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Dejean, A., Compin, A., Delabie, J. H. C., Azémar, F., Corbara, B., & Leponce, M. (2019). Biotic and abiotic determinants of the formation of ant mosaics in primary Neotropical rainforests. Ecol Entomol, 44(4), 560–570.
Abstract: 1. Ants are widespread in tropical rainforests, including in the canopy where territorially dominant arboreal species represent the main part of the arthropod biomass.
2. By mapping the territories of dominant arboreal ant species and using a null model analysis and a pairwise approach this study was able to show the presence of an ant mosaic on the upper canopy of a primary Neotropical rainforest (c. 1ha sampled; 157 tall trees from 28 families). Although Neotropical rainforest canopies are frequently irregular, with tree crowns at different heights breaking the continuity of the territories of dominant ants, the latter are preserved via underground galleries or trails laid on the ground.
3. The distribution of the trees influences the structure of the ant mosaic, something related to the attractiveness of tree taxa for certain arboreal ant species rather than others.
4. Small-scale natural disturbances, most likely strong winds in the area studied (presence of canopy gaps), play a role by favouring the presence of two ant species typical of secondary formations: Camponotus femoratus and Crematogaster levior, which live in parabiosis (i.e. share territories and nests but lodge in different cavities) and build conspicuous ant gardens. In addition, pioneer Cecropia myrmecophytic trees were recorded.
Keywords: Ant mosaics; connections on the ground; host tree attractiveness; indicators of disturbance; primary Neotropical rainforest; territoriality
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Sprenger, P. P., Hartke, J., Feldmeyer, B., Orivel, J., Schmitt, T., & Menzel, F. (2019). Influence of Mutualistic Lifestyle, Mutualistic Partner, and Climate on Cuticular Hydrocarbon Profiles in Parabiotic Ants. J Chem Ecol, 45(9), 741–754.
Abstract: A vital trait in insects is their cuticular hydrocarbon (CHC) profile, which protects the insect against desiccation and serves in chemical communication. Due to these functions, CHC profiles are shaped by both climatic conditions and biotic interactions. Here, we investigated CHC differentiation in the neotropical parabiotic ant species Crematogaster levior and Camponotus femoratus, which mutualistically share a nest. Both consist of two cryptic species each (Cr. levior A and B and Ca. femoratus PAT and PS) that differ genetically and possess strongly different CHC profiles. We characterized and compared CHC profiles of the four cryptic species in detail. Our results suggest that Cr. levior A, Ca. femoratus PAT and Ca. femoratus PS adapted their CHC profiles to the parabiotic lifestyle by producing longer-chain CHCs. At the same time, they changed their major CHC classes, and produce more alkadienes and methyl-branched alkenes compared to Cr. levior B or non-parabiotic species. The CHC profiles of Cr. levior B were more similar to related, non-parabiotic species of the Orthocrema clade than Cr. levior A, and the chain lengths of B were similar to the reconstructed ancestral state. Signals of both the parabiotic partner (biotic conditions) and climate (abiotic conditions) were found in the CHC profiles of all four cryptic species. Our data suggest that mutualisms shaped the CHC profiles of the studied species, in particular chain length and CHC class composition. Beside this, signals of the parabiotic partners indicate potential impacts of biotic interactions, via chemical mimicry or chemical camouflage.
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Piponiot, C., Rutishauser, E., Derroire, G., Putz, F. E., Sist, P., West, T. A. P., et al. (2019). Optimal strategies for ecosystem services provision in Amazonian production forests. Environmental Research Letters, 14(12), 124090.
Abstract: Although tropical forests harbour most of the terrestrial carbon and biological diversity on Earth they continue to be deforested or degraded at high rates. In Amazonia, the largest tropical forest on Earth, a sixth of the remaining natural forests is formally dedicated to timber extraction through selective logging. Reconciling timber extraction with the provision of other ecosystem services (ES) remains a major challenge for forest managers and policy-makers. This study applies a spatial optimisation of logging in Amazonian production forests to analyse potential trade-offs between timber extraction and recovery, carbon storage, and biodiversity conservation. Current logging regulations with unique cutting cycles result in sub-optimal ES-use efficiency. Long-term timber provision would require the adoption of a land-sharing strategy that involves extensive low-intensity logging, although high transport and road-building costs might make this approach economically unattractive. By contrast, retention of carbon and biodiversity would be enhanced by a land-sparing strategy restricting high-intensive logging to designated areas such as the outer fringes of the region. Depending on management goals and societal demands, either choice will substantially influence the future of Amazonian forests. Overall, our results highlight the need for revaluation of current logging regulations and regional cooperation among Amazonian countries to enhance coherent and trans-boundary forest management.
