Developing a Unified Theoretical Framework for Linking Biodiversity, Ecosystem Functioning, and Human Wellbeing in Nigerian Tropical Ecosystems

The relationship between biodiversity, ecosystem functioning, and human wellbeing is one of the most consequential questions in contemporary ecology, yet theoretical integration of these three pillars remains fragmented, particularly in the context of tropical African ecosystems. This study develops and tests a unified theoretical framework that explicitly links species diversity, functional redundancy, ecosystem process rates, and human wellbeing outcomes across contrasting Nigerian tropical ecosystems including rainforest, derived savanna, freshwater wetlands, and coastal mangroves. The framework draws on the biodiversity-ecosystem functioning literature, ecosystem services cascade models, and resilience theory, synthesising their assumptions into a single testable causal architecture. Structural equation models were parameterised using a multi-site dataset compiled from over 200 plots across four geopolitical zones, integrating plant, invertebrate, and vertebrate diversity data with ecosystem process measurements and household wellbeing surveys. Results confirm that the biodiversity-functioning-wellbeing pathway operates in Nigerian tropical systems but is strongly mediated by land use intensity and institutional governance quality, which can either amplify or suppress the translation of ecosystem processes into realised human wellbeing. Functional redundancy emerged as a critical buffer mechanism that stabilises ecosystem process delivery under biodiversity loss. The unified framework generates novel predictions about threshold effects and cross-scale feedbacks not derivable from existing partial theories. The study makes a substantial original theoretical contribution and recommends embedding the framework within Nigeria's National Biodiversity Strategy and Action Plan revision process. Keywords: biodiversity-ecosystem functioning, theoretical framework, ecosystem services, Nigeria, functional redundancy.