Doctor of Philosophy / Department of Electrical and Computer Engineering / Caterina Scoglio / Vector-borne diseases not only cause devastating economic losses, they also significantly impact human health in terms of morbidity and mortality. From an economical and humane point of view, mitigation and control of vector-borne diseases are essential. Studying dynamics of vector-borne disease transmission is a challenging task because vector-borne diseases show complex dynamics impacted by a wide range of ecological factors. Understanding these factors is important for the development of mitigation and control strategies. Mathematical models have been commonly used to translate assumptions concerning biological (medical, demographical, behavioral, immunological) aspects into mathematics, linking biological processes of transmission and dynamics of infection at population level. Mathematical analysis translates results back into biology. Classical deterministic epidemic models do not consider spatial variation, assuming space is homogeneous. Spatial spread of vector-borne diseases observed many times highlights the necessity of incorporating spatial dynamics into mathematical models. Heterogeneous demography, geography, and ecology in various regions may result in different epidemiological characteristics. Network approach is commonly used to study spatial evolution of communicable diseases transmitted among connected populations. In this dissertation, the spread of vector-borne diseases in time and space, is studied to understand factors that contribute to disease evolution. Network-based models have been developed to capture different features of disease transmission in various environments. Network nodes represent geographical locations, and the weights represent the level of contact between regional pairings. Two competent vector populations, Aedes mosquitoes and Culex mosquitoes, and two host populations, cattle and humans were considered. The deterministic model was applied to the 2010 Rift Valley fever outbreak in three provinces of South Africa. Trends and timing of the outbreak in animals and humans were reproduced. The deterministic model with stochastic parameters was applied to hypothetical Rift Valley fever outbreak on a large network in Texas, the United States. The role of starting location and size of initial infection in Rift Valley fever virus spread were studied under various scenarios on a large-scale network. The reproduction number, defined as the number of secondary infections produced by one infected individual in a completely susceptible population, is typically considered an epidemic threshold of determining whether a disease can persist in a population. Extinction thresholds for corresponding Continuous-time Markov chain model is used to predict whether a disease can perish in a stochastic setting. The network level reproduction number for diseases vertically and horizontally transmitted among multiple species on heterogeneous networks was derived to predict whether a disease can invade the whole system in a deterministic setting. The complexity of computing the reproduction number is reduced because the expression of the reproduction number is the spectral radius of a matrix whose size is smaller than the original next generation matrix. The expression of the reproduction number may have a wide range of applications to many vector-borne diseases. Reproduction numbers can vary from below one to above one or from above one to below one by changing movement rates in different scenarios. The observations provide guidelines on executing movement bans in case of an epidemic. To compute the extinction threshold, corresponding Markov chain process is approximated near disease free equilibrium. The extinction threshold for Continuous-time Markov chain model was analytically connected to the reproduction number under some assumptions. Numerical simulation results agree with analytical results without assumptions, proposing a mathematical problem of proving the existence of the relationships in general. The distance of the extinction threshold were shown to be closer to one than the reproduction number. Consistent trends of probability of extinction varying with disease parameters observed through numerical simulations provide novel insights into disease mitigation, control, and elimination.

A wide range of ecological communities ranging from polar terrestrial to tropical marine environments are affectedby global climate change. Over the last century, atmospheric temperature has increased by an average of 0. 60 C andis expected to rise by 1.1- 6.40C over the next 100 years. This rising temperature has increased the intensity andfrequency of weather extremes due to which a large number of species are facing risk of extinction. Studies haveshown that species existing on lower latitude are more sensitive to temperature variability compared to speciesexisting on higher latitude but temperature is increasing rapidly in higher latitude compare to lower latitude. Thisuneven distribution of temperature sensitive species and warming rate has highlighted the need for combined studiesof temperature variability and sensitiveness of species to predict how the ecosystems will respond to increasinglyvariable climate. Using a generalized Rosenzweig-MacArthur model, I explored how temperature variability andsensitivity of species will affect the extinction risks of species and how the connectance and species-richness ofecological communities will govern this response. This study showed that the risk of extinction of species mostlydepends on their sensitivity to temperature deviation from the optimum value and level of temperature variability.Among these two, sensitivity of species to temperature deviation was most prominent factor affecting extinction risk.In this study, connectance did not show any effect on mean extinction risk and time taken by a certain proportion ofspecies to reach pre-defined extinction thresholds. But, species-richness showed some effect on mean extinction riskof species. It was found that risk of extinction of species in species-rich communities was higher compared tospecies-poor communities. Species-rich communities also took shorter time before they lost 1/6 of the species. Thepresent study also suggests a possible tipping point due to increasing temperature variability in near future. In furtherstudies, different sensitivity of species at different trophic levels and the possible evolution of sensitivity of speciesshould also be consider while predicting how ecological communities will respond to changing climate in the longrun.

