Date of Award

Fall 12-1-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Steven L. Lima

Second Advisor

William A. Mitchell

Third Advisor

Michael J. Angilletta

Abstract

Several researchers have proposed that warm-adapted organisms should outperform cold-adapted organisms because of the greater rates ofreactions at higher temperatures. This hypothesis-commonly referred to as 'hotter is better'-predicts that maximal performance should increase as the thermal optimum increases. I used published thermal reaction norms for 23 species of fish to test the hypothesis that hotter is better for individual growth rate. These studies reported a wide range of thermal optima among species. Using a phylogenetic hypothesis derived from multiple published sources, I calculated independent contrasts of thermal optima and maximal growth rates. The maximal growth rate appears unrelated to the thermal optimum (/3 = -0.34 for untransformed data and /J = -0.21 for independent contrasts). This result differs from recent findings that suggest hotter is better for rates of population growth. I believe the lack of a relationship in my study stems from the complex processes of acquisition, allocation, and specialization that underlie variation in thermal reaction norms among species. Many comparative studies have shown that highly variable thermal environments may allow for greater performance at warmer temperatures without changing an organism's mean body temperature. In order to predict how thermodynamic effects can change the shape of a performance curve I introduced a thermodynamic effect into a model of optimal performance curves and generated performance landscapes for several combinations of stochastic and seasonal variations in temperature.

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