Functional trait responses of macroinvertebrates to anthropogenic activities in a tropical stream in North-Central Nigeria

In the tropical regions of the world, freshwater ecosystems are increasingly being subjected to intense human activities, which in turn alter their unique features and biodiversity. In this study, we assessed the responses of macroinvertebrate functional traits to several environmental gradients in the Emu Stream, a rural stream located in North-Central Nigeria. The samples were collected and analysed using standard methods and procedures for a period of twelve months (January to December 2022) across the four (4) sampling stations of the stream. A total of 11 biological traits comprising 45 trait attributes were selected and analysed using fuzzy coding. Multivariate approaches, including two-way MANOVA, RLQ ordination, and fourth-corner analysis, were employed to explore the relationships between environmental variables, macroinvertebrate assemblages, and functional traits. The results indicated spatial and seasonal variability in physicochemical conditions, with turbidity and electrical conductivity showing significant differences across stations. The RLQ analysis shows strong trait-environment associations, with the first two axes accounting for 79.98% of the total inertia. Traits related to body size, mobility, respiration, feeding habits, and tolerance to oxygen depletion were strongly structured along gradients of flow, nutrient enrichment, organic pollution and seasonal hydrology. Fourth-corner analysis further confirmed significant positive and negative associations between specific traits and key environmental stressors. Generally, the study demonstrates that macroinvertebrate functional traits respond predictably to anthropogenic disturbances and seasonal variability in a tropical freshwater ecosystem, particularly in regions experiencing rapid land use change.