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PubMed2003

Biodiversity, habitat area, resource growth rate and interference competition.

For the majority of species, per capita growth rate correlates negatively with population density. Although the popular logistic equation for the growth of a single species incorporates this intraspecific competition, multi-trophic models often ignore self-limitation of the consumers. Instead, these models often assume that the predator-prey interactions are purely exploitative, employing simple Lotka-Volterra forms in which consumer species lack intraspecific competition terms. Here we show that intraspecific interference competition can account for the stable coexistence of many consumer species on a single resource in a homogeneous environment. In addition, our work suggests a potential mechanism for field observations demonstrating that habitat area and resource productivity strongly positively correlate to biodiversity. In the special case of a modified Lotka-Volterra model describing multiple predators competing for a single resource, we present an ordering procedure that determines the deterministic fate of each specific consumer. Moreover, we find that the growth rate of a resource species is proportional to the maximum number of consumer species that resource can support. In the limiting case, when the resource growth rate is infinite, a model with intraspecific interference reduces to the conventional Lotka-Volterra competition model where there can be an unlimited number of coexisting consumers. This highlights the crucial role that resource growth rates may play in promoting coexistence of consumer species.

Animals↗
PubMed2003

Effect of ammonia toxicity on the competition among three species of cladocerans (Crustacea: Cladocera).

Among the natural abiotic variables affecting the species density and composition of cladocerans, ammonia is important. Using population growth data as tool, we studied the competitive outcome of three cladoceran species (Ceriodaphnia dubia, Daphnia pulex, and Moina macrocopa) grown alone and together at three different concentrations (0, 25, and 100 mg L(-1)) of ammonia at one density (1 x 10(6)cells ml(-1)) of the microalga Chlorella vulgaris. Regardless of the presence or absence of competing species, C. dubia showed little population growth at 100 mg L(-1) of ammonia. At 25 mg L(-1) of ammonia, the population density of C. dubia increased but the value was much lower than that in control. D. pulex was able to grow at the ammonia concentration of 25 mg L(-1), comparable to controls. However, at 100 mg L(-1) of ammonia, the population declined and more rapidly when competed with other cladocerans. M. macrocopa showed decreased population density with increasing ammonia concentration in the medium. This trend was accelerated by the presence of competing cladocerans. M. macrocopa was benefited by the presence of D. pulex at 0 and 25 mg L(-1) of ammonia in the medium. The peak population density of C. dubia varied from 0.5 to 9 ind.ml(-1), whereas for D. pulex and M. macrocopa, these values varied from 1 to 3 ind.ml(-1) and 7 to 18 ind.ml(-1), respectively, depending on the ammonia concentration and the presence of competing species. The rates of population increase per day of C. dubia, D. pulex, and M. macrocopa ranged from -0.12+/-0.001 to 0.30+/-0.01, 0.04+/-0.001 to 0.22+/-0.002, and 0.201+/-0.028 to 0.235+/-0.019, respectively, depending on the ammonia concentration and the presence of competitors. Our study showed that while competition within the chosen cladoceran species caused suppression of one or two competing species, the presence of ammonia expedited this process based on the relative sensitivities of the tested zooplankton.

Ammonia↗
PubMed2002

Anabolic androgenic steroid affects competitive behaviour, behavioural response to ethanol and brain serotonin levels.

The present study investigated whether anabolic androgenic steroid (AAS) treatment (daily subcutaneous injections during 2 weeks with nandrolone decanoate; 15 mg/kg) affects competitive behaviour, and locomotor activity response to a sedative dose of ethanol (0.5 g ethanol/kg). In addition, levels of brain monoamines were assessed. The results showed that AAS treated animals exhibited enhanced dominant behaviour in the competition test compared to controls. The AAS groups' locomotor activity was not affected by ethanol in contrast to the controls who showed a sedative locomotor activity. AAS animals had significant lower levels of serotonin in basal forebrain and dorsal striatum compared to controls. These findings further strengthen the fact that AAS affects behaviour, as well as biochemical parameters. Based on previous studies and results from the present study, we hypothesize that AAS abuse may constitute a risk factor for disinhibitory behaviour, partly by affecting the serotonergic system.

Anabolic Agents↗
PubMed2002

Attenuation of context-specific inhibition on reversal learning of a stimulus-response task in rats with neurotoxic hippocampal damage.

Rats with hippocampal or sham lesions were trained on a stimulus-response task developed for the 8-arm radial maze. After reaching a stringent learning criterion, different context manipulations were performed. In Experiment I, the different groups were transferred to an identical radial maze in a different room to determine the context specificity of the discrimination learning. Experiment I revealed that although rats with hippocampal lesions did not show a normal context detection effect, the expression of the discrimination was not context dependent for either the lesion or sham groups. In Experiment II, animals were trained to criterion on the discrimination task and then both groups were divided into sub-groups based on whether they would experience reversal training in the same or different context from original training. Experiment II indicated that animals with hippocampal lesions and shams reversed in a different context were significantly enhanced in reaching the learning criterion compared to either counterparts that were reversed in the same context. Reversal learning in rats with hippocampal lesions was faster than sham animals in the same context suggesting that the context-specific inhibition effect was hippocampal-based. After learning the reversal task, the groups of animals trained and reversed in different contexts were brought back into the original training context to test for competitive effects. Animals with hippocampal lesions that were reversed in the different context, did not show a competition between the most recently acquired discrimination and a context-specific association acquired during original training whereas sham animals in the same condition did. Taken together these results suggest that rats with hippocampal lesions do not acquire normal context-specific inhibition during discrimination learning.

