Intraspecific Variation in Crayfish Behaviour Alters Stream Ecosystem Functions

Human-induced environmental changes are reshaping animal behavioural traits, yet their ecological consequences remain poorly understood. We demonstrate that among-population variation in the behavioural traits of two freshwater crayfish species profoundly affects key ecosystem functions in streams. Crayfish movement behaviour was strongly linked to increased water column metabolism in both natural streams and controlled mesocosm experiments. Movement also influenced nutrient cycling, highlighting the role of bioturbation in ecosystem dynamics. In contrast, boldness negatively impacted leaf litter breakdown, suggesting that less bold individuals rely more on leaf litter as refuge and food. Notably, within-species behavioural differences often outweighed species identity in determining ecological impacts. Our findings reveal that shifts in animal movement behaviour can drive fundamental ecological processes and emphasise the overlooked importance of within-species trait variation. These results advance our understanding of how behavioural diversity influences ecosystem functions and underscore the need to incorporate intraspecific variation into ecological frameworks.