Jonathan Davies
Relevant Thesis-Based Degree Programs
Affiliations to Research Centres, Institutes & Clusters
Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Biodiversity loss worldwide coincides with an increase in epidemics. This loss of species and reassembly of species communities is thought to be connected to disease transmission via two, opposing, theories: (1) the dilution effect predicts that high species richness can buffer diseases, and therefore higher host diversity lowers disease prevalence or outbreak potential (R0); (2) the amplification effect states that more host diversity creates more opportunity for disease transmission, increasing disease prevalence. Both theories are predicated on the mode of disease transmission (Chapter 2), and the abundance and disease competence of hosts in the community. Defining host competence is complex, but research shows that more closely related species have a higher probability of sharing a pathogen, and thus host competence may reflect phylogeny. To elucidate the mechanisms underlying dilution and amplification effects, this thesis explores the role of host phylogenetic structure on disease outbreak, using epidemiological models that assume the probability of transmission co-varies with the phylogenetic distance between hosts. From a review of multi-host disease transmission (Chapter 3), I compose a multi-host SI model using host phylogeny as a proxy for probability of disease- sharing, and show that even when host species richness has an amplifying effect on disease outbreak potential, it is possible to observe a phylogenetic dilution effect: more phylogenetically diverse host communities have a reduced R0 compared to phylogenetically clustered communities (Chapter 4). I apply this model to an empirical system, bovine Tuberculosis in South Africa, using camera-trap data to infer host contact-rates, which, combined with the phylogenetic host structure, informs transmission rates between species (Chapter 5). I show that the effect of host phylogenetic structure, and the phylogenetic position of the reservoir host (African Buffalo, Syncerus caffer) is more important than contact structure in determining disease outbreak potential, assuming transmission is scaled by the phylogenetic distance between the reservoir (donating) and receiving host. This model suggests that bovine Tuberculosis dynamics are primarily driven by intraspecific transmission within the reservoir host. This work contributes to the disease-diversity debate, and reveals how host phylogenetic community structure may be an important mechanism underlying disease-outbreak potential.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Glacial refugia have likely been important in shaping diversity gradients outside the tropics. However, the biogeographical histories of most species within glacial refugia remain unclear. In this thesis, I examine the geographic range structure and phylogenetic attributes of the mosses of Haida Gwaii, a putative glacial refugium and ‘hotspot’ of moss diversity off the northwest coast of British Columbia. I show that many species have widespread, but disjunct distributions, typically with few close relatives on the islands. I suggest that these features reflect the imprint of glacial history, whereby species within refugia represent isolated populations of previously more widespread species that may have diversified elsewhere. The phylogenetic dispersion of species within high elevation habitats, which best match the climatic regime of the historical glacial refugium, is consistent with the filtering of evolutionarily distinct glacial relicts, and contrasts markedly with the patterns of phylogenetic clustering observed across other habitat types. My study illustrates how the present-day phylogenetic structure of species composition and diversity can reveal the signal of glacial refugia, and help explain why some taxa are more diverse outside of the tropics.
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