Diet selection in captivity by a generalist herbivorous rodent ( Octodon degus ) from the Chilean coastal desert Julio R. Guti´ errez* & Francisco Bozinovic† *Departamento de Biologia, Universidad de La Serena, Casilla 599, La Serena, Chile †Departamento de Ecologia, P. Universidad Cat´ olica de Chile, Casilla 114-D, Santiago, Chile ( Received 28 October 1996, accepted 11 March 1998) Five captive adult female degus ( Octodon degus ) were offered leaves and twigs to eat from three woody ( A desmia bedwellii, Porlieria chilensis and Proustia pungens ) and two suffruticose ( Baccharis paniculata and Chenopodium petiolase ) shrubs that provide cover in their natural habitat. The degus discriminated among the plant species, consuming lower amounts of P. chilensis . Daily body mass losses of degus were significantly higher when they were fed upon P. pungens and P. chilensis . The nutritional value of plants, concomitant with degu nutritional requirements, may explain changes in shrub cover previously found to follow removal of degus from experimental plots. ©1998 Academic Press Keywords: herbivory; feeding ecology; vegetation structure; Chilean desert; Octodon degus Introduction Plant communities are known to be affected by foraging behaviour of small mammals (Davidson et al ., 1985; Palo & Robbins, 1991; Meserve et al ., 1993). The protein to fibre ratio of plants may determine food preferences of mammalian herbivores (Milton, 1979), so that foraging has a differential impact on the structure of plant communities. Herbivorous rodents such as N eotoma and Octodon degus Mol, for example, behaviourally reduce the fibre content of their diet (Justice & Smith, 1992; Bozinovic, 1995). In a Chilean coastal desert (Parque Nacional Fray Jorge), the cover response of shrubs and ephemeral plants to experimental removal of the principal herbivorous rodent ( O. degus , the degu) for a 6-year period (1989–1994) was described by Gutti´ errez et al . (1997). Although diversity and species composition of plant communities at the study site are know to be largely regulated by rainfall, removal of degus had significant effects on shrubs and ephemerals. For example, we found that the shrubs A desmia bedwellii, Baccharis paniculata and Chenopodium petiolare increased their cover after removal of degus. In contrast, cover of the dominant thorn shrubs, Journal of Arid Environments (1998) 39: 601–607 Article No. ae980412 0140–1963/98/040601+ 07 $30.00/0 © 1998 Academic Press