Can widespread generalist predators affect keystone prey? A case study with red foxes and European rabbits in their native range

Widespread generalist predators may affect declining keystone prey populations. However, this phenomenon is not well understood. In this paper, we assessed whether the abundance and population growth of European rabbits Oryctolagus cuniculus, a keystone prey species in Mediterranean Iberia, was related to the abundance and diet of red foxes, Vulpes vulpes, a widespread generalist predator. In a locality in central Spain, where rabbit population abundance declined, we estimated rabbit abundance during almost 3 years and determined fox abundance and diet during two concurrent years. We calculated a fox predation index (percentage of consumed rabbit biomass × fox abundance) to assess the importance of rabbits to foxes. We employed a multi–model approach to explain rabbit abundance and population growth. Foxes consumed between 60 and 99 % rabbit biomass in their diets, and this was independent of rabbit abundance. Periods of higher fox predation index coincided with lower rabbit density and vice versa. Two models best explained rabbit abundance and four rabbit population growth. They included the fox predation index and its interaction with rabbit abundance during the previous month. Altogether, fox predation, intraspecific density dependence, and their interaction partly explained rabbit population dynamics. We conclude that in order to propel the recovery of the rabbit in Iberia, it is essential to better understand the role of these factors in driving the abundance of the species.
This is a partial result from the I+D National Plan Projects CGL2005-02340, CGL2009-10741 and CGL2013-43197, funded by the Spanish Ministry of Science and Innovation and EU FEDER funds. JFdS benefitted from a FPI PhD scholarship (BES- 2006-12562) funded by the Spanish Ministry of Science and Innovation and the European Social Fund. J. Fernandez-de-Simon and F. Díaz-Ruiz are currently holding a postdoctoral fellowship from Junta de Castilla-La Mancha and the European Social Fund (Operational Programme FSE 2007/2013). M. Delibes-Mateos is currently funded by Junta de Andalucía and the EU FP7, under grant agreement 267226.