Jean-Paul Lachaud | ECOSUR - Academia.edu (original) (raw)
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Papers by Jean-Paul Lachaud
Sociobiology
regular dispersion patterns in the spatial distribution of ant nests are linked to both defense o... more regular dispersion patterns in the spatial distribution of ant nests are linked to both defense of foraging areas and competition for food. They are frequently observed amongst colonies of conspecifics when the availability of colony foundation sites is homogeneous. In order to evaluate the degree of intraspecific competition in the dominant Neotropical ectatommine ant Ectatomma ruidum and the importance of interactions with another dominant sympatric ectatommine ant, E. tuberculatum, we examined the spatial relationships among colonies of these two species in an area with a naturally very high nest density (up to 11500 and 1500 nests/ha, respectively). Data were analyzed by calculation of the clark and Evans nearest neighbor index and by statistical comparison of the observed mean distance to the nearest neighbor and a theoretical value obtained by Monte-carlo simulation. The latter procedure allowed analysis of spatial relationships despite the nonhaphazard location of E. tuberculatum nests, which were always found at the base of a tree. Whatever the nest density, the mean distance between nearest neighbor nests of E. ruidum was always higher than that expected for random distribution. This regular dispersion pattern strongly supports the hypothesis that E. ruidum colonies are monodomous. In the three quadrats where they co-occurred, E. ruidum and E. tuberculatum were independently distributed, suggesting a low level of interaction between them. Even at high colony densities, the dominant character of each of these species does not appear to be incompatible with their co-existence, due to the low degree of niche overlap between them.
Environmental Entomology, 2015
Parasitism of ants that nest in rotting wood by eucharitid wasps was studied in order to examine ... more Parasitism of ants that nest in rotting wood by eucharitid wasps was studied in order to examine whether habitat and season influence ant parasitism, vegetation complexity and agrochemical use correlate with ant parasitism, and whether specific local and landscape features of agricultural landscapes correlate with changes in ant parasitism. In a coffee landscape, 30 coffee and 10 forest sites were selected in which local management (e.g., vegetation, agrochemical use) and landscape features (e.g., distance to forest, percent of rustic coffee nearby) were characterized. Rotten logs were sampled and ant cocoons were collected from logs and cocoons were monitored for parasitoid emergence. Sixteen ant morphospecies in three ant subfamilies (Ectatomminae, Ponerinae, and Formicinae) were found. Seven ant species parasitized by two genera of Eucharitidae parasitoids (Kapala and Obeza) were reported and some ant-eucharitid associations were new. According to evaluated metrics, parasitism did not differ with habitat (forest, high-shade coffee, low-shade coffee), but did increase in the dry season for Gnamptogenys ants. Parasitism increased with vegetation complexity for Gnamptogenys and Pachycondyla and was high in sites with both high and low agrochemical use. Two landscape variables and two local factors positively correlated with parasitism for some ant genera and species. Thus, differences in vegetation complexity at the local and landscape scale and agrochemical use in coffee landscapes alter ecological interactions between parasitoids and their ant hosts.
Journal of Insect Physiology, 2015
Communication in ants is based to a great extent on chemical compounds. Recognition of intruders ... more Communication in ants is based to a great extent on chemical compounds. Recognition of intruders is primarily based on cuticular hydrocarbon (CHC) profile matching but is prone to being cheated. Eucharitid wasps are specific parasitoids of the brood of ants; the immature stages are either well integrated within the colony or are protected within the host cocoons, whereas adult wasps at emergence must leave their host nest to reproduce and need to circumvent the ant recognition system to escape unscathed. The behavioral interactions between eucharitid wasps and workers of their host, the Neotropical ant Ectatomma tuberculatum, are characterized. In experimental bioassays, newly emerged parasitoids were not violently aggressed. They remained still and were grabbed by ants upon contact and transported outside the nest; host workers were even observed struggling to reject them. Parasitoids were removed from the nest within five minutes, and most were unharmed, although two wasps (out of 30) were killed during the interaction with the ants. We analyzed the CHCs of the ant and its two parasitoids, Dilocantha lachaudii and Isomerala coronata, and found that although wasps shared all of their compounds with the ants, each wasp species had typical blends and hydrocarbon abundance was also species specific. Furthermore, the wasps had relatively few CHCs compared to E. tuberculatum (22-44% of the host components), and these were present in low amounts. Wasps, only partially mimicking the host CHC profile, were immediately recognized as alien and actively removed from the nest by the ants. Hexane-washed wasps were also transported to the refuse piles, but only after being thoroughly inspected and after most of the workers had initially ignored them. Being recognized as intruder may be to the parasitoids' advantage, allowing them to quickly leave the natal nest, and therefore enhancing the fitness of these very short lived parasitoids. We suggest that eucharitids take advantage of the hygienic behavior of ants to quickly escape from their host nests.
