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At least 811 records · Page 45Linked to original sources
PubMed1983

Density dependent selection incorporating intraspecific competition 1. A haploid model.

A haploid model is introduced and analyzed in which intraspecific competition is incorporated within a density dependent framework. It is assumed that each genotype has a unique carrying capacity corresponding to the equilibrium population size when fixed for that type. Each genotypic fitness at a single multi-allelic locus is a function of a distinctive effective population size formed by adding the numbers of each genotype present, weighted by an intraspecific competition coefficient. As a result, the fitnesses depend upon the relative frequencies of the various genotypes as well as the total population size. Intergenotypic interactions can have a profound effect upon the outcome of the population. In particular, when the density effect of one individual upon another depends upon their respective genotypes, a unique stable interior equilibrium is possible in which all alleles are present. This stands in contrast to the purely density dependent haploid system in which the only possible stable state corresponds to fixation for the type with the highest carrying capacity. In the present model selective advantage is determined by a balance between carrying capacity and sensitivity to density pressures from other genotypes. Fixation for the genotype with the highest carrying capacity, for instance, will not be stable if it exerts a sufficiently weak competitive effect upon the other genotypes. In the diallelic case, maintenance of both alleles at a stable equilibrium requires that the net intragenotypic competition between individuals of like genotype be stronger than that between unlike types. As for purely density regulated systems, there may be no stable equilibria and/or regular and chaotic cycling may occur. The results may also be interpreted in terms of a discrete time model of interspecific competition with each haplotype representing a different species.

Animals↗
PubMed1995

Increased activation as a limiting factor of performance in sharp shooters.

The measurement of autonomic nervous system (ANS) activity was performed on 10 male and five female sharp shooters (rifle) during competitions. Electrodermal, thermovascular, cardiorespiratory variables and two indices of performance were recorded simultaneously. When the subjects fired shots that hit the target, they had a higher number of negative skin potential responses than when they missed. The responses had lower amplitude but lasted longer than when the shots missed the target. Good performance seemed to depend on high levels of motivation (increase in negative potential response), better mastery of the emotional reactivity (low amplitude response), and greater concentration time (increased duration of response).

Autonomic Nervous System↗
PubMed1988

Competition between lever-pressing behavior and thermoregulatory behavior on exposure to heat in intracranial self-stimulating rats.

To investigate the relationship between the thermoregulatory system and the brain-reward system, we examined effects of heat exposure and tail amputation on lever-pressing behavior in intracranial self-stimulating rats. Rats that continuously pressed a lever voluntarily for 1 hour at an ambient temperature (Ta) of 22 degrees C interrupted lever pressing and showed heat loss behaviors, such as grooming and body extension, at a Ta of 36 degrees C. Hypothalamic temperature (Thy) at the time of the first body extension was higher than that after 1 hour of lever-pressing at a Ta of 22 degrees C. Tail amputation experiments showed the same result. Thy at the onset of the body extension after tail amputation was higher than that at the end of 1 hour of lever-pressing under control conditions. The data suggest that thermal factors, especially Thy, are important in the control of lever-pressing behavior.

Amputation, Surgical↗
PubMed1991

Does snatching frequency really indicate food ingestion in the Nile tilapia?

The fitness of the snatching frequency as an indicator of food intake in Nile tilapia fingerlings, Oreochromis niloticus (L), was studied. Five groups of four individuals each were used after a two-day starvation period. The hierarchical rank among individuals in the same group was registered. Food in the form of tiny pellets (ranging from 1.30 to 1.95 mm in diameter) was offered, and the individual snatching frequency was observed during a 20-min period. The animals were then sacrificed for evaluation of stomach contents. It was concluded that snatching frequency is not a good parameter to indicate individual food intake in this species when fed as a group with pellets crushed into tiny particles. This raises a problem for investigations that require evaluation of the cumulative effect of competition on food intake, such as growth or conversion efficiency studies. Furthermore, a very low correlation between snatching frequency and food intake was shown in the third hierarchical rank. It is suggested that the linearity assumed in such hierarchies should be reconsidered.

Animals↗