Parasite-mediated and direct competition in a two-host shared macroparasite system

Area of Science:

• Ecology
• Population Dynamics
• Mathematical Biology

Background:

• Understanding species interactions is crucial for ecology.
• Competition and parasitism significantly influence population dynamics.
• Deterministic models are valuable tools for studying ecological systems.

Purpose of the Study:

• To investigate the local dynamical behavior of a deterministic model with two host species.
• To analyze the combined effects of direct, apparent (parasite-mediated), and intra-specific competition.
• To provide a comprehensive overview of system stability, feasibility, and potential dynamical behaviors.

Main Methods:

• Utilized a geometric approach in parameter space, constructing maps structured by bifurcation surfaces.
• Avoided algebraic intractability by focusing on qualitative changes in system behavior.
• Analyzed stability and feasibility structures of system equilibria.

Main Results:

• The system is sensitive to infection's effect on fecundity, readily generating cycles via Hopf bifurcations.
• Apparent competition, mediated by macroparasites, is sufficient to explain host exclusion across many parameter values.
• Direct competition reinforces parasite-mediated exclusion, expanding the exclusion region.
• A simple condition for host exclusion was derived, applicable to both micro- and macroparasite models.

Conclusions:

• Macroparasite-mediated apparent competition is a potent driver of host exclusion, even without direct competition.
• The interplay between direct and parasite-mediated competition significantly shapes population dynamics and can lead to exclusion.
• The developed geometric mapping technique is broadly applicable to nonlinear population models beyond host-parasite systems.