Optimal Population Density Research Articles

Factors affecting the output rate of Spirulina platensis with reference to mass cultivation

The disappointingly low yields of Spirulina cultivated in large, commercial-scale reactors prompted our attempt to elucidate some of the reasons for this phenomenon. The results show the importance of maintaining the pH as high as possible, at a point, however, where it does not yet limit growth. To check the growth of contaminating algae, such as Chlorella spp., the pH was elevated to a point higher than the optimal for Spirulina. Close to pH 11·0, signs of deterioration became evident, but the culture recuperated readily when the pH was lowered back to the optimum (pH 10·5). The depth of the culture had no effect on the maximal areal output of dry biomass, but exerted a very marked effect on the optimal population density. At a culture depth of 150 mm the optimal cell density was at an optical density of 0·5 absorbancy units, whereas at a culture depth of 75 mm the optimal cell density was 0·7 absorbancy units. The stirring rate also affected the optimal population density. At slow stirring speeds (58 cm s −1, which were neverthe3ess approximately twice as fast as that maintained in large commercial ponds) there was a substantial reduction in the output rate at high population densities. Similar results were obtained at high stirring rates, but the effect was much reduced and was only observed at the highest cell densities. The chlorophyll: phaeophytin ratio altered signficantly throughout the year, being highest in mid-winter and declining in summer. A practical conclusion drawn from these results was that there is a clear advantage in operating the slow flowing cultures in large reactors at as shallow a culture depth as practically possible. This increases the optimal cell density to a level that may be easier to harvest and maintain in large-scale reactors. The inefficiency of harvesting large volumes of low cell densities has lead to the general practice of allowing cell densities to increase far above the optimum. Our results indicate that this may have detrimental effects on the output rate considering the relatively low stirring rates which commonly prevail in large reactors.

Culture of Isolated Microspores of Saccharum spontaneum)

Summary Microspore culture of Saccharum spontaneum L. was investigated as a means to produce haploid plants. Isolated and cultured microspores initiated sporophytic development which in 4 to 6 weeks resulted in procalli and calli. The percentage of microspores producing multicellular procalli was increased by removing the nonviable microspores before initiating the culture, establishing an optimum population density, and using nutrient media relatively low in sucrose and NH4NO3. The procalli produced from microspore culture ceased development at about the same stage as did procalli within anthers in culture. Thus, a factor or factors other than the anther wall must be responsible for the low yield of haploids from S. spontaneum. The effect of temperature and of sucrose and 2,4-D in the media changed during the development of calli from unicellular microspores. The apparently different requirements for specific stages of development indicates that successful production of haploid plants from microspore culture will require a series of environmental and cultural manipulations.

Production and carrying capacity for the earthworm Lumbricus terrestris in culture

Approximately 8 h were required at 25°C for food to pass from mouth to anus in the earthworm Lumbricus terrestris. Gut load per unit transit appeared inversely related to nitrogen content; values of about 2 and 44 mg dry castings per 100mg dry worm were obtained with activated sludge and mineral soil, respectively. Production of biomass was greater in a substrate of activated sludge and loam relative to activated sludge and cellulose, despite higher concentrations of nitrogen in the latter. Optimum population density was about 8 earthworms (31 g live wt) in 1000cm 3 2:1 sludge:soil. Growth occurred at a maximum rate between 15 and 25°C. A yield of approximately 4% biomass (dry wt) was obtained on a mixture of activated sludge and loam, based on the content of organic matter present.

Optimal Population Density and Random vs. Selective Elimination of Genotypes Under a Modified Single‐Seed Descent Method with Spring Oats1

A modified single‐seed descent (SSD) method of generation advance is used in the Univ. of Illinois spring oat (Avena Saliva L.) breeding program. The method couples high plant density with limited soil fertility and moisture levels to produce a population with a high proportion of single or few seeded plants, along with some barren plants. Questions regarding the technique are twofold: 1) what population density will yield a high proportion of plants with one or very few seeds and a minimum of barren plants, and 2) are the genotypes which are lost due to barrenness randomly or selectively eliminated?In a series of population densities, ranging from 10 to 150 seeds per 15‐cm clay pot in 10 seed increments, 30 to 40% of the plants grown at densities of 100 to 150 seedlings per pot produced single seeds. Populations of 120 to 150 seedlings per pot allows adaptation of the technique to the SSD principle with a considerable savings in harvest time and greenhouse space.To determine whether barren plants were randomly or selectively eliminated, progenies of two segregating crosses were grown at high (60 seedlings per pot) and low (10 seedlings per pot) population densities. After two generations of modified SSD, 34.5% of the original population was lost due to barrenness at the high density in one cross and 26.5% in the other. Seed of surviving genotypes was increased for a replicated field trial where maturity (days after 1 June), plant height (cm), oil content (nuclear magnetic resonancevalue), and grain yield (g/hill plot) were measured. Means and variances between progenies advanced under high or low densities generally did not differ for any of the traits, leading to the conclusion that the genotypes eliminated due to barren plants were randomly and not selectively eliminated due to selection pressures of the technique.

