Authors: Byron Adams, Elias Johnson, D Alejandro Espinosa-Lucas, R Darío Perez-García, Israel Solano-Zavaleta, J Jaime Zúñiga-Vega, Gonzalo A Ramirez-Cruz
Mentors: Byron Adams
Insitution: Brigham Young University
Urbanization has forced animals to respond to novel environments. One of the challenges of urban ecology is that it is unknown if the ecological processes that take place in wild conditions also occur in urban environments. In natural ecosystems, key predators can limit prey abundance and have a widespread effect on trophic levels. Here, we examine a predator-prey interaction in Mexico City, an urban ecosystem where prey can be evaluated in the presence or absence of apex predators. Nearly all original ecosystems in Mexico City have been converted into man-made structures. Many of the green spaces in the city contain populations of the Mexican gray squirrel. These green spaces are also inhabited by different species of raptors, the most frequent being Harris’s hawk, Cooper’s hawk, and sharp-shinned hawk. Little is known about interactions between raptors and squirrels in terms of demographic parameters. We do know, however, that raptors prey on squirrels. We predicted that in parks where raptors were present, there would be fewer squirrels than in parks where there were no raptors. We studied the relationship between raptors and squirrels using occupancy models to determine the environmental factors that affect the presence of both squirrels and raptors. We then tested if the presence of raptors influenced the occupancy probability of squirrels. Lastly, we estimated the abundance of squirrels in parks, both where raptors are present and where they are absent. Contrary to our predictions, we found no evidence that predators predict squirrel abundance. However, we did find evidence that the presence of raptors can be predicted by the abundance of squirrels. These results suggest that this predator-prey interaction in Mexico City parks could be relatively recent and still not in equilibrium, or that other factors may be affecting the dynamics between these two urban populations.