| Home | [31–40] << 41 42 43 44 45 46 47 48 49 50 >> [51–60] |
|
Zinger, L., Donald, J., Brosse, S., Gonzalez, M. A., Iribar, A., Leroy, C., et al. (2020). Advances and prospects of environmental DNA in neotropical rainforests. Adv. Ecol. Res., 62, 331–373.
Abstract: The rainforests of the Neotropics shelter a vast diversity of plant, animal and microscopic species that provide critical ecosystem goods and services for both local and worldwide populations. These environments face a major crisis due to increased deforestation, pollution, and climate change, emphasizing the need for more effective conservation efforts. The adequate monitoring of these ecosystems has proven a complex and time consuming endeavour, which depends on ever dwindling taxonomic expertise. To date, many species remain undiscovered, let alone described, with otherwise limited information regarding known species population distributions and densities. Overcoming these knowledge shortfalls and practical limitations is becoming increasingly possible through techniques based on environmental DNA (eDNA), i.e., DNA that can be obtained from environmental samples (e.g. tissues, soil, sediment, water, etc.). When coupled with high-throughput sequencing, these techniques now enable realistic, cost-effective, and standardisable biodiversity assessments. This opens up enormous opportunities for advancing our understanding of complex and species-rich tropical communities, but also in facilitating large-scale biomonitoring programs in the neotropics. In this review, we provide a brief introduction to eDNA methods, and an overview of their current and potential uses in both terrestrial and aquatic ecosystems of neotropical rainforests. We also discuss the limits and challenges of these methods for our understanding and monitoring of biodiversity, as well as future research and applied perspectives of these techniques in neotropical rainforests, and beyond. © 2020 Elsevier Ltd
Keywords: Biomonitoring; Conservation biology; DNA metabarcoding; eDNA; Environmental genomics; Neotropics; Rainforests
|
|
Sayer, E. J., Rodtassana, C., Sheldrake, M., Bréchet, L. M., Ashford, O. S., Lopez-Sangil, L., et al. (2020). Revisiting nutrient cycling by litterfall—Insights from 15 years of litter manipulation in old-growth lowland tropical forest. Adv. Ecol. Res., 62, 173–223.
Abstract: The crucial role of tropical forests in the global carbon balance is underpinned by their extraordinarily high biomass and productivity, even though the majority of tropical forests grow on nutrient-poor soils. Nutrient cycling by litterfall has long been considered essential for maintaining high primary productivity in lowland tropical forests but few studies have tested this assumption experimentally. We review and synthesise findings from the Gigante Litter Manipulation Project (GLiMP), a long-term experiment in lowland tropical forest in Panama, Central America, in which litter has been removed from or added to large-scale plots for 15 years. We assessed changes in soil and litter nutrient concentrations in response to the experimental treatments and estimated nutrient return and nutrient use efficiency to indicate changes in nutrient cycling. The soil concentrations of most nutrients increased with litter addition and declined with litter removal. Litter removal altered nitrogen, potassium, manganese and zinc cycling, demonstrating the importance of litter inputs for maintaining the availability of these elements to plants. By contrast, litter addition only altered nitrogen cycling and, despite low concentrations of available soil phosphorus, the effects of litter manipulation on phosphorus cycling were inconsistent. We discuss potential mechanisms underlying the observed changes, and we emphasise the importance of decomposition processes in the forest floor for retaining nutrient elements, which partially decouples nutrient cycling from the mineral soil. Finally, by synthesising GLiMP studies conducted during 15 years of litter manipulation, we highlight key knowledge gaps and avenues for future research into tropical forest nutrient cycling. © 2020 Elsevier Ltd
Keywords: Forest floor; Litter addition; Litter removal; Litterfall; Nutrient cycling; Nutrient use efficiency; Soil fertility; Trace elements; Tropical lowland forest
|
|
Delaval, M., & Charles-Dominique, P. (2006). Edge effects on frugivorous and nectarivorous bat communities in a neotropical primary forest in French Guiana. Rev. Ecol.-Terre Vie, 61(4), 343–352.
