Date of Award
Thesis and Dissertation
Master of Science (MS)
School of Biological Sciences
Angelo P. Capparella
Tropical rainforests in the Amazon Basin show an extraordinarily high degree of biodiversity, the reasons for which are poorly understood. A number of biogeographical models have been proposed to account for the variation present within and among species, including birds. This study tests the predictive ability of six major historical vicariant biogeographical models (Andean uplift, marine incursion, Amazonian lake, river barrier, refuge, and river refuge) using a large data set of morphological characters in the Wedge-billed Woodcreeper (Glyphorynchus spirurus), a small understory songbird found mostly in terra firme tropical rain forest. It also characterizes variation in key morphological characters and tests the validity of the fourteen current subspecies in this species. Canonical discriminant analyses paired with cluster analyses and goodness-of-fit tests were used to test the biogeographical models, and discriminant function analyses were used in the subspecies revision. In all cases, measures were taken to address geographic uncertainty. We discovered that none of the six tested models fully predicted the observed morphological patterns in this species, that the marine incursion, lake, and Andean uplift models could be excluded entirely, and that the river barrier, refuge, and river refuge models showed predictive power in limited locations but not across the entire range. We also found that extensive clinal variation exists in the characters under study, and that at a diagnosability level of 95% only one current subspecies remained valid, but that several more exist as distinct entities at 90% and 75% levels of diagnosability. The use of a very high diagnosability level may impede the recognition of existing geographic variation and should be carefully considered. Various sources of geographic uncertainty were not found to have any effect on the trends discovered, but sparse sampling in some areas remains a problem. These results corroborate recent genetic studies which have questioned the current subspecies rankings, but they fail to recover the same biogeographical patterns found in other studies. Morphological variation in this species captures such a complex history that no single biogeographical model can be distinguished, a phenomenon which we name the palimpsest model.
Tito, Gregory, "Exploring The Biogeography Of South American Rainforest Understory Birds Using Morphological Variation In The Wedge-Billed Woodcreeper (glyphorynchus Spirurus)" (2017). Theses and Dissertations. 779.
Available for download on Tuesday, September 25, 2018