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PubMed2006

The evolution of altruism: game theory in multilevel selection and inclusive fitness.

Although the prisoner's dilemma (PD) has been used extensively to study reciprocal altruism, here we show that the n-player prisoner's dilemma (NPD) is also central to two other prominent theories of the evolution of altruism: inclusive fitness and multilevel selection. An NPD model captures the essential factors for the evolution of altruism directly in its parameters and integrates important aspects of these two theories such as Hamilton's rule, Simpson's paradox, and the Price covariance equation. The model also suggests a simple interpretation of the Price selection decomposition and an alternative decomposition that is symmetrical and complementary to it. In some situations this alternative shows the temporal changes in within- and between-group selection more clearly than the Price equation. In addition, we provide a new perspective on strong vs. weak altruism by identifying their different underlying game structures (based on absolute fitness) and showing how their evolutionary dynamics are nevertheless similar under selection (based on relative fitness). In contrast to conventional wisdom, the model shows that both strong and weak altruism can evolve in periodically formed random groups of non-conditional strategies if groups are multigenerational. An integrative approach based on the NPD helps unify different perspectives on the evolution of altruism.

Altruism↗
PubMed2004

A functionally diverse population growth model.

The present work deals with a single species population growth model, exhibiting diverse functional modes. The model is based on the principle of limiting factors for population growth. This paradigm was adapted from the law of the minimum, and the law of the tolerance. In the framework presented here, rates of natality and mortality are controlled by extreme values of limiting factors. The formal expression of these ideas corresponds to what we call a functionally diverse model. This model permits the identification of thresholds of viability, starvation, intraspecific cooperation and competition. The performance of the model is evaluated using data for populations growing under experimental or natural conditions.

Animals↗
PubMed2006

Competition in chemostat-type equations with two habitats.

Competition on a model with nutrient recycling is considered. The model is based on a chemostat-type equation which is used to study population dynamics of microorganisms. The model consists of four organisms competing for a limiting nutrient. Nutrient is supplied both from the in-flow of medium and a recycling with delay, the latter is generated from dead organisms by bacterial decomposition. This paper shows that the model undergoes a Hopf bifurcation through a critical value of time delay when the in-flow is small. Coexistence of four organisms competing for one limiting nutrient is indicated by numerical simulation results.

Bacteria↗
PubMed2006

Movement toward better environments and the evolution of rapid diffusion.

We study a reaction-diffusion-advection model for two ecologically equivalent competitors with different dispersal strategies inhabiting a spatially heterogeneous environment. The competitors represent different phenotypes of the same species. One is assumed to disperse by simple diffusion, the other by diffusion together with directed movement toward more favorable environments. We show that under suitable conditions on the underlying spatial domain, the competitor that moves toward more favorable environments may have a competitive advantage even if it diffuses more rapidly than the other competitor. This is in contrast with the case in which both competitors disperse by pure diffusion, where the competitor that diffuses more slowly always has the advantage. We determine competitive advantage by examining the invasibility, i.e. stability or instability, of steady states with only one competitor present. The mathematical approach is a perturbation analysis of principal eigenvalues.

Algorithms↗
PubMed2005

Competitive coexistence of two Pneumocystis species.

Pneumocystis are fungal pathogens of mammalian lungs that can cause lethal pneumonia in immunocompromised hosts. In some mammals, coinfections of genetically distinct Pneumocystis populations have been identified, but the nature of their interaction and its significance are unknown. Two species that infect rats, Pneumocystis carinii and Pneumocystis wakefieldiae, were studied over a 6-year period, representing approximately 700 generations of Pneumocystis. Population densities of each species were analyzed within the framework of the Lotka-Volterra competition model, which revealed the two species were in competition and predicted competitive exclusion of one species. However, stable coexistence was observed in 460 replicate populations. Selected extrinsic factors that might mitigate the extinction were evaluated. Logistic-regression analyses showed that higher relative humidity and higher organism lung burdens were associated with infections comprised of P. carinii alone, while lower temperatures and an increased rat census were associated with the presence of P. wakefieldiae. PCR and immunofluorescent analysis of rat lung tissue showed that both species were present within the same alveoli, excluding habitat heterogeneity as a mechanism of coexistence. These data suggest that P. carinii and P. wakefieldiae were in competitive coexistence, which was influenced in part by extrinsic factors. To our knowledge, this is the first report to evaluate interactions of pathogenic fungal species within a mammalian host using ecological models.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Orientation of nurses towards formal and informal learning: motives and perceptions.

