The effect of host density on ectoparasite distribution: An example of a rodent parasitized by fleas

The pattern of parasitism of the flea species Xenopsylla dipodilli and Nosopsyllus iranus theodori on the desert rodent species Gerbillus dasyurus was studied to test the hypothesis that the relationships between flea abundance and host density conform to pre-existing models of R. M. Anderson and R. M. May, with the correction that the density of those host individuals that possess permanent burrows (residents) is substituted for the overall host density. It was predicted that: (1) the intensity of flea infestation would increase in curvilinear fashion with increase of host density to a plateau that would be attained at a lower level of host density than would be expected from the basic model, and (2) the prevalence of flea infestation plotted against host density would be hump-shaped. The results indicated that intensity of flea infestation increased in either curvilinear fashion to an asymptote (for X. dipodilli) or linearly (for N. i. theodori) with increase of host density. As host density increased, the prevalence of infestation changed either unimodally (X. dipodilli) or logarithmically (N. i. theodori). In addition, there was a positive relationship between the mean number of fleas per host and the percentage of hosts infested. Both basic and corrected models describing the relationships between flea burden and host density fit the observational data well. However, simulations of the fraction of resident hosts demonstrated that this parameter influences the relationship between host density and flea burden only when residents comprise ≤50% of all host individuals.