Abstract
Emerging infectious vector-borne diseases, that is diseases transmitted by blood-sucking insects that are rapidly increasing in their geographic or phylogenetic range, are on the rise worldwide, having widespread and catastrophic effects on immunologically naïve species. For instance, populations of native wildlife in multiple aquatic and terrestrial systems have been decimated in the past few decades by diseases, altering species abundance and assemblage composition at both small and broad spatial scales, disturbing ecosystem integrity. Interestingly, the common driver behind these emergences lies in anthropogenization of the landscape. Humans, by modifying pristine landscapes toward pastures and encroaching further into natural habitats, have directly or indirectly accelerated the spread of diseases in wildlife. Studying patterns and drivers of such emergences should therefore be of prime importance to disease ecologists. However, the two questions that matter the most to understand disease patterns, the “when” and “where”, are also the most difficult to answer when considering spatial scale, both requiring massive investment in time and resources. Thus, while we have a relatively good knowledge of disease drivers in local systems, it remains difficult to make predictions for other systems or on a broader geographical scale. This thesis focuses on bridging the gap between local processes and large geographical scales, progressing along an increasing ecosystem complexity gradient, using avian malaria - a vector-borne disease - as a model. Avian malaria occurrence has been shown to be on the rise in the New Zealand avifauna, potentially threatening indigenous bird species that are considered to be the most extinction-prone in the world. However, both spatial and temporal transmission patterns are poorly understood despite the impressive body of literature on this disease. Therefore, the goal of my PhD project was to investigate the spatial transmission dynamics of this disease along a spatial continuum ranging from local (~150 km span), to regional (~150000 km2 area), to worldwide scale. In this thesis, I explore the fine-scale spatial and temporal interactions between the intermediate and definitive hosts of this disease, its spread along a longitudinal gradient with the potential for undisturbed landscape to create ecological refuges for endemic species, and the worldwide factors influencing global dynamics of avian malaria among its bird hosts. My results show that avian malaria prevalence in New Zealand wildlife and around the world is mainly driven by abiotic drivers at regional and global scales, but that life history traits of species seems to be the predominant driver at more local scale. For instance, I show that the breeding period of bird species seems to play an important role in synchronizing contact rates between mosquito vectors and bird hosts at local scale, hence increasing avian malaria transmission in wildlife. In addition, increasing the spatial scale of ecosystems also changes the importance of diseases drivers, with temperature and precipitation predominantly shaping the disease landscape. With the current rate of global climate change, I show that an increase in vector-borne disease prevalence is a strong possibility, having potential widespread effects on native fauna around the world.