Studien syftar till att testa teorier om effekter av habitatstorlek, konnektivitet, områdesskydd, habitatmängd och fragmentering på enskilda arters förekomstmönster, samt undersöka existensen av fragmenteringströskel och utdöendetröskel. Förekomstdata för revlummer Lycopodium annotinum och mattlummer Lycopodium clavatum har insamlats i 61 skogsfragment utspridda i 10 kartrutor à 2,5×2,5 km i landskapet Södermanland. I vardera skogsfragment undersöktes en yta om 500m2. Revlummer förekom i 13 och mattlummer i 10 av de undersökta skogsfragmenten. I 7 kartrutor förekom revlummer i minst 1 skogsfragment, för mattlummer var motsvarande siffra 8 kartrutor. Resultaten visar att habitatstorlek har en signifikant positiv effekt på förekomst av revlummer och mattlummer samt att konnektivitet har en signifikant positiv effekt på förekomst av mattlummer. Områdesskydd, habitatmängd och fragmentering i landskapet har ingen påvisad effekt på förekomst av dessa arter och ingen fragmenteringströskel eller utdöendetröskel har hittats. Dessa resultat indikerar att ett bevarande av skogsfragment med stor storlek och hög konnektivitet är viktigt för de undersökta arternas fortsatta livskraft. / The aim of this study is to test theories of the effects of habitat size, connectivity, area protection, habitat amount and fragmentation on the occurrence of single species, plus examining the existence of a fragmentation threshold and an extinction threshold. Occurrence of stiff clubmoss Lycopodium annotinum and stag’s-horn clubmoss Lycopodium clavatum was examined in 61 forest fragments scattered over 10 large 2,5×2,5 km plots, located in the county of Stockholm in Sweden. In each forest an area covering 500m2 was searched for the two species. Lycopodium annotinum occured in 13 and L. clavatum in 10 of the investigated fragments. Lycopodium annotinum occurred in at least 1 fragment in 7 large plots, 8 large plots was the corresponding number for L. clavatum. The results showed a significant positive effect of habitat size on the occurrence of both species and a significant positive effect of connectivity on the occurrence of Lycopodium clavatum. Area protection, habitat amount and fragmentation had no observed effect on the occurrence of these species, and no fragmentation threshold or extinction threshold was found. These results indicate the importance of preserving large forest fragments with high connectivity, to assure continued viability of the examined species.

Noteworthy species endemic to the Galapagos Islands off Ecuador are two flightless birds, the Galapagos Penguin (Spheniscus mendiculus) and Flightless Cormorant (Phalacrocrax harrisi). Both adapted increased swimming ability at the cost of flight. This however has limited their ability to find richer feeding grounds in times of low resource availability, or to escape potential predators. Their population numbers, though small, were stable. Stress on this stability has increased since human arrival. Various invasive species from pets, farm animals and rats to even mosquito vectors of avian disease accompanied humans. . El Nino Southern Oscillation or ENSO cycles of warm waters in the Pacific Ocean south of the Equator cause drastic drops in food sources for all Galapagos seabirds. Serious ENSO events in 1983 and 1998 caused some species’ populations to drop by as much as 77%. Periodic less severe cycles may help explain how population recovery has not rebounded to earlier numbers. Reduced chick survival and adult fecundity seem to occur in concert with mild events. With available data and use of a modeling approach, this study focuses and explores their situations. Restoring population stability may include use of models, species monitoring, conservation and limiting invasive species. Usher matrices based on different climate conditions were produced using data combined from current and past census counts and weather. Models are used to compare available census data and test reliable predictors. Climate data from National Oceanic and Atmospheric Administration and the University of Florida provides for testing predictions of current and probable future climate change. Life histories of both species are regarded. Results suggest the current Cormorant population is still stable. The Penguin, however, faces a 20% probability of extinction in 100 years if current conditions remain. Extinction probability rises to 60% if climate change continues to worsen. Interventions such as captive breeding could be suitable for population recovery.