Nymphal Ixodes dammini: models of the temporal abundance patterns.

A difference equation model was developed to explore the sensitivity of the temporal pattern of relative abundance of active, host-seeking nymphal Ixodes dammini. Inputs to the model were the temporal patterns of recruitment of nymphs into the active class, mortality and successful acquisition of hosts by the ticks. Input parameters were varied both in the temporal pattern (shape) and in the cumulative level (summed over the period of activity). The output of the models, the temporal abundance pattern, was examined for (1) overall shape and (2) the timing of the peak abundance of host-seeking nymphs. The shape of the temporal pattern of nymphal abundance was not sensitive to changes in the shape of the functions used as input for host-finding. The time of peak abundance of nymphs is slightly sensitive to changes in the overall level of host-finding and mortality. When more ticks are removed from the active class (host-finding or mortality increasing), the time of the peak abundance of the nymphs shifts earlier. However, this shift is small compared to variation in field data. The general shape of the activity pattern was sensitive to changes in the temporal pattern of recruitment. A left-skewed distribution produced output which most resembles field data. The temporal pattern of nymphs entering the active class is important, and is an area which needs further empirical work.