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Delaval, M., Henry, M., & Charles-Dominique, P. (2005). Interspecific competition and niche partitioning: Example of a neotropical rainforest bat community. Rev. Ecol.-Terre Vie, 60(2), 149–165.
Abstract: To understand the organization of a bat community and the coexistence of sympatric species, it is essential to understand how species use and share common resources. First, we describe a bat community in a primary rainforest of French Guiana. The presence of particular roosting sites, such as caves, and the absence of disturbances are important local factors in structuring communities. In the course of this study, we focused on the three most common species of three vegetarian bat guilds (understorey frugivores, canopy frugivores and nectarivores). The local coexistence of these species is possible thanks to space, food and/or time partitioning. Space partitioning is consistent with the hypothesis that smaller bats with a more manoeuvrable flight tend to occupy more cluttered space less attractive to their competitors and have smaller home range. We observed a time partitioning that is likely to reduce competition among some frugivorous bat species by reducing direct interference during foraging. Besides an interest for the field community ecology, this study of a community living in a primary forest can be used as a reference for non disturbed habitat for conservation purposes.
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Christensen-Dalsgaard, K. K., Ennos, A. R., & Fournier, M. (2008). Interrelations between hydraulic and mechanical stress adaptations in woody plants. Plant. Signal. Behav., 3(7), 463–465.
Abstract: The fields of plant water relations and plant biomechanics have traditionally been studied separately even though often the same tissues are responsible for water transport and mechanical support. There is now increasing evidence that hydraulic and mechanical adaptations may influence one another. We studied the changes in the hydraulic and mechanical properties of the wood along lateral roots of two species of buttressed trees. In these roots, the mechanical contstraints quantified by strain measurements are known to decrease distally. Further, we investigated the effect of mechanical loading on the vessel anatomy in these and four other species of tropical trees. We found that as the strain decreased, the wood became progressively less stiff and strong but the conductivity increased exponentially. This was reflected in that adaptations towards re-enforcing mechanically loaded areas resulted in xylem with fewer and smaller vessels. In addition a controlled growth experiment on three tree species showed that drought adaptation may results in plants with stronger and stiffer tissue. Our results indicate that hydraulic and mechanical stress adaptations may be interrelated, and so support recent studied suggesting that physiological responses are complex balances rather than pure optimisations. ©2008 Landes Bioscience.
Keywords: Conductivity; Modulus of elasticity; Strain; Tree ecophysiology; Tropical trees; Wood anatomy; Yield stress
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Bossu, J., Lehnebach, R., Corn, S., Regazzi, A., Beauchene, J., & Clair, B. (2018). Interlocked grain and density patterns in Bagassa guianensis: changes with ontogeny and mechanical consequences for trees. Trees, 32(6), 1643–1655.
Abstract: Interlocked grain and basic density increase from pith to bark in Bagassa guianensis and greatly improve trunk torsional stiffness and wood tenacity in the radial plane.
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Doughty, C. E., Wolf, A., Baraloto, C., & Malhi, Y. (2016). Interdependency of plants and animals in controlling the sodium balance of ecosystems and the impacts of global defaunation. Ecography, 39(2), 204–212.
Abstract: Sodium, an element which is needed by animals but often toxic in high concentrations to plants, may be deficient and limit animal abundance in inland continental regions, but may be overabundant and limit plant productivity in coastal regions. Here we present data from 50 independent plots (including leaf data from more than 2480 individual trees) showing that leaves in the Amazon basin uptake high amounts of sodium (Na) in a manner more similar to the essential cation potassium (K) than to the toxic cation aluminium (Al). Leaf Na increases linearly with soil Na concentrations, and there is no apparent mechanism for selective exclusion of Na in comparison to K, a key attribute of halophytes. This indicates that the Amazon basin is broadly non-halophytic and increased sodium concentrations in non-halophyte plants often decrease plant productivity. Total Na concentrations are ∼ 10 times higher in coastal regions than inland regions. Such concentration gradients in nutrients may have been reduced in the past because large animals that were abundant in the Pleistocene have been hypothesized to play a large role in reducing nutrient concentration gradients at continental scales. We use a diffusion model and a Na loss rate based on empirical data to estimate that large animals may have moved significant quantities of Na inland away from coastal regions in the Amazon Basin. Therefore, our simple model suggests that large animals may play an important, yet diminishing, role in maintaining the sodium balance of the planet. © 2016 Nordic Society Oikos.
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Aguilos, M., Stahl, C., Burban, B., Hérault, B., Courtois, E., Coste, S., et al. (2018). Interannual and seasonal variations in ecosystem transpiration and water use efficiency in a tropical rainforest. Forests, 10(1).
