Final Population Size Research Articles

Survival of Pseudomonas fluorescens inocula of different physiological stages in soil

The influence of different soil conditioning and incubation temperatures and the effect of variability between different batches of inocula of Pseudomonas fluorescens on its survival in the soil were investigated. Bacterial numbers decreased exponentially as described by the function Y = A + B × (1 − R) t, based on the Gompertz equation, where Y is the logarithm of bacterial numbers at time t; A represents the logarithm of the final population; B is the difference between the logarithm of the initial bacterial numbers and A; R is the daily reduction factor and t the time in days. At both 5 and 15°C numbers of P. fluorescens changed similarly and stabilized between 2.2 × 10 3 and 1.8 × 10 3 cfu g −1 oven-dry soil. The daily reduction factors (R) were 0.075 at 5°C and 0.034 at 15°C. At 25°C, the competition between P. fluorescens and the endogenous microbial population reduced the numbers of P. fluorescens more abruptly, resulting in stable numbers of 1.3 × 10 2 bacteria g −1 oven-dry soil and a higher daily reduction factor of 0.132. A higher soil conditioning temperature (15°C) resulted in slightly better survival. At 15°C, P. fluorescens stabilized at 9.53 × 10 3 cells g −1 dry soil with a lower daily reduction factor (0.110); at 5°C, the final population size was 4.45 × 10 3 cells g −1 and the R value 0.169. Microcalorimetric measurements were made to characterize and standardize bacterial cultures of P. fluorescens. A significant correlation between heat output (time integral of the power-time curve) and bacterial numbers (correlation coefficient r 2 adjof 0.98) was obtained in a batch-culture experiment. The inoculum size affected the duration of the lag before heat production (a 10-fold increase in inoculum size reduced the lag by 3.5–4 h) but not the apparent growth rate. The growth stage of the inoculum (derived from the microcalorimetric output) affected both the duration of the lag and the specific growth rate upon reinoculation into the same medium. In a second experiment, it was established that introducing an inoculum from the late exponential phase (when the power output of the culture reached its maximum) into soil resulted in a higher stabilization level and a lower death rate than when early exponential or stationary phase inocula were used.

Quantitative Sampling of Fish Populations with a Mobile Rising Net

Abstract A modified pop net (i.e., an inflatable lift net), used to estimate fish population size, was evaluated in a small northern Colorado lake having a stocked population of rainbow trout Oncorhynchus mykiss of known initial size. At the conclusion of pop-net sampling, the lake was treated with rotenone to estimate final fish population size and the instantaneous daily mortality rate. This rate was used to determine the expected fish population size for each day of sampling. A target value for the population estimates based on pop-net samples was defined as the mean of the expected daily population sizes. Seven estimators were used to predict total fish population size from pop-net sampling; 95% confidence intervals for all ratio estimators included the target value. A volume-based stratified ratio estimator best predicted the fish population size in the study lake.

Influence of the inoculum density on the growth and survival of Rhizobium leguminosarum biovar trifolii introduced into sterile and non-sterile loamy sand and silt loam

After the introduction of Rhizobium leguminosarum biovar trifolii into natural loamy sand and silt loam, bacterial numbers increased only directly after inoculation. Thereafter, bacterial numbers decreased until an equilibrium was reached. This decrease was exponential on a log scale and could be described by the function Y = A + B − R′, where Y is the log number of rhizobial cells at time: T; A represents the lgo of the final population size; B is the difference between the log (initial number of bacteria) and A; R is the daily reduction factor of Y−A and t is time in days after inoculation. The final population sizes increased with increasing inoculum densities (10 4−10 8 bacteria/g soil). In sterilized soil, however, the populations increased up to an equilibrium, which was not affected by the inoculum density. The final population sizes were higher in silt loam than in loamy sand in natural, as well as in sterilized soil. The final population size was reached earlier in natural silt loam than in loamy sand. Also the growth rate in sterilized soil was higher in silt loam than in loamy sand. The growth rate of low inoculum densities in silt loam was exponential and approximately the same as in yeast extract mannitol broth. The growth rate in loamy sand could be improved by incresing the bulk density of the soil from 1.0 to 1.4 g/cm 3.

