About the Influences of Some Major Biotic Drivers on the Population Dynamics in Host-parasite Systems: Interpretative Lessons from an Extended Nicholson-Bailey Model

Population dynamics within host-parasite systems in insects is governed by a series of factors, both endogenous and exogenous. Among them, five factors may be considered as major drivers: the respective inherent rates of increase of the host and of the parasite, the level of resource available to the host, the respective immigration rates of the host and of the parasite. While only the first two (the inherent rates of increase of host and parasite) are considered in the original Nicholson and Bailey model, an extended version of the model includes also the other three parameters, thus providing a broader (although still schematic) approach to the host-parasite population dynamics. A brief analysis of the respective influences of each of these five driving parameters on the main features of host-parasite dynamics is derived accordingly, based upon this extended model. Finally, specific attention is paid to the major concerns due to the cyclic outbreaks of both the host and the parasite, regarding in particular the amplitude, the periodicity and the conditions of onset of the cyclicity. Both the practical aspects of the cyclic regime and its possible adaptative significance are discussed. As a whole, this approach aims to provide some general clues for the interpretation of various features of the host-parasite dynamics, as reported from field observations.