Abstract

Island ecosystems are widely studied as "natural laboratories” for biological change. Animals that colonize islands frequently exhibit differences from their mainland counterparts in morphology, physiology, and behavior. Some of the most striking features include changes in body size and shape, with extreme examples being dwarfism, gigantism, and flightlessness. These changes are generally driven by isolation and reduction in predators and competitors. The 10 woodpecker species belonging to the Centurus clade of genus Melanerpes are ideally suited to study evolutionary changes associated with island conditions because they include numerous populations restricted to islands, allowing comparisons among island and continent ecosystems. To test specific hypotheses regarding overall body size, overall shape, and differences between the sexes in size (sexual size dimorphism, SSD) and shape (sexual body component dimorphism, SBCD), I analyzed six morphological measures in >1,500 museum specimens representing 43 taxa or populations, of which 20 were island forms. In contrast to prior studies of island birds, we computed overall body size as geometric mean of the six measurements to derive a reliable measure of body size. Although insular effects of body size and shape have been widely studied in birds, island effects on sexual dimorphism have been largely ignored, for which use of an unbiased reference character is essential. For overall body size, I found no support at either the interspecific or intraspecific level for the island rule that small and large mainland taxa converge on an intermediate body size after colonizing islands. Sexual size dimorphism existed in all taxa and populations, with males being larger than females, but no consistent differences between island and mainland populations were detected at either taxonomic level. For overall body shape, island populations consistently exhibited relatively shorter wings, which followed the general trend for insular birds that places them on a trajectory toward flightlessness. For SBCD, males consistently possessed larger bill dimensions, whereas females had consistently longer wings, tails, and legs relative to overall size; however, no differences between island and mainland populations existed at either taxonomic level. Collectively, these findings augment our understanding of how island conditions influence the morphology of birds.

LLU Discipline

Biology

Department

Biology

School

School of Medicine

First Advisor

William K. Hayes

Second Advisor

Anthony I. Metcalf

Third Advisor

Kevin E. Nick

Fourth Advisor

Melissa R. Price

Fifth Advisor

Michael E. Akresh

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

2019

Date (Title Page)

6-2019

Language

English

Library of Congress/MESH Subject Headings

Melanerpine woodpeckers; Sex Characteristics; Body Size

Type

Thesis

Page Count

xi, 59 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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