Zur chemischen Zusammensetzung der CtenophorePleurobrachia pileus in der Kieler Bucht

The chemical composition of the ctenophorePleurobrachia pileus was investigated in March, May and July 1981 in Kiel Bight, western Baltic. The results of all determinations yielded low values compared with other zooplankton groups. Dry weight made up 1.95 to 2.28% wet weight with a minimum occurring in may. Ash-free dry weight amounted to 28–37% of the dry weight but exhibited a maximum in May. Carbon and nitrogen analyses yielded amounts of between 2.6–4.7% of the dry weight and 0.5–1.0% of the dry weight, respectively. Both elements reached lowest levels in May. Proteins reached a minimum in May, too, and values ranged between 2.5 and 5.1% of the dry weight. However, lipids as well as carbohydrates exhibited highest values in May and ranged from 0.8 to 1.6% and 0.8–1.1% of the dry weight, respectively. The C∶N values increased between March and July from 3.7∶1 to 6.7∶1, indicating a decline in protein content. To relate the biochemical compounds to organic matter I used three different approaches: (1) On the basis of ashfree dry weight, carbohydrates remained constant whereas lipids increased from March to July. A minimum of proteins occurred in May. The three compounds made up only 14–22% of ash-free dry weight. (2) Organic matter approximately equals organic carbon content multiplied by 2. Proteins, lipids and carbohydrates summed up reached 61–100% of this reference value and the seasonal course of these compounds changed in a drastic way: proteins decreased, whereas lipids as well as carbohydrates showed a relative maximum in May. (3) Finally, the carbon content of each biochemical compound was calculated in relation to total carbon content measured via C/N analysis. On this basis, 63–105% of total carbon were recovered, and the course of seasonal changes agreed with that of the second approach. A comparison of these three approaches suggests that comparative calculations based on carbon measurements are more valid than those based on ash-free dry weight. The results show that seasonal changes in the amount of organic matter and the biochemical composition occurred. Dry weight was lowest in May, which could be due to the low salinity environment recorded at that time and the corresponding low salt content of the tissue. The observed relative maxima of lipids and carbohydrates in May may be explained by good food conditions since high zooplankton densities are characteristic for this month in Kiel Bight.      

Nitrogen Constituents in Manganese-Deficient Lemon Leaves

Total (Kjeldahl) nitrogen content of manganese-deficient lemon leaves was found to be about 40% higher (on a dry weight basis) than in the analog control leaves. The nitrate-N content rose in the deficient leaves from 18.2 mg/100 g to 95.6 mg/100 g dry weight. Among the N constituents studied, the free amino acids increased by about 42%, the protein amino acids by about 22%, and the total protein by more than 22%, all on a fresh weight basis. Acrylamide gel electrophoresis and ammonium sulfate fractionation showed qualitative differences in the various proteins. The increase of the protein fraction in the -Mn leaves may be attributed in part to the decrease of dry matter in these leaves (25.8% as compared to 30.7% in the control leaves) and in part to accumulation of apparent proteinous material in manganese-deficient tissues.     

The balance of nitrogen and composition of proteins inPleurotus ostreatus grown on natural substrates

The balance of nitrogen and nitrogen compounds in Pleurotus ostreatus, cultivated on waste materials, corn straw and maize residues, was investigated. The results show that this organism has a considerable ability to fix atmospheric nitrogen, fixing 312 g of total nitrogen per 100 kg dry weight. When recalculating with respect to a decrease of the substrate during growth of the organism a value of 9.7 mg per 1 g of the decrease in material is obtained. Fruiting bodies, as well as the produced substrate contain 17-19 amino acids. In the produced substrate the content of the protein nitrogen represents only 30% of the total. It can concluded that Pleurotus ostreatus yields a suitable raw material in the food industry and possibly also a fodder based on the basis of solid, cellulose-containing wastes.     

