WenJun Zhang School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China Computational Ecology and Software ISSN 2220-721X http://www.iaees.org/publications/journals/ces/online-version.asp 2026 16 3 243 272 International Academy of Ecology and Environmental Sciences Hong Kong 2 April 2026 11 May 2026 1 September 2026 species diversity latitudinal gradient niche theory species-energy hypothesis evolutionary time metabolic theory unified theory macroecology The geographical patterning of species diversity, most famously the latitudinal gradient, one of the oldest and most celebrated patterns in ecology, still lacks a unified mechanistic explanation. Existing hypotheses, including the species-energy hypothesis, the environmental heterogeneity hypothesis, the area hypothesis, neutral theory, metabolic theory, maximum entropy theory, and historical-evolutionary hypotheses, each capture a critical dimension of diversity generation. Yet none alone can explain why regions with identical energy inputs can differ so dramatically in species richness. After systematically reviewing these classical and cutting-edge theories, I propose a novel integrative framework: the Niche-Energy-Time triadic synergy hypothesis (NET hypothesis) in present paper. The NET hypothesis starts from three irreducible ultimate constraints: a thermodynamic constraint, available energy flux (E) sets the upper limit on the total biomass and number of individuals a community can sustain; a structural constraint, multidimensional niche space volume (H) determines the fineness with which that energy flow can be partitioned among species; and a historical constraint, the effective evolutionary and community assembly time (T) determines the degree to which that niche space has been filled. I argue that species diversity is an emergent outcome of these three constraints acting as a serial filter not a linear function of any single factor. I present the core mathematical structure of the NET hypothesis, demonstrate its logical necessity by deriving it from population energy allocation, the niche-width-species-number trade-off, and the macro-dynamics of speciation-extinction balance, and show its power to unify a wide range of classical diversity patterns, including the latitudinal gradient, elevational patterns, and island species-area relationships, as well as anomalous cases. The NET hypothesis does not overturn existing hypotheses but embeds energy, heterogeneity, area, and time into the E, H, and T dimensions, revealing the synergistic mechanisms by which they act as necessary but not sufficient conditions. It provides a testable, quantifiable, mechanistic foundation for predicting biodiversity change and guiding conservation planning. http://www.iaees.org/publications/journals/ces/articles/2026-16(3)/Niche-Energy-Time-triadic-synergy-hypothesis.pdf