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Schmitt, S., Derroire, G., Tysklind, N., Heuertz, M., & Hérault, B. (2021). Topography shapes the local coexistence of tree species within species complexes of Neotropical forests. Oecologia, 196, 389–398.
Abstract: Forest inventories in Amazonia include around 5000 described tree species belonging to more than 800 genera. Numerous species-rich genera share genetic variation among species because of recent speciation and/or recurrent hybridisation, forming species complexes. Despite the key role that tree species complexes play in understanding Neotropical diversification, and their need to exploit a diversity of niches, little is known about the mechanisms that allow local coexistence of tree species complexes and their species in sympatry. In this study, we explored the fine-scale distribution of five tree species complexes and 22 species within these complexes. Combining forest inventories, botanical determination, and LiDAR-derived topographic data over 120 ha of permanent plots in French Guiana, we used a Bayesian modelling framework to test the role of fine-scale topographic wetness and tree neighbourhood on the occurrence of species complexes and the relative distribution of species within complexes. Species complexes of Neotropical trees were widely spread across the topographic wetness gradient at the local scale. Species within complexes showed pervasive niche differentiation along with topographic wetness and competition gradients. Similar patterns of species-specific habitat preferences were observed within several species complexes: species more tolerant to competition for resources grow in drier and less fertile plateaus and slopes. If supported by partial reproductive isolation of species and adaptive introgression at the species complex level, our results suggest that both species-specific habitat specialisation within species complexes and the broad ecological distribution of species complexes might explain the success of these species complexes at the regional scale.
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Leponce, M., Dejean, A., Mottl, O., & Klimes, P. (2021). Rapid assessment of the three-dimensional distribution of dominant arboreal ants in tropical forests. Insect Conservation and Diversity, 14(4), 426–438.
Abstract: Ants are omnipresent in tropical forests, especially territorially dominant arboreal ants whose territories are spatially segregated forming ‘ant mosaics’. These ecologically important species are rarely used in conservation monitoring because of the difficulty in collecting them. We developed a standardised baitline protocol to study the distribution of dominant ants on canopy trees and also a procedure to objectively define species dominance, even in unknown ant assemblages.
Besides eliminating the need to climb trees, this protocol allows live arboreal ant specimens to be sampled at different heights. Behavioural aggressiveness assays between the collected workers provide data on the three-dimensional distribution of colonies and on interactions between species. We compared the results of the behavioural tests to those from null models.
In the New Guinean lowland forest studied, we show that the canopy was either shared by multiple territorial species or inhabited by a single species with a large territory. The baitline protocol collected up to half of the arboreal ant species found in a felling census. However, the proportion of species collected at baits decreased with the increasing spatial dominance of single territorial species.
Behavioural observations used in the protocol allowed a more efficient detection of ant mosaics than null models. Territorially dominant ants were active on both understorey and canopy trees.
The protocol is fast and easy to replicate. It is a potential tool for understanding and monitoring the spatiotemporal dynamics of arboreal ant assemblages and can detect populous colonies, including those of invasive species
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Barr, C. B., Cerdan, A., Clavier, S., & Murienne, J. (2021). Amazonopsis cerdani (Coleoptera: Elmidae: Elminae), a New Species of RiffleBeetle from French Guiana with Habitat Observations. The Coleopterists Bulletin, 75(2), 427–439.
Abstract: A third species of Amazonopsis , Amazonopsis cerdani Barr and Cerdan, new species (Coleoptera: Elmidae), is herein described from French Guiana. One female paratype of Amazonopsis theranyi Barr from Peru is tentatively reassigned to A. cerdani as a non-paratype. Photographic images of the male and female habitus, and the male genitalia, are provided, as is a distribution map and a key to the species. Amazonopsis cerdani differs from A. theranyi from Peru and Amazonopsis camachoi Barr from Venezuela by the presence of prominent spines on protarsomeres 1–4 of males, among other characters. The habitat of this species is small, shallow, lowland streams with sandy-silty substrates and low flow. Specimens were collected from unconsolidated leaf litter in depositional areas, and from stick and leaf packs lodged in the current. Genetic analysis conducted on three specimens from two localities, a male and two females, showed that they are conspecific.
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Guzman, L. M., Trzcinski, M. K., Barberis, I. M., Cereghino, R., Srivastava, D. S., Gilbert Benjamin, et al. (2021). Climate influences the response of community functional traits to local conditions in bromeliad invertebrate communities. Ecography, 44(3), 440–452.
