My main scientific interests focus on biotic interactions among organisms. I explore how animals and plants interact with each other and among themselves. A major goal is to improve our understanding of the functioning of biological communities, by identifying both the proximal mechanisms and the underlying selective forces that shape complex relationships such as mutualism and competition. My works also fit into efforts to better integrate biotic interactions into studies of major ecological changes such as biological invasions.

To date, I have focused on different kinds of interactions that insects have both among them and with various organisms including plants or fungi. Using approaches of behavioural, nutritional or chemical ecology, I combine field and laboratory experiments to exlpore the complex, sometimes indirect ways through which these organisms interact.

Ecological interactions and conservation 

(Temporary teaching and research assistant - Université Lyon 1, France)

As a research assistant in the ECC team of the LEHNA, I investigated the importance of both inter- and intra-specific interactions in conservation issues.

Some argue that species interactions must be an integral part of conservation efforts. This is particularly obvious when a threatened species maintain close associations with other organisms. Such is the case of some Lycaenid butterflies whose complete life cycle requires specific plants and ants. I took part in a study characterizing the relationships among the abundances of the three interacting species in grasslands of the Rhône-Alpes french region. This work will provide both methodological recommendations for conservation managers and new insights in the community context of the plant-butterfly-ant interactions.

Intra-specific interactions, on the other hand, are more commonly taken into account in conservation strategies. In some systems, however, their detailed study is still crucially needed to improve our understanding of challenging ecological problems. I undertook such an approach by conducting experiments to unravel the social organization of the invasive ant Lasius neglectus and, ultimately, uncover its invasion history at a regional scale in the Rhône valley.

Impact of an invasive wasp on native ant communities

(Post-doc Victoria University of Wellington, New Zealand)

The common wasp, Vespula vulgaris was accidentally introduced in New Zealand in the late 1970's, and quickly invaded the whole country. Beech forests are particularly favorable to the species: abundant scale insects live there, and produce a large amount of honeydew. This sugar-rich resource is heavily used by wasps, so that their population density in this habitat is now one of the highest in the world. As a predator and competitor, V. vulgaris can negatively affect a wide range of native organisms. 

Working in the team led by Phil Lester at the CBRE,
my aim was to assess the impacts of invasive wasps on native ant communities. I examined how ants and wasps interact in the field, wether they interact directly (when foraging for the same prey) or indirectly (when honeydew collection by wasps reduce the amount of this resource for other consumers like ants). I also studied how ants respond, both individually and collectively, to variations in macronutrient availability.

This work showed that behavioural plasticity can play an important role not only in the ecological success of invasive species, but also in the ability of native species to co-exist with invaders. It also highlights the needs for more studies linking diet and behaviour, because they can shed light on the mechanisms behind biological invasions and food competition in general.

Obligate ant-plant mutualism

(PhD - EDB/Université Toulouse III, France - Supervisors: A. Dejean and J. Orivel)

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.ThèseJG-pdf

Ecology of  the little fire ant
Wasmannia auropunctata in its native range

(Master - EDB/Université Toulouse III, France - Supervisor: J. Orivel)

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 French Guiana. My contribution to this project concerned the populations found in human-disturbed areas, such as forest fragments or roadsides.
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: B. Holzer and M. Chapuisat)

(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: G. Lempérière).