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Trees play a key role in the structure and function of many ecosystems worldwide. In the Mediterranean Basin, forests cover approximately 22% of the total land area hosting a large number of endemics (46 species). Despite its particularities and vulnerability, the biodiversity of Mediterranean trees is not well known at the taxonomic, spatial, functional, and genetic levels required for conservation applications. The WOODIV database fills this gap by providing reliable occurrences, four functional traits (plant height, seed mass, wood density, and specific leaf area), and sequences from three DNA-regions (rbcL, matK, and trnH-psbA), together with modelled occurrences and a phylogeny for all 210 Euro-Mediterranean tree species. We compiled, homogenized, and verified occurrence data from sparse datasets and collated them on an INSPIRE-compliant 10 × 10 km grid. We also gathered functional trait and genetic data, filling existing gaps where possible. The WOODIV database can benefit macroecological studies in the fields of conservation, biogeography, and community ecology.

Environmental DNA (eDNA) metabarcoding has recently gain much attention to assess aquatic environment biodiversity. A great variety of protocols have been developed to collect, extract, and analyze eDNA, some of which are continuously evolving and optimized with technological improvements. Such technological shifts might deprecate the biological data produced with earlier protocols, leading to a loss of biological knowledge. Here, we investigated the robustness of an aquatic eDNA metabarcoding method through the comparison of two biodiversity datasets generated by two optimized protocols with different collection and extraction steps. To this end, we compared fish community richness and composition of 12 streams and 3 rivers from French Guiana, sampled with two distinct protocols commonly used in aquatic eDNA studies. Although sample collection with each protocol was not achieved the same year, our results show that species richness and species composition were only slightly affected by the protocol choice, both protocols producing similar fish assemblages at each sample site. Both protocols had a higher replicability in streams than in rivers, strengthening the importance to adapt sampling effort to waterbody type as rivers host a larger number of species than small streams. Despite the need for a standardized approach in eDNA metabarcoding studies, testing the robustness of datasets to protocol variations remains crucial to valorize old data, time series, or data collected in difficult to access locations.

Freshwater ecology templates were developed in temperate streams, but whether they also apply to tropical streams that harbour a higher biological diversity than their temperate counterparts remains uncertain. This is particularly true for tropical fish assemblages inhabiting small streams that have been less studied than larger, higher-order lowland streams. Here, we disentangled the strength of spatial (longitudinal and environmental) drivers, and scale-specific (drainage basin, reach and local scale) determinants of species richness and composition of freshwater fish assemblages inhabiting small streams in French Guiana. We found that species richness increased from upstream to downstream but also with increasing local habitat structural diversity independently of stream position in the upstream–downstream gradient. This pattern was shared by the two most speciose fish orders (Characiformes and Siluriformes), demonstrating that species addition rather than species replacement shaped species richness in these assemblages. Species composition of fish assemblages was determined equally by their spatial structure within drainage and by the environment, and assemblages differed both with distance and along an upstream–downstream gradient. The environmental effect on species assemblages indicated by the fact that almost all environmental descriptors had slight but nonetheless significant effects on assemblage composition, probably reflecting species-specific responses to the local environment. In contrast, despite a strong micro-endemism between drainages for some taxa, assemblages were only slightly affected by river drainage identity, since widespread species were a common constituent of assemblages in all rivers. We identified five species assemblages characterising different local habitat features from torrential areas to lowland muddy areas. We also distinguished fish assemblages from confluence areas with larger rivers, which differed from the other five assemblages. The fish zonation patterns we report can constitute a benchmark for future studies measuring the impact of anthropogenic disturbances on Neotropical forest streams.

Aim Differences in dispersal limitation and environmental filtering have been proposed to explain differences in diversity patterns between regions. Incorporating functional traits into studies of assembly rules allows the relative strengths of such processes to be distinguished. We test the predictions that assemblages in a similar environment under strong dispersal limitation should be differentiated taxonomically but not functionally, whereas strong environmental filtering should more differentiate assemblages functionally. Location French Guiana and France. Methods We used two datasets on fish assemblage composition: one for French Guiana and one for continental France. We constrained both dataset to have similar geographical extent and similar environment using site location and topographic variables of the French Guiana dataset to select continental France data. We estimated functional diversity using a combination of 15 fish morphological traits. We computed species and functional richness at regional and local scales for both regions. We calculated taxonomic and functional turnover between sites and compared them within and between regions. Results Taxonomic and functional richness were higher in tropical fish assemblages than in temperate ones both on regional and local scales. Species richness differences between the two regions resulted in very similar functional richness. Temperate assemblages showed a higher functional turnover than tropical assemblages, but a lower taxonomic turnover. We found a stronger turnover in taxonomic diversity than in functional diversity between tropical assemblages, and the opposite pattern between temperate ones. Main conclusions The higher functional richness in tropical assemblages was mainly caused by an increased number of species compared to temperate assemblages, probably linked with an increase in available niches. Dispersal limitation was the predominant process in structuring Guianese stream fish assemblages causing strong species replacement, whereas French stream fish assemblages were mainly under strong environmental filtering resulting in local adaptations to different environments.

International audience; The statistical reliability of a pollen count in representing the true composition of modern and fossil pollen assemblages depends on the minimum number of pollen grains counted. In palynological literature this number varies between b150 and N1000, but very few studies have probed the question using robust statistical approaches. Here, we use the Pearson-Brown Prophecy formula and apply it to different fossil pollen counts from two large lake systems in Iran to calculate the minimum terrestrial and total pollen count necessary to obtain a reliable representativity of pollen assemblages. Our results surprisingly show that a pollen count of b150 is sufficient to achieve a reliability of 0.90 with no additional significant information obtained when counting more pollen. If the upland vegetation reconstruction is important, then terrestrial pollen counts as low as 67 could be sufficient. It seems that the statistically significant pollen counts are site-specific and vary between different environments and even within the same type of environment. We suggest that this value should be calculated for each pollen site so that the pollen analysts can more efficiently manage their time when counting pollen slides.

Determining the species compositions of local assemblages is a prerequisite to understanding how anthropogenic disturbances affect biodiversity. However, biodiversity measurements often remain incomplete due to the limited efficiency of sampling methods. This is particularly true in freshwater tropical environments that host rich fish assemblages, for which assessments are uncertain and often rely on destructive methods. Developing an efficient and nondestructive method to assess biodiversity in tropical freshwaters is highly important. In this study, we tested the efficiency of environmental DNA (eDNA) metabarcoding to assess the fish diversity of 39 Guianese sites. We compared the diversity and composition of assemblages obtained using traditional and metabarcoding methods. More than 7,000 individual fish belonging to 203 Guianese fish species were collected by traditional sampling methods, and ~17 million reads were produced by metabarcoding, among which ~8 million reads were assigned to 148 fish taxonomic units, including 132 fish species. The two methods detected a similar number of species at each site, but the species identities partially matched. The assemblage compositions from the different drainage basins were better discriminated using metabarcoding, revealing that while traditional methods provide a more complete but spatially limited inventory of fish assemblages, metabarcoding provides a more partial but spatially extensive inventory. eDNA metabarcoding can therefore be used for rapid and large-scale biodiversity assessments, while at a local scale, the two approaches are complementary and enable an understanding of realistic fish biodiversity.