Department Aquatic Ecology

Ecosystem ecology needs a framework that explicitly considers the roles of organic compounds. The ecology of molecules integrates compound identity, diversity, and interactions to understand ecosystem processes, such as nutrient and carbon cycling. This approach leverages advances in analytical chemistry and molecular biology to unravel the complex chemical interplay within ecosystems.

1. Cryptic species are an important part of freshwater biodiversity, yet it remains unclear how these species integrate into communities from local to regional geographic scales. To protect biodiversity, particularly overlooked cryptic species, an accurate understanding of the underlying processes and adequate level of protection is needed.
2. We analysed patterns of syntopies (local co-occurrences) and sympatries (regional range overlap) to explore how the phylogenetic origin of cryptic species shapes biodiversity patterns. We hypothesised (i) that syntopies were more common among distantly than closely related cryptic species, and (ii) that the existing sympatries were an outcome of phylogenetic relatedness and dispersal.
3. The hypotheses were tested on a polyphyletic species complex of subterranean amphipod species (Niphargus rhenorhodanensis complex) by deploying molecular species delimitation, time-calibrated phylogenies, and co-occurrence analyses with probabilistic and generalised linear models (GLM).
4. The studied complex comprised 37–48 molecular operational taxonomic units (MOTUs) from nine different clades, with syntopies occurring at random or less frequently than expected. GLM indicated age of divergence did not predict species sympatries, although they emerged more frequently among MOTUs from different clades. Sympatries, however, emerged through dispersal, in MOTUs with large geographic ranges. These mostly overlapped at the foothills of the Alps, the Jura and the Central Massif.
5. We conclude that the observed spatial patterns are mainly driven by dispersal and presumably reflect the geographic circumstances of speciation. While species richness on a local scale may be an outcome of competition and dispersal, regional biodiversity patterns presumably arise through a clade-level cascade of historical events, including orogeny and climatic shifts.

Temperate streams are subsidized by inputs of leaf litter peaking in fall. Yet, stream communities decompose dead leaves and integrate their energy into the aquatic food web throughout the whole year. Most studies investigating stream decomposition largely overlook long-term trajectories, which must be understood for an appropriate temporal upscaling of ecosystem processes. Using mesocosms, we quantified changes in carbon, nitrogen, and phosphorus content of three leaf species during decomposition at weekly to multi-month intervals for up to a year; then, we tested how decomposition duration affected the subsequent consumption by a keystone amphipod macroinvertebrate. Over a year, nitrogen and phosphorus percentage increased across all leaf species, but only the recalcitrant species maintained initial levels of absolute nitrogen and phosphorus. Prolonged decomposition barely affected or impaired amphipod consumption of labile leaf species, whereas it enhanced feeding on the recalcitrant species. Overall, we demonstrate that recalcitrant leaves might serve as longer stored potential resources for when labile species have already been consumed and that their increasing palatability observed over multi-month intervals of sustained decomposition may stabilize fluctuations in the rates of leaf litter integration into aquatic food webs. This yearlong perspective highlights the relevancy of slow-decomposing leaves for aquatic detrital communities.

Biodiversity–ecosystem functioning experiments have established generally positive species richness-productivity relationships in plots of single ecosystem types, typically grassland or forest. However, it remains unclear whether these findings apply in real-world landscapes that resemble a heterogeneous mosaic of different ecosystem and plant types that interact through biotic and abiotic processes. Here, we show that landscape-level diversity, measured as number of land-cover types (different ecosystems) per 250×250 m, is positively related to landscape-wide remotely-sensed primary production across all of North America, covering 16 of 18 ecoregions of Earth. At higher landscape diversity, productivity was temporally more stable, and 20-year greening trends were accelerated. These effects occurred independent of local species diversity, suggesting emergent mechanisms at hitherto neglected levels of biological organization. Specifically, mechanisms related to interactions among land-cover types unfold at the scale of entire landscapes, similar to, but not necessarily resulting from, interactions between species within single ecosystems.