Abstract: Functional traits determine an organism's performance in a given environment and as such determine which organisms will be found where. Species respond to local conditions, but also to larger scale gradients, such as climate. Trait ecology links these responses of species to community composition and species distributions. Yet, we often do not know which environmental gradients are most important in determining community trait composition at either local or biogeographical scales, or their interaction. Here we quantify the relative contribution of local and climatic conditions to the structure and composition of functional traits found within bromeliad invertebrate communities. We conclude that climate explains more variation in invertebrate trait composition within bromeliads than does local conditions. Importantly, climate mediated the response of traits to local conditions; for example, invertebrates with benthic life-history traits increased with bromeliad water volume only under certain precipitation regimes. Our ability to detect this and other patterns hinged on the compilation of multiple fine-grained datasets, allowing us to contrast the effect of climate versus local conditions. We suggest that, in addition to sampling communities at local scales, we need to aggregate studies that span large ranges in climate variation in order to fully understand trait filtering at local, regional and global scales.
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Migliavacca, M., Musavi, T., Mahecha, M. D., Nelson, J. A., Knauer, J., Baldocchi, D. D., et al. (2021). The three major axes of terrestrial ecosystem function. Nature, 598(7881), 468–472.
Abstract: The leaf economics spectrum1,2 and the global spectrum of plant forms and functions3 revealed fundamental axes of variation in plant traits, which represent different ecological strategies that are shaped by the evolutionary development of plant species2. Ecosystem functions depend on environmental conditions and the traits of species that comprise the ecological communities4. However, the axes of variation of ecosystem functions are largely unknown, which limits our understanding of how ecosystems respond as a whole to anthropogenic drivers, climate and environmental variability4,5. Here we derive a set of ecosystem functions6 from a dataset of surface gas exchange measurements across major terrestrial biomes. We find that most of the variability within ecosystem functions (71.8%) is captured by three key axes. The first axis reflects maximum ecosystem productivity and is mostly explained by vegetation structure. The second axis reflects ecosystem water-use strategies and is jointly explained by variation in vegetation height and climate. The third axis, which represents ecosystem carbon-use efficiency, features a gradient related to aridity, and is explained primarily by variation in vegetation structure. We show that two state-of-the-art land surface models reproduce the first and most important axis of ecosystem functions. However, the models tend to simulate more strongly correlated functions than those observed, which limits their ability to accurately predict the full range o
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Gonzalès-Melo, A., Posada, J. M., Beauchêne, J., Lehnebach, R., Leviennois, S., Rivera, K., et al. (2021). Radial variations in wood functional traits in a rain forest from eastern Amazonia. Trees, 36, 569–581.
Abstract: Trees can modify their wood structure in response to changes in mechanical, hydraulic and storage demands during their life-cycles. Thus, examining radial variations in wood traits is important to expand our knowledge of tree functioning and species ecological strategies. Yet, several aspects of radial changes in wood functional traits are still poorly understood, especially in angiosperm trees from tropical humid forests. Here, we examined radial shifts in wood traits in trunks of tropical forest species and explored their potential ecological implications. We first examined radial variations in wood specific gravity (WSG). Then, we asked what anatomical traits drove radial variations in WSG, and whether WSG, vessel fraction and specific hydraulic conductivity vary independently from each other along the radius gradients. We measured WSG and eight wood anatomical traits, at different radial positions along the trunks, in 19 tree species with contrasting shade-tolerance from a lowland tropical forest in eastern Amazonia. Most species had significant radials shifts in WSG. Positive radial gradients in WSG (i.e., increments from pith to bark) were common among shade-intolerant species and were explained by different combinations of fiber and parenchyma traits, while negative radial shifts in WSG (e.g., decreases towards the bark) were present in shade-tolerants, but were generally weakly related to anatomical traits. We also found that, in general, WSG was unrelated to vessel fraction and specific hydraulic conductivity in any radial position. This study illustrates the contrasting radial variations in wood functional traits that occur in tree species from a humid lowland tropical forest. In particular, our results provide valuable insights into the anatomical traits driving WSG variations during tree development. These insights are important to expand our knowledge on tree ecological strategies by providing evidence on how wood allocation varies as trees grow, which in turn can be useful in studying trait-demography associations, and in estimating tree above-ground biomass.
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Dejean, A., Petitclerc, F., Azémar, F., & Rossi, V. (2021). Nutrient provisioning of its host myrmecophytic tree by a temporary social parasite of a plant-ant. Biological Journal of the Linnean Society, 133(3), 744–750.
