Simulation of population dynamics of the parasite Haematoloechus coloradensis Cort 1915 (Digenea: Haematolochidae) in its 3 host species: effects of environmental temperature and precipitation

Abstract

This study describes development and evaluation of a simulation model representing the life cycle of the parasite Haematoloechus coloradensis, and use of the model to examine effects of variations in temperature and precipitation on parasite population dynamics. The model consists of 4 submodels, each representing dynamics of a different developmental stage of the parasite and population dynamics of its associated host species. The parasite egg submodel represents dynamics of parasite eggs in the environment as a function of parasite recruitment and mortality, and snail infection. Snail, odonate, and frog submodels represent population dynamics and infection of the 3 host species, and parasite development within each host. In the snail submodel parasites are affected by recruitment of susceptible individuals, snail infection, cercariae shedding, and snail and cercaria mortality. Snail infection is determined by encounter rate between parasite eggs and susceptible snails. In both odonate and frog submodels recruitment and mortality of hosts constitute the source of susceptible hosts and parasite mortality, respectively. Odonate infection is determined by encounter rate between cercariae and susceptible odonates. Frog infection is determined by encounter rate between infected odonates and susceptible frogs. Simulated population dynamics and seasonal variations in prevalences of infection for second (odonate) and definitive (frog) hosts generally agreed with field observations (Dronen, 1978). Differences between simulated and observed variations in prevalence for the first intermediate host (snail), probably were due to failure of the model to represent (1) effects of temperature on parasite development within snails and (2) parasite-induced host mortality. High precipitation and short summers (favorable conditions for host populations) resulted in higher stable prevalences than baseline conditions for the 3 host species. Simulated effects of low precipitation and extended summers (unfavorable conditions for host species) indicated that temperature had a greater impact on parasite population dynamics than precipitation. Susceptible host abundances were decreased during extended summers to levels below which encounter rate could maintain the parasite population. Overall, results suggest that timing of occurrence of a given disturbance may be as important in determining impact on parasite population dynamics as the specific nature of the disturbance.