POPULATION ECOLOGY - ORIGINAL PAPER High red deer density depresses body mass of roe deer fawns Emmanuelle Richard • Jean-Michel Gaillard • Sonia Saı ¨d • Jean-Luc Hamann • Franc ¸ois Klein Received: 25 July 2009 / Accepted: 24 November 2009 / Published online: 24 December 2009 Ó Springer-Verlag 2009 Abstract Many previous studies have pointed out that, when resources are limited, the potential for competition should be high among sympatric species that display overlaps in habitat and nutritional niches. However, reli- able evidence of competition between red deer (Cervus elaphus) and roe deer (Capreolus capreolus) has not been yet reported for life history traits directly measuring per- formance such as body mass, reproduction, or survival. From long-term monitoring of deer populations in the reserve of La Petite Pierre (France), we measured the sex- specific responses of roe deer fawn body mass to changes in red deer density after accounting for possible con- founding effects of date of shooting, climatic conditions, and roe deer density. As expected under the hypothesis of competition, red deer density in a given year had a marked negative influence on body mass of roe deer fawns born the same year and the following year. Fawn mass of roe deer males and females responded in similar ways to changes in red deer density. Our study provides the first evidence of a negative response of roe deer performance to high red deer density. Keywords Inter-specific competition Á Herbivores Á Density dependence Á Individual performance Á Sympatric species Introduction Interactions among individuals influence population dynamics and thereby species distribution (Begon et al. 2006). For example, on northern European coasts, Brent Geese have better feeding conditions thanks to facilitation by herbivores such as hare, rabbit, cattle and sheep (van der Wal et al. 2000). Competition is expected to be the most common interaction for large herbivores in the absence of large predators (Putman 1996). The most frequent type of competition among large herbivores is exploitation com- petition (Dolman and Wa ¨ber 2008), which occurs when the use of a resource by one individual reduces the availability of that resource to another individual [Johnson et al. (2000) for an example in mule deer Odocoileus hemionus and elk Cervus elaphus]. Many studies have suggested that, when resources are limited, the potential for competition is high among sympatric species of large herbivores, which often have overlaps in habitats and nutritional niches [Bartos et al. (2002) for white-tailed deer Odocoileus virginianus, fallow deer Dama dama, red deer Cervus elaphus, and roe deer Capreolus capreolus; Focardi et al. (2006) for roe deer and fallow deer; Hemami et al. (2004) for roe deer and muntjac Muntiacus reevesi; Marshal et al. (2008) for feral ass Equus asinus and mountain sheep Ovis canadensis]. However, even if competition is possible, deer species of different size can coexist by having different rates of food extraction (Jarman 1974). This corresponds to the Jarman-Bell principle developed to explain the coexistence among African ungulates by a partitioning of food Communicated by Jo ¨rg Ganzhorn. E. Richard Á J.-M. Gaillard (&) Unite ´ Mixte de Recherche no. 5558, Biome ´trie et Biologie Evolutive, Universite ´ Lyon 1, 43 boulevard du 11 novembre 1918, 696220 Villeurbanne Cedex, France e-mail: gaillard@biomserv.univ-lyon1.fr S. Saı ¨d Á J.-L. Hamann Á F. Klein Office National de la Chasse et de la Faune Sauvage, Centre National d’Etudes et de Recherches Applique ´es, Cervide ´s Sanglier, 1 place Exelmans, 55000 Bar Le Duc, France 123 Oecologia (2010) 163:91–97 DOI 10.1007/s00442-009-1538-z