How antibiotic exposure affect predator-prey interactions by population dynamics in ciliates?

Biodiversity loss resulting from environmental pollution is a global concern. While interspecific interactions are central to ecology, the impact of environmental pollution on predator-prey interactions and its ecological consequences, such as extinction and biodiversity loss, remain unclear. To investigate the effects of antibiotic exposure on predation strength and the resulting ecological consequence, the Didinium-Paramecium was utilized as a predator-prey model and exposed to nitrofurazone or erythromycin, two common pollutants, respectively. Initially, we determined prey population growth dynamics, body size, and predator numerical-functional responses. Subsequently, these above parameters were integrated into a mathematical model of predator-prey predation. Then both the long time-series data and phase portraits obtained through model simulation were used to estimate interaction strength and to predict the outcome of predator-prey coexistence. Our results revealed that exposure to either antibiotic significantly reduced prey population growth parameters (e.g., µmax and K) while increasing individual body size. The combined effects of antibiotic exposure and predation pressure on population growth inhibition or body size promotion were variable, mostly additive, with a few cases of synergy and extremely rare antagonism, depending on antibiotic exposure concentration. As antibiotic exposure concentration increased, the predator rmax generally declined, while functional responses varied depending on specific parameters, implying a decrease in predator-prey interaction strength. Analyses of phase portrait features showed that the population oscillation amplitude decreased with increasing antibiotic exposure concentrations, the cycle length of adjacent peaks increased, and prey extinction occurred earlier. In conclusion, antibiotic exposure reduced both predator and prey fitness, underlying the reason antibiotics reduces the strength of predator-prey interaction. Despite the indirect benefits of prey gain from this, the presence of predators can expedite the process of prey extinction caused by antibiotic exposure.

Different Microeukaryotic Trophic Groups Show Different Latitudinal Spatial Scale Dependences in Assembly Processes across the Continental Shelves of China.

The relative role of stochasticity versus determinism is critically dependent on the spatial scale over which communities are studied. However, only a few studies have attempted to reveal how spatial scales influence the balance of different assembly processes. In this study, we investigated the latitudinal spatial scale dependences in assembly processes of microeukaryotic communities in surface water and sediment along the continental shelves of China. It was hypothesized that different microeukaryotic trophic groups (i.e., autotroph, heterotroph, mixotroph, and parasite) showed different latitudinal scale dependences in their assembly processes. Our results disclosed that the relative importance of different assembly processes depended on a latitudinal space scale for planktonic microeukaryotes. In surface water, as latitudinal difference increased, the relative contributions of homogenous selection and homogenizing dispersal decreased for the entire community, while those of heterogeneous selection and drift increased. The planktonic autotrophic and heterotrophic groups shifted from stochasticity-dominated processes to heterogeneous selection as latitudinal differences surpassed thresholds of 8° and 16°, respectively. For mixotrophic and parasitic groups, however, the assembly processes were always dominated by drift across different spatial scales. The balance of different assembly processes for the autotrophic group was mainly driven by temperature, whereas that of the heterotrophic group was driven by salinity and geographical distance. In sediment, neither the entire microeukaryotic community nor the four trophic groups showed remarkable spatial scale dependences in assembly processes; they were always overwhelmingly dominated by the drift. This work provides a deeper understanding of the distribution mechanisms of microeukaryotes along the continental shelves of China from the perspective of trophic groups.