The Minimum Carbon Theory: A Physiological Basis for Species Coexistence

Lei Chen

Understanding how species coexist and why diversity varies across regions remains a central challenge in ecology. Although existing theories such as niche theory, neutral theory, and modern coexistence theory have yielded important insights into species coexistence and diversity, their reliance on abstract parameters lacking direct physiological grounding limits empirical validation and constrains cross-scale integration. To address this limitation, the minimum carbon theory is proposed, defining Cₘᵢₙ as the minimum net carbon gain required for survival, grounded in the first principle that autotrophic organisms must maintain a positive carbon balance to persist. Coexistence occurs when multiple species each sustain net carbon gains above their Cₘᵢₙ under shared environmental regimes. The Cₘᵢₙ theory provides a physiological foundation for understanding species coexistence and diversity, integrating existing ecological theories under the common constraint of carbon balance. Because carbon is the universal currency of life, the Cₘᵢₙ can be applied across taxa and ecological scales, providing a broadly applicable framework for diverse domains, including biological invasions, ecosystem functioning, ecological stability, and evolutionary biogeography. In a biosphere increasingly shaped by global climate change, the Cₘᵢₙ theory provides a unifying physiological lens on how individual carbon thresholds scale up to shape species diversity and ecosystem function.