The evolution of local co-occurrence in birds in relation to latitude, sympatry, and range symmetry

We studied evolution of secondary syntopy (local co-occurrence) in almost 900 species of songbirds (Passeriformes) from the whole word in relation to latitude. We expected a positive relationship due to recent findings that speciation rate and transition of species from allopatry into secondary sympatry is higher in temperate areas. After selecting species pairs according to breeding range overlap and age of split criteria, we correlated syntopy with sympatry, range symmetry and pair age. In most of the analyses, syntopy indeed increased with latitude from Southern to Northern Hemisphere.