Population regulation in trichostrongylids of ruminants
International Journal for Parasitology 17(2): 531-540
Since regulation of population size requires the existence of one or more density-dependent processes affecting parasite numbers, the literature was examined for evidence of density-dependence in establishment, reproduction and mortality of trichostrongylids of ruminants. Because of differences between the two environments required for completion of the trichostrongylid life-cycle, this evidence was sought in processes occurring within the host, rather than in dung-pats or on pasture. Evidence was found of at least one density-dependent population process in several economically important species of the genera Haemonchus, Ostertagia and Trichostrongylus, although further observations on populations derived from continuous infection at several rates of larval intake are required to substantiate much of this evidence. It is suggested that populations of trichostrongylids of ruminants are regulated at the level of the suprapopulation by density-dependent constraints on egg production of constituent infrepopulations; rates of larval intake may play a central role in coordinating regulation within each ecosystem.