1 research outputs found
A preliminary threshold model of parasitism in the Cockle\emph{Cerastoderma edule} using delayed exchange of stability
Thresholds occur in the dynamics of many biological communities. Here we
model a persistence type threshold which has been shown experimentally to exist
in hyperparasitised flukes in the cockle, a shellfish. Our model consists of a
periodically driven slow-fast host-parasite system of equations for a slow
flukes population and a fast Unikaryon hyperparasite population. The model
exhibits two branches of the critical curve crossing in a transcritical
bifurcation scenario. We discuss two thresholds due to immediate and delayed
exchange of stability effects; and we derive algebraic relationships for
parameters of the periodic solution in the limit of the infinite ratio of the
time scales. Flukes parasitise cockles and in turn are hyperparasitised by the
microsporidian Unikaryon legeri; the life cycle of flukes includes several life
stages and a number of different hosts. That is, the flukes-hyperparasite
system in a cockle is part of a larger estuarine ecosystem of species involving
parasites, shellfish and birds which prey on shellfish. A population dynamics
model which accounts for such multi-species interactions and includes the
fluke-hyperparasite model in a cockle as a subsystem is presented. We provide
evidence that the threshold effect we observed in the flukes-hyperparasite
subsystem remains apparent in the multi-species system. Assuming that flukes
damage cockles, and taking into account that the hyperparasite is detrimental
to flukes, it is natural to suggest that the hyperparasitism may support the
abundance of cockles and, thereby, the persistence of the ecosystem, including
shellfish and birds. We confirm the possibility of this scenario in our model
by removing the hyperparasite and demonstrating that this may result in a
substantial drop in cockle numbers. The result indicates a possible significant
role for the microparasite in this estuarine ecosystem