The aim of this exploratory study was to gain information on the current orientation of registered nurses towards continuing education and lifelong learning. The population (N=162) consists of 2nd and 1st Level nurses who have or are currently taking part in continuing education. Qualitative empirical data were obtained through semi structured one to one interviews. The research questions sought information related to some of the reasons and motives for the participants' taking part in various categories of learning. Also explored was what factors might influence these participants' learning activities and the views and perceptions of their learning experiences. For many of these nurses, the initial motive for taking part in continuing education was the perception that they were being left behind by the higher educational level of nurses entering the profession. Contrary to some anecdotal views, the participants generally felt that higher education (HE) contributed to enhanced client care, reporting additional personal and professional satisfaction. Alleged poor support from managers for continuing education and the lack of parity, often within the same organisation regarding the selection criteria to take part in a variety of learning activities, was a source of dissatisfaction for some of these participants. Their determination to learn, however, remained strong.

Adult↗
PubMed2004

Coping with competitive situations in humans.

The analysis of effects of competitive situations in our species may contribute to acquiring deeper knowledge about the effects of social stress and its relationship with different pathologies. The latest studies indicate that the neuroendocrine response to competition depends more on subjective factors related to the cognitive evaluation of the situation than on the outcome itself. Findings suggest that when subjects cope with a competition, they assess it in such a way that it activates a psychobiological coping response. The pattern of this response may correspond to a predominant active or passive coping strategy, the choice ultimately depending on factors such as the importance of the competition for the subject, the subject's involvement or perceived possibilities of control of outcome or success (e.g. past experience in similar competitions, judge or rank of the opponent), among others. More important than winning or losing is the coping pattern displayed by the subject, which determines the hormonal changes experienced when facing competition and its outcome.

Adaptation, Psychological↗
PubMed2004

The neural bases of cooperation and competition: an fMRI investigation.

Cooperation and competition are two basic modes of social cognition that necessitate monitoring of both one's own and others' actions, as well as adopting a specific mental set. In this fMRI, study individuals played a specially designed computer game, according to a set of predefined rules, either in cooperation with or in competition against another person. The hemodynamic response during these conditions was contrasted to that of the same subjects playing the game independently. Both cooperation and competition stances resulted in activation of a common frontoparietal network subserving executive functions, as well as the anterior insula, involved in autonomic arousal. Moreover, distinct regions were found to be selectively associated with cooperation and competition, notably the orbitofrontal cortex in the former and the inferior parietal and medial prefrontal cortices in the latter. This pattern reflects the different mental frameworks implicated in being cooperative versus competitive with another person. In accordance with evidence from evolutionary psychology as well as from developmental psychology, we argue that cooperation is a socially rewarding process and is associated with specific left medial orbitofrontal cortex involvement.

Adult↗
PubMed2004

Timing between ejaculations changes paternity success.

It is believed that when two male rats copulate with a single female, the last one that ejaculates fathers significantly more pups than the first one. To determine the effects of order and elapsed time between two males copulating with the same female, albino Wistar (W) and pigmented Long-Evans (LE) male rats copulated with a W female. Paternity was confirmed by the pups' pigmentation. Three groups were made according to the elapsed time between the first male's ejaculation and the placement of the female with the second male; T0 (0-min group); T5 (5-min group); and T10 (10-min group). Male order was counterbalanced in each group. The results showed that the second male had the advantage in T0, but the first males had the advantage in T5 and T10. These data indicate that in a two-male situation, the advantage in paternity for a second male occurs only during copulations following the first few minutes of a first male's ejaculation. After 5 min, a second male has no advantage in fathering pups.

