Darwin's entangled bank through deep time: Structural stability of mutualistic networks over evolutionary timescales

Mutualistic interactions form species-rich, complex networks that play essential roles for ecosystem function. Over macroevolutionary time scales, global- and continental-level networks change as species emerge and go extinct, yet the stability of their structural organization remains poorly understood. Here, we show that ancestral interaction networks can be reconstructed from present-day phylogenetic and interaction data. We infer the ancestral networks of plant mutualisms involving arbuscular mycorrhizal fungi, bat pollinators, and bird seed dispersers at large biogeographic scales. We find that these mutualistic networks exhibit a modular structure that has persisted for millions of years, maintained by the evolutionary conservatism of species interactions. As species diversify, they show limited shifts in mutualistic partners. This minimal evolutionary rewiring results in a remarkable long-term stability of mutualistic network structure at large spatial scales.