Avian diversification along elevational zones in the Tropical Andes: density-dependent cladogenesis of tanagers, ecological speciation and climate-driven population genetic differentiation
- Author(s): Sedano Cruz, Raul E
- Advisor(s): Smith, Thomas B
- et al.
Examining patterns of biodiversity in the Tropical Andes provides insight into ecological and evolutionary processes leading to accumulation of lineages in montane regions. In the Tropical Andes, the dramatic changes in topographic and environmental conditions over short distances constitute an ideal system for studying morphological adaptation and geographic discontinuities. These patterns of biodiversity along elevational gradients in the Tropical Andes remains intriguing because there is no comprehensive theory that explains, species richness, high levels of endemism, and the extraordinary variation in traits that are ecologically relevant, in a region that occupies less than 1% of global surface. In particular, I examine phylogenies, eco morphology and population genetics of birds in the Tropical Andes.
In chapter one, I use phylogenetic-based methods to assess slowdown in evolution of body size, changes among lineages in elevational-range overlap and rate-shifts in cladogenesis. Interspecific phylogenetic comparative analysis of the Core Tanager clade supports an overall density-dependent cladogenesis consistent with tenets of adaptive radiation. In chapter two, I use explicit spatial hypotheses of the distribution of the Andean Purplish-Mantled Tanager for present-day and to the past ice-age 18,000-22,000 years ago to test for concordant patterns between population genetic structure using microsatellites loci and mtDNA sequence variation, and potential effects of climate change. Topographical and environmental determinants explain a large proportion of spatial genetic variation in this tanager, but demographic history does not appear to be responding to the expansion of suitable area since last ice-age. In the third chapter, I use coalescent methods for a multilocus data set to examine demographic history between of The Olive-striped and Streak-necked Flycatcher (the montane Mionectes) and between populations for each of these species. The amount of differentiation between species that barely overlap ranges along elevation is similar to the differentiation observed between populations within the same species across the Andean ranges. Because divergence times broadly overlapped between and within the same species, discordant patterns of differentiation in plumage and vocal traits between populations within the same species as compared with distinctive plumage and vocal phenotypes between species cannot be simply explained by rapid differentiation due to genetic drift alone.