Ecological and Evolutionary Determinants of Invasive Plant Success in Degraded Tropical Ecosystems of South West Nigeria

Invasive plant species pose a growing threat to biodiversity and ecosystem functioning in degraded tropical landscapes, yet the ecological and evolutionary mechanisms underpinning their success in West African systems remain poorly understood. This study investigates the ecological and evolutionary determinants of invasive plant establishment and spread in degraded ecosystems across South West Nigeria, using a combination of comparative trait analysis, phylogenetic methods, population genomics, and field invasion ecology. Eight invasive plant species including Chromolaena odorata, Tithonia diversifolia, and Lantana camara were studied across a network of sixty degraded plots in Oyo, Osun, and Ekiti States. Functional traits associated with invasive success were compared between invasive and co-occurring native species using phylogenetically controlled regressions. Population genomic analysis using genotyping-by-sequencing characterised the evolutionary origins, admixture, and adaptive differentiation of Nigerian populations of two focal invaders relative to native range populations. Field experiments manipulated disturbance intensity and native competitor diversity to test mechanistic hypotheses about competitive displacement and niche pre-emption. Results demonstrate that rapid local adaptation in functional traits, particularly specific leaf area and phenotypic plasticity, significantly enhances invasive performance in Nigerian conditions beyond what is attributable to species identity alone. Competitive exclusion of native species was driven primarily by early-season resource capture rather than allelopathy. Novel weapons and enemy release hypotheses received only partial support. The study provides the most comprehensive ecological and evolutionary analysis of plant invasions in South West Nigeria to date and develops a predictive risk framework for screening future invasive threats. Keywords: invasive plants, ecological determinants, evolutionary adaptation, South West Nigeria, population genomics.