The biochemical composition and calorie density of the walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> in the Sea of Okhotsk

In tissues of the walleye pollock Theragra chalcogramma the dry matter content averages 18.5%. The lipid content of the raw material is 0.7%, the protein content is 15.3%, carbohydrates are 0.6%, and ash is 1.3%. The average calorie density is 940 cal/g wet weight and 5080 cal/g dry weight. The dry matter content of gonads varies within 14.9–28.0% in females and 14.5–17.0% in males. The lipid content of the raw material is 0.9–3.0% in females and 1.3–1.8% in males; the protein content is 10.2–21.5% and 10.7–13.4%, respectively. The calorie density of female gonads is 702–1537 cal/g wet weight and 4426–5482 cal/g dry weight; for the male gonads it is 760–960 cal/g wet weight and 4952–5641 cal/g dry weight. The dry matter content of the liver varies within 42.2–62.2% for females and 34.4–62.4 for males. The lipid content of the raw material is 25.6–44.5% for females and 16.6–41.3% for males; the protein content is 6.3–9.8% and 8.1–12.3%, respectively. The calorie density of the liver in females varies within 2918–4601 cal/g wet weight and 6370–7395 cal/g dry weight; in males it is 2291–4357 cal/g wet weight and 6392–7492 cal/g dry weight. The minimum calorie density of the liver is observed in juvenile pollock: 963 cal/g wet weight and 2045 cal/g dry weight. The dry-matter content of feces in different size groups varies within 15.0–18.4%. Values of the average lipid content of raw material range from 1.1 to 1.6%; the protein content is from 1.8 to 3.8% and carbohydrates are from 0.9 to 1.4%. The calorie density of feces from variously-sized walleye pollock varies within a narrow range, from 308 to 362 cal/g wet weight. The energy equivalent ranges, depending on body size, from 259 to 2377 cal. The share of energy concentrated in the somatic (muscle) tissue of variously-sized walleye pollock during ontogenesis constitutes 56.5–93.9%; in female gonads it is 0.9–26.6%; in male gonads it is 0.4–7.3%, in the female liver it is 7.9–27.2%, and in the male liver it is 5.7–26.9%. The amount of energy (cal), concentrated in the female liver and gonads is on average 1.5 and 3 times as high as that in the male liver and gonads, respectively. The maximum total energy loss (15–30%) in mature walleye pollock of various-sizes occurs in the spawning period, during the transition from the maturity stage 5 to stage 6. The total amount of energy accumulated during the lifecycle from small juveniles (<17 cm) to very large individuals (>60 cm) averages 1964 kcal for females and 1465 kcal for males. The difference in the amount of energy is explained by the fact that oogenesis requires more energy than spermatogenesis.     

Utilization of household food waste for the production of ethanol at high dry material content

Background

Environmental issues and shortage of fossil fuels have turned the public interest to the utilization of renewable, environmentally friendly fuels, such as ethanol. In order to minimize the competition between fuels and food production, researchers are focusing their efforts to the utilization of wastes and by-products as raw materials for the production of ethanol. household food wastes are being produced in great quantities in European Union and their handling can be a challenge. Moreover, their disposal can cause severe environmental issues (for example emission of greenhouse gasses). On the other hand, they contain significant amounts of sugars (both soluble and insoluble) and they can be used as raw material for the production of ethanol.

Results

Household food wastes were utilized as raw material for the production of ethanol at high dry material consistencies. A distinct liquefaction/saccharification step has been included to the process, which rapidly reduced the viscosity of the high solid content substrate, resulting in better mixing of the fermenting microorganism. This step had a positive effect in both ethanol production and productivity, leading to a significant increase in both values, which was up to 40.81% and 4.46 fold, respectively. Remaining solids (residue) after fermentation at 45% w/v dry material (which contained also the unhydrolyzed fraction of cellulose), were subjected to a hydrothermal pretreatment in order to be utilized as raw material for a subsequent ethanol fermentation. This led to an increase of 13.16% in the ethanol production levels achieving a final ethanol yield of 107.58 g/kg dry material.

