Ant Diversity, from Local to Global Scales: Effects of Environmental Conditions, Community Structure and Biological Invasions

Our understanding of global diversity patterns is largely based on the study of vertebrates and plants. However, the vast majority of described species (and probably undescribed species) are insects. As a consequence, the effort to protect biodiversity is skewed toward a visible minority of organisms while the impacts of human activities on the majority of species are less well known. While the study of diversity of all insects at a large scale or at a global scale is at this point impossible; the study of specific groups of insects, as surrogates for most insect groups, is feasible. The results shown here represent the first attempt to understanding the global distribution of a large group of insects, ants (Formicidae). Ants have been shown to be one of the best surrogates at local and regional scales and are ecologically relevant for the stability and composition of ecosystems. Our results demonstrate that diversity hotspots in ants differ from those observed in vertebrates suggesting that conservation plans established on the basis of the diversity of vertebrate groups might not be optimal for insects. Based on our actual knowledge of ants, two models were designed to identify regions of the globe that have been poorly explored. These described "hotspots of ignorance" also appear to be the most threatened regions in terms of deforestation, therefore leading to the conclusion that many species in these areas could disappear even before they are discovered. Our results bring to light that the development of biodiversity surveys and conservation programs with a special focus on insects is in urgent need.;A key first step in moving from the identification of regions where conservation is critical is documenting the known distribution of species and other taxa. Toward this end, I developed global distribution maps for each of the 300 extant ant genera. Similarly, the inventory of ants of China, the third largest country in the world, represents an important contribution to our knowledge on ant distribution. The Chinese ant fauna is composed of almost 900 species from both the Palearctic and Oriental regions. The analysis also suggests the presence of a third distinct regional fauna on the Tibetan plateau. Finally, the knowledge of ants of China is likely incomplete and comparison of species listed from various regions of Asia suggests evidence for the presence of more diverse fauna in several Chinese provinces.;Among the native species found in Asia, Pachycondyla chinensis represents an interesting example of a successful invasive species in North America. This species was introduced in the United States no later than the 1930s and is now one of the most widespread invasive species in North America. Results from varied forested habitats show that this species can reach very high population density and directly impact the community composition of native species. In areas where P. chinensis was present, both diversity and abundance of native species was negatively affected. This represents one of the few examples of the ability of an invasive species to invade and succeed in habitats that are relatively undisturbed, thus challenging the idea that invasive ants are passengers of human disturbance and not drivers of native species decline.;During the study of P. chinensis, a novel foraging behavior was described, "tandem carrying". This behavior may represent one the most simple recruitment techniques known to ants. To recruit nestmates, a successful scout grabs a worker with its mandibles and carries it directly to the food resource intended for exploitation. Despite its simplicity, the flexibility of this behavior in space and time is important for the effective acquisition of resources in a dynamic and competitive environment.