An Agent-Based Model of Golden Eagle Predation on the Santa Cruz Island Fox
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During the 1990s, the endemic Santa Cruz island (SCI) fox (Urocyon littoralis santacruzae) population experienced heavy predation from invasive golden eagles (Aquila chrysaetos) and nearly went extinct. The Island Fox Recovery Program instituted in 2002 has since reestablished the population to normal levels. We have constructed an agent-based model (ABM), which simulates the population dynamics of the SCI foxes in both the absence and presence of golden eagle predation. Geographic information system (GIS) data are integrated into the model to replicate the distribution of multiple vegetation types on the island, and the location of golden eagles’ nests and hunting territories. Using the model, we determine how both island vegetation and predation by golden eagles impacted the spatial density and distribution of the foxes across SCI. Model analysis shows the 10 golden eagles known to reside on the island during the 1990s and 2000s were sufficient to have caused this rapid population decline even without the presence of other factors such as disease or competition. Additionally, model analysis shows that while removal of the golden eagles was necessary for the survival of the SCI fox population, the remaining population of 75–100 foxes had a 90% survival probability without aid. The model we present provides a powerful tool for understanding the spatial and temporal dynamics of the SCI fox population, can be used and adapted to facilitate the further management of the population, and provides a working example in integrating GIS data with ABMs.