Exploring macroinvertebrate community assembly rules: unraveling the effects of flow intermittency and poor ecological potential on environmental filtering and limiting similarity through functional traits

Flow intermittency and poor environmental conditions can occur separately or simultaneously, affecting the occurrence of trait states in stream macroinvertebrate assemblages. Within the framework of limiting similarity theory, we investigate whether environmental filtering or limiting similarity serves as the primary driver force under three environmental conditions: unstressed (perennial environment and good ecological potential), single-stressed (intermittent condition or poor ecological potential), and multi-stressed (intermittent condition and poor ecological potential) environments. Our analysis validated neutral trait states that are not influenced by different environmental stressors. In unstressed environments, limiting similarity is the primary driver force shaping the macroinvertebrate community. In stressed environments, however, the type of stress determines the influence of environmental filtering. It is not the quantity but rather the quality of stress that increases the influence of environmental filtering. Flow intermittency has a more pronounced effect on the aquatic community than poor ecological potential because it eliminates living conditions, while poor ecological conditions merely restrict them. As anticipated, we observed that certain trait states have specific responses indicating that different driver forces influence them across various environmental conditions. Our study provides valuable insights for managing freshwater habitats and developing adaptive conservation strategies considering increasing drought frequency worldwide.