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Thesis Abstract – Schultz (2009)


The Size-Grain Hypothesis: A Field Test of Wing Length Proportions of Beetles and a Study of Pogonomyrmex californicus Locomotion

Author and college:

Emily Schultz, Scripps College


April 27, 2009


Bachelor of Arts in Organismal Biology and Ecology


Diane Thomson, Joint Science Department of Claremont McKenna, Pitzer, and Scripps Colleges


The size-grain hypothesis asserts that the landscape is more rugged for small organisms, making it energetically beneficial for them to have short appendages, such as legs or wings, in proportion to their body size. The hypothesis also predicts that organisms evolving in more rugged habitats should have different allometry than those in more evenly grained environments. This study tested the size-grained hypothesis in two contexts: a field test to characterize allometric relationships in different habitats and a lab test of the underlying assumptions about energetic costs. Beetles were collected using pitfall traps in two habitats with distinct grain and structure (coastal sage scrub and grassland) with the goal of comparing wing length to body size proportions. The collections indicated that the diversity of beetles during the season when the study took place was not sufficient for an analysis of their allometric relationships. The lab experiment investigating energetic of locomotion examined the path length, vertical movement, and velocity of Pogonomyrmex californicus on artificial landscapes of varying rugosity to test the assumption that environmental grain strongly influences locomotion behavior and energetic costs. The path length and vertical movement increased on more rugged landscapes, while velocity decreased. This demonstrates that rugged environments increase the energetic costs of locomotion, providing support for the size-grain hypothesis.

For more information:

Contact Diane Thomson – dthomson@kecksci.claremont.edu

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