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PubMed2002

Competition and species packing in patchy environments.

In models of competition in which space is treated as a continuum, and population size as continuous, there are no limits to the number of species that can coexist. For a finite number of sites, N, the results are different. The answer will, of course, depend on the model used to ask the question. In the Tilman-May-Nowak ordinary differential equation model, the number of species is asymptotically C log N with most species packed in at the upper end of the competitive hierarchy. In contrast, for metapopulation models with discrete individuals and stochastic spatial systems with various competition neighborhoods, we find a traditional species area relationship CN(a), with no species clumping along the phenotypic gradient. The exponent a is larger by a factor of 2 for spatially explicit models. In words, a spatial distribution of competitors allows for greater diversity than a metapopulation model due to the effects of recruitment limitation in their competition.

Competitive Behavior↗
PubMed2002

Stabilizing dispersal delays in predator-prey metapopulation models.

Time delays produced by dispersal are shown to stabilize Lotka-Volterra predator-prey models. The models are formulated as integrodifferential equations that describe local predator-prey dynamics and either intrapatch or interpatch dispersal. Dispersing individuals may (or may not) differ in the duration of their trips; these differences are captured via a distributed delay in the models. Our results include those of previous studies as special cases and show that the stabilizing effect continues to operate when the dispersal process is modeled more realistically.

Animals↗
PubMed2002

Simulated moving bed chromatography (SMB) for application in bioseparation.

Simulated Moving Bed (SMB) technology is of rising interest in the field of bioseparation. This is particularly due to its advantages such as reduction of solvent consumption, high productivity and final purities as well as low investment costs in comparison to eluent chromatography. SMB units can operate under high productivity overloaded conditions. This leads to non-linear competitive adsorption behavior, which has to be accounted for when designing and optimizing new SMB separations. The so called "Triangle Theory", which is briefly reviewed in this chapter, provides explicit criteria for the choice of the operating conditions of SMB units to achieve the prescribed separation of a mixture characterized by Langmuir, modified Langmuir and bi-Langmuir isotherms. The application of the SMB-technique to the downstream processing of biotechnological products requires some specific changes to meet the special demands of bioproduct isolation. Some exemplary applications are given including separations of sugars, proteins, monoclonal antibodies, ionic molecules and optical isomers and for desalting.

Animals↗
PubMed1986

Evolutionary games and two species population dynamics.

Competition between species has long been modeled by population dynamics based on total numbers of each species. Recently, the evolution of strategy frequencies has been used successfully for competition models between individuals. In this paper, we illustrate that these two views of competition are compatible. It is shown that the rate of intra and interspecific competitions between individuals largely determines the population dynamics. Competition models over a single common resource and predator-prey models are developed from this individual competition approach. In particular, the equilibrium strategies in a co-evolving predator-prey system are shown to be more stable than the predicted strategy cycling of standard evolutionary game theory.

Animals↗
PubMed1984

The effects of interference competition on stability, structure and invasion of a multi-species system.

An interference competition model for a many species system is presented, based on Lotka-Volterra equations in which some restrictions are imposed on the parameters. The competition coefficients of the Lotka-Volterra equations are assumed to be expressed as products of two factors: the intrinsic interference to other individuals and the defensive ability against such interference. All the equilibrium points of the model are obtained explicitly in terms of its parameters, and these equilibria are classified according to the concept of sector stability. Thus survival or extinction of species at a stable equilibrium point can be determined analytically. The result of the analysis is extended to the successional processes of a community. A criterion for invasion of a new species is obtained and it is also shown that there are some characteristic quantities which show directional changes as succession proceeds.

Animals↗
PubMed1985

Cardiovascular changes and hearing threshold shifts in men under complex exposures to noise, whole body vibrations, temperatures and competition-type psychic load.

