RESEARCH ARTICLE Ownership, size and reproductive status affect the outcome of food ball contests in a dung roller beetle: when do enemies share? Ivette A. Chamorro-Florescano • Mario E. Favila • Rogelio Macı ´as-Ordo ´n ˜ez Received: 30 October 2009 / Accepted: 4 September 2010 / Published online: 19 September 2010 Ó Springer Science+Business Media B.V. 2010 Abstract Theory predicts that asymmetry between contenders influences their ability to defend resources. More recently, some theoretical approaches have also examined the circumstances that might promote sharing of the disputed resources. We tested these hypotheses in males of the ball roller beetle Canthon cyanellus cyanellus. Males fight for possession of a food ball, which is a vital resource used for nesting. We evaluated the role of food resource ownership, body size and reproductive status on the outcome of contests (win, lose or share) between males that rolled a food ball (owners or finders) either alone or with a female partner, when faced with male intruders (or joiners). Large owners of a food ball had a higher probability of victory than small intruders, and small owners had a high probability of losing when faced with large intruders. The reproductive status of both contenders also influenced their chances of winning: previously mated owners of a food ball had a higher probability of winning than virgin owners. Males of a similar size tended to split the food ball, thereby sharing the resource. Our results suggest that competitors may adjust the intensity of their aggression depending at least on their own resource holding power (RHP), the value of the resource in dispute and perhaps even the RHP of their opponents. Sharing the food ball emerges as a fresh solution between similarly matched contestants. Keywords Asymmetric contests Á Canthon cyanellus cyanellus Á Foraging competition Á Resource holding power Á Food sharing Á Roller beetles I. A. Chamorro-Florescano Facultad de Ciencias Biolo ´gicas y Agropecuarias, Universidad Veracruzana, Campus Tuxpan. Carretera Tuxpan a Tampico km. 7.5, C.P. 92860 Tuxpan Veracruz, Mexico M. E. Favila (&) Red de Ecoetologı ´a, Instituto de Ecologı ´a, A.C, Apartado Postal 63, C.P. 91000 Xalapa, Veracruz, Mexico e-mail: mario.favila@inecol.edu.mx R. Macı ´as-Ordo ´n ˜ez Red de Biologı ´a Evolutiva, Instituto de Ecologı ´a, A.C, Apartado Postal 63, C.P. 91000 Xalapa, Veracruz, Mexico 123 Evol Ecol (2011) 25:277–289 DOI 10.1007/s10682-010-9428-8