Master of Arts
Date of Defense
Patricia Parker, PhD
The recently discovered presence of a species of Plasmodium infecting the endangered Galapagos penguin (Spheniscus mendiculus) potentially threatens their long-term persistence. However, not much information is available on the transmission dynamics of Plasmodium in Galapagos or the impact of the parasite on infected penguins. The present work takes the model of the Galapagos penguin population devised by Vargas et al. (2007)—which did not include any impacts from disease—and adds a simple model of infection. Two variables—the probability of an individual becoming infected each year, and the increase in annual mortality caused by infection—define the dynamics of the disease component of the model; the stress from El Niño events could also affect infected individuals in different ways, and so three forms of stress-induced relapse are explored as well. The entirety of parameter space is explored for all three relapse scenarios. All the models show a high impact due to mortality from infection, and there are large parts of parameter space that have a 0% probability of persistence over the next 100 years. The probability of persistence decreases substantially if relapse events occur during all El Niño events, weak and strong. Increasing the breeding success of the population provides a modest benefit, but does not reverse the overall trend. In order to estimate the mortality that might be associated with Plasmodium infection, a comparison was made between census data from 1998–2009 and model predictions based on these same years. The models differed in their level of mortality from infection, and a range of plausible parameter values was determined from the best-fitting models; these ranged from 0–10% to 0–15%, depending on the type of relapse modeled. Even at these relatively low levels of impact, Plasmodium infection still has the potential to drastically reduce the probability of persistence of the penguin population over the next 100 years.
Meile, Robert James, "Modeling the potential effects of Plasmodium infection on the Galapagos penguin (Spheniscus mendiculus)" (2012). Theses. 35.