Abstract: One of the most advanced ant–plant mutualisms is represented by myrmecophytes sheltering colonies of some plant-ant species in hollow structures called domatia. In turn, the myrmecophytes benefit from biotic protection and sometimes nutrient provisioning (myrmecotrophy). Furthermore, over the course of evolution, some ant species have become social parasites of others. In this general context, we studied the relationship between its host trees and Azteca andreae (Dolichoderinae), a temporary social parasite of the plant-ant Azteca ovaticeps, and, as such, obligatorily associated with myrmecophytic Cecropia obtusa trees (Urticaceae). A first experiment showed that the δ15N values of the young leaves of Cecropia sheltering a mature A. andreae colony were very similar to those for trees sheltering Azteca alfari or A. ovaticeps, two typical Cecropia mutualists for which myrmecotrophy is known. In a second experiment, by injecting a 15N-labelled glycine solution into locusts given as prey to A. andreae colonies, we triggered an increase in δ15N in the young leaves of their host Cecropia. Thus, 15N passed from the prey to the host trees, explaining the outcomes of the first experiment. We discuss these results in light of the notion of ‘by-product benefits’.
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Valverde-Barrantes, O. J., Authier, L., Schimann, H., & Baraloto, C. (2021). Root anatomy helps to reconcile observed root trait syndromes in tropical tree species. American Journal of Botany, 108(5), 744–755.
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Quéméré, E., Aucourt, M., Troispoux, V., Brosse, S., Murienne, J., Covain, R., et al. (2021). Unraveling the dietary diversity of Neotropical top predators using scat DNA metabarcoding: A case study on the elusive Giant Otter. Environmental DNA, 3(5), 889–900.
Abstract: Large carnivores play a pivotal regulating role in maintaining healthy and balanced ecosystems; however, most of them are rare and elusive, and knowledge about their resource consumption is scarce. Traditional methods based on morphological identification of undigested remains are labor intensive and often not sufficiently accurate, leading to errors and biased ecological inferences. Here, we developed a multi-marker DNA metabarcoding approach to analyze the dietary diversity of giant otters (Pteronura brasiliensis) from fecal DNA while controlling predator species identity. We combined two mitochondrial markers, 12S rRNA and cytochrome c oxidase 1 (COI) gene, that target the full range of potential vertebrate and invertebrate prey. We compiled a local reference database of DNA barcodes for most potentially ingested fish, which were used to evaluate the specificity of the metabarcoding primers in silico. Most prey are identified at the species level (>90%) and the dietary profiles provided independently by the two markers are highly similar, whether in terms of list of prey or frequency of occurrences, hence validating the approach. We detected a higher number of rare fish prey with the 12S primers that amplified solely Teleost species while the degenerate COI primers revealed non-fish prey (e.g., amphibians, snakes, birds, and earthworms) and confirmed predator species identity. This study demonstrated that scat DNA metabarcoding is particularly useful to provide in-depth information on elusive carnivorous dietary profile. Our methodology opens up new opportunities to understand how top carnivores diet cope with the effects of anthropogenic alteration of ecosystems and identify conflicts with humans and livestock.
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Vleminckx, J., Fortunel, C., Valverde-Barrantes, O., Paine, C. E. T., Engel, J., Petronelli, P., et al. (2021). Resolving whole-plant economics from leaf, stem and root traits of 1467 Amazonian tree species. Oikos, 130(7), 1193–1208.
Abstract: It remains unclear how evolutionary and ecological processes have shaped the wide variety of plant life strategies, especially in highly diverse ecosystems like tropical forests. Some evidence suggests that species have diversified across a gradient of ecological strategies, with different plant tissues converging to optimize resource use across environmental gradients. Alternative hypotheses propose that species have diversified following independent selection on different tissues, resulting in a decoupling of trait syndromes across organs. To shed light on the subject, we assembled an unprecedented dataset combining 19 leaf, stem and root traits for 1467 tropical tree species inventoried across 71 0.1-ha plots spanning broad environmental gradients in French Guiana. Nearly 50% of the overall functional heterogeneity was expressed along four orthogonal dimensions, after accounting for phylogenetic dependences among species. The first dimension related to fine root functioning, while the second and third dimensions depicted two decoupled leaf economics spectra, and the fourth dimension encompassed a wood economics spectrum. Traits involved in orthogonal functional strategies, five leaf traits in particular but also trunk bark thickness, were consistently associated with a same gradient of soil texture and nutrient availability. Root traits did not show any significant association with edaphic variation, possibly because of the prevailing influence of other factors (mycorrhizal symbiosis, phylogenetic constraints). Our study emphasises the existence of multiple functional dimensions that allow tropical tree species to optimize their performance in a given environment, bringing new insights into the debate around the presence of a whole plant economic spectrum in tropical forest tree communities. It also emphasizes the key role that soil heterogeneity plays in shaping tree species assembly. The extent to which different organs are decoupled and respond to environmental gradients may also help to improve our predictions of species distribution changes in responses to habitat modification and environmental changes.
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