My main scientific interests focus on biotic interactions among organisms. I am interested in identifying both the proximal mechanisms and the underlying selective forces that shape complex relationships such as mutualism and competition. To date, I have focused on different kinds of interactions involving social insects, combining field and laboratory experiments.
- Competitive and mutualistic interactions
Role of competition in the structuration of communities
- Biological invasions
Interactions between native and introduced species
Comparison of native and introduced populations
- Social insects (ants, wasps)
- Plant/insect interactions
- Tropical and temperate communities
- Behavioural and chemical ecology approaches
2008-present: Impact of an invasive wasp on native ant communities
(Post-doctoral fellowship - School of Biological Sciences, Victoria University of Wellington, New Zealand - Director: Dr. Phil Lester)The common wasp (Vespula vulgaris) has been introduced in New Zealand in the late 1970’s. These wasps have successfully invaded the beech forests, where they consume the abundant honeydew produced by endemic scale-insects. They reach very high densities here and, as a predator and competitor, they could have an impact on a variety of native animals. My aim is to study the impacts that Vespula vulgaris could have on native ant communities through food competition. This requires studying how ants and wasps interact but also getting a better biological knowledge of the little-known native ant species.
2004-2008: Obligate ant-plant mutualism
The evolutionary stability of mutualisms, or mutually beneficial interactions between species, raises a lot of questions. In theory, shifts to unidirectional exploitation are often possible as former mutualists evolve towards parasitism or because external non-mutualist organisms interfere with established associations. Paradoxically, mutualisms are everywhere. How can they persist in the face of these destabilizing pressures?
I explored this question in the Guianian myrmecophyte Hirtella physophora, a shrub bearing leaf pouches that lives in pristine rainforests, and its almost exclusive inhabitant, the ant Allomerus decemarticulatus. First, I examined all the effects that the partners have on each other. Ants represent an optimal, indirect defence against herbivores, mainly as a by-product of their foraging activity. Plants provide shelter and nectar, as well as conditions favoring the use of an exclusive territory. I argue that the global functioning of this mutualism corresponds to the concept of pseudoreciprocity, a situation limiting the possibilities of conflict between partners. Besides, I studied the encounter of the two partners to determine what prevents the presence of intruders. I experimentally tested the role interspecific competition, selective filters and host recognition by the queens could have. The last mechanism, rarely demonstrated, proved to be prominent and could contribute to the structuring of a compartmentalized community that favors the perpetuation of very specific associations.
Grangier J. 2008. Stabilité évolutive d'un mutualisme plante/fourmis obligatoire et spécifique. Thèse de doctorat, Université Paul Sabatier,183pp.
2003-04: Ecology of the little fire ant Wasmannia auropunctata in its native range
Native to the Neotropics, the little fire ant Wasmannia auropunctata is one of the most problematic invasive ants known, with accompanying ecological and economical consequences in the numerous areas where it has been introduced.
One of the aims of our group was to study the ecology of this ant species in its native range, in
I collected extensive demographic data that confirmed the dominant status of these native populations. I also evaluated the possible mechanisms behind a surprising coexistence between such dominant populations and Cyphomyrmex fungus-growing ants, by using both behavioural and chemical approaches.
Grangier J. 2004. Les populations envahissantes de la fourmi Wasmannia auropunctata (Roger) dans sa zone d'origine: caractérisation, comparaison avec une zone d'introduction, et interactions avec l'entomofaune. Mémoire de DEA, Université de Toulouse,29pp.
Previous research works
2003 (3 months)Supercolonies in the wood-ant Formica paralugubris: recognition and aggressiveness (Institut d'Ecologie, Lausanne, Switzerland - Supervisors: Dr B. Holzer and Pr. M. Chapuisat)
2001-02 (4 months)
Mountain forest ecology: snag management and conservation of the fauna associated to dead wood (Coleoptera and Hymenoptera) (University of Grenoble I / Parc Naturel Régional des Hauts-Plateaux du Vercors, France - Supervisor: Pr. G. Lempérière).