Acorn preference under field and laboratory conditions by two flightless Iberian dung beetle species (Thorectes baraudi and Jekelius nitidus): implications for recruitment and management of oak forests in central Spain

Abstract

1. Recently, a mutualistic relationship has been described between some dung beetles (Thorectes lusitanicus and Mycotrupes lethroides) and oak species (Quercus suber, Q. canariensis, and Q. rubra), which could be crucial for ensuring seedling recruitment and sustaining the equilibrium of oak populations. For T. lusitanicus, a diet based on acorns during the reproductive period improved resistance to low-temperature conditions and improved ovarian development. 2. In this paper, we conducted field and laboratory experiments to investigate the interaction between two potential acorn-eating beetles, Thorectes baraudi and Jekelius nitidus, with Quercus suber. We determined the feeding preferences of both beetle species and estimated the rates of acorn manipulation by beetles according to habitat structure and several characteristics of the acorn, such as seed size and acorn infestation by weevils. 3. Results demonstrated the positive interaction between the dung beetle Thorectes baraudi and Quercus trees. Thorectes baraudi was clearly more attracted to volatiles of acorns than to dung. Jekelius nitidus, on the contrary, was either not or anecdotally attracted to acorns. On the contrary, in the case of Jekelius nitidus, the acorn attraction could be considered anecdotal or even accidental. Our field results demonstrated the acorn burying behaviour of T. baraudi in the oak forests of the Cabaneros National Park (Spain), suggesting a potential role of this beetle species as an active secondary acorn disperser. 4. This unexpected behaviour could be particularly important in Mediterranean oak forests and savannahs, where most Quercus species are strongly recruitment limited because of serious overgrazing problems.