Upstream trophic structure modulates downstream community dynamics via resource subsidies

Trophic Conditions Influence Widespread Distribution of Aster-Like Nanoparticles Within Aquatic Environments

Aster-like nanoparticles (ALNs) are newly described femto-entities. Their ecology (e.g., geographic distribution, spatial dynamic, preferences, forcing factors) is still unknown. Here, we report that these entities, which have largely been ignored until now, can develop or maintain themselves in most aquatic environments in the Loire River catchment, France. We observed a significant influence of the trophic state on ALN ecological distributions. A positive relationship between prokaryotic abundance and ALN (r² = 0.72, p < 0.01) has been identified, but its exact nature remains to be clarified. Combined with their ubiquitous distribution and high abundances (up to 7.9 × 10⁶ ALNs mL^-1) recorded in our samples, this probably makes ALNs an overlooked functional component in aquatic ecosystems.

Cross-ecosystem carbon flows connecting ecosystems worldwide

Ecosystems are widely interconnected by spatial flows of material, but the overall importance of these flows relative to local ecosystem functioning remains unclear. Here we provide a quantitative synthesis on spatial flows of carbon connecting ecosystems worldwide. Cross-ecosystem flows range over eight orders of magnitude, bringing between 10⁻³ and 10⁵ gC m⁻² year⁻¹ to recipient ecosystems. Magnitudes are similar to local fluxes in freshwater and benthic ecosystems, but two to three orders of magnitude lower in terrestrial systems, demonstrating different dependencies on spatial flows among ecosystem types. The strong spatial couplings also indicate that ecosystems are vulnerable to alterations of cross-ecosystem flows. Thus, a reconsideration of ecosystem functioning, including a spatial perspective, is urgently needed.

Material flows between ecosystems, though the degree to which ecosystems are coupled is under investigation. Here Gounand et al. analyze cross-ecosystem carbon flows and relate them to in situ functions, and report different dependencies on spatial flows across numerous ecosystems.

Upstream trophic structure modulates downstream community dynamics via resource subsidies

In many natural systems, the physical structure of the landscape dictates the flow of resources. Despite mounting evidence that communities' dynamics can be indirectly coupled by reciprocal among ecosystem resource flows, our understanding of how directional resource flows might indirectly link biological communities is limited. We here propose that differences in community structure upstream should lead to different downstream dynamics, even in the absence of dispersal of organisms. We report an experimental test of the effect of upstream community structure on downstream community dynamics in a simplified but highly controlled setting, using protist microcosms. We implemented directional flows of resources, without dispersal, from a standard resource pool into upstream communities of contrasting interaction structure and then to further downstream communities of either one or two trophic levels. Our results demonstrate that different types of species interactions in upstream habitats may lead to different population sizes and levels of biomass in these upstream habitats. This, in turn, leads to varying levels of detritus transfer (dead biomass) to the downstream communities, thus influencing their population densities and trophic interactions in predictable ways. Our results suggest that the structure of species interactions in directionally structured ecosystems can be a key mediator of alterations to downstream habitats. Alterations to upstream habitats can thus cascade down to downstream communities, even without dispersal.