Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
We assessed the occurrence of algae in five species of tank-bromeliads found in contrasting environmental sites in a Neotropical, primary rainforest around the Nouragues Research Station, French Guiana. The distributions of both algal abundance and biomass were examined based on physical parameters, the morphological characteristics of bromeliad species and with regard to the structure of other aquatic microbial communities held in the tanks. Algae were retrieved in all of the bromeliad species with mean densities ranging from ∼10(2) to 10(4) cells/mL. Their biomass was positively correlated to light exposure and bacterial biomass. Algae represented a tiny component of the detrital food web in shaded bromeliads but accounted for up to 30 percent of the living microbial carbon in the tanks of Catopsis berteroniana, located in a highly exposed area. Thus, while nutrient supplies are believed to originate from wind-borne particles and trapped insects (i.e., allochtonous organic matter), our results indicate that primary producers (i.e., autochtonous organic matter) are present in this insectivorous bromeliad. Using a 24-h incubation of size-fractionated and manipulated samples from this plant, we evaluated the impact of mosquito foraging on algae, other microorganisms and rotifers. The prey assemblages were greatly altered by the predation of mosquito larvae. Grazing losses indicated that the dominant algal taxon, Bumilleriopsis sp., like protozoa and rotifers, is a significant part of the diet of mosquito larvae. We conclude that algae are a relevant functional community of the aquatic food web in C. berteroniana and might form the basis of a complementary non-detrital food web.
ISSN: 1932-6203

hal-00819161
https://hal.archives-ouvertes.fr/hal-00819161
https://hal.archives-ouvertes.fr/hal-00819161/document
https://hal.archives-ouvertes.fr/hal-00819161/file/Brouard2011_AreAlgae.pdf
DOI : 10.1371/journal.pone.0020129

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Background and AimsEpiphytism imposes physiological constraints resulting from the lack of access to the nutrient sources available to ground-rooted plants. A conspicuous adaptation in response to that lack is the phytotelm (plant-held waters) of tank-bromeliad species that are often nutrient-rich. Associations with terrestrial invertebrates also result in higher plant nutrient acquisition. Assuming that tank-bromeliads rely on reservoir-assisted nutrition, it was hypothesized that the dual association with mutualistic ants and the phytotelm food web provides greater nutritional benefits to the plant compared with those bromeliads involved in only one of these two associations.MethodsQuantitative (water volume, amount of fine particulate organic matter, predator/prey ratio, algal density) and qualitative variables (ant-association and photosynthetic pathways) were compared for eight tank- and one tankless-bromeliad morphospecies from French Guiana. An analysis was also made of which of these variables affect nitrogen acquisition (leaf N and δ(15)N).Key ResultsAll variables were significantly different between tank-bromeliad species. Leaf N concentrations and leaf δ(15)N were both positively correlated with the presence of mutualistic ants. The amount of fine particulate organic matter and predator/prey ratio had a positive and negative effect on leaf δ(15)N, respectively. Water volume was positively correlated with leaf N concentration whereas algal density was negatively correlated. Finally, the photosynthetic pathway (C3 vs. CAM) was positively correlated with leaf N concentration with a slightly higher N concentration for C3-Tillandsioideae compared with CAM-Bromelioideae.ConclusionsThe study suggests that some of the differences in N nutrition between bromeliad species can be explained by the presence of mutualistic ants. From a nutritional standpoint, it is more advantageous for a bromeliad to use myrmecotrophy via its roots than to use carnivory via its tank. The results highlight a gap in our knowledge of the reciprocal interactions between bromeliads and the various trophic levels (from bacteria to large metazoan predators) that intervene in reservoir-assisted nutrition.
ISSN: 0305-7364

hal-00849045
https://hal.archives-ouvertes.fr/hal-00849045
DOI : 10.1093/aob/mct147
PUBMED : 23864002

