This is volume 204 issue 6 of The American Naturalist. Since its inception in 1867, The American Naturalist has maintained its position as one of the world’s premier peer-reviewed publications in ecology, evolution, and behavior research. Its goals are to publish articles that are of broad interest to the readership, pose new and significant problems, introduce novel subjects, develop conceptual unification, and change the way people think. The American Naturalist emphasizes sophisticated methodologies and innovative theoretical syntheses — all in an effort to advance the knowledge of organic evolution and other broad biological principles.