Abstract: Warmer and drier climates over Amazonia have been predicted for the next century with expected changes in regional water and carbon cycles. We examined the impact of interannual and seasonal variations in climate conditions on ecosystem-level evapotranspiration (ET) and water use efficiency (WUE) to determine key climatic drivers and anticipate the response of these ecosystems to climate change. We used daily climate and eddyflux data recorded at the Guyaflux site in French Guiana from 2004 to 2014. ET and WUE exhibited weak interannual variability. The main climatic driver of ET and WUE was global radiation (Rg), but relative extractable water (REW) and soil temperature (Ts) did also contribute. At the seasonal scale, ET and WUE showed a modal pattern driven by Rg, with maximum values for ET in July and August and for WUE at the beginning of the year. By removing radiation effects during water depleted periods, we showed that soil water stress strongly reduced ET. In contrast, drought conditions enhanced radiation-normalized WUE in almost all the years, suggesting that the lack of soil water had a more severe effect on ecosystem evapotranspiration than on photosynthesis. Our results are of major concern for tropical ecosystem modeling because they suggest that under future climate conditions, tropical forest ecosystems will be able to simultaneously adjust CO2 and H2O fluxes. Yet, for tropical forests under future conditions, the direction of change in WUE at the ecosystem scale is hard to predict, since the impact of radiation on WUE is counterbalanced by adjustments to soil water limitations. Developing mechanistic models that fully integrate the processes associated with CO2 and H2O flux control should help researchers understand and simulate future functional adjustments in these ecosystems.
Keywords: Drought; Evapotranspiration; Radiation; Tropical rainforest; Water use efficiency; Atmospheric radiation; Carbon dioxide; Climate change; Drought; Efficiency; Evapotranspiration; Forestry; Heat radiation; Radiation effects; Soil moisture; Tropics; Water supply; Climate condition; Drought conditions; Interannual variability; Mechanistic models; Seasonal variation; Tropical ecosystems; Tropical rain forest; Water use efficiency; Ecosystems
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Fanin, N., Hättenschwiler, S., Schimann, H., & Fromin, N. (2015). Interactive effects of C, N and P fertilization on soil microbial community structure and function in an Amazonian rain forest. Funct. Ecol., 29(1), 140–150.
Abstract: Resource control over abundance, structure and functional diversity of soil microbial communities is a key determinant of soil processes and related ecosystem functioning. Copiotrophic organisms tend to be found in environments which are rich in nutrients, particularly carbon, in contrast to oligotrophs, which survive in much lower carbon concentrations. We hypothesized that microbial biomass, activity and community structure in nutrient-poor soils of an Amazonian rain forest are limited by multiple elements in interaction. We tested this hypothesis with a fertilization experiment by adding C (as cellulose), N (as urea) and P (as phosphate) in all possible combinations to a total of 40 plots of an undisturbed tropical forest in French Guiana. After 2 years of fertilization, we measured a 47% higher biomass, a 21% increase in substrate-induced respiration rate and a 5-fold higher rate of decomposition of cellulose paper discs of soil microbial communities that grew in P-fertilized plots compared to plots without P fertilization. These responses were amplified with a simultaneous C fertilization suggesting P and C colimitation of soil micro-organisms at our study site. Moreover, P fertilization modified microbial community structure (PLFAs) to a more copiotrophic bacterial community indicated by a significant decrease in the Gram-positive : Gram-negative ratio. The Fungi : Bacteria ratio increased in N fertilized plots, suggesting that fungi are relatively more limited by N than bacteria. Changes in microbial community structure did not affect rates of general processes such as glucose mineralization and cellulose paper decomposition. In contrast, community level physiological profiles under P fertilization combined with either C or N fertilization or both differed strongly from all other treatments, indicating functionally different microbial communities. While P appears to be the most critical from the three major elements we manipulated, the strongest effects were observed in combination with either supplementary C or N addition in support of multiple element control on soil microbial functioning and community structure. We conclude that the soil microbial community in the studied tropical rain forest and the processes it drives is finely tuned by the relative availability in C, N and P. Any shifts in the relative abundance of these key elements may affect spatial and temporal heterogeneity in microbial community structure, their associated functions and the dynamics of C and nutrients in tropical ecosystems.
Keywords: Ecosystem functioning; Functional significance; Microbial community structure; Multiple resource limitation; Phospholipid fatty acids (PLFA); Phosphorus; Soil functioning; Tropical forest
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Fournier, M., Dlouhá, J., Jaouen, G., & Almeras, T. (2013). Integrative biomechanics for tree ecology: Beyond wood density and strength. J. Exp. Bot., 64(15), 4793–4815.
Abstract: Functional ecology has long considered the support function as important, but its biomechanical complexity is only just being elucidated. We show here that it can be described on the basis of four biomechanical traits, two safety traits against winds and self-buckling, and two motricity traits involved in sustaining an upright position, tropic motion velocity (MV) and posture control (PC). All these traits are integrated at the tree scale, combining tree size and shape together with wood properties. The assumption of trait constancy has been used to derive allometric scaling laws, but it was more recently found that observing their variations among environments and functional groups, or during ontogeny, provides more insights into adaptive syndromes of tree shape and wood properties. However, oversimpli-fed expressions have often been used, possibly concealing key adaptive drivers. An extreme case of oversimplification is the use of wood basic density as a proxy for safety. Actually, as wood density is involved in stiffiness, loads, and construction costs, the impact of its variations on safety is non-trivial. Moreover, other wood features, especially the microfibril angle (MFA), are also involved. Furthermore, wood is not only stiff and strong, but it also acts as a motor for MV and PC. The relevant wood trait for this is maturation strain asymmetry. Maturation strains vary with cell-wall characteristics such as MFA, rather than with wood density. Finally, the need for further studies about the ecological relevance of branching patterns, motricity traits, and growth responses to mechanical loads is discussed. © The Author 2013.