Conclusions

In conclusion, the ability of utilizing household food waste for the production of ethanol at elevated dry material content has been demonstrated. A separate liquefaction/saccharification process can increase both ethanol production and productivity. Finally, subsequent fermentation of the remaining solids could lead to an increase of the overall ethanol production yield.     

赤腹松鼠能量代谢和营养需要的初步研究

在饲养条件下,赤腹松鼠(Callosciurus erythraeus)每天摄入干物质为7.06—9.91克/只,摄入能最为525.4—562.2千焦耳/千克~0.75每天每只摄入蛋白质:1.26—2.00克,脂肪0.69—2.79克。松鼠对能量、干物质、蛋白质和脂肪的消化率分别为85.7％—89.3％;84.7％—87.0％;75.9％—82.7％和79.1％—94.0％。赤腹松鼠喜食含脂量高的食物,对脂肪的消化能力高于蛋白质。营造种子含脂量高的多种树种混交林,提供松鼠足够的食物,是防止松鼠危害的有效途径。     

Responses to sucrose and glutamine by soybean embryos grown in vitro

Immature soybean (Glycine max [L.] Merr. cv. Ransom) embryos were grown in vitro in the presence of different concentrations of sucrose and glutamine to examine how availability of carbohydrate and nitrogen affects dry matter accumulation and embryo composition. Embryos were transferred to fresh medium every 4 days to maintain sucrose and glutamine concentrations of the culture medium. In all experiments, accumulation of dry matter and protein content increased when the sucrose concentration of the culture medium was increased from 1.5 to 150 mM: however, a relatively greater enhancement of dry matter than of protein accumulation resulted in a lower protein concentration at 150 than at 1.5 mM sucrose. Both content and concentration of protein were increased by the increases in glutamine supply to concentrations exceeding 68% protein at 120 mM glutamine. In combination with 150 mM sucrose, however, oil increased as glutamine supply was increased from 0.6 to 6 mM and then decreased as glutamine supply was increased from 6 lo 120 mM. Varying the concentration of sucrose available during seed development also affected embryo composition. Decreased availability of sucrose during either the early or late portion of the culture period resulted in lower accumulation of dry mailer as well as oil. Protein concentration was actually higher for embryos transferred from 150 to 1.5 nM sucrose than for those remaining in 150 mM throughout the culture period: however, the greater percentage of protein was due lo a decrease in accumulation of dry weight. In addition, embryo composition was affected by altering the availability of glutamine during culture, indicating that variation in the level of nitrogen assimilate delivered during seed development can change embryo composition. Decreasing the glutamine concentration of the medium lowered both protein and oil content. In contrast, increasing the glutamine concentration of the medium from 0.6 to 6 mM 8 days after initiation of culture increased the protein content and concentration of the embryo while oil content was not affected.     

Environmental constraints on the foraging behaviour of a dwarf antelope (Madoqua kirkii)

Dik-diks (Madoqua sp.) inhabit semi-arid regions and experience very different conditions of food availability and quality between wet and dry seasons. By comparing the behaviour of dik-diks between these two seasons, we identified environmental constraints affecting their feeding strategies. In both seasons foraging time was limited by high mid day temperatures. In the wet season a high intake rate compensates for the loss in foraging time, but in the dry season water and protein become limiting. To meet minimum daily water requirements in the dry season dik-diks fed on plant species that they avoided during the wet season. Analysis at the plant species level showed higher species selectivity in the wet season than in the dry season. In a multiple regression analysis food species preferences were best explained by relative abundance and water content in the dry season, and by dry matter content in the wet season. In the wet season the daily dry-matter intake of dik-diks in the field was only about 10% higher than the theoretically predicted minimum for a ruminant of this body weight, while protein and water intake were about 3 times as high. This suggests that the most limiting dietary component in the wet season is energy. In the dry season the daily intake of all dietary components is lower than the theoretical minimum required, and also lower than the values suggested by laboratory studies of dik-diks. This dry season deficit is presumably met from body reserves. Dry season water intake was approximately 30% of the intake observed in laboratory studies indicating that dikdiks are even better adapted to arid conditions than suggested by physiological experiments.     

