Functional Redundancy and Ecological Insurance in Degraded Floodplain Fish Communities of the Middle Niger, Nigeria

This research investigated the concept of functional redundancy and its role as ecological insurance in fish communities of degraded floodplain ecosystems along the Middle Niger River in Kogi and Niger states, North Central Nigeria. Functional redundancy, defined as the extent to which multiple species perform equivalent ecological functions, is theorised to provide resilience against biodiversity loss by buffering ecosystem function against species extinction. Whether this insurance mechanism operates effectively in heavily disturbed tropical floodplain systems has remained empirically unresolved. Fish community surveys were conducted at 20 stations across a disturbance gradient ranging from near-intact floodplain sections to heavily degraded areas affected by agricultural encroachment, sand dredging, and fishing pressure. Functional trait data including trophic guild, reproductive strategy, habitat affinity, body size, and hypoxia tolerance were compiled for all recorded species. Functional diversity indices including functional redundancy, functional evenness, and functional divergence were computed. Redundancy-ecosystem function relationships were tested using structural equation modelling with empirical fish biomass and secondary production as function proxies. Results demonstrated that functional redundancy declined steeply with increasing disturbance but at a significantly faster rate than species richness, indicating that redundancy loss preceded measurable biodiversity decline and was therefore a more sensitive indicator of ecological degradation. Degraded sites exhibited highly uneven functional space occupation, with several critical functional groups, including large-bodied piscivores and migratory species, represented by only one or two species. Loss of these irreplaceable functional groups significantly impaired secondary production potential. The study delivers original theory-building and empirical evidence for the ecological insurance value of functional redundancy in Nigerian floodplain fisheries and recommends its incorporation into biodiversity assessment standards for freshwater impact assessment in Nigeria. Keywords: functional redundancy, ecological insurance, floodplain fish communities, Middle Niger, functional diversity