Cascading Trophic Effects of Large Carnivore Extirpation on Vegetation Structure in North Central Nigerian Savanna Ecosystems

The extirpation of large carnivores from savanna ecosystems is hypothesised to trigger trophic cascades that release herbivore populations from top-down regulation, leading to vegetation overgrazing and structural degradation. However, empirical evidence for trophic cascades in West African savanna systems is extremely sparse. This study tests the trophic cascade hypothesis rigorously using a replicated comparative design across protected areas in North Central Nigeria with contrasting large carnivore presence and absence histories, including Kainji Lake National Park, Borgu Game Reserve, and several community-managed conservation areas. Carnivore presence was characterised using intensive camera trap arrays. Herbivore population structure and behaviour were assessed through distance sampling and activity budget observations. Vegetation structure, woody cover, grass biomass, and tree sapling recruitment were measured across carnivore presence and absence sites using identical plot-based methods. Results reveal significantly higher medium-sized herbivore densities in carnivore-absent areas and substantially altered herbivore behavioural patterns, including reduced vigilance and more uniform space use. Vegetation structure in carnivore-absent sites showed lower woody sapling density, reduced structural complexity, and altered grass community composition consistent with higher browsing and grazing pressure. Path analysis confirmed that carnivore presence effects on vegetation operated through both density-mediated and behaviour-mediated indirect effects. These findings provide the first rigorous empirical evidence for large carnivore-driven trophic cascades in a Nigerian savanna ecosystem and have significant implications for rewilding and carnivore restoration strategies in North Central protected areas. Keywords: trophic cascade, large carnivores, savanna vegetation, North Central Nigeria, rewilding.