The effect of level of CaCO3, inoculation and lime pelleting on the nodulation and growth of beans in five acid soils

Summary The effect of level of CaCO₃, inoculation and lime pelleting on the nodulation, dry matter yield and % N content of common bean plants (Phaseolus vulgaris) grown in five acid soils was investigated in a greenhouse study. The soils represented a range in pH from 3.9 to 5.1, in exchangeable Al from 0.0 to 4 meq/100 gm, in exchangeable Mn from 0.35 to 2.32 me/100 gm, and in %C from 0.69 to 5.60.Nodule weight decreased with increasing %C and for the soil with highest %C (5.60) no nodules were observed. In soils with low organic matter and low exchangeable Al and Mn, inoculation increased nodule weight, dry matter yield and %N especially at the lowest pH level. Where the seeds were not inoculated, nodule weight and dry matter yield increased with soil pH. No such increases were observed where the seeds were inoculated. There was no apparent advantage in lime pelleting in such soils.In soils with low organic matter content and with substantial amounts of Al and/or Mn, liming increased nodule weight and dry matter yield, and decreased exchangeable Al and/or Mn. Lime pelleting was superior to mere inoculation in increasing nodule weight particularly at low lime rates.In soils with relatively high organic matter content, nodulation was very low or none at all. Low lime rates had little effect on exchangeable Al and Ca and dry matter yield. Higher lime rates, however, decreased exchangeable Al and dry matter yield but increased exchangeable Ca.     

Biological efficiency and nutritional value of Pleurotus ostreatus cultivated on spent beer grain

Unpretreated spent beer grains were successfully used as a basic substrate material for the cultivation of Pleurotus ostreatus. The effects of spent grain types, additives, substrate moisture content, and substrate packing density on the yield and nutrition of fruit bodies were investigated. The cultivation results showed that few fruit bodies were formed on spent grain alone; however, a significantly high biological efficiency (19.1%) was obtained with the addition of wheat bran to (45%). The chemical analysis of fruit bodies indicated that P. ostreatus cultivated on spent grain substrate had a higher nutritional value than those grown on other reported types of substrates. The total amino acid content in the fruit bodies was 347.5 mg/g dry matter, and the crude protein content was as high as 53.3% on a dry weight basis. It was also found that the cultivation of P. ostreatus increased the crude protein content, while it decreased the ratio of lignin to cellulose, of the spent grain substrate.     

Long-term operation of slurry bioreactor for decomposition of food wastes

A pilot scale slurry bioreactor was used for the treatment of food wastes. Food wastes were continuously added (750 g wet weight per day) into the reactor and successfully decomposed to inorganic carbon without intermittent removal of suspended solids. During operation for 90 days, 91% reduction of food wastes was achieved. Microorganisms actively grew during the initial 20 days of operation, and reached a stationary phase with a cell concentration of around 5 x 10(10) cells ml(-1), which indicated that food waste was utilized as a respiratory substrate during this phase. Using data for time variation of dissolved oxygen, the oxygen requirement for decomposition of food wastes was estimated to be 5.0 g O2 g(-1) dry weight of food wastes.     

Responses of pocket gophers (Thomomys bottae) to changes in diet quality

Summary We examined digestibility of dry matter, nutrients, and fiber, and food intake, metabolic fecal losses, weight change, and gut size of pocket gophers (Thomomys bottae) in relation to diet quality in the laboratory. Pocket gophers were maintained for 15–20 days on one of seven diets which contained from 18% to 56% neutral detergent fiber (NDF). NDF content of the diet was an excellent predictor of diet quality. Digestibility of dry matter, NDF, and nitrogen all decreased with increasing NDF content of the diet. In general, pocket gophers compensated for low diet quality by increasing dry matter intake, but those given high quality forage before the lowest quality diet reduced their intake. Thus, the response of pocket gophers to low quality diets may depend on their body condition. Because increased food intake resulted in increased total metabolic fecal losses and metabolic fecal nitrogen losses, decreasing food intake on low-quality diets may be advantageous. A further response of pocket gophers to decreased food quality was an increase in size of cecum and large intestine, suggesting that fermentation of cell walls became increasingly important as diet quality decreased.     