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Ghislain, B., Engel, J., Clair, B., Donaldson, L., & Baas, P. (2019). Diversity of anatomical structure of tension wood among 242 tropical tree species. IAWA Journal, 40(4), 765–784.
Abstract: Angiosperm trees produce tension wood to actively control their vertical position. Tension wood has often been characterised by the presence of an unlignified inner fibre wall layer called the G-layer. Using this definition, previous reports indicate that only one-third of all tree species have tension wood with G-layers. Here we aim to (i) describe the large diversity of tension wood anatomy in tropical tree species, taking advantage of the recent understanding of tension wood anatomy and (ii) explore any link between this diversity and other ecological traits of the species. We sampled tension wood and normal wood in 432 trees from 242 species in French Guiana. The samples were observed using safranin and astra blue staining combined with optical microscopy. Species were assigned to four anatomical groups depending on the presence/absence of G-layers, and their degree of lignification. The groups were analysed for functional traits including wood density and light preferences. Eighty-six% of the species had G-layers in their tension wood which was lignified in most species, with various patterns of lignification. Only a few species did not have G-layers. We found significantly more species with lignified G-layers among shade-tolerant and shade-demanding species as well as species with a high wood density. Our results bring up-to-date the incidence of species with/without G-layers in the tropical lowland forest where lignified G-layers are the most common anatomy of tension wood. Species without G-layers may share a common mechanism with the bark motor taking over the wood motor. We discuss the functional role of lignin in the G-layer.
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Ruiz-González, M. X., Leroy, C., Dejean, A., Gryta, H., Jargeat, P., Carrión, A. D. A., et al. (2019). Do host plant and associated ant species affect microbial communities in myrmecophytes? Insects, 10(11), 391.
Abstract: Ant-associated microorganisms can play crucial and often overlooked roles, and given the diversity of interactions that ants have developed, the study of the associated microbiomes is of interest. We focused here on specialist plant-ant species of the genus Allomerus that grow a fungus to build galleries on their host-plant stems. Allomerus-inhabited domatia, thus, might be a rich arena for microbes associated with the ants, the plant, and the fungus. We investigated the microbial communities present in domatia colonised by four arboreal ants: Allomerus decemarticulatus, A. octoarticulatus, A. octoarticulatus var. demerarae, and the non-fungus growing plant-ant Azteca sp. cf. depilis, inhabiting Hirtella physophora or Cordia nodosa in French Guiana. We hypothesized that the microbial community will differ among these species. We isolated microorganisms from five colonies of each species, sequenced the 16S rRNA or Internal TranscribedSpacer (ITS) regions, and described both the alpha and beta diversities. We identified 69 microbial taxa, which belong to five bacterial and two fungal phyla. The most diverse phyla were Proteobacteria and Actinobacteria. The microbial community of Azteca cf. depilis and Allomerus spp. differed in composition and richness. Geographical distance affected microbial communities and richness but plant species did not. Actinobacteria were only associated with Allomerus spp.
Keywords: Allomerus decemarticulatus; Allomerus octoarticulatus; Azteca sp; Cf; Cordia nodosa; Depilis; Domatia; Hirtella physophora; Microbial diversity
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Leponce, M., Delabie, J. H. C., Orivel, J., Jacquemin, J., Calvo Martin, M., & Dejean, A. (2019). Tree-dwelling ant survey (Hymenoptera, Formicidae) in Mitaraka, French Guiana. Zoosystema, 40(sp1), 163–179.
