co-infection with a larger and more diverse range of nematode parasites
is pervasive in wildlife (Petney and Andrews, 1998; Lello
et al., 2004) and has been shown in feral Soay sheep (Wimmer
et al., 2004; Craig et al., 2006), which have not been subject to
intensification and management. In addition to those species such
as T. circumcincta and T. vitrinus that are common in managed
sheep flocks, in the study flock of Soay sheep there was a relatively
high abundance of parasitic nematode species such as T.
axei and B. trigonocephalum that have become rare elsewhere. Livestock
management practices create niches that are suited to the
development and survival of free-living stages of helminth parasites;
enhance sheep exposure to infective stages of the parasites;
and alter the host innate or adaptive immune responses to infection
(Shaw and Dobson, 1995). Better understanding is needed
of the manner whereby these factors may upset the equilibrium
between different nematode species or populations, allowing some
to predominate and potentially become pathogenic, while limiting
others, thereby reducing nematode parasite species diversity, and
allowing for sequential variation in the predominance of individual
species. Thus, consideration ofthose factors that allowed for the
diversity and seasonal abundance of individual nematode parasite
species in the study flock of Soay sheep is pertinent