PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Competitive Behavior”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed1995

Is there value in audition extramurals?

BACKGROUND: It has become common for fourth-year medical students interested in surgical careers to leave their parent university to take extramural elective rotations in surgery at other institutions. These "audition extramurals," while of some educational value, are often repetitions of prior clerkships and may not broaden the student's educational horizons. Instead, they are intended to enhance a student's competitiveness in the match. While recent opinions and questionnaires have suggested that such extramural rotations are not valuable in general surgery, no study has formally evaluated the effect of extramural electives on the residency match. METHODS: Over a 6-year period, the authors reviewed the outcome in 99 students who took extramural elective rotations in surgery. Of the 99 students, 28 were from the authors' institution who left to do extramural rotations elsewhere and 71 were outside students who came to the University of South Florida for an elective. While the elective rotation increased the probability of an interview, it did not alter ranking or probability of matching. RESULTS: For general surgery students, the elective rotation may actually decrease competitiveness, while for specialty students, it appears necessary but not sufficient to improve match outcome. The elective might facilitate placement for students who did not match, but did not do so predictably. CONCLUSIONS: The authors conclude that extramural elective rotations should be taken for educational value only and not as auditions for residency.

Career Mobility↗
PubMed1980

Sexual behaviour and reproductive competition in male wild and domestic Norway rats.

The copulatory behaviour of male wild Norway rats (Rattus norvegicus) exposed individually to females in hormone-induced oestrus is characterized by fewer mounts and intromissions per ejaculatory series, shorter ejaculation latencies, and longer ejaculatory clasps than the copulatory behaviour of domestic males. Competition between wild and domestic males testes simultaneously in pairs produced only minor changes in copulatory behaviour. The reproductive success of wild and domestic male pair simultaneously exposed to naturally cycling females was nearly equal in both the laboratory and an outdoor enclosure. Genotype of the female had little effect on male copulatory behaviour. The copulatory behaviour of sexually naive and experienced domestic rats did not differ. However, most sexually naive wild males failed to exhibit copulatory behaviour under the test conditions employed.

Animals↗
PubMed2000

Soft tissue injuries to USA paralympians at the 1996 summer games.

OBJECTIVE: To report the soft tissue injuries sustained by the members of four disabled sports organizations (DSOs) who competed as the USA Team at the 1996 Paralympic Games. SETTING: 1996 Paralympic Games, Atlanta, Georgia. METHODS: Soft tissue (strain, sprain, tendonitis, bursitis, or contusion) injury frequencies sustained by Disabled Sports USA (DSUSA, n = 66), the United States Association for Blind Athletes (USABA, n = 53), the United States Cerebral Palsy Athletic Association (USCPAA, n = 56), and Wheelchair Sports USA (WSUSA, n = 129) athletes were compared by body region with chi-square tests (p<.05) and standardized residual assessment. RESULTS: A total of 254 soft tissue injuries (67% acute onset, 170/254) were sustained by the participant DSO members. Statistical design limitations and poor USCPAA athlete homogeneity prompted their exclusion from group comparisons (descriptive results are reported). The most common injury regions for specific DSOs were shoulder (26%), hip-thigh (14%), and ankle (12%) for DSUSA; hip-thigh (21%), cervicothoracic region (19%), and shoulder (17%) for USABA; lumbar region (14%), foot-toe (13%), and ankle (9%) for USCPAA; and shoulder (18%), arm-elbow (12%), forearm-wrist (12%), and lumbar region (9%) for USUSA. Chi-square residual analysis showed that the USABA athletes contributed more to cervicothoracic and lower leg region injury frequencies than DSUSA or WSUSA athletes. The WSUSA athletes contributed more to elbow-arm and forearm-wrist region injury frequencies than DSUSA or USABA athletes. The DSUSA athletes contributed more to ankle region injury frequencies than USABA or WSUSA athletes. CONCLUSIONS: Differences in soft tissue injury frequency among athletes of differing DSOs suggest that the competitive use of adaptive or assistive devices, in combination with sport-specific stressors and the athletes' disabilities, is related to the development of predictable soft tissue injury patterns. The decreased incidence of shoulder injury among WSUSA athletes suggests that the injury prevention advice provided by previous studies is being implemented among athletes at this competitive level. The increased incidence of ankle injuries among DSUSA athletes suggests lower extremity load imbalances (prosthetic vs. uninvolved) during running. The increased incidence of lower leg injuries among USABA athletes suggests "overuse" injury patterns typical of nondisabled runners, or inadvertent contacts (contused shins), whereas the increased incidence of cervicothoracic injuries suggests injuries related to falls, "near falls," or sudden directional changes prompted by guidance aids.