Density-dependent fecundity in Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

An experiment to assess the effect of population density upon the fecundity of Sitophilus oryzae (L.) is described. The range of densities employed is rather wider and somewhat lower than used in the earlier study of MacLagan and Dunn (1935). Whereas the results of this earlier study suggested a hyperbolic relationship between fecundity and population density, the present study suggests that there is an optimum population density above and below which fecundity is reduced. A mathematical model is fitted to the data. The implications of this more complex relationship are discussed.

Reproductive potential of the earthworm Eisenia foetida.

Regression equations are provided for the earthworm Eisenia foetida with respect to age at which 50% of the population became clitellate at 25° C in relation to population density in activated sludge and in horse manure. Regression equations are provided for progeny per cocoon versus weight of cocoon, and weight of cocoon in relation to weight of parent; from these an equation is derived for progeny per cocoon relative to worm weight. Regression equations are given on (a) number of cocoons produced per adult in relation to age and population density from onset of adulthood to median peak production of cocoons, age 10 weeks, and from age 10 weeks to age 27 weeks, and (b) weight of worm in relation to population density and age between ages 5 and 27 weeks. From (a) and (b) a family of equations (c) are derived giving progeny per cocoon in relation to age of adult and population density. From equations (a) and (c) two families of equations are generated giving progeny per adult in relation to ascent to, and descent from, the median week of peak cocoon production in relation to population density. Data also are provided on age at which reproduction terminates in relation to population density, optimum population density for reproduction, and hatchability.

Canopy Architecture at Various Population Densities and the Growth and Grain Yield of Corn1

Parameters of canopy architecture were related to light interception and productivity using data from a field experiment with corn grown at population densities from 17,500 to 125,000 plants per hectare. With nutrients and soil moisture nonlimiting, the amount of solar radiation intercepted by the foliage canopy was a major determinant of crop growth during the vegetative stage. Leaf arrangements with a preponderance of erect leaves, occurring just before the tassels emerged, allowed the deepest penetration of light into the foliage canopy and gave the highest crop growth rates. Computer simulation of photosynthetic production using the measured foliage display characteristics closely approximated measured rates of growth before anthesis. The yield of grain correlated well with crop growth rates up to an optimum population density, but then became negatively associated with density as further increases in the numbers of growing pouits apparently placed too great a demand on the community's metabolite‐producing ability.

Feeding Space, Population Density and Growth of Young Chickens

ADEQUATE feeding space and optimum population density (floor space) are generally considered necessary for maximum growth of broiler chickens. Recommended space allowances vary somewhat, with the recommendations published by the Nutrition Council of the American Feed Manufacturers Association (1952) representing the majority of institutions making recommendations. Their recommendation for floor space per bird is: ½ sq. ft. through 6 weeks and 1 sq. ft. for 7 through 12 weeks. For feeding space per 100 birds the recommendation is: 0–2 weeks 100 linear inches; 3–6 weeks 175 inches; 7–12 weeks 300 inches; these allowances should be increased during warm weather.Less than the recommended space allowance in either category is often referred to as a stress upon the chickens. Frequently in popular articles and talks the suggestion is made that when floor space per chick is below the recommended level, feeding space should be increased. The theory behind …

Fruity and other mutants of the cellular slime mould, Dictyostelium discoideum: a study of developmental aberrations.

Summary: Study of three mutants of Dictyostelium discoideum—Fruity, Bushy and Dwarf—provide specific examples of aberrant behaviour during aggregation and the construction of fruiting bodies. The proportion of initiator cells in the population and the optimal population density for aggregation have been shown to be under genetic control. In the Fruity mutant, the great increase in the number of initiator cells leads to the formation of aggregates composed of very few individuals and correspondingly tiny fruits. The morphology of the aggregates and fruits and the regulatory properties of this morphogenetic system have been examined.

The Behaviour of the Robin.—Part I. The Life‐history, with special reference to Aggressive Behaviour, Sexual Behaviour, and Territory. Part II. A Partial Analysis of Aggressive and Recognitional Behaviour

The Behaviour of the Robin.—Part I. The Life‐history, with special reference to Aggressive Behaviour, Sexual Behaviour, and Territory. Part II. A Partial Analysis of Aggressive and Recognitional Behaviour