Everything old is new again: robust predictive frameworks for shifting host-pathogen interactions in the face of global change
Disease ecology urgently requires powerful predictive tools that anticipate the links between global change and emerging infectious disease. However, the ecological context of emerging disease remains poorly understood, especially given that the majority of parasites in any given ecosystem have no direct impact on human health. This dissertation explores a global change biology approach to host-pathogen interactions, focused on understanding both positive and negative impacts of climate change on parasites and pathogens. Chapter 1 reviews current theory surrounding extinction, including mathematical modeling approaches at scales from population extirpation up through global extinction rates. Community-level approaches to extinction risk estimation are applied in Chapter 2, which includes forecasts for climate-driven range shifts based on the largest macroparasite occurrence dataset yet assembled. Up to a third of parasites could face extinction in a changing climate, especially accounting for co-extinction with hosts. However, we find no evidence that wildlife parasites face better or worse odds of survival (or have different hotspots of diversity) based on their potential to infect humans. The results of this study indicate the hundreds of thousands, or potentially millions, of parasitic species on Earth are likely to be redistributed around the globe in a hard to predict pattern, with unknown effects on wildlife and human health. The same species distribution modeling methods from Chapter 2 are used in Chapter 3 to predict the global distribution of Zika virus, an emerging infection from 2016 with a still largely unresolved eco-epidemiology. The conflict among different models and modeling approaches surrounding Zika's distribution is considered in Chapter 4, by interfacing these models with simulations of potential epidemics in the United States. Overall, this dissertation addresses the idea that in the face of global change, ecologists will play an increasingly important role in predicting shifting landscapes of disease. However, the overwhelming focus on emergence ignores the importance of extinction as a potentially complementary phenomenon within ecosystems; and the varied approaches within ecology, and the short timescale on which ecologists work during current outbreaks, pose a disciplinary problem with no clear answer.