Athletic Injuries↗
PubMed2003

Phased infectivity in Heterorhabditis megidis: the effects of infection density in the parental host and filial generation.

Entomopathogenic nematodes can develop through two or more generations in the cadavers of killed insect hosts. Non-feeding infective juveniles from each generation emerge and may spend prolonged periods searching for a new host. The infectivity of the infective juveniles of Heterorhabditis megidis varies with time after emergence and may not reach a maximum until several weeks have passed. 'Phased infectivity' hypotheses propose that this pattern is adaptive, tending to reduce competition in new hosts. Here we provide further evidence that infectivity is phased in H. megidis. In addition, we show that the basic pattern is modified by infection density in the parental host and by filial generation. Two general patterns were observed: first, infective juveniles that developed under the least crowded conditions (F(1) infective juveniles produced in hosts infected with 16 parent nematodes) reached maximum infectivity after only 15 days, compared to 27 or 39 days for infective juveniles that developed under more crowded conditions (F(1) produced in hosts infected with 103 or 424 parent nematodes or F(2) infective juveniles). Second, infective juveniles had lower infectivity overall when produced under the most crowded conditions (F(2) versus F(1); highest versus lowest infection density). We propose that while lower overall infectivity is a necessary consequence of limited resource availability during infective juvenile development, the difference in the timing of peak infectivity reflects a shift in the fitness gains associated with being maximally infective either 'early' or 'late'. F(1) infective juveniles emerge several days before F(2) infective juveniles, and we suggest that filial generation and infection density in the parental host function as indicators of the potential risk of competition within new hosts.

Analysis of Variance↗
PubMed2002

Influence of environmental factors on shot put and hammer throw range.

On the rotating Earth, in addition to the Newtonian gravitational force, two additional relevant inertial forces are induced, the centrifugal and Coriolis forces. Using computer modelling for typical release heights and optimal release angles, we compare the influence of Earth rotation on the range of the male hammer throw and shot put with that of air resistance, wind, air pressure and temperature, altitude and ground obliquity. Practical correction maps are presented, by which the ranges achieved at different latitudes and/or with different release directions can be corrected by a term involving the effect of Earth rotation. Our main conclusion and suggestion is that the normal variations of certain environmental factors can be substantially larger than the smallest increases in the world records as acknowledged by the International Amateur Athletic Federation and, therefore, perhaps these should be accounted for in a normalization and adjustment of the world records to some reference conditions. Although this suggestion has certainly been made before, the comprehensiveness of our study makes it even more compelling. Our numerical calculations contribute to the comprehensive understanding and tabulation of these effects, which is largely lacking today.

Acceleration↗
PubMed2003

Resistance may be futile: dispersal scales and selection for disease resistance in competing plants.

If a host species shares a pathogen with competing species, the disease may provide a net benefit. Selection for resistance will depend on the trade-off between the damage done by the disease and the positive effects resulting from infection of competitors. This paper presents a simple, spatially explicit model of a plant that shares a disease with a superior competitor. The phenotypic evolution of cost-free resistance is studied by using the method of pair approximation to analyse the small-scale spatial structure of the interacting populations. Selection favors lower resistance when disease transmission is spatially local and the damage to the competitor is sufficient to outweigh the direct effects of infection. This suggests that local spatial structure may be critical in determining the coevolution of host-host-pathogen systems.

Competitive Behavior↗
PubMed2003

Founder control and coexistence in a simple model of asymmetric competition for light.

Size asymmetry in plant light acquisition complicates predictions of competitive outcomes in light-limited communities. We present a mathematically tractable model of asymmetric competition for light and discuss its implications for predicting outcomes of competition during establishment in two-, three-, and many-species communities. In contrast to the resource-reduction model of symmetric competition for a single resource, the model we present predicts that outcomes of asymmetric competition for light will sometimes depend on the timing of establishment and the consequent hierarchy among species in canopy position. Competitive outcomes in the model depend on the minimum light requirements (L(c)) and self-shading of species lower in the canopy compared to the light available (L(out)(*)) beneath species higher in the canopy. Succession progresses towards species with decreasing values for L(c), but arrested successions occur when initial dominants have relatively high values for L(c) but low values for L(out)(*), leading to founder control. A theoretically limitless number of species may coexist in competition for light when dominance is founder controlled. These model predictions have implications for an array of applied ecological questions, including methods to control invasive species in light-limited restored ecosystems.

