Original article Symbiotic mutualism with a community of opportunistic ants: protection, competition, and ant occupancy of the myrmecophyte Barteria nigritana (Passifloraceae) Champlain Djiéto-Lordon a , Alain Dejean b , Marc Gibernau b , Martine Hossaert-McKey c , Doyle McKey c, * a Laboratoire de Zoologie, Faculté des Sciences, BP 812, Yaoundé, Cameroon b Laboratoire d’Ecologie Terrestre, Université Toulouse III, 118, Route de Narbonne, 31062, Toulouse cedex, France c Centre d’Ecologie Fonctionnelle et Evolutive, CNRS, 1919 route de Mende, 34293, Montpellier cedex 5, France Received 18 July 2003; accepted 8 March 2004 Available online 17 July 2004 Abstract Barteria nigritana is a myrmecophyte tree of Lower Guinea coastal vegetation. Unlike the more specialised B. fistulosa, which harbours a single host-specific mutualistic ant, B. nigritana is associated with several opportunistic ants. Such symbiotic, yet opportunistic, ant–plant associations have been little studied. On 113 clumps of B. nigritana, we censused ant associates and herbivores and compared herbivory on plants occupied by different ants. In addition to these correlative data, protection conferred by different ant species was compared by herbivore-placement experiments. Identity of ant associate changed predictably over plant ontogeny. Pheidole megacephala was restricted to very small plants; saplings were occupied by either Oecophylla longinoda or Crematogaster sp., and the latter species was the sole occupant of larger trees. Damage by caterpillars of the nymphalid butterfly Acraea zetes accounted for much of the herbivory to leaves. Ant species differed in the protection provided to hosts. While P. megacephala provided no significant protection, plants occupied by O. longinoda and Crematogaster sp. suffered less damage than did unoccupied plants or those occupied by P. megacephala. Furthermore, O. longinoda provided more effective protection than did Crematogaster sp. Herbivore-placement experiments confirmed these results. Workers of O. longinoda killed or removed all larval instars of A. zetes. Crematogaster preyed on only the two first larval instars, and P. megacephala preyed mainly on eggs, only rarely attacking the two first larval instars. Opportunistic ants provided significant protection to this relatively unspecialised myrmecophyte. The usual associate of mature trees was not the species that provided most protection. © 2004 Elsevier SAS. All rights reserved. Keywords: Barteria nigritana; Crematogaster sp.; Oecophylla longinoda; Pheidole megacephala; Acraea zetes; Ant–plant interactions; Protection mutualism 1. Introduction Myrmecophytes, or ant-plants, offer lodging to ants in the form of domatia (e.g., hollow stems or thorns, leaf pouches) and also furnish food, directly in the form of extrafloral nectar and/or food bodies, or indirectly via the excretions of hemipteran trophobionts (“Homoptera” is now recognised to be a paraphyletic grouping within Hemiptera [von Dohlen and Moran, 1995]). Many myrmecophytes are associated with specialist ‘plant-ants’ that nest only in myrmecophytes, often being restricted to a few closely related or ecologically similar host plants. Plant-ants may effectively protect the host-plant against herbivores and sometimes encroaching vines (e.g., Vasconcelos, 1991; Davidson and McKey, 1993; Maschwitz and Fiala, 1995; Vasconcelos and Casimiro, 1997; Moog et al., 1998; Renner and Ricklefs, 1998; Fiala et al., 1999). However, usually more than one species of ant is associated with individuals of a population of myrmeco- phytes, and the degree of protection can vary among ants (e.g., Janzen, 1975; Fowler, 1993; Longino, 1991; Gaume and McKey, 1999). Some myrmecophytes host ant species that are not spe- cialist plant-ants (Alonso, 1998; Rickson et al., 2003). Colo- nies opportunistically occupy myrmecophytes, along with * Corresponding author. E-mail address: mckey@cefe.cnrs-mop.fr (D. McKey). Acta Oecologica 26 (2004) 109–116 www.elsevier.com/locate/actoec © 2004 Elsevier SAS. All rights reserved. doi:10.1016/j.actao.2004.03.007