Abstract: Ants constitute a substantial part of the arthropod biomass in rainforests. Most studies have focused on ground-dwelling ants, which constitute almost half of the diversity of the ant assemblage. We report here the results of the first survey of tree-dwelling ants in French Guiana on a plateau and in a swamp palm forest (Euterpe oleracea Mart.) in the Mitaraka Mountains. We were interested in seeing the effect of topography and geographic distance on species richness and composition and to gather information on the species distribution on tree trunks. The fauna of Mitaraka was compared with one from a site 350 km distant (Petit Saut). In total 105 trees were sampled (30, 30, 45 in the plateau and the swamp forests of Mitaraka, and in Petit Saut plateau forest, respectively). Arboreal ants were attracted using tuna and honey baits spread along a rope reaching an upper branch, except for the palm swamp forest where the baits were only placed at 2 m high. A total of 34, 13 and 22 species were observed in these three respective sites. Six of these species are new records for French Guiana. In Mitaraka Camponotus femoratus (Fabricius, 1804) and Crematogaster leviorLongino, 2003 co-occurred on trees (parabiotic association) and were among the most common species, along with Crematogaster tenuiculaForel, 1904 which was found on other trees (species exclusion). The Mitaraka Mountains appeared more species rich and had a species composition distinct from Petit Saut. Topography also influenced ant species composition. Almost half of the species collected by the baitline method were exclusively foraging in the canopy.
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Piponiot, C., Rödig, E., Putz, F. E., Rutishauser, E., Sist, P., Ascarrunz, N., et al. (2019). Can timber provision from Amazonian production forests be sustainable? Environmental Research Letters, 14(6), 064014.
Abstract: Around 30 Mm3 of sawlogs are extracted annually by selective logging of natural production forests in Amazonia, Earth’s most extensive tropical forest. Decisions concerning the management of these production forests will be of major importance for Amazonian forests’ fate. To date, no regional assessment of selective logging sustainability supports decision-making. Based on data from 3500 ha of forest inventory plots, our modelling results show that the average periodic harvests of 20 m3 ha−1 will not recover by the end of a standard 30 year cutting cycle. Timber recovery within a cutting cycle is enhanced by commercial acceptance of more species and with the adoption of longer cutting cycles and lower logging intensities. Recovery rates are faster in Western Amazonia than on the Guiana Shield. Our simulations suggest that regardless of cutting cycle duration and logging intensities, selectively logged forests are unlikely to meet timber demands over the long term as timber stocks are predicted to steadily decline. There is thus an urgent need to develop an integrated forest resource management policy that combines active management of production forests with the restoration of degraded and secondary forests for timber production. Without better management, reduced timber harvests and continued timber production declines are unavoidable.
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Van Langenhove, L., Depaepe, T., Vicca, S., van den Berge, J., Stahl, C., Courtois, E., et al. (2019). Regulation of nitrogen fixation from free-living organisms in soil and leaf litter of two tropical forests of the Guiana shield. Plant Soil, .
Abstract: Background and aims: Biological fixation of atmospheric nitrogen (N 2 ) is the main pathway for introducing N into unmanaged ecosystems. While recent estimates suggest that free-living N fixation (FLNF) accounts for the majority of N fixed in mature tropical forests, the controls governing this process are not completely understood. The aim of this study was to quantify FLNF rates and determine its drivers in two tropical pristine forests of French Guiana. Methods: We used the acetylene reduction assay to measure FLNF rates at two sites, in two seasons and along three topographical positions, and used regression analyses to identify which edaphic explanatory variables, including carbon (C), nitrogen (N), phosphorus (P) and molybdenum (Mo) content, pH, water and available N and P, explained most of the variation in FLNF rates. Results: Overall, FLNF rates were lower than measured in tropical systems elsewhere. In soils seasonal variability was small and FLNF rates differed among topographies at only one site. Water, P and pH explained 24% of the variation. In leaf litter, FLNF rates differed seasonally, without site or topographical differences. Water, C, N and P explained 46% of the observed variation. We found no regulatory role of Mo at our sites. Conclusions: Rates of FLNF were low in primary rainforest on poor soils on the Guiana shield. Water was the most important rate-regulating factor and FLNF increased with increasing P, but decreased with increasing N. Our results support the general assumption that N fixation in tropical lowland forests is limited by P availability. © 2019, The Author(s).