许氏平鲉幼鱼的赖氨酸需求量

通过8周的生长实验确定了许氏平(Sebastes schlegeli)幼鱼的赖氨酸需求量。饲料必需氨基酸组成(除赖氨酸外)参照鱼体肌肉蛋白的氨基酸模式,配制赖氨酸含量为1.542、.04、2.54、3.04、3.54和4.04%的等氮等能的六种半精制饲料。研究结果表明,随着饲料中赖氨酸含量的增加,增重率逐渐提高,当饲料中赖氨酸含量为3.54%时,达到最大值(P0.05)。基础饲料组的蛋白质贮积率最低,且显著低于3.54%组(P0.05),和其他组之间差异不显著(P0.05)。随着饲料中赖氨酸含量的增加,饲料系数逐渐降低,当饲料中赖氨酸含量为3.54%时达最小值,随着饲料中赖氨酸含量继续增加饲料系数呈上升趋势(P0.05)。饲料中赖氨酸水平对鱼体的干物质、蛋白质、脂肪、灰分和能量含量均无显著影响(P0.05)。饲料中赖氨酸水平对血清谷丙转氨酶(ALT)、谷草转氨酶(AST)活性有显著性影响(P0.05),而对血清甘油三酯及胆固醇含量没有显著性影响(P0.05)。通过回归分析,得出许氏平幼鱼最大生长的饲料赖氨酸需求量2.99%,占饲料蛋白的6.16%。       

The composition and nutritional status of the diet of Oreochromis niloticus in Lake Chamo, Ethiopia

The stomach contents of Oreochromis niloticus from L. Chamo were microscopically examined and chemically analysed in order to study the relationship between food quality, growth and condition. More than 20 genera of phytoplankton plus Copepoda, Rotifera and nauplii were present in the stomach contents. The diatom, Melosira , was the most dominant alga in the diet, contributing about 30% of the organic matter. The composition of the food in terms of organic nutrients was dominated by carbohydrate (20.3% dry weight). Both protein and fat made low contributions to the diet; 10% and 5.8% dry weight, respectively. The overall performance of the fish in assimilating food was high: 43.3% for ash free dry weight, 61.2% for protein, 57.2% for lipid, 29% for carbohydrate and 55.7% for energy. The digestible protein-energy ratio was 15.7 mg kJ⁻¹, suggesting that the food was qualitatively good both for fast growth and for maintaining good condition. It was concluded that the small amount of good quality food ingested, the low fish population density in the lake and the high temperature of the water are the major factors responsible for making O. niloticus a fast-growing fish in Lake Chamo.     

The amount of food ingested in a single meal by rainbow trout offered chopped herring, dry and wet diets