Abstract: The impact of a road crossing a continuous Guyana primary forest was studied through the analysis of qualitative and quantitative changes in a frugivorous and nectarivorous bat community at different distances from forest edge. Bats were captured along three 3-km forest transects perpendicular to the edge, and at the Nouragues Station located 150 km in the interior of the primary forest block, in an uninhabited area. Along the 3-km transects, we caught over seven times more individuals than in primary forest, this value decreasing according to the distance from the edge. Moreover, at the very edge, species richness was higher than along transects, probably due to exchanges between primary forest and the open habitats. On the contrary, diversity values at forest edges were lower than in primary forest, with a demographic explosion of a few opportunistic phyllostomid species such as Carollia perspicillata and Artibeus jamaicensis. Species restricted to degraded habitat like Glossophaga soricina and Artibeus cinereus were still present 3 km away from the edge, where the proportion of C perspicillata was seven times higher than in primary forest at Nouragues. These changes in the community of bats have important consequences on seed and pollen dispersal. So edge effects may significantly affect both faunal and floral assemblage. We conclude that changes in bat community occur up to at least 3 km from forest edge, i. e. at a greater distance than that found for all other vertebrates previously studied. By their implications our results should be considered in habitat and species conservation management plans.
|
|
Amusant, N., Beauchene, J., Fournier, M., Janin, G., & Thevenon, M. F. (2004). Decay resistance in Dicorynia guianensis Amsh.: analysis of inter-tree and intra-tree variability and relations with wood colour. Ann. For. Sci., 61(4), 373–380.
Abstract: Dicorynia guianensis Amsh. is very widespread in the forests of French Guiana and moreover is the leading species harvested in this area, but its main defect remains the great variability of wood durability, especially with respect to fungal decay. The aim of this work was to study this inter- and intra-tree variability in order to identify the parameters responsible for this variation (growth area, height and radial position) within the tree. The resistance decrease from the outer heartwood to the pith. Measurement of colour variation using the CIELAB (L*, a*, b*, C*, h*) system was performed at the intra-tree level to highlight the longitudinal and radial gradients of variation. Dicorynia guianensis becomes less red and dark from the outer to the inner heartwood and from the base to the top. Lastly, variations of colour and durability were correlated: the wood is less resistant the redder and darker it is.
Keywords: Dicorynia guianensis; Amazonian wood; wood colour/decay resistance; heartwood; variability
|
|
Almeras, T., Derycke, M., Jaouen, G., Beauchene, J., & Fournier, M. (2009). Functional diversity in gravitropic reaction among tropical seedlings in relation to ecological and developmental traits. J. Exp. Bot., 60(15), 4397–4410.
Abstract: Gravitropism is necessary for plants to control the orientation of their axes while they grow in height. In woody plants, stem re-orientations are costly because they are achieved through diameter growth. The functional diversity of gravitropism was studied to check if the mechanisms involved and their efficiency may contribute to the differentiation of height growth strategies between forest tree species at the seedling stage. Seedlings of eight tropical species were grown tilted in a greenhouse, and their up-righting movement and diameter growth were measured over three months. Morphological, anatomical, and biomechanical traits were measured at the end of the survey. Curvature analysis was used to analyse the up-righting response along the stems. Variations in stem curvature depend on diameter growth, size effects, the increase in self-weight, and the efficiency of the gravitropic reaction. A biomechanical model was used to separate these contributions. Results showed that (i) gravitropic movements were based on a common mechanism associated to similar dynamic patterns, (ii) clear differences in efficiency (defined as the change in curvature achieved during an elementary diameter increment for a given stem diameter) existed between species, (iii) the equilibrium angle of the stem and the anatomical characters associated with the efficiency of the reaction also differed between species, and (iv) the differences in gravitropic reaction were related to the light requirements: heliophilic species, compared to more shade-tolerant species, had a larger efficiency and an equilibrium angle closer to vertical. This suggests that traits determining the gravitropic reaction are related to the strategy of light interception and may contribute to the differentiation of ecological strategies promoting the maintenance of biodiversity in tropical rainforests.
Keywords: Biomechanics; French Guiana; functional diversity; gravitropism; reaction wood; tropical rainforest
|
|
Chang, S. S., Clair, B., Ruelle, J., Beauchene, J., Di Renzo, F., Quignard, F., et al. (2009). Mesoporosity as a new parameter for understanding tension stress generation in trees. J. Exp. Bot., 60(11), 3023–3030.
Abstract: The mechanism for tree orientation in angiosperms is based on the production of high tensile stress on the upper side of the inclined axis. In many species, the stress level is strongly related to the presence of a peculiar layer, called the G-layer, in the fibre cell wall. The structure of the G-layer has recently been described as a hydrogel thanks to N-2 adsorption-desorption isotherms of supercritically dried samples showing a high mesoporosity (pores size from 2-50 nm). This led us to revisit the concept of the G-layer that had been, until now, only described from anatomical observation. Adsorption isotherms of both normal wood and tension wood have been measured on six tropical species. Measurements show that mesoporosity is high in tension wood with a typical thick G-layer while it is much less with a thinner G-layer, sometimes no more than normal wood. The mesoporosity of tension wood species without a G-layer is as low as in normal wood. Not depending on the amount of pores, the pore size distribution is always centred around 6-12 nm. These results suggest that, among species producing fibres with a G-layer, large structural differences of the G-layer exist between species.
