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Biomedical subjects

H I Freedman

Publications and source records attributed to H I Freedman.

12 recordsLinked to original sources
PubMed1992

Hopf bifurcation in three-species food chain models with group defense.

Three-species food-chain models, in which the prey population exhibits group defense, are considered. Using the carrying capacity of the environment as the bifurcation parameter, it is shown that the model without delay undergoes a sequence of Hopf bifurcations. In the model with delay it is shown that using a delay as a bifurcation parameter, a Hopf bifurcation can also occur in this case. These occurrences may be interpreted as showing that a region of local stability (survival) may exist even though the positive steady states are unstable. A computer code BIFDD is used to determine the stability of the bifurcation solutions of a delay model.

Animals↗
PubMed1991

Models for the effect of toxicant in single-species and predator-prey systems.

Models of single-species and predator-prey systems in a polluted closed environment are developed and partially analyzed. Three cases are considered: a single influx of toxicant, a constant influx of toxicant, and a periodic pollution of the environment. In the case of single-species growth we are able to determine some local and global dynamics. In the case of predator-prey systems, we investigate the existence of steady states for a small constant influx of toxicant.

Environmental Pollution↗
PubMed1990

A model of predator-prey dynamics as modified by the action of a parasite.

A predator-prey population is described in which the prey population may be either a secondary host or a primary host to a parasite, but the predator is always a primary host. Those prey that have been invaded by the parasite have their behavior modified so as to make them more susceptible to predation. The model is described by a system of three autonomous ordinary differential equations. Conditions for persistence of all populations are given in the case that both populations are primary hosts. A brief discussion of the stability of the interior equilibrium is given.

Animals↗
PubMed1990

A time-delay model of single-species growth with stage structure.

A single-species growth model with stage structure consisting of immature and mature stages is developed using a discrete time delay. It is shown that under suitable hypotheses there exists a globally asymptotically stable positive equilibrium. Questions concerning oscillation and nonoscillation of solutions are addressed analytically and numerically. The effect of the delay on the populations at equilibrium is also considered.

Animals↗
PubMed1989

Predator-prey populations with parasitic infection.

A predator-prey model, where both species are subjected to parasitism, is developed and analyzed. For the case where there is coexistence of the predator with the uninfected prey, an epidemic threshold theorem is proved. It is shown that in the case where the uninfected predator cannot survive only on uninfected prey, the parasitization could lead to persistence of the predator provided a certain threshold of transmission is surpassed.

Animals↗
PubMed1989

Population diffusion in a two-patch environment.

A model of a single-species population diffusing in a two-patch environment is proposed. It is shown that there exists a positive, monotonic, continuous steady-state solution with continuous flux, in the cases of both reservoir and no-flux boundary conditions, that is asymptotically stable. In the case of patches with equal carrying capacities, it is shown that the uniform steady state is globally asymptotically stable.

Ecology↗