Two-year-old 1·5-kg rainbow trout were held in cages and conditioned by feeding either on low-fat chopped herring (H trout) or dry pellets (P trout) for 15 weeks. Their satiation amounts were then determined under standard conditions. On a wet weight basis H trout ate 2·5-3·5 times more food than P trout; this was sufficient to compensate for the high water content of herring and thereby maintain the dry matter intake. When P trout were offered herring (PH trout) they consumed more food than when offered dry pellets but not as much as H trout. Stomach capacity restricted the intake and their dry matter intake was reduced by c. 40%. When H trout were offered dry pellets (HP trout) they adjusted their intake immediately close to the level of P trout although their larger stomachs could have accommodated more than twice this volume of dry food. The return of appetite after a satiation meal was almost linear with time. Appetite increased at c. 556 mg g^-1 body weight h^-1 for H trout and at 142 mg g^-1 bw h^-1 for P trout. The return of appetite in PH trout was significantly slower (c. 370 mg g^-1 bw h^-1) than in H trout; the previous dietary history of the PH trout limited their capacity to process larger volumes of wet food in a single meal. Fish offered dry diet (P and HP trout) had similar rates of appetite return despite their previous feeding history suggesting that the property of the dry feed itself might limit meal size. The total gastric emptying time of diets of similar dry matter content (with and without large amounts of water) was similar, but the delay time before gastric emptying starts tended to be longer for dry diets. Dry pellets appear to impose a demand for water that prolongs the gastric delay. This water demand is met partly by drinking since the trout fed on dry pellets drank significantly more (436 ± 189 mg kg^-1 h^-1) than unfed and herring-fed trout which drank little or not at all (65 ± 113 and 70 ± 66 mg kg^-1 h^-1 respectively). Dietary water facilitated food processing and increased daily dry matter intake of trout when fed four times a day. When only one satiation meal per day was allowed, dietary water had no effect. It is concluded from this work that, in addition to gastric volume, a short-term limitation on the size of satiation meals in the rainbow trout is the availability of water to moisturize the food and thus to promote gastric digestion and emptying.     

Determinants of the dramatic seasonal changes in the intake of energy and protein by Japanese monkeys in a cool temperate forest

Daily intake of gross energy (DGEI) and protein (DGPI) of Japanese monkeys in a cool temperature forest were investigated in different four seasons. As a result, dramatic seasonal differences in DGEI and DGPI were found: DGEI and DGPI in winter were significantly lower than those in spring and autumn, being only about 17–42% of those in the two seasons. DGEI and DGPI in summer were also lower than those in autumn and spring, being only about 29–52% of those in the two latter seasons. Seasonal comparisons of some variables on food qualities revealed that much lower values of DGEI and DGPI in winter and summer were influenced srongly not so much by the lower calorie and protein content of food as by the lower speed of dry weight intake. Multiple regression analyses for each food item revealed that the unit weight was a more important factor in determining the speed of dry weight intake than was the speed of unit intake. In addition, the speed of dry weight intake contributed much more to the speed of calorie and protein intake than did the content of calorie and protein. Multiple regression analyses, employing DGEI and DGPI (as dependent variables) and daily mean values of some variables related to food quality (as independent variables), revealed that the mean values of speed of calorie and protein intake on food items eaten in a day could explain 79.0% and 85.9% of the variance in DGEI and DGPI, respectively. In addition, the mean value of the speed of dry weight intake of food items eaten in a day can be used to explain 74.3% and 52.8% of the variance in DGEI and DGPI, respectively. These findings suggested that not only nutritional content of food but also the speed of dry weight intake strongly determined the nutritional condition of nonhuman primates. Am. J. Primatol. 41:267–288, 1997. © 1997 Wiley-Liss, Inc.     

我国淡水优质草食性鱼类的营养和能量学研究 Ⅱ.草鱼、团头鲂对七种水生高等植物的最大摄食量和消化率的测定

作者采用常规生化分析法测定草食性鱼类天然食料(七种水生高等植物)的生化成分和能值。在实验室特定条件下测定了草鱼和团头鲂的系列体重组对七种水生高等植物的最大摄食量和消化率。1.七种水生高等植物的生化成分的含量和能值的分析结果表明,菹草、黄丝草、聚草、苦草、小茨草、轮叶黑藻和紫背浮萍的水分百分含量范围为80.85—92.72%、蛋白质为1.69—4.96%、脂肪为0.35—1.09%、灰分为0.98—2.6%、纤维素为0.66—2.17%、无氮浸出物为2.3—9.95%。七种水生植物的蛋白质均含有常见十七种氨基酸,包括鱼体必需氨基酸九种和非必需氨基酸八种。其中菹草的氨基酸含量最高(36.63mg/g 湿重)、苦草最低(12.92mg/g 湿重);菹草的能值最高(3.36KJ/g 湿重)、小茨藻最低(1.28KJ/g 湿重)。2.草鱼、团头鲂对七种水生植物的最大摄食量(Y,g/24h)及消化率(Y,%)与鱼体重(X,g)相关显著,关系式为 Y=aX~b。从结果表明,随着鱼体重的增加,鱼对七种食料的相对摄食量下降(绝对摄食量上升),消化率提高。草鱼的最大摄食量一般比团头鲂高,而消化率一般比团头鲂低。       