Animals↗
PubMed2005

Male expulsion in cooperative Mongolian gerbils (Meriones unguiculatus).

Mongolian gerbils are territorial rodents of steppes and semideserts of Mongolia and Northern China. At least under laboratory conditions, the family life is characterized by long-term harmonious and short-term aggressive periods in which some members are expelled. The purpose of this study was to clarify which features of male offspring promote their expulsion. Therefore body mass, absolute and relative weight of testes and epididymis, histology of testes and testosterone concentrations were analyzed in males derived from five families living in semi-natural enclosures with food and water ad libitum. Males expelled (EFM, n=40) had significantly higher relative testes and relative epididymis weight and higher testosterone concentrations in harmonious periods than it did non-attacked ones (IFM, n=13). A stepwise discriminant analysis has established the relative testes weight as decisive for the affiliation to EFM or IFM. Based on this parameter, 71.7% of the offspring could be classified correctly. Moreover, histological results showed that 50.0% of integrated and 29.4% of the expelled family members had incomplete spermiogenesis, indicating a reduced fertility. It is concluded, that males do compete for reproduction within the families which triggers the expulsion of the males with the highest reproductive capacity.

Aggression↗
PubMed2005

Intercollegiate soccer: saliva cortisol and testosterone are elevated during competition, and testosterone is related to status and social connectedness with team mates.

Men and women from a southern university's intercollegiate varsity soccer teams gave saliva samples before and after league matches. For the men, samples were collected for a single game ending in victory. For the women, samples were collected for two games, one of which ended in victory and the other in defeat. For both men and women, match competition substantially increased saliva cortisol (C) and testosterone (T). For women, play-related increases in saliva C and T were similar in victory and defeat. For both men and women, saliva T (but not C) was highly correlated with teammate ratings of playing abilities--one measure of status with teammates--and self-ratings of social connectedness with teammates, but the nature of the relationship was different according to sex. For men, play-related changes in T were positively correlated with these variables, but before-game T was not. For women, before-game T was positively related to each of these variables, but play-related changes in T were not. Status and social connectedness are pertinent to understanding interpersonal dynamics in most social groups, and these results--which link T and these variables in an athletic context--may have relevance for understanding social relationships in other settings.

Adolescent↗
PubMed2006

Rank in a food competition test and humoral immune functions in male Brandt's voles (Lasiopodomys brandtii).

Social status can influence an animal's immune and reproductive functions, eventually leading to alterations in immunocompetence and reproductive success. Here, we report that rank assessed in a food competition test, considered as an index of social status, has significant influences on humoral immune functions in male Brandt's voles (Lasiopodomys brandtii) living in a group. Our data reveal a negative correlation of the spleen mass and serum antibody levels with social status, as well as a positive correlation of serum cortisol levels with social status. Males winning in food competition had a smaller spleen, a lower level of serum antibodies, and a higher level of serum cortisol than did their conspecific counterparts. These data indicate interactions between social status and humoral immune functions and might illustrate a trade-off between infection risks and reproductive success in male Brandt's voles.

Animals↗
PubMed2007

Effects of ability- and chance-determined competition outcome on testosterone.

Winning competitions has been shown to lead to higher testosterone (T) relative to losing in men and males of other species. In Experiment 1, 38 women and 37 men provided a saliva sample, completed a novel computer-based vocabulary competition task at which they won or lost based on their own ability, provided feedback about the competition via questionnaire, and then produced a second saliva sample. Task outcome and performance was not sexually differentiated, and overall task performance was negatively correlated with T. Male but not female winners had lower baseline and post-competition T, and male losers had a larger decrease in T from baseline to post-competition. In Experiment 2, 31 men and 43 women completed the same as above, but were randomly assigned to win or lose. In this case, competition outcome did not affect T for men but there was an effect such that women who would have had an ability-determined loss showed a larger decrease in T than women who would have had an ability-determined win. Thus, earned wins appear to attenuate a decline in T in men, consistent with past research into the competition effect and T, and perhaps women under complex circumstances.