Biomass↗
PubMed2003

Seed-cache exchange promotes coexistence and coupled consumer oscillations: a model of desert rodents as resource processors.

Most models of resource competition assume that coexistence of consumers depends on tradeoffs in their abilities to exploit shared resources along dimensions of environmental heterogeneity generated by factors external to the consumers. However, consumers may create heterogeneity themselves by modifying resources that they do not immediately consume; such "resource processing" is predicted to allow coexistence if consumers vary in use of resources in primary vs. modified form. To explore whether external food storage (caching) represents a form of resource processing that contributes to observed patterns of species coexistence, we developed a biologically explicit simulation model of competition for a well-studied system, seed-eating desert heteromyid rodents. Here we present the model, compare competitive outcomes with and without inter-specific exchange of cached food, and describe population dynamics of coexisting competitors. The model predicts stable coexistence only when there is exchange of cached seeds via scavenging of caches left undefended by mortality or by pilferage of defended caches. Net interactions between coexisting consumers ranged from competition (10% of cases) to host-parasite (77%), commensalism (12%), and mutualism (1%). Population dynamics of coexisting consumers often showed strong periodicity and coupled synchronous or slightly lagged cycles, a possibility not previously anticipated for desert rodents occupying constant environments. Our model confirms that caching does represent a form of resource processing likely to play a significant role in the dynamics and diversity of communities of desert rodents and other caching animals.

Animals↗
PubMed2003

Baseline criteria and the evolution of hosts and parasites: D0, R0 and competition for resources between strains.

Our understanding of the evolution of diseases has been greatly aided by the use of baseline criteria. Here we examine the theoretical and biological relationships of the well known baseline criteria for the evolution of disease (R0) and the recently introduced corresponding criterion for the evolution of resistance in hosts (D0). We show that there is a formal theoretical equivalence between the two criteria and discuss the characteristics of seperability that determine whether the criteria define the course of evolution. These theoretical determinants correspond biologically to whether strains compete for resources or not. We discuss the biological application of the criteria and argue that D0 may be less widely applicable than R0, but does determine the evolution of resistance in populations with fixed carrying capacities.

Animals↗
PubMed1984

Local resource competition and the evolution of male-biased sex ratios.

In many mammalian species, maturing males disperse from their natal groups, while females remain near their places of birth. If sources are limited locally, related females may be forced to compete with one another for access to resources, while mature males will compete primarily with unrelated individuals in non-natal groups. Clark (1978) suggested that under such circumstances the extent of competition among females could be reduced if females uniformly skewed the sex ratio of their offspring in favor of males. Skewed secondary sex ratios and investment patterns in galagos and red deer appear to be consistent with this hypothesis. Several authors have recently demonstrated that the evolution of skewed sex ratios may be influenced by population structure, and Wilson & Colwell (1981) have shown that male-biased sex ratios can evolve in structured haplodiploid populations. Here, I construct an intrademic group selection model to simulate the effects of density-dependent mortality upon diploid populations structured much as Clark describes: males disperse, females remain near their female relatives, and local resource competition limits the size of local groups. The results confirm that male-biased sex ratios can evolve in a diploid species, even when groups are large and the skew in sex ratio is substantial.

Alleles↗
PubMed2001

Optimal harvesting and stability for a two-species competitive system with stage structure.

In this paper, we consider a stage-structured competitive population model with two life stages, immature and mature, with a mature population of harvesting. We obtain conditions for the existence of a globally asymptotically stable positive equilibrium and a threshold of harvesting for the mature population. The optimal harvesting of the mature population is also considered.

Animals↗
PubMed2003

Periodic coexistence of four species competing for three essential resources.

We show the existence of a periodic solution in which four species coexist in competition for three essential resources in the standard model of resource competition. By assuming that species i is limited by resource i for each i near the positive equilibrium, and that the matrix of contents of resources in species is a combination of cyclic matrix and a symmetric matrix, we obtain an asymptotically stable periodic solution of three species on three resources via Hopf bifurcation. A simple bifurcation argument is then employed which allows us to add a fourth species. In principle, the argument can be continued to obtain a periodic solution adding one new species at a time so long as asymptotic stability can be assured at each step. Numerical simulations are provided to illustrate our analytical results. The results of this paper suggest that competition can generate coexistence of species in the form of periodic cycles, and that the number of coexisting species can exceed the number of resources in a constant and homogeneous environment.

Animals↗