Beyond the triad: why ecological theory must anchor One Health

One Health has been highly effective at emphasizing the interconnectedness of human, animal, and environmental health. However, One Health must more explicitly incorporate ecological theory to move beyond documenting pathogen presence or co-location toward understanding the mechanisms that lead to infection and transmission. Here, we argue that ecological theory provides the missing mechanistic layer between pathogen detection and prevention, and we identify four practical areas where this matters: landscape connectivity and contact networks, biodiversity and microbiomes, ecological interpretation of environmental sampling, and long-term ecological capacity. Together, these areas can help identify which human-animal-environment connections matter most for disease dynamics and where prevention efforts can most effectively interrupt transmission. Therefore, ecological theory can move One Health from documenting connections toward identifying mechanisms, directing prevention, supporting wildlife conservation, and promoting human well-being.