This study deals with changes in the temporary hearing threshold (TTS2), heart rate (HR), R-wave amplitude (RWA), diastolic blood pressure (DBP), systolic blood pressure (SBP), pulse pressure (PP) and reaction time (RT) in subjects (n = 108) who, while working on a choice reaction apparatus, were exposed in an exposure chamber to combinations of noise and vibration at dry bulb temperatures of 20 degrees and 30 degrees C. The study was carried out as a type 2-3-3 factorial experiment, the number of the exposure combinations thus being 18. To find out the effects of competition-type psychic stress, some of the subjects were placed in a competitive group and some in a non-competitive group. The members of the competitive group were given financial encouragement and information on their progress during the test, whereas those in the non-competitive group worked at the rate they considered best without any monetary rewards or interim information. The noise classes were: no noise, a stable broadband (bandwidth 0.2-16.0 kHz) A-weighted noise of 90 dB not related to competition, and a stable broadband A-weighted noise of 90 dB related to competition about the fastest reaction time. The vibration classes were: no vibration, sinusoidal whole body vibration (Z-axis) at a frequency of 5 Hz, and stochastic broadband (bandwidth 2.8-11.2 Hz) whole body vibration (Z-axis). The acceleration (rms) of both vibrations was 2.12 m/s2. One experiment consisted of a control period of 30 min, three consecutive exposure periods of 16 min with an interval of 4 min, and a 15-min recovery period. The variance analysis model best explained the variation in TTS2 values at 4 kHz and second best the variation in TTS2 values at 6 kHz; it explained the variation in HR values third best, the variation in SBP values fourth best and the variation in PP values fifth best. On the other hand, the model explained least well the variation in DBP and RWA values. In general, the explanatory power of the model increased together with the number of exposures. The psychic stress caused by competition accelerated the growth of the TTS2 values, HR values and SBP values, when the subjects were simultaneously exposed to noise or to a combination of noise and vibration. An interesting finding for the continuation of the research project was that sinusoidal and stochastic vibration affected the cardiovascular changes, temporary hearing threshold and reaction times in different ways.

Adolescent↗
PubMed1989

Biofeedback training versus simple instructions to reduce heart rate reactivity to a psychological stressor.

The effectiveness of cardiac education and visual biofeedback of heart rate as a training procedure to teach people to control their heart rate to a psychological stressor was investigated with 36 students, half of whom acted as control subjects. Training took 5 weeks and consisted of 30-min per week of awareness training, plus exercises to increase and decrease heart rate under rest and stressful conditions, with monetary rewards for success. Effects were tested by pre-post test comparisons between the control and the experimental groups, and results indicated that the group which received training significantly lowered its heart rate reactivity even though not specifically instructed to do so. However, when instructed to control heart rate reactivity for a monetary reward, the control group also succeeded at this task, raising several issues regarding the efficacy of reactivity training.

Adult↗
PubMed1987

Comparison of three worksite weight-loss competitions.

Competition is an effective means of promoting weight loss in worksite programs. This study was designed to determine the most effective structure of competition through a comparison of two kinds of competition within one worksite. Two competitions were between teams and one was among individuals. While all three competitions produced significant weight loss and lower attrition than previous worksite programs, the team competitions produced significantly lower attrition rates and significantly greater weight loss than the individual competition. Patterns of loss over time and the distribution of losses for groups also differed, with a smaller proportion of successful participants in the individual competition. The results suggest that team support as well as competition is a necessary component of effective worksite weight loss competitions.

Adult↗
PubMed1979

Student physical symptoms and the social climate of college living groups.

Student physical symptoms were related to the social climates of university living groups. A Physical Symptom Risk Scale, a new subscale of the University Residence Environment Scale, which relates consistently to physical symptom complaints for male, female, and coed living groups, was developed. Living groups characterized by high student physical symptoms were perceived by students as low in involvement and support, high in competition, and low in student influence. The results indicate that certain types of social environments may be "high risk" settings in that they support and possibly facilitate complaints of physical symptoms. These settings may be amenable to early "environmental diagnosis," preventive counseling, and change-oriented social systems intervention.

Competitive Behavior↗
PubMed1982

Immune parameters in athletes before and after strenuous exercise.

Secretory IgA levels were studied in nationally ranked Nordic skiers before and after the national cross-country races held in February 1981. Comparing the skiers with age-matched controls, there was significantly lower level of salivary IgA before the race. Concentrations of IgA decreased further following the competition (50 kn for males; 20 km for females) to very low levels. There also were a significant increase in the percentage of B lymphocytes and a decrease in the null population (non-T, non-B) in the athletes after the race compared with the controls. The mechanism responsible for these changes is unknown, but the low salivary IgA levels may result from depletion of nasal fluid and/or malfunction of the mucosal plasma cells due to a decrease temperature in the mucous membranes. We speculated that a temporary antibody deficiency on the mucosal surface might lead to a susceptibility to acquiring viral and bacterial infections, especially during the interval immediately following strenuous exercise.

Adult↗
PubMed1980

Relative male age, fertility, and competitive mating success in Drosophila melanogaster.

Female choice experiments were used to investigate the effect of relative male age on mating success in D. melanogaster. Experiments were conducted with a Canton-S (CS) strain, in which two virgin males of different ages (2, 4, or 8 days old) were offered to virgin females. Older males were found to be more successful under competitive conditions in another group of experiments, vermilion (v) males of different ages competed with CS males of different ages. The competitive success of v males was found to increase with their relative age. Male fertility at 2, 4, and 8 days of age was documented for both male genotypes mated with CS females. CS males fathered more offspring per copulation than v males, and the fertility of all males was found to increase with age. Discussion focuses on the changes in male mating success and fertility with age and genotype.

Age Factors↗