Abstract: Group hunting, nomadism, wingless queens and colony fission characterize army ants, allowing them to have become the main tropical arthropod predators, mostly of other social insects. We studied the reactions of different ant species to the New World army ants Eciton burchellii (WESTWOOD, 1842) and E. hamatum (FABRICIUS, 1782) (Ecitoninae). We compiled our results with those already known in a synthetic appendix. A wide range of ant species react to the ap-proach of army ant raids by evacuating their nests with several workers transporting brood. The Eciton plunder a large part of the brood but rarely kill workers or queens, so that the latter return to their nest and resume colony activity. One exception is Paratrechina longicornis (LATREILLE, 1802) colonies that quickly evacuate their nest, so that the entire col-ony can generally escape a raid. Another is Leptogenys mexicana (MAYR, 1870) that leave their nests in columns while some nestmates resist the attack; they therefore lose only a few larvae. We noted that colonies can avoid being raided if the army ants ignore them (Atta cephalotes (LINNAEUS, 1758)), or if the workers produce a repellent substance (Azteca associated with myrmecophytic Cecropia) or are repellent themselves (Pachycondyla villosa (FABRICIUS, 1804), Ec-tatomma spp.). In the other cases, a part of the brood is lost. When an Eciton raid approached the base of their host-tree trunk, Azteca andreae GUERRERO, DELABIE and DEJEAN, 2010 workers dropped a part of their brood on the ground. While numerous Eciton workers were gathering up this brood, the front of the column advanced, so that the Azteca andreae nests were not plundered. Pheidole megacephala (FABRICIUS, 1793) nests were partly plundered as the workers reacted aggressively, blocking the Eciton inside their nests during a long time. When the latter returned toward their bivouac, they were attacked and killed by their nestmates whether or not they had retrieved Pheidole brood. Consequently, the front of the column turned away from the Pheidole nest.

Abstract: The diversion of a host's energy by a symbiont for its own benefit is a major source of instability in horizontally-transmitted mutualisms. This instability can be counter-balanced by the host's retaliation against exploiters. Such responses are crucial to the maintenance of the relationship. We focus on this issue in an obligate ant-plant mutualism in which the ants are known to partially castrate their host plant. We studied plant responses to various levels of castration in terms of (1) global vegetative investment and (2) investment in myrmecophytic traits. Castration led to a higher plant growth rate, signalling a novel case of gigantism induced by parasitic castration. On the other hand, completely castrated plants produced smaller nesting and food resources (i.e. leaf pouches and extra floral nectaries). Since the number of worker larvae is correlated to the volume of the leaf pouches, such a decrease in the investment in myrmecophytic traits demonstrates for the first time the existence of inducible retaliation mechanisms against too virulent castrating ants. Over time, this mechanism promotes an intermediate level of castration and enhances the stability of the mutualistic relationship by providing the ants with more living space while allowing the plant to reproduce. © 2013 Springer Science+Business Media New York.

Abstract: The strongly fragrant thermogenic inflorescences of Taccarum ulei (Araceae) are highly attractive to nightactive scarab beetles of Cyclocephala celata and C. cearae (Scarabaeidae, Cyclocephalini), which are effective pollinators of plants in the wild in northeastern Brazil. GC-MS analysis of headspace floral scent samples of T. ulei established that two constituents, (S)-2-hydroxy-5- methyl-3-hexanone (an aliphatic acyloin rarely detected in flowers) and dihydro-b-ionone (an irregular terpene) accounted for over 96% of the total scent discharge. Behavioral tests (in both field and cages) showed that male and female C. celata and C. cearae were attracted to traps baited with a synthetic mixture of both compounds; however, they were also responsive to (S)-2-hydroxy-5-methyl-3-hexanone alone, which thus functions as a specific attractive cue. These findings support other recent research in suggesting that angiosperms pollinated by cyclocephaline scarab beetles release floral odors of limited complexity in terms of numbers of compounds, but often dominated by unusual compounds that may ensure attraction of specific pollinator species. © 2013 Elsevier B.V.

Abstract: The future of tropical managed forests is threatened by climate change. In anticipation of the increase in the frequency of drought episodes predicted by climatic models for intertropical regions, it is essential to study commercial trees' resilience and vulnerability to water stress by identifying potential interaction effects between selective logging and stress due to a lack of water. Focusing on 14 species representing a potential or acknowledged commercial interest for wood production in the Guiana Shield, a joint model coupling growth and mortality for each species was parametrized, including a climatic variable related to water stress and the quantity of aboveground biomass lost after logging. For the vast majority of the species, water stress had a negative impact on growth rate, while the impact of logging was positive. The opposite results were observed for the mortality. Combining results from growth and mortality models, we generate vulnerability profiles and ranking from species apparently quite resistant to water stress (Chrysophyllum spp., Goupia glabra Aubl., Qualea rosea Aubl.), even under logging pressure, to highly vulnerable species (Sterculia spp.). In light of our results, forest managers in the Guiana Shield may want to conduct (i) a conservation strategy of the most vulnerable species and (ii) a diversification of the logged species. Conservation of the already-adapted species may also be considered as the most certain way to protect the tropical forests under future climates. © 2016 by the authors.

Abstract: While attention on logging in the tropics has been increasing, studies on the long-term effects of silviculture on forest dynamics and ecology remain scare and spatially limited. Indeed, most of our knowledge on tropical forests arises from studies carried out in undisturbed tropical forests. This bias is problematic given that logged and disturbed tropical forests are now covering a larger area than the so-called primary forests. A new network of permanent sample plots in logged forests, the Tropical managed Forests Observatory (TmFO), aims to fill this gap by providing unprecedented opportunities to examine long-term data on the resilience of logged tropical forests at regional and global scales. TmFO currently includes 24 experimental sites distributed across three tropical regions, with a total of 490 permanent plots and 921 ha of forest inventories. To improve our knowledge of the resilience of tropical logged forests, 20 research institutes are now collaborating on studies on the effects of logging on forest structure, productivity, biodiversity and carbon fluxes at large spatial and temporal scales. These studies are carried out in the Tropical managed Forests Observatory (TmFO), an international network including 24 sites and 490 permanent sample plots across South America, Africa and South East Asia.