Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology

Date of Defense

7-18-2006

Graduate Advisor

Bette A. Loiselle, Ph.D.

Co-Advisor

Robert E. Ricklefs, Ph.D.

Committee

Elizabeth A. Kellogg, Ph.D.

J. Van Remsen, Ph.D.

Shannon J. Hackett, Ph.D.

Abstract

Ecological and historical approaches to studying species¿ geographic ranges have yet to be unified. Ideal scenarios for integrating ecology with evolutionary biology in biogeography are those where contemporary ecological interactions may have influenced species¿ distributions historically, driving the evolution of ecological niches. I focused on understanding the origin of elevational distributions of species, and specifically on the role of interspecific competition in the origin of complementary elevational ranges. To test hypotheses about the origin of elevational distributions, I followed a combined approach involving molecular phylogenetics, phylogeography, population genetics, and ecological niche modeling. I focused on Buarremon torquatus and B. brunneinucha (Aves, Emberizinae), whose elevational distributions appear to be influenced by interspecific competition. The hypothesis that elevational distributions in Buarremon changed in opposite directions as a result of competition is untenable because: (1) a historical expansion of the range of B. brunneinucha into areas occupied by B. torquatus was not accompanied by a shift in the elevational range of the former species, (2) when B. brunneinucha colonized the range of B. torquatus, lineages with disparate elevational distributions had already diverged, and (3) historical trends in effective population size do not suggest populations with elevational ranges abutting those of putative competitors have declined as would be expected if competition caused range contractions. In addition, explicit analyses relating elevation to environmental variables that limit distributions directly indicate some distribution patterns can be more parsimoniously explained by hypotheses alternative to competition. The role of competition in elevational zonation may be to act as a sorting mechanism that allows the coexistence along mountain slopes only of ecologically similar species that differ in elevational distributions prior to attaining sympatry. A comprehensive assessment of species limits within B. torquatus based on phylogenetic, vocal, morphological, and ecological data indicates that B. torquatus comprises multiple species. Although examining the origin of the contrasting elevational ranges of different species is still sensible because the B. torquatus complex is a clade, when viewed in comparison to those of genera with multiple species, the patterns of elevational distribution of ¿B. torquatus¿ do not appear as unique as traditionally thought.

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Biology Commons

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