Influence of the inoculum density on the growth and survival ofRhizobium leguminosarumbiovartrifoliiintroduced into sterile and non-sterile loamy sand and silt loam

Abstract After the introduction of Rhizobium leguminosarum biovar trifolii into natural loamy sand and silt loam, bacterial numbers increased only directly after inoculation. Thereafter, bacterial numbers decreased until an equilibrium was reached. This decrease was exponential on a log scale and could be described by the function Y = A + B −R′, where Y is the log number of rhizobial cells at time: T; A represents the lgo of the final population size; B is the difference between the log (initial number of bacteria) and A; R is the daily reduction factor of Y−A and t is time in days after inoculation. The final population sizes increased with increasing inoculum densities (104−108 bacteria/g soil). In sterilized soil, however, the populations increased up to an equilibrium, which was not affected by the inoculum density. The final population sizes were higher in silt loam than in loamy sand in natural, as well as in sterilized soil. The final population size was reached earlier in natural silt loam than in loamy sand. Also the growth rate in sterilized soil was higher in silt loam than in loamy sand. The growth rate of low inoculum densities in silt loam was exponential and approximately the same as in yeast extract mannitol broth. The growth rate in loamy sand could be improved by incresing the bulk density of the soil from 1.0 to 1.4 g/cm3.

Spatial distribution, life history and estimates of survivorship in a fourteen‐species assemblage of larval dragonflies (Odonata: Anisoptera)

SUMMARY. 1. Spatial and temporal changes in larval densities were used to infer patterns of habitat use and survivorship in a fourteen‐species assemblage of dragonflies (Odonata: Anisoptera) in a small fishless pond. The density of all species combined peaked at >1000 m−2 in late summer, Most species (e.g. Libellula spp.) were restricted to shallow, nearshore habitats (<1.0m in depth), but a few (e.g. Epitheca spp.) also used deeper areas of the pond. Only Perithemis tenera was most abundant in deep habitats.2. Because many species exhibited temporal shifts in their use of habitats, it was necessary to estimate survival from changes in population size, calculated as the product of density and habitat area, summed across habitats. In most species, periods of high mortality in autumn and spring were separated by 3–4 months of negligible mortality in winter. Survivorship was linear only in the two species that completed all of larval development in summer (Sympetrum vicinum and Pantala flavescens). Average survival rates for these two species (−0.0049 and −0.0079 log density d−1) were similar to those in previous studies (Lawton, 1970; Benke & Benke, 1975).3. Survivorship in many species was confounded by other life history phenomena such as (i) mixed voltinism, (ii) overlapping migrant and resident cohorts, and (iii) asynchronous development within species. Asynchrony made it difficult to estimate initial and final population sizes, hence total larval survivorship. However, based on emergence data, only 0.4–3% of larvae survived after peak abundance. None of this mortality can be ascribed to vertebrate predation, and only a little to overwintering stress and starvation. Thus, predation by invertebrates might play a major role in the regulation of these populations.

Friends and strangers: a test of the Charnov-Finerty Hypothesis.

We tested the hypothesis that populations composed of unrelated animals should perform worse than those composed of related animals by setting up two moderatedly dense field populations in adjacent enclosures: one was composed of related females and one of unrelated females; both had unrelated males. The survival and reproductive success of a number of litters located by spooling were determined. Final population size, pregnancy success, number of young recruited per pregnancy, and survival were similar in both populations. Thus, differences in relatedness produced no differences in demography. We conclude that the Charnov-Finerty Hypothesis in unlikely to be an explanation for microtine population fluctuations.

Estimation of mutation rates in cultured mammalian cells

The factors that affect reliable estimations of mutation rates (μ) in cultured mammalian somatic cell populations by fluctuation analysis are studied experimentally and statistically. We analyze the differential effect of the final cell population size in each culture ( N t) and the number of parallel cultures ( C) on the variation in the rate estimates ( μ ) inferred from the P 0 method. The analysis can be made after the derivation of the variance of μ , which is a measure of variation of μ for a given combination of N t and C in a number of repeat experiments. The variance of μ is inversely proportional to C and to the square of N t. N t determines the probability of occurrence of mutation in a cell culture. By influencing the size of P 0, N t also determines whether a rate estimate is obtainable from the experiment. Since P o is estimated from the fraction of cultures containing no mutation in a set of C cultures, C becomes a determining factor for the accuracy of μ . The rate estimated from P ̂ 0 is biased, but the bias is in general 2 orders of magnitude smaller than μ . By the selection of an appropriate combination of N t and C for the experiment, this bias can be reduced even further. Based on the notion of comparing two proportions, we propose a test statistic and have applied it to experimental results for a test of equality of mutation rates in different cell lines. This development places the comparison of mutation rates on a statistical basis.