Keywords: Biomechanics; Ecological strategy; Gravitropism; Shape; Size; Trees; Wood
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Baraloto, C., Marcon, E., Morneau, F., Pavoine, S., & Roggy, J. C. (2010). Integrating functional diversity into tropical forest plantation designs to study ecosystem processes. Ann. For. Sci., 67(3), 303.
Abstract: The elucidation of relationships between biodiversity and ecosystem processes has been limited by the definition of metrics of biodiversity and their integration into experimental design. Functional trait screening can strengthen the performance of these designs. We suggest the use of Rao's quadratic entropy to measure both functional diversity and phylogenetic diversity of species mixtures proposed for an experimental design, and demonstrate how they can provide complementary information. We also present an index assessing the statistical performance of these independent variables in different experimental designs. Measurement of independent variables as continuous vs. discrete variables reduces statistical performance, but improves the model by quantifying species differences masked by group assignments. To illustrate these advances, we present an example from a tropical forest tree community in which we screened 38 species for nine functional traits. The proposed TropiDEP design is based on the relative orthogonality of two multivariate trait axes defined using principal component analysis. We propose that independent variables describing functional diversity might be grouped to calculate independent variables describing suites of different traits with potentially different effects on particular ecosystem processes. In other systems these axes may differ from those reported here, yet the methods of analysis integrating functional and phylogenetic diversity into experimental design could be universal.
Keywords: complementarity; ecosystem function; functional groups; leaf economics spectrum; nitrogen fixation; quadratic entropy
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Fine, P. V. A., Metz, M. R., Lokvam, J., Mesones, I., Zuniga, J. M. A., Lamarre, G. P. A., et al. (2013). Insect herbivores, chemical innovation, and the evolution of habitat specialization in Amazonian trees. Ecology, 94(8), 1764–1775.
Abstract: Herbivores are often implicated in the generation of the extraordinarily diverse tropical flora. One hypothesis linking enemies to plant diversification posits that the evolution of novel defenses allows plants to escape their enemies and expand their ranges. When range expansion involves entering a new habitat type, this could accelerate defense evolution if habitats contain different assemblages of herbivores and/or divergent resource availabilities that affect plant defense allocation. We evaluated this hypothesis by investigating two sister habitat specialist ecotypes of Protium subserratum (Burseraceae), a common Amazonian tree that occurs in white-sand and terra firme forests. We collected insect herbivores feeding on the plants, assessed whether growth differences between habitats were genetically based using a reciprocal transplant experiment, and sampled multiple populations of both lineages for defense chemistry. Protium subserratum plants were attacked mainly by chrysomelid beetles and cicadellid hemipterans. Assemblages of insect herbivores were dissimilar between populations of ecotypes from different habitats, as well as from the same habitat 100 km distant. Populations from terra firme habitats grew significantly faster than white-sand populations; they were taller, produced more leaf area, and had more chlorophyll. White-sand populations expressed more dry mass of secondary compounds and accumulated more flavone glycosides and oxidized terpenes, whereas terra firme populations produced a coumaroylquinic acid that was absent from white-sand populations. We interpret these results as strong evidence that herbivores and resource availability select for divergent types and amounts of defense investment in white-sand and terra firme lineages of Protium subserratum, which may contribute to habitat-mediated speciation in these trees. © 2013 by the Ecological Society of America.
Keywords: Amazonia; Ecological speciation; Ecotypes; Herbivory; Natural enemies; Plant defense; Protium subserratum; Terra firme forests; Tropical rain forests; White-sand forests
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Masse, P. S. M., Kenne, M., Mony, R., Dejean, A., & Tindo, M. (2011). Initial behavior in colony fragments of an introduced population of the invasive ant Wasmannia auropunctata. C. R. Biol., 334(7), 572–576.
Abstract: We investigated in the laboratory the initial behavior of propagules of the invasive ant Wasmannia auropunctata in Cameroon where it has been introduced. Both workers and queens at first feigned death (thanatosis), and then the workers slowly moved around the experimental arena; the queens did the same about 10 seconds later. Each queen antennated selected workers that then aggregated together by grasping the hind leg of another ant with their mandibles. When encountering the queen again, the lead worker climbed up the queen's hind leg and onto her back, followed by some other individuals. The remaining workers followed the queen to a location in the experimental arena. When brood was present, the workers transferred it to this location. Orphaned workers did not aggregate, but gathered the brood together and took care of it. By permitting propagules to survive, these behaviors likely contribute to the success of W. auropunctata as an invader. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Keywords: Aggregation; Death feigning; Thanatosis; Worker transportation; Biological invasion; Little fire ant
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