A Phylogenetic Model of Established and Enabled Biome Shifts

Where each species actually lives is distinct from where it could potentially survive and persist. This suggests it is important to distinguish established biome affinities (where species live) from enabled affinities (where species could live) when considering how ancestral species moved and evolved among major habitat types, yet typical phylogenetic approaches modeling biome shifts only consider established affinities while disregarding enabled ones. We introduce a new phylogenetic method, called RFBS (Realized & Fundamental Biome Shifts), to model how anagenetic and cladogenetic events cause established and enabled biome affinities (or, more generally, other discrete realized versus fundamental niche states) to shift over evolutionary timescales. We provide practical guidelines for how to assign established and enabled biome affinity states to extant taxa, using the flowering plant clade Viburnum as a case study. Through a battery of simulation experiments, we show that RFBS performs well, even when we have realistically imperfect knowledge of enabled biome affinities for most analyzed species. We also show that RFBS reliably discerns established from enabled affinities, with similar accuracy to Dispersal-Extinction-Cladogenesis models that ignore the existence of enabled biome affinities. Lastly, we apply RFBS to Viburnum to infer ancestral biomes throughout the tree and to highlight instances where repeated shifts between established affinities for warm and cold temperate forest biomes were enabled by a stable and slowly-evolving enabled affinity for both temperate biomes.