Time Distributions for Describing Appearance of Specific Culms of Winter Wheat1

AbstractCereal plants emerge and develop tillers in response to the field environment in which they are planted and grown. If the pattern of development of productive culms can be recognized and measured, impacts of different field conditions upon plants can be assessed. This study presents a method for describing emergence and tiller appearance patterns and illustrates the use of these patterns in comparing crop development responses to field environments. Desirable environments will produce uniform populations of culms with regularly spaced appearance patterns while stressful environments cause a variety of irregular patterns.Characteristics of the populations of appearing culms can be described fundamentally by the logistic distribution function or can be approximated by the normal distribution function. The cumulative form of both functions is a sigmoid curve. The mean of the normal coincides with the 50% appearance time of the logistic. When the dispersion coefficient (s) of the normal function and the rate coefficient (k) of the logistic equation are related by ks = 1.69, the two curves differ by less than 1% of the final population size at any point. Culm appearance populations from good seedbeds appear as normal or logistic curves (considered to be the same curve) when appearances are timed by degree‐days (3°C base). Fifty percent emergence for Stephens winter wheat (Triticum aestivum L.) occurs near 100 degree‐days from planting, and tillers Tl, T2, and T3 occur at about 250, 300, and 375 degree‐days, respectively, in a fertile seedbed with adequate water. Culm appearance data that are not normally distributed may be converted to normal form with transforms or population splitting procedures. The nature of the transformation required to normalize the data may help characterize the field condition causing non‐normal appearance.

LEAF AND FLOWER DEMOGRAPHY OF TRIFOLIUM REPENS L.

SummaryTwo clones of Trifolium repens L., differentiated in response to their neighbours, the grasses Dactylis glomerata L. and Poa pratensis L., were grown as single ramets in mixture with these same two grasses. At weekly intervals for 59 weeks, births and deaths of leaves and flowers, and extension of stolons were recorded. These birth and death statistics were used to calculate life spans, natality and mortality rates, age class distributions and other demographic parameters of the populations of leaves and Bowers of T. repens L. For both individuals recruitment and death of leaves occurred throughout most of the year. Flowers were produced from early May to mid September by one individual and from late March to mid September by the other. The average life span of leaves does not vary significantly between the four treatments but the timing of birth has a strong influence on the expectation of life. For leaves and flowers from both white clover plants, the population flux was more rapid when growing with P. pratensis L. than with D. glomerata L., yet in both treatments the final population sizes were similar.

The Turnover Ratio in Production Ecology of Freshwater Invertebrates

The turnover ratio of freshwater benthic invertebrates, expressed as the ratio of a cohort's production to the mean standing crop, has been observed to be relatively constant, about 2.5 to 5, with a mode of about 3.5. Turnover ratios were computed from Allen growth-survivorship curves under various combinations of hypothetical conditions to determine the theoretical range. The effects of varying curve shape, initial individual weight relative to maximum, final population size in numbers relative to initial population, and growth pattern were tested with several series of Allen curves. With moderate variation in these factors around the most probable conditions, the theoretical turnover ratio varied from about 3 to 4 for aquatic insects, but it is probable somewhat larger for crustaceans. Turnover ratios were also considered as equal to instantaneous growth rates computed over an entire single life cycle for several invertebrate species. These were similar to those obtained with the Allen curves, although about 1 unit larger on the average.

A Method of Estimating Mortality Rates from Change in Composition

This paper examines the problem of estimating mortality rates from knowledge of catch and of the change in composition caused by selective fishing on one of two classes of a closed population.Estimators of fishing mortality in the presence and in the absence of natural mortality are given. An estimator of natural mortality is shown for the special case where final population size is known.A numerical example illustrates the method. Certain problems are discussed and two types of application are suggested.