Multiple source pools and dispersal barriers for Galapagos plant species distribution

We reexamined geographic factors explaining the number of plant species on islands in the Galapagos Archipelago. We hypothesized that plant species ri chness (S) was related to the number of source pools and that plant species dispersal preferentially followed direct, oceanic pathways. To test differ ent dispersal pathways from multiple source pools, the total number of isla nds within a given dispersal radius (i) was posed as the sum of the number of line-of-sight islands (C-i) and of the number of islands without line-of -sight connection (B-i). In partial regression analyses, controlling for ne arest island area (A(2)) and for recipient island elevation (E) and area (I nA), C-i and C-i x E were found to be positively correlated with S in the G alapagos for nearly all dispersal ranges from 10 km to 419 km (maximum inte r-island separation). In contrast, B-i x E was negatively correlated with S at the longest dispersal ranges. The connectivity index, C-i, multiplied b y elevation, E, explained more variation in S in the Galapagos than prior r egression models using additive forms of E, InA, A(2), and isolation from t he central island. Using the variables C-i x E and InA, multiple-regression models explained >90% of the variance in both endemic and total plant spec ies richness in the Galapagos Archipelago.