Keywords: Free-living nitrogen fixation; French Guiana; Molybdenum; Nutrients; Phosphorus; Tropical forest
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Taureau, F., Robin, M., Proisy, C., Fromard, F., Imbert, D., & Debaine, F. (2019). Mapping the mangrove forest canopy using spectral unmixing of very high spatial resolution satellite images. Remote Sens., 11(3), 367.
Abstract: Despite the lowtree diversity and scarcity of the understory vegetation, the high morphological plasticity of mangrove trees induces, at the stand level, a very large variability of forest structures that need to be mapped for assessing the functioning of such complex ecosystems. Fully constrained linear spectral unmixing (FCLSU) of very high spatial resolution (VHSR) multispectral images was tested to fine-scale map mangrove zonations in terms of horizontal variation of forest structure. The study was carried out on three Pleiades-1A satellite images covering French island territories located in the Atlantic, Indian, and Pacific Oceans, namely Guadeloupe, Mayotte, and New Caledonia archipelagos. In each image, FCLSU was trained from the delineation of areas exclusively related to four components including either pure vegetation, soil (ferns included), water, or shadows. It was then applied to the whole mangrove cover imaged for each island and yielded the respective contributions of those four components for each image pixel. On the forest stand scale, the results interestingly indicated a close correlation between FCLSU-derived vegetation fractions and canopy closure estimated from hemispherical photographs R 2 = 0.95) and a weak relation with the Normalized Difference Vegetation Index (R 2 = 0.29). Classification of these fractions also offered the opportunity to detect and map horizontal patterns of mangrove structure in a given site. K-means classifications of fraction indeed showed a global view of mangrove structure organization in the three sites, complementary to the outputs obtained from spectral data analysis. Our findings suggest that the pixel intensity decomposition applied to VHSR multispectral satellite images can be a simple but valuable approach for (i) mangrove canopy monitoring and (ii) mangrove forest structure analysis in the perspective of assessing mangrove dynamics and productivity. As with Lidar-based surveys, these potential new mapping capabilities deserve further physically based interpretation of sunlight scattering mechanisms within forest canopy. © 2019 by the authors.
Keywords: Forest structure; Guadeloupe; Hemispherical photographs; Mangrove; Mayotte; New Caledonia; Remote sensing; Image resolution; Photography; Photomapping; Pixels; Remote sensing; Satellites; Vegetation; Forest structure; Guadeloupe; Hemispherical photographs; Mangrove; Mayotte; New Caledonia; Forestry
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Fichaux, M., Béchade, B., Donald, J., Weyna, A., Delabie, J. H. C., Murienne, J., et al. (2019). Habitats shape taxonomic and functional composition of Neotropical ant assemblages. Oecologia, 189(2), 501–513.
Abstract: Determining assembly rules of co-occurring species persists as a fundamental goal in community ecology. At local scales, the relative importance of environmental filtering vs. competitive exclusion remains a subject of debate. In this study, we assessed the relative importance of habitat filtering and competition in structuring understory ant communities in tropical forests of French Guiana. Leaf-litter ants were collected using pitfall and Winkler traps across swamp, slope and plateau forests near Saül, French Guiana. We used a combination of univariate and multivariate analyses to evaluate trait response of ants to habitat characteristics. Null model analyses were used to investigate the effects of habitat filtering and competitive interactions on community assembly at the scale of assemblages and sampling points, respectively. Swamp forests presented a much lower taxonomic and functional richness compared to slope and plateau forests. Furthermore, marked differences in taxonomic and functional composition were observed between swamp forests and slope or plateau forests. We found weak evidence for competitive exclusion based on null models. Nevertheless, the contrasting trait composition observed between habitats revealed differences in the ecological attributes of the species in the different forest habitats. Our analyses suggest that competitive interactions may not play an important role in structuring leaf-litter ant assemblages locally. Rather, habitats are responsible for driving both taxonomic and functional composition of ant communities.
Keywords: Formicidae; Functional diversity; Habitat filtering; Rainforest; Traits; Formicidae
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