Keywords: Growth stress; hydrogel; mesoporosity; tension wood
|
|
Scotti, I., & Delph, L. F. (2006). Selective trade-offs and sex-chromosome evolution in Silene latifolia. Evolution, 60(9), 1793–1800.
Abstract: Alleles of sexually antagonistic genes (i.e., genes with alleles affecting fitness in opposite directions in the two sexes) can avoid expression in the sex to which they are detrimental via two processes: they are subsumed into the nonrecombining, sex-determining portion of the sex chromosomes or they evolve sex-limited expression. The former is considered more likely and leads to Y-chromosome degeneration. We mapped quantitative trait loci of major effect for sexually dimorphic traits of Silene latifolia to the recombining portions of the sex chromosomes and found them to exhibit sex-specific expression, with the Y chromosome in males controlling a relatively larger proportion of genetic variance than the X in females and the average autosome. Both reproductive and ecophysiological traits map to the recombining region of the sex chromosomes. We argue that genetic correlations among traits maintain recombination and polymorphism for these genes because of balancing selection in males, whereas sex-limited expression represses detrimental alleles in females. Our data suggest that the Y chromosome of S. latifolia plays a major role in the control of key metabolic activities beyond reproductive functions.
Keywords: antagonistic genes; linkage map; quantitative trait loci; sex-specific expression; Y chromosome
|
|
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.
|
|
Bardet, S., Beauchene, J., & Thibaut, B. (2003). Influence of basic density and temperature on mechanical properties perpendicular to grain of ten wood tropical species. Ann. For. Sci., 60(1), 49–59.
Abstract: The influence of temperature on transverse mechanical properties of 10 tropical species in green condition was studied in radial compression (0 to 99 degreesC), transverse shear with longitudinal-radial shearing plane and rupture of the longitudinal-tangential plane (20 to 80 degreesC). Basic density ranged from 0.21 to 0.91 g cm(-3). Load-displacement curves were characterised by initial rigidity, yield stress, yield strain and strain energy at 20% strain level. The relation between each criterion and basic density was expressed by a power law. The dependency on temperature evidenced a sharp glassy transition, except for the fracture energy only slightly influenced by temperature. An empirical model allowed evaluating a transition temperature between 51 and 69 degreesC, depending on the species and the criterion, which was attributed to lignin. Detailed analysis of the apparent modulus in radial compression suggested that complex relaxation phenomena occur around 10 degreesC and that the rubbery state is not fully reached at 80 degreesC.
Keywords: green wood; tropical wood; transverse mechanical properties; basic density; softening temperature
|
|
Sist, P., Picard, N., & Gourlet-Fleury, S. (2003). Sustainable cutting cycle and yields in a lowland mixed dipterocarp forest of Borneo. Ann. For. Sci., 60(8), 803–814.
Abstract: Based on a 6 year monitoring of the dynamics of a mixed dipterocarp forest in East Borneo (1990-1996), we built a matrix model to predict the sustainable cutting cycle in relation with the extraction and damage rates. Plots were ordered according to three main groups of damage and logging intensity. The first group G1 gathered slightly damaged plots with a remaining basal area greater than or equal to80% of the original (mean logging intensity = 6 trees ha(-1)). Plots belonging to G2, had a remaining basal area varying between 70 and 79% of the original one (mean logging intensity = 8 trees ha(-1)). Finally, G3 gathers highly damaged plots with a remaining basal area < 70% of the original one and a high logging intensity (mean = 14 trees ha(-1)). The mean sustainable cutting cycles predicted in the three groups were significantly different and equal 27, 41 and 89 years in G1, G2 and G3 respectively. However, the respective mean annual extracted volumes were similar: 1.6, 1.8 and 1.4 m(3) ha(-1) year(-1), respectively in G1, G2 and G3. The model suggests that a 40 year cycle, extracting 8 trees ha(-1) (60 m(3) ha(-1)) and an annual volume of 1.5 m(3) ha(-1) year(-1) is the best option to preserve ecological integrity of the forest, to ensure yield sustainability and, according to existing cost analysis, economic profitability. This result is also consistent with other studies which already demonstrated that logging damage reduction using RIL techniques could be only significant with a moderate felling intensity not exceeding 8 trees ha(-1). This felling intensity threshold can be easily achieved by applying simple harvesting rules.
|