prey density to an asymptotic value. Cannibalism took place even when phytoplankton was available as an alternative food supply. Based on a daily ration, the optimal prey stages for CVI females, Cni-IV and CI-II are NI-VI, NI-IV and NI-II respectively. Under average, natural prey density (10 nauplii I1), 5 tenellus can achieve only a small fraction (max 9%) of the daily minimum food requirement by cannibalistic feeding. However, the impact of cannibalism on naupliar survivorship can be significant. When adult females occur at a density of 10 I1, the mortality due to cannibalism attains 99.2% during the naupliar stages.

Density-dependent natural selection does not increase efficiency

Summary Populations of Drosophila melanogaster kept at high population density (K-selected) for 125 generations have higher larval viability than populations kept at low densities (r-selected) when both are raised under crowded conditions. In addition K-selected adults that emerge from crowded cultures are larger than their r-selected counterparts. These differences cannot be explained by differences in efficiency of food use. The minimum food required for successful pupation is actually greater in the K-selected populations. I conjecture that there may be a trade-off between minimum food requirements and competitive ability, which has changed substantially in the K-selected populations. The possibility that K-selected larvae can dig more more deeply and gain access to unused food is examined and rejected as a possible explanation of the viability differences. Evidence is provided supporting the hypothesis that the differences in viability may be due to an increased tendency of the K-selected larvae to pupate off the surface of the medium.