Population dynamics of rodents and their parasite communities in a naturally fragmented landscape

Paterson, Victoria Louise (2012) Population dynamics of rodents and their parasite communities in a naturally fragmented landscape. PhD thesis, University of Glasgow.

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An island system with corresponding mainland sites, was used to study
woodland rodent dynamics and their parasite communities within a naturally
fragmented landscape. The study site, hosts and parasite species investigated
within this thesis allowed the investigation of how natural fragmentation affects
demographic and population dynamics of rodents (chapter 3). Reduced habitat
connectivity is known to affect nearly every process in biology. Low degrees of
fragmentation and high connectivity between habitats have been shown to
provide the most stable conditions for populations to persist, as movement of
organisms is less restricted. It is shown that in contrast to previous studies on
fragmented populations, the fragmented landscape of the islands had little
effect on the demographic characteristics of rodent populations in comparison to
those on the mainland. There were few difference found in the demographics of
wood mice and bank voles when compared to mainland sites. The results from
this study then allowed the broader question of how parasites dynamics are
affected by the spatial structure of a host population to be addressed.
Theory predicts that parasites are unable to persist in small, isolated host
populations, due to small host population size as well as potential genetic
factors increasing the risk of extinction. However parasites may become more
prevalent in isolated populations as hosts may have a reduced ability to deal
with infection. It is shown (chapter 4) that within this study system that despite
some island populations being extremely small, there is no overall reduction in
parasite species found within fragmented habitats. Furthermore, extinction of
the parasites investigated within wood mice and bank voles is unlikely due to the
direct life cycle of these parasites. Variation was seen in the prevalence of
infection, however the majority of the parasite species on islands did not show a
reduced prevalence of infection compared to mainland sites.
Finally parasite co-infection and co-aggregation and their dependency on
host characteristics in woodland rodents (chapter 5) were investigated. Parasite
species infecting hosts are normally studied individually, however this is not
what is seen within natural populations. Co-infection is an important concept
within natural systems as there is a vast diversity of parasite species that create ample opportunity for concurrent infections. Therefore, it is proposed that
studies should be focused on parasite interactions, as within host interactions
can in turn affect the abundance and distribution at the level of the host
population. This study focused on seven parasite taxa, and it was found that the
maximum number of parasite species any individual was found to be infected
with was five, with the mean number for both host species at around two.
Parasites associations were also more common than expected within the same
functional groups with co-occurrence being more common between parasite
species associated with ectoparasites. Within this study, host aggregation was
positively correlated with differing parasite taxa. Furthermore, looking at
patterns of co-aggregation could aid in our understanding of parasite
interactions within hosts. The nature of these interactions will determine
whether aggregation is positively or negatively correlated across different
parasite taxa. A small number of hosts maybe responsible for transmitting the
majority of infections (20/80 rule). Identifying these individuals would be
informative in helping to control disease spread. Host characteristics have been
found to be informative in terms of single parasite species infections. Within this
study it was found that juvenile bank voles were more likely to be co-infected
than those within other age classes. No host characteristic explained patterns of
co-infection in wood mice.
In conclusion I found that natural fragmentation does not have an overall
negative effect on rodent host dynamics nor does it reduce the number or
prevalence of infection of parasite species able to infect hosts. This thesis has
highlighted the importance for using natural wildlife systems in empirical
studies, and the need to further address multiple parasite interactions within a
host community.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QH Natural history > QH301 Biology
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
Supervisor's Name: Biek, Dr. Roman
Date of Award: 2012
Depositing User: Dr Victoria Louise Paterson
Unique ID: glathesis:2012-4028
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 16 Apr 2013 09:30
Last Modified: 16 Apr 2013 09:30
URI: https://theses.gla.ac.uk/id/eprint/4028

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