Patterns and Processes of Diversification: Speciation and Historical Congruence in Some Neotropical Birds.

This paper documents congruence in geographical patterns of speciation for four clades of birds having taxa endemic to the same areas within the Neotropics. Two genera, Pionopsitta parrots and Selenidera toucans, corroborate a well known biogeographic disjunction in which taxa endemic to southern Central America and the Chocó region of northwestern South America are the sister-group to a radiation within the Amazon basin. These two genera, along with two lineages within the toucan genus Pteroglossus, also document a pattern of historical interrelationships for four well known areas of endemism within Amazonia: Guyanan + (Belém-Pará + (Inambari + Napo)). These generalized historical patterns are interpreted to have arisen via fragmentation (vicariance) of a widespread ancestral biota. A review of the paleogeographic evidence suggests that these vicariance events could have originated as a result of several different mechanisms operating at various times during the Cenozoic. The inference that diversification of the Neotropical biota is primarily the result of the most recent of these possible vicariance events, namely isolation within Quaternary forest refugia, is unwarranted, given present data. These patterns of historical congruence are also interpreted as direct evidence against the hypothesis that diversification of the forest biota was a consequence of parapatric differentiation along recently established ecological gradients.