Sarah Groc

Defense: December, 9th. 2011

Diversity and structure of leaf-litter ant assemblages in French Guianese pristine forests and anthropized areas (agroecosystems).

Among invertebrates, which are not commonly recognized as good indicators of terrestrial ecosystem health, ants are the exception. Indeed, they are currently used for evaluating and monitoring environmental changes in some parts of the world.

The overall aim of my Ph.D. research is to describe and understand the diversity patterns of leaf-litter ant assemblages at regional and local scales, in French Guianese pristine and anthropized forested areas.

At regional scale, the diversity patterns of leaf-litter ant assemblages are expected to change depending on the east-west gradient, because of the geographic distance, the pluviometry or environmental gradients. Likewise, at local scale, these parameters are influenced by environmental and microclimatic conditions in pristine forests, while they are neither lightly nor deeply changed in plantations of more or less exotic essences.

Ants were collected with two sampling methods in four French Guianese localities following a standard protocol. At lab, they were sorted, mounted to constitute several reference collections, and finally identified to species level. Incidence matrices were then made, before being integrated in an ant dataset and treated with different statistic tools.

Specific richness, species density per m² as well as taxonomic and functional structures of leaf-litter ant assemblages both vary at regional and local scales. Locally, these variations lead to more or less heterogeneous assemblages, which are composed of wide-distributed species associated with a group of more or less habitat-specific species. In pristine forests, the specific diversity is particularly high, and several species new to science were discovered. Finally, at local scale, replacing forest by plantations generally deeply changes the leaf-litter ant assemblages, and can favor the introduction of species well adapted to disturbance (like tramp or invasive species). However, cacao plantations seem to shelter ant assemblages close to that of the surrounding forest matrix contrary to the plantations of acacias, heveas or Caribbean pines.

Directors

- Alain Dejean

- Jacques Delabie, Cocoa Research Center (CEPEC), Santa Cruz State University (UESC) – Bahia, Brazil.

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