Trophic cascades and predator-prey dynamics in freshwater ecosystems subjected to thermal fluctuations

Abstract

This study examines how thermal fluctuations influence predator–prey dynamics and trophic cascades in freshwater ecosystems, with a focus on ecosystem stability under climate variability. A six-week mesocosm experiment was conducted using four thermal treatments: control (19°C), constant warming (23°C), fluctuating (17–27°C), and extreme pulse (30°C peaks). A three-level trophic web (phytoplankton, Daphnia magna, and Notonecta glauca) was set up. Measured key variables were phytoplankton biomass (chlorophyll a), zooplankton density, predator survival, strength of interaction (OI), trophic transfer efficiency (TTE), and ecosystem stability (σ2). Statistical tests were repeated-measures ANOVA and Gaussian process regression. These conditions of constant warming (~22.8 µg L⁻¹) created a larger phytoplankton biomass than the control (~15.0 µg L⁻¹) and more variability with extreme pulse conditions (~11.4 µg L⁻¹). Zooplankton density declined from 28.5 ± 3.1 to 12.5 ± 3.0 individuals L⁻¹ under combined thermal stress and predation. Predator–prey interaction strength was highest under constant warming (0.035 ± 0.006) and lowest under extreme pulse conditions (0.024 ± 0.008). Under constant warming, the trophic transfer efficiency was maximum at 22.7% and 15.6% but low at limiting conditions. There was a significant decrease in ecosystem stability and the variance, which rose to 6.38 (extreme pulse) compared to a control of 1.85, showing non-linear threshold responses. One important cause of trophic dynamics and ecosystem stability is not mean warming, but thermal variability. Middle levels of warming are beneficial in terms of productivity and energy flow, but severe thermal events interfere with the ecological interactions and make the system less resilient.