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Although ants may induce community-wide effects via changes in physical habitats in terrestrial environments, their influence on aquatic communities living in plant-held waters remains largely underexplored. The neotropical tank-bromeliad Aechmea mertensii (Bromeliaceae) occurs along forest edges in ant-gardens initiated by Camponotus femoratus or by Pachycondyla goeldii. Its leaves form wells that hold rainwater and provide suitable habitats for many aquatic organisms. We postulated that these ant-plant mutualisms indirectly affect the microbial community structure via changes in the environmental conditions experienced by the plants. To test this hypothesis, we analyzed the protist communities from 63 tank-bromeliads associated with either C. femoratus or P. goeldii (hereafter Cf-Aechmea and Pg-Aechmea) along a forest edge in French Guiana. For each plant, a large number of environmental variables (including habitat structure, food resources, incident radiation and the presence of aquatic invertebrates) were quantified to determine their relative importance in driving any observed differences across ant-associated plants. Pg-Aechmea are located in sun-exposed areas and hold low volumes of water and low amounts of detritus, whereas Cf-Aechmea are located in partially shaded areas and accumulate higher amounts of water and detritus. Protists (i.e., protozoa and algae) inhabiting Cf-Aechmea exhibit greater richness and abundances than those in Pg-Aechmea. Variations in detritus content, number of leaves, incident radiation, and the epiphyte richness of the ant-garden were the main factors explaining the variation in protist richness. A shift in the functional group composition of protists between bromeliads tended by different ant species suggested that mutualistic ants indirectly mediate changes in the microbial food web.
Basic and Applied Ecology

hal-00913126
https://hal.archives-ouvertes.fr/hal-00913126
https://hal.archives-ouvertes.fr/hal-00913126/document
DOI : 10.1016/j.baae.2012.10.002
OATAO : 10190

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. A substantial fraction of the freshwater available in neotropical forests is impounded within the rosettes of bromeliads that form aquatic islands in a terrestrial matrix. The ecosystem functioning of bromeliads is known to be influenced by the composition of the contained community but it is not clear whether bromeliad food webs remain functionally similar against a background of variation in the understorey environment. 2. We considered a broad range of environmental conditions, including incident light and incoming litter, and quantified the distribution of a very wide range of freshwater organisms (from viruses to macroinvertebrates) to determine the factors that influence the functional structure of bromeliad food webs in samples taken from 171 tank-bromeliads. 3. We observed a gradient of detritus-based to algal-based food webs from the understorey to the overstorey. Algae, rotifers and collector and predatory invertebrates dominated bromeliad food webs in exposed areas, whereas filter-feeding insects had their highest densities in shaded forest areas. Viruses, bacteria and fungi showed no clear density patterns. Detritus decomposition is mainly due to microbial activity in understorey bromeliads where filter feeders are the main consumers of microbial and particulate organic matter (POM). Algal biomass may exceed bacterial biomass in sun-exposed bromeliads where amounts of detritus were lower but functional diversity was highest. 4. Our results provide evidence that tank-bromeliads, which grow in a broad range of ecological conditions, promote aquatic food web diversity in neotropical forests. Moreover, although bromeliad ecosystems have been categorised as detritus-based systems in the literature, we show that algal production can support a non-detrital food web in these systems.
ISSN: 0046-5070

hal-00819103
https://hal.archives-ouvertes.fr/hal-00819103

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Although ants may induce community-wide effects via changes in physical habitats in terrestrial environments, their influence on aquatic communities living in plant-held waters remains largely underexplored. The neotropical tank-bromeliad Aechmea mertensii (Bromeliaceae) occurs along forest edges in ant-gardens initiated by Camponotus femoratus or by Pachycondyla goeldii. Its leaves form wells that hold rainwater and provide suitable habitats for many aquatic organisms. We postulated that these ant-plant mutualisms indirectly affect the microbial community structure via changes in the environmental conditions experienced by the plants. To test this hypothesis, we analyzed the protist communities from 63 tank-bromeliads associated with either C. femoratus or P. goeldii (hereafter Cf-Aechmea and Pg-Aechmea) along a forest edge in French Guiana. For each plant, a large number of environmental variables (including habitat structure, food resources, incident radiation and the presence of aquatic invertebrates) were quantified to determine their relative importance in driving any observed differences across ant-associated plants. Pg-Aechmea are located in sun-exposed areas and hold low volumes of water and low amounts of detritus, whereas Cf-Aechmea are located in partially shaded areas and accumulate higher amounts of water and detritus. Protists (i.e., protozoa and algae) inhabiting Cf-Aechmea exhibit greater richness and abundances than those in Pg-Aechmea. Variations in detritus content, number of leaves, incident radiation, and the epiphyte richness of the ant-garden were the main factors explaining the variation in protist richness. A shift in the functional group composition of protists between bromeliads tended by different ant species suggested that mutualistic ants indirectly mediate changes in the microbial food web.
ISSN: 1439-1791

hal-00817519
https://hal.archives-ouvertes.fr/hal-00817519