Achievement↗
PubMedDate not supplied

Readiness for future managerial leadership roles: nursing students' perceived importance of organizational values.

This study explored the values held by nursing students attending a baccalaureate program. Our aim was to determine whether nursing students' values change after being exposed to educators as well as mentors and ethics education and after experiencing today's challenging work environment, with an emphasis on the organizational domain of the students' values set. The conceptual framework that underpins the approach to values presented in this study argues that the total values set of a working person consists of three domains: personal, professional, and organizational values. Our sample consisted of first, third, and fourth year nursing students (N = 496) attending the Tel Aviv University in Israel. Participants were requested to answer a questionnaire and to rate their perceived importance of 30 values. The results revealed significant differences in the participants' perceived importance of the three values domains. The organizational values--the new business values--were perceived significantly to be least important. Sex was found to be significantly related to perception of values' importance. Year of study was not found to be significantly correlated to perception of values. The findings reflect that senior nursing students are only moderately prepared for their future managerial leadership roles and point out the need to provide students with more stimulating and supportive learning experiences.

Adult↗
PubMed2006

Long-term effects of athletics meet on the perceived competence of individuals with intellectual disabilities.

The purpose was to examine the effects of the type of athletic program (integrated versus segregated) and of the type of sport (basketball versus swimming) on two domains of perceived competence (athletic competence and social acceptance), and general self-worth. Participants were 48 adolescent females with intellectual disabilities (ID) divided equally into six groups: (a) segregated basketball, (b) integrated basketball, (c) segregated swimming, (d) integrated swimming, (e) physical education (PE), and (f) sedentary. The experimental treatment was 21 months long; for sport groups, this involved 2h of training each week and 12 competitive meets. We administrated Harter's (Harter, S. (1985). Manual for the self-perception profile for children. Denver: University of Denver) Self-Perception Profile for Children seven times to determine changes in perceived competence, and general self-worth. Results indicated: (a) no changes in perceived social acceptance; (b) significantly lower perceived athletic competence for the integrated groups; (c) significantly lower general self-worth for the basketball groups compared to the PE group. The integrated environment helps adolescents with ID to adopt a more realistic evaluation of their physical competence.

Adolescent↗
PubMed2004

The competitive dynamics of metapopulations subject to the Allee-like effect.

It is well recognized that individuals of many species can benefit from the presence of conspecifics, a concept broadly referred to as the Allee effect. At the metapopulation level, there is an analogous but essentially different phenomenon called the Allee-like effect that leads to metapopulation extinction thresholds at low habitat occupancy. But so far not adequate attention has been paid to this phenomenon. In this paper, the Allee-like effect is introduced into a metapopulation model of one species and also that of a three-state two-species competitive system. Phase plane analysis is used to investigate the dynamics of these models. We demonstrate that the Allee-like effect alone could lead to multiple stable states in three-state two-species competitive systems at the metapopulation level, and the number of stable states decrease as the Allee-like effect becomes more severe. Severe Allee-like effects may make coexistence impossible and may even lead to the extinction of both species even if their initial habitat occupancies are high and suitable habitats are enough. It is especially noticeable that depending on their initial conditions one species may exclude the other one that subjects to a weaker Allee-like effect than the former, while the second species always excludes the first one when both species are assumed to be in the absence of the Allee-like effect. We also investigate the habitat destructive effect on the Allee-like system mentioned above. Research indicates that the existence of the Allee-like effect makes a metapopulation more susceptible to habitat destruction. All in all, the Allee-like effect is probably a destabilizing factor that, together with habitat destruction, would affect the continuous existence of species. These conclusions may have important implications for conservation and metacommunity organization.

China↗