Rethinking angiosperm diversification through the functional integration of mutualisms

Akira Yamawo 

Flowering plants have generated and maintained exceptional diversity for over 100 million years despite repeated environmental change and mass extinction events. Explaining this evolutionary success requires understanding not only how new lineages arise, but also how they persist after divergence. Although multiple ecological traits and interactions are known to influence angiosperm diversification, less attention has been paid to whether different interactions contribute asymmetrically to lineage generation and lineage persistence. Here, I develop the Functionally Integrated Symbiotic System (FISS) as an organizational and testable hypothesis in which ecological interactions are functionally integrated when they make distinct and complementary contributions across demographic and evolutionary bottlenecks. Pollination is expected to contribute disproportionately to lineage generation through reproductive isolation, whereas seed dispersal and mycorrhizal symbioses may contribute more strongly to persistence-related processes by promoting spatial expansion, successful recruitment, and environmental buffering. These three mutualisms are treated as an illustrative set spanning reproductive, dispersal, and establishment stages rather than as an exhaustive set of interactions affecting diversification. FISS therefore predicts that mutualistic traits should show asymmetric associations with lineage generation and persistence, and that their joint functional configuration should provide greater explanatory or predictive information about long-term diversification than individual interactions alone. FISS provides a basis for testing how the functional organization of ecological interactions may shape macroevolutionary dynamics.