Theoretical Contributions to Understanding Trophic Cascade Dynamics Following Predator Removal in Nigerian Inland Lake Ecosystems

Trophic cascade theory predicts that the removal of apex predators triggers cascading effects through aquatic food webs, yet the specific dynamics and management implications of trophic cascades in Nigerian inland lake ecosystems have not been theoretically developed or empirically tested in the recent literature. This study makes original theoretical contributions to understanding trophic cascade dynamics following the documented depletion of Lates niloticus populations through intensive fishing in Kainji Lake, Niger State. A theoretical food web model for Kainji Lake was constructed from published diet composition studies, trophic level data, and biomass estimates, and parameterised using six years of catch monitoring data from the National Institute for Freshwater Fisheries Research field station. Ecopath with Ecosim was used to simulate the ecological consequences of different Lates niloticus exploitation levels on intermediate predator, forage fish, zooplankton, and phytoplankton biomass trajectories. Sensitivity analysis and Monte Carlo uncertainty estimation were applied to quantify model robustness. Simulation results predicted that continued depletion of Lates niloticus biomass below 15% of its unfished level would trigger a trophic cascade resulting in forage fish population collapse, zooplankton release from predation, and consequent phytoplankton bloom intensification. This cascade dynamic was supported by field observations of declining forage fish yields and increasing algal bloom frequency over the study period. The study introduces the concept of trophic cascade vulnerability index as a novel diagnostic tool for identifying food web configurations in Nigerian inland lakes most susceptible to cascade-driven regime shifts.

Keywords: trophic cascade, Lates niloticus, Ecopath with Ecosim, Kainji Lake, food web dynamics