Animals↗
PubMed1998

Mating competitiveness of irradiated flies for screwworm fly eradication campaigns.

Should the screwworm fly invade Australia, the sterile insect technique (as used successfully overseas) is currently the only feasible method of eradication. Used in conjunction with chemical control methods, it relies on large numbers of factory-reared, sterilized males competing successfully with wild males for the wild females. However, laboratory and field studies have shown that the processes of mass rearing, irradiation and distribution seriously impair the competitiveness of the sterilized flies. This study collates and analyses the relatively sparse information on the relative mating competitiveness of sterilized screwworm flies, from both controlled experiments and large-scale field studies. A population dynamics example then demonstrates that competitiveness will be a key parameter in the effectiveness and economic feasibility of any future eradication campaign.

Animals↗
PubMed2003

Relative effects of harassment, frustration, and task characteristics on cardiovascular reactivity.

Effects of anger induction procedures such as frustration and harassment on cardiovascular reactivity have been demonstrated in a wide range of experimental situations. Similarly, heightened cardiovascular reactivity has been associated with a diverse range of tasks involving active coping, competition and interpersonal interaction. The present study sought to directly compare the relative effects of these two important ways of inducing cardiovascular changes. One hundred and five university students performed two tasks that differed in the degree of active coping and interpersonal competition: a competitive psychomotor task and a problem-solving task. States of anger were induced during both tasks by means of harassment, frustration or frustration+harassment. Task-related changes in heart rate, systolic blood pressure, diastolic blood pressure, pulse volume amplitude and respiratory sinus arrhythmia amplitude were monitored. The competitive psychomotor task produced greater cardiovascular reactivity than did the problem-solving task. Harassment and frustration+harassment provoked more cardiovascular reactivity than did frustration alone. However, harassment and frustration+harassment had the greatest cardiovascular effects in the competitive task, whereas frustration had the greatest cardiovascular effects in the problem-solving task. In this sense, the increases on cardiovascular reactivity seem to depend on the interaction between anger induction procedures and the context in which anger is provoked.

Adaptation, Psychological↗
PubMed2003

Psychosocial aspects of women's lives: work, family, and life cycle issues.

Over the past century and continuing to evolve into the twenty-first century, there have been dramatic changes in work and personal/family lives within the United States. These changes, though strongly affecting men and children, have impacted most dramatically on women's lives, particularly white, middle-class women. Psychiatrists and other mental health clinicians need to be aware of the scope and nature of these changes and to recognize that their own personal experiences and values might differ from those of women of different generations as well as different socioeconomic and cultural backgrounds.

Adaptation, Psychological↗
PubMed2002

Effects of opiate ligands on intraspecific aggression in crickets.

In the cricket Gryllus bimaculatus, the opiate antagonist naloxone, 30 microg in 50 microl into hemolymph per animal, caused a release of intraspecific aggression in male-losers and in females. Naloxone had no significant effect on the aggression of winners and isolated males. The agonist of mu-opiate receptors DAGO, 45 microg, suppressed aggression in male winners and decreased the percentage and duration of contact fights between previously isolated males. The results suggest that, during social contacts, the activity of the endogenous opioid system may contribute to suppressing aggression in subordinate males, as well as in females.

Aggression↗
PubMed1996

Obstetric care: competition or co-operation.

OBJECTIVE: The aim of this study was to determine the feasibility of co-operation within maternity and obstetric care between midwives, general practitioners (GPs) and obstetricians. DESIGN: descriptive correlational study. SETTING: The Netherlands. Policy is towards more co-operation between primary and secondary health care. However, in Dutch health care midwives, GPs and obstetricians may also have conflicts of interests. PARTICIPANTS: members of obstetric co-operation groups (91 midwives, 53 GPs, 31 obstetricians) completed a questionnaire. MEASUREMENTS AND FINDINGS: in the questionnaire information was collected on what members of obstetric co-operative groups expect from co-operation. Findings indicated that consensus existed about experienced advantages and disadvantages of co-operation, tasks that should be achieved, and how obstetric co-operative groups could be set up. Nevertheless, there was evidence of competition and there were also conflicting ideas about co-operation. KEY CONCLUSIONS AND IMPLICATIONS FOR PRACTICE: it is concluded that the findings have implications for the organisation of an obstetric co-operative group. If professionals want to start such a group it is preferable to start with topics that benefit all participants (win-win situation) and motivate them to participate actively. A second step may be an attempt to reach agreement about how to communicate with each other in the case of referrals and consultations. During this phase mutual trust and respect may grow, so that finally more difficult problems can be discussed (mixed-motives situation).

Attitude of Health Personnel↗