Prediction of tick abundance requires taking into account: (i) the abiotic properties of the site, which reflect how ticks can survive and populate a site and (ii) the movements of hosts through the landscape patches, which explain the densities of host populations.
Since the rate of contact between infected and susceptible hosts (i.e., the nodes of a transmission network) are crucial determinants of epidemic dynamics [35], [36], the number of connections per highly-connected node should increase as a function of host population density and size.
The spread of the disease needs a minimum threshold support of host population density (36 ).
The extent of parasite-induced reduction of host population density is expected to correlate with initial parasite prevalence.
Based on experiments with other Daphnia microparasites [ 25, 26], we predict a parasite-induced reduction of host population density.
Long-term direct monitoring of host population density and prevalence of hantavirus infection in North American deer mice provided early warning of elevated risk for HPS in the southwestern United States (CDC 1998, 1999; Yates et al. 2002).
Great gerbils usually have few visible symptoms of plague infection, and only moderate increases in mortality [ 12, 20], and there seems to be a critical threshold of host population density necessary for plague to persist in an area [ 10, 12, 21].
Biological control agents require time to acclimate, and build up populations to reach effective density for control of host populations and dispersal.
The density of the host population and the transmission rate of the parasite are two of the most important of these ecological factors.
Any increase in the basic rate of increase of a feminising parasite will tend to increase the equilibrium density of the host population due to the increase in the proportion of female hosts.
These factors act both through their direct effects upon the parasite's basic rate of increase, and indirectly, by altering the equilibrium density of the host population.
