Content area
Abstract
Understanding how diversity is attained and maintained is one of the central questions in biology. In the Neotropics most attention has centered on the Amazonian lowlands, despite the recognized importance of the role of the Andes in South American diversity. In this dissertation, I address the question by using Nothoprocta tinamous as a model case for examining diversification in the Andes. As a group, they are a manageable size, they exhibit near-restriction to the Andes, they show multi-species parapatric distributions, and they have presumed limited dispersal ability. These are all useful attributes for a system to study speciation and diversification.
First, I constructed the phylogenetic framework with a molecular phylogeny based on one nuclear and two mitochondrial genes. This phylogeny has the richest taxon-sampling of any yet produced for tinamous. High Bayesian posterior probabilities (>0.95) for all of the higher-level relationships supported the traditional subfamily division as well as the monophyly of all genera. Within Nothoprocta, the main finding was the paraphyly of Nothoprocta pentlandii, which requires that the northern populations (Nothoprocta oustaleti) be elevated to species rank.
Second, I analyzed the distributions of all Nothoprocta taxa using niche modeling. With 407 different existing localities and 100 new localities obtained during my fieldwork, I used Maxent to produce a likelihood of occurrence for each species using seven environmental variables. Six of the species show “parapatric stratified distributions.” The current distribution pattern in Nothoprocta at the specific and subspecific levels is not characterized by isolation by geographical barriers or distance, but rather by extensively parapatric distributions.
Finally, I combined the data presented in the previous chapters in an effort to find explanations to the striking parapatric stratified diversity pattern of Nothoprocta. I analyzed this pattern of distribution with respect to the evolutionary relationships within clades, species, and subspecies. I did not find evidence of parapatric speciation among members of Nothoprocta and concluded that the most likely mechanism driving speciation in this group is the fracturing of long, narrow, montane distributions, followed by diversification in allopatry and possibly through posterior secondary contact.
