Effects of parasite communities on willow ptarmigan population dynamics
Evidence that parasites interact to affect host population dynamics, and that external factors affect infection in general.
Author(s): P. R. Holmstad, P.J. Hudson, & A. Skorping
Title: The influence of a parasite community on the dynamics of a host population: a longitudinal study on willow ptarmigan and their parasites
Journal: Oikos 111: 377-319
Most empirical studies of the way that parasites affect host populations have concentrated on just one parasite species at a time. However, host individuals are often infected by more than one parasite simultaneously.
In a study of willow ptarmigan (Lagopus lagopus) in Norway, Peter Hudson and collaborators have found evidence that parasites interact to affect host population dynamics.
Two helminth parasites in particular (Trichostrongylus tenuis and Hymenolepis microps) had negative effects on bird body mass and breeding mortality, but data showed a significant additional effect of the remainder of the parasite community (although none of the other parasites appeared to have a significant effect on its own).
The researchers also found that the prevalence of parasites — even ones which were quite taxonomically dissimilar — often covaried within years, suggesting that something is affecting infection by parasites in general. For example, environmental conditions such as snow cover might affect exposure to a variety of parasites