Sociobiology
regular dispersion patterns in the spatial distribution of ant nests are linked to both defense o... more regular dispersion patterns in the spatial distribution of ant nests are linked to both defense of foraging areas and competition for food. They are frequently observed amongst colonies of conspecifics when the availability of colony foundation sites is homogeneous. In order to evaluate the degree of intraspecific competition in the dominant Neotropical ectatommine ant Ectatomma ruidum and the importance of interactions with another dominant sympatric ectatommine ant, E. tuberculatum, we examined the spatial relationships among colonies of these two species in an area with a naturally very high nest density (up to 11500 and 1500 nests/ha, respectively). Data were analyzed by calculation of the clark and Evans nearest neighbor index and by statistical comparison of the observed mean distance to the nearest neighbor and a theoretical value obtained by Monte-carlo simulation. The latter procedure allowed analysis of spatial relationships despite the nonhaphazard location of E. tuberculatum nests, which were always found at the base of a tree. Whatever the nest density, the mean distance between nearest neighbor nests of E. ruidum was always higher than that expected for random distribution. This regular dispersion pattern strongly supports the hypothesis that E. ruidum colonies are monodomous. In the three quadrats where they co-occurred, E. ruidum and E. tuberculatum were independently distributed, suggesting a low level of interaction between them. Even at high colony densities, the dominant character of each of these species does not appear to be incompatible with their co-existence, due to the low degree of niche overlap between them.
Environmental Entomology, 2015
Parasitism of ants that nest in rotting wood by eucharitid wasps was studied in order to examine ... more Parasitism of ants that nest in rotting wood by eucharitid wasps was studied in order to examine whether habitat and season influence ant parasitism, vegetation complexity and agrochemical use correlate with ant parasitism, and whether specific local and landscape features of agricultural landscapes correlate with changes in ant parasitism. In a coffee landscape, 30 coffee and 10 forest sites were selected in which local management (e.g., vegetation, agrochemical use) and landscape features (e.g., distance to forest, percent of rustic coffee nearby) were characterized. Rotten logs were sampled and ant cocoons were collected from logs and cocoons were monitored for parasitoid emergence. Sixteen ant morphospecies in three ant subfamilies (Ectatomminae, Ponerinae, and Formicinae) were found. Seven ant species parasitized by two genera of Eucharitidae parasitoids (Kapala and Obeza) were reported and some ant-eucharitid associations were new. According to evaluated metrics, parasitism did not differ with habitat (forest, high-shade coffee, low-shade coffee), but did increase in the dry season for Gnamptogenys ants. Parasitism increased with vegetation complexity for Gnamptogenys and Pachycondyla and was high in sites with both high and low agrochemical use. Two landscape variables and two local factors positively correlated with parasitism for some ant genera and species. Thus, differences in vegetation complexity at the local and landscape scale and agrochemical use in coffee landscapes alter ecological interactions between parasitoids and their ant hosts.
Journal of Insect Physiology, 2015
Communication in ants is based to a great extent on chemical compounds. Recognition of intruders ... more Communication in ants is based to a great extent on chemical compounds. Recognition of intruders is primarily based on cuticular hydrocarbon (CHC) profile matching but is prone to being cheated. Eucharitid wasps are specific parasitoids of the brood of ants; the immature stages are either well integrated within the colony or are protected within the host cocoons, whereas adult wasps at emergence must leave their host nest to reproduce and need to circumvent the ant recognition system to escape unscathed. The behavioral interactions between eucharitid wasps and workers of their host, the Neotropical ant Ectatomma tuberculatum, are characterized. In experimental bioassays, newly emerged parasitoids were not violently aggressed. They remained still and were grabbed by ants upon contact and transported outside the nest; host workers were even observed struggling to reject them. Parasitoids were removed from the nest within five minutes, and most were unharmed, although two wasps (out of 30) were killed during the interaction with the ants. We analyzed the CHCs of the ant and its two parasitoids, Dilocantha lachaudii and Isomerala coronata, and found that although wasps shared all of their compounds with the ants, each wasp species had typical blends and hydrocarbon abundance was also species specific. Furthermore, the wasps had relatively few CHCs compared to E. tuberculatum (22-44% of the host components), and these were present in low amounts. Wasps, only partially mimicking the host CHC profile, were immediately recognized as alien and actively removed from the nest by the ants. Hexane-washed wasps were also transported to the refuse piles, but only after being thoroughly inspected and after most of the workers had initially ignored them. Being recognized as intruder may be to the parasitoids' advantage, allowing them to quickly leave the natal nest, and therefore enhancing the fitness of these very short lived parasitoids. We suggest that eucharitids take advantage of the hygienic behavior of ants to quickly escape from their host nests.