This thesis investigates aspects of the community ecology of rabbit parasites with particular
emphasis upon the gut helminths, utilising a 23 (later extended to 26) year time series of
rabbits and their parasites. A clearer understanding of parasite communities can lead to
more effective biological control strategies. Rabbits are regarded as a serious pest species
throughout Europe and the Antipodes and the use of the myxomatosis virus, as a biological
control agent, has already been tried and failed. However, a clearer picture of the parasite
community may offer future possibilities for control. Additionally, the rabbit is a good
model for other grazing species, as it carries a similar gut helminth community. Drug
resistance is an increasing problem in a wide range of parasites. A clearer appreciation of
parasite communities could also aid in the search for effective and environmentally sound
pathogen control strategies (e.g. via cross immunity or competition with benign species).
Theoretical models have revealed the importance of aggregation to the stability of the host
parasite relationship, to parasite evolution and to interspecific parasite interactions. A
number of models have considered the effect of varying aggregation upon these dynamics
with differing outcomes to those where aggregation was a fixed parameter. Here the
stability of the distribution for each of the rabbit helminths was examined using Taylor’s
power law. The analyses revealed that aggregation was not a stable parameter but varied
with month, year, host sex, host age, and host myxomatosis status.
Evidence for the existence of interspecific parasite interactions in natural systems has been
equivocal. Factors influencing parasite intensity were evaluated for the gut helminth. A
network of potential interactions between the parasites was revealed. Only month was
shown to be of greater influence on the community.
Following, from the above analyses, a community model was constructed which
incorporated both seasonal forcing and interspecific parasite interactions, with interaction
mediated via host immunity. One unexpected emergent property was an interaction between
the seasonality and the immune decay rate with slower immune decay resulting in a shift of
the immune response out of phase with the species against which it was produced. The
model was also used to assess the potential effects of two control strategies, an anticestodal
and a single species vaccine. The vaccine had greater effects on the whole community than
the anticestodal because of the immune- mediated interactions.
The host is also an integral part of the community as the parasite dynamics are linked with
that of their host. Therefore an assessment of the parasites’ impact upon host condition and
fecundity was also undertaken. This revealed a variety of positive and negative associations
between the parasites and their host, with potential implications for future host control
strategies.
This study has shown that ignoring parasite-parasite or parasite-host interactions and
interactions of both the host and the parasite with the external environment, could result in a
poor description of the community dynamics. Such complexities need to be considered and
incorporated into theory if future control strategies for either host or parasites are to be
effective.