限制食粪对东方田鼠食物消化和体重生长的影响

食粪行为是植食性小型哺乳动物为满足其营养需求所采取的一种适应对策。实验室条件下,限制1月龄和12月龄东方田鼠摄食粪便,测定了限制食粪对食物消化率和体重生长的影响,旨在进一步揭示食粪行为在植食性小型哺乳动物的营养及消化对策中的作用。结果表明,限制食粪使1月龄和12月龄东方田鼠的干物质消化率分别下降27.64 %和7.89 %,粗蛋白消化率分别下降21.39 %和12.68 %;限制食粪可显著抑制东方田鼠的体重增长,且限制食粪对幼体体重的影响较成体明显。因此,研究结果充分验证了限制食粪可降低东方田鼠的食物消化率及抑制其体重生长的假设。     

Food choice by Blue-gray Tanagers in relation to protein content

We tested discriminatory ability and food choice in relation to protein content of the diet in wild-caught Blue-gray Tanagers (Thraupis episcopus), a generalist tropical frugivorous bird. In two sets of experiments we offered to five individual birds in pair-wise choice trials two nearly iso-caloric experimental diets differing in their protein content only. Protein contents of the experimental diets were 4.6 vs. 1.4% in the first experiment and 3.2 and 1.5% (dry matter basis) in the second experiment. Response varied among individual tanagers, but 6 of the 10 birds showed a clear preference for the food highest in protein. Two individuals displayed a strong positional preference. When testing each treatment group, birds ate daily significantly more of the food that had higher protein content. We conclude that Blue-gray Tanagers prefer richer nitrogen foods. Our results also demonstrate that Blue-gray Tanagers have remarkable discriminatory abilities, they reacted to differences in protein content as small as 0.09% fresh matter. We show for the first time discriminatory ability and preference of wild frugivorous birds for foods richer in protein under controlled conditions. Our findings support the hypothesis that frugivorous birds can act as selective agents for fruit pulp composition.     

Buoyant Densities and Dry-Matter Contents of Microorganisms: Conversion of a Measured Biovolume into Biomass

Several isolates of bacteria and fungi from soil, together with cells released directly from soil, were studied with respect to buoyant density and dry weight. The specific volume (cubic centimeters per gram) of wet cells as measured in density gradients of colloidal silica was correlated with the percent dry weight of the cells and found to be in general agreement with calculations based on the partial specific volume of major cell components. The buoyant density of pure bacterial cultures ranged from 1.035 to 1.093 g/cm³, and their dry-matter content ranged from 12 to 33% (wt/wt). Average values proposed for the conversion of bacterial biovolume into biomass dry weight are 1.09 g/cm³ and 30% dry matter. Fungal hyphae had buoyant densities ranging from 1.08 to 1.11 g/cm³, and their dry-matter content ranged from 18 to 25% (wt/wt). Average values proposed for the conversion of hyphal biovolume into biomass dry weight are 1.09 g/cm³ and 21% dry matter. Three of the bacterial isolates were found to have cell capsules. The calculated buoyant density and percent dry weight of these capsules varied from 1.029 g/cm³ and 7% dry weight to 1.084 g/cm³ and 44% dry weight. The majority of the fungi were found to produce large amounts of extracellular material when grown in liquid cultures. This material was not produced when the fungi were grown on either sterile spruce needles or membrane filters on an agar surface. Fungal hyphae in litter were shown to be free from extracellular materials.