Niche theory for within-host parasite dynamics: Analogies to food web modules via feedback loops

Why do parasites exhibit a wide dynamical range within their hosts? For instance, why can a parasite only sometimes successfully infect its host? Why do some parasites exhibit large fluctuations? Why do two parasites coinfect, exclude each other, or win only sometimes over another (via priority effects)? For insights, we turn to food webs. An omnivory model (IGP) blueprints one parasite competing with immune cells for host energy (PIE), and a competition model (keystone predation, KP) mirrors a new coinfection model (2PIE). We then draw analogies between models using feedback loops. We translate those loops into the intraspecific direct (DE) and indirect effects (IE) that create various dynamics. Three points arise. First, a prey or parasite can flip between stable and oscillatory coexistence with their enemy with weakening IE and strengthening DE. Second, even with comparable loop structure, a parasite cannot exhibit priority effects seen in IGP due to constraints imposed by production of immune cells. Third, despite simpler loop structure, KP predicts parallel outcomes in the two-parasite model due to comparable structure of interactions between competing victims and their resources and enemies. Hence, food web models offer powerful if imperfect analogies to feedbacks underlying the dynamical repertoire of parasites within hosts.

Host-Parasitoid Model With Intraspecific Competitions

In this paper a discrete-time host-parasitoid model with intraspecific competitions is proposed. Phase portraits are drawn for different types of intraspecific competitions to notice the effects of intraspecific competitions for biologically reasonable range of parameter values. Bifurcation analysis is done with respect to instantaneous search rate as well as handling time for different types of intraspecific competitions. Many forms of complex dynamics such as chaos, periodic windows etc. are observed. The stable coexistence as well as oscillatory coexistence of host and parasitoid are shown under different types of intraspecific competitions. The Hopf point and attractor crises exist for different intraspecific competitions.

COMPETITION BETWEEN TWO MICROORGANISMS IN THE CHEMOSTAT WITH GENERAL VARIABLE YIELDS AND GENERAL GROWTH RATES

A model of competition between two organisms in the chemostat is studied in this paper, where it is assumed that the yield coefficients and growth rates are general functions of the nutrient concentration. We give a characterization of the outcome of this competition in terms of the relevant parameters in hyperbolic cases: conditions of the existence and local stability of the rest points are obtained, and the global asymptotic behavior of the solutions is analyzed. In contrast to the corresponding model with constant yields rate, it is demonstrated that the variability of the yield coefficient may lead to oscillatory coexistence of two microorganisms in continuous culture.