Origins of the Macaronesian flora: Dispersal and diversification shape a meta-archipelago

Ancestors of oceanic insular floras arrived via long-distance dispersal as a function of the geographic location, climatic habitats, and geologic age of the island. As a result, these floras comprise a mix of lineages, derived from distinct colonization events with different continental and insular origins.

We assembled distributional data for native plant species in four Macaronesian archipelagoes (Azores, Madeira, Canary Islands, and Cabo Verde). Drawing from phylogenetic studies, we assigned each endemic species to a lineage. Five regions represent where the closest relatives of these lineages occur: American, temperate northern Europe, Mediterranean, Saharan, and African. We then estimated the total number of colonization events to Macaronesia as a whole and each constituent archipelago deriving from each region.

The distribution of the origins of native non-endemic lineages broadly reflects the range of climates available in a given archipelago, such that a habitat filter model best explains their distributions. In contrast, for endemic lineages, combinations involving the Mediterranean region predominate across all four archipelagoes. The most species-rich lineages most commonly originate in the Canaries and subsequently disperse to younger, more isolated archipelagoes, reflecting a progression rule pattern.

Different theoretical models apply depending on the scale of endemism. One pattern that transcended existing models involved instances where an archipelago that promotes ecological diversification serves as a stepping stone for the colonization of more distant archipelagoes that otherwise may not have been suitable for ancestral continental taxa, which we term the island springboard effect.