Département Ecologie aquatique

The late Smithian and Smithian-Spathian boundary (SSB) witnessed significant conodont extinction approximately 2.7 million years after the major Permian-Triassic boundary extinction. This study offers a detailed examination of the Smithian-Spathian transition at the Guryul Ravine section in the Srinagar district, Kashmir, focusing on conodonts and δ¹³C_carb values. The section features an unprecedented conodont taxonomic richness, with 53 species from 17 genera, including three newly formalized species: Neospathodus aristatus n. sp., Neospathodus guryulensis n. sp. and Borinella? prima n. sp. Additionally, Borinella ex gr. buurensis and Scythogondolella ex gr. milleri are subdivided into multiple morphotypes, facilitating a refined biochronological scheme.
A high-resolution δ¹³C_carb record spanning the Early Triassic captures global carbon isotope excursions. The integration of δ¹³C_carb with conodont biostratigraphy enhances global correlation of the Smithian-Spathian transition. The late Smithian conodont extinction aligns with a globally observed positive δ¹³C_carb excursion, reaching an exceptional value of + 12 ‰, likely of diagenetic origin.
This study proposes a new conodont biochronological framework based on the Unitary Association Method (UAM). Placing the SSB between the extinction climax and re-diversification onset, the framework relies on a rich conodont collection from Guryul Ravine, Kashmir, and a comprehensive reassessment of conodont data from 19 other sections along the northern Gondwana margin. The resulting 16 Unitary Association Zones (UAZs) are cross-referenced with lithological, chemostratigraphical (δ¹³C_carb), and ammonoid markers, establishing an unprecedentedly robust basis for defining the SSB. The proposed boundary is within UAZ₈ but allows for future refinements.

Aquatic and terrestrial ecosystems are linked through the reciprocal exchange of materials and organisms. Aquatic-to-terrestrial subsidies are relatively small in most terrestrial ecosystems, but they can provide high contents of limiting resources that increase consumer fitness and ecosystem production. However, they also may carry significant contaminant loads, particularly in anthropogenically impacted watersheds. Global change processes, including land use change, climate change and biodiversity declines, are altering the quantity and quality of aquatic subsidies, potentially shifting the balance of costs and benefits of aquatic subsidies for terrestrial consumers. Many global change processes interact and impact both the bright and dark sides of aquatic subsidies simultaneously, highlighting the need for future integrative research that bridges ecosystem as well as disciplinary boundaries. We identify key research priorities, including increased quantification of the spatiotemporal variability in aquatic subsidies across a range of ecosystems, greater understanding of the landscape-scale extent of aquatic subsidy impacts and deeper exploration of the relative costs and benefits of aquatic subsidies for consumers.

Global efforts aimed at safeguarding and restoring biodiversity require methods to monitor progress towards conservation objectives. Such methods should provide a systematic and robust assessment of biodiversity for the lowest cost. River environmental DNA (eDNA) metabarcoding has been successfully applied to measure biodiversity in dendritic riverine habitats and is increasingly used to describe communities of terrestrial vertebrates in ecosystems that are challenging to survey using traditional methods. However, interpreting eDNA surveys in riverine habitats requires an understanding of the influence of eDNA transport, decay, and production on the distribution of eDNA. To this end, the hydrology-based eDITH (eDNA Integrating Transport and Hydrology) model incorporates such factors and can recover reliable spatial biodiversity patterns for aquatic taxa, but its potential to successfully model terrestrial taxa is so far unexplored. Here, we applied eDITH to eDNA metabarcoding data for terrestrial mammals collected over two mountainous catchments (575 and 745 km²) in British Columbia, Canada. We assessed prediction transferability between neighboring catchments and compared model predictions with observations from camera trapping. We found that for 9 out of 15 taxa detected by both eDNA and camera traps, predicted distributions predominantly matched observations from camera trap surveys, illustrating that eDITH can uncover patterns of mammal distribution in mountainous catchments. While lacking knowledge of actual taxon density prevents us from determining whether discrepancies stem from data limitations or complex eDNA production-density relationships, good transferability of predictions to the neighboring catchments suggests that eDNA distribution of some terrestrial and semi-aquatic mammals is partly determined by habitat preference and hydrology. Downstream sampling can recover most biodiversity across the catchment, but the inclusion of upstream samples can aid in detecting elusive species. This study underscores the broader applications of river eDNA beyond aquatic species and illustrates its potential use in addressing terrestrial mammal biodiversity monitoring objectives with tailored sampling approaches.