Trophic downgrading decreases species asynchrony and community stability regardless of climate warming

Abstract

Theory and some evidence suggest that biodiversity promotes stability. However, evidence of how trophic interactions and environmental changes modulate this relationship in multitrophic communities is lacking. Given the current scenario of biodiversity loss and climate changes, where top predators are disproportionately more affected, filling these knowledge gaps is crucial. We simulated climate warming and top predator loss in natural microcosms to investigate their direct and indirect effects on temporal stability of microbial communities and the role of underlying stabilising mechanisms. Community stability was insensitive to warming, but indirectly decreased due to top predator loss via increased mesopredator abundance and consequent reduction of species asynchrony and species stability. The magnitude of destabilising effects differed among trophic levels, being disproportionally higher at lower trophic levels (e.g. producers). Our study unravels major patterns and causal mechanisms by which trophic downgrading destabilises large food webs, regardless of climate warming scenarios.

Temporal variability declines with increasing trophic levels and spatial scales in freshwater ecosystems

“…The movement of top consumers from low prey density patches for more profitable high-density patches should also promote more spatially asynchronous fluctuations in resources, which should in turn decrease prey variability at the regional scale. Recent experimental evidence suggests that the extinction of a top predator led to more unstable communities due to an increase in synchrony of lower trophic levels caused by mesopredator pressure 28 . We thus suggest that top mobile consumers can be seen as stabilizers of their abundances and of entire metacommunities.…”

Environmental DNA Biomonitoring Reveals the Interactive Effects of Dams and Nutrient Enrichment on Aquatic Multitrophic Communities

“…In comparison, high modularity represents that the fluctuation of taxa in one module will not spread to other modules due to limited linkages across different modules, isolating different taxa from disturbance intensity. , The synergistic manner identified by modularity and coherence further shows that the negative interaction effects of stressors are accumulated and amplified at the food web level. Because, on the one hand, the cascade effect has its own amplification effect across trophic levels in the food web, ,, and, on the other hand, the bio-interactions among taxa in the food web are relevant to the material and energy metabolism in the ecosystem, , the simplified food webs inevitably reduce the ecosystem process and stability, , inhibit the transfer efficiency of C/N/P elements across trophic levels, further lead to water eutrophication and water security risks, and ultimately drive the secondary variation of aquatic communities.…”

“…Because, on the one hand, the cascade effect has its own amplification effect across trophic levels in the food web, 25,26,72 and, on the other hand, the bio-interactions among taxa in the food web are relevant to the material and energy metabolism in the ecosystem, 29,30 the simplified food webs inevitably reduce the ecosystem process and stability, 53,73 inhibit the transfer efficiency of C/N/P elements across trophic levels, further lead to water eutrophication and water security risks, and ultimately drive the secondary variation of aquatic communities.…”

“…River systems inhabit highly diverse aquatic organisms, including microbiota, invertebrates, and fish. ,, These groups are in different niches that do their part in ecosystems, and there are close biotic interactions between them. , A recent study suggested that dams alter the structure of river food webs through bottom-up and top-down pathways . On the one hand, dams affect the energy and material transfer from debris or primary producers by changing the availability of basic food resources in rivers (e.g., the reduction of coarse detritus); , on the other hand, dams hinder the dispersal of fish species and migration routes for spawning or foraging; ,, fish determine the spatiotemporal patterns of their prey communities through top-down control and trophic cascades. , Moreover, the enrichment of nitrogen and phosphorus in rivers can eliminate the nutrient limitation of plankton communities and increase their biomass . These changes further increase the energy flow from primary productivity and then transfer it to a higher trophic level (e.g., herbivorous fish), and finally change the structure and composition of the food web. − While these pieces of evidence suggest that dams and nutrient enrichment drive the aquatic communities from the multiple taxonomic groups or multitrophic levels, most studies only focus on a single taxonomic group (e.g., fish and algae).…”

“…21 On the one hand, dams affect the energy and material transfer from debris or primary producers by changing the availability of basic food resources in rivers (e.g., the reduction of coarse detritus); 22,23 on the other hand, dams hinder the dispersal of fish species and migration routes for spawning or foraging; 4,9,24 fish determine the spatiotemporal patterns of their prey communities through top-down control and trophic cascades. 25,26 Moreover, the enrichment of nitrogen and phosphorus in rivers can eliminate the nutrient limitation of plankton communities and increase their biomass. 27 These changes further increase the energy flow from primary productivity and then transfer it to a higher trophic level (e.g., herbivorous